Title of Invention	"PROCESS FOR PRODUCING BISPHENOL A"
Abstract	There is provided a process for producing bisplenol (BPA) which includes steps of treating a part of a mother liquor obtained in the process for production of bisphenol A to remove impurities therefrom and then feeding again the thus treated mother liquor to the reaction system, which is capable of preventing a BPA production catalyst used therein from being deteriorated in catalytic activity. The process for producing bisphenol A according to the present invention includes a reaction step of reacting acetone and phenol (PL) to obtain a reaction mixture containing BPA and PL; a low-boiling component separation step of separating a BPA-containing component from the reaction mixture; a BPA separation step of separating the BPA-containing component into a material flow containing BPA as a main component and a mother liquor containing PL and reaction impurities as main components; a light component separation step of subjecting at least a part of the mother liquor to heat treatment and distillation in the presence of an alkali to separate the mother liquor into a light component and a heavy component; and a recombination reaction step of treating the thus separated light component in the presence of a catalyst to allow PL and isopropenyl phenol contained in the light component to be recombined with each other and converted into bisphenol A, in which a content of isopropyl phenol in a reactdoil out ionoit ined in the reaction step is controlled to not more than 4% by weight.

Title of Invention

"PROCESS FOR PRODUCING BISPHENOL A"

Abstract

There is provided a process for producing bisplenol (BPA) which includes steps of treating a part of a mother liquor obtained in the process for production of bisphenol A to remove impurities therefrom and then feeding again the thus treated mother liquor to the reaction system, which is capable of preventing a BPA production catalyst used therein from being deteriorated in catalytic activity. The process for producing bisphenol A according to the present invention includes a reaction step of reacting acetone and phenol (PL) to obtain a reaction mixture containing BPA and PL; a low-boiling component separation step of separating a BPA-containing component from the reaction mixture; a BPA separation step of separating the BPA-containing component into a material flow containing BPA as a main component and a mother liquor containing PL and reaction impurities as main components; a light component separation step of subjecting at least a part of the mother liquor to heat treatment and distillation in the presence of an alkali to separate the mother liquor into a light component and a heavy component; and a recombination reaction step of treating the thus separated light component in the presence of a catalyst to allow PL and isopropenyl phenol contained in the light component to be recombined with each other and converted into bisphenol A, in which a content of isopropyl phenol in a reactdoil out ionoit ined in the reaction step is controlled to not more than 4% by weight.

