POROUS ELECTRODE FOR THE ELECTROCHEMICAL REACTION OF ORGANIC COMPOUNDS IN TWO IMMISCIBLE PHASES IN AN ELECTROCHEMICAL FLOW REACTOR

Abstract

A method for the electrochemical reaction of an organic material, and a device in which a corresponding method is carried out including a porous electrode for the electrochemical reaction of organic compounds in two immiscible phases in an electrochemical flow reactor. A first nonpolar solvent and a first polar electrolyte or a first organic material in the form of a liquid or gas and the first polar electrolyte form a first phase boundary with one another in such a form that the first phase boundary in the electrochemical conversion is at least partly within a first electrode, preferably at an interface between a first lipophilic layer and a second hydrophilic layer.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International Application No. PCT/EP2018/097087 filed 28 Dec. 2018, and claims the benefit thereof. The International Application claims the benefit of German Application No. DE 10 2018 201 287.3 filed 29 Jan. 2018. All of the applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The present invention relates to a method of the electrochemical conversion of an organic material and to an apparatus in which a corresponding method can be conducted.

BACKGROUND OF INVENTION

The use of electrochemical methods in the synthesis of bulk and fine chemicals has always been a major challenge. Many organic substrate molecules are only sparingly soluble in water, but have much better solubility in nonpolar solvents, i.e. organic solvents.

However, the use of electrolytes based on organic solvents brings some significant disadvantages for electrochemistry.

Firstly, organic solvents and lipophilic organic salts are much more expensive than water and inorganic salts.

Secondly, organic electrolytes typically have a significantly poorer conductivity than aqueous electrolytes, which leads to high cell voltages and high ohmic losses.

Thirdly, the electrolyte in electrochemical processes is often a consumable material. Even though the overall reaction does not relate to water, it can be consumed locally and then regenerated in the bulk electrolyte. Every electrochemical process requires a counterpart reaction at the counterelectrode. Many electrochemical conversions, especially organic electrochemical conversions, also include protons that have to be generated or consumed by the counterpart reactions. In the case of water, this is typically either the reduction or oxidation of water to hydrogen or oxygen. In organic electrolytes, the organic solvent assumes the role of water, and is broken down at the counterelectrode. This can be avoided by the use of sacrificial agents or sacrificial materials, but these in turn massively increase process costs. At high current density, proton transport by the electrolyte can even be inadequate for the reaction rate, which can lead to protonation or deprotonation and subsequent breakdown of the electrolyte at the electrodes.

Therefore, the use of aqueous electrolytes appears very desirable for electrochemical synthesis. However, the often poor solubility of the reagent molecules in water or even electrolytes having high ionic strength severely limit substrate supply to the electrodes and hence the current densities.

At present, no general solution to this problem is being employed. Proposals by Beck et al. relate to very thin capillary cells, as discussed, for example, in Fritz Beck, Berichte der Bunsen-Gesellschaft 1973, 77 (10/11), p. 810-817 and F. Beck, H. Guthke, Chemie-Ing.-Techn. 1969, 41 (17), p. 943-950.

US 2013/0228470 A1 discloses a method of converting carbon-based gases and carbon oxides to longer-chain organic gases.

US 2013/0087451 A1 discloses a membrane-electrode arrangement and an organic hybrid production apparatus.

The description of U.S. Pat. No. 4,834,847 discloses an electrochemical cell and a method of the electrolysis of an aqueous solution of an alkali metal halide and the preparation of a halogenated hydrocarbon.

There is therefore a need for an effective method of electrochemical conversion of organic compounds, especially of organic compounds having zero or sparing solubility in water.

SUMMARY OF INVENTION

The inventors have found that an electrochemical reaction of organic compounds can effectively be conducted at a phase boundary when this is within a multilayer porous electrode comprising a hydrophilic layer and a lipophilic layer.

In a first aspect, the present invention relates to a method of electrochemical conversion of a first organic material which is soluble in or miscible with a first nonpolar solvent, comprising introducing the first organic material into the first nonpolar solvent to produce a first organic solvent or mixture; providing an electrolysis cell comprising—a porous first electrode comprising at least one first lipophilic layer and at least one second hydrophilic layer, where the first lipophilic layer and the second hydrophilic layer are porous, and—a second electrode; introducing the first organic solution or mixture into the electrolysis cell in such a way that the first organic solution or mixture makes contact with the first lipophilic layer of the first electrode; introducing a first polar electrolyte into the electrolysis cell in such a way that the first polar electrolyte makes contact with the second hydrophilic layer of the first electrode and the second electrode; and electrochemically converting the first organic material at the first electrode; or providing an electrolysis cell comprising—a porous first electrode comprising at least one first lipophilic layer and at least one second hydrophilic layer, where the first lipophilic layer and the second hydrophilic layer are porous, and—a second electrode; introducing the first organic material in the form of a liquid or gas into the electrolysis cell in such a way that the first organic material makes contact with the first lipophilic layer of the first electrode; introducing a first polar electrolyte into the electrolysis cell in such a way that the first polar electrolyte makes contact with the second hydrophilic layer of the first electrode and the second electrode; and electrochemically converting the first organic material at the first electrode; wherein—the first nonpolar solvent and the first polar electrolyte or—the first organic material in the form of a liquid or gas and the first polar electrolyte form a first phase boundary with one another in such a form that the first phase boundary in the electrochemical conversion is at least partly within the first electrode, preferably at an interface between the first lipophilic layer and the second hydrophilic layer.

In a further aspect, the invention relates to an apparatus for electrochemical conversion of a first organic material which is soluble in or miscible with a first nonpolar solvent, comprising an electrolysis cell, wherein the electrolysis cell comprises—a porous first electrode comprising at least one first lipophilic layer and at least one second hydrophilic layer, wherein the first lipophilic layer and the second hydrophilic layer are porous, and—a second electrode; at least one first supply device for the supply of a first solution or mixture of a first organic material which is soluble in or miscible with a first nonpolar solvent in or with a first nonpolar solvent, or for the supply of a first organic material which is soluble in or miscible with a first nonpolar solvent, which is set up to supply the first solution or mixture of the first organic material in or with the first nonpolar solvent, or to supply the first organic material, to the electrolysis cell in such a way that the first organic solution or mixture or the first organic material makes contact with the first lipophilic layer of the first electrode; and at least one first removal device for the removal of the remaining first solution or mixture and optionally at least one first product of the electrochemical conversion of the first organic material, or of the remaining first organic material and optionally at least one first product, or of the remaining first nonpolar solvent and optionally at least one first product, or of at least one first product, which is set up to remove the remaining first solution or mixture and optionally at least the first product of the electrochemical conversion of the first organic material, or the remaining first organic material and optionally at least the first product, or the remaining first nonpolar solvent and optionally at least the first product, or at least the first product from the electrolysis cell; further comprising at least one second supply device for a first polar electrolyte, which is set up to supply the first polar electrolyte to the electrolysis cell in such a way that the first polar electrolyte makes contact with the second hydrophilic layer of the first electrode and the second electrode, and/or a second removal device for the first polar electrolyte and optionally at least one first product of the electrochemical conversion of the first organic material, which is set up to remove the first polar electrolyte and optionally at least one first product of the electrochemical conversion of the first organic material from the electrolysis cell.

Further aspects of the present invention can be inferred from the dependent claims and the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended drawings are intended to illustrate embodiments of the present invention and impart further understanding thereof. In association with the description, they serve to elucidate concepts and principles of the invention. Other embodiments and many of the advantages mentioned are apparent with regard to the drawings. The elements of the drawings are not necessarily shown true to scale with one another. Elements, features and components that are the same, have the same function and the same effect are each given the same reference numerals in the figures of the drawings, unless stated otherwise.

FIGS. 1 to 6 show, in schematic form, illustrative embodiments of an apparatus of the invention with which the method of the invention can be performed.

FIGS. 7 and 8 show results that have been achieved in an example of the method of the invention.

DETAILED DESCRIPTION OF INVENTION

Unless defined differently, technical and scientific expressions used herein have the same meaning as commonly understood by a person skilled in the art in the technical field of the invention.

Figures given in the context of the present invention relate to % by weight, unless otherwise stated or apparent from the context. In the gas diffusion electrode of the invention, the percentages by weight add up to 100% by weight.

In the context of the present invention, hydrophobic is understood to mean water-repellent. According to the invention, hydrophobic pores and/or channels are those that repel water. More particularly, hydrophobic properties, according to the invention, are associated with substances or molecules having nonpolar groups.

By contrast, hydrophilic is understood to mean the ability to interact with water and other polar substances.

Lipophilic is understood to mean the property possessed by a substance that has good solubility in fats and oils or in which fats and oils have good solubility in turn. More particularly, lipophilic substances are understood to mean those that do not mix with and/or dissolve in, and/or repel, a first polar solvent of the first polar electrolyte, and which are especially hydrophobic, i.e. water-repellent.

