Title of Invention	"PROCESS FOR PRODUCING HIGH-PURITY TEREPHTHALIC ACID"
Abstract	A method for producing high purity terephthalic acid having a step (a) of forming crude terephthalic acid, a disso-lution step (b) of dissolving the crude terephthalic acid in a water solvent, a reduction step(c), a crystallization step (d), a separation step (e), a washing step (f) and a drying step (g), which further comprises a recovering step (h) wherein a solid contained in the washing wastewater discharged from the above washing step (f) is recovered and the resultant solid is fed to the above crystallization step (d) or to the above separation step (e), and a reuse step (i) wherein the washing waslewater having been subjected to the recovery of a solid in the above recovering step (h) is used as a solvent for the above dissolution step (b). The above method allows the reuse of a washing wastewater with an apparatus being compact in size, in the production of high purity terephthalic acid.

Title of Invention

"PROCESS FOR PRODUCING HIGH-PURITY TEREPHTHALIC ACID"

Abstract

A method for producing high purity terephthalic acid having a step (a) of forming crude terephthalic acid, a disso-lution step (b) of dissolving the crude terephthalic acid in a water solvent, a reduction step(c), a crystallization step (d), a separation step (e), a washing step (f) and a drying step (g), which further comprises a recovering step (h) wherein a solid contained in the washing wastewater discharged from the above washing step (f) is recovered and the resultant solid is fed to the above crystallization step (d) or to the above separation step (e), and a reuse step (i) wherein the washing waslewater having been subjected to the recovery of a solid in the above recovering step (h) is used as a solvent for the above dissolution step (b). The above method allows the reuse of a washing wastewater with an apparatus being compact in size, in the production of high purity terephthalic acid.

