GB1001429A - Process for producing polyethylene terephthalate - Google Patents

Abstract

Polyethylene terephthalate is made by a continuous process in which bis-(2-hydroxyethyl) terephthalate or a low polymer thereof is continuously polycondensed in the presence of an added reactant adapted to react with the liberated ethylene glycol, the added reactant being a dicarboxylic acid or a lower dialky ester thereof. Specified reactants are terephthalic, isophthalic, succinic, adipic, glutaric, sebacic, xylidinic, dipheny-p,p1-dicarboxylic, naphthalene - 1,5 - dicarboxylic, naphthalene - 3,7 - dicarboxylic and durene-1,4-dicarboxylic acids and their dimethyl, diethyl, dipropyl and diisopropyl esters. Preferably 0.05 to 1.0 mole of added reactant is used per mol. of bis-(2-hydroxyethyl) terephthalate. The polyesterification process preferably comprises (1) continuously reacting dimethyl terephthalate and ethylene glycol in an ester interchange column from which the liberated methanol is removed; (2) feeding the resulting bis-(2-hydroxyethyl) terephthalate to a prepolymerization zone comprising vertically mounted heat-exchangers down which the ester-interchange product flows in the form of thin annular films and from which the liberated ethylene glycol is removed; (3) mixing a stream of the resulting prepolymer having a degree of polymerization of 8 to 18 with the added reactant and (4) feeding the mixture to a screw conveyer type final poly-condensation vessel from which the water or monohydric alcohol liberated by reaction between the added reactant and the liberated ethylene glycol is removed.