Full Text	TITLE OF INVENTION PROCESS FOR PRODUCING BISPHENOL A FIELD OF THE INVENTION The present invention relates to a process for producing bisphenol A, and more particularly, to a process for producing bisphenol A including steps of treating a part of a mother liquor separated in a bisphenol A separation step to remove impurities therefrom and then recycling the thus treated mother liquor to the reaction system, which process is capable of preventing a bisphenol A production catalyst used therein from being deteriorated in catalytic activity. RELATED ARTS Bisphenol A has been usually produced by using phenol and acetone as raw materials. As a typical method for production of bisphenol A, there is known the method of reacting the above raw materials with each other in the presence of an acid catalyst such as cation exchange resins. However, the reaction mixture obtained by the above conventional method contains, in addition to the aimed bisphenol A, unreacted phenol, unreacted acetone, water produced by the reaction, and reaction by-products such as colored substances. The reaction by-products are usually separated from the reaction mixture by a distillation method. In the distillation method, the reaction mixture is distilled within a distillation column at a temperature lower than a boiling point of phenol to recover low-boiling components such as unreacted acetone, water produced by the reaction and a part of unreacted phenol from a top of the distillation column and obtain a bisphenol A-containing component from a bottom thereof. Then, the bisphenol A-containing component obtained from the bottom of the distillation column is separated into a material flow containing bisphenol A as a main component and a mother liquor containing phenol and reaction impurities as main components. A large part of the mother liquor is recycled to the reaction system. However, in order to prevent isomers or high-boiling impurities from being accumulated in the reaction system, a part of the mother liquor is usually withdrawn from the reaction system to remove the impurities therefrom. The impurities are generally removed from the mother liquor by the method of subjecting the mother liquor to heating reaction by adding an alkali thereto to decompose bisphenol A and isomers thereof into phenol and isopropenyl phenol. In this case, a part of the other impurities are converted into heavy components and discharged as tar out of the reaction system. The decomposition reaction is usually conducted by a reaction distillation method, and phenol and isopropenyl phenol produced by the decomposition reaction are supplied to a recombination reactor filled with an acid ion exchange resin catalyst to produce bisphenol A therefrom (refer to Japanese Patent Publication (KOKOKU) No. 49-48319 and Japanese Patent Application Laid-open (KOKAI) Nos. 1-230538 and 5-331088). The reaction solution discharged from the recombination reactor is recycled to the reaction system together with the mother liquor subjected to no removal of impurities therefrom. However, even though a part of the mother liquor is withdrawn from the reaction system and subjected to alkali heat treatment to remove impurities therefrom, the acid ion exchange resin catalyst used in the reaction step tends to be deteriorated, thereby failing to conduct a stable production of bisphenol A for a long period of time. Further, as a result of study for the deterioration of catalyst activity by isopropyl phenol, it has been found that methanol contained in the material acetone promotes the deterioration of catalyst activity by isopropyl phenol. In the material acetone, methanol is contained as an impurity and it is known that the activity of aminothiol carried-type ion exchange resin catalyst is deteriorated by the methanol (refer to Japanese Patent Application Laid-Opens (KOKAI) No. 6-92889, 6-25047 or the like). The promotion effect of deterioration of catalyst activity together with alkyl phenol such as isopropyl phenol was not known. DISCLOSURE OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION The present invention has been made in view of the above conventional problems. An object of the present invention is to provide a process for producing bisphenol A including steps of treating at least a part of a mother liquor obtained in a bisphenol A separation step to remove impurities therefrom and then recycling the thus treated mother liquor to the reaction system, which is capable of preventing a bisphenol A production catalyst used therein from being deteriorated in catalytic activity. MEANS FOR SOLVING PROBLEM As a result of the present inventors' earnest study for solving the above conventional problems, it has been found that isopropyl phenol by-produced upon subjecting the mother liquor to heat treatment in the presence of an alkali to remove impurities therefrom, is a substance which promotes deterioration of catalytic activity of the acid ion exchange resin catalyst used in the reaction step, and, therefore, when an amount of isopropyl phenol contained in the reaction solution being present in the reaction step is controlled to a specific range, the acid ion exchange resin catalyst used in the reaction step can be prevented from being deteriorated in catalytic activity thereof. The present invention has been attained on the basis of the above finding. That is, to accomplish the aim, in an aspect of the present invention, there is provided a process for producing bisphenol A comprising at least a reaction step of reacting acetone and phenol as raw materials in the presence of an acid ion exchange resin catalyst to obtain a reaction mixture containing bisphenol A and phenol; a low-boiling component separation step of separating the reaction mixture into a bisphenol A-containing component and a low-boiling component containing unreacted acetone; a bisphenol A separation step of separating the bisphenol A-containing component into a material flow containing bisphenol A as a main component and a mother liquor containing phenol as main components; a light component separation step of subjecting at least a part of the thus separated mother liquor to heat treatment and distillation in the presence of an alkali to separate the mother liquor into a light component and a heavy component; a recombination reaction step of treating the thus separated light component in the presence of an acid ion exchange resin catalyst to allow phenol and isopropenyl phenol contained in the light component to be recombined with each other and converted into bisphenol A; and a recombination reaction solution recycling step of recycling a recombination reaction solution obtained in the recombination reaction step to the above reaction step, in which a content of isopropyl phenol in a reaction solution being present in the reaction step is controlled to not more than 4% by weight. EFFECT OF THE INVENTION In the process for producing bisphenol A according to the present invention which process includes steps of treating at least a part of a mother liquor obtained in a bisphenol A separation step to remove impurities therefrom and then recycling the thus treated mother liquor to the reaction system, it is possible to prevent a bisphenol A production catalyst used therein from being deteriorated in catalytic activity. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a flow diagram showing the process for producing bisphenol A according to the present invention. Fig. 2 is a flow diagram showing a pilot plant used in Example I. EXPLANATION OF REFERENCE NUMERALS la: Methanol removal apparatus; 2: Reactor; 4: Distillation column; 5: Crystallizer; 6: Solid/liquid separator; 7: Re-dissolver; 8: Re-crystallizer; 9: Solid/liquid separation and rinsing system; 11: Crystal adduct decomposition apparatus; 12: Purifier; 13a: Alkali decomposition column; 13b: Recombination reactor; 13c: Mother liquor concentration column, 14: Tank; 20: Separation system; 20a: Purifier; 22: Phenol storage tank PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION The present invention is described in detail hereinunder. The following descriptions are merely concerned with a typical example of preferred embodiments of the present invention, and it is therefore not intended to limit the scope of the present invention thereto. The process for producing bisphenol A according to the present invention includes at least a reaction step of reacting acetone and phenol as raw materials in the presence of an acid ion exchange resin catalyst to obtain a reaction mixture containing bisphenol A and phenol; a low-boiling component separation step of separating the reaction mixture into a bisphenol A-containing component and a low-boiling component containing unreacted acetone; a bisphenol A separation step of separating the bisphenol A-containing component into a material flow containing bisphenol A as a main component and a mother liquor containing phenol and reaction by-products as main components; a light component separation step of subjecting at least a part of the thus separated mother liquor to heat treatment and distillation in the presence of an alkali to separate the mother liquor into a light component and a heavy component; a recombination reaction step of treating the thus separated light component in the presence of an acid ion exchange resin catalyst to allow phenol and isopropenyl phenol contained in the light component to be recombined with each other and converted into bisphenol A; and a recombination reaction solution recycling step of recycling a recombination reaction solution obtained in the recombination reaction step to the above reaction step. Further, the process of the present invention may also include, if required, an acetone recycling step of separating and recovering unreacted acetone from the low-boiling component obtained in the low-boiling component separation step and recycling the thus recovered unreacted acetone to the reaction step, a mother liquor recycling step of recycling a part of the mother liquor separated to the reaction step without treating the mother liquor, etc. First, for facilitated understanding of the present invention, the process for producing bisphenol A according bo the present invention is generally described by referring to the flow diagram shown in Fig. 1. However, it should be noted that the production process of the present invention can be carried out in various embodiments. Acetone and phenol as raw materials are fed to a reactor (2) through a line (1). A reaction mixture discharged from the reactor (2) is introduced into a distillation column (4) through a line (3). A low-boiling component containing acetone, water, phenol, etc., which is withdrawn from a top of the distillation column (4) is delivered to a separation system (20) where the low-boiling component is separated by distillation, etc., into acetone, water and phenol. The thus separated acetone is delivered to a methanol removing apparatus (la) as the below-mentioned purifier through a line (21) and a line (A). Water separated is withdrawn from the separation system (20) and discharged out of the system. The separated phenol is fed from the separation system (20) to the purifier (20a) and subjected to purification treatment therein, and then delivered to a phenol storage tank (22). A bottom component in the distillation column (4) is delivered to a crystallizer (5) to crystallize a crystal adduct of bisphenol A and phenol therefrom. The crystal adduct is fed to a solid/liquid separator (6) and separated into a solid component and a liquid component, re-dissolved in a re-dissolver (7), recrystallized in a recrystallizer (8), and then treated by a solid/liquid separation and rinsing system (9) constituted from a centrifugal separator, etc. In this case, the crystal adduct is rinsed (washed) with clean phenol fed from the tank (22). A rinsing waste water is delivered to the re-dissolver (7) through a line (10) (or fed to the solid/liquid separator (6) through a line (17) and used for rinsing the crystal adduct). The rinsed crystal adduct is fed to an adduct decomposition apparatus (11) where the crystal adduct is heated and decomposed into bisphenol A and phenol. The resultant bisphenol A is then treated in a purifier (12) to obtain a bisphenol A product. The phenol separated in the adduct decomposition apparatus (11) and the purifier (12) is delivered to the tank (22). At least a part of the liquid (mother liquor) separated in the solid/liquid separator (6) is fed through an impurity removal line (13') to remove impurities therefrom. Upon the removal treatment of impurities, at least a part of the mother liquor is concentrated in the mother liquor concentration column (13c), and thereafter it is heat-treated in the presence of an alkali in an alkali decomposition column (13a), and then separated into a light component and a heavy component. The light component is fed to a recombination reactor (13b) and subjected to a recombination reaction treatment, and returned to the line (13). Meanwhile, a part of the mother liquor may be delivered to a mother liquor tank (14) through the line (13) The mother liquor in the mother liquor tank (14) is delivered to the line (1) through a line (15), mixed with acetone and then fed to the reactor (2). Further, the mother liquor in the mother liquor tank (14) is also delivered to the line (3) through a line (16). The amount of the mother liquor fed from the line (15) to the line (1) is controlled such that a ratio between acetone and phenol in a mixed solution composed of the mother liquor and acetone which is fed to the reactor (2), lies within a predetermined range. By controlling the ratio between acetone and phenol contained in the mixed solution to be fed to the reactor (2) to the predetermined range, a quality and a yield of a bisphenol A product are stabilized. Meanwhile, the mother liquor tank (14) serves as a buffer tank for equalizing an amount of the mother liquor recycled through the line (13). Next, the respective steps of the process of the present invention are described in detail. In the reaction conducted in the reactor (2), phenol and acetone as raw materials are reacted with each other under such a condition that phenol is used in a stoichiometrically excessive amount relative to acetone. The molar ratio of phenol to acetone (phenol/acetone) is usually 3 to 30 and preferably 5 to 20. The reaction temperature is usually 50 to 100°C, and the reaction pressure is usually from normal pressure to 600 kPa (absolute pressure). As the material acetone, there can be used one which is industrially available with no limitation. For instance, there can be used a purified acetone which is newly fed from the out of system, an acetone obtained by separating unreacted acetone in the low-boiling component separation step and further treating it in the acetone recycling step, and a mixture thereof. As the catalyst, there is usually used a strong acid cation exchange resin such as sulfonic acid type cation exchange resins, and preferably a resin obtained by partially modifying the strong acid cation exchange resin with a sulfur-containing amine compound. In particular, when using such a resin obtained by partially modifying the strong acid cation exchange resin with a sulfur-containing amine compound such as 2-aminoethane thiol and 2-(4-pyridyl)ethane thiol, the effects of the present invention can be more remarkably exhibited. The degree of modification with the sulfur-containing amine compound may be controlled such that the sulfur-containing amine compound is used in an amount of usually 2 to 30 mol% and preferably 5 to 20 mol% based on an acid group (sulfonic group) contained in the acid ion exchanger. The condensation reaction between phenol and acetone is usually conducted by a fixed bed flow method or a suspension type batch method. In the fixed bed flow method, the raw mixture is fed to the reactor at an hourly liquid space velocity of usually 0.2 to 50/h. In the suspension type batch method, the amount of the acid ion exchange resin catalyst used varies depending upon reaction temperature and reaction time, and is usually 20 to 100% by weight. The reaction time is usually 0.5 to 5 hr. The reaction mixture obtained in the reaction step is separated into a bisphenol A-containing component and a low-boiling component containing unreacted acetone. As the separating method, as described above by referring to the flow diagram shown in Fig. 1, there is used such a method in which using the distillation column (4), the reaction mixture obtained in the reaction step is subjected to distillation to separate the low-boiling component containing unreacted acetone from a top of the distillation column. The bottom liquid in the distillation column is a liquid component containing bisphenol A. As the distillation column, there may be used known distillation columns. When the distillation is conducted under normal pressure, the distillation temperature is not higher than a boiling point of phenol, and the distillation procedure is preferably conducted under reduced pressure. The distillation under reduced pressure is usually conducted at a temperature of 50 to 150°C under a pressure of 50 to 300 mmHg. The distillation procedure is preferably conducted under such a condition that a predetermined amount of unreacted phenol contained in the reaction mixture is withdrawn from a bottom of the distillation column to form an adduct with bisphenol A in the subsequent crystallization step. The component separated from the top of the distillation column (4) contains unreacted acetone, water, methanol and isopropyl phenol as impurities, unreacted phenol, etc. By adjusting an amount of the isopropyl phenol withdrawn from the top of the column, the concentration of the isopropyl phenol contained in the reaction solution can be well controlled. For example, in order to reduce an amount of isopropyl phenol contained in the reaction solution obtained in the distillation column (4), the amount of phenol recovered on the top side of the column may be increased, the reflux ratio of the column may be reduced, or phenol may be supplied to the distillation column (4) from an outside, thereby efficiently conducting the above control procedure. The above distillation procedure is preferably conducted such that the ratio of the amount of isopropyl phenol recovered on the top side of the column to the amount of the same substance being fed thereto is usually not less than 0.8% by weight and preferably not less than 1.5% by weight. The concentration of bisphenol A contained in the bottom liquid which is obtained after separating the above low-boiling component from the top of the column is usually 20 to 50% by weight. When the concentration of bisphenol A contained in the bottom liquid is less than 20% by weight, the yield of bisphenol A tends to be lowered. When the concentration of bisphenol A contained in the bottom liquid is more than 50% by weight, a viscosity of the concentrated mixed solution tends to be increased, so that it may be difficult to deliver the solution through the reaction system. The bottom liquid is delivered to the bisphenol A separation step where bisphenol A as the aimed product is recovered. When the process includes the above acetone recycling step, the low-boiling component separated in the low-boiling component separation step which contains unreacted acetone, water, phenol and isopropyl phenol, is fed to the acetone recycling step constituted from the separation system (20) where acetone is separated therefrom, for example, by distillation. The thus separated acetone is preferably fed back to the methanol removing apparatus (la) disposed on an upstream side of the reaction step to remove methanol as an impurity therefrom before the acetone is fed as raw acetone to the reaction system. In view of deterioration of catalyst activity, it is preferred to reduce the amount of methanol in the material acetone as possible. However, in order to remove a small amount of methanol from the material acetone, it is required to provide plural distillation columns having large number plates so that the system is enlarged, the economical cost is large and it is not practical. In consideration of these, the methanol content in the material acetone is usually 10 to 500 ppm by weight, preferably 30 to 500 ppm by weight, more preferably 50 to 300 ppm by weight. When the methanol content is within