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EP0627020B1 - Electrochemical process for preparing glyoxylic acid - Google Patents

Electrochemical process for preparing glyoxylic acid Download PDF

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Publication number
EP0627020B1
EP0627020B1 EP93917417A EP93917417A EP0627020B1 EP 0627020 B1 EP0627020 B1 EP 0627020B1 EP 93917417 A EP93917417 A EP 93917417A EP 93917417 A EP93917417 A EP 93917417A EP 0627020 B1 EP0627020 B1 EP 0627020B1
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mol
acid
cathode
metals
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German (de)
French (fr)
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EP0627020A1 (en
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Bernd Scharbert
Stephen Dapperheld
Pierre Babusiaux
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Hoechst AG
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Hoechst AG
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Priority claimed from DE4217336A external-priority patent/DE4217336C2/en
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    • 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 production of glyoxylic acid by electrochemical reduction of oxalic acid.
  • Glyoxylic acid is an important intermediate for the production of technically relevant compounds and can be produced either by a controlled oxidation of glyoxal or by an electrochemical reduction of oxalic acid.
  • electrochemical reduction of oxalic acid to glyoxylic acid has long been known and is generally carried out in aqueous, acidic medium, at low temperature, on electrodes with high hydrogen overvoltage, for example on electrodes made of lead, cadmium or mercury, with or without the addition of mineral acids and in the presence an ion exchange membrane performed (DE-AS 163 842, 292 866, 458 438).
  • the object of the present invention is to provide a process for the electrochemical reduction of oxalic acid to glyoxylic acid which avoids the disadvantages mentioned above, in particular has a high selectivity, reaches the lowest possible oxalic acid concentration at the end of the electrolysis and a cathode with a high one Long-term stability used.
  • the cathode should be from a technically well available or material to be processed without problems.
  • Selectivity is understood to mean the ratio of the amount of glyoxylic acid produced to the total amount of products formed during the electrolysis, namely glyoxylic acid plus by-products, for example glycolic acid, acetic acid and formic acid.
  • the object was achieved in that the electrochemical reduction of oxalic acid on cathodes which consist of carbon or at least 50% by weight of at least one of the metals Cu, Ti, Zr, V, Nb, Ta, Fe, Co, Ni, Zn , Al, Sn and Cr, is carried out and the electrolyte is or contains salts of metals with a hydrogen overvoltage of at least 0.25 V at a current density of 2500 A / m.
  • the present invention thus relates to a process for the preparation of glyoxylic acid by electrochemical reduction of oxalic acid in aqueous solution in divided or undivided electrolysis cells, characterized in that the cathode is made of carbon or at least 50% by weight of at least one of the metals Cu, Ti , Zr, V, Nb, Ta, Fe, Co, Ni, Zn, Al, Sn and Cr and the aqueous electrolysis solution in the undivided cells or in the cathode compartment of the divided cells also contains at least one salt of metals with a hydrogen overvoltage of at least 0, 25 V, preferably at least 0.40 V, based on a current density of 2500 A / m, which in the case of a carbon cathode has a minimum concentration of 10 von% by weight in the aqueous electrolysis solution.
  • All materials which are at least 50% by weight, preferably at least 80% by weight, in particular at least 93% by weight, of one or more of the metals Cu, Ti, Zr, are suitable as cathodes for the process according to the invention.
  • V, Nb, Ta, Fe, Co, Ni, Zn, Al, Sn and Cr, preferably Fe, Co, Ni, Cr, Cu and Ti consist, or also all carbon electrode materials, for example electrode graphites, impregnated graphite materials, carbon felts and also glassy carbon.
  • the above-mentioned metallic materials can also be alloys of two or more of the above-mentioned metals, preferably Fe, Co, Ni, Cr, Cu and Ti.
  • Cathodes made of at least 80% by weight, preferably 93 to 96% by weight, of an alloy of two or more metals mentioned above and 0 to 20% by weight, preferably 4 to 7% by weight , from any other metal, preferably Mn, Ti, Mo or a combination thereof, and 0 to 3% by weight, preferably 0 to 1.2% by weight, of a non-metal, preferably C, Si, P , S or a combination thereof.
  • the advantage of using the cathode materials according to the invention is that technically available, inexpensive or easily processable materials can be used. Stainless steel or graphite is particularly preferred.
  • stainless chromium-nickel steels with the material numbers (according to DIN 17 440) 1.4301, 1.4305, 1.4306, 1.4310, 1.4401, 1.4404, 1.4435, 1.4541, 1.4550, 1.4571, 1.4580, 1.4583, 1.4828, 1.4841 and 1.4845 can be used whose compositions are given in percent by weight in the table below.
  • the method according to the invention is carried out in undivided or preferably in divided cells.
  • the usual diaphragms made of polymers or other organic or inorganic materials, such as glass or ceramics, which are stable in the aqueous electrolysis solution, are used to divide the cells into anode and cathode compartments.
  • ion exchange membranes in particular cation exchange membranes made from polymers, preferably polymers with carboxyl and / or sulfonic acid groups.
  • stable anion exchange membranes is also possible.
  • the electrolysis can be carried out in all customary electrolysis cells, such as, for example, in beaker or plate and frame cells or cells with fixed bed or fluidized bed electrodes. Both the monopolar and the bipolar circuit of the electrodes can be used.
  • All materials on which the corresponding anode reactions take place can be used as anode material.
  • lead, lead dioxide on lead or other carriers, platinum, metal oxides on titanium, for example titanium dioxide doped with noble metal oxides such as platinum oxide, are suitable for the development of oxygen from dilute sulfuric acid.
  • carbon or titanium dioxide on titanium doped with noble metal oxides are used, for example, for the development of chlorine from aqueous alkali metal chloride solutions.
  • Aqueous mineral acids or solutions of their salts such as, for example, dilute sulfuric or phosphoric acid, dilute or concentrated hydrochloric acid, sodium sulfate or sodium chloride solutions, can be used as anolyte liquids.
  • the aqueous electrolysis solution in the undivided cell or in the cathode compartment in the divided cell contains the oxalic acid to be electrolyzed in a concentration expediently between about 0.1 mol of oxalic acid per liter of solution and the saturation concentration of oxalic acid in the aqueous electrolysis solution at the electrolysis temperature used.
  • Salts of metals with a hydrogen overvoltage of at least 0.25 V are added to the aqueous electrolysis solution in the undivided cell or in the cathode space of the divided cell.
  • Such salts are mainly the salts of Cu, Ag, Au, Zn, Cd, Fe, Hg, Sn, Pb, Tl, Ti, Zr, Bi, V, Ta, Cr, Ce, Co or Ni, preferably the salts of Pb, Sn, Bi, Zn, Cd and Cr, particularly preferably the salts of Pb.
  • the preferred anions of these salts are chloride, sulfate, nitrate or acetate.
  • the salts can be added directly or, for. B. by adding oxides, carbonates, in some cases also the metals themselves, in the solution.
  • the salt concentration of the aqueous electrolysis solution in the undivided cell or in the cathode compartment of the divided cell is expediently from 10 ⁇ 7 to 10% by weight, preferably to 10 ⁇ 6 to 0.1% by weight, in particular 10 ⁇ 5 to 0, 04 wt .-%, each based on the total amount of the aqueous electrolysis solution, adjusted.
  • a salt concentration of 10 ⁇ 6 to 10% by weight preferably 10 ⁇ 5 to 10 ⁇ 1% by weight, in particular 10 ⁇ 4 to 4 x 10 ⁇ % by weight, is expedient.
  • metal salts can also be used which form poorly soluble metal oxalates after addition to the aqueous electrolysis solution, for example the oxalates of Cu, Ag, Au, Zn, Cd, Sn, Pb, Ti, Zr, V, Ta, Ce and Co.
  • the added metal ions from the product solution can be removed very easily by filtration after the electrolysis to the saturation concentration.
  • the addition of the salts mentioned can be dispensed with if the above-mentioned metal ions increase in the above-mentioned concentration ranges Start of electrolysis are present in the aqueous electrolyte solution of the undivided cell or in the cathode compartment of the divided cell. It should be noted that the added metal ions must not be present as a metallic alloy component with more than 20% by weight in the cathode material. In this case, the addition of the salts mentioned is necessary in the concentration ranges mentioned above.
  • the presence of the above-mentioned metal ions in the above-mentioned concentration ranges at the beginning of the electrolysis is always to be expected even without the addition of the salts if, after an interruption in operation, for example after a trial in a batch process, a new trial with new catholyte liquid is started without the cathode is changed. In the event of a longer interruption, the cathode can be kept under protective current and the catholyte under inert gas.
  • the current density of the method according to the invention is advantageously between 10 and 10,000 A / m, preferably 100 to 5000 A / m, in the case of a carbon cathode between 10 and 5000 A / m, preferably 100 to 4000 A / m.
  • the cell voltage of the method according to the invention is dependent on the current density and is expediently between 1 V and 20 V, preferably between 1 V and 10 V, based on an electrode spacing of 3 mm.
  • the electrolysis temperature can range from - 20 ° C to + 40 ° C. Surprisingly, it was found that at electrolysis temperatures below + 18 ° C, even at oxalic acid concentrations less than 1.5% by weight, the formation of glycolic acid as a by-product can be less than 1.5 mol% compared to the glyoxylic acid formed. The proportion of glycolic acid increases at higher temperatures.
  • the electrolysis temperature is therefore preferably between + 10 ° C and + 30 ° C, in particular between + 10 ° C and + 18 ° C.
  • the catholyte flow rate of the process according to the invention is between 1 and 10,000, preferably 50 and 2000, in particular 100 and 1000, liters per hour.
  • the product solution is worked up using customary methods.
  • the electrochemical reduction is stopped when a certain turnover has been reached.
  • the resulting glyoxylic acid is separated from any oxalic acid still present in accordance with the prior art mentioned above.
  • the oxalic acid can be selectively fixed to ion exchange resins and the aqueous solution free of oxalic acid can be concentrated in order to obtain a commercial 50% by weight glyoxylic acid.
  • the glyoxylic acid is continuously extracted from the reaction mixture by customary methods and the corresponding equivalent proportion of fresh oxalic acid is added simultaneously.
  • the reaction by-products in particular glycolic acid, acetic acid and formic acid, are not or not completely separated from the glyoxylic acid by these methods. It is therefore important to achieve high selectivity in the process in order to avoid complex cleaning processes.
  • the process according to the invention is characterized in that the proportion of the sum of by-products can be kept very low. It is between 0 and 5 mol%, preferably below 3 mol%, in particular below 2 mol%, relative to the glyoxylic acid.
  • the selectivity of the process according to the invention is all the more remarkable in that, even at a low final concentration of oxalic acid, ie in the range from 0.1 to 0.2 mol of oxalic acid per liter of electrolysis solution, the proportion of by-products is preferably below 3 mol%, based on glyoxylic acid. lies.
  • Another advantage of the method according to the invention is the long-term stability of the cathodes used in comparison to the lead cathodes which have been customary to date.
  • a divided circulation cell which is constructed as follows:
  • the quantitative analysis of the components was carried out by means of HPLC, the chemical yield is defined as the amount of glyoxylic acid produced, based on the amount of oxalic acid consumed.
  • the current yield relates to the amount of glyoxylic acid produced.
  • the selectivity has already been defined above.
  • Example 3 Connection attempt to Example 2
  • Example 5 Connection test to electrolysis according to Example 4
  • Example 6 as example 4, but using a stainless steel cathode with material no. 1.4541 (according to DIN 17 440).
  • Example 7 as example 4,
  • the quantitative analysis of the components was carried out by means of HPLC, the chemical yield is defined as the amount of glyoxylic acid produced, based on the amount of oxalic acid consumed.
  • the current yield relates to the amount of glyoxylic acid produced.
  • the selectivity has already been defined above.
  • Example 1 The procedure was as in Example 1, except that no lead salt was added, but the electrolysis cell was kept between the electrolysis under protective current and the catholyte under inert gas. The immediately preceding electrolysis was the electrolysis carried out according to Example 1.
  • This example demonstrates the achievement of a high glyoxylic acid concentration at a low oxalic acid concentration while maintaining the high selectivity.
  • the electrolysis time was 10395 Ah without intermediate treatment of the electrochemical cell.
  • the example illustrates that the high selectivity is maintained at an oxalic acid concentration of less than 0.2 mol / l. Chemical yield and current yield are somewhat lower than at higher oxalic acid concentrations.
  • the cathode was rinsed with 10% nitric acid at about 25 ° C for at least 30 minutes.
  • the amount of hydrogen developed cathodically was as follows: a) 26 l, b) 5.5 l c) 12 l, d) 6.1 l, e) 19 l.
  • the example shows that the side reaction of the cathodic hydrogen evolution is suppressed when the metal salts are metered in.

