TWI328002B - Process for producing high-purity terephthalic acid - Google Patents

Description

1328002 IX. Description of the invention: [Technical field to which the invention pertains] The present invention relates to a method for producing high-purity terephthalic acid. [Prior Art]

In the process of producing high-purity terephthalic acid, in order to produce high-purity terephthalic acid from bismuth, the raw material is first oxidized to produce para-xylene, and then contained therein. The 4-carboxybenzaldehyde which is an intermediate product is reduced to be p-toluic acid and removed to produce high-purity terephthalic acid. The steps are as follows. The raw material p-xylene is oxidized to terephthalic acid by a catalyst in a high temperature and high pressure acetic acid solution. At this time, the intermediate 4-carboxybenzaldehyde will be formed along with the stearic dicarboxylic acid. The slurry containing the same is subjected to crystallization and solid-liquid separation to obtain a crude p-phthalic acid. Then, the crude terephthalic acid crystal is dissolved in water under high temperature and high pressure to form an aqueous solution, and the 4-carboxybenzofural contained in the crude terephthalic acid is hydrogen-reduced to become a highly water-soluble para-benzene. Formic acid. Thereafter, it was pressure-cooled to precipitate a low water-soluble terephthalic acid from the aqueous solution, and was recovered as high-purity terephthalic acid. Here, in the primary separation mother liquid in which the high-purity terephthalic acid has been separated, the active components such as terephthalic acid and p-toluic acid are dissolved, and in order to improve productivity and reduce the drainage load, it is known that crystallization is performed. A method in which the tank is cooled while being stirred and precipitated to recover secondary crystals (Patent Document 1 and Patent Document 2). However, if this separation mother liquid is once cooled to a predetermined final temperature, 3] 2XP/Invention Manual (Supplement)/94-09/94117424 1328002 The crystal grain size will be fine, and recovered by a recovery device such as a filter. In the case of secondary crystallization, there is a disadvantage that the clogging of the filter and the recovery rate are reduced. Further, the secondary crystals have high adhesion, and when the crystals of the propeller type agitating blades or the paddle type agitating blades are precipitated, they are not sufficiently stirred to the vicinity of the inner wall, and deposits are formed on the inner wall side. Further, the fine powder accompanying the vapor generated by the above-described crystal precipitation treatment in the form of a cornice adheres to the side surface of the gas phase portion in the crystal deposition tank. When the deposits of the devices and the like are grown and detached, the cause of the blockage of the pipeline or the like is caused. Therefore, it is necessary to perform the cleaning operation of periodically stopping and washing the equipment φ. (Patent Document 1) Japanese Patent Laid-Open Publication No. Hei. No. 5-2 - No. 2 2 3 3 4 (Patent Document 2) Japanese Patent Laid-Open Publication No. Hei No. Hei-5-5 8 9 8 (Invention) [Problems to be Solved by the Invention] )

The present invention provides a method for producing a high-purity terephthalic acid, which is capable of improving the recovery rate of the secondary crystals precipitated by cooling the primary separation mother liquid when the high-purity terephthalic acid is produced. Secondary separation of mother liquor from turbidity (SS concentration). Further, it is intended to provide a method for producing high-purity terephthalic acid which can prevent the formation of deposits in the system and the occurrence of agglomerates during the cooling treatment. (Means for Solving the Problem) The inventors of the present invention have made intensive studies to solve the above problems. As a result, the inventors of the present invention have found that the above-mentioned problems can be solved by performing pressure-cooling in a plurality of stages of the separation of the mother liquid, thereby completing the present invention. That is, the gist of the present invention is as follows (1) to (1 1 ). 8 312XP / Inventive Manual (Supplement) / 94-09/94117424 1328002, wherein the separation mother liquid obtained by the filtration step (g) is contacted with the synthetic adsorption material to remove p-toluic acid, and then supplied to the dissolution step (b) . (11) The method for producing high-purity terephthalic acid according to any one of the above (6) to (10) wherein the concentration of the suspended matter in the separated mother liquid obtained by the filtration step (g) is 200 mg/L or less. (effect of the invention)

According to the present invention, it is possible to provide a method for producing high-purity terephthalic acid, which is capable of improving the recovery rate of secondary crystals which are cooled and precipitated in the primary separation mother liquid in the production of high-purity p-dicarboxylic acid, thereby obtaining low turbidity. Secondary separation of the mother liquor (SS concentration). Further, it is possible to provide a method for producing high-purity terephthalic acid capable of suppressing the formation of deposits in the system and the occurrence of agglomerates during the cooling treatment. [Embodiment] Hereinafter, the present invention will be described in detail. The method for producing high-purity terephthalic acid of the present invention comprises: an oxidation step (a), which is obtained by oxidizing p-dioxane to obtain crude terephthalic acid containing 4-carboxybenzaldehyde; and a dissolving step (b) The crude terephthalic acid is dissolved in an aqueous solvent under high temperature and high pressure to obtain a crude aqueous solution of terephthalic acid; and the reducing step (c) is carried out in the presence of a catalyst in the presence of a catalyst. Contacting with oxygen to obtain a reduction reaction solution for reducing the above 4-carboxybenzaldehyde to p-benzoic acid; and crystallization step (d), subjecting the reduction reaction solution to pressure evaporation and cooling to 1 2 0 to 2 0 0 ° C, the high purity of the crystal of the succinic acid is blocked 11 312XP / invention instructions (supplement) / 94-09 / 94117424 1328002 crystallization; solid-liquid separation step (e), the above crystallization step (d The obtained slurry is solid-liquid separated into crystals and separation mother liquid formed by the above-mentioned high-purity terephthalic acid crystal; and the crystal precipitation step (f) is to cool the separation mother liquid, which is mainly composed of the above solid-liquid separation step (e) Income Crystallized from crystals of terephthalic acid and p-toluic acid contained in the mother liquor; characterized in that

