FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE
Specification
(See Section 10; Rule 13)
A COMPOSITION FOR PREPARING TEREPHTHALIC ACID
RELIANCE INDUSTRIES LIMITED
an Indian Company
of 3rd Floor, Maker Chamber - IV, 222, Nariman Point,
Mumbai 400 021, Maharashtra, India
INVENTORS:
1. JAIN SURESH SHANTILAL
2. ADURI PAVANKUMAR
3. UPPARA PARASU VEERA
4. TANGADE PRASHANT SUDHAKAR
The following specification particularly describes the invention and the manner in which it is
to be performed.

FIELD
The present disclosure relates to a composition for preparing terephthalic acid. The present disclosure also relates to a process for the preparation of terephthalic acid.
BACKGROUND
Terephthalic acid is an organic compound with formula C6H4(COOH)2- This colourless solid
is a commodity chemical, used principally as a precursor to the polyester PET, used to make clothing and plastic bottles. World production in 1970 was around 1.75 million tonnes. By 2006, global purified terephthalic acid (PTA) demand had exceeded 30 million tonnes. There is a smaller, but nevertheless significant, demand for terephthalic acid in the production of polybutylene terephthalate and several other engineering .polymers. In the research laboratory, terephthalic acid has been popularized as a component for the synthesis of metal-organic frameworks. Terephthalic acid is also used as filler in some military smoke grenades, most notably the American M83 smoke grenade, producing a thick white smoke when burned. Due to the wider applications of terephthalic acid, many methods for its manufacturing and purification have been developed in the recent years. Some of the prior art documents which disclose the processes for the synthesis of terephthalic acids are as follows.
US patent 2833816 discloses a process for producing aromatic carboxylic acid such as terephthalic acid by oxidation of aromatic compounds such as para-xylene at 120 to 275°C in the presence of acetic acid, metal catalyst and a bromine source. During the oxidation reaction, major intermediates that are formed are p-toulic acid and 4-carboxy-benzaldehyde (4-CBA). Para-toulic acid remain in soluble state in the solvent. However, 4-CBA co-crystallizes with product due to its similar crystal structure. Terephthalic acid which contains 4-CBA is typically termed as crude terephthalic acid. The crude terephthalic acid (CTA) containing 4-CBA is highly undesirable in producing polyester as it as act as a chain

terminating agent during the polymerization. Hence CTA is required to be further purified by additional steps.
US patent 7094925 discloses a process for the oxidation of an alkyl-aromatic compound which comprises admixing the aromatic compound with an oxidizing agent or sulfur compound in the presence of an ionic liquid and a nitrogen oxyacid species. Ionic liquid used in the process comprises an organic anion selected from the group consisting of trifluoroacetate, acetate, methanesulfonate, and combinations thereof or an anion based on sulfur, nitrogen, phosphorous, silicon, selenium, tellurium, arsenic, antimony, bismuth, or oxoanions of a metal. The process disclosed in US7094925 is carried out under Bronsted acidic conditions.
US2009/0326265 discloses the use of l-ethyl-3-methylimidazolium bromide as a bromine source during the oxidation. It is disclosed that the use of molecular bromine typically releases free bromine which causes corrosion to the equipment, whereas Ionic liquid based bromine source does not release the free bromine and hence advantageous during the manufacturing.
In US patent 6355835, the use of methylethlyketone (MEK) as a promoter to replace the bromine source is disclosed. However, the process disclosed in US6355835 requires high amount of catalysts. Another disadvantage of the process is that the organic promoter may undergo oxidation at the process operating conditions, further complicating purification steps.
US Patent 6153790 discloses utilization of a catalyst system which is a combination of cobalt and zirconium species for the preparation of aromatic carboxylic acids. The process disclosed in US6153790 avoids utilization of a halide promoter.

