TW201516029A - Process for producing terephthalic acid - Google Patents

Abstract

The present disclosure provides a process for preparing terephthalic acid; said process comprising oxidizing p-xylene with an oxidizing agent in the presence of a carboxylic acid solvent, at least one catalyst and at least one ionic liquid.

Description

Process for producing terephthalic acid

The present invention relates to a process for producing terephthalic acid.

Terephthalic acid is an organic compound of the formula C ₆ H ₄ (COOH) ₂ . This colorless solid is a general-purpose chemical used primarily as a polyester PET precursor for the production of garments and plastic bottles. The world production in 1970 was about 1.75 million tons. By 2006, the global demand for pure terephthalic acid (PTA) has exceeded 30 million tons. In the production of polybutylene terephthalate and other engineering polymers, there is a small but still considerable demand for terephthalic acid. In research laboratories, terephthalic acid has been commonly used as a component of synthetic metal-organic frameworks. Terephthalic acid is also used as a filler for some military smoke bombs, such as the most famous American M83 smoke bomb, which produces white smoke when burned. Due to its wide application, many methods for producing and purifying terephthalic acid have been developed in recent years.

The process for synthesizing terephthalic acid disclosed in some prior art documents is as follows: U.S. Patent 2,831,816 discloses a process for producing a polyaromatic acid such as terephthalic acid, which is obtained by placing an aromatic compound such as xylene in acetic acid. The metal catalyst and the bromine source are oxidized at 120 to 275 °C. In the oxidation reaction, the main intermediates formed are p-methylbenzoic acid and 4-carboxybenzaldehyde (4-CBA), and p-methylbenzoic acid is present in a solvent in a dissolved state. However, since both have a similar crystal structure, 4-CBA and the product will form a eutectic. The general term for terephthalic acid containing 4-CBA is crude terephthalic acid. It is highly undesirable to produce crude terephthalic acid (CTA) containing 4-CBA in the production of polymers because of its The role in the polymerization process is the chain terminator. Therefore, additional steps are required to further purify the CTA.

U.S. Patent 7,094,925 discloses a process for oxidizing an alkyl aromatic compound which comprises blending an aromatic compound with an oxidizing agent or sulfide in an ionic liquid and a nitrogen oxyacid. The ionic liquid used in the process comprises an organic anion selected from the group consisting of trifluoroacetate, acetate, methanesulfonate and combinations thereof, or a sulfur, nitrogen, phosphorus, ruthenium, An anion of selenium, tellurium, arsenic, antimony or bismuth, or an oxyanion of a metal. The process disclosed in U.S. Patent 7,094,425 is carried out under Bronsted acidic conditions.

U.S. Patent No. 2009/0326265 discloses the use of 1-ethyl-3-methylimidazolium bromide as a source of bromine during oxidation. According to the published information, the use of molecular bromine usually releases free bromine, causing corrosion of the equipment, while ionic liquids based on bromine sources do not release free bromine, which is advantageous for production.

In U.S. Patent 6,565,835, the use of methyl ethyl ketone (MEK) as a promoter is disclosed to replace the bromine source. However, the process disclosed in U.S. Patent 6,565,835 requires a large amount of catalyst. Another disadvantage of this process is that the organic promoter may be oxidized under process operating conditions, complicating the purification step.

U.S. Patent No. 6,153,790 discloses the use of a catalyst system comprising a combination of cobalt and zirconium to produce an aromatic carboxylic acid. The process disclosed in U.S. Patent No. 6,153,790 avoids the use of halogen promoters.

US Patent No. 2010/0174111 discloses a process for providing crystals of terephthalic acid, the process comprising: a) providing a component comprising terephthalic acid and one or more ionic liquids, and b) administering the components of step a) Combined with a non-solvent (water) to crystallize terephthalic acid.

US Patent No. 20120004449 discloses a process for oxidizing an alkyl aromatic compound, the process comprising forming a mixture comprising an alkyl aromatic compound, a solvent, a bromine source, and a catalyst. Contacting the mixture with an oxidizing agent to produce a solid oxide comprising at least one of an aromatic aldehyde, an aromatic alcohol, an aromatic ketone, and an aromatic carboxylic acid; wherein the solvent comprises a carboxylic acid having 1 to 7 carbon atoms and an ion a liquid selected from the group consisting of an imidazole ionic liquid, a pyridinium ionic liquid, a phosphonium ionic liquid, a tetraalkylammonium ionic liquid, and combinations thereof.

