Patent ID: 6277947
Filing Date: 2001-08-21
Classification: C08G

Abstract:
A process of producing polytrimethylene terephthalate (PTT) with an intrinsic viscosity of 0.75 up to at least 1.15 dl/g by esterification of terephthalic acid (Twith trimethylene glycol (TMG) in the presence of a catalytic titanium compound to obtain an esterification product, precondensation of the esterification product to obtain a precondensation product and polycondensation of the precondensation product to obtain PTT, characterized in thata) the esterification is performed in at least two stages, a first, initial stage and at least one second subsequent esterification step,b) a catalyst feed is provided wherein the catalyst is a compound of a metal which may be titanium or zirconium,c) a major quantity between 65 and 100 wt % of said catalyst feed containing 35 to 110 ppm metal is introduced into the at least one subsequent esterification stage, which is operated at a temperature of 240 to 275.degree. C. and a pressure of 0.7 to 1.5 bar,d) a minor quantity of said catalyst feed containing 0 to 40 ppm metal and up to 35 wt % of the total catalyst is directly fed to the initial esterification stage which is operated at a temperature of 240 to 275.degree. C., a total molar TMG to TPA feed ratio of 1.15 to 2.5, and a pressure of 1 to 3.5 bar,e) the precondensation is performed at a temperature of 250 to 270.degree. C. under a reduced pressure between 2 and 200 mbar, andf) the polycondensation is carried out in the melt phase at a pressure of 0.2 to 2.5 mbar and a temperature of 250 to 270.degree. C.