KR100744754B1 - Preparation method of aromatic carboxylic acid - Google Patents

Abstract

The present invention relates to a method for producing an aromatic carboxylic acid, and more particularly, supplying the hot mother liquor of the purification process to the upper part of the dehydration column and supplying the hot condensate obtained from the first condenser to the upper part (first step); The condenser is installed in three or four stages, the hot condensate from the first condenser is refluxed to the dehydration tower, and the exhaust gas from the first or second condenser is removed from the stripper in the condensate of the third condenser. The carboxylic acid and methyl acetate are removed, and the exhaust gas at 80-130 ° C. from the second or third condenser is fed to the hydrolysis tower to convert methyl acetate to acetic acid, and the condensate under the stripper needs hot water during the purification process. Supplying to the place, and removing the rest to the wastewater treatment plant (second step); And the exhaust gas from the last condenser is fed to the bottom of the absorber to absorb unreacted alkyl substituted aromatic compounds and unreacted lower aliphatic carboxylic acid esters in the exhaust gas by lower aliphatic carboxylic acids, and the liquid discharged from the lower portion of the absorber is oxidized. Recycled to the process, the upper end of the absorber provides an aromatic carboxylic acid production process comprising the step of absorbing the lower aliphatic carboxylic acid in the exhaust gas (water). According to the present invention, it is possible to eliminate the blockage of the dehydration tower, improve energy recovery efficiency, and significantly reduce the amount of unreacted alkyl substituted carboxylic acid and lower aliphatic carboxylic acid.

Description

Preparation method of aromatic carboxylic acid

1 is a view showing a manufacturing process of an aromatic carboxylic acid according to the present invention.

1: alkyl substituted aromatic compound 2: heavy metal catalyst and bromine

3: oxidation reactor 4: dehydration tower

5a: first condenser 5b: second condenser

6: stripper 7: third condenser

8: methyl acetate reactor 9: fourth condenser

10: absorber 11: lower aliphatic carboxylic acid

12: water 13: heat exchanger

14: air inflator 15: motor

16: steam turbine 17: air compressor

18: regenerative pyrolysis oxidation reactor 19: cooler

20: air 21: first crystallization tank

22: heat exchanger at the top of the crystal bath 24: reservoir

25: solid-liquid separator 26: dryer

27: liquid storage tank 28: inlet mixing tank

29: removed from process 31: refinery mixing tank

32: preheater 33: reduction reactor

34: 2nd crystal tank 35: 1st solid-liquid separation facility

36: secondary solid-liquid separation plant 37: dryer

38: product reservoir 39: condensate

The present invention provides a method for producing an aromatic aromatic carboxylic acid which liquid phase oxidizes an alkyl aromatic compound containing an alkyl substituent or a partially oxidized alkyl substituent with an oxygen-containing gas, thereby eliminating clogging of the dehydration tower and improving energy recovery efficiency. It is about.

Generally, aromatic aromatic carboxylic acids are used as basic raw materials for textiles, resins, etc., and also as basic raw materials for PET bottles. As a method for producing an aromatic carboxylic acid, an alkyl-substituted aromatic compound is molecularly formed in a reaction solvent containing heavy metal compounds such as cobalt and manganese and bromine compounds in an oxidation reactor, and containing lower aliphatic carboxylic acids such as acetic acid. Liquid phase oxidation by contact with an oxygen-containing gas is commercially available.

The oxidizing exhaust gas discharged from the liquid phase oxidation oxidation reactor contains a solvent. Therefore, a method of installing a distillation tower on top of the oxidation reactor for recovering and reusing it, distilling using heat of exhaust gas, recovering a solvent, and refluxing the oxidation reactor is known (US Patent 5,463,113).

In this method, the exhaust gas from the distillation column is cooled with cooling water in the condenser to condense the water vapor in the exhaust gas, and the condensate is refluxed in the distillation column for use in distillation. However, since the exhaust gas obtained from the distillation column contains a small amount of acetic acid or other corrosive substances and scaling components, there is a problem in that an air expander has problems such as corrosion and scaling.

In addition, as a method for recovering energy in the apparatus for installing a distillation column above the oxidation reactor, a method of recovering energy by heating the exhaust gas of the distillation column, burning it using a catalyst, and supplying it to an air expander has been proposed. (US Patent 5,723,656).

