Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B3/00—Electrolytic production of organic compounds
  • C25B3/20—Processes
  • C25B3/25—Reduction
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B3/00—Electrolytic production of organic compounds
  • C25B3/20—Processes
  • C25B3/29—Coupling reactions

Definitions

• ..204 59 R, 260/538 membrane and the Catholyte is an Organic Solvent- [511 Int 29/06, C076 51/40, C07c 55/06 Tetraethylammonium perchlorate, tetraethylammoni- [58] Field of Search ..204/59, 72- 260/538 bmmide tetrabulylammmium Perchlmte, tetrabutylammonium iodide and tetraethylammonium 5 f p-toluenesulfonate are the preferred solutes for the 6] Re erences catholyte.
• Oxalic acid and oxalate salts are produced commercially to fill a great variety of end uses. For example, they are used in laundries as a rust and ink remover, as the chief constituent in automobile radiator scale removers, as an electrolyte in the anodic oxidation of aluminum, as a bleaching agent for such materials as straw, cork, rosin and wood, as reagents in chemical analysis and in the manufacture of miscellaneous chemical derivatives.
• Oxalic acid is prepared commercially by four general methods:
• an oxalate salt capable of being converted to form oxalic acid is prepared by an electrolytic technique.
• My invention relates to the cationic reduction of carbon dioxide in an electrolytic cell whereby it is converted to an oxalate salt.
• the electrolytic dimerization of carbon dioxide to the oxalate salt is conducted in an electrolytic cell wherein the anode and cathode compartments are separated by a porous membrane.
• the catholyte comprises a nonaqueous solvent having dissolved therein tetraethylammonium or tetrabutylammonium salts of perchloric acid, hydrobromic acid, hydriodic acid or p-toluenesulfonic acid.
• Coulombic yields as high as 75 percent are obtained where the catholyte is used as the anolyte while yields of sodium oxalate as high as 97 percent are obtained when the anolyte is an aqueous solution of sodium chloride.
• my invention relates to the production of oxalic acid by an electrolytic means. More specifically, my invention is directed to the preparation of an oxalate salt by means of the electrochemical dimerization of carbon dioxide followed by the acidification of the oxalate to produce oxalic acid. More particularly, my invention relates to the improvement of producing an oxalate salt in an electrolytic cell wherein the cell has an anode compartment and a cathode compartment separated by a cationic exchange porous membrane. The improvement comprises:
• the oxalate salt may be converted to oxalic acid by contacting the salt with an acid to produce a salt of the acid and oxalic acid.
• the electrolytic cell employed may embody some of the various mechanical designs known heretofore.
• the cell will comprise two compartments separated by a porous membrane to prevent the admixing of the electrolytes. Mechanical agitation of the catholyte or circulation of the catholyte through the cathode compartment is not essential but is preferred.
• An electrode is located in each compartment. Heating and cooling should be provided to maintain the operating temperature within the desired limits.
• the anode chamber may be constructed from the same materials used in electrolytic chlorine cells such as carbon steel.
• the cathode compartment may be constructed from carbon steel. Interior surfaces of the anode and cathode compartments may be lined with non-metallic materials such as polyvinylchloride or nylon.
• the electrodes may be constructed from a variety of materials.
• the cathode material should have a high hydrogen overvoltage. Carbon, platinum, tin or zinc cathodes result in the generation of a gas and are not preferred. Copper or lead amalgamated cathodes as well as mercury, lead, or stainless steel cathodes produce the desired results. Because of corrosion problems in the anode compartment, inert or corrosion resistant anodes are employed. Generally, carbon or graphite anodes are preferred.
• the anode and cathode compartments are separated by a membrane which prevents the anolyte and catholyte from mixing while being sufficiently porous to permit the passage of cations.
• a membrane which prevents the anolyte and catholyte from mixing while being sufficiently porous to permit the passage of cations.
• porous membranes constructed of sintered glass and cation exchange resin are useful while cation exchange resin is preferred.
• each half cell may be separately constructed and joined together with the porous membrane located at the junction.
• the cell may comprise a single compartment divided by a wall, a portion or all of which may constitute the porous membrane.
• the half-cell compartments may comprise concentrically positioned chambers with the porous membrane located in the wall of the inner chamber.
• One means to accomplish this is to provide a fritted disc or sparger in the compartment to introduce the carbon dioxide into the catholyte as a series of small bubbles. Improved contact between the gaseous carbon dioxide and the catholyte may be provided through mixing means located in the cathode compartment.
• Another means to introduce carbon dioxide into the cathode compartment is to add it to a circulating stream of catholyte at a point external to the cell. The circulating stream also provides a means of mixing the contents of the cathode compartment.
• the desired reaction is conducted by employing a catholyte comprising a quaternary ammonium salt as an electrolyte dissolved in a non-aqueous solvent.
• Catholyte solvents which may be usefully employed include N,N-dimethyl-formamide (DMF), dimethylacetamide (DMA), dimethyl sulfoxide (DM- SO) and hexamethylphosphoramide (HMPA) with N,N-dimethylformamide being preferred.
• the electrolyte is dissolved in the solvent and is a quaternary ammonium salt.
