Process for the production of polyethylene terephthalate copolyester, copolyester obtained thereby and its use and catalyst useful in the process

Abstract

The present invention relates to a process for the production of polyethylene terephthalate copolyester from terephthalic acid, isophthalic acid and ethylene glycol, comprising the steps of: a) preparing a catalyst composition comprising a zinc compound being present such that the elemental zinc content is in a range of about 50 to about 500 ppm, preferably about 200 to about 500 ppm, most preferably about 180 to about 260 ppm, based on the copolyester, b) placing the catalyst composition, terephthalic acid, isophthalic acid and ethylene glycol in a vessel, and c) reacting the terephthalic acid, isophthalic acid and ethylene glycol in an esterification step and a polycondensation step to obtain polyethylene terephthalate copolyester; to the copolyester obtained thereby and its use, as well as to a catalyst composition suitable in the inventive process.

Description

Technical field

[0001] The present invention relates to a method for preparing polyethylene terephthalate copolyester, the obtained copolyester and its use, and a catalyst composition suitable for the method. Background technique

[0002] PET is prepared in two steps by one of two methods, the DMT and PTA methods (or transesterification and direct esterification methods, respectively). Applications of PET include fiber and filament, film and bottle grade chips. Modern factories use the PTA method and, in addition, directly form products (fibers and filaments, films) by extruding the melt obtained from the final polycondensation reactor.

[0003] First, let's compare DMT and PTA methods. The main difference is the starting material. Earlier methods used dimethyl terephthalate (DMT) and ethylene glycol (EG) as starting materials. This is because terephthalic acid of sufficient purity cannot be obtained in the early years of polyester preparation. In the DMT method, in the first ste...