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EP0457320B1 - Process for partial electrolyte dehalogenation dichloro- and trichloro-acetic acids and electrolysis solution - Google Patents

Process for partial electrolyte dehalogenation dichloro- and trichloro-acetic acids and electrolysis solution Download PDF

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Publication number
EP0457320B1
EP0457320B1 EP91107944A EP91107944A EP0457320B1 EP 0457320 B1 EP0457320 B1 EP 0457320B1 EP 91107944 A EP91107944 A EP 91107944A EP 91107944 A EP91107944 A EP 91107944A EP 0457320 B1 EP0457320 B1 EP 0457320B1
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EP0457320A1 (en
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Steffen Dr. Dapperheld
Rudolf Rossmeissl
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Hoechst AG
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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

  • Monochloroacetic acid and its derivatives are important intermediates in industrial organic synthesis. They are used for the production of adhesives, pesticides or pharmaceutical products.
  • the production of monochloroacetic acid by chlorinating acetic acid is always associated with the formation of di- and trichloroacetic acid.
  • electrochemical dehalogenation is also available for removing di- and trichloroacetic acid from the product mixture (EP-B 0 241 685).
  • the latter dehalogenation is carried out using graphite cathodes in the presence of small amounts of metal salts with a hydrogen overvoltage of at least 0.4 V (at a current density of 4000 A / m 2 ), preferably in water-containing, acidic electrolytes.
  • This process has a high selectivity because the thermodynamically favored reduction of protons to hydrogen takes place at the cathode at low concentrations of the partially dehalogenated di- and trichloroacetic acid. In this way, undesired dehalogenation of the monochloroacetic acid is avoided, but the di- and trichloroacetic acid are also dehalogenated only with poor current efficiency.
  • This method is not suitable for dehalogenation down to a very low concentration level of di- and trichloroacetic acid, since an increasing proportion of the electrical charge is used for the reduction of protons to hydrogen.
  • An economical implementation of dehalogenation to monochloroacetic acid at a low concentration of di- and trichloroacetic acid has therefore only been insufficient to date (comparative example).
  • the task was therefore to selectively dehalogenate di- and trichloroacetic acid with very extensive conversion to monochloroacetic acid, that is to say not completely.
  • Nekrasov et al. investigated the dehalogenation of trichloroacetic acid and monochloroacetic acid in the presence of tetramethylammonium or tetraethylammonium salt in a non-protic electrolyte (Nekrasov et al., Elektrokhimiya 1988, 24, 560-563). The effects they observed in no way suggest that ammonium salts in an aqueous electrolyte could inhibit the above-mentioned undesired reduction of protons to hydrogen.
  • di- and trichloroacetic acid can be dehalogenated continuously or discontinuously to form monochloroacetic acid with very extensive conversion in divided electrolysis cells if electrolysis is carried out in aqueous solutions in which, in addition to metal salts, a hydrogen overvoltage of at least 0.4 V (at a Current density of 4000 A / m 2 ) quaternary ammonium and / or phosphonium salts are still dissolved.
  • Another object is an electrolysis solution for the partial dehalogenation of tri- and / or dichloroacetic acid, which contains at least one of these two acids, one or more metal salts with a hydrogen overvoltage of at least 0.4 V (at a current density of at least 4000 A / m 2 ) contains at least one compound selected from the group of compounds of the formula I to V.
  • the compounds of the formulas I to V are used in concentrations of 1 to 5000 ppm, preferably 10 to 1000 ppm, but in particular 50 to 500 ppm.
  • the metal salts with a hydrogen overvoltage of at least 0.4 V are generally the soluble salts of Cu, Zn, Cd, Hg, Sn, Pb, Ti, Bi, V, Ta and / or Ni, preferably the soluble salts of Cu, Zn, Cd, Sn, Hg and Pb.
  • CI-, Br-, SO 4 2- , NO 3 - or CH 3 COO- are preferably used as anions, the anion being chosen so that a soluble metal salt is formed (for example PbN0 3 ).
  • the salts can be added directly to the electrolysis solution or, e.g. by adding oxides or carbonates - or by adding the metals themselves, such as Zn, Cd, Sn, Pb, Ni - in the solution.
  • the salt concentration in the catholyte is expediently set to about 0.1 to 5000 ppm, preferably to about 10 to 1000 ppm.
  • the starting material for the process is di- and / or trichloroacetic acid or mixtures thereof with monochloroacetic acid which are inevitably formed in the acetic acid chlorination.
  • the proportion by weight of di- and trichloroacetic acid in the total amount of chlorinated acetic acids is less than 10% by weight. This proportion by weight can easily be less than 5% by weight, or even less than 2% by weight, which was particularly surprising.
  • the catholyte can also contain mineral acids (eg HCl, H 2 S0 4 etc.).
  • the anolyte is preferably an aqueous mineral acid, in particular an aqueous hydrochloric acid or sulfuric acid.
  • the same material as that for the cathode can generally be used as the anode material.
  • other customary electrode materials which, however, must be inert under the electrolysis conditions, for example titanium, coated with titanium dioxide and doped with a noble metal oxide, such as e.g. Ruthenium dioxide.
  • Cation exchange membranes made of perfluorinated polymers with carboxyl and / or sulfonic acid groups are generally used to divide the cells into the anode and cathode compartments. It is also generally possible to use anion exchange membranes which are stable in the electrolyte, diaphragms made of polymers or inorganic materials.
  • the electrolysis temperature should generally be below 100 ° C, preferably between 10 and 90 ° C.
  • the electrolysis can be carried out either continuously or batchwise.
  • a continuous process is preferred, especially at a low concentration of di- and trichloroacetic acid.
  • chloride is constantly consumed due to the anodic chlorine evolution. In general, the chloride consumption is then compensated for by continuously introducing gaseous HCl or aqueous hydrochloric acid.
  • the electrolysis product is worked up in a known manner, e.g. by distillation.
  • the metal salts and the quaternary ammonium and phosphonium compounds remain in the residue and can be returned to the process.
  • the invention is illustrated by the following examples. Examples 1-9 are followed by a comparative example.
  • the comparative example shows that under the electrolysis conditions of EP-B 0 241 685, when a dichloroacetic acid concentration of 31% (based on the total amount of dissolved acetic acids) is reached, the major part of the electrical charge is used for the reduction of protons to hydrogen .

