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

• ABSTRACT Glyoxylic acid is prepared by a process facilitating recovery of glyoxylic acid, the process being electrolytic reduction of oxalic acid in an electrolysis cell in which a. the cathode is solid and metallic with a hydrogen overvoltage which is greater than the potential for the reduction of oxalic acid to glyoxylic acid,
• the separating diaphragm is a cation exchange membrane
• the catholyte comprises an aqueous solution of oxalic acid which is free of a strong inorganic acid
• the temperature of the catholyte is between 0 and 70C.
• the present invention relates to a process for the preparation of glyoxylic acid by the cathodic reduction of oxalic acid.
• German Pat. Specification No. 204,787 which is a Patent of Addition to 194,038 mentioned above describes the use of hydrochloric acid as the electrolyte but the other characteristics of the process remain essentially the same.
• the isolation of the glyoxylic acid from the reactionmedium is complicated by the presence of the strong inorganic acid. 1f the reaction mixture consists of an aqueous solution of oxalic and glyoxylic acids concentrating the solution and cooling it to to 5C precipitates the oxalic acid, leaving a solution of glyoxylic acid which can be either sold commercially as it is, or can be concentrated to obtain crystalline glyoxylic acid.
• the reaction mixture consists of an aqueous solution of oxalic, glyoxylic and sulphuric acids, it is necessary, in addition to the'cooling, to remove the sulphuric acid from the mixture, for example through precipitation with the aid of alkaline earth hydroxides or salts (German Pat. 163,842, Example 1; Belgian Pat. 757,106, Example 2).
• German Pat. Specification No. 204,787 describes aiding the removal of this auxiliary electrolyte by replacing thesulphuric acid by hydrochloric acid, which can. be removed by evaporation.
• hydrochloric acid has other disadvantages, principally due to its corrosive character; it is also difficult to remove completely by simple evaporation, be cause the evaporation cannot be carried out at a high temperature because of the risks of degrading the glyoxylic acid.
• the present invention provides a process for the preparation of glyoxylic acid by cathodic reduction of oxalic acid, which comprises performing the cathodic reduction in an electrolysis cell having a cathode compartment containing a catholyte and solid metallic cathode with a hydrogen overvoltage, which is greater than the potential for the reduction of oxalic acid to glyoxylic acid, and an anode compartment containing an anolyte and an anode, the cathode and anode compartments being separated by a cation exchange membrane diaphragm, the catholyte moving in a closed path by being passed into the cathode compartment, over the surface of the cathode, being removed from there and returned to the cathode compartment, the catholyte being at a temperature of 0 to 70C, preferably 5 to 35C and comprising an aqueous solution of oxalic acid, which is free of strong inorganic acid, but can contain glyoxylic
• the cathode, and anode and the separating diagraphm are preferably coated in parallel planes; advantageously, several of the elementary electrolysis cells can be combined in the manner of a filter press.
• cathode surface examples include lead; solid amalgams of lead; alloys of lead with silver, antimony, tin or bismuth; and cadmium.
• the cathode interior and surface are usually of the same material, e.g., a lead plate, but can be different, e.g., a lead plate'with a load amalgam surface.
• Anode of the electrolysis cells usually consists of a' solid electrically conducting material which is electrochemically stable in the anolyte and under the operating conditions considered.
• Such materials are metals and metalloids such as platinum, platinised titanium, graphite, lead and its alloys, particularly with silver, antimony or tin.
• Any known cation exchange membrane can be used to separate the catholyte from the anolyte, but membranes of the homogeneous type and membranes of the heterogeneous type are preferred.
• Thes membranes can optionally be reinforced with a screen.
• membranes which do not swell and which are stable to the action of the various constituents of the catholyte and the anolyte. Examples of such membranes are those described in the specifications of US. Pat. No. 2,681,320 and French Pat. Nos. 1,568,994, 1,575,782, 1,578,019, 1,583,089 and 1,584,187.
