DESC:FIELD
The present disclosure relates to a process for the purification of crude aromatic carboxylic acid.
BACKGROUND
Polyesters are polymers formed from a chemical reaction between an acid and an alcohol. Polymer grade or "purified" aromatic carboxylic acid is the starting material in the synthesis of polyester resin, which is the principal polymer in the manufacture of polyester fibers, polyester films, resins, and the like. Polyester resin is used for making commercial materials having a variety of applications, depending on how they have been produced and the resulting orientation of the polymer chains.
Usually, purified aromatic carboxylic acid is produced from relatively less pure, technical grade or "crude" aromatic carboxylic acid by various purification processes. Purification of the crude terephthalic acid by hydrogenation using a suitable catalyst is a well-known in the art.
Various techniques have been explored to purify crude carboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid and the like. Conventionally, crude terephthalic acid is subjected to catalytic hydrogenation to convert 4-carboxybenzaldehyde (4-CBA) into p-toluic acid; the latter is then separated and eliminated from the system. Hydrogenation is carried out at very high temperature and pressure conditions which makes the overall process energy inefficient. There are some techniques which use catalysts such as 5% Pd/C to produce purified terephthalic acid from crude terephthalic acid.
Further, some methods disclose reacting crude carboxylic acids with a Lewis base to effect formation of a salt or an adduct of the acid with the base. This adduct is subsequently crystallized and de-adducted to leave behind the purified carboxylic acid. Such processes, however, require longer time periods and have higher complexity levels.
Therefore there is felt a need for a simple process for the purification of crude aromatic carboxylic acid
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 ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide a process for the purification of crude aromatic carboxylic acid.
Another object of the present disclosure is to provide a process for the purification of crude terephthalic acid to produce purified/pure terephthalic acid having low 4-CBA content.
Still another object of the present disclosure is to provide a process to separate an adduct of Lewis based-aromatic carboxylic acid selectively.
Yet another object of the present disclosure is to provide an environment friendly, simple, safe, and cost effective process for the purification of the crude aromatic carboxylic acid.
Another object of the present disclosure is to provide a process for the purification of the crude aromatic carboxylic acid by reducing impurities and metal contents.
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
The present disclosure provides a process for the purification of crude aromatic carboxylic acid. In the first step of the process of the present disclosure, the crude aromatic carboxylic acid is reacted with at least one Lewis base in a first fluid medium at a temperature in the range of 20 oC to 200 oC and at a pressure in the range of 1 bar to 40 bar to obtain a clear solution (resultant mass) comprising Lewis base-aromatic carboxylic acid adducts in dissolved form. The clear solution is subjected to selective crystallization at a temperature lower than the temperature at which the reaction of Lewis base with the crude aromatic carboxylic acids is carried out, to obtain at least one adduct of Lewis base-aromatic carboxylic acid. The adduct of Lewis base-aromatic carboxylic acid is at least one selected from the group consisting of Lewis base-terephthalic acid formed during the purification of the crude terephthalic acid and Lewis base-orthophthalic acid formed during the purification of the crude orthophthalic acid. The crystals obtained after the step of crystallization are selectively separated from the resultant mass to obtain crystals of Lewis base-aromatic carboxylic acid adduct. The separated crystals of the selected adduct are subjected for de-adduction by treating it with a second fluid medium to obtain a purified/pure aromatic carboxylic acid.
Lewis base and the fluid media used in the process of the present disclosure can be separated, recovered, reused, and recycled in the process continuously.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWING
Figure 1 illustrates the structure of an adduct of terephthalic acid and 1-methyl imidazole- in accordance with the present disclosure.

