JP3864561B2 - 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.
[0003]
As a method for producing an aromatic carboxylic acid, in general, a methyl-substituted aromatic compound containing molecular oxygen is contained in a reaction solvent containing a lower aliphatic carboxylic acid such as acetic acid using a heavy metal compound and a bromine compound as a catalyst in an oxidation reactor. 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
[0004]
Since the oxidation exhaust gas discharged from the oxidation reactor is accompanied by a solvent, a catalyst, etc., in order to collect and reuse it, a distillation column connected to the upper part of the oxidation reaction tank is provided and the heat of the exhaust gas is used. There is a method in which the solvent is recovered by distillation and refluxed to the oxidation reaction tank (Japanese Patent Publication No. 54-14098). In this method, exhaust gas from the distillation tower is cooled with cooling water in a condenser to condense the vapor in the exhaust gas, and the condensed water is refluxed to the distillation tower and used for distillation.
[0005]
Thus, in an apparatus provided with a distillation tower at the upper part of the oxidation reactor, in order to recover energy, the exhaust gas of the distillation tower is heated or further burned and supplied to a turbine (expander) to recover energy. A method has been proposed (Japanese Patent Publication No. 9-511253, WO 97/27168). In general, energy recovery by a turbine requires a large heat drop, so in the above method, the exhaust gas is heated and supplied to the turbine without reducing the temperature by installing a condenser after the distillation column. Energy is recovered.
[0006]
However, since the exhaust gas obtained from the distillation tower contains acetic acid and other corrosive substances or scaling components in a small amount, there is a problem that the turbine is liable to be corroded or scaled. Further, in the above method, since the mother liquor separated from the purification step is circulated to the distillation tower, there is a problem that the remaining crystals are likely to be clogged due to accumulation in the distillation tower.
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide an aromatic group capable of efficiently recovering energy without obstructing the turbine, and capable of efficiently producing an aromatic carboxylic acid by performing distillation without clogging the distillation column. It is to propose a method for producing carboxylic acid.
[0008]
[Means for Solving the Problems]
The present invention is the following method for producing an aromatic carboxylic acid.
(1) Oxidation that generates an aromatic carboxylic acid under high temperature and high 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 in an oxidation reactor. Process,
Distillation step of introducing oxidation exhaust gas from the oxidation reactor into the distillation tower and performing distillation, and refluxing the fraction containing the reaction solvent to the oxidation reactor,
A condensing process that cools the exhaust gas from the distillation tower with a condenser to recirculate the condensed water to the distillation tower and newly generates water vapor,
A method for producing an aromatic carboxylic acid, comprising: a combustion process in which exhaust gas emitted from a condenser is combusted in a combustor; and an energy recovery process in which energy is recovered from water vapor obtained from the condenser and combustion exhaust gas obtained from the combustor.
(2) The method according to (1), wherein the condensing step sequentially condenses using a multi-stage condenser.
(3) The method according to (1) or (2) above, wherein the condenser has a kettle shape.
(4) The method according to any one of (1) to (3) above, wherein the temperature of exhaust gas from the condensation step is set to 50 to 150 ° C. and methyl acetate is maintained on the exhaust gas side.
(5) The method according to any one of (1) to (4), wherein energy is recovered by a steam turbine and a gas turbine in the energy recovery step.
(6) The method according to any one of (1) to (5) above, wherein the oxygen-containing gas is pressurized with the recovered energy and supplied to the oxidation reactor.
(7) The method according to any one of (1) to (6) above, wherein a liquid extraction part is provided in the distillation column.
[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]
An aromatic compound having a partially oxidized alkyl substituent is a compound in which an alkyl group in the above compound is partially oxidized and oxidized to the aldehyde group, acyl group, carboxyl group, hydroxyalkyl group or the like. 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 ppm, preferably 100 to 5000 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. If air is used as gas containing molecular oxygen, 2 to 20 nm ³ of the aromatic compound 1kg of the oxidizing material, preferably it is desirable to supply to the reaction system at a ratio of 2.5~15Nm ^3.
[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, the oxidation exhaust gas from the oxidation reactor is introduced into a distillation column (high pressure distillation column) connected to the upper part of the oxidation reactor, distillation is performed using the heat generated in the oxidation reactor, and the fraction containing the reaction solvent is removed. Reflux to the oxidation reactor from the bottom of the column, and vapor and non-condensable gas are discharged from the top of the column. The distillation column may be independent from the oxidation reactor as shown in JP-A-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 preferred. In this case, a means for collecting fine solids such as aromatic carboxylic acid crystals and catalysts, for example, a solid collection tray is used as the packed bed. What is provided in the lower side is preferable.
