Basf Wyandotte Corporation

Other

Shyam D Argade

Edward N Balko

James E Shrewsburg

Thomas G Coker

Arvind S Patil

Stephen M Collins

Eugene Y Weissman

John J Bortak

David A Kramer

William Francis Schmitt

Douglas A Porath

In a process for making chlorine electrolytically in which a build-up of nitrogen trichloride occurs in the bottoms of cooling apparatus, a method and apparatus is provided wherein the nitrogen trichloride is dissolved in an organic solvent such as carbon tetrachloride, the chlorine removed, and the solution treated to destroy the otherwise hazardous nitrogen trichloride. The solvent is then separated and recycled to avoid environmentally undesirable waste products.

Apparatus for removing nitrogen trichloride from chlorine gas

Discrete thermoplastic fibers of fluorohydrocarbons and other self-bonding thermoplastic fibers are deployed as separators or diaphragms in electrochemical cells.

Thermoplastic fibers as separator or diaphragm in electrochemical cells

Small quantities of metal ions can be removed from an aqueous solution by subjecting the solution to an electric current in the presence of an anode and a fibrous metal cathode. The invention also provides an electrolytic apparatus having such electrodes. The process is particularly adaptable to the removal of mercury contamination from liquid brine streams.

Method for the recovery of mercury and other heavy metal ions from a

Initial cell voltages are reduced by decreasing the resistance of the diaphragm through a degassing procedure prior to or at installation thereof. This degassing procedure involves subjecting the diaphragm to subatmospheric pressure while contacting the diaphragm with electrolyte, said electrolyte being an aqueous saline solution having a surface active agent therein in an amount sufficient to reduce the surface tension below the critical surface tension for wetting the fibers, and increasing the pressure to atmospheric or cell working pressure to force electrolyte solution into the interstices of the diaphragm.

Process for installing synthetic fiber diaphragms in chlor-alkali cell

Fibers about micron size in cross-section of certain fluorine-containing polymers can be treated after being deposited as a diaphragm, either during operation or separately before installation, so that they develop a 0.25-millimeter-thick ply on either side of a central body which is substantially different in chemical composition. This yields a diaphragm 1 to 5 millimeters thick which has a Mullen burst strength approximately three to five times greater than that of an untreated diaphragm (20-25 pounds per square inch versus 5 to 7 pounds per square inch) and a remarkably improved service life in the treated diaphragm (200 days and up) in comparison with such untreated diaphragm (30 days or less). Use of a polymer based upon a major proportion of chlorotrifluoroethylene appears to be required. This discovery is economically significant, in that it is an essential element in the technology of the replacement of asbestos diaphragms now used with a synthetic material. Health-hazard and pollution-control considerations have made it desirable to replace asbestos, and this invention provides the key to the solution of the problem. Moreover, a synthetic-polymer diaphragm has two significant advantages that an asbestos one lacks--it will withstand washing or cleaning with an acid solution, and it does not swell in service and resists erosion, so that a closer electrode spacing can be used and the cell voltage can thus be lower.

Electrolysis of alkali-metal halides

An especially efficient and durable electrolytic cell is provided by utilizing a combined cathode and diaphragm unit wherein the cathode is made by spray coating a ferrous metal substrate with a powder metal having lower hydrogen overvoltage than said substrate to form a protected cathode surface having a larger surface area than the substrate, and vacuum depositing a polymer impregnated asbestos fiber diaphragm onto a spray coated surface of the cathode to form a fibrous diaphragm thereon. Preferably, the cathode surface is made with nickel and the polymer impregnated asbestos diaphragm contains from about 10 to about 30 percent based on the weight of asbestos of an organic cementing agent such as a fluorohydrocarbon polymer.

Combined cathode and diaphragm unit for electrolytic cells

An especially efficient and durable electrolytic cell is provided by utilizing a combined cathode and diaphragm unit wherein the cathode is made by spray coating a ferrous metal substrate with a powder metal having lower hydrogen overvoltage than said substrate to form a protected cathode surface having a larger surface area than the substrate, and vacuum depositing fluorinated hydrocarbon polymer fibers onto the spray coated surface of the cathode to form a fibrous diaphragm securely adhered thereto. Preferably, the cathode surface is made with nickel and the fluorinated hydrocarbon polymer is selected from the group consisting of homopolymers of chlorotrifluoroethylene and copolymers of chlorotrifluoroethylene and at least one compatible monomer with units of chlorotrifluoroethylene accounting for at least 80 percent of the monomeric units of said copolymer.

Method for removing nitrogen trichloride from chlorine gas

Chlorotrifluoroethylene containing polymer diaphragm

Synthetic-fiber diaphragms are further improved by incorporating in the diaphragm an effective proportion of a suitable inorganic material such as TiO.sub.2, BaSO.sub.4 or K.sub.2 Ti.sub.8 O.sub.17, which is more hydrophilic than the fluoropolymer forming the diaphragm. This is done either by mixing the inorganic material with the resin before it is made into fiber or by supplying sub-micron-sized particles of the inorganic material, during or even after diaphragm formation. A principal benefit is that this lowers the cell voltage which is required during an initial period (up to about 300 hours) of the operation of a chlor-alkali cell provided with such a diaphragm, making it possible to avoid such drawbacks as suffering an initial period of low production or the necessity of providing external cooling to the cell during such an initial period.

Diaphragms for chlor-alkali cells

An improvement in the recovery of mercury from aqueous streams is achieved by the use of polytetrafluoroethylene filters.

Polytetrafluoroethylene membrane filters for mercury recovery

A ferrous metal cathode used in a chlor-alkali electrolytic cell has a metallic coating deposited thereon. The metallic coating is applied by either flame spraying or plasma spraying a powdered metal onto the ferrous metal surface. The metals which are utilized are those having a lower hydrogen overvoltage than iron.

Sprayed cathodes

Electrolytic filter press cell frames are provided with a polymeric protective covering which is either directly laminated thereonto or otherwise secured thereto. The protective covering is, preferably, a fluorinated hydrocarbon.

Protective covering for electrolytic filter press cell frames

Brine from a conventional treatment process is pre-filtered prior to the electrolysis of same by a method which includes the steps of: (a) heating the brine, (b) adding sodium carbonate thereto, (c) stirring the solution, (d) allowing the solution to settle, and (e) passing the solution through an absolute membrane filter. The filter 'polishes' the brine feed by removing the high hardness ions.

Removal of low level hardness impurities from brine feed to chlorine

In the process of producing chlorine and caustic soda employing mercury amalgam electrolytic cells, mercury losses occur in both solid and liquid plant waste streams. This invention provides for an integrated system in which mercury is extracted from plant waste streams, the waste streams are discharged, and the mercury recovered by electro-reduction in the plant electrolytic cells.

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Woodhaven, MI, United States of America

Shyam D Argade