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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)
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  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Abstract

PCT No. PCT/EP93/00232 Sec. 371 Date Oct. 24, 1994 Sec. 102(e) Date Oct. 24, 1994 PCT Filed Feb. 2, 1993 PCT Pub. No. WO93/17151 PCT Pub. Date Sep. 2, 1993.The present invention describes a process for preparing glyoxylic acid by electrochemical reduction of oxalic acid in aqueous solution in divided or undivided electrolytic cells, wherein the cathode comprises carbon or at least 50% by weight of at least one of the metals Cu, Ti, Zr, V, Nb, Ta, Fe, Co, Ni, Zn, Al, Sn and Cr and the aqueous electrolysis solution in the undivided cells or in the cathode compartment of the divided cells in addition contains at least one salt of metals having a hydrogen overpotential of at least 0.25 V, based on a current density of 2500 A/m2. The process according to the invention has the advantage that inexpensive materials available on an industrial scale, in particular stainless chromium-nickel steels or graphite can be employed as the cathode material.

Description

Die vorliegende Erfindung betrifft ein Verfahren zur Herstellung von Glyoxylsäure durch elektrochemische Reduktion von Oxalsäure.The present invention relates to a process for the production of glyoxylic acid by electrochemical reduction of oxalic acid.

Glyoxylsäure ist ein wichtiges Zwischenprodukt zur Herstellung von technisch relevanten Verbindungen und läßt sich entweder durch eine kontrollierte Oxidation von Glyoxal oder durch eine elektrochemische Reduktion von Oxalsäure herstellen.Glyoxylic acid is an important intermediate for the production of technically relevant compounds and can be produced either by a controlled oxidation of glyoxal or by an electrochemical reduction of oxalic acid.

Die elektrochemische Reduktion von Oxalsäure zu Glyoxylsäure ist seit langem bekannt und wird im allgemeinen in wäßrigem, saurem Medium, bei niedriger Temperatur, an Elektroden mit hoher Wasserstoffüberspannung, beispielsweise an Elektroden aus Blei, Cadmium oder Quecksilber, mit oder ohne Zusatz von Mineralsäuren sowie in Gegenwart einer Ionenaustauschermembran durchgeführt (DE-AS 163 842, 292 866, 458 438).The electrochemical reduction of oxalic acid to glyoxylic acid has long been known and is generally carried out in aqueous, acidic medium, at low temperature, on electrodes with high hydrogen overvoltage, for example on electrodes made of lead, cadmium or mercury, with or without the addition of mineral acids and in the presence an ion exchange membrane performed (DE-AS 163 842, 292 866, 458 438).

Bei den bisher üblichen Elektrolyseverfahren von Oxalsäure im technischen Maßstab oder bei Versuchen mit längerer Elektrolysedauer wurden keine befriedigenden Ergebnisse erzielt, da im Verlauf der Elektrolyse die Stromausbeute deutlich sank (DE-AS 347 605) und die Wasserstoffentwicklung zunahm.Satisfactory results have not been achieved with the electrolysis processes of oxalic acid which have been customary up to now on an industrial scale or in experiments with a longer electrolysis time, since the current yield decreased significantly in the course of the electrolysis (DE-AS 347 605) and the evolution of hydrogen increased.

Um diesen Nachteilen zu begegnen, wurde die Reduktion von Oxalsäure an Bleikathoden in Gegenwart von Zusatzstoffen, beispielsweise tertiären Aminen oder quartären Ammoniumsalzen, durchgeführt (DE-OS 22 40 759, 23 59 863). Die Konzentration des Zusatzstoffes liegt dabei zwischen 10⁻⁵ % und 1 %. Dieser Zusatzstoff ist dann im Produkt Glyoxylsäure enthalten und muß durch ein Trennverfahren abgetrennt werden. Über die Selektivität des Verfahrens werden in den genannten Dokumenten keine näheren Angaben gemacht.In order to counter these disadvantages, the reduction of oxalic acid on lead cathodes was carried out in the presence of additives, for example tertiary amines or quaternary ammonium salts (DE-OS 22 40 759, 23 59 863). The concentration of the additive is between 10⁻⁵% and 1%. This additive is then contained in the product glyoxylic acid and must be separated by a separation process. The selectivity of the process is described in the specified documents are not specified.

In Goodridge et al., J. Appl. Electrochem., 10, 1 (1980), S. 55 - 60 werden verschiedene Elektrodenmaterialien hinsichtlich ihrer Stromausbeute bei der elektrochemischen Reduktion von Oxalsäure untersucht. Dabei hat sich gezeigt, daß eine hochreine Bleikathode (99,999 %) für den genannten Zweck am besten geeignet ist, während eine Graphitkathode eine deutlich geringere Stromausbeute bewirkt.In Goodridge et al., J. Appl. Electrochem., 10, 1 (1980), pp. 55-60, various electrode materials are examined with regard to their current efficiency in the electrochemical reduction of oxalic acid. It has been shown that a high-purity lead cathode (99.999%) is best suited for the purpose mentioned, while a graphite cathode has a significantly lower current efficiency.

In der internationalen Patentanmeldung WO-91/19832 wird ebenfalls ein elektrochemisches Verfahren zur Herstellung von Glyoxylsäure aus Oxalsäure beschrieben, in dem jedoch hochreine Bleikathoden mit einem Reinheitsgrad über 99,97 % in Gegenwart geringer Mengen von in der Elektrolyselösung gelösten Bleisalzen verwendet werden. Bei diesem Verfahren werden die Bleikathoden periodisch mit Salpetersäure gespült, wodurch sich die Lebensdauer der Kathoden vermindert. Ein weiterer Nachteil dieses Verfahrens besteht darin, daß die Oxalsäurekonzentration während der Elektrolyse ständig im Bereich der Sättigungskonzentration gehalten werden muß. Die Selektivität liegt dabei nur bei 95 %.International patent application WO-91/19832 also describes an electrochemical process for the production of glyoxylic acid from oxalic acid, in which, however, high-purity lead cathodes with a degree of purity of over 99.97% are used in the presence of small amounts of lead salts dissolved in the electrolysis solution. In this process, the lead cathodes are periodically rinsed with nitric acid, which reduces the life of the cathodes. Another disadvantage of this process is that the oxalic acid concentration must be kept constantly in the range of the saturation concentration during the electrolysis. The selectivity is only 95%.

Bisher ist nur die Verwendung von Graphitkathoden und Kathoden mit hoher Wasserstoffüberspannung wie Blei, Quecksilber oder Cadmium und Legierungen dieser Metalle beschrieben. Für eine technische Verwendung des besagten Verfahrens haben diese Materialien schwerwiegende Nachteile hinsichtlich der Toxizität und der Anwendung und Verarbeitbarkeit in einer elektrochemischen Zelle.So far, only the use of graphite cathodes and high hydrogen overvoltage cathodes such as lead, mercury or cadmium and alloys of these metals has been described. For a technical use of the said method, these materials have serious disadvantages with regard to toxicity and the application and processability in an electrochemical cell.

Die Aufgabe der vorliegenden Erfindung besteht darin, ein Verfahren zur elektrochemischen Reduktion von Oxalsäure zu Glyoxylsäure zur Verfügung zu stellen, das die vorstehend genannten Nachteile vermeidet, insbesondere eine hohe Selektivität aufweist, am Ende der Elektrolyse eine möglichst niedrige Oxalsäurekonzentration erreicht und eine Kathode mit einer hohen Langzeitstabilität benutzt. Dabei soll die Kathode aus einem technisch gut verfügbaren oder unproblematisch zu verarbeitendem Material bestehen. Unter Selektivität wird das Verhältnis der Menge an produzierter Glyoxylsäure zur Menge der insgesamt während der Elektrolyse gebildeten Produkte, nämlich Glyoxylsäure plus Nebenprodukte, beispielsweise Glykolsäure, Essigsäure und Ameisensäure, verstanden.The object of the present invention is to provide a process for the electrochemical reduction of oxalic acid to glyoxylic acid which avoids the disadvantages mentioned above, in particular has a high selectivity, reaches the lowest possible oxalic acid concentration at the end of the electrolysis and a cathode with a high one Long-term stability used. The cathode should be from a technically well available or material to be processed without problems. Selectivity is understood to mean the ratio of the amount of glyoxylic acid produced to the total amount of products formed during the electrolysis, namely glyoxylic acid plus by-products, for example glycolic acid, acetic acid and formic acid.