the above range, the practical operation which is prevented from deterioration of catalyst activity can be conducted without large load of acetone purification. As the separation system (20), there may be usually used a multi-stage distillation column. The separated and recovered phenol is usually purified together with fresh phenol in the purifier (20a), and then stored in the storage tank (22) for clean phenol and used for rinsing the below-mentioned crystal adduct. In the purifier (20a), isopropyl phenol is purged out of the system by distillation, etc. When the isopropyl phenol is purged out of the system by distillation, there may be used such a method in which isopropyl phenol contained in phenol is purged together with heavy substances contained in phenol fed from outside, from a bottom of the purifier (20a), for example, by conducting the distillation at a temperature of 150 to 190°C under an absolute pressure of 300 to 760 mmHg. In the bisphenol A separation step, a material flow containing bisphenol A as a main component is separated from the bisphenol A-containing component obtained in the low-boiling component separation step. The material flow may be separated by using any suitable known methods without particular limitations. The "material flow containing bisphenol A as a main component" used herein means a material flow comprising 50% by weight of bisphenol A. Namely, this means a material flow in the form of a solid, a liquid, a gas, a slurry or a cake containing bisphenol A as a main component such as a cake or a slurry of a crystal adduct of bisphenol A and phenol or a crystal of bisphenol A solely, a melt of bisphenol A and gasified bisphenol A. These material flows may also contain phenol or impurities such as reaction by-products. As the method for separating the material flow, there may be used, for example, such a method of separating the bisphenol A-containing component by crystallization into a material flow composed of a cake of the crystal adduct of bisphenol A and phenol, and a material flow containing, in addition to bisphenol A, reaction byproducts such as 2,4-bisphenol A and chroman (i.e., a so-called mother liquor). Examples of the other methods for separating the material flow may include the method of adding a third component such as water and acetone to the bisphenol A-containing solution to directly precipitate a crystal of bisphenol A without forming the adduct and then subjecting the resultant reaction mixture to solid/liquid separation to separate bisphenol A therefrom, the method of subjecting the bisphenol A-containing material flow to distillation under a high vacuum condition using a distillation column to allow bisphenol A to be distilled from a top of the column and separated therefrom, etc. In the followings, there are explained the crystallization step and the bisphenol A-recovering step conducted in the typical method in which the bisphenol A-containing component is subjected to crystallization and then solid/liquid separation to separate the component into the crystal adduct of bisphenol A and phenol and the mother liquor. (1) Crystallization Step The bottom liquid from which the low-boiling component is separated in the low-boiling component separation step (liquid component containing bisphenol A) is successively subjected to a crystallization step. In the crystallization step, the bottom liquid is cooled from a temperature of 70 to 140°C to a temperature of 35 to 60°C in the crystallizer (5) to crystallize the crystal adduct and obtain a slurry containing the crystal adduct. The thus obtained slurry is fed to the solid/liquid separator (6) and subjected to solid/liquid separation treatment therein. As the crystallizer (5), there may be usually employed a crystallization vessel equipped with one or plural operation-switchable external coolers. In the case where a plurality of external coolers are operated while changing- over the operation therebetween, the non-operated external cooler is switched to start its operation after dissolving crystals adhered to an inside thereof under heating, thereby enabling a continuous operation of the crystallization step while maintaining a high performance thereof. Meanwhile, upon changing-over the operation between the external coolers, crystallization characteristics in the crystallization vessel tend to be varied, so that the amount of the mother liquor separated in the solid/liquid separator (6) also tends to be changed. In order to prevent occurrence of such a change in amount of the mother liquor fed from the line (15) to the line (1), a part of the mother liquor may be usually bypassed to a downstream side of the reactor (2) through the line (16). In the case where a crystallization vessel equipped with a jacketed cooler is used as the crystallizer (5), a scraper for removing crystals adhered to a heat transfer surface thereof is preferably fitted to the crystallization vessel. (2) Bisphenol A Recovering Step The crystal adduct recovered in the solid/liquid separator (6) is dissolved again in phenol in the re-dissolver (7), re-crystallized in the re-crystallizer (8) to enhance a purity thereof, and then subjected to solid/liquid separation and rinsed with clean phenol in the solid/liquid separation and rinsing system (9) constituted from a centrifugal separator, etc. The thus rinsed crystal adduct is then delivered to the crystal adduct decomposition system (11). Meanwhile, a large part of the liquid component separated in the solid/liquid separation and rinsing system (9) and the rinsing waste solution can be used as phenol for re-dissolution of the crystal adduct in the re-dissolver (7) as well as a rinsing solution to be fed to the solid/liquid separator (6). A part of the liquid component separated in the solid/liquid separation and rinsing system (9) is circulated together with the recycled mother liquor to the tank (14). In the crystal adduct decomposition apparatus (11), there may be usually used such a method in which the crystal adduct is melted under heating at a temperature of 100 to 160°C, and the thus obtained molten solution is distilled to remove a large part of phenol therefrom. In the purifier (12), there may be usually used such a method in which the reaction product is subjected to steam stripping, etc., to remove residual phenol therefrom and obtain purified bisphenol A. These methods are described, for example, in Japanese Patent Application Laid-open (KOKAI) Nos. 2-28126 and 63-132850, etc. The "mother liquor" used herein means a liquid obtained by removing the material flow containing bisphenol A as a main component from the bisphenol A-containing component in the bisphenol A separation step, for example, a liquid obtained by separating the adduct of bisphenol A and phenol therefrom by the solid/liquid separator (6) after crystallizing the adduct. A part (for example, 85 to 96%) of the liquid component (mother liquor) obtained by solid/liquid separation in the solid/liquid separator (6) is circulated to an upstream side of the reaction step through the line (13) and then the line (15), and/or circulated to a downstream side of the reaction step through the line (16). In the process of the present invention, although the mother liquor recycling step is not essential, when the mother liquor recycling step is used in combination with the below-mentioned light component separation step, it is possible to efficiently remove heavy substances and continuously conduct a stable operation of the process. More specifically, the mother liquor obtained from the solid/liquid separator (6) usually comprises 65 to 85% by weight of phenol, 10 to 20% by weight of bisphenol A and 5 to 15% by weight of by-products such as 2,4'-isomer. Thus, the mother liquor contains a large amount of impurities such as 2,4'-isomer. In order to prevent these impurities from being accumulated in the process, a part of the mother liquor obtained from the solid/liquid separator (6) is fed to the below-mentioned light component separation step. In this case, the operation of a pump (not shown) for feeding the mother liquor from the tank (14) to the line (15) may be controlled such that the molar ratio of phenol contained in the mother liquor to a sum of fresh acetone (a) fed to the line (1) and the recovered acetone (b) fed through the line (21) (a + b) (phenol/acetone) lies within the above-mentioned constant mixing ratio. In the light component separation step, at least a part of the mother liquor separated in the previous step is subjected to heat treatment and distillation in the presence of an alkali and separated into a light component and a heavy component. More specifically, at least a part of the mother liquor is branched from the line (13) to the impurity removal line (13') and fed to the alkali decomposition column (13a). In the alkali decomposition column (13a), the mother liquor is subjected to heat treatment and distillation in the presence of an alkali and separated into a light component and a heavy component. Preferably, at least a part of the thus branched mother liquor is fed to the mother liquor concentration column (13c) and distilled thereby distilling out a large part of isopropyl phenol together with a part of phenol therefrom from the column top and/or column side as a light component liquid, and then heated in the presence of an alkali substance to decompose bisphenol A and isomers thereof contained in the mother liquor into phenol and isopropenyl phenol. Hereinafter, a case obtaining the light component liquid from the top of column is explained as an example embodiment. The phenol recovered from a top of the mother liquor concentration column (13c) contains a large amount of isopropyl phenol. Therefore, at least a part of the solution containing the recovered phenol is branched and purged out of the system through the line (13d), or at least a part of the solution branched is fed to the purifier (20a) to purify and remove isopropyl phenol therefrom, thereby enabling the concentration of isopropyl phenol contained in the reaction solution to be well controlled. When conducting the present step in combination with the separation procedure for separating isopropyl phenol in the distillation column (4), the concentration of isopropyl phenol can be more efficiently controlled. In the phenol recovered from the top of mother liquor concentration column (13c), the phenol which is not purged to the out of system through the line (13d) is used for quenching the top of alkali decomposition column (13a). The isopropyl phenol content contained in the phenol purged to the out of system through the line (13d) is preferably not less than 5% by weight, more preferably 5 to 20% by weight, especially preferably 7 to 15% by weight of isopropyl phenol provided to the mother liquor concentration column (13c). When the content of withdrawn isopropyl phenol is less than the above range, there is a possibility that it is difficult to maintain the content of isopropyl phenol contained in the reaction solution in the reaction step to the prescribed range. Further, in order to increase the amount of phenol purged to the out of system through the line (13d), it is necessary to increase the amount of purged phenol to lead the loss of phenol. Especially, in case where the phenol is not purged to the out of system through the line (13d) is used for quenching the top of alkali decomposition column (13a), there is a possibility that the amount of phenol used for the quenching is decreased so that the quenching is insufficient, and this is not preferred. Further, when the amount of phenol used for the quenching is too small, the concentration of isopropenyl phenol in the light component obtained from the alkali decomposition column (13a) as described hereinafter is increased. When the concentration of isopropenyl phenol is high, there is a possibility that the dimerization of isopropenyl phenol occurs and the selectivity in the recombination reaction step as described hereinafter is deteriorated, and this is not preferred. In the mother liquor concentration column (13c), by increasing the amount of phenol recovered on the top side of the column or decreasing the reflux ratio thereof, a ratio of the amount of isopropyl phenol distilled out and recovered on the top side of the column to the amount of the same substance fed to the column is controlled to usually not less than 0.6 and preferably not less than 0.8. The ratio of the distillated solution to be branched and discharged is preferably not less than 0.1. In this case, when it is required to control the ratio between phenol and isopropenyl phenol owing to reduction in amount of phenol fed to the recombination reactor (13b) in the subsequent step, such a procedure of feeding phenol from outside may be conducted in combination with the control procedure. The above decomposition reaction is preferably performed by a reaction distillation method in which the mother liquor is fed together with the alkali substance to the alkali decomposition column (13a) and heated to a temperature of 200 to 300°C to decompose bisphenol A and isomers thereof contained therein. As the alkali substance, there may be used any suitable known alkali substances, e.g., hydroxides, carbonates and phenol salts of alkali metals such as sodium and potassium, hydroxides and phenol salts of alkali earth metals such as magnesium and calcium, etc. These alkali substances are preferably fed in the form of an aqueous solution thereof, etc. The decomposition rate of bisphenol A and isomers thereof in the alkali decomposition step is usually not less than 30%, preferably not less than 50% and more preferably not less than 60%. The above mother liquor may be previously concentrated and then subjected to the decomposition reaction as described in Japanese Patent Application Laid-open (KOKAI) No. 10-218814(1998). Alternatively, the mother liquor may also be directly subjected to the decomposition reaction without the concentration procedure. This is because even though the mother liquor is directly subjected to the decomposition reaction, phenol contained in the mother liquor is immediately evaporated therefrom, resulting in concentration of the mother liquor. In the alkali decomposition column (13a), the mother liquor to be treated for removing impurities therefrom is not only subjected to alkali decomposition, but also separated into a light component containing phenol and isopropenyl phenol and a heavy component containing tar, etc. The thus separated heavy component is discharged out of the system. The above light component is subjected to recombination reaction treatment in the recombination reactor (13b). More specifically, the above isopropenyl phenol is a polymerizable substance and readily forms a polymer thereof. Therefore, when the light component containing isopropenyl phenol is directly fed to the mother liquor recycling line (13), there tends to arise such a problem that the resultant bisphenol A product is undesirably colored by the polymer. For this reason, the light component (phenol and isopropenyl phenol) distilled off from the top of the alkali decomposition column (13a) is immediately condensed and fed to the recombination reactor (13b) to conduct a recombination reaction thereof in the presence of an acid ion exchange resin, thereby preventing production of the polymer as a coloring component. The recombination reaction is usually conducted at a temperature of 50 to 85°C. As the acid ion exchange resin used in the recombination reaction, there may be usually used strong acid cation exchange resins such as sulfonic acid-type cation exchange resins. Meanwhile, the acid ion exchange resin used in the recombination reaction may be the same as the sulfonic acid-type strong acid cation exchange resin used in the reaction step which is partially neutralized with the sulfur-containing compound. In the recombination reaction, there tends to occur dimerization of isopropenyl phenol as a side reaction. Therefore, the molar ratio of phenol to isopropenyl phenol fed to the recombination reactor (13b) is preferably controlled to not less than 40, thereby considerably preventing occurrence of the side reaction. In order to control the molar ratio of phenol to isopropenyl phenol to not less than 40, an additional amount of phenol (such as phenol used for rinsing the crystal in the crystallization step) is preferably added from outside. The recombination reaction solution (solution of bisphenol A produced) obtained in the above step is returned to the mother liquor recycling line (13). The process for producing bisphenol A according to the present invention is characterized by controlling the content of isopropyl phenol in the reaction solution obtained in the reaction step to not more than 4% by weight, preferably not more than 2% by weight, more preferably not more than 1% by weight and still more preferably not more than 0.5% by weight. It has been found by the present inventors that isopropyl phenol (including o-, m- and p-isomers and a mixture thereof) contained as an impurity in the reaction solution obtained in the reaction step is a substance which accelerates deterioration of catalytic activity of the acid ion exchange resin catalyst used in the reaction step. Further, it has also been found that isopropyl phenol is by-produced upon the heat treatment conducted in the presence of the alkali in the impurity treatment step. Therefore, in the process for producing bisphenol A which includes the above impurity treatment step, the inclusion of isopropyl phenol is inevitably caused. The more frequently the impurity treatment is repeated, the more the isopropyl phenol is accumulated in the system. For this reason, in the present invention, the content of isopropyl phenol in the reaction solution obtained in the reaction step is controlled to not more than 4% by weight, so that the acid ion exchange resin catalyst used in the reaction step can be prevented from being deteriorated in catalytic activity. The concentration of isopropyl phenol in the reaction solution obtained in the reaction step may be determined based on the value measured at any of an inlet, an inside and an outlet of the reactor. However, in order to prevent deterioration of the ion exchange resin, the concentration of isopropyl phenol is preferably controlled based on the value measured at an inlet of the reactor. As the method for controlling the content of isopropyl phenol in the reaction solution obtained in the reaction step, there is preferably used such a method of separating 5 to 20% by weight and preferably 5 to 15% by weight of the mother liquor fed to the light component separation step as a heavy component. This method is based on the present inventors' finding that the amount of an alkyl phenol produced in the system has a correlation with the amount of the heavy component (tar component) discharged from the alkali decomposition column (13a). The conditions for controlling an amount of the heavy component discharged include a residence time of the mother liquor, an alkali concentration, a decomposition temperature, a degree of pressure reduction, etc., in the alkali decomposition column (13a). The amount of the heavy component discharged may be controlled to the above-specified range by adequately selecting and combining these conditions. More specifically, the residence time of the mother liquor in the alkali decomposition column (13a) is usually 1 to 20 hr and preferably 2 to 10 hr. The alkali concentration (concentration of alkali contained in the heavy component discharged out of the system in the light component separation step) is usually 100 to 4000 ppm by weight and preferably 200 to 2000 ppm by weight in terms of metallic sodium. The decomposition temperature is usually 170 to 300°C and preferably 200 to 250°C. The degree of pressure reduction is usually 10 to 100 Torr and preferably 20 to 50 Torr. Also, the content of isopropyl phenol in the reaction solution being present in the reaction step may also be controlled by the method of adjusting a rate of separation of the mother liquor branched from the line (13) to the impurity removal line (13'), the method of changing a ratio of phenol distilled off from the mother liquor concentration column (13c) before the addition of alkali because isopropyl phenol is withdrawn together with the phenol, or the method of controlling the amount of the reaction solution withdrawn