Full Text	DESCRIPTION PROCESS FOR PRODUCING HIGH-PURITY TEREPHTHALIC ACID Technical Field [0001] The present invention relates to a process for producing high-purity terephthalic acid. Background Art [0002] For obtaining crystals of high-purity terephthalic acid, it is necessary that the intermediates which have generated as by-products of the oxidation of p-xylene and include 4-carboxybenzaldehyde as a major component (the intermediates are effective ingredients convertible into terephthalic acid but are impurities after mixing with product terephthalic acid) should be removed as much as possible from crude terephthalic acid crystals obtained by the oxidation. For this purpose, a purification step is conducted in which the 4-carboxybenzaldehyde is reduced to p-toluic acid, which has higher water solubility than terephthalic acid, and terephthalic acid crystallization is then conducted to obtain high-purity terephthalic acid crystals. This procedure, for example, comprises the following steps as shown in Fig. 2. [0003] First, in a dissolution step, crude terephthalic acid a is slurried with water b in a slurrying vessel 1 and the resultant initiation slurry c is made to have a high temperature and high pressure with a pump la and a heater Ib to dissolve the crude terephthalic acid a in the water and thereby obtain an aqueous crude-terephthalic-acid solution c'. A reduction step is then conducted in which the aqueous crude-terephthalic-acid solution c' is introduced into a hydrogenation reactor 2 and brought into contact with hydrogen d in the presence of a catalyst to thereby reduce the 4-carboxybenzaldehyde into p-toluic acid. The liquid reduction reaction mixture e thus obtained, which contains p-toluic acid and terephthalic acid, is introduced into crystallization vessels 3 arranged in series to conduct a crystallization step, in which crystallization is caused by pressure-release cooling. Since terephthalic acid has lower water solubility than p-toluic acid, high-purity crystals of terephthalic acid can be separated out in this step by controlling crystallization conditions. A separation step is subsequently conducted, in which a slurry f containing the high-purity crystals of terephthalic acid which have thus separated out is introduced into a solid-liquid separator 4 optionally with pressure control with a pump 3a. The slurry is thus subjected to solid-liquid separation in which the reduction-reaction mother liquor g is separated and a high-purity terephthalic acid cake h is recovered. This high-purity terephthalic acid cake h is subjected to a washing step, in which a washing operation with a cleaning fluid i is performed in a washing apparatus 5 and a solid-liquid separation operation is performed in a solid-liquid separator 6 to obtain a washed cake k. Furthermore, a drying step is conducted, in which the washed cake k obtained is dried with a dryer 8 to obtain high-purity terephthalic acid crystals m. On the other hand, since the reduction-reaction mother liquor g still contains effective ingredients including terephthalic acid and p-toluic acid, these effective ingredients are recovered as much as possible. Furthermore, the washings j discharged after the washing operation are reused as a solvent in the dissolution step. [0004] In the crystallization step/ the final crystallization vessel is generally operated at a temperature of 120-180°C in order to prevent the p-toluic acid from forming a eutectic with the terephthalic acid. Because of this, the procedure heretofore in use comprises subjecting the slurry f obtained through crystallization to solid-liquid separation with a solid bowl type centrifugal separator while keeping the slurry f in a high-temperature and high-pressure state to thereby separate the reduction-reaction mother liquor g, washing the resultant high-purity terephthalic acid cake h by suspension washing at an elevated pressure, releasing the suspension from the pressure, conducting solid-liquid separation again at ordinary pressure, and discharging the washings j. [0005] Recently, a process for terephthalic acid production including a simplified step for the purification is described in patent documents 1 and 2. In this process, a solid-liquid separation/washing apparatus 7 in which both the solid-liquid separation operation and the washing operation can be conducted (corresponding to the apparatus surrounded by the broken line in the figure) is used to integrally conduct solid-liquid separation and a washing step at an elevated pressure. In this case, the washings j to be discharged are in a high-temperature high-pressure state. [0006] The washings j are accompanied by part of the solid matter to be recovered as a high-purity terephthalic acid cake h, because of, e.g., leakage through the washing screen. When the washings j containing the solid matter are reused, without any treatment, as a solvent in the slurrying vessel 1, then the amount of the solid matter which should be treated in the purification step system is increased and this requires each apparatus to have a larger size because of the necessity of keeping the slurry concentration in the system constant. Furthermore, when solid-liquid separation and a washing operation are conducted in a united apparatus at a high temperature and high pressure, a larger amount of terephthalic acid dissolves in the washings. This also results in an increase in solid matter amount in the system and hence in the necessity of apparatus enlargement. Patent Document 1: WO 92/18454 Patent Document 2: WO 93/24440 Disclosure of the Invention Problem that the Invention is to Solve [0007] An object of the invention is to provide a process for producing high-purity terephthalic acid in which washings can be reused with a small apparatus in producing high-purity terephthalic acid. Means for Solving the Problem [0008] The present inventors made intensive investigations in order to overcome the problem described above. As a result, they have found that the problem can be eliminated by removing beforehand the solid matter which has accompanied the washings. It has been further found that the solid matter removed can be reused without influencing product quality by recycling the solid matter to a step before the separation step. The invention has been thus completed. Essential points of the invention reside in the following (1) to (10). [0009] (1) A process for producing high-purity terephthaiic acid which comprises a crude terephthalic acid production step (a) in which p-xylene is oxidized to produce crude terephthalic acid containing 4-carboxybenzaldehyde, a dissolution step (b) in which the crude terephthalic acid obtained in the crude terephthalic acid production step (a) is dissolved in a water solvent at a high temperature and a high pressure to obtain an aqueous solution of the crude terephthalic acid, a reduction step (c) in which the 4-carboxybenzaldehyde in the aqueous crude-terephthaiic-acid solution is reduced to p-toluic acid with hydrogen in the presence of a catalyst to obtain a liquid of reduction reaction mixture, a crystallization step (d) in which the liquid of reduction reaction mixture is cooled to 120-200°C to cause crystals of the terephthalic acid and thereby obtain a slurry, a separation step (e) in which the slurry is subjected to solid-liquid separation to separate the slurry into a terephthalic acid cake comprising the terephthalic acid crystals as the main component and the mother liquor in the reduction reaction, a washing step (f) in which the terephthalic acid cake is washed with a cleaning fluid, and a drying step (g) in which the cake washed in the washing step (f) is dried to obtain crystals of high-purity terephthalic acid, the process further including a recovery step (h) in which a solid matter contained in the washings discharged from the washing step (f) is recovered and the solid matter obtained is sent to the crystallization step (d) or the separation step (e) and a reuse step (i) in which the washings from which a solid matter has been recovered in the recovery step (h) are used as a solvent for the dissolution step (b) . [0010] (2) The process for producing high-purity terephthalic acid as described under (1) above wherein in the recovery step (h), the solid matter is recovered after the washings discharged from the washing step (f) are cooled. [0011] (3) The process for producing high-purity terephthalic acid as described under (2) above wherein the washings discharged from the washing step (f) have a temperature exceeding 100°C and the solid matter is recovered therefrom after the washings are cooled to 0-100°C. [0012] (4) The process for producing high-purity terephthalic acid as described under (2) or (3) above wherein the washings are cooled by pressure-release evaporation. [0013] (5) The process for producing high-purity terephthalic acid as described under any one of (1) to (4) above wherein the recovery of a solid matter in the recovery step (h) is conducted with a cyclone or a thickener. [0014] (6) The process for producing high-purity terephthalic acid as described under any one of (1) to (5) above wherein the separation step (e) is conducted at a pressure higher than the pressure in a final crystallization vessel in the crystallization step (d). [0015] (7) The process for producing high-purity terephthalic acid as described under anyone of (1) to (6) above wherein the separation step (e) and the washing step (f) are conducted with a united apparatus. [0016] (8) The process for producing high-purity terephthalic acid as described under (7) above wherein the united apparatus for conducting the separation step (e) and the washing step (f) is any of a screen bowl type centrifugal separator, a rotary pressure filter, and a horizontal belt filter. [0017] (9) The process for producing high-purity terephthalic acid as described under any one of (1) to (8) above wherein the solid matter contained in the washings discharged from the washing step (f) accounts for 1-10% by weight of the terephthalic acid crystals contained in the slurry supplied to the separation step (e) . [0018] (10) The process for producing high-purity terephthalic acid as described under any one of (1) to (8) above wherein the crystallization step (d) is composed of crystallization vessels arranged in two or more stages and the solid matter recovered in the recovery step (h) is sent to the final crystallization vessel among the crystallization vessels arranged in two or more stages. Advantage of the Invention [0019] According to the invention, a process for producing high-purity terephthalic acid can be provided in which washings can be reused with a small apparatus in producing high-purity terephthalic acid. Brief Description of the Drawings [0020] [Fig. 1] Fig. 1 is a flow diagram illustrating an embodiment of the process for producing high-purity terephthalic acid according to the invention. [Fig. 2] Fig. 2 is a flow diagram illustrating an example of related-art processes for producing high-purity terephthalic acid. Description of the Reference Numerals and Sings [0021] 1, 11 slurrying vessel la, lla pump Ib, lib heater 2, 12 hydrogenation reactor 3, 13 crystallization vessel 3a, 13a pump 4, 6 solid-liquid separator 5 washing apparatus 7, 17 solid-liquid separation/washing apparatus 8, 18 dryer 19 cooler 20 separator a, A crude terephthalic acid b, B water c, C initiation slurry c1, C' aqueous crude-terephthalic-acid solution d, D hydrogen e, E liquid reduction reaction mixture f, F slurry g, G reduction-reaction mother liquor h high-purity terephthalic acid cake i, I cleaning fluid j, J washings k washed cake K high-purity terephthalic acid cake m, M high-purity terephthalic acid crystals N recovered slurry O recovered solid matter P recovered waste liquid Best Mode for Carrying Out the Invention [0022] The invention will be explained below in detail. [0023] The process of the invention for producing high-purity terephthalic acid comprises a crude terephthalic acid production step (a) in which p-xylene is oxidized to produce crude terephthalic acid containing 4-carboxybenzaldehyde, a dissolution step (b) in which the crude terephthalic acid obtained in the crude terephthalic acid production step (a) is dissolved in a water solvent at a high temperature and a high pressure to obtain an aqueous solution of the crude terephthalic acid, a reduction step (c) in which the 4-carboxybenzaldehyde in the aqueous crude-terephthalic-acid solution is reduced to p-toluic acid with hydrogen in the presence of a catalyst to obtain a liquid reduction reaction mixture, a crystallization step (d) in which the liquid reduction reaction mixture is cooled to 120-200°C to cause crystals of the terephthalic acid and thereby obtain a slurry, a separation step (e) in which the slurry i s subjected to solid-liquid separation to separate the slurry into a terephthalic acid cake comprising the terephthalic acid crystals as the main component and the mother liquor in the reduction reaction, a washing step (f) in which the terephthalic acid cake is washed with a cleaning fluid, and a drying step (g) in which the cake washed in the washing step (f) is dried to obtain crystals of high-purity terephthalic acid, the process being characterized by further including a recovery step (h) in which a solid matter contained in the washings discharged from the washing step (f) is recovered and the solid matter obtained is sent to the crystallization step (d) or the separation step (e) and a reuse step (i) in which the washings from which a solid matter has been recovered in the recovery step (h) are used as a solvent for the dissolution step (b) . The production process of the invention is explained by reference to Fig. 1. [0024] The term "effective ingredients" hereinafter means terephthalic acid and other compounds capable of being converted to terephthalic acid through, e.g./ oxidation, and includes both dissolved ingredients and precipitated ingredients. The term "solid matter" means precipitated ingredients among the effective ingredients. [0025] First, in the crude