Die Aufgabe wurde dadurch gelöst, daß die elektrochemische Reduktion von Oxalsäure an Kathoden, die aus Kohlenstoff oder mindestens zu 50 Gew.-% aus mindestens einem der Metalle Cu, Ti, Zr, V, Nb, Ta, Fe, Co, Ni, Zn, Al, Sn und Cr bestehen, durchgeführt wird und der Elektrolyt Salze von Metallen mit einer Wasserstoffüberspannung von mindestens 0,25 V bei einer Stromdichte von 2500 A/m ist oder enthält.The object was achieved in that the electrochemical reduction of oxalic acid on cathodes which consist of carbon or at least 50% by weight of at least one of the metals Cu, Ti, Zr, V, Nb, Ta, Fe, Co, Ni, Zn , Al, Sn and Cr, is carried out and the electrolyte is or contains salts of metals with a hydrogen overvoltage of at least 0.25 V at a current density of 2500 A / m.

Gegenstand der vorliegenden Erfindung ist somit ein Verfahren zur Herstellung von Glyoxylsäure durch elektrochemische Reduktion von Oxalsäure in wäßriger Lösung in geteilten oder ungeteilten Elektrolysezellen, dadurch gekennzeichnet, daß die Kathode aus Kohlenstoff oder mindestens zu 50 Gew.-% aus mindestens einem der Metalle Cu, Ti, Zr, V, Nb, Ta, Fe, Co, Ni, Zn, Al, Sn und Cr besteht und die wäßrige Elektrolyselösung in den ungeteilten Zellen oder im Kathodenraum der geteilten Zellen noch mindestens ein Salz von Metallen mit einer Wasserstoffüberspannung von mindestens 0,25 V, vorzugsweise mindestens 0,40 V, bezogen auf eine Stromdichte von 2500 A/m, enthält, welches im Fall einer Kohlenstoffkathode eine Mindestkonzentration von 10⁻⁶ Gew % in der wäßrigen Elektrolyselösung hat.The present invention thus relates to a process for the preparation of glyoxylic acid by electrochemical reduction of oxalic acid in aqueous solution in divided or undivided electrolysis cells, characterized in that the cathode is made of carbon or at least 50% by weight of at least one of the metals Cu, Ti , Zr, V, Nb, Ta, Fe, Co, Ni, Zn, Al, Sn and Cr and the aqueous electrolysis solution in the undivided cells or in the cathode compartment of the divided cells also contains at least one salt of metals with a hydrogen overvoltage of at least 0, 25 V, preferably at least 0.40 V, based on a current density of 2500 A / m, which in the case of a carbon cathode has a minimum concentration of 10 von% by weight in the aqueous electrolysis solution.

Als Kathode für das erfindungsgemäße Verfahren sind alle Materialien geeignet, die mindestens zu 50 Gew.-%, vorzugsweise mindestens zu 80 Gew.-%, insbesondere mindestens zu 93 Gew.-%, aus einem oder mehreren der Metalle Cu, Ti, Zr, V, Nb, Ta, Fe, Co, Ni, Zn, Al, Sn und Cr, vorzugsweise Fe, Co, Ni, Cr, Cu und Ti, bestehen, oder auch alle Kohlenstoff-Elektrodenmaterialien, beispielsweise Elektrodengraphite, imprägnierte Graphitwerkstoffe, Kohlefilze und auch glasartiger Kohlenstoff. Die vorstehend genannten metallischen Materialien können auch Legierungen aus zwei oder mehreren der vorstehend genannten Metalle, vorzugsweise Fe, Co, Ni, Cr, Cu und Ti sein. Von besonderem Interesse sind Kathoden, die zu mindestens 80 Gew.-%, vorzugsweise zu 93 bis 96 Gew.-%, aus einer Legierung aus zwei oder mehreren vorstehend genannten Metalle und zu 0 bis 20 Gew.-%, vorzugsweise zu 4 bis 7 Gew.-%, aus einem beliebigen anderen Metall, vorzugsweise Mn, Ti, Mo oder eine Kombination davon, und zu 0 bis 3 Gew.-%, vorzugsweise zu 0 bis 1,2 Gew.-%, aus einem Nichtmetall, vorzugsweise C, Si, P, S oder eine Kombination davon, bestehen.All materials which are at least 50% by weight, preferably at least 80% by weight, in particular at least 93% by weight, of one or more of the metals Cu, Ti, Zr, are suitable as cathodes for the process according to the invention. V, Nb, Ta, Fe, Co, Ni, Zn, Al, Sn and Cr, preferably Fe, Co, Ni, Cr, Cu and Ti, consist, or also all carbon electrode materials, for example electrode graphites, impregnated graphite materials, carbon felts and also glassy carbon. The above-mentioned metallic materials can also be alloys of two or more of the above-mentioned metals, preferably Fe, Co, Ni, Cr, Cu and Ti. Are of particular interest Cathodes made of at least 80% by weight, preferably 93 to 96% by weight, of an alloy of two or more metals mentioned above and 0 to 20% by weight, preferably 4 to 7% by weight , from any other metal, preferably Mn, Ti, Mo or a combination thereof, and 0 to 3% by weight, preferably 0 to 1.2% by weight, of a non-metal, preferably C, Si, P , S or a combination thereof.

Der Vorteil der Verwendung der erfindungsgemäßen Kathodenmaterialien liegt darin, daß technisch verfügbare, preiswerte oder leicht verarbeitbare Materialien eingesetzt werden können. Besonders bevorzugt ist Edelstahl oder Graphit.The advantage of using the cathode materials according to the invention is that technically available, inexpensive or easily processable materials can be used. Stainless steel or graphite is particularly preferred.

Beispielsweise können nichtrostende Chrom-Nickel-Stähle mit den Werkstoff-Nummern (nach DIN 17 440) 1.4301, 1.4305, 1.4306, 1.4310, 1.4401, 1.4404, 1.4435, 1.4541, 1.4550, 1.4571, 1.4580, 1.4583, 1.4828, 1.4841 und 1.4845 verwendet werden, deren Zusammensetzungen in Gewichtsprozent in nachstehender Tabelle angegeben sind. Bevorzugt sind die Edelstähle mit den Werkstoff-Nummern 1.4541 mit 17 - 19 % Cr, 9 bis 12 % Ni, ≤ 2 % Mn, ≤ 0,8 % Ti und ≤ 1,2 % Nichtmetallanteil (C, Si, P, S) und der Werkstoff-Nr. 1.4571 mit 16,5 - 18,5 % Cr, 11 - 14 % Ni, 2,0 - 2,5 % Mo, ≤ 2 % Mn, ≤ 0,8 % Ti und ≤ 1,2 % Nichtmetallanteil (C, Si, P, S).

Figure imgb0001
For example, stainless chromium-nickel steels with the material numbers (according to DIN 17 440) 1.4301, 1.4305, 1.4306, 1.4310, 1.4401, 1.4404, 1.4435, 1.4541, 1.4550, 1.4571, 1.4580, 1.4583, 1.4828, 1.4841 and 1.4845 can be used whose compositions are given in percent by weight in the table below. Preference is given to stainless steels with material numbers 1.4541 with 17-19% Cr, 9 to 12% Ni, ≤ 2% Mn, ≤ 0.8% Ti and ≤ 1.2% non-metal content (C, Si, P, S) and the material no. 1.4571 with 16.5 - 18.5% Cr, 11 - 14% Ni, 2.0 - 2.5% Mo, ≤ 2% Mn, ≤ 0.8% Ti and ≤ 1.2% non-metal content (C, Si , P, S).
Figure imgb0001

Das erfindungsgemäße Verfahren wird in ungeteilten oder vorzugsweise in geteilten Zellen durchgeführt. Zur Teilung der Zellen in Anoden- und Kathodenraum werden die üblichen, in der wäßrigen Elektrolyselösung stabilen Diaphragmen aus Polymeren oder anderen organischen oder anorganischen Werkstoffen, wie beispielsweise Glas oder Keramik verwendet. Vorzugsweise verwendet man lonenaustauschermembranen, insbesondere Kationenaustauschermembranen aus Polymeren, vorzugsweise Polymeren mit Carboxyl- und/oder Sulfonsäuregruppen. Die Verwendung von stabilen Anionenaustauschermembranen ist ebenfalls möglich.The method according to the invention is carried out in undivided or preferably in divided cells. The usual diaphragms made of polymers or other organic or inorganic materials, such as glass or ceramics, which are stable in the aqueous electrolysis solution, are used to divide the cells into anode and cathode compartments. It is preferred to use ion exchange membranes, in particular cation exchange membranes made from polymers, preferably polymers with carboxyl and / or sulfonic acid groups. The use of stable anion exchange membranes is also possible.

Die Elektrolyse kann in allen üblichen Elektrolysezellen, wie beispielsweise in Becherglas- oder Platten- und Rahmenzellen oder Zellen mit Festbett- oder Fließbettelektroden, durchgeführt werden. Es ist sowohl die monopolare als auch die bipolare Schaltung der Elektroden anwendbar.The electrolysis can be carried out in all customary electrolysis cells, such as, for example, in beaker or plate and frame cells or cells with fixed bed or fluidized bed electrodes. Both the monopolar and the bipolar circuit of the electrodes can be used.

Es ist möglich, die Elektrolyse sowohl kontinuierlich als auch diskontinuierlich durchzuführen.It is possible to carry out the electrolysis both continuously and batchwise.

Als Anodenmaterial können alle Materialien verwendet werden, an denen die korrespondierenden Anodenreaktionen ablaufen. Beispielsweise sind Blei, Bleidioxid auf Blei oder anderen Trägern, Platin, Metalloxide auf Titan, beispielsweise mit Edelmetalloxiden wie Platinoxid dotiertes Titandioxid auf Titan, für die Sauerstoffentwicklung aus verdünnter Schwefelsäure geeignet. Kohlenstoff oder mit Edelmetalloxiden dotiertes Titandioxid auf Titan werden beispielsweise zur Entwicklung von Chlor aus wäßrigen Alkalichlorid-Lösungen eingesetzt.All materials on which the corresponding anode reactions take place can be used as anode material. For example, lead, lead dioxide on lead or other carriers, platinum, metal oxides on titanium, for example titanium dioxide doped with noble metal oxides such as platinum oxide, are suitable for the development of oxygen from dilute sulfuric acid. Carbon or titanium dioxide on titanium doped with noble metal oxides are used, for example, for the development of chlorine from aqueous alkali metal chloride solutions.

