RU2375500C2 - Method of producing hydrogen peroxide and chlorate - Google Patents

Abstract

FIELD: chemistry. ^ SUBSTANCE: invention relates to a method of producing chlorate of alkali metal, involving: provision for an electrochemical cell, which has an anode and a cathode in separate anode and cathode chambers; bringing the cathode into contact with electrolyte, containing at least one organic mediator and one or more organic or inorganic acids; reacting the organic mediator on the cathode with formation of at least one reduced form of this mediator; reacting said at least one reduced form of mediator with oxygen with formation of hydrogen peroxide; bringing the anode into contact with the anolyte, which contains chloride of alkali metal; reacting chloride on the anode with formation of chlorine, which is hydrolysed; and reacting the hydrolysed chlorine with formation of chlorate. ^ EFFECT: increased efficiency of producing chlorate of alkali metal. ^ 19 cl, 4 dwg, 1 ex

Description

The present invention relates to a method for the production of alkali metal chlorate in a diaphragm electrochemical cell.

Alkali metal chlorate and especially sodium chlorate is an important chemical reagent, especially in the pulp and paper industry as a raw material for the production of chlorine dioxide, which is widely used in bleaching. Traditionally, alkali metal chlorate is produced by electrolysis of alkali metal chlorides in open diaphragm-free electrolytic cells equipped with hydrogen evolution cathodes. The general chemical reaction taking place in such cells is as follows:

MCl + 3H ₂ O → MClO ₃ + 3H ₂ ,

where M is an alkali metal.

This method is very effective, although hydrogen gas released at the cathode creates some overvoltage, which increases energy consumption.

Hydrogen peroxide is also widely used in the pulp and paper industry and is usually produced by the anthraquinone method with alternating hydrogenation and oxidation of anthraquinones and / or tetrahydroantraquinones in a working solution. This method, although it is very effective, is difficult to operate and requires a variety of equipment. To date, no alternative competitive methods have been proposed, except in very special cases.

WO 2004/005583 describes the production of an alkali metal chlorate in an electrolytic cell divided by a cation-selective separator into an anode chamber in which an anode is located and a cathode chamber in which a gas diffusion electrode is located. Oxygen is supplied to the cathode chamber and subjected to electrolysis to form an alkali metal hydroxide.

The electrochemical production of an alkaline hydrogen peroxide solution by reducing oxygen at the cathode is described, for example, in US 6322690.

The electrochemical production of an alkaline solution of hydrogen peroxide by reducing oxygen at the cathode while producing sodium chlorate is described in E.E. Kalu and C. Oloman, Simultaneous Electrosynthesis of Alkaline Hydrogen Peroxide and Sodium Chlorate, Simultaneous Electrosynthesis of Alkaline Hydrogen Peroxide and Sodium Chlorate, Journal of Applied Electrochemistry, 20 (1990), 932-940.

E.L. Gyenge and C.W. Oloman in “Electrosynthesis of hydrogen peroxide in acidic solutions by mediated oxygen”, Part I: The structure of the emulsion, the kinetics of electrode processes and periodic electrolysis reduction in a three-phase (aqueous / organic / gaseous) system Part I: Emulsion structure, electrode kinetics and batch electrolysis "), Journal of Applied Electrochemistry, (2003), 33 (8), 655-663; and “Electrosynthesis of hydrogen peroxide in acidic solutions by mediated oxygen” and “Electrosynthesis of hydrogen peroxide in acidic solutions by mediated oxygen”. reduction in a three-phase (aqueous / organic / gaseous) system. Part II: Experiments in flow-by fixed-bed electrochemical cells with three-phase flow "), Journal of Applied Electrochemistry, (2003), 33 (8), 665-674, describe the production of hydrogen peroxide by electrolytic reduction of 2-ethyl-9,10-anthraquinone to the corresponding anthrahydroquinone dissolved in an organic phase emulsified in water. This anthrahydroquinone is reacted with gaseous oxygen to produce hydrogen peroxide.

JP 61-284591 and US 4067787 describe the production of hydrogen peroxide by reducing a water-soluble derivative of anthraquinone in an aqueous solution, followed by reaction with oxygen.

A. Huissoud and P. Tissot in "Electrochemical reduction of 2-ethyl-9,10-anthraquinone on reticulated vitreous carbon and mediated formation of hydrogen peroxide "), Journal of Applied Electrochemistry (1998), 28 (6), 653-657, describe the electrochemical reduction of 2-ethyl-9,10-anthraquinone in dimethoxyethane containing 5% water and 0.1 mol / liter of tetrafluoroborate tetraethylammonium.

Electrochemical oxygen reduction on a carbon cathode with grafted anthraquinone is described, for example, in WO 02/02846, Mirkhalaf, Fakhradin; Tammeveski, Kaido; Schiffrin, David J., “Substituent effects on the electrocatalytic reduction of oxygen on quinone-modified glassy carbon electrodes”, Phys. Chem. Chem. Phys. (2004), 6 (6), 1321-1327; and Vaik, Katri; Schiffrin, David J .; Tammeveski, Kaido, "Electrochemical reduction of oxygen on anodically pre-treated and chemically grafted glassy carbon electrodes in alkaline solutions", Electrochemistry Communications (2004), 6 (1), 1-5.

Vaik, Katri; Sarapuu, Ave; Tammeveski, Kaido; Mirkhalaf, Fakhradin; Schiffrin, David J., Oxygen reduction on phenanthrenequinone-modified glassy carbon electrodes in 0.1 M KOH, Journal of Electroanalytical Chemistry (2004), 564 ( 1-2), 159-166, describe the use of a cathode with a grafted phenanthrene quinone.

WO 03/004727 describes the electrosynthesis of organic compounds by electrochemical conversion of a compound in the presence of an electrolyte containing an ionic liquid at room temperature and recovering the product.

The objective of the invention is to provide an effective method for the production of alkali metal chlorate.

Another objective of the invention is the provision of a method that enables the simultaneous production of alkali metal chlorate and hydrogen peroxide.

The invention relates to a method for the production of alkali metal chlorate, including:

providing an electrochemical cell containing the anode and cathode in separate anode and cathode chambers;

contacting the cathode with a catholyte containing at least one organic mediator and one or more organic or inorganic acids;

reacting the organic mediator at the cathode with the formation of at least one reduced form of this mediator;

reacting said at least one reduced form of a mediator with oxygen to form hydrogen peroxide;

contacting the anode with an anolyte containing alkali metal chloride;

the reaction of chloride at the anode with the formation of chlorine, which is hydrolyzed; and

the reaction of hydrolyzed chlorine with the formation of chlorate.

Preferably, hydrogen peroxide is separated from catholyte as a product or used as a reagent for the production of other chemicals without isolation from the electrolyte. However, if hydrogen peroxide is not needed at this production site, it can also be simply destroyed, for example, by catalytic decomposition.

