Method for manufacturing polyethylene terephthalate containing low amounts of diethylene glycol in the presence of monocarboxylic acid

Abstract

A method is described for the manufacture of polyethylene terephthalate from terephthalic acid and ethylene glycol in the presence of a monocarboxylic acid, which comprises the steps of: (a) in a first reaction step, esterifying a saturated solution of terephthalic acid with ethylene glycol in a mixture of a monocarboxylic acid with water or another suitable solvent to obtain as an intermediate a monoethylene glycol terephthalate carboxylate, a diethylene glycol terephthalate carboxylate, or oligomers thereof, wherein the ethylene glycol is employed in a molar amount equal to or less than the sum of the molar amounts of terephthalic acid and monocarboxylic acid together; and (b) in a second reaction step, converting the monoethylene glycol terephthalate carboxylate or the diethylene glycol terephthalate carboxylate, or the oligomers thereof to polyethylene terephthalate containing less than 0.1% by weight of diethylene glycol.