Als Anolytflüssigkeiten können wäßrige Mineralsäuren oder Lösungen ihrer Salze, wie beispielsweise verdünnte Schwefel- oder Phosphorsäure, verdünnte oder konzentrierte Salzsäure, Natriumsulfat- oder Natriumchloridlösungen, verwendet werden.Aqueous mineral acids or solutions of their salts, such as, for example, dilute sulfuric or phosphoric acid, dilute or concentrated hydrochloric acid, sodium sulfate or sodium chloride solutions, can be used as anolyte liquids.

Die wäßrige Elektrolyselösung in der ungeteilten Zelle oder im Kathodenraum in der geteilten Zelle enthält die zu elektrolysierende Oxalsäure in einer Konzentration zweckmäßigerweise zwischen etwa 0,1 mol Oxalsäure pro Liter Lösung und der Sättigungskonzentration von Oxalsäure in der wäßrigen Elektrolyselösung bei der angewendeten Elektrolysetemperatur.The aqueous electrolysis solution in the undivided cell or in the cathode compartment in the divided cell contains the oxalic acid to be electrolyzed in a concentration expediently between about 0.1 mol of oxalic acid per liter of solution and the saturation concentration of oxalic acid in the aqueous electrolysis solution at the electrolysis temperature used.

Der wäßrigen Elektrolyselösung in der ungeteilten Zelle oder im Kathodenraum der geteilten Zelle werden Salze von Metallen mit einer Wasserstoffüberspannung von mindestens 0,25 V (bezogen auf eine Stromdichte von 2500 A/m) zugesetzt. Als derartige Salze kommen hauptsächlich infrage die Salze von Cu, Ag, Au, Zn, Cd, Fe, Hg, Sn, Pb, Tl, Ti, Zr, Bi, V, Ta, Cr, Ce, Co oder Ni, vorzugsweise die Salze von Pb, Sn, Bi, Zn, Cd und Cr, insbesondere bevorzugt die Salze von Pb. Die bevorzugten Anionen dieser Salze sind Chlorid, Sulfat, Nitrat oder Acetat.Salts of metals with a hydrogen overvoltage of at least 0.25 V (based on a current density of 2500 A / m) are added to the aqueous electrolysis solution in the undivided cell or in the cathode space of the divided cell. Such salts are mainly the salts of Cu, Ag, Au, Zn, Cd, Fe, Hg, Sn, Pb, Tl, Ti, Zr, Bi, V, Ta, Cr, Ce, Co or Ni, preferably the salts of Pb, Sn, Bi, Zn, Cd and Cr, particularly preferably the salts of Pb. The preferred anions of these salts are chloride, sulfate, nitrate or acetate.

Die Salze können direkt zugesetzt oder auch, z. B. durch Zugabe von Oxiden, Carbonaten, in einigen Fällen auch der Metalle selbst, in der Lösung erzeugt werden.
Die Salzkonzentration der wäßrigen Elektrolyselösung in der ungeteilten Zelle bzw. im Kathodenraum der geteilten Zelle wird zweckmäßig auf 10⁻⁷ bis 10 Gew.-%, vorzugsweise auf 10⁻⁶ bis 0,1 Gew.-%, insbesondere 10⁻⁵ bis 0,04 Gew.-%, jeweils bezogen auf die Gesamtmenge der wäßrigen Elektrolyselösung, eingestellt.
Im Falle der Kohlenstoffkathode ist eine Salzkonzentration von 10⁻⁶ bis 10 Gew.-%, vorzugsweise 10⁻⁵ bis 10⁻¹ Gew.-%, insbesondere 10⁻⁴ bis 4 x 10⁻ Gew.-%, zweckmäßig.The salts can be added directly or, for. B. by adding oxides, carbonates, in some cases also the metals themselves, in the solution.
The salt concentration of the aqueous electrolysis solution in the undivided cell or in the cathode compartment of the divided cell is expediently from 10⁻⁷ to 10% by weight, preferably to 10⁻⁶ to 0.1% by weight, in particular 10⁻⁵ to 0, 04 wt .-%, each based on the total amount of the aqueous electrolysis solution, adjusted.
In the case of the carbon cathode, a salt concentration of 10⁻⁶ to 10% by weight, preferably 10⁻⁵ to 10⁻¹% by weight, in particular 10⁻⁴ to 4 x 10⁻% by weight, is expedient.

Überraschenderweise wurde festgestellt, daß auch solche Metallsalze eingesetzt werden können, die nach Zugabe in die wäßrige Elektrolyselösung schwerlösliche Metalloxalate bilden, beispielsweise die Oxalate von Cu, Ag, Au, Zn, Cd, Sn, Pb, Ti, Zr, V, Ta, Ce und Co. Auf diese Weise können die zugesetzten Metallionen aus der Produktlösung durch Filtration nach der Elektrolyse bis zur Sättigungskonzentration sehr einfach entfernt werden.Surprisingly, it was found that metal salts can also be used which form poorly soluble metal oxalates after addition to the aqueous electrolysis solution, for example the oxalates of Cu, Ag, Au, Zn, Cd, Sn, Pb, Ti, Zr, V, Ta, Ce and Co. In this way, the added metal ions from the product solution can be removed very easily by filtration after the electrolysis to the saturation concentration.

Auf die Zugabe der genannten Salze kann verzichtet werden, wenn die vorstehend genannten Metallionen in den vorstehend genannten Konzentrationsbereichen zu Beginn der Elektrolyse in der wäßrigen Elektrolytlösung der ungeteilten Zelle oder im Kathodenraum der geteilten Zelle vorhanden sind. Dabei ist zu beachten, daß die zugesetzten Metallionen nicht als metallischer Legierungsbestandteil mit mehr als 20 Gew.-% im Kathodenmaterial vorliegen dürfen. In diesem Fall ist die Zugabe der genannten Salze in den vorstehend genannten Konzentrationsbereichen erforderlich.The addition of the salts mentioned can be dispensed with if the above-mentioned metal ions increase in the above-mentioned concentration ranges Start of electrolysis are present in the aqueous electrolyte solution of the undivided cell or in the cathode compartment of the divided cell. It should be noted that the added metal ions must not be present as a metallic alloy component with more than 20% by weight in the cathode material. In this case, the addition of the salts mentioned is necessary in the concentration ranges mentioned above.

Die Anwesenheit der vorstehend genannten Metallionen in den vorstehend genannten Konzentrationsbereichen zu Beginn der Elektrolyse ist immer dann auch ohne Zugabe der Salze zu erwarten, wenn nach einer Betriebsunterbrechung, beispielsweise nach einem Versuch im diskontinuierlichen Verfahren, ein neuer Versuch mit neuer Katholytflüssigkeit gestartet wird, ohne daß die Kathode verändert wird. Bei längerer Unterbrechung kann die Kathode unter Schutzstrom und der Katholyt unter Inertgas gehalten werden.The presence of the above-mentioned metal ions in the above-mentioned concentration ranges at the beginning of the electrolysis is always to be expected even without the addition of the salts if, after an interruption in operation, for example after a trial in a batch process, a new trial with new catholyte liquid is started without the cathode is changed. In the event of a longer interruption, the cathode can be kept under protective current and the catholyte under inert gas.

Zu Beginn einer Elektrolyse können 10⁻⁷ bis 10 Gew.-%, vorzugsweise 10⁻⁵ bis 0,1 Gew.-%, Mineralsäure wie Phosphorsäure, Salzsäure, Schwefelsäure oder Salpetersäure oder organische Säuren, beispielsweise Trifluoressigsäure, Ameisensäure oder Essigsäure, in die Katholytflüssigkeit zugegeben werden.At the beginning of an electrolysis 10⁻⁷ to 10 wt .-%, preferably 10⁻⁵ to 0.1 wt .-%, mineral acid such as phosphoric acid, hydrochloric acid, sulfuric acid or nitric acid or organic acids, for example trifluoroacetic acid, formic acid or acetic acid, in the Catholyte fluid can be added.

Die Stromdichte des erfindungsgemäßen Verfahrens liegt zweckmäßigerweise zwischen 10 und 10000 A/m, bevorzugt bei 100 bis 5000 A/m, im Falle einer Kohlenstoff-Kathode zwischen 10 und 5000 A/m, vorzugsweise bei 100 bis 4000 A/m.The current density of the method according to the invention is advantageously between 10 and 10,000 A / m, preferably 100 to 5000 A / m, in the case of a carbon cathode between 10 and 5000 A / m, preferably 100 to 4000 A / m.

Die Zellspannung des erfindungsgemäßen Verfahrens ist abhängig von der Stromdichte und liegt zweckmäßigerweise zwischen 1 V und 20 V, vorzugsweise zwischen 1 V und 10 V, bezogen auf einen Elektrodenabstand von 3 mm.The cell voltage of the method according to the invention is dependent on the current density and is expediently between 1 V and 20 V, preferably between 1 V and 10 V, based on an electrode spacing of 3 mm.

Die Elektrolysetemperatur kann im Bereich von - 20 °C bis + 40 °C liegen. Überraschenderweise wurde festgestellt, daß bei Elektrolysetemperaturen unter + 18 °C, selbst bei Oxalsäurekonzentrationen kleiner als 1,5 Gew.-%, die Bildung von Glykolsäure als Nebenprodukt unter 1,5 Mol-% im Vergleich zur gebildeten Glyoxylsäure liegen kann. Bei höheren Temperaturen nimmt der Anteil der Glykolsäure zu. Die Elektrolysetemperatur liegt deshalb vorzugsweise zwischen + 10 °C und + 30 °C, insbesondere zwischen + 10 °C und + 18 °C.The electrolysis temperature can range from - 20 ° C to + 40 ° C. Surprisingly, it was found that at electrolysis temperatures below + 18 ° C, even at oxalic acid concentrations less than 1.5% by weight, the formation of glycolic acid as a by-product can be less than 1.5 mol% compared to the glyoxylic acid formed. The proportion of glycolic acid increases at higher temperatures. The electrolysis temperature is therefore preferably between + 10 ° C and + 30 ° C, in particular between + 10 ° C and + 18 ° C.

Der Katholytdurchfluß des erfindungsgemäßen Verfahrens liegt zwischen 1 und 10000, vorzugsweise 50 und 2000, insbesondere 100 und 1000, Liter pro Stunde.The catholyte flow rate of the process according to the invention is between 1 and 10,000, preferably 50 and 2000, in particular 100 and 1000, liters per hour.