DETAILED DESCRIPTION
During the wet oxidation process of para-xylene, crude terephthalic acid is obtained as the main product and intermediates such as para-tolualdehyde, para-toluic acid, 4-carboxybenzhaldehyde (4-CBA) and side products such as isophthalic acid, phthalic acid, meta or ortho-tolualdehyde, meta or ortho-toluic acid, 2 or 3-carboxybenzhaldehyde, 3 or 4-bromo methyl benzoic acid, benzoic acid, trimellitic acid, trimesic acid, benzaldehyde, phthalaldehyde, ethylbenzaldehyde, methylstyrene, diphenic acid, 2- biphenyl carboxylic acid, hemi mellitic acid, dimethyl terephthalate, methyl p-toulate, 3-hydroxy 4-methyl benzoic acid, terephthaldehyde, styrene, phenol, toluene, benzene, ethylbenzene, methylethylbenzene, formaldehyde, 1,3-cyclopentadiene, indene, methylnaphthalene, anthracene, phenantrene, phenylacetylene, methylbiphenyl, diphenylbutane, naphthalene, and 4,4-dimethylbibenzyl, vinylacetylene are produced.
Terephthalic acid containing at least one of the above listed intermediates, by-products, side products, catalyst is termed as crude terephthalic acid. The intermediates are formed in large quantities and eventually are converted into crude terephthalic acid during the wet oxidation of para-xylene. However, the side products formed are in small quantities.
In order to use terephthalic acid as a starting material, for example, in the preparation of polyethylene terephthalate, the content of 4-carboxybenzaldehyde (4-CBA) is recommended to be preferably below 100 ppm.
During the production of terephthalic acid, 4-CBA is produced in the range of 4000 ppm to 10000 ppm and para-toluic acid is produced in the range of 150 ppm to 5000 ppm. Therefore, reducing the 4-CBA impurity is very important for further use of terephthalic acid. 4-CBA, if it exists in large quantities in terephthalic acid, acts as a chain terminator during the PET polymerization process, and hence the desired PET molecular weight may not be achieved. Conventionally, crude terephthalic acid is subjected to hydrogenation to convert 4-CBA into p-toluic acid and subsequently p-toluic acid is separated.
Conventional hydrogenation is a high energy intensive process with requirement of noble material as a catalyst. Therefore, the inventors of the present disclosure envisaged a simple and cost effective process for the purification of the crude aromatic carboxylic acid. The chemicals used in the purification process of the present disclosure can be recovered and reused and hence, the process of the present disclosure is economic.
In accordance with the present disclosure, there is provided a process for purifying the crude aromatic carboxylic acid involving the following steps:
In the first step, the crude aromatic carboxylic acid, at least one Lewis base and at least one first fluid medium are mixed and stirred in a reactor, wherein the reactor is maintained at a temperature in the range of 20 oC to 200 oC to obtain an adduct of the aromatic carboxylic acid and Lewis base. The formed adduct appears as homogenous solution, i.e., it is completely dissolved in the resultant mass. The stirring speed of the reactor during the reaction is in the range of 5 rpm to 800 rpm. In this step, water can be added, in the range of 1 % to 10% (w/w), to the first fluid medium to get purified/pure carboxylic acid. In one embodiment, purified carboxylic acid is purified terephthalic acid of PET grade.
The crude aromatic carboxylic acid comprises crude terephthalic acid, and crude orthophthalic acid. In one embodiment the crude carboxylic acid comprises 4-carboxy benzaldehyde, p-toluic acid, isophthalic acid, orthophthalic acid, benzoic acid, and trimellitic acid as the major acid impurities, and cobalt, magnesium, chromium, copper, nickel, vanadium, iron, molybdenum, tin, cerium, zirconium, cesium, sodium, and titanium as the major metal impurities. In an exemplary embodiment the crude carboxylic acid is crude terephthalic acid.
Lewis base that can be used in the present disclosure include substituted and non-substituted linear, branched, cyclic, polycyclic, heterocyclic, and heteroaryl Lewis base and any combinations thereof. Non-limiting examples of Lewis base include linear, and branched substituted and non-substituted mono, di, and trialkyl amine and phosphine, linear and branched substituted and non-substituted mono and dialkyl sulfide, substituted and non-substituted imidazole, pyrazole, thiazole, isothiazole, azathiozole, oxothiazole, oxazine, oxazoline, oxazaborole, dithiozole, triazole, selenozole, oxahosphole, pyrrole, borole, furan, thiphene, phosphole, pentazole, indole, indoline, oxazole, isothirazole, tetrazole, benzofuran, dibenzofuran, benzothiophene, dibenzothoiphene, thiadiazole, pyridine, pyrimidine, pyrazine, pyridazine, piperazine, piperidine, morpholine, pyran, aniline, phthalazine, quinazoline, quinoxaline, tromethamine, triethanoamine, pyrrolidine 1-(2-hydroxyethyl), morpholine 4-(2-hydroxyethyl), L-Lysine, hydrabamine, N-methyl glucamine, ethylene diamine, ethanoamine, 2-dimethylamino ethanol, diethanolamine, deanol, choline, benzathine, benethamine, L-arginine, ammonia and any combinations thereof. In an exemplary embodiment Lewis base is 1-methyl imidazole.
