JP2002326970A - Method of production for aromatic carboxylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of production for aromatic carboxylic acid capable of effectively separating and collecting an aliphatic carboxylic acid from unnecessary by-products for the reaction such as water, a alcohol or the like even lowering the tower height of a distillation tower and capable of using collected aliphatic acid in the reaction by an effective concentration of the acid and capable of producing the aromatic carboxylic acid using a reactor composed of an inexpensive material. SOLUTION: This method of production for the aromatic carboxylic acid carries out a liquid phase oxidation of an alkylaromatic compound by a gas including oxygen in the presence of an oxidizing catalyst in a reaction solvent including the aliphatic carboxylic acid in an oxidizing reactor 1, produces the aromatic carboxylic acid under high pressure and high temperature, introduces the exhaust gas of the oxidation to a distillation tower 2 and distills, refluxes the fraction including the reaction solvent to the oxidizing reactor 1, cools the exhaust gas from the distillation tower 2 by a condenser 3 and produces the condensed water, and subjects the condensed water to a membrane separator 8 permeating methanol and water to the permeate side and concentrating the aliphatic carboxylic acid to the concentrate side and returns the concentrate to the middle of the distillation tower 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing an aromatic carboxylic acid by subjecting an alkyl aromatic compound containing an alkyl substituent or a partially oxidized alkyl substituent to liquid phase oxidation with an oxygen-containing gas.

[0002]

2. Description of the Related Art Aromatic carboxylic acids are important as basic chemicals, and aromatic dicarboxylic acids are particularly useful as raw materials for fibers, resins and the like. For example, the demand for terephthalic acid as a polyester raw material has been increasing in recent years. As a method for producing an aromatic carboxylic acid, generally, in an oxidation reactor, a heavy metal compound and a bromine compound are used as catalysts, and an alkyl-substituted aromatic compound is molecularly oxygen-containing in a reaction solvent containing a lower aliphatic carboxylic acid such as acetic acid. A method of contacting with a gas to perform liquid phase oxidation is employed. In such a production method, an oxidation reaction is carried out by introducing an alkyl-substituted aromatic compound such as para-xylene, a mixture of acetic acid and a catalyst as a raw material, and an oxygen-containing gas such as air into a oxidation reactor, and performing terephthalic acid. And other aromatic carboxylic acids.

[0003] Since the oxidizing exhaust gas discharged from the oxidizing reactor is accompanied by a solvent, a catalyst, and the like, the condensate obtained by condensing the oxidizing exhaust gas in the oxidizing exhaust gas condenser is collected and reused in a distillation column in order to recover and reuse the oxidizing exhaust gas. There is a method in which distillation is carried out after introduction, and a fraction containing a reaction solvent is refluxed to an oxidation reactor. Further, there is a method in which a distillation column is provided at the upper part of the reaction tank, and the solvent is recovered by using the heat of the oxidation exhaust gas to recover the solvent and refluxed to the oxidation reaction tank (Japanese Patent Publication No. 54-14098, JP-A-6-14098). 279
353). In this method, the exhaust gas discharged from the distillation column is cooled by cooling water in a condenser to condense the steam in the exhaust gas, and the condensed water is returned to the distillation column and used for distillation.

In the method of distilling an oxidizing exhaust gas or a condensate thereof, since the boiling points of acetic acid and water or alcohol are close to each other, a solvent such as acetic acid is completely separated and recovered from water or alcohol in a distillation column. Requires a higher column height of the distillation column, and lowering the column height causes some of the solvent to migrate to the condensed water side. Since water is generated in the oxidation reaction, a part of the condensed water must be discharged to the outside of the system, and the solvent and other components flow out into the wastewater, so that the treatment is also difficult.

[0005]

The object of the present invention is to efficiently separate aliphatic carboxylic acids from by-products such as water and alcohol unnecessary for the reaction even if the height of the distillation column is reduced. A method for producing an aromatic carboxylic acid which can be recovered, and which can be used for the reaction by efficiently concentrating the recovered aliphatic carboxylic acid and which can produce an aromatic carboxylic acid using an inexpensive material apparatus It is to propose.

[0006]

