Diamond Shamrock Corporation

Andrew D Babinsky

Charles J Hora

Nicholas Shuster

Leo L Benezra

William E Kidon

Ronald L Dotson

Edward J Peters

Thomas G Strempel

Thomas J Gilligan, Iii

Wayne P Zeman

Martin M Dorio

Chromic acid is now efficiently prepared in a process using dichromate, such as the dichromate typically available as an intermediate in the chromic acid production from chrome ore. In the process, the dichromate is introduced into the center compartment of a three-compartment electrolytic cell and dichromate-containing center compartment electrolyte flows through a porous diaphragm into the anode compartment of the cell. Electrolyte is introduced to the cell cathode compartment which is separated from the center compartment by a substantially hydraulically impermeable cation-exchange membrane means. During electrolysis, chromic acid is prepared in the anolyte and alkali product is produced in the catholyte.

Production of chromic acid in a three-compartment cell

The invention is directed to an electrolytic process for converting alkali metal carbonates to alkali metal hydroxides at high current efficiencies.

Electrolysis of carbonates to produce hydroxides

Chromic acid production is now simplified in a process using the concentrated dichromate typically available at an intermediate stage when chromic acid is produced from chrome ore. In the process, the dichromate is treated in a three-compartment cell as, for example, after removal of the sulfate or carbonate salt evolved in the overall production process. The dichromate feed enters the center compartment of the three-compartment cell and then flows through a porous diaphragm to the anode compartment of the cell and is electrolyzed at elevated current density. Depleted feed solution may be withdrawn from the center compartment and recirculated for reuse. Concentrated, water-white alkali product is produced in the cathode compartment. The anolyte from the cell, rich in chromic acid, can be concentrated, cooled, and the chromic acid recovered. Liquid removed from chromic acid recovery can be recirculated for subsequent electrolysis, as by combination with the feed. Both alkali product and anolyte chromic acid can be produced at enhanced current efficiency.

Chromic acid production process using a three-compartment cell

Chromic acid is now produced in simplified processing that also reduces acid contaminants, while using the alkali metal chromate typically available at an early stage in chromic acid production from chrome ore. In the process, chromate is converted to dichromate in the anode compartment of either a two-compartment, or three-compartment, electrolytic cell. During electrolysis, metal ion contamination is reduced. Withdrawn anolyte from this first cell may then be concentrated. The dichromate feed, possibly concentrated, is then introduced to the center compartment of a three-compartment electrolytic cell and flows through a porous diaphragm to the anode compartment of the cell. The anolyte from this later electrolytic cell, rich in chromic acid, can be concentrated, cooled, and the chromic acid recovered. Liquid removed from chromic acid recovery can be recycled. Alkali product is produced in the cathode compartment of each cell.

Production of chromic acid using two-compartment and three-compartment

In an electrolytic cell of the membrane type wherein the anolyte and catholyte are separated by a hydraulically impermeable membrane, the improvement comprising limiting the hydraulically impermeable membrane portion of the divider between anolyte and catholyte chambers to that area which is between the active areas of the anode and cathode while all other areas between catholyte and anolyte chambers are nonpermeable so as to minimize back-migration of undesirable ions which decrease overall current efficiency. Specifically, in a chlor-alkali cell an electrode would be enclosed in a fluorinated ethylene propylene enclosure having window-like openings therein made from Nafion type hydraulically impermeable cation exchange membrane, said window-like openings exposing only active electrode areas.

Membrane assembly for electrolytic cells

Disclosed is a method for converting a diaphragm electrolytic cell to a membrane electrolytic cell by using the standard diaphragm cell equipment and applying a membrane over top of a matting material upon the cathode surface. This method permits a manufacturer having diaphragm electrolytic cells to convert those cells to membrane electrolytic cells without significant capital expenditure to achieve the desirable characteristics of a membrane electrolytic cell.

Converting a diaphragm electrolytic cell to a membrane electrolytic cell

Disclosed are a sulfonyl group containing fluorocarbon polymer cation-exchange membrane which has been fabric reinforced and, on one side of which has been treated, after the fabric reinforcing has been applied in a heat-pressure application, to a depth of at least 10 microns with a primary amine or a secondary amine or mixtures thereof to aminate a majority of said sulfonyl groups.

Reverse-side treatment of fabric reinforced membranes

Disclosed is a method and apparatus for the concentration and purification of a cell liquor containing sodium or potassium hydroxide wherein the three compartment electrolytic cell has a porous catalytic anode, a porous asbestos diaphragm separating the anode compartment and a central compartment having a stratification network, a cation-exchange membrane separating the central compartment and a cathode compartment having cathode disposed therein such that an electrolyzing current may be passed between the anode and cathode. Hydrogen gas emanating from the cathode and anode compartments is fed into the porous catalytic anode to decrease the potential across the cell below the evolution potential for chlorine and coincidently reduce the power requirements of the cell, which is operated at elevated temperatures.

Apparatus for concentration and purification of a cell liquor in an

Disclosed are a sulfonyl group containing fluorocarbon polymer cation-exchange membrane, one side of which has been amine treated to a depth of at least 10 microns, as well as a chlor-alkali electrolytic cell employing same.

Polyamine modified membranes and chlor-alkali electrolysis cells

Optimum current efficiencies are attained and maintained in a membrane chlor-alkali electrolytic cell by the constant, precise control of both the brine and caustic concentrations at each membrane phase boundary. Such control requires recycling through external holding tanks wherein the concentrations are adjusted to 560 grams per liter caustic and 190 grams per liter brine. Turbulent flow of such concentrations in the cells helps maintain the optimum concentration and also decreases the diffusion layer.

Process for brine membrane cell operation with external caustic and NaCl

Disclosed is a method for converting a diaphragm electrolytic cell to a membrane electrolytic cell by using the standard diaphragm cell equipment and applying a membrane over top of a matting material upon the cathode surface. This method permits a manufacturer having a diaphragm electrolytic cells to convert those cells to membrane electrolytic cells without significant capital expenditure to achieve the desirable characteristics of a membrane electrolytic cell.

Disclosed is a method and apparatus for the concentration and purification of a cell liquor containing sodium or potassium hydroxide wherein the three compartment electrolytic cell has a porous catalytic anode, a porous asbestos diaphragm separating the anode compartment and a central compartment having a stratification network, a cation-exchange membrane separating the central compartment and a cathode compartment having cathode disposed therein such that an electrolyzing current may be passed between the anode and cathode. Hydrogen gas emanating from the cathode and anode compartments is fed into the porous catalytic anode to decrease the potential across the cell below the evolution potential for chlorine and coincidentally reduce the power requirements of the cell, which is operated at elevated temperatures.

Method for concentration and purification of a cell liquor in an

Cation-exchange membranes for use in the electrolysis of alkali metal chloride solutions are treated in order to introduce hydrated alkali metal ions throughout the membrane and are subsequently installed in a cell and subjected to an applied voltage not in excess of about 6.5 to 8.5, passage of current and electrolysis occurring immediately.

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Chagrin Falls, OH, United States of America

Andrew D Babinsky