The first fluid medium used in the process the present disclosure is at least one selected from the group consisting of tetrahydrofuran, substituted tetrahydrofuran, water, 1,4-dioxane and substituted 1,4-dioxane. Typically, the first fluid medium is tetrahydrofuran.
In one embodiment of the present disclosure, 1-methyl imidazole is reacted with the crude terephthalic acid in tetrahydrofuran to obtain an adduct of 1-methyl imidazole and terephthalic acid. In another embodiment, 1-methyl imidazole is reacted with the crude orthophthalic acid in tetrahydrofuran to obtain the adduct of 1-methyl imidazole and orthophthalic acid.
The adduct formation takes place due to dipole-dipole interaction between the nitrogen atom of 1-methyl imidazole and hydrogen atom of the aromatic carboxylic acids group present in terephthalic acid and orthophthalic acid.
In an exemplary embodiment of the present disclosure, the dipole-dipole interaction between the nitrogen atom of 1-methyl imidazole and hydrogen atom of terephthalic acid is depicted in Figure 1 by dotted line.
In another embodiment of the present disclosure, the mole ratio of Lewis base to the crude aromatic carboxylic acid is in the range of 1:1 to 50:1, more particularly in the range of 2:1 to 12:1 and even more particularly is in the range of 2:1 to 10:1.
In yet another embodiment of the present disclosure, the mole ratio of Lewis base to the first fluid medium is in the range of 1:1 to 1:30, more particularly is in the range of 1:2 to 1:15 and even more particularly is in the range of 1:3 to 1:8.
The ratio of the amount of Lewis base to the crude aromatic carboxylic acid is such that all adducts formed of the aromatic carboxylic acid, its intermediates and impurities remain soluble in the resultant mass at a predetermined temperature.
In the second step, the so obtained homogenous (clear) solution of the resultant mass containing the adduct of Lewis base-aromatic carboxylic acid undergoes selective crystallization at a temperature lower than the temperature in the first step to obtain the crystals of at least one adduct of the aromatic carboxylic acid. In this step, optionally a few pure crystals of the adduct of the carboxylic acid and Lewis base are seeded to get selective crystallization of the adduct of the carboxylic acid and Lewis base. In one embodiment the crystallization can be done under stirring at a stirring speed in the range of 1 rpm to 400 rpm. In another embodiment at least one chelating agent is added to remove the metals from the aromatic carboxylic acid to obtain purified/pure carboxylic acid Lewis base adduct. In still another embodiment purified terephthalic acid of PET grade is obtained.
The chelating agent is at least one selected from the group consisting of EDTA (ethylenediamine tetraacetate), DTPA (Diethylenetriaminepentaacetic acid), and NTA (Nitrilotriacetic acid).
In an exemplary embodiment, the adduct of Lewis base-aromatic carboxylic acid is at least one selected from the group consisting of Lewis base-terephthalic acid adduct formed during the purification of the crude terephthalic acid and Lewis base-orthophthalic acid formed during the purification of the crude orthophthalic acid.
In the third step, the selected crystals obtained in the above step are separated by filtration i.e., filtering the solids from the mother liquor followed by washing the crystals optionally with the first fluid medium to obtain separated crystals of Lewis base-aromatic carboxylic acid. In an exemplary embodiment, the separated crystals are the crystals of Lewis base-terephthalic acid adduct and Lewis base-orthophthalic acid obtained from crude terephthalic acid and crude orthophthalic acid, respectively.