US2010/0174111 discloses a process for providing crystalline terephthalic acid comprising: a) providing a composition comprising terephthalic acid and one or more ionic liquids; and b) combining the composition of step (a) with a non-solvent (water), thereby crystallizing terephthalic acid.
US20120004449 discloses a process for oxidizing an alkyl-aromatic compound which comprises forming a mixture comprising the alkyl-aromatic compound, a solvent, a bromine source, and a catalyst; and contacting the mixture with an oxidizing agent to produce a solid oxidation product 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 from 1 to 7 carbon atoms and an ionic liquid selected from the group consisting of an imidazolium ionic liquid, a pyridinium ionic liquid, a phosphonium ionic liquid, a terra alkyl ammonium ionic liquid, and combinations thereof.
US2012/0004450 discloses a process for producing terephthalic acid from para-xylene which comprises forming a mixture comprising the para-xylene, a solvent, a bromine source, and a catalyst; and oxidizing the para-xylene by contacting the mixture with an oxidizing agent to produce a solid oxidation product comprising terephthalic acid, 4-carboxybenzaldehyde, and para-toluic acid; wherein the solvent comprises a carboxylic acid having from 1 to 7 carbon atoms, a dialkyl imidazolium ionic liquid, and optionally water.
US2012/0004451discloses a process for producing terephthalic acid from para-xylene which comprises forming a mixture comprising the para-xylene, a solvent, a bromine source, a catalyst and ammonium acetate; and oxidizing the para-xylene by contacting the mixture with an oxidizing agent to produce a solid oxidation product comprising terephthalic acid, 4-carboxybenzaldehyde, and para-toluic acid; wherein the solvent comprises a carboxylic acid having from 1 to 7 carbon atoms.

US2012/0004454 discloses a mixture for oxidizing an alkyl-aromatic compound comprising: the alkyl-aromatic compound, a solvent, a bromine source, and a catalyst; wherein the solvent comprises a carboxylic acid having from 1 to 7 carbon atoms and an ionic liquid selected from the group consisting of an imidazolium ionic liquid, a pyridinium ionic liquid, a phosphonium ionic liquid, a tetra alkyl ammonium ionic liquid, and combinations thereof.
The prior art patent documents mainly focused on preparation of terephthalic acid by oxidation of xylene in the presence of catalyst, solvent and bromine source such as HBr, NaBr, KBr, NR4Br. The solvents utilized include acetic acid, water and ionic liquids. These known processes are not able to produce highly pure terephthalic acid. i.e. these processes are not able to reduce the formation of intermediates such as 4-carboxy-benzaldehyde. Therefore, these processes inherently require additional purification steps. Further, these processes utilize excess amount of bromine and the metal catalyst.
Accordingly, it is desirable to develop a mixture which can undergo oxidation and produce terephthalic acid which is substantially free of intermediates such as 4-carboxy-benzaldehyde.
OBJECTS
Some of the objects of the present disclosure which at least one embodiment herein satisfies
are as follows:
It is an object of the present disclosure to provide a composition for the preparation of terephthalic acid.
It is another object of the present disclosure to provide a composition for the preparation of purified terephthalic acid, which is capable of reducing the formation of undesired intermediates.

