FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)
A PROCESS FOR RECOVERY OF DICARBOXYLIC ACID FROM AN EFFLUENT GENERATED DURING POLYESTER FABRIC
PROCESSING
RELIANCE INDUSTRIES LIMITED
an Indian Organization
of 3rd Floor, Maker Chamber-IV, 222, Nariman Point,
Mumbai 400 021, Maharashtra, India
Inventors:
1. NAYAK SHILPA GIRISH
2. LABDE JAYPRAKASH VINAYAK
3. SUBBIAH VENKATACHALAM
4. KELKAR ANIL KRISHNA
5. BHARADWAJ SANJAY KUMAR
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF THE DISCLOSURE:
The present disclosure relates to a process for recovering a monomeric substituent from an effluent. The present disclosure particularly relates to a process of recovering dicarboxylic acid from an effluent.
BACKGROUND:
Fabric processing with polyester is generally carried out to achieve the desired fabric properties such as improved comfort, feel, drape, wrinkle free, higher durability, moisture regain and the like. The fabric processing is mostly carried out in an aqueous alkali solution. During processing, polyester tends to dissolve in an aqueous alkali solution resulting in 5-45% weight reduction of the polyester used. Presently, this waste is drained as an effluent after insufficient or without treatment. The drained effluent is environmentally hazardous as it possesses very high chemical oxygen demand (COD) value i.e., about 36000 ppm. The high chemical oxygen demand is generally due to the dissolved organic and inorganic constituents. Therefore, to make the effluent environmentally safe, it is desirable to recover the organic/inorganic constituents. Further, it would also be economical if the recovery process results in high recovery of the constituent with high purity without excessive loss through decomposition or side reactions. The highly pure constituents recovered from the effluent may be reused to make the fabric processing further economical.
One of the prior arts disclose a method of isolating terephthalic acid by heating polyethylene terephthalate and 18 wt % solution of NaOH at 100 °C for 2 hrs and separating sodium salt of terephthalic acid from the reaction mixture. The sodium salt of terephthalic acid is then acidified, filtered, rinsed and dried to obtain terephthalic acid.

Another prior art discloses a process for recovering terephthalic acid from a composition comprising water, poly-e-caproamide and polyethylene terphthlate by heating with a solution of sodium hydroxide at temperatures of 210-250 °C followed by acidification.
In yet another prior art the polyester is contacted with an alkali metal hydroxide to form a hydrolyzed mixture containing an alkali metal carboxylic acid salt. The hydrolyzed mixture is then oxidized using an oxidizing agent such as air, hydrogen peroxide, ozone, oxygen, and mixtures thereof to form an oxidized mixture containing insoluble impurities followed by removing the insoluble impurities, and acidifying the oxidized mixture followed by recovering dicarboxylic acid from the acidified mixture.
Yet another prior art discloses the recovery of terephthalic acid by treating effluent with an aqueous ammonia solution followed by acidification using sulfuric acid and then filtration.
Recovery of terephthalic acid in 87-95 % from the waste containing polyethylene terephthalate and methyl benzoate after hydrolyzing the waste with sodium hydroxide has been reported in one of the prior arts.
One of the drawbacks associated with the prior art processes is the presence of considerable amount of impurities in the recovered terephthalic acid. These impurities tend to impart color to the recovered terephthalic acid making it unfit to be recycled for the preparation of the colorless polyethylene terephthalate articles.
Another drawback of the prior art processes is that they need elevated temperatures, high pressures and/or expensive equipment. Moreover, none of the processes is known wherein the recovery is achieved quickly with higher terephthalic acid yield. Other drawback with some of the prior arts is that the process for recovering terephthalic acid is complex and uneconomic.

Accordingly, it is desirable to provide an effective process which can recover dicarboxylic acid such as terephthalic acid in high yield and purity.
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.
It is another object of the present disclosure to provide a process for recovering dicarboxylic acid from an effluent.
It is still another object of the present disclosure to provide a process for recovering dicarboxylic acid which is simple and economic.
It is still another object of the present disclosure to provide a process for recovering dicarboxylic acid in high yield and purity.
It is still another object of the present disclosure to provide a process for recovering dicarboxylic acid which results in an environmentally safe effluent.
Other objects and advantages of the present disclosure will be more apparent from the following description when read in conjunction with the accompanying figures, which are not intended to limit the scope of the present disclosure.
In accordance with the present disclosure there is provided a process for recovery of dicarboxylic acid from an effluent comprising dissolved organic and inorganic constituents, said process comprising the following steps:
a. purging the effluent with a substantially oxygen free inert gas for a time period ranging between 12 hours and 48 hours followed by acidification to obtain a precipitate containing dicarboxylic acid; and

