JPS6167784A - Production of glyoxalic acid by electrochemical anodic oxidation of glyoxal - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for producing glyoxylic acid by anodic electrochemical oxidation of glyoxal.

with nitric acid (French Patents Nos. 1,326,605 and 23)
It is known to oxidize glyoxal to glyoxylic acid in an aqueous medium by electrochemical methods (see French Patent Application No. 2,443,517) or by electrochemical methods (see French Patent Application No. 2,443,517).

More generally, cathodic reduction of oxalic acid (French patent no.
151150), ethylene glycol or tartaric acid anodization (e.g. Acta, Cbim, Acad
, Soi, Hung, 1978, Vol. 98, No. 49
Pages to pages 66, 367 to 373; Magyar
Kem, Folyoirat, l 973 No. 84
Vol. 61-68, 217-225, No. 2
It is known that certain electrochemical methods can produce glyoxylic acid, such as (see pages 55-362 and 469-475).

However, such known methods have drawbacks. For example, (a) nitric acid oxidation of glyoxal requires significant investment for separation of glyoxylic acid and for denitration of wash water; (b) t, oxalic acid and tartaric acid are not economical raw materials; (C) ethylene glycol (d) glyoxal anodization requires the use of an electrolytic cell with an ion conversion membrane.

However, the inventors have surprisingly discovered an anodic electrochemical glyoxal oxidation process which allows glyoxylic acid to be produced in good yields and with good selectivity while avoiding the drawbacks of known processes.

The method according to the invention consists of a cathode and at least one cathode compartment containing the cathode, at least one anode compartment containing the anolyte and an anode consisting of an aqueous solution of glyoxal and an electrolyte, and between these two compartments there is at least one cathode compartment containing the anode. O in an electrolytic cell containing one separator with stirring.
It consists of subjecting an aqueous solution of glyoxal to an anodic electrochemical oxidation at a temperature between 70 °C and 70 °C, in which the anode is made of metal surface adatoms selected from the group consisting of silver, bismuth, copper, tin, thallium ( It is characterized by being doped with a small amount (6 datom).

According to another feature, the separator is advantageously made from sintered glass. Such a sintered glass separator has 5 to
Preferably it has an average pore diameter of 15/Zm.

According to a further advantageous embodiment, the separator is made of an anion exchange membrane, in contrast to the cation exchange membranes already used in the known method of electrochemical glyoxal oxidation (see FR 2 443 517). Such an anion exchange membrane on the one hand prevents the migration of the cations used for doping the anode towards the cathode and on the other hand makes it possible to keep the chloride ion concentration constant in the anode chamber.

Furthermore, such anion exchange membranes enhance glyoxal consumption, increase glyoxylic acid yield, and provide glyoxylic acid with little residual glyoxal.

Examples of anionic membranes that can be used according to the invention include anionic membranes of very different origins and types, such as anionic membranes with quaternary ammonium groups on a textured or untextured polyvinyl skeleton, polystyrene, polyvinylidene fluoride. can be given.

Especially commercially available RAIPORE 50
35L or IONAC 3475. The former is commercially available from RAI Research Corporation, Marcus Boulevard Haupouche, Long Island, New York, USA, and the latter is commercially available from Ionac Chemical Company, Birmingham, New York, USA.

Although the precise role played by such surface adatoms is unknown, the inventors have shown that they favor the oxidation of glyoxal and that they yield aqueous solutions of glyoxylic acid containing almost no unconverted glyoxal. To my surprise, I discovered that I could do it.

The anode is doped with such surface-absorbing atoms beforehand or by electrodeposition during the process according to the invention, silver nitrate,
According to bismuth (I) oxide, cuprous chloride, the anode can be doped with the same or different types of surface adatoms.

Preferred surface adatoms for doping the anode are silver and tin.