The present invention relates to the following method for producing an aromatic carboxylic acid. (1) Oxidation in which an alkyl aromatic compound is liquid-phase oxidized with an oxygen-containing gas in a reaction solvent containing an aliphatic carboxylic acid in an oxidation reactor in the presence of an oxidation catalyst to produce an aromatic carboxylic acid under high temperature and high pressure. A distillation step in which an oxidizing exhaust gas from an oxidation reactor or a condensate obtained by condensing an oxidizing exhaust gas with an oxidizing exhaust gas condenser is introduced into a distillation column to perform distillation, and a fraction containing a reaction solvent is refluxed to the oxidation reactor. A condensing step in which the gas at the top of the tower is cooled by a condenser to produce condensed water, the condensed water is separated by membrane using a membrane separator, water and alcohol are passed through the permeate, and the aliphatic carboxylic acid is concentrated. A method for producing an aromatic carboxylic acid, comprising: a membrane separation step of concentrating and collecting a concentrated solution on a side thereof; (2) The method according to the above (1), wherein the theoretical plate height in the distillation step is 10 to 70 theoretical plates. (3) The method according to (2), wherein the theoretical plate height in the distillation step is 20 to 40 theoretical plates. (4) The concentrated liquid from the membrane separation step is counted from the top of the column for 5 minutes.
The method according to any one of the above (1) to (3), wherein the water is returned to a stage below the theoretical plate height and above five theoretical plate heights counted from the column bottom. (5) The concentrated liquid from the membrane separation step is counted from the top of the column for 1 hour.
The method according to the above (4), wherein the composition is returned to 0 to 25 theoretical plates. (6) The method according to any one of (1) to (5) above, wherein the material of the distillation column is titanium and the material of the membrane separation device is stainless steel. (7) The method according to the above (6), wherein the material of the condenser of the distillation column is stainless steel. (8) The method according to any one of (1) to (7) above, wherein the membrane separation step performs membrane separation using a reverse osmosis membrane. (9) The method according to any one of (1) to (8) above, wherein the volume concentration ratio in the membrane separation step is 2 to 20 times. (10) The volume concentration ratio in the membrane separation step is 5 to 15
The method according to the above (9), which is twice as large. (11) An apparatus for producing an aromatic carboxylic acid under high temperature and pressure by subjecting an alkyl aromatic compound to liquid phase oxidation with an oxygen-containing gas in a reaction solvent containing an aliphatic carboxylic acid in an oxidation reactor in the presence of an oxidation catalyst. The method according to any one of the above (1) to (10), wherein there are two or more series, wherein the distillation step is carried out in a distillation column attached to each oxidizing apparatus, and the membrane separation step is performed in a concentrated manner for all series. (12) An apparatus for producing an aromatic carboxylic acid under high temperature and high pressure by subjecting an alkyl aromatic compound to liquid phase oxidation with an oxygen-containing gas in a reaction solvent containing an aliphatic carboxylic acid in an oxidation reactor in the presence of an oxidation catalyst. There are two or more series, and the distillation step is performed in the distillation column attached to each oxidizer, and the membrane separation step is intensively processed in the entire series, and the concentrated liquid is distilled by the apparatus for producing one aromatic carboxylic acid. The method according to (11), wherein the liquid is returned to the tower.

In the present invention, the reaction is carried out while removing water and alcohol generated by the oxidation reaction by membrane separation.
In this case, it is preferable to combine a distillation step and a membrane separation step in order to efficiently separate an aliphatic carboxylic acid such as acetic acid used as a solvent from unnecessary components such as generated water and alcohol. When the above separation is performed only by distillation,
As described above, it is necessary to increase the tower height, and if separation is performed only by membrane separation, the separation efficiency is poor, and a multi-stage membrane separation device is required. If most of the acid is separated, and the remainder of the low-concentration liquid is separated by membrane separation, the separation can be performed efficiently with a small-scale apparatus.

As the oxidizing raw material for producing an aromatic carboxylic acid in the method of the present invention, an aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent (hereinafter sometimes simply referred to as an oxidizing raw material) is used. Can be used. Such an aromatic compound may be monocyclic or polycyclic. Examples of the alkyl substituent include an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an n-propyl group, and an isopropyl group. Examples of the partially oxidized alkyl group include an aldehyde group, an acyl group, a carboxyl group, and a hydroxyalkyl group.

Specific examples of aromatic compounds having an alkyl substituent, ie, alkyl-substituted aromatic hydrocarbons, include, for example, m-diisopropylbenzene, p-diisopropylbenzene, m-cymene, p-cymene, m-xylene, An alkyl group having 1 to 4 carbon atoms such as p-xylene, trimethylbenzenes and tetramethylbenzenes is
Di or polyalkyl benzenes having from 2 to 4 di or polyalkyl naphthalenes having from 2 to 4 alkyl groups having 1 to 4 carbon atoms, such as dimethyl naphthalenes, diethyl naphthalenes and diisopropyl naphthalenes;
And polyalkylbiphenyls having 2 to 4 alkyl groups having 1 to 4 carbon atoms, such as dimethylbiphenyls.

In the aromatic compound having a partially oxidized alkyl substituent, a part of the alkyl group in the aromatic compound having a plurality of alkyl groups is oxidized to form the aldehyde group, acyl group, carboxyl group or hydroxyalkyl group. A compound that has been oxidized to a group or the like. Specific examples include 3-methylbenzaldehyde and 4-methylbenzaldehyde.
Examples include methylbenzaldehyde, m-toluic acid, p-toluic acid, 3-formylbenzoic acid, 4-formylbenzoic acid, and 2-methyl-6-formylnaphthalenes. These are used alone or as a mixture of two or more.

In the method of the present invention, a heavy metal compound and a bromine compound are used as catalysts. Examples of such compounds are as follows. That is,
As the heavy metal in the heavy metal compound, for example, cobalt, manganese, nickel, chromium, zirconium, copper,
Lead, hafnium, cerium and the like can be mentioned. These can be used alone or in combination, but it is particularly preferable to use a combination of cobalt and manganese. Such heavy metal compounds include, for example, acetate, nitrate, acetylacetonate, naphthenate, stearate, bromide, etc., with acetate being particularly preferred.