Gas diffusion electrodes (GDE) in general are electrodes in which liquid, solid and gaseous phases are present, and where a conductive catalyst in particular catalyzes an electrical reaction between the liquid phase and the gaseous phase.

Different types of design are possible, for example in the form of a porous “all-active material catalyst” optionally with auxiliary layers to adjust the hydrophobicity, in which case, for example, it is possible to produce a membrane-GDE composite, e.g. AEM-GDE composite; of a conductive porous support to which a catalyst can be applied in a thin layer, in which case it is likewise again possible to produce a membrane-GDE composite, e.g. AEM-GDE composite; or of a catalyst which is porous in the composite and may be applied, optionally with additive, directly to a membrane, for example an AEM, and may then form a catalyst-coated membrane (CCM) in the composite.

Standard pressure is 101 325 Pa=1.01325 bar.

Electro-osmosis: Electro-osmosis is understood to mean an electrodynamic phenomenon in which a force in the cathode direction acts on particles having a positive zeta potential that are present in solution, and a force in the anode direction acts on all particles having a negative zeta potential. If a conversion takes place at the electrodes, i.e. if there is galvanic current flow, there is also a stream of matter of the particles having positive zeta potential toward the cathode, irrespective of whether or not the species is involved in the conversion. The same is also true of a negative zeta potential and the anode. If the cathode is porous, the medium is also pumped through the electrode. This is also referred to as an electro-osmotic pump.

The streams of matter that result from electro-osmosis can also flow counter to concentration gradients. Diffusion-related currents that compensate for the concentration gradients can be overcompensated as a result.

A separator is a two-dimensional structure designed to separate electrodes and/or electrolytes or the reaction spaces or half-cells in an electrolysis cell from one another. It is electrically insulating in respect of the electrodes of an electrolysis cell itself and can, especially in particular embodiments, at least partly prevent, preferably essentially prevent, the mixing of two electrolytes and/or, if appropriate, of product gases and/or reaction gases of an electrochemical reaction in half-cells separated by the separator. More particularly, a separator can prevent the mixing of product gases and/or reaction gases of half-cells separated thereby. However, a separator permits adequate exchange of mass and in particular of charge carriers with an electrolyte medium, in order to enable ionic flow. As separators, for example, frits, membranes, diaphragms etc. generally allow diffusive mass transfer of liquids and dissolved substances.

A diaphragm is a specific separator which is designed to electrically insulate electrodes from one another but does not have any intrinsic ion conductivity or marked transport selectivity. More particularly, a diaphragm, in particular embodiments, can also prevent the mixing of reaction gases in electrolyte streams. It is a two-dimensional component, for example a paper-like or porous composite material. Ion conductivity is achieved in a diaphragm via the absorptivity of the diaphragm toward the electrolyte. Diaphragms therefore frequently have a very sharp pore size distribution.

A membrane is an electrically insulating polymer film designed to electrically insulate electrodes from one another and preferably to essentially prevent the mixing of two electrolytes and gas bubbles present therein, especially to prevent the mixing of gas bubbles at least present therein. However, the membrane may have an active ion transport function by virtue of appropriate chemical groups. If this ion transport is ion-selective for one or more ions, for example cations and/or protons or anions, reference is also made to an ion-selective membrane. An ion-selective membrane is correspondingly an electrically insulating polymer film for the electrodes of the electrolysis cell, which is designed to electrically insulate electrodes from one another and especially to essentially prevent the mixing of two electrolytes and gas bubbles present therein, especially to prevent the mixing of gas bubbles at least present therein. The polymer in such an ion-selective membrane bears charged functional groups with mobile counterions and therefore constitutes a macromolecular salt, an acid and/or a base. Swollen in a pure solvent, for example water, these membranes have intrinsic ion conductivity. In electrolyte solutions, they generally also have selectivity with respect to the nature of the charge carrier transported. The ionic functionalization under potential can also lead to formation of new charge carriers in the membrane that are then responsible for ion transport in the membrane.

In a first aspect, the present invention relates to a method of electrochemical conversion of a first organic material which is soluble in or miscible with a first nonpolar solvent, comprising introducing the first organic material into the first nonpolar solvent to produce a first organic solvent or mixture; providing an electrolysis cell comprising—a porous first electrode comprising at least one first lipophilic layer and at least one second hydrophilic layer, where the first lipophilic layer and the second hydrophilic layer are porous, and—a second electrode; introducing the first organic solution or mixture into the electrolysis cell in such a way that the first organic solution or mixture makes contact with the first lipophilic layer of the first electrode; introducing a first polar electrolyte into the electrolysis cell in such a way that the first polar electrolyte makes contact with the second hydrophilic layer of the first electrode and the second electrode; and electrochemically converting the first organic material at the first electrode; or providing an electrolysis cell comprising—a porous first electrode comprising at least one first lipophilic layer and at least one second hydrophilic layer, where the first lipophilic layer and the second hydrophilic layer are porous, and—a second electrode; introducing the first organic material in the form of a liquid or gas into the electrolysis cell in such a way that the first organic material makes contact with the first lipophilic layer of the first electrode; introducing a first polar electrolyte into the electrolysis cell in such a way that the first polar electrolyte makes contact with the second hydrophilic layer of the first electrode and the second electrode; and electrochemically converting the first organic material at the first electrode; wherein—the first nonpolar solvent and the first polar electrolyte or—the first organic material in the form of a liquid or gas and the first polar electrolyte form a first phase boundary with one another in such a form that the first phase boundary in the electrochemical conversion is at least partly within the first electrode, preferably at an interface between the first lipophilic layer and the second hydrophilic layer.

In the method of the invention, the first organic material is not particularly restricted, provided that it is soluble in or miscible with a first nonpolar solvent. In this case, as is clear in the second embodiment of the method of the invention, it is not even necessary for the first nonpolar solvent to be employed in the method if the first organic material is liquid or gaseous. It is important merely that a phase boundary forms within the first electrode. For this purpose, it is consequently also sufficient for the first organic material and the first polar electrolyte to form a phase boundary, i.e. two separate phases. For this purpose, it is sufficient, for example, when the first organic material, in particular embodiments, is nonpolar.

In the first embodiment of the present method, this phase boundary is formed between the first solution or mixture in which the nonpolar solvent has been mixed with or has dissolved the first organic material, and the first polar electrolyte. In this respect, it is pointed out that, in this first embodiment of the method of the invention, the first organic material may take the form of a solid, liquid or gas that can then be dissolved in or mixed with the first nonpolar solvent. The first organic material here need not necessarily be nonpolar if it dissolves in or mixes with the first nonpolar solvent.

The first organic material can be introduced here in the form of a liquid or gas, especially liquid, into a nonpolar solvent, for example in order to adjust the viscosity of the first organic material, in order that it can achieve better ingress to and can preferably penetrate into the first electrode, it being simpler to reach the triphasic interface in the first electrode especially in the case that the first electrode takes the form of a gas diffusion electrode. Moreover, it is more easily possible through the mixing with the first nonpolar solvent or the dissolving in the first nonpolar solvent to adjust the concentration of the first organic material through the dilution, by means of which the reaction at the electrode can be better controlled, and overreduction can especially be reduced or avoided.

In the method of the invention, there are thus two variants for electrochemical conversion of the first organic material, depending on whether or not it is in the form of a fluid, i.e. liquid or gas. If the first organic material is in the form of a fluid, it can also be introduced directly as such into the electrolysis cell since it can form a first phase boundary with the first polar electrolyte. If the first organic material is in solid form, it must be dissolved in a first nonpolar solvent for it to be able to be introduced into the electrolysis cell and for the first nonpolar solvent to form the first phase boundary with the first polar electrolyte therein. In addition, it is of course also possible for the first organic material in the form of a fluid to be mixed with or dissolved in a first nonpolar solvent, for example in order to be able to form a better first phase boundary with the first polar electrolyte.

Apart from that, there is no further restriction in the first organic material that is soluble in or miscible with a first nonpolar solvent.

Nor is there any particular restriction in the first organic material with regard to possible classes of compounds. It may be a saturated, unsaturated and/or aromatic hydrocarbon which is substituted or unsubstituted, where the substituents are not particularly restricted, provided that the first organic material is soluble in or miscible with a first nonpolar solvent. For example, it is also possible to use polar substituents when the first organic material itself is still soluble in or miscible with a first nonpolar solvent. For that reason, the nature of the substituents is not particularly restricted either, nor is the number of carbons in the first organic material. In particular embodiments, the first organic material is aromatic or at least comprises an aromatic moiety in the structure. For example, the first organic material for a reduction may be selected from unsaturated hydrocarbons, aldehydes, ketones, nitro compounds, nitroso compounds, nitriles, etc.; and for an oxidation may be selected from alcohols, unsaturated hydrocarbons, amines, mercaptans, etc.

In particular embodiments, the first organic material is especially immiscible with water and/or insoluble in water as solvent in the first polar electrolyte. In particular embodiments, the first organic material is hydrophobic, especially when it is in the form of a liquid or gas.

