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

Definitions

• the present invention relates to a process for the manufacture of glyoxylic acid by electrochemical reduction of oxalic acid.
• Glyoxylic acid is a synthetic industrial intermediate commonly used to access various raw materials such as p- h ydroxymandelic acid, p-hydroxyphenylglycine. It is mainly obtained by gentle oxidation of glyoxal or by electrochemical reduction of oxalic acid.
• the electrochemical reduction of oxalic acid to glyoxylic acid has been known for a very long time and it is generally carried out in an acid medium, at low temperature, with electrodes with a high hydrogen overvoltage, in the presence or not of a protonic mineral acid such as than sulfuric acid, an ion exchange membrane and it is usually carried out with a circulation of the electrolyte (German patents n 8 163.842, 194.038. 204.787, 210.693, 292.866. 347.605, 458.436; French patents no. 2.062.822, 2.151.150; Indian Patent No. 148,412; W. HOHRSCHULZ. Z. Elektrochem. 1926.82, 449; S. AVERY et al, Ber.
• the Applicant has surprisingly discovered a simple and economical process for the electrochemical reduction of oxalic acid to glyoxylic acid which overcomes this drawback.
• This process carried out at a temperature between 0 ° C and 30 ° C in a having electrolyzer, at least one anode compartment containing an anode and an anolyte, at least one cathode compartment containing a cathode and a catholyte consisting of an aqueous solution of oxalic acid and, between these two compartments at least one separator, is characterized in that the anode is constituted by a solid conductor uniformly covered with lead dioxide.
• the coating of lead dioxide is uniform, compact, adherent to the substrate and it has a thickness of 0.2 to 5 mm.
• a thin metallic intermediate layer constituted by a metal chosen from copper, silver, gold.
• the coating of lead dioxide is carried out by means known per se.
• it can be carried out by electrolytic deposition on the solid conductive support chosen, previously cleaned, in an electrolyser equipped with a copper cathode and containing an electrolyte constituted by an acidic aqueous solution of lead (II) nitrate and nitrate.
• the uniformity of the deposit as well as its adhesion, its compactness and its thickness which is easily adjusted by the duration of the electrolytic deposit, are easily controlled by observation with a scanning electron microscope of the surface of the deposit and of the wafer after breaking of the electrode.
• the solid conductive support is chosen from the materials commonly used in electrochemical processes, such as lead and its alloys, dense graphite, vitreous carbon, titanium, gold, platinum.
• the solid support is made of dense graphite or of titanium, and preferably, it is of titanium.
• the cathode is made of lead or one of its alloys, advantageously with bismuth.
• the anode and the cathode can take various forms, in particular they can be in the form of plate, disc, grid. They can also have a compact or porous structure permeable to gases.
• the anode and the cathode have a gas-permeable structure.
• the method according to the invention is carried out at a temperature between 0 ° C and 30 ° C, advantageously at a temperature of 20 ° C, which very often involves a cooling of the cell, and / or anolyte and catholyte.
• the anolyte consists of an acidic aqueous solution.
• this anolyte is not characteristic of the invention because it essentially aims to ensure the electrical conductivity between the two electrodes.
• aqueous solutions of sulfuric, phosphoric acid are used.
• concentration of these solutions is generally understood between 0.1 and 5 moles / liter, preferably between 0.5 and 2 moles / liter.
• the catholyte at the start of electrolysis, is an aqueous solution of oxalic acid with a concentration of between 0.1 M and its saturation at the temperature considered.
• the concentration of sulfuric acid in the anolyte is advantageously 1 M.
• the concentrations of oxalic acid and of glyoxylic acid formed can be either constant, when operating continuously, or variable when we operate discontinuously.
• the concentration of oxalic acid in the catholyte is 0.7 + 0.1M.
• the parasitic current for reduction of glyoxylic acid is proportional to its concentration in the reaction medium.