The anolyte can have a concentration of chloride ions up to saturation, preferably from about 30 to about 300 g / l, more preferably from about 50 to about 250 g / l, most preferably from about 80 to about 200 g / l, based on chloride sodium. Typically, the anolyte also contains at least some chlorate, preferably from about 1 to about 1200 g / l, based on sodium chlorate. In one embodiment, its preferred content is from about 300 to about 650 g / l, most preferably from about 500 to about 650 g / l, based on sodium chlorate. In another embodiment, its preferred content is from about 1 to about 50 g / l, most preferably from about 1 to about 30 g / l, based on sodium chlorate.

To stimulate the hydrolysis of chlorine, the pH in the volume of the anolyte is preferably at least about 4, most preferably from about 4 to about 10. It should be understood that there may be local deviations in pH and, in particular, local zones with significantly more low pH, as protons are formed.

To suppress undesirable side reactions, it is possible to introduce chromate, an alkali metal dichromate, or other suitable pH buffer into the anolyte. If chromate or dichromate is present in the anolyte, its content is preferably from about 0.01 to about 10 g / l, most preferably from about 0.01 to about 6 g / l, based on sodium chromate. However, it is also possible to work essentially in the absence of chromate in the anolyte.

Unless otherwise indicated, all concentrations in g / l are given relative to the volume of the real solution.

The temperature of the anolyte is preferably from about 20 to about 100 ° C., Most preferably from about 40 to about 90 ° C.

Accordingly, most of the chlorine formed in the anode chamber dissolves in the anolyte solution. Dissolved chlorine spontaneously undergoes partial hydrolysis with the formation of hypochlorous acid in accordance with the equation

Cl ₂ + H ₂ O → HClO + HCl

Hypochlorous acid undergoes a disproportionation (in some literature referred to as “autooxidation”) to chlorate in accordance with the general equation

2HClO + ClO ^- → ClO ₃ ^- + 2Cl ^- + 2H ⁺

Disproportionation can take place in a given cell, in a separate chlorate reactor, or both.

Preferably, the anolyte from the anode chamber, also referred to as “chlorate electrolyte” and usually containing chlorine and / or hypochlorous acid, is fed to a chlorate reactor for disproportionation reactions to produce chlorate. The chlorate reactor may be of the usual type, for example as described in US 5,419,818, and may include one or more chlorate vessels.

When the disproportionation is sufficiently completed, the chlorate electrolyte can be fed to the crystallizer to precipitate and recover solid alkali metal chlorate. The mother liquor from the crystallizer, usually containing unreacted chloride ions, hypochlorite and chlorate, is then preferably recycled to the anode chamber of the electrochemical cell to form the anolyte together with freshly added alkali metal chloride. You can also use chlorate electrolyte as such without crystallization, for example, as raw materials supplied to the chlorine dioxide generator. Such an embodiment is advantageous in an integrated process in which a depleted solution in a generator from chlorine dioxide production is returned to the anode chamber of an electrochemical cell for chlorate production.

The production of alkali metal chlorate can be carried out continuously, batchwise or in a mixed mode.

The organic mediator in catholyte is preferably dissolved in a predominantly aqueous or predominantly organic continuous liquid phase, preferably having electrical conductivity under process conditions of at least about 0.1 S / m, more preferably at least about 1 S / m, most preferably at least at least about 3 S / m. However, it is also possible that the organic mediator is dissolved in a predominantly organic phase emulsified in a continuous, predominantly aqueous, phase.

An organic mediator is a substance capable of electrochemically reacting at the cathode to form one or more reduced forms, which, in turn, are capable of reacting with preferably molecular oxygen and converting back to its original form, thereby enabling a cyclic process. The reaction of the reduced forms of the mediator with oxygen preferably occurs in the presence of protons. However, in the absence of a suitable proton source, formation of peroxide salts, for example Na ₂ O ₂ , is possible, which can subsequently be hydrolyzed to produce hydrogen peroxide. Outside of any theory, it is assumed that the reaction scheme for the formation of hydrogen peroxide involves the transfer of two electrons and two protons that occurs in separate or combined simultaneous reactions, and, as expected, involving O ₂ ^- ·, НОО ·, and НОО as intermediate particles ^- .

Examples of classes of organic compounds that form redox systems and are useful as mediators include quinones, flavoquinones, pyridine derivatives such as nicotinamides, and ketones.

Suitable quinones include molecules containing a (benzo) quinone moiety (ortho or para forms), among which anthraquinones, tetrahydroquinones, naphthoquinones, benzoquinones and their derivatives are preferred. Anthraquinones, naphthoquinones and benzoquinones are preferably substituted, for example, alkyl substituted, such as 2-alkyl-9,10-anthraquinones. Specific examples include 2-ethyl-9,10-anthraquinone, 2-tert-butyl-9,10-anthraquinone, 2-hexenyl-9,10-anthraquinone, eutectic mixtures of alkyl-9,10-anthraquinones, mixtures of 2-amyl-9, 10-anthraquinones, all of which have high stability. Specific examples of alkyl substituted naphthoquinones include 2-methyl-1,4-naphthoquinone, 2-ethyl-1,4-naphthoquinone, 2-propyl-1,4-naphthoquinone, 2-tert-butyl-1,4-naphthoquinone, 2-tertamyl-1 4-naphthoquinone, 2-isoamyl-1,4-naphthoquinone, 2,3-dimethyl-1,4-naphthoquinone. Other examples of substituents suitable for controlling the reactivity and solubility of quinones include —SO ₃ H / —SO ₃ ^- , —PO ₂ R ^- , —OPO ₃ R ^- , —NO ₂ , —OCH ₃ , —SO ₂ CH ₃ , -OPh, -SPh, -SO ₂ Ph, -COOH / -COO ^- , -CN, -OH, -COCH ₃ , -F, -Cl, -Br, -CF ₃ , -NH ₂ / -NH ₃ ⁺ , -NRH / -NRH ₂ ⁺ , -NR ₂ / -NR ₂ H ⁺ , -NR ₃ ⁺ , -PH ₂ / -NH ₃ ⁺ , -SR ₂ ⁺ , -PRH / -PRH ₂ ⁺ , -PR ₂ / - PR ₂ H ⁺ and -PR ₃ ⁺ , where R is preferably, independently of one another, optionally substituted alkyl, alkenyl, or aryl, or hydrogen. Anthraquinone may be mono- or multisubstituted with some combination of the above and / or other substituents. Quinone derivatives with substituents carrying a common charge, which give the molecule an ionic character, can also be used. Specific examples of non-alkyl substituted quinone derivatives include anthraquinone-2-sulfonate, 5,6,7,8-tetrahydro-9,10-anthraquinone-2-sulfonate, anthraquinone-2,6-disulfonate, naphthoquinone-2-sulfonate, 2- methoxy-1,4-naphthoquinone, 2-ethoxy-1,4-naphthoquinone, 2-aminoanthraquinone, 2-aminonaphthoquinone, 2- (alkylamino) -anthraquinone, 2- (dialkylamino) -anthraquinone, 2- (trialkylammonium) -anthraquinone, 2- (alkylamino) naphthoquinone, 2- (dialkylamino) naphthoquinone, 2- (trialkylammonium) naphthoquinone. Naphthoquinones can, for example, be substituted at any position on the side ring, for example naphthoquinone-6-sulfonate or 6-trialkylammonium naphthoquinone. It may also be advantageous to have one substituent on each ring, such as, for example, in 6-amylnaphthaquinone-2-sulfonate or 6-ethyl-2-triethylammonium naphthoquinone. Suitable examples for benzoquinone are benzoquinone-2-sulfonate and 2- (ethyl, dimethyl) ammonium. Anthraquinones and naphthoquinones with partially hydrogenated side rings can also be used, for example, 1,2,3,4-tetrahydroantraquinone, 5,6,7,8-tetrahydro-2-ethylantraquinone, 5,6,7,8-tetrahydronaphthoquinone. This also applies to substituted anthra and naphthoquinones, including those corresponding to the above types.

