JP4431812B2 - Method for producing aromatic carboxylic acid - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
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]
[Prior art]
Aromatic carboxylic acids are important as basic chemicals. In particular, aromatic dicarboxylic acids are useful as raw materials for fibers, resins and the like. For example, the demand for terephthalic acid is increasing as a polyester raw material in recent years. As a method for producing an aromatic carboxylic acid, in general, in an oxidation reactor, a heavy metal compound and a bromine compound are used as catalysts, and an alkyl-substituted aromatic compound contains molecular oxygen in a reaction solvent containing a lower aliphatic carboxylic acid such as acetic acid. A method of liquid phase oxidation by contacting with gas 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 the oxidation reactor. An aromatic carboxylic acid such as
[0003]
Since the exhaust gas discharged from the oxidation reactor is accompanied by a solvent, catalyst, etc., in order to recover and reuse it, a condensate obtained by condensing the exhaust gas from the oxidation exhaust gas condenser is introduced into the distillation tower. There is a method of performing distillation and refluxing a fraction containing a reaction solvent to an oxidation reactor. There is also a method in which a distillation column connected to the upper part of the reaction tank is provided, distillation is performed using the heat of the oxidation exhaust gas, and the solvent is recovered and refluxed to the oxidation reaction tank (Japanese Patent Publication No. 54-14098, Japanese Patent Laid-Open No. 6-1994). 279353). In this method, the exhaust gas emitted from the distillation tower is cooled with cooling water in a condenser to condense water vapor in the exhaust gas, and the condensed water is refluxed to the distillation tower and used for distillation.
[0004]
Thus, in the method of distilling oxidized exhaust gas or its condensate, the boiling points of acetic acid and water or alcohol are close to each other, so that a solvent such as acetic acid is completely separated from water or alcohol and recovered in a distillation column. It is necessary to raise the tower height of the tower, and when the tower height is lowered, a part of the solvent moves to the condensed water side. Since water is generated in the above oxidation reaction, it is necessary to discharge a part of the condensed water to the outside of the system, and since the solvent and other components flow out into the waste water, the treatment is also difficult.
[0005]
In addition, aliphatic carboxylic acid esters such as methyl acetate produced by the oxidation reaction are absorbed and recovered by washing water, and this is hydrolyzed using ion exchange resin as a catalyst, and aliphatic carboxylic acids such as acetic acid are recovered as a solvent. However, it is difficult to separate aliphatic carboxylic acid and alcohol by hydrolysis.
[0006]
[Problems to be solved by the invention]
The problem of the present invention is that even if the column height of the distillation column is lowered, the aliphatic carboxylic acid can be efficiently separated and recovered from by-products such as water and alcohol unnecessary for the reaction, and wastewater treatment is also possible. It is to propose an easy method for producing an aromatic carboxylic acid.
Another object of the present invention is to propose a method for producing an aromatic carboxylic acid capable of efficiently hydrolyzing an aliphatic carboxylic acid ester produced in a reaction system and recovering a useful product.
[0007]
[Means for Solving the Problems]
The present invention is the following method for producing an aromatic carboxylic acid.
( 1 In the oxidation reactor Low An oxidation step of producing an aromatic carboxylic acid under high temperature and pressure by liquid phase oxidation of an alkyl aromatic compound with an oxygen-containing gas in the presence of an oxidation catalyst in a reaction solvent containing an aliphatic carboxylic acid;
A distillation step of introducing oxidation exhaust gas from the oxidation reactor, or a condensate obtained by condensing the oxidation exhaust gas in the oxidation exhaust gas condenser to the distillation tower, performing distillation, and refluxing the fraction containing the reaction solvent to the oxidation reactor,
A condensing step of cooling the top gas exiting the distillation tower with a condenser to produce condensed water; and
Condensed water A separation membrane consisting of a reverse osmosis membrane Membrane separation , Water and alcohol Low molecular weight nonionic substances containing To the permeate side, Low Membrane separation process for collecting and recovering aliphatic carboxylic acid to concentrate
including Production of aromatic carboxylic acids Method.
( 2 The above-mentioned (including the absorption step of contacting the exhaust gas from the condensation step with the cleaning liquid to absorb the aliphatic carboxylic acid ester and supplying the absorption liquid to the membrane separation step ( 1 ) The method described.