It is another object of the present disclosure to a simple, safe and cost effective process for preparation of purified terephthalic acid.
Other objects and advantages of the present disclosure will be more apparent from the following description which is not intended to limit the scope of the present disclosure.
SUMMARY:
In accordance with the present disclosure there is provided a composition for preparing
purified 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,
said composition adapted to reduce the formation of 4-carboxy-benzaldehyde (4-CBA) to less than 2000ppm during the preparation of terephthalic acid.
Typically, the proportion of the ionic liquid to the carboxylic acid solvent ranges between 1:1 and 1:20.
Typically, the ionic liquid is at least one selected from the group consisting of alkyl ionic liquids and aryl alkyl ionic liquids.
Typically, 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 aryl alkyl ionic liquid selected from the group consisting of 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.
In another embodiment the ionic liquid is at least one alkyl ionic liquid selected from the group consisting of 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. In another embodiment the ionic liquid comprises a combination of at least one alkyl ionic liquid and at least one aryl alkyl ionic liquid.
Typically, 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.
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.
In another embodiment the composition further comprises at least one bromine source selected from the group consisting of HBr, NaBr, KBr, NR4Br, benzylbromide, monobromoacetic acid, di-bromo acetic acid, bromoacetyl bromide, tetrabromomethane and ethylene di-bromide.
In accordance with another aspect of the present disclosure there is provided a process for preparing purified terephthalic acid; said process comprising 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 to 250°C and at a pressure of 10 to 60 bar to obtain purified terephthalic acid,
said process characterized by 4-carboxy-benzaldehyde (4-CBA) content in terephthalic acid is less than 2000ppm.
Typically, the proportion of the ionic liquid to the carboxylic acid solvent ranges between 1:1 and 1:20.
In one embodiment the process further comprising a step of incorporating at least one bromine source selected from the group consisting of HBr, NaBr, KBr, NH4Br, benzylbromide, monobromoacetic acid, di-bromo acetic acid, bromoacetyl bromide, tetrabromomethane and ethylene di-bromide in said composition.
Typically, 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.
Typically, the ionic liquid is at least one aryl alkyl ionic liquid selected from the group consisting of 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.
Typically, the ionic liquid is at least one alkyl ionic liquid selected from the group consisting of 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.
Typically, the carboxylic acid solvent is acetic acid.
Typically, 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.
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.
DETAILED DESCRIPTION
Conventionally terephthalic acid is produced by wet oxidation of para-xylene. In the process of wet oxidation, acetic acid is used as solvent, cobalt and manganese acetates are used as catalyst and hydrogen bromide used as a promoter.
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.
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.
To overcome the drawbacks associated with the prior art process, the inventors of the present disclosure focused on developing a starting mixture or composition which can be successfully oxidized to produce pure terephthalic acid.
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.
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.
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 adapted to reduce the formation of 4-carboxy-benzaldehyde (4-CBA) to less than 2000ppm during the preparation of terephthalic acid.
In the present composition the proportion of the ionic liquid to the carboxylic acid solvent is maintained between 1:1 and 1:20.
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.
In one embodiment the ionic liquid is at least one aryl alkyl ionic liquid which includes but is not limited to 1-benzyl, 3-methyI 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.
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.
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.
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.
The composition of the present disclosure further comprises at least one bromine source selected from the group consisting of HBr, NaBr, KBr, NH4Br, benzylbromide, monobromoacetic acid, di-bromo acetic acid, bromoacetyl bromide, tetrabromomethane and ethylene di-bromide.
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:
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 2000ppm.
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.
The process of the present disclosure further comprising a step of incorporating at least one bromine source selected from the group consisting of HBr, NaBr, KBr, NH4Br, benzylbromide, monobromoacetic acid, di-bromo acetic acid, bromoacetyl bromide, tetrabromomethane and ethylene di-bromide in said composition.
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.
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.
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-mediyl 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.
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.
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):
- Preparation of mixtures which are devoid of p-Toluic acid and their oxidation
Procedure:
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.
The composition of each mixture is provided in table No. 1. Table No. 1

Without p-Toluic acid
Example 1 Example 2 Example 3 Example 4 Example 5
p-xylene (81.83 grams) p-xylene
(81.83 grams) p-xylene (69.9 grams) p-xylene (81.83
grams) p-xylene (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 acetate. cobalt cobalt acetate.
acetate.4H20 acetate.4H20 4H2O acetate.4H2O 4H2O
(0.63 grams) (3.3 grams) (2.8 grams) (3.5 grams) (3.5 grams)
manganese manganese manganese manganese manganese
acetate. 4H2O acetate. 4H2O acetate. 4H2O acetate.4H2O acetate.4H2O
(0.89 grams) (2.5 grams) (2.1 grams) (2.5 grams) (2.5 grams)
48 % HBr 1-butyl, 3- 1-butyl, 3- Tetra butyl Tetra butyl
methyl methyl phosphonium phosphonium
(0.58 grams) imidazolium imidazolium bromide (20 %) bromide (81.83
chloride (35%) methane (81.83 grams) grams)
(143.17 grams) sulfonate +
+48 % HBr (33%) (139.8 48 % HBr (2.8
(3.3 grams) grams) + 48 % HBr (2.8 grams) grams)
Temperature Temperature Temperature Temperature ( Temperature (V)
(°C):215 (°C):215 (°C).: 215 °C):215 : 215
Pressure (Bar): Pressure(Bar): Pressure(Bar): Pressure(Bar): Pressure (Bar): 40
40 40 40 40 Time (hours): 3
Time (hours): 3 Time (hours): 3 Time (hours): 3 Time (hours): 3
Intermediate (4- Intermediate Intermediate (4- Intermediate (4- Intermediate (4-
CBA) content : (4-CBA) CBA) content : CBA) content : CBA) content :
5600ppm content : 91000ppm 85000ppm 19000ppm 42000ppm
B: Examples (6 to 10):
- Preparation of mixtures which essentially contains p-Toluic acid and their oxidation
Procedure:
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.
The composition of each mixture is provided in table No. 1.