• the permeation selectivity of the membranes used (defined in and measured as in French Pat.
• the catholyte can consist essentially of water and oxalic acid with, optionally, glyoxylic acid; the catholyte can contain oxalic acid without glyoxylic acid only at the start of electrolysis; in the same way, the catholyte can contain glyoxylic acid without oxalic acid only at the end of electrolysis.
• concentrations of oxalic and glyoxylic acids can be either constant when the reaction is carried out continuously, or variable when the reaction is carried out discontinuously or at the start of a continuous operation.
• the concentration of oxalic acid is less than the saturation concentration at the temperature of electrolysis; generally, this concentration is greater than 2% by weight, and preferably greater than 3% when the current density is high, these values relating particularly to the constant concentration when the reaction is carried out continuously and to the final concentration when the reaction is carried out discontinuously.
• the concentration of glyoxylic acid is usually between 3 and 25% by weight, and preferably between and 15% by weight, these values relating particularly to the constant concentration of glyoxylic acid when the reaction is carried out continuously and to the final concentration of this acid when e i is ri d Q Qi QP "E9".
• the catholyte can also contain reaction by-products in small amounts, e.g., generally less than 1% by Wei
• An aqueous acid solution is preferably used as the anolyte, though any other anolyte capable of providing electrical conductivity between the two electrodes can be used.
• Aqueous solutions of sulphuric or phosphoric acids are usually employed in a concentration generally of 0.l to 5 m ols/litre, and pre ferably 0 5 to 2 mols/litre.
• the current density at the cathode is preferably 3 to 50 A/dm especially lO to 3 5 A/dn 1 g g
• the flow of the catholytein a closed circuit is usually achieved by means of a pump; the circuit can in addition contain attached devices such as a heat exchanger or an expansion vessel.
• the expansion vessel enables oxalic acid to be added to the catholyte and also some catholyte to be withdrawn in order to extract the glyoxylic acid.
• At least one spacer is preferablypresent iii'i'fi'iiitfie and/or cathode compartments; these spacers serve to prevent deformations of the cation exchange membrane, and contact between this membrane and the electrodes and also help to render the catholyte of uniform concentration.
• These spacers are generally manufactured from synthetic polymers which are chemically inert and which do not conduct electricity; they can be made in the form of interlaced, interwined, knotted or welded yarns (e.g., woven fabrics, grids or nets) or they can be in the form of plates possessing holes or grooves. In practice, these spacers are oriented along planes which are parallel to those of the electrodes and the separating diaphragm.
• the s'b'tVifififi' speed of the catholyte i.e. the speed in the cathode compartment, assumed to contain no spacer
• the s'b'tVifififi' speed of the catholyte is usually greater than 1 cm/second, and preferably greater than cm/second.
• the catholyte is preferably degassed in the expansion 5 vessel with the aid of a stream of inert gas, e.g., nitrogen.
• the glyoxylic acid is isolated by the known means, especially in the manner described above by concentrating and cooling the catho- 10 lyte, optionally under reduced pressure.
• the cooling is especially in the manner described above by concentrating and cooling the catho- 10 lyte, optionally under reduced pressure.
• the degree of concentration and the cooling temperature naturally vary according to the degree of purity desired for the glyoxwhich do not contain strong inorganic acid, e.g., sulphuric or hydrochloric acid and hence facilitate work up and recovery of the glyoxylic acid: it allows electrolysis cells to be produced which are compact and easy to dismantle; it allows the gases which are produced at the anode, especially oxygen, which are capable of creating regions of lower or even zero current density, to be removed easily.
• EXAMPLE l The reduction of oxalic acid to glyoxylic acid is carried out in an electrolysis cell possessing the following characteristics: both electrodes are rectangular plates of lead, the usable surface area of each of which is 0.8 dm the the cation exchange membrane separating anode and cathode compartments is of the heterogeneous type consisting of a cross-linked, sulphonated styrene/divinylbenzene copolymer, dispersed in a matrix of vinyl chloride polymer, and it is reinforced with a woven fabric of polyethylene glycol terephthalate.