( 3 The above (including the absorption step of contacting the exhaust gas from the oxidation exhaust gas condenser with the cleaning liquid to absorb the aliphatic carboxylic acid ester and supplying the absorption liquid to the distillation process ( 1 ) The method described.
( 4 ) Condensed water, absorption liquid, permeate or concentrated liquid obtained by membrane separation of these is contacted with a hydrolysis catalyst to hydrolyze the aliphatic carboxylic acid ester, and a hydrolysis process for supplying the hydrolysis liquid to the membrane separation process is included. the above( 1 ) Or ( 3 ) Any one of the methods.
( 5 ) Hydrolysis catalyst is an ion exchange resin 4) The method described.
( 6 ) The whole or a part of the condensed water is subjected to membrane separation, and the concentrated solution is refluxed to the distillation step. 5 ) Any one of the methods.
( 7 ) The membrane separation step is performed in a plurality of stages (1) to ( 6 ) Any one of the methods.
[0008]
In the present invention, water and alcohol produced by an oxidation reaction Low molecular weight nonionic substances containing The reaction is carried out while removing by membrane separation. In this case, such as acetic acid used as a solvent Low Combines distillation and membrane separation processes to efficiently separate aliphatic carboxylic acids from unwanted components such as water and alcohol Separation. If the above separation is performed only by distillation, it is necessary to increase the tower height as described above. If the separation is performed only by membrane separation, the separation efficiency is poor and a multistage membrane separation apparatus is required. A low-distillation tower, Low If most of the aliphatic carboxylic acid is separated and the remainder of the low-concentration liquid is separated by membrane separation, the separation can be efficiently performed with a small-scale apparatus.
[0009]
As an 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) can be used. Such 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.
[0010]
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.
[0011]
In addition, 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, hydroxyalkyl group or the like. 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 give. These may be used alone or as a mixture of two or more.
[0012]
In the method of the present invention, a heavy metal compound and a bromine compound are used as catalysts. Examples of these compounds are as follows. That is, 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 being particularly preferred.
[0013]
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, benzyl bromide, bromo Examples thereof include organic bromine compounds such as methyltoluene, dibromoethane, tribromoethane, and tetrabromoethane. These bromine compounds are also used alone or as a mixture of two or more.
[0014]
In the present invention, the catalyst composed of a combination of the above heavy metal compound and bromine compound is desirably composed of 0.05 to 10 moles, preferably 0.1 to 2 moles of bromine atoms with respect to 1 mole of heavy metal atoms. Such a catalyst is normally used in the range of 10 to 10000 wt-ppm, preferably 100 to 5000 wt-ppm as the heavy metal concentration in the reaction solvent.
[0015]
In the method of the present invention, in an oxidation reactor as an oxidation step, an aromatic compound serving as an oxidation raw material is liquid-phase oxidized with a molecular oxygen-containing gas in a reaction solvent containing a lower aliphatic carboxylic acid in the presence of the catalyst. As a result, an aromatic carboxylic acid as a product is obtained.
[0016]
Examples of the molecular oxygen-containing gas include oxygen and air, but air is preferably used practically. The molecular oxygen-containing gas is supplied in excess of the amount necessary 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, 2 to 20 Nm with respect to 1 kg of the aromatic compound as the oxidation raw material ³ , Preferably 2.5-15 Nm ³ It is desirable to supply the reaction system at a ratio of
[0017]
Specific examples of the lower aliphatic carboxylic acid used as the reaction solvent include acetic acid, propionic acid, butyric acid, and the like. 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 acetic acid, propionic acid, butyric acid and a mixture thereof, or a mixture of these lower aliphatic carboxylic acid and water. In these, the mixture of an acetic acid and water is preferable, and the mixture which mixed 1-20 weight part of water with respect to 100 weight part of acetic acid, Preferably 5-15 weight part is desirable.
[0018]
The temperature of the oxidation reaction is usually 100 to 250 ° C, preferably 150 to 220 ° C. Moreover, the reaction pressure should just be more than the pressure which can maintain a reaction system in a liquid phase.