The selected crystals obtained from the purification of the crude carboxylic acid in the above step in the process of the present disclosure are characterized by X-ray crystallography and other spectrometry analysis.
In the fourth step, the separated, selected crystals of Lewis base-aromatic carboxylic acid are treated with at least one second fluid medium for de-adduction to obtain a purified aromatic carboxylic acid. The de-adduction (separation) is carried out by the addition of the crystals of the selected adduct in the second fluid medium under stirring, either at room temperature or optionally heating the mixture of the second fluid medium and the crystals of Lewis base-aromatic carboxylic acid adduct at a temperature in the range of 20 oC to 140 oC and at second predetermined pressure. After de-adduction, the solid obtained is filtered off and dried to obtain solid pure aromatic carboxylic acid, whereas the impurities remain in the filtrate/ mother liquor.
The solid obtained after the fourth step is optionally, subjected to washing using the first fluid medium at a temperature in the range of 30 oC to 100 oC and autogenously generated pressure before drying.
The second fluid medium is at least one selected from the group comprising methanol, ethanol, propanol, benzyl alcohol, and water. The second fluid can be recovered after the step of de-adduction.
In an exemplary embodiment, the amount of combined quantity of 4-carboxy benzaldehyde and p-toluic acid in the purified/pure terephthalic acid is below 190 ppm.
In the present disclosure, the washing fluid medium is referred to as the third fluid medium. The separated adduct is washed with at least one third fluid medium to remove/reduce the different impurities adhered to the surface of crystals of the adduct of the aromatic carboxylic acid-Lewis base. The third fluid medium is at least one selected from the group consisting of tetrahydrofuran, methyl acetate, ethyl acetate, acetonitrile, dichloromethane, dichloroethane, and 1-methyl imidazole.
The fluid media and the chemicals/reagents used in the process of the present disclosure can be recovered and recycled for further use.
In the present disclosure, the process for preparing the adduct is carried out in a reactor. Non-limiting examples of the reactors for the formation of the complex or adduct include single or series of continuously stirred flow reactors, static mixers, plug flow reactors, fixed bed reactors, fluidized bed reactors, packed bed reactors and combinations thereof.
The present disclosure is further illustrated herein below with the help of the following experiments. The experiments 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 embodiments herein. The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. These laboratory scale experiments can be scaled up to industrial/commercial scale.
EXPERIMENTAL DETAILS:
In order to obtain polymer grade terephthalic acid, different solvents were employed to prepare the adduct of terephthalic acid-1-methyl imidazole (TA-MIM adduct). The first fluid medium was selected from dimethylformamide, acetonitrile, monoethylene glycol, and tetrahydrofuran. Experiment 1 was carried out by using tetrahydrofuran as the first fluid medium.
Experiment 1: Purification of crude terephthalic acid in accordance with the present disclosure-
49.8 grams of crude terephthalic acid, 99.6 grams of 1-methyl imidazole in 1:2 molar ratio and 300 gm of tetrahydrofuran (first fluid medium) were taken in a round bottom flask to obtain a resultant mixture. The so obtained resultant mixture was stirred and maintained at a temperature of 72 oC and at atmospheric pressure for 2 hours to obtain a homogenous mixture having an adduct of terephthalic acid and 1-methyl imidazole. The homogeneous mixture was then cooled to 30 oC and allowed to stand for 50 minutes to obtain crystals of the adduct of terephthalic acid and 1-methyl imidazole.
The crystals obtained from the homogeneous mixture after crystallization were separated by filtration under vacuum. The separated crystals were washed with 200 gm of tetrahydrofuran. The crystals obtained from the above step were further taken in a round bottom flask and 800 ml of Methanol (second fluid medium) was added to obtain mixture of methanol and crystals. The so obtained mixture was stirred at a speed of 400 rpm at 30 oC for 20 minutes to obtain pure terephthalic acid.
The 4-CBA content in the purified/pure terephthalic acid was reduced to 264 ppm from its initial content in the crude terephthalic acid of 3118 ppm.
Experiments 2-4: Purification of crude terephthalic acid using other first fluid media-
A similar experiment as described in experiment 1 was carried out by replacing the first fluid medium with dimethylformamide, acetonitrile, and monoethylene glycol in place of tetrahydrofuran.
