Process for depolymerizing polyalkylene terephthalate in a mixture with low-melting-point polyolefins

Abstract

The present invention relates to a process for depolymerizing at least one polymer P1 in a polymer mixture, wherein the polymer mixture also includes at least one polyolefin PO having a lower melting point than P1, and in particular polyethylene PE or polypropylene PP. Polymer P1 is a polyalkylene terephthalate, i.e., a polymer comprising terephthalic acid units and alkylene glycol units, in particular polyethylene terephthalate PET or polybutylene terephthalate PBT. The process according to the present invention comprises two steps: In the first step, polymer P1 is reacted with glycol compound G to obtain a cleavage product P2 having essentially a shorter chain length than P1. In the second step, the cleavage product P2 and any polymer P1 not converted in the first step are reacted with additionally added glycol compound G and are at least partially cleaved into monomer units. The first step is performed at the melting temperature T of the polyolefin PO. PO The second step is carried out at a higher temperature than the first, and the second step is to melt the polyolefin PO at the melting temperature T PO This process is carried out at a lower temperature. This allows for the simple and efficient separation of solid polyolefin (PO) from the mixture obtained after the second step.

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