In the case where the quinone is substituted and contains one or more optionally substituted alkyl, alkenyl or aryl groups, it is preferable that these groups, independently from each other, have from 1 to 12 carbon atoms, most preferably from 1 to 8 carbon atoms. If there is more than one such group, then they preferably have a mixed chain length. Alkyl, alkenyl and aryl groups may also be substituted, for example, by one or more hydroxyl groups.

Quinones, including anthraquinones, tetrahydroantraquinones, naphthoquinones, benzoquinones and their derivatives, can be reduced to the corresponding hydroquinones by sequential addition of two electrons and two protons. Along with quinone and hydroquinone, it is believed that a number of intermediate forms are present and active, such as the semiquinone radical and the semiquinone anion, as well as the main forms of acid hydroquinone. All of these reduced forms can react with oxygen and contribute to the general reaction of hydrogen peroxide and starting quinone formation.

Other mediator systems capable of reducing oxygen to superoxide and subsequently hydrogen peroxide include flavoquinones, for example flavin (see, for example, H. Tatsumi et al. In “Mechanistic study of the autooxidation” of reduced flavin and quinone compounds ") in Journal of Electroanalytical Chemistry (1998), 443, 236-242) and pyridine derivatives such as nicotinamide and derivatives thereof.

Other mediator systems are formed by ketones and their corresponding alcohols. The ketone can be electrochemically reduced to the corresponding alcohol, which reacts with oxygen to form hydrogen peroxide and the starting ketone. Secondary alcohols and especially phenyl are preferred. Suitable alcohols include isopropyl alcohol, benzyl alcohol, diphenylmethanol, methylphenylmethanol. Secondary alcohols optionally containing a charge-carrying group may also be used.

The content of the organic mediator, including its reduced forms, in the catholyte is preferably at least about 0.1 wt.%, More preferably at least about 1 wt.%, Most preferably at least about 3 wt.%. It is limited from above only by solubility, which depends on the mediator used and the composition of the liquid phase, but in many cases it can reach about 10 wt.% Or about 20 wt.% Or even more. In one embodiment, in which a significant portion of hydrogen peroxide is formed outside the cell, the content of the organic mediator is preferably at least about 1 wt.%, More preferably at least about 3 wt.%, Most preferably at least about 10 wt.% .

If the catholyte contains predominantly an aqueous continuous phase in which the organic mediator is dissolved, this phase preferably contains at least about 50 wt.%, Most preferably at least about 80 wt.% Of water and other inorganic components. Then it is preferred that the mediator is selected from those that have high solubility in water, for example quinones having one or more hydrophilic groups, such as —SO ₃ H / —SO ₃ ^- , —NO ₂ , —COOH / —COO ^- , -OH, -NH ₂ / -NH ₃ ⁺ , -NRH / -NRH ₂ ⁺ , -NR ₂ / -NR ₂ H ⁺ , -NR ₃ ⁺ , -PH ₂ / -NH ₃ ⁺ , -PRH / -PRH ₂ ⁺ , -PR ₂ / -PR ₂ H ⁺ and -PR ₃ ⁺ , where R preferably represents, independently of one another, hydrogen or optionally substituted alkyl or alkenyl.

If the catholyte contains predominantly an organic continuous phase in which the organic mediator is dissolved, this phase preferably contains at least about 50 wt.%, Most preferably at least about 80 wt.%, Organic components and in extreme cases may essentially not contain inorganic components. However, it is preferred that at least about 5 wt.%, Most preferably at least about 20 wt.%, Of the inorganic components are contained. These inorganic components can be, for example, inorganic ions of salts formed by both organic and inorganic ions.

The continuous liquid phase of the catholyte preferably contains at least partially an organic salt containing at least one kind of organic cation and / or organic anion. Its content in the continuous liquid phase is preferably from about 20 wt.% To about 99 wt.%, More preferably from about 40 wt.% To about 95 wt.%, Most preferably from about 60 wt.% To about 90 wt.% .

The continuous liquid phase of the catholyte preferably has a pH of less than 7. If this liquid phase is predominantly organic, then this pH corresponds to the pH obtained in water maintained in equilibrium with the predominantly organic liquid phase.

At least partially, the organic salt may be selected from the group of salts referred to as ionic liquids, i.e. a wide class of liquids essentially consisting of ions. The ionic liquid can be simple and contain one kind of anion and one kind of cation, or it can be complex and contain a mixture of different anions and / or different cations. Some ionic liquids have a low melting point and negligible vapor pressure near or below room temperature and are often called room temperature ionic liquids. Such ionic liquids usually remain liquid over a wide temperature range.

At least partially, the organic salt can also be selected from salts which alone cannot be classified as ionic liquids, but which possess such properties when present together with a neutral cosolvent such as water or a low molecular weight alcohol such as methanol, ethanol or propanol, of which water is preferred. The weight ratio of salt to co-solvent is preferably from about 1: 1 to about 1000: 1, more preferably from about 2: 1 to about 100: 1, most preferably from about 5: 1 to about 20: 1.

It is preferable to use at least partially an organic salt which alone or in combination with a neutral cosolvent forms a liquid phase at atmospheric pressure below about 130 ° C, preferably below about 100 ° C, most preferably below about 80 ° C. In addition, the partial pressure of this salt at 100 ° C is preferably below about 10 kPa, more preferably below about 1 kPa, most preferably below about 0.1 kPa (excluding the partial pressure of an optional neutral cosolvent).

A fluid with suitable physical properties may contain one at least partially organic salt or a mixture of two or more at least partially organic salts, preferably in combination with one or more neutral cosolvents, of which water is preferred. It may also contain anions and cations, which themselves do not form salts with suitable properties.

