JP2005247839A - Method for producing aromatic carboxylic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an aromatic carboxylic acid with which energy possessed by a separation mother liquor is effectively utilized and an active component dissolved in the mother liquor is effectively recovered when the separated mother liquor obtained by carrying out solid-liquid separation of an oxidation reaction slurry in a high-temperature and a high-pressure state at the high temperature under the high pressure is treated in the method for producing the aromatic carboxylic acid from an alkyl aromatic compound. <P>SOLUTION: A pressure state above atmospheric pressure pressurized in an oxidation step is retained in steps thereafter in production steps of the aromatic carboxylic acid having the oxidation step (11), a recovery step (14), recycling steps (H and I) and concentrating steps (16, 17 and 18). The pressure is utilized in concentration (16) in the concentrating steps. In the concentrating steps, a solvent T in the mother liquor I is evaporated without carrying out heating, compressing, etc. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing an aromatic carboxylic acid.

  In general, a process for producing terephthalic acid, which is an aromatic carboxylic acid, is performed, for example, as shown in FIG. Xylene a is oxidized with air b to produce terephthalic acid. The produced terephthalic acid is a slurry in which a part thereof is dissolved in a solvent, and this reaction slurry c is introduced into the crystallization tank 2 and evaporated under pressure to further precipitate terephthalic acid to obtain a crystallization slurry d. . This crystallization slurry d is separated into a terephthalic acid cake e and a separation mother liquor f through a solid-liquid separation step in which the solid-liquid separation device 3 separates the crystallization slurry d. Among these, the terephthalic acid cake e is dried by the drying device 4 to obtain terephthalic acid crystals g.

  The separated mother liquor f can be reused as the recycled mother liquor h as a solvent for the oxidation reaction step. However, if impurities contained in the separated mother liquor f accumulate in the system, the quality of the resulting terephthalic acid crystals g will be affected. . Therefore, in order to suppress the accumulation of impurities, a part of the separated mother liquor f is purged out of the system as a purge mother liquor i. However, this purge mother liquor i contains not only impurities but also an oxidation catalyst and a solvent component, and it is necessary to recover these effective components.

  In general, first, the solvent component of the purge mother liquor i is evaporated by the solvent evaporation device 5, high-boiling components such as an oxidation catalyst and impurities are concentrated, and the oxidation catalyst is recovered from the concentrated residue j by a process such as extraction. . In addition, the evaporated solvent vapor k is usually reused as the solvent in the oxidation reaction step and the washing liquid in the solid-liquid separation step. . Here, the purge mother liquor i is accompanied by solids such as terephthalic acid and its oxidation intermediate due to leakage in the solid-liquid separator 3. If the purge mother liquor accompanied by the solid content is mixed into the residue by the concentration process, it becomes difficult to recover the solid content, leading to a decrease in productivity.

  Therefore, in Patent Document 1, the separation mother liquor f is branched, one of them is recycled mother liquor h and returned to the oxidation reaction step, and the other is concentrated as purge mother liquor i. Describes a method for solid-liquid separation of the solid content contained in.

  Further, the reaction slurry c is solid-liquid separated in a state of maintaining a high temperature and high pressure directly without passing through the crystallization tank 2 or without releasing to normal pressure even when the pressure evaporates in the crystallization tank 2. Methods are described in US Pat. Thereby, the drying process of the downstream separated terephthalic acid cake e can be simplified, and the heat energy consumed in the purification process of the dried terephthalic acid crystals g can be reduced.

JP 2000-504741 Gazette JP 2001-139514 A JP 2002-336687 A

  However, the high-temperature and high-pressure separation mother liquor obtained by solid-liquid separation under high temperature and high pressure has higher solubility than the separation mother liquor obtained by solid-liquid separation under lower temperature and low pressure, so terephthalic acid and its oxidation Many active ingredients such as intermediates are dissolved, and if the concentration operation is performed once until the residue is obtained by purging the separation mother liquor with high temperature and high pressure, terephthalic acid dissolved in the high temperature and high pressure separation mother liquor and its oxidation intermediate Active ingredients such as the body are mixed into the residue, leading to a decrease in productivity. On the other hand, when the recycled mother liquor is cooled by pressure-release evaporation and supplied to the reactor, a large amount of energy is required to raise the temperature of the reaction product to a predetermined oxidation reaction temperature, which reduces the recovery efficiency of oxidation reaction energy. It becomes.

  Therefore, the present invention provides a method for producing an aromatic carboxylic acid from an alkylaromatic compound. In processing a separation mother liquor obtained by solid-liquid separation of an oxidation reaction slurry in a high temperature and high pressure state at a high temperature and high pressure, An object of the present invention is to produce an aromatic carboxylic acid by recovering an active ingredient dissolved in a mother liquor by efficiently using the energy it has to concentrate.

The present invention includes (A) an oxidation step in which an alkyl aromatic compound is oxidized in an acetic acid solvent in the presence of a catalyst under a pressure exceeding normal pressure to produce an aromatic carboxylic acid,
(B) a solid-liquid separation step in which the slurry containing the produced aromatic carboxylic acid crystals is separated into an aromatic carboxylic acid and a mother liquor under a pressure exceeding normal pressure;
(C) The mother liquor recycling step in which the mother liquor is branched while maintaining a pressure exceeding normal pressure, and one of them is returned to the (A) oxidation step,
(D) In the method for producing an aromatic carboxylic acid, comprising the step (C) of concentrating the other mother liquor branched in the mother liquor recycling step.
In the concentration step (D), the other mother liquor is evaporated under reduced pressure to a pressure equal to or lower than the vapor pressure at the initial temperature of the other mother liquor to precipitate an aromatic carboxylic acid, and then the precipitated aroma By recovering the group carboxylic acid, the above problems were solved.