The first nonpolar solvent is likewise not particularly restricted, provided that it forms a phase boundary with the first polar electrolyte. This may be a pure compound, for example optionally substituted alkanes such as pentane, hexane, heptane, octane, etc., partly or fully halogenated alkanes such as dichloromethane, etc.; substituted or unsubstituted aromatics such as benzene, toluene, etc.; alkenes; alkynes; esters; ethers such as diethyl ether, tetrahydrofuran, etc. It is also possible to use mixtures of nonpolar solvents. The first nonpolar solvent is especially not soluble with water or in water as solvent in the first polar electrolyte, i.e. in particular hydrophobic.

The first nonpolar solvent need not be electrically conductive, but it is not impossible that conductive nonpolar solvents such as ionic liquids (ILs) are used, provided that they are stable and immiscible with the first polar electrolyte, especially an aqueous phase. Since hydrophobic organic salt melts in particular, for example Bu₃MeP⁺ ((CF₃)SO₂)N⁻, as ionic liquids often have very desirable dissolution properties, they can also be used in place of the first nonpolar solvent. The hydrophobic ionic liquids here are not particularly restricted.

A first nonpolar solvent is employed, for example, in the embodiments set out above for the first organic compound. In addition, a nonpolar solvent may also be required if a first organic product which is solid at the reaction temperature of the electrochemical conversion is formed at the porous first electrode in the electrochemical reaction, does not dissolve in the first polar electrolyte and is accordingly to be removed again from the first electrode with the first polar solvent.

What is meant here by the expression “miscible with a first nonpolar solvent” is that the mixing with nonpolar solvent does not form two phases, i.e. a phase boundary.

The introducing of the first material into the first nonpolar solvent for preparation of a first organic solution or mixture is not particularly restricted. For example, it can be mixed, added dropwise, stirred, etc. However, preference is given to preparing a homogeneous solution in the introducing of the first organic material into the first nonpolar solvent.

The first polar electrolyte is likewise not particularly restricted. In particular embodiments, the first polar electrolyte is liquid. In particular embodiments, the first polar electrolyte is protic. In particular embodiments, the first polar electrolyte especially comprises at least one first polar solvent such as, for example, water; alcohols such as methanol, ethanol, propanol, butanol, phenol, etc.; carboxylic acids such as formic acid, acetic acid, propionic acid, etc.; aldehydes such as acetaldehyde, etc., ketones such as acetone; acids such as H₂SO₄, HCl, HBr, etc.; sulfones; amines; nitriles; amides; lactones; sulfoxides; etc., and mixtures; and especially water as polar solvent. In addition, it comprises compounds such as conductive salts that are soluble in the at least one first polar solvent and enable ionic contacting of the electrodes, i.e. of the first and second electrodes of the electrolysis cell, such that charge carrier transport, for example ion transport, can take place. The conductive salt is not particularly restricted, and comprises, for example, salts of alkali metals and/or alkaline earth metals, for example of lithium, sodium, potassium, magnesium, calcium, etc., for example halides, sulfates, etc. In addition, the first polar electrolyte may also contain substances typically present in electrolytes, for example pH regulators, buffers, etc.

As well as the first polar solvents mentioned, it is also possible to use other, especially protic, solvents in the first polar electrolyte, either alone as solvent or in combination with the abovementioned polar solvents. At low temperatures of <15° C., it is also possible to use HF, for example. It is also equally possible here to use salt melts or ionic liquids such as ethylmethylimidazolium hydrogensulfate and/or triethanolmethylammonium methylsulfate, provided that they are polar. More particularly, it is possible to use those further, preferably protic, solvents in reactions in the electrolysis cell that neither consume nor produce water—for example with regard to the second electrode, provided that the reaction takes place within their stability window. The polar solvent can be suitably chosen accordingly.

In particular embodiments, the first polar electrolyte contains water and optionally at least one salt, for example one of those specified above. In particular embodiments, the first polar electrolyte—also referred to hereinafter as first phase if appropriate—is an aqueous solution of salts that can serve as electrolyte and optionally consumable materials, i.e. can accordingly, if appropriate, be supplied to the electrolysis cell via a feed device and removed from the electrolysis cell via a removal device.

By contrast, the first organic solution or mixture, or the first organic material in the form of a liquid or gas, forms a second phase which is a nonpolar phase that contains the first organic material as substrate. This nonpolar phase has only limited or zero miscibility with the polar electrolyte as the first phase, for example the aqueous electrolyte, such that a phase boundary forms. As already set out above, the first organic material as substrate must be soluble in or miscible with a nonpolar solvent, but may be solid, liquid or gaseous. It is also possible for the first organic material to be the nonpolar phase in the form of a pure substrate. The nonpolar phase need not be electrically conductive. In particular embodiments in the first variant, the substrate is a substrate solution in a nonpolar organic solvent.

The providing of an electrolysis cell comprising a porous first electrode comprising at least one first lipophilic layer and at least one second hydrophilic layer, wherein the first lipophilic layer and the second hydrophilic layer are porous, and a second electrode is likewise not particularly restricted. Apart from the two electrodes, wherein the second electrode is not particularly restricted, the electrolysis cell is likewise not particularly restricted in terms of its material and its configuration. Illustrative configurations of the electrolysis cell are described hereinafter.

The first electrode is porous, i.e. has pores, and comprises at least one first lipophilic layer and at least one second hydrophilic layer. However, it is not impossible that the first electrode also comprises regions that do not have a porous configuration, for example a grid for electrical contact connection, in which case, however, a layer may optionally be pressed into the grid in order to form a porous structure in turn. The first lipophilic layer is porous. The second hydrophilic layer is porous. More particularly, the first lipophilic layer and the second hydrophilic layer are in contact with one another. If the two layers are in contact and the two layers are porous, it is possible to reduce or prevent the formation of by-products that have to be removed, for example of OH⁻ in the case of use of water in the polar electrolyte.

The pore size here is not particularly restricted, but in particular embodiments is in the range from 0.1 to 500 μm, for example in the range from 0.2 to 100 μm, e.g. 0.5 to 10 μm. Pore size can be suitably determined, for example, by means of porosimetry. The first electrode thus has at least one region with pores, especially with pores present in the region in which the electrochemical conversion of the first organic material is effected, i.e. especially in the region in which the first lipophilic layer and the second hydrophilic layer adjoin one another. In this region, in particular embodiments, there is also accordingly at least one first electrocatalyst or catalyst for the electrochemical conversion of the first organic material which is not particularly restricted. The first electrocatalyst may comprise, for example, metals and/or compounds thereof, for example Cu, Ag, Au, Pd, Zr, Zn, Cd, Pb, Ir, Sn, Zn, Pb, Ti, Fe, Ni, Co, Rh, Ru, W, Mo, and compounds thereof, for example oxides or suitable polymorphs of carbon etc., and mixtures and or alloys thereof, and may be suitably adapted to a desired electrochemical conversion. For example, it may also be introduced into the second hydrophilic layer. Preferably, however, the first electrocatalyst is not present in the first lipophilic layer.

However, the first electrode may as a whole also consist only of materials comprising pores, i.e. in particular embodiments comprises solely porous layers. With porous layers, good separation of the two phases in the process in particular is possible, i.e. of the nonpolar phase of the nonpolar solution or mixture or of the nonpolar solvent, and of the polar phase of the polar electrolyte. In this way too, it is possible to increase the area-based current density within the electrode, especially when the first lipophilic layer and/or the second hydrophilic layer are conductive. Moreover, the electrochemically catalyzed reaction to give the desired product is improved by the pore structure. In particular embodiments, the first electrode consists of the first lipophilic layer and the second hydrophilic layer, and optionally a material for electrical contact connection. It is optionally possible for the first electrode in such embodiments also to be coated, for example on the lipophilic layer on the side which is in contact with the first nonpolar solution or mixture, or the first organic solvent in the form of a liquid or gas, as bulk, and/or on the hydrophilic layer on the side which is in contact with the first polar electrolyte as bulk.

Within the present concept, i.e. in relation to the present process and also the present apparatus, the first electrode forms a “three-phase half-cell” within the electrolysis cell. Within the concept, at least one electrochemical half-cell thus comprises three phases, namely the solid but porous electrode that lies between two immiscible fluid phases, one of which is nonpolar and contains the substrate, and the other is a polar electrolyte that carries the ion current and can optionally serve as consumable material. The electrolyte phase here is that directed toward the counterelectrode.

The porous first electrode has amphiphilic character and comprises at least two layers, one of which is more hydrophilic and the other more lipophilic. Both layers here are preferably electrically conductive and porous. Since electrodes, owing to electrochemical stress, generally become more hydrophilic, it is also possible to introduce the electrical contact or electrical contact connection into the hydrophilic layer or into the layer boundary.

The first lipophilic layer is not particularly restricted provided that it is lipophilic. In particular embodiments, it is hydrophobic. The first lipophilic layer is porous, i.e. has pores. As a result, the transport of the first organic material, optionally dissolved in or mixed with the first nonpolar solvent, can be controlled, such that, if appropriate, no excess reaction takes place. The first lipophilic layer may also be constructed, for example, as a grid or the like, although this is not preferred.

