Title of Invention

METHOD FOR PRODUCING PRILLS OF BISPHENOL A

Abstract

There is provided a process for producing a prill of bisphenol A, comprising the step of dropping a melt of bisphenol A from a nozzle plate disposed at an upper portion of a granulating column and flowing a cooling gas upwardly from a lower portion of the granulating column, said process satisfying the following conditions (a) to (c): (a) a diameter of respective orifices of the nozzle being in the range of 0.3 to 1.0 mm; (b) a discharge velocity of the melt of bisphenol A from the nozzle being in the range of 0.5 to 1.8 m/s; and (c) a flow rate of the cooling gas being in the range of 0.7 to 2.0 m/s.

Full Text

DESCRIPTION METHOD FOR PRODUCING PRILLS OF BISPHENOL A TECHNICAL FIELD The present invention relates to a process for producing a prill of bisphenol A [2,2-bis(4-hydroxyphenyl)propane] (hereinafter occasionally referred to merely as "BPA"). The present invention more particularly relates to a process capable of stably producing bisphenol A, preventing adhesion or deposition of BPA onto a bottom of a granulating column, and effectively producing a granulated product of bisphenol A, i.e., a prill of bisphenol A having a uniform particle size, a high fluidity, a large bulk density and a high hardness, by defining an orifice diameter of a nozzle, a discharge velocity of a melt of bisphenol A from the nozzle, a flow rate of a cooling gas, a distance between orifices of the nozzle, etc. BACKGROUND ART It is known that bisphenol A is an important compound as a raw material of engineering plastics such as polycarbonate resins and polyallylate resins, or epoxy resins. In recent years, the need of BPA tends to increase more and more. BPA is produced by subjecting an excess amount of phenol and acetone to a condensation reaction in the presence of an acid catalyst and, if required, a co-catalyst such as a sulfur compound. BPA products are usually in the form of granules or flakes because BPA has a melting point as high as 157°C. Of these products, granules are preferred in view of a good fluidity thereof. The process for production of BPA usually includes a granulating step in which heat-melted BPA is granulated into a granular product (prill). In the granulating step, BPA is formed into droplets and then cooled and solidified, for example, using a granulating apparatus such as a spray dryer to obtain granules. If the BPA droplets have a large size in the granulating step, a_ temperature of the BPA prill tends to increase due to the insufficient cooling effect in the step of cooling and solidifying the droplets. The thus produced BPA prill is received in a flexible container bag, etc., for shipment thereof. If the BPA prill has a high temperature, there arise problems concerning safety upon transportation thereof. To solve these problems, there is provided a secondary cooling step of cooling the BPA prill to about 35°C using a gas slide cooler, etc., resulting in high facility costs. Conventionally, the granulation of BPA has been conducted by maintaining the melt of BPA at a temperature of 200°C or lower, adjusting a liquid depth of the melt of BPA to 300 to 2000 mm at an outlet of the nozzle, and setting a height of the granulating column to at least 10000 mm. However, the conventional methods fail to specify a velocity of the cooling gas (for example, refer to Japanese Patent Publication No. Showa 47(l972)-8060). Also, there has been proposed the method in which in order to reduce an amount of BPA fine particles produced, the cooling gas velocity Vg is defined so as to satisfy the formula- O.lVp Further, there has also been proposed the method of granulating the melt of BPA while applying a vibration thereto. However, the method requires the use of a vibrating device (for example, refer to Japanese Patent Application No. 2002-302978). Further, there is also known the method of granulating ammonium nitrate under the conditions in which the liquid height of ammonium nitrate is 75 mm, a nozzle orifice diameter is 0.75 to 2 mm, a distance between adjacent orifices of the nozzle is 5 to 20 mm, and a flow rate of a cooling gas is 0.3 to 1.2 m/s. However, the method fails to specify the range of a discharge velocity of a melt of the ammonium nitrate (for example, refer to Japanese Patent Publication No. Showa 55(l980)-22137). In addition, there has been proposed the method in which a replaceable nozzle is provided such that granulation is conducted while always keeping an injection port of the nozzle in a clean condition by replacing the nozzle with a new one. However, in order to ensure a sufficient strength of the nozzle body and a nozzle plate, it is required to broaden a distance between the adjacent nozzle ports, resulting in poor throughput per unit area. For this reason, the above method has such a problem that if the amount of granules