Table No. 2:

With p-Toluic acid
Example 6 Example 7 Example 8 Example 9 Example 10
p-xylene (74.04 p-xylene (74.04 p-xylene (77.93 p-xylene (77.93 p-xylene (81.83
grams) grams) grams) grams) 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 cobalt cobalt cobalt cobalt
acetate.4H2O
(0.63 grams) acetate.4H20
(0.63 grams) acetate.4H2O (0.63 grams) acetate.4H20
(0.63 grams) acetate.4H2O
(0.63 grams)
manganese acetate.4H2O (0.89 grams) manganese acetate.4H2O (0.89 grams) manganese acetate.4H2O (0.89 grams) manganese acetate.4H20 (0.89 grams) manganese acetate.4H2O (0.89 grams)
1-butyl , 3-
methyl
imidazolium 1-butyl , 3-
methyl
imidazolium tetra butyl phosphonium bromide (20.91 tetra butyl phosphonium bromide (20.91 48%HBr(0.58
grams)
acetate (81.83 grams) acetate (81.83 grams)
+ grams) + 1-butyl , 3-methyl imidazolium grams) + 1-butyl,
3-methyl
imidazolium
48%HBr (5.23 grams) acetate (78.93 grams) acetate (78.93 grams) + 48% HBr(0.58 grams)
p-Toluic acid: p-Toluic acid: p-Toluic acid: p-Toluic acid: p-Toluic acid:
2% 2% 1% 1% 1%
(10 grams) (10 grams) (5 grams) (5 grams) (5 grams)
Temperature( Temperature (oC) Temperature Temperature (oC) Temperature(
°C):215 : 215 (°C):215 : 215 °C):215
Pressure (Bar): Pressure(Bar): 40 Pressure(Bar): Pressure(Bar): 40 Pressure(Bar):
40 Time (hours): 3 40 Time (hours): 3 40
Time (hours): 3 Time (hours): 3 Time (hours): 3
No Intermediate (4- Intermediate (4- Intermediate (4- Intermediate
terephtbalic acid formed CBA) content : 5600 ppm CBA) content : 1600ppm CBA) content : 8700ppm (4-CBA) content : 5600 ppm

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.
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 1600ppm 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.
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.
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.
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.
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.

We claim:
1. A composition for preparing purified terephthalic acid; said composition
comprises:
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 adapted to reduce the formation of 4-carboxy-benzaldehyde (4-CBA) to less than 2000 ppm during the preparation of terephthalic acid.
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 ionic liquid is at least one aryl alkyl ionic liquid selected from the group consisting of 1-benzyl, 3-methyl imidazolium bromide; 1-benzyl, 3-methyl imidazolram 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.
7. The composition as claimed in claim 1, wherein the ionic liquid is at least one alkyl ionic liquid selected from the group consisting of 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.
8. 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.
9. 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.
10. The composition as claimed in claim 1 further comprises at least one bromine source selected from the group consisting of HBr, NaBr, KBr, NH4Br,

benzylbromide, monobromoacetic acid, di-bromo acetic acid, bromoacetyl bromide, tetrabromomethane and ethylene di-bromide.
11. The composition as claimed in claim 1, wherein the carboxylic acid solvent is acetic acid.
12. A process for preparing purified terephthalic acid; said process comprising 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 to 250 °C and at a pressure of 10 to 60 bar to obtain purified terephthalic acid,
said process characterized by 4-carboxy-benzaldehyde (4-CBA) content in terephthalic acid is less than 2000 ppm.
13. The process as claimed in claim 12, wherein the proportion of the ionic liquid
to the carboxylic acid solvent ranges between 1:1 and 1:20.

14. The process as claimed in claim 12, further comprising a step of incorporating at least one bromine source selected from the group consisting of HBr, NaBr, KBr, NH4Br, benzylbromide, monobromoacetic acid, di-bromo acetic acid, bromoacetyl bromide, tetrabromomethane and ethylene di-bromide in said composition.
15. The process as claimed in claim 12, 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.
16. The process as claimed in claim 12, wherein the ionic liquid is at least one selected from the group consisting of alkyl ionic liquids and aryl alkyl ionic liquids.
17. The process as claimed in claim 12, wherein the ionic liquid comprises a combination of at least one alkyl ionic liquid and at least one aryl alkyl ionic liquid.
18. The process as claimed in claim 12, wherein the ionic liquid is at least one aryl alkyl ionic liquid selected from the group consisting of 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.
19. The process as claimed in claim 12, wherein the ionic liquid is at least one alkyl ionic liquid selected from the group consisting of 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; I-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. 20. The process as claimed in claim 12, wherein the carboxylic acid solvent is acetic acid.
21. The process as claimed in claim 12, 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.
22. The process as claimed in claim 12, 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.