from the line (13d) to the purifier (20a). In particular, among these methods, the method of controlling the amount of the reaction solution withdrawn from the line (13d) to the purifier (20a) is preferred since isopropyl phenol can be removed more efficiently. In addition, the content of isopropyl phenol in the reaction solution obtained in the reaction step may also be controlled by the method of adjusting an amount of the recombination reaction solution fed to the recombination reactor (13b) to the line (13) or the method of adjusting an amount of fresh phenol contained in the raw phenol. Further, although isopropyl phenol may be removed by distillation from the light component obtained in the alkali decomposition column (13a), the removal of isopropyl phenol is preferably conducted by the method of controlling operation conditions of the alkali decomposition column (13a) in view of simplicity thereof. Meanwhile, in the production process of the present invention, in addition to the above procedures, hydrated phenol generated in the dehydration procedure upon initiation of using the reaction catalyst may be fed little by little to the distillation columns disposed within the process during the operation thereof to remove water therefrom for reusing the thus dehydrated phenol. The above procedure is preferable since the obtained phenol can be reused as the raw phenol. As described above, in the preferred embodiment of the present invention, acetone is fed together with a largely excessive amount of phenol to the reactor filled with the sulfonic acid-type ion exchange resin modified with an aminothiol compound to allow the condensation reaction therebetween to proceed, thereby producing bisphenol A. In this case, when the reaction for production of bisphenol A is conducted for a long period of time, the sulfonic acid-type ion exchange resin used therein as the catalyst tends to lose its effects owing to deterioration of the aminothiol compound acting as a co-catalyst, or tends to be deteriorated in catalytic activity owing to adhesion of heavy substances such as by-produced tar to the surface of the ion exchange resin which results in covering the surface of the catalyst therewith. For this reason, it is required to periodically withdrawn the catalyst from the reactor and replace the catalyst with new one. The catalyst to be added to the reactor upon the replacement may be a fresh catalyst newly produced, or the sulfonic acid-type ion exchange resin catalyst obtained by treating the used catalyst withdrawn from the reactor which is deteriorated in catalytic activity, with an acid, etc., to remove tar and the deteriorated co-catalyst from the surface thereof, and then immersing the thus treated catalyst again in a solution containing an aminothiol compound to modify the resin with the aminothiol compound. The ion exchange resin catalyst may be usually charged into the reactor frequently in a water-swelled state. Therefore, the ion exchange resin catalyst filled in the reactor is preferably subjected to dehydration procedure before initiating the reaction for production of bisphenol A. The dehydration procedure of the ion exchange resin catalyst is usually performed by roughly removing water from the catalyst and then contacting the catalyst with phenol. The water-swelled ion exchange resin tends to undergo rapid reduction of its volume upon the dehydration procedure, resulting in the risk of breakage of the ion exchange resin itself. Therefore, the initial dehydration procedure is preferably conducted using a mixed solution containing phenol and water at a mixing ratio of about 9:1. By such a method, the ion exchange resin can be prevented from suffering from rapid reduction of its volume and, therefore, breakage thereof. As the method of contacting the catalyst with phenol upon the dehydration procedure, there may be used a batch method in which the catalyst is immersed in phenol in a batch manner, or a continuous method in which phenol is continuously flowed through the catalyst. The phenol used in the dehydration procedure may be either purified phenol or the filtrate (mother liquor) generated in the solid/liquid separation step which is circulated and reused through the process for production of bisphenol A. The phenol used in the dehydration procedure contains water, acid components dissociated from the sulfonic acid-type ion exchange resin, etc. Therefore, the phenol is preferably purified for reuse. The method of purifying the phenol used in the dehydration procedure is not particularly limited, and there may be used, for example, the method of purifying the phenol while returning the phenol little by little into the process upon restarting the operation after storing the phenol in the tank, etc., or the method of purifying the phenol using a special distillation column therefor, etc. Also, in the case where two or more reactors are operated in parallel, while operating one or more reactors, the other one or more non-operated reactors may be subjected to dehydration treatment of phenol at the same time, and the thus dehydrated but unpurified phenol generated in the treatment is returned to the process. When returning the unpurified phenol to the process, the unpurified phenol may be fed to the distillation column used in the low-boiling component separation step for removing unreacted acetone, water, etc., which is disposed on a downstream side of the reactor, or may be fed to an upstream side of the impurity removal treatment step for purifying the phenol. Also, these procedures may be conducted in combination with each other. In general, since there may be present such a risk that the acid components contained in the unpurified phenol is mixed in the bisphenol A product, the unpurified phenol is preferably fed to the upstream side of the impurity removal treatment step. However, if such a phenol having a large water content which is generated at an initial stage of the dehydration procedure is fed to the impurity removal treatment step, water tends to be mixed in the alkali decomposition column used for the impurity removal treatment, so that it may be difficult to suitably conduct the alkali decomposition step operated under high-temperature (not less than 200°C) and high-vacuum pressure (not more than 80 mmHg) conditions, because the high-vacuum condition in the step is no longer kept owing to a vapor pressure of water mixed therein. For this reason, the phenol having a large water content which is generated at an initial stage of the dehydration procedure is preferably first treated in the low-boiling component separation step, and then fed to the upstream side of the impurity removal treatment step by switching the operation after reducing the water content in the phenol. The thus purified phenol may be used as phenol for rinsing the crystal adduct obtained in the solid/liquid separation step. EXAMPLES The present invention is described in more detail by the following examples. However, these examples are only illustrative and not intended to limit the scope of the present invention. (1) Analyzing Method for Acetone The analysis for acetone was conducted using a gas chromatograph "GC-14B" manufactured by Shimadzu Corporation and equipped with a fused silica capillary column and a TCD detector. (2) Analyzing Method for Isopropyl Phenol The analysis for isopropyl phenol was conducted using a gas chromatograph "GC-14B" manufactured by Shimadzu Corporation and equipped with a fused silica capillary column and a FID detector. (3) Conversion of acetone The conversion of acetone was calculated from the following equation. Conversion of acetone (%) = [{(Feed amount of material acetone (kg/h)) - (Acetone concentration in the line 3 (% by weight)) X (Flow rate of liquid in the line 3 (kg/h))}/(Feed amount of material acetone (kg/h))] X 100 Example 1: Using a pilot plant shown in Fig. 2, bisphenol A was continuously produced. A reactor (2) having a diameter of 660 mm was disposed in the reaction step, and filled with 340 L of an ion exchange resin as a catalyst which was obtained by modifying 20 mol% of sulfonic groups contained in a sulfonic acid-type cation exchange resin "DIA-ION SK-104H" produced by Mitsubishi Chemical Corporation, with 2-(4-pyridyl)ethane thiol. A mother liquor fed through a line (15) and a distillation-purified phenol/acetone mixed solution (composed of 82% by weight of phenol, 4% by weight of acetone, 8% by weight of bisphenol A and 6% by weight of other components, and the concentration of methanol in the acetone was 100 ppm by weight) were fed at a rate of 400 kg/hr, and reacted with each other at 65°C. The obtained reaction solution was fed through a line (3) to a distillation column (4) packed with a filler such that the number of theoretical plates was 7, and a distillate was withdrawn from a top of the column at a rate of 62 kg/hr. In this time, the amount of isopropyl phenol in the distillate withdrawn from the top of the distillation column (4) was 1.6% by weight of the feed amount. The column bottom liquid in the distillation column (4) was fed to a crystallization column (5) and a crystal adduct of bisphenol A and phenol was precipitated. The thus obtained crystal adduct was fed together with the purified phenol (120 kg/h) used for rinsing the crystal adduct to a solid/liquid separation apparatus (6) and separated into a solid (78 kg/hr) and a mother liquor (385 kg/hr). The solution flowed through a line (13') was fed to a mother liquor concentration column (13c) packed with a filler such that the number of theoretical plates was 3, and a distillate was withdrawn from a top of the column at a rate of 29 kg/hr. About 11% of the resultant solution was branched and discharge to the out of system through the line (13d) thereby remove isopropyl phenol therefrom. In this time, the amount of isopropyl phenol discharged to the out of system was 10% of the amount fed to the mother liquor concentration column (13c). 347 kg/hr of the mother liquor (90% by weight based on a total weight of the mother liquor) was directly fed again to the reaction step through a line (13), whereas remaining 38 kg/hr of the mother liquor (10% by weight based on a total weight of the mother liquor) was subjected to the treatment in the mother liquor concentration column (13c) and the column top liquid and column bottom liquid which were not discharged to the out of system were fed to an alkali decomposition column (13a). In the alkali decomposition column (13a), after adding a 25 wt% sodium hydroxide aqueous solution thereto at a rate of 0.22 kg/hr, the mother liquor was subjected to alkali decomposition reaction and distillation for a residence time of 4 hr at 210°C under a pressure of 40 Torr to separate 3.8 kg/hr of a heavy component (purging rate of heavy component: 10% by weight) therefrom. The resultant light component from which the heavy component (tar component) was removed, was fed to a recombination reactor (13b) maintained at 65°C and packed with the sulfonic acid-type cation exchange resin "DIA-ION SK-104H" produced by Mitsubishi Chemical Corporation, which was not modified with a sulfur-containing amine compound, to react isopropenyl phenol produced by the alkali decomposition reaction with phenol, thereby producing bisphenol A. Thereafter, the resultant reaction solution was fed again to the reaction system through the line (13). According to the above procedure, the process was continuously operated for 4000 hr. After the elapse of 250 hr from initiation of the operation, the amount of impurities within the reaction system was stabilized, and no change in amount of impurities within the reaction system was caused until 4000 hr elapsed. At this time, the concentration of p-isopropyl phenol in the raw material fed to the reactor (2) was 0.3% by weight. The amount of isopropyl phenol withdrawn from the top of distillation column (4) was 1.5% by weight of the fed isopropyl phenol and the amount of isopropyl phenol withdrawn to the out of system through the line (13d) was 10% by weight of isopropyl phenol fed to the mother liquor concentration column (13c). In addition, the conversion of acetone was 98.5% after the elapse of 1 hr from initiation of feeding acetone to the reaction system, and thereafter reduced to 93.1% after the process was operated for 4000 hr. Example 2; The same procedure as defined in Example 1 was conducted except that a part of the distillate withdrawn from the mother liquor concentration column (13c) was not discharged to the out of system through the line (13d). As a result, it was confirmed that the concentration of isopropyl phenol in the raw material fed to the reactor (2) was stabilized at 0.8% by weight. The conversion of acetone was 98.5% after the elapse of 1 hr from initiation of feeding acetone to the reaction system, and thereafter reduced to 91.8% after the process was operated for 4000 hr. Example 3; The same procedure as defined in Example 1 was conducted except that isopropyl phenol was not discharged to the out of system from the distillate of distillation column (4). As a result, it was confirmed that the concentration of isopropyl phenol in the raw material fed to the reactor (2) was stabilized at 1.2% by weight. The conversion of acetone was 98.5% after the elapse of 1 hr from initiation of feeding acetone to the reaction system, and thereafter reduced to 90.4% after the process was operated for 4000 hr. Example 4; The same procedure as defined in Example 1 was conducted except that methanol having acetone in amount of 650 ppm by weight was used as the reaction material. As a result, it was confirmed that the concentration of isopropyl phenol in the raw material fed to the reactor (2) was stabilized at 0.4% by weight. The conversion of acetone was 98.0% after the elapse of 1 hr from initiation of feeding acetone to the reaction system, and thereafter reduced to 88.6% after the process was operated for 4000 hr. Example 5: The same procedure as defined in Example 1 was conducted except that the temperature of alkali decomposition column (13a) in the low-boiling component separation step was 250°C, 0.9 kg/hr of a heavy component was separated (purging rate of heavy component: 2.3% by weight), the amount of phenol purged to the out of system through the line (13d) from the top of mother liquor concentration column (13c) was 20% by weight of amount fed to the mother liquor concentration column (13c), and the amount of isopropyl phenol withdrawn from the top of distillation column (4) was 2.5% by weight of amount fed to the distillation column (4). As a result, it was confirmed that the concentration of isopropyl phenol in the raw material fed to the reactor (2) was stabilized at 2.1% by weight. The conversion of acetone was 98.5% after the elapse of 1 hr from initiation of feeding acetone to the reaction system, and thereafter reduced to 88.3% after the process was operated for 4000 hr. Comparative Example 1; The same procedure as defined in Example 1 was conducted except that the conditions for reaction distillation by the alkali decomposition were changed, and the reaction distillation procedure was conducted at 250°C. Since the alkali decomposition temperature was higher than that used in Example 1, the alkali decomposition more rapidly proceeded as compared to that in Example 1, so that the amount of the heavy component withdrawn from the bottom of the column was reduced to 0.8 kg/hr (purging rate of heavy component: 2.3% by weight). After the elapse of 250 hr from initiation of the operation, the amount of impurities within the reaction system was stabilized, and no change in amount of impurities was caused until 4000 hr elapsed. At this time, the concentration of p-isopropyl phenol in the raw material fed to the reactor (2) was 6.3% by weight. In addition, the conversion of acetone was 98.5% after the elapse of 1 hr from initiation of feeding acetone to the reaction system, and thereafter largely reduced to 80.9% after the process was operated for 4000 hr. As a result, it was confirmed that the sulfonic acid-type cation exchange resin catalyst was considerably deteriorated. Comparative Example 2; The same procedure as defined in Comparative Example 1 was conducted except that methanol having acetone in amount of 650 ppm by weight was used as the reaction material. As a result, it was confirmed that the concentration of isopropyl phenol in the raw material fed to the reactor (2) was stabilized at 6.3% by weight. The conversion of acetone was 97.5% after the elapse of 1 hr from initiation of feeding acetone to the reaction system, and thereafter reduced to 71.1% after the process was operated for 4000 hr. Table 1 (Table Removed) Although the present invention is described above with respect to embodiments which are considered to be most practical and preferable at the present time, the present invention is not limited to these embodiments, and various changes and modifications will be appropriately made within the scope of claims and a whole of a specification of this application unless departing from the subject matter and concept of the present invention, and it should be construed that the changes and modifications are involved within a technical range of the present invention. WHAT IS CLAIMED IS; 1. A process for producing bisphenol A comprising at least a reaction step of reacting acetone and phenol as raw materials in the presence of an acid ion exchange resin catalyst to obtain a reaction mixture containing bisphenol A and phenol; a low-boiling component separation step of separating the reaction mixture into a bisphenol A-containing component and a low-boiling component containing unreacted acetone; a bisphenol A separation step of separating the bisphenol A-containing component into a material flow containing bisphenol A as a main component and a mother liquor containing phenol as main components; a light component separation step of subjecting at least a part of the thus separated mother liquor to heat treatment and distillation in the presence of an alkali to separate the mother liquor into a light component and a heavy component; a recombination reaction step of treating the thus separated light component in the presence of an acid ion exchange resin catalyst to allow phenol and isopropenyl phenol contained in the light component to be recombined with each other and converted into bisphenol A; and a recombination reaction solution recycling step of recycling a recombination reaction solution obtained in the recombination reaction step to the above reaction step, in which a content of isopropyl phenol in a reaction solution being present in the reaction step is controlled to not more than 4% by weight. 2. A process according to claim 1, wherein the acid ion exchange resin catalyst used in the reaction step is a modified acid ion exchange resin catalyst obtained by modifying an acid ion exchange resin with an alkyl aminothiol. 3. A process according to claim 2, wherein the alkyl aminothiol is 2-aminoethane thiol and/or 2-(4-pyridyl)ethane thiol. 4. A process according to any one of claims 1 to 3, wherein in the light component separation step, the heavy component is separated in an amount corresponding to 5 to 20% by weight of the mother liquor fed thereto. 5. A process according to any one of claims 1 to 4, wherein in the light component separation step there is a mother liquor concentration column prior to the heat treatment, not less than 5% by weight of isopropyl phenol provided to the mother liquor concentration column is withdrawn from the light component separation step as a purged product when at least a part of the light component distilled solution obtained from the mother liquor concentration column is discharged from the light component separation step as the purged product. 6. A process according to any one of claims 1 to 5, wherein in the low-boiling component separation step, not less than 0.8% by weight of isopropyl phenol fed thereto is separated together with the low-boiling component. 7. A process according to any one of claims 1 to 6, wherein the content of methanol contained in the acetone as the material provided to the reaction step is 10 to 500 ppm by weight. 8. A process according to claim 1, which is substantially as hereinbefore described with reference to any one of the foregoing examples and the accompanying drawings. 9. Bisphenol A produced according to the process of any one of claims 1 to 8.