terephthalic acid production step (a) , p-xylene is oxidized in a liquid phase with molecular oxygen in an acetic acid solvent in the presence of a catalyst to thereby produce crude terephthalic acid. This step is well known, and the catalyst, which has been known to be conventionally used in this reaction, is used. Examples thereof include compounds of heavy metals, such as cobalt compounds, manganese compounds, iron compounds, and chromium compounds, and bromine compounds. In the reaction system, these compounds are present in a dissolved state. Preferred of these is a combination of a cobalt compound or manganese compound with a bromine compound. In this case, these compounds are generally used in such amounts that the amounts of cobalt atoms, manganese atoms, and bromine atoms are 10-5,000 ppm, 10-5,000 ppm, and 10-10,000 ppm, respectively, of the solvent. [0026] As the molecular oxygen is generally used a gas mixture comprising an inert gas and oxygen. For example, air or oxygen-enriched air is used. The molar proportion of the molecular oxygen to the p-xylene to be fed to the reactor is generally 3-20 times by mole, preferably 2-4 times by mole. [0027] The proportion of the p-xylene to the acetic acid to be supplied to the reactor is generally 1-50% by weight. The concentration of water in the reaction system is generally 5-20% by weight, preferably 5-15% by weight. [0028] The temperature in the oxidation reaction is generally 160-260°C/ preferably 170-210°C. The reaction may be conducted at any pressure at which the reaction system can retain a liquid phase at the reaction temperature. The pressure is generally 0.5-5 MPa, preferably 1-2 MPa. The residence time is generally 10-200 minutes. [0029] Terephthalic acid is not easy to dissolve in the acetic acid serving as a solvent. Because of this, the terephthalic acid yielded in the oxidation reaction step precipitates as crystals to form a slurry. However, terephthalic acid may be dissolved depending on the amount of the solvent, reaction temperature, and pressure. In this case, a crystallization step for, e.g., cooling the liquid reaction mixture is conducted to precipitate the terephthalic acid and thereby form a slurry. This slurry is subjected to solid-liquid separation to obtain crude terephthalic acid crystals. Although the terephthalic acid slurry obtained in the oxidation reaction step is in a pressurized state/ this slurry may be subjected as it is to solid-liquid separation or may be subjected to pressure-release cooling or the like and then to solid-liquid separation. For the solid-liquid separation, any method may be used as long as the crystals can be separated from the mother liquor. Examples thereof include filtration and centrifugal separation. If necessary, washing and drying are conducted. Thus, crude terephthalic acid crystals are obtained. [0030] The teem "crude terephthalic acid" in the invention means terephthalic acid containing 4-carboxybenzaldehyde in an amount of 1,000-10,000 ppm. [0031] In the dissolution step (b) , the crude terephthalic acid A (crude terephthalic acid containing 4-carboxybenzaldehyde and obtained by oxidizing p-xylene) is sent to a slurrying vessel 11 and dissolved in water B in a high-temperature and high-pressure environment. The crude terephthalic acid A is one obtained by oxidizing p-xylene in an aliphatic carboxylic acid solvent such as acetic acid. This crude terephthalic acid contains, as by-products, intermediates in which one of the alkyl groups has not been completely oxidized, such as, e.g., 4-carboxybenzaldehyde. For producing the high-purity terephthalic acid, it is necessary that these impurities should be removed as much as possible from the crude terephthalic acid A. [0032] The terephthalic acid has low solubility in water. It is necessary that the crude terephthalic acid A should be slurried with water B in the slurrying vessel 11 and the resultant initiation slurry C should be regulated with a pump lla and a heater lib so as to have a high temperature and high pressure at which the terephthalic acid can be dissolved in the water. The temperature in such high-temperature and high-pressure conditions depends on the slurry concentration. However, the temperature should be 200°C or higher and be not higher than the temperatures which the apparatus can withstand, and desirably is 230°C or higher and 320°C or lower. The pressure in the high-temperature and high-pressure conditions should be one at which a liquid phase can be maintained at a temperature in that range, and desirably is 2.8 MPa or higher and 11.3 MPa or lower. [0033] The concentration of the slurry obtained in the dissolution step (b) is generally 20-40 wt%, preferably 25-35 wt%. Too high slurry concentrations cause clogging in the apparatus. Too low slurry concentrations result in an increased mother liquor amount and this necessitates a larger apparatus size suitable for the production amount. From the standpoint of clogging prevention, it is preferred to maintain a constant slurry concentration. [0034] In the subsequent reduction step (c) , the aqueous crude-terephthaiic-acid solution C1 obtained through the dissolution step (b) is sent to a hydrogenation reactor 12 and catalytically reduced in the presence of a catalyst with hydrogen D introduced to thereby obtain a liquid reduction reaction mixture E. The catalyst and the conditions in the hydrogenation reactor 12 should be ones which reduce the 4-carboxybenzaldehyde and do not reduce the terephthalic acid. This is intended to reduce the 4-carboxybenzaldehyde contained in the aqueous crude-terephthalic-acid solution C1 to p-toluic acid, which has higher solubility in water than the terephthalic acid. It is desirable that this reduction should be conducted to the highest possible level. This hydrogenation also is well known. As the hydrogenation catalyst may be used a catalyst comprising a Group 8-10 (according to IUPAC Nomenclature of Inorganic Chemistry, revised edition (1998)) metal such as ruthenium, rhodium, palladium, platinum, or osmium. Usually, such a catalyst is supported on a support, e.g., activated carbon, and used as a fixed bed. Preferred of those is palladium supported on activated carbon. The temperature in the hydrogenation is generally 260-320°C, preferably 270-300°C, and the partial pressure of hydrogen is generally 0.5-20 kg/cm2G. [0035] Furthermore, in the crystallization step (d) , the liquid reduction reaction mixture E obtained in the reduction step (c) is introduced into a crystallization vessel 13. The temperature and pressure are reduced to such a degree that the p-toluic acid remains dissolved. Thus, the terephthalic acid is crystallized to obtain a slurry F. It is more desirable that two or more, preferably three to six, crystallization vessels 13 be arranged in series and the pressure be reduced by stages to cool the reaction mixture E (cooling by pressure-release evaporation) and crystallize the terephthalic acid. Although two crystallization vessels 13 have been disposed in Fig. 1, three or more crystallization vessels may be disposed. The temperature in the final crystallization vessel which is the last of the crystallization vessels 13 may be regulated so as to result in temperature conditions under which the p-toluic acid does not form a eutectic with the terephthalic acid. Specifically, the temperature is desirably 120°C or higher and 200°C or lower, more desirably 130°C or higher and 180°C or lower. The pressure in this case is desirably 0.20 MPa or higher and 1.56 MPa or lower, more desirably 0.27 MPa or higher and 1.00 MPa or lower. [0036] Subsequently, in the separation step (e) , the slurry F is introduced into a solid-liquid separator at a pressure higher than the pressure of the slurry obtained in the crystallization step (d) to separate a reduction-reaction mother liquor G and obtain a high-purity terephthalic acid cake including the terephthalic acid crystals having a high purity. Furthermore, the washing step (f) is conducted in which this high-purity terephthalic acid cake is washed while keeping the cake in a pressurized state. It is preferred that a solid-liquid separation/washing apparatus 17 in which the separation step (e) and the washing step (f) can be simultaneously conducted should be used as that solid-liquid separator in this operation. Employing this apparatus can simplify a series of steps. [0037]When the separation step (e) and the washing step (f) are conducted with the solid-liquid separation/washing apparatus 17 only, the procedure is as follows. The slurry F and a cleaning fluid I are introduced into the solid-liquid separation/washing apparatus 17. Water having a temperature equal to or higher than the operating temperature of the solid-liquid separation/washing apparatus 17 is generally used as the cleaning fluid I. Immediately after the solid-liquid separation of the slurry F is conducted, the resultant cake is washed with the cleaning fluid I in the same apparatus. And then, a high-purity terephthalic acid cake K which has been washed is separated and taken out, and the reduction-reaction mother liquor G and washings J consisting mainly of the cleaning fluid I are discharged. [0038] It is desirable that the operating temperature of the solid-liquid separation/washing apparatus 17 be equal to the temperature in the final crystallization vessel in the crystallization step (d) and be 120°C or higher and 200°C or lower. More desirably, the operating temperature is 130°C or higher and 180°C or lower. The pressure should be higher than the pressure in the final crystallization vessel in the crystallization step (d) in order to inhibit a temperature decrease caused by pressure release. Specifically, it is desirable that the pressure in the apparatus 17 be higher by 0-1 MPa than the pressure in the final crystallization vessel in the crystallization step (d) . In case where the reaction mixture which has undergone crystallization in the final crystallization vessel further undergoes a pressure reduction, cooling by pressure-release evaporation occurs and ingredients dissolved in the mother liquor may precipitate. This may raise a trouble in the separation step (e) in the solid-liquid separation/washing apparatus 17. On the other hand, raising the pressure to a high degree requires the apparatus to be reinforced so as to withstand that. Examples of the solid-liquid separation/washing apparatus 17, in which both of solid-liquid separation and washing can be conducted as described above, include a screen bowl type centrifugal separator, rotary vacuum filter, and horizontal belt filter. Especially preferred is a screen bowl type centrifugal separator. [0039] The high-purity terephthalic acid cake K thus obtained is dried with a dryer 18 in the drying step (g) to thereby remove the residual adherent liquid. Thus, high-purity terephthalic acid crystals M can be obtained. Examples of the dryer 18 include a steam tube dryer and a fluidized-bed dryer. It is also possible to use a method in which releasing the pressure from the high-purity terephthalic acid cake K having a high temperature and a high pressure vaporize at least part of the solvent ingredient adherent to the cake. Examples of the dyer 18 include a rotary dryer and a fluidized-bed dryer. The drying may be conducted in the presence of a flowing gas at a drying outlet operating temperature of 70-180°C using steam or the like as a heat source. [0040] On the other hand, the reduction-reaction mother liquor G also contains the effective ingredients, e.g., terephthalic acid and p-toluic acid, and it is necessary to recover these ingredients as much as possible. Examples of methods for the recovery include a method which comprises introducing the mother liquor G into one or more pressure-release cooling vessels, cooling the mother liquor G to precipitate the effective ingredients contained therein to obtain a slurry, filtering the slurry to separate it into a secondary mother liquor and secondary crystals, introducing the secondary crystals into the oxidation step in which the dialkylaromatic compound is oxidized to yield the crude aromatic carboxylic acid, and using the secondary mother liquor directly or indirectly in place of the water B in the slurrying vessel 11 or using the secondary liquor as a cleaning fluid in the washing step (f) . [0041] The pressure-release cooling vessels are vessels regulated so as to have a pressure which is lower than the pressure of the liquid to be introduced thereinto and at which the boiling point of the main component of the liquid is not higher than the temperature of the liquid before introduction. When a liquid is introduced into this pressure-release cooling vessel, part of the liquid vaporizes and the remainder of the liquid is cooled to the boiling point at the pressure after the change. In this operation, when the liquid is a solution, the solute is precipitated in an amount by which the solute amount exceeds the solubility after the cooling. [0042] Furthermore, the washings J (the term "washings" in the invention means the liquid discharged after the terephthalic acid cake obtained through solid-liquid separation is washed with a cleaning fluid) also contain the effective ingredients. Especially when the solid-liquid separation/washing apparatus 17 is employed to stably conduct both of solid-liquid separation and washing therein, the solid matter, which is not dissolved in the washings J, is apt to come into the washings J. The amount of this solid matter is desirably 1% by weight or larger and 10% by weight or smaller, more desirably 3% by weight or larger and 8% by weight or smaller, based on the terephthalic acid crystals in the slurry F supplied to the solid-liquid separation/washing apparatus 17. In case where it is attempted to reduce the content of the solid matter to below 1% by weight, there is a possibility that the operation of the solid-liquid separation/washing apparatus 17 might become unstable. On the other hand, in case where the content thereof exceeds 10% by weight, it becomes necessary to enlarge the