US Patent No. 2012/0004450 discloses a process for producing terephthalic acid using para-xylene, the process comprising forming a mixture comprising para-xylene, a solvent, a bromine source, a catalyst, and ammonium acetate (optional); The oxidizing agent is contacted to oxidize p-xylene to produce a solid oxide comprising terephthalic acid, 4-carboxybenzaldehyde and p-methylbenzoic acid; wherein the solvent comprises a carboxylic acid having 1 to 7 carbon atoms, a dialkyl group Imidazolium ionic liquid and water (optional).

US Patent 2012/0004451 discloses a process for producing terephthalic acid using para-xylene, the process comprising forming a mixture comprising para-xylene, a solvent, a bromine source, a catalyst, and ammonium acetate; oxidizing by contacting the mixture with an oxidizing agent. Para-xylene produces a solid oxide comprising terephthalic acid, 4-carboxybenzaldehyde and p-methylbenzoic acid; wherein the solvent comprises a carboxylic acid having from 1 to 7 carbon atoms.

US Patent No. 2012/0004454 discloses a mixture for oxidizing an alkyl aromatic compound, the mixture comprising: an alkyl aromatic compound, a solvent, a bromine source, and a catalyst; wherein the solvent comprises a carboxylic acid having 1 to 7 carbon atoms and An ionic liquid selected from the group consisting of an imidazole ionic liquid, a pyridinium ionic liquid, a phosphonium ionic liquid, a tetraalkylammonium ionic liquid, and combinations thereof.

U.S. Patent No. 2012/0004455 A1 discloses a component in solid terephthalic acid comprising terephthalic acid, p-toluic acid and 4-carboxybenzaldehyde; wherein the content of 4-carboxybenzaldehyde is less than about 4,000 ppm. The content of p-toluic acid is greater than about 2,000 ppm.

U.S. Patent No. 2012/0004456 A1 discloses the purification of crude terephthalic acid (first time) A process for containing impurities when concentrated, the process comprising: contacting crude terephthalic acid with a solvent comprising an ionic liquid to produce a solid terephthalic acid product, wherein the second concentration of impurities in the product is less than the first concentration. The ionic liquid used is selected from the group consisting of imidazolium ionic liquids, pyridinium ionic liquids, phosphonium ionic liquids, tetraalkylammonium ionic liquids, and combinations thereof.

The processes disclosed in the above patent documents do not discuss various other intermediates and by-products in the production of terephthalic acid. Moreover, these processes use an excess of bromine source as a promoter. Further, in these known inventions, different ionic liquids are used as a solvent in the oxidation step and the purification step. Therefore, it is desirable to develop a simple and economical process for the preparation of terephthalic acid which can reduce the number of chemicals and produce high purity terephthalic acid.

[purpose]

The present invention has the following objects: It is an object of the present invention to provide a process for preparing purified terephthalic acid.

Another object of the present invention is to provide an integrated process for the preparation and purification of terephthalic acid.

Still another object of the present invention is to provide a process for preparing terephthalic acid from a small scale to a large scale.

It is yet another object of the present invention to provide a simple, safe and cost effective process for the preparation of terephthalic acid.

According to the present invention, there is provided a process for the preparation of purified terephthalic acid, the process comprising the steps of: - oxidizing p-xylene using an oxidizing agent in the presence of a carboxylic acid solvent, at least one catalyst and at least one ionic liquid, Obtaining a mixture containing crude terephthalic acid; - separating the mixture for the first time to obtain crude terephthalic acid and a first mother liquor comprising an ionic liquid, a residual solvent, a catalyst and impurities; - dissolving the crude terephthalic acid in at least one ionic liquid and then recrystallizing the benzene Dicarboxylic acid; and treating terephthalic acid by using at least one ionic liquid, and second separating and purifying terephthalic acid, aiming to obtain purified terephthalic acid and a second mother liquor comprising ionic liquid and impurities; Process characteristics: a. The formed 4-carboxybenzaldehyde (4-CBA) is less than 4000 ppm; b. the ionic liquid used in the oxidation step, the dissolution step and the purification step are the same; and c. the ionic liquid content and para-xylene Just proportional.

In one embodiment, the process further includes the step of using a second mother liquor in a loop comprising the ionic liquid from the purification step to the oxidation step.

In another embodiment, the process further includes the step of using a first mother liquor in a loop, the mother liquor comprising an ionic liquid from a first separation step to an oxidation step or a purification step.

Typically, the ionic liquid used in the oxidation step, the dissolution step, and the purification step is a fresh ionic liquid or an ionic liquid present in the first or second mother liquor.

In one embodiment of the invention, the process further comprises the steps of: - separating the ionic liquid, the carboxylic acid solvent and the catalyst from the first mother liquor using a method selected from the group consisting of fractionation, extraction and membrane filtration. At least one of them, and - separate loops using the separated ionic liquid, carboxylic acid solvent, and catalyst.