Die Aufarbeitung der Produktlösung erfolgt nach üblichen Methoden. Bei diskontinuierlicher Arbeitsweise wird die elektrochemische Reduktion abgebrochen, wenn ein bestimmter Umsatz erreicht ist. Die entstandene Glyoxylsäure wird von noch vorhandener Oxalsäure nach dem vorstehend genannten Stand der Technik abgetrennt. Beispielsweise kann die Oxalsäure selektiv an Ionenaustauscherharzen fixiert und die wäßrige oxalsäurefreie Lösung aufkonzentriert werden, um eine kommerzielle 50 gew.-%ige Glyoxylsäure zu erhalten. Bei einer kontinuierlichen Arbeitsweise wird die Glyoxylsäure kontinuierlich aus dem Reaktionsgemisch nach üblichen Methoden extrahiert und simultan dazu der entsprechende äquivalente Anteil an frischer Oxalsäure zugeführt.The product solution is worked up using customary methods. In the case of discontinuous operation, the electrochemical reduction is stopped when a certain turnover has been reached. The resulting glyoxylic acid is separated from any oxalic acid still present in accordance with the prior art mentioned above. For example, the oxalic acid can be selectively fixed to ion exchange resins and the aqueous solution free of oxalic acid can be concentrated in order to obtain a commercial 50% by weight glyoxylic acid. In the case of a continuous procedure, the glyoxylic acid is continuously extracted from the reaction mixture by customary methods and the corresponding equivalent proportion of fresh oxalic acid is added simultaneously.

Die Reaktionsnebenprodukte, insbesondere Glykolsäure, Essigsäure und Ameisensäure, werden nach diesen Methoden nicht oder nicht vollständig von der Glyoxylsäure abgetrennt. Es ist deshalb wichtig, eine hohe Selektivität in dem Verfahren zu erreichen, um aufwendige Reinigungsprozesse zu umgehen. Das erfindungsgemäße Verfahren zeichnet sich dadurch aus, daß der Anteil der Summe an Nebenprodukten sehr gering gehalten werden kann. Er liegt zwischen 0 und 5 Mol-%, bevorzugt unter 3 Mol-%, insbesondere unter 2 Mol-%, relativ zur Glyoxylsäure.The reaction by-products, in particular glycolic acid, acetic acid and formic acid, are not or not completely separated from the glyoxylic acid by these methods. It is therefore important to achieve high selectivity in the process in order to avoid complex cleaning processes. The process according to the invention is characterized in that the proportion of the sum of by-products can be kept very low. It is between 0 and 5 mol%, preferably below 3 mol%, in particular below 2 mol%, relative to the glyoxylic acid.

Die Selektivität des erfindungsgemäßen Verfahrens ist umso bemerkenswerter, als daß auch bei niedriger Oxalsäure-Endkonzentration, d. h. im Bereich von 0,1 bis 0,2 mol Oxalsäure pro Liter Elektrolyselösung, der Anteil an Nebenprodukten vorzugsweise unter 3 Mol-%, bezogen auf Glyoxylsäure, liegt.The selectivity of the process according to the invention is all the more remarkable in that, even at a low final concentration of oxalic acid, ie in the range from 0.1 to 0.2 mol of oxalic acid per liter of electrolysis solution, the proportion of by-products is preferably below 3 mol%, based on glyoxylic acid. lies.

Ein weiterer Vorteil des erfindungsgemäßen Verfahrens besteht in der Langzeitstabilität der verwendeten Kathoden im Vergleich zu den bisher üblichen Bleikathoden.Another advantage of the method according to the invention is the long-term stability of the cathodes used in comparison to the lead cathodes which have been customary to date.

In den nachfolgenden Beispielen, die die vorliegende Erfindung näher erläutern, wird eine geteilte Umlaufzelle verwendet, die wie folgt aufgebaut ist:In the following examples, which explain the present invention in more detail, a divided circulation cell is used, which is constructed as follows:

Umlaufzelle mit 0,02 m Elektrodenfläche, Elektrodenabstand 3 mm.

  • A)
    Kathode:
    Edelstahl, Werkstoff Nr. 1.4571 (nach DIN 17440), wenn nicht anders vermerkt.
    Anode:
    dimensionsstabile Anode für Sauerstoff-Entwicklung auf Basis Iridiumoxid auf Titan
    Kationaustauschermembran:
    2-Schichtmembran aus Copolymerisaten aus Perfluorsulfonylethoxyvinylether + Tetrafluorethylen. Auf der Kathodenseite befindet sich eine Schicht mit dem Äquivalentgewicht 1300, auf der Anodenseite eine solche mit dem Äquivalentgewicht 1100, beispielsweise ®Nafion 324 der Firma DuPont;
    Abstandhalter:
    Polyethylennetze
Circulation cell with 0.02 m electrode area, electrode spacing 3 mm.
  • A)
    Cathode:
    Stainless steel, material no.1.4571 (according to DIN 17440), unless otherwise noted.
    Anode:
    Dimensionally stable anode for oxygen development based on iridium oxide on titanium
    Cation exchange membrane:
    2-layer membrane made from copolymers of perfluorosulfonylethoxy vinyl ether + tetrafluoroethylene. On the cathode side there is a layer with the equivalent weight 1300, on the anode side one with the equivalent weight 1100, for example ®Nafion 324 from DuPont;
    Spacers:
    Polyethylene nets

Die quantitative Analyse der Komponenten erfolgte mittels HPLC, die chemische Ausbeute ist definiert als Menge an produzierter Glyoxylsäure, bezogen auf die Menge an verbrauchter Oxalsäure. Die Stromausbeute bezieht sich auf die hergestellte Menge an Glyoxylsäure. Die Selektivität wurde vorstehend bereits definiert.The quantitative analysis of the components was carried out by means of HPLC, the chemical yield is defined as the amount of glyoxylic acid produced, based on the amount of oxalic acid consumed. The current yield relates to the amount of glyoxylic acid produced. The selectivity has already been defined above.

Beispiel 1 (Vergleichsbeispiel) ohne SalzzusatzExample 1 (comparative example) without added salt

Elektrolysebedingungen:

Stromdichte:
2500 A/m
Zellspannung:
4 - 6 V
Katholyttemperatur:
16°C
Katholytdurchfluß:
400 l/h
Anolyt:
2 normale Schwefelsäure
Ausgangskatholyt:
2418 g (19,2 Mol) Oxalsäure-Dihydrat in 24 l wäßriger Lösung.Electrolysis conditions:
Current density:
2500 A / m
Cell voltage:
4 - 6 V
Catholyte temperature:
16 ° C
Catholyte flow:
400 l / h
Anolyte:
2 normal sulfuric acid
Starting catholyte:
2418 g (19.2 mol) oxalic acid dihydrate in 24 l aqueous solution.

Nach 5 Minuten Elektrolysezeit wurde die Stromausbeute für die Bildung von Wasserstoff zu 84 % ermittelt, eine Bildung von Glyoxylsäure fand dagegen kaum statt.After 5 minutes of electrolysis time, the current yield for the formation of hydrogen was found to be 84%, whereas there was hardly any formation of glyoxylic acid.

Beispiel 2Example 2

Elektrolysebedingungen und Ausgangskatholyt wie in Beispiel 1.Electrolysis conditions and starting catholyte as in Example 1.

Es wurden jedoch 1,76 g Blei(ll)acetat-Trihydrat dem Katholyt zugesetzt. Nach 5 Minuten Elektrolysezeit wurde die Stromausbeute für Wasserstoff zu 6 % ermittelt. Nach 945 Ah übertragener Ladung wurde der Katholyt in einen Sammelbehälter abgelassen und analysiert: Gesamtvolumen 25,4 l 0,21 mol/l Oxalsäure (5,33 Mol) 0,54 mol/l Glyoxylsäure (13,7 Mol) 0,0015 mol/l Glykolsäure (0,04 Mol) 0,0004 mol/l Ameisensäure (0,01 Mol) 0,0004 mol/l Essigsäure (0,01 Mol)

Chemische Ausbeute an Glyoxylsäure
99 %
Stromausbeute
78 %
Selektivität
99,6 %
However, 1.76 g of lead (II) acetate trihydrate was added to the catholyte. After 5 minutes of electrolysis, the current yield for hydrogen was found to be 6%. After 945 Ah of transferred charge, the catholyte was drained into a collection container and analyzed: Total volume 25.4 l 0.21 mol / l Oxalic acid (5.33 mol) 0.54 mol / l Glyoxylic acid (13.7 moles) 0.0015 mol / l Glycolic acid (0.04 mol) 0.0004 mol / l Formic acid (0.01 mol) 0.0004 mol / l acetic acid (0.01 mol)
Chemical yield of glyoxylic acid
99%
Current efficiency
78%
selectivity
99.6%

Beispiel 3: Anschlußversuch an Beispiel 2Example 3: Connection attempt to Example 2

Elektrolysebedingungen wie Beispiel 2Electrolysis conditions as example 2

Ausgangskatholyt:
2418 g (19,2 Mol) Oxalsäure-Dihydrat in 24 l wäßriger Lösung unter Zusatz von 0,088 g Blei(II)acetat-Dihydrat und 2,6 ml 65 %iger SalpetersäureStarting catholyte:
2418 g (19.2 mol) oxalic acid dihydrate in 24 l aqueous solution with the addition of 0.088 g lead (II) acetate dihydrate and 2.6 ml 65% nitric acid

Nach 945 Ah übertragener Ladung wurde eine Probe genommen und die Stromausbeute für Glyoxylsäure zu 80 % ermittelt. Nach 1045 Ah übertragener Ladung wurde der Katholyt abgelassen und analysiert. Gesamtvolumen: 25,3 l 0,17 mol/l Oxalsäure (4,30 Mol) 0,58 mol/l Glyoxylsäure (14,7 Mol) 0,0024 mol/l Glykolsäure (0,06 Mol)

Chemische Ausbeute an Glyoxylsäure
99 %
Stromausbeute
76 %
Selektivität
99,6 %.
A sample was taken after 945 Ah of transferred charge and the current yield for glyoxylic acid was found to be 80%. After 1045 Ah transferred charge, the catholyte was drained and analyzed. Total volume: 25.3 l 0.17 mol / l Oxalic acid (4.30 moles) 0.58 mol / l Glyoxylic acid (14.7 moles) 0.0024 mol / l Glycolic acid (0.06 mol)
Chemical yield of glyoxylic acid
99%
Current efficiency
76%
selectivity
99.6%.