solid-liquid separation/washing apparatus 17 for obtaining the high-purity terephthalic acid crystals M in a desired amount. [0043] In the recovery step (h), the effective ingredients are recovered as the solid matter from the washings J as much as possible. Since the washings J have a high temperature (generally exceeding 100°C) , the effective ingredients are contained therein in a dissolved state in a large amount besides being contained as the solid matter. It is therefore desirable to cool the washings J in order to precipitate the effective ingredients dissolved. More desirably, the washings J are cooled to 100°C or lower. However, the temperature to which the washings J are to be cooled should be not lower than the solidifying point of the washings J, and is preferably 60°C or higher and 100°C or lower. In case where the cooling temperature is too high, the terephthalic acid dissolved in the washings cannot be sufficiently recovered. In case where the cooling temperature is too low, energy is necessary for preheating in reusing the washings in the dissolution step (b) and the apparatus is required to be enlarged. The cooling may be conducted with a cooler 19 which is a pressure-release cooling vessel, or may be conducted by heat exchange. From the standpoint of apparatus simplification, it is preferred to use a pressure-release cooling vessel. Cooling to below 100°C may be attained by employing an ejector or the like and operating it under reduced pressure. [0044] It is desirable that the solid matter be recovered with a separator 20, such as, e.g., a cyclone (centrifugal settler) or a thickener (precipitation/concentration vessel), from the recovered slurry N in which the effective ingredients have been crystallized by the cooling. The recovered solid matter O thus recovered is introduced into the crystallization step (d) (e.g., the crystallization vessel 13) or the separation step (e) (e.g. , the solid-liquid separation/washing apparatus 17) (the solid matter O may be introduced into both of the crystallization step (d) and the separation step (e)) . In particular, when the crystallization step (d) employs two or more crystallization vessels 13, it is more desirable to introduce the solid matter O into the final crystallization vessel. [0045] The crystallization vessels 13 and the solid-liquid separation/washing apparatus 17 are operated under such temperature and pressure conditions that the p-toluic acid dissolves and the terephthalic acid precipitates. Because of this, the p-toluic acid can be kept in a dissolved state and be separated from the solid matter and discharged together with the reduction-reaction mother liquor G or washings J, while keeping the terephthalic acid in a precipitated state. Thus, most of the terephthalic acid contained in the solid matter can be obtained as high-purity terephthalic acid crystals M. [0046] In the reuse step (i) , the washings from which the solid matter has been recovered in the recovery step (h) are supplied as part of the water B to the slurry ing vessel 11 in the dissolution step (b) . [0047] The invention will be explained below in detail by reference to Example. EXAMPLE [0048] An acetic acid solution containing p-xylene and a catalyst (an acetic acid solution of cobalt acetate and manganese acetate and hydrogen bromide), a separated mother liquor recycled from a later solid-liquid separation step, and air were continuously supplied to a stirring vessel. An oxidation reaction was conducted at an operating temperature of 190°C and an operating pressure of 1.23 MPa (absolute pressure) while controlling the liquid level so as to result in a residence time of 1 hour. The distillate vapor was cooled to a final .temperature of 40°C with condensers disposed in multi- stage arrangement. The apparatus was operated while controlling the discharge gas so as to have an oxygen concentration of 2.5 vol%. The condensates obtained through the respective condensers were mixed together and refluxed to the oxidation reactor, and that part thereof was discharged so that the mother liquor in the slurry-discharged after the reaction had a water concentration of 10% by weight. The slurry discharged from the oxidation reactor had a slurry concentration of 35% by weight, and the cobalt/manganese/bromine concentrations in the reaction mother liquor were 300/300/1,000 ppm by weight. [0049] The slurry discharged from the oxidation reactor was continuously fed to a stirring vessel together with air. A low-temperature additional oxidation reaction was conducted at an operating temperature of 181°C and an operating pressure of 1.15 MPa (absolute pressure) while controlling the liquid level so as to result in a residence time of 15 minutes. The distillate vapor was cooled to a final temperature of 40°C with condensers disposed in multi-stage arrangement. The apparatus was operated while controlling the discharge gas so as to have an oxygen concentration of 6 vol%. The condensates obtained through the respective condensers were mixed together and refluxed to the low-temperature additional-oxidation reactor. [0050] The slurry discharged from the low-temperature additional-oxidation reactor was cooled to 90°C to cause crystallization. The resultant slurry after the crystallization was supplied to a rotary vacuum filter to conduct solid-liquid separation and washing. The operating pressure in this operation was the atmospheric pressure. The crude terephthalic acid cake separated was dried with a steam rotary dryer to obtain crude terephthalic acid crystals. [0051] This crude terephthalic acid was subjected to the steps for high-purity terephthalic acid production shown in Fig. 1. First, in the slurrying vessel 11 in the dissolution step (b), an initiation slurry C containing 30% by weight the crude terephthalic acid was obtained using water B as a solvent. This slurry was converted to an aqueous crude-terephthalic-acid solution C' having a high temperature and high pressure of 290°C and 8.54 MPa with the pump lla and the heater lib, and this solution was sent to the hydrogenation reactor 12 in the reduction step (c) shown in Fig. 1. In the hydrogenation reactor 12, the aqueous crude-terephthalic-acid solution C' was reduced with hydrogen D in the presence of a palladium catalyst at 290°C and 8.54 MPa. [0052] In the subsequent crystallization step (d) , five crystallization vessels 13 arranged in series were used to cause pressure-release evaporation by stages. Thus, the pressure and temperature were finally reduced to 0.63 MPa and 161°C, respectively, to crystallize terephthalic acid. The slurry F obtained by the crystallization was treated with a screen bowl type centrifugal separator as the solid-liquid separation/washing apparatus 17 in the following manner. First, in the separation step (e) , the slurry F was separated, by solid-liquid separation, into a terephthalic acid cake and a reduction-reaction mother; liquor G. Subsequently, in the washing step (f) , the terephthalic acid cake separated was washed with water as the cleaning fluid I and a high-purity terephthalic acid cake K was recovered. The operating conditions for this solid-liquid separation/washing apparatus 17 included a pressure of 0.73 MPa and a temperature of 161°C. The temperature of the water supplied as the cleaning fluid I was 161°C. The amount of the cleaning fluid used was 0.8 parts by weight per part by weight of the terephthalic acid cake separated by solid-liquid separation. [0053] The washings J discharged from the washing part contained a solid matter which had leaked out through the screen, the solid matter being contained in an amount corresponding to 5% by weight of the solid matter contained in the slurry F supplied to the solid-liquid separation/washing apparatus 17. The washings J further contained terephthalic acid dissolved therein in an amount, corresponding to 0.3% by weight. The recovery step (h) was hence conducted in which the washings J were introduced into the cooler 19 and released the pressure to the atmospheric pressure and cooled to 100°C to thereby precipitate the terephthalic acid dissolved in the washings J. Thereafter, employing the thickener (sedimentation separator) 20, the terephthalic acid crystals contained in the washings J were recovered as a. recovered solid matter O. [0054] The recovered solid matter O, which comprised high-purity terephthalic acid crystals, was returned to the final crystallization vessel in the crystallization step (d) , while the recovered waste liquid P from which the solid matter had been recovered was sent to the slurrying vessel 11 in the dissolution step (b) as a solvent for the dissolution step. The amount of the recovered solid matter O thus sent corresponded to 5% by weight based on the crude terephthalic acid fed to the slurrying vessel 11. COMPARATIVE EXAMPLE [0055] The same procedure as in Example was conducted, except that the washings J were directly sent to the slurrying vessel 11 in the dissolution step (b) without being sent to the recovery step (h). (Results) In the process according to the invention, the amount of the terephthalic acid to be fed to the slurrying vessel 11 could be reduced by 5% by weight by recovering beforehand the solid matter contained in the washings J and then returning the washings J to the slurrying vessel 11. Thus, the necessity of plant apparatus enlargement for maintaining a given slurry concentration at the production step could be removed. [0056] While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. [0057] This application is based on a Japanese patent application filed on May 28, 2004 (Application No. 2004-159897), the contents thereof being herein incorporated by reference. Industrial Applicability [0058] According to the invention, a process for producing high-purity terephthalic acid can be provided in which washings can be reused in a small apparatus in producing high-purity terephthalic acid. The invention has a significant industrial value. We Claim: [1] A process for producing high-purity terephthalic acid which comprises; a crude terephthalic acid production step (a) in which p-xylene is oxidized to produce crude terephthalic acid containing 4-carboxybenzaldehyde, a dissolution step (b) in which the crude terephthalic acid obtained in the crude terephthalic acid production step (a) is dissolved in a water solvent at a high temperature and a high pressure to obtain an aqueous solution of the crude terephthalic acid, a reduction step (c) in which the 4-carboxybenzaldehyd in the aqueous crude terephthalic acid solution is reduced to p-toluic acid with hydrogen in the presence of a group 8-10 metal catalyst to obtain a liquid of reduction reaction mixture, a crystallization step (d) in crystallization vessel in which the liquid of reduction reaction mixture is cooled to.120 - 200°C to cause crystals of the terephthalic acid and thereby obtain a slurry, a separation step (e) is carried out in united apparatus in which the slurry is subjected to solid-liquid separation to separate the slurry into a terephthalic acid cake comprising the terephthalic acid crystals as the main component and the mother liquor in the reduction reaction, a washing step (f) is carried out in the united apparatus in which the tcrephthalic acid cake is washed with a cleaning fluid, thereby obtaining washing discharge having solid matters, and a drying step (g) in which the cake washed in the washing step (f) is dried to obtain crystals of high-purity terephthalic acid, characterized in that the process further includes a recovery step (h) in which a solid matter contained in the washings discharged from the washing step (f) is recovered and the solid matter obtained is sent to the crystallization step (d) or the separation step (e) and a reuse step (i) in which the washings from which a solid matter has been recovered in the recovery step (h) are used as a solvent for the dissolution step (b). [2] The process for producing high-purity terephthalic acid as claimed in claim 1, wherein in the recovery step (h), the solid matter is recovered after the washings discharges from the washing step (f) are cooled. [3] The process for producing high-purity terephthalic acid as claimed in claim 2, wherein the washings discharged from the washing step (f) have a temperature exceeding 100° C and the solid matter is recovered therefrom after the washings are cooled to 0-100°C [4] The process for producing high-purity terephthalic acid as claimed in claim 2, wherein the washings are cooled by pressure-release evaporation. [5] The process for producing high-purity terephthalic acid as claimed in claim 1, wherein the recovery of a solid matter in the recovery step (h) is conducted with a cyclone or a thickener. [6] The process for producing high-purity terephthalic acid as claimed in claim 1, - wherein the separation step (e) is conducted at a pressure higher than the pressure in a final crystallization vessel in the crystallization step (d). [7] The process for producing high-purity terephthalic acid as claimed in claim 1, wherein the separation step (e) and the washing step (f) are conducted with a united apparatus. [8] The process for producing high-purity terephthalic acid as claimed in claim 7, wherein the united apparatus for conducting the separation step (e) and the washing step (f) is any of a screen bowl type centrifugal separator, a rotary pressure filter, and a horizontal belt filter. [9] The process for producing high-purity terephthalic acid as claimed in claim 1, wherein the solid matter contained in the washings discharges from the washing step (f) accounts for 1-10% by weight of the terephthalic acid crystals contained in the slurry supplied to the separation step (e). (10\| The process for producing high-purity terephthalic acid as claimed in claim 1, wherein the crystallization step (d) is composed of crystallization vessels arranged in two or more stages and the solid matter recovered in the recovery step (h) is sent to the final crystallization vessels among the crystallization vessels arranged in two or more stages.