Experiment 5: Purification of crude terephthalic acid without using the First fluid medium:
A similar experiment as described in experiment 1 was carried out in the absence of first fluid medium and using higher quantity of 1-methyl imidazole i.e., using 49.8 gms of crude terephthalic acid and 150 gms of 1-methylimidazole.
The results for the experiments 1-5 are presented in table 1.
Table 1: Effect of different fluid media (solvents)
Expt. No. First Fluid medium 4-CBA content (ppm)
1 Tetrahydrofuran 264
2 Acetonitrile 1570
3 Monoethyleneglycol 1257
4 Dimethylformamide 920
5 No first fluid medium 900

It is clear from table 1 that there is a substantial reduction in 4-CBA in presence of tetrahydrofuran (as a fluid medium) as compared to dimethylformamide, acetonitrile, and monoethylene glycol.
No adduct separation was observed in case of monoethylene glycol as solvent, hence the reaction mass was further cooled to 0 oC and the adduct so obtained was analyzed for 4-CBA (4carboxybenzaldehyde) using Hg-polarography.

Experiment 6: Effect of THF wash to TA-MIM adduct_Ist stage
In order to see the effect of washing, the adduct obtained in experiment 1 was washed with tetrahydrofuran at 70 oC. A 50% reduction in 4-CBA was observed in comparison with TA-MIM adduct that was not washed with THF. The experimental results are presented in Table 2. The quantity of THF used for washing was 2 times the adduct quantity.
Experiments 7 & 8: Effect of THF wash to TA-MIM adduct_IInd stage
The experiments were carried out to see the further reduction of 4-CBA content in the second stage. The adduct obtained in experiment 1 (adduct of terephthalic acid-1-methyl imidazole) was further dissolved in a mixture of fresh tetrahydrofuran and 1-methyl imidazole. 99 gms of terephthalic acid – 1-methyl imidazole adduct was dissolved in the mixture containing 300 gms tetrahydrofuran and 49.8 gms 1-methyl imidazole. After de-adduction and separation, the 4-CBA content in the purified/pure terephthalic acid was found to be 66 ppm.
The so obtained terephthalic acid was further washed with tetrahydrofuran. It was observed that 4-CBA content reduced to 37 ppm. The combined 4-CBA and p-toluic acid content in the purified/pure terephthalic acid was found to be 40 ppm.
Table 2: Effect of THF wash to TA-MIM adduct
Experiment No. Condition 4-CBA content (ppm)
1 TA from 1st stage adduct without THF wash 264
6 TA from 1st stage adduct after THF wash 140
7 TA from 2nd stage adduct without THF wash 66
8 TA from 2nd stage adduct with THF wash 37

Experiment 9: Effect of seeding of PTA-MIM adduct:
49.8 grams of crude terephthalic acid, 99.6 grams of 1-methyl imidazole in 1:2 molar ratio and 300 gm of tetrahydrofuran (first fluid medium) were taken in a round bottom flask to obtain a resultant mixture. The so obtained resultant mixture was stirred at a temperature of 72 oC and at atmospheric pressure for 2 hours to obtain a homogenous mixture having an adduct of terephthalic acid and 1-methyl imidazole. The homogeneous mixture was then cooled to 30 oC and allowed to stand for 50 minutes to obtain crystals of the adduct of terephthalic acid and 1-methyl imidazole. A few crystals of TA-MIM adduct were added to grow an uniform needle type crystals of TA-MIM adduct when the cooling was started.
The so obtained crystals were separated by filtration under vacuum. The separated crystals were washed with 200 gm of tetrahydrofuran. The crystals obtained from the above step were further taken in a round bottom flask and 800 ml of Methanol (second fluid medium) was added to obtain a mixture of methanol and crystals. The mixture of methanol and crystals was stirred at a speed of 400 rpm at 30 oC for 20 minutes to obtain pure terephthalic acid.
The 4-CBA content in the purified terephthalic acid was reduced to 240 ppm from its initial content in the crude terephthalic acid of 3118 ppm.
