Method for producing a polyester terephthalate incorporating a depolymerization method

Patent metadata

Field	Value
Publication number	US-2022127416-A1
Application number	US-202017427450-A
Country	US
Kind code	A1
Filing date	Jan 27, 2020
Priority date	Feb 1, 2019
Publication date	Apr 28, 2022
Grant date	—

Abstract

The invention relates to a process for producing a terephthalate polyester from at least one feedstock of polyester to be recycled, integrating a process of depolymerization, advantageously by glycolysis, of the polyester to be recycled in order to produce a diester intermediate compatible with the specifications of the polymerization steps and comprising an optimized system for recycling the streams.

First claim

1 . Process for producing a terephthalate polyester from at least one feedstock of polyester to be recycled, comprising at least the following steps:
a) a step of depolymerization of said feedstock of polyester to be recycled, comprising at least one reaction section fed with said feedstock of polyester to be recycled and with a glycol feedstock, wherein said reaction section is operated, at a temperature between 150° C. and 400° C., preferably between 180° C. and 300° C., preferably between 200° C. and 280° C., at a pressure of at least 0.1 MPa, preferentially at least 0.4 MPa, and with a residence time per reactor of between 0.05 and 10 h, in order to obtain a depolymerization reaction effluent, b) a separation step, comprising at least one separation section fed with said depolymerization reaction effluent obtained at the end of the depolymerization step a), in order to obtain at least one glycol effluent and one diester effluent, c) a step for purifying the diester effluent obtained at the end of step b), comprising at least one separation section that is fed with said diester effluent obtained at the end of step b) and operated at a temperature below or equal to 250° C., at a pressure less than or equal to 0.001 MPa, and with a liquid residence time per section of the less than equal to 10 min, then a discolourationsection operated at a temperature between 100° C. and 250° C. and at a pressure of between 0.1 and 1.0 MPa, in the presence of an adsorbent, in order to obtain a liquid purified diester effluent, d) a step for preparing a polymerization feedstock comprising at least one mixing section fed with at least one terephthalic feedstock, and at least one fraction of said purified diester effluent obtained in step c) in liquid form, wherein the amounts of at least said terephthalic feedstock and said fraction of the purified diester effluent, introduced into said mixing section, is adjusted so that the ratio of the total number of moles of diol units of formula —[C(n +1) H (2n+2) O 2 ]—, n being an integer greater than or equal to 1, introduced into said mixing section, relative to the total number of moles of terephthalate units of formula —[CO—(C 6 H 4 )—CO]—, introduced into said mixing section, is between 1.0 and 2.0, wherein said mixing section is operated at a temperature between 25° C. and 250° C. and at a pressure greater than or equal to 0.1 MPa, e) a step for condensing said polymerization feedstock resulting from step d), in order to produce at least one condensation reaction effluent, one diol effluent and one aqueous effluent or one methanol effluent, wherein said condensation step comprises at least one reaction section operated at a temperature between 150° C. and 400° C., at a pressure between 0.05 and 1 MPa, and with a residence time of between 0.5 and 10 h, and at least one separation section, f) a step of polycondensation of said condensation reaction effluent obtained in step e) in order to obtain at least said terephthalate polyester and a diol effluent, wherein said polycondensation step comprises at least one reaction section that comprises at least one reactor in which the polycondensation is carried out and that is operated at a temperature between 200° C. and 400° C., at a pressure between 0.0001 and 0.1 MPa, with a residence time between 0.1 and 5 h, said reaction section also comprising at least one drawing-off of said diol effluent, g) a step for treating the diols, comprising a recovery section fed at least by all or part of the glycol effluent resulting from step b) and all or part of the diol effluent resulting from step f), in order to obtain a diol stream to be treated, and a section for purification of said diol stream to be treated in order to obtain a purified diol stream.

2 . Production process according to claim 1 , wherein said feedstock of polyester to be recycled comprises at least 10% by weight of opaque PET, very preferably at least 15% by weight of opaque PET.

3 . Production process according to claim 1 , wherein said feedstock of polyester to be recycled comprises 0.1% and 10% by weight of pigments, notably between 0.1% and 5% by weight of pigments.

4 . Production process according to claim 1 , wherein the reaction section of step a) is fed with said feedstock of polyester to be recycled and with said glycol feedstock so that the amount of the glycol compound contained in said glycol feedstock corresponds, at the inlet of said reaction section, to 1 to 20 mol, preferably 3 to 10 mol, of glycol compound per mole of basic repeating unit of the polyester contained in said feedstock of polyester to be recycled.

5 . Production process according to claim 1 , wherein the separation section of step b) comprises a succession of 1 to 5 gas-liquid separations, carried out at a temperature of between 100° C. and 250° C. and at a pressure of between 0.00001 and 0.2 MPa.

6 . Production process according to claim 1 , wherein the separation section of the purification step c) uses a system of falling film or wiped film evaporation, by falling film or wiped film short path distillation, or by a succession of several falling film or wiped film short path distillations and/or evaporations, at a temperature below or equal to 250° C., preferably below or equal to 230° C., very preferably below or equal to 200° C., and at a pressure less than or equal to 0.001 MPa, preferably less than or equal to 0.0001 MPa, preferably less than or equal to 0.00005 MPa.

7 . Production process according to claim 1 , wherein the adsorbent of the discolouration section of step c) is an activated carbon.

8 . Production process according to claim 1 , wherein the amounts of terephthalate feedstock, and of purified diester effluent, introduced into said mixing section of step d) are adjusted so that the ratio of the total number of moles of diol units introduced into said mixing section, relative to the total number of moles of terephthalate units introduced into said mixing section, is between 1.0 and 1.5, preferentially between 1.0 and 1.3.

9 . Production process according to claim 1 , wherein said mixing section in step d) is operated at a temperature of between 60° C. and 200° C., preferably between 100° C. and 150° C.

Assignees

• Ifp Energies Now

Inventors

• Thinon Olivier
• Gauthier Thierry

Classifications

• C08G63/183 Primary

  Terephthalic acids · CPC title

• C07C51/43

  by change of the physical state, e.g. crystallisation · CPC title

• C07C69/82

  Terephthalic acid esters · CPC title

• C07C67/03

  by reacting an ester group with a hydroxy group · CPC title

• C07C67/56

  by solid-liquid treatment; by chemisorption · CPC title