Full Text

DESCRIPTION
PROCESS FOR PRODUCING HIGH-PURITY TEREPHTHALIC ACID Technical Field [0001]
The present invention relates to a process for producing high-purity terephthalic acid. Background Art [0002]
For obtaining crystals of high-purity terephthalic acid, it is necessary that the intermediates which have generated as by-products of the oxidation of p-xylene and include 4-carboxybenzaldehyde as a major component (the intermediates are effective ingredients convertible into terephthalic acid but are impurities after mixing with product terephthalic acid) should be removed as much as possible from crude terephthalic acid crystals obtained by the oxidation. For this purpose, a purification step is conducted in which the 4-carboxybenzaldehyde is reduced to p-toluic acid, which has higher water solubility than terephthalic acid, and terephthalic acid crystallization is then conducted to obtain high-purity terephthalic acid crystals. This procedure, for example, comprises the following steps as shown in Fig. 2. [0003]
First, in a dissolution step, crude terephthalic acid a is slurried with water b in a slurrying vessel 1
and the resultant initiation slurry c is made to have a high temperature and high pressure with a pump la and a heater Ib to dissolve the crude terephthalic acid a in the water and thereby obtain an aqueous crude-terephthalic-acid solution c'. A reduction step is then conducted in which the aqueous crude-terephthalic-acid solution c' is introduced into a hydrogenation reactor 2 and brought into contact with hydrogen d in the presence of a catalyst to thereby reduce the 4-carboxybenzaldehyde into p-toluic acid. The liquid reduction reaction mixture e thus obtained, which contains p-toluic acid and terephthalic acid, is introduced into crystallization vessels 3 arranged in series to conduct a crystallization step, in which crystallization is caused by pressure-release cooling. Since terephthalic acid has lower water solubility than p-toluic acid, high-purity crystals of terephthalic acid can be separated out in this step by controlling crystallization conditions. A separation step is subsequently conducted, in which a slurry f containing the high-purity crystals of terephthalic acid which have thus separated out is introduced into a solid-liquid separator 4 optionally with pressure control with a pump 3a. The slurry is thus subjected to solid-liquid separation in which the reduction-reaction mother liquor g is separated and a high-purity terephthalic acid cake h is recovered. This high-purity terephthalic acid cake h is
subjected to a washing step, in which a washing operation with a cleaning fluid i is performed in a washing apparatus 5 and a solid-liquid separation operation is performed in a solid-liquid separator 6 to obtain a washed cake k. Furthermore, a drying step is conducted, in which the washed cake k obtained is dried with a dryer 8 to obtain high-purity terephthalic acid crystals m. On the other hand, since the reduction-reaction mother liquor g still contains effective ingredients including terephthalic acid and p-toluic acid, these effective ingredients are recovered as much as possible. Furthermore, the washings j discharged after the washing operation are reused as a solvent in the dissolution step. [0004]
In the crystallization step/ the final crystallization vessel is generally operated at a temperature of 120-180°C in order to prevent the p-toluic acid from forming a eutectic with the terephthalic acid. Because of this, the procedure heretofore in use comprises subjecting the slurry f obtained through crystallization to solid-liquid separation with a solid bowl type centrifugal separator while keeping the slurry f in a high-temperature and high-pressure state to thereby separate the reduction-reaction mother liquor g, washing the resultant high-purity terephthalic acid cake h by suspension washing at an elevated pressure, releasing the
suspension from the pressure, conducting solid-liquid separation again at ordinary pressure, and discharging the washings j. [0005]
Recently, a process for terephthalic acid production including a simplified step for the purification is described in patent documents 1 and 2. In this process, a solid-liquid separation/washing apparatus 7 in which both the solid-liquid separation operation and the washing operation can be conducted (corresponding to the apparatus surrounded by the broken line in the figure) is used to integrally conduct solid-liquid separation and a washing step at an elevated pressure. In this case, the washings j to be discharged are in a high-temperature high-pressure state. [0006]
The washings j are accompanied by part of the solid matter to be recovered as a high-purity terephthalic acid cake h, because of, e.g., leakage through the washing screen. When the washings j containing the solid matter are reused, without any treatment, as a solvent in the slurrying vessel 1, then the amount of the solid matter which should be treated in the purification step system is increased and this requires each apparatus to have a larger size because of the necessity of keeping the slurry concentration in the system constant. Furthermore, when
solid-liquid separation and a washing operation are
conducted in a united apparatus at a high temperature and
high pressure, a larger amount of terephthalic acid
dissolves in the washings. This also results in an
increase in solid matter amount in the system and hence in
the necessity of apparatus enlargement.
Patent Document 1: WO 92/18454
Patent Document 2: WO 93/24440
Disclosure of the Invention
Problem that the Invention is to Solve
[0007]
An object of the invention is to provide a process for producing high-purity terephthalic acid in which washings can be reused with a small apparatus in producing high-purity terephthalic acid. Means for Solving the Problem
[0008]
The present inventors made intensive investigations in order to overcome the problem described above. As a result, they have found that the problem can be eliminated by removing beforehand the solid matter which has accompanied the washings. It has been further found that the solid matter removed can be reused without influencing product quality by recycling the solid matter to a step before the separation step. The invention has been thus completed. Essential points of the invention reside in
the following (1) to (10).
[0009]
(1) A process for producing high-purity terephthaiic acid
which comprises
a crude terephthalic acid production step (a) in which p-xylene is oxidized to produce crude terephthalic acid containing 4-carboxybenzaldehyde,
a dissolution step (b) in which the crude terephthalic acid obtained in the crude terephthalic acid production step (a) is dissolved in a water solvent at a high temperature and a high pressure to obtain an aqueous solution of the crude terephthalic acid,
a reduction step (c) in which the 4-carboxybenzaldehyde in the aqueous crude-terephthaiic-acid solution is reduced to p-toluic acid with hydrogen in the presence of a catalyst to obtain a liquid of reduction reaction mixture,
a crystallization step (d) in which the liquid of reduction reaction mixture is cooled to 120-200°C to cause crystals of the terephthalic acid and thereby obtain a slurry,
a separation step (e) in which the slurry is subjected to solid-liquid separation to separate the slurry into a terephthalic acid cake comprising the terephthalic acid crystals as the main component and the mother liquor in the reduction reaction,
a washing step (f) in which the terephthalic acid cake is washed with a cleaning fluid, and
a drying step (g) in which the cake washed in the washing step (f) is dried to obtain crystals of high-purity terephthalic acid,
the process further including
a recovery step (h) in which a solid matter contained in the washings discharged from the washing step (f) is recovered and the solid matter obtained is sent to the crystallization step (d) or the separation step (e) and
a reuse step (i) in which the washings from which a solid matter has been recovered in the recovery step (h) are used as a solvent for the dissolution step (b) . [0010]
(2) The process for producing high-purity terephthalic
acid as described under (1) above wherein in the recovery
step (h), the solid matter is recovered after the washings
discharged from the washing step (f) are cooled.
[0011]
(3) The process for producing high-purity terephthalic
acid as described under (2) above wherein the washings
discharged from the washing step (f) have a temperature
exceeding 100°C and the solid matter is recovered
therefrom after the washings are cooled to 0-100°C.
[0012]
(4) The process for producing high-purity terephthalic
acid as described under (2) or (3) above wherein the
washings are cooled by pressure-release evaporation.
[0013]
(5) The process for producing high-purity terephthalic
acid as described under any one of (1) to (4) above
wherein the recovery of a solid matter in the recovery
step (h) is conducted with a cyclone or a thickener.
[0014]
(6) The process for producing high-purity terephthalic
acid as described under any one of (1) to (5) above
wherein the separation step (e) is conducted at a pressure
higher than the pressure in a final crystallization vessel
in the crystallization step (d).
[0015]
(7) The process for producing high-purity terephthalic
acid as described under anyone of (1) to (6) above wherein
the separation step (e) and the washing step (f) are
conducted with a united apparatus.
[0016]
(8) The process for producing high-purity terephthalic
acid as described under (7) above wherein the united
apparatus for conducting the separation step (e) and the
washing step (f) is any of a screen bowl type centrifugal
separator, a rotary pressure filter, and a horizontal belt
filter.
[0017]
(9) The process for producing high-purity terephthalic
acid as described under any one of (1) to (8) above
wherein the solid matter contained in the washings
discharged from the washing step (f) accounts for 1-10% by
weight of the terephthalic acid crystals contained in the
slurry supplied to the separation step (e) .
[0018]
(10) The process for producing high-purity terephthalic
acid as described under any one of (1) to (8) above
wherein the crystallization step (d) is composed of
crystallization vessels arranged in two or more stages and
the solid matter recovered in the recovery step (h) is
sent to the final crystallization vessel among the
crystallization vessels arranged in two or more stages.
Advantage of the Invention
[0019]
According to the invention, a process for producing high-purity terephthalic acid can be provided in which washings can be reused with a small apparatus in producing high-purity terephthalic acid. Brief Description of the Drawings
[0020]
[Fig. 1] Fig. 1 is a flow diagram illustrating an embodiment of the process for producing high-purity terephthalic acid according to the invention.
[Fig. 2] Fig. 2 is a flow diagram illustrating an example
of related-art processes for producing high-purity
terephthalic acid.
Description of the Reference Numerals and Sings
[0021]
1, 11 slurrying vessel
la, lla pump
Ib, lib heater
2, 12 hydrogenation reactor
3, 13 crystallization vessel
3a, 13a pump
4, 6 solid-liquid separator
5 washing apparatus