produced is the same, a granulating column having a larger diameter must be used therein (for example, refer to Japanese Patent Publication No. Heisei 8(l996)-4737). DISCLOSURE OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION Under these circumstances, an object of the present invention is to provide a process which is capable of stably producing bisphenol A, preventing adhesion or deposition of BPA onto a bottom of a granulating column to thereby reduce occurrence of out-of-spec products due to adhesion or deposition of BPA and omit a vibration device upon the granulation of BPA, and effectively producing a prill of bisphenol A having a uniform particle size, a high fluidity, a large bulk density and a high hardness, by defining a diameter of respective orifices of a nozzle, a discharge velocity of a melt of bisphenol A from the nozzle, a flow rate of a cooling gas and a distance between the adjacent orifices of the nozzle. As a result of extensive researches in view of the above problems, the inventors have found that the above object can be achieved by defining a diameter of respective orifices of a nozzle, a discharge velocity of a melt of bisphenol A from the nozzle and a flow rate of the cooling gas to specific values upon conducting granulation of bisphenol A by dropping the melt of bisphenol A from a nozzle plate disposed at an upper portion of a granulating column and flowing the cooling gas upwardly from a bottom of the granulating column. The present invention has been accomplished on the basis of the above findings. Thus, the present invention provides^ (1) A process for producing a prill of bisphenol A, comprising the step of dropping a melt of bisphenol A from a nozzle plate disposed at an upper portion of a granulating column and flowing a cooling gas upwardly from a lower portion of the granulating column, said process satisfying the following conditions (a) to (c): (a) a diameter of respective orifices of the nozzles being in the range of 0.3 to 1.0 mm; (b) a discharge velocity of the melt of bisphenol A from the nozzle being in the range of 0.5 to 1.8 m/s; and (c) a flow rate of the cooling gas being in the range of 0.7 to 2.0 m/s; and (2) the process as descried in the above aspect (l), wherein a distance between the adjacent orifices of the nozzle is in the range of 5 to 12 mm. EFFECT OF THE INVENTION In accordance with the present invention, by defining an orifice diameter of a nozzle, a discharge velocity of a melt of bisphenol A from the nozzle, a flow rate of a cooling gas and a distance between adjacent orifices of the nozzle to specific ranges, bisphenol A can be stably produced, and adhesion or deposition of BPA onto a bottom of a granulating column can be prevented, thereby enabling a prill of bisphenol A having a uniform particle size, a high fluidity, a large bulk density and a high hardness to be produced at a high efficiency. Further, since adhesion or deposition of BPA onto a bottom of a granulating column can be prevented, no procedure for removing adherends from the bottom of the granulating column by complicated hammering operations is required, thereby ensuring a long-term operation thereof as well as attaining a large economical advantage. BRIEF DESCRIPTION OF DRAWING Fig. 1 is a schematic view showing an example of a granulating apparatus usable in the present invention. Explanation of Reference Numerals 1- granulating nozzle?" % granulating column! 3^ inlet for cooling gas! 4-outlet for products! 5: outlet for cooling gas BEST MODE FOR CARRYING OUT THE INVENTION Bisphenol A used in the present invention may be produced, for example, by the process comprising the steps of (A) obtaining a mixed reaction solution by subjecting an excess amount of phenol and acetone to a condensation reaction in the presence of an acid catalyst! (B) concentrating the mixed reaction solution! (C) crystallizing and separating an adduct of bisphenol A and phenol from a residual concentrated solution obtained in the step (B); (D) dissolving the adduct of bisphenol A and phenol thus crystallized and separated in the step (C) using a phenol-containing solution! (E) crystallizing and separating the adduct of bisphenol A and phenol from the solution obtained in the step (D) and, if required, repeating a procedure of dissolving the adduct using a phenol-containing solution and then crystallizing and separating the adduct from the resultant solution one or more times! and (F) heat-melting the adduct of bisphenol A and phenol crystallized and separated in the step (E) and then distilling off phenol from the resultant adduct. Step (A) In the step (A) of the process for production of bisphenol A, an excess amount of phenol and acetone are subjected to a condensation reaction in the presence of an acid catalyst to produce bisphenol A. As the acid catalyst, there may be used acid-type ion exchange