Cooling the cooling solution by evaporating the water solvent in the mother liquor by lowering the pressure, cooling the plurality of stages, depressurizing the last cooling tank to below atmospheric pressure, and setting the temperature of the last cooling tank to 40-70 °C. First, in the crude terephthalic acid production step (a), p-diphenylbenzene is subjected to liquid phase oxidation with molecular oxygen in an acetic acid solvent in the presence of a catalyst to form crude p-benzoic acid. This step is known as a catalyst which is conventionally used for the reaction, and specific examples thereof include a heavy metal compound such as a cobalt compound, a manganese compound, an iron compound, and a chromium compound, and a bromine compound. These are present in the reaction system in a dissolved state. Among them, a cobalt compound or a combination of a manganese compound and a bromine compound is preferred. In this case, usually, these compounds are used in such a manner that the solvent is 10 to 50,000 p p m of cobalt atoms, 10 to 5,000 ppm of manganese atoms, and 10 to 10,000 ppm of bromine atoms. As the molecular oxygen, a mixed gas of an inert gas and oxygen is usually used, for example, air or oxygen-enriched air is used. The molar ratio of the molecular oxygen to the reactor is usually 3 to 20 moles, preferably 2 to 4 12 312 XP / invention specification (supplement) / 94-09/94117424 1328002 Moer times. The ratio of p-xylene to acetic acid supplied to the reactor is usually from 1 to 50% by weight. The water concentration in the reaction system is usually 5 to 20% by weight, preferably 5 to 15% by weight. The temperature of the oxidation reaction is usually 160 °, 260 ° C, preferably 170 ° 2 to 1 0 ° C; the pressure may be maintained at a reaction temperature above the pressure of the reaction system in the liquid phase, usually It is 0.5 to 5 MPa, preferably 1 to 2 MPa; the residence time is usually from 10 to 200 minutes.

Since terephthalic acid is insoluble in acetic acid which is a solvent, the terephthalic acid which is usually formed in the oxidation reaction step is crystallized and forms a slurry. However, depending on the amount of the solvent, the reaction temperature and the pressure, there is also a case where terephthalic acid is dissolved. In this case, a crystallization step of cooling the reaction system or the like is provided to precipitate a stearic acid to form a slurry. The slurry was subjected to solid-liquid separation to obtain crude terephthalic acid crystals. The p-benzoic acid syrup system obtained in the oxidation reaction step is in a pressurized state, and can be directly subjected to solid-liquid separation, or subjected to pressure-pressure cooling or the like, followed by solid-liquid separation. The method for solid-liquid separation may be any one which can separate the crystal from the mother liquid, and examples thereof include filtration and centrifugation. Washing and drying as needed to obtain crude terephthalic acid crystals (crude terephthalic acid C). Further, the "crude terephthalic acid" of the present invention means terephthalic acid containing from 10 to 1000 ppm of 4-carboxybenzaldehyde. In the oxidation step (a), when the dimethyl group A is oxidized, not only the above-mentioned terephthalic acid but also 4-carboxybenzaldehyde which is not completely oxidized by a single-sided alkyl group is formed (hereinafter) The product referred to as "4CBA" is the product of the Deputy 13 312XP / Invention Manual (supplement) / 94-09/94117424 1328002. In order to remove these by-products from the crude terephthalic acid c and obtain high purity terephthalic acid, the following steps were carried out.