• Useful electrolytes include the C -C alkyl quaternary ammonium salts soluble in the selected solvent, particularly the C -C alkyl quaternary ammonium salts.
• Preferred electrolytes include the tetraethylammonium, tetrapropylammonium and tetrabutylammonium salts of perchloric acid,
• TEPC tetraethylammonium perchlorate
• TEBr tetraethylammonium bromide
• TBPC tetrabutylammonium perchlorate
• TBI tetrabutylammonium iodide
• TBI tetraethylammonium p-toluenesulfon
• an oxalate salt which may be converted to oxalic acid
• aqueous salt solutions may be usefully employed as the anolyte while permitting coulombic yields as high as 97 percent of the oxalate salt.
• Aqueous solutions of such salts as sodium chloride, sodium hydroxide and sodium bicarbonate have been usefully employed in the anode compartment.
• sodium salts are preferred because with the migration of the sodium ion to the cathode compartment the resultant sodium oxalate is readily converted to oxalic acid following its recovery from the compartment.
• the oxalate produced is a quaternary ammonium oxalate which may be recovered from the catholyte by causing it to precipitate by the addition of diethyl ether.
• sodium oxalate is produced in the catholyte as a white precipitate and may be recovered by filtration of the catholyte. Washing of the oxalate with an organic solvent, such as acetone, is followed by a drying step.
• the sodium oxalate is often recovered from the catholyte admixed with other salts, such as sodium bicarbonate. The oxalate may be recovered therefrom by combining the mixed salts with a mixture of aqueous acetic acid and acetone.
• the white suspension of sodium oxalate may be recovered by filtration and then acidified with an acid, such as hydrochloric acid to produce oxalic acid and sodium chloride. Addition of acetone results in sodium chloride crystals and a solution of oxalic acid in acetone. The sodium chloride crystals may be removed by filtration and the filtrate evaporated to dryness to yield oxalic acid. Altemately, the mixed salts may be mixed with hydrochloric acid followed by the addition of acetone to produce the oxalic acid.
• EXAMPLE I A series of runs demonstrating my invention were conducted in an electrolytic cell having two compartments separated by a cationic porous membrane consisting of cationic exchange resin.
• the cathode compartment was equipped with a lead electrode having a cross sectional area of 9.7 cm, a gas inlet tube and a magnetic stirring bar.
• the anode compartment was equipped with a carbon electrode having a cross sectional area of 12 cm.
• the catholyte was deaerated with a nitrogen stream for approximately five minutes and then carbon dioxide was introduced into the cathode compartment.
• Runs 6 to 14 show that higher yields of oxalate are obtained when an aqueous solution of sodium salt serves as the anolyte with yields as high as 97.8 percent being obtained.
• TEPC-Tetraethylammonium perchlorate DMSO- Dimethyl sulfoxide; DMA-Dimethylacetamide; HMPA-Hexamethylphosphoraniide; DMFN,N-dimethylde; TEBr-Tetraethylammonlum bromide.
• TBI-Tetrabutylammonium iodide TEPC-Tetraethylammonium perchlorate
• TBPCTetrabutylammonium perchlorate TEBr-Tetraethylammonlum bromide
• TEP'ISTetraethylammonium p-tolucnesulionate DMF-N,N-dimethyllormamide.
• EXAMPLE V Typically, the sodium oxalate formed in the cathode compartment as in Examples ll-IV was recovered, when desired, by filtering the catholyte with suction. The resulting white solid was washed with acetone and dried in a vacuum oven under partial vacuum. The dried product consisted of sodium oxalate admixed with sodium bicarbonate. The mixed salt was treated with an aqueous solution of acetic acid and then with acetone. Filtering out the white precipitate yielded sodium oxalate which was collected and dried. The white product was then mixed with concentrated hydrochloric acid and the resultant slurry treated with acetone and filtered under suction. The white solid recovered was washed with acetone, dried and identified as sodium chloride. Evaporation of the filtrate to dryness yielded oxalic acid. The yield of oxalic acid was quantative, i.e., 100 percent.
• quaternary ammonium salt is a C,-C alkyl quaternary ammonium salt.
• a process according to claim 2 wherein the quaternary ammonium salt is selected from the group consisting of the tetraethylammonium tetraprop'ylammonlum and tetrabutylammonium salts of perc loric acid, hydrobromic acid, hydriodic acid and ptoluenesulfonic acid.
• the quaternary ammonium salt is selected from the group consisting of tetraethylammonium perchlorate, tetraethylammonium bromide, tetrabutylammonium perchlorate, tetrabutylammonium iodide and tetraethylammonium p-toluenesulfonate.
• anolyte is selected from the group consisting of the catholyte, aqueous NaCl, aqueous NaOH and aqueous NaHCO;.
• cathode materials are selected from the group consisting of copper amalgam, lead amalgam, lead, mercury and stainless steel.
• a process according to claim 1 including the following additional steps:

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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Cited By (33)

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Citations (3)

• 0
  • BE BE791653D patent/BE791653A/xx unknown
• 1971
  • 1971-12-28 US US00213206A patent/US3720591A/en not_active Expired - Lifetime
• 1972
  • 1972-10-14 DE DE19722250522 patent/DE2250522B2/de not_active Withdrawn
  • 1972-10-25 GB GB4916772A patent/GB1382518A/en not_active Expired
  • 1972-11-07 JP JP47110858A patent/JPS4875513A/ja active Pending
  • 1972-11-17 FR FR7240863A patent/FR2165883B1/fr not_active Expired
  • 1972-11-29 IT IT32222/72A patent/IT971321B/it active
  • 1972-12-01 NL NL7216305A patent/NL7216305A/xx unknown

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