General Electric Company

Oronzio Denora Impianti Elettrochimici S.p.a.

United Technologies Corporation

Oronzio De Nora Permelec S.p.a.

Thomas G Coker

Anthony B LaConti

Russell M Dempsey

Anthony R Fragala

Edward N Balko

Anthony B La Conti

George B McGray

John F Austin

Chlorine is generated by electrolyzing aqueous alkali metal chloride in a cell wherein the anode and cathode are separated by and in contact with an ion exchange diaphragm and wherein the anode and/or cathode contains particles of an electroconductive catalytic material along with particles of an electroconductive extender bonded to the membrane.

Production of halogens by electrolysis of alkali metal halides in an

A unitary membrane-electrode assembly includes a structure with multiple layers having different overvoltages for the desired electrochemical reaction. The layer attached to the membrane has a higher overvoltage for the electrochemical reaction than the electrode layer attached to its upper surface thereby preferentially locating the electrochemical reaction zone a small but controlled distance away from the membrane surface. In an alkali metal halide or alkali metal sulfate electrolysis process the use of a unitary dual layer structure with a bonded remote electrode is particularly useful as a cathode side structure because it eliminates formation of concentrated caustic at the membrane surface. As a result, back migration of OH.sup.- ions is reduced and cathodic current efficiency is increased.

Multi-layer structure for electrode membrane-assembly and electrolysis

A process for fabricating a unitary membrane-electrode structure by attaching an electrode to a permselective membrane while the latter is in a non-hydrated (and essentially non-dissociated) form. The electrode, in the form of a bonded aggregate of catalytic and polymeric binder particles, is attached to a membrane having less than 0.01 grams of matrix water per gram of dry membrane by the application of heat and pressure. The membrane is then hydrated causing the membrane to swell by a controlled amount and converting it to the dissociated form. A membrane-electrode structure fabricated in this manner is particularly useful in the electrolysis of alkali metal halides because it is characterized by improved cathodic current efficiency and by reduced susceptibility to permeation of gaseous hydrogen.

Dry process for fabricating a unitary membrane-electrode structure

A halogen, such as chlorine, is generated by electrolysis of an aqueous solution of an alkali metal halide such as sodium chloride, in a cell having anolyte and catholyte chambers separated by a solid polymer electrolyte in the form of a stable, selectively cation permeable, ion exchange membrane. One or more catalytic electrodes including at least one thermally stablized, reduced oxide of a platinum group metal are bonded to the surface of the membrane. An aqueous brine solution is brought into contact with the anode and water or an aqueous NaOH solution is brought into contact with the cathode. The brine is electrolyzed to produce chlorine at the anode and hydrogen and caustic at the cathode. The cell membrane preferably has an anion rejecting cathode side barrier layer which rejects hydroxyl ions to block back migration of caustic to the anode thereby enhancing the cathode current efficiency of the cell and of the process.

A unitary membrane-electrode assembly includes an electrode structure with multiple layers having different overvoltages for the desired electrochemical reaction. In the preferred arrangement the layer attached to the membrane has the higher overvoltage thereby preferentially locating the reaction zone a small but controlled distance away from the electrode membraneinterface. In a NaCl brine electrolysis process the use of a dual layer electrode as the cathode is particularly useful because it eliminates formation of concentrated caustic at the membrane surface. As a result, back migration of OH.sup.- ions is reduced and cathodic current efficiency is increased.

Multi-layer electrode membrane-assembly and electrolysis process using

A halogen, such as chlorine, is generated by electrolysis of an aqueous solution of an alkali metal halide such as sodium chloride, in a cell having anolyte and catholyte chambers separated by a solid polymer electrolyte in the form of a stable, selectively cation permeable, ion exchange membrane. One or more catalytic electrodes including at least one thermally stabilized, reduced oxide of a platinum group metal are bonded to the surface of the membrane. An aqueous brine solution is brought into contact with the anode and water or an aqueous NaOH solution is brought into contact with the cathode. The brine is electrolyzed to produce chlorine at the anode and hydrogen and caustic at the cathode. The cell membrane preferably has an anion rejecting cathode side barrier layer which rejects hydroxyl ions to block back migration of caustic to the anode thereby enhancing the cathode current efficiency of the cell and of the process.

A process for producing sulfuric acid and caustic soda by the electrolysis of an alkali metal sulfate in a membrane cell having a hydrogen depolarized anode. Hydrogen gas in the anode chamber is oxidized to produce hydrogen cations which combine with the sulfate anions from the aqueous alkali metal sulfate solution to produce sulfuric acid. Alkali metal ions are transported across the membrane to the cathode to produce caustic and gaseous hydrogen. By oxidizing hydrogen at the anode, the cell voltage for the electrolysis of the alkali metal sulfate is substantially reduced.

Electrolysis of alkali metal salts with hydrogen depolarized anodes

A novel, electrocatalytic material comprising at least one reduced platinum group metal oxide is subsequently heated in the presence of oxygen at a temperature high enough to stabilize the catalyst in acidic and halogen environments. The catalyst optionally contains other thermally stabilized, reduced platinum group metal oxides, electroconductive extenders of the group consisting of graphite and oxides of transition or valve metals. A novel electrode structure includes the catalyst and a polymeric binder. A novel method of preparing the electrocatalytic material is described as well as a unitary electrolyte electrode structure which has a bonded electrode containing the novel electrocatalytic material, bonded to at least one side of a membrane-electrolyte.