As the bromine compound, for example, molecular bromine,
Inorganic bromine compounds such as hydrogen bromide, sodium bromide, potassium bromide, cobalt bromide and manganese bromide; methyl bromide, methylene bromide, bromoform, benzyl bromide, bromomethyltoluene, dibromoethane, tribromoethane and Organic bromine compounds such as tetrabromoethane can be mentioned. These bromine compounds are also used alone or as a mixture of two or more.

In the present invention, the catalyst comprising the combination of the heavy metal compound and the bromine compound is used in an amount of 0.05 to 10 mol, preferably 0.1 mol, of bromine atom per 1 mol of heavy metal atom.
Those having a range of 2 to 2 mol are desirable. Such a catalyst is usually used as a heavy metal concentration in a reaction solvent of 10 to 100.
00 wt-ppm, preferably 100-5000 wt-
Used in the ppm range.

In the method of the present invention, an aromatic compound as an oxidizing raw material is reacted with a molecular oxygen-containing gas in a reaction solvent containing a lower aliphatic carboxylic acid in the presence of the catalyst in an oxidation reactor as an oxidation step. By phase oxidation,
Obtain aromatic carboxylic acid as product.

The molecular oxygen-containing gas includes, for example, oxygen and air, but practically, air is preferably used. The molecular oxygen-containing gas is supplied in excess of the amount required to oxidize the aromatic compound serving as the oxidation raw material to the aromatic carboxylic acid. When air is used as the molecular oxygen-containing gas, aromatic compound 1 serving as an oxidation raw material
2 to 20 Nm ³ , preferably 2.5 to 15 kg / kg
It is desirable to supply Nm ^{3 to} the reaction system at a ratio of Nm ³ .

Specific examples of the lower aliphatic carboxylic acid used as the reaction solvent include acetic acid, propionic acid and butyric acid. The lower aliphatic carboxylic acid can be used alone as a reaction solvent, or can be mixed with water and used as a reaction solvent in the form of a mixture. Specific examples of the reaction solvent include, for example, acetic acid, propionic acid, butyric acid and mixtures thereof,
Alternatively, a mixture of these lower aliphatic carboxylic acids and water can be used. Among these, a mixture of acetic acid and water is preferable, and a mixture of 1 to 20 parts by weight of water, preferably 5 to 15 parts by weight of water is particularly desirable with respect to 100 parts by weight of acetic acid.

The temperature of the oxidation reaction is usually 100 to 250 ° C.
Preferably, the range of 150 to 220 ° C is desirable. Also,
The reaction pressure may be any pressure as long as the reaction system can be maintained in a liquid phase.

By reacting in this manner, an aromatic carboxylic acid corresponding to the aromatic compound to be used as an oxidation raw material is obtained. Specific examples of aromatic carboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 4,4′-biphenyldicarboxylic acid; and aromatic dicarboxylic acids such as trimellitic acid and trimesic acid. Aromatic tricarboxylic acids such as pyromellitic acid; and the like.

The method of the present invention is preferably applied to the production of an aromatic dicarboxylic acid or an aromatic carboxylic acid insoluble or hardly soluble in a reaction solvent, particularly preferably to the production of terephthalic acid.

The generated aromatic carboxylic acid such as terephthalic acid precipitates as a crystal and forms a slurry. This slurry is extracted from the oxidation reaction tank and the crystals are collected by solid-liquid separation to obtain crude terephthalic acid and the like. Things are obtained. Oxidation reaction intermediates and impurities are entrained in the crystals of the crude product thus obtained, and the crude product is dissolved, and crystals such as terephthalic acid are precipitated through purification steps such as oxidation treatment and reduction treatment. Then, a slurry containing crystals is obtained.
When crystals are recovered from such a slurry, a purified product such as purified terephthalic acid is obtained.

In the distillation step, the oxidizing exhaust gas is preferably introduced into a distillation column (high-pressure distillation column) connected to the upper part of the oxidation reactor, and distillation is performed by utilizing the heat generated by the oxidation reactor. The condensed liquid condensed in the condenser may be introduced into a distillation column (normal pressure distillation column) to perform distillation. In any case, the fraction containing the reaction solvent was refluxed from the bottom to the oxidation reactor,
An overhead gas containing water and a non-condensable gas is discharged from the overhead. The distillation column may be independent of the oxidation reactor as shown in JP-B-54-14098.
As shown in -279353, it may be installed at the top of the oxidation reactor. The distillation column may be a plate column,
A packed tower is preferable, and in this case, a means for collecting fine solids such as aromatic carboxylic acid crystals, for example, a solid collecting tray provided below the packed bed is preferable.

The distillation column used in the distillation step preferably has a theoretical plate height of 10 to 70 theoretical plates, preferably 20 to 40 theoretical plates. In addition, the distillation column is constructed so that a plurality of columns are continuously provided, the exhaust gas is sequentially distilled in the next column, and the distillate in the subsequent stage is sequentially refluxed to the previous stage. It is preferable that the liquid is drawn out of the system to prevent the concentration and temperature of the reaction liquid in the oxidation reaction tower from decreasing.