In one embodiment of the invention, the process further comprises the step of adding at least one bromine source: HBr, NaBr, KBr, NH ₄ Br, benzyl bromide, monobromoacetic acid, dibromoacetic acid, bromide bromide, tetra Methyl bromide and ethylene dibromide.

Generally, the ionic liquid is at least one selected from the group consisting of an alkyl ionic liquid and an arylalkyl ionic liquid.

Typically, the ionic liquid comprises a cation selected from the group consisting of quaternary ammonium salts, choline salts, guanidines, phosphines, hydrazines, imidazolium, pyridinium, pyrrolidinium, morpholinium, quinolinium, isoquinolines. a group consisting of pyrene, pyrazolium and acridinium; further comprising an anion selected from the group consisting of chloride, bromide, fluoride, iodide, mesylate, tosylate, hydrosulfate, A group consisting of sulfates, alkyl sulfonates, phosphates, phosphonates, alkyl phosphates, nitrates, nitrites, carbonates, acetates, bicarbonates, hydroxides, and oxides.

In one embodiment, the ionic liquid comprises an organic cation selected from the group consisting of quaternary ammonium salts, choline salts, guanidine, phosphine ruthenium, osmium, imidazolium, pyridinium, pyrrolidinium, morpholinium, quinoline. a group consisting of hydrazine, isoquinolinium, pyrazolium and acridinium; and bromide as an anion.

In one embodiment of the invention, the ionic liquid is an arylalkyl ionic liquid selected from the group consisting of 1-benzyl-3-methylimidazolium bromide, 1-benzyl-3-methylimidazolium chloride , 1-benzyl-3-methylimidazolium acetate, 1-benzyl-3-methylimidazolium mesylate, 1-benzyl-3-methylimidazolium phosphate, benzyl tributylphosphonium bromide Benzyltributylammonium bromide, 1-phenyl-3-methylimidazolidinium, 1-phenyl-3-methylimidazolium bromide, 1-phenyl-3-methylimidazolium acetate, 1 -Phenyl-3-methylimidazolium mesylate, 1-phenyl-3-methylimidazolium phosphate, phenyltributylphosphonium bromide, phenyltributylammonium bromide, 1,3-two Benzylimidazolium chloride, 1,3-dibenzylammonium bromide, 1,3-dibenzylimidazolium acetate, 1,3-dibenzylimidazolium mesylate, and 1,3-dibenzylimidazole a group of phosphates.

In another embodiment of the invention, the ionic liquid is an alkyl ionic liquid selected from the group consisting of 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazole, 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium mesylate, 1-butyl 3-methylimidazolium phosphate, 1-ethyl-3-methylimidazole, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium acetate, 1 -ethyl-3-methylimidazolium mesylate, 1-ethyl-3-methylimidazolium phosphate, tetrabutylphosphonium chloride, tetrabutylphosphonium bromide, tetrabutylphosphonium acetate, tetra Butylphosphonium methanesulfonate, tetrabutylphosphonium phosphonium phosphate, trihexyltetradecylphosphine chloride, trihexyltetradecylphosphonium bromide, trihexyltetradecylphosphine acetate, trihexyl Tetradecylphosphonium decanoate, tetrabutylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium acetate, tetrabutylammonium methanesulfonate, tetrabutylammonium phosphate, choline chloride, bromine a group consisting of alkali, choline acetate, and choline mesylate.

Usually, the oxidation step is carried out at a temperature of from 100 to 250 ° C and a pressure of from 10 to 60 bar.

Generally, the step of dissolving terephthalic acid in an ionic liquid is carried out at a temperature of from 25 to 225 °C.

Generally, the concentration of the ionic liquid used in the oxidation step relative to the total reaction mass ranges from 0.04 to 50%.

Typically, the oxidant is oxygen or air.

Typically, the carboxylic acid solvent is acetic acid.

Typically, the catalyst comprises at least one metal compound selected from the group consisting of cobalt, magnesium, chromium, copper, nickel, vanadium, iron, molybdenum, tin, cerium, zirconium, hafnium and titanium.

Usually, the catalyst is selected from the group consisting of cobalt acetate, manganese acetate, barium acetate, potassium acetate, barium acetate, zirconium acetate, copper acetate, cobalt oxalate, manganese oxalate, barium oxalate, potassium oxalate, barium oxalate, zirconium oxalate, copper oxalate. At least one of the groups.

Typically, the ratio of ionic liquid to carboxylic acid solvent ranges from 1:1 to 1:20.

Generally, the concentration of the catalyst relative to the total reactive species ranges from 0.02 to 2.5%.