Thermally stabilized reduced platinum oxide electrocatalyst

A three layer cation transporting membrane in which the interior layer has the best hydroxyl ion (OH) rejection characteristics. The outer layers are preferably porous.

Multi layer ion exchanging membrane with protected interior hydroxyl ion

The performance of a permselective cation transporting membrane is improved by making the membrane a three or more layer structure in which the layer having the best hydroxyl (OH) ion rejection characteristic is in the interior of the membrane. The OH ion rejection layer, which typically has sulfonamide or carboxylic functional groups, is covered by a cation transporting layer having sulfonate functional groups to which the cathode electrode is attached by bonding or otherwise. This keeps the high caustic concentrations present at the membrane-electrode interface away from the sulfonamide, etc. rejection layer.

A halogen, such as chlorine, is generated in an electrolysis cell in which at least one of the cell electrodes is bonded to the surface of a solid but porous membrane which separates the cell into anode and cathode chambers. A pressurized aqueous metal halide such as brine is electrolyzed at the anode to produce chlorine. Brine anolyte and sodium ions are hydraulically transported across the porous membrane to produce caustic (NaOH) at the cathode. By bonding at least one gas permeable, porous electrode to the hydraulically permeable membrane, the cell voltage for electrolysis of brine is considerably lower than that required for asbestos diaphragm cells, while achieving high cathodic current efficiencies by minimizing back migration of caustic to the anode.

Cell having catalytic electrodes bonded to a membrane separator

A halogen, such as chlorine, is generated by electrolysis of an aqueous solution of an alkali metal halide such as sodium chloride, in a cell having anolyte and catholyte chambers separated by a solid polymer electrolyte in the form of a stable, selectively cation permeable, ion exchange membrane. One or more catalytic electrodes including at least one thermally stabilized, reduced oxide of a platinum group metal are bonded to the surface of the membrane. An aqueous brine solution is brought into contact with the anode and water or an aqueous NaOH solution is brought into contact with the cathode. The brine is electrolyzed to produce chlorine at the anode and hydrogen and caustic at the cathode. The cell membrane preferably has an anion rejecting cathode side barrier layer which rejects hyroxyl ions to block back migration of caustic to the anode thereby enhancing the cathode current efficiency of the cell and of the process.

The invention describes a pressurized, three compartment membrane cell for the electrolyzing aqueous alkali metal halides at low cell voltages and with high cathodic current efficiencies. Unitary electrode-electrolyte structures, in the form electrochemically active electrodes physically bonded to ion transporting permselective membranes divide the cell into anode, cathode and buffer compartments. The buffer compartment feed is pressurized to maintain at a positive pressure differential with respect to the anode and cathode compartment feeds. The flexible unitary electrode-membrane electrolytes are forced outwardly against electronically conductive anode and cathode current collectors to provide uniform, constant and controllable contact between the bonded electrodes and thereby minimizing ohmic losses. A three compartment cell operated in this fashion not only minimizes the voltage required to electrolyze the halide solution, but also increases the cathodic current efficiency at high caustic concentrations by providing multiple hydroxide rejection stages in a single cell process. The improvement in cathodic current efficiency is realized by forming a lower caustic concentration in the buffer compartment than in the cathode compartment thereby reducing backmigration of OH.sup.- ions into the anode compartment.

Electrolysis of alkali metal halides in a three-compartment cell with a

The invention describes a self pressurized three compartment, membrane cell and a process for electrolyzing aqueous halide solutions at low cell voltages and high cathode current efficiencies. Electrochemically active electrodes are physically bonded to ion exchanging membranes which divide the cell into three compartments. The mass transport characteristics of the membranes are selected so that water brought into the center or buffer compartment along with the halide ions exceeds water transport out of the compartment. This results in good electrode to current collector contact as the membranes to which the electrochemically active electrodes are permanently bonded are forced against the current collectors. The instant invention relates to a process and apparatus for the electrolytic production of halogens and alkali metal hydroxides from aqueous alkali metal halide solutions. More particularly, it relates to the electrolysis of brine in a three compartment membrane cell having catalytic anode and cathode electrodes physically bonded to the permselective membranes which divide the cell into three compartments.

Electrolysis of alkali metal halides in a three compartment cell with

A halogen such as chlorine is produced by the electrolysis of an aqueous solution of a hydrogen halide such as hydrochloric acid in an electrolysis cell having anolyte and catholyte chambers separated by a solid polymer electrolyte in the form of a stable, selectively permeable, hydrated ion exchange membrane. Catalytic electrodes in the form of fluorocarbon bonded, thermally stabilized, reduced oxides of platinum group metals are bonded to at least one surface of the membrane and an aqueous hydrochloric acid solution is brought in contact with the bonded anode to generate chlorine at the anode and hydrogen at the cathode.

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Waltham, MA, United States of America

Thomas G Coker