Mechanochemistry-assisted depolymerization process for preparation of di-octyl terephthalate

Abstract

The present invention relates to process for preparation of green plasticizer Di-Octyl Terephthalate (DOTP) from polyethylene terephthalate (PET) post-consumer plastics waste through mechanically assisted degrative transesterification. More particularly, the present invention relates to continuous process for preparation of Di-Octyl Terephthalate using mechano-chemical assisted degradative transesterification of post consumed PET bottles. The mechanically assisted depolymerization under elevated pressure provides milling-assisted depolymerization under elevated pressure with the mass ratio of the PET to the secondary alcohol 1:3-4, temperature in the range of 200 to 220°C, and reaction time in the range of 3 to 4 hours, the degradation rate of the PET can reach 100 %, and the yield of the DOTP reaches to upto 90%. The process has the characteristics of a fast reaction rate, avoiding the formation of side chain oligomers and thereby attaining a high diester yield.

Description

[0001] P_IN 105466

[0002] MECHANOCHEMISTRY-ASSISTED DEPOLYMERIZATION PROCESS FOR PREPARATION OF DI-OCTYL TEREPHTHALATE

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to process for preparation of green plasticizer Di-Octyl Terephthalate (DOTP) from polyethylene terephthalate (PET) post-consumer plastics waste through mechanically assisted degrative transesterification. More particularly, the present invention relates to continuous process for preparation of Di-Octyl Terephthalate using mechano-chemical assisted degradative transesterification of post consumed PET bottles. The mechanically assisted depolymerization under elevated pressure provides milling-assisted depolymerization under elevated pressure with the mass ratio of the PET to the secondary alcohol 1:3-4, temperature in the range of 200 to 220°C, and reaction time in the range of 3 to 4 hours, the degradation rate of the PET can reach 100 %, and the yield of the DOTP reaches to upto 90%. The process has the characteristics of a fast reaction rate, avoiding the formation of side chain oligomers and thereby attaining a high diester yield.

[0005] BACKGROUND OF THE INVENTION:

[0006] PET excellent performance makes it ideal polymeric material for beverage bottles, fibers, films, film bases, and electrical insulation. However, rising PET consumption poses waste management challenges. Inadequate recycling leads to resource depletion and environmental pollution, stressing the need for effective waste management solutions.

[0007] The primary method for treating post-consumer waste PET is thermal recycling, but over the repeat recycling of same material that faces challenges such as diminished physical properties, transparency, and hygiene due to impurities and thermal degradation. Other methods, including landfill, incineration, and thermal cracking, have limitations. As alternative, depolymerization of polymer to produce high value-added products offers a promising recycling solution.

[0008] Dioctyl terephthalate (DOTP) is a superior green plasticizer for polyvinyl chloride (PVC) plastics, exhibiting enhanced properties compared to Di-isooctyl Phthalate (DOP). DOTP offers advantages such as heat and cold resistance, low volatility, extraction resistance, flexibility, and excellent electrical insulation and it is eco-friendly. It demonstrates superior durability, soap resistance, and low-temperature flexibility. The low volatility of DOTP ensures compliance with temperatureP_IN 105466

[0009] resistance requirements for wire and cable applications, making it suitable for 70°C resistant cable materials (IEC standard) and various other PVC soft products.

[0010] In addition to its extensive application in cable materials and PVC, DOTP is utilized in the production of artificial leather films. Its excellent compatibility extends to its use as a plasticizer for acrylonitrile derivatives, polyvinyl butyral, nitrile rubber, and nitrocellulose. Furthermore, DOTP is employed as a plasticizer for synthetic rubber, a paint additive, a precision instrument lubricant, a lubricant additive, and a paper softener. Consequently, synthesizing DOTP from postconsumer waste PET provides dual environmental and economic benefits, attracting significant interest.

[0011] References may be made to CN patent CN 102241592 A, wherein process for producing dioctyl terephthalate from polyester waste in presence of metatitanic acid lipid material as a catalyst disclsoed. It further discusses the transesterification reaction condition temperature 180 °C~

[0012] 240 °C, pressure -0.01MPa~-during 0.03MPa. and decolorization of reaction mixture using granular activated carbon.

[0013] References may be made to IN patent application IN202011035841, wherein Transition Metal Based Heterogeneous catalyst for the Production of Plasticizer Dioctyl terephthalate disclosed. Transition Metal Based Heterogeneous catalyst is comprised of transition metals such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn, more specifically Fe or a mixture of Fe and one of the metals from first transition metal series dispersed on biomass derived activated carbon. Further the catalyst is recovered using centrifugation.

[0014] References may be made to CN patent CN102617352A, wherein method for preparing dioctyl terephthalate (DOTP) from waste and old polyethylene glycol terephthalate (PET) through near- critical alcoholysis disclosed the reaction was proceeded without catalyst under critical temperature is 3()()~350 °C, and the reaction times is 3~4h.

[0015] References may be made to CN patent CN 112521279 described the synthesis of environment-friendly plasticizer DOTP by Esterification of Terephthalic acid obtain from crushed PET waste. Crushed PET mixed with 8-15% NaOH methanol solution, added with catalyst, heated to 190 °C then mixture heated to to 250-300 °C, evaporating and recovering the ethylene glycol obtained in the reaction, and adding acid to obtain terephthalic acid. Further decolorization and alkali wash is performed to remove color, acidic and alkaline contaminants.P_IN 105466

[0016] References may be made to US patent US11117853B2 described methods for manufacturing and decolorizing dioctyl terephthalate by transesterification of PET using Tetraisopropyl titanate, tetraisobutyl titanate, and tetra (2-ethylhexyl) titanate catalyst followed by alkali wash and decolorization of unpurified DOTP. Further for color removal reducing agent among thiourea dioxide aqueous solution, hydrogen peroxide, and an aqueous solution of sodium borohydride and sodium hydroxide used.

[0017] The following discussion presents a review of the existing literature pertaining to batch process for preparation and decolorizing dioctyl terephthalate by transesterification of PET, rendering an overview of the prior art references in this field. These references serve as a testament to the extensive research conducted in this area and provide valuable insights into the techniques and methodologies employed in the preparation of dioctyl terephthalate by transesterification of PET. The above information disclosed is only for the enhancement of understanding of the background of the invention.

[0018] However, the above investigations and inventions are restricted to batch processes that lack control over the transesterification rate and report a minimum production rate. The reactors used are conventional batch reactors without any process intensification. The down streaming steps are time-consuming, especially during alkali wash and neutralization. Scalability is another issue, with difficulties in maintaining efficiency and cost-effectiveness at larger scales.

