Process for producing a constant purity DMT intermediate and process for reworking the product to very pure DMT and / or medium to high purity terephthalic acid

摘要

The invention relates to a process for the production of a DMT intermediate product as well as its working up to fibregrade DMT and to medium pure and pure terephthalic acid. The DMT intermediate product is moreover produced by combined oxidation of a predominantly para-xylene (p-X) and para-toluic acid methyl ester (p-TE) containing mixture in liquid phase with an oxygen containing gas, esterification of the acids being produced with methanol, distillative or rectificative separation of the esterification products being produced into a p-TE rich fraction I, a fraction II containing more than 99% by weight DMT and its isomers and a high boiling residue fraction III as well as feeding back the p-TE fraction I into the oxidation, with the residue fraction III having a DMT content of 15 to 70% by weight and the DMT fraction II being purified by single solvent recrystallisation in methanol to form the DMT intermediate product to such an extent that the amounts of hydroxymethylbenzoic acid methyl ester (HM-BME) and terephthalic acid methyl ester (TAE) in the DMT intermediate product amount together to less than 200 ppm.