20‧‧‧Oxidation section

30‧‧‧ Crystallized section

40‧‧‧purification section

50‧‧‧Separation section

1 to 20 and 7A‧‧‧ pipelines

Figure 1 illustrates a process for producing terephthalic acid in accordance with an exemplary embodiment of the present invention.

Traditionally, terephthalic acid is produced by wet oxidation of para-xylene. In the wet In the oxidation process, acetic acid is used as a solvent, cobalt acetate and manganese acetate are used as catalysts, and hydrogen bromide is used as a promoter.

The molecular species detected during the wet oxidation process of para-xylene are: terephthalic acid (crude terephthalic acid) as main product; p-tolualdehyde, p-toluic acid and 4-carboxybenzaldehyde, etc. Intermediates; and by-products such as isophthalic acid, phthalic acid, m- or o-tolualdehyde, m- or o-toluenesulfonic acid, 2 or 3-carboxybenzaldehyde, 3 or 4-bromomethylbenzoic acid, Terephthalaldehyde, styrene, phenol, toluene, benzene, ethylbenzene, methyl ethylbenzene, formaldehyde, 1,3-cyclopentadiene, anthracene, methylnaphthalene, anthracene, phenanthrene, phenylacetylene, methylbiphenyl, two Phenylbutane, dimethyl fumarate, and 4,4-dimethylbibenzyl, vinyl acetylene. The intermediate is formed in large amounts and, in the wet oxidation of para-xylene, is finally converted to crude terephthalic acid. However, only a small amount of by-products are formed. Importantly, the product, intermediates, and by-products remain in solution during the reaction to achieve complete conversion. In the conventional process, the terephthalic acid crystals formed during the oxidation process enclose some intermediates such as 4-CBA. In order to produce PET with terephthalic acid, it is necessary to make the 4-CBA content in terephthalic acid not exceed 100 ppm. Therefore, in the conventional process, the terephthalic acid containing impurities also needs to be hydrogenated, and is intended to convert 4-CBA into p-toluic acid. After that, p-methylbenzoic acid also needs to be separated to obtain pure terephthalic acid.

To overcome the shortcomings of the prior art process, the present invention provides a simple, economical, and efficient process for the synthesis of pure terephthalic acid involving the use of ionic liquids. The inventors of the present process have found that in the production of terephthalic acid, the ionic liquid can be used both as a promoter and as a cosolvent.

The ionic compounds used in the process of the invention are capable of dissolving intermediates and by-products during the oxidation and purification stages. Advantageously, these intermediates remain dissolved in the ionic liquid and are further oxidized to the desired product during the terephthalic acid production process. Therefore, the concentration of the intermediate can be reduced by itself in the oxidation stage, thereby omitting the hydrogenation stage unlike the conventional production process. However, it is impossible to completely omit the purification stage because in the oxidation stage, Due to the similar structure of the two compounds, 4-CBA co-crystallization with terephthalic acid occurs. Extraction or controlled crystallization of 4-CBA from the crude terephthalic acid dissolved compound is required.

According to the present invention, the ionic liquid used in the process for preparing terephthalic acid is at least one selected from the group consisting of an alkyl ionic liquid and an arylalkyl ionic liquid. Typically, the ionic liquid comprises a cation selected from the group consisting of quaternary ammonium salts, choline salts, guanidines, phosphines, hydrazines, imidazolium, pyridinium, pyrrolidinium, morpholinium, quinolinium, isoquinolines. a group consisting of pyrene, pyrazolium and acridinium; further comprising an anion selected from the group consisting of chloride, bromide, fluoride, iodide, mesylate, tosylate, hydrosulfate, A group consisting of sulfates, alkyl sulfonates, phosphates, phosphonates, alkyl phosphates, nitrates, nitrites, carbonates, acetates, bicarbonates, hydroxides, and oxides. In a preferred embodiment, the ionic liquid comprises an organic cation selected from the group consisting of quaternary ammonium salts, choline salts, guanidines, phosphines, guanidines, imidazolium, pyridinium, pyrrolidinium, morpholinium, quinolin a group consisting of oxonium, isoquinolinium, pyrazolium and acridinium; and bromide as an anion. It has been found that the use of an ionic compound containing a bromine anion in the oxidation step and the purification step omits the need to add HBr, KBr, and the like.