• the substitution resistance of the membrane is 7 9 cm (measurement made in 0.6 M KCl solution) and its permeation selectivity is 77.5%; the distance from the electrode to the membrane is 3 mm; two pumps cause the catholyte and the anolyte to circulate in the electrolysis cell; and the anolyte and the catholyte circulating in external circuits each contain an expansion vessel equipped with supply and removal pipe- ,lines; the catholyte circuits also contain a cooling
• the electrolysis conditions are as follows:
• oxalic acid added to the catholyte 0.4 I/hour of a 9.65% aqueous solution of oxalic acid.
• EXAMPLE 2 An electrolysis is carried out in the same apparatus as in Example 1, under the following conditions:
• Crystalline glyoxylic acid is prepared from the above solution by the following method. This solution is concentrated at 30C in vacuo, cooled to 0C and filtered;
• the filtrate has a glyoxylic acid content of 45% (weight/weight) whilst the precipitate has an oxalic acid content of 99.5% (weight/weight).
• Example 3 The reduction of oxalic acid to glyoxylic acid is carried out in an electrolysis cell similar to that of Example 1, but the usable surface area of each electrode of which is 2.5 dm
• the electrolysis conditions are as follows:
• This solution is electrolysed for 7 hours 15 minutes, adding fresh catholyte at a rate of 0.542 l/hour with a 14.08% solution of oxalic acid and simultaneous removal of catholyte sufficient to keep the volume of the catholyte constant.
• the following catholyte then contained 3.07% oxalic acid and 3% glyoxylic acid.
• Electrolysis is then carried out continuously for 24 hours, supplying fresh catholyte at a rate of 1.14 l/hour with a 8.5% solution of oxalic acid and simultaneous removal in corresponding amounts as before.
• the volume of the catholyte was reduced to 7 1; this second stage is a stage of continuous operation in that the concentration of glyoxylic acid remains substantially constant (about 3%).
• the catholyte at the end of the experiment contains 4.28% oxalic acid and 3.03% glyoxylic acid.
• Example 4 In this experiment, the apparatus is the same as in Ex ample 3.
• Catholyte originally introduced: 6.3 l of a 3.82% strength solution of oxalicacid.
• This'solution is electrolysed for 7 hours, supplying it at a rate of 0.495 l/hour with a 15.85% solution of oxalic' acid with removal of the catholyte sufficient to keep its volume constant.
• Electrolysis is then carried out continuously for 34 hours 30 minutes (the concentrations remaining substantially constant), supplying the catholyte at the rate of 0.810 l/hour with 10.58% oxalic acid. During this second period, the volume of the catholyte is kept constant at 9 l. The catholyte at the end of the experiment contains 4.8% glyoxylic acid and 3.79% oxalic acid.
• EXAMPLE 5 In this experiment, the assembly is the same as in Example 3, but the cathode is a lead alloy containing 5% of silver.
• This solution is electrolysed for 7 hours 40 minutes, supplying fresh catholyte at a rate of 0.495 l/hour with a 16% solution of oxalic acid and simultaneous removal as in previous Examples. Electrolysis is then carried out under conditions of continuous operation for 10 hours, supplying the catholyte at a rate of 0.790 l/hr. with a 10.7% solution. During this period the volume of the catholyte is kept constant and equal to 9 1.
• the catholyte contains 4.22% glyoxylic acid and 4.4% oxalic acid.
• Example 6 The apparatus described in Example 3 is used with the following electrolysis conditions current density: 25 A/dm voltage: 5.45 V
• This solution is electrolysed for 5 hours minutes, supplying the catholyte with 0.8 l/hour of a solution containing 16.7% by weight of oxalic acid and removal to constant volume as in previous Examples. Electrolysis is then contained for 14 hours 45 minutes, supplying the catholyte with 1.460 l/hour ofa 10.65% solution of oxalic acid. During this last period, the volume of the catholyte is kept at 9 1. At the end of the experiment, the catholyte contains 4.64% glyoxylic acid and 4.18% oxalic acid.