Such an at least partially organic salt can be formed by various combinations of cations and anions, among which at least one type of ion is organic. These ions are preferably monovalent. Examples of cations include 1-alkyl-3-methylimidazolium, 1-butyl-3-methylimidazolium [BMIM], 1-ethyl-3-methylimidazolium [EMIM], 1,2,3-trimethylimidazolium, n-alkylpyridinium, n-butylpyridinium [BPY ], pyrrolidinium, guanidinium and alkylguanidino, izourony, PR ₄ ^+, NR ₄ ^+, SR ₃ ^+, tetramethylammonium, choline, cocomonium, and mixtures thereof, wherein R preferably represent, independently of each other, optionally substituted alkyl, alkenyl, or aryl , or hydrogen. Other examples include substituted quinones, referred to herein as [Q-NR ₃ ⁺ ] and [Q-PR ₃ ⁺ ], where Q is quinone, such as anthraquinone, naphthoquinone or benzoquinones, and R is the same as above. Examples of anions include hexafluorophosphate [HFP], tetrafluoroborate [TFB], fluorosulfonate, hexafluoroantimonate, hexafluoroarsenate, chloroaluminate, bromoaluminate, bis (trifluoromethyl sulfonyl) imide, tris (trifluoromethyl sulfonyl) methide, trifluoronated, tri-trifluoromethanesulfonate , nitrate, sulfate, phosphate, RPO ₄ ^2- , R ₂ PO ₄ ^- , R ₂ PO ₂ ^- (e.g. dialkyl phosphinate), perchlorate, acetate, alkyl sulfonate, bis (2-ethylhexyl) sodium sulfosuccinate, diethylene glycol monomethyl ether sulfate, alkyl oligoester, tetraal ilborat, propionate, succinate, saccharinate, glycolate, stearate, lactate, malate, tartrate, citrate, ascorbate, glutamate, benzoate, salicylate, methanesulfonate, toluenesulfonate, and mixtures thereof, wherein R means the same as above. Other examples include substituted quinones, referred to herein as [Q- (O) -SO ₃ ^- ] and [Q- (O) -PO ₃ R ^- ], where Q is quinone such as anthraquinone, naphthoquinone or benzoquinones, (O) means optional oxygen (e.g., sulfate / sulfonate and phosphate / phosphonate), and R means the same as above.

In the case where any cation or anion contains one or more optionally substituted alkyl, alkenyl or aryl groups, it is preferable that these groups, independently from each other, have from 1 to 12 carbon atoms, most preferably from 1 to 8 carbon atoms. If there is more than one such group, then they preferably have a mixed chain length. Alkyl, alkenyl and aryl groups may also be substituted, for example, by one or more hydroxyl groups.

Examples of salts useful in the present invention include any combination of the following cations: [1,3-dialkylimidazolium], [trialkylammonium], [tetraalkylammonium], [trialkylphosphonium], [tetraalkylphosphonium], [alkylpyridinium], [choline], [Q-NR ₃ ⁺ ] and [Q-PR ₃ ⁺ ], in combination with any of the following anions: [sulfate], [phosphate], [alkyl sulfate], [alkyl sulfonate], [dialkyl phosphate], [alkyl phosphonate], [Q- (O) -SO ₃ ^- ] and [Q- (O) -PO ₃ R ^- ], where Q, (O) and R mean the same as above.

Particular group combinations include [1,3-dialkylimidazolium] [alkylsulfonate] such as any of the following: [1-butyl-3-methylimidazolium] [methyl-SO ₃ ^- ], [1-ethyl-3-methylimidazolium] [ ethyl sulfonate], [1-hexyl-3-methylimidazolium] [tosylate], [1-butyl-3-methylimidazolium] [anthraquinone-2-sulfonate] or [1-butyl-3-methylimidazolium] [5-tertamylnaphthoquinone-2-sulfonate ]; [tetraalkylammonium] [Q- (O) -SO ₃ ^- ] such as any of the following: [methyl, triethylammonium] [5-tertamylnaphthoquinone-2-sulfonate], [methyl, diethyl, butylammonium] [anthraquinone-2-sulfonate] or [choline] [5-amylbenzoquinone-2-sulfonate]; or [Q-NR ₃ ⁺ ] [alkyl sulfonate] such as [5,6,7,8-tetrahydroantraquinone-2-aminium, n, n, n- (methyl, diethyl)] [methyl sulfonate]; [tetraalkylphosphonium] [dialkylphosphate] such as any of the following: [ethyl tributylphosphonium] [diethyl phosphate], [phenyltriethylphosphonium] [diisobutyl phosphate].

Without regard to specific group combinations, many combinations are possible, such as any of the following: [triisobutyl (methyl) phosphonium] [tosylate], [trihexyl (tetradecyl) phosphonium] [bis-2,4,4-trimethylpentylphosphinate] [tetrabutylammonium] [methanesulfonate ] [1-ethyl-3-methylimidazolium] [HFP], [tripentylsulfonium] [dipentyl, benzylammonium], [benzoquinone-2-amino-n, n, n-diethyl, phenyl] [5,6,7,8-tetrahydro -9,10-anthraquinone-2-sulfonate], [choline] [5-ethoxy-1,4-naphthoquinone-6-sulfate], [n-propylpyridinium] [saccharinate].

In addition to those mentioned above, other types of commercially available or otherwise known ionic liquids or salts having such properties in combination with a neutral cosolvent can also be used.

You can also use a salt in which at least one of the ions also acts as a mediator, which undergoes a reaction at the cathode with the formation of the reduced form and thus participates in the cyclic process of producing hydrogen peroxide. In this case, the mediator used may partially or completely consist of ions of such a salt. Examples include salts containing a cation or anion of a substituted quinone or a nicotinamide derivative such as those mentioned above.

The use of at least partially an organic salt as described above in the continuous electrolyte phase provides the advantages of combining the high solubility of organic mediators, such as quinones, with good electrical conductivity. Another advantage is the very low flammability, which makes it possible to safely react with oxygen at higher oxygen concentrations and higher temperatures than would be possible with conventional flammable solvents. It also facilitates the separation of hydrogen peroxide from it, for example, by evaporation or extraction, and thereby the production of hydrogen peroxide, either of high purity, or in a mixture to be further processed with the selected compound, for example water. Another example is a methanol / hydrogen peroxide mixture for use as a reagent in an epoxidation reaction. The use of ionic liquids to form a medium suitable for carrying out reactions involving hydrogen peroxide was described by B. Chhikara et al. “Oxidation of alcohols with hydrogen peroxide, catalyzed by a new imidazolium ion based on the phosphoric tungstate complex in an ionic liquid” catalyzed by a new imidazolium ion based phosphotungstate complex in ionic liquid "), Journal of Catalysis 230 (2005, 436-439).

The catholyte additionally contains one or more organic or inorganic acids, such as formic acid, acetic acid, monochloroacetic acid, benzoic acid, sulfonic acids, phosphonic acids, nitric acid, sulfuric acid, hydrochloric (hydrochloric) acid, hydroiodic acid, hydrobromic acid, perchloric acid or phosphoric acid.

