Patent ID: 6800718
Filing Date: 2004-10-05
Classification: C08G

Abstract:
A process of producing polytrimethylene terephthalate (PTT) with an intrinsic viscosity of at least 0.75 dl/g by esterification of terephthalic acid (TPA) with 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 stage connected to a process column, b) a liquid catalyst feed is prepared on base of TMG having a concentration of less than 5 wt-% titanium in the form of a titanium compound stabilized by a bifunctional organic acid, c) a major quantity between 65 and 100% of said liquid catalyst feed containing 35 to 110 ppm titanium, is introduced into the at least one subsequent esterification stage, operated at a temperature of 245 to 260Â° C., and a pressure of 0.7 to 1.2 bar, d) a minor quantity of said liquid catalyst feed containing 0 to 40 ppm titanium and equal in maximum to 35% of the total catalyst is directly fed to the initial esterification stage usually together with the raw materials, which direct catalyst feed can be partially or completely substituted by the same quantity of catalyst in a reaction product, which may be recycled from any further reaction stages and which is mixed to the raw materials for further reaction in said initial esterification stage in connection with a total molar TMG to TPA feed ratio of 1.15 to 2.5, a temperature of 240 to 270Â° C. and a pressure of 1-3.5 bar, e) the precondensation is performed at a temperature of 245 to 260Â° C. under a reduced pressure between 2 and 200 mbar, f) the polycondensation is carried out in the melt phase at a pressure of 0.2 to 2.5 mbar, a temperature of 252 to 267Â° C., basically increasing from the entry to the exit of the polycondensation reactor during agitation and formation of steadily renewed, large film surfaces of the re action product for evaporation of the split products, and g) for generating the vacuum to perform the precondensation and polycondensation vapor-jet pumps are used to remove the released TMG and PTT oligomers and low boilers from the gas phase of the reactors, and the vapor-jet pumps are operated with TMG vapor, and the vapors sucked off and compressed by the vapor-jet pumps and said TMG vapors are condensed by spraying them with a liquid which predominantly consists of TMG.