Bayer Aktiengesellschaft

Bernd Makowka

Hans-Dieter Block

Rainer Weber

Helmut Klotz

Norbert Lonhoff

Bernhard Wehling

Bernhard Spreckelmeyer

Helga Rosentreter

Gertrud Klein, Heir

Heinz-Gunter Klein, Deceased

A process for the production of chromic acid by the multistage electrolysis of dichromate and/or monochromate solutions in two-compartment electrolysis cells, of which the anode and cathode compartments are separated by cation exchanger membranes, at temperatures in the range from 50.degree. to 90.degree. C., the dichromate and/or monochromate solutions being obtained by the digestion of chrome ores and leaching, the improvement wherein, optionally after the removal of aluminum, vanadium and other impurities, the monochromate solution obtained after leaching is adjusted at 20.degree. to 110.degree. C. to a pH value of from 8 to 12 by the addition and/or in situ formation of carbonate in a quantity of from 0.01 to 0.18 mol/l (for 300 to 500 g/l Na.sub.2 CrO.sub.4, converted with CO.sub.2 under pressure into a dichromate-containing solution, the dichromate-containing solution is introduced into the anode compartment of the electrolysis cell, a solution containing chromic acid, in which the molar ratio of Na ions to chromic acid is from 0.45:0.55 to 0.30:0.70, is electrolytically produced and the chromic acid is worked up by crystallization, washing and drying.

Electrochemical process for the production of chromic acid

Crome tanning of pickled animal hides with a tanning agent comprising a reaction product of a basic chromium (III) sulfate and aliphatic C.sub.4 -C.sub.6 dicarboxylic acids or their salts is improved by preparing the reaction product in an aqueous solution from basic chromium (III) sulfate and 0.2 to 0.8 mol of the aliphatic dicarboxylic acids per mol chromium oxide of the basic chromium sulfate with subsequent adjustment of the theoretical basicity to 0 to 50% with alkali metal hydroxide or carbonate, the reaction product being added to a hide pickling liquor in the form of an aqueous solution having a chromium oxide content of at least 5% or in powder form in a quantity of 0.9 to 1.5% chromium oxide, based on hide weight, with a liquor volume less than 100%, based on hide weight, the final pH value being above 4.0 and the final temperature above 40.degree. C.

High-extraction chrome tanning process

An improved process for the preparation of dimethylmaleate by the esterification of maleic acid anhydride, maleic acid monomethylester, maleic acid or mixtures thereof with methanol in the presence of catalytic quantities of sulphuric acid, which comprises carrying out the esterification reaction within 20 to 120 minutes in a multistage bubble cap column reactor at temperatures of from 90.degree. to 140.degree. C. and with methanol excesses of from 0.4 to 2.0 mole per mole of the dimethylmaleate to be produced.

Process for the preparation of dimethylmaleate

Growing community of inventors

Bergisch-Gladbach, Germany

Bernd Makowka