Full Text

TITLE OF INVENTION
PROCESS FOR PRODUCING BISPHENOL A
FIELD OF THE INVENTION
The present invention relates to a process for producing bisphenol A, and more particularly, to a process for producing bisphenol A including steps of treating a part of a mother liquor separated in a bisphenol A separation step to remove impurities therefrom and then recycling the thus treated mother liquor to the reaction system, which process is capable of preventing a bisphenol A production catalyst used therein from being deteriorated in catalytic activity.
RELATED ARTS
Bisphenol A has been usually produced by using phenol and acetone as raw materials. As a typical method for production of bisphenol A, there is known the method of reacting the above raw materials with each other in the presence of an acid catalyst such as cation exchange resins. However, the reaction mixture obtained by the above conventional method contains, in addition to the aimed bisphenol A, unreacted phenol, unreacted acetone, water produced by the reaction, and reaction by-products such as colored substances. The reaction by-products are usually
separated from the reaction mixture by a distillation method. In the distillation method, the reaction mixture is distilled within a distillation column at a temperature lower than a boiling point of phenol to recover low-boiling components such as unreacted acetone, water produced by the reaction and a part of unreacted phenol from a top of the distillation column and obtain a bisphenol A-containing component from a bottom thereof. Then, the bisphenol A-containing component obtained from the bottom of the distillation column is separated into a material flow containing bisphenol A as a main component and a mother liquor containing phenol and reaction impurities as main components.
A large part of the mother liquor is recycled to the reaction system. However, in order to prevent isomers or high-boiling impurities from being accumulated in the reaction system, a part of the mother liquor is usually withdrawn from the reaction system to remove the impurities therefrom. The impurities are generally removed from the mother liquor by the method of subjecting the mother liquor to heating reaction by adding an alkali thereto to decompose bisphenol A and isomers thereof into phenol and isopropenyl phenol. In this case, a part of the other impurities are converted into heavy components and discharged as tar out of the reaction system. The decomposition reaction is usually
conducted by a reaction distillation method, and phenol and isopropenyl phenol produced by the decomposition reaction are supplied to a recombination reactor filled with an acid ion exchange resin catalyst to produce bisphenol A therefrom (refer to Japanese Patent Publication (KOKOKU) No. 49-48319 and Japanese Patent Application Laid-open (KOKAI) Nos. 1-230538 and 5-331088). The reaction solution discharged from the recombination reactor is recycled to the reaction system together with the mother liquor subjected to no removal of impurities therefrom.
However, even though a part of the mother liquor is withdrawn from the reaction system and subjected to alkali heat treatment to remove impurities therefrom, the acid ion exchange resin catalyst used in the reaction step tends to be deteriorated, thereby failing to conduct a stable production of bisphenol A for a long period of time.
Further, as a result of study for the deterioration of catalyst activity by isopropyl phenol, it has been found that methanol contained in the material acetone promotes the deterioration of catalyst activity by isopropyl phenol. In the material acetone, methanol is contained as an impurity and it is known that the activity of aminothiol carried-type ion exchange resin catalyst is deteriorated by the methanol (refer to Japanese Patent Application Laid-Opens (KOKAI) No. 6-92889, 6-25047 or the like). The
promotion effect of deterioration of catalyst activity together with alkyl phenol such as isopropyl phenol was not known.
DISCLOSURE OF THE INVENTION
PROBLEM TO BE SOLVED BY THE INVENTION
The present invention has been made in view of the above conventional problems. An object of the present invention is to provide a process for producing bisphenol A including steps of treating at least a part of a mother liquor obtained in a bisphenol A separation step to remove impurities therefrom and then recycling the thus treated mother liquor to the reaction system, which is capable of preventing a bisphenol A production catalyst used therein from being deteriorated in catalytic activity.
MEANS FOR SOLVING PROBLEM
As a result of the present inventors' earnest study for solving the above conventional problems, it has been found that isopropyl phenol by-produced upon subjecting the mother liquor to heat treatment in the presence of an alkali to remove impurities therefrom, is a substance which promotes deterioration of catalytic activity of the acid ion exchange resin catalyst used in the reaction step, and, therefore, when an amount of isopropyl phenol contained in the reaction
solution being present in the reaction step is controlled to a specific range, the acid ion exchange resin catalyst used in the reaction step can be prevented from being deteriorated in catalytic activity thereof. The present invention has been attained on the basis of the above finding.
That is, to accomplish the aim, in an aspect of the present invention, there is provided a process for producing bisphenol A comprising at least a reaction step of reacting acetone and phenol as raw materials in the presence of an acid ion exchange resin catalyst to obtain a reaction mixture containing bisphenol A and phenol; a low-boiling component separation step of separating the reaction mixture into a bisphenol A-containing component and a low-boiling component containing unreacted acetone; a bisphenol A separation step of separating the bisphenol A-containing component into a material flow containing bisphenol A as a main component and a mother liquor containing phenol as main components; a light component separation step of subjecting at least a part of the thus separated mother liquor to heat treatment and distillation in the presence of an alkali to separate the mother liquor into a light component and a heavy component; a recombination reaction step of treating the thus separated light component in the presence of an acid ion exchange resin catalyst to allow phenol and
isopropenyl phenol contained in the light component to be recombined with each other and converted into bisphenol A; and a recombination reaction solution recycling step of recycling a recombination reaction solution obtained in the recombination reaction step to the above reaction step, in which a content of isopropyl phenol in a reaction solution being present in the reaction step is controlled to not more than 4% by weight.
EFFECT OF THE INVENTION
In the process for producing bisphenol A according to the present invention which process includes steps of treating at least a part of a mother liquor obtained in a bisphenol A separation step to remove impurities therefrom and then recycling the thus treated mother liquor to the reaction system, it is possible to prevent a bisphenol A production catalyst used therein from being deteriorated in catalytic activity.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 is a flow diagram showing the process for producing bisphenol A according to the present invention.
Fig. 2 is a flow diagram showing a pilot plant used in Example I.
EXPLANATION OF REFERENCE NUMERALS
la: Methanol removal apparatus; 2: Reactor; 4: Distillation column; 5: Crystallizer; 6: Solid/liquid separator; 7: Re-dissolver; 8: Re-crystallizer; 9: Solid/liquid separation and rinsing system; 11: Crystal adduct decomposition apparatus; 12: Purifier; 13a: Alkali decomposition column; 13b: Recombination reactor; 13c: Mother liquor concentration column, 14: Tank; 20: Separation system; 20a: Purifier; 22: Phenol storage tank
PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION
The present invention is described in detail hereinunder. The following descriptions are merely concerned with a typical example of preferred embodiments of the present invention, and it is therefore not intended to limit the scope of the present invention thereto. The process for producing bisphenol A according to the present invention includes at least a reaction step of reacting acetone and phenol as raw materials in the presence of an acid ion exchange resin catalyst to obtain a reaction mixture containing bisphenol A and phenol; a low-boiling component separation step of separating the reaction mixture into a bisphenol A-containing component and a low-boiling component containing unreacted acetone; a bisphenol A separation step of separating the bisphenol A-containing
component into a material flow containing bisphenol A as a main component and a mother liquor containing phenol and reaction by-products as main components; a light component separation step of subjecting at least a part of the thus separated mother liquor to heat treatment and distillation in the presence of an alkali to separate the mother liquor into a light component and a heavy component; a recombination reaction step of treating the thus separated light component in the presence of an acid ion exchange resin catalyst to allow phenol and isopropenyl phenol contained in the light component to be recombined with each other and converted into bisphenol A; and a recombination reaction solution recycling step of recycling a recombination reaction solution obtained in the recombination reaction step to the above reaction step. Further, the process of the present invention may also include, if required, an acetone recycling step of separating and recovering unreacted acetone from the low-boiling component obtained in the low-boiling component separation step and recycling the thus recovered unreacted acetone to the reaction step, a mother liquor recycling step of recycling a part of the mother liquor separated to the reaction step without treating the mother liquor, etc.
First, for facilitated understanding of the present invention, the process for producing bisphenol A according

bo the present invention is generally described by referring to the flow diagram shown in Fig. 1. However, it should be noted that the production process of the present invention can be carried out in various embodiments.
Acetone and phenol as raw materials are fed to a reactor (2) through a line (1). A reaction mixture discharged from the reactor (2) is introduced into a distillation column (4) through a line (3). A low-boiling component containing acetone, water, phenol, etc., which is withdrawn from a top of the distillation column (4) is delivered to a separation system (20) where the low-boiling component is separated by distillation, etc., into acetone, water and phenol. The thus separated acetone is delivered to a methanol removing apparatus (la) as the below-mentioned purifier through a line (21) and a line (A). Water separated is withdrawn from the separation system (20) and discharged out of the system. The separated phenol is fed from the separation system (20) to the purifier (20a) and subjected to purification treatment therein, and then delivered to a phenol storage tank (22).
A bottom component in the distillation column (4) is delivered to a crystallizer (5) to crystallize a crystal adduct of bisphenol A and phenol therefrom. The crystal adduct is fed to a solid/liquid separator (6) and separated into a solid component and a liquid component, re-dissolved
in a re-dissolver (7), recrystallized in a recrystallizer (8), and then treated by a solid/liquid separation and rinsing system (9) constituted from a centrifugal separator, etc. In this case, the crystal adduct is rinsed (washed) with clean phenol fed from the tank (22). A rinsing waste water is delivered to the re-dissolver (7) through a line (10) (or fed to the solid/liquid separator (6) through a line (17) and used for rinsing the crystal adduct). The rinsed crystal adduct is fed to an adduct decomposition apparatus (11) where the crystal adduct is heated and decomposed into bisphenol A and phenol. The resultant bisphenol A is then treated in a purifier (12) to obtain a bisphenol A product. The phenol separated in the adduct decomposition apparatus (11) and the purifier (12) is delivered to the tank (22).
At least a part of the liquid (mother liquor) separated in the solid/liquid separator (6) is fed through an impurity removal line (13') to remove impurities therefrom. Upon the removal treatment of impurities, at least a part of the mother liquor is concentrated in the mother liquor concentration column (13c), and thereafter it is heat-treated in the presence of an alkali in an alkali decomposition column (13a), and then separated into a light component and a heavy component. The light component is fed to a recombination reactor (13b) and subjected to a
recombination reaction treatment, and returned to the line (13). Meanwhile, a part of the mother liquor may be delivered to a mother liquor tank (14) through the line (13) The mother liquor in the mother liquor tank (14) is delivered to the line (1) through a line (15), mixed with acetone and then fed to the reactor (2). Further, the mother liquor in the mother liquor tank (14) is also delivered to the line (3) through a line (16).
The amount of the mother liquor fed from the line (15) to the line (1) is controlled such that a ratio between acetone and phenol in a mixed solution composed of the mother liquor and acetone which is fed to the reactor (2), lies within a predetermined range. By controlling the ratio between acetone and phenol contained in the mixed solution to be fed to the reactor (2) to the predetermined range, a quality and a yield of a bisphenol A product are stabilized. Meanwhile, the mother liquor tank (14) serves as a buffer tank for equalizing an amount of the mother liquor recycled through the line (13).
Next, the respective steps of the process of the present invention are described in detail.

In the reaction conducted in the reactor (2), phenol and acetone as raw materials are reacted with each other under such a condition that phenol is used in a
stoichiometrically excessive amount relative to acetone. The molar ratio of phenol to acetone (phenol/acetone) is usually 3 to 30 and preferably 5 to 20. The reaction temperature is usually 50 to 100°C, and the reaction pressure is usually from normal pressure to 600 kPa (absolute pressure).
As the material acetone, there can be used one which is industrially available with no limitation. For instance, there can be used a purified acetone which is newly fed from the out of system, an acetone obtained by separating unreacted acetone in the low-boiling component separation step and further treating it in the acetone recycling step, and a mixture thereof.
As the catalyst, there is usually used a strong acid cation exchange resin such as sulfonic acid type cation exchange resins, and preferably a resin obtained by partially modifying the strong acid cation exchange resin with a sulfur-containing amine compound. In particular, when using such a resin obtained by partially modifying the strong acid cation exchange resin with a sulfur-containing amine compound such as 2-aminoethane thiol and 2-(4-pyridyl)ethane thiol, the effects of the present invention can be more remarkably exhibited. The degree of modification with the sulfur-containing amine compound may be controlled such that the sulfur-containing amine compound
is used in an amount of usually 2 to 30 mol% and preferably 5 to 20 mol% based on an acid group (sulfonic group) contained in the acid ion exchanger.
The condensation reaction between phenol and acetone is usually conducted by a fixed bed flow method or a suspension type batch method. In the fixed bed flow method, the raw mixture is fed to the reactor at an hourly liquid space velocity of usually 0.2 to 50/h. In the suspension type batch method, the amount of the acid ion exchange resin catalyst used varies depending upon reaction temperature and reaction time, and is usually 20 to 100% by weight. The reaction time is usually 0.5 to 5 hr.

