| abstract |
Process of producing polytrimethylene terephthalate (PTT) by esterification of terephthalic acid (TPA) with trimethylene glycol (TMG) in the presence of a catalytic titanium compound, precondensation and polycondensation. The esterification is effected in at least two stages, where in the first stage a molar ratio of TMG to TPA of 1.15 to 2.5, a content of titanium of 0 to 40 ppm, a temperature of 240 to 275° C., and a pressure of 1 to 5.0 bar, preferably 3.5 bar are used. In the at least one subsequent stage a content of titanium is adjusted which is higher than in the initial stage by 35 to 110 ppm. |