Claims:WE CLAIM:
1. A process for recovering monomers and oligomers from polymer waste, said process comprising the following steps:
a. collecting polymer waste and separating polyester and non-polyester from said polymer waste;
b. pulverizing separated polyester waste to obtain pulverized polyester waste;
c. introducing said pulverized polyester waste in a pressure reactor and adding water to said pulverized polyester to obtain a slurry;
d. heating said slurry at a first predetermined temperature and at a predetermined pressure followed by adding a catalyst in said pressure reactor to obtain a reaction mass;
e. subjecting said reaction mass to selective crystallization at a second pre-determined temperature to obtain a biphasic mixture comprising solid phase comprising crystals of terephthalic acid and mother liquor;
f. separating said solid phase followed by drying to obtain monomers comprising terephthalic acid and oligomers comprising unreacted polyethylene terephthalate; and
g. distilling said mother liquor obtained in step (e) to obtain monomers comprising monoethylene glycol and diethylene glycol.
2. The process as claimed in claim 1, wherein a bleaching agent is added in step c) when said pulverized polyester waste is colored.
3. The process as claimed in claimed 1, wherein a bleaching agent is added in step f) when said solid phase is colored.
4. The process as claimed in claim 2 or claim 3, wherein said bleaching agent is selected from the group consisting of Linear alkyl benzene sulphonic acid (C10-C14).

5. The process as claimed in claim 1, wherein said polyester waste is selected from the group consisting of polyester bottles, polyester chips, polyester construction material, and polyester cloths.
6. The process as claimed in claim 1, wherein said catalyst is selected from the group consisting of an bleaching agent, organic acid, anionic surfactant and a combination thereof.
7. The process as claimed in claim 6, wherein said organic acid is at least one of non-substituted and substituted organic acid.
8. The process as claimed in claim 6 or claim 7, wherein said organic acid is at least one selected from the group consisting of oxalic acid, citric acid, malic acid, malonic acid, and benzene sulphonic acid.
9. The process as claimed in claim 6, wherein the concentration of said catalyst is in the range of 0.1% to 50% w/v.
10. The process as claimed in claim 6 or claim 7 or claim 8, wherein the concentration of said organic acid is in the range of 0.1% to 20% w/v.
11. The process as claimed in claim 6, wherein said anionic surfactant is selected from compounds having a carbon content in the range of C12-C48.
12. The process as claimed in claim 6 or claim 11, wherein said anionic surfactant is at least one selected from the group consisting of linear alkyl benzene sulphonic acid with alkyl chain from C10-C14, and heavy alkyl benzene sulfonic acid with alkyl chain from C20-C28 and C30-C42.
13. The process as claimed in claim 1, wherein said pulverized polyester waste is melted before introducing it into the pressure reactor in step (c).
14. The process as claimed in claim 1, wherein said first predetermined pressure is an autogenous pressure in the range of 10 bar to 100 bar.