[0019] Currently, Dioctyl terephthalate (DOTP) is primarily synthesized from post-consumer waste PET through alkaline hydrolysis or alcoholysis methods. Alkaline hydrolysis involves intricate processes, high expenses, and low yields, constraining its practical application. Alcoholysis directly converts post-consumer PET with iso-octyl alcohol, requiring catalysts like zinc acetate or titanic acid to enhance DOTP yield. However, alcoholysis faces challenges such as catalyst hydrolysis susceptibility, elevated costs, environmental impact, prolonged reaction times, and purification complexities due to high solvent residue and presence of yellowish color. Despite improvements over alkaline hydrolysis, these factors limit the widespread adoption of the alcoholysis method for DOTP production from post-consumer PET waste.

[0020] Thus, keeping in view the drawbacks of the hitherto reported prior arts, there are still opportunities to enhance this process, making it more environmentally sustainable and effective.

[0021] In view of the above and obviate the drawbacks of existing prior arts, present invention relates to continuous process for preparation of Di-Octyl Terephthalate using mechano-chemical assisted degradative transesterification of post consumed PET bottles in a short period of time, which is anP_IN 105466

[0022] environmentally sustainable Process. The continuous process consisting the conversion of batch system into continuous mode of operation using Continuous Stirred Tank Reactors [CSTR] configuration along with a melt feeder and attrition reactor for the PET dissolution and conversion via degradative transesterification reaction and product recovery.

[0023] OBJECTIVE OF THE INVENTION

[0024] The main objective of the present invention is to provide a process for the continuous production of Di-Octyl Terephthalate using mechano-chemical assisted degradative transesterification of post consumed PET bottles.

[0025] Another objective of the present invention is provided use of organo metallic catalyst to enhance reaction time and yield of Di-Octyl Terephthalate product.

[0026] Another objective of the present invention is to continuous process consisting the conversion of batch system into continuous mode of operation using Continuous Stirred Tank Reactors [CSTR] configuration along with a melt feeder and attrition reactor for the PET dissolution and conversion via degradative transesterification reaction and product recovery.

[0027] Another objective of the present invention is to recover used catalyst from the system through high-speed centrifugation before product downstream.

[0028] Another objective of the present invention is to decolorized & remove impurities from the product mixture in high-speed centrifugation system.

[0029] SUMMARY OF THE INVENTION

[0030] Additional features and embodiments of the present disclosure will be better understood through the techniques and other aspects of the disclosure. Other embodiments of the invention are described in detail herein and are considered a part of the claimed disclosure.

[0031] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description section. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0032] The following is a condensed description of the disclosure to give the reader with a basic understanding. Its main goal is to present some of the principles described in this document in a simpler version as a prologue to the more extensive exposition that follows.P_IN 105466

[0033] The present invention, and in accordance with main aspect of the present invention relates to continuous process for preparation of Di-Octyl Terephthalate using mechano-chemical assisted degradative transesterification of post consumed PET bottles in a short period of time, which is an environmentally sustainable Process.

[0034] An aspect of the present invention to provide Mechano-chemical assisted degrative transesterification to overcome technical challenges of slow dissolution and reaction rate in alcoholysis of post-consumer PET waste to green plasticizer (DOTP) in view of prior art.

[0035] An aspect of the present invention, continuous mechano-chemical reactor system [S102] using continuous stirred tank reactor (CSTR) configuration for producing green plasticizer Di-Octyl Terephthalate (DOTP) from post-consumer polyethylene terephthalate (PET) waste, comprises of:

[0036] a) attrition mill / ball mill reactor

[0101] ;

[0037] b) nitrogen purging tube [102a-c];

[0038] c) condenser [103a-c];

[0039] d) decanter (Dean-Stark apparatus) [104a-c];

[0040] e) vent valves (105a-c);

[0041] f) metering pump for solvent charging

[0106] ;

[0042] g) gravity feeder

[0107] ;

[0043] h) melt extruder

[0108] ;

[0044] i) jacketed reactors [109a-b];

[0045] j) buffer tank [HO];

[0046] k) pumps [llla-c];

[0047] l) tubular bowl centrifuge [112a-b];

[0048] m) stirring tanks [113,114];

[0049] n) heteroazetropic distillation tower

[0115] ;

[0050] wherein, the attrition mill / ball mill reactor

[0101] comprises a vessel and zirconia ball having a diameter ranging from 5-8 mm along with an agitator shaft; wherein, the gravity feeder (107) is operating at the control process in a range of 10 g / min to 75 g / min.

[0051] Another aspect of the present invention is to provide novel batch and continuous mechano-chemical reactor system for producing green plasticizer (DOTP) from post-consumer PET waste to solve the above technical problems comprising: a pre -retreatment of post-consumer PET waste (S100), Mechanical assisted continuous degrative transesterification (S102), catalyst recoveryP_IN 105466

[0052] (S104), a decolorization (S106), a neutralization / washing system (S108), a Heteroazeotropic distillation system (S110), a filtration (S112) and obtained purified DOTP, characterized in that:

[0053] S100 - Pretreatment: The post-consumer PET waste sorted from polymer mix then it is washed with solvent and dried and crushed into particles with a side length of about 0.5 to 2 mm.

[0054] S102 - Mechanical assisted degrative transesterification: This system comprises a solvent and feed tanks, a Mechanical assisted degrative transesterification reactor, decanter, reflux condenser, pressuring regulator, condensation and collection tank,

[0055] S104 - Catalyst recovery: After the reaction completed, the crude mixture allows to centrifuge (Bowl centrifuge) for remove / recover used catalyst in the system.

[0056] S106 - Decolorization: This present invention S102 providing an unpurified dioctyl terephthalate; mixing the unpurified dioctyl terephthalate with a reducing agent, stirring for 0.5 to 1 hours, keeping for layer separation, to obtain a first decolorizing product; wherein the decolorizing adsorbent material has an acid value between 0.1 and 2 mg KOH / g, a relative humidity between 2 and 10%, and a fineness between 80 and 100 cm2 / g. (in tubular centrifuge)

[0057] S108 - Neutralization / washing: This system includes a neutralization / washing tank of crude DOTP. In this the product pH is maintained.

[0058] S110 - Heteroazeotropic distillation system: the neutralized product is purified from organic impurities by using water as an extractive distillate.

[0059] An another aspect of the present invention, wherein continuous mechano-chemical reactor system, the flow rates of 106 and 107 are maintained in a specific ratio of 1:2.5 -3.5 with a dissolution temperature in range of 200-220°C in

[0101] under a total pressurized condition in the range of 1.5-2.5 bar for a residence time period in the range of 30-90 min and a complete degradative transesterification undergoes in 109 a & b under temperature in the range of 190- 195 °C under 0.5-1 bar pressure with a total residence period in the range 180-240 min.