[0019]
By making it react in this way, the aromatic carboxylic acid corresponding to the aromatic compound used as an oxidation raw material is obtained. Specific examples of the aromatic carboxylic acid 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 acids; aromatic polycarboxylic acids such as pyromellitic acid.
[0020]
The method of the present invention is preferably applied to the production of an aromatic dicarboxylic acid or an aromatic carboxylic acid that is insoluble or hardly soluble in the reaction solvent, and particularly preferably to the production of terephthalic acid.
[0021]
The produced aromatic carboxylic acid such as terephthalic acid is precipitated as crystals and becomes a slurry. By removing this slurry from the oxidation reaction tank and recovering the crystals by solid-liquid separation, a crude product such as crude terephthalic acid is obtained. It is done.
Oxidation reaction intermediates and impurities are accompanied in the crude product crystals 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. And a slurry containing crystals. When crystals are recovered from such a slurry, a purified product such as purified terephthalic acid is obtained.
[0022]
In the distillation step, it is preferable to introduce oxidation exhaust gas into a distillation column (high pressure distillation column) connected to the upper part of the oxidation reactor and perform distillation using the heat generated in the oxidation reactor. Distillation may be performed by introducing the condensed condensate into a distillation column (atmospheric distillation column). In either case, the fraction containing the reaction solvent is refluxed from the column bottom to the oxidation reactor, and the column top gas containing water and non-condensable gas is discharged from the column top. The distillation column may be independent from the oxidation reactor as shown in JP-B-54-14098, or may be installed at the top of the oxidation reactor as shown in JP-A-6-279353. The distillation column may be a plate column, but a packed column is preferable. In this case, a means for collecting fine solids such as crystals of aromatic carboxylic acid, for example, a solid collection tray is provided below the packed bed. What is provided in is preferable.
In addition, the distillation tower is constructed by continuously installing multiple towers and distilling the exhaust gas in the next tower in order to return the distillate in the subsequent stage to the previous stage in sequence, and distilling from the middle of each tower during an emergency stop. It is preferable to withdraw the liquid out of the system and prevent the concentration and temperature of the reaction liquid in the oxidation reaction tower from decreasing.
[0023]
By distilling the oxidation exhaust gas or the condensate obtained by condensing the oxidation exhaust gas in the oxidation exhaust gas condenser in such a distillation tower, the fraction containing the reaction solvent discharged along with the oxidation exhaust gas is refluxed to the oxidation reactor. . This fraction is refluxed to the oxidation reactor as a column bottom liquid in a state in which unreacted alkyl aromatic compound, generated aromatic carboxylic acid, catalyst and the like are concentrated in addition to the reaction solvent. Among these, solids such as aromatic carboxylic acid crystals and catalysts, and components with high boiling points are trapped or distilled off at the bottom of the distillation column, and have low boiling points. Low A reaction solvent such as an aliphatic carboxylic acid is distilled at a relatively upper portion.
[0024]
Such a fraction is refluxed as it is to the oxidation reactor, but a distillate with a high acetic acid concentration is withdrawn at the bottom of the distillation column and used as an absorbent for aliphatic carboxylic acid esters. In addition, it can be used as a crystal washing liquid obtained by solid-liquid separation of the slurry extracted from the 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 drawing it out of the system.
[0025]
In the condensation step, the tower top gas exiting from the distillation tower is cooled with cooling water by a condenser to condense the water vapor in the tower top gas to produce condensed water. The condenser may be connected to the distillation column, or may be provided separately, or may be a single one or divided into a plurality. The condensation temperature may be a temperature at which water vapor is condensed, and the aliphatic carboxylic acid ester may or may not be condensed. The total amount of the condensed water may be sent to the membrane separation step, or part of it may be refluxed to the distillation column and part of it may be sent to the membrane separation step.
[0026]
Membrane separation process is a by-product such as water and alcohol by membrane separation part or all of the condensed water Low molecular weight nonionic substances containing To the permeate side, Low In this step, the aliphatic carboxylic acid is concentrated to the concentrate side and separated. As a separation membrane for such separation, a reverse osmosis membrane The use You The Reverse osmosis membranes include polyamide, aromatic polyamide, polyacrylonitrile, polypropylene, polyvinylidene fluoride, polyfluorinated ethylene, polyvinyl alcohol, polyester, polyimide, polysulfone, polyethersulfone, acetic acid Cellulose-based, cellulose ester-based, triacetylcellulose-based, uric acid polyether-based, polypiperazamide-based, polyfuran-based, and polyethyleneimine-based are available, and a crosslinked aromatic polyamide-based reverse osmosis membrane is particularly preferable.