15. The process as claimed in claim 1, wherein said first predetermined temperature is in the range of 160 oC to 220 oC and second predetermined temperature is in the range of 10 oC to 40 oC.
, Description:FIELD
The present disclosure relates to a process for recovery of monomers and oligomers from polyester waste.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.
The term “monomer” as used herein refers to a molecule that can undergo polymerization thereby contributing constitutional units to the essential structure of a macromolecule.
The term "oligomer" as used herein refers to a molecule that consists of a few monomer units. For example dimers, trimers, and tetramers are the oligomers composed of two, three, and four monomers, respectively.
The term “polymer” as used herein refers to a molecule where the number of monomers is not limited.
The term “autogenous pressure” as used herein refers to a vapor pressure of a solvent created in a reactor at a higher temperature (up to 200 oC). The autogenous pressure can be in the range of 10 bar to 100 bar based on the use of the solvent.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
The common existence of polyester is for packaging, storage of household items, water, and different beverages. Polyethylene terephthalate (PET) is polyester manufactured by using polymer grade terephthalic acid and monoethylene glycol. There are various industrial applications of polyethylene terephthalate such as use in different grades of film, fiber, and bottle, use in textile industries, and in pharmaceutical industries.
Fiber grade polyester can blend with natural polymer such as cotton for making various clothing applications. Polyesters can be 100% recycled. However, the biodegradability is a major concern in respect of polyesters. Millions of tons of polyester waste is generated which creates an environmental burden. Increased environmental awareness, statutory measures, and public demand for environmental sustainability are leading to a noticeable interest in plastic recycling. Various types of chemical recycling of polyesters such as poly (ethylene terephthalate) (PET) are under study. Some of the promising chemical recycling processes are glycolysis, methanolysis, acid-base hydrolysis, aminolysis, glycolysis-hydrolysis, etc.
However, the aforestated conventional processes use metal acetates for glycolysis, strong acid like H2SO4, and HCl in acid hydrolysis, strong base like NaOH, and KOH for base hydrolysis and triethanol amine for aminolysis for recycling of PET. Further, the conventional depolymerization processes recover mainly Bis (hydroxy ethylene) terephthalate as a main monomer.
Therefore, there remains a need to develop a process for recovery of monomers and oligomers that overcome the drawbacks as described hereinabove.
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 simple, cost effective and a single step process for recovery of monomers, and oligomers from polyethylene terephthalate waste.
Another object of the present disclosure is to provide a process for recovery of monomers comprising terephthalic acid and monoethylene glycol, and oligomers comprising unreacted polyethylene terephthalate from polyester waste, which is environment friendly.
Still another object of the present disclosure is to provide a process for recovery of terephthalic acid, monoethylene glycol, diethylene glycols, and polyethylene terephthalate from polyester waste.
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 relates to a process for recovery of monomers comprising terephthalic acid and monoethylene glycol, and oligomers from Polyester waste. The process comprises acid hydrolysis of polyester waste using a catalyst selected from the group consisting of an organic acid, anionic surfactant, and a combination thereof, at a predetermined temperature and a predetermined pressure for a predetermined time to obtain a reaction mass comprising the monomers and oligomers. The monomers and oligomers can be separated from the reaction mass to obtain monomers comprising terephthalic acid and monoethylene glycol and oligomers comprising unreacted polyethylene terephthalate.
DETAILED DESCRIPTION
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed elements.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.

Polyesters are commonly used in packaging such as packaging for storage of household items, water, and different beverages, clothing and have various commercial applications. Although polyesters can be recycled, the biodegradability is a major concern to the environment. There are various types of chemical polyester recycling processes such as glycolysis, methanolysis, acid-base hydrolysis, aminolysis, glycolysis-hydrolysis etc.
However, the conventional chemical recycling processes use strong chemicals (strong acids/strong bases) for recycling of polyesters, which is not environment friendly. Further, bis (hydroxyethylene) terephthalate is the main monomer obtained from the conventional methods, which is a burden for disposal.