b. filtering the precipitate containing dicarboxylic acid and iteratively washing it to obtain a dicarboxylic acid having a purity of at least 85%.
Typically, the method step of purging is carried out at a temperature ranging between 20 °C and 40 °C.
Typically, the method step of acidification is carried out using acid having higher dissociation constant than that of the dicarboxylic acid.
Typically, the method step of acidification is carried out at a pH ranging between 1 and 6.
In one embodiment of the present disclosure the effluent is wastage generated during polyester fabric processing.
Typically, the dicarboxylic acid is at least one selected from the group consisting of terephthalic acid, isophthalic acid, phthalic acjd and adipic acid.
Typically, the organic constituent is at least one selected from the group consisting of benzoic acid, toluic acid, acetaldehyde, ethylene glycol and diethylene glycol.
Typically, the substantially oxygen free inert gas is at least one selected from the group consisting of argon, nitrogen, and substantially oxygen free air.
Typically, the method step of purging is carried out at a purging rate ranging between 30 mL/min and 80 mL/min.
In accordance with yet another embodiment of the present disclosure the method step of purging is carried out using air at a temperature 20 to 40°C and at a rate ranging between 30 mL/min and 80 mL/min to avoid oxidation of any of the organic/inorganic constituents present in the effluent.

In accordance with yet another embodiment of the present disclosure the recovered dicarboxylic acid is at least 99.99% pure.
Typically, the acid is at least one mineral acid selected from the group of acids consisting of aqueous hydrochloric acid, gaseous hydrochloric acid, sulfuric acid, nitric acid oleium and phosphoric acid.
Typically, the chemical oxygen demand of the effluent before and after the recovery of dicarboxylic acid is 36000 ppm and 1000 ppm respectively.
DETAILED DESCRIPTION:
Tonnes of alkaline effluent generated during polyester fabric processing are being drained without any reuse. This effluent is harmful to the environment as its chemical oxygen demand value is too high. To reduce chemical oxygen demand value either partly or fully it is desirable to recover the dicarboxylic acid present in the effluent.
The inventors of the present invention employ this effluent as a raw material and also to recover value added product such as dicarboxylic acid generally, and terephthalic acid particularly. The process developed by the inventors of the present disclosure for treating an effluent and recovering dicarboxylic acid is efficient, cost effective and environment friendly.
In accordance with one aspect of the present disclosure there is provided a process for recovery of dicarboxylic acid from the effluent comprising dissolved organic and inorganic constituents in addition to the dicarboxylic acid. The dicarboxylic acid to be recovered is at least one selected from the group consisting of terephthalic acid, isophthalic acid, phthalic acid and adipic acid. The effluent is particularly generated during polyester fabric processing.
In the first step, the effluent is purged with substantially oxygen free inert gas. The purging is carried out at a temperature ranging between 20 °C and 40 °C for

a time period ranging between 12 hours and 48 hours to obtain a purged effluent. The substantially oxygen free inert gas is purged through the effluent at a rate ranging between 30 mL/min and 80 mL/min. The substantially oxygen free inert gas employed to carry out purging is at least one selected form the group consisting of argon, nitrogen and substantially oxygen free air.
The substantially oxygen free inert gas can also be air with an adequate precautions being taken to obviate the reaction such as oxidation of the organic or inorganic components present in the effluent. Form the numerous experiments conducted by the inventors; it is found that the oxidation reaction takes place if the air is purged at a temperature ranging between 20° C and 40° C at a bubbling rate ranging between 30 mL/min and 80 mL/min. If purging conditions while purging air are not maintained within the limits then it may result in the formation of undesirable oxidized impurities which may contaminate terephthalic acid while precipitation. The purging of argon, nitrogen and substantially oxygen free air or normal air is carried out for the purpose of evaporating or venting relatively volatile organic components present in the effluent. This process helps either completely or a greater extent to get rid of the undesirable organic components that may otherwise co-precipitate with terephthalic acid during precipitation. The organic components that are evaporated during purging comprise benzoic acid, toluic acid, acetaldehyde, ethylene glycol and diethylene glycol. The organic components are either evaporated or vented is evident from the fall in the chemical oxygen demand value. In an exemplary embodiment of the present disclosure, if chemical oxygen demand value of the unpurged effluent is 36000 ppm then the chemical oxygen demand value falls to 25000 ppm after purging substantially oxygen free inert gas. Another advantage of purging an inert gas with an intention to avoid oxidation is that terephthalic acid loss due to oxidation is prevented to recover it in maximum yield.