resins. The acid-type ion exchange resins are not particularly limited, and there may be used those conventional acid-type ion exchange resins ordinarily used as a catalyst for production of bisphenol A. Of these resins, sulfonic acid-type cation exchange resins are preferred, in particular, in view of catalytic activity, etc. The sulfonic acid-type cation exchange resins are not particularly limited as long as they are strong acid cation exchange resins having a sulfonic group. Examples of the sulfonic acid-type cation exchange resins include sulfonated styrene-divinyl benzene copolymers, sulfonated crosslinked styrene polymers, phenol formaldehyde-sulfonic acid resins, and benzene formaldehyde-sulfonic acid resins. These resins may be used singly or in the combination of any two or more thereof. In the above production process, the acid-type ion exchange resin may be usually used in combination with mercaptans as a co-catalyst. The mercaptans are compounds containing free SH groups in a molecule thereof. Examples of the mercaptans include alkyl mercaptans, or alkyl mercaptans having one or more substituent groups such as carboxyl, amino andhydroxyl, e.g., mercaptocarboxylic acids, aminoalkanethiols and mercaptoalcohols. Specific examples of such mercaptans include alkyl mercaptans such as methyl mercaptan, ethyl mercaptan, n~butyl mercaptan and n-octyl mercaptan, thiocarboxylic acids such as thioglycolic acid and p-mercaptopropionic acid, aminoalkanethiols such as 2-aminoethanethiol, and mercaptoalcohols such as mercaptoethanol. Of these mercaptans, especially preferred are alkyl mercaptans in view of their good effect as a co-catalyst. These mercaptans may be used singly or in the combination of any two or more thereof. These mercaptans may be fixed on the above acid-type ion exchange resin to function as a co-catalyst. The amount of the mercaptans used is usually in the range of 0.1 to 20 mol% and preferably 1 to 10 mol% based on the raw acetone. The ratio between amounts of phenol and acetone used is not particularly limited, and the amount of unreacted acetone is preferably as low as possible in view of facilitated purification of bisphenol A produced and economical advantages. Therefore, phenol is usefully used in an excess amount relative to a stoichiometric amount thereof. Phenol is usually used in an amount of 3 to 30 mol and preferably 5 to 15 mol per mol of acetone. Upon production of bisphenol A, no reaction solvent is generally required except that the reaction solution has a too high viscosity or the reaction is conducted at a low temperature at which it might become difficult to continue the reaction due to undesired solidification. The condensation reaction of phenol and acetone in the above production process may be conducted by either a batch method or a continuous method. The condensation reaction may be advantageously conducted by such a fixed bed continuous reaction method in which phenol, acetone and mercaptans (in the case where the mercaptans are not fixed on the acid-type ion exchange resin) are continuously fed into a reaction column filled with the acid-type ion exchange resin. In the fixed bed continuous reaction method, either a single reaction column or two or more reaction columns may be used. In particular, a fixed bed multistage continuous reaction method using two or more reaction columns which are filled with the acid-type ion exchange resin and connected in series to each other is preferably used from the industrial viewpoints. The reaction conditions of the fixed bed continuous reaction method are explained below. First, the molar ratio of acetone to phenol is usually in the range of 1/30 to 1/3 and preferably 1/15 to 1/5. If the molar ratio of acetone to phenol is less than 1/30, the reaction rate tends to be too slow. If the molar ratio of acetone to phenol is more than 1/3, the amount of impurities produced tends to be increased, and the selectivity to bisphenol A tends to be lowered. On the other hand, in the case where the mercaptans are not fixed on the acid-type ion exchange resin, the molar ratio of the mercaptans to acetone is usually in the range of 0.1/100 to 20/100 and preferably 1/100 to 10/100. If the molar ratio of the mercaptans to acetone is less than 0.1/100, the reaction rate and the selectivity to bisphenol A may fail to be improved sufficiently. Even if the molar ratio of the mercaptans to acetone is more than 20/100, the effect corresponding to the use of such a large amount of the mercaptans tends to be no longer attainable. The reaction temperature is usually in the range of 40 to 150°C and preferably 60 to 110°C. If the reaction temperature is lower than 40°C, the reaction rate tends to be too slow, and the viscosity of the reaction solution tends to be too high, resulting in occurrence of undesired solidification thereof in some cases. If the reaction