Bayer Aktiengesellschaft

Helmut Klotz

Rainer Weber

Hans-Dieter Block

Norbert Lonhoff

Hans D Pinter

Hans G Fitzky

Bernhard Spreckelmeyer

Wolfgang Ohlendorf

Lothar Sesterhenn

Bernd Makowka

Walter Kornfeld

Wolfgang Isenhagen

Ernst Tepe

Klaus Bloch

In the preparation of a graphite body suitable for use as a cathode in an electrolytic process, comprising the steps of

Preparation of stable graphite

A dimensionally stable anode comprised of

Dimensionally stable anodes and their use in the preparation of alkali

A process for the preparation of alkali metal dichromates and/or chromic acid by electrolysis of alkali metal monochromate and/or alkali metal dichromate solution in electrolysis cells, the anode and cathode compartments of which are separated by cation exchange membranes, wherein the cation exchange membranes are single-layer membranes based on perfluorinated polymers having sulfonic acid groups as cation exchange groups, and an aqueous solution having a pH of 4 to 14 is produced in the cathode compartment of the cells.

Process for the preparation of alkali metal dichromates and chromic acid

The invention relates to a process for the preparation of alkali metal dichromates and chromic acid by the electrolysis of monochromate and/or dichromate solutions in a multi-chamber cell, wherein the anode chamber is shielded from the solution of chromate, dichromate and/or chromic acid by a bipolar ion exchanger membrane.

Preparation of chromic acid using bipolar membranes

A process for the preparation of alkali metal dichromates and chromic acid by the electrolysis of monochromate and/or dichromate solutions in an electrolytic cell in which the anode and cathode chamber are separated by a cation exchanger membrane anolyte fluid containing dichromate and/or chromic acid being formed in the anode chamber and alkaline catholyte fluid containing alkali metal ions being formed in the cathode chamber, the improvement wherein the catholyte fluids are periodically replaced by a solution which is at a pH below 6.

Processes for the preparation of alkali metal dichromates and chromic

A process for the preparation of chromic acid by the electrolysis of dichromate and/or monochromate solutions in electrolytic cells in which the anode chamber and the cathode chamber are separated by a cation exchanger membrane, the improvement wherein the chromic acid content of the solution in the anode chamber is periodically increased above that of a continuous operating state.

Process for the preparation of chromic acid

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

A process for the preparation of alkali metal dichromates and chromic acid by the electrolysis of monochromate and/or dichromate solutions in an electrolytic cell in which the anode and cathode chambers are separated by cation exchange member, the improvement wherein the formation of deposits on the membrane is prevented comprising continuously introducing a solution containing chromate at a pH of about 3 to 10 into the cathode chamber during the electrolysis.

A process for the production of alkali dichromates and chromic acid by electrolysis of alkali monochromate or alkali dichromate solutions wherein the anodes used in the electrolysis are dimensionally stable anodes of valve metals activated by electrodeposition of noble metals and/or noble compounds from melts containing noble metal salts.

Process for the production of alkali dichromates and chromic acid

A woven diaphragm for a diaphragm electrolysis cell for electrolysis of aqueous solutions containing ions such as alkali metal ions, chloride ions, and sulfate ions which diaphragm comprises warp threads and weft threads. Both warp threads and weft threads are of multifil filaments. Weft threads contain less than about 200 per meter and warp threads contain less than 400 per meter.

Woven diaphragm for aqueous electrolytes

In the treatment of a perfluorinated polymer membrane containing acid ion exchanger groups in a corona discharge, the improvement which comprises employing a membrane containing carboxyl groups and maintaining the membrane at a temperature below about 80.degree. C. during the discharge treatment. Advantageously the corona discharge treatment is carried out intermittently, the temperature is maintained at about -10.degree. to +22.degree. C., during the treatment the average rate of irradiation is below about 2 Ah/m.sup.2, the frequency of the corona discharge is from about 5 to 15 kHz, the voltage for producing the corona discharge is from about 1 to 20 kV and the dose is from about 0.1 to 10 Ah/m.sup.2 of membrane surface. The resulting membranes exhibit lowered resistance resulting in lower cell voltages when used in the electrolysis of sodium chloride.

Treatment of perfluorinated polymer membranes containing carboxyl groups

In an electrolytic cell for the production of chlorine and hydrogen from hydrochloric acid, the cell comprising a plurality of spaced bipolar electrodes each provided with vertical grooves for the passage of gas, and a plurality of diaphragms each subdividing the space between adjacent electrodes, the improvement which comprises providing the grooves with a depth of about 18 to 35 mm at least in the upper part of the electrodes. Advantageously the grooves have a width of about 2 to 3 mm and the spacing between adjacent grooves of each electrode is about 4 to 6 mm, the depth of the grooves at their bottoms is about 12 to 15 mm and increases in upward direction to about 20 to 30 mm, and the distance between the electrodes and the diaphragms is from about 0.05 to 1 mm. The voltage drop and energy consumption are less than with different groove configurations and the chlorine content of the hydrogen gas is reduced.

Hydrochloric acid electrolytic cell for the preparation of chlorine and

The sodium concentration in the amalgam of an electrolysis cell is automatically monitored by periodically removing an amalgam sample of predetermined quantity from the end compartment of the electrolysis cell, introducing the sample into a reference cell containing a reference electrolyte, thereby to form a galvanic element in said reference cell, discharging the galvanic element, and measuring the charge flowing out when the galvanic element is discharged, the charge being an index of the sodium concentration. Advantageously the reference electrolyte is a dilute solution of at least one of sodium hydroxide and sodium chloride. The apparatusincludes many cells and a common distant monitoring station. A voltage which is proportional to the decomposition current of the galvanic element formed by the amalgam and reference electrolyte is fed to the input of a voltage/frequency converter which determines the charge, and the output of the converter is integrated by a subsequent counter chain until the decomposition current is damped.

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Bergisch Gladbach, Germany

Helmut Klotz