[0023]
By performing distillation in such a distillation column, a 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 them, solids such as aromatic carboxylic acid crystals and catalysts and components having a high boiling point are captured or distilled at the lower part of the distillation column, and reaction solvents such as aliphatic carboxylic acids having a low boiling point are distilled at a relatively upper part.
[0024]
Such fractions are directly refluxed to the oxidation reactor, but by providing a liquid extraction part in the distillation column, a large amount of reflux water enters the oxidation reactor and dilutes the reaction liquid when the reaction is stopped urgently. Can be prevented. In addition, the distillate can be always extracted from the liquid extraction part and used for washing the crystals separated into solid and liquid.
[0025]
In the condensation process, the exhaust gas from the distillation tower is cooled by cooling water with a condenser to condense the vapor in the exhaust gas, generate condensed water and recirculate it to the distillation tower, and evaporate the cooling water to newly generate water vapor. Let A plurality of condensers are used, and exhaust gas is sequentially passed through and condensed in stages, whereby low energy steam can be obtained separately from high energy steam.
[0026]
By using a kettle type condenser, water vapor can be generated without providing a container for generating water vapor. And by controlling the temperature of the condenser so that the temperature of the exhaust gas coming out of the condensation process is 80 ° C. or more, most of the methyl acetate and other impurities can be retained in the exhaust gas. It can be used effectively, for example, by refluxing it to the surface or by washing the crystal.
[0027]
In the combustion process, the exhaust gas emitted from the condenser is combusted in the combustor. At this time, if necessary, the exhaust gas is heated, and if necessary, auxiliary fuel is added and allowed to pass through the catalyst layer, so that combustible substances contained in the exhaust gas burn. In this case, methyl acetate may be recovered and returned to the oxidation reactor, but may be burned without recovery if recovery is expensive. Combustion decomposes pollutants such as methyl bromide and raises the temperature and pressure of the exhaust gas.
[0028]
In the energy recovery process, energy is recovered from water vapor obtained in the condensation process and exhaust gas obtained in the combustion process. By introducing these into separate steam turbines and gas turbines and recovering them as rotational energy, energy recovery can be carried out using a small device, but even if they are introduced into one gas turbine and recovered Good. When the condensers are installed in a plurality of stages, steam with different energy levels can be obtained, and these are introduced into different parts of the steam turbine to recover energy.
[0029]
The energy recovered in this way can be used to pressurize the oxygen-containing gas and introduce it into the oxidation reactor to efficiently perform the oxidation reaction, and can also be recovered as electric power. Specifically, by connecting the rotation shafts of the gas compressor and the generator directly to the rotation shafts of the steam turbine and the gas turbine and making these rotation shafts common, it is possible to improve the efficiency of energy recovery and utilization.
[0030]
Since the oxidation reaction is an exothermic reaction, energy is continuously generated. By recovering and utilizing this, the reaction can be made more efficient and the reaction cost can be reduced.
[0031]
【The invention's effect】
In the present invention, the steam in the exhaust gas coming out of the distillation tower is condensed, the condensed water is refluxed to the distillation tower, and water vapor is newly generated, and energy is recovered from this water vapor and combustion exhaust gas. It is possible to efficiently recover energy without giving water, and to efficiently produce an aromatic carboxylic acid by performing distillation without clogging the distillation column.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings for the production of terephthalic acid. FIG. 1 is a system diagram showing a method for producing terephthalic acid according to an embodiment. In FIG. 1, 1 is an oxidation reactor, a packed bed type distillation column 2 is directly connected to the upper part, and a plurality of kettle type condensers 3a, 3b, 3c,. Yes.
[0033]
The production method of terephthalic acid is to supply para-xylene as raw material alkyl aromatic compound, acetic acid as reaction solvent, heavy metal compound and bromine compound as catalyst from line L1 to oxidation reactor 1 and air as oxygen-containing gas from line L2. Supply and perform liquid phase oxidation under high temperature and high pressure to produce terephthalic acid. The produced terephthalic acid is precipitated as crystals, forming a slurry.
[0034]
The oxidation exhaust gas from the oxidation reactor 1 enters the distillation column 2 in a high temperature and high pressure state, and distillation is performed while passing through the packed bed. The solids contained in the oxidation exhaust gas are removed and refluxed by the lower solids collection tray. In the distillation column 2, the by-product of the high-boiling fraction is distilled at the lower part, and the acetic acid of the low-boiling fraction is distilled relatively at the upper part. These fractions are refluxed to the oxidation reactor 1 together with the solids as a bottom liquid.