temperature exceeds 150°C, it might be difficult to suitably control the reaction, the selectivity to bisphenol A (p,pf-isomer) tends to be lowered, and the acid-type ion exchange resin as a catalyst tends to be decomposed or deactivated. Further, the LHSV (liquid hourly space velocity) of the raw mixture is usually in the range of 0.2 to 30 hr"1 and preferably 0.5 to 10 hr1. In the above production process, the mixed reaction solution thus obtained is preferably first filtered using a filter. Thus, by subjecting the solution of bisphenol A to filtration using a filter, foreign substances contained in the solution is removed therefrom, so that bisphenol A can be prevented from being decomposed under high temperature conditions in the subsequent steps. As a result, the obtained product can be prevented from undergoing formation of undesirable colored substances, thereby obtaining a bisphenol A product having a good hue. The above filtration procedure enables removal of catalyst residues and crushed catalyst particles which tend to promote decomposition of bisphenol A and deteriorate the hue of the bisphenol A product. In the post treatments of the mixed reaction solution or post treatments conducted subsequent to the above filtration procedure, in addition to the below-mentioned steps (B) to (F), the filtration procedure using a filter may be performed in at least one of periods between the step of dissolving the adduct of bisphenol A and phenol using the phenol-containing solution, and the step of crystallizing and separating the adduct from the solution. Next, the steps (B) to (F) are explained. Step (B): In the step (B), the mixed reaction solution containing substantially no acid-type ion exchange resin is concentrated. In this concentration step, usually, the mixed reaction solution is first subjected to distillation under reduced pressure using a distillation column to remove unreacted acetone, water by-produced and low-boiling substances such as alkyl mercaptans therefrom. The distillation under reduced pressure may be generally performed under a pressure of about 6.5 to 80 kPa at a temperature of about 70 to 180°C. In this case, the unreacted phenol undergoes azeotropy, so that a part of the unreacted phenol is discharged and removed out of the distillation column together with the low-boiling substances. In the distillation step, in order to prevent thermal decomposition of bisphenol A, the temperature of a heating source used is preferably controlled to 190°C or lower. Next, a bottom liquid obtained by removing the low-boiling substances from the reaction mixture which contains bisphenol A, phenol, etc., is further subjected to distillation under reduced pressure to distil off phenol therefrom and concentrate bisphenol A. The conditions of the above concentration step are not particularly limited, and the concentration step may be usually conducted at a temperature of about 100 to 170°C under a pressure of about 5 to 70 kPa. If the temperature used in the concentration step is lower than 100°C, a high vacuum tends to be required. If the temperature used in the concentration step is higher than 170°C, removal of excessive heat tends to be required in the subsequent crystallization step. Also, the concentration of bisphenol A contained in the concentrated residual solution is preferably in the range of 20 to 50% by mass and more preferably 20 to 40% by mass. If the concentration of bisphenol A in the concentrated residual solution is less than 20% by mass, the recovery rate of bisphenol A tends to be lowered. If the concentration of bisphenol A in the concentrated residual solution exceeds 50% by mass, the transportation of the resultant slurry after the crystallization step tends to become difficult. Step (C): In the step (C), a 1^1 adduct of bisphenol A and phenol (hereinafter referred to merely as "phenol adduct") is crystallized and separated from the concentrated residual solution obtained in the step (B). In this step, first, the above concentrated residual solution is cooled to a temperature of about 40 to 70°C to crystallize the phenol adduct therefrom and form a slurry. In this case, the above cooling may be conducted using an external heat exchanger, or may be conducted by a vacuum cooling crystallization method in which the concentrated residual solution is mixed with water, and cooled using a latent heat of vaporization of water under reduce pressure. In the vacuum cooling crystallization method, about 3 to 20% by mass of water is added to the concentrated residual solution, and the resultant mixture is subjected to crystallization treatment usually at a temperature of 40 to 70°C under a pressure of 3 to 13 kPa. If the amount of water added is less than 3% by mass, the heat removal capability tends to be insufficient. If the amount of water added exceeds 20% by mass, the dissolving loss