7, 17 solid-liquid separation/washing apparatus
8, 18 dryer

19 cooler
20 separator
a, A crude terephthalic acid
b, B water
c, C initiation slurry
c1, C' aqueous crude-terephthalic-acid solution
d, D hydrogen
e, E liquid reduction reaction mixture
f, F slurry
g, G reduction-reaction mother liquor
h high-purity terephthalic acid cake
i, I cleaning fluid j, J washings k washed cake
K high-purity terephthalic acid cake m, M high-purity terephthalic acid crystals N recovered slurry O recovered solid matter P recovered waste liquid Best Mode for Carrying Out the Invention [0022]
The invention will be explained below in detail. [0023]
The process of the invention for producing high-purity terephthalic acid comprises
a crude terephthalic acid production step (a) in which p-xylene is oxidized to produce crude terephthalic acid containing 4-carboxybenzaldehyde,
a dissolution step (b) in which the crude terephthalic acid obtained in the crude terephthalic acid production step (a) is dissolved in a water solvent at a high temperature and a high pressure to obtain an aqueous solution of the crude terephthalic acid,
a reduction step (c) in which the 4-carboxybenzaldehyde in the aqueous crude-terephthalic-acid solution is reduced to p-toluic acid with hydrogen in the presence of a catalyst to obtain a liquid reduction
reaction mixture,
a crystallization step (d) in which the liquid reduction reaction mixture is cooled to 120-200°C to cause crystals of the terephthalic acid and thereby obtain a slurry,
a separation step (e) in which the slurry i s subjected to solid-liquid separation to separate the slurry into a terephthalic acid cake comprising the terephthalic acid crystals as the main component and the mother liquor in the reduction reaction,
a washing step (f) in which the terephthalic acid cake is washed with a cleaning fluid, and
a drying step (g) in which the cake washed in the washing step (f) is dried to obtain crystals of high-purity terephthalic acid,
the process being characterized by further including
a recovery step (h) in which a solid matter contained in the washings discharged from the washing step (f) is recovered and the solid matter obtained is sent to the crystallization step (d) or the separation step (e) and
a reuse step (i) in which the washings from which a solid matter has been recovered in the recovery step (h) are used as a solvent for the dissolution step (b) . The production process of the invention is explained by reference to Fig. 1.
[0024]
The term "effective ingredients" hereinafter means terephthalic acid and other compounds capable of being converted to terephthalic acid through, e.g./ oxidation, and includes both dissolved ingredients and precipitated ingredients. The term "solid matter" means precipitated ingredients among the effective ingredients. [0025]
First, in the crude terephthalic acid production step (a) , p-xylene is oxidized in a liquid phase with molecular oxygen in an acetic acid solvent in the presence of a catalyst to thereby produce crude terephthalic acid. This step is well known, and the catalyst, which has been known to be conventionally used in this reaction, is used. Examples thereof include compounds of heavy metals, such as cobalt compounds, manganese compounds, iron compounds, and chromium compounds, and bromine compounds. In the reaction system, these compounds are present in a dissolved state. Preferred of these is a combination of a cobalt compound or manganese compound with a bromine compound. In this case, these compounds are generally used in such amounts that the amounts of cobalt atoms, manganese atoms, and bromine atoms are 10-5,000 ppm, 10-5,000 ppm, and 10-10,000 ppm, respectively, of the solvent. [0026]
As the molecular oxygen is generally used a gas
mixture comprising an inert gas and oxygen. For example, air or oxygen-enriched air is used. The molar proportion of the molecular oxygen to the p-xylene to be fed to the reactor is generally 3-20 times by mole, preferably 2-4 times by mole. [0027]
The proportion of the p-xylene to the acetic acid to be supplied to the reactor is generally 1-50% by weight. The concentration of water in the reaction system is generally 5-20% by weight, preferably 5-15% by weight. [0028]
The temperature in the oxidation reaction is generally 160-260°C/ preferably 170-210°C. The reaction may be conducted at any pressure at which the reaction system can retain a liquid phase at the reaction temperature. The pressure is generally 0.5-5 MPa, preferably 1-2 MPa. The residence time is generally 10-200 minutes. [0029]
Terephthalic acid is not easy to dissolve in the acetic acid serving as a solvent. Because of this, the terephthalic acid yielded in the oxidation reaction step precipitates as crystals to form a slurry. However, terephthalic acid may be dissolved depending on the amount of the solvent, reaction temperature, and pressure. In this case, a crystallization step for, e.g., cooling the
liquid reaction mixture is conducted to precipitate the terephthalic acid and thereby form a slurry. This slurry is subjected to solid-liquid separation to obtain crude terephthalic acid crystals. Although the terephthalic acid slurry obtained in the oxidation reaction step is in a pressurized state/ this slurry may be subjected as it is to solid-liquid separation or may be subjected to pressure-release cooling or the like and then to solid-liquid separation. For the solid-liquid separation, any method may be used as long as the crystals can be separated from the mother liquor. Examples thereof include filtration and centrifugal separation. If necessary, washing and drying are conducted. Thus, crude terephthalic acid crystals are obtained. [0030]
The teem "crude terephthalic acid" in the invention means terephthalic acid containing 4-carboxybenzaldehyde in an amount of 1,000-10,000 ppm. [0031]
In the dissolution step (b) , the crude terephthalic acid A (crude terephthalic acid containing 4-carboxybenzaldehyde and obtained by oxidizing p-xylene) is sent to a slurrying vessel 11 and dissolved in water B in a high-temperature and high-pressure environment. The crude terephthalic acid A is one obtained by oxidizing p-xylene in an aliphatic carboxylic acid solvent such as
acetic acid. This crude terephthalic acid contains, as by-products, intermediates in which one of the alkyl groups has not been completely oxidized, such as, e.g., 4-carboxybenzaldehyde. For producing the high-purity terephthalic acid, it is necessary that these impurities should be removed as much as possible from the crude terephthalic acid A.
[0032]
The terephthalic acid has low solubility in water. It is necessary that the crude terephthalic acid A should be slurried with water B in the slurrying vessel 11 and the resultant initiation slurry C should be regulated with a pump lla and a heater lib so as to have a high temperature and high pressure at which the terephthalic acid can be dissolved in the water. The temperature in such high-temperature and high-pressure conditions depends on the slurry concentration. However, the temperature should be 200°C or higher and be not higher than the temperatures which the apparatus can withstand, and desirably is 230°C or higher and 320°C or lower. The pressure in the high-temperature and high-pressure conditions should be one at which a liquid phase can be maintained at a temperature in that range, and desirably is 2.8 MPa or higher and 11.3 MPa or lower.
[0033]
The concentration of the slurry obtained in the
dissolution step (b) is generally 20-40 wt%, preferably 25-35 wt%. Too high slurry concentrations cause clogging in the apparatus. Too low slurry concentrations result in an increased mother liquor amount and this necessitates a larger apparatus size suitable for the production amount. From the standpoint of clogging prevention, it is preferred to maintain a constant slurry concentration.
[0034]
In the subsequent reduction step (c) , the aqueous crude-terephthaiic-acid solution C1 obtained through the dissolution step (b) is sent to a hydrogenation reactor 12 and catalytically reduced in the presence of a catalyst with hydrogen D introduced to thereby obtain a liquid reduction reaction mixture E. The catalyst and the conditions in the hydrogenation reactor 12 should be ones which reduce the 4-carboxybenzaldehyde and do not reduce the terephthalic acid. This is intended to reduce the 4-carboxybenzaldehyde contained in the aqueous crude-terephthalic-acid solution C1 to p-toluic acid, which has higher solubility in water than the terephthalic acid. It is desirable that this reduction should be conducted to the highest possible level. This hydrogenation also is well known. As the hydrogenation catalyst may be used a catalyst comprising a Group 8-10 (according to IUPAC Nomenclature of Inorganic Chemistry, revised edition
(1998)) metal such as ruthenium, rhodium, palladium,
platinum, or osmium. Usually, such a catalyst is supported on a support, e.g., activated carbon, and used as a fixed bed. Preferred of those is palladium supported on activated carbon. The temperature in the hydrogenation is generally 260-320°C, preferably 270-300°C, and the partial pressure of hydrogen is generally 0.5-20 kg/cm2G. [0035]
Furthermore, in the crystallization step (d) , the liquid reduction reaction mixture E obtained in the reduction step (c) is introduced into a crystallization vessel 13. The temperature and pressure are reduced to such a degree that the p-toluic acid remains dissolved. Thus, the terephthalic acid is crystallized to obtain a slurry F. It is more desirable that two or more, preferably three to six, crystallization vessels 13 be arranged in series and the pressure be reduced by stages to cool the reaction mixture E (cooling by pressure-release evaporation) and crystallize the terephthalic acid. Although two crystallization vessels 13 have been disposed in Fig. 1, three or more crystallization vessels may be disposed. The temperature in the final crystallization vessel which is the last of the crystallization vessels 13 may be regulated so as to result in temperature conditions under which the p-toluic acid does not form a eutectic with the terephthalic acid. Specifically, the temperature is desirably 120°C or higher and 200°C or lower, more
desirably 130°C or higher and 180°C or lower. The pressure in this case is desirably 0.20 MPa or higher and 1.56 MPa or lower, more desirably 0.27 MPa or higher and 1.00 MPa or lower.
[0036]
Subsequently, in the separation step (e) , the slurry F is introduced into a solid-liquid separator at a pressure higher than the pressure of the slurry obtained in the crystallization step (d) to separate a reduction-reaction mother liquor G and obtain a high-purity terephthalic acid cake including the terephthalic acid crystals having a high purity. Furthermore, the washing step (f) is conducted in which this high-purity terephthalic acid cake is washed while keeping the cake in a pressurized state. It is preferred that a solid-liquid separation/washing apparatus 17 in which the separation step (e) and the washing step (f) can be simultaneously conducted should be used as that solid-liquid separator in this operation. Employing this apparatus can simplify a series of steps.
[0037]When the separation step (e) and the washing step
(f) are conducted with the solid-liquid separation/washing apparatus 17 only, the procedure is as follows. The slurry F and a cleaning fluid I are introduced into the solid-liquid separation/washing apparatus 17. Water
having a temperature equal to or higher than the operating temperature of the solid-liquid separation/washing apparatus 17 is generally used as the cleaning fluid I. Immediately after the solid-liquid separation of the slurry F is conducted, the resultant cake is washed with the cleaning fluid I in the same apparatus. And then, a high-purity terephthalic acid cake K which has been washed is separated and taken out, and the reduction-reaction mother liquor G and washings J consisting mainly of the cleaning fluid I are discharged. [0038]
It is desirable that the operating temperature of the solid-liquid separation/washing apparatus 17 be equal to the temperature in the final crystallization vessel in the crystallization step (d) and be 120°C or higher and 200°C or lower. More desirably, the operating temperature is 130°C or higher and 180°C or lower. The pressure should be higher than the pressure in the final crystallization vessel in the crystallization step (d) in order to inhibit a temperature decrease caused by pressure release. Specifically, it is desirable that the pressure in the apparatus 17 be higher by 0-1 MPa than the pressure in the final crystallization vessel in the crystallization step (d) . In case where the reaction mixture which has undergone crystallization in the final crystallization vessel further undergoes a pressure reduction, cooling by
pressure-release evaporation occurs and ingredients dissolved in the mother liquor may precipitate. This may raise a trouble in the separation step (e) in the solid-liquid separation/washing apparatus 17. On the other hand, raising the pressure to a high degree requires the apparatus to be reinforced so as to withstand that. Examples of the solid-liquid separation/washing apparatus 17, in which both of solid-liquid separation and washing can be conducted as described above, include a screen bowl type centrifugal separator, rotary vacuum filter, and horizontal belt filter. Especially preferred is a screen bowl type centrifugal separator. [0039]
The high-purity terephthalic acid cake K thus obtained is dried with a dryer 18 in the drying step (g) to thereby remove the residual adherent liquid. Thus, high-purity terephthalic acid crystals M can be obtained. Examples of the dryer 18 include a steam tube dryer and a fluidized-bed dryer. It is also possible to use a method in which releasing the pressure from the high-purity terephthalic acid cake K having a high temperature and a high pressure vaporize at least part of the solvent ingredient adherent to the cake. Examples of the dyer 18 include a rotary dryer and a fluidized-bed dryer. The drying may be conducted in the presence of a flowing gas at a drying outlet operating temperature of 70-180°C using