[0060] Another aspect of the present invention, wherein continuous mechano-chemical reactor system, the recovery of the organometallic catalyst from crude product is done by high-speed tubular centrifuge (112a) before product downstream through decolorization

[0113] and neutralization

[0114] and purification

[0115] .

[0061] Yet another aspect of the present invention, wherein S 102 step is under a reaction pressure between 1-3 bar, a reaction temperature between 190 and 220° C., and a reaction time between 3 to 4 hours. Yet another aspect of the present invention, wherein the C3-C12 secondary alcohol is at least one selected from the group consisting of n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol,P_IN 105466

[0062] pentanol, hexanol, heptanol, octanol, isooctanol, 2-ethylhexanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether and ethylene glycol monobutyl ether.

[0063] Another aspect of the present invention, a process for preparation of green plasticizer Di-Octyl Terephthalate (DOTP) from polyethylene terephthalate (PET) post-consumer plastics waste through a continuous mechano-chemical reactor system by mechanically assisted degrative transesterification, comprising the steps of;

[0064] a) vacuuming the attrition reactor (101) and refilled with nitrogen though nitrogen purging tube (102a) by maintain back pressure rate (BPR) with vent valves (105A);

[0065] b) adding pretreated polyethylene terephthalate (PET) waste in melt extruder (108) through hopper of gravity feeder (107);

[0066] c) melting PET waste in melt extruder (108) at temperature in the range of 200-240°C;

[0067] d) passing melted PET waste through a 0.5mm die as a melted filament into an attrition mill / ball mill (101);

[0068] e) charging mixture of secondary alcohol and organometallic catalyst through metering pump (106) simultaneously in attrition mill / ball mill (101);

[0069] f) heating the attrition reactor (101) at the temperature in the range of 200-250 °C for the time period in the ranges 30-90 minutes under a total pressurized condition in the range of 1.5-2.5 bar;

[0070] g) refluxing to remove the excess secondary alcohol by distillation in condenser (103a) and collected in Decanter (104a) using Dean-Stark apparatus and passed in the attrition reactor (101) to obtain homogenized reaction mixture;

[0071] h) passing the homogenized reaction mixture to jacketed reactor (109a) and further (109b); i) heating the jacketed reactor (109a, b) at the temperature in the range of 190-195°C under 0.5- 1 bar pressure with a total residence period in the range of 180-240 min;

[0072] j) refluxing back the excess secondary alcohol by distillation in condenser (103b,c) and collected in decanter (104b, c) using Dean-Stark apparatus to pass in the jacketed reactor (109a, b) for the completion of degradative transesterification of PET to obtain crude DOTP; k) collecting crude DOTP in the buffer tank (110);

[0073] l) pumping the crude DOTP by pump (Illa) to tubular bowl centrifuge (112a);

[0074] m) centrifuging the crude DOTP by the rotation ranges from 10000-15000 rpm to settle down the crude DOTP to the bottom of the tubular bowl to separate the catalyst from the crude product; n) passing crude DOTP to stirring tanks (113) and added base solution;P_IN 105466

[0075] o) pumping the mixture by pump (111b) to tubular bowl centrifuge (112b);

[0076] p) centrifuging the mixture by the rotation ranges from 10000-15000 rpm to settle down the crude DOTP to the bottom of the tubular bowl to remove oligomers;

[0077] q) passing crude DOTP to stirring tanks (114) and added water for pH adjustment;

[0078] r) pumping the crude DOTP by pump (111c) with continuous water flow to heteroazetropic distillation tower (115);

[0079] s) collecting the purified DOTP at the boom of heteroazeotropic distillation column;

[0080] Another aspect of the present invention, wherein PET waste is taken as the raw material.

[0081] Another aspect of the present invention, wherein the secondary alcohol (C3-C12) is selected from n-propanol, isopropanol, n-butanol, sec -butanol, tert-butanol, pentanol, hexanol, heptanol, octanol, isooctanol, 2-ethylhexanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether or ethylene glycol monobutyl ether in degrative transesterification step.

[0082] Yet another aspect of the present invention, wherein the PET waste and secondary alcohol is mixed in the mass ratio of 1:3-4.

[0083] Still yet another aspect of the present invention, wherein organo-metallic catalyst is selected from the stannous acid or butyl acetonic acid in the 0.1-2% of the weight ratio of PET waste in degrative transesterification step to enhance reaction time and yield of DOTP product.

[0084] Still yet another aspect of the present invention, wherein base is selected from alkali hydroxides with a normality range of 0.3-2.0N and weight ratio of 0.5-2.0 with respective crude DOTP in the neutralization step.

[0085] Still yet another aspect of the present invention, wherein ethylene glycol is formed as by product and collected with water in Dean-Stark apparatus.

[0086] Still yet another aspect of the present invention, wherein the pretreatment of polyethylene terephthalate (PET), consisting the steps of;

[0087] a) collecting and sorting the post-consumer polyethylene terephthalate (PET) waste from polymer mix;

[0088] b) washing the sorted polyethylene terephthalate (PET) waste with solvent and dried through centrifugation followed air drying to ensure that PET waste moisture < 0.5% to inhibit product quality and process inefficiency;

[0089] c) shredding the dried PET waste into particles with a side length of about 0.5 to 2 mm.

[0090] Still yet another aspect of the present invention, wherein detergent is used as washing compound to remove impurities like dirt, grease, food residues, and labels from the PET waste.P_IN 105466

[0091] Still yet another aspect of the present invention, wherein polyethylene terephthalate (PET) bottle caps which is made up of High-Density Polyethylene (HDPE) are sorted.

[0092] Yet another aspect of the present invention, wherein catalyst is at least one selected from the group consisting of organo-metallic compound such as stannous acid, butyl acetonic acid.

[0093] Yet another aspect of the present invention, wherein base solution includes: 0.3 to 2 N alkali hydroxide based on a total amount of the product mixture.

[0094] Yet another aspect of the present invention, wherein the reactor is assisted to provide attrition phenomena through attrition milling for mechano-chemical synchronization.

[0095] Yet another aspect of the present invention, wherein the ball mill consists of zirconia not limited to steel, tungsten carbide, or silicon nitride as milling media

[0096] Yet another aspect of the present invention, wherein PET melting taken place in melt extruder to assist reaction with PET filament.

[0097] Yet another aspect of the present invention, wherein S104-S108 taken place in tubular centrifuge for catalyst recovery and to assist downstream of DOTP purification.