In general, since a large drop in heat is required for energy recovery by the turbine, the condenser is installed at the rear end of the distillation column so that the temperature is not lowered, and the exhaust gas is heated and supplied to the turbine to recover energy.

On the other hand, the exhaust gas of the oxidation reactor is directly condensed in the condenser, the condensate is distilled to circulate acetic acid to the oxidation reactor, and methyl acetate in the exhaust gas of the condenser is adsorbed onto the activated carbon. It is known to decompose it with steam, hydrolyze it to regenerate acetic acid, and circulate this acetic acid with an oxidation reactor (Japanese Patent Application Laid-Open No. 4-169551A).

Since this method condenses the exhaust gas of the oxidation reactor directly in the condenser, it is necessary to separate each component from both the condensate and the condenser exhaust gas, and the adsorption, desorption of activated carbon and the hydrolysis of methyl acetate for the separation of methyl acetate. There is such a problem that the operation becomes complicated due to this.

In Korean Patent Laid-Open No. 2000-5733, the exhaust gas discharged from the oxidation reactor is condensed at 50-150 ° C. in a condenser, a part of the condensate is refluxed to a distillation column, a part is supplied to a purification process, and the exhaust gas after condensation is Disclosed is a method for recovering energy from an air expander by recovering aliphatic carboxylic acid with washing water and then burning in a combustor.

This method maintains the aliphatic carboxylic acid ester in the condensation gas and burns it or recovers it to the absorption liquid containing aliphatic carboxylic acid and feeds it to the oxidation reactor.

In the former method, the aliphatic carboxylic acid ester cannot be recovered by burning the exhaust gas immediately.In the latter method, even when the aliphatic carboxylic acid ester is recovered, it accumulates in the oxidation reactor and only the concentration of the aliphatic carboxylic acid in the exhaust gas rises. There is a problem in that the combustion is discharged to the combustor through the absorber.

That is, the aliphatic carboxylic acid used in the method of producing the aromatic carboxylic acid occupies a large part in the cost of producing the aromatic carboxylic acid. The above method does not recover the aliphatic carboxylic acid ester, so the manufacturing cost increases. There is this.

In addition, when the exhaust gas is combusted and then supplied to the air expander, bromine generated from bromine compound combustion during exhaust gas combustion causes serious corrosion problems in the pipe and the air expander. In addition, in the above method, since the cooled condensate is refluxed in the distillation column, the high pressure steam generated in the cooler is reduced, thereby reducing the amount of electricity generated in the steam turbine.

A method of hydrolyzing by installing an ion exchange resin on the top of the dehydration column has also been proposed, but there is a problem that there is no commercialized ion exchange resin that can be used in this temperature range because the top of the dehydration column is maintained at a high temperature of 160 ° C or higher.

In order to solve the problems of the prior art, the present inventors effectively recover the aliphatic carboxylic acid ester and the unreacted alkyl substituted carboxylic acid generated in the preparation of the aromatic carboxylic acid. In addition, the present invention was completed by developing an aromatic carboxylic acid production method which increases energy recovery efficiency by preventing clogging of the dehydration tower using high-temperature condensate supplied from the condenser to the upper part of the dehydration tower.

In addition, another object of the present invention is to condense the high temperature condensed in the condenser after the dehydration column of the oxidation process instead of heating the purified water with a heat exchanger in order to supply the hot water of 100 ℃ or more used in the slurrying of the solid components in the purification process It is to provide an aromatic carboxylic acid production method by simplifying the equipment by supplying the condensate of.

Other objects and advantages of the invention will be described below and will be appreciated by the embodiments of the invention. In addition, the objects and advantages of the invention may be realized by the means and combinations indicated in the claims.

In order to achieve the above object, the present invention provides an aromatic carboxylic acid comprising oxidizing and purifying an alkyl aromatic compound, distillation, condensation and combustion of exhaust gas discharged after oxidation, and energy recovery from steam and combustion exhaust gas. In the manufacturing method,