The catholyte may also contain other components. For example, a predominantly organic continuous liquid phase may contain, as previously mentioned, a neutral cosolvent, preferably water. The amount of neutral co-solvent is preferably up to about 50 wt.%, Most preferably from about 1 to about 20 wt.%. A particularly preferred neutral co-solvent content may be, for example, from about 1 to about 5 wt.% Or from about 5 to about 10 wt.%. Examples of other optional additives include hydrogen peroxide stabilizers, emulsifiers, corrosion inhibitors, anti-foaming agents, buffers, conductivity enhancers, viscosity reducers, etc. Examples of hydrogen peroxide stabilizers include stabilizers widely used for this purpose, such as phosphoric acid, phosphonic acid complexing agents, alkali metal stannate protective colloids and pyridinecarboxylic acid radical scavengers. Examples of phosphonic acid-based complexing agents include 1-hydroxyethylidene-1,1-diphosphonic acid, 1-aminoethane-1,1-diphosphonic acid, aminotri (methylene phosphonic acid), ethylene diamine tetra (methylene phosphonic acid), hexamethylene diamine tetra (methylene diphosphonate) (methylenephosphonic acid), diethylene triaminex (methylenephosphonic acid), 1-aminoalkane-1,1-diphosphonic acids (such as morpholine methane diphosphonic acid, n, n-dimethylaminodimethyldiphosphonic acid, aminomethyldipho sphonic acid), their reaction products and their salts, preferably sodium salts.

Preferably, the predominantly organic liquid phase in the catholyte has a viscosity under operating conditions below about 100 MPa · s, more preferably below about 30 MPa · s, and most preferably below about 10 MPa · s. In addition, due to the dangers associated with handling substantially pure hydrogen peroxide, the product recovered is preferably a mixture of hydrogen peroxide with water or low molecular weight alcohols, for example methanol. The partial pressure at 100 ° C. of the liquid components that do not form part of the product mixture should preferably be below about 10 kPa, more preferably below about 1 kPa, most preferably below 0.1 kPa.

The electrochemical cell may include only one chamber for the anode and one for the cathode, or may additionally include one or more chambers in between, for example, an electrodialysis package that allows any known electrodialysis. The means for separating these chambers may be a non-selective physical barrier, such as a porous membrane or diaphragm, or it may be selectively permeable to certain particles, such as cations or anions. A combination of membranes, such as bipolar membranes, can be used to separate water into protons and hydroxide ions. Non-selective barriers can be made, for example, from asbestos, ceramics, glass, polyolefins, polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), etc. Cation selective membranes can be made, for example, from organic polymers such as PTFE, polystyrene, styrene / divinylbenzene or vinylpyridine / divinylbenzene modified with acidic groups such as sulfonate, carboxylate or phosphonate. Anion selective membranes can be made, for example, from organic polymers such as PTFE, polystyrene, styrene / divinylbenzene or vinylpyridine / divinylbenzene modified with basic groups such as quaternary ammonium. Bipolar membranes may contain an anion-permeable membrane and a cation-permeable membrane, layered together, optionally with a catalyst layer between them. Ion-selective and bipolar membranes are commercially available, for example, under the trademarks Nafion ™, Flemium ™, Neosepta bipolar®.

The electrolyte in the cathode chamber may contain one, two or more liquid phases. In a system with a single liquid phase, there is only a predominantly organic or predominantly aqueous liquid phase of the electrolyte. In a system with two liquid phases, the non-continuous phase can be emulsified or simply mixed in the continuous liquid phase. If there is more than one liquid phase, then the components in the electrolyte will be distributed between these phases depending on their solubility properties. In addition to the liquid phase or phases, gas and / or solids may also be present.

The temperature and pressure in the cathode chamber may be the same as in the anode chamber, or different from the anode chamber, and is preferably set so that the catholyte is a liquid. High temperature contributes to low viscosity, high electrical conductivity and high mass transfer rates, while low temperature contributes to the stability of hydrogen peroxide and components in the electrolyte. Typically, the temperature is preferably from about 0 to about 200 ° C., more preferably from about 40 to about 150 ° C., most preferably from about 60 to about 100 ° C. The pressure is preferably from about 10 to about 30,000 kPa, more preferably from about 80 to about 2000 kPa, most preferably from about 100 to about 800 kPa.

The reaction of one or more reduced forms of the mediator and oxygen with the formation of hydrogen peroxide can occur inside the cell or in a separate container or both, and there, usually leading to the formation of hydrogen peroxide in catholyte and the re-formation of the mediator to participate in another reaction cycle. Typically, molecular oxygen is added to the electrolyte containing the reduced mediator, but part of it can come from oxygen generated during anode reactions and transferred through the electrolyte in the cell, optionally through a membrane, or isolated as a separate stream and reintroduced into the cell. Molecular oxygen can be added dissolved in a liquid or in the form of any oxygen-containing gas, such as air, oxygen-enriched air or essentially pure oxygen. Adding at least part of the oxygen in the form of gas directly to the cell provides the advantage of improving mixing, and can also create a gas lift for transferring electrolyte from the cell, alternatively contributing to the distillation of hydrogen peroxide from the electrolyte. Adding oxygen directly to the cell may allow the complete catalytic cycle of the mediator to complete within the cell, essentially eliminating the need to withdraw the stream containing the reduced form of the mediator and to supply the stream containing the mediator. The reactions resulting in the formation of hydrogen peroxide are facilitated by the presence of protons, which can come from any available source, such as water, hydroquinone, protons formed at the anode, or any acid that has been added to the electrolyte. If the reaction with oxygen occurs in a separate container, conditions in it such as temperature, pressure, etc. may be the same as or prevailing in the cell, or different from them. The temperature is preferably from ambient, for example, about 20 ° C., to an upper limit determined by either the flammability of the solvent or the stability of hydrogen peroxide, for example, to about 70 ° C. The pressure is preferably from about atmospheric to about 5 bar gauge pressure. Usually, it is preferable to use a bubble column either packed or with sieve plates. The oxygen-containing gas is preferably supplied from below, and the liquid flows either from bottom to top or from top to bottom.

Various methods can be used to separate hydrogen peroxide from the electrolyte, such as evaporation, extraction, or membrane techniques. Such separation can occur in the cell, in separate equipment, from which the remaining electrolyte is then recycled back to the cell, or both.

In one embodiment, hydrogen peroxide is evaporated from the predominantly organic phase of the electrolyte, preferably together with water and, optionally, with other volatile substances that may be present. Evaporation can be carried out directly from the cell or from a separate container, for example, by distillation with any gas, for example oxygen, air or nitrogen, or by distillation at atmospheric pressure or below atmospheric pressure. The low vapor pressure of the at least partially organic salt and other organic substances optionally present in the electrolyte and not part of the desired product mixture promotes the use of evaporation techniques to separate hydrogen peroxide. In this embodiment, it is possible to obtain a high purity product stream containing hydrogen peroxide without complex purification steps.

