Reducing waste from polycondensation of ethylene terephthalate - with aid of series of vacuum aggregates, pumps and vapour ejectors driven by recycled glycol vapours

摘要

Removal of vaporous reaction prods. in mfr. of polyesters, esp. polyethylene terephthalate, as in parent patent, is effected with the aid of vacuum units connected via suction lines with the vapour chambers of the reactors. At least the first 2 stages of the vacuum units are designed as vapour ejectors driven by glycol vapour. The process also uses condensers up or downstream of the vacuum units. Final compression of any reaction prods. not condensed in the condensers dof preceding stages, and of uncondensed, entrained, gases, up to atmospheric pressure, is carried out by a ring pump installed downstream and driven by liq. glycol. In this addn., the glycol-vapour-driven condensers are mixing condensers from each of which the condensate is conveyed into an associated, separate, container. Part of that condensate is recycled, after cooling, to its respective mixing condenser to serve as coolant; whilst part of the condensate is evaporated and conveyed to the vapour ejector upstream of the associated mixing condenser, and used to drive it. The amounts of fresh glycol used to operate this process are kept at a minimum, whilst ensuring constant vacuum.