of bisphenol A tends to become undesirably large. In such a crystallization procedure, if the crystallization temperature is less than 40°C, the solution to be crystallized tends to be increased in viscosity or solidified. If the crystallization temperature exceeds 70°C, the dissolving loss of bisphenol A tends to become undesirably large. Next, the slurry containing the thus crystallized phenol adduct is separated into the phenol adduct and a crystallization mother liquor containing reaction byproducts by known methods such as filtration and centrifugal separation. Step (D): In the step (D), the phenol adduct crystallized and separated in the above step (C) is dissolved using a phenol-containing solution. The phenol-containing solution used in the step (D) is not particularly limited. Examples of the phenol-containing solution include phenol recovered in the concentration step (B), a washing solution for the phenol adduct produced in the crystallization and separation step (C), a mother liquor obtained from the solid-liquid separation of the phenol adduct crystallized which is obtained in the step subsequent to this step (D), and a washing solution for the phenol adduct. The above phenol-containing solution is added to the phenol adduct obtained in the step (C), and the resultant mixture is heated to a temperature of about 80 to 110°C to dissolve the phenol adduct therein under heating, thereby preparing a bisphenol A-containing solution having a bisphenol A concentration suitable for the subsequent crystallization procedure. The thus prepared bisphenol A-containing solution is relatively easy to handle since the solution has a low viscosity even at a relatively low temperature. Therefore, the bisphenol A-containing solution is suitable for subjecting the phenol adduct crystallized in the subsequent step to solid-liquid separation using a filter. Step (E): In the step (E), the phenol adduct is crystallized and separated from the bisphenol A-containing solution obtained in the above step (D). If required, in order to obtain a higher purity product, the procedure of dissolving the thus obtained phenol adduct using a phenol-containing solution and then crystallizing and separating the phenol adduct from the solution may be repeated one or more times. In this step, the procedure of crystallizing and separating the phenol adduct and the procedure of dissolving the phenol adduct using a phenol-containing solution are the same as those in the steps (C) and (D), respectively. Step (F): In the step (F), the phenol adduct crystallized and separated in the above step (E) is melted under heating and then subjected to distillation to remove phenol therefrom. In this step, the phenol adduct is first heated to a temperature of about 100 to 160°C and melted to form a liquid mixture. Then, the liquid mixture is subjected to distillation under reduced pressure to distil off phenol therefrom, thereby recovering molten bisphenol A. The distillation under reduced pressure may be generally conducted under a pressure of 1 to 11 kPa at a temperature of 150 to 190°C. The residual phenol in the solution may be removed therefrom by further subjecting the solution to steam-stripping or nitrogen-stripping. The granulating column is equipped a top thereof with a nozzle plate for forming the melt of BPA into droplets at, and at a bottom thereof with a duct for blowing a cooling gas thereinto. As the nozzle plate, there may be used a metal plate provided with a number of pores or orifices, etc., which can be heated by an electric heater or steam in order to prevent solidification of BPA. The height of the granulating column may be determined depending upon a cooling time of the BPA droplets, and is usually in the range of about 10 to 50 m. As the granulating column, there may be used, for example, the apparatus as shown in Fig, 1. The melt of BPA purified in the step (F) is discharged from a granulating nozzle 1 to form BPA droplets, and then dropped in the form of a shower within a granulating column 2. The BPA droplets are cooled by a gas introduced through a inlet for cooling gas 3 and formed into prills of BPA which are discharged through a outlet for products 4. The gas used for cooling the BPA droplets is discharged through a outlet for cooling gas 5. The temperature of the melt of BPA is preferably in the range of 157 to 200°C and more preferably 157 to 180°C. If the temperature of the melt of BPA is less than 157°C, the melt of BPA tends to be solidified. If the temperature of the melt of BPA exceeds 200°C, the resultant prills of BPA tends to undergo undesirable discoloration. The granulating nozzle 1 is constituted of a plate with a nozzle. In the present invention, respective orifices formed in the nozzle have an orifice size (diameter) of 0.3 to 1.00 mm, preferably 0.4 to 0.7 mm and more preferably 0.5 to 0.6 mm, thereby enabling