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Description

Monochloressigsäure und ihre Derivate sind wichtige Zwischenprodukte in der industriellen organischen Synthese. Sie werden zur Herstellung von Klebstoffen, Pflanzenschutzmitteln oder pharmazeutischen Produkten verwendet.
Die Herstellung von Monochloressigsäure durch Chlorieren von Essigsäure ist immer mit der Bildung von Di- und Trichloressigsäure verbunden. Zur Entfernung von Di- und Trichloressigsäure aus dem Produktgemisch steht neben der katalytischen Hydrierung der Di- und Trichloressigsäure zu Monochloressigsäure auch die elektrochemische Enthalogenierung zur Verfügung (EP-B 0 241 685).Monochloroacetic acid and its derivatives are important intermediates in industrial organic synthesis. They are used for the production of adhesives, pesticides or pharmaceutical products.
The production of monochloroacetic acid by chlorinating acetic acid is always associated with the formation of di- and trichloroacetic acid. In addition to the catalytic hydrogenation of di- and trichloroacetic acid to monochloroacetic acid, electrochemical dehalogenation is also available for removing di- and trichloroacetic acid from the product mixture (EP-B 0 241 685).

Die letztgenannte Enthalogenierung wird unter Verwendung von Graphitkathoden in Gegenwart kleiner Mengen an Metallsalzen mit einer Wasserstoffüberspannung von mindestens 0,4 V (bei einer Stromdichte von 4000 A/m2) durchgeführt, und zwar bevorzugt in wasserhaltigen, sauren Elektrolyten.The latter dehalogenation is carried out using graphite cathodes in the presence of small amounts of metal salts with a hydrogen overvoltage of at least 0.4 V (at a current density of 4000 A / m 2 ), preferably in water-containing, acidic electrolytes.

Dieses Verfahren hat eine hohe Selektivität, da an der Kathode bei niedrigen Konzentrationen der teilweise zu enthalogenierenden Di- und Trichloressigsäure die thermodynamisch begünstigte Reduktion von Protonen zu Wasserstoff stattfindet. Auf diese Weise wird zwar eine unerwünschte Enthalogenierung der Monochloressigsäure vermieden, jedoch werden auch die Di- und die Trichloressigsäure nur noch mit schlechter Stromausbeute enthalogeniert. Für eine Enthalogenierung bis zu einem sehr niedrigen Konzentrationsniveau der Di- und Trichloressigsäure ist dieses Verfahren nicht geeignet, da ein immer größerer Anteil der elektrischen Ladung für die Reduktion von Protonen zu Wasserstoff verbraucht wird. Eine wirtschaftliche Durchführung der Enthalogenierung zu Monochloressigsäure bei einer niedrigen Konzentration der Di- und Trichloressigsäure ist daher bisher nur unzureichend möglich (Vergleichsbeispiel).This process has a high selectivity because the thermodynamically favored reduction of protons to hydrogen takes place at the cathode at low concentrations of the partially dehalogenated di- and trichloroacetic acid. In this way, undesired dehalogenation of the monochloroacetic acid is avoided, but the di- and trichloroacetic acid are also dehalogenated only with poor current efficiency. This method is not suitable for dehalogenation down to a very low concentration level of di- and trichloroacetic acid, since an increasing proportion of the electrical charge is used for the reduction of protons to hydrogen. An economical implementation of dehalogenation to monochloroacetic acid at a low concentration of di- and trichloroacetic acid has therefore only been insufficient to date (comparative example).

Es bestand somit die Aufgabe, Di- und Trichloressigsäure bei sehr weitgehendem Umsatz selektiv zu Monochloressigsäure - also nicht vollständig - zu enthalogenieren.The task was therefore to selectively dehalogenate di- and trichloroacetic acid with very extensive conversion to monochloroacetic acid, that is to say not completely.

Aus EP-A-0 280 120 ist nun bekannt, daß eine vollständige Entchlorierung von 3,3-Dichlor-2-fluoracryl- säure in Anwesenheit von protoniertem Dimethylanilin eintritt, insbesondere wenn die Entchlorierung diskontinuierlich durchgeführt wird.It is now known from EP-A-0 280 120 that complete dechlorination of 3,3-dichloro-2-fluoroacrylic acid occurs in the presence of protonated dimethylaniline, especially if the dechlorination is carried out batchwise.