In another embodiment, hydrogen peroxide is extracted from the predominantly organic liquid phase with any suitable solvent, such as water or methanol. All widely used extraction technologies can be applied, such as in one or more settling mixers, columns with sieve plates, columns with a packing layer. If an electrolyte is used that also contains a predominantly aqueous phase, then hydrogen peroxide will automatically be enriched in this phase, which can be recovered as a product, alternatively distilled or otherwise purified and recycled back to the cell.

In yet another embodiment, membrane separation is used. Examples of such methods include membrane extraction, pervaporation (evaporation through a semipermeable membrane), and nanofiltration.

In yet another embodiment, the mediator and its reduced forms are dissolved in a predominantly aqueous phase. If the oxidation of the reduced forms of the mediator also occurs in the predominantly aqueous phase, then hydrogen peroxide can be separated by, for example, distillation. Another option is to keep the predominantly aqueous phase essentially free of oxygen and transfer, for example, by extraction the reduced forms of the mediator into the predominantly organic phase and then carry out the oxidation.

In yet another embodiment, hydrogen peroxide is not recovered from the electrolyte, but used directly as a reagent in the production of other chemicals. The electrolyte remaining after such reactions can then be recycled to the cell.

Such production of hydrogen peroxide is preferably carried out continuously, either with the flow of electrolyte through the cell, or with the continuous release of hydrogen peroxide from the electrolyte in the cell. It is preferable to ensure proper mixing, especially around the cathode, for example, gas purging, mechanical stirring, electrolyte circulation, or combinations thereof. The gas purge is preferably carried out with oxygen or an oxygen-containing gas such as air. In a cell with a substantially vertical flow, gas purge can also create a gas lift that enhances the transfer of electrolyte through the cell, alternatively by distilling off hydrogen peroxide, optionally together with water or any other component that is volatile at operating temperature and pressure.

In order to avoid harmful accumulation of impurities from the starting chemicals or decomposition products resulting from side reactions, in some cases it may be appropriate to discharge part of the electrolyte from the system and / or purify it in various ways, such as electrodialysis, adsorption, recrystallization, precipitation, washing, ion exchange , evaporation or stripping with a carrier gas, reactive regeneration with acid / base or reduction / oxidation stages.

Since hydrogen gas may form at the cathode as a result of a side reaction, it may be useful to have a gas analyzer and an inert gas purge device.

The temperature can be controlled by any suitable means, for example, using heat exchangers at any appropriate flow. Cooling can also be carried out by evaporation, for example, in an electrochemical cell, followed by condensation of steam. If cooling by evaporation is carried out using water, it may be appropriate to add water specifically for this purpose.

The anode may be made of any suitable material, for example titanium, a titanium alloy. The anode is preferably coated, for example, from RuO ₂ / TiO ₂ , RuO ₂ / TiO ₂ / IrO ₂ or Pt / Ir. Particularly preferred anodes are DSA ™ (dimensionally stable anode).

Various types of cathodes may be used. Preferably, the cathode is made of a material that suppresses parasitic reactions, such as hydrogen evolution, direct reduction of oxygen to water, and decomposition of an organic mediator, ionic liquid, or hydrogen peroxide formed. In most cases, it is preferable to use a cathode with a hydrophobic surface. Examples of cathode materials include carbon based materials such as boron-doped diamond, graphite, glassy carbon, highly oriented pyrolytic graphite, carbon net and conductive polymers. Examples of conductive polymers include poly (para) phenylene, polypyrrole, polythiophene and polyaniline. The conductive polymer may be applied as a thin film with a preferred thickness of from about 0.1 to about 100 microns on any suitable substrate, such as Pt or stainless steel. Such a polymer film can be obtained by chemical synthesis or preferably electrosynthesis. A specific example is the cathode obtained by electrosynthesis of a polypyrrole film on stainless steel. Other examples of cathode materials include metals such as iron, steel, lead, nickel, titanium or platinum, or conductive metal oxides such as PbO ₂ , NiO ₂ , Ti ₄ O ₇ , NiCo ₂ O ₄ or RuO ₂ . Other examples include electrocatalytic cathodes made of a material such as titanium or a titanium alloy coated, in whole or in part, with particles of noble metals such as gold, platinum, palladium, or grafted catalysts for anthraquinones.

The cathode and anode can be made with various geometric shapes and can, for example, take the form of a flat sheet or plate, a curved (non-planar) surface, a curved surface, a perforated plate, a woven wire mesh, a stretched mesh sheet, rod or tube. However, preferably the anode and cathode are flat in shape, most preferably in the form of a sheet, grid or plate.

Any conventional cell design may be used, preferably with the smallest possible distance between the anode and cathode. The divided cell may, for example, be of the “zero gap” type of cells in which at least one of the electrodes is pressed against the membrane separating the cell.

A typical production plant includes many cells to achieve the desired performance. These cells can be arranged in a monopolar or bipolar manner in an electrolytic cell in accordance with any conventional construction.

Next, some embodiments of the invention will be further described in connection with the accompanying schematic drawings. However, the scope of the invention is not limited to these embodiments. Figure 1 shows a schematic diagram of the cathode part of the method, and figure 2, 3 and 4 shows schematic designs of various electrochemical cells.

Turning to FIG. 1, the electrochemical reduction of the mediator occurs in a predominantly organic continuous phase of the electrolyte in the cell chamber 1, which may be a cathode chamber or a single-chamber cell. The feed stream 14 supplies the cell chamber 1 with any substances that are consumed in this process, such as oxygen, or are discharged in any non-recycle product stream, such as water or an inert gas, such as nitrogen. If oxygen is present, then a reaction between the reduced form or forms of the mediator and oxygen can also occur in the cell chamber 1 with the formation of hydrogen peroxide or alkali metal peroxide. If this reaction proceeds to a sufficiently large degree, then it is sufficient to remove hydrogen peroxide together with, for example, water in the form of stream 6. If the reaction with the formation of hydrogen peroxide or alkali metal peroxide does not proceed to the end, then the electrolyte is withdrawn and this reaction is completed to the desired degree in the oxidation reactor 2, to which additional oxygen can be supplied 15. The resulting stream 7 contains hydrogen peroxide or alkali metal peroxide in one or more forms depending on the conditions used, for example , As a vapor or dissolved in a liquid phase. If there is both a gas and at least one liquid phase, they are sent to a gas-liquid separator 3, from which the gas stream 8 is sent to the condenser 4. The product hydrogen peroxide 10 is removed from the condenser 4, and the remaining gas 13, for example oxygen, water vapor and other optional components, either recycle to any place where oxygen can be used, such as the cell chamber 1 or the oxidation reactor 2, or discharged through 16. The liquid stream 9 from the separator 3 is recycled to the cell chamber 1. If the liquid stream 9 contains hydrogen peroxide, then it is first sent to a separator 5, which may be, for example, an extraction unit or a membrane separation unit. Here, this stream 5 is separated into a stream 11 of a product 11 containing hydrogen peroxide and a recycle stream 12 containing a predominantly organic electrolyte.