• the method according to the invention is implemented in an electrolyser equipped with at least one separation membrane delimiting at least one anode compartment and at least one cathode compartment.
• This membrane is an ion exchange membrane, advantageously a cation exchange membrane.
• the nature of this is not characteristic of the invention; this is how any known membrane can be used, in particular membranes of the homogeneous type and membranes of the heterogeneous type.
• the permselectivity of the membranes used is preferably greater than 60% (determination made according to French patent No. 8 1,584,187).
• the anode and the cathode, having a structure permeable to gases, are plated on either side of the separation membrane.
• the current density at the cathode is generally between 3 and 50 A / dm 2 .
• the evacuation of the gases formed both at the cathode and at the anode is favored by an upward circulation of the anolyte and of the catholyte along the respective electrodes.
• the anolyte can be circulated faster than the catholyte.
• the electrolysis cell can be equipped with a total anode surface greater than the total cathode surface, advantageously this difference is about 20 Z.
• a 2239 quality graphite disc from LE CARBONE-LORRAINE, with a geometric surface of 12.5 cm 2 is carefully etched by polarization anodic for 30 minutes in sodium hydroxide at 10% by weight under a current density of the order of 4 mA / cm 2 , then after washing with distilled water it is placed in an aqueous solution of nitric acid at 10% by weight for 10 minutes and finally it is washed with distilled water.
• the deposit lead dioxide on the anode is carried out under a current density of 30-50 mA / cm 2 , at 60 ⁇ 5 ° C, and maintaining the pH of the electrolyte at around 2 by additions of lead (II) oxide and copper (II) carbonate.
• the electrolysis is stopped when the thickness of lead dioxide deposited on the anode is close to 0.4 mm.
• An examination of this deposit under a scanning electron microscope shows that it is uniform, compact and adherent to the substrate and that it consists of pyramidal grains with projecting faces.
• Electrolysis is started at 20 ⁇ 1 ° C, at an electrical voltage of 8 volts, a current density of 100 mA / cm 2 and a circulation of the catholyte and the anolyte, maintained at 20 + 1 ° C, d '' about 400 cm / min.
• a titanium plate of 99.6% purity and a thickness of 0.25 mm is deployed in the form of a grid having identical meshes 3-34-25. Then, this grid, carefully sanded and rinsed successively with acetone, alcohol and water, is uniformly covered with lead dioxide according to a process identical to that described in Example 1-A-. Its active surface determined after deposition by electrochemical control is 9cm 2 .
• the electrolysis is started at 20 ⁇ 1 ° C under an electrical voltage of 3.2 volts, a current density of 100 mA / cm2 and a circulation of the catholyte and the anolyte maintained at 20 ⁇ 1 ° C 400 cm 3 / min.
• Example 1-B is reproduced by replacing the dense graphite anode covered with lead dioxide with a lead anode of identical shape. During the electrolysis, there is a consumption of this anode of 1.64 mmol of lead by Faraday.
• Example 1-8 is repeated, replacing the dense graphite anode covered with lead dioxide with a dense graphite anode of the same quality and identical shape. During electrolysis, a consumption of this anode of 341.3 mmol of carbon is observed by Faraday.
• Example 2-8 When reproducing Example 2-8 by replacing the titanium anode covered with lead dioxide with a titanium anode of the same quality and identical shape, a rapid stopping of the electrolysis is observed due to the formation on the anode of an insulating layer of titanium oxide.

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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)
• Electrolytic Production Of Metals (AREA)

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• 1985
  • 1985-09-10 FR FR8513385A patent/FR2587039B1/fr not_active Expired - Lifetime
• 1986
  • 1986-08-29 US US06/901,792 patent/US4692226A/en not_active Expired - Fee Related
  • 1986-09-03 CA CA000517410A patent/CA1295967C/en not_active Expired - Lifetime
  • 1986-09-09 EP EP86401970A patent/EP0221790A1/de not_active Withdrawn

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