Nekrasov et al. untersuchten die Enthalogenierung von Trichloressigsäure und Monochloressigsäure in Anwesenheit von Tetramethylammonium- oder Tetraethylammoniumsalz in einem nicht-protischen Elektrolyten (Nekrasov et al., Elektrokhimiya 1988, 24, 560-563). Die von ihnen beobachteten Effekte legen jedoch in keiner Weise nahe, daß in einem wäßrigen Elektrolyten Ammoniumsalze die oben erwähnte unerwünschte Reduktion von Protonen zu Wasserstoff hemmen könnten.Nekrasov et al. investigated the dehalogenation of trichloroacetic acid and monochloroacetic acid in the presence of tetramethylammonium or tetraethylammonium salt in a non-protic electrolyte (Nekrasov et al., Elektrokhimiya 1988, 24, 560-563). The effects they observed in no way suggest that ammonium salts in an aqueous electrolyte could inhibit the above-mentioned undesired reduction of protons to hydrogen.

Es wurde nun überraschenderweise gefunden, daß man Di- und Trichloressigsäure mit sehr weitgehendem Umsatz in geteilten Elektrolysezellen kontinuierlich oder diskontinuierlich zu Monochloressigsäure enthalogenieren kann, wenn man in wäßrigen Lösungen elektrolysiert, in denen neben Metallsalzen mit einer Wasserstoffüberspannung von mindestens 0,4 V (bei einer Stromdichte von 4000 A/m2) noch quartäre Ammonium- und/oder Phosphoniumsalze gelöst sind.It has now surprisingly been found that di- and trichloroacetic acid can be dehalogenated continuously or discontinuously to form monochloroacetic acid with very extensive conversion in divided electrolysis cells if electrolysis is carried out in aqueous solutions in which, in addition to metal salts, a hydrogen overvoltage of at least 0.4 V (at a Current density of 4000 A / m 2 ) quaternary ammonium and / or phosphonium salts are still dissolved.

Ein Gegenstand der Erfindung ist daher ein Verfahren zur teilweisen Enthalogenierung von Tri- und Dichloressigsäure zu Monochloressigsäure durch Elektrolyse wäßriger Lösungen dieser Säuren in geteilten Zellen in Anwesenheit eines oder mehrerer Metallsalze mit einer Wasserstoffüberspannung von mindestens 0,4 V (bei einer Stromdichte von 4000 A/m2) unter Verwendung von Kohlenstoffkathoden, gekennzeichnet durch Zusatz von mindestens einer Verbindung ausgewählt aus der Gruppe der Verbindungen der Formel I bis V,

Figure imgb0001
Figure imgb0002
Figure imgb0003
Figure imgb0004
Figure imgb0005
worin bedeuten:

  • X Stickstoff oder Phosphor,
  • R1 bis R21, gleich oder verschieden unabhängig voneinander, Wasserstoff, geradkettiges oder verzweigtes C1-C18-Alkyl, C3-C18-Cycloalkyl oder C1-C18-Alkyl-Aryl, wobei der Arylrest 6 bis 12 Kohlenstoffatome hat, und die Reste R2 bis R16 außerdem noch unabhängig voneinander folgende Bedeutung haben können:
  • R2 eine Gruppe der Formel -((CH2)n-O)m-R, wobei für R dieselben Reste infrage kommen wie für R1, aber R1 und R unabhängig voneinander sind, wobei n eine ganze Zahl von 1 bis 12 und ebenso m eine ganze Zahl von 1 bis 12 ist,
  • R3 und R4 zusammen, R5 und R6 zusammen und/oder R7 und R8 zusammen unabhängig voneinander eine Kette von 2 bis 8 CH2-Gruppen oder eine Gruppe der Formel -CH2(Z)CH2-mit Z = Stickstoff, Sauerstoff, Schwefel,
  • R12 und R13 zusammen, R13 und R14 zusammen, R14 und R15 zusammen und/oder R15 und R16 zusammen unabhängig voneinander eine Gruppe der Formel
    Figure imgb0006
  • Y eine Gruppe der Formel -(CH2)p- oder -CH2-[O-(CH2)p]q-O-(CH2)2-, wobei p eine ganze Zahl von 1 bis 12 und q eine ganze Zahl von 0 bis 6 ist und
  • A- eines der Anionen OH-, F-, CI-, Br-, J-, S04 2-, HS04-, NO3-, CH3C00-, BF4- oder CH3OSO3-.
The invention therefore relates to a process for the partial dehalogenation of tri- and dichloroacetic acid to monochloroacetic acid by electrolysis of aqueous solutions of these acids in divided cells in the presence of one or more metal salts with a hydrogen overvoltage of at least 0.4 V (at a current density of 4000 A / m 2 ) using carbon cathodes, characterized by the addition of at least one compound selected from the group of the compounds of the formula I to V,
Figure imgb0001
Figure imgb0002
Figure imgb0003
Figure imgb0004
Figure imgb0005
 in which mean:
  • X nitrogen or phosphorus,
  • R 1 to R 21 , identical or different independently of one another, are hydrogen, straight-chain or branched C 1 -C 18 alkyl, C 3 -C 18 cycloalkyl or C 1 -C 18 alkyl aryl, the aryl radical having 6 to 12 carbon atoms and the radicals R 2 to R 16 can also independently of one another have the following meanings:
  • R 2 is a group of the formula - ((CH 2 ) n -O) m -R, where R is the same radical as R 1 , but R 1 and R are independent of one another, where n is an integer from 1 to 12 and likewise m is an integer from 1 to 12,
  • R 3 and R 4 together, R 5 and R 6 together and / or R 7 and R 8 together independently of one another are a chain of 2 to 8 CH 2 groups or a group of the formula -CH 2 (Z) CH 2 -with Z = Nitrogen, oxygen, sulfur,
  • R 12 and R 13 together, R 13 and R 14 together, R 14 and R 15 together and / or R 15 and R 16 together independently of one another are a group of the formula
    Figure imgb0006
  • Y is a group of the formula - (CH 2 ) p- or -CH 2 - [O- (CH 2 ) p] qO- (CH 2 ) 2 -, where p is an integer from 1 to 12 and q is an integer from Is 0 to 6 and
  • A- one of the anions OH-, F-, CI-, Br-, J-, S0 4 2 -, HS0 4 -, NO 3 -, CH 3 C00-, BF 4 - or CH 3 OSO 3 -.