[0027]
The separation membrane can be of any shape such as flat membrane, tubular, spiral, hollow fiber. Such a separation membrane separates by molecular diameter, ionicity, etc., and is a by-product such as water and alcohol. Low molecular weight nonionic substances containing To the permeate side, Low Aliphatic carboxylic acid can be concentrated and concentrated on the concentrate side Reverse osmosis membrane Can be used. About 20% of the aliphatic carboxylic acid ester permeates and about 80% remains on the concentration side. The membrane separation step may be performed in a single stage, but is preferably performed in a plurality of stages.
[0028]
Unnecessary water produced by reaction and alcohol and other by-products such as methanol by membrane separation of condensed water Low molecular weight nonionic substances containing Is permeated to the permeate side and separated. Such as acetic acid used as solvent Low The aliphatic carboxylic acid remains on the concentrate side and is concentrated. Since acetic acid and water have close boiling points, it is necessary to increase the tower height to separate them by distillation. By using reverse osmosis membranes, It is easily separated by membrane separation due to the difference in molecular diameter and ionicity. If the separation is not complete, the membrane separation can be performed in multiple stages.
[0029]
The permeate can be separated from water and alcohol and other by-products by separation means such as distillation and discharged out of the system, or used as washing water for the aromatic carboxylic acid produced. The concentrated liquid is refluxed to the oxidation step, and at this time, it is preferable that all or part of the concentrated liquid is returned to the upper part of the distillation column and used for distillation.
[0030]
By limiting the condensation temperature in the condensation step, the aliphatic carboxylic acid ester can be condensed or moved to the exhaust gas side, but when moving to the exhaust gas side, the exhaust gas is brought into contact with the cleaning liquid in the absorption step. Absorb. As the cleaning liquid, water can be used, but acetic acid may be used. The absorbing solution can be sent to the membrane separation step as it is, but can also be hydrolyzed in the hydrolysis step and sent to the membrane separation step.
[0031]
In the hydrolysis step, the condensed carboxylic acid ester is hydrolyzed by bringing the condensed water, the absorption liquid, the permeate or the concentrated liquid obtained by membrane separation into contact with the hydrolysis catalyst. When using a room temperature distillation column, it is preferable to hydrolyze the entire permeated liquid separated from the membrane. As the hydrolysis catalyst, an H-type ion exchange resin, preferably a strong acid cation exchange resin, particularly a macroporous ion exchange resin is preferred, but other acid or alkali catalysts may be used.
[0032]
Aliphatic carboxylic acid ester is obtained by hydrolysis. Low Since it is decomposed into an aliphatic carboxylic acid and an alcohol, these are separated as described above by membrane separation of the hydrolyzate. When the permeate or concentrate in the membrane separation process is hydrolyzed, the membrane is separated in the next stage membrane separation process. In the case of the concentrate, it is returned to the oxidation process and then becomes condensed water and recycled to the membrane separation process. May be separated at a certain stage.
[0033]
【The invention's effect】
According to the present invention, water and alcohol produced by an oxidation reaction Use reverse osmosis membrane for low molecular weight non-ionic substances including By performing the reaction while removing by membrane separation, water and alcohol and other by-products that are unnecessary for the reaction Lower aliphatic carboxylic acid Efficient separation and recovery are possible, and wastewater treatment is easy.
In addition, by combining distillation and membrane separation, the column height of the distillation column can be lowered. Low Aliphatic carboxylic acid can be efficiently separated and recovered from by-products such as water and alcohol unnecessary for the reaction, and waste water treatment is also easy.
