Process for the depolymerization of a polyester comprising opaque polyethylene terephthalate

Process for the depolymerization of a polyester feedstock comprising opaque PET, the said feedstock comprising from 0.1% to 10% by weight of pigment, the said process comprising at least the following stages:

• a) a conditioning stage fed by the said polyester feedstock;
• b) a stage of depolymerization by glycolysis fed at least by the effluent from stage a) and by a contribution of diol, carried out at a temperature of between 200 and 400° C., with from 1 to 20 mol of diol per mole of diester in the said polyester feedstock and a residence time of the polyester of between 0.1 and 5 h, converting the PET into BHET monomer and BHET oligomers;
• c) a stage of separation of the diol fed at least by the effluent from stage b), carried out at a temperature of between 100 and 250° C., at a lower pressure than that of stage b) and producing a diol effluent and a liquid effluent rich in monomers, carried out in 1 to 5 successive gas/liquid separation sections, the liquid effluent from the preceding section feeding the subsequent section, all of the gas effluents being condensed to form the diol effluent, the liquid effluent resulting from the final gas/liquid separation section constituting the liquid effluent rich in monomers;
• d) a stage of separation of the liquid effluent rich in monomers resulting from stage c) into a heavy impurities effluent and a prepurified monomers effluent carried out at a temperature of less than 250° C. and a pressure of less than 0.001 MPa with a liquid residence time of less than 10 min;
• and
• e) a stage of decolouration of the prepurified monomers effluent, carried out at a temperature of between 100 and 250° C. and at a pressure of between 0.1 and 1.0 MPa in the presence of an adsorbent and producing a purified monomers effluent.