[0098] Still yet another aspect of the present invention is to provide continuous process consisting the conversion of batch system into continuous mode of operation using Continuous Stirred Tank Reactors [CSTR] configuration along with a melt feeder and attrition reactor for the PET dissolution and conversion via degradative transesterification reaction and product recovery. Still yet another aspect of the present invention is to provide a novel batch and continuous mechano-chemical reactor system for producing green plasticizer (DOTP) from post-consumer PET waste to solve the above technical problems.

[0099] BRIEF DESCRIPTION OF THE DRAWING

[0100] The invention has other advantages and features which will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which:

[0101] Figure-1 is a schematic flow chart of a process for producing dioctyl terephthalate

[0102] Figure-2 is a schematic scheme for batch production dioctyl terephthalate in pressurized attrition mill

[0103] Figure-3 is a schematic scheme for continuous production dioctyl terephthalate pressurized attrition mill followed by CSTR

[0104] Figure-4 is a schematic scheme for continuous downstream for production of dioctyl terephthalateP_IN 105466

[0105] DETAILED DESCRIPTION OF THE INVENTION

[0106] The foregoing detailed description of the disclosure is elaborated to provide a clear understanding to the person who is skilled in the art. Additional features, embodiments, and advantages of the invention will be described hereinafter which form the subject of the claims of the disclosure, however, the set forth disclosure provided in the specification will best be understood in conjunction with the appended claims and figures as provided heretofore. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent processes do not depart from the spirit and scope of the disclosure as set forth in the appended claims. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure.

[0107] While the invention has been disclosed with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the invention without departing from its scope.

[0108] Throughout the specification and claims, the following terms take the meanings explicitly associated herein unless the context clearly dictates otherwise. The meaning of "a", "an", and "the" include plural references. The meaning of "in" includes "in" and "on." Referring to the drawings, like numbers indicate like parts throughout the views. Additionally, a reference to the singular includes a reference to the plural unless otherwise stated or inconsistent with the disclosure herein. In line with the above objectives, the present invention relates to continuous process for preparation of Di-Octyl Terephthalate using mechano-chemical assisted degradative transesterification of post consumed PET bottles. The continuous process for preparation of Di-Octyl Terephthalate comprises: a pre -retreatment of post-consumer PET waste (S100), Mechanical assisted continuous degrative transesterification (S102), catalyst recovery (S104), a decolorization (S106), a neutralization / washing system (S108), a Heteroazeotropic distillation system (S110), a filtration (S112) and obtained purified Di-Octyl Terephthalate [DOTP]. The continuous process ioP_IN 105466

[0109] consists of a thermally assisted attrition reactor operating under variable pressure suitable for the PET dissolution and conversion via degradative transesterification reaction and product recovery. The continuous process consisting the conversion of batch system into continuous mode of operation using Continuous Stirred Tank Reactors [CSTR] configuration along with a melt feeder and attrition reactor respectively.

[0110] The present invention is to introduce an intensified batch and continuous mechano chemical degradative transesterification method for producing a terephthalate plasticizer with high-purity, using polyethylene terephthalate (PET) waste as the raw material. The present invention also addresses the limitations of conventional terephthalate plasticizer production methods, particularly when using PET waste, by tackling the issue of dissolution / homogenization, long reaction time, product and by-product purification, recovery of monomer from effluent stream and catalyst recovery, which are the significant challenge faced by process industry.

[0111] An embodiment of the present invention, continuous mechano-chemical reactor system [S102] using continuous stirred tank reactor (CSTR) configuration for producing green plasticizer Di-Octyl Terephthalate (DOTP) from post-consumer polyethylene terephthalate (PET) waste, comprises of:

[0112] a. attrition mill / ball mill reactor

[0101] ;

[0113] b. nitrogen purging tube [102a-c];

[0114] c. condenser [103a-c];

[0115] d. decanter (Dean-Stark apparatus) [104a-c];

[0116] e. vent valves (105a-c);

[0117] f. metering pump for solvent charging

[0106] ;

[0118] g. gravity feeder

[0107] ;

[0119] h. melt extruder

[0108] ;

[0120] i. jacketed reactors [109a-b];

[0121] j. buffer tank [HO];

[0122] k. pumps [llla-c];

[0123] l. tubular bowl centrifuge [112a-b];

[0124] m. stirring tanks [113,114];

[0125] n. heteroazetropic distillation tower

[0115] ;P_IN 105466

[0126] wherein, the attrition mill / ball mill reactor

[0101] comprises a vessel and zirconia ball having a diameter ranging from 5-8 mm along with an agitator shaft; wherein, the gravity feeder (107) is operating at the control process in a range of 10 g / min to 75 g / min.

[0127] Another embodiment of the present invention is to provide novel batch and continuous mechanochemical reactor system for producing green plasticizer (DOTP) from post-consumer PET waste to solve the above technical problems comprising: a pre -retreatment of post-consumer PET waste (S100), Mechanical assisted continuous degrative transesterification (S102), catalyst recovery (S104), a decolorization (S106), a neutralization / washing system (S108), a Heteroazeotropic distillation system (S110), a filtration (S112) and obtained purified DOTP, characterized in that:

[0128] S100 - Pretreatment: The post-consumer PET waste sorted from polymer mix then it is washed with solvent and dried and crushed into particles with a side length of about 0.5 to 2 mm.

[0129] S102 - Mechanical assisted degrative transesterification: This system comprises a solvent and feed tanks, a Mechanical assisted degrative transesterification reactor, decanter, reflux condenser, pressuring regulator, condensation and collection tank,

[0130] S104 - Catalyst recovery: After the reaction completed, the crude mixture allows to centrifuge (Bowl centrifuge) for remove / recover used catalyst in the system.

[0131] S106 - Decolorization: This present invention S102 providing an unpurified dioctyl terephthalate; mixing the unpurified dioctyl terephthalate with a reducing agent, stirring for 0.5 to 1 hours, keeping for layer separation, to obtain a first decolorizing product; wherein the decolorizing adsorbent material has an acid value between 0.1 and 2 mg KOH / g, a relative humidity between 2 and 10%, and a fineness between 80 and 100 cm2 / g. (in tubular centrifuge)

[0132] S108 - Neutralization / washing: This system includes a neutralization / washing tank of crude DOTP. In this the product pH is maintained.

[0133] S110 - Heteroazeotropic distillation system: the neutralized product is purified from organic impurities by using water as an extractive distillate.