Therefore, the present disclosure envisages a simple process for the recovery of monomers comprising terephthalic acid and monoethylene glycol; and oligomers comprising unreacted polyethylene terephthalate from polyester waste using mild reactants.
In an aspect of the present disclosure, there is provided a process for recovery of monomers comprising terephthalic acid and monoethylene glycol; and oligomers from Polyester waste. The process is described in detail.
First, the polymer waste is collected from various sources. In an embodiment, the polyester waste can be collected from food malls, hotel, grocery stores, apartments, municipal plastic waste and the like
The polymer waste can be separated into polyester waste and non-polyester waste. The polyester waste can be polyethylene terephthalate bottles, polyester cloths, polyester cloths blended with cotton, polyester material used in the constructions, and the like. The polyester waste can be transparent material or colored material.
The separated polyester waste is pulverized to obtain a pulverized polyester waste. The pulverized polyester waste can be in the form of powder, chips, flakes and the like.
The pulverized polyester waste is introduced in a pressure reactor followed by adding water and optionally bleaching agent to obtain slurry. The pressure reactor has motorized stirrer with digital controller to control and monitor temperature, pressure and stirring speed. In one embodiment the temperature of the pressure reactor is in the range of 160 oC to 220 oC, pressure is in the range of 10 bar to 100 bar and stirring speed is in the range of 25 rpm to 1500 rpm. In an embodiment the temperature of the pressure reactor is 200 oC, pressure is 50 bar and the stirring speed is 1000 rpm.
The ratio of pulverized polyester waste to water is in the range of 1:18 to 1:750. In an embodiment the ratio of pulverized polyester waste to water is 1:550.
In another embodiment the pulverized polyester waste can be melted before introducing it into the pressure reactor.
The addition of bleaching agent to the pulverized polyester waste along with water in the pressure reactor is optional due to the fact that the bleaching agent is used for removing color of the polyester waste. In an embodiment the bleaching agent is not added when the polyester waste is transparent. In another embodiment the bleaching agent is added when the polyester waste is colored.
The so obtained slurry is heated in the pressure reactor at a first predetermined temperature and at a predetermined pressure followed by adding a catalyst in the reactor to obtain a reaction mass.
In one embodiment, the catalyst is added in the pressure reactor along with water, which is mixed separately before the addition. In another embodiment the mixture of water and catalyst is heated at a temperature in the range of 50 oC to 75 oC prior to the addition in the pressure reactor.
The catalyst can be selected from an organic acid catalyst, an anionic surfactant, and a combination thereof.
The organic acid used can be at least one catalyst selected from non-substituted and substituted organic acid. The organic acid can be at least one selected from the group consisting of oxalic acid, citric acid, malic acid, malonic acid and benzene sulphonic acid and combinations thereof. Typically, the organic acid is oxalic acid.
The anionic surfactant can play a dual role in the reaction, namely, it acts as a catalyst for hydrolysis and also as a bleaching agent to remove the color of the polyester waste. The anionic surfactant used as a catalyst can be anionic surfactant with a carbon content ranging from C12-C48. Particularly, the anionic surfactant can be at least one selected from linear alkyl benzene sulphonic acid with alkyl chain from C10-C14, and heavy alkyl benzene sulfonic acid with alkyl chain from C20-C28 and C30-C42.
The concentration of the organic acid used in the process of the present disclosure can be in the range of 0.1% to 20% w/v of the total reaction mass. In one embodiment the concentration of the organic acid is 5% w/v.
In the present disclosure, the ratio of the polyester waste and the organic acid can be in the range of 0.25-50 w/w. In one embodiment, the ratio of the polyester waste and the acid is 20 w/w.
In accordance with the present disclosure, the first predetermined temperature can be in the range of 160 oC to 220 oC. In an embodiment the first predetermined temperature is 175 oC.
The predetermined pressure can be an autogenous pressure generated due to the water vapors in the pressure reactor. The autogenous pressure in the pressure reactor can be in the range of 10 bar to 100 bar. The autogenous pressure in accordance with the present disclosure depends on the solvents and catalyst used in the reactor.
The so obtained reaction mass can be subjected to selective crystallization at a temperature in the range of 20 oC to 40 oC to obtain a biphasic mixture comprising solid phase comprising monomers and oligomers and mother liquor comprising monoethylene glycol and diethylene glycol. The solid phase comprising monomers comprises crystals of terephthalic acid which can be separated by filtration and the so obtained crystals of terephthalic acid can be washed with water, followed by drying to obtain dried crystals of terephthalic acid. In one embodiment crystallization is carried out at 25 oC.
The solid phase comprising oligomers comprises unreacted polyethylene terephthalate that can be further processed to obtain oligomers.
Further, the mother liquor is subjected to distillation at a temperature in the range of 50 oC to 300 oC to obtain monoethylene glycol as a monomer. Diethylene glycol is also separated from further distilling the mother liquor at a temperature in the range of 200 oC to 250 oC as a byproduct, which can be further used in various applications.
The process of the present disclosure is a single step process and hence is simple and cost effective. The process of the present disclosure uses organic acid catalyst which can be recycled after reaction and may be reused. Therefore the process of the present disclosure is environment friendly.
EXPERIMENTAL DETAILS
Experiment 1:
2.5 gms of small pieces of transparent PET bottles were taken as a waste. The waste was introduced in the pressure reactor having motorized stirrer with digital controller to control and monitor Temperature, pressure and stirring speed. 50 gm water was added into the pressure reactor containing pieces of transparent PET bottles. 4.5% w/v concentration of oxalic acid was added in the reactor. The reactor was heated to 200 oC wherein 30 bar autogenous pressure was generated in the reactor. The reaction was kept for 480 minutes to obtain 1.6 g of terephthalic acid.