In particular embodiments, the first lipophilic layer is electrically conductive. In particular embodiments, the first lipophilic layer is electrochemically inactive as catalyst, especially when it is introduced into the first polar electrolyte, for example an aqueous electrolyte. In this way, it is especially possible to ensure that no electrochemical reactions take place when a portion of this layer comes into contact with the electrolyte. Otherwise, the electroosmotic pressure in the porous electrode can draw the electrolyte into the lipophilic layer and force the liquid-liquid interface out of the first electrode, such that the substrate supply thereof can be cut off as a result.

The construction of the first lipophilic layer is not particularly restricted, and it may be constructed in a meshlike manner, as a scrim, loop-drawn knit or loop-formed knit, in a spongelike manner, etc. In particular embodiments, the first lipophilic layer is realized by binding particles that are especially inert, conductive and/or hydrophobic, e.g. hydrophobic carbon and/or glassy carbon, with a hydrophobic binder material such as PTFE (polytetrafluoroethylene), PCTFE (polychlorotrifluoroethylene), PFA (perfluoroalkoxy) and/or FEP (fluoroethylene-propylene). The production of the first lipophilic layer may be simultaneous with the production of the second hydrophilic layer and optionally further layers, for example by means of joint rolling, coextrusion, etc., or separately therefrom, in which case the layers can subsequently be suitably bonded.

In particular embodiments, the first lipophilic layer has essentially zero catalytic activity in respect of the first polar electrolyte, i.e. has a high overvoltage for the competing reaction with the first polar electrolyte, for example a high overvoltage for the evolution of hydrogen or evolution of oxygen, according to how the electrode is connected. In particular embodiments, the first lipophilic layer comprises hydrophobic, preferably conductive, first particles and/or at least one first hydrophobic binder. If the first lipophilic layer of the first electrode is in contact with a gas as first organic material, the first electrode may also take the form of a gas diffusion electrode, and so the first lipophilic layer may be designed accordingly.

The second hydrophilic layer is not particularly restricted either and is especially wettable with the first polar electrolyte, especially water. In particular embodiments, the second hydrophilic layer comprises a first electrocatalyst and optionally at least one second binder. In particular embodiments, the hydrophilic layer is thus the electrochemically active layer. It contains or even consists essentially of the first electrocatalyst. It is preferably also hydrophilic, porous and/or electrically conductive.

In principle, the second hydrophilic layer may also be realized with bound particles, optionally with at least one binder. By contrast, however, these particles are at least partially electrochemically active catalyst particles. This layer preferably consists of the first electrocatalyst in a large portion. However, embedding of the first electrocatalyst into an inert conductive matrix is also possible. The binder used may also, for example, be PTFE or PTFCE. In order to further increase the hydrophilic character of this layer, these polymers may, however, also be partly replaced by hydrophilic binder polymers such as polyarylsulfones, e.g. PPSU (polyphenylene-sulfone).

It is also possible to introduce hydrophilic additives, e.g. metal oxides, for example Al₂O₃, TiO₂, ZnO, Y₂O₃, etc., into the second hydrophilic layer. In particular embodiments, the second hydrophilic layer thus comprises first hydrophilic additives, especially metal oxides.

In particular embodiments, the second hydrophilic layer may also comprise an inherently ion-conductive additive such as a cation or anion exchanger. To achieve inherent ion conductivity, it is thus possible to introduce ion conductivity additives such as ion exchange resins or other solid electrolytes into this layer, which are not particularly restricted. In particular embodiments, the second hydrophilic layer comprises a first ion-conducting additive, especially a cation or anion exchanger.

As well as the first lipophilic layer and the second hydrophilic layer, the first electrode may also comprise further “layers”.

For better current distribution in large electrodes, it is possible, for example, to add a first current collector which is not particularly restricted in terms of material and form and may comprise, for example, a metal, a conductive oxide, a ceramic, a conductive polymer, etc., which may take the form, for example, of a lattice, braid, loop-formed knit, loop-drawn knit or the like. Since the first current collector should not come into contact with the first polar electrolyte, especially an aqueous electrolyte, it is preferably connected to the first lipophilic layer. In particular embodiments, the first electrode thus comprises a first current collector which is preferably not in contact with the second hydrophilic layer. It is also possible for a first current collector to be realized, for example, as an incomplete metal coating, for example, of the first lipophilic layer. Preference is given to using a metal braid since it can also offer additional mechanical support. The first current collector, for example, may lie on or be embedded in the first lipophilic layer, for example in that it is rolled with said layer.

As well as the first lipophilic layer and the second hydrophilic layer and optionally the first current collector, the first electrode may also comprise further additional layers. For example, a protective layer may be provided as a “top layer” on the second hydrophilic layer, for example in the form of a hydrophilic membrane for the second hydrophilic layer for protection of the layer. The hydrophilic membrane may optionally be soaked and passed through by the electrolyte. The main function of this layer is the protection of the electrode from erosion. This layer may also form an additional flow barrier in order to prevent migration of the liquid-liquid boundary. In particular embodiments, such a membrane on the second hydrophilic layer is porous.

It is also or alternatively possible to provide, for example, a protective layer as “backing layer” on the first lipophilic, e.g. hydrophobic, layer, for example in the form of a hydrophobic membrane for the first lipophilic layer, for example for better wetting with the nonpolar phases, for example based on polyamide, etc., in order to prevent erosions and/or avoid flows through the electrode. Since this side, however, is on the opposite side from the counterelectrode, however, it is preferably used for electrical contact connection, which correspondingly means that such a hydrophobic membrane is not very practicable. In such a case, the layer should thus then preferably not be continuous, and, for example, wires of the current collector, if present, may protrude therefrom.

The second hydrophilic layer may also be fused to an ion-conductive membrane. In particular, inherent ion conductivity of the second hydrophilic layer is preferable here, said layer especially corresponding to the ion-conductive membrane. Like the top layer discussed above, this layer also offers erosion protection and flow resistance. However, it may additionally be used to increase the total charge transport between the first electrode and the first polar electrolyte. For example, anion exchange membranes may be used in order to limit charge transport in cathodes to anions that leave the first electrode in the polar electrolytes and to protons that penetrate via the Grotthuss mechanism. In a corresponding manner, it is possible to use cation exchange membranes, for example, at the anode. This can be used to control the electroosmotic pressure and/or to protect the electrode from electrolyte cations and/or anions. Just like cathodes, it is thus also possible to shield anodes from electrolyte anions Like the top layer and the backing layer, the anion and/or cation exchange membranes are also not particularly restricted. The anion and/or cation exchange membranes may be realized, for example, as anion exchange membrane (AEM), cation exchange membrane (CEM), or bipolar membrane in either direction.

In addition, in the first electrode, at least one support construction may be incorporated as mechanical support, for example in the form of insulation polymer mats, etc., for example including into each layer of the electrode.

In the electrolysis cell, the first electrode may be connected as cathode or anode, according to the desired electrochemical conversion, i.e. reduction or oxidation.

In addition, the electrolysis cell comprises a second electrode which is not particularly restricted. In terms of its construction, it may be similar to or different than that of the first electrode, according to the desired half-cell reaction. For instance, the second electrode may take the form of an all-active electrode or solid electrode, of a gas diffusion electrode, of a porous bound catalyst structure, of a particulate catalyst on a support, of a coating of a particulate catalyst on a membrane, of a porous conductive support into which a catalyst has been impregnated, and/or of a noncontinuous sheetlike structure. Water can also be electrolyzed to H₂ or O₂ at the second electrode, for example in the case of an aqueous first polar electrolyte.

The second electrode may also be executed as a direct catalyst coating on a membrane or in direct contact with a membrane, especially if it is a noncontinuous planar construction such as mesh, for example. The second electrode may also be insulated by a separator in order to protect the first electrode from gases that form at the second electrode.

In the above cases, in particular embodiments, a first organic material is converted at the first electrode, while there is preferably a conversion of the first polar electrolyte or a constituent thereof, for example water, at the second electrode.

The arrangement of the electrodes is not particularly restricted. For example, they may be arranged essentially in parallel, such that it is correspondingly possible to form electrode stacks, or else they may be in a concentric arrangement, etc.

In particular embodiments, the second electrode comprises at least one third lipophilic layer and at least one fourth hydrophilic layer, wherein the third lipophilic layer and the fourth hydrophilic layer are preferably porous, wherein the first polar electrolyte makes contact with the fourth hydrophilic layer of the second electrode, further comprising introducing—a second organic material in the form of a liquid or gas, or—a second organic solution or mixture comprising a second organic material which is soluble in or miscible with a second nonpolar solvent, and a second nonpolar solvent, into the electrolysis cell in such a way that the first organic material or the second organic solution or mixture makes contact with the third lipophilic layer of the second electrode, wherein the second organic material is electrochemically converted at the second electrode. In this case, for example, two organic substrates may be converted simultaneously in the manner of a tandem electrolysis.