  That is, (A) the pressure state exceeding the normal pressure pressurized in the oxidation step is maintained also in the subsequent steps (B) and (C), and the pressure is utilized during the concentration in the (D) concentration step. (D) It was possible to evaporate the solvent in the mother liquor without performing heating, compression, etc. from the beginning in the concentration step.

  According to the present invention, in the method for producing an aromatic carboxylic acid, when concentrating the purge mother liquor of the mother liquor to be treated separated from the obtained aromatic carboxylic acid, the energy of the mother liquor is used as part of the concentration. As a result, the recovery rate of useful components contained in the purge mother liquor can be increased. Recycled mother liquor, which is the remainder of the mother liquor, is recycled to an oxidation reactor that oxidizes while maintaining high temperature and pressure, thereby reducing the energy required for temperature rise and enabling effective recovery of oxidation reaction energy. It becomes.

Hereinafter, the present invention will be described in detail with reference to FIG.
This invention is an aromatic carboxylic acid production method comprising (A) an oxidation step, (B) a solid-liquid separation step, (C) a mother liquor recycling step, and (D) a concentration step.

  In the oxidation step (A), the aromatic alkyl carboxylic acid slurry C is obtained by liquid phase oxidation of the alkyl aromatic compound A in the reaction medium. When the aromatic carboxylic acid to be produced is terephthalic acid, the alkyl aromatic compound A is p-xylene. At this time, it is desirable to oxidize 90% by weight or more of p-xylene as the alkyl aromatic compound A to terephthalic acid, and more desirably 95% by weight or more can be oxidized.

  Moreover, an acetic acid solvent is used as a reaction medium in the (A) oxidation step. When manufacturing said terephthalic acid, it is preferable that the usage-amount of this acetic acid solvent is 2 weight times or more with respect to p-xylene. If the amount of the acetic acid solvent used is less than 2 times by weight, the reaction slurry temperature may be too high, leading to troubles such as clogging. On the other hand, the amount of the acetic acid solvent used is preferably 6 times by weight or less, more preferably 4 times by weight or less. If it exceeds 6 times by weight, the amount of solvent in the system with respect to the product production amount becomes large, and there is a need to increase the size of the equipment, which is economically undesirable. As the acetic acid solvent, the recycled mother liquor H obtained in the later-described solid-liquid separation step (B) and the recovered acetic acid M collected from the solvent vapor obtained in the concentration step (D) can be reused. At this time, it is preferable to dehydrate the solvent vapor obtained in the (D) concentration step by distillation or the like in order to prevent the water generated by the oxidation reaction from increasing in the solvent.

  The acetic acid solvent in the present invention is preferably a mixture of acetic acid and water, and is usually 1 part by weight or more, and preferably 5 parts by weight or more with respect to 100 parts by weight of acetic acid. This is because if it is attempted to use acetic acid that is less than 1 part by weight of water and is close to pure, it is not preferable in terms of energy and economy because it takes too much time to recycle the solvent mixed with water by distillation or the like. On the other hand, it is usually 20 parts by weight or less and preferably 15 parts by weight or less with respect to 100 parts by weight of acetic acid. It is because there exists a possibility that reaction efficiency may fall when water exceeds 20 weight part.

  As the alkyl aromatic compound A in the present invention, an aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent can be used. Such alkyl aromatic compounds may be monocyclic or polycyclic. As said alkyl substituent, C1-C4 alkyl groups, such as a methyl group, an ethyl group, n-propyl group, and an isopropyl group, can be mention | raise | lifted, for example. Examples of partially oxidized alkyl groups include aldehyde groups, acyl groups, carboxyl groups, and hydroxyalkyl groups.

  Specific examples of the aromatic compound having an alkyl substituent, that is, an alkyl-substituted aromatic hydrocarbon include, for example, m-diisopropylbenzene, p-diisopropylbenzene, m-cymene, p-cymene, m-xylene, and p-xylene. Di- or polyalkylbenzenes having 2 to 4 alkyl groups having 1 to 4 carbon atoms such as trimethylbenzenes and tetramethylbenzenes; 1 to 4 carbon atoms such as dimethylnaphthalenes, diethylnaphthalenes and diisopropylnaphthalenes Examples thereof include di- or polyalkylnaphthalenes having 2 to 4 alkyl groups; polyalkylbiphenyls having 2 to 4 alkyl groups having 1 to 4 carbon atoms such as dimethylbiphenyls.

  In addition, in the aromatic compound having a partially oxidized alkyl substituent, the alkyl group in the aromatic compound having the alkyl substituent is partially oxidized to form the aldehyde group, acyl group, carboxyl group or hydroxyalkyl group. It is an oxidized compound. Specific examples include 3-methylbenzaldehyde, 4-methylbenzaldehyde, m-toluic acid, p-toluic acid, 3-formylbenzoic acid, 4-formylbenzoic acid and 2-methyl-6-formylnaphthalene. Can be mentioned. These may be used alone or as a mixture of two or more.