Experiments 2- 16:
Experiments 2-16 was repeated using various catalysts, different concentration of catalyst, various types of waste material, different temperature and pressure, different residence time. The results are summarized in Table 1 below.
Table 1
Expt. No. Waste PET PET : Water mole ratio Catalyst Name and conc. in w/w Temperature
in 0C Pressure in bar Bleaching Agent Conc. in w/w Reaction Time in min. % yield in terms of
TA recovery Remarks
1 Transparent PET bottles cut in small pieces 1:210
i.e., 2.5 g of PET waste in 50g. water Oxalic acid 4.5 % 200 Autogenous - 30 Not required 480 75%
1.6 g. white powder collected ? Powder was dissolved in Caustic and regenerated by HCl.
? Powder was analyzed on HPLC and compared and confirmed by authentic Terephthalic Acid.
? Mother liquor was not analyzed.
2 Transparent PET bottles cut in small pieces 1:18 i.e., 122.5g of PET in 211.6 water Oxalic acid 4.5 % 200 Autogenous - 50 Not required 480 91%
96g of white powder collected ? Powder was dissolved in Caustic and regenerated by HCl
? Powder was analyzed on HPLC analysis was compared and confirmed by authentic Terephthalic Acid.
? Mother liquor was analyzed and confirmed presences of Ethylene Glycol (EG), Di-ethylene Glycol (DEG) by GC-MS method with authentic Ethylene glycol (EG) and Di-ethylene glycol.
? 78% EG, 4% DEG and 18% of unknown were formed.
3 Light Green PET bottles cut in small pieces 1:40 i.e 10g. Of PET in 37.50g. of water Oxalic acid 4.5% 200 Autogenous - 40 - 180 85% 7.2g of white powder ? Powder was dissolved in Caustic and regenerated by HCl
? Powder was analyzed on HPLC.
HPLC analysis was compared and confirmed by authentic Terephthalic Acid.
? During dissolving in Caustic, unreacted PET polymer separated by decantation which was 2% on the basis on PET.
? Mother liquor was not analyzed
4 Blue PET bottles cut in small pieces 1:60 i.e 30g PET in 170g of water HABS (Laboratory made )
5% 175 Autogenous - 15 Work as catalyst as well as Bleaching agent 180 60% i.e. 15 g of white powder ? Paste type mass was observed.
? Treated with alkaline water and toluene.
? Separated Aq. alkaline layer was treated with O-phosphoric acid, white powder appeared.
? HPLC analysis was confirmed by authentic Terephthalic Acid.
5 Mixed (20 % each of Green ,Blue, Brown and white) PET bottles cut in small pieces 1:40 i.e 15 g PET in 55 g of water HABS (Laboratory made )
5% 175 Autogenous - 15 Work as catalyst as well as Bleaching agent 60% i.e. 7.7 g of white powder ? Paste type mass was observed.
? Treated with alkaline water and toluene.
? Aq. alkaline layer separated was treated with O-phosphoric acid, white powder appeared

6 Mixed (20 % each of Green ,Blue, Brown and white) PET bottles cut in small pieces 1:40
i.e., 15 g PET in 55 g of water HABS (Laboratory made )
0.15% 200 Autogenous - 12 Work as catalyst as well as Bleaching agent 180 90%
11g. white powder collected ? No Paste type mass was observed.
? Greenish white solids observed turned white after washing with hot water.
? HPLC analysis was confirmed by authentic Terephthalic Acid.

7 Blue PET bottles cut in small pieces 1:40
i.e., 15 g PET in 55 g of water LAS (90% Pure)
0.9% 200 Autogenous - 12 Work as catalyst as well as Bleaching agent 180 96%
11.45 g of white –off white powder collected ? White –off white powder.
? HPLC analysis was confirmed by authentic Terephthalic Acid.
? 75% Mother Liquor was collected and recycled.

8 Blue PET bottles cut in small pieces 1:40 i.e 15 g PET in Recycled (45g)
Mother liquor with(10 g) 20% make up with water
LAS (90% Pure)
0.20%
Make up catalyst 200 Autogenous - 12 Work as catalyst as well as Bleaching agent 180 96% 11.43 g of white –off white powder collected ? White –off white powder.
? HPLC analysis was confirmed by authentic Terephthalic Acid.
? Mother liquor recycling was successfully achieved.
9 Green PET bottles with other polymer like PP caps, Labelle and rings which cut in small pieces 1:50 i.e 9.9g PET with 0.33g PP ring,1.18g of PP cap and 0.16g of PP Labelle in 170g of water LAS (90% Pure)
0.8% 200 Autogenous - 15 Work as catalyst as well as Bleaching agent 180 90% i.e., 7.62 g of white powder ? White –off white powder.
? HPLC analysis was confirmed by authentic Terephthalic Acid.
? 85% Mother Liquor was collected.
? PP polymer agglomerated and forms one lump.

