METHOD OF RECOVERY OF CATALYST FROM HIGH-BOILING RESIDUE AFTER DISTILLATION OF CRUDE ESTER

摘要

1. Process for the recovery and reuse of heavy metal oxidation catalyst from the Witten process for the production of dimethyltherephthalate proceeding from high boiling distillation residues with a cobalt content of 1 to 10 g/kg and possibly a manganese content of 0.1 to 5 g/kg residue and/or a nickel content of 0.1 to 5 g/kg of residue, which accumulate in the oxidation of p-xylene and/or p-toluic acid methyl ester-containing mixtures in the liquid phase with oxygen or an oxygen-containing gas at a pressure of 4 to 8 bar and a temperature of 140 to 170 degrees C in the presence of dissolved heavy metal oxidation catalyst, subsequent esterification of the oxidation product with methanol at a pressure of 20 to 30 bar and a temperature of 230 to 280 degrees C and distillative separation of the esterification product into a p-toluic acid methyl ester-rich fraction, a dimethylterephthalate-rich fraction and a high boiling distillation residue, by extraction of the heavy metal oxidation catalyst with water, diluted mineral acids, aqueous low molecular aliphatic monocarboxylic acid with 1 to 4 C-atoms or alcohols with heating, optionally after combustion of the high boiling distillation residues, characterized in that a) the aqueous, acidic, heavy metal oxidation catalyst-containing extract with a cobalt content of 0.2 to 20 g/l, where appropriate a manganese content of 0.05 to 10 g/l and where appropriate a nickel content of 0.05 to 10 g/l is treated with a strongly acid cation exchanger resin in alkali metal form, for example Na**+- or K**+-form at elevated temperature up until its exchanger capacity is attained, b) the cation exchanger resin is washed at elevated temperature and is regenerated at room temperature with Na**+- or K**+-acetate-containing solutions with displacement of the catalyst components and receipt of an aqueous acetic acid catalyst solution containing the catalyst components, and c) the regenerated catalyst solution is employed again directly in the oxidation of p-xylene and/or p-toluic acid methyl ester.