  Among the above alkyl aromatic compounds A, m-xylene and p-xylene are preferable, and p-xylene is more preferable.

  In the (A) oxidation step, the alkyl aromatic compound A may be usually oxidized with the molecular oxygen-containing gas B. As the molecular oxygen-containing gas B, for example, a gas containing molecular oxygen such as air, oxygen diluted with an inert gas, or oxygen-enriched air is used. Of these, air is preferably used practically.

  Examples of the aromatic carboxylic acid obtained in the present invention include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 4,4′-biphenyldicarboxylic acid; aromatics such as trimellitic acid and trimesic acid Aromatic tricarboxylic acid; aromatic polycarboxylic acid such as pyromellitic acid.

  The method of the present invention is preferably applied to the production of an aromatic dicarboxylic acid or an aromatic carboxylic acid that is sparingly soluble in the reaction solvent, and particularly preferably to the production of terephthalic acid using p-xylene as a raw material. .

  The catalyst used for oxidizing the alkyl aromatic compound A is not particularly limited as long as it has an ability to oxidize the alkyl aromatic compound A and convert it into an aromatic carboxylic acid. A bromine compound may be used as a catalyst aid if necessary. Examples of the heavy metal in the heavy metal compound include cobalt, manganese, nickel, chromium, zirconium, copper, lead, hafnium and cerium. These can be used alone or in combination, but it is particularly preferable to use cobalt and manganese in combination. Examples of such heavy metal compounds include acetate, nitrate, acetylacetonate, naphthenate, stearate and bromide, with acetate and bromide being particularly preferred.

  Examples of the bromine compound include inorganic bromine compounds such as molecular bromine, hydrogen bromide, sodium bromide, potassium bromide, cobalt bromide and manganese bromide, methyl bromide, methylene bromide, bromoform, odor And organic bromine compounds such as benzyl bromide, bromomethyltoluene, dibromoethane, tribromoethane and tetrabromoethane. These bromine compounds are also used alone or as a mixture of two or more.

  Specific examples of the catalyst used for oxidizing the alkyl aromatic compound A include a combination of cobalt, manganese and bromine, and a combination of cobalt acetate, manganese acetate and hydrogen bromide is particularly preferable.

  In the present invention, the catalyst comprising a combination of the heavy metal compound and the bromine compound is usually 0.05 mol or more, preferably 0.1 mol or more, per 1 mol of the heavy metal atom. On the other hand, it is usually 10 mol or less of bromine atom, preferably 5 mol or less. Moreover, such a catalyst is 10 ppm or more normally as a heavy metal density | concentration in a reaction solvent, Preferably it is 100 ppm or more. On the other hand, it is usually 10,000 ppm or less and preferably 3000 ppm or less.

  The reaction temperature for the oxidation of the alkyl aromatic compound A in the reactor 11 in the figure is usually 140 ° C. or higher, preferably 150 ° C. or higher, more preferably 170 ° C. or higher. A reaction temperature of less than 140 ° C. is not preferable because the reaction rate tends to decrease. On the other hand, it is usually 230 ° C. or lower, preferably 210 ° C. or lower, and more preferably 200 ° C. or lower. If the reaction temperature exceeds 230 ° C. and is too high, the amount of acetic acid solvent lost due to combustion tends to increase, such being undesirable.

  Moreover, the reaction pressure for the oxidation of the alkyl aromatic compound A in the reactor 11 in the figure needs to be at least the pressure at which the mixture can maintain the liquid phase at the above reaction temperature, and is a pressure exceeding the normal pressure. There is a need. Specifically, the absolute pressure is preferably 0.2 MPa or more, and more preferably 1 MPa or more. On the other hand, the absolute pressure is preferably 5 MPa or less, and more preferably 2 MPa or less. Specifically, the pressure is a pressure at which the composition of the reaction mixture and the boiling state at the set reaction temperature are maintained.

  The above oxidation reaction is usually carried out continuously, and the reaction time (average residence time) is preferably 30 minutes or more, particularly preferably 40 minutes or more. This is because if it is less than 30 minutes, the reaction becomes insufficient and the desired product quality may not be obtained. On the other hand, it is preferably 300 minutes or less, and more preferably 150 minutes or less. If it exceeds 300 minutes, the combustion of acetic acid increases, which is not economical. Moreover, it is not economical also in the point which the capacity | capacitance of the reactor 11 becomes large.

  The water concentration of the acetic acid solvent as the reaction solvent can be adjusted by, for example, purging a part of the condensate O obtained by condensing the reaction gas N generated in the reactor 11 out of the system.

  The reactor 11 is preferably a tank equipped with a stirrer, but does not necessarily need to be equipped with a stirrer and may be of a bubble column type. A supply port for the molecular oxygen-containing gas B is provided in the lower part of the reactor 11, and a condenser 11 a may be provided in the upper part of the reactor 11 as necessary. The molecular oxygen-containing gas B supplied from the lower part is used for the oxidation reaction of the alkyl aromatic compound A, and then extracted from the reactor 11 as a reaction gas N accompanied by a large amount of acetic acid vapor. After the condensate O mainly composed of acetic acid is condensed and separated in the vessel 11a, it is discharged as exhaust gas P. The condenser 11a may be a single stage or a plurality of stages. The supply amount of the molecular oxygen-containing gas B is in accordance with the oxygen concentration in the exhaust gas P or in the exhaust gas P1 of the final-stage condenser when the condenser 11a has a plurality of stages, and preferably 1 to 10 volumes. %, More preferably 2 to 8% by volume. Usually, the condensate O contains water, and a part of the condensate O is purged outside the system to adjust the water in the system, and the rest is refluxed to the reactor 11. Further, the exhaust gas P may be branched into two flows, one being discharged out of the system and the other being continuously circulated and supplied to the reactor 11.