Supplying the high temperature mother liquor of the purification process to the upper part of the dehydration column installed on the oxidation reactor and supplying the high temperature condensate obtained from the first condenser to the upper part (first step); The condenser is installed in three or four stages, the hot condensate from the first condenser is refluxed to the dehydration tower, and the exhaust gas from the first or second condenser is removed from the stripper in the condensate of the third condenser. The substituted carboxylic acid and methyl acetate are removed, and the exhaust gas at 80-130 ° C. from the second or third condenser is fed to the hydrolysis tower to convert methyl acetate to acetic acid, and the condensate under the stripper is subjected to hot water during the purification process. Supplying it to the place where it is needed, and removing the rest to the wastewater treatment plant (second step); And the exhaust gas from the last condenser is fed to the bottom of the absorber to absorb unreacted alkyl substituted aromatic compounds and unreacted lower aliphatic carboxylic acid esters in the exhaust gas by lower aliphatic carboxylic acids, and the liquid discharged from the lower portion of the absorber is oxidized. Recycled to the process, the upper end of the absorber provides a method for producing an aromatic carboxylic acid comprising the step (third step) of absorbing the lower aliphatic carboxylic acid in the exhaust gas with water.

Here, it is preferable to further supply purified water to the upper part of the dehydration column for supplying the hot condensate water obtained in the first condenser.

In addition, the stripper lower condensate is preferably supplied to the refinery mixing tank or the first solid-liquid separation facility during the purification process.

Furthermore, the acetic acid obtained by the methyl acetate hydrolysis step in the hydrolysis column is preferably recovered by an oxidation reactor.

In addition, the steam generated in each condenser is supplied to the steam turbine is converted into energy, the exhaust steam from the steam turbine is preferably heated up in the heat exchanger after condensation and supplied to each condenser.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Prior to this, terms or words used in the present specification and claims should not be construed as being limited to the common or dictionary meanings, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention.

Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiments of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

In the present invention, an aromatic compound having an alkyl substituent may be used as a raw material for producing an aromatic carboxylic acid. Such an aromatic compound may be a monocyclic or polycyclic compound, and examples of the alkyl substituent include alkyl groups having 1 to 4 carbon atoms such as methyl group, ethyl group n-propyl group, and isopropyl group, but are not limited thereto. . In addition, some oxidized alkyl substituents may include, for example, an aldehyde group, a carboxyl group G hydroxy alkyl group, and the like.

In the present invention, it is preferable to use a heavy metal compound and a bromine compound as a catalyst. Heavy metals include cobalt, manganese, nickel, chromium, copper, titanium, cerium, and the like. These may be used alone or in combination, but it is particularly preferable to use a combination of cobalt and manganese.

Examples of the bromine compound include inorganic bromine compounds such as molecular bromine, hydrogen bromide, potassium bromide, cobalt bromide and manganese bromide, and organic bromine compounds such as bromobenzyl and tetrabromoethane. These bromine compounds are used individually or in mixture of 2 or more types.

As the molecular oxygen-containing gas, oxygen, air, and the like can be cited, but air is generally used.

On the other hand, examples of the lower aliphatic carboxylic acid used as the reaction solvent include acetic acid, propionic acid and butyric acid. Lower aliphatic carboxylic acids may be used alone or in admixture with water as a reaction solvent.

In addition, the temperature of the oxidation reaction is usually 150-220 ° C, preferably 180-200 ° C. If the temperature of the oxidation reaction is less than 150 ℃ causes a problem that the oxidation reaction does not proceed, if the temperature exceeds 220 ℃ may cause a problem that the yield of the alkyl substituent aromatic compound combustion reaction with oxygen in the air is sharply lowered yield Can be. In addition, the reaction pressure should just be a pressure more than the pressure which can maintain a reaction system in a liquid phase.

The present invention applies to the preparation of aromatic carboxylic acids, and particularly to the preparation of terephthalic acid.

In the present invention, the condensate vapor in the exhaust gas from the dewatering tower is condensed, once the condensate generated in the condenser is refluxed to the dehydration tower to remove the blockage caused by solid components in the mother liquor entering the dehydration tower, the top of the dehydration tower Minimize the flow rate of the supplied cold water, and in this process, increase the generation of high pressure steam to improve energy recovery efficiency.

Conventionally, the aliphatic carboxylic acid ester is absorbed into the absorbent liquid containing aliphatic carboxylic acid and circulated to the oxidation reactor, thereby attempting to suppress the generation of the aliphatic carboxylic acid ester in the oxidation reactor, but the results are insignificant.

Therefore, a method of hydrolyzing by installing an ion exchange resin on top of the dehydration column has also been proposed, but since the top of the dehydration tower is maintained at a high temperature of 160 ° C. or higher, there is no commercialized ion exchange resin that can be used in this temperature range.

In the present invention, the aliphatic carboxylic acid ester may be converted into aliphatic carboxylic acid in a hydrolysis tower packed with an ion exchange resin usable up to 130-140 ° C. and reused in an oxidation reaction process.