By distilling the oxidized exhaust gas or the condensate obtained by condensing the oxidized exhaust gas with the oxidized exhaust gas condenser in such a distillation column, the fraction containing the reaction solvent discharged along with the oxidized exhaust gas is converted to the oxidized reactor. Reflux. This fraction is refluxed to the oxidation reactor as a bottom liquid in a state where the unreacted alkyl aromatic compound, the generated aromatic carboxylic acid, the catalyst and the like in addition to the reaction solvent are concentrated. Among these, solids such as aromatic carboxylic acid crystals and catalysts and components having a high boiling point are trapped or distilled at the lower portion of the distillation column, and reaction solvents such as aliphatic carboxylic acids having a low boiling point are distilled relatively at the upper portion.

Such a distillate is directly refluxed to the oxidation reactor, but a distillate having a high aliphatic carboxylic acid concentration is extracted by providing a distillate at the lower part of the distillation column to remove the aliphatic carboxylic acid. Not only can it be used as an ester absorbing liquid, but also can be used as a washing liquid for crystals obtained by solid-liquid separation of a slurry extracted from an oxidation reactor. When the reaction is urgently stopped, it is possible to prevent a large amount of reflux water from entering the oxidation reactor and diluting the reaction solution by extracting the reaction solution from the system.

In the condensing step, the overhead gas discharged from the distillation tower is cooled by cooling water in a condenser to condense the water vapor in the overhead gas to generate condensed water. The condenser may be connected to the distillation column, may be separately provided, or may be a single condenser or a plurality of condensers. The condensation temperature may be a temperature at which water vapor condenses, and the aliphatic carboxylic acid ester may or may not condense. All of the condensed water may be sent to the membrane separation step, or a part may be refluxed to the distillation column and a part may be sent to the membrane separation step.

In the membrane separation step, part or all of the condensed water is subjected to membrane separation in the membrane separation step to allow water and by-products such as alcohol to pass through the permeate, and to concentrate the aliphatic carboxylic acid into the concentrate. This is the step of separating. As a separation membrane for performing such separation, a reverse osmosis membrane can be used. As a reverse osmosis membrane, polyamide-based, aromatic polyamide-based, polyacrylonitrile-based, polypropylene-based, polyvinylidene fluoride-based, polyfluorinated ethylene-based, polyvinyl alcohol-based,
Polyester-based, polyimide-based, polysulfone-based, polyethersulfone-based, cellulose acetate-based, cellulose ester-based, triacetylcellulose-based, uric acid polyether-based, polypiperazamide-based, polyfuran-based, and polyethyleneimine-based. Crosslinked aromatic polyamide reverse osmosis membranes are preferred.

The shape of the separation membrane may be any shape such as a flat membrane, a tubular membrane, a spiral, or a hollow fiber. Such a separation membrane separates by molecular diameter, ionicity, etc., and allows water and alcohol and other by-products to permeate through the permeate, and allows aliphatic carboxylic acid to be concentrated and separated into the concentrate. Can be used. About 20% of the aliphatic carboxylic acid ester permeates, and about 80% remains on the concentrate side. The membrane separation step may be performed in a single stage, but is preferably performed in a plurality of stages.

By membrane-condensing the condensed water, unnecessary water produced by the reaction and alcohol and other by-products such as methanol permeate to the permeate side to be separated. Aliphatic carboxylic acids such as acetic acid used as a solvent remain on the concentrate side and are concentrated. Since acetic acid and water have close boiling points, it is necessary to increase the tower height in order to separate them by distillation, but they are easily separated by membrane separation due to differences in molecular diameter and ionicity. If the separation is not complete, membrane separation can be performed over multiple stages. The volume concentration ratio in the membrane separation step is 2-2.
It can be 0 times, preferably 5 to 15 times.

The permeate can be separated from water and alcohol and other by-products by a separation means such as distillation and discharged out of the system, or can be used as washing water for the aromatic carboxylic acid produced. The concentrate is refluxed to the oxidation step, and at this time, all or part of the liquid is returned to the middle stage of the distillation column in the return step and used for distillation.

In the return step, the concentrated liquid from the membrane separation step is returned to the middle stage of the distillation column. The middle stage of the distillation column means an intermediate portion other than the top and bottom stages of the distillation column, but a stage below the height of 5 theoretical plates counted from the top of the column and above 5 theoretical plates counted from the bottom of the column. It is particularly preferred to return to 10 to 25 theoretical stages counted from the top of the column.

The return position of the concentrated liquid in such a return step is preferably a position where the concentration of the aliphatic carboxylic acid in the distillation column substantially coincides with the concentration of the aliphatic carboxylic acid in the concentrated liquid. That is, when the aliphatic carboxylic acid is distilled off in the distillation column, it flows down in a state of being dissolved in the liquid refluxed from the condenser. Therefore, the aliphatic carboxylic acid concentration is low at the top of the column and high at the bottom of the column. Therefore, if the concentrated liquid is returned to the position where the concentration of the aliphatic carboxylic acid is substantially the same, the distillation can be performed efficiently.