  In the present invention, (A) in the oxidation step, after the oxidation reaction in the reactor 11, as shown in FIG. 2, additional treatment is performed as necessary using the additional oxidation reactor 11 ′. Also good. This additional treatment refers to a reaction mixture obtained by the oxidation reaction (hereinafter referred to as “first reaction zone”) in the first stage at a temperature lower than that of the first reaction zone and an alkyl aromatic compound. If A is p-xylene, in the second reaction zone maintained at a temperature of 5 to 20 ° C. lower than the first reaction zone, an additional oxidation treatment (hereinafter referred to as “low temperature additional oxidation”) is carried out without supplying the alkyl aromatic compound A. "). The pressure during this low temperature additional oxidation needs to be at least the pressure at which the internal mixture can maintain the liquid phase at least at the reaction temperature, and is desirably 0.2 MPa or more in absolute pressure. On the other hand, the absolute pressure is desirably 5 MPa or less. The low temperature additional oxidation reaction is preferably carried out continuously, and the reaction time is preferably 5 minutes or longer. On the other hand, it is good for it to be 120 minutes or less. The low temperature additional oxidation may be performed twice or more. Further, if necessary, in the third reaction zone, additional oxidation treatment (hereinafter referred to as “high temperature additional oxidation”) may be performed at a higher temperature than the first reaction zone or the second reaction zone. If it is less than 5 minutes, the reaction becomes insufficient and the desired product quality cannot be obtained. On the other hand, if it exceeds 120 minutes, the apparatus becomes large and not economical.

  As the molecular oxygen-containing gas B ′ supplied for performing the low temperature additional oxidation or the high temperature additional oxidation, as in the first reaction zone, air, oxygen diluted with an inert gas, oxygen-enriched air, etc. In practice, air is preferably used. In addition, the supply amount of the reaction gas N ′ discharged from the additional oxidation reactor 11 ′ that has performed this reaction, in the case of a single condenser 11a ′, in the condensed exhaust gas P ′ that has been condensed, When there are a plurality of stages of condensers 11a ', the oxygen concentration in the exhaust gas P1' after the final stage of condensation is preferably 1 to 10% by volume, more preferably 2 to 8% by volume. It is good that it is 1 / 10,000 or more of the quantity supplied to the oxidation reaction performed in one reaction zone, and it is more preferred that it is 1/100 or more. On the other hand, it is preferably 1/5 or less, and more preferably 1/10 or less. In addition, if it is a reactor of the same type as the said 1st reaction zone, it can be used as the said 3rd reaction zone which performs the said 2nd reaction zone which performs this low temperature additional oxidation, or the said high temperature additional oxidation.

  The aromatic carboxylic acid slurry C, which is the obtained reaction mixture, whether or not subjected to the above-mentioned additional oxidation treatment, recovers aromatic carboxylic acid crystals in the following (B) solid-liquid separation step. Prior to this, the crystallization treatment may be performed under a pressure exceeding the normal pressure as necessary. The aromatic carboxylic acid slurry C is cooled by releasing pressure under a lower pressure than in the above oxidation step, and the aromatic carboxylic acid dissolved in the solvent is further precipitated, resulting in aromatic carboxylic acid crystals. The amount of recovered is increased. However, when cooled by crystallization, the separation operation temperature obtained in the solid-liquid separation step (B) is lowered. As a result, the temperature of the separation mother liquor and the separation cake is also lowered, so that the effect of the technology of the present invention is reduced. In addition, in order to perform solid-liquid separation described below under a pressure exceeding normal pressure, the final aromatic carboxylic acid slurry C is maintained at a high temperature, specifically 110 ° C. to oxidation, while maintaining the pressure exceeding normal pressure. It is necessary to keep the reaction temperature high.

  In the (B) solid-liquid separation step, the aromatic carboxylic acid slurry C is solid-liquid separated into the aromatic carboxylic acid cake E and the mother liquor F under a pressure exceeding normal pressure by the solid-liquid separator 12. To do. Among those separated by the solid-liquid separator 12, the mother liquor F is sent to the mother liquor recycling step (C) while maintaining a pressure exceeding the normal pressure. In addition, the pressure exceeding the normal pressure in this invention means a pressure larger than the vapor pressure of the mother liquor at the temperature of the mother liquor contained in the aromatic carboxylic acid slurry C. By maintaining the pressure in this manner, the mother liquor F is prevented from being evaporated and cooled, and the temperature level of the aromatic carboxylic acid slurry C is substantially maintained.

  In the present invention, (B) the pressure at the time of solid-liquid separation of the slurry containing the aromatic carboxylic acid crystals produced in the solid-liquid separation step into the aromatic carboxylic acid cake E and the mother liquor F is a pressure higher than normal pressure. Specifically, the absolute pressure is preferably 0.2 MPa or more, and more preferably 0.3 MPa or more. When the pressure is less than 0.2 MPa, there are few active ingredients that dissolve in the separated mother liquor, so the effect of adopting the present invention becomes small. On the other hand, the upper limit is the pressure of the slurry obtained from the (A) oxidation step, and the absolute pressure is preferably 1.5 MPa or less.