The various settings shown in FIG. 1 can be combined in a variety of ways. For example, oxygen can be introduced into the cell chamber 1 in various ways, for example, separately or together with any liquid feed or recycle stream. Oxygen can also be introduced at a location above the electrodes to separate electrochemical reactions and oxidation. The oxidation reactor 2 and the gas-liquid separator 3 can be combined, for example, by using a bubble column. If the operating conditions are set so that gas is not formed, and only the liquid phase is discharged from the cell chamber 1, then the gas-liquid separator 3 and the condenser 4 can be excluded.

Turning to FIG. 2, an electrochemical cell operating in accordance with the invention includes an anode 21 in an anode chamber 23 and a cathode 22 in a cathode chamber 24. This cell also includes a middle chamber 25 separated from the anode and cathode chambers 23 and 24 by ion-selective membranes 26 and 27. In one embodiment, membrane 26 is permeable to anions, and membrane 27 is permeable to cations. In another embodiment, both membranes 26 and 27 are cation permeable. In the cathode chamber 24 contains catholyte containing the organic mediator according to the invention. Oxygen-containing gas is supplied via the inlet stream 28 to the cathode chamber 24, and the outlet stream 29 containing hydrogen peroxide and / or the reduced mediator is sent to the installation 30, where further processing takes place. Such further processing may include the oxidation of the reduced mediator to produce hydrogen peroxide and its separation, leading to the formation of a product stream 31 containing hydrogen peroxide and, optionally, other substances, such as water, that may remain in the final product, and others that can be isolated later, and recirculated stream 32, containing, for example, catholyte with an organic mediator obtained by the oxidation of its reduced forms. In the anode chamber 23 serves the input stream 33, which may have different compositions depending on the desired reactions. An anolyte containing reaction products is discharged as an effluent 34 to a product separator 35 from which product 36 is withdrawn, and the remaining electrolyte 37 is recycled to the anode chamber 23. Into the middle chamber 25 is an inlet stream 38 with preferably an aqueous solution, the composition of which depends on desired general reactions. The stream 39 exiting the middle chamber 25 may be recycled or used in any other way.

If the cell of FIG. 2 is used in an embodiment in which the membrane 26 is anion selective, the membrane 27 is cation selective and the chloride is reacted at the anode to form chlorine, which can be hydrolyzed further to produce hypochlorous acid and eventually chlorate, then the anolyte is preferably is an aqueous solution containing NaCl, NaClO ₃ or the corresponding potassium salts KCl or KClO ₃ and, optionally, a buffer, such as chromate, dichromate or any other suitable salt. Anolyte product stream 34 is diverted and sent to a product separator 35, where the alkali metal chlorate is crystallized and 36 is withdrawn, and the remaining electrolyte is recycled 37 to the anode chamber 23. It is also possible to provide a plant (not shown), for example, a chlorate reactor, for further reactions with the formation of chlorate by disproportionation of hypochlorous acid in the product effluent 34 prior to crystallization. In one embodiment, a water-type solvent containing HCl or NaCl is preferably supplied to the middle chamber 39 through an inlet stream 38, and chloride ions are transferred through the anion-selective membrane 26 to the anode chamber 23, where they are consumed on the anode 21 to form chlorine in the first stage . Then, Na ⁺ or K ^{+ is} supplied to the cathode chamber 23 by the inlet stream 33, for example, in the form of NaOH or KOH. In another embodiment, OH ^- , for example, in the form of NaOH or KOH, is fed into the middle chamber through the inlet stream 38, hydroxide ions will be transported through the anion-selective membrane 26, and then, through the inlet stream 33, chloride ions, for example, in the form of NaCl . In any of these embodiments, cations, typically Na ⁺ or H ⁺ , are transferred from the middle chamber 25 through the cation selective membrane 27 to the cathode chamber 24.

Turning to FIG. 3, an electrochemical cell operating according to the invention includes an anode 21 in an anode chamber 23 and a cathode 22 in a cathode chamber 24. However, unlike the cell in FIG. 2, there is only one ion-selective membrane 27, which is preferably cation selective, and the middle chamber is absent. In all other respects, this cell is identical to the cell of FIG. 2, to the description of which the reader is referred.

If the cell of FIG. 3 is provided with a cation selective membrane 27 and is used in an embodiment in which chloride reacts on anode 21 to produce chlorine, which then hydrolyzes to form chlorate, then the anolyte is preferably an aqueous solution containing NaCl, NaClO ₃ or the corresponding potassium salts KCl or KClO ₃ and a buffer such as chromate, dichromate or any other suitable salt. NaCl or KCl is fed into the anode chamber 23 by an inlet stream 33, while cations such as Na ⁺ or H ⁺ are transferred through the membrane 27 to the cathode chamber 24. To compensate for the decrease in Na ⁺ or K ⁺ through the membrane 27 and neutralize H ⁺ generated during anodic reactions, it may be appropriate to add a certain amount of NaOH or KOH to any suitable place, for example, to the inlet stream 33 or the recycle stream 37. In all other respects, such as the manipulation of the product stream 34 and the recycle stream 37, the functioning of the equiv corresponding valence embodiment is implemented in a cell of FIG. 2, to the description of which the reader is referred.

Referring to FIG. 4, an electrochemical cell operating according to the invention includes an anode 21 in an anode chamber 23 and a cathode 22 in a cathode chamber 24. However, unlike the cell in FIG. 2, the middle chamber is replaced by a bipolar membrane 40 separating the chambers 23 and 24 cells. The bipolar membrane 40 includes an anion selective membrane 26 and a cation selective membrane 27 laminated together on both sides of the catalyst layer 45. Water from the anolyte passes into the catalyst layer, where it splits into protons passing into the cathode chamber 24, and hydroxide ions passing into the anode chamber 23. In all other respects, this cell is identical to the cells of FIGS. 2 and 3, the description of which is referred to reader.

If the cell of FIG. 4 is used in an embodiment in which chloride reacts on anode 21 to form chlorine, which then undergoes further reaction to chlorate, then the anolyte is preferably an aqueous solution containing NaCl, NaClO ₃ or the corresponding potassium salts KCl or KClO ₃ and a buffer such as chromate, dichromate or any other suitable salt. NaCl or KCl is fed into the anode chamber 23 by an inlet stream 33. Inside the bipolar membrane, water is split into protons and hydroxide ions. Protons move into the cathode chamber 24 and assist in the oxidation of the reduced mediator to form hydrogen peroxide, and hydroxide ions move into the anode chamber 23, facilitating the hydrolysis of chlorine. In all other respects, such as manipulating the product stream 34 and the recycled stream 37, the operation is equivalent to the corresponding embodiment implemented in the cell of FIG. 2, to the description of which the reader is referred.

In all the embodiments described with reference to FIGS. 2-4, the cathodic process can be identical, that is, to restore the mediator on the cathode 22 and transfer cations of the Na ⁺ or H ^{+ type} from the middle chamber 25 or the anode chamber 23 through the cation selective membrane 27.