Ein weiterer Gegenstand ist eine Elektrolyselösung zur teilweisen Enthalogenierung von Tri- und/oder Dichloressigsäure, welche mindestens eine dieser beiden Säuren, ein oder mehrere Metallsalze mit einer Wasserstoffüberspannung von mindestens 0,4 V (bei einer Stromdichte von mindestens 4000 A/m2) und noch mindestens eine Verbindung ausgewählt aus der Gruppe der Verbindungen der Formel I bis V enthält.Another object is an electrolysis solution for the partial dehalogenation of tri- and / or dichloroacetic acid, which contains at least one of these two acids, one or more metal salts with a hydrogen overvoltage of at least 0.4 V (at a current density of at least 4000 A / m 2 ) contains at least one compound selected from the group of compounds of the formula I to V.

Bevorzugt sind, Verbindungen der Formel I, bei denen unabhängig voneinander

  • R1 bis R4 = Wasserstoff oder C1-C16-Alkyl ist,
    sowie Verbindungen der Formel III, bei denen
  • R11 = C4-C16-Alkyl und
  • R12 bis R16 unabhängig voneinander = H oder C4-C16-Alkyl ist.
Preferred compounds of the formula I are those in which they are independent of one another
  • R 1 to R 4 = hydrogen or C 1 -C 16 alkyl,
    and compounds of the formula III in which
  • R 11 = C 4 -C 16 alkyl and
  • R 12 to R 16 independently of one another = H or C 4 -C 16 alkyl.

Ferner sind Verbindungen der Formel II bevorzugt, bei denen unabhängig voneinander

  • R5 bis R10 = C4-C6-Alkyl, Cyclohexyl oder geradkettiges und geradzahliges C8-C16-Alkyl ist.
Compounds of the formula II are further preferred, in which independently of one another
  • R 5 to R 10 = C 4 -C 6 alkyl, cyclohexyl or straight-chain and even-numbered C 8 -C 16 alkyl.

Besonders bevorzugt sind

  • A) Verbindungen der Formel I, bei denen X = Stickstoff oder Phosphor, R1 = C1-C3-Alkyl und unabhängig voneinander R2 bis R4 = C1-C4-Alkyl ist,
  • B) Verbindungen der Formel III, bei denen R11 = C8-C16-Alkyl und R12 bis R16 = H ist

Beim erfindungsgemäßen Verfahren wird mindestens eine Verbindung der Formel I oder II oder III oder IV oder V oder es werden beliebige Gemische von Verbindungen der Formeln I, II, III, IV und V in der Elektrolyse eingesetzt.Are particularly preferred
  • A) compounds of the formula I in which X = nitrogen or phosphorus, R 1 = C 1 -C 3 -alkyl and independently of one another R 2 to R 4 = C 1 -C 4 -alkyl,
  • B) Compounds of the formula III in which R 11 = C 8 -C 16 alkyl and R 12 to R 16 = H

In the process according to the invention, at least one compound of the formula I or II or III or IV or V or any mixtures of compounds of the formulas I, II, III, IV and V are used in the electrolysis.

Die Verbindungen der Formeln I bis V werden in Konzentrationen von 1 bis 5000 ppm, vorzugsweise 10 bis 1000 ppm insbesondere aber 50 bis 500 ppm verwendet.The compounds of the formulas I to V are used in concentrations of 1 to 5000 ppm, preferably 10 to 1000 ppm, but in particular 50 to 500 ppm.

Als Metallsalze mit einer Wasserstoffüberspannung von mindestens 0,4 V (bei einer Stromdichte von 4000 A/m2) werden im allgemeinen die löslichen Salze von Cu, Zn, Cd, Hg, Sn, Pb, Ti, Bi, V, Ta und/oder Ni, vorzugsweise die löslichen Salze von Cu, Zn, Cd, Sn, Hg und Pb eingesetzt. Als Anionen werden vorzugsweise CI-, Br-, SO4 2-, NO3- oder CH3COO- verwendet, wobei das Anion so gewählt wird, daß ein lösliches Metallsalz entsteht (z.B. PbN03).The metal salts with a hydrogen overvoltage of at least 0.4 V (at a current density of 4000 A / m 2 ) are generally the soluble salts of Cu, Zn, Cd, Hg, Sn, Pb, Ti, Bi, V, Ta and / or Ni, preferably the soluble salts of Cu, Zn, Cd, Sn, Hg and Pb. CI-, Br-, SO 4 2- , NO 3 - or CH 3 COO- are preferably used as anions, the anion being chosen so that a soluble metal salt is formed (for example PbN0 3 ).

