Method of polyester manufacturing using crossflow membrane filtration

An improved process for the manufacture of polyester resin from the esterification of an aromatic acid with a glycol followed by polycondensation in the presence of a metal oxide catalyst in which spent glycol is removed during the course of the polycondensation reaction along with insolubles, unpolymerized monomers, large particulates, low molecular weight oligomers, metal oxide catalyst, cation impurities and anion impurities, and trace amounts of other additives and impurities, comprising the steps of:

• (a) increasing the temperature of the spent glycol to maintain the monomer dissolved in solution;
• (b) passing the spent glycol through a coarse filter screen to remove large particulates;
• (c) passing the spent glycol to a crossflow membrane filtration device with sufficient fluid velocity across the crossflow membrane filtration device to maintain turbulent flow such that a glycol permeate is produced that is free of insolubles but retains the dissolved monomer;
• (d) collecting the glycol permeate from the crossflow membrane filtration device;
• (e) recycling the glycol permeate to the esterification process;
• (f) purging the retentate containing the concentrated insolubles;
• and
• (g) separating the concentrated insolubles from the purged retentate.