The invention will now be further described using the following example. Unless otherwise indicated, all proportions and percentages are expressed as fractions and percentages by weight.

Example

A solution containing 50 ml of ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM] [HFP] with 0.8 g of 2-ethyl-9,10-anthraquinone (EAQ) was poured into the cathode chamber of a small reactor. This solution was purged with nitrogen gas saturated with water for 30 minutes to dissolve the gases in the solution and to saturate the solution with water to a calculated content of about 3-5 wt.%. An aqueous phase of 40 ml of 0.5 M H ₂ SO _{4 was} added over the organic phase to supply protons. A cathode in the form of a circular platinum network with a diameter of 3 cm was placed in the organic phase, and the anode of the platinum network was placed in a separate chamber containing a 10 mM aqueous NaOH solution. The anode and cathode chambers were separated by a non-selective ceramic membrane (diaphragm). The catholyte was mixed using a magnetic rod located in the organic phase in the cathode chamber. To control the cathode potential, a calomel reference electrode was placed in the cathode chamber near the cathode. The anode chamber contained an aqueous solution of 150 g / l NaCl and 10 g / l sodium dichromate. At a temperature of 68 ° C, a current of 0.2 A was passed between the cathode and anode. During this experiment, a few drops of NaOH (1 M) were added to the anolyte to maintain a pH between 6 and 7. Hydrogen peroxide was formed in the cathode chamber. In the anode chamber, chloride was oxidized to chlorine, which eventually formed chlorate. After 20 minutes, the experiment was completed and the current efficiency was calculated for the formation of chlorate, which amounted to 59%.

Claims (19)

1. The method of production of alkali metal chlorate, including:
providing an electrochemical cell containing the anode and cathode in separate anode and cathode chambers;
contacting the cathode with an electrolyte containing at least one organic mediator and one or more organic or inorganic acids;
reacting the organic mediator at the cathode with the formation of at least one reduced form of this mediator;
reacting said at least one reduced form of a mediator with oxygen to form hydrogen peroxide;
contacting the anode with an anolyte containing alkali metal chloride;
the reaction of chloride at the anode with the formation of chlorine, which is hydrolyzed; and
the reaction of hydrolyzed chlorine with the formation of chlorate. 2. The method according to claim 1, in which the concentration of chloride ions in the anolyte is from about 30 to about 300 g / l per sodium chloride. 3. The method according to claim 1, in which the pH in the volume of the anolyte is from about 4 to about 10. 4. The method according to any one of claims 1 to 3, in which the electrochemical cell contains at least one chamber between the anode and cathode chambers. 5. The method according to any one of claims 1 to 3, in which the organic mediator is selected from the group consisting of quinones, flavoquinones, pyridine derivatives and ketones. 6. The method according to claim 5, in which the organic mediator is selected from the group consisting of quinones containing a (benzo) quinone fragment. 7. The method according to claim 6, in which the organic mediator is selected from the group consisting of anthraquinones, tetrahydroantraquinones, naphthoquinones, benzoquinones and their derivatives. 8. The method according to any one of claims 1 to 3, in which the content of the organic mediator, including its reduced forms, in the catholyte is at least about 1 wt.%. 9. The method according to any one of claims 1 to 3, in which the catholyte contains at least partially an organic salt, including at least one type of organic cation and / or organic anion. 10. The method according to claim 9, in which the content of the at least partially organic salt in the catholyte is from about 20 wt.% To about 99 wt.%. 11. The method according to claim 9, in which said at least partially organic salt is present together with a neutral co-solvent, and the mass ratio of salt to co-solvent is from about 1: 1 to about 1000: 1. 12. The method according to claim 9, in which the catholyte is present neutral cosolvent in an amount up to about 50 wt.%. 13. The method according to claim 9, in which said at least partially organic salt, by itself or in combination with a neutral cosolvent forms a liquid phase at atmospheric pressure below about 130 ° C. 14. The method according to claim 9, in which said at least partially organic salt at 100 ° C has a partial pressure of less than about 10 kPa. 15. The method according to claim 9, in which said at least partially organic salt contains a cation selected from the group consisting of 1-alkyl-3-methylimidazolium, 1-butyl-3-methylimidazolium [BMIM], 1-ethyl-3 -methylimidazolium [EMIM], 1,2,3-trimethylimidazolium, n-alkylpyridinium, n-butylpyridinium [BPY], pyrrolidinium, guanidinium and alkylguanidinium, isouronium, PR ₄ ⁺ , NR ₄ ⁺ , SR ₃ ⁺ , tetramethylammonium, choline, cocomine and mixtures thereof, R are, independently of one another, optionally substituted alkyl, alkenyl or aryl, or hydrogen. 16. The method according to claim 9, in which said at least partially organic salt contains a cation selected from the group consisting of substituted quinones. 17. The method according to claim 9, wherein said at least partially organic salt comprises an anion selected from the group consisting of hexafluorophosphate [HFP], tetrafluoroborate [TFP], fluorosulfonate, hexafluoroantimonate, hexafluoroarsenate, chloroaluminate, bromoaluminate, bis (trifluoromethyl sulfonate) imide, tris (trifluoromethylsulfonyl) methide, tricyanomethide, dicyanamide, nonafluorobutanesulfonate, trifluoromethanesulfonate, 2,2,2-trifluoroethanesulfonate, nitrate, sulfate, phosphate, RPO4 ^2- , R ₂ PO ₄ ^- , R ₂ PO ₂ ^- (for example, dialkylphosphine , perchlorate, acetate, alkylsulfo Nata, bis (2-ethylhexyl) sodium sulfosuccinate, diethylene glycol monomethyl ether sulfate, alkyl oligoester sulfate, pivalate, tetraalkyl borate, propionate, succinate, saccharinate, glycolate, stearate, lactate, benzoic acid tartrate, nitrate, nitrate, nitrate, nitrate, mixtures, R are, independently of one another, optionally substituted alkyl, alkenyl or aryl, or hydrogen. 18. The method according to claim 9, in which said at least partially organic salt contains an anion selected from the group consisting of substituted quinones. 19. The method according to claim 9, in which said at least partially organic salt contains a cation selected from the group consisting of [1,3-dialkylimidazolium], [trialkylammonium], [tetraalkylammonium], [trialkylphosphonium], [tetraalkylphosphonium], [alkylpyridinium], [choline], [Q-NR ₃ ^+] and [Q-PR ₃ ^+] and an anion selected from the group consisting of [sulphate], [phosphate], [alkyl sulphate], [alkyl sulphonate], [ dialkyl phosphate], [alkyl phosphonate], [Q- (O) -SO ₃ ^- ] and [Q- (O) -PO ₃ R ^- ], where Q represents quinone, (O) represents optional oxygen, R represents, whatever dr g from each other, optionally substituted alkyl, alkenyl or aryl, or hydrogen.

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