FIELD: chemistry.
SUBSTANCE: invention relates to a method of producing a polyester, particularly polyethylene terephthalate (PET), involving a process of depolymerisation of secondary polyester material, particularly containing opaque polyester. Method of producing polyester terephthalate from at least one secondary polyester material containing at least 10 wt.% of opaque polyethylene terephthalate, which enables to reduce consumption of raw material and energy, involving at least the following steps: a) a step for depolymerising said secondary polyester feedstock, comprising at least one reaction section, to which said secondary polyester feedstock and a glycolic feedstock containing ethylene glycol, wherein said reaction section operates at temperature of 150 °C to 400 °C, at pressure of at least 0.1 MPa, and with a residence time in one reactor from 0.05 to 10 hours, to obtain a stream with a depolymerisation reaction, b) a separation step comprising at least one separation section to which said depolymerisation reaction stream obtained at the outlet of the depolymerisation step a) is fed to obtain at least one glycol stream and one diester stream, c) a step for purifying the diester stream obtained at the outlet of step b), comprising at least one separation section to which said diester stream obtained at the outlet of step b) is supplied, and which operates at temperature less than or equal to 250 °C, pressure less than or equal to 0.001 MPa, and when the liquid in one section is less than or equal to 10 minutes, then the decolouration section operating at temperature of 100 °C to 250 °C and pressure from 0.1 to 1.0 MPa, in the presence of an adsorbent to obtain a liquid purified diester stream which contains bis (2-hydroxyethyl) terephthalate BHET, d) a step for preparing a polymerisation feedstock, comprising at least one mixing section, to which at least one terephthalic feedstock containing terephthalic acid or dimetiterephthalate is fed, and at least a portion of said purified diester stream obtained in step c) in liquid form, wherein the amounts of at least said terephthalic feedstock and said portion of the purified diester stream are introduced into said mixing section, are selected so that the ratio of the total number of moles of diol links of formula -[C(n+1)H(2n+2)O2]-, where n is an integer greater than or equal to 1 introduced into said mixing section, to the total number of moles of terephthalate links of formula -[CO-(C6H4)-CO]- introduced into said mixing section ranged from 1.0 to 2.0, wherein said mixing section operates at temperature of 100 °C to 150 °C and pressure greater than or equal to 0.1 MPa, e) a step of condensing said polymerisation feedstock obtained in step d) to obtain at least one condensation stream, a diol stream and an aqueous stream or methanol stream, wherein said condensation step includes at least one reaction section operating at temperature of 150 °C to 400 °C, pressure from 0.05 to 1 MPa and with residence time from 1 to 10 hours, as well as at least one separation section, f) a step for polycondensation of said condensation reaction stream obtained in step e) to obtain at least said polyester terephthalate and a diol stream, wherein said polycondensation step includes at least one reaction section comprising at least one reactor in which polycondensation is carried out and which operates at temperature of 200 °C to 400 °C, pressure of 0.0001 to 0.1 MPa and with a residence time of 0.1 to 5 hours, wherein said reaction section also comprises at least one outlet for said diol stream, g) a step for treating diols, comprising a recuperation section, to which at least part or all of the glycol stream exiting from step b) is supplied, and all or part of the diol stream exiting step f) to obtain a diol stream to be treated, and a purification section of said diol stream to be treated to obtain a purified diol stream.
EFFECT: providing a method of producing polyester, without deterioration of the quality of the produced polyester, at least partially from a compound obtained from recycled polyester, wherein the secondary polyester contains an opaque polyester in a sufficiently significant amount corresponding to that found in the polyester material from collection and sorting systems, also with the possibility of obtaining a liquid purified intermediate diester, which meets the specifications of the polymerisation process and which can be directly supplied to polymerisation steps without an intermediate purification step and/or conditioning, which enables to avoid additional manipulations and significant energy consumption, and at the same time introduction of the purified intermediate diester, obtained in liquid form at the outlet of the depolymerisation steps, to the polymerisation steps, in particular, into a monomer mixture, enables to reduce the amount of monomer diol raw material fed to the polymerisation process while maintaining good processability.
12 cl, 1 dwg, 2 tbl, 4 ex