[0034]
By providing the absorption step, the aliphatic carboxylic acid ester can be recovered from the exhaust gas of the condensation step. Also, by hydrolyzing the aliphatic carboxylic acid ester Low The utilization efficiency can be increased by separating the aliphatic carboxylic acid and the alcohol by membrane separation. At this time, by combining the hydrolysis step and the membrane separation step, separation of the aliphatic carboxylic acid and alcohol generated by the hydrolysis is facilitated. Furthermore, by combining the absorption process, hydrolysis process and membrane separation process, the aliphatic carboxylic acid ester in the exhaust gas can be recovered and effectively used, Low Separation efficiency of aliphatic carboxylic acid and alcohol can be increased.
[0035]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings for a method for producing terephthalic acid.
[0036]
FIGS. 1 to 3 are flowcharts showing a method for producing terephthalic acid in an embodiment using a high-pressure distillation column, and FIGS. 4 and 5 are embodiments in which an atmospheric distillation column is used. 1 to 3, reference numeral 1 denotes an oxidation reactor, and a high-pressure distillation column is directly connected to the upper portion as a distillation column 2. 3 is a condenser, 4 and 5 are coolers, 6 is an absorption tower, and 7 is a pump. Reference numerals 8 and 8a are membrane separation devices, which have separation membranes 9 and 9a made of reverse osmosis membranes. 10 and 10a are hydrolysis tanks having catalyst layers 11 and 11a made of an ion exchange resin.
[0037]
1 to 3, the terephthalic acid production method of FIG. 1 to FIG. 3 supplies para-xylene as a raw material alkylaromatic compound, acetic acid as a reaction solvent, heavy metal compound and bromine compound as catalysts from a line L1 to an oxidation reactor 1, Air is supplied as an oxygen-containing gas, and liquid phase oxidation is performed at high temperature and pressure to produce terephthalic acid. The produced terephthalic acid is precipitated as crystals to form a slurry, which is taken out from the line L3.
[0038]
In FIG. 1, oxidation exhaust gas enters the distillation column 2 in a high temperature and high pressure state, and distillation is performed while passing through the packed bed 12. Most of acetic acid as a solvent is distilled together with the raw material paraxylene contained in the oxidation exhaust gas and the catalyst, and the fraction containing these is refluxed to the oxidation reactor. The exhaust gas containing a part of acetic acid and low-boiling by-products such as methanol enters the condenser 3 and is cooled, and the remaining acetic acid, water, methanol, and other by-products are condensed to produce condensed water. Part of methyl acetate, which is an aliphatic carboxylic acid ester, also condenses.
[0039]
A part of the condensed water is refluxed as it is to the distillation column 2, and a part is collected by the water receiving unit 13, taken out from the line L 4 and cooled by the cooler 4. Then, the pressure is increased by the pump 7 and sent to the concentrated liquid chamber 14 of the membrane separation device 8, and low molecular weight nonionic substances such as water and methanol permeate the permeated liquid chamber 15 through the separation membrane 9 by membrane separation. The permeate is discharged from the line L5, and the concentrate is refluxed from the line L6 to the top of the distillation column 2.
[0040]
The exhaust gas exiting from the upper part of the condenser 3 enters the cooler 5 from the line L7, is cooled, enters the absorption tower 6, contacts the cleaning liquid supplied from the line L8 while passing through the packed bed 16, and is contained in the gas. Methyl acetate is absorbed into the cleaning solution. The exhaust gas from which methyl acetate has been removed is discharged from the line L9. The absorption liquid that has absorbed methyl acetate merges from line L10 to line L4, is mixed with condensed water, and is supplied to the membrane separation device 8. Depending on the separation performance of the separation membrane 9, there are methyl acetate that remains on the concentrate side and circulates and that that permeates the permeate side, both of which can be hydrolyzed by an appropriate method.
[0041]
In FIG. 2, the hydrolysis tank 10 is provided on the cooler 5, and the catalyst layer 11 is formed. For this reason, when the methyl acetate in the exhaust gas cooled by the cooler 5 passes through the hydrolysis tank 10, it is decomposed into acetic acid and methanol by hydrolysis. Acetic acid and methyl acetate remaining in the exhaust gas that has passed through the hydrolysis tank 10 are recovered by contacting with water from the line L8 in the absorption tower 6. When the hydrolyzed liquid joins the lines L10 to L4 and is supplied to the membrane separation device 8 together with the condensed water, acetic acid remains on the concentrate side, and methanol permeates on the permeate side and is separated. Therefore, even when acetic acid is used as the cleaning liquid in the absorption tower 6, the acetic acid is recovered and supplied to the distillation tower 2. Other configurations and operations are the same as those in FIG.