Preliminary electrodeposition is carried out by methods known per se. Generally it is achieved in an electrolytic cell with three electrodes, namely a reference electrode (e.g. calomel KCI saturated electrode), an auxiliary electrode of platinum and an electrode to be doped, the electrolyte of the electrolyte being in the form of a solution, 1xio-' ~I X 10-'
The selected metal is then electrochemically doped with approximately 20 ± 10 coulombs per electrode 1d containing one or more water-soluble derivatives of the selected surface adatoms to a molar concentration of (7゛). Attach to target. Such electrodeposition is I
This can also be achieved by introducing one or more water-soluble derivatives of surface adatoms into the anode chamber at the beginning of the process to a molar concentration of X 10-''.

The method according to the invention is carried out at temperatures between 0 and 70°C, preferably between 20 and 70°C.
C. and preferably at a temperature of 50.degree.

The cell cathode consists of a conductive material that is chemically and electrochemically stable in the catholyte under operating conditions. Such materials include platinum, stainless steel, among others.

The anode is made from platinum or vitreous carbon. The anolyte contains essentially water, glyoxal, an electrolyte, and preferably one or more water-soluble derivatives of selected surface adatoms to dope the anode in low concentrations. Conventionally used electrolytes are highly water-soluble inorganic products containing anions selected from the group consisting of chloride, nitrite, nitrate and sulfate anions. Advantageously, the electrolyte is chloride ions, preferably supplied by hydrogen chloride.

The catholyte contains substantially water and an electrolyte that is generally qualitatively and quantitatively the same as that present in the anolyte. However, it can also be different. In this case 1 it contains hydroxyl ions.

The molar concentration of glyoxal in the anolyte can vary within a wide range, but usually consists of 0.2-5M, advantageously they contain 0.5-2M.

If the anodic oxidation reaction is continued, the anolyte will react according to the following reaction formula (1)
(accordingly, glyoxal becomes insufficient) and glyosylic acid increases.

(1) OHC-1CHO+HO-2e-→o, ac
-COOH+2H+ From the equation (1), it is necessary to use 193,000 coulombs to oxidize 1 mole of glyoxal, and this value is simply expressed.

The glyoxylic acid formed can also be electrochemically oxidized to oxalic acid according to equation (2).

(2) OHCC0OH+HzO2e--+HOOC-C
OOH+2H+ and finally the oxalic acid can be decomposed by decarboxylation oxidation according to equation (3).

(3) HOOC-C0OH+H, O-2e-1→2
COz+H*O+2H+Glyoxal oxidation to glyoxylic acid is therefore a competition between the oxidation of the glyoxylic acid formed to oxalic acid on the one hand, and the oxidative decarboxylation degradation of the oxalic acid that may be present on the other hand.

At the completion of the reaction, the anolyte contains essentially water, unconverted glyoxal (glyoxylic acid), electrolyte, and optionally oxalic acid. The amount of residual glyoxal is small,
The use of a doped anode according to the invention makes it possible to obtain an anolyte containing only small amounts of residual glyoxal at the end of the reaction.

The larger the ratio ρ = □ (Q is the amount of electricity consumed, and Qth is the amount of theoretical electricity), the higher the concentration of oxalic acid becomes. .

The current density at the cathode is generally 0.1 to IQA/dm", preferably 0.5 to 5 A/dm", advantageously IA/dm".
dm”.

The potential difference (hereinafter referred to as V) applied to the electrodes is a function of the electrical resistivity bottles of the solutions contained in each chamber and their electrolyte concentration.

Generally, a potential difference of 2 to IOV is sufficient to maintain the current density applied to the electrodes. Usually 1. By using electrolytes as described above at concentrations of 0.26 to 3, expressed in -1 equivalents, anolytes and catholytes which provide satisfactory electrical resistivities are obtained. Such electrolytes are in particular hydrogen chloride, potassium nitrite, potassium nitrate, sodium chloride, sodium sulfate.

A preferred electrolyte is hydrogen chloride at a molar concentration of 1±0.3.