In such embodiments, the second electrode is similar to the first electrode or relatively large parts or the entirety thereof may even correspond thereto. If, for example, the first electrode is the cathode, the second electrode could be constructed, in a mirror image, as the anode in the layer structure toward the middle of the electrolysis cell (between the two electrodes).

In such a second electrode, the third lipophilic layer may be formed from the same material as the first lipophilic layer, or from another material mentioned for the first lipophilic layer. It is likewise possible for the fourth hydrophilic layer to be constructed from the same material as the second lipophilic layer, or from another material. More particularly, the fourth hydrophilic layer may include the same electrocatalyst as the second hydrophilic layer as the second electrocatalyst, or a different one, but preferably one selected from the materials mentioned above for the first electrocatalyst. Any desired combinations are possible here, including with regard to the presence of further layers in the second electrode, for instance a second current collector may correspond to the first current collector or else may be different therefrom, but may be made of one of the materials mentioned for the first current collector. With regard to the form as well, the individual layers may be the same or different. Preferably, however, the third lipophilic layer and/or the fourth hydrophilic layer are porous. Preferably, the third lipophilic layer and the fourth hydrophilic layer are in contact with one another. It is also possible, in a manner corresponding to the first electrode, for membranes to be applied to the layers of the second electrode in such embodiments, for example a hydrophobic membrane on the third lipophilic layer and/or a hydrophilic membrane or ion exchange membrane on the fourth hydrophilic layer. Here too, the materials usable may correspond to those in the abovementioned corresponding analogous layers, wherein the layers may be the same or different. It is also possible for at least one support construction to be provided in the second electrode, for example including for all layers.

In addition, the second organic material may correspond to the first organic material or may be different therefrom. Since, however, different reactions can proceed at the anode than at the cathode, the first organic material and the second organic material are different, for example including with regard to the aggregate form and with regard to whether or not they are in a solution or mixture. Correspondingly, it is also possible for the second nonpolar solvent, if it is used in the process, to correspond to the first nonpolar solvent, if it is used, or be different therefrom.

In the embodiments with the second electrode comprising the fourth hydrophilic layer, this is typically in contact with the first polar electrolyte. However, it is also conceivable that the electrolysis cell comprises at least one separator, for example a diaphragm and/or a membrane—which are not particularly restricted—between the first electrode and the second electrode, such that the space between the two electrodes is divided into two component spaces, in which case it is possible for a first polar electrolyte to be introduced into one component space—for example adjoining the second hydrophilic layer of the first electrode—and for a second polar electrolyte that may correspond to the first polar electrolyte or be different therefrom to be introduced into another component space—for example adjoining the fourth hydrophilic layer of the second electrode or generally the second electrode, although the materials for this second two polar electrolyte may be the same as mentioned for the first polar electrolyte. However, this is not preferred. In particular embodiments, the second hydrophilic layer of the first electrode makes at least partial contact with a first separator.

Alternatively or additionally, it is also optionally possible to use further separators and optionally further polar electrolytes with which product extraction from the first polar electrolyte is possible, for example when the electrochemical conversion generates an organic product soluble in the first polar electrolyte at the first and optionally second electrodes. In that case, it is easily possible here to purify the organic product.

In particular embodiments, the second hydrophilic layer of the first electrode and the fourth hydrophilic layer of the second electrode make at least partial contact with a first separator on opposite sides of the first separator. In such embodiments, the first polar electrolyte is at least partly present in the first separator. In particular embodiments, the first separator has been swollen by the first polar electrolyte. In this way, it is possible to enable good contact between the two electrodes with a small electrolyte volume. This is advantageous especially when the first polar electrolyte is not converted, i.e. not consumed, or can easily be replenished.

As well as separators, the electrolysis cell may also comprise further constituents that are typically used for electrolysis cells, such as corresponding feed and drain devices for the first polar electrolyte, the first nonpolar solution or mixture or the first organic material in the form of a liquid or gas, and optionally for the second nonpolar solution or mixture or the second organic material in the form of a liquid or gas, heating and/or cooling devices, pumps, valves, housing, etc. However, the electrolysis cell comprises at least one power source.

In the method of the invention, the introducing of the first organic solution or mixture, or of the first organic material in the form of a liquid or gas, into the electrolysis cell in such a way that the first organic solution or mixture or the first organic material makes contact with the first lipophilic layer of the first electrode, the introducing of a first polar electrolyte into the electrolysis cell in such a way that the first polar electrolyte makes contact with the second hydrophilic layer of the first electrode and the second electrode, and any introducing of the second organic solution or mixture comprising a second organic material or the second organic material in the form of a liquid or gas in such a way that the second organic solution or mixture or the second organic material makes contact with the third lipophilic layer of the second electrode are not particularly restricted, and the introduction can be effected simultaneously or at different times.

After the introducing of the first organic solution or mixture, or of the first organic material in the form of a liquid or gas, as nonpolar phase, and after the introducing of the first polar electrolyte as polar phase, the nonpolar phase and polar phase form a first phase boundary in such a form that the first phase boundary in the electrochemical conversion is at least partly within the first electrode, preferably at an interface between the first lipophilic layer and the second hydrophilic layer. The use of the first hydrophilic layer and of the first lipophilic layer can ensure here that the first phase boundary forms at least partly and preferably completely in the first electrode in the electrochemical conversion, such that the first organic material can arrive there for electrochemical conversion, but it is simultaneously also possible to establish a suitable cell voltage by means of the first polar electrolyte. The first phase boundary as liquid-liquid phase boundary must thus be at least partly in contact with the electrode surface. In this way, it is also possible to form a triphasic interface at which an electrocatalyst of the first electrode, for example the first catalyst, simultaneously has access to electrical contact, ion contact, optionally protons from the first polar electrolyte, and the first organic material as substrate. In order to achieve high current densities, the total area of these three phase interfaces should be at a maximum. For this purpose, it is possible to position the liquid-liquid interface within a porous electrode.

In order that the liquid-liquid boundary remains at or within the electrode, it is necessary for the electrode to have an amphiphilic character, as achieved by virtue of the lipophilic layer and the hydrophilic layer, with the side toward the counterelectrode being wettable by the polar, for example aqueous, phase, while the other side is wettable by the nonpolar phase. The electrode thus has at least two layers. In order, however, to bring the phases into contact, the second hydrophilic layer preferably also includes a certain amount of lipophilic pores, for example ≤30%, preferably ≤25%, further preferably ≤20%, based on the pores of the hydrophilic layer.

Corresponding considerations relate to the second electrode if it has the third lipophilic layer and the fourth hydrophilic layer and a second phase boundary forms between the first polar electrolyte (or another, for example second, polar electrolyte) and the second nonpolar solution or mixture or the second organic material in the form of a liquid or gas.

The electrochemical conversion of the first organic material or of the first organic material in the form of a liquid or gas at the first electrode, and if appropriate the electrochemical conversion of the second organic material, or of the second organic material in the form of a liquid or gas, are not particularly restricted and may be suitably adapted to a reactant and a desired product.

The electrochemical conversion of the first organic material gives rise to at least one first organic product which, according to its solubility and polarity, can be removed from the first electrode via the first nonpolar phase, i.e. first nonpolar solution or mixture or first organic material, or the first polar electrolyte as polar phase. It can either be discharged from the electrolysis cell via the corresponding phase and then optionally removed/extracted outside and optionally purified, or extracted into further phases in the electrolysis cell, for example by means of suitable separators, and hence optionally separated from by-products.

It should be noted here that, as well as the electrochemical conversion at the first electrode—in which at least one first organic product is formed—an electrochemical conversion also takes place at the second electrode, in which at least one second inorganic product, for example chlorine, oxygen, etc., or at least one second organic product may form, for example with the second electrode comprising the third lipophilic layer and the fourth hydrophilic layer. It is of course possible in that case, in the method of the invention, for the first organic product to be reacted further with the second inorganic or organic product, preferably after previous removal and purification thereof, such that it is possible by the method of the invention not just to perform an organic synthesis step by electrochemical means, but simultaneously also to obtain a further reactant for a subsequent step, in which case it is also possible, for example, to use waste heat from the electrochemical conversion for this further conversion in the subsequent step.

As set out above, the method of the invention may also be followed by an extraction. In some cases, for example the cathodic reduction of nitro compounds or the anodic oxidation of aldehydes, hydrophilicity of the product is increased, which leads to partial extraction into the electrolyte. In this case, the electrolyte, after leaving the cell, in particular embodiments, will go through an extraction vessel with pure organic solvent to recover the product.

For these applications, the electrolyte gap can also be provided with an unlimited number of separators, e.g. 2, 3, 4, 5, 6, 7, 8, 9, 10 or more separators, as also set out above, to simplify the extraction.