Experiment 10: Effect of water on metal reduction in purified terephthalic acid
49.8 grams of crude terephthalic acid, 99.6 grams of 1-methyl imidazole in 1:2 molar ratio, and 285 grams of tetrahydrofuran, and 15 grams demineralized water (first fluid medium) were taken in a round bottom flask to obtain a resultant mixture. The so obtained resultant mixture was stirred at a temperature of 72 oC and at atmospheric pressure for 2 hours to obtain a homogenous mixture comprising an adduct of terephthalic acid and 1-methyl imidazole. The homogeneous mixture was then cooled to 30 oC and allowed to stand for 50 minutes to obtain crystals of the adduct of terephthalic acid and 1-methyl imidazole.
The crystals obtained from the homogeneous mixture after crystallization were separated by filtration under vacuum. The separated crystals were washed with 200 gm of tetrahydrofuran. The crystals obtained from the above step were further taken in a round bottom flask and 800 ml of Methanol (second fluid medium) was added to obtain a mixture of methanol and crystals. The so obtained mixture of methanol and crystals was stirred at a speed of 400 rpm at 30 oC for 20 minutes to obtain pure terephthalic acid.
The metal content in the crude terephthalic acid and purified terephthalic acid is presented in table 3 below
Table 3: Effect of water on metal reduction in purified terephthalic acid
Metals (ppm) Co Mn Cr Total
Crude terephthalic acid (CTA) 24.0 25.0 0.2 49.2
Metals in purified terephthalic acid 0.2 0.1 0.4 0.7
Analysis was done by using Atomic absorption spectroscopy instrument.
Experiment 11: Effect of chelating agent on metal reduction in purified terephthalic acid
25 grams of crude terephthalic acid, 49.5 grams of 1-methyl imidazole in 1:2 molar ratio, 148.5 grams of tetrahydrofuran, 2 grams demineralized water (first fluid medium) and 0.47 grams ethylenediamine tetraacetate (EDTA) as chelating agent were taken into a round bottom flask to obtain a resultant mixture. The so obtained resultant mixture was stirred at a temperature of 72 oC and at atmospheric pressure for 2 hours to obtain a homogenous mixture having an adduct of terephthalic acid and 1-methyl imidazole. The homogeneous mixture was then cooled to 30 oC and allowed to stand for 50 minutes to obtain crystals of the adduct of terephthalic acid and 1-methyl imidazole.
The crystals obtained from the homogeneous mixture after crystallization were separated by filtration under vacuum. The separated crystals were washed with 100 gm of tetrahydrofuran. The crystals obtained from the above step were further taken in a round bottom flask and 400 ml of Methanol (second fluid medium) was added to obtain a mixture of methanol and crystals The so obtained mixture of methanol and crystals was stirred at a speed of 400 rpm at 30 oC for 20 minutes to obtain pure terephthalic acid.
The cobalt and manganese content in the crude terephthalic acid were 24 and 25 ppm respectively and in purified terephthalic acid the cobalt and manganese content were found to be 0.3 and 0.2 ppm respectively. Analysis was done by using Atomic absorption spectroscopy.
TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE:
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of:
? a process for the purification of crude aromatic carboxylic acid that reduces the formation of 4-carboxybenzaldehyde;
? a process that can be carried out at moderate temperature and atmospheric pressure;
? a process for the purification of crude aromatic carboxylic acid that facilitates in reducing the formation of color bodies and metal impurities in the final product;
? a process in which the fluid medium and the chemicals (reagents) can be regenerated, recycled and reused; and
? a process for purifying the aromatic carboxylic acid that is simple and environmental friendly.