production of prills of BPA having an average particle size of about 0.5 to 1.5 mm. In the present invention, it is required that the discharge velocity of the melt of BPA discharged from the granulating nozzle 1 is controlled to 0.5 to 1.8 m/s, preferably 1.0 to 1.8 m/s and more preferably 1.4 to 1.8 m/s. When the discharge velocity of the melt of BPA is 0.5 m/s or more, the BPA droplets are prevented from being merged with each other and formed into large particles. When the discharge velocity of the melt of BPA is 1.8 m/s or less, the BPA droplets are not merged with each other, thereby forming particles having a uniform size. Since too large particles of the BPA droplets are difficult to cool, the BPA droplets still held in the form of the melt of BPA reach the bottom of the granulating column and attached or deposited thereonto. Meanwhile, the discharge velocity of the melt of BPA may be controlled by adjusting a flow rate of the melt of BPA fed to the nozzle, etc. Also, the distance between the adjacent orifices of the nozzle is in the range of 5 to 12 mm, preferably 7 to 11 mm and more preferably 8 to 10 mm. Meanwhile, the distance between the adjacent orifices of the nozzle means a distance between centers of the adjacent orifices. If the distance between the adjacent orifices of the nozzle exceeds 12 mm, the distance between the BPA droplets discharged becomes broadened and are difficult to merge with each other even though the melt of BPA is discharged in a somewhat inclined state from the nozzle. However, in such a case, if the amount of the melt of BPA fed becomes large, it is required to use a large number of the nozzle plates, so that the diameter of the granulating column must be inevitably increased. That is, when the distance between the adjacent orifices of the nozzle is 12 mm or less, the number of the nozzle plates is appropriate, so that it is unnecessary to increase the diameter of the granulating column. In addition, if the melt of BPA is discharged out of the nozzle in a deviated state due to contamination of the orifices of the nozzle, the BPA droplets tend to be merged with each other. However, when the distance between the adjacent orifices of the nozzle is 5 mm or more, the BPA droplets are prevented from merging with each other even though such a deviated flow of the melt of BPA occurred. As the gas introduced through inlet for cooling gas 3, there may be usually used inert nitrogen since BPA tends to be readily oxidized. The velocity of the cooling gas flowing through the granulating column 2 is in the range of 0.7 to 2.0 m/s, preferably 0.9 to 1.8 m/s and more preferably 1.0 to 1.6 m/s. When the velocity of the cooling gas flow is in the range of 0.7 to 2.0 m/s, the temperature within the granulating column 2 can be controlled to 40 to 90°C, so that the prills of BPA can be cooled to a temperature of 50 to 60°C. If the velocity of the cooling gas flow is 0.7 m/s or more, the melt of BPA can be appropriately cooled. On the other hand, if the velocity of the cooling gas flow is 2.0 m/s or less, the BPA droplets tend to be smoothly dropped and, as a result, prevented from being impinged against each other, resulting in reduction of BPA fine particles produced as well as increase in yield of prills of BPA. Further, as the material of apparatuses or equipments used in the process from the step (A) through the granulating column, there may be generally used SUS304, SUS316, SUS316L, etc. EXAMPLES Next, the present invention will be described in more detail by referring to the following examples and comparative examples. However, it should be noted that these examples are only illustrative and not intended to limit the invention thereto. REFERENCE EXAMPLE 1 A mixture containing phenol and acetone at a molar ratio of 10:l together with ethyl mercaptan were continuously flowed through a fixed bed-type reaction column filled with a cation exchange resin "DIAION SK104H" available from Mitsubishi Chemical Corp., at a LHSV of 3 hr1 to react with each other at 75°C. The resultant reaction mixture was subjected to distillation under a reduced pressure of 67 kPa at a bottom temperature of 170°C to remove acetone, water, ethyl mercaptan, etc., therefrom. Then, the reaction mixture was further subjected to distillation under a reduced pressure of 14 kPa at 130°C to remove phenol therefrom, and concentrate the mixture until the concentration of bisphenol A therein reached 40% by mass to obtain a phenol solution of bisphenol A. The thus obtained phenol solution of bisphenol A having a bisphenol A concentration of 40% by mass was mixed with water, and cooled to 50°C under reduced pressure and held under the conditions to crystallize an adduct of bisphenol A and phenol, thereby obtaining a slurry. Next, the thus obtained slurry was subjected to solid-liquid separation, thereby separating the adduct of