The reaction mixture obtained in the reaction step is separated into a bisphenol A-containing component and a low-boiling component containing unreacted acetone. As the separating method, as described above by referring to the flow diagram shown in Fig. 1, there is used such a method in which using the distillation column (4), the reaction mixture obtained in the reaction step is subjected to distillation to separate the low-boiling component containing unreacted acetone from a top of the distillation column. The bottom liquid in the distillation column is a liquid component containing bisphenol A. As the distillation column, there may be used known distillation
columns. When the distillation is conducted under normal pressure, the distillation temperature is not higher than a boiling point of phenol, and the distillation procedure is preferably conducted under reduced pressure. The distillation under reduced pressure is usually conducted at a temperature of 50 to 150°C under a pressure of 50 to 300 mmHg. The distillation procedure is preferably conducted under such a condition that a predetermined amount of unreacted phenol contained in the reaction mixture is withdrawn from a bottom of the distillation column to form an adduct with bisphenol A in the subsequent crystallization step. The component separated from the top of the distillation column (4) contains unreacted acetone, water, methanol and isopropyl phenol as impurities, unreacted phenol, etc. By adjusting an amount of the isopropyl phenol withdrawn from the top of the column, the concentration of the isopropyl phenol contained in the reaction solution can be well controlled. For example, in order to reduce an amount of isopropyl phenol contained in the reaction solution obtained in the distillation column (4), the amount of phenol recovered on the top side of the column may be increased, the reflux ratio of the column may be reduced, or phenol may be supplied to the distillation column (4) from an outside, thereby efficiently conducting the above control procedure. The above distillation procedure is preferably
conducted such that the ratio of the amount of isopropyl phenol recovered on the top side of the column to the amount of the same substance being fed thereto is usually not less than 0.8% by weight and preferably not less than 1.5% by weight.
The concentration of bisphenol A contained in the bottom liquid which is obtained after separating the above low-boiling component from the top of the column is usually 20 to 50% by weight. When the concentration of bisphenol A contained in the bottom liquid is less than 20% by weight, the yield of bisphenol A tends to be lowered. When the concentration of bisphenol A contained in the bottom liquid is more than 50% by weight, a viscosity of the concentrated mixed solution tends to be increased, so that it may be difficult to deliver the solution through the reaction system. The bottom liquid is delivered to the bisphenol A separation step where bisphenol A as the aimed product is recovered.
When the process includes the above acetone recycling step, the low-boiling component separated in the low-boiling component separation step which contains unreacted acetone, water, phenol and isopropyl phenol, is fed to the acetone recycling step constituted from the separation system (20) where acetone is separated therefrom, for example, by distillation. The thus separated acetone is preferably fed
back to the methanol removing apparatus (la) disposed on an upstream side of the reaction step to remove methanol as an impurity therefrom before the acetone is fed as raw acetone to the reaction system.
In view of deterioration of catalyst activity, it is preferred to reduce the amount of methanol in the material acetone as possible. However, in order to remove a small amount of methanol from the material acetone, it is required to provide plural distillation columns having large number plates so that the system is enlarged, the economical cost is large and it is not practical. In consideration of these, the methanol content in the material acetone is usually 10 to 500 ppm by weight, preferably 30 to 500 ppm by weight, more preferably 50 to 300 ppm by weight. When the methanol content is within the above range, the practical operation which is prevented from deterioration of catalyst activity can be conducted without large load of acetone purification.
As the separation system (20), there may be usually used a multi-stage distillation column. The separated and recovered phenol is usually purified together with fresh phenol in the purifier (20a), and then stored in the storage tank (22) for clean phenol and used for rinsing the below-mentioned crystal adduct. In the purifier (20a), isopropyl phenol is purged out of the system by distillation, etc. When the isopropyl phenol is purged out of the system by
distillation, there may be used such a method in which isopropyl phenol contained in phenol is purged together with heavy substances contained in phenol fed from outside, from a bottom of the purifier (20a), for example, by conducting the distillation at a temperature of 150 to 190°C under an absolute pressure of 300 to 760 mmHg.

In the bisphenol A separation step, a material flow containing bisphenol A as a main component is separated from the bisphenol A-containing component obtained in the low-boiling component separation step. The material flow may be separated by using any suitable known methods without particular limitations. The "material flow containing bisphenol A as a main component" used herein means a material flow comprising 50% by weight of bisphenol A. Namely, this means a material flow in the form of a solid, a liquid, a gas, a slurry or a cake containing bisphenol A as a main component such as a cake or a slurry of a crystal adduct of bisphenol A and phenol or a crystal of bisphenol A solely, a melt of bisphenol A and gasified bisphenol A. These material flows may also contain phenol or impurities such as reaction by-products. As the method for separating the material flow, there may be used, for example, such a method of separating the bisphenol A-containing component by crystallization into a material flow composed of a cake of
the crystal adduct of bisphenol A and phenol, and a material flow containing, in addition to bisphenol A, reaction byproducts such as 2,4-bisphenol A and chroman (i.e., a so-called mother liquor). Examples of the other methods for separating the material flow may include the method of adding a third component such as water and acetone to the bisphenol A-containing solution to directly precipitate a crystal of bisphenol A without forming the adduct and then subjecting the resultant reaction mixture to solid/liquid separation to separate bisphenol A therefrom, the method of subjecting the bisphenol A-containing material flow to distillation under a high vacuum condition using a distillation column to allow bisphenol A to be distilled from a top of the column and separated therefrom, etc. In the followings, there are explained the crystallization step and the bisphenol A-recovering step conducted in the typical method in which the bisphenol A-containing component is subjected to crystallization and then solid/liquid separation to separate the component into the crystal adduct of bisphenol A and phenol and the mother liquor. (1) Crystallization Step
The bottom liquid from which the low-boiling component is separated in the low-boiling component separation step (liquid component containing bisphenol A) is successively subjected to a crystallization step. In the crystallization
step, the bottom liquid is cooled from a temperature of 70 to 140°C to a temperature of 35 to 60°C in the crystallizer
(5) to crystallize the crystal adduct and obtain a slurry
containing the crystal adduct. The thus obtained slurry is
fed to the solid/liquid separator (6) and subjected to
solid/liquid separation treatment therein. As the
crystallizer (5), there may be usually employed a
crystallization vessel equipped with one or plural
operation-switchable external coolers. In the case where a
plurality of external coolers are operated while changing-
over the operation therebetween, the non-operated external
cooler is switched to start its operation after dissolving
crystals adhered to an inside thereof under heating, thereby
enabling a continuous operation of the crystallization step
while maintaining a high performance thereof. Meanwhile,
upon changing-over the operation between the external
coolers, crystallization characteristics in the
crystallization vessel tend to be varied, so that the amount
of the mother liquor separated in the solid/liquid separator
(6) also tends to be changed. In order to prevent
occurrence of such a change in amount of the mother liquor
fed from the line (15) to the line (1), a part of the mother
liquor may be usually bypassed to a downstream side of the
reactor (2) through the line (16). In the case where a
crystallization vessel equipped with a jacketed cooler is
used as the crystallizer (5), a scraper for removing crystals adhered to a heat transfer surface thereof is preferably fitted to the crystallization vessel. (2) Bisphenol A Recovering Step
The crystal adduct recovered in the solid/liquid separator (6) is dissolved again in phenol in the re-dissolver (7), re-crystallized in the re-crystallizer (8) to enhance a purity thereof, and then subjected to solid/liquid separation and rinsed with clean phenol in the solid/liquid separation and rinsing system (9) constituted from a centrifugal separator, etc. The thus rinsed crystal adduct is then delivered to the crystal adduct decomposition system (11).
Meanwhile, a large part of the liquid component separated in the solid/liquid separation and rinsing system (9) and the rinsing waste solution can be used as phenol for re-dissolution of the crystal adduct in the re-dissolver (7) as well as a rinsing solution to be fed to the solid/liquid separator (6). A part of the liquid component separated in the solid/liquid separation and rinsing system (9) is circulated together with the recycled mother liquor to the tank (14).
In the crystal adduct decomposition apparatus (11), there may be usually used such a method in which the crystal adduct is melted under heating at a temperature of 100 to
160°C, and the thus obtained molten solution is distilled to remove a large part of phenol therefrom. In the purifier (12), there may be usually used such a method in which the reaction product is subjected to steam stripping, etc., to remove residual phenol therefrom and obtain purified bisphenol A. These methods are described, for example, in Japanese Patent Application Laid-open (KOKAI) Nos. 2-28126 and 63-132850, etc.

The "mother liquor" used herein means a liquid obtained by removing the material flow containing bisphenol A as a main component from the bisphenol A-containing component in the bisphenol A separation step, for example, a liquid obtained by separating the adduct of bisphenol A and phenol therefrom by the solid/liquid separator (6) after crystallizing the adduct. A part (for example, 85 to 96%) of the liquid component (mother liquor) obtained by solid/liquid separation in the solid/liquid separator (6) is circulated to an upstream side of the reaction step through the line (13) and then the line (15), and/or circulated to a downstream side of the reaction step through the line (16). In the process of the present invention, although the mother liquor recycling step is not essential, when the mother liquor recycling step is used in combination with the below-mentioned light component separation step, it is possible to

efficiently remove heavy substances and continuously conduct a stable operation of the process.
More specifically, the mother liquor obtained from the solid/liquid separator (6) usually comprises 65 to 85% by weight of phenol, 10 to 20% by weight of bisphenol A and 5 to 15% by weight of by-products such as 2,4'-isomer. Thus, the mother liquor contains a large amount of impurities such as 2,4'-isomer. In order to prevent these impurities from being accumulated in the process, a part of the mother liquor obtained from the solid/liquid separator (6) is fed to the below-mentioned light component separation step. In this case, the operation of a pump (not shown) for feeding the mother liquor from the tank (14) to the line (15) may be controlled such that the molar ratio of phenol contained in the mother liquor to a sum of fresh acetone (a) fed to the line (1) and the recovered acetone (b) fed through the line (21) (a + b) (phenol/acetone) lies within the above-mentioned constant mixing ratio.