[0042]
In FIG. 3, the exhaust gas from the distillation tower 2 enters the condenser 3 from the entire line L7 and is condensed. Here, the condensed water and the mixed solution of the absorbing solution having absorbed the methyl acetate in the absorption tower 6 enter the membrane separation device 8 from the line L10 and are separated into acetic acid, methanol and water by membrane separation. A part of methyl acetate remains on the concentrate side, and a part permeates on the permeate side.
[0043]
The permeate enters the hydrolysis tank 10a, and methyl acetate is hydrolyzed by the catalyst layer 11a to decompose into acetic acid and methanol. By subjecting the hydrolyzed solution to membrane separation by the membrane separation device 8a, acetic acid remains on the concentrate side, and methanol and water permeate to the permeate side. The concentrated liquids of the membrane separators 8 and 8a join together and enter the line L6, where methyl acetate is hydrolyzed in the hydrolysis tank 10 and refluxed to the upper part of the distillation column 2. Here, acetic acid and methanol refluxed to the oxidation reactor 1 are separated by the membrane separation device 8 when circulated as oxidation exhaust gas.
[0044]
4 and 5, an atmospheric distillation column is connected to the upper portion of the oxidation reactor 1 via the oxidation exhaust gas condenser 3 a and the pressure reducing valve 18 as the distillation column 2, and the condenser 3 is connected to the distillation column 2. . A cooler 5 and an absorption tower 6 are connected to the oxidation exhaust gas condenser 3a.
[0045]
4 and FIG. 5, the terephthalic acid production method of FIG. 4 and FIG. 5 supplies para-xylene as a raw material alkylaromatic compound, acetic acid as a reaction solvent, and a heavy metal compound and a bromine compound as a catalyst from a line L1 to an oxidation reactor 1. Air is supplied as an oxygen-containing gas, and liquid phase oxidation is performed at high temperature and pressure to produce terephthalic acid. The produced terephthalic acid is precipitated as crystals to form a slurry, which is taken out from the line L3.
[0046]
In FIG. 4, the oxidation exhaust gas enters the oxidation exhaust gas condenser 3a from the line L11 in a high-temperature and high-pressure state and is cooled. A part of the condensate is refluxed as it is to the oxidation reactor 1, and a part of the condensate passes through the pressure reducing valve 18 to Enters the distillation column 2 and is distilled by heating the reboiler 17. The exhaust gas from the oxidation exhaust gas condenser 3a enters the cooler 5 from the line L13, is cooled, enters the absorption tower 6, contacts the cleaning liquid supplied from the line L8 while passing through the packed bed 16, and is contained in the gas. Methyl acetate is absorbed into the cleaning solution. The exhaust gas from which methyl acetate has been removed is discharged from the line L9. The absorbing liquid that has absorbed methyl acetate merges from the line L10 to the line L12, is mixed with the condensate, and is supplied to the distillation column 2.
[0047]
In the distillation column 2, most of the acetic acid contained in the oxidation exhaust gas is distilled off and refluxed to the oxidation reactor 1. Distillation tower top vapor containing a part of acetic acid and low-boiling by-products such as methanol is cooled by entering condenser 3 from line L14, and the remaining acetic acid, water, methanol and other by-products are condensed and condensed. Water is produced. Part of methyl acetate, which is an aliphatic carboxylic acid ester, also condenses.
[0048]
The condensed water is directly pressurized by the pump 7 and sent to the concentrated liquid chamber 14 of the membrane separation device 8, and low molecular weight nonionic substances such as water and methanol permeate through the separation membrane 9 to the permeate liquid chamber 15 by membrane separation. To do. The permeate is discharged from the line L5, and the concentrate is refluxed from the line L6 to the top of the distillation column 2.
[0049]
In FIG. 5, the cooler 5 is omitted, the hydrolysis tank 10 is provided in the line L6, and the catalyst layer 11 is formed. For this reason, when the methyl acetate in the permeate of the membrane separation device 8 passes through the hydrolysis tank 10, it is decomposed into acetic acid and methanol by hydrolysis and refluxed to the upper part of the distillation column 2.