In one embodiment of the invention, the ionic liquid employed is an arylalkyl ionic liquid selected from the group consisting of 1-benzyl-3-methylimidazolium bromide and 1-benzyl-3-methyl chloride. Imidazole, 1-benzyl-3-methylimidazolium acetate, 1-benzyl-3-methylimidazolium mesylate, 1-benzyl-3-methylimidazolium phosphate, benzyl tributyl bromide Phosphine, benzyl tributylammonium bromide, 1-phenyl-3-methylimidazole, 1-phenyl-3-methylimidazolium bromide, 1-phenyl-3-methylimidazolium acetate , 1-phenyl-3-methylimidazolium mesylate, 1-phenyl-3-methylimidazolium phosphate, phenyltributylphosphonium bromide, phenyltributylammonium bromide, 1,3 -dibenzylimidazolium chloride, 1,3-dibenzylammonium bromide, 1,3-dibenzylimidazolium acetate, 1,3-dibenzylimidazolium mesylate, and 1,3-dibenzyl A group consisting of pyrimidyl phosphates.

In another embodiment of the invention, the ionic liquid employed is an alkyl ion a liquid selected from the group consisting of 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazole imidazole, 1-butyl-3-methylimidazolium acetate, 1-butyl -3-methylimidazolium mesylate, 1-butyl-3-methylimidazolium phosphate, 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium mesylate, 1-ethyl-3-methylimidazolium phosphate, tetrabutylphosphonium chloride, tetrabutyl Phosphine bromide, tetrabutylphosphonium phthalate acetate, tetrabutylphosphonium methanesulfonate, tetrabutylphosphonium phosphonium phosphate, trihexyltetradecylphosphine chloride, trihexyltetradecylphosphonium bromide , trihexyltetradecylphosphine acetate, trihexyltetradecylphosphonium citrate, tetrabutylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium acetate, tetrabutylammonium methanesulfonate, A group consisting of tetrabutylammonium phosphate, choline chloride, choline bromide, choline acetate, and choline mesylate.

The invention provides an integrated process for synthesizing pure terephthalic acid, which comprises the steps of oxidation, purification, product crystallization, and recovery and reuse/recycling of solvents, ionic compounds and catalysts.

In particular, the integrated process of the present invention involves the steps of: in a first step, oxidizing p-xylene using an oxidizing agent in the presence of a carboxylic acid solvent, at least one catalyst, and at least one ionic liquid, with the aim of obtaining a crude p-benzene a mixture of dicarboxylic acids. Usually, the oxidation step is carried out at a temperature of from 100 to 250 ° C and a pressure of from 10 to 60 bar. In the oxidation step, the concentration of the ionic liquid relative to the total reaction mass is maintained between 0.04 and 50%. Typically, the oxidant is oxygen or air. Typically, the carboxylic acid solvent is acetic acid. Typically, the ratio of ionic liquid to carboxylic acid solvent is maintained between 1:1 and 1:20.

According to the invention, in the oxidation step, the catalyst used comprises at least one metal compound selected from the group consisting of cobalt, magnesium, chromium, copper, nickel, vanadium, iron, molybdenum, tin, cerium, zirconium, hafnium and titanium. Group. Usually, the catalyst is selected from the group consisting of cobalt acetate, manganese acetate, barium acetate, potassium acetate, barium acetate, zirconium acetate, copper acetate, cobalt oxalate, manganese oxalate, barium oxalate, potassium oxalate, barium oxalate, zirconium oxalate, copper oxalate. At least one of the groups.

Generally, the concentration of the catalyst used relative to the total reaction mass ranges from 0.02 to 2.5%.

The resulting mixture is then subjected to a first separation to obtain crude terephthalic acid and a first mother liquor comprising an ionic liquid, a residual solvent, a catalyst and impurities.

In the second step, the crude terephthalic acid is dissolved in at least one ionic liquid and then the terephthalic acid is recrystallized. Usually, the step of dissolving the crude terephthalic acid in the ionic liquid is carried out at a temperature of from 25 to 225 °C.

In addition, the dissolution process can also be carried out in stages. The crude terephthalic acid is dissolved in the ionic compound or ionic liquid mixture. Additionally, the dissolution step disclosed herein is followed by extraction of impurities in the same or another container.

The extraction of impurities is carried out in an ionic compound, a mixture of several ionic compounds or a mixture of ionic compounds and molecular solvents. The molecular solvent used in the present invention is selected from the group consisting of acetic acid, aliphatic or aromatic alcohols, water, or a combination of such solvents.

In the next step, terephthalic acid is treated by using at least one ionic liquid, and terephthalic acid is separated and purified a second time to obtain purified terephthalic acid and a second mother liquor comprising ionic liquids and impurities. The remaining mother liquor for each step is then recovered. The solid pure terephthalic acid obtained by the process of the present invention can be further filtered, washed and dried as needed.

The process of the present invention has the following characteristics: 4- formed 4-carboxybenzaldehyde (4-CBA) less than 4000ppm; ̇ used in the oxidation step, dissolution step and purification step are the same ionic liquid; and hydrazine ionic liquid content and paraxylene In direct proportion.