• EXAMPLE 7 The assembly described in Example 1 is used.
• the cathode is a plate of pure lead which has been amalgamated at the surface with mercury (0.5 cm Hg for a total surface area of 2 dm).
• the usable cathode surface area is 0.8 dm
• EXAMPLE 8 in this embodiment, an assembly of the filter press type is produced, with 4 cells of 2.5 dm each one being similar to that described in Example 3.
• Electrolysis is carried out for 7 hours 35 minutes, supplying 0.660 l/hour of a 36.7% solution of oxalic acid, and removal to'constant volume as in previous Examples.
• Process for the preparation of glyoxylic acid by cathodic reduction of oxalic acid which comprises performing the cathodic reduction in an electrolysis cell having a cathode compartment containing a catholyte and a solid metallic cathode which a hydrogen overvoltage, which is greater than the potential for the reduction of oxalic acid to glyoxylic acid, and an anode compartment containing an anolyte and an anode, the cathode and anode compartments being separated by a cation exchange membrane diaphragm, the catholyte moving in a closed path by being passed into the cathode compartment, over the surface of the cathode, being removed from there and returned to the cathode compartment, the catholyte being at a temperature of 0 to C and comprising an aqueous solution of oxalic acid, which is free of strong inorganic acid.
• At least the surface thereof consists of acomposition selected from the group consisting of cadmium, lead, a solid amalgam of lead, and an alloy of lead with a metal selected from the group consisting of silver, antimony, tin and bismuth.
• catholyte contains between 3 and 25% by weight of glyoxylic acid.
• a process according to claim 3 wherein the cathode current density is 3 to 50 Aldm 6.
• a process according to claim 1 wherein the cathode compartment is free from any spacer and the speed at which the catholyte circulates in the cathode compartment is greater than 10 cm/sec.
• the cathode is selected from the group consisting of lead, an alloy of lead with 5% silver, and lead with an amalgamated lead surface
• the cathode current density is 12.5 25 Aldm
• the cation exchange diaphagm is of the heterogeneous type consisting of a cross-linked sulphonated styrene divinylbenzene copolymer dispersed in a matrix of vinyl chloride polymer
• the catholyte and anolyte are both circulated outside the cell
• the speed at which the catholyte and anolyte pass over the cathode and anode respectively is cm/sec
• the catholyte temperature is 20 30C
• the catholyte is degassed with nitrogen
• oxalic acid is added continuously to the catholyte and catholyte is withdrawn continuously in order to extract the glyoxylic acid from it.

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  • BE BE787770D patent/BE787770A/xx unknown
• 1971
  • 1971-08-20 FR FR7130395A patent/FR2151150A5/fr not_active Expired
• 1972
  • 1972-08-11 NL NL7211021A patent/NL7211021A/xx unknown
  • 1972-08-17 BR BR005614/72A patent/BR7205614D0/pt unknown
  • 1972-08-17 JP JP47081858A patent/JPS4829720A/ja active Pending
  • 1972-08-18 GB GB3872472A patent/GB1364761A/en not_active Expired
  • 1972-08-18 AT AT716372A patent/AT326624B/de not_active IP Right Cessation
  • 1972-08-18 DD DD165131A patent/DD98281A5/xx unknown
  • 1972-08-18 CA CA149,775A patent/CA974477A/en not_active Expired
  • 1972-08-18 CH CH1226672A patent/CH541535A/fr not_active IP Right Cessation
  • 1972-08-18 US US00281742A patent/US3779876A/en not_active Expired - Lifetime
  • 1972-08-18 DE DE2240731A patent/DE2240731C3/de not_active Expired
  • 1972-08-19 IT IT28322/72A patent/IT964101B/it active

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