In the light component separation step, at least a part of the mother liquor separated in the previous step is subjected to heat treatment and distillation in the presence of an alkali and separated into a light component and a heavy component. More specifically, at least a part of the mother liquor is branched from the line (13) to the impurity
removal line (13') and fed to the alkali decomposition column (13a). In the alkali decomposition column (13a), the mother liquor is subjected to heat treatment and distillation in the presence of an alkali and separated into a light component and a heavy component. Preferably, at least a part of the thus branched mother liquor is fed to the mother liquor concentration column (13c) and distilled thereby distilling out a large part of isopropyl phenol together with a part of phenol therefrom from the column top and/or column side as a light component liquid, and then heated in the presence of an alkali substance to decompose bisphenol A and isomers thereof contained in the mother liquor into phenol and isopropenyl phenol. Hereinafter, a case obtaining the light component liquid from the top of column is explained as an example embodiment.
The phenol recovered from a top of the mother liquor concentration column (13c) contains a large amount of isopropyl phenol. Therefore, at least a part of the solution containing the recovered phenol is branched and purged out of the system through the line (13d), or at least a part of the solution branched is fed to the purifier (20a) to purify and remove isopropyl phenol therefrom, thereby enabling the concentration of isopropyl phenol contained in the reaction solution to be well controlled. When conducting the present step in combination with the
separation procedure for separating isopropyl phenol in the distillation column (4), the concentration of isopropyl phenol can be more efficiently controlled.
In the phenol recovered from the top of mother liquor concentration column (13c), the phenol which is not purged to the out of system through the line (13d) is used for quenching the top of alkali decomposition column (13a). The isopropyl phenol content contained in the phenol purged to the out of system through the line (13d) is preferably not less than 5% by weight, more preferably 5 to 20% by weight, especially preferably 7 to 15% by weight of isopropyl phenol provided to the mother liquor concentration column (13c). When the content of withdrawn isopropyl phenol is less than the above range, there is a possibility that it is difficult to maintain the content of isopropyl phenol contained in the reaction solution in the reaction step to the prescribed range. Further, in order to increase the amount of phenol purged to the out of system through the line (13d), it is necessary to increase the amount of purged phenol to lead the loss of phenol. Especially, in case where the phenol is not purged to the out of system through the line (13d) is used for quenching the top of alkali decomposition column (13a), there is a possibility that the amount of phenol used for the quenching is decreased so that the quenching is insufficient, and this is not preferred.
Further, when the amount of phenol used for the quenching is too small, the concentration of isopropenyl phenol in the light component obtained from the alkali decomposition column (13a) as described hereinafter is increased. When the concentration of isopropenyl phenol is high, there is a possibility that the dimerization of isopropenyl phenol occurs and the selectivity in the recombination reaction step as described hereinafter is deteriorated, and this is not preferred.
In the mother liquor concentration column (13c), by increasing the amount of phenol recovered on the top side of the column or decreasing the reflux ratio thereof, a ratio of the amount of isopropyl phenol distilled out and recovered on the top side of the column to the amount of the same substance fed to the column is controlled to usually not less than 0.6 and preferably not less than 0.8. The ratio of the distillated solution to be branched and discharged is preferably not less than 0.1. In this case, when it is required to control the ratio between phenol and isopropenyl phenol owing to reduction in amount of phenol fed to the recombination reactor (13b) in the subsequent step, such a procedure of feeding phenol from outside may be conducted in combination with the control procedure.
The above decomposition reaction is preferably performed by a reaction distillation method in which the
mother liquor is fed together with the alkali substance to the alkali decomposition column (13a) and heated to a temperature of 200 to 300°C to decompose bisphenol A and isomers thereof contained therein. As the alkali substance, there may be used any suitable known alkali substances, e.g., hydroxides, carbonates and phenol salts of alkali metals such as sodium and potassium, hydroxides and phenol salts of alkali earth metals such as magnesium and calcium, etc. These alkali substances are preferably fed in the form of an aqueous solution thereof, etc. The decomposition rate of bisphenol A and isomers thereof in the alkali decomposition step is usually not less than 30%, preferably not less than 50% and more preferably not less than 60%.
The above mother liquor may be previously concentrated and then subjected to the decomposition reaction as described in Japanese Patent Application Laid-open (KOKAI) No. 10-218814(1998). Alternatively, the mother liquor may also be directly subjected to the decomposition reaction without the concentration procedure. This is because even though the mother liquor is directly subjected to the decomposition reaction, phenol contained in the mother liquor is immediately evaporated therefrom, resulting in concentration of the mother liquor. In the alkali decomposition column (13a), the mother liquor to be treated for removing impurities therefrom is not only subjected to
alkali decomposition, but also separated into a light component containing phenol and isopropenyl phenol and a heavy component containing tar, etc. The thus separated heavy component is discharged out of the system.
The above light component is subjected to recombination reaction treatment in the recombination reactor (13b). More specifically, the above isopropenyl phenol is a polymerizable substance and readily forms a polymer thereof. Therefore, when the light component containing isopropenyl phenol is directly fed to the mother liquor recycling line (13), there tends to arise such a problem that the resultant bisphenol A product is undesirably colored by the polymer. For this reason, the light component (phenol and isopropenyl phenol) distilled off from the top of the alkali decomposition column (13a) is immediately condensed and fed to the recombination reactor (13b) to conduct a recombination reaction thereof in the presence of an acid ion exchange resin, thereby preventing production of the polymer as a coloring component.
The recombination reaction is usually conducted at a temperature of 50 to 85°C. As the acid ion exchange resin used in the recombination reaction, there may be usually used strong acid cation exchange resins such as sulfonic acid-type cation exchange resins. Meanwhile, the acid ion
exchange resin used in the recombination reaction may be the same as the sulfonic acid-type strong acid cation exchange resin used in the reaction step which is partially neutralized with the sulfur-containing compound.
In the recombination reaction, there tends to occur dimerization of isopropenyl phenol as a side reaction. Therefore, the molar ratio of phenol to isopropenyl phenol fed to the recombination reactor (13b) is preferably controlled to not less than 40, thereby considerably preventing occurrence of the side reaction. In order to control the molar ratio of phenol to isopropenyl phenol to not less than 40, an additional amount of phenol (such as phenol used for rinsing the crystal in the crystallization step) is preferably added from outside.
The recombination reaction solution (solution of bisphenol A produced) obtained in the above step is returned to the mother liquor recycling line (13).
The process for producing bisphenol A according to the present invention is characterized by controlling the content of isopropyl phenol in the reaction solution obtained in the reaction step to not more than 4% by weight, preferably not more than 2% by weight, more preferably not more than 1% by weight and still more preferably not more than 0.5% by weight. It has been found by the present
inventors that isopropyl phenol (including o-, m- and p-isomers and a mixture thereof) contained as an impurity in the reaction solution obtained in the reaction step is a substance which accelerates deterioration of catalytic activity of the acid ion exchange resin catalyst used in the reaction step. Further, it has also been found that isopropyl phenol is by-produced upon the heat treatment conducted in the presence of the alkali in the impurity treatment step. Therefore, in the process for producing bisphenol A which includes the above impurity treatment step, the inclusion of isopropyl phenol is inevitably caused. The more frequently the impurity treatment is repeated, the more the isopropyl phenol is accumulated in the system. For this reason, in the present invention, the content of isopropyl phenol in the reaction solution obtained in the reaction step is controlled to not more than 4% by weight, so that the acid ion exchange resin catalyst used in the reaction step can be prevented from being deteriorated in catalytic activity. The concentration of isopropyl phenol in the reaction solution obtained in the reaction step may be determined based on the value measured at any of an inlet, an inside and an outlet of the reactor. However, in order to prevent deterioration of the ion exchange resin, the concentration of isopropyl phenol is preferably controlled based on the value measured at an inlet of the reactor.
As the method for controlling the content of isopropyl phenol in the reaction solution obtained in the reaction step, there is preferably used such a method of separating 5 to 20% by weight and preferably 5 to 15% by weight of the mother liquor fed to the light component separation step as a heavy component. This method is based on the present inventors' finding that the amount of an alkyl phenol produced in the system has a correlation with the amount of the heavy component (tar component) discharged from the alkali decomposition column (13a). The conditions for controlling an amount of the heavy component discharged include a residence time of the mother liquor, an alkali concentration, a decomposition temperature, a degree of pressure reduction, etc., in the alkali decomposition column (13a). The amount of the heavy component discharged may be controlled to the above-specified range by adequately selecting and combining these conditions.
More specifically, the residence time of the mother liquor in the alkali decomposition column (13a) is usually 1 to 20 hr and preferably 2 to 10 hr. The alkali concentration (concentration of alkali contained in the heavy component discharged out of the system in the light component separation step) is usually 100 to 4000 ppm by weight and preferably 200 to 2000 ppm by weight in terms of metallic sodium. The decomposition temperature is usually
170 to 300°C and preferably 200 to 250°C. The degree of pressure reduction is usually 10 to 100 Torr and preferably 20 to 50 Torr. Also, the content of isopropyl phenol in the reaction solution being present in the reaction step may also be controlled by the method of adjusting a rate of separation of the mother liquor branched from the line (13) to the impurity removal line (13'), the method of changing a ratio of phenol distilled off from the mother liquor concentration column (13c) before the addition of alkali because isopropyl phenol is withdrawn together with the phenol, or the method of controlling the amount of the reaction solution withdrawn from the line (13d) to the purifier (20a). In particular, among these methods, the method of controlling the amount of the reaction solution withdrawn from the line (13d) to the purifier (20a) is preferred since isopropyl phenol can be removed more efficiently. In addition, the content of isopropyl phenol in the reaction solution obtained in the reaction step may also be controlled by the method of adjusting an amount of the recombination reaction solution fed to the recombination reactor (13b) to the line (13) or the method of adjusting an amount of fresh phenol contained in the raw phenol. Further, although isopropyl phenol may be removed by distillation from the light component obtained in the alkali decomposition column (13a), the removal of isopropyl phenol
is preferably conducted by the method of controlling operation conditions of the alkali decomposition column (13a) in view of simplicity thereof.
Meanwhile, in the production process of the present invention, in addition to the above procedures, hydrated phenol generated in the dehydration procedure upon initiation of using the reaction catalyst may be fed little by little to the distillation columns disposed within the process during the operation thereof to remove water therefrom for reusing the thus dehydrated phenol. The above procedure is preferable since the obtained phenol can be reused as the raw phenol.
As described above, in the preferred embodiment of the present invention, acetone is fed together with a largely excessive amount of phenol to the reactor filled with the sulfonic acid-type ion exchange resin modified with an aminothiol compound to allow the condensation reaction therebetween to proceed, thereby producing bisphenol A. In this case, when the reaction for production of bisphenol A is conducted for a long period of time, the sulfonic acid-type ion exchange resin used therein as the catalyst tends to lose its effects owing to deterioration of the aminothiol compound acting as a co-catalyst, or tends to be deteriorated in catalytic activity owing to adhesion of heavy substances such as by-produced tar to the surface of
the ion exchange resin which results in covering the surface of the catalyst therewith. For this reason, it is required to periodically withdrawn the catalyst from the reactor and replace the catalyst with new one.
The catalyst to be added to the reactor upon the replacement may be a fresh catalyst newly produced, or the sulfonic acid-type ion exchange resin catalyst obtained by treating the used catalyst withdrawn from the reactor which is deteriorated in catalytic activity, with an acid, etc., to remove tar and the deteriorated co-catalyst from the surface thereof, and then immersing the thus treated catalyst again in a solution containing an aminothiol compound to modify the resin with the aminothiol compound.
The ion exchange resin catalyst may be usually charged into the reactor frequently in a water-swelled state. Therefore, the ion exchange resin catalyst filled in the reactor is preferably subjected to dehydration procedure before initiating the reaction for production of bisphenol A. The dehydration procedure of the ion exchange resin catalyst is usually performed by roughly removing water from the catalyst and then contacting the catalyst with phenol. The water-swelled ion exchange resin tends to undergo rapid reduction of its volume upon the dehydration procedure, resulting in the risk of breakage of the ion exchange resin itself. Therefore, the initial dehydration procedure is
preferably conducted using a mixed solution containing phenol and water at a mixing ratio of about 9:1. By such a method, the ion exchange resin can be prevented from suffering from rapid reduction of its volume and, therefore, breakage thereof.
As the method of contacting the catalyst with phenol upon the dehydration procedure, there may be used a batch method in which the catalyst is immersed in phenol in a batch manner, or a continuous method in which phenol is continuously flowed through the catalyst. The phenol used in the dehydration procedure may be either purified phenol or the filtrate (mother liquor) generated in the solid/liquid separation step which is circulated and reused through the process for production of bisphenol A.
The phenol used in the dehydration procedure contains water, acid components dissociated from the sulfonic acid-type ion exchange resin, etc. Therefore, the phenol is preferably purified for reuse. The method of purifying the phenol used in the dehydration procedure is not particularly limited, and there may be used, for example, the method of purifying the phenol while returning the phenol little by little into the process upon restarting the operation after storing the phenol in the tank, etc., or the method of purifying the phenol using a special distillation column therefor, etc. Also, in the case where two or more reactors
are operated in parallel, while operating one or more reactors, the other one or more non-operated reactors may be subjected to dehydration treatment of phenol at the same time, and the thus dehydrated but unpurified phenol generated in the treatment is returned to the process.
When returning the unpurified phenol to the process, the unpurified phenol may be fed to the distillation column used in the low-boiling component separation step for removing unreacted acetone, water, etc., which is disposed on a downstream side of the reactor, or may be fed to an upstream side of the impurity removal treatment step for purifying the phenol. Also, these procedures may be conducted in combination with each other. In general, since there may be present such a risk that the acid components contained in the unpurified phenol is mixed in the bisphenol A product, the unpurified phenol is preferably fed to the upstream side of the impurity removal treatment step. However, if such a phenol having a large water content which is generated at an initial stage of the dehydration procedure is fed to the impurity removal treatment step, water tends to be mixed in the alkali decomposition column used for the impurity removal treatment, so that it may be difficult to suitably conduct the alkali decomposition step operated under high-temperature (not less than 200°C) and high-vacuum pressure (not more than 80 mmHg) conditions,
because the high-vacuum condition in the step is no longer kept owing to a vapor pressure of water mixed therein. For this reason, the phenol having a large water content which is generated at an initial stage of the dehydration procedure is preferably first treated in the low-boiling component separation step, and then fed to the upstream side of the impurity removal treatment step by switching the operation after reducing the water content in the phenol.
The thus purified phenol may be used as phenol for rinsing the crystal adduct obtained in the solid/liquid separation step.
EXAMPLES
The present invention is described in more detail by the following examples. However, these examples are only illustrative and not intended to limit the scope of the present invention.
(1) Analyzing Method for Acetone
The analysis for acetone was conducted using a gas chromatograph "GC-14B" manufactured by Shimadzu Corporation and equipped with a fused silica capillary column and a TCD detector.
(2) Analyzing Method for Isopropyl Phenol
The analysis for isopropyl phenol was conducted using a gas chromatograph "GC-14B" manufactured by Shimadzu
Corporation and equipped with a fused silica capillary column and a FID detector.
(3) Conversion of acetone
The conversion of acetone was calculated from the following equation.
Conversion of acetone (%) = [{(Feed amount of material acetone (kg/h)) - (Acetone concentration in the line 3 (% by weight)) X (Flow rate of liquid in the line 3 (kg/h))}/(Feed amount of material acetone (kg/h))] X 100
Example 1:
Using a pilot plant shown in Fig. 2, bisphenol A was continuously produced. A reactor (2) having a diameter of 660 mm was disposed in the reaction step, and filled with 340 L of an ion exchange resin as a catalyst which was obtained by modifying 20 mol% of sulfonic groups contained in a sulfonic acid-type cation exchange resin "DIA-ION SK-104H" produced by Mitsubishi Chemical Corporation, with 2-(4-pyridyl)ethane thiol. A mother liquor fed through a line (15) and a distillation-purified phenol/acetone mixed solution (composed of 82% by weight of phenol, 4% by weight of acetone, 8% by weight of bisphenol A and 6% by weight of other components, and the concentration of methanol in the acetone was 100 ppm by weight) were fed at a rate of 400 kg/hr, and reacted with each other at 65°C. The obtained
reaction solution was fed through a line (3) to a distillation column (4) packed with a filler such that the number of theoretical plates was 7, and a distillate was withdrawn from a top of the column at a rate of 62 kg/hr. In this time, the amount of isopropyl phenol in the distillate withdrawn from the top of the distillation column (4) was 1.6% by weight of the feed amount. The column bottom liquid in the distillation column (4) was fed to a crystallization column (5) and a crystal adduct of bisphenol A and phenol was precipitated. The thus obtained crystal adduct was fed together with the purified phenol (120 kg/h) used for rinsing the crystal adduct to a solid/liquid separation apparatus (6) and separated into a solid (78 kg/hr) and a mother liquor (385 kg/hr). The solution flowed through a line (13') was fed to a mother liquor concentration column (13c) packed with a filler such that the number of theoretical plates was 3, and a distillate was withdrawn from a top of the column at a rate of 29 kg/hr. About 11% of the resultant solution was branched and discharge to the out of system through the line (13d) thereby remove isopropyl phenol therefrom. In this time, the amount of isopropyl phenol discharged to the out of system was 10% of the amount fed to the mother liquor concentration column (13c).
347 kg/hr of the mother liquor (90% by weight based on a total weight of the mother liquor) was directly fed again to the reaction step through a line (13), whereas remaining 38 kg/hr of the mother liquor (10% by weight based on a total weight of the mother liquor) was subjected to the treatment in the mother liquor concentration column (13c) and the column top liquid and column bottom liquid which were not discharged to the out of system were fed to an alkali decomposition column (13a). In the alkali decomposition column (13a), after adding a 25 wt% sodium hydroxide aqueous solution thereto at a rate of 0.22 kg/hr, the mother liquor was subjected to alkali decomposition reaction and distillation for a residence time of 4 hr at 210°C under a pressure of 40 Torr to separate 3.8 kg/hr of a heavy component (purging rate of heavy component: 10% by weight) therefrom. The resultant light component from which the heavy component (tar component) was removed, was fed to a recombination reactor (13b) maintained at 65°C and packed with the sulfonic acid-type cation exchange resin "DIA-ION SK-104H" produced by Mitsubishi Chemical Corporation, which was not modified with a sulfur-containing amine compound, to react isopropenyl phenol produced by the alkali decomposition reaction with phenol, thereby producing bisphenol A. Thereafter, the resultant reaction solution was fed again to the reaction system through the line (13).
According to the above procedure, the process was continuously operated for 4000 hr. After the elapse of 250 hr from initiation of the operation, the amount of impurities within the reaction system was stabilized, and no change in amount of impurities within the reaction system was caused until 4000 hr elapsed. At this time, the concentration of p-isopropyl phenol in the raw material fed to the reactor (2) was 0.3% by weight. The amount of isopropyl phenol withdrawn from the top of distillation column (4) was 1.5% by weight of the fed isopropyl phenol and the amount of isopropyl phenol withdrawn to the out of system through the line (13d) was 10% by weight of isopropyl phenol fed to the mother liquor concentration column (13c). In addition, the conversion of acetone was 98.5% after the elapse of 1 hr from initiation of feeding acetone to the reaction system, and thereafter reduced to 93.1% after the process was operated for 4000 hr.
Example 2;
The same procedure as defined in Example 1 was conducted except that a part of the distillate withdrawn from the mother liquor concentration column (13c) was not discharged to the out of system through the line (13d). As a result, it was confirmed that the concentration of isopropyl phenol in the raw material fed to the reactor (2)
was stabilized at 0.8% by weight. The conversion of acetone was 98.5% after the elapse of 1 hr from initiation of feeding acetone to the reaction system, and thereafter reduced to 91.8% after the process was operated for 4000 hr.
Example 3;
The same procedure as defined in Example 1 was conducted except that isopropyl phenol was not discharged to the out of system from the distillate of distillation column (4). As a result, it was confirmed that the concentration of isopropyl phenol in the raw material fed to the reactor (2) was stabilized at 1.2% by weight. The conversion of acetone was 98.5% after the elapse of 1 hr from initiation of feeding acetone to the reaction system, and thereafter reduced to 90.4% after the process was operated for 4000 hr.
Example 4;
The same procedure as defined in Example 1 was conducted except that methanol having acetone in amount of 650 ppm by weight was used as the reaction material. As a result, it was confirmed that the concentration of isopropyl phenol in the raw material fed to the reactor (2) was stabilized at 0.4% by weight. The conversion of acetone was 98.0% after the elapse of 1 hr from initiation of feeding
acetone to the reaction system, and thereafter reduced to 88.6% after the process was operated for 4000 hr.
Example 5:
The same procedure as defined in Example 1 was conducted except that the temperature of alkali decomposition column (13a) in the low-boiling component separation step was 250°C, 0.9 kg/hr of a heavy component was separated (purging rate of heavy component: 2.3% by weight), the amount of phenol purged to the out of system through the line (13d) from the top of mother liquor concentration column (13c) was 20% by weight of amount fed to the mother liquor concentration column (13c), and the amount of isopropyl phenol withdrawn from the top of distillation column (4) was 2.5% by weight of amount fed to the distillation column (4). As a result, it was confirmed that the concentration of isopropyl phenol in the raw material fed to the reactor (2) was stabilized at 2.1% by weight. The conversion of acetone was 98.5% after the elapse of 1 hr from initiation of feeding acetone to the reaction system, and thereafter reduced to 88.3% after the process was operated for 4000 hr.
Comparative Example 1;
The same procedure as defined in Example 1 was conducted except that the conditions for reaction distillation by the alkali decomposition were changed, and the reaction distillation procedure was conducted at 250°C. Since the alkali decomposition temperature was higher than that used in Example 1, the alkali decomposition more rapidly proceeded as compared to that in Example 1, so that the amount of the heavy component withdrawn from the bottom of the column was reduced to 0.8 kg/hr (purging rate of heavy component: 2.3% by weight). After the elapse of 250 hr from initiation of the operation, the amount of impurities within the reaction system was stabilized, and no change in amount of impurities was caused until 4000 hr elapsed. At this time, the concentration of p-isopropyl phenol in the raw material fed to the reactor (2) was 6.3% by weight. In addition, the conversion of acetone was 98.5% after the elapse of 1 hr from initiation of feeding acetone to the reaction system, and thereafter largely reduced to 80.9% after the process was operated for 4000 hr. As a result, it was confirmed that the sulfonic acid-type cation exchange resin catalyst was considerably deteriorated.
Comparative Example 2;
The same procedure as defined in Comparative Example 1 was conducted except that methanol having acetone in amount
of 650 ppm by weight was used as the reaction material. As a result, it was confirmed that the concentration of isopropyl phenol in the raw material fed to the reactor (2) was stabilized at 6.3% by weight. The conversion of acetone was 97.5% after the elapse of 1 hr from initiation of feeding acetone to the reaction system, and thereafter reduced to 71.1% after the process was operated for 4000 hr.
Table 1
(Table Removed)
Although the present invention is described above with respect to embodiments which are considered to be most practical and preferable at the present time, the present invention is not limited to these embodiments, and various changes and modifications will be appropriately made within the scope of claims and a whole of a specification of this application unless departing from the subject matter and concept of the present invention, and it should be construed
that the changes and modifications are involved within a technical range of the present invention.