[0134] An another embodiment of the present invention, wherein continuous mechano-chemical reactor system, the flow rates of 106 and 107 are maintained in a specific ratio of 1:2.5 -3.5 with a dissolution temperature in range of 200-220°C in

[0101] under a total pressurized condition in the range of 1.5-2.5 bar for a residence time period in the range of 30-90 min and a complete degradative transesterification undergoes in 109 a & b under temperature in the range of 190-195°C under 0.5-1 bar pressure with a total residence period in the range 180-240 min.P_IN 105466

[0135] Another embodiment of the present invention, wherein continuous mechano-chemical reactor system, the recovery of the organometallic catalyst from crude product is done by high-speed tubular centrifuge (112a) before product downstream through decolorization

[0113] and neutralization

[0114] and purification

[0115] .

[0136] Yet another embodiment of the present invention, wherein S102 step is under a reaction pressure between 1-3 bar, a reaction temperature between 190 and 220° C., and a reaction time between 3 to 4 hours.

[0137] Yet another embodiment of the present invention, wherein the C3-C12 secondary alcohol is at least one selected from the group consisting of n-propanol, isopropanol, n-butanol, sec-butanol, tertbutanol, pentanol, hexanol, heptanol, octanol, isooctanol, 2-ethylhexanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether and ethylene glycol monobutyl ether.

[0138] Another embodiment of the present invention, a process for preparation of green plasticizer Di-Octyl Terephthalate (DOTP) from polyethylene terephthalate (PET) post-consumer plastics waste through a continuous mechano-chemical reactor system by mechanically assisted degrative transesterification, comprising the steps of;

[0139] a) vacuuming the attrition reactor (101) and refilled with nitrogen though nitrogen purging tube (102a) by maintain back pressure rate (BPR) with vent valves (105A);

[0140] b) adding pretreated polyethylene terephthalate (PET) waste in melt extruder (108) through hopper of gravity feeder (107);

[0141] c) melting PET waste in melt extruder (108) at temperature in the range of 200-240°C;

[0142] d) passing melted PET waste through a 0.5mm die as a melted filament into an attrition mill / ball mill (101);

[0143] e) charging mixture of secondary alcohol and organometallic catalyst through metering pump (106) simultaneously in attrition mill / ball mill (101);

[0144] f) heating the attrition reactor (101) at the temperature in the range of 200-250 °C for the time period in the ranges 30-90 minutes under a total pressurized condition in the range of 1.5-2.5 bar;

[0145] g) refluxing to remove the excess secondary alcohol by distillation in condenser (103a) and collected in Decanter (104a) using Dean-Stark apparatus and passed in the attrition reactor (101) to obtain homogenized reaction mixture;

[0146] h) passing the homogenized reaction mixture to jacketed reactor (109a) and further (109b);P_IN 105466

[0147] i) heating the jacketed reactor (109a, b) at the temperature in the range of 190-195°C under 0.5- 1 bar pressure with a total residence period in the range of 180-240 min;

[0148] j) refluxing back the excess secondary alcohol by distillation in condenser (103b,c) and collected in decanter (104b, c) using Dean-Stark apparatus to pass in the jacketed reactor (109a,b) for the completion of degradative transesterification of PET to obtain crude DOTP; k) collecting crude DOTP in the buffer tank (110);

[0149] l) pumping the crude DOTP by pump (Illa) to tubular bowl centrifuge (112a);

[0150] m) centrifuging the crude DOTP by the rotation ranges from 10000-15000 rpm to settle down the crude DOTP to the bottom of the tubular bowl to separate the catalyst from the crude product; n) passing crude DOTP to stirring tanks (113) and added base solution;

[0151] o) pumping the mixture by pump (111b) to tubular bowl centrifuge (112b);

[0152] p) centrifuging the mixture by the rotation ranges from 10000-15000 rpm to settle down the crude DOTP to the bottom of the tubular bowl to remove oligomers;

[0153] q) passing crude DOTP to stirring tanks (114) and added water for pH adjustment;

[0154] r) pumping the crude DOTP by pump (111c) with continuous water flow to heteroazetropic distillation tower (115);

[0155] s) collecting the purified DOTP at the boom of heteroazeotropic distillation column;

[0156] Another embodiment of the present invention, wherein PET waste is taken as the raw material; Another embodiment of the present invention, wherein the secondary alcohol (C3-C12) is selected from n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, pentanol, hexanol, heptanol, octanol, isooctanol, 2-ethylhexanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether or ethylene glycol monobutyl ether in degrative transesterification step.

[0157] Yet another embodiment of the present invention, wherein the PET waste and secondary alcohol is mixed in the mass ratio of 1:3-4.

[0158] Still yet another embodiment of the present invention, wherein organo-metallic catalyst is selected from the stannous acid or butyl acetonic acid in the 0.1-2% of the weight ratio of PET waste in degrative transesterification step to enhance reaction time and yield of DOTP product.

[0159] Still yet another embodiment of the present invention, wherein base is selected from alkali hydroxides with a normality range of 0.3-2.0N and weight ratio of 0.5-2.0 with respective crude DOTP in the neutralization step.

[0160] Still yet another embodiment of the present invention, wherein ethylene glycol is formed as by product and collected with water in Dean-Stark apparatus.P_IN 105466

[0161] Still yet another embodiment of the present invention, wherein the pretreatment of polyethylene terephthalate (PET), consisting the steps of;

[0162] a) collecting and sorting the post-consumer polyethylene terephthalate (PET) waste from polymer mix;

[0163] b) washing the sorted polyethylene terephthalate (PET) waste with solvent and dried through centrifugation followed air drying to ensure that PET waste moisture < 0.5% to inhibit product quality and process inefficiency;

[0164] c) shredding the dried PET waste into particles with a side length of about 0.5 to 2 mm.

[0165] Still yet another embodiment of the present invention, wherein detergent is used as washing compound to remove impurities like dirt, grease, food residues, and labels from the PET waste. Still yet another embodiment of the present invention, wherein polyethylene terephthalate (PET) bottle caps which is made up of High-Density Polyethylene (HDPE) are sorted.

[0166] Yet another embodiment of the present invention, wherein catalyst is at least one selected from the group consisting of organo-metallic compound such as stannous acid, butyl acetonic acid.

[0167] Yet another embodiment of the present invention, wherein base solution includes: 0.3 to 2 N alkali hydroxide based on a total amount of the product mixture.

[0168] Yet another embodiment of the present invention, wherein the reactor is assisted to provide attrition phenomena through attrition milling for mechano-chemical synchronization.

[0169] Yet another embodiment of the present invention, wherein the ball mill consists of zirconia not limited to steel, tungsten carbide, or silicon nitride as milling media

[0170] Yet another embodiment of the present invention, wherein PET melting taken place in melt extruder to assist reaction with PET filament.