On the other hand, when the concentrated liquid is returned to the top of the column, a part of the aliphatic carboxylic acid in the concentrated liquid is carried into the condenser along with the exhaust gas and corrodes the condenser.
It dissolves in the condensed liquid and circulates to the membrane separation step, thereby reducing the membrane separation effect. When returned to the bottom of the column, a low-concentration, low-temperature concentrated liquid is introduced into the lower portion of the distillation column, thereby lowering the distillation efficiency and lowering the efficiency of the oxidation reaction.

In the present invention, by returning the concentrated solution to the middle stage of the distillation column, the distillation efficiency can be increased and the aliphatic carboxylic acid can be concentrated and refluxed to the oxidation step, thereby increasing the oxidation reaction efficiency. be able to. Further, the membrane separation efficiency can be increased. The amount of the aliphatic carboxylic acid introduced into the condensation step can be reduced to reduce the corrosion of the condenser, and the amount of the aliphatic carboxylic acid circulated from the distillation column to the membrane separation device can be reduced.

In the present invention, since the corrosion of the condenser can be reduced, the material of the condenser can be a low-cost material such as stainless steel even in the case of high-pressure distillation. The oxidation reactor and the high-pressure distillation tower are preferably made of a corrosion-resistant material such as titanium. The membrane separation device can be made of the same stainless steel as the condenser.

When the concentrated solution is returned to the distillation column, the membrane separation device cannot return the concentrated solution due to troubles such as failure, which may affect the distillation column. The effect on the distillation column can be reduced by reducing the amount of concentrated liquid to be returned by increasing the concentration.

In the present invention, the alkyl aromatic compound is subjected to liquid phase oxidation with an oxygen-containing gas in a reaction solvent containing an aliphatic carboxylic acid in a reaction solvent containing an aliphatic carboxylic acid in an oxidation reactor to convert the aromatic carboxylic acid under high temperature and high pressure. It is preferable that there are two or more systems for the production, and that the distillation step is performed by a distillation column attached to each oxidizing apparatus, and that the membrane separation step is performed by concentrating the entire system. In this case, by returning the concentrated solution of the membrane separation step to the distillation column of the apparatus for producing one aromatic carboxylic acid, the influence on the distillation step due to the failure of returning the concentrated solution due to a trouble in the membrane separation apparatus is reduced. Limited to one distillation column,
The effect on the whole can be avoided.

The aliphatic carboxylic acid ester can be condensed or transferred to the exhaust gas side by limiting the condensation temperature in the condensation step. It can be brought into contact and absorbed. Although water can be used as the cleaning liquid, acetic acid may be used. The absorbing solution can be sent to the membrane separation step as it is, or can be hydrolyzed in the hydrolysis step and sent to the membrane separation step.

[0038]

According to the present invention, by performing a reaction while removing water and alcohol generated by the oxidation reaction by membrane separation, the water and alcohol unnecessary for the reaction can be efficiently separated and recovered from by-products such as alcohol. And wastewater treatment is easy. Also, by combining distillation and membrane separation, even if the height of the distillation column is lowered, aliphatic carboxylic acids can be efficiently separated and recovered from by-products such as water and alcohol unnecessary for the reaction, Wastewater treatment is also easy.

Further, by returning the concentrated liquid in the membrane separation step to the middle stage of the distillation column, the collected concentrated liquid can be further concentrated and refluxed to the oxidation step. In this case, the distillation efficiency can be increased and the recovered fat can be recovered. The group carboxylic acid can be prevented from flowing out to the condensation step, thereby preventing corrosion of the condenser, enabling the use of low-cost materials, and increasing the efficiency of membrane separation.

[0040]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of the present invention will be described with reference to the drawings for a method for producing terephthalic acid.

1 and 2 are flow charts showing an embodiment using a high-pressure distillation column, and FIG. 3 is a flow chart showing a method for producing terephthalic acid in an embodiment using a normal-pressure distillation column. A case in which manufacturing is performed using two series of apparatuses will be described. In FIGS. 1 and 2, reference numerals 1 and 1a denote oxidation reactors, and a high-pressure distillation column is directly connected as a distillation column 2 or 2a at the top. Three, three
a is a condenser, 4, 4a and 5 are coolers, and 7 is a high-pressure pump. Reference numeral 8 denotes a membrane separation device having a separation membrane 9 made of a reverse osmosis membrane.

In the method for producing terephthalic acid shown in FIG. 1, para-xylene as a raw material alkyl aromatic compound, acetic acid as a reaction solvent, a heavy metal compound and a bromine compound as a catalyst are supplied from a line L1 to an oxidation reactor 1, and a line L2 is supplied from a line L2. Air is supplied as an oxygen-containing gas, and liquid phase oxidation is performed at high temperature and high pressure to generate terephthalic acid. The generated terephthalic acid precipitates as crystals to form a slurry, which is taken out from the line L3.