A further aspect of the present invention is directed to an apparatus for electrochemical conversion of a first organic material which is soluble in or miscible with a first nonpolar solvent, comprising an electrolysis cell, wherein the electrolysis cell comprises—a porous first electrode comprising at least one first lipophilic layer and at least one second hydrophilic layer, wherein the first lipophilic layer and the second hydrophilic layer are porous, and—a second electrode; at least one first supply device for the supply of a first solution or mixture of a first organic material which is soluble in or miscible with a first nonpolar solvent in or with a first nonpolar solvent, or for the supply of a first organic material which is soluble in or miscible with a first nonpolar solvent, which is set up to supply the first solution or mixture of the first organic material in or with the first nonpolar solvent, or to supply the first organic material, to the electrolysis cell in such a way that the first organic solution or mixture or the first organic material makes contact with the first lipophilic layer of the first electrode; and at least one first removal device for the removal of the remaining first solution or mixture and optionally at least one first product of the electrochemical conversion of the first organic material (according to whether or not it is polar and can accordingly be transferred to the first polar electrolyte), or of the remaining first organic material and optionally at least one first product, or of the remaining first nonpolar solvent and optionally at least one first product, or of at least one first product, which is set up to remove the remaining first solution or mixture and optionally at least the first product of the electrochemical conversion of the first organic material, or the remaining first organic material and optionally at least the first product, or the remaining first nonpolar solvent and optionally at least the first product, or at least the first product from the electrolysis cell; further comprising at least one second supply device for a first polar electrolyte, which is set up to supply the first polar electrolyte to the electrolysis cell in such a way that the first polar electrolyte makes contact with the second hydrophilic layer of the first electrode and the second electrode, and/or a second removal device for the first polar electrolyte and optionally at least one first product of the electrochemical conversion of the first organic material, which is set up to remove the first polar electrolyte and optionally at least one first product of the electrochemical conversion of the first organic material from the electrolysis cell.

The apparatus of the invention comprises at least one second supply device for the first polar electrolyte which is set up to supply the first polar electrolyte to the electrolysis cell in such a way that the first polar electrolyte makes contact with the second hydrophilic layer of the first electrode and the second electrode, if appropriate the fourth hydrophilic layer of the second electrode, and/or a second removal device for the first polar electrolyte and optionally at least one first product of the electrochemical conversion of the first organic material, which is set up to remove the first polar electrolyte and optionally at least one first product of the electrochemical conversion of the first organic material from the electrolysis cell. These are likewise not particularly restricted, provided that they are suitable for the corresponding materials, and can also be executed in the form of pipes, conduits, etc. However, if the first polar electrolyte is not converted or does not undergo any overall change in the electrochemical conversion in the electrolysis cell, and also no product from the electrochemical conversion of the first organic material and optionally of the first nonpolar solvent is transferred into it, it would also be conceivable that the second supply device and/or the second removal device is dispensed with, for example when no water is consumed in the electrolysis in an aqueous first polar electrolyte. For heat-related reasons, however, even in such cases, the first polar electrolyte is supplied and removed, and so the corresponding supply and removal device is present.

If at least one first polar product (and/or second polar product given the appropriate configuration of the second electrode) is formed in the electrochemical conversion and is transferred to the first (and/or second) polar electrolyte, extraction (optionally by means of one or more separators) can also be effected into further polar electrolytes within the first electrolysis cell, such that, correspondingly, further supply and removal devices may also be provided for further polar electrolytes.

The apparatus of the invention can especially be used to perform the method of the invention. Correspondingly, the above details of the method of the invention, especially those relating to constituents of the apparatus such as an electrolysis cell and components thereof, are also applicable in the case of the apparatus of the invention, and reference is thus made here to this as well. Particularly the configurations of the first and second electrodes in the case of the apparatus of the invention correspond to those as discussed above for the method of the invention. In addition, the electrolysis cell in the apparatus of the invention comprises at least one power source, and may additionally also comprise the constituents that have been mentioned for the method of the invention, such as separators, pumps, valves, heating and/or cooling devices, etc.

In particular embodiments, the first electrode and/or optionally the second electrode (especially when it comprises the third lipophilic layer and the fourth hydrophilic layer) comprises a current collector which is not in contact with the second hydrophilic layer or, if appropriate, with the fourth hydrophilic layer. This type of electrode is advantageous when the solubility of a substrate, i.e. of the corresponding organic material, in aqueous electrolytes is too low to achieve suitable current densities or the separation of the product from the electrolytes is very costly.

The first and/or second electrode may also take the form of vapor diffusion electrodes/gas diffusion electrodes. In this electrolyte design, the first and/or second organic material as substrate may be borne by a nonpolar phase that flows through, or through the reverse side of, the electrode. In principle, this phase may also be a substrate vapor, a vapor carrier gas mixture or else a clean gaseous substrate. In this latter specific case, the amphiphilic electrode would become a gas diffusion electrode. It is not impossible that the organic material undergoes a phase transition during the electrochemical process. A liquid substrate can also lead to a gaseous product. A gaseous substrate may also result in a product having a higher boiling point that condenses after the conversion.

In particular embodiments, the first lipophilic layer comprises hydrophobic, preferably conductive, first particles and/or at least one first hydrophobic binder.

In particular embodiments, the second hydrophilic layer comprises a first electrocatalyst and optionally at least one second binder. In particular embodiments, the second hydrophilic layer comprises a first ion-conducting additive, especially a cation or anion exchanger, and/or first hydrophilic additives, especially metal oxides.

In particular embodiments, the second hydrophilic layer of the first electrode makes at least partial contact with a first separator. It has already been stated that the electrodes may contain a fused membrane. This membrane may also be utilized jointly by both electrodes in particular embodiments. In this case, the membrane swollen with the first polar electrolyte, for example a water-swollen membrane, becomes the polar, for example aqueous, phase, and a membrane-electrode assembly (MEA) may be formed. Especially in the case of non-water-releasing reactions, however, saturation of the organic phase with water may possibly be required. The membrane is not limited in terms of its ion conductivity. The functionalization of the membrane polymers can be matched to the demands of the specific reaction. Therefore, this membrane can be realized as a cation exchange membrane, anion exchange membrane or bipolar membrane in either direction.

The first supply device and the first removal device are not particularly restricted, provided that they are suitable for the supply and removal of the corresponding material, and may take the form, for example, of pipes, conduits, etc.

In particular embodiments, the second electrode comprises at least one third lipophilic layer and at least one fourth hydrophilic layer, wherein the third lipophilic layer and the fourth hydrophilic layer are preferably porous, wherein the second hydrophilic layer and the fourth hydrophilic layer are opposite one another but preferably not in contact with one another in the electrolysis cell, further comprising at least one further supply device for the supply of a second solution or mixture of a second organic material which is soluble in or miscible with a second nonpolar solvent in or with a second nonpolar solvent, or for the supply of a second organic material which is soluble in or miscible with a second nonpolar solvent, which is set up to supply the second solution or mixture of the second organic material in or with the second nonpolar solvent, or the second organic material, to the electrolysis cell in such a way that the second organic solution or mixture or the second organic material makes contact with the third lipophilic layer of the second electrode; and at least one further removal device for the removal of the remaining second solution or mixture and optionally at least one second product of the electrochemical conversion of the second organic material, or of the remaining second organic material and optionally at least one second product, or of the remaining second nonpolar solvent and optionally at least one second product, or of at least one second product, which is set up to remove the remaining second solution or mixture and optionally at least the second product of the electrochemical conversion of the second organic material, or the remaining second organic material and optionally at least the second product, or the remaining second nonpolar solvent and optionally at least the second product, or at least the second product from the electrolysis cell.

If, in such embodiments, at least one first polar (organic) product is formed at the first electrode and at least one second polar (organic) product at the second electrode, it is not impossible that both are transferred into the first polar electrolyte. Preference is given here, however, to providing a separator between the two electrodes, such that the at least one first polar product is transferred into the first polar electrolyte and the at least one second polar product into a further (e.g. second) polar electrolyte that may be different than or correspond to the first polar electrolyte. When the at least one first polar product and the at least one second polar product are transferred into the first polar electrolyte, however, it is not impossible that the two are then allowed to react.

In these embodiments, the second hydrophilic layer and the fourth hydrophilic layer are opposite one another in the electrolysis cell, but preferably do not make contact, especially when they are both conductive. However, they may make partial contact if they are nonconductive provided that it can be ensured that the first electrode and the second electrode come into contact with the first polar electrolyte. However, this is not preferred.

The at least one further supply device for supply of a second solution or mixture of a second organic material which is soluble in or miscible with a second nonpolar solvent in or with a second nonpolar solvent, or for the supply of a second organic material which is soluble in or miscible with a second nonpolar solvent, and the at least one further removal device for the removal of the remaining second solution or mixture and optionally at least one second product of the electrochemical conversion of the second organic material, or of the remaining second organic material and optionally at least one second product, or of the remaining second nonpolar solvent and optionally at least one second product, or of at least one second product, are also not particularly restricted, provided that they are suitable for supply and removal of the corresponding material, and may take the form, for example, of pipes, conduits, etc.