The process also includes the step of recycling a second mother liquor comprising an ionic liquid from a purification step to an oxidation step.

The process also includes the step of using a first mother liquor in a loop comprising an ionic liquid from a first separation step to an oxidation step or a purification step.

Generally, the ionic liquid used in the oxidation step, the dissolution step, and the purification step is Fresh ionic liquid or ionic liquid present in the first or second mother liquor.

The above process further comprises the steps of: separating the ionic liquid, the carboxylic acid solvent and the catalyst from the first mother liquor by a method selected from at least one of the group consisting of fractionation, extraction and membrane filtration; Ionic liquid, carboxylic acid solvent and catalyst.

The process of the present invention also includes the step of adding at least one source of bromine in the oxidation step. Typically, a bromine source selected from the group consisting of HBr, the group consisting of NaBr, KBr, NH ₄ Br, benzyl bromide, a bromo acetic acid, dibromo acetic acid, bromo-acetyl bromide, methyl bromide and ethylene dibromide four.

A process for producing terephthalic acid according to an exemplary embodiment of the present invention is shown in FIG.

The raw materials for the production of terephthalic acid, namely p-xylene, acetic acid and catalyst, enter the oxidation section (20) from lines 1, 2 and 3, respectively. The ionic liquid enters the oxidation section (20) through line 4. The reaction slurry line 5 is connected to a crystallization section (30) which functions to separate crude terephthalic acid (CTA). The separated CTA is sent to the purification section (40) through line 6 for purification. The mother liquor from the crystallization section (30) is passed through the line 7 into the oxidation section (20) for use in the loop. The mother liquor from the crystallization section (30) can also be transported through line 7A to the ionic liquid separation section (50) where it is separated by acetic acid and catalyst by fractional distillation, extraction, membrane filtration or a combination thereof. The recovered acetic acid and the catalyst are looped back to the oxidation section (20) through the line 8, and the separated ionic liquid is sent to the purification section (40) through the line 9 to purify the CTA. Further, the fresh ionic liquid can be supplied through the line 12. From the CTA purification section (40), through the line 10, the ionic liquid containing 4-CBA and other intermediate solutions are looped back to the oxidation section (20). The purified terephthalic acid is separated from the purification section (40) through a line 11.

The process of the present invention is further illustrated by the following examples. The sole purpose of the examples herein is to provide a Therefore, the examples should not be construed as limiting the scope of the embodiments in the specification.

Example: example 1:

A mixture of acetic acid, 1-butyl-3-methylimidazolium acetate and 1-benzyl-3-methylimidazolium bromide in a mixing ratio of 76:20:4 was used as a solvent at a temperature of 215 ° C and a pressure of 40 bar. Oxidized p-xylene (40.91 g). Cobalt acetate and manganese acetate (300 ppm and 400 ppm, respectively) were used as catalysts. After reacting for 3 hours, crude terephthalic acid (CTA) was separated from the mother liquor by filtration. CTA (61 g) was then sent to the purification section. By fractional distillation, 321 g of acetic acid was separated from the mother liquor, and at the same time, the organic matter and the catalyst were separated by a precipitation method. The obtained purified product of 1-butyl-3-methylimidazolium acetate and 1-benzyl-3-methylimidazolium bromide (105 g) was then sent to purify CTA. After CTA purification, the composition of 1-butyl-3-methylimidazolium acetate and 1-benzyl-3-methylimidazolium bromide was further recycled back to oxidation for the next round. In the purified terephthalic acid, the final content of 4-CBA was 150 ppm, and in CTA it was 252 ppm.

Example 2:

A mixture of acetic acid and tetrabutylphosphonium bromide in a mixing ratio of 80:20 was used as a solvent, and p-xylene (82 g) was oxidized at a temperature of 215 ° C and a pressure of 40 bar. Cobalt acetate and manganese acetate (1650 ppm and 1120 ppm, respectively) were used as catalysts. After reacting for 3 hours, crude terephthalic acid (CTA) was separated from the mother liquor by filtration. The obtained CTA (120 g) was sent to the purification section. By fractional distillation, 300 g of acetic acid was separated from the mother liquor, and at the same time, the organic matter and the catalyst were separated by a precipitation method. The purified tetrabutylphosphonium bromide was fed to the CTA purification section with fresh tetrabutylphosphonium bromide. After CTA purification, the tetrabutylphosphonium bromide is recycled back to oxidation for the next round. In the purified terephthalic acid, the final content of 4-CBA was 1%, and in CTA it was 1.9%.