10 100% White polyester cloth 1 : 535
i.e., 1g of cloth in 50 g of water 0.15% LAS (90% pure) 200 14 Work as catalyst as well as Bleaching agent 120 65% i.e., 0.55 g of white powder ? White off white powder.
? HPLC analysis was confirmed by authentic Terephthalic Acid.
? 90% Mother Liquor was collected.

11 100% (Dark Brown) colored polyester cloth 2.5 g of cloth in 50 g water. 5% Sodium hypochloride 60 and 90 1 atm. Bleaching agent 180 Color extraction observed ? Extraction was not observed at 60 oC
? Hence temperature was raised to 90 oC where no complete bleaching of polyester cloth was occurred.
? Mother liquor was colorless.
12 100% (Dark Brown) colored polyester cloth 2.5 g of cloth in 50 g water. 5% LAS (90% pure) 60 and 90 1 atm. Color extraction 180 Color extraction observed ? Extraction was observed at 60 oC
? For better extraction temperature was raised to 90 oC where no complete bleaching was occurred.
? Color pigment gets extracted in Mother Liquor and was turned brown.
13 100% (Dark Brown) colored polyester cloth 2% loading on weight basis i.e., 1 gm of Polyester cloth and 50 g of Benzyl alcohol : Isopropanol in 40:60 ratio Color extraction 150 Autogenous - 10 Benzyl alcohol : Isopropanol in 40:60 ratio -Color extraction 60 Color extraction observed ? Dark Brown polyester color extraction achieved and it became white to off white fiber
? Mother liquor extracts color pigment.
? Colored Mother Liquor was distillated and colorless solvent was recovered and reused for further extractions experimentations.
14 Extracted polyester fiber 1 : 535 i.e.1g extracted polymer in 50 ml water LAS (90% pure) 0.33% 200 Autogenous - 12 Work as catalyst as well as Bleaching agent 30 20% i.e., 0.2 g of white powder ? White/ off white powder.
? HPLC analysis was confirmed by authentic Terephthalic Acid.
? 90% Mother Liquor was collected.
? Unreacted solubilized PET has recrystallized after 24 hrs storage.
15 100% (Dark Brown) colored polyester cloth 2% loading on weight basis i.e. 1 gm of Polyester cloth and 49 g of LAS LAS (90% pure) as solvent 200 Autogenous - 14 Work as catalyst as well as Bleaching agent 180 Color extraction observed ? Thick mass was observed
? Water was added to thick mass Buff Colored powder observed.
16 100% (Dark Brown) colored polyester cloth 2% loading on weight basis i.e. 1 gm of Polyester cloth and 50% of LAS in water LAS (50% pure) as solvent 200 Autogenous - 14 Work as catalyst as well as Bleaching agent 180 Color extraction observed ? White/ off white powder.
? HPLC analysis was confirmed by authentic Terephthalic Acid.
? 90% Mother Liquor was collected.
LAS-Linear alkyl sulfonate
HABS-heavy alkyl benzene sulfonate

From table 1, it is observed that terephthalic acid is recovered/obtained from the polymer waste by using the catalyst, i.e. oxalic acid, LAS (Linear alkyl sulfonate) and HABS (heavy alkyl benzene sulfonate) in accordance with the process of the present disclosure. The catalyst is also acting as a bleaching agent in some reactions. Therefore, the process of the present disclosure is economic and environment friendly. The authenticity of so obtained terephthalic acid, monoethylene glycol and diethylene glycol are confirmed by various advanced analytical techniques like LCMS, GCMS, HPLC, TGA analysis.

TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE
The present disclosure described herein above has several technical advantages including, but not limited to, a process for recovery of monomers and oligomers from polyester waste, wherein the process is:
? a single step process, and hence cost effective; and
? environment friendly.

The foregoing description of the specific embodiments so fully reveals the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
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.