As the dissolving step (b), the crude terephthalic acid C is slurried in the slurrying tank 12 by water D, and the starting slurry E is made into a high temperature and a high pressure by the pump 12a and the heater 12b. And dissolved in water to become an aqueous solution E'. The above-mentioned terephthalic acid has low solubility in water, and the above-mentioned high temperature and high pressure are necessary for the state in which the above terephthalic acid is soluble in water. This temperature varies depending on the slurry concentration, and is preferably 2,300 ° C or more and 3 2 0 ° C or less. If it is less than 2 30 °C, the solubility is not sufficient. If it exceeds 3 2 0 °C, energy is wasted, and if the temperature is too high, there will be decomposition of terephthalic acid to produce other substances. Further, the pressure is necessary for maintaining the liquid phase in the above temperature range, and is preferably 2.8 MPa or more and 11.3 MPa or less. Further, the concentration of the slurry obtained in the dissolution step (b) is usually from 20 to 40% by weight, preferably from 25 to 35% by weight. If the slurry concentration is too high, it will cause blockage in the device. If it is too low, the amount of mother liquor will increase, and the equipment for production will be enlarged. From the standpoint of preventing clogging, it is preferable to keep the slurry concentration constant. Next, as the reduction step (c), the aqueous solution E' of the terephthalic acid obtained by the above dissolution step is sent to the hydrogenation reactor 13 to carry out contact reduction by introducing hydrogen F in the presence of a catalyst. The reduction reaction solution G was obtained. The conditions in the catalyst and hydrogenation reactor 13 must be those which reduce the above 4 C B A but do not reduce the above-mentioned terephthalic acid. It is used to reduce the 4 C B A contained in the aqueous solution E' to a highly water-soluble p-formic acid. This reduction is best done with as high a efficiency as possible. This hydrogenation reaction is also known; the hydrogenation catalyst uses 8 to 10 groups of ruthenium, rhodium, palladium, platinum, etc. (according to IUPAC Inorganic Chemicals 14 312XP / Invention Specification (supplement) / 94-09/94117424 1328002 The metal catalyst is usually used as a fixed bed in a supported carrier such as activated carbon. Among these, palladium supported on activated carbon is preferred. The hydrogenation temperature is usually from 2 6 0 to 3 2 0 ° C, preferably from 2 7 0 to 300 ° C, and the partial pressure of hydrogen is usually from 0.5 to 20 kg/cm 2 G. Further, as the first crystallization step (d), the reduction reaction liquid G obtained in the reduction step (c) is introduced into the crystallization chamber 14 to lower the temperature and pressure while maintaining the dissolution of the ruthenium bismuth acid. The above-mentioned terephthalic acid crystals are precipitated into a slurry. Here, the crystallization tank is provided in series of φ in multiple stages, preferably in the range of 3 to 6, to gradually reduce the pressure and to cool (depressurization evaporative cooling) to precipitate the above-mentioned terephthalic acid crystals more preferably. The temperature of the final crystal precipitation tank 14 may be controlled to a temperature condition in which p-toluic acid is not co-crystallized with terephthalic acid, and specifically, it is required to be 1 2 0 ° C or more and 200 ° C or less. It is preferably 1 3 0 ° C or more and 1 80 ° C or less. The pressure at this time must be 0.20 MPa or more and 1.56 MPa or less, and preferably 0.27 MPa or more and 1.00 Μ P a or less. If these conditions are lower temperature and low pressure, not only the above-mentioned terephthalic acid but also pyromellitic acid will be co-crystallized, and the purity of the obtained high-purity β-degree benzoic acid crystal will decrease. On the other hand, if higher temperature and pressure are maintained under these conditions, the amount of crystallization of the obtained stearic acid will be reduced and the efficiency will be deteriorated. Next, as the solid-liquid separation step (e), the slurry is introduced into a solid-liquid separator, and the mother liquid J is separated and separated once from the slurry to obtain a high-purity pair of the above-mentioned terephthalic acid crystals having high purity. Phthalate filter cake. The high-purity terephthalic acid filter cake is washed in a washing device and then dried to form a primary crystal formed by high-purity terephthalic acid crystals to be more than 15 312 ΧΡ / invention specification (supplement) / 94 -09/94 η 7424 1328002 Preferably, if the steps of the above-described solid-liquid separator and the above-described cleaning apparatus are integrated in one solid-liquid separation and cleaning apparatus 15, the steps can be simplified and further improved. As described above, the operation of separating and cleaning the slurry tamping liquid by one solid-liquid separation and cleaning device 15 is as follows. The slurry mash and the cleaning solution I are introduced into a solid-liquid separation and cleaning device 15 . As the cleaning liquid I, water is preferred. The slurry is subjected to solid-liquid separation, and the separated filter cake is washed with the cleaning solution I, and the high-purity terephthalic acid filter cake L is separated from the primary separation liquid J, and the separation mother liquid J is discharged once and the main The effluent mash consisting of the components of the cleaning solution I. Here, the temperature of the primary separation mother liquid J discharged from the solid-liquid separation and cleaning device 15 is the same as the crystallization precipitation condition in the first crystallization precipitation step (d), and is 1 2 0 ° C or higher and 2 0 0 Preferably, the temperature is lower than °C, and more preferably 130 ° C or more and 180 ° C or less; in addition, regarding the pressure, in order to suppress the temperature drop caused by the pressure release, it is necessary to be the final stage of the crystallization precipitation step (d). The pressure in the crystallization chamber is higher. Specifically, it is preferably higher than the pressure of the final crystallization tank of the crystallization step (d) by 0 to 1 Μ P a . In the solid-liquid separation step (e), it is preferred to operate the slurry without being cooled by the supplied slurry. The solid-liquid separation and cleaning device 15 which can be integrated and subjected to solid-liquid separation and washing is, for example, a screenbowl-type centrifugal separator, a vacuum-reducing vacuum thickener, a horizontal belt filter, etc., particularly preferably a screen bowl type. Centrifugal separator. The thus obtained high-purity terephthalic acid filter cake L is dried in a drying device 16 to remove the residual adhering liquid, thereby obtaining a high-purity bismuth dipic acid crystallization. The drying device 16 may be, for example, a tumbling dryer or a flow 312 ΧΡ / invention specification (supplement) / 94-09/94117424 1328002 bed dryer, etc., in the presence of aeration gas, using a heat source such as water vapor, It is carried out at a dry outlet operating temperature of 70 ° C to 180 ° C. On the other hand, in the above-mentioned primary separation liquid J and the cleaning discharge liquid K, the active ingredient is still contained, and it is necessary to recover as much as possible to obtain high-purity terephthalic acid. Further, the above-mentioned effective component means the above-mentioned terephthalic acid and other compounds which can be produced by oxidizing to the above-mentioned terephthalic acid, for example, and which contain a dissolved component and a solid component. Further, the above solid fraction refers to a component precipitated from the above active ingredient.

