Dynamit Nobel Aktiengesellschaft

Rudolf Cordes

Heinrich Bunger

Gerhart Hoffmann

Karl Irlweck

Gerhard Hoffmann

The yield of dimethyl terephthalate obtained by the oxidation of a mixture of p-xylene and methyl p-toluate, preferably with air, and esterification of the thus-produced acids is increased by utilizing a mixture of cobalt and manganese compounds as the oxidation catalyst.

Process for the preparation of dimethyl terephthalate

A process for the recovery and reuse of heavy metal oxidation catalyst from residues in the Witten DMT process by extraction, which involves mixing and settling of the residue with water or dilute aqueous solutions of water-soluble, low-molecular, aliphatic monocarboxylic acids at 70.degree.-160.degree. C. and recycling of the extract of the high-boiling distillation residues into the DMT process. The high-boiling distillation residue and the extractant are used in a quantitative ratio of 1:0.9 to 1:0.1, preferably 1:0.5 to 1:0.3.

Process for the recovery and reuse of heavy metal oxidation catalyst

A process for effecting the recovery and use of a heavy metal oxidation catalyst from a high-boiling distillation residue obtained during the Witten process for the production of dimethyl terephthalate involves the extraction of the high-boiling distillation reside with water or dilute aqueous solution of low molecular weight aliphatic monocarboxylic acids or alcohols and recycling of the extract into the oxidation stage of the Witten process. In the extract the quantitative ratio of the sum of the amount of trimellitic acid and monomethyl ester of trimellitic acid to the amount of heavy metal catalyst is controlled to be at a value of no more than 1.8:1 and in the oxidation stage of the Witten process the catalyst concentration (c), expressed in p.p.m., is represented by the formula:

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Niederkassel, Germany

Rudolf Cordes