WHAT IS CLAIMED IS;
1. A process for producing bisphenol A comprising at least a reaction step of reacting acetone and phenol as raw materials in the presence of an acid ion exchange resin catalyst to obtain a reaction mixture containing bisphenol A and phenol; a low-boiling component separation step of separating the reaction mixture into a bisphenol A-containing component and a low-boiling component containing unreacted acetone; a bisphenol A separation step of separating the bisphenol A-containing component into a material flow containing bisphenol A as a main component and a mother liquor containing phenol as main components; a light component separation step of subjecting at least a part of the thus separated mother liquor to heat treatment and distillation in the presence of an alkali to separate the mother liquor into a light component and a heavy component; a recombination reaction step of treating the thus separated light component in the presence of an acid ion exchange resin catalyst to allow phenol and isopropenyl phenol contained in the light component to be recombined with each other and converted into bisphenol A; and a recombination reaction solution recycling step of recycling a recombination reaction solution obtained in the recombination reaction step to the above reaction step, in which a content of isopropyl phenol in a reaction solution
being present in the reaction step is controlled to not more than 4% by weight.
2. A process according to claim 1, wherein the acid ion
exchange resin catalyst used in the reaction step is a
modified acid ion exchange resin catalyst obtained by
modifying an acid ion exchange resin with an alkyl
aminothiol.
3. A process according to claim 2, wherein the alkyl
aminothiol is 2-aminoethane thiol and/or 2-(4-pyridyl)ethane
thiol.
4. A process according to any one of claims 1 to 3,
wherein in the light component separation step, the heavy
component is separated in an amount corresponding to 5 to
20% by weight of the mother liquor fed thereto.
5. A process according to any one of claims 1 to 4,
wherein in the light component separation step there is a
mother liquor concentration column prior to the heat
treatment, not less than 5% by weight of isopropyl phenol
provided to the mother liquor concentration column is
withdrawn from the light component separation step as a
purged product when at least a part of the light component

distilled solution obtained from the mother liquor concentration column is discharged from the light component separation step as the purged product.
6. A process according to any one of claims 1 to 5, wherein in the low-boiling
component separation step, not less than 0.8% by weight of isopropyl phenol
fed thereto is separated together with the low-boiling component.
7. A process according to any one of claims 1 to 6, wherein the content of
methanol contained in the acetone as the material provided to the reaction step
is 10 to 500 ppm by weight.
8. A process according to claim 1, which is substantially as hereinbefore
described with reference to any one of the foregoing examples and the
accompanying drawings.
9. Bisphenol A produced according to the process of any one of claims 1 to 8.

Documents:

6302-delnp-2008-Abstract-(03-02-2014).pdf

6302-delnp-2008-abstract.pdf

6302-delnp-2008-Claims-(03-02-2014).pdf

6302-delnp-2008-claims.pdf

6302-delnp-2008-Correspondence Others-(03-02-2014).pdf

6302-DELNP-2008-Correspondence-Others (06-11-2009).pdf

6302-delnp-2008-correspondence-others.pdf

6302-DELNP-2008-Description (Complete).pdf

6302-delnp-2008-drawings.pdf

6302-delnp-2008-form-1.pdf

6302-delnp-2008-form-13.pdf

6302-DELNP-2008-Form-18 (06-11-2009).pdf

6302-DELNP-2008-Form-2.pdf

6302-delnp-2008-form-26.pdf

6302-DELNP-2008-Form-3.pdf

6302-DELNP-2008-Form-5.pdf

6302-delnp-2008-GPA-(03-02-2014).pdf

6302-delnp-2008-pct-210.pdf

6302-delnp-2008-pct-301.pdf

6302-delnp-2008-pct-304.pdf

6302-delnp-2008-pct-308.pdf

6302-delnp-2008-Petition-137-(03-02-2014).pdf

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Patent Number

259696

Indian Patent Application Number

6302/DELNP/2008

PG Journal Number

13/2014

Publication Date

28-Mar-2014

Grant Date

24-Mar-2014

Date of Filing

18-Jul-2008

Name of Patentee

MITSUBISHI CHEMICAL CORPORATION

Applicant Address

14-1 SHIBA 4-CHOME MINATO-KU TOKYO JAPAN.

Inventors:

#	Inventor's Name	Inventor's Address
1	NAGAOKA, MICHIHIRO	C/O MITSUBISHI CHEMICAL COORPORATION 17-1 TOWADA KAMISU -SHI IBARAKI-KEN JAPAN.
2	TANAKA, TATSUO	C/O MITSUBISHI CHEMICAL COORPORATION 17-1 TOWADA KAMISU -SHI IBARAKI-KEN JAPAN.
3	KIMURA, HIROAKI	C/O MITSUBISHI CHEMICAL COORPORATION 17-1 TOWADA KAMISU -SHI IBARAKI-KEN JAPAN.
4	HAYASHI, HIDETO	C/O MITSUBISHI CHEMICAL COORPORATION 17-1 TOWADA KAMISU -SHI IBARAKI-KEN JAPAN.
5	NAKAJIMA,IWAO	C/O MITSUBISHI CHEMICAL COORPORATION 17-1 TOWADA KAMISU -SHI IBARAKI-KEN JAPAN.

PCT International Classification Number

C07 37/20

PCT International Application Number

PCT/JP2007/000027

PCT International Filing date

2007-01-24

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2006-01638	2006-01-25	Japan