steam or the like as a heat source. [0040]
On the other hand, the reduction-reaction mother liquor G also contains the effective ingredients, e.g., terephthalic acid and p-toluic acid, and it is necessary to recover these ingredients as much as possible. Examples of methods for the recovery include a method which comprises introducing the mother liquor G into one or more pressure-release cooling vessels, cooling the mother liquor G to precipitate the effective ingredients contained therein to obtain a slurry, filtering the slurry to separate it into a secondary mother liquor and secondary crystals, introducing the secondary crystals into the oxidation step in which the dialkylaromatic compound is oxidized to yield the crude aromatic carboxylic acid, and using the secondary mother liquor directly or indirectly in place of the water B in the slurrying vessel 11 or using the secondary liquor as a cleaning fluid in the washing step (f) . [0041]
The pressure-release cooling vessels are vessels regulated so as to have a pressure which is lower than the pressure of the liquid to be introduced thereinto and at which the boiling point of the main component of the liquid is not higher than the temperature of the liquid before introduction. When a liquid is introduced into
this pressure-release cooling vessel, part of the liquid vaporizes and the remainder of the liquid is cooled to the boiling point at the pressure after the change. In this operation, when the liquid is a solution, the solute is precipitated in an amount by which the solute amount exceeds the solubility after the cooling. [0042]
Furthermore, the washings J (the term "washings" in the invention means the liquid discharged after the terephthalic acid cake obtained through solid-liquid separation is washed with a cleaning fluid) also contain the effective ingredients. Especially when the solid-liquid separation/washing apparatus 17 is employed to stably conduct both of solid-liquid separation and washing therein, the solid matter, which is not dissolved in the washings J, is apt to come into the washings J. The amount of this solid matter is desirably 1% by weight or larger and 10% by weight or smaller, more desirably 3% by weight or larger and 8% by weight or smaller, based on the terephthalic acid crystals in the slurry F supplied to the solid-liquid separation/washing apparatus 17. In case where it is attempted to reduce the content of the solid matter to below 1% by weight, there is a possibility that the operation of the solid-liquid separation/washing apparatus 17 might become unstable. On the other hand, in case where the content thereof exceeds 10% by weight, it
becomes necessary to enlarge the solid-liquid separation/washing apparatus 17 for obtaining the high-purity terephthalic acid crystals M in a desired amount. [0043]
In the recovery step (h), the effective ingredients are recovered as the solid matter from the washings J as much as possible. Since the washings J have a high temperature (generally exceeding 100°C) , the effective ingredients are contained therein in a dissolved state in a large amount besides being contained as the solid matter. It is therefore desirable to cool the washings J in order to precipitate the effective ingredients dissolved. More desirably, the washings J are cooled to 100°C or lower. However, the temperature to which the washings J are to be cooled should be not lower than the solidifying point of the washings J, and is preferably 60°C or higher and 100°C or lower. In case where the cooling temperature is too high, the terephthalic acid dissolved in the washings cannot be sufficiently recovered. In case where the cooling temperature is too low, energy is necessary for preheating in reusing the washings in the dissolution step (b) and the apparatus is required to be enlarged. The cooling may be conducted with a cooler 19 which is a pressure-release cooling vessel, or may be conducted by heat exchange. From the standpoint of apparatus simplification, it is preferred to use a pressure-release
cooling vessel. Cooling to below 100°C may be attained by employing an ejector or the like and operating it under reduced pressure. [0044]
It is desirable that the solid matter be recovered with a separator 20, such as, e.g., a cyclone (centrifugal settler) or a thickener (precipitation/concentration vessel), from the recovered slurry N in which the effective ingredients have been crystallized by the cooling. The recovered solid matter O thus recovered is introduced into the crystallization step (d) (e.g., the crystallization vessel 13) or the separation step (e) (e.g. , the solid-liquid separation/washing apparatus 17) (the solid matter O may be introduced into both of the crystallization step (d) and the separation step (e)) . In particular, when the crystallization step (d) employs two or more crystallization vessels 13, it is more desirable to introduce the solid matter O into the final crystallization vessel. [0045]
The crystallization vessels 13 and the solid-liquid separation/washing apparatus 17 are operated under such temperature and pressure conditions that the p-toluic acid dissolves and the terephthalic acid precipitates. Because of this, the p-toluic acid can be kept in a dissolved state and be separated from the solid matter and
discharged together with the reduction-reaction mother liquor G or washings J, while keeping the terephthalic acid in a precipitated state. Thus, most of the terephthalic acid contained in the solid matter can be obtained as high-purity terephthalic acid crystals M. [0046]
In the reuse step (i) , the washings from which the solid matter has been recovered in the recovery step (h) are supplied as part of the water B to the slurry ing vessel 11 in the dissolution step (b) . [0047]
The invention will be explained below in detail by reference to Example. EXAMPLE [0048]
An acetic acid solution containing p-xylene and a catalyst (an acetic acid solution of cobalt acetate and manganese acetate and hydrogen bromide), a separated mother liquor recycled from a later solid-liquid separation step, and air were continuously supplied to a stirring vessel. An oxidation reaction was conducted at an operating temperature of 190°C and an operating pressure of 1.23 MPa (absolute pressure) while controlling the liquid level so as to result in a residence time of 1 hour. The distillate vapor was cooled to a final .temperature of 40°C with condensers disposed in multi-
stage arrangement. The apparatus was operated while controlling the discharge gas so as to have an oxygen concentration of 2.5 vol%. The condensates obtained through the respective condensers were mixed together and refluxed to the oxidation reactor, and that part thereof was discharged so that the mother liquor in the slurry-discharged after the reaction had a water concentration of 10% by weight. The slurry discharged from the oxidation reactor had a slurry concentration of 35% by weight, and the cobalt/manganese/bromine concentrations in the reaction mother liquor were 300/300/1,000 ppm by weight. [0049]
The slurry discharged from the oxidation reactor was continuously fed to a stirring vessel together with air. A low-temperature additional oxidation reaction was conducted at an operating temperature of 181°C and an operating pressure of 1.15 MPa (absolute pressure) while controlling the liquid level so as to result in a residence time of 15 minutes. The distillate vapor was cooled to a final temperature of 40°C with condensers disposed in multi-stage arrangement. The apparatus was operated while controlling the discharge gas so as to have an oxygen concentration of 6 vol%. The condensates obtained through the respective condensers were mixed together and refluxed to the low-temperature additional-oxidation reactor.
[0050]
The slurry discharged from the low-temperature additional-oxidation reactor was cooled to 90°C to cause crystallization. The resultant slurry after the crystallization was supplied to a rotary vacuum filter to conduct solid-liquid separation and washing. The operating pressure in this operation was the atmospheric pressure. The crude terephthalic acid cake separated was dried with a steam rotary dryer to obtain crude terephthalic acid crystals.
[0051]
This crude terephthalic acid was subjected to the steps for high-purity terephthalic acid production shown in Fig. 1. First, in the slurrying vessel 11 in the dissolution step (b), an initiation slurry C containing 30% by weight the crude terephthalic acid was obtained using water B as a solvent. This slurry was converted to an aqueous crude-terephthalic-acid solution C' having a high temperature and high pressure of 290°C and 8.54 MPa with the pump lla and the heater lib, and this solution was sent to the hydrogenation reactor 12 in the reduction step (c) shown in Fig. 1. In the hydrogenation reactor 12, the aqueous crude-terephthalic-acid solution C' was reduced with hydrogen D in the presence of a palladium catalyst at 290°C and 8.54 MPa.
[0052]
In the subsequent crystallization step (d) , five crystallization vessels 13 arranged in series were used to cause pressure-release evaporation by stages. Thus, the pressure and temperature were finally reduced to 0.63 MPa and 161°C, respectively, to crystallize terephthalic acid. The slurry F obtained by the crystallization was treated with a screen bowl type centrifugal separator as the solid-liquid separation/washing apparatus 17 in the following manner. First, in the separation step (e) , the slurry F was separated, by solid-liquid separation, into a terephthalic acid cake and a reduction-reaction mother; liquor G. Subsequently, in the washing step (f) , the terephthalic acid cake separated was washed with water as the cleaning fluid I and a high-purity terephthalic acid cake K was recovered. The operating conditions for this solid-liquid separation/washing apparatus 17 included a pressure of 0.73 MPa and a temperature of 161°C. The temperature of the water supplied as the cleaning fluid I was 161°C. The amount of the cleaning fluid used was 0.8 parts by weight per part by weight of the terephthalic acid cake separated by solid-liquid separation. [0053]
The washings J discharged from the washing part contained a solid matter which had leaked out through the screen, the solid matter being contained in an amount corresponding to 5% by weight of the solid matter
contained in the slurry F supplied to the solid-liquid separation/washing apparatus 17. The washings J further contained terephthalic acid dissolved therein in an amount, corresponding to 0.3% by weight. The recovery step (h) was hence conducted in which the washings J were introduced into the cooler 19 and released the pressure to the atmospheric pressure and cooled to 100°C to thereby precipitate the terephthalic acid dissolved in the washings J. Thereafter, employing the thickener (sedimentation separator) 20, the terephthalic acid crystals contained in the washings J were recovered as a. recovered solid matter O. [0054]
The recovered solid matter O, which comprised high-purity terephthalic acid crystals, was returned to the final crystallization vessel in the crystallization step (d) , while the recovered waste liquid P from which the solid matter had been recovered was sent to the slurrying vessel 11 in the dissolution step (b) as a solvent for the dissolution step. The amount of the recovered solid matter O thus sent corresponded to 5% by weight based on the crude terephthalic acid fed to the slurrying vessel 11. COMPARATIVE EXAMPLE [0055]
The same procedure as in Example was conducted, except that the washings J were directly sent to the