Example 3:

A mixture of acetic acid and 1-benzyl-3-methylammonium imidazole in a mixing ratio of 70:30 was used as a solvent, and p-xylene (82 g) was oxidized at a temperature of 215 ° C and a pressure of 40 bar. Use B Cobalt acid and manganese acetate (300 ppm and 400 ppm, respectively) were used as catalysts. After reacting for 3 hours, crude terephthalic acid (CTA) was separated from the mother liquor by filtration. The obtained CTA (109 g) was sent to the purification section. By fractional distillation, 260 g of acetic acid was separated from the mother liquor, and at the same time, the organic matter and the catalyst were separated by a precipitation method. The purified 1-benzyl-3-methylimidazolium bromide was fed to the CTA purification section with fresh 1-benzyl-3-methylimidazolium bromide. After purification of the CTA, 1-benzyl-3-methylammonium bromide was oxidized back to oxidation for the next round. In the purified terephthalic acid, the final content of 4-CBA is 1000 ppm, and in CTA it is 3100 ppm.

Technological advancement and economic significance:

- The process of the present invention can reduce the formation of impurities such as 4-carboxybenzaldehyde (4-CBA) in the production of terephthalic acid, thereby producing high purity terephthalic acid.

- The process of the present invention omits additional steps such as hydrogenation.

- The process of the invention uses both ionic liquids and co-solvents as promoters.

- In one embodiment, the process of the invention uses the same ionic liquid in both steps (ie, oxidation and purification), after which the terephthalic acid, 4-CBA, other intermediates and by-products are maintained in solution form.

- The ionic compound containing a bromine anion is used in the oxidation and purification stages of the process of the present invention, and other bromine sources such as HBr, NaBr and KBr are omitted.

- The process of the present invention is economical due to repeated use/return recovery of solvent, ionic liquid and catalyst.

The word "comprise" (including) or its variants such as "comprises" or "comprising" as used throughout this specification shall be understood to include the stated elements, the whole or the steps, or a group of elements, Or steps included, but without exposing any other elements, elements or steps, nor a set of other elements, elements or steps.

The use of the expression "at least one", "at least" or "at least one" means that one or more elements, components or quantities are used, and such usage may occur in the disclosed embodiments. Designed to achieve one or more desired goals or outcomes. The values of the various physical parameters, the dimensions and the quantities given are only approximations, and the designation is greater or less than the value of these physical parameters, dimensions and quantities, and is intended to be within the scope of the invention and the claims.

Although certain embodiments of the invention have been disclosed, these embodiments are not intended to limit the scope of the invention. Variations or modifications of the various parts of the invention may be made by those skilled in the art after reviewing the invention disclosed herein. Such changes or modifications are in accordance with the spirit of the invention.

20‧‧‧Oxidation section

30‧‧‧ Crystallized section

40‧‧‧purification section

50‧‧‧Separation section

1 to 20 and 7A‧‧‧ pipelines

Claims (20)