In particular embodiments, the third lipophilic layer comprises hydrophobic, preferably conductive, third particles that may correspond to or be different than the first particles, and/or at least one second hydrophobic binder that may correspond to or be different than the second hydrophobic binder.

In particular embodiments, the fourth hydrophilic layer comprises a second electrocatalyst that may correspond to or be different than the first electrocatalyst, and optionally at least one fourth binder that may correspond to or be different than the second binder. In particular embodiments, the fourth hydrophilic layer comprises a second ion-conducting additive that may correspond to or be different than the first ion-conducting additive, especially a cation or anion exchanger, and/or second hydrophilic additives, especially metal oxides, that may correspond to or be different than the first hydrophilic additives.

In particular embodiments, the second hydrophilic layer of the first electrode and the fourth hydrophilic layer of the second electrode make at least partial contact with a first separator on opposite sides of the first separator. In such embodiments, a first polar electrolyte is at least partly present in the first separator. In particular embodiments, the first separator has been swollen by the first polar electrolyte.

In particular embodiments, the apparatus of the invention is an electrolysis system. In particular embodiments, an electrolysis system of the invention comprises a multitude of electrolysis cells that may be constructed in accordance with the electrolysis cell detailed by way of example.

In particular embodiments, the apparatus of the invention further comprises at least one recycling device for the first nonpolar solvent and/or the first organic material, the first polar electrolyte, optionally further polar electrolytes and/or optionally the second polar solvent and/or the second organic material, optionally also comprising corresponding separation devices and/or purifying devices for provision thereof.

In particular embodiments, the apparatus of the invention further comprises an external device for electrolyte treatment at least of the first polar electrolyte, optionally with a feed for lost electrolyte or constituents thereof.

By the method of the invention and with the apparatus of the invention, it is possible to conduct a multitude of electrochemical conversions of organic compounds, some of which are set out hereinafter by way of example.

Examples of cathodic transformations: Many organic conversions can be conducted electrochemically. These may include various hydrogenation reactions of polar and nonpolar multiple bonds. Reductive bond cleavages are also possible.

Examples of anodic transformations: Oxidations of alcohols or oxidative compounds are also possible. The Kolbe coupling of adipic monoesters to give dialkyl sebacates has been the subject of intense study in the past, but has not been implementable owing to the high cell voltages as a result of the acetonitrile-based solvent. It is also possible to oxidatively couple alkynes.

The method of the invention is also of interest for pharmaceutical syntheses since the avoidance of catalysts present in solution or suspension in the synthesis here means that these can correspondingly also be avoided in the product—for example in the case of heavy-metal catalysts.

For the apparatus of the invention—as becomes clear from the above variations—various cell concepts are possible, some of which are described by way of example hereinafter.

A first illustrative embodiment of an electrolysis cell with an amphiphilic electrode is shown in schematic form in FIG. 1.

A working electrode 1 here comprises a first lipophilic layer 2 which is preferably hydrophobic and is in contact with a nonpolar phase 5, and a second hydrophilic layer which is in contact with a first polar electrolyte 6. The first polar electrolyte is additionally in contact with the counterelectrode 4.

Further embodiments based on this embodiment are shown in FIGS. 2 to 4, these embodiments showing a basic mode of operation for these amphiphilic electrodes in combination with a water-consuming counterelectrode that evolves H₂ or O₂.

In FIG. 2, the nonpolar phase is routed here through the first cell space I, forming a nonpolar product P from an organic material as reagent R, while the first polar electrolyte E is pumped through the second cell space II. A large part of the construction in FIG. 3 corresponds to that in FIG. 2, except that the second electrode 4 adjoins the first electrode 1, with insulation correspondingly present here between the two electrodes. The second electrode 4 here is porous in order that the first polar electrolyte E can make contact with the first electrode 1. In FIG. 4, the cell space II is divided into two cell spaces II, II⁺, as a result of which liquid flows around the second electrode 4. For protection of the first electrode 1, the second electrode 4 adjoins a separator S.

It is more sensible, however, to execute both electrodes in the cell by means of amphiphilic electrodes, as shown by way of example in FIG. 5 and FIG. 6. In this case, both electrodes can be used for electrochemical conversions of nonpolar reagents R1, R2 to nonpolar products P1, P2 in the amphiphilic cells as cathode K and anode A with additional benefits, with the two electrodes in FIG. 6 divided by a common separator S, here by way of example in the form of a common membrane containing polar electrolyte. The maximum Faraday efficiency in that case is 200%. Since all electroorganic transformations are proton transfers, transformations in this cell type can be divided into three categories. (Hereinafter: RED: reduction; OX: oxidation; REDOX: redox reaction; R: organic radical; Et: ethyl)

Non-water-consuming or water-generating processes: in these processes, water is converted locally into OH⁻ or H⁺, but the water is regenerated in the bulk electrolyte. These systems (theoretically) do not require any electrolyte.

e.g.: aldehyde reduction+Kolbe coupling of adipic acid
RED: R—CHO+2e⁻+2H₂O→R—CH₂—O +2OH⁻
OX: 2EtO₂C—(CH₂)₄—CO₂H→EtO₂C—(CH₂)₈—CO₂Et+2e⁻+2H⁺+2CO₂
Electrolyte: −2H₂O+2OH⁻+2H⁺=0
REDOX: R—COH+2EtO₂C—(CH₂)₄—CO₂H→R—CH₂—OH+2CO₂+EtO₂C—(CH₂)₈—CO₂Et

Water-consuming processes: in these processes, water is consumed overall. The electrolyte therefore has to be supplemented continuously with water.

e.g.: aldehyde reduction+alcohol oxidation
RED: R—CHO+2e⁻+2H₂O→R—CH₂—OH+2OH⁻I×2
OX: R—CH₂—OH+H₂O→R—COOH+4e⁻+4H⁺
Electrolyte: −2H₂O+2OH⁻—H₂O+2H⁺=−H2O
REDOX: 2R—COH+R—CH₂—OH+H₂O→2R—CH₂—OH+R—COOH

Water-generating processes: in these processes, water is released overall. The electrolyte thus has to be continuously concentrated.

e.g.: nitro reduction+oxidative alkyne coupling
RED: R—NO₂+6e⁻+4H₂O→R—NH₂+6OH⁻
OX: 2R—CCH→R—CC—CC—R+2e⁻+2H⁺I×3
Electrolyte: −4H₂O+6OH⁻+6H⁺=+2H₂O
REDOX: R—NO₂+6R—CCH→R—NH₂+3R—CC—CC—R+2H₂O

Further possible applications of the method of the invention and also of the apparatus of the invention can be found, for example, in Fritz Beck, Berichte der Bunsen-Gesellschaft 1973,77 (10/11), 810-817; F. Beck, H. Guthke Chemie-Ing.-Technik. 1969, 41 (17), 943-950; DE1643693A1; DE2023080A1; DE2336288A1; DE2345461A1; and DE3615472A1.

The present invention is notable here for the use of specific electrodes for performance of the electroorganic redox processes at a phase boundary.

The above embodiments, configurations and developments can be combined with one another as desired if viable. Further possible configurations, developments and implementations of the invention also include combinations, not specified explicitly, of features of the invention that have been described above or are described hereinafter in the working examples. More particularly, the person skilled in the art will also add individual aspects as improvements or supplementations to the respective basic form of the present invention.

The invention is elucidated further in detail hereinafter with reference to various examples thereof. However, the invention is not limited to these examples.

EXAMPLE 1

An illustrative cell construction was realized according to FIG. 1.

In this case, the electroreduction of nitrobenzene to aniline was demonstrated. The first polar electrolyte was realized by an aqueous 0.5 M K₂SO₄ solution. The counterelectrode, an IrO₂-coated Ti sheet, as second electrode consumed water in a 2.5 M KOH and was separated by a CEM, Nafion N11, in order to prevent reoxidation of the partly water-soluble aniline product. The nonpolar organic phase was a 5 M solution of nitrobenzene in diethyl ether (50 times the concentration compared to the maximum solubility in pure water). The phases were pumped along either side of the working electrode as first electrode. The latter consisted of a carbon GDL (Freudenberg H23 C2) as hydrophobic layer (in contact with the nonpolar phase) and a dendritic copper catalyst bound to an anion exchange resin as hydrophilic layer (in contact with the first polar electrolyte). The dendritic copper catalyst bound to anion exchange resin was described in: “Selective Electroreduction of CO₂ toward Ethylene on Nano-Dendritic Copper Catalysts at High Current Density”; Christian Reller,* Ralf Krause, Elena Volkova, Bernhard Schmid, Sebastian Neubauer, Andreas Rucki, Manfred Schuster, and Gunter Schmid; Adv. Energy Mater. 2017, 1602114

FIG. 7 shows the working electrode potential E_WE versus a silver-silver chloride electrode in nitrobenzene bulk electrolysis.