  It is desirable that the separated aromatic carboxylic acid cake E is washed with impurities and by-products with the washing liquid Q in the washing device 13 before being dried with the drying device 15. Here, acetic acid, water, or the like is used as the cleaning liquid Q.

  Further, when the solid-liquid separation device 12 and the washing device 13 perform the solid-liquid separation step and the washing device 13 as shown in FIG. The process can be simplified and is more desirable. Examples of the solid-liquid separation / washing device 14 that can perform the two steps in this way include, for example, a screen bowl type centrifugal separator, a rotary vacuum filter, a horizontal belt filter, and the like. A screen bowl type centrifuge having excellent heat resistance even in a high temperature range close to the above temperature is preferred.

  The obtained washing cake R is dried in the drying device 15 to remove the adhering liquid remaining on these cakes, thereby obtaining aromatic carboxylic acid crystals G. Here, the drying device 15 may be composed of a plurality of devices. Among them, as an apparatus for removing at least a part of the adhering liquid, by transferring the cake and the adhering liquid adhering to the cake to a lower pressure state, the adhering liquid adhering to the cake is contained in the inside. It is desirable to use a device that evaporates under pressure by energy. Here, the pressure release evaporation means that the liquid in a high pressure state is suddenly shifted to a low pressure state where the temperature before the transition is equal to or higher than the boiling point at the pressure after the transition, and a part of the boiling point at the pressure after the transition. It is cooled to the following and / or partially evaporates due to their internal energy. Although it is more desirable if as much of the adhering liquid as possible can be evaporated by the above-mentioned pressure-release evaporation, when drying is insufficient only by pressure-release, further heating is necessary.

  In addition, since the said acetic acid solvent, the said aromatic carboxylic acid, etc. are contained in the washing | cleaning drainage liquid S after wash | cleaning said aromatic carboxylic acid cake E, said reaction with recycling mother liquor H or independently. If returned to the vessel 11, the yield of the entire manufacturing process is improved, which is desirable.

  In the recycling step (C), the mother liquor F is branched into the recycle mother liquor H and the purge mother liquor I while maintaining the pressure exceeding the normal pressure. “While maintaining a pressure exceeding normal pressure” is a pressure level at which the operation pressure of the (B) solid-liquid separation step is substantially maintained. The ratio of branching to the recycle mother liquor H and the purge mother liquor I can be arbitrarily adjusted according to the situation of the entire manufacturing process. ) Is 40% or more, preferably 60% or more. On the other hand, it is usually 95% or less, preferably 90% or less. The recycled mother liquor H and the purge mother liquor I are desirably maintained at a pressure exceeding the above normal pressure, and more desirably substantially maintained at the operation pressure in the (B) solid-liquid separation step. .

  By maintaining the operating pressure in the above-mentioned (B) solid-liquid separation step, the recycled mother liquor H and the cleaning waste liquid S are substantially cooled without releasing the recycled mother liquor H by depressurization evaporation. While maintaining the operation temperature of the solid-liquid separation step, the reactor 11 can be returned to the oxidation step (A) described above, and energy for pressurizing and heating again can be saved to satisfy the predetermined oxidation reaction condition. The generated energy (oxidation reaction heat) can be effectively recovered and utilized from the distillate vapor.

  Since the (B) solid-liquid separation step is processed under high-temperature and high-pressure operating conditions, the mother liquor F contains the aromatic carboxylic acid and other active ingredients as compared with the case of solid-liquid separation under normal temperature and normal pressure conditions. Many are dissolved. Therefore, the aromatic carboxylic acid is precipitated and collected in the (D) concentration step with respect to the purge mother liquid I branched from the mother liquid F. When the operation of concentrating the purge mother liquor I at a time until a residue is obtained, the aromatic carboxylic acid and other active ingredients that have been dissolved are almost mixed into the residue and cannot be recovered. Productivity will be reduced. For this reason, the concentration step (D) comprises a two-stage concentration, and the aromatic carboxylic acid is precipitated in the first concentration process, the precipitated aromatic carboxylic acid is recovered, and the aromatic carboxylic acid is recovered. A method of performing a second stage concentration treatment on the subsequent mother liquor to evaporate and recover the solvent component is preferred.

  In the concentration step (D), first, the purge mother liquor I is pressure-evaporated to perform a first-stage concentration process to evaporate a part of the solvent component, and then the first-stage concentration. The solid content precipitated by the treatment is recovered. Furthermore, the mother liquor from which the aromatic carboxylic acid has been separated by this recovery is subjected to a second stage concentration treatment to evaporate the remaining solvent components and recover the solvent. Here, until the purge mother liquor I and the recycled mother liquor H are branched from the mother liquor F, the temperature of the separated mother liquor is maintained at the operating temperature of the (B) solid liquor separation process by maintaining the operating pressure of the (B) solid liquor separation process. It is desirable to do.