bisphenol A and phenol therefrom. The resultant adduct was mixed with phenol, and then heated to 90°C, thereby preparing a solution containing 60% by mass of phenol and 40% by mass of bisphenol A. The resultant solution was subjected again to similar vacuum cooling crystallization and solid-liquid separation to obtain the adduct of bisphenol A and phenol. Then, the resultant adduct was washed with purified phenol, thereby obtaining crystals of the adduct of bisphenol A and phenol. The obtained crystals of the adduct were melted under heating to 130°C and then dephenolated to obtain bisphenol A. The resultant bisphenol A was heated at 220°C for 40 min in air. As a result of visual observation of a hue of the bisphenol A based on an APHA standard color, it was confirmed that the bisphenol A exhibited a hue of APHA15. EXAMPLE 1 A nitrogen gas is fed to a granulating column having a diameter of 2.2 m and a height of 30 m from a bottom thereof at a gas velocity of 1.6 m/s. The granulating column was fitted, at top thereof, with a nozzle plate having orifices with a diameter of 0.5 mm adjacent two of which were spaced from each other at a distance of 9 mm. The melt of bisphenol A at 170°C was fed to the nozzle plate such that a discharge velocity of the melt of bisphenol A from the nozzle was 1.4 m/s, thereby granulating BPA. As a result, it was confirmed that prills of BPA having an average particle size of 1.0 mm were stably produced over 2 weeks. After the elapse of 2 weeks, when the granulating column was inspected, it was confirmed that substantially no adherent substance such as BPA was deposited on a bottom of the granulating column. The results are shown in Table 1. EXAMPLE 2 Using the same nozzle plate and the same granulating column as used in EXAMPLE 1, a nitrogen gas at 40°C was fed to the granulating column at a gas velocity of 1.0 m/s, and the melt of bisphenol A at 170°C was fed thereto such that a discharge velocity of the melt of bisphenol A from the nozzle was 1.8 m/s, thereby granulating BPA. As a result, it was confirmed that prills of BPA having an average particle size of 1.1 mm were stably produced over 2 weeks. After the elapse of 2 weeks, when the granulating column was inspected, it was confirmed that substantially no adherent substance such as BPA was deposited on the bottom of the granulating column. The results are shown in Table 1. EXAMPLE 3 The same granulating column as used in EXAMPLE 1 was fitted, at top thereof, with a nozzle plate having orifices with a diameter of 0.6 mm adjacent two of which were spaced from each other at a distance of 5 mm. A nitrogen gas at 40°C was fed to the granulating column at a gas velocity of 1.6 m/s, and the melt of bisphenol A at 170°C was fed thereto such that a discharge velocity of the melt of bisphenol A from the nozzle was 1.5 m/s, thereby granulating BPA. As a result, it was confirmed that prills of BPA having an average particle size of 1.1 mm were stably produced over 2 weeks. After the elapse of 2 weeks, when the granulating column was inspected, it was confirmed that substantially no adherent substance such as BPA was deposited on the bottom of the granulating column. The results are shown in Table 1. EXAMPLE 4 The same granulating column as used in EXAMPLE 1 was fitted, at top thereof, with a nozzle plate having orifices with a diameter of 0.5 mm adjacent two of which were spaced from each other at a distance of 5 mm. A nitrogen gas at 40°C was fed to the granulating column at a gas velocity of 1.1 m/s, and the melt of bisphenol A at 170°C was fed thereto such that a discharge velocity of the melt of bisphenol A from the nozzle was 1.8 m/s, thereby granulating BPA. As a result, it was confirmed that prills of BPA having an average particle size of 1.1 mm were stably produced over 2 weeks. After the elapse of 2 weeks, when the granulating column was inspected, it was confirmed that substantially no adherent substance such as BPA was deposited on the bottom of the granulating column. The results are shown in Table 1. COMPARATIVE EXAMPLE 1 Into the same granulating column as used in EXAMPLE 4 which was fitted with a nozzle plate having orifices with a diameter of 0.5 mm adjacent two of which were spaced from each other at a distance of 5 mm, a nitrogen gas at 40°C was fed at a gas velocity of 1.1 m/s, and the melt of bisphenol A at 170°C was fed such that a discharge velocity of the melt of bisphenol A from the nozzle was 2.9 m/s, thereby granulating BPA. As a result, it was confirmed that prills of BPA having an average particle size of 1.6 mm were stably produced over 2 weeks. However, after the elapse of 2 weeks, when the granulating column was inspected, it was confirmed that about 10 mnrthick BPA was deposited on the bottom of the granulating column. The adherent substance was readily separated from the bottom of the granulating column by