A process for degrading polyethylene terephthalate to dimethyl terephthalate

摘要

Dimethyl terephthalate is prepared by mixing polyethylene terephthalate with up to 50 per cent of its weight of dimethyl terephthalate and heating the mixture at 10-35 atmospheres gauge pressure to a temperature of up to 210 DEG C. in the presence of methanol and a transesterification catalyst in a proportion of 0.5-10 per cent by weight of the polyethylene terephthalate. Suitable catalysts are zinc, zinc oxide, magnesium oxide, zinc acetate, lead oxide, lead acetate, magnesium and iron. The pressure is preferably 10 to 19 atmospheres gauge. Examples are given illustrating the reaction using varying proportions of dimethyl terephthalate and different polyethylene terephthalate wastes, viz.: polyethylene terephthalate waste fibres, and chips. A comparative example is also given of the degradation of polyethylene terephthalate, in the absence of dimethyl terephthalate.