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 “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.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
,CLAIMS:WE CLAIM:
1. A process for the purification of crude aromatic carboxylic acid, said process comprising the following steps:
a) reacting said crude aromatic carboxylic acid with at least one Lewis base in a first fluid medium at a temperature ranging from 20 oC to 200 oC, under stirring and at a pressure ranging from 1 bar to 40 bar to obtain Lewis base-aromatic carboxylic acid adducts in the resultant mass;
b) selectively crystallizing at least one of said Lewis base-aromatic carboxylic acid adducts at a temperature lower than the temperature, and pressure at which the reaction in step (a) is carried out, under stirring, to obtain crystals of the selected Lewis base-aromatic carboxylic acid adduct;
c) separating said crystals of the selected Lewis base-aromatic carboxylic acid adduct from the resultant mass to obtain separated crystals of the selected Lewis base-aromatic carboxylic acid adduct;
d) de-adducting said separated crystals of the selected Lewis base-aromatic carboxylic acid adduct of step (c), by treating it with a second fluid medium to obtain a solid containing pure selected aromatic carboxylic acid; and
e) separating said solid followed by drying to obtain pure selected aromatic carboxylic acid.
2. The process as claimed in claim 1, wherein said crude aromatic carboxylic acid is at least one of crude terephthalic acid, and crude orthophthalic acid.
3. The process as claimed in claim 1, wherein said Lewis base is at least one selected from the group consisting of substituted and non-substituted linear, branched, cyclic, polycyclic, heterocyclic, and aromatic Lewis base.
4. The process as claimed in claim 1, wherein said first fluid medium is at least one selected from the group consisting of tetrahydrofuran, substituted tetrahydrofuran, water, 1,4-dioxane, substituted 1,4-dioxane and said second fluid medium is at least one selected from the group consisting of methanol, ethanol, propanol, benzyl alcohol, and water.
5. The process as claimed in claim 1, wherein said crude aromatic carboxylic acid is crude terephthalic acid, said Lewis base is 1-methyl imidazole and said first fluid medium is tetrahydrofuran.
6. The process as claimed in claim 1, wherein the molar ratio of said Lewis base to said crude aromatic carboxylic acid is in the range of 1:1 to 50:1 and the molar ratio of said Lewis base to said first fluid medium is in the range of 1:1 to 1:30.
7. The process as claimed in claim 1, wherein said Lewis base-aromatic carboxylic acid adducts of step (b) are at least one selected from the group consisting of Lewis base-terephthalic acid adduct, and Lewis base-orthophthalic acid adduct.
8. The process as claimed in claim 1, wherein said crystals of said adduct of said aromatic carboxylic acid and said Lewis base are subjected to washing with a third fluid medium prior to breaking said adduct of said aromatic carboxylic acid and said Lewis base, wherein said third fluid medium is at least one selected from the group consisting of tetrahydrofuran, substituted tetrahydrofuran, 1,4-dioxane, substituted 1,4-dioxane, methyl acetate, ethyl acetate, dichloromethane, dichloroethane, acetonitrile, and 1-methyl imidazole.
9. The process as claimed in claim 1, wherein the step of de-adducting said adduct with said second fluid medium further comprises heating said mixture of said second fluid medium and said crystals of said Lewis base-aromatic carboxylic acid adduct at a temperature is in the range of 20 oC to 140 oC and at a pressure in the range of 1 bar to 30 bar to obtain said pure aromatic carboxylic acid.
10. The process as claimed in claim 1, wherein 4- carboxy benzaldehyde content in said pure selected aromatic carboxylic acid is less than 40 ppm.
11. The process as claimed in claim 1, wherein said step (b) further comprises seeding of pure crystals of said adduct of said carboxylic acid and said Lewis base to achieve selective crystallization to obtain pure adduct of said carboxylic acid and said Lewis base.
12. The process as claimed in claim 1, wherein said step (a) further comprises addition of water in the range of 1% to 10% (w/w) into said first fluid medium to obtain pure carboxylic acid.
13. The process as claimed in claim 1, wherein said step (b) further comprises the addition of chelating agent to remove the metal impurities from said crude carboxylic acid to obtain pure carboxylic acid.
14. The process as claimed in claim 13, wherein said crude carboxylic acid has metal impurities selected from the group consisting of cobalt, manganese, iron, and chromium.
15. The process as claimed in claim 1, wherein said solid obtained in step (d) is subjected, before step (e), to washing using said first fluid medium at a temperature in the range of 30 oC to 100 oC and at autogenously generated pressure.
16. The process as claimed in claim 1, wherein combined quantity of 4-carboxy benzaldehyde and p-toluic acid in pure carboxylic acid is below 190 ppm.