A modification of the process according to the invention consists in using an aqueous catholyte which gives a pH greater than 7 and is made up essentially of alkali metal hydroxide and water.

The alkali metal hydroxide is sodium hydroxide or potassium hydroxide, with a molar concentration of 1 sodium hydroxide being preferred.

This modification according to the invention can be realized in a conventional electrolytic cell with two chambers separated by a sintered glass diaphragm or advantageously in an electrolytic cell with three chambers in series separated by a sintered glass diaphragm. The anode chamber contains an anode and an anolyte, the cathode chamber contains a cathode and a catholyte,
The central intermediate chamber contains the same solution as the catholyte used.

It will be appreciated that the diffusion of the different species present in each chamber is small.

The following examples illustrate, but do not limit, the invention.

Concentrations of glyoxal, glyoxylic acid and oxalic acid are expressed in mM/t unless otherwise stated.

The chemical yield Rc and electric rate Re were calculated using the following formulas.

The electrolytic cell used in Examples 1-13 has two units separated by a sintered glass diaphragm with an average pore diameter of 10±5, am.

The cathode chamber is an 8'Oct chamber equipped with a platinum cathode.

The anode chamber is a 120 d chamber with an anode having an effective area of 15 cvll.

The electrolytic cells used in Examples 4 to 16 had (1) an 80 cJ cathode chamber equipped with a platinum cathode, and (II) +10± in series.
A central chamber of 30QIF separated from the anode and cathode chambers by a sintered glass diaphragm with an average pore diameter of 5fim, (Ill) from three groups of anode chambers of 120d with an anode and magnetic stirrer with an effective area of 15 al. Become.

Note: In all other examples the surface adatoms were electrodeposited onto a platinum anode.

Table 2 shows that by carrying out the present invention using surface adatoms of seeds, glyoxylic acid power (obtained) with almost no residual glyoxal when compared with the method carried out under the same conditions without anodic doping. It shows.

Notes: (1) Anode doping was carried out by introducing 14 wg of silver nitrate into the anode chamber at the start of electrolysis.

From an inspection of the table it is clear that by applying the modified embodiment of the invention an anolyte containing the ion OH- and glyoxylic acid with almost no residual glyoxal therein is obtained.

The example below shows another modification, in this case using a two-chamber electrolyzer separated by a commercially available anionic membrane, these two chambers having a volume of approximately 25 cd, each containing Platinum anodes and cathodes, a magnetic stirrer, and a refrigerant were provided to prevent water evaporation when the test was conducted at temperatures above 20°C.

The results obtained are shown in Table 3 below.

When examining the above table, it can be seen that the simultaneous use of an anionic membrane and a doped anode results in higher electrical efficiency and yield than the results obtained using a sintered glass separator.

Furthermore, a comparison of Example 17 with Examples 18-20 shows the beneficial effect of the use of a doped anode on the residual glyoxal percentage.

Claims (1)

[Scope of Claims] 1. At least one catholyte chamber containing a cathode and a catholyte, at least one anolyte chamber containing an anolyte and an anolyte consisting of an aqueous solution of glyoxal and an electrolyte, and a space between these two chambers. A method for producing glyoxylic acid by electrochemical oxidation of glyoxal in an aqueous solution at temperatures between 0 and 70° C. in an electrolytic cell consisting of at least one separator, the anode comprising silver, bismuth, copper, tin and thallium. An improved method characterized in that the metal surface is doped with adatoms selected from the group consisting of: 2. The method according to claim 1, wherein the separator is sintered glass. 3. The method according to claim 1, wherein the separator is an anionic membrane. 4. The method according to claim 1, wherein the electrolyte is an aqueous solution of an alkali metal hydroxide. 5. The method of claim 1, wherein the anolyte is a glyoxal solution in 1±0.3N hydrochloric acid. 6. The method according to claim 4, wherein the catholyte is a 1N solution of sodium hydroxide.