In addition, according to the present invention, since the exhaust gas from the steam turbine is not supplied to the condenser immediately after condensing in the cooler, but is supplied to the condenser after the primary heating through heat exchange in the upper part of the crystal bath, the amount of steam generated in the condenser is supplied. Increase by more than 10%.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. However, the scope of the present invention is not limited only to the description of these examples.

1 is a view showing a manufacturing process of an aromatic carboxylic acid according to the present invention. In FIG. 1, 1 is an alkyl substituted aromatic compound, 2 is a heavy metal catalyst and a bromine compound, 3 is an oxidation reactor, and the dehydration tower 4 is installed in the upper part of an oxidation reactor.

First, three water supply pipes are installed in the upper part of the dehydration tower 4 so that the lowermost pipe is supplied with the mother liquid supplied from the primary solid-liquid separation facility 35, and the upper part of the mother liquid pipe is supplied from the first condenser 5a. The high temperature condensate being supplied.

Next, the mother liquor supplied from the refining process separation equipment 35 contains 1-3 wt% of solid components, which may cause clogging in the dehydration tower 4, thereby supplying purified water at low temperature. Rather than supplying hot condensate at 130-165 ° C. as in the present invention, the solid component solubility may be increased to effectively remove the solid component. In addition, a small amount of purified water is supplied to the top to minimize organic compounds going to the condenser.

In addition, the condenser may be composed of three or four stages, the first condenser (5a) generates hot steam and hot condensate, the hot condensate is refluxed to the dehydration tower (4) as described above.

In addition, in the second condenser 5b and the third condenser 7, medium level steam and condensate are generated, and the exhaust gas from the first condenser 5a or the second condenser 5b is discharged from the stripper 6. The unreacted alkyl substituted carboxylic acid and methyl acetate in the condensate of the third condenser 7 are removed, and the exhaust gas at 80-130 ° C. from the third condenser 7 is fed to the methyl acetate hydrolysis tower 8. Convert methyl acetate to acetic acid.

The condensed water in the lower portion of the stripper 6 is supplied where hot water is needed during the purification process such as the purification mixing tank 31 and the primary solid-liquid separation facility 35, and the rest is supplied to the wastewater treatment plant. In addition, the liquid from the lower part of the hydrolysis tower 8 is supplied to the inlet mixing tank 28.

The absorber 10 is composed of upper and lower parts, and the lower part absorbs unreacted methyl acetate and unreacted alkyl substituted aromatic compound in the exhaust gas with a low temperature aliphatic carboxylic acid, and the upper part is exhaust gas using water 12. Absorb the aliphatic carboxylic acid in. In addition, the liquid exiting the absorber bottom is fed to the inlet mixing tank 28 and recovered to the oxidation reactor 3.

On the other hand, the exhaust gas discharged from the upper end of the absorber 10 is heated up in the heat exchanger 13 using the high-pressure steam generated in the condenser as a high temperature heat source, and then supplied to the air expander 14 to recover energy, Impurities are treated in a high efficiency regenerative thermal oxidizer (18) of 95% or higher and then released into the atmosphere.

In addition, the steam generated in the condenser is supplied to the steam turbine 16 is converted into energy, the air 20 is supplied to the oxidation reactor at a high temperature and high pressure through the air compressor 17, the power used in the air compressor is a steam turbine It is supplied through the 16, the air expander 14, and the motor 15. The exhaust steam generated in the steam turbine 16 is condensed in the cooler 19, and then heated up in the crystal bath upper heat exchanger 22 and supplied to the condensers 5a, 5b, and 7 again.

Next, the high temperature and high pressure slurry from the oxidation reactor 3 is decompressed in the first crystal bath 21, and the steam generated is condensed in the heat exchanger 22 located above the first crystal bath 21. It is refluxed to the first crystal bath 21.

At this time, the first crystal bath 21 may be composed of two stages to four stages, and in order to increase product yield, secondary oxidation may be performed by additionally supplying compressed air of an air compressor to the first crystal tank 21. . In addition, after the secondary oxidation, it may be elevated to high temperature and high pressure, and the third oxidation may be performed to minimize impurities in the reactant.