A process for preparing purified terephthalic acid, the process comprising the steps of: i. oxidizing p-xylene using an oxidizing agent in the presence of a carboxylic acid solvent, at least one catalyst, and at least one ionic liquid, with the aim of obtaining a coarse pair a mixture of phthalic acid; ii. separating the mixture for the first time to obtain crude terephthalic acid and a first mother liquor comprising an ionic liquid, a residual solvent, a catalyst and impurities; iii. dissolving the crude terephthalic acid in at least one ion In the liquid, then recrystallizing terephthalic acid; and iv. treating the terephthalic acid by using at least one ionic liquid, and separating and purifying the terephthalic acid for the second time, aiming to obtain purified terephthalic acid and containing ions a second mother liquor of liquid and impurities; characterized by: a. 4-carboxybenzaldehyde (4-CBA) formed less than 4000 ppm; b. the same ionic liquid used in the oxidation step, the dissolution step, and the purification step; c. The ionic liquid content is proportional to p-xylene. The process of claim 1 further comprising the step of using a second mother liquor in a loop comprising the ionic liquid from the purification step to the oxidizing step. The process of claim 1, further comprising the step of using a first mother liquor in a loop, the mother liquor comprising an ionic liquid from the first separation step to the oxidation step or the purification step. The process of claim 1, wherein the ionic liquid used in the oxidizing step, the dissolving step, and the purifying step is a fresh ionic liquid or an ionic liquid present in the first or second mother liquor. The process of claim 1, further comprising the steps of: i. separating the ionic liquid, the carboxylic acid solvent and the catalyst from the first mother liquor by a method; the method is selected from at least one of the group consisting of fractionation, extraction and membrane filtration; ii. separately using the separated ionic liquid , carboxylic acid solvent and catalyst. The process of claim 1, further comprising the step of adding at least one bromine source: HBr, NaBr, KBr, NH ₄ Br, benzyl bromide, monobromoacetic acid, dibromoacetic acid, bromoethylene bromide, tetrabromomethane and dibromo Ethylene. The process of claim 1, wherein the ionic liquid is at least one selected from the group consisting of an alkyl ionic liquid and an arylalkyl ionic liquid. The process of claim 1, wherein the ionic liquid comprises a cation selected from the group consisting of a quaternary ammonium salt, a choline salt, a guanidine, a phosphonium, a guanidine, an imidazolium, a pyridinium, a pyrrolidinium, a morpholinium, a quin a group consisting of oxonium, isoquinolinium, pyrazolium and acridinium; further comprising an anion selected from the group consisting of chloride, bromide, fluoride, iodide, mesylate, toluene Esters, hydrosulfates, sulfates, alkyl sulfonates, phosphates, phosphonates, alkyl phosphates, nitrates, nitrites, carbonates, acetates, hydrogencarbonates, hydroxides and oxides The group formed. The process of claim 1 wherein the ionic liquid comprises an organic cation selected from the group consisting of quaternary ammonium salts, choline salts, guanidines, phosphonium ruthenium, osmium, imidazolium, pyridinium, pyrrolidinium, morpholinium, a group consisting of quinolinium, isoquinolinium, pyrazolium and acridinium; and bromide as an anion. The process of claim 1, wherein the ionic liquid is an arylalkyl ionic liquid selected from the group consisting of 1-benzyl-3-methylimidazolium bromide, 1-benzyl-3-methylimidazole, 1-benzyl-3-methylimidazolium acetate, 1-benzyl-3-methylimidazolium mesylate, 1-benzyl-3-methylimidazolium phosphate, benzyltributylphosphonium bromide, Benzyltributylammonium bromide, 1-phenyl-3-methylimidazolidinium, 1-phenyl-3-methylimidazolium bromide, 1-phenyl- 3-methylimidazolium acetate, 1-phenyl-3-methylimidazolium mesylate, 1-phenyl-3-methylimidazolium phosphate, phenyl tributylphosphonium bromide, phenyl tributyl Ammonium bromide, 1,3-dibenzylimidazolium chloride, 1,3-dibenzylammonium bromide, 1,3-dibenzylimidazolium acetate, 1,3-dibenzylimidazolium mesylate, And a group consisting of 1,3-dibenzylimidazolium phosphate. The process of claim 1, wherein the ionic liquid is an alkyl ionic liquid selected from the group consisting of 1-butyl-3-methylimidazolium bromide, 1-benzyl-3-methylimidazole, 1- Butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium mesylate, 1-butyl-3-methylimidazolium phosphate, 1-ethyl-3-methyl chlorination Imidazole, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium mesylate, 1-ethyl-3- Methylimidazolium phosphate, tetrabutylphosphonium chloride, tetrabutylphosphonium bromide, tetrabutylphosphonium acetate, tetrabutylphosphonium methanesulfonate, tetrabutylphosphonium phosphate, trihexyl-14 Alkylphosphine chloride, trihexyltetradecylphosphonium bromide, trihexyltetradecylphosphine acetate, trihexyltetradecylphosphonium citrate, tetrabutylammonium chloride, tetrabutyl bromide Groups of ammonium, tetrabutylammonium acetate, tetrabutylammonium methanesulfonate, tetrabutylammonium phosphate, choline chloride, choline bromide, choline acetate, and choline mesylate. The process of claim 1, wherein the oxidizing step is carried out at a temperature of from 100 to 250 ° C and a pressure of from 10 to 60 bar. The process of claim 1, wherein the step of dissolving the crude terephthalic acid in the ionic liquid is carried out at a temperature of from 25 to 225 °C. The process of claim 1, wherein the concentration of the ionic liquid to the total reaction material used in the oxidizing step ranges from 0.04 to 50%. The process of claim 1 wherein the oxidant is oxygen or air. The process of claim 1 wherein the carboxylic acid solvent is acetic acid. The process of claim 1 wherein the catalyst comprises at least one metal compound selected from the group consisting of cobalt, magnesium, chromium, copper, nickel, vanadium, iron, molybdenum, tin, cerium, zirconium, hafnium. And a group of titanium. The process of claim 1, wherein the catalyst is selected from the group consisting of cobalt acetate, manganese acetate, barium acetate, potassium acetate, barium acetate, zirconium acetate, copper acetate, cobalt oxalate, manganese oxalate, barium oxalate, potassium oxalate, barium oxalate, zirconium oxalate. And at least one of the group consisting of copper oxalate. The process of claim 1, wherein the ratio of the ionic liquid to the carboxylic acid solvent ranges from 1:1 to 1:20. The process of claim 1 wherein the concentration of the catalyst relative to the total reactive species ranges from 0.02 to 2.5%.