[0171] Yet another embodiment of the present invention, wherein S104-S108 taken place in tubular centrifuge for catalyst recovery and to assist downstream of DOTP purification.

[0172] Still yet another embodiment of the present invention is to provide continuous process consisting the conversion of batch system into continuous mode of operation using Continuous Stirred Tank Reactors [CSTR] configuration along with a melt feeder and attrition reactor for the PET dissolution and conversion via degradative transesterification reaction and product recovery. Still yet another embodiment of the present invention is to provide a novel batch and continuous mechano-chemical reactor system for producing green plasticizer (DOTP) from post-consumer PET waste to solve the above technical problems.P_IN 105466

[0173] In another embodiment of the present invention, process simplifies the catalyst recovery, washing and neutralization commonly required in previous state of art. The solution involves reacting PET waste with a secondary alcohol unit in the presence of a specific organo-metallic catalyst, initiating a degrative transesterification reaction. These steps are followed by a purification process to achieve the desired purity for the plasticizer required for the PVC processing industries.

[0174] In another embodiment of the present invention, process streamlined, reducing the complexity of prior processes while enhancing the quality of the final product. Further details and technical specifics of the invention will be elaborated in subsequent sections.

[0175] Pretreatment of PET waste

[0176] The post-consumer PET waste involves several steps to prepare the material for further processing. The defined steps ensure that contaminants are removed which won’t hinder the reaction by making side reaction and provide additional impurities in the product mixer. The pretreatment steps consist of Sorting, washing, drying and shredding.

[0177] Sorting: The post-consumer PET waste is collected and sorted according to the processing condition. The PET bottle caps which is made up of HDPE (High-Density Polyethylene) are sorted and allowed only PET material. This step ensure that only PET materials are processed further and done manually by density separation.

[0178] Washing: The sorted PET bottle undergoes intense washing using detergent and friction to remove impurities like dirt, grease, food residues, and labels from the PET waste. This step ensure that eliminate contaminants that could affect the quality of PET waste and a cleaner final product. Drying: After washing, the PET waste was dried to prevent moisture from affecting transesterification process. The PET waste is dried through centrifugation followed air drying to ensure that PET waste moisture < 0.5% to inhibit product quality and process inefficiency.

[0179] Shredding: The present process developed on the size reduced PET waste due to the easier access of dissolution and melting. The shredding ensure that PET waste is reduced to the scrap size < 2 mm.

[0180] Proper pretreatment of PET waste, through the mentioned techniques ensures that the PET is clean, dry, and appropriately sized for the degradative transesterification process to DOTP. These steps prevent contamination and improve the efficiency of the reactions, leading to a higher-quality green plasticizer product.P_IN 105466

[0181] Mechanical-assisted degradative transesterification

[0182] The degradative transesterification was carried out in a mechanical assisted reactor in batch and continuous mode of operation as shown in Fig 2 and Fig 3

[0183] The batch system 101 consists of a thermally assisted attrition reactor operating under variable pressure suitable for the PET dissolution and conversion via degradative transesterification reaction and product recovery. The temperature in the reactor for the dissolution and transesterification of PET is maintained in the range of 190-220°C with 1-4 bar pressure. The reaction is conducted under inert atmosphere using Nitrogen (N2) and back pressure regulator (BPR) to maintain the desired pressure for the dissolution and maintain the boiling point of solvent / secondary alcohol or mixture of solvent above the optimum reaction temperature.

[0184] The reactor 101 in Fig 2 comprises of 10 L vessel with 5-8mm zirconia ball along with agitator shaft capable of being heated till 300°C and having a 2 L Dean and Stark apparatus attached to the reactor with an overhead condenser and BPR for maintain a continuous flow inert gas into the system. Considerably 1 -2 kg of PET waste at size (< 2 mm) added in the reactor through hopper and simultaneously 3-6 kg of secondary alcohol is charged along with 5- 10 g of organo- metallic catalyst in the reactor to form a mixture of reactant to initiate the reaction. The reactor is vacuumized till 10- 50 mmHg and then refilled with nitrogen till 0.5-1 bar pressure from line 102.

[0185] The reactor is heated to a temperature of 220°C and above for fast rate dissolution of PET waste under a generated total pressurized condition between of 3-4 bar for the duration of 30-90 min. After the dissolution of PET waste to complete homogenized solution, the reactor temperature was decreased to 190-195°C and maintained for 3-4 h for the completion of degradative transesterification of PET to crude DOTP plasticizer. Ethylene glycol formed as by product during the course of reaction is distilled along with secondary alcohol, condensed 103 and collected in Dean-Stark apparatus 104. The excess secondary alcohol is refluxed back to the reactor 101. The suitable amount ranges of 1-1.5 L water used in the Dean-Stark apparatus.

[0186] In one aspect, the batch system converted into continuous mode of operation using CSTR configuration along with a melt feeder and attrition reactor as shown in Fig 3 respectively. In this type of configuration, PET waste is metered through a gravimetric feeder 107 into a melt extruder 108 which is connected to an attrition reactor 101 for PET dissolution and homogenization and followed by CSTR configurations for degradative transesterification of PET waste to crude DOTP. In this configuration, the melt feeder is operated in a temperature range to obtain a melted filament in size range 0.5- 1mm into attrition mill controlled in the temperature 190-220°C with 1-4 barP_IN 105466

[0187] pressure. The series of CSTR 109 a,b is operated in a temperature range of 190 to 195°C for the completion of the degradative transesterification reaction.

[0188] Fig 3, illustrate the continuous setup of degradative transesterification of PET waste to DOTP. The pretreated PET waste is metered in melt extruder 106 via a 107 gravimetric feeder operating in a range of 10 g / min-75 g / min. The melted PET is passed continuously through a 0.5mm die as a filament into a 10110 L attrition reactor with a melted PET-to-ball ratio of 1:1-3 at a given instant. Simultaneously, a continuous flow of secondary alcohol is fed through a metering pump 106 operated in a range of 30 ml / min-150 ml / min with a dispersed concentration of organo-metallic catalyst at 0.01-0.05%. The transesterification catalyst dosage is 0.1-2% of the weight of PET waste. The flow rates of 106 and 107 are maintained in a specific ratio of 1:2.5 -3.5 with a dissolution temperature of 220°C under a total pressurized condition between 1.5-2.5 bar for a residence time of 30-90 min. The temperature of reactors 101, 109a, b is maintained through an external heating system supplying hot oil to the outer jacket of the reactor. In 101, the level of the reaction mixture is maintained through an overflow or a delivery pump connected to reactor 109a.