Beispiel 4:Example 4:

Elektrolysebedingungen wie Beispiel 1Electrolysis conditions as example 1

Ausgangskatholyt:Starting catholyte:

403 g (3,2 Mol) Oxalsäure-Dihydrat in 4000 ml wäßriger Lösung, Zusatz von 1,46 g Blei(ll)acetat-Trihydrat. Nach 171 Ah übertragener Ladung wurde der Katholyt abgelassen und analysiert.
Endkatholyt:   Gesamtvolumen 4270 ml 0,15 Mol/l Oxalsäure 0,57 Mol/l Glyoxylsäure 0,0038 Mol/l Glykolsäure 0,0004 Mol/l Ameisensäure 0,0019 Mol/l Essigsäure.
Chemische Ausbeute:  95 %
Stromausbeute:  76 %
Selektivität:  98,9 %.403 g (3.2 mol) oxalic acid dihydrate in 4000 ml aqueous solution, addition of 1.46 g lead (II) acetate trihydrate. After 171 Ah of transferred charge, the catholyte was drained and analyzed.
Final catholyte: Total volume 4270 ml 0.15 mol / l Oxalic acid 0.57 mol / l Glyoxylic acid 0.0038 mol / l Glycolic acid 0.0004 mol / l Formic acid 0.0019 mol / l Acetic acid.
Chemical yield: 95%
Current efficiency: 76%
Selectivity: 98.9%.

Beispiel 5: Anschlußversuch an Elektrolyse gemäß Beispiel 4Example 5: Connection test to electrolysis according to Example 4

Elektrolysebedingungen wie Beispiel 1Electrolysis conditions as example 1

Ausgangskatholyt:
403 g (3,2 Mol) Oxalsäure-Dihydrat in 4000 ml wäßriger Lösung, Zusatz von 30 mg Blei(II)acetat-Dihydrat.Starting catholyte:
403 g (3.2 mol) of oxalic acid dihydrate in 4000 ml of aqueous solution, addition of 30 mg of lead (II) acetate dihydrate.

Nach Durchgang von jeweils 171 Ah wurde der Katholyt in ein Sammelgefäß abgelassen, 270 ml Wasser dem Anolyt zugesetzt und eine frische Ausgangskatholyt-Lösung eingefüllt. Nach insgesamt 684 Ah wurde die gesammelte Katholyt-Lösung analysiert.
Endkatholyt:   Gesamtvolumen 17,1 l 0,13 Mol/l Oxalsäure 0,55 Mol/l Glyoxylsäure 0,0056 Mol/l Glykolsäure 0,0006 Mol/l Ameisensäure 0,0002 Mol/l Essigsäure.
Chemische Ausbeute:  89 %
Stromausbeute:  73 %
Selektivität:  98,8 %After passing through 171 Ah each, the catholyte was drained into a collecting vessel, 270 ml of water were added to the anolyte and a fresh starting catholyte solution was introduced. After a total of 684 Ah, the collected catholyte solution was analyzed.
Final catholyte: Total volume 17.1 l 0.13 mol / l Oxalic acid 0.55 mol / l Glyoxylic acid 0.0056 mol / l Glycolic acid 0.0006 mol / l Formic acid 0.0002 mol / l Acetic acid.
Chemical yield: 89%
Power yield: 73%
Selectivity: 98.8%

Beispiel 6: wie Beispiel 4, aber unter Verwendung einer Edelstahl-Kathode mit der Werkstoff-Nr. 1.4541 (nach DIN 17 440).Example 6: as example 4, but using a stainless steel cathode with material no. 1.4541 (according to DIN 17 440).


Endkatholyt:   Gesamtvolumen 4270 ml 0,19 Mol/l Oxalsäure 0,52 Mol/l Glyoxylsäure 0,0027 Mol/l Glykolsäure 0,0012 Mol/l Essigsäure
Chemische Ausbeute:  93 %
Stromausbeute:  70 %
Selektivität:  99,3 %.
Final catholyte: Total volume 4270 ml 0.19 mol / l Oxalic acid 0.52 mol / l Glyoxylic acid 0.0027 mol / l Glycolic acid 0.0012 mol / l acetic acid
Chemical yield: 93%
Current efficiency: 70%
Selectivity: 99.3%.

Beispiel 7: wie Beispiel 4,Example 7: as example 4,

aber unter Verwendung einer Kupferkathode mit der Kurzbezeichnung SF-CuF20 (nach DIN 17 670) mit einem Mindestgehalt an Kupfer von 99,9 %.
Endkatholyt:   Gesamtvolumen 4260 ml 0,17 Mol/l Oxalsäure 0,55 Mol/l Glyoxylsäure 0,0073 Mol/l Glykolsäure 0,0026 Mol/l Essigsäure
Chemische Ausbeute:  95 %
Stromausbeute:  73 %
Selektivität:  98,2 %.but using a copper cathode with the short name SF-CuF20 (according to DIN 17 670) with a minimum copper content of 99.9%.
Final catholyte: Total volume 4260 ml 0.17 mol / l Oxalic acid 0.55 mol / l Glyoxylic acid 0.0073 mol / l Glycolic acid 0.0026 mol / l acetic acid
Chemical yield: 95%
Power yield: 73%
Selectivity: 98.2%.

  • B)
    Kathode:
    Werkstoff Graphit, beispielsweise ®Diabon N der Firma Sigri, Meitingen
    Anode:
    dimensionsstabile Anode für Sauerstoff-Entwicklung auf Basis Iridiumoxid auf Titan
    Kationaustauschermembran:
    2-Schichtmembran aus Copolymerisaten aus Perfluorsulfonylethoxyvinylether + Tetrafluorethylen. Auf der Kathodenseite befindet sich eine Schicht mit dem Äquivalentgewicht 1300, auf der Anodenseite eine solche mit dem Äquivalentgewicht 1100, beispielsweise ®Nafion 324 der Firma DuPont;
    Abstandhalter:
    Polyethylennetze
    B)
    Cathode:
    Graphite material, for example ®Diabon N from Sigri, Meitingen
    Anode:
    Dimensionally stable anode for oxygen development based on iridium oxide on titanium
    Cation exchange membrane:
    2-layer membrane made from copolymers of perfluorosulfonylethoxy vinyl ether + tetrafluoroethylene. On the cathode side there is a layer with the equivalent weight 1300, on the anode side one with the equivalent weight 1100, for example ®Nafion 324 from DuPont;
    Spacers:
    Polyethylene nets

Die quantitative Analyse der Komponenten erfolgte mittels HPLC, die chemische Ausbeute ist definiert als Menge an produzierter Glyoxylsäure, bezogen auf die Menge an verbrauchter Oxalsäure. Die Stromausbeute bezieht sich auf die hergestellte Menge an Glyoxylsäure. Die Selektivität wurde vorstehend bereits definiert.The quantitative analysis of the components was carried out by means of HPLC, the chemical yield is defined as the amount of glyoxylic acid produced, based on the amount of oxalic acid consumed. The current yield relates to the amount of glyoxylic acid produced. The selectivity has already been defined above.

Beispiel 1:Example 1:

Elektrolysebedingungen

Stromdichte:
2500 A m⁻
Zellspannung:
5,1 - 6,5 V
Katholyttemperatur:
16 °C
Katholytdurchfluß:
300 l/h
Anolyt:
2-normale Schwefelsäure
Ausgangskatholyt:
101 g Oxalsäure-Dihydrat (0,8 Mol) in 1010 ml wäßriger Lösung; Zusatz von 360 mg Blei(II)acetat-Trihydrat (200 ppm Pb⁺)
Endkatholyt:
Gesamtvolumen 1080 ml;
0,16 mol/l Oxalsäure (0,17 Mol);
0,57 mol/l Glyoxylsäure (0,61 Mol);
0,0085 mol/l Glykolsäure (0,009 Mol);
0,0028 mol/l Essigsäure (0,003 Mol).
Electrolysis conditions
Current density:
2500 A m⁻
Cell voltage:
5.1 - 6.5 V
Catholyte temperature:
16 ° C
Catholyte flow:
300 l / h
Anolyte:
2-normal sulfuric acid
Starting catholyte:
101 g oxalic acid dihydrate (0.8 mol) in 1010 ml aqueous solution; Addition of 360 mg lead (II) acetate trihydrate (200 ppm Pb⁺)
Final catholyte:
Total volume 1080 ml;
0.16 mol / l oxalic acid (0.17 mol);
0.57 mol / l glyoxylic acid (0.61 mol);
0.0085 mol / l glycolic acid (0.009 mol);
0.0028 mol / l acetic acid (0.003 mol).

Chemische Ausbeute an Glyoxylsäure:Chemical yield of glyoxylic acid:
97 %97%
Stromverbrauch:Power consumption:
43 Ah43 Ah
Stromausbeute:Current efficiency:
76 %76%
Selektivität:Selectivity:
98,1 %98.1%
Beispiel 2:Example 2:

Es wurde wie in Beispiel 1 verfahren, nur daß kein Bleisalz zugesetzt, sondern die Elektrolysezelle zwischen den Elektrolysen unter Schutzstrom und der Katholyt unter Inertgas gehalten wurde. Die unmittelbar vorangegangene Elektrolyse war die gemäß Beispiel 1 durchgeführte Elektrolyse.The procedure was as in Example 1, except that no lead salt was added, but the electrolysis cell was kept between the electrolysis under protective current and the catholyte under inert gas. The immediately preceding electrolysis was the electrolysis carried out according to Example 1.

Elektrolysebedingungen

Stromdichte:
2500 A m⁻
Zellspannung:
5,1 - 7,1 V
Katholyttemperatur:
16 °C
Katholytdurchfluß:
300 l/h
Anolyt:
2-normale Schwefelsäure
Electrolysis conditions
Current density:
2500 A m⁻
Cell voltage:
5.1 - 7.1 V
Catholyte temperature:
16 ° C
Catholyte flow:
300 l / h
Anolyte:
2-normal sulfuric acid

Ausgangskatholyt:Starting catholyte:
101 g Oxalsäure-Dihydrat (0,8 Mol) in 1000 ml wäßriger Lösung101 g oxalic acid dihydrate (0.8 mol) in 1000 ml aqueous solution
Endkatholyt:Final catholyte:
Gesamtvolumen 1050 ml;
0,15 mol/l Oxalsäure (0,16 Mol);
0,60 mol/l Glyoxylsäure (0,63 Mol);
0,0086 mol/l Glykolsäure (0,009 Mol);
weitere Nebenprodukte konnten nicht festgestellt werden.Total volume 1050 ml;
0.15 mol / l oxalic acid (0.16 mol);
0.60 mol / l glyoxylic acid (0.63 mol);
0.0086 mol / l glycolic acid (0.009 mol);
no other by-products could be identified.