In the second step, the purged effluent is acidified to a pH ranging between 1 and 6 to obtain a precipitate containing dicarboxylic acid. The acidification is carried out using an acid having higher dissociation constant than that of the dicarboxylic acid to be precipitated. The acid having higher dissociation constant than the dicarboxylic acid to be recovered is at least one selected from the group consisting of aqueous hydrochloric acid, gaseous hydrochloric acid, sulfuric acid, nitric acid, oleium and phosphoric acid. In the final step, the precipitate containing dicarboxylic acid is filtered. The residue is washed repeatedly with water to obtain a dicarboxylic acid having a purity of at least 99%. In accordance with one of the embodiment of the present disclosure the purity of the recovered dicarboxylic acid is at least 85 %. In accordance with another embodiment of the present disclosure the purity of the recovered dicarboxylic acid is at least 99.99 %.
In one of the embodiments the dicarboxylic acid is terephthalic acid. In an exemplary embodiment of the present disclosure the chemical oxygen demand value of the effluent after the recovery of dicarboxylic acid i.e., terephthalic acid is less than 1000 ppm.
The present disclosure is further described in light of the following examples which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure.
Example 1:
10 ml of HC1 was added to lOOg of effluent which was generated during the polyester fabric processing to precipitate terephthalic acid (pH 4). The precipitated terephthalic acid was washed with 200 ml of water for three times and dried to obtain 6.5g of terephthalic acid. The purity of the recovered terephthalic acid and COD value of the effluent after recovery of terephthalic acid were recorded and are represented in table 1.4

Example 2:
Argon gas was bubbled through lOOg of effluent which was generated during the polyester fabric processing for 48 hours at room temperature and at a rate of 60 mL/minute to obtain purged effluent. The purged effluent was acidified at pH 4 with 10 ml of HO to precipitate terephthalic acid. The terephthalic acid was filtered, washed with water and dried to obtain 6.5g of terephthalic acid. The purity of the recovered terephthalic acid and COD value of the effluent after recovery of terephthalic acid were recorded and are represented in table 1.
Table 1

Initial COD Final COD Terephthalic % purity of
value of an value of an acid per 100 terephthalic
effluent (ppm) effluent (ppm) gm of effluent acid
Example 1 36000 1100 6.5 g 83.0
Example 2 36000 1000 6.5 g 99.5
From the above results, it can be concluded that the purging of argon results in higher purity terephthalic acid.
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 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 specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment 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.

We Claim;
1. A process for recovery of dicarboxylic acid from an effluent comprising
dissolved organic and inorganic constituents, said process comprising the
following steps:
a. purging the effluent with a substantially oxygen free inert gas for a
time period ranging between 12 hours and 48 hours followed by
acidification to obtain a precipitate containing dicarboxylic acid;
and
b. filtering the precipitate containing dicarboxylic acid and iteratively
washing it to obtain a dicarboxylic acid having a purity of at least
85%.
2. The process as claimed in claim 1, wherein the method step of purging is carried out at a temperature ranging between 20 °C and 40 °C.
3. The process as claimed in claim 1, wherein the method step of acidification is carried out using acid having higher dissociation constant than that of the dicarboxylic acid.
4. The process as claimed in claim 1, wherein the method step of acidification is carried out at a pH ranging between 1 and 6.
5. The process as claimed in claim 1, wherein the effluent is wastage generated during polyester fabric processing.
6. The process as claimed in claim 1, wherein the dicarboxylic acid is at least one selected from the group consisting of terephthalic acid, isophthalic acid, phthalic acid and adipic acid.
7. The process as claimed in claim 1, wherein the organic constituent is at least one selected from the group consisting of benzoic acid, toluic acid, acetaldehyde, ethylene glycol and diethylene glycol.

8. The process as claimed in claim 1, wherein the substantially oxygen free
inert gas is at least one selected from the group consisting of argon,
nitrogen, and substantially oxygen free air.
9, The process as claimed in claim 1, wherein the method step of purging is
carried out at a purging rate ranging between 30 mL/min and 80 mL/min.
10.The process as claimed in claim 1, wherein the method step of purging is carried out using air at a temperature 20 to 40°C and at a rate ranging between 30 mL/min and 80 mL/min to avoid oxidation of any of the organic/inorganic constituents present in the effluent.
11.The process as claimed in claim 1, wherein the recovered dicarboxylic acid is at least 99.99% pure.
12.The process as claimed in claim 1, wherein the acid is at least one mineral acid selected from the group of acids consisting of aqueous hydrochloric acid, gaseous hydrochloric acid, sulfuric acid, nitric acid oleium and phosphoric acid.
13.The process as claimed in claim 1, wherein the chemical oxygen demand of the effluent before and after the recovery of dicarboxylic acid is 36000 ppm and 1000 ppm respectively.