【Example】
Examples of the present invention will be described below. In each example,% and ppm are based on weight unless otherwise stated.
[0050]
Reference example 1
In the oxidation reactor of FIG. 1, paraxylene was oxidized at 190 ° C. and 1.2 MPa to produce terephthalic acid, and the oxidized exhaust gas was distilled in the distillation tower 2 and condensed at 160 ° C. in the condenser 3. Mixing of 50 kg / hr of absorption liquid in which exhaust gas from the distillation tower 2 is brought into contact with 10 kg / hr of 35 ° C. water as absorption liquid in the absorption tower 6 to absorb methyl acetate and 55 kg / hr of condensed water taken out from the condenser The liquid 105 kg / hr was discharged out of the system. The mixture was 1.5% acetic acid, 2650 ppm methyl acetate, and 1040 ppm methanol. The exhaust gas from the absorption tower was 0.1 volume ppm of acetic acid, 1020 volume ppm of methyl acetate, and 106 ppm of methanol.
[0051]
Example 1
In Reference Example 1, the condensed water taken out from the condenser 3 is set to 205 kg / hr, and the mixed solution 255 kg / hr mixed with the absorbing solution 50 kg / hr from the absorption tower 6 is increased to 4.9 MPa and sent to the membrane separation device 8. The membrane was separated, 150 kg / hr of the concentrated liquid was refluxed to the distillation column 2, and 105 kg / hr of the permeate was discharged out of the system. The separation membrane was a reverse osmosis membrane SU-820 (trade name, manufactured by Toray Industries, Inc.) made of a crosslinked polyamide composite membrane, and the permeate was 0.3% acetic acid, 303 ppm methyl acetate, and 1010 ppm methanol. The exhaust gas was 0.1 ppm by volume of acetic acid, 1530 ppm by volume of methyl acetate, and 305 ppm of methanol.
[0052]
Example 2
In FIG. 2, the amount of washing water in the absorption tower 6 is 50 kg / hr, and a mixed liquid 295 kg / hr in which 90 kg / hr of the hydrolyzed absorption liquid is mixed with 205 kg / hr of the condensate 3 from the condenser 3 is mixed. The membrane was separated with a membrane separator 8, 150 kg / hr of the concentrated solution was refluxed to the distillation column 2, and 145 kg / hr of the permeate was discharged out of the system. The hydrolysis catalyst is a macroporous strongly acidic cation exchange resin (manufactured by Organo Corporation, Amberlyst 15, trade name). Others were performed in the same manner as in Example 1. The permeate was 0.5% acetic acid, 550 ppm methyl acetate, and 1700 ppm methanol. The exhaust gas was 0.5 ppm by volume of acetic acid, 103 ppm by volume of methyl acetate, and 1100 ppm of methanol.
[0053]
Example 3
In FIG. 3, the washing water in the absorption tower 6 was 10 kg / hr, and the absorption liquid 900 kg / hr was boosted to 7.8 MPa by the pump 7 and supplied to the membrane separation devices 8 and 8a and the hydrolysis devices 10 and 10a. The concentrated liquids 650 kg / hr and 145 kg / hr of the membrane separators 8 and 8a were joined and refluxed to the distillation column 2 through the hydrolysis tank 10, and the permeate 105 kg / hr of the membrane separator 8a was discharged out of the system. Others were the same as in Example 2. The permeate was 0.1% acetic acid, 50 ppm methyl acetate, and 2010 ppm methanol. Further, the exhaust gas was 0.1 volume ppm, methyl acetate 212 volume ppm, and methanol 1050 ppm.