The supply with organic phase was switched on 3 min after the current. A spontaneous rise in the working electrode potential is observed, which suggests that the electrode has switched from hydrogen production to nitro reduction. The drop in gas evolution at the working electrode was also observed.

After 38 min, the organic phase was stopped, which led to irreversible saturation of the entire electrode in the aqueous phase. After switch-on, it was no longer possible to continue the supply, which shows that the substrate is indeed supplied directly from the organic phase and not by extraction of the substrate into the aqueous phase.

1H NMR analysis of the aqueous and organic phase showed that the only product of this conversion was aniline. FIG. 8 shows the NMR spectrum of the organic phase after the electrolysis. No products are observed apart from aniline.

Claims

1. A method of electrochemical conversion of a first organic material which is soluble in or miscible with a first nonpolar solvent, the method comprising:

introducing the first organic material into the first nonpolar solvent to produce a first organic solvent or mixture;

providing an electrolysis cell comprising a porous first electrode comprising at least one first lipophilic layer and at least one second hydrophilic layer, where the first lipophilic layer and the second hydrophilic layer are porous, and a second electrode;

introducing the first organic solution or mixture into the electrolysis cell in such a way that the first organic solution or mixture makes contact with the first lipophilic layer of the first electrode;

introducing a first polar electrolyte into the electrolysis cell in such a way that the first polar electrolyte makes contact with the second hydrophilic layer of the first electrode and the second electrode; and

electrochemically converting the first organic material at the first electrode; or

providing an electrolysis cell comprising a porous first electrode comprising at least one first lipophilic layer and at least one second hydrophilic layer, where the first lipophilic layer and the second hydrophilic layer are porous, and a second electrode;

introducing the first organic material in the form of a liquid or gas into the electrolysis cell in such a way that the first organic material makes contact with the first lipophilic layer of the first electrode;

introducing a first polar electrolyte into the electrolysis cell in such a way that the first polar electrolyte makes contact with the second hydrophilic layer of the first electrode and the second electrode; and

electrochemically converting the first organic material at the first electrode;

wherein the first nonpolar solvent and the first polar electrolyte or the first organic material in the form of a liquid or gas and the first polar electrolyte form a first phase boundary with one another in such a form that the first phase boundary in the electrochemical conversion is at least partly within the first electrode, preferably at an interface between the first lipophilic layer and the second hydrophilic layer.

2. The method as claimed in claim 1,

wherein the first polar electrolyte is liquid.

3. The method as claimed in claim 1,

wherein the first electrode comprises a first current collector which is not in contact with the second hydrophilic layer.

4. The method as claimed in claim 1,

wherein the first lipophilic layer has zero catalytic activity in respect of the first polar electrolyte, and/or

wherein the first lipophilic layer comprises hydrophobic first particles and/or at least one first hydrophobic binder.

5. The method as claimed in claim 1,

wherein the second hydrophilic layer comprises a first electrocatalyst and optionally at least one second binder, and/or

wherein the second hydrophilic layer comprises a first ion-conducting additive, and/or first hydrophilic additives.

6. The method as claimed in claim 1,

wherein the second hydrophilic layer of the first electrode makes at least partial contact with a first separator.

7. The method as claimed in claim 1,

wherein the second electrode comprises at least one third lipophilic layer and at least one fourth hydrophilic layer,

wherein the third lipophilic layer and the fourth hydrophilic layer are preferably porous, wherein the first polar electrolyte makes contact with the fourth hydrophilic layer of the second electrode,

further comprising introducing—a second organic material in the form of a liquid or gas, or—a second organic solution or mixture comprising a second organic material which is soluble in or miscible with a second nonpolar solvent, and a second nonpolar solvent, into the electrolysis cell in such a way that the first organic material or the second organic solution or mixture makes contact with the third lipophilic layer of the second electrode,

wherein the second organic material is electrochemically converted at the second electrode.

8. The method as claimed in claim 7,

wherein the second hydrophilic layer of the first electrode and the fourth hydrophilic layer of the second electrode make at least partial contact with a first separator on opposite sides of the first separator, wherein the first polar electrolyte is at least partly present in the first separator.

9. An apparatus for electrochemical conversion of a first organic material which is soluble in or miscible with a first nonpolar solvent, comprising:

an electrolysis cell, wherein the electrolysis cell comprises a porous first electrode comprising at least one first lipophilic layer and at least one second hydrophilic layer, wherein the first lipophilic layer and the second hydrophilic layer are porous, and a second electrode;

at least one first supply device for the supply of a first solution or mixture of a first organic material which is soluble in or miscible with a first nonpolar solvent in or with a first nonpolar solvent, or for the supply of a first organic material which is soluble in or miscible with a first nonpolar solvent, which is set up to supply the first solution or mixture of the first organic material in or with the first nonpolar solvent, or to supply the first organic material, to the electrolysis cell in such a way that the first organic solution or mixture or the first organic material makes contact with the first lipophilic layer of the first electrode; and

at least one first removal device for the removal of the remaining first solution or mixture and optionally at least one first product of the electrochemical conversion of the first organic material, or of the remaining first organic material and optionally at least one first product, or of the remaining first nonpolar solvent and optionally at least one first product, or of at least one first product, which is set up to remove the remaining first solution or mixture and optionally at least the first product of the electrochemical conversion of the first organic material, or the remaining first organic material and optionally at least the first product, or the remaining first nonpolar solvent and optionally at least the first product, or at least the first product from the electrolysis cell; and

at least one second supply device for a first polar electrolyte, which is set up to supply the first polar electrolyte to the electrolysis cell in such a way that the first polar electrolyte makes contact with the second hydrophilic layer of the first electrode and the second electrode, and/or a second removal device for the first polar electrolyte and optionally at least one first product of the electrochemical conversion of the first organic material, which is set up to remove the first polar electrolyte and optionally at least one first product of the electrochemical conversion of the first organic material from the electrolysis cell.

10. The apparatus as claimed in claim 9,

wherein the first electrode comprises a first current collector that is not in contact with the second hydrophilic layer.

11. The apparatus as claimed in claim 9,

wherein the first lipophilic layer comprises hydrophobic first particles and/or at least one first hydrophobic binder.

12. The apparatus as claimed in claim 9,

wherein the second hydrophilic layer comprises a first electrocatalyst and optionally at least one second binder, and/or

wherein the second hydrophilic layer comprises a first ion-conducting additive, and/or first hydrophilic additives.

13. The apparatus as claimed in claim 9,

wherein the second hydrophilic layer of the first electrode makes at least partial contact with a first separator.

14. The apparatus as claimed in claim 9,

wherein the second electrode comprises at least one third lipophilic layer and at least one fourth hydrophilic layer,

wherein the third lipophilic layer and the fourth hydrophilic layer are porous,

wherein the second hydrophilic layer and the fourth hydrophilic layer are opposite one another but not in contact with one another in the electrolysis cell,

further comprising:

at least one further supply device for the supply of a second solution or mixture of a second organic material which is soluble in or miscible with a second nonpolar solvent in or with a second nonpolar solvent, or for the supply of a second organic material which is soluble in or miscible with a second nonpolar solvent, which is set up to supply the second solution or mixture of the second organic material in or with the second nonpolar solvent, or the second organic material, to the electrolysis cell in such a way that the second organic solution or mixture or the second organic material makes contact with the third lipophilic layer of the second electrode; and

at least one further removal device for the removal of the remaining second solution or mixture and optionally at least one second product of the electrochemical conversion of the second organic material, or of the remaining second organic material and optionally at least one second product, or of the remaining second nonpolar solvent and optionally at least one second product, or of at least one second product, which is set up to remove the remaining second solution or mixture and optionally at least the second product of the electrochemical conversion of the second organic material, or the remaining second organic material and optionally at least the second product, or the remaining second nonpolar solvent and optionally at least the second product, or at least the second product from the electrolysis cell.

15. The apparatus as claimed in claim 14,

wherein the second hydrophilic layer of the first electrode and the fourth hydrophilic layer of the second electrode make at least partial contact with a first separator on opposite sides of the first separator, wherein a first polar electrolyte is at least partly present in the first separator.

16. The method as claimed in claim 2,

wherein the first polar electrolyte contains water and optionally at least one salt.

17. The method as claimed in claim 4,

wherein the first lipophilic layer comprises hydrophobic, conductive, first particles.

18. The method as claimed in claim 5,

wherein the second hydrophilic layer comprises a first ion-conducting additive comprising a cation or anion exchanger, and/or first hydrophilic additives comprising metal oxides.

19. The method as claimed in claim 8,

wherein the first separator has been swollen by the first polar electrolyte.

20. The apparatus as claimed in claim 11,

wherein the first lipophilic layer comprises hydrophobic, conductive, first particles.

21. The apparatus as claimed in claim 12,

wherein the second hydrophilic layer comprises a first ion-conducting additive comprising a cation or anion exchanger, and/or first hydrophilic additives comprising metal oxides.

22. The apparatus as claimed in claim 15,

wherein the first separator has been swollen by the first polar electrolyte.