First, since the content of the terpene phthalic acid in the cleaning effluent K is small, it is preferable to directly return to the solvent as the above-mentioned dissolution step (b). Further, in the case where the cleaning effluent K contains a solid component, it may be subjected to solid-liquid separation by another solid-liquid separation device before returning to the dissolution step (b). The reason for this is that when the solid-liquid separation and cleaning device 15 described above is integrated and subjected to solid-liquid separation and washing, since the leakage is likely to occur, the cleaning discharge liquid K contains a solid component. Further, before the separation by the other solid-liquid separation device described above, if the crystallization is carried out in advance, the amount of the component recoverable by the solid-liquid separation is improved. In this case, the solid matter may be collected and collected in the crystallization tank 14 or the like, or the separated liquid may be used as the solvent used in the slurry tank 1 2 . Next, regarding the primary separation of the mother liquid J, the second crystal precipitation step (f) is to separate the primary separation mother liquid J by using a plurality of stages of the pressure-cooling cooling tank, and to separate the above-mentioned terephthalic acid and the paralysis contained in the mother liquid J. A secondary crystal composed of benzoic acid or the like is crystallized and recovered. The plural section refers to a structure in which the pressure-relieving cooling tanks are arranged in series of two or more stages, and the corresponding pressures in the respective tanks are lowered by the temperature of each of the 17 312XP/invention specification (supplement)/94-09/94117424 1328002, thereby separating the dissolved components. Further, the pressure-releasing cooling tank means a tank having a pressure lower than that of the liquid to be introduced, and the boiling point of the main component of the liquid in the pressure in the tank is equal to or lower than the temperature of the liquid before introduction. If liquid is introduced into the discharge cooling bath, a portion of the liquid evaporates and the remaining liquid is cooled to the boiling point of the pressure after the change. At this time, in the case where the liquid is a solution, the solute which exceeds the solubility component after cooling precipitates crystals.

The stepwise cooling is performed by using the above-mentioned pressure-releasing cooling tank of the plurality of stages to cause the crystal precipitation to be crystallized as compared with the cooling by a single stage of pressure-cooling or a combination of pressure-cooling cooling and heat exchange. Since the cooling and/or crystallization precipitation non-uniformity can be suppressed, the amount of the solid matter obtained by performing more thorough crystal precipitation increases, and the properties of the obtained solid matter become easy to handle. Further, it is possible to suppress the crystal of the above-mentioned effective component from adhering to the pressure-reducing cooling tank or the line introduced into the pressure-releasing cooling tank. Therefore, in the plurality of pressure-release cooling tanks of the plurality of stages, the pressure of the first pressure-release cooling tank 17 which is the first pressure-release cooling tank is preferably equal to or higher than the atmospheric pressure, and is not discharged by the solid-liquid separation step (e). The pressure of the mother liquid J is separated once, preferably at a temperature of 100 ° C or more, and is less than the temperature of the primary mother liquid J separated by the solid-liquid separation step (e) (for example, pressure-evaporating and cooling to 100 ° C to no The temperature at the solid-liquid separation in the solid-liquid separation step (e) may be, and the pressure-evaporation is preferably a pressure-evaporation to atmospheric pressure). If the pressure is reduced to less than atmospheric pressure once, the pressure reduction range is too large, the crystal precipitation will be non-uniform, or the size of the obtained crystal will be too small, and the meaning of the pressure-reducing cooling tank in which a plurality of stages are provided will be lost. In addition, since the boiling point of water at atmospheric pressure is 100 ° C, the temperature is 18 312 XP / invention manual (supplement) / 94-09/941 丨 7424