Die Salze können der Elektrolyselösung direkt zugesetzt werden oder auch z.B. durch Zugabe von Oxiden oder Carbonaten - oder durch Zugabe der Metalle selbst, wie bei Zn, Cd, Sn, Pb, Ni - in der Lösung erzeugt werden.The salts can be added directly to the electrolysis solution or, e.g. by adding oxides or carbonates - or by adding the metals themselves, such as Zn, Cd, Sn, Pb, Ni - in the solution.

Die Salzkonzentration im Katholyten wird zweckmäßig auf etwa 0,1 bis 5000 ppm, vorzugsweise auf etwa 10 bis 1000 ppm, eingestellt.The salt concentration in the catholyte is expediently set to about 0.1 to 5000 ppm, preferably to about 10 to 1000 ppm.

Beim erfindungsgemäßen Verfahren tritt im allgemeinen eine außerordentlich geringe Wasserstoffentwicklung an der Kathode auch bei sehr niedrigen Konzentrationen der mehrfach chlorierten Essigsäuren ein, ohne daß sich bei Dauerbetrieb die hohe Selektivität der Elektrolyse verschlechtert. Das erfindungsgemäße Verfahren ist daher außerordentlich wirtschaftlich, was nach dem Stand der Technik in keiner Weise zu erwarten war. Auch eine kontinuierliche Verfahrensweise bei niedrigen Konzentrationen der Ausgangsverbindungen führt nur in sehr geringem Umfang zu Essigsäure.In the process according to the invention, there is generally an extremely low evolution of hydrogen at the cathode, even at very low concentrations of the multiply chlorinated acetic acids, without the high selectivity of the electrolysis deteriorating during continuous operation. The process of the invention is therefore extremely economical, which was not to be expected in any way from the prior art. Even a continuous procedure with low concentrations of the starting compounds leads to acetic acid only to a very small extent.

Als Ausgangsmaterial für das Verfahren werden Di- und/oder Trichloressigsäure oder deren bei der Essigsäurechlorierung zwangsläufig entstehenden Mischungen mit Monochloressigsäure verwendet.The starting material for the process is di- and / or trichloroacetic acid or mixtures thereof with monochloroacetic acid which are inevitably formed in the acetic acid chlorination.

Im allgemeinen können, insbesondere als Katholyt, wäßrige Lösungen der chlorierten Essigsäuren in allen möglichen Konzentrationen (ca. 1 bis ca. 95 Gew.-%) verwendet werden.In general, especially as a catholyte, aqueous solutions of chlorinated acetic acids in all possible concentrations (approx. 1 to approx. 95% by weight) can be used.

Besonders vorteilhaft ist es, wenn der Gewichtsanteil der Di- und Trichloressigsäure an der Gesamtmenge der chlorierten Essigsäuren kleiner als 10 Gew.-% ist. Dabei kann dieser Gewichtsanteil ohne weiteres kleiner als 5 Gew.-%, oder sogar kleiner als 2 Gew.-% sein, was besonders überraschend war.
Der Katholyt kann zusätzlich noch Mineralsäuren (z.B. HCI,H2S04 etc.) enthalten.It is particularly advantageous if the proportion by weight of di- and trichloroacetic acid in the total amount of chlorinated acetic acids is less than 10% by weight. This proportion by weight can easily be less than 5% by weight, or even less than 2% by weight, which was particularly surprising.
The catholyte can also contain mineral acids (eg HCl, H 2 S0 4 etc.).

Der Anolyt ist vorzugsweise eine wäßrige Mineralsäure, insbesondere eine wäßrige Salzsäure oder Schwefelsäure.The anolyte is preferably an aqueous mineral acid, in particular an aqueous hydrochloric acid or sulfuric acid.

Als Kohlenstoffkathoden kommen im Prinzip alle üblichen Kohle-Elektrodenmaterialien in Frage wie z.B. Elektrodengraphite, imprägnierte Graphitwerkstoffe oder auch glasartiger Kohlenstoff.In principle, all common carbon electrode materials, such as e.g. Electrode graphites, impregnated graphite materials or glassy carbon.

Als Anodenmaterial kann im allgemeinen das gleiche Material wie für die Kathode verwendet werden. Darüberhinaus ist auch der Einsatz anderer üblicher Elektrodenmaterialien möglich, die jedoch unter den Elektrolysebedingungen inert sein müssen, beispielsweise Titan, beschichtet mit Titandioxid und dotiert mit einem Edelmetalloxid, wie z.B. Rutheniumdioxid.The same material as that for the cathode can generally be used as the anode material. In addition, it is also possible to use other customary electrode materials which, however, must be inert under the electrolysis conditions, for example titanium, coated with titanium dioxide and doped with a noble metal oxide, such as e.g. Ruthenium dioxide.