Chemische Ausbeute an Glyoxylsäure:Chemical yield of glyoxylic acid:
98 %98%
Stromverbrauch:Power consumption:
43 Ah43 Ah
Stromausbeute:Current efficiency:
79 %79%
Selektivität:Selectivity:
98,6 %98.6%
Beispiel 3:Example 3:

Anschlußversuch an Elektrolyse gemäß Beispiel 2Connection test to electrolysis according to example 2

Elektrolysebedingungen

Stromdichte:
2500 A m⁻
Zellspannung:
zwischen 5 und 7 V
Katholyttemperatur:
16 °C
Katholytdurchfluß:
300 l/h
Anolyt:
2-normale Schwefelsäure
Electrolysis conditions
Current density:
2500 A m⁻
Cell voltage:
between 5 and 7 V.
Catholyte temperature:
16 ° C
Catholyte flow:
300 l / h
Anolyte:
2-normal sulfuric acid

Ausgangskatholyt:Starting catholyte:
101 g Oxalsäure-Dihydrat (0,8 Mol) in 1010 ml wäßriger Lösung, Zusatz von 7,2 mg Blei(II)acetat-Trihydrat (4 ppm Pb⁺).
Nach Durchgang von jeweils 43 Ah wurde eine Probe zur Analyse genommen und der Katholyt in ein Sammelgefäß abgelassen, 70 ml Wasser dem Anolyt zugesetzt und eine frische Ausgangskatholyt-Lösung eingefüllt. Nach insgesamt 946 Ah wurde die gesammelte Katholytlösung analysiert. 101 g oxalic acid dihydrate (0.8 mol) in 1010 ml aqueous solution, addition of 7.2 mg lead (II) acetate trihydrate (4 ppm Pb⁺).
After passing through 43 Ah each, a sample was taken for analysis and the catholyte was drained into a collecting vessel, 70 ml of water were added to the anolyte and a fresh starting catholyte solution was introduced. After a total of 946 Ah, the collected catholyte solution was analyzed.
Endkatholyt:Final catholyte:
Gesamtvolumen 23,5 l;
0,19 mol/l Oxalsäure (4,47 Mol);
0,54 mol/l Glyoxylsäure (12,7 Mol);
0,0043 mol/l Glykolsäure (0,10 Mol);
0,0021 mol/l Ameisensäure (0,05 Mol).Total volume 23.5 l;
0.19 mol / l oxalic acid (4.47 mol);
0.54 mol / l glyoxylic acid (12.7 mol);
0.0043 mol / l glycolic acid (0.10 mol);
0.0021 mol / l formic acid (0.05 mol).

Chemische Ausbeute an Glyoxylsäure:Chemical yield of glyoxylic acid:
97 %97%
Stromverbrauch:Power consumption:
946 Ah946 Ah
Stromausbeute:Current efficiency:
72 %72%

Die Stromausbeute bleibt über den Verlauf des gesamten Versuches im Rahmen statistischer Schwankungen konstant.

Selektivität:
98,8 %
The current yield remains constant over the course of the entire experiment within the framework of statistical fluctuations.
Selectivity:
98.8%

Beispiel 4:Example 4:

Elektrolysebedingungen

Stromdichte:
2500 A m⁻
Zellspannung:
5,1 - 6,0 V
Katholyttemperatur:
16 °C
Katholytdurchfluß:
400 l/h
Anolyt:
2-normale Schwefelsäure
Electrolysis conditions
Current density:
2500 A m⁻
Cell voltage:
5.1 - 6.0 V
Catholyte temperature:
16 ° C
Catholyte flow:
400 l / h
Anolyte:
2-normal sulfuric acid

Ausgangskatholyt:Starting catholyte:
2418 g Oxalsäure-Dihydrat (19,2 Mol) in 24 l wäßriger Lösung, Zusatz von 1,76 g Blei(II)acetat-Trihydrat (40 ppm Pb⁺)2418 g oxalic acid dihydrate (19.2 mol) in 24 l aqueous solution, addition of 1.76 g lead (II) acetate trihydrate (40 ppm Pb⁺)
Endkatholyt:Final catholyte:
Gesamtvolumen 25,2 l;
0,20 mol/l Oxalsäure (5,04 Mol);
0,53 mol/l Glyoxylsäure (13,4 Mol);
0,0036 mol/l Glykolsäure (0,089 Mol);
0,0003 mol/l Ameisensäure (0,008 Mol);
0,0006 mol/l Essigsäure (0,015 Mol).Total volume 25.2 l;
0.20 mol / l oxalic acid (5.04 mol);
0.53 mol / l glyoxylic acid (13.4 mol);
0.0036 mol / l glycolic acid (0.089 mol);
0.0003 mol / l formic acid (0.008 mol);
0.0006 mol / l acetic acid (0.015 mol).

Chemische Ausbeute an Glyoxylsäure:Chemical yield of glyoxylic acid:
95 %95%
Stromverbrauch:Power consumption:
945 Ah945 Ah
Stromausbeute:Current efficiency:
76 %76%
Selektivität:Selectivity:
99,2 %99.2%
Beispiel 5:Example 5:

Elektrolysebedingungen

Stromdichte:
2500 A m⁻
Zellspannung:
5 - 7 V
Katholyttemperatur:
16 °C
Katholytdurchfluß:
400 l/h
Anolyt:
2-normale Schwefelsäure
Electrolysis conditions
Current density:
2500 A m⁻
Cell voltage:
5 - 7 V
Catholyte temperature:
16 ° C
Catholyte flow:
400 l / h
Anolyte:
2-normal sulfuric acid

Ausgangskatholyt:
a) 302 g (2,4 Mol) Oxalsäure-Dihydrat in 3000 ml Wasser, Zusatz von 1,08 g Blei(ll)acetat-Trihydrat (200 ppm Pb⁺)
b) Nach Durchgang von 128 Ah wurde der Katholyt abgelassen und analysiert, 200 ml Wasser dem Anolyt zugesetzt und eine frische Katholytlösung eingefüllt, die 302 g (2,4 Mol) Oxalsäure-Dihydrat in 3000 ml Wasser enthielt, Zusatz von 21 mg Blei(ll)acetat-Trihydrat (4 ppm Pb⁺).
c) Nach Durchgang weiterer 128 h wurde wie unter b) verfahren und erneut elektrolysiert. Allerdings wurden diesmal weitere 2,4 Mol Oxalsäure zusätzlich in fester Form während laufender Elektrolyse zudosiert und die doppelte Ladung, entsprechend 257 Ah, übertragen.
Die Ergebnisse sind in folgender Tabelle festgehalten: a) b) c) eingesetzte Oxalsäure 2,4 Mol 2,4 Mol 4,8 Mol übertragene Ladung: 128 Ah 128 Ah 257 Ah Endkatholyt:    Gesamtvolumen 3,2 l 3,2 l 3,4 l    Oxalsäure 0,11 Mol/l 0,11 Mol/l 0,13 Mol/l    Glyoxylsäure 0,60 Mol/l 0,62 Mol/l 1,02 Mol/l    Glykolsäure 0,0024 Mol/l 0,0068 Mol/l 0,013 Mol/l    Ameisensäure - - 0,002 Mol/l    Essigsäure 0,0024 Mol/l 0,0025 Mol/l 0,0031 Mol/l Chem. Ausbeute 94 % 97 % 80 % Stromausbeute 80 % 83 % 72 % Selektivität 99,2 % 98,5 % 98,2 % Starting catholyte:
a) 302 g (2.4 mol) oxalic acid dihydrate in 3000 ml water, addition of 1.08 g lead (II) acetate trihydrate (200 ppm Pb⁺)
b) After passing through 128 Ah, the catholyte was drained off and analyzed, 200 ml of water were added to the anolyte and a fresh catholyte solution was added which contained 302 g (2.4 mol) of oxalic acid dihydrate in 3000 ml of water, addition of 21 mg of lead ( ll) acetate trihydrate (4 ppm Pb⁺).
c) After a further 128 h, the procedure was as under b) and electrolysis was carried out again. This time, however, an additional 2.4 mol of oxalic acid was added in solid form during the ongoing electrolysis and the double charge, corresponding to 257 Ah, was transferred.
The results are shown in the following table: a) b) c) Oxalic acid used 2.4 moles 2.4 moles 4.8 moles transferred charge: 128 Ah 128 Ah 257 Ah Final catholyte: Total volume 3.2 l 3.2 l 3.4 l Oxalic acid 0.11 mol / l 0.11 mol / l 0.13 mol / l Glyoxylic acid 0.60 mol / l 0.62 mol / l 1.02 mol / l Glycolic acid 0.0024 mol / l 0.0068 mol / l 0.013 mol / l Formic acid - - 0.002 mol / l acetic acid 0.0024 mol / l 0.0025 mol / l 0.0031 mol / l Chemical yield 94% 97% 80% Current efficiency 80% 83% 72% selectivity 99.2% 98.5% 98.2%

Dieses Beispiel demonstriert das Erreichen einer hohen Glyoxylsäurekonzentration bei niedriger Oxalsäurekonzentration unter Beibehaltung der hohen Selektivität.This example demonstrates the achievement of a high glyoxylic acid concentration at a low oxalic acid concentration while maintaining the high selectivity.

Beispiel 6: LangzeitstabilitätExample 6: Long-term stability

Folgeversuch von Beispiel 4, Elektrolysebedingungen wie Beispiel 4Follow-up experiment of example 4, electrolysis conditions as example 4

Die Elektrolysedauer betrug 10395 Ah ohne Zwischenbehandlung der elektrochemischen Zelle.The electrolysis time was 10395 Ah without intermediate treatment of the electrochemical cell.