1328002 is set to 100 °c or more. On the other hand, if the temperature at which the mother liquid J is separated at one time does not decrease, crystal precipitation cannot be performed. Further, in the above-mentioned plurality of pressure-release cooling grooves of the plurality of stages, it is preferable that at least the agitating blades have a distance of 10 mm or more from the inner wall of the pressure-relieving cooling groove. Further, in the stirring blade, the portion closer to the inner wall of the groove at the above interval is preferably as long as possible, and the anchor type stirring blade is preferable. In the above-mentioned pressure-releasing cooling tank, since the purity is low, the precipitation of dioxin is precipitated, and only the above-mentioned stirring blade is used to adhere the above-mentioned terephthalic acid or the like to the wall surface. Then, by the agitating blade which is turned close to the wall of the groove, the liquid in the vicinity of the wall surface flows appropriately, and it is possible to inhibit the adhesion of terephthalic acid or the like to the wall surface. However, if the pressure-reducing cooling tank itself is too close, the agitating blade is preferably spaced apart from the wall by 10 m or more. In particular, since it is highly probable that the amount of crystal precipitation of the pressure cooling tank 107 in the initial pressure cooling tank is the highest, it is more preferable to provide the above-mentioned stirring blade in the pressure cooling tank 17. Further, the agitating blades may be provided in a plurality of stages of the pressure reducing cooling grooves. In the above-mentioned pressure-relieving cooling tank, when the above-mentioned anchor type stirring blade is used to crystallize the upper crystal from the primary separation mother liquid J, the anchor type stirring rotation number is preferably 3.0 rpm or more and 30 rpm or less, more preferably 5 rpm or more. If the temperature is less than 3.0 rpm, the agglomerated fruit cannot be fully utilized, and the crystals having crystallized crystals adhere to the surface below the liquid surface in a lump. On the other hand, if it is 30 rpm, it can be fully mixed. Even if it is faster, not only wastes energy, but also the primary separation liquid is scattered in the pressure-relieving cooling tank, and becomes the liquid surface 312XP/invention manual of the crystal knot attached to the tank ( Replenishment) /94-09/94]17424 Pressure and one of the 50 mm to release the cold as the crystal face of the more acid crystals, avoiding the first between the damaged surfaces and the first place After the '2 0 rpm - the effect of the inner wall side of the stirring J will also be the main reason for the above 19 1328002. Further, in the above-mentioned plurality of pressure-release cooling tanks, it is preferable that not only the above-mentioned terephthalic acid but also the above-mentioned para-benzoic acid and other by-product crystals are precipitated. In the second crystallization step (f), the precipitated component is not crystallized, and since the filtration step (g) described later cannot be recovered and is discharged as the secondary separation mother liquid, the substance which is crystallized is not limited to the above-mentioned benzene. The dicarboxylic acid is carried out in such a manner that all of the active ingredients are crystallized and returned as much as possible.

Therefore, in the present invention, the pressure of the final pressure-relieving cooling tank 18 of the final pressure-relieving cooling tank in the plurality of stages of the pressure-release cooling tank is reduced to less than atmospheric pressure, so that the temperature of the cooling tank becomes 40 to 8 0 ° C, preferably 5 0 to 7 (TC. Specifically, the pressure of the final pressure-relieving cooling bath 18 is 0.007 MPa or more and 0.03 MPa or less, preferably 0.02 to 0.03 MPa. If the pressure exceeds 0. 0 3 Μ P a, or the temperature is too high, the crystallization is not complete, and the recovery will be insufficient. On the other hand, if the pressure is less than 0.007 MPa and the temperature is too low, the final pressure is reduced due to the high degree of pressure reduction. The burden on the cooling tank 18 is too large. Further, between the first pressure-releasing cooling tank 17 and the final pressure-cooling cooling tank 18, a single or a plurality of pressure-relieving cooling tanks may be further provided to carry out the staged crystallization. In the second crystallization step (f), the secondary slurry 0 obtained by crystallizing the above-mentioned terephthalic acid or the like is introduced into the filter 1 and 9 in the filtration step (g). The mother liquor P is separated from the secondary crystal Q solid solution. The filter used here can filter The downstream side of the device becomes a pressure state above atmospheric pressure, and the upstream side of the filter of the filter becomes a secondary slurry for solid-liquid solution than the downstream side of the filter of 20 312XP/invention specification (supplement)/94-09/94117424 1328002 The second crystallization is precipitated and the second crystallization is separated and separated from the φ side of the mother liquid p by cross-linking the filter cake layer, and the above-mentioned two are used, for example, Ishikawa Machinery Co., Ltd. Active ingredients

The above-mentioned secondary reduction is the above-mentioned oxidation of benzene, and the high purity of the invention is preferably 200 mg/L on the other hand. Further, this higher pressure state and separation makes it easy to filter. Although it is easy to handle by the above plural, it is difficult to carry out. Further, on the side to which the above step (f) is sent, the side of the mother liquid P flows in the forward direction by the above-mentioned transition device. Further, the filter cake as described above captures particles, and the filter cake layer is a mechanism for filtering the filter cake layer. The secondary crystal Q of the crecket filter manufactured by Shimadaka Heavy Industries Co., Ltd. is preferably returned, and in particular, it is returned to the above-mentioned crystal Q to contain not only the above-mentioned impurity dicarboxylic acid such as pyromellitic acid. Therefore, the impurities can be made into the production of the upper terephthalic acid, and the above-mentioned secondary separation mother liquid F is a suspended matter concentration system of 100 mg/L or less.