The oxidized exhaust gas is supplied to the line L4 at high temperature and high pressure.
The distillation is performed while passing through the packed bed through the packed bed 2. Most of the solvent, acetic acid, together with the raw material paraxylene and the catalyst contained in the oxidized exhaust gas are distilled off, and the fraction containing these is refluxed to the oxidation reactor 1 from the line L5. Exhaust gas containing a part of acetic acid and low-boiling by-products such as methanol enters the condenser 3 from the line L6 and is cooled, and the remaining acetic acid, water, methanol, and other by-products are condensed to generate condensed water. . Methyl acetate, which is an aliphatic carboxylic acid ester, also partially condenses.

A part of the condensed water is directly returned to the distillation column 2 from the line L7, and a part is taken out from the line L8 and cooled by the cooler 5. At this time, the exhaust gas discharged from the upper part of the condenser 3 is introduced into the cooler 4 from the line L9 to be cooled, and the condensed water is joined from the line L10 to the line L8. The exhaust gas from the cooler 4 is discharged from the line L11. The condensed water cooled by the cooler 5 is pressurized by the high-pressure pump 7 and
From 12, it is sent to the concentrated liquid chamber 11 of the membrane separation device 8, and low molecular weight nonionic substances such as water and methanol permeate into the permeated liquid chamber 12 through the separation membrane 9 by membrane separation. The permeate is discharged from line L13 and the concentrate is
To the middle stage of the distillation column 2.

By returning the concentrated solution of the membrane separation device to the middle stage of the distillation column 2, the collected concentrated solution containing acetic acid is subjected to distillation in the distillation column 2, and the outflow of acetic acid to the condenser 3 is prevented. And the distillation efficiency is increased.

In FIG. 2, a production apparatus 10 comprising an oxidation reactor 1, a distillation column 2, a condenser 3, a condenser 4, and lines L1 to L11, an oxidation reactor 1a, a distillation column 2a, a condenser 3
a, a cooler 4a and lines L1a to L11a, two systems of a manufacturing apparatus 10a are provided, each having the same configuration as that of FIG. Then, the condensed liquids of the respective lines L8 and L8a merge and are sent to the cooler 5,
It is cooled by a series of coolers 5, pressurized by a high-pressure pump 7, and subjected to membrane separation by a membrane separation device 8. The concentrate of the membrane separation device 8 is supplied from the line L14 to the middle stage of the distillation column 2a of one of the manufacturing devices 10a. Thereby, even in the case of emergency stop of the membrane separation device 8, the influence is limited to one distillation column 2a, and the influence on the other distillation column 2 is prevented.

In FIG. 3, the atmospheric pressure distillation column is connected as the distillation column 2 to the upper part of the oxidation reactor 1 via the oxidation exhaust gas condenser 13 and the pressure reducing valve 14, and the condenser 3 is connected to the distillation column 2. . An absorption tower 15 is connected to the oxidizing exhaust gas condenser 13.

In the method for producing terephthalic acid shown in FIG. 3, para-xylene as a raw material alkyl aromatic compound, acetic acid as a reaction solvent, heavy metal compounds and bromine compounds as catalysts are supplied to an oxidation reactor 1 from a line L1, and Air is supplied as an oxygen-containing gas, and liquid phase oxidation is performed at high temperature and high pressure to generate terephthalic acid. The generated terephthalic acid precipitates as crystals to form a slurry, which is taken out from the line L3.

The oxidizing exhaust gas enters the oxidizing exhaust gas condenser 13 at a high temperature and a high pressure from the line L4 and is cooled. A part of the condensate is returned to the oxidizing reactor 1 from the line L16 as it is, and a part is passed through the pressure reducing valve 14. The distillation column 2 enters the distillation column 2 from the line L17, and distillation is performed by heating the reboiler 17.
The exhaust gas of the oxidizing exhaust gas condenser 13 enters the absorption tower 15 from a line L18, and passes through a line L1 while passing through a packed bed 16.
In contact with the cleaning liquid supplied from 9, the methyl acetate in the gas is absorbed by the cleaning liquid. The exhaust gas from which methyl acetate has been removed is discharged from line L20. The absorption liquid that has absorbed the methyl acetate merges into the line L8 from the line L21, is mixed with the condensate, and is supplied to the distillation column 2.

In the distillation column 2, most of the acetic acid contained in the oxidized exhaust gas is distilled and returned to the oxidation reactor 1 through the line L 5. The distillation column overhead vapor containing a part of acetic acid and low-boiling by-products such as methanol enters the condenser 3 from the line L6, is cooled, and the remaining acetic acid, water, methanol, and other by-products are condensed, Condensed water is produced. Methyl acetate, which is an aliphatic carboxylic acid ester, also partially condenses.

A part of the condensed water is returned to the distillation column 2 from the line L7, and the other part is pressurized by the high pressure pump 7 and sent to the concentrated liquid chamber 11 of the membrane separation device 8, where water and methanol are separated by the membrane separation. A low molecular weight nonionic substance such as the above permeates into the permeate chamber 12 through the separation membrane 9. The permeate is line L13
, And the concentrated liquid is returned to the middle stage of the distillation column 2 from the line L14.

