The synthesis method of PBT can adopt two process routes:
(1) The transesterification method, that is, the transesterification of dimethyl terephthalate (DMT) and 1,4-butanediol (BDO) is carried out first, and then the polycondensation is carried out. The characteristic of the transesterification method is its mature technology. The amount of BDO is small, which is a homogeneous reaction and produces less by-product tetrahydrofuran (THF).
(2) Direct esterification method, namely, direct esterification of purified terephthalic acid (PTA) and 1,4-butanediol, and then polycondensation to prepare PBT. The main advantage of the direct esterification method is that it does not generate methanol, THF is easy to separate and recover, and it consumes less energy. The disadvantage is that the esterification is a heterogeneous reaction, and the reaction speed is slow; PTA can promote the decomposition of BDO to produce THF.
The main technical key of the two routes is how to reduce the amount of BDO and reduce the production of THF.