[0054]
Reference example 2
In the oxidation reactor shown in FIG. 4, para-xylene was oxidized at 190 ° C. and 1.2 MPa to produce terephthalic acid, and the oxidized exhaust gas was cooled to 120 ° C. by the oxidized exhaust gas condenser 3a and condensed. The exhaust gas from the oxidation exhaust gas condenser 3 a is cooled to 40 ° C. by the cooler 5, and the absorption liquid 210 kg / hr which has absorbed methyl acetate by contacting with 10 kg / hr of 35 ° C. water as the cleaning liquid in the absorption tower 6 is oxidized. A mixed liquid 685 kg / hr mixed with 465 kg / hr of condensate taken out from the exhaust gas condenser 3a is distilled at a reflux ratio 4 in the atmospheric pressure distillation tower 2, and 105 kg / hr of distillate from the top of the tower is discharged out of the system. did. The effluent was 1.5% acetic acid, 1.6% methyl acetate, and 0.1% methanol. The exhaust gas from the absorption tower was acetic acid 0.1 volume ppm, methyl acetate 500 volume ppm, and methanol 30 ppm.
[0055]
Example 4
In Reference Example 2, the condensed water taken out from the condenser 3 is pressurized to 4.9 MPa and sent to the membrane separation device 8 for membrane separation, and the concentrated solution 525 kg / hr is refluxed to the distillation column 2 and the permeate 105 kg / hr is supplied. It was discharged out of the system. The separation membrane was a reverse osmosis membrane SU-820 (trade name, manufactured by Toray Industries, Inc.) made of a crosslinked polyamide composite membrane, and the permeate was 0.3% acetic acid, 0.3% methyl acetate, and 0.08% methanol. It was. The exhaust gas was 0.1 ppm by volume of acetic acid, 700 ppm by volume of methyl acetate, and 50 ppm of methanol.
[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.
FIG. 4 is a flowchart showing a method for producing terephthalic acid according to still another embodiment.
FIG. 5 is a flowchart showing a method for producing terephthalic acid according to still another embodiment.
[Explanation of symbols]
1 Oxidation reactor
2 Distillation tower
3 Condenser
3a Oxidation exhaust gas condenser
4, 5 Cooler
6 Absorption tower
7 Pump
8, 8a Membrane separator
9, 9a Separation membrane
10, 10a Hydrolysis tank
11, 11a catalyst layer
12, 16 packed bed
13 Water receiving section
14 Concentrated liquid chamber
15 Permeate chamber
17 Reboiler
18 Pressure reducing valve

Claims (7)

An oxidation step for producing an aromatic carboxylic acid under high temperature and pressure by liquid phase oxidation of an alkyl aromatic compound with an oxygen-containing gas in a reaction solvent containing a lower aliphatic carboxylic acid in an oxidation reactor in the presence of an oxidation catalyst;
A distillation step of introducing oxidation exhaust gas from the oxidation reactor, or a condensate obtained by condensing the oxidation exhaust gas in the oxidation exhaust gas condenser to the distillation tower, performing distillation, and refluxing the fraction containing the reaction solvent to the oxidation reactor,
A condensation process in which the top gas from the distillation tower is cooled by a condenser to produce condensed water, and the condensed water is membrane-separated by a separation membrane consisting of a reverse osmosis membrane to produce a low molecular weight non-ionic substance containing water and alcohol A method for producing an aromatic carboxylic acid, comprising a membrane separation step of allowing the substance to permeate to the permeate side and concentrating and collecting the lower aliphatic carboxylic acid to the concentrate side. The exhaust gases leaving the condensation step is contacted with a washing liquid to absorb the aliphatic carboxylic acid esters, method of claim 1, including an absorption step for supplying the absorbing solution in the membrane separation step. The exhaust gases leaving the oxidation waste gas condenser is brought into contact with washing liquid to absorb the aliphatic carboxylic acid esters, method of claim 1, including an absorption step for supplying the absorbing solution in the distillation step. The invention includes a hydrolysis step in which condensed water, an absorption liquid, a permeate or a concentrate obtained by membrane separation of these is contacted with a hydrolysis catalyst to hydrolyze an aliphatic carboxylic acid ester, and the hydrolysis liquid is supplied to the membrane separation step. Item 4. The method according to any one of Items 1 to 3 . The method according to claim 4 , wherein the hydrolysis catalyst is an ion exchange resin. The method according to any one of claims 1 to 5 , wherein all or part of the condensed water is subjected to membrane separation, and the concentrate is refluxed to the distillation step. The method according to any one of claims 1 to 6 , wherein the membrane separation step is performed in a plurality of stages.

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