Ausgangskatholyt:Starting catholyte:

2418 g (19,2 Mol) Oxalsäure-Dihydrat in 24 1 Wasser und Zusätze von 22 mg Blei(ll)acetat-Trihydrat (0,5 ppm Pb⁺) und 0,86 ml 65 %iger HNO₃ (33 ppm HNO₃) Nach jeweils 945 Ah übertragener Ladung wurde eine Probe zur Bestimmung der Stromausbeute genommen, der Katholyt in einen Sammelbehälter abgelassen, 1200 ml Wasser dem Anolyt zugegeben und eine frische Katholytlösung entsprechend dem Ausgangskatholyt eingefüllt. Nach insgesamt 10395 Ah (208 h Elektrolysedauer) wurden die gesammelten Katholyte analysiert.2418 g (19.2 mol) of oxalic acid dihydrate in 24 l of water and additions of 22 mg of lead (II) acetate trihydrate (0.5 ppm Pb⁺) and 0.86 ml of 65% HNO₃ (33 ppm HNO₃) after For each charge of 945 Ah transferred, a sample was taken to determine the current efficiency, the catholyte was drained into a collecting container, 1200 ml of water were added to the anolyte and a fresh catholyte solution was filled in according to the starting catholyte. After a total of 10395 Ah (208 h electrolysis time), the collected catholytes were analyzed.

Endkatholyt:Final catholyte:
Gesamtvolumen 277 l;
0,24 Mol/l Oxalsäure (66,5 Mol);
0,50 Mol/l Glyoxylsäure (139 Mol);
0,0038 Mol/l Glykolsäure (1,1 Mol);
0,0012 Mol/l Ameisensäure (0,33 Mol);
Chem. Ausbeute 96 %
Stromausbeute 72 %
Selektivität 99,0 %Total volume 277 l;
0.24 mol / l oxalic acid (66.5 mol);
0.50 mol / l glyoxylic acid (139 mol);
0.0038 mol / l glycolic acid (1.1 mol);
0.0012 mol / l formic acid (0.33 mol);
Chemical yield 96%
Current efficiency 72%
Selectivity 99.0%

Der Verlauf der Stromausbeute nach jeweils 945 Ah war im Rahmen statistischer Schwankungen bei (72 ± 6) % konstant. Über die Dauer des Versuchs ließ sich kein Trend zu erhöhter oder erniedrigter Stromausbeute feststellen.The course of the current yield after every 945 Ah was constant in the context of statistical fluctuations at (72 ± 6)%. No trend towards increased or decreased current yield could be determined over the duration of the experiment.

Beispiel 7:Example 7:

Folgeversuch von Beispiel 6Follow-up experiment of example 6

Elektrolysebedingungen wie Beispiel 4 und 6Electrolysis conditions as examples 4 and 6

Ausgangskatholyt wie Beispiel 6.Starting catholyte as example 6.

Nach Durchgang von 945 Ah (entsprechend 92 % der theoretischen Ladungsmenge) und nach 1040 Ah (entsprechend 101 % der theoretischen Ladungsmenge) wurden Proben analysiert.Samples were analyzed after passing through 945 Ah (corresponding to 92% of the theoretical amount of charge) and after 1040 Ah (corresponding to 101% of the theoretical amount of charge).

Endkatholyt:

Figure imgb0002
Figure imgb0003
 Final catholyte:
Figure imgb0002
Figure imgb0003

Das Beispiel verdeutlicht, daß bei einer Oxalsäurekonzentration kleiner als 0,2 Mol/l die hohe Selektivität erhalten bleibt. Chemische Ausbeute und Stromausbeute sind etwas niedriger als bei höheren Oxalsäurekonzentrationen.The example illustrates that the high selectivity is maintained at an oxalic acid concentration of less than 0.2 mol / l. Chemical yield and current yield are somewhat lower than at higher oxalic acid concentrations.

Beispiel 8: Katalytische Wirkung zugegebener MetallsalzeExample 8: Catalytic effect of added metal salts

Vor jedem Versuch wurde die Kathode mindestens 30 Minuten bei etwa 25°C mit 10%iger Salpetersäure gespült.Before each experiment, the cathode was rinsed with 10% nitric acid at about 25 ° C for at least 30 minutes.

Elektrolysebedingungen wie Beispiel 5.Electrolysis conditions as example 5.

Während des Versuchs wurde die Menge des kathodisch entwickelten Wasserstoffs gemessen.During the experiment, the amount of hydrogen developed cathodically was measured.

Ausgangskatholyt:Starting catholyte:

302 g (2,4 Mol) Oxalsäure-Dihydrat in 3000 ml Wasser

  • a) ohne weiteren Zusatz,
  • b) mit 1,08 g Blei(ll)acetat-Trihydrat,
  • c) mit 1,25 g Zinkchlorid,
  • d) mit 1,39 g Wismut(III)nitrat-Pentahydrat und
  • e) mit 1,51 g Kupfer(II)-sulfat-Pentahydrat.
302 g (2.4 mol) oxalic acid dihydrate in 3000 ml water
  • a) without further addition,
  • b) with 1.08 g of lead (II) acetate trihydrate,
  • c) with 1.25 g of zinc chloride,
  • d) with 1.39 g bismuth (III) nitrate pentahydrate and
  • e) with 1.51 g of copper (II) sulfate pentahydrate.

Nach Durchgang von 128 Ah (entsprechend 100 % der theoretisch zu übertragenden Ladungsmenge) war die kathodisch entwickelte Wasserstoffmenge wie folgt: a) 26 l, b) 5,5 l c) 12 l, d) 6,1 l, e) 19 l.After passing through 128 Ah (corresponding to 100% of the amount of charge theoretically to be transferred), the amount of hydrogen developed cathodically was as follows: a) 26 l, b) 5.5 l c) 12 l, d) 6.1 l, e) 19 l.

Das Beispiel zeigt, daß die Nebenreaktion der kathodischen Wasserstoffentwicklung bei Zudosierung der Metallsalze zurückgedrängt wird.The example shows that the side reaction of the cathodic hydrogen evolution is suppressed when the metal salts are metered in.

Claims (18)

  1. A process for preparing glyoxylic acid by electrochemical reduction of oxalic acid in aqueous solution in divided or undivided electrolytic cells, wherein the cathode comprises carbon or at least 50% by weight of at least one of the metals Cu, Ti, Zr, V, Nb, Ta, Fe, Co, Ni, Sn, Zn, Al and Cr, and the aqueous electrolysis solution in the undivided cells or in the cathode compartment of the divided cells in addition contains at least one salt of metals having a hydrogen overpotential of at least 0.25 V, based on a current density of 2500 A/m, which salt, in the case of a carbon cathode, has a minimum concentration of 10⁻⁶% by weight in the aqueous electrolysis solution.
  2. The process as claimed in claim 1, wherein the cathode comprises at least 50% by weight, preferably at least 80% by weight, of at least one of the metals Fe, Co, Ni, Cr, Cu and Ti.
  3. The process as claimed in claim 1, wherein the cathode comprises at least 50% by weight, preferably at least 80% by weight, of an alloy of two or more of the metals Cu, Ti, Zr, V, Nb, Ta, Fe, Co, Ni, Sn, Zn, Al and Cr.
  4. The process as claimed in claim 2, wherein the cathode comprises at least 80% by weight, preferably at least 93% by weight, of an alloy of two or more of the metals Fe, Co, Ni, Cr, Cu and Ti.
  5. The process as claimed in claim 1 or 2, wherein the cathode comprises at least 80% by weight, preferably from 93 to 96% by weight, of an alloy of two or more of the metals mentioned in claim 1 or 2, and from 0 to 20% by weight, preferably from 4 to 7% by weight, of any other metal, preferably Mn, Ti, Mo or a combination thereof, and from 0 to 3% by weight, preferably from 0 to 1.2% by weight, of a nonmetal, preferably C, Si, P, S or a combination thereof.
  6. The process as claimed in claim 1 or 2, wherein the cathode is composed of alloy steel.
  7. The process as claimed in claim 6, wherein the alloy steel is a stainless chromium-nickel steel.
  8. The process as claimed in claim 1, wherein the cathode is composed of graphite.
  9. The process as claimed in at least one of claims 1 to 7, wherein the concentration of the salts of metals having a hydrogen overpotential of at least 0.25 V, based on a current density of 2500 A/m, in the aqueous electrolysis solution in the undivided cell or in the cathode compartment of the divided cell is from 10⁻⁷ to 10% by weight, preferably from 10⁻⁶ to 0.1% by weight, especially from 10⁻⁵ to 0.04% by weight.
  10. The process as claimed in claim 8, wherein the concentration of the salts of metals having a hydrogen overpotential of at least 0.25 V, based on a current density of 2500 A/m, in the aqueous electrolysis solution in the undivided cell or in the cathode compartment of the divided cell is from 10⁻⁶ to 10% by weight, preferably from 10⁻⁵ to 10⁻¹% by weight, especially from 10⁻⁴ to 4 × 10⁻% by weight.
  11. The process as claimed in at least one of claims 1 to 10, which comprises using, as salts of metals having a hydrogen overpotential of at least 0.25 V, based on a current density of 2500 A/m, the salts of Cu, Ag, Au, Zn, Cd, Fe, Hg, Sn, Pb, Tl, Ti, Zr, Bi, V, Ta, Cr, Ce, Co, Ni, preferably of Pb, Sn, Bi, Zn, Cd, Cr, or a combination thereof, especially Pb salts.
  12. The process as claimed in at least one of claims 2 to 7, wherein the current density is between 10 and 10,000 A/m, preferably between 100 and 5000 A/m.
  13. The process as claimed in claim 8, wherein the current density is between 10 and 5000 A/m, preferably between 100 and 4000 A/m.
  14. The process as claimed in at least one of claims 1 to 13, wherein the electrolysis temperature is between -20°C and +40°C, preferably +10°C and +30°C, especially +10°C and +18°C.
  15. The process as claimed in at least one of claims 1 to 8, wherein the oxalic acid concentration in the electrolysis solution is between 0.1 mol per liter of electrolysis solution and the saturation concentration of oxalic acid in the electrolysis solution at the electrolysis temperature used.
  16. The process as claimed in at least one of claims 1 to 15, wherein the aqueous electrolysis solution contains from 10⁻⁷ to 10% by weight, preferably from 10⁻⁵ to 10⁻¹% by weight, of a mineral acid or organic acid.
  17. The process as claimed in at least one of claims 1 to 16, wherein the electrolysis is carried out in divided electrolytic cells.
  18. The process as claimed in claim 17, wherein the membrane material used in the divided electrolytic cells are cation exchanger membranes made of polymers containing carboxylic acid groups or sulfonic acid groups or both.
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EP0627020A1 (en) 1994-12-07
US5474658A (en) 1995-12-12
WO1993017151A1 (en) 1993-09-02
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DE59302695D1 (en) 1996-06-27
ATE138425T1 (en) 1996-06-15
CA2130552A1 (en) 1993-08-23

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