[0035]
When the exhaust gas from the distillation tower 2 sequentially passes through the condensers 3a, 3b, 3c from the line L3, the steam in the exhaust gas is condensed by the cooling water on the shell side, and enters the steam separator 4 from the line L4. The condensed water is partly refluxed to the distillation column 2 from the line L5. In the condensers 3a, 3b, and 3c, the cooling water on the shell side evaporates by heat exchange, and water vapor is newly generated. This steam is high energy at high temperature and high pressure on the condenser 3a side, and the energy on the condenser 3c side is sequentially low energy. , L7 enters the condenser 6 to become condensate, and is branched from the line L8 to the lines L8a, L8b, L8c and circulated as cooling water to the condensers 3a, 3b, 3c.
[0036]
The exhaust gas separated by the steam separator 4 controls the temperature on the outlet side of the condenser 3c to 50 to 150 ° C., preferably 90 to 120 ° C., thereby maintaining methyl acetate and other impurities in a gas state. And introduced into the heater 7 from the line L9 and heated. The heated exhaust gas is introduced from the line L10 into the combustor 8 and passes through the catalyst layer to be burned. The combustion gas is introduced from the line L11 to the gas turbine 9 and expanded to recover energy as the rotational force of the turbine. The exhaust gas exiting the gas turbine 9 is introduced into the exhaust gas treatment device 10 from the line L12, and bromine compounds and the like are removed by adsorption or the like, and the exhaust gas is discharged from the line L13.
[0037]
The steam turbine 5 and the gas turbine 9 are connected to the same rotating shaft 11 to constitute an energy recovery device, and a gas compressor 12 and a generator 13 are connected to the rotating shaft 11 as a load. Thereby, the gas compressor 12 is driven using the rotational energy recovered by the steam turbine 5 and the gas turbine 9, the air supplied from the line L14 is compressed, and the oxygen-containing gas is supplied from the line L2 to the oxidation reactor 1. Then, an oxidation reaction is performed, and the generator 13 is rotated to recover energy as electric power.
[0038]
When starting up the apparatus, power is supplied to the generator 13 to drive the gas compressor 12, the steam turbine 5 and the gas turbine 9 to start the oxidation reaction, and the steam is sequentially discharged from the oxidation exhaust gas discharged as the oxidation reaction proceeds. Energy is recovered by the turbine 5 and the gas turbine 9. In the steady operation, the oxidation reaction is an exothermic reaction. Therefore, energy is continuously recovered from the heat generation, and the operation is performed by using the power of the pump and the like as well as the gas compressor 12 and heating.
[0039]
In the oxidation reactor 1, terephthalic acid is generated by the oxidation reaction and precipitates as crystals to form a slurry. The slurry is extracted from the line L 15 and is solid-liquid separated by the first solid-liquid separator 14. A part of the separated mother liquor is discharged from the line L16 in order to prevent accumulation of impurities, and most of the mother liquor is circulated from the line L17 to the oxidation reactor 1 via the line L1. The separated crystals are transferred from the line L18 to the second solid-liquid separator 15, and at this time, they are washed with acetic acid water extracted from the lower part of the distillation column 2 to the line L19 to be separated into solid and liquid. The line L20 is provided to draw out dilute acetic acid water from the distillation column 2 and prevent dilution of the reaction liquid in the oxidation reactor 1 during an emergency stop of the apparatus, and is normally closed.
[0040]
The mother liquor separated by the second solid-liquid separator 15 is circulated from the line L21 to the oxidation reactor 1, and the crystals are introduced from the line L22 into the dryer 16 and dried to obtain crude terephthalic acid (CTA). The first and second solid-liquid separators 14 and 15 use a single device, and may be washed with acetic acid water in the middle thereof, and the pressure is increased at an arbitrary position in the middle or front and rear thereof. May be reduced to a low pressure.
[0041]
The crude terephthalic acid dried in the dryer 16 is slurried with water that enters the mixer 17 from the line L23 and circulates through the line L24. The slurried crude terephthalic acid is dissolved by raising the temperature in the heating device 18. The dissolved crude terephthalic acid is introduced into a reduction reactor 19 filled with a palladium catalyst or the like and subjected to hydrogenation treatment, so that the impurities represented by 4-carboxybenzaldehyde (4-CBA) are reduced. Is done.
[0042]
After the reduction treatment, the reaction solution is introduced into the crystallization tank 20, the pressure is lowered, and the temperature of the mother liquor is evaporated to lower the temperature, thereby depositing purified terephthalic acid. The evaporated mother liquor water vapor is supplied to the heating device 18 from the line L28 and used as a part of the heat source. Heat that is insufficient in the warming device 18 due to dissolution of the crude terephthalic acid is compensated by high-pressure steam, hot oil, or the like. The slurry on which the purified terephthalic acid is deposited is separated into mother liquor and purified terephthalic acid by the solid-liquid separators 21 and 22.