applying an impact thereto from outside. The results are shown in Table 1. COMPARATIVE EXAMPLE 2 Into the same granulating column as used in EXAMPLE 1 which was fitted with a nozzle plate having orifices with a diameter of 0.5 mm adjacent two of which were spaced from each other at a distance of 9 mm, a nitrogen gas at 40°C was fed at a gas velocity of 0.5 m/s, and the melt of bisphenol A at 170°C was fed such that a discharge velocity of the melt of bisphenol A from the nozzle was 1.8 m/s, thereby granulating BPA. As a result, it was confirmed that prills of BPA having an average particle size of 1.3 mm were stably produced over 2 weeks. However, after the elapse of 2 weeks, when the granulating column was inspected, it was confirmed that about 50 mnrthick BPA was deposited on the bottom of the granulating column. The adherent substance was readily separated in a plate shape from the bottom of the granulating column by applying an impact thereto from outside. The results are shown in Table 1. COMPARATIVE EXAMPLE 3 Into the same granulating column as used in EXAMPLE 1 which was fitted with a nozzle plate having orifices with a diameter of 0.5 mm adjacent two of which were spaced from each other at a distance of 9 mm, a nitrogen gas at 40°C was fed at a gas velocity of 1.6 m/s, and the melt of bisphenol A at 170°C was fed such that a discharge velocity of the melt of bisphenol A from the nozzle was 0.4 m/s, thereby granulating BPA. As a result, it was confirmed that droplets of the melt of BPA were merged together to form large size particles, dropped and impinged to the bottom of the granulating column before being completely solidified, and then deposited thereon, thereby finally causing plugging of the granulating column. The results are shown in Table 1. COMPARATIVE EXAMPLE 4 Into the same granulating column as used in EXAMPLE 3 which was fitted with a nozzle plate having orifices with a diameter of 0.6 mm adjacent two of which were spaced from each other at a distance of 5 mm, a nitrogen gas at 40°C was fed at a gas velocity of 2.5 m/s, and the melt of bisphenol A at 170°C was fed such that a discharge velocity of the melt of bisphenol A from the nozzle was 1.5 m/ss thereby granulating BPA. As a result, it was confirmed that although prills of BPA having an average particle size of 1.2 mm were stably produced over 2 weeks, BPA fine particles deposited in the nitrogen gas outlet were increased. After the elapse of 2 weeks, when the granulating column was inspected, it was confirmed that although substantially no BPA was deposited on the bottom of the granulating column, the yield of the prills of BPA was lowered. The results are shown in Table 1. COMPARATIVE EXAMPLE 5 Into the same granulating column as used in EXAMPLE 1 which was fitted with a nozzle plate having orifices with a diameter of 0.5 mm adjacent two of which were spaced from each other at a distance of 3 mm, a nitrogen gas at 40° C was fed at a gas velocity of 1.0 m/s, and the melt of bisphenol A at 170°C was fed such that a discharge velocity of the melt of bisphenol A from the nozzle was 1.8 m/s, thereby granulating BPA. As a result, it was confirmed that prills of BPA having an average particle size of 1.6 mm were stably produced over 2 weeks. However, after the elapse of 2 weeks, when the granulating column was inspected, it was confirmed that about 30 mnrthick BPA was deposited on the bottom of the granulating column. The results are shown in Table 1. CLAIMS 1. A process for producing a prill of bisphenol A, comprising the step of dropping a melt of bisphenol A from a nozzle plate disposed at an upper portion of a granulating column and flowing a cooling gas upwardly from a lower portion of the granulating column, said process satisfying the following conditions (a) to (c): (a) a diameter of respective orifices of the nozzle being in the range of 0.3 to 1.0 mm; (b) a discharge velocity of the melt of bisphenol A from the nozzle being in the range of 0.5 to 1.8 m/s; and (c) a flow rate of the cooling gas being in the range of 0.7 to 2.0 m/s. 2. The process for producing a prill of bisphenol A as described in claim 1, wherein a distance between the adjacent orifices of the nozzle is in the range of 5 to 12 mm.

Documents:

2786-CHENP-2006 AMENDED PAGES OF SPECIFICATION 13-10-2011.pdf

2786-CHENP-2006 AMENDED CLAIMS 13-10-2011.pdf

2786-CHENP-2006 CORRESPONDENCE OTHERS 05-08-2011.pdf

2786-CHENP-2006 FORM-3 13-10-2011.pdf

2786-CHENP-2006 OTHER PATENT DOCUMENT 13-10-2011.pdf

2786-CHENP-2006 EXAMINATION REPORT REPLY RECEIVED 13-10-2011.pdf

2786-chenp-2006-abstract.pdf

2786-chenp-2006-claims.pdf

2786-chenp-2006-correspondnece-others.pdf

2786-chenp-2006-description(complete).pdf

2786-chenp-2006-drawings.pdf

2786-chenp-2006-form 1.pdf

2786-chenp-2006-form 26.pdf

2786-chenp-2006-form 3.pdf

2786-chenp-2006-form 5.pdf

2786-chenp-2006-pct.pdf