Process of producing polytrimethylene terephthalate (PTT)

摘要

A process for the preparation of polytrimethylene terephthalate (PTT), having an intrinsic viscosity of at least 0.75 dl/g, comprises esterification of terephthalic acid (TPA) with tri-methylene glycol (TMG) in the presence of a catalytic titanium compound to obtain an esterification product followed by pro-condensation and poly-condensation to yield PTT. A process for the preparation of polytrimethylene terephthalate (PTT), having an intrinsic viscosity of at least 0.75 dl/g, comprises esterification of terephthalic acid (TPA) with tri-methylene glycol (TMG) in the presence of a catalytic titanium compound to obtain an esterification product followed by pro-condensation and poly-condensation to yield PTT, whereby (A) the esterification is preformed by pre-condensation and poly-condensation to yield PTT, whereby (A) the esterification is performed in at least two stages with the second stage connected to a process column (B) a liquid catalyst feed is prepared on a base of TMG having a concentration of less than 5 wt.% Ti in the form of a titanium compound stabilized by a bifunctional organic acid. (C) 65-100 % of the liquid catalyst feed containing 35-110 ppm Ti is introduced into at least one subsequent esterification stage at 245-260 [deg]C and 0.7-1.2 bar (D) up to 35 % of the liquid catalyst feed is directly fed to the initial esterification stage together with the raw materials and is optionally at least partially substituted by the same quantity of catalyst in a reaction product, optionally recycled from any further reaction stages and which is mixed with the raw material for further reaction in the initial esterification stage with a total TMG feed ratio of 1.25-2.5, at 245-260 [deg]C and 1-3.5 bar (E) the precondensation is carried out at 245-260 [deg]C and 2-150 mbar (F) the polycondensation is carried out at 0.2-2 mbar and 252-267 [deg]C, increasing from the entry to the exit of the reactor during agitation and formation of steadily renewed, large film surfaces of the reaction product for evaporation of the split products and (G) using vapor-jet pumps to generate the vacuum in steps (E) and (F) to remove released TMG and PTT oligomers and low boilers from the gas phase of the reactors. The vapor-jet pumps are operated with TMG vapor and the vapors are sucked off and compressed by the vapor-jet pumps and the TMG vapors are condensed by spraying them with a liquid that consists predominantly of TMG.