[0189] The speed of the delivery pump controls the delivery volume of the homogenized reaction mixture to reactor 109a and further to 109b. The temperature of 109a, b was maintained in the temperature range of 190-195°C under 0.5-1 bar pressure with a total residence time of 180-240 min for the completion of degradative transesterification of PET to crude DOTP and collected in the buffer tank 110. Ethylene glycol formed as by product during the course of reaction in the reactor 101, 109a, b is distilled along with secondary alcohol, condensed 103a, b, c and collected in Dean-Stark apparatus 104a, b, c. The excess secondary alcohol refluxed back to the reactor while ethylene glycol collected in water. The suitable amount ranges of 1-1.5 L water used in the Dean-Stark apparatus.

[0190] Catalyst recovery

[0191] The crude DOTP from the degradative transesterification reaction is pumped into a tubular bowl centrifuge 112a through a pump from the buffer tank 110 before which the excess secondary alcohol is recovered from the crude product mixture. The operating condition for the removal of secondary alcohol varies from 5-10 mmHg with a temperature range of 140-160°C. The tubular bowl centrifuges comprise several key parts that separate the catalyst from the crude reaction mixture. The centrifuge bowl featured an elongated tubular design consisting of a motor and a drive shaft that rotates the bowl at 10000-15000 rpm. The crude DOTP is fed continuously to theP_IN 105466

[0192] bottom of the tubular bowl, where the high-speed centrifugal force separates the catalyst from the crude product.

[0193] Product purification

[0194] Crude DOTP is further processed to remove oligomers with a base / neutral solution using a tubular bowl centrifuge that has the ability to separate heavy and light phases. The light phase consists of a product mixture, while the base / neutral solution, along with oligomers and impurities, is separated as the heavy phase, continuously following the principle of density difference. The base solution, preferably with a normality range of 0.3-2.0N, is used with a weight ratio of 0.5-2.0 with respective crude DOTP. The product mixture from 112a is collected in 113 stirrer tanks where the base solution is added and sent to tubular bowl centrifuge 112b to separate the light and heavy phases from the product mixture. The collected light phase mainly consists of diester and secondary alcohol, which is purified to azeotropic distillation 105. The water is used as an entraining agent for the removal of secondary alcohol as the distillate, while the purified product is collected in the bottom stream in a continuous operative heteroazeotropic distillation column.

[0195] EXAMPLES

[0196] The following examples, which include preferred embodiments, will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purpose of illustrative discussion of preferred embodiments of the invention.

[0197] Example-1:- Preparation of Dioctyl Terephthalate in pressurized Batch mechano-chemical reactor.

[0198] Typically, a PET bottle is sorted, washed, dried and shredded to a scrap size of 1.5 mm. In the attrition reactor, 1800 g of PET is mixed with 5400 g of 2-ethylhexanol and added with 9 g of Butyl stannous acid catalyst with 3600 g zirconium ball (12 mm). Initially, the reaction is conducted at 220 °C under nitrogen atmosphere with BPR regulating at 3 bar pressure for duration 30 min for complete dissolution of PET scrap. The reaction is continued further for 180 min at 190°C with a maintained pressure of 1 bar using inert flow for completion of degradative transesterification of PET to crude DOTP.

[0199] Example-2:- Preparation of Dioctyl Terephthalate in continuous mechano-chemical reactor configuration.P_IN 105466

[0200] 8.2 g / min of melted PET and 2-ethyl hexanol with 0.03% catalyst concentration is continuously charged along with catalyst dispersed as in example Ifeed in to and catalyst mixture in 1:0.01 proportion is feed to extruder hopper 101 continuously molten PET and catalyst pass through 102 Nozzle which is operating at 220 °C, 102 Nozzle connected to 1st attrition mill reactor 103 and two CSTR 108a, 108b in series, simultaneously 45 g / min 2-ethylhexanol through deep leg is charged in 103 through 104 inlet pipe. After the residence time of 2 h in each reactor reaction mixture transfer through overflow outlet pipe to next reactor. Ethylene glycol formed during the reaction is collected in condenser 107a, 107b and 107c decanter 106a, 106b and 106c arrangement.

[0201] 103, 108a and 108b operating at 185 °C and atmospheric pressure under continuous Nitrogen flow in each reactor through 105a, 105b and 105c purging tube. Output from the reactor is coming from overflow pipe to maintained residence time. In output inlet pipe one restrictor mesh is used to restrict flow of undissolved PET. Sample collection is done from last reactor after CSTRs attain steady state condition.

[0202] Example-3:- Downstream for purification of Dioctyl Terephthalate.

[0203] Crude DOTP was collected in tank 110 from examples 1 & 2 to get purified from catalyst and oligomers through centrifugation 112 a, b and distillation 115 operations. In a 100 ml / min flow rate, crude DOTP has passed to the tubular centrifuge 112a from 110 through a pump Illa to recover the catalyst. The deposited catalyst was scrubbed down from the centrifuge bowl, and DOTP was collected from the lower limp of the centrifuge. The collected DOTP passes to stirring tank 113 to remove the oligomers from the DOTP. 0.7N base solution has been added at a flow rate of 25 ml / min in a continuous stirring. The mixer was sent to tubular centrifuge 112b at a 100 ml / min flow rate through 111b to separate the aqueous (Base) and organic (DOTP) layers. The organic layer was sent to stirrer tank 114 to get pH adjusted to 6.5 by the addition of water at 25 ml / min at continuous stirring. The pH-adjusted DOTP was mixed with excess water in a ratio of 1 8 for hetero azeotropic distillation column 115 to remove secondary alcohol and distillate containing 95% purified DOTP.

[0204] ADVANTAGES OF THE INVENTION

[0205] The main advantages of the present invention are:

[0206] 1. Faster reaction rate, avoiding the formation of side chain oligomers and thereby attaining a high diester yield.P_IN 105466

[0207] 2. Mechanochemistry-assisted depolymerization process processes precisely control over the transesterification rate and report a maximum production rate of green plasticizer Di-Octyl Terephthalate (DOTP) from polyethylene terephthalate (PET).

[0208] 3. Preparation of Di-Octyl Terephthalate using mechano-chemical assisted degradative transesterification of post consumed PET bottles in a shorter period of time offers an environmentally sustainable Process.

[0209] The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously, many modifications and variations are possible in the light of the above teaching.

[0210] The embodiments were chosen and described to best explain the principles of the present invention and its practical application, to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated.

[0211] It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.