  First, in the first-stage concentration step, the remaining purge mother liquor I obtained by removing the recycled mother liquor H from the mother liquor F is released at a pressure equal to or lower than the vapor pressure of the mother liquor at the liquid temperature of the purge mother liquor I. Introducing into the evaporation device 16 (hereinafter, this operation is referred to as “releasing pressure”), the first stage concentration treatment for releasing pressure evaporation and the accompanying cooling treatment are carried out, and a part of the solvent component is removed from the solvent vapor T. And concentrated and cooled to obtain concentrate U. The temperature after this cooling treatment corresponds to the boiling point of the mother liquor at the pressure after releasing the pressure. The amount of the solvent evaporated by the concentration in the first stage is usually 10% by weight or more, preferably 20% by weight or more of the total solvent contained in the purge mother liquid I. If it is less than 10% by weight, the amount of active ingredient recovered is small and the effect is not sufficient. On the other hand, it is usually 50% by weight or less and preferably 40% by weight or less. If the amount to be evaporated exceeds 50% by weight, not only the active ingredient but also impurities that affect the quality of the product are precipitated, which is not preferable.

  At this time, the operation pressure of the pressure release evaporator 16 (the operation pressure for the first stage concentration) is a pressure equal to or lower than the vapor pressure of the mother liquor at the temperature of the purge mother liquor I for efficient concentration. Is desirable. Specifically, the absolute pressure is preferably 0.05 MPa or more. When the operating pressure is less than 0.05 MPa, not only the active ingredient but also impurities that affect the quality of the product are precipitated by concentration and cooling, which is not preferable. On the other hand, the pressure is preferably equal to or lower than the vapor pressure of the mother liquor at the temperature of the purge mother liquor I. If the pressure is too high, the amount of active ingredient recovered is small and the effect is not sufficient. Thus, by maintaining the pressurized state pressurized in the oxidation step (A) with the purge mother liquor I and using the pressurized state during the concentration, the purge mother liquor I can be used without heating or the like. The solvent in the inside can be evaporated, and efficient concentration can be performed.

  The solvent vapor T evaporated during the concentration is mainly composed of acetic acid as a solvent component. In order to use this acetic acid again as a solvent, as shown in FIG. 1, the above-mentioned (A) oxidation step is indirectly performed as recovered acetic acid M which is treated with a dehydrating device 19 such as distillation to remove the oxidation product water L. Alternatively, as shown in FIG. 2, the condensate M ′ obtained by cooling the solvent vapor T with the condenser 20 or the like and returning it to the liquid is directly returned to the (A) oxidation step. Also good. Furthermore, these may be used as the cleaning liquid Q.

  In the concentrated liquid U obtained by the above-mentioned concentration in the first stage, precipitates are generated by pressure-release evaporation. In order to collect the precipitate, in the solid content recovery step, the solid content W is separated from the separated mother liquor V by the solid content recovery device 17, and the solid content W including the precipitate by the above-described pressure-release evaporation is recovered. Examples of the solid content recovery device 17 include a filter, a centrifuge, a cyclone, and a thickener.

  This solid content W is an active ingredient such as the aromatic carboxylic acid or its intermediate, and the productivity can be improved by returning it to the reactor 11 in the oxidation step (A).

  Furthermore, it is preferable that the separated mother liquor V is introduced into the solvent evaporation apparatus 18 as a second concentration process, and is heated to further evaporate the remaining solvent components and concentrate. The operation here may be carried out using a method similar to the conventional one, and for example, the solvent component is evaporated with a heat medium such as steam. Usually, the separated mother liquor V is introduced into a solvent evaporation device 18 comprising a tank, and the solvent component is cooked from the outside using steam as a heat source under an operating pressure of 0.03 MPa (absolute pressure) to 0.15 MPa (absolute pressure). And concentrate the high-boiling components such as catalyst components, by-products and impurities 10 to 40 times. For example, as shown in FIG. 2, the concentrated solution Y may be continuously or indirectly extracted from the solvent evaporation device 18, and the solvent component may be evaporated by the heating device 21 to recover the residual solvent Z. Since the solvent vapor X evaporated from the solvent evaporation apparatus 18 is mainly composed of acetic acid, which is a solvent component, as in the case of the solvent vapor T described above, the (A) oxidation step is directly performed after cooling back to liquid. Alternatively, after the treatment with the dehydrating device 19 such as distillation to remove the oxidation product water L, the recovered acetic acid M may be indirectly returned to the (A) oxidation step. Similarly, these may be used as the cleaning liquid Q. The dehydration process may be performed by integrating the solvent vapor T and the solvent vapor X.

  Residue J that has not evaporated in the second stage concentration treatment contains the by-product of the aromatic carboxylic acid, the catalyst used in the reactor 11, and the like. It is desirable that the residue J is subjected to an appropriate treatment such as extraction to recover a catalyst component, and the recovered catalyst is regenerated and reused in a catalyst regeneration step.

  According to the present invention, in the aromatic carboxylic acid production process, by using the energy of the mother liquor for the concentration of the purge mother liquor as part of the concentration, the recovery rate of useful components contained in the purge mother liquor can be increased. Furthermore, by recycling the mother liquor at high temperature and high pressure to the oxidation process that oxidizes alkyl aromatic compounds to aromatic carboxylic acids, the energy required for the reaction conditions can be reduced, so the energy generated by the oxidation reaction can be used effectively. can do.

  EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely using FIG. 2, this invention is not limited to a following example at all.