The crystallization of the tears is formed by filtering on the lower holes of the above-mentioned finger-distributing sub-distributor, and the above-mentioned part of the island can be used as the ^ ( a ) as the special liquid P if the filter is carried out in the forward direction by the filter cake. The pressure-relieving cooling tank of the good state is in a state of easy adhesion, and the upstream side of the filter means that the downstream side of the filter refers to the secondary slurry 0 and the upstream side of the filter toward the filter filter finger to filter fine Immediately after the filter surface, the oxidizing step (a) is better for the F η丨daba 丨C filter of the filter 1 ί, which is operated as described above. The phthalic acid also contains > but these cannot be directly caused by the above-mentioned oxidation step, the benzoic acid > can be extracted as a whole. The yield 〇P is preferably the concentration of the suspended substance is better, 50 ι ng / L The following refers to the 312XP / hair relative to the second separation mother The specification (supplement)/94-09/94]] 7424 21 1328002 The weight of the float of benzoic acid or the like which is not dissolved in the solvent and is dispersed in the solvent is analyzed according to the method described in JIS K0101. Since the at least one portion of the secondary separation mother liquid p is discharged to the outside of the system so as not to cause the impurity concentration in the system to be excessively high, the para-benzoic acid contained in the secondary separation mother liquid P is discarded, thereby causing the present invention. The overall yield of the terephthalic acid production method is lowered. Further, in the case where at least a part of the secondary separation mother liquid P is directly or indirectly reused as a solvent in the production step, it is necessary to suppress the accumulation of p-toluic acid in the system.

In order to remove the para-benzoic acid contained in P in the second separation mother liquid, there is a method of bringing P in the secondary separation mother liquid into contact with the synthetic adsorption material. As the synthetic adsorbent, an organic synthetic adsorbent is generally used. The synthesis of styrene-divinylbenzene such as SEPABEADS SP825' SP850, SP207 (SEPABEADS is a registered trademark of Mitsubishi Chemical Corporation), AMBERLITE XAD-4, XAD-16UMBERLITE is a registered trademark of Rohm & Haas Co., Ltd., etc. Adsorbent; DIAI 0 Ν Η P 2 MG (DIAI 0 N is a registered trademark of Mitsubishi Chemical Corporation), AMBERLITE XAD-7, XAD-8 and other acrylic synthetic adsorbents. Preferably, it is a non-polar organic synthetic adsorbent, in particular, a synthetic adsorbent composed of a porous copolymer of a monovinyl compound and a polyvinyl compound, wherein a synthetic adsorbent using a styrene-divinyl stupid system is used. good. Since p-toluic acid has a benzene ring, it is easily adsorbed to a synthetic adsorbent of styrene-divinylbenzene. The specific surface area of the adsorbent is generally 400 to 1500 m 2 /g, preferably 600 to 1000 m 2 /g, and the pore volume is generally 0.5 to 3 m L / g, preferably 1. 0 to 2. 0 m L / g, the pore diameter is generally 1 0 ~ 1 0 0 0 A > preferably 5 0 ~ 5 0 0 A. The adsorbent is generally filled in the adsorption tower 22 312XP / invention manual (supplement) / 94-09 / 94117424 1328002 and becomes a filling layer height of about 1.5 ~ 4. 0 m. Although there is a difference in when the supply of the liquid to be treated is stopped, generally, if the height of the packed bed is too low, the utilization efficiency of the adsorbent is lowered. The supply rate of the liquid to be treated in the adsorption tower is generally 0.5 to 30 m/hr, and SV is generally 0.5 to 20 hr. After the second separation of the mother liquor by the adsorption treatment, the concentration of the phthalic acid is reduced, and it is preferable to use it as a solvent for the dissolution step and a separation filter cake after the solid-liquid separation step. Further, p-toluic acid is an oxidized intermediate in which p-xylene is oxidized to terephthalic acid, and is adsorbed to a synthetic fluorene-containing benzoic acid-based detachment solution, preferably supplied to an oxidation step. . Hereinafter, the present invention will be specifically described by way of examples. [Method for Measuring Suspension Concentration (JISK 0 1 0 1 )] The suspended substance (substance suspended in water) is subjected to the following operation, and the sample is filtered to remove the substance remaining on the filter material by 1 0 5 to 1 1 Dry at 0 °C and measure the mass.

(a) When a glass fiber filter paper is used, it is preliminarily attached to a filter, and is sufficiently sucked and washed with water. The filter material is placed on the watch glass and heated at about 1 0 5 to 1 10 ° C. After the temperature is released in the moisture-proof box, the quality is measured. (b) The filter material is attached to the filter, and an appropriate amount of the sample is injected into the filter for suction filtration. The material adhering to the wall of the sample container and the filter tube was washed with water and dropped onto the filter material, and the residual material on the filter material was mixed, and this was washed several times with water. (c) The residue is carefully taken out from the filter together with the filter material using a tweezers, etc., and transferred to the watch glass used in (a), heated at 1 0 5 to 1 10 ° C for 2 hours, 23 3 ] 2XP/ BRIEF DESCRIPTION OF THE INVENTION (Spread)/94-09/94〗 17424 1328002 After cooling in a previous moisture barrier, the mass is measured. (d) The suspended matter (mg/l) was calculated according to the following formula.