[0052]

Embodiments of the present invention will be described below. In each case,% and ppm are by weight unless otherwise stated.

Reference Example 1 The apparatus of FIG. 1 was changed to connect the line L14 to the line 7, and the concentrated liquid was combined with the condensed liquid and returned to the top of the distillation column 2. In this case, 190 ° C, 1.2MP in an oxidation reactor
a) oxidizes para-xylene to produce terephthalic acid,
The oxidation exhaust gas is distilled in a titanium steel distillation column 2 and a condenser 3
At 100 ° C. Stainless steel condenser 3
After cooling to 40 ° C. in a stainless steel cooler 4, mixing with a liquid condensed in a condenser 3, cooling to 40 ° C. in a stainless steel cooler 5, and a stainless steel high-pressure pump 7. The pressure was increased to 6.0 MPa, and the solution was sent to a stainless steel membrane separator 8 where the membrane was separated, and the permeate was discharged out of the system. The theoretical height of the distillation column was 30 theoretical plates, and the separation membrane used was a reverse osmosis membrane AD-8040F (trade name) manufactured by Osmonics, USA, and the volume concentration ratio was 1.5 times. The concentrated liquid of the reverse osmosis membrane was mixed with the condensed liquid of the condenser 3 at the top of the distillation tower 2 and refluxed. The condensate of the stainless steel condenser 3 is 2.5% of acetic acid, and the permeate of the membrane separation device 8, which is wastewater, is 0.8% of acetic acid. 1 part by weight. The feed amount of the condensate to the membrane separation device 8 required 1322 parts by weight with respect to 1000 parts by weight of para-xylene. The stainless steel condenser 3 corroded until it could not be used in six months.

Example 1 In the oxidation reactor shown in FIG. 1, terephthalic acid was produced by oxidizing para-xylene at 190 ° C. and 1.2 MPa. At 1
Condensation was performed at 00 ° C. The exhaust gas from the stainless steel condenser 3 is cooled to 40 ° C. in the stainless steel cooler 4, mixed with the liquid condensed in the condenser 3, cooled to 40 ° C. in the stainless steel cooler 5, and The pressure was increased to 6.0 MPa by a stainless steel high-pressure pump 7, sent to a stainless steel membrane separator 8 to separate the membrane, the concentrated solution was returned to the middle stage of the distillation column 2, and the permeate was discharged out of the system. . The theoretical plate height of the distillation column 2 was 30 theoretical plates, the separation membrane used was a reverse osmosis membrane AD-8040F (trade name) manufactured by Osmonix, USA, and the volume concentration ratio was 9.1 times. The concentrated solution of the reverse osmosis membrane was returned to the 20th theoretical plate, counting from the top of the distillation column 2. The condensate of the condenser 3 is 1.3% of acetic acid, and the permeate of the membrane separation device 8 which is wastewater is 0.2% of acetic acid.
The acetic acid loss amount was 0.9 parts by weight with respect to 0 parts by weight, which was 1/3 or less of Reference Example 1. The feed amount of the condensate to the membrane separation device 8 is 46 parts per 1000 parts by weight of para-xylene.
4 parts by weight, which is 35% of that of Reference Example 1, and accordingly, the cooling water amount of the cooler 4 and the power consumption of the high-pressure pump are also reduced.
35%.

Example 2 In the oxidation reactor 1 of the manufacturing apparatus 10 shown in FIG.
Paraxylene was oxidized at 1.2 ° C. at 1.2 ° C. to produce terephthalic acid, and the oxidized exhaust gas was distilled in a titanium distillation column 2 and condensed at 100 ° C. in a condenser 3. The exhaust gas from the stainless steel condenser 3 was cooled to 40 ° C. by the cooler 4. Also in the oxidation reactor 1a of the manufacturing apparatus 10a, 19
Paraxylene was oxidized at 0 ° C. and 1.2 MPa to produce terephthalic acid, and the oxidized exhaust gas was distilled in a titanium distillation column 2a and condensed at 100 ° C. in a stainless steel condenser 3a. The exhaust gas from the stainless steel condenser 3a was cooled to 40 ° C. by the stainless steel cooler 4a. The condensed liquids of the manufacturing apparatuses 10 and 10a are mixed, cooled to 40 ° C. by a stainless steel cooler 5, and then pressurized to 6.0 MPa by a stainless steel high pressure pump 7 to form a stainless steel membrane separation apparatus 8 And the membrane is separated.
And the permeate was discharged out of the system. Distillation columns 2 and 2
The theoretical plate height of a was 30 theoretical plates, and the separation membrane used was a reverse osmosis membrane AD-8040F (trade name) manufactured by Osmonix, USA, and the volume concentration ratio was 9.7 times. The concentrated liquid of the reverse osmosis membrane was returned to the 20th theoretical plate, counting from the top of the distillation column 2a. The condensate in the condensers 3 and 3a is acetic acid 1.
The permeate of the membrane separation device 8 which is 3% and the wastewater is 0.2% acetic acid
And the total amount of para-xylene feed of the two series is 1000
The acetic acid loss amount was 0.9 parts by weight with respect to parts by weight, which was the same as in Example 1, although the two-line treatment was performed. The feed amount of the condensate to the membrane separation device 8 was 464 parts by weight with respect to 1000 parts by weight of the total amount of para-xylene fed in the two lines, which was the same as in Example 1.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a method for producing terephthalic acid according to an embodiment.