(Example 1)
3.35 parts by weight of acetic acid solution (water content: 14% by weight) containing catalyst (cobalt acetate, manganese acetate in acetic acid and hydrogen bromide) per 1 part by weight of p-xylene, solid-liquid separation in the latter stage Separation mother liquor (recycle mother liquor H) recycled from the process 6.24 parts by weight and air (molecular oxygen-containing gas B) 3.57 Nm ³ are continuously supplied to the reactor 11 which is a stirring tank, and the operation temperature The oxidation reaction was carried out while adjusting the liquid level so that the residence time was 1 hour at 190 ° C. and an operating pressure of 1.23 MPa (absolute pressure). Further, the reaction gas N as the distilled steam was finally cooled to 40 ° C. by the multistage condenser 11a, and the oxygen concentration in the exhaust gas P was adjusted to 2.5% by volume. Further, the condensate O obtained from each condenser 11a was integrated and refluxed to the reactor 11, and a part of the condensate O was extracted so that the moisture concentration in the mother liquor of the aromatic carboxylic acid slurry C was 10% by weight. As a result, the breakdown of the aromatic carboxylic acid slurry C extracted from the reactor 11 is 2.05 parts by weight of crude terephthalic acid, 3.79 parts by weight of the mother liquor, and the concentration of cobalt / manganese / bromine in the reaction mother liquor is 300/300/1000. The weight ppm and the slurry concentration were 35% by weight.

The aromatic carboxylic acid slurry C withdrawn from the reactor 11: 5.84 parts by weight was stirred in a stirred tank together with 0.08 Nm ^{3 of} air (molecular oxygen-containing gas B ′) before being sent to the solid-liquid separator 12. It is continuously supplied to a supplementary oxidation reactor 11 ′ that performs a certain low temperature supplemental oxidation, and is adjusted at a low temperature while adjusting the liquid level so that the residence time is 15 minutes at an operational temperature of 181 ° C. and an operational pressure of 1.15 MPa (absolute pressure). An oxidation reaction was performed. In addition, the reaction gas N ′ which is the distilled steam in this low temperature additional oxidation reaction is finally cooled to 40 ° C. by the multistage condenser 11a ′, and the oxygen concentration in the exhaust gas P1 ′ discharged from the final stage condenser Was adjusted to be 6% by volume. Further, the condensate O ′ obtained from each condenser 11a ′ was integrated and refluxed to the additional oxidation reactor 11 ′.

  The aromatic carboxylic acid slurry C ′ extracted from the additional oxidation reactor 11 ′ was supplied to a screen bowl type centrifuge serving as the solid-liquid separation / washing device 14 for solid-liquid separation. Here, the operating pressure was 1.18 MPa (absolute pressure). The crude terephthalic acid cake, which is the aromatic carboxylic acid cake E centrifuged in the centrifugal separator corresponding to the solid-liquid separator 12, is in the screen portion (corresponding to the cleaning device 13) in the screen bowl type centrifugal separator. Crude terephthalic acid which is aromatic carboxylic acid crystal G is dried by evaporating the liquid adhering to the cake after being washed with 2.99 parts by weight of acetic acid which is cleaning liquid Q and then letting the liquid discharged from the discharge valve to atmospheric pressure at once. 1.56 parts by weight of crystals were obtained.

  On the other hand, the mother liquor F recovered by the solid-liquid separation branched 20% as the purge mother liquor I while maintaining the solid-liquid separation operation pressure. Further, the remaining 80% was recycled to the reactor 11 as a recycled mother liquor H together with the cleaning waste liquid S generated in the above washing as 6.24 parts by weight of recycled mother liquor (mother liquor recycling rate 80%).

  Purge mother liquor I: 0.91 part by weight is supplied to the first concentration tank corresponding to the pressure release evaporator 16 in a state having a pressure of 1.18 MPa (absolute pressure) and a temperature of 183 ° C., and is 0 using a steam ejector. By releasing the pressure to 0.05 MPa (absolute pressure), 0.35 part by weight of the solvent component in the mother liquor was evaporated. As a result, the first concentration tank was cooled to 90 ° C., and 0.01 part by weight of terephthalic acid dissolved in the purge mother liquor I was precipitated. As a result of recovering the solid content of the slurry extracted from the first concentration tank with a centrifuge, 94% of the terephthalic acid dissolved in the purge mother liquor I was recovered. The solvent vapor T distilled out in the first concentration tank was condensed in the condenser 20, and 0.35 parts by weight of the obtained condensate M ′ was sent to the reactor 11.

  The separated mother liquor V after the solid content W is recovered by the solid content recovery device 17: 0.56 parts by weight is supplied to the second concentration tank corresponding to the solvent evaporation device 18 and heated externally with steam to evaporate the solvent component. Then, the concentration treatment was carried out so that the concentration of impurities and catalysts as high-boiling components was concentrated 20 times. The solvent vapor X distilled out in the second concentration tank was supplied to a dehydrating distillation column which is a dehydrating device 19, and the acetic acid solvent was recovered as recovered acetic acid M. On the other hand, the concentrated liquid Y was indirectly extracted, and further heated externally using a heat transfer oil in the heating device 21, and the residual solvent Z of the concentrated liquid Y was cooked and collected in the second concentrated tank to obtain a residue J. .