Zur Teilung der Zellen in Anoden- und Kathodenraum werden im allgemeinen Kationenaustauschermembranen aus perfluorierten Polymeren mit Carboxyl- und /oder Sulfonsäuregruppen benutzt. Auch die Verwendung von im Elektrolyten stabilen Anionenaustauschermembranen, Diaphragmen aus Polymeren oder anorganischen Werkstoffen ist im allgemeinen möglich.
Die Elektrolysetemperatur soll im allgemeinen unter 100 °C liegen, vorzugsweise zwischen 10 und 90 °C.Cation exchange membranes made of perfluorinated polymers with carboxyl and / or sulfonic acid groups are generally used to divide the cells into the anode and cathode compartments. It is also generally possible to use anion exchange membranes which are stable in the electrolyte, diaphragms made of polymers or inorganic materials.
The electrolysis temperature should generally be below 100 ° C, preferably between 10 and 90 ° C.

Die Elektrolyse kann sowohl kontinuierlich als auch diskontinuierlich durchgeführt werden. Bevorzugt ist ein kontinuierliches Verfahren vor allem bei niedriger Konzentration der Di- und Trichloressigsäure.The electrolysis can be carried out either continuously or batchwise. A continuous process is preferred, especially at a low concentration of di- and trichloroacetic acid.

Wird als Anolyt wäßrige Salzsäure verwendet, dann wird durch die anodische Chlorentwicklung ständig Chlorid verbraucht. Im allgemeinen wird dann der Chloridverbrauch durch kontinuierliches Einleiten von gasförmigem HCI oder von wäßriger Salzsäure ausgeglichen.If aqueous hydrochloric acid is used as the anolyte, then chloride is constantly consumed due to the anodic chlorine evolution. In general, the chloride consumption is then compensated for by continuously introducing gaseous HCl or aqueous hydrochloric acid.

Die Aufarbeitung des Elektrolyseproduktes erfolgt auf bekannte Weise, z.B. durch Destillation. Die Metallsalze und die quartären Ammonium- und Phosphoniumverbindungen bleiben dabei im Rückstand und können wieder in den Prozeß zurückgeführt werden.The electrolysis product is worked up in a known manner, e.g. by distillation. The metal salts and the quaternary ammonium and phosphonium compounds remain in the residue and can be returned to the process.

Die Erfindung wird nun durch die folgenden Beispiele näher erläutert. Nach den Beispielen 1-9 folgt noch ein Vergleichsbeispiel. Aus dem Vergleichsbeispiel geht hervor, daß unter den Elektrolysebedingungen des EP-B 0 241 685 bereits beim Erreichen einer Dichloressigsäure-Konzentrationen von 31 % (bezogen auf die Gesamtmenge der gelösten Essigsäuren) der Hauptanteil der elektrischen Ladung für die Reduktion von Protonen zu Wasserstoff verbraucht wird.The invention is illustrated by the following examples. Examples 1-9 are followed by a comparative example. The comparative example shows that under the electrolysis conditions of EP-B 0 241 685, when a dichloroacetic acid concentration of 31% (based on the total amount of dissolved acetic acids) is reached, the major part of the electrical charge is used for the reduction of protons to hydrogen .

Beispiele 1 bis 8Examples 1 to 8 ElektrolysebedingungenElectrolysis conditions

Umlaufzelle mit 0,0015 m2 Elektrodenfläche;

  • Elektrodenabstand 5 mm
  • Elektroden: imprägnierter Graphit ODiabon (der Fa. Sigri, Meitingen, Deutschland)
  • Kationenaustauschermembran: ONafion 324 (der Fa. DuPont, Wilmington, Del., USA, 2-Schichtenmembran aus Copolymerisaten aus Perfluorsulfonylethoxyvinylether und Tetrafluorethylen. Auf der Kathodenseite befindet sich eine Schicht mit dem Äquivalentgewicht 1300, auf der Anodenseite eine solche mit dem Äquivalentgewicht 1100)
  • Abstandshalter: Polyethylennetze
  • Durchfluß: 100 I/h
  • Temp.: 30 - 42 °C
  • Anolyt: konzentrierte Salzsäure, kontinuierlich ergänzt durch gasförmiges HCI
  • Katholyt: 800 g Wasser, 350 g Monochloressigsäure, 7 g Dichloressigsäure (im Beispiel 2 Trichloressigsäure). Die Di- bzw. Trichloressigsäure wird dem Katholyten in gleichbleibenden Mengen, bis zum Erreichen der in der Tabelle angegebenen Menge, im Abstand von ca. 10 Minuten zugeführt. Die Konzentrationen des Metallsalzes und der jeweils eingesetzten Verbindung der Formel 1 bzw. III sind aus der Tabelle ersichtlich.
Circulation cell with 0.0015 m 2 electrode area;
  • Distance between electrodes 5 mm
  • Electrodes: impregnated graphite ODiabon (from Sigri, Meitingen, Germany)
  • Cation exchange membrane: ONafion 324 (from DuPont, Wilmington, Del., USA, 2-layer membrane made from copolymers of perfluorosulfonylethoxy vinyl ether and tetrafluoroethylene. On the cathode side there is a layer with the equivalent weight 1300, on the anode side one with the equivalent weight 1100).
  • Spacers: polyethylene nets
  • Flow: 100 l / h
  • Temp .: 30 - 42 ° C
  • Anolyte: concentrated hydrochloric acid, continuously supplemented by gaseous HCI
  • Catholyte: 800 g water, 350 g monochloroacetic acid, 7 g dichloroacetic acid (in the example 2 trichloroacetic acid). The di- or trichloroacetic acid is fed to the catholyte in constant amounts until the amount specified in the table is reached at intervals of about 10 minutes. The concentrations of the metal salt and the compound of formula 1 or III used in each case can be seen from the table.

