Composition for preparing terephthalic acid

Abstract

The present disclosure provides a composition for preparing terephthalic acid; said composition comprises p-Toluic acid in an amount of 0.05% to 4% with respect to the total mass of the composition; at least one catalyst in an amount of 0.02% to 2.5% with respect to the total mass of the composition; at least one ionic liquid in an amount of 0.04% to 50% with respect to the total mass of the composition; at least one carboxylic acid solvent; and p-xylene. The present disclosure also provides a process for preparing terephthalic acid.

Claims

1. A composition for preparing terephthalic acid; said composition consisting essentially of: i. p-Toluic acid in an amount of 0.05% to 4% with respect to the total mass of the composition; ii. at least one catalyst in an amount of 0.02% to 2.5% with respect to the total mass of the composition; iii. at least one ionic liquid in an amount of 0.04% to 50% with respect to the total mass of the composition; iv. at least one carboxylic acid solvent; and v. p-xylene, said composition when used in the preparation of terephthalic acid, results in the formation of less than 2000 ppm of 4-carboxy-benzaldehyde (4-CBA).

2. The composition as claimed in claim 1, wherein the proportion of the ionic liquid to the carboxylic acid solvent ranges between 1:1 and 1:20.

3. The composition as claimed in claim 1, wherein the ionic liquid is at least one selected from the group consisting of alkyl ionic liquids and aryl alkyl ionic liquids.

4. The composition as claimed in claim 1, wherein the ionic liquid comprises an organic cation selected from the group consisting of quaternary ammonium, cholinium, sulfonium, phosphonium, guanidinium, imidazolium, pyridinium, pyrrolidinium, morpholinium, quinolinium, isoquinolium, pyrazolium and piperidinium; and an anion selected from the group consisting of chloride, bromide, fluoride, iodide, mesylate, tosylate, hydrogen sulfate, sulfate, alkyl sulfonate, phosphates, phosphonates, akyl phosphates, nitrates, nitrites, carbonates, acetates, bicarbonates, hydroxides and oxides.

5. The composition as claimed in claim 1, wherein the ionic liquid comprises a combination of at least one alkyl ionic liquid and at least one aryl alkyl ionic liquid.

6. The composition as claimed in claim 1, wherein the catalyst comprises at least one metal compound, the metal being selected from the group consisting of cobalt, magnesium, chromium, copper, nickel, vanadium, iron, molybdenum, tin, cerium, zirconium, cesium and titanium.

7. The composition as claimed in claim 1, wherein the catalyst is at least one selected from the group consisting of cobalt acetate, manganese acetate, cerium acetate, potassium acetate, cesium acetate, zirconium acetate, copper acetate, cobalt oxalate, manganese oxalate, cerium oxalate, potassium oxalate, cesium oxalate, zirconium oxalate and copper oxalate.

8. The composition as claimed in claim 1, wherein the carboxylic acid solvent is acetic acid.

9. A process for preparing terephthalic acid; said process consisting essentially of the following steps: preparing a composition comprising p-Toluic acid in an amount of 0.05% to 4% with respect to the total mass of the composition; at least one catalyst in an amount of 0.02% to 2.5% with respect to the total mass of the composition; at least one ionic liquid in an amount of 0.04% to 50% with respect to the total mass of the composition; at least one carboxylic acid solvent and p-xylene; and oxidizing said composition in the presence an oxidizing agent selected from the group consisting of oxygen and air, at a temperature of 100 to250° C. and at a pressure of 10 to 60 bar to obtain terephthalic acid, the content of 4-carboxy-benzaldehyde (4-CBA) being less than 2000 ppm.