Manufacturing process diagram of aromatic carboxylic acid crystal according to the present invention Production process diagram of terephthalic acid crystals in Examples Production process diagram of conventional terephthalic acid crystals

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reactor 2 Crystallization tank 3 Solid-liquid separation device 4 Drying device 5 Solvent evaporation device 6 Dehydration device 11 Reactor 11 'Additional oxidation reactor 11a, 11a' Condenser 12 Solid-liquid separation device 13 Washing device 14 Solid-liquid separation and Cleaning device 15 Drying device 16 Pressure release evaporator 17 Solid content recovery device 18 Solvent evaporation device 19 Dehydration device 20 Condenser 21 Heating device a p-xylene b Air c Reaction slurry d Crystallization slurry e Terephthalic acid cake f Separation mother liquor g Terephthalate Acid crystal h Recycle mother liquor i Purge mother liquor j Residual k Solvent vapor l Oxidized water m Recovered acetic acid A Alkyl aromatic compound B, B 'Molecular oxygen-containing gas C Aromatic carboxylic acid slurry E Aromatic carboxylic acid cake F Mother liquor G Aroma Group carboxylic acid crystal H recycle mother liquor I purge mother liquor J residue L oxidation product water M recovered acetic acid M 'condensate N, N' reaction gas O condensate P, 'Exhaust gas P1, P1' final stage exhaust gas Q cleaning liquid R washed cake S wash effluent T solvent vapor U concentrate V separated mother liquor W solid X solvent vapor Y concentrate Z residual solvent after condensation of

Claims (10)

(A) an oxidation step in which an alkylaromatic compound is oxidized in an acetic acid solvent at 140 to 230 ° C. in the presence of a catalyst under a pressure exceeding normal pressure to produce an aromatic carboxylic acid;
(B) a solid-liquid separation step in which the slurry containing the produced aromatic carboxylic acid crystals is separated into an aromatic carboxylic acid and a mother liquor under a pressure exceeding normal pressure;
(C) The mother liquor recycling step in which the mother liquor is branched while maintaining a pressure exceeding normal pressure, and one of them is returned to the (A) oxidation step,
(D) A concentration step of concentrating the other mother liquor branched in the (C) mother liquor recycling step,
A process for producing an aromatic carboxylic acid having
In the concentration step (D), the other mother liquor is evaporated under reduced pressure to a pressure equal to or lower than the vapor pressure at the initial temperature of the other mother liquor to precipitate an aromatic carboxylic acid, and then the precipitated aroma A process for producing an aromatic carboxylic acid, comprising recovering an aromatic carboxylic acid.   The (D) concentration step comprises two-stage concentration, and the other mother liquor is sent to the first-stage concentration process at a pressure higher than normal pressure, and the pressure is equal to or lower than the vapor pressure at the initial temperature of the other mother liquor. The first stage of concentration treatment is performed by evaporation under pressure to precipitate the aromatic carboxylic acid, and then the precipitated aromatic carboxylic acid is recovered, and the second stage is added to the mother liquor after the recovery of the aromatic carboxylic acid. The method for producing an aromatic carboxylic acid according to claim 1, wherein the solvent component is evaporated and recovered by performing a concentration treatment.   The method for producing an aromatic carboxylic acid according to claim 1 or 2, wherein the aromatic carboxylic acid recovered in the (D) concentration step is returned to the (A) oxidation step. (A) an oxidation step in which an alkyl aromatic compound is oxidized in an acetic acid solvent in the presence of a catalyst under a pressure exceeding normal pressure to produce an aromatic carboxylic acid;
(B) a solid-liquid separation step in which the slurry containing the produced aromatic carboxylic acid crystals is separated into an aromatic carboxylic acid and a mother liquor under a pressure exceeding normal pressure;
(C) A mother liquor recycling step in which the mother liquor is branched while maintaining a pressure higher than normal pressure, and one of them is returned to the (A) oxidation step,
(D) The concentration step of concentrating the other mother liquor branched in the (C) mother liquor recycling step,
A process for producing an aromatic carboxylic acid having
The (D) concentration step consists of two-stage concentration, and the other mother liquor is sent to the first-stage concentration process at a pressure higher than normal pressure, and the pressure is equal to or lower than the vapor pressure at the initial temperature of the other mother liquor. The first stage of concentration treatment is performed by evaporation under reduced pressure to precipitate the aromatic carboxylic acid, and then the precipitated aromatic carboxylic acid is recovered and returned to the oxidation step (A) to recover the aromatic carboxylic acid. A method for producing an aromatic carboxylic acid, comprising subjecting the mother liquor to a second concentration process to evaporate and recover the solvent component.   5. The method according to claim 1, wherein in the (C) mother liquor recycling step, the one of the branched mother liquors is returned to the (A) oxidation step while maintaining a pressure higher than normal pressure. A process for producing an aromatic carboxylic acid according to claim 1.   The solvent component evaporated in the first-stage concentration treatment and / or the second-stage concentration treatment is directly or indirectly returned to the (A) oxidation step. 6. A process for producing an aromatic carboxylic acid according to any one of 5 above.   The (B) solid-liquid separation step includes a step of washing the aromatic carboxylic acid obtained by solid-liquid separation with a washing liquid, and the above-mentioned solid-liquid separation step and the above washing step include The method for producing an aromatic carboxylic acid according to any one of claims 1 to 6, wherein the method is carried out in an integrated solid-liquid separator.   The method for producing an aromatic carboxylic acid according to claim 7, wherein the solid-liquid separator is a screen bowl type centrifuge.   The method for producing an aromatic carboxylic acid according to claim 7 or 8, wherein the cleaning liquid is acetic acid or water.   The method for producing an aromatic carboxylic acid according to any one of claims 1 to 9, wherein the alkyl aromatic compound is p-xylene, and the aromatic carboxylic acid is terephthalic acid.

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