[0043]
The mother liquor separated by the solid-liquid separator 21 is cooled by a cooling device 23 to precipitate impurities such as p-toluic acid. The deposited impurities are separated from the mother liquor by the separation device 24 and discharged out of the system from the line L30. The mother liquor from which the precipitated impurities have been removed is introduced into the extraction device 25, where it is combined with the mother liquor supplied from the line L28 and condensed in the heating device 18, and impurities that are not precipitated are extracted by paraxylene supplied from the line L31. After removal, it is sent to the line L32 as washing water, where it is mixed with the washing water supplied from the line L33 and mixed with the terephthalic acid crystals separated by the solid-liquid separator 21 and reslurried to carry out washing. Solid-liquid separation is performed in the separator 22.
[0044]
The separated liquid is returned from the line L24 to the mixer as reslurry water, and the crystals are dried by the dryer 26 and taken out from the line 34 as purified terephthalic acid (PTA). The excess water purified by the extraction device 25 is discharged from the line L35. In this case, since the reaction solvent and by-products are removed, the waste water treatment is easy. The paraxylene extracted by the extraction device 25 is introduced into the oxidation reactor 1 from the line L36 through the line L1.
[0045]
In the above method, the steam in the exhaust gas exiting the distillation tower 2 is condensed by the condensers 3a, 3b, 3c and then recovered by the gas turbine 9, so that the gas turbine is damaged by acetic acid or other corrosive substances or scaled substances. It is possible to recover energy by preventing the above. Since the cooling water used for condensation can be evaporated and recovered as steam by the steam turbine 5, there is little reduction in recovery efficiency compared to the case where energy is recovered from the entire exhaust gas. In this case, by performing condensation over several stages, water vapor having different energies can be recovered, and the energy recovery efficiency is increased.
[0046]
Further, the condensed water in the condensers 3a, 3b, and 3c is refluxed to the distillation column 2 to prevent the distillation column 2 from being clogged, thereby allowing efficient distillation. The water held in the distillation column 2 at the time of the emergency stop of the apparatus is extracted from the line L20, so that the reaction liquid in the oxidation reactor 1 can be prevented from being diluted and the apparatus can be easily restarted.
[0047]
In the above description, the washing water in the lines L32 and L33 may be changed to be introduced into the mixer 17. Further, two solid-liquid separators 14, 15 or 21, 22 are used in combination, but when using a device equipped with a washing mechanism such as a rotary screen or a centrifugal separator, one device can be used. .
[Brief description of the drawings]
FIG. 1 is a system diagram showing a method for producing terephthalic acid according to an embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Oxidation reactor 2 Distillation towers 3a, 3b, 3c Condenser 4 Steam separator 5 Steam turbine 6 Condenser 7 Heater 8 Combustor 9 Gas turbine 10 Exhaust gas treatment device 11 Rotating shaft 12 Gas compressor 13 Generator 14 , 15, 21, 22 Solid-liquid separators 16, 26 Dryer 17 Mixer 18 Heating device 19 Reduction reactor 20 Crystallization tank 23 Cooling device 24 Separation device 25 Extraction device

Claims (7)

An oxidation step for producing an aromatic carboxylic acid under high temperature and high 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 in an oxidation reactor;
A distillation step of introducing the oxidation exhaust gas from the oxidation reactor into the distillation column to perform distillation, and refluxing the fraction containing the reaction solvent to the oxidation reactor;
A condensing step for cooling the exhaust gas from the distillation tower with a condenser to recirculate the condensed water to the distillation tower and newly generating water vapor,
A method for producing an aromatic carboxylic acid, comprising: a combustion step of combusting exhaust gas emitted from a condenser in a combustor; and an energy recovery step of recovering energy from water vapor obtained from the condenser and combustion exhaust gas obtained from the combustor. The method according to claim 1, wherein the condensing step sequentially condenses with a plurality of stages of condensers. 3. A process according to claim 1 or 2, wherein the condenser is kettle shaped. The method according to any one of claims 1 to 3, wherein the temperature of exhaust gas from the condensation step is set to 50 to 150 ° C and methyl acetate is maintained on the exhaust gas side. The method according to claim 1, wherein energy is recovered by a steam turbine and a gas turbine in the energy recovery step. 6. The method according to claim 1, wherein the oxygen-containing gas is pressurized with the recovered energy and supplied to the oxidation reactor. The method according to any one of claims 1 to 6, wherein a liquid extraction part is provided in the distillation column.

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