Beispiel 9Example 9

Wie Elektrolysezelle 1, aber mit folgenden Änderungen: Elektrodenfläche: 0,02 m2

  • Kationenaustauschermembran: ONafion 423 (Fa. DuPont, 1-Schichtenmembran aus Copolymerisaten aus Perfluorsulfonylethoxyvinylether und Tetrafluorethylen mit einem Äquivalentgewicht von 1200)
  • Durchfluß: 400 I/h
  • Katholyt: 2400 g Wasser, 1050 g Monochloressigsäure, 60 g Dichloressigsäure. Die Konzentrationen des Metallsalzes und der Verbindung der Formel 1 sind aus der Tabelle ersichtlich.
Like electrolysis cell 1, but with the following changes: Electrode area: 0.02 m 2
  • Cation exchange membrane: ONafion 423 (DuPont, 1-layer membrane made from copolymers of perfluorosulfonylethoxy vinyl ether and tetrafluoroethylene with an equivalent weight of 1200)
  • Flow: 400 l / h
  • Catholyte: 2400 g water, 1050 g monochloroacetic acid, 60 g dichloroacetic acid. The concentrations of the metal salt and the compound of formula 1 can be seen from the table.

VergleichsbeispielComparative example

Elektrolyse nach EP-B 0 241 685

  • Elektrolysebedingungen wie bei den Beispielen 1 bis 8 mit Ausnahme von:
    • Katholyt: 2 kg Wasser, 0,4 kg Dichloressigsäure, 532 ppm CdC12
    • Stromdichte: 4000 A/m2
    • Zellspannung: 4,5 V
    • Ladungsverbrauch. 145 Ah
    • Elektrolyseergebnis:
    • Dichloressigsäure:0,1 kg (= 31,1 Gew.-%)
    • Monochloressigsäure: 0,221 kg (= 68,9 Gew.-%)
  • Während der Elektrolyse wurden 36 % der Ladungsmenge für die Reduktion von Protonen zu Wasserstoff verbraucht. Die Wirtschaftlichkeit des erfindungsgemäßen Verfahrens wird bei Gegenüberstellung des Vergleichsbeispiels und Beispiel 6 besonders deutlich. Im Beispiel 6 beträgt der Anteil der elektrischen Ladung, die für die Reduktion von Protonen zu Wasserstoff verbraucht wird, bei einem Dichloressigsäureanteil von 1 Gew.-% nur 2,1 %.
    Figure imgb0007
    Figure imgb0008
Electrolysis according to EP-B 0 241 685
  • Electrolysis conditions as in Examples 1 to 8 with the exception of:
    • Catholyte: 2 kg water, 0.4 kg dichloroacetic acid, 532 ppm CdC1 2
    • Current density: 4000 A / m 2
    • Cell voltage: 4.5 V
    • Charge consumption. 145 Ah
    • Electrolysis result:
    • Dichloroacetic acid: 0.1 kg (= 31.1% by weight)
    • Monochloroacetic acid: 0.221 kg (= 68.9% by weight)
  • During electrolysis, 36% of the charge was used to reduce protons to hydrogen. The economy of the method according to the invention is particularly clear when comparing the comparative example and example 6. In example 6, the proportion of electrical Charge that is used for the reduction of protons to hydrogen with a dichloroacetic acid content of 1% by weight is only 2.1%.
    Figure imgb0007
    Figure imgb0008

Claims (22)