Description

DETAILED DESCRIPTION

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

(2) Molecular species that are detected during the wet oxidation process of para-xylene are terephthalic acid as a main product (crude terephthalic acid), intermediates such as para-tolualdehyde, para-toluic acid,4-carboxybenzhaldehyde and side products such as isophthalic acid, phthalic acid, meta or ortho-tolualdehyde, metaor ortho-toluic acid, 2 or 3-carboxybenzhaldehyde, 3 or 4-Bromo methyl benzoic acid, benzoic acid, trimelliticacids, trimesic acid, benzaldehyde, phthalaldehyde, ethylbenzaldehyde, methylstyrene, diphenic acid, 2-biphenyl carboxylic acid, hemi melitic acid, dimethyl terephthalate, methyl p-toulate, 3-hydroxy 4-methyl benzoic acid, terephthal aldehyde, styrene, phenol, toluene, benzene, ethylbenzene, methylethylbenzene, formaldehyde, 1,3-cyclopentadiene, indene, methylnaphthalene, anthracene, phenantrene, phenylacetylene, methylbiphenyl, diphenylbutane, naphthalene, and 4,4-dimethylbibenzyl, vinylacetylene. The intermediates form in large amount and eventually convert into crude terephthalic acid during the wet oxidation of para-xylene.

(3) It is important that the product, intermediates and side-products remain in soluble state during the reaction for complete conversion. In the conventional process, terephthalic acid crystals formed during the oxidation trap some of intermediates such as 4-CBA. It is known that to produce PET from terephthalic acid, it is essential to have 4-CBA content as low as 100 ppm in terephthalic acid. Therefore, in the conventional process, the impure Terephthalic acid again needs to be subjected to hydrogenation to convert 4-CBA into p-toulic acid. Subsequently, p-toulic acid needs to be separated to obtain pure Terephthalic acid.

(4) The inventors of the present disclosure have developed a starting mixture or composition which can be successfully oxidized to produce pure terephthalic acid.

(5) Initially, the inventors of the present disclosure found that the ionic liquids can be used as a promoter as well as co-solvent. The ionic compounds solubilize the intermediates and side products during the oxidation. It is advantageous to keep these intermediates in dissolved form in the ionic compounds, as they can be further oxidized into the desired product during the manufacturing of terephthalic acid. Thus the concentration of intermediates can be reduced during the oxidation stage itself, thereby eliminating hydrogenation stage as against the conventional manufacturing process.

(6) Further, the inventors of the present disclosure surprisingly found that incorporation of p-Toulic acid in the mixture or composition meant for oxidation significantly reduces the 4-carboxy-benzaldehyde (4-CBA) content in the terephthalic acid which in turn provides terephthalic acid in a highly pure form. Accordingly, the present disclosure provides a composition for preparing purified terephthalic acid, which essentially comprises p-Toluic acid. The effect of initial addition of p-Toluic acid is illustrated in the examples.

(7) In accordance with the first aspect of the present disclosure there is provided a composition for preparing purified terephthalic acid. The composition contains p-Toluic acid in an amount of 0.05% to 4% with respect to the total mass of the composition; at least one catalyst in an amount of 0.02% to 2.5% with respect to the total mass of the composition; at least one ionic liquid in an amount of 0.04% to 50% with respect to the total mass of the composition; at least one carboxylic acid solvent; and p-xylene. The composition is adapted to reduce the formation of 4-carboxy-benzaldehyde (4-CBA) to less than 2000 ppm during the preparation of terephthalic acid.

(8) In the present composition the proportion of the ionic liquid to the carboxylic acid solvent is maintained between 1:1 and 1:20.

(9) In accordance with the present disclosure the ionic liquid is at least one selected from the group consisting of alkyl ionic liquids and aryl alkyl ionic liquids. The ionic liquid comprises an organic cation selected from the group consisting of quaternary ammonium, cholinium, sulfonium, phosphonium, guanidinium, imidazolium, pyridinium, pyrrolidinium, morpholinium, quinolinium, isoquinolium, pyrazolium and piperidinium; and an anion selected from the group consisting of chloride, bromide, fluoride, iodide, mesylate, tosylate, hydrogen sulfate, sulfate, alkyl sulfonate, phosphates, phosphonates, akyl phosphates, nitrates, nitrites, carbonates, acetates, bicarbonates, hydroxides and oxides.