In addition, the slurry from the first crystal bath 21 is supplied to a storage tank 24 operated at atmospheric pressure and 100 ° C., and is supplied to the solid-liquid separator 25. The solid component in the solid-liquid separator 25 may be transferred to a dryer 26 and then transferred to a tablet mixing tank 31 after drying, or may be used as a low quality terephthalic acid. In addition, the liquid from the solid-liquid separator 25 is transferred to the liquid storage tank 27 and then supplied to the inlet mixing tank 28, some of which is removed 29 in the process for removing impurities.

Subsequently, water and terephthalic acid are mixed in the purification mixing tank 31 and then transferred to a reduction reactor 33 through a preheater 32. In the reduction reactor 33, impurities in terephthalic acid are converted into hydrogen. Remove

Subsequently, the slurry is transferred to the second crystal bath 34 to reduce the temperature. The steam generated at this time is supplied to a heat source of the preheater 32, and a part of the condensed water 39 generated after heat exchange in the preheater is reused as purified water. The rest is transferred to a wastewater treatment plant.

In addition, the slurry from the second crystal bath 34 is separated into a solid and a liquid in the first solid-liquid separation plant 35, the liquid is recovered in the dehydration tower (4), the solid is again 50% by weight of the slurry After the production is supplied to the secondary solid-liquid separation equipment 36, it is transferred to the product storage tank 38 through the dryer 37. The solid-liquid separation plant is preferably secondary, but may be primary.

As described above, although the present invention has been described by means of a limited embodiment and drawings, the present invention is not limited thereto and is described below by the person skilled in the art to which the present invention pertains. Various modifications and variations are possible without departing from the scope of the appended claims.

As described above, the process for preparing the aromatic carboxylic acid of the present invention provides the following effects.

First, the high-temperature condensed water generated in the first condenser can be refluxed to the dehydration tower to remove the blockage due to the solid component in the mother liquid entering the dehydration tower.

Second, it minimizes the flow rate of the cold water supplied to the top of the dehydration tower, and in this process can increase the generation of high-pressure steam to improve the energy recovery efficiency.

Third, the exhaust steam generated in the steam turbine can be condensed in the cooler and then heated up in the crystallization top heat exchanger and supplied to the condenser at the rear end of the dehydration tower to maximize steam generation.

Fourth, by converting and recovering the by-product methyl acetate to acetic acid using an ion exchange resin in a methyl acetate hydrolysis column maintained at 80-130 ℃, not only reduces the amount of acetic acid used in the production more than 10-20%, Unreacted alkyl substituted aromatic compounds can be recovered back to the process to increase product yield.

Claims (5)

In the method of producing an aromatic carboxylic acid comprising the step of oxidizing and purifying an alkyl aromatic compound, distillation, condensation and combustion of exhaust gas discharged after oxidation, and energy recovery from steam and combustion exhaust gas, Supplying the high temperature mother liquor of the purification process to the upper part of the dehydration column installed on the oxidation reactor and supplying the high temperature condensate obtained from the first condenser to the upper part (first step); The condenser is installed in three or four stages, the hot condensate from the first condenser is refluxed to the dehydration tower, and the exhaust gas from the first or second condenser is removed from the stripper in the condensate of the third condenser. The substituted carboxylic acid and methyl acetate are removed, and the exhaust gas at 80-130 ° C. from the second or third condenser is fed to the hydrolysis tower to convert methyl acetate to acetic acid, and the condensate under the stripper is subjected to hot water during the purification process. Supplying it to the place where it is needed, and removing the rest to the wastewater treatment plant (second step); And The exhaust gas from the last condenser is fed to the bottom of the absorber to absorb unreacted alkyl substituted aromatic compounds and unreacted aliphatic carboxylic acid esters in the exhaust gas by aliphatic carboxylic acid, and the liquid discharged from the lower portion of the absorber is recycled to the oxidation process. At the top of the absorber, absorbing aliphatic carboxylic acid in the exhaust gas with water (third step) Method for producing an aromatic carboxylic acid, characterized in that comprises a. The method of claim 1, And further supplying purified water to the upper part of the dehydration tower for supplying the high-temperature condensed water obtained in the first condenser. The method of claim 1, The stripper lower condensate is supplied to a refinery mixing tank or a first solid-liquid separation facility during the refining process. The method of claim 1, The acetic acid obtained in the hydrolysis column is recovered by an oxidation reactor. The method of claim 1, The steam generated in each condenser is supplied to the steam turbine is converted into energy, the exhaust steam from the steam turbine is heated up in the heat exchanger after condensation is supplied to each condenser.

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