1. A process for the partial dehalogenation of trichloroacetic and dichloroacetic acid to give monochloroacetic acid by the electrolysis of aqueous solutions of these acids in divided cells in the presence of one or more metal salts having a hydrogen overvoltage of at least 0.4 V (at a current density of 4000 A/m2), using carbon cathodes, which comprises adding at least one compound selected from the group consisting of compounds of the formula I to V
Figure imgb0027
Figure imgb0028
Figure imgb0029
Figure imgb0030
Figure imgb0031
in which
X is nitrogen or phosphorus,
R1 to R21 are identical or different and independently of one another are hydrogen, linear or branched C1-C18-alkyl, C3-C18-cycloalkyl or C1-C18-alkylaryl, the aryl radical having 6 to 12 carbon atoms and the radicals R2 to R16 being able, in addition, independently of one another to have the following meaning:
R2 is a group of the formula -((CH2)n-O)m-R in which the same radicals are suitable for R as for R1, but R1 and R are independent of one another, n being an integer from 1 to 12 and m being also an integer from 1 to 12,
R3 and R4 together, R5 and R6 together and/or R7 and R8 together are, independently of one another, a chain of 2 to 8 CH2 groups or a group of the formula -CH2(Z)CH2- in which Z is nitrogen, oxygen or sulfur,
R12 and R13 together, R13 and R14 together, R14 and R15 together and/or R15 and R16 together are, independently of one another, a group of the formula
Figure imgb0032
Y is a group of the formula -(CH2)p- or -CH2-[O-(CH2)p]q-O-(CH2)2- in which p is an integer from 1 to 12 and q is an integer from 0 to 6, and
A- is one of the anions OH-, F-, CI-, Br-, I-, SO4 2-, HSO4-, NO3-, CH3COO-, BF4-or CH3OSO3-.
2. The process as claimed in claim 1, which comprises adding at least one compound of the formula I.
3. The process as claimed in claim 1, which comprises adding at least one compound of the formula II.
4. The process as claimed in claim 1, which comprises adding at least one compound of the formula III.
5. The process as claimed in claim 1, which comprises adding at least one compound of the formula IV.
6. The process as claimed in claim 1, which comprises adding at least one compound of the formula V.
7. The process as claimed in one of claims 1 and 2, wherein, in formula I, R1 to R4 independently of one another are hydrogen or C1-C16-alkyl.
8. The process as claimed in one of claims 1 and 2, wherein, in formula I, X is nitrogen or phosphorus, R1 is C1-C3-alkyl and R2 to R4 independently of one another are C1-C4-alkyl.
9. The process as claimed in one of claims 1 and 3, wherein, in formula II, R5 to R10 independently of one another are linear or branched C4-C6-alkyl, cyclohexyl or linear and even-numbered C8-C16-alkyl.
10. The process as claimed in one of claims 1 and 4, wherein, in formula III, R11 is C4-C16-alkyl and R12 to R16 independently of one another are H or C4-C16-alkyl.
11. The process as claimed in one of claims 1 and 4, wherein, in formula III, R11 is C8-C16-alkyl and R12 to R 16 are H.
12. The process as claimed in at least one of claims 1 to 11, wherein the compounds of the formulae I-V are employed in concentrations of 1 to 5000 ppm.
13. The process as claimed in at least one of claims 1 to 11, wherein the compounds of the formulae I-V are employed in concentrations of 10 to 1000 ppm.
14. The process as claimed in at least one of claims 1 to 11, wherein the compounds of the formulae I-V are employed in concentrations of 50 to 500 ppm.
15. The process as claimed in at least one of claims 1 to 14, wherein the soluble salts of Cu, Zn, Cd, Hg, Sn, Pb, Ti, Bi, V, Ta and/or Ni are used as the metal salts having a hydrogen overvoltage of at least 0.4 V (at a current density of at least 4000 A/m2).
16. The process as claimed in at least one of claims 1 to 14, wherein the soluble salts of Cu, Zn, Cd, Sn, Hg and Pb are used as the metal salts having a hydrogen overvoltage of at least 0.4 V (at a current density of at least 4000 A/m2).
17. The process as claimed in at least one of claims 1 to 16, wherein the concentration of the metal salts is 0.1 to 5000 ppm.
18. The process as claimed in at least one of claims 1 to 16, wherein the concentration of the metal salts in the electrolysis solution is 10 to 1000 ppm.
19. The process as claimed in at least one of claims 1 to 18, wherein the electrolysis is carried out continuously.
20. An electrolysis solution for the partial dehalogenation of trichloroacetic and/or dichloroacetic acid, which contains at least one of the two acids, one or more metal salts having a hydrogen overvoltage of at least 0.4 V (at a current density of at least 4000 A/m2) and also at least one compound selected from the group consisting of the compounds of the formula I to V
Figure imgb0033
Figure imgb0034
Figure imgb0035
Figure imgb0036
Figure imgb0037
in which:
X is nitrogen or phosphorus,
R1 to R21 are identical or different and independently of one another are hydrogen, linear or branched C1-C18-alkyl, C3-C18-cycloalkyl or C1-C18-alkylaryl, the aryl radical having 6 to 12 carbon atoms and the radicals R2 to R16 being able, in addition, independently of one another to have the following meaning:
R2 is a group of the formula -((CH2)n-O)m-R in which the same radicals are suitable for R as for R1, but R1 and R are independent of one another, n being an integer from 1 to 12 and m being also an integer from 1 to 12,
R3 and R4 together, R5 and R6 together and/or R7 and R8 together are, independently of one another, a chain of 2 to 8 CH2 groups or a group of the formula -CH2(Z)CH2- in which Z is nitrogen, oxygen or sulfur,
R12 and R13 together, R13 and R14 together, R14 and R15 together and/or R15 and R16 together are a group of the formula
Figure imgb0038
Y is a group of the formula -(CH2)p- or -CH2-[O-(CH2)p]q-O-(CH2)2- in which p is an integer from 1 to 12 and q is an integer from 0 to 6, and
A- is one of the anions OH-, F-, CI-, Br-, I-, S04 2-, HSO4-, NOa-, CHaC00-, BF4-or CHaOSOa-.
21. An electrolysis solution as claimed in claim 20, in which the soluble salts of Cu, Zn, Cd, Hg, Sn, Pb, Ti, Bi, V, Ta and/or Ni are employed as the metal salts having a hydrogen overvoltage of at least 0.4 V (at a current density of at least 4000 A/m2).
22. An electrolysis solution as claimed in at least one of claims 20 to 21, in which the compounds of the formulae I-V are employed in a concentration of 1 to 5000 ppm.
EP91107944A 1990-05-18 1991-05-16 Process for partial electrolyte dehalogenation dichloro- and trichloro-acetic acids and electrolysis solution Expired - Lifetime EP0457320B1 (en)

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