(10) In one embodiment the ionic liquid is at least one aryl alkyl ionic liquid which includes but is not limited to 1-benzyl, 3-methyl imidazolium bromide; 1-benzyl, 3-methyl imidazolium chloride; 1-benzyl, 3-methyl imidazolium acetate; 1-benzyl, 3-methyl imidazolium methane sulfonate; 1-benzyl, 3-methyl imidazolium phosphate; Benzyl tributyl phosphonium bromide, Benzyl tributyl ammonium bromide; 1-phenyl, 3-methyl imidazolium chloride; 1-phenyl, 3-methyl imidazolium bromide; 1-phenyl, 3-methyl imidazolium acetate; 1-phenyl, 3-methyl imidazolium methane sulfonate; 1-phenyl, 3-methyl imidazolium phosphate; Phenyl tributyl phosphonium bromide; Phenyl tributyl ammonium bromide; 1,3-dibenzyl imidazolium chloride; 1,3-dibenzyl imidazolium bromide; 1,3-dibenzyl imidazolium acetate; 1,3-dibenzyl imidazolium methane sulfonate; and 1,3-dibenzyl imidazolium phosphate.

(11) In another embodiment the ionic liquid is at least one alkyl ionic liquid which includes but is not limited to 1-butyl, 3-methyl imidazolium bromide; 1-butyl, 3-methyl imidazolium chloride; 1-butyl, 3-methyl imidazolium acetate; 1-butyl, 3-methyl imidazolium methane sulfonate; 1-butyl, 3-methyl imidazolium phosphate; 1-ethyl, 3-methyl imidazolium chloride; 1-ethyl, 3-methyl imidazolium bromide; 1-ethyl, 3-methyl imidazolium acetate; 1-ethyl, 3-methyl imidazolium methane sulfonate; 1-ethyl, 3-methyl imidazolium phosphate; Tetrabutyl phosphonium chloride; Tetrabutyl phosphonium bromide; Tetrabutyl phosphonium acetate; Tetrabutyl phosphonium methane sulfonate; Tetrabutyl phosphonium phosphate; Trihexyl Tetradecyl phosphonium chloride; Trihexyl Tetradecyl phosphonium bromide; Trihexyl Tetradecyl phosphonium acetate; Trihexyl Tetradecyl phosphonium decanoate; Tetrabutyl ammonium chloride; Tetrabutyl ammonium bromide; Tetrabutyl ammonium acetate; Tetrabutyl ammonium methane sulfonate; Tetrabutyl ammonium phosphate; Choline chloride; Choline bromide; choline acetate; and choline methane sulfonate.

(12) In accordance with another embodiment of the present disclosure the ionic liquid employed in the composition comprises a combination of at least one alkyl ionic liquid and at least one aryl alkyl ionic liquid.

(13) The catalyst employed in the composition comprises at least one metal compound, the metal being selected from the group consisting of cobalt, magnesium, chromium, copper, nickel, vanadium, iron, molybdenum, tin, cerium, zirconium, cesium and titanium. In one embodiment the catalyst is at least one selected from the group consisting of cobalt acetate, manganese acetate, cerium acetate, potassium acetate, cesium acetate, zirconium acetate, copper acetate, cobalt oxalate, manganese oxalate, cerium oxalate, potassium oxalate, cesium oxalate, zirconium oxalate and copper oxalate.

(14) The composition of the present disclosure further comprises at least one bromine source selected from the group consisting of HBr, NaBr, KBr, NH.sub.4Br, benzylbromide, monobromoacetic acid, di-bromo acetic acid, bromoacetyl bromide, tetrabromomethane and ethylene di-bromide.

