Dynamit Nobel Aktiengesellschaft

Huls Aktiengesellschaft

Ralf Wirges

Anton Schoengen

Hermann-Josef Korte

Rudolf Modic

Jorg Porschen

Johann H Schroeder

Hans U Neutzler

Anton Miletic

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.

Process for the production of DMT-intermediate product of specific

Process for the production of DMT-intermediate product of specific purity

A process for the production of terephthalic acid from p-xylene and methanol by way of the dimethyl terephthalate obtained by oxidation, in the liquid phase with atmospheric oxygen in the presence of dissolved heavy metal compounds as the catalyst, of a mixture of p-xylene and a fraction containing predominantly methyl p-toluate, which fraction is recycled into the oxidation, to obtain an oxidation product containing primarily p-toluic acid and monomethyl terephthalate at a temperature of 140.degree.-170.degree. C. and under a pressure of 4-8 bar; by esterification of the oxidation product in a reactor with liquid and subsequently vaporized methanol brought to an elevated pressure, at a temperature of 220.degree.-280.degree. C. and under a pressure of 20-25 bar to obtain a raw ester containing primarily methyl p-toluate and dimethyl terephthalate; by withdrawing the raw ester fraction and a methanol-containing vapor fraction from the esterification reactor; by distillatory separation of the raw ester into a methyl p-toluate fraction and a fraction rich in terephthalic aldehyde methyl ester, which fractions are recycled into the oxidation, a raw dimethyl terephthalate fraction, and a residual fraction; and by hydrolysis of the raw dimethyl terephthalate fraction with water, obtaining the thus-formed terephthalic acid and separation of a methanol-water mixture. In this process, the methanol-containing vapor fraction and the methanol-water mixture are separated by rectification under elevated pressure and elevated temperature into a methanol-rich head fraction and an aqueous sump phase, the methanol formed at the head of the rectification stage is withdrawn in vapor phase under elevated pressure, and esterification of the oxidation product is conducted with the methanol-containing vapor brought by compression to esterification pressure and esterification temperature.

Process for producing terephthalic acid from p-xylene and methanol by

A process for the production of dimethyl terephthalate from p-xylene and methanol by oxidation in a reactor, in the liquid phase with atmospheric oxygen in the presence of dissolved heavy metal compounds as a catalyst, of a mixture of p-xylene and a fraction containing predominantly methyl p-toluate, which fraction is recycled into the oxidation, to obtain an oxidation product containing primarily p-toluic acid and monomethyl terephthalate, at a temperature of 140.degree.-170.degree. C. and under a pressure of 4-8 bar; by esterification of the oxidation product with liquid and subsequently vaporized methanol brought to an elevated pressure, at a temperature of 220.degree.-280.degree. C. and under a pressure of 20-25 bar in a reactor to obtain a raw ester containing primarily p-toluate and dimethyl terephthalate; by withdrawing the raw ester fraction and a methanol-containing vapor fraction from the esterification stage, by distillatory separation of the raw ester into a p-toluate fraction which is recycled into the oxidation, a raw dimethyl terephthalate fraction which is subjected to further processing by recrystallization in methanol, and a residual fraction which is optionally subjected to a thermal aftertreatment or a reactive treatment with methanol and is partially recycled into the process after a subsequent working-up step by distillation. In this process, the esterification of the oxidation product is conducted with a methanol-containing vapor, brought by compression to the elevated pressure and elevated temperature required for esterification, which methanol-containing vapor has been obtained from the filtrate of the recrystallization of the raw dimethyl terephthalate fraction by vaporization or also by rectification of the methanol-containing vapor fraction and optionally additional methanol-containing process streams, under a pressure lying below the pressure utilized in the esterification reactor.

Process for the production of dimethyl terephthalate from p-xylene and

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Niederkassel, Germany

Ralf Wirges