Dimethyl terephthalate prepn. by oxidn. process - comprising methanol treatment of recycled distn. residue or extract contg. catalyst

摘要

Dimethyl terephthalate, (I), prepn. by oxidn. of p-xylene and/or Me p-toluate with O2 or an O2-contg. gas in the presence of a heavy metal catalyst, esterification of oxidn. reaction mixt. with MeOH, distn. of esterification mixt. to separate (I) from fractions having a lower b. pt. and recycling to oxidn. step of (A) distn. residue contg. the heavy metal catalyst and/or (B) heavy metal catalyst -contg. extract obtd. after further extn. of (A), takes place by process in which (A) and/or (B) is contacted with MeOH before recycling. (I) is used as starting material in prepn. of fibre- and film-forming polyesters. Contact of (A) or (B) with MeOH before recycling to oxidn. step, (i) increases yield of (I), (ii) reduces colour of oxidn. reaction mixt. and (iii) facilitates subsequent purification.