slurrying vessel 11 in the dissolution step (b) without being sent to the recovery step (h). (Results)
In the process according to the invention, the amount of the terephthalic acid to be fed to the slurrying vessel 11 could be reduced by 5% by weight by recovering beforehand the solid matter contained in the washings J and then returning the washings J to the slurrying vessel 11. Thus, the necessity of plant apparatus enlargement for maintaining a given slurry concentration at the production step could be removed. [0056]
While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. [0057]
This application is based on a Japanese patent application filed on May 28, 2004 (Application No. 2004-159897), the contents thereof being herein incorporated by reference.
Industrial Applicability [0058]
According to the invention, a process for producing high-purity terephthalic acid can be provided in which
washings can be reused in a small apparatus in producing high-purity terephthalic acid. The invention has a significant industrial value.

We Claim:
[1] A process for producing high-purity terephthalic acid which comprises;
a crude terephthalic acid production step (a) in which p-xylene is oxidized to produce crude terephthalic acid containing 4-carboxybenzaldehyde,
a dissolution step (b) in which the crude terephthalic acid obtained in the crude terephthalic acid production step (a) is dissolved in a water solvent at a high temperature and a high pressure to obtain an aqueous solution of the crude terephthalic acid,
a reduction step (c) in which the 4-carboxybenzaldehyd in the aqueous crude terephthalic acid solution is reduced to p-toluic acid with hydrogen in the presence of a group 8-10 metal catalyst to obtain a liquid of reduction reaction mixture,
a crystallization step (d) in crystallization vessel in which the liquid of reduction reaction mixture is cooled to.120 - 200°C to cause crystals of the terephthalic acid and thereby obtain a slurry,
a separation step (e) is carried out in united apparatus in which the slurry is subjected to solid-liquid separation to separate the slurry into a terephthalic acid cake comprising the terephthalic acid crystals as the main component and the mother liquor in the reduction reaction,
a washing step (f) is carried out in the united apparatus in which the tcrephthalic acid cake is washed with a cleaning fluid, thereby obtaining washing discharge having solid matters, and
a drying step (g) in which the cake washed in the washing step (f) is dried to obtain crystals of high-purity terephthalic acid,
characterized in that the process further includes
a recovery step (h) in which a solid matter contained in the washings discharged from the washing step (f) is recovered and the solid matter obtained is sent to the crystallization step (d) or the separation step (e) and
a reuse step (i) in which the washings from which a solid matter has been recovered in the recovery step (h) are used as a solvent for the dissolution step (b).
[2] The process for producing high-purity terephthalic acid as claimed in claim 1, wherein in the recovery step (h), the solid matter is recovered after the washings discharges from the washing step (f) are cooled.
[3] The process for producing high-purity terephthalic acid as claimed in claim 2, wherein the washings discharged from the washing step (f) have a temperature exceeding 100° C and the solid matter is recovered therefrom after the washings are cooled to 0-100°C
[4] The process for producing high-purity terephthalic acid as claimed in claim 2, wherein the washings are cooled by pressure-release evaporation.
[5] The process for producing high-purity terephthalic acid as claimed in claim 1, wherein the recovery of a solid matter in the recovery step (h) is conducted with a cyclone or a thickener.
[6] The process for producing high-purity terephthalic acid as claimed in claim 1, - wherein the separation step (e) is conducted at a pressure higher than the pressure in a final crystallization vessel in the crystallization step (d).
[7] The process for producing high-purity terephthalic acid as claimed in claim 1, wherein the separation step (e) and the washing step (f) are conducted with a united apparatus.
[8] The process for producing high-purity terephthalic acid as claimed in claim 7, wherein the united apparatus for conducting the separation step (e) and the washing step (f) is any of a screen bowl type centrifugal separator, a rotary pressure filter, and a horizontal belt filter.
[9] The process for producing high-purity terephthalic acid as claimed in claim 1, wherein the solid matter contained in the washings discharges from the washing step (f) accounts for 1-10% by weight of the terephthalic acid crystals contained in the slurry supplied to the separation step (e).
(10| The process for producing high-purity terephthalic acid as claimed in claim 1, wherein the crystallization step (d) is composed of crystallization vessels
arranged in two or more stages and the solid matter recovered in the recovery step (h) is sent to the final crystallization vessels among the crystallization vessels arranged in two or more stages.

Documents:

7224-DELNP-2006-Abstract.pdf

7224-DELNP-2006-Claims-(07-12-2011).pdf

7224-delnp-2006-Claims-(13-04-2011).pdf

7224-delnp-2006-claims.pdf

7224-DELNP-2006-Correspondence Others-(07-12-2011).pdf

7224-delnp-2006-Correspondence Others-(13-04-2011).pdf

7224-DELNP-2006-Correspondence Others-(21-11-2011).pdf

7224-DELNP-2006-Correspondence Others-(31-10-2011).pdf

7224-delnp-2006-correspondence-others-1.pdf

7224-delnp-2006-correspondence-others.pdf

7224-delnp-2006-description (complete).pdf

7224-DELNP-2006-Drawings-(07-12-2011).pdf

7224-delnp-2006-Drawings-(13-04-2011).pdf

7224-delnp-2006-drawings.pdf

7224-DELNP-2006-Form-1.pdf

7224-delnp-2006-form-18.pdf

7224-delnp-2006-form-2.pdf

7224-delnp-2006-form-26.pdf

7224-DELNP-2006-Form-3-(07-12-2011).pdf

7224-delnp-2006-Form-3-(13-04-2011).pdf

7224-DELNP-2006-Form-3-(21-11-2011).pdf

7224-DELNP-2006-Form-3-(31-10-2011).pdf

7224-DELNP-2006-Form-3.pdf

7224-delnp-2006-form-5.pdf

7224-DELNP-2006-GPA-(07-12-2011).pdf

7224-delnp-2006-GPA-(13-04-2011).pdf

7224-delnp-2006-pct-304.pdf

7224-delnp-2006-pct-search report.pdf

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Patent Number

252544

Indian Patent Application Number

7224/DELNP/2006

PG Journal Number

21/2012

Publication Date

25-May-2012

Grant Date

22-May-2012

Date of Filing

30-Nov-2006

Name of Patentee

MITSUBISHI CHEMICAL CORPORATION

Applicant Address

14-1,SHIBA 4-CHOME,MINATO-KU,TOKYO 108-0014 JAPAN

Inventors:

#	Inventor's Name	Inventor's Address
1	MOTOKI NUMATA	C\O MITSUBISHI CHEMICAL CORPORATION,1-1,KUROSAKISHIROISHI,YAHATANISHI-KU KITAKYUSHU-SHI,FUKUOKA 806-0004,JAPAN
2	TAKAYUKI ISOGAI	C\O MITSUBISHI CHEMICAL CORPORATION,1-1,KUROSAKISHIROISHI,YAHATANISHI-KU KITAKYUSHU-SHI,FUKUOKA 806-0004,JAPAN
3	TOMOHIKO OGATA	C\O MITSUBISHI CHEMICAL CORPORATION,1-1,KUROSAKISHIROISHI,YAHATANISHI-KU KITAKYUSHU-SHI,FUKUOKA 806-0004,JAPAN

PCT International Classification Number

C07C 51/43

PCT International Application Number

PCT/JP2005/009462

PCT International Filing date

2005-05-24

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	204-159897	2004-05-28	Japan