(15) In accordance with another aspect of the present disclosure there is provided a process for preparing purified terephthalic acid. The process involves the following steps:

(16) In the first step a composition comprising p-Toluic acid in an amount of 0.05% to 4% with respect to the total mass of the composition; at least one catalyst in an amount of 0.02% to 2.5% with respect to the total mass of the composition; at least one ionic liquid in an amount of 0.04% to 50% with respect to the total mass of the composition; at least one carboxylic acid solvent and p-xylene is prepared. In the next step, the composition is oxidized in the presence an oxidizing agent selected from the group consisting of oxygen and air, at a temperature of 100 to 250° C. and at a pressure of 10 to 60 bar to obtain purified terephthalic acid. The carboxylic acid solvent employed is acetic acid. The process of the present disclosure is mainly characterized by 4-carboxy-benzaldehyde (4-CBA) content in terephthalic acid is less than 2000 ppm.

(17) In accordance with the present disclosure the proportion of the ionic liquid to the carboxylic acid solvent is maintained between 1:1 and 1:20.

(18) The process of the present disclosure further comprises a step of incorporating at least one bromine source selected from the group consisting of HBr, NaBr, KBr, NH.sub.4Br, benzylbromide, monobromoacetic acid, di-bromo acetic acid, bromoacetyl bromide, tetrabromomethane and ethylene di-bromide in said composition.

(19) In accordance with the present disclosure the ionic liquid comprises an organic cation selected from the group consisting of quaternary ammonium, cholinium, sulfonium, phosphonium, guanidinium, imidazolium, pyridinium, pyrrolidinium, morpholinium, quinolinium, isoquinolium, pyrazolium and piperidinium; and an anion selected from the group consisting of chloride, bromide, fluoride, iodide, mesylate, tosylate, hydrogen sulfate, sulfate, alkyl sulfonate, phosphates, phosphonates, akyl phosphates, nitrates, nitrites, carbonates, acetates, bicarbonates, hydroxides and oxides. In one embodiment the ionic liquid is at least one selected from the group consisting of alkyl ionic liquids and aryl alkyl ionic liquids. In another embodiment the ionic liquid comprises a combination of at least one alkyl ionic liquid and at least one aryl alkyl ionic liquid.

(20) The aryl alkyl ionic liquid includes but is not limited to 1-benzyl, 3-methyl imidazolium bromide; 1-benzyl, 3-methyl imidazolium chloride; 1-benzyl, 3-methyl imidazolium acetate; 1-benzyl, 3-methyl imidazolium methane sulfonate; 1-benzyl, 3-methyl imidazolium phosphate; Benzyl tributyl phosphonium bromide, Benzyl tributyl ammonium bromide; 1-phenyl, 3-methyl imidazolium chloride; 1-phenyl, 3-methyl imidazolium bromide; 1-phenyl, 3-methyl imidazolium acetate; 1-phenyl, 3-methyl imidazolium methane sulfonate; 1-phenyl, 3-methyl imidazolium phosphate; Phenyl tributyl phosphonium bromide; Phenyl tributyl ammonium bromide; 1,3-dibenzyl imidazolium chloride; 1,3-dibenzyl imidazolium bromide; 1,3-dibenzyl imidazolium acetate; 1,3-dibenzyl imidazolium methane sulfonate; and 1,3-dibenzyl imidazolium phosphate.

(21) The alkyl ionic liquid includes but is not limited to 1-butyl, 3-methyl imidazolium bromide; 1-butyl, 3-methyl imidazolium chloride; 1-butyl, 3-methyl imidazolium acetate; 1-butyl, 3-methyl imidazolium methane sulfonate; 1-butyl, 3-methyl imidazolium phosphate; 1-ethyl, 3-methyl imidazolium chloride; 1-ethyl, 3-methyl imidazolium bromide; 1-ethyl, 3-methyl imidazolium acetate; 1-ethyl, 3-methyl imidazolium methane sulfonate; 1-ethyl, 3-methyl imidazolium phosphate; Tetrabutyl phosphonium chloride; Tetrabutyl phosphonium bromide; Tetrabutyl phosphonium acetate; Tetrabutyl phosphonium methane sulfonate; Tetrabutyl phosphonium phosphate; Trihexyl Tetradecyl phosphonium chloride; Trihexyl Tetradecyl phosphonium bromide; Trihexyl Tetradecyl phosphonium acetate; Trihexyl Tetradecyl phosphonium decanoate; Tetrabutyl ammonium chloride; Tetrabutyl ammonium bromide; Tetrabutyl ammonium acetate; Tetrabutyl ammonium methane sulfonate; Tetrabutyl ammonium phosphate; Choline chloride; Choline bromide; choline acetate; and choline methane sulfonate.