Claims

P_IN 105466We Claim1. A continuous mechano-chemical reactor system [S102] using continuous stirred tank reactor (CSTR) configuration for producing green plasticizer Di-Octyl Terephthalate (DOTP) from post-consumer polyethylene terephthalate (PET) waste, comprises of:a) attrition mill / ball mill reactor [101];b) nitrogen purging tube [102a-c];c) condenser [103a-c];d) decanter (Dean-Stark apparatus) [104a-c];e) vent valves (105a-c);f) metering pump for solvent charging [106];g) gravity feeder [107];h) melt extruder [108];i) jacketed reactors [109a-b];j ) buffer tank [110];k) pumps [11 la-c];l) tubular bowl centrifuge [ 112a-b] ;m) stirring tanks [113,114];n) heteroazetropic distillation tower [115];wherein, the attrition mill / ball mill reactor [101] comprises a vessel and zirconia ball having a diameter ranging from 5-8 mm along with an agitator shaft; wherein, the gravity feeder (107) is operating at the control process in a range of 10 g / min to 75 g / min.

2. The continuous mechano-chemical reactor system as claimed in claim 1, wherein the flow rates of [106] and [107] are maintained in a specific ratio of 1:2.5 -3.5 with a dissolution temperature in range of 200-220°C in [101] under a total pressurized condition in the range of 1.5-2.5 bar for a residence time period in the range of 30-90 min and a complete degradative transesterification undergoes in 109 a & b under temperature in the range of 190- 195 °C under 0.5-1 bar pressure with a total residence period in the range of 180-240 min.P_IN 1054663. The continuous mechano-chemical reactor system as claimed in claim 1 , wherein the recovery of the organometallic catalyst from crude product is done by high-speed tubular centrifuge (112a) before product downstream through decolorization (113) and neutralization (114) and purification (115).

4. A process for preparation of green plasticizer Di-Octyl Terephthalate (DOTP) from polyethylene terephthalate (PET) post-consumer plastics waste through a continuous mechano-chemical reactor system as claimed in claim 1 by mechanically assisted degrative transesterification, comprising the steps of;a) vacuuming the attrition reactor (101) and refilled with nitrogen though nitrogen purging tube (102a) by maintain back pressure rate (BPR) with vent valves (105A);b) adding pretreated polyethylene terephthalate (PET) waste in melt extruder (108) through hopper of gravity feeder (107);c) melting PET waste in melt extruder (108) at temperature in the range of 200-240°C; d) passing melted PET waste through a 0.5mm die as a melted filament into an attrition mill / ball mill (101);e) charging mixture of secondary alcohol and organometallic catalyst through metering pump (106) simultaneously in attrition mill / ball mill (101);f) heating the attrition reactor ( 101 ) at the temperature in the range of 200-250 °C for the time period ranges from 30-90 minutes under a total pressurized condition in the range of 1.5- 2.5 bar;g) refluxing to remove the excess secondary alcohol by distillation in condenser (103a) and collected in Decanter (104a) using Dean-Stark apparatus and passed in the attrition reactor (101) to obtain homogenized reaction mixture;h) passing the homogenized reaction mixture to jacketed reactor (109a) and further 109b; i) heating the jacketed reactor (109a,b) at the temperature range of 190-195 °C under 0.5-1 bar pressure with a total residence time of range 180-240 min;j) refuxing back the excess secondary alcohol by distillation in condenser (103b, c) and collected in decanter (104b,c) using Dean-Stark apparatus to pass in the jacketed reactorP_IN 105466(109a,b) for the completion of degradative transesterification of PET to obtain crude DOTP;k) collecting crude DOTP in the buffer tank (110);l) pumping the crude DOTP by pump (11 la) to tubular bowl centrifuge (112a);m) centrifuging the crude DOTP by the rotation ranges from 10000-15000 rpm to settle down the crude DOTP to the bottom of the tubular bowl to separate the catalyst from the crude product;n) passing crude DOTP to stirring tanks (113) and added base solution;o) pumping the mixture by pump (11 lb) to tubular bowl centrifuge (112b);p) centrifuging the mixture by the rotation ranges from 10000-15000 rpm to settle down the crude DOTP to the bottom of the tubular bowl to remove oligomers;q) passing crude DOTP to stirring tanks (114) and added water for pH adjustment;r) pumping the crude DOTP by pump (111c) with continous water flow to hetero azetropic distillation tower (115);s) collecting the purified DOTP at the boom of heteroazeotropic distillation column;5. The process of preparation of green plasticizer DOTP as claimed in claim 4, wherein PET waste is taken as the raw material.

6. The process of preparation of green plasticizer DOTP as claimed in claim 4, wherein the secondary alcohol (C3-C12) is selected from n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, pentanol, hexanol, heptanol, octanol, isooctanol, 2-ethylhexanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether or ethylene glycol monobutyl ether in degrative transesterification step.

7. The process of preparation of green plasticizer DOTP as claimed in claim 4, wherein the PET waste and secondary alcohol is mixed in the mass ratio of 1:3-4.

8. The process of preparation of green plasticizer DOTP as claimed in claim 4, wherein organometallic catalyst is selected from the stannous acid or butyl acetonic acid in the 0.1 -2% of the weight ratio of PET waste in degrative transesterification step to enhance reaction time and yield of DOTP product.P_IN 1054669. The process of preparation of green plasticizer DOTP as claimed in claim 4, wherein base is selected from alkali hydroxides with a normality range of 0.3-2.0N and weight ratio of 0.5- 2.0 with respective crude DOTP in the neutralization step.

10. The process of preparation of green plasticizer DOTP as claimed in claim 4, wherein ethylene glycol is formed as by product and collected with water in Dean-Stark apparatus.

11. The process for preparation of green plasticizer Di-Octyl Terephthalate (DOTP) from polyethylene terephthalate (PET) as claimed in claim 4, wherein the pretreatment of polyethylene terephthalate (PET), consisting the steps of;a) collecting and sorting the post-consumer polyethylene terephthalate (PET) waste from polymer mix;b) washing the sorted polyethylene terephthalate (PET) waste with solvent and dried through centrifugation followed air drying to ensure that PET waste moisture < 0.5% to inhibit product quality and process inefficiency;c) shredding the dried PET waste into particles with a side length of about 0.5 to 2 mm.

12. The process of preparation of green plasticizer DOTP as claimed in claim 11, wherein detergent is used as washing compound to remove impurities like dirt, grease, food residues, and labels from the PET waste.

13. The process for preparation of green plasticizer DOTP from PET as claimed in claim 11, the polyethylene terephthalate (PET) bottle caps which is made up of High-Density Polyethylene (HDPE) are sorted.

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