S=(a - b)xl 0 0 0 /V Here, S: suspended matter (mg / 1); a: mass of filter material and surface glass containing suspended matter (mg); b: transition material and The mass of the recorded glass (mg); V: sample (m 1 ) 0 (Example 1) The acetic acid solution of p-terephthalic acid, catalyst (cobalt acetate, manganese acetate solution and bromine φ hydrogen) The separated mother liquor and air recovered in the solid-liquid separation step in the latter stage are continuously supplied to the stirring tank at an operating temperature of 1 90 ° C and an operating pressure of 1. 2 3 Μ P a (absolute pressure) with a residence time of 1 hour. The liquid level is adjusted and the oxidation reaction is carried out at the same time. Further, the distillate vapor was finally cooled to 40 ° C by a multistage condenser, and the oxygen concentration in the exhaust gas was adjusted to 2·5 νο 1 % to carry out the operation. Further, the condensate obtained from each condenser was integrated and refluxed to the oxidation reactor, and a part of the reaction was taken out so that the water concentration in the mother liquor of the slurry became 10% by weight. The slurry extracted from the oxidation reactor has a slurry concentration of 35 wt% and a cobalt/manganese/bromine concentration in the reaction mother liquor of 300/300/1000 ppm by weight. The slurry taken out from the oxidation reactor was continuously supplied to the stirring tank together with the air, and the liquid level was adjusted for 15 minutes at an operating temperature of 181 ° C and an operating pressure of 1.15 MPa (absolute pressure), and the low temperature was simultaneously added. Oxidation reaction. Further, the distillate vapor was finally cooled to 40 °C by a multistage condenser, and the oxygen concentration in the exhaust gas was adjusted to 6 vol% to carry out the operation. Further, the condensate obtained by each condenser was integrated and refluxed to a low temperature additional oxidation counter 24 312 XP / invention manual (supplement) / 94-09 / 94117424 1328002. The slurry taken out from the low-temperature addition oxidation reactor is crystallized to 9 (TC, and the slurry obtained by precipitation of the crystal is supplied to a vacuum filter for solid-liquid separation and washing. The operating pressure here is atmospheric pressure. The separated crude terephthalic acid filter cake is dried by a steam tumble dryer to obtain crude terephthalic acid. The crude terephthalic acid is supplied to the high purity p-benzoic acid shown in FIG. A step of producing formic acid. Using water D as a solvent, a high-temperature high-pressure aqueous solution E' containing 30 weight%/〇φ of crude terephthalic acid is obtained. In the step shown in Fig. 1, it is sent to the hydrogenation reactor 13 The temperature and pressure of the aqueous solution E' were set to 290 ° C and 8.7 MPa (89 kgf / cm 2 · recording pressure), respectively.

In the first crystallization step (d) in which the crystallization is continued, the crystallization tank 14 having five crystallization tanks connected in series is used, and is cooled by stepwise pressure evaporation to be cooled to a final temperature of 15 5 °. C, the solute crystals are precipitated. The slurry obtained by crystal precipitation is separated into a high-purity terephthalic acid filter cake L containing primary crystals and a primary separation mother liquid J by a solid-liquid separation and washing apparatus 15 to obtain the above-mentioned high-purity p-benzoquinone. The acid cake L was washed with washing water, dried by a drying device 16 and recovered as high-purity terephthalic acid crystal ruthenium. On the other hand, in the first pressure-release cooling tank 17 provided with the anchor type stirring blade, the pressure is lowered to atmospheric pressure, and the primary separation mother liquid J is pressure-cooled to 100 ° C to perform the second stage of the first stage. The crystallization of the precipitation step (f) is precipitated. The number of revolutions of the anchor type stirring blade was set to 10 rpm, and the gap between the anchor type stirring blade and the side wall of the inner wall was set to 10 m. 25 312XP/Invention Manual (supplement)/94-09/94117424

1328002 Next, the obtained intermediate slurry N at 100 °C was introduced into the final pressure-relieving cooling tank 18 with an ejector, and the operating pressure was changed to 0. 0 2 Μ P a pressure was cooled to 60 °C. The secondary slurry 0 thus obtained was placed in a Fundabac filter (R 5 6 - 8 6 - 2 5 type) manufactured by Ishikawa Harima Heavy Industries Co., Ltd. as a machine 19, and subjected to solid-liquid separation. The second obtained here: The concentration of the suspended matter of the mother liquid P was measured by the above method, and as a result, it was 30 mg / 1 〇, and the first pressure-relieving cooling tank 17 and the final pressure-release cooling were 18. In the course of one month, no precipitates adhered and grew on the side of the inner wall, and the secondary crystallization Q was recovered. The present invention has been described in detail above with reference to the specific embodiments thereof, and it is understood that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on the patent (Special Wish 2 0 0 4 - 1 5 9 7 8 6) filed on May 28, 2004, and its contents are also extracted hereto as reference (industrially available) According to the present invention, it is possible to provide a method for producing high-purity p-dicarboxylic acid, which is capable of improving the recovery rate of secondary crystals in which the primary mother liquid is cooled and precipitated when producing high-purity terephthalic acid. Secondary separation of mother liquor with low turbidity concentration). Further, it is possible to provide a method for producing high-purity terephthalic acid which inhibits the formation of deposits in the system and causes a blockage during the cooling treatment. Industrial Value of the Invention [Simplified Description of the Drawings] Fig. 1 is a view showing an example of the method for producing terephthalic acid of the present invention 312XP/invention specification (supplement)/94-09/941Π424 The process of the application is completed by the stability of the separation (SS can occur. Flow 26 1328002). [Main component symbol description] 12 slurry tank 12a pump 12b heater 13 hydrogenation reactor 14 crystallization chamber 15 solid-liquid separation and washing Net device φ 1 6 Drying device 17 First pressure relief cooling tank 18 Final pressure relief cooling tank 19 Filter A p-xylene B Oxygen-containing gas C Crude to p-dicarboxylic acid D water