(22) The catalyst employed in the composition of the present disclosure comprises at least one metal compound, the metal being selected from the group consisting of cobalt, magnesium, chromium, copper, nickel, vanadium, iron, molybdenum, tin, cerium, zirconium, cesium and titanium. In one embodiment the catalyst includes but is not limited to cobalt acetate, manganese acetate, cerium acetate, potassium acetate, cesium acetate, zirconium acetate, copper acetate, cobalt oxalate, manganese oxalate, cerium oxalate, potassium oxalate, cesium oxalate, zirconium oxalate and copper oxalate.

(23) The present disclosure is further illustrated herein below with the help of the following examples. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

EXAMPLES

A: Comparative Examples (1 to 5)

(24) Preparation of Mixtures which are Devoid of p-Toluic Acid and their Oxidation

(25) Procedure

(26) Oxidation of p-xylene was carried out at 215° C. and 20-40 bar pressure using a mixture of acetic acid and ionic liquid with or without HBr in the presence of cobalt acetate and manganese acetate as catalyst.

(27) The composition of each mixture is provided in table No. 1.

(28) TABLE-US-00001 TABLE NO. 1 Without p-Toluic acid Example 1 Example 2 Example 3 Example 4 Example 5 p-xylene p-xylene p-xylene p-xylene p-xylene (81.83 grams) (81.83 grams) (69.9 grams) (81.83 grams) (81.83 grams) acetic acid acetic acid acetic acid acetic acid acetic acid (416.07 grams) (265.88 grams) (282.6 grams) (327.6 grams) (327.6 grams) cobalt cobalt cobalt cobalt cobalt acetate•4H.sub.2O acetate•4H.sub.2O acetate•4H.sub.2O acetate•4H.sub.2O acetate•4H.sub.2O (0.63 grams) (3.3 grams) (2.8 grams) (3.5 grams) (3.5 grams) manganese manganese manganese manganese manganese acetate•4H.sub.2O acetate•4H.sub.2O acetate•4H.sub.2O acetate•4H.sub.2O acetate•4H.sub.2O (0.89 grams) (2.5 grams) (2.1 grams) (2.5 grams) (2.5 grams) 48% HBr 1-butyl, 3-methyl 1-butyl, 3-methyl Tetra butyl Tetra butyl (0.58 grams) imidazolium imidazolium methane phosphonium phosphonium chloride (35%) sulfonate (33%) bromide (20%) bromide (143.17 grams) + (139.8 grams) + (81.83 grams) (81.83 grams) + 48% HBr (3.3 grams) 48% HBr (2.8 grams) 48% HBr (2.8 grams) Temperature Temperature Temperature Temperature Temperature (° C.): 215 (° C.): 215 (° C.): 215 (° C.): 215 (° C): 215 Pressure (Bar): 40 Pressure(Bar): 40 Pressure(Bar): 40 Pressure(Bar): 40 Pressure (Bar): 40 Time (hours): 3 Time (hours): 3 Time (hours): 3 Time (hours): 3 Time (hours): 3 Intermediate Intermediate Intermediate Intermediate Intermediate (4-CBA) content: (4-CBA) content: (4-CBA) content: (4-CBA) content: (4-CBA) content: 5600 ppm 91000 ppm 85000 ppm 19000 ppm 42000 ppm

B: Examples (6 to 10)

(29) Preparation of Mixtures which Essentially Contains p-Toluic Acid and their Oxidation

(30) Procedure

(31) Oxidation of p-xylene was carried out at 215° C. and 20-40 bar pressure using a mixture of p-Toluic acid, acetic acid and ionic liquid with or without HBr in the presence of cobalt acetate and manganese acetate as catalyst.