FIG. 2 is a flowchart showing a method for producing terephthalic acid according to another embodiment.

FIG. 3 is a flowchart showing a method for producing terephthalic acid according to still another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 1a Oxidation reactor 2, 2a Distillation tower 3, 3a Condenser 4, 4a, 5 Cooler 7 High-pressure pump 8 Membrane separation device 9 Separation membrane 10, 10a Production equipment 11 Concentrated liquid room 12 Permeate liquid room 13 Oxidation exhaust gas condensation Vessel 14 pressure reducing valve 15 absorption tower 16 packed bed 17 reboiler

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Michio Umeda Inventor F-term (reference) 4D006 GA03 JA01C JA53A KA01 KA71 KB18 MA01 MA02 MA03 MC16 MC18 MC23 MC28 MC29 MC33 MC39 MC45 MC48 MC51 MC54 MC58 MC62 MC63 PA03 PB12 PB70 4D076 AA06 AA16 AA22 BB04 BC01 CA19 FA02 FA04 FA12 FA19 FA34 HA03 JA03 JA06 4H006 AA02 AB46 AD11 AD19 BA16 BA20 BA32 BA37 BA60 BB17 BD53 BD40 BD40 BD40 BE30 BJ50 BS30 4H039 CA65 CC30

Claims (12)

[Claims] 1. An alkyl carboxylic acid is liquid-phase oxidized with an oxygen-containing gas in a reaction solvent containing an aliphatic carboxylic acid in a reaction solvent containing an aliphatic carboxylic acid in an oxidation reactor to produce an aromatic carboxylic acid under high temperature and high pressure. An oxidation step in which an oxidation exhaust gas or a condensate obtained by condensing an oxidation exhaust gas in an oxidation exhaust gas condenser from an oxidation reactor is introduced into a distillation column for distillation, and a fraction containing a reaction solvent is refluxed to the oxidation reactor. A condensation step in which the overhead gas coming out of the distillation tower is cooled by a condenser to generate condensed water, and the condensed water is subjected to membrane separation by a membrane separation device to allow water and alcohol to permeate into the permeated liquid side to remove aliphatic carboxylic acid. A method for producing an aromatic carboxylic acid, comprising: a membrane separation step of concentrating and recovering a concentrated solution to a concentrate side; and a return step of returning a concentrated solution in the membrane separation step to a middle stage of a distillation column. 2. The theoretical plate height in the distillation step is 10 to 7
2. The method of claim 1, wherein the number of theoretical plates is zero. 3. The theoretical plate height in the distillation step is 20-4.
3. The method of claim 2, wherein the number of theoretical plates is zero. 4. The method according to claim 1, wherein the concentrated liquid from the membrane separation step is returned to the lower stage from the height of 5 theoretical plates counted from the top of the column and to the upper stage from the height of 5 theoretical plates counted from the bottom of the column. The method according to any of the above. 5. The method according to claim 4, wherein the concentrated liquid from the membrane separation step is returned to 10 to 25 theoretical stages counted from the top of the column. 6. The method according to claim 1, wherein the material of the distillation column is titanium, and the material of the membrane separation device is stainless steel. 7. The method according to claim 6, wherein the material of the condenser of the distillation column is stainless steel. 8. The method according to claim 1, wherein in the membrane separation step, the membrane is separated using a reverse osmosis membrane. 9. The volume concentration ratio in the membrane separation step is 2 to 9.
The method according to any one of claims 1 to 8, which is 20 times. 10. The volume concentration ratio in the membrane separation step is 5
10. The method of claim 9, wherein the factor is ~ 15. 11. An aromatic carboxylic acid is produced under high temperature and high pressure by subjecting an alkyl aromatic compound to liquid phase oxidation with an oxygen-containing gas in a reaction solvent containing an aliphatic carboxylic acid in an oxidation reactor in the presence of an oxidation catalyst. The method according to any one of claims 1 to 10, wherein there are two or more systems for performing the distillation, wherein the distillation step is performed in a distillation column attached to each oxidizing apparatus, and the membrane separation step is performed in a concentrated manner for all the series. 12. An aromatic carboxylic acid is produced at high temperature and pressure by subjecting an alkyl aromatic compound to liquid phase oxidation with an oxygen-containing gas in a reaction solvent containing an aliphatic carboxylic acid in an oxidation reactor in the presence of an oxidation catalyst. There are two or more systems that perform the distillation process, and the distillation process is performed by the distillation column attached to each oxidation device. The membrane separation process is a process that concentrates and processes the entire system to produce one aromatic carboxylic acid from the concentrated solution. Claim 1 which is returned to the distillation column
2. The method according to 1.