E Starting slurry E' Aqueous solution F Hydrogen G Reduction reaction solution Η Slurry I Washing liquid J Primary separation of mother liquor Κ Washing effluent 312ΧΡ/Invention manual (supplement)/94-09/941]7424 27

1328002 L High purity terephthalic acid filter cake Μ High purity terephthalic acid crystal Ν Intermediate slurry 0 Secondary slurry 二次 Secondary separation mother liquor Q Secondary crystallization

312ΧΡ/Invention Manual (supplement)/94-09/94117424 28

Claims (1)

1328002 Yi) ^PR 1 3 2010 X. Patent application scope: j Revision of this book. 1. A method for manufacturing high-purity terephthalic acid, which has the following steps: oxidation step (a), the system will be two The benzene is oxidized to obtain a crude terephthalic acid containing 4-carboxybenzaldehyde; and the dissolving step (b) is to dissolve the crude terephthalic acid in an aqueous solvent under high temperature and high pressure to obtain a crude terephthalic acid f. An aqueous acid solution; a reduction step (c), wherein the crude terephthalic acid aqueous solution is contacted with hydrogen in the presence of a contact medium to obtain a reduction reaction solution for reducing the above 4-carboxyphenylfurfural to p-benzoic acid; The crystallization precipitation step (d) is carried out by subjecting the reduction reaction solution to pressure evaporation and cooling to 1 2 0 to 200 ° C to crystallize the high purity terephthalic acid crystal; the solid-liquid separation step (e) And solid-liquid separating the slurry obtained in the above crystallization precipitation step (d) into a crystal and separation mother liquid formed by the above-mentioned high-purity terephthalic acid crystal; The crystallization step (f) is carried out by cooling the separation mother liquid, and crystallizing the terephthalic acid and the para-benzoic acid-based crystal contained in the separation mother liquid obtained by the solid-liquid separation step (e); The crystallization step (f) is performed by using a plurality of cooling tanks to cool the final cooling tank to a temperature less than atmospheric pressure, and the temperature of the last cooling tank is set to 40 to 7 (TC, The cooling bath evaporates the aqueous solvent in the mother liquor by reducing the pressure. 2. The method for producing high purity p-triconic acid according to the first aspect of the patent application 29 94117424 1328002, wherein the crystallization step (f) In the cooling tank used, the first cooling tank is cooled by evaporation and cooled to 100 ° C~ the temperature at the time of solid-liquid separation in the solid-liquid separation step (e). 3 · As claimed in the second paragraph of the patent application A method for producing high-purity terephthalic acid, wherein the first cooling tank is subjected to pressure-evaporation to atmospheric pressure. 4. The method for producing high-purity terephthalic acid according to the first aspect of the patent application, wherein the crystallization step (f) The cooling tank used in the present invention has an anchor type stirring wing. 5. The method for producing high-purity terephthalic acid according to claim 1, wherein at least one of the cooling grooves used in the crystallization step (f) has an interval of 10 mm from an inner wall of the cooling groove thereof. Above and below 50mm stirring wings. 6. The method for producing high-purity terephthalic acid according to the first aspect of the invention, wherein the slurry obtained by the crystallization precipitation step (f) is subjected to solid-liquid separation into a crystallization and separation mother liquid using a filter (g) ). 7. The method for producing high purity terephthalic acid according to item 6 of the patent application, wherein the crystal separated by the filtering step (g) is supplied to the oxidation step 8. The method for producing high-purity terephthalic acid according to claim 6, wherein in the filtering step (g), the downstream side of the filter of the filter is set to a pressure state higher than atmospheric pressure, and the filtration is performed. The upstream side of the filter of the machine is set to a higher pressure state than the downstream side of the filter, and the filter cake is filtered in the forward direction of the filter to perform solid-liquid separation. 9. The method of producing high purity terephthalic acid according to claim 6 of the invention, wherein the separation mother liquid obtained by the filtration step (g) is directly or fed to the dissolution step (b). 10. The method of claim 6, wherein the separation mother liquid obtained by the filtration step (g) is contacted with the mixture to remove the para-benzoic acid, and then supplied to the dissolution step (b). ). The high purity p-benzoquinone® method of claim 6, wherein the separation in the separation mother liquid obtained by the filtration step (g) is 200 mg/L or less. Between the grounding supply and the manufacture of the absorbing material L 94117424 31