(32) The composition of each mixture is provided in table No. 2.

(33) TABLE-US-00002 TABLE NO. 2 With p-Toluic acid Example 6 Example 7 Example 8 Example 9 Example 10 p-xylene p-xylene p-xylene p-xylene p-xylene (74.04 grams) (74.04 grams) (77.93 grams) (77.93 grams) (81.83 grams) acetic acid acetic acid acetic acid acetic acid acetic acid (327.38 grams) (327.38 grams) (315.71 grams) (315.13 grams) (411.07 grams) cobalt acetate•4H.sub.2O cobalt acetate•4H.sub.2O cobalt acetate•4H.sub.2O cobalt acetate•4H.sub.2O cobalt acetate•4H.sub.2O (0.63 grams) (0.63 grams) (0.63 grams) (0.63 grams) (0.63 grams) manganese manganese manganese manganese manganese acetate•4H.sub.2O acetate•4H.sub.2O acetate•4H.sub.2O acetate•4H.sub.2O acetate•4H.sub.2O (0.89 grams) (0.89 grams) (0.89 grams) (0.89 grams) (0.89 grams) 1-butyl, 3-methyl 1-butyl, 3-methyl tetra butyl tetra butyl 48% HBr imidazolium acetate imidazolium phosphonium phosphonium (0.58 grams) (81.83 grams) acetate bromide bromide (81.83 grams) + (20.91 grams) + (20.91 grams) + 48% HBr 1-butyl, 3-methyl 1-butyl, 3-methyl (5.23 grams) imidazolium acetate imidazolium acetate (78.93 grams) (78.93 grams) + 48% HBr (0.58 grams) p-Toluic acid: p-Toluic acid: p-Toluic acid: p-Toluic acid: p-Toluic acid: 2% (10 grams) 2% (10 grams) 1% (5 grams) 1% (5 grams) 1% (5 grams) Temperature Temperature Temperature Temperature Temperature (° C.): 215 (° C): 215 (° C.): 215 (° C): 215 (° C.): 215 Pressure (Bar): 40 Pressure(Bar): 40 Pressure(Bar): 40 Pressure(Bar): 40 Pressure(Bar): 40 Time (hours): 3 Time (hours): 3 Time (hours): 3 Time (hours): 3 Time (hours): 3 No terephthalic Intermediate Intermediate Intermediate Intermediate acid formed (4-CBA) content: (4-CBA) content: (4-CBA) content: (4-CBA) content: 5600 ppm 1600 ppm 8700 ppm 5600 ppm

(34) From the results as shown in tables 1 and 2, it is clear that incorporation of external p-Toluic acid reduces the 4-carboxy-benzaldehyde (4-CBA) content in terephthalic acid.

(35) Particularly, it is found that when a mixture/composition containing p-Toluic acid and ionic liquid is used during the oxidation of p-xylene, there is significant reduction in formation 4-CBA. Example 8 clearly shows that the formation of 4-CBA is reduced to 1600 ppm i.e. the formation of 4-CBA is 3.5 times less than the conventional process for preparation of terephthalic acid. This in turn suggests that the mixture of the present disclosure is capable of producing terephthalic acid in a highly pure form.

(36) Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

(37) The use of the expression “a”, “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.

(38) The numerical values given for various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher or lower than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the disclosure and the claims unless there is a statement in the specification to the contrary.

(39) While certain embodiments of the disclosure have been described, these embodiments have been presented by way of examples only, and are not intended to limit the scope of the disclosure. Variations or modifications in the composition of this disclosure, within the scope of the disclosure, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this disclosure.