U.S. patent application number 16/959717 was filed with the patent office on 2020-12-10 for porous electrode for the electrochemical reaction of organic compounds in two immiscible phases in an electrochemical flow reactor.
This patent application is currently assigned to Siemens Aktiengesellschaft. The applicant listed for this patent is Siemens Aktiengesellschaft. Invention is credited to Christian Reller, Bernhard Schmid, Gunter Schmid.
Application Number | 20200385875 16/959717 |
Document ID | / |
Family ID | 1000005079583 |
Filed Date | 2020-12-10 |
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United States Patent
Application |
20200385875 |
Kind Code |
A1 |
Schmid; Bernhard ; et
al. |
December 10, 2020 |
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.
Inventors: |
Schmid; Bernhard; (Duren,
DE) ; Reller; Christian; (Minden, DE) ;
Schmid; Gunter; (Hemhofen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Siemens Aktiengesellschaft |
Munich |
|
DE |
|
|
Assignee: |
Siemens Aktiengesellschaft
Munich
DE
|
Family ID: |
1000005079583 |
Appl. No.: |
16/959717 |
Filed: |
December 28, 2018 |
PCT Filed: |
December 28, 2018 |
PCT NO: |
PCT/EP2018/097087 |
371 Date: |
July 2, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25B 3/04 20130101; C25B
9/08 20130101; C25B 11/0415 20130101; C25B 11/035 20130101; C25B
11/0405 20130101; C25B 11/0489 20130101 |
International
Class: |
C25B 11/03 20060101
C25B011/03; C25B 3/04 20060101 C25B003/04; C25B 11/04 20060101
C25B011/04; C25B 9/08 20060101 C25B009/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 29, 2018 |
DE |
10 2018 201 287.3 |
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.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] 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
[0002] 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
[0003] 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.
[0004] However, the use of electrolytes based on organic solvents
brings some significant disadvantages for electrochemistry.
[0005] Firstly, organic solvents and lipophilic organic salts are
much more expensive than water and inorganic salts.
[0006] Secondly, organic electrolytes typically have a
significantly poorer conductivity than aqueous electrolytes, which
leads to high cell voltages and high ohmic losses.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] US 2013/0228470 A1 discloses a method of converting
carbon-based gases and carbon oxides to longer-chain organic
gases.
[0011] US 2013/0087451 A1 discloses a membrane-electrode
arrangement and an organic hybrid production apparatus.
[0012] 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.
[0013] 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
[0014] 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.
[0015] 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.
[0016] 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.
[0017] Further aspects of the present invention can be inferred
from the dependent claims and the detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] 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.
[0019] 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.
[0020] FIGS. 7 and 8 show results that have been achieved in an
example of the method of the invention.
DETAILED DESCRIPTION OF INVENTION
[0021] 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.
[0022] 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.
[0023] 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.
[0024] By contrast, hydrophilic is understood to mean the ability
to interact with water and other polar substances.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] Standard pressure is 101 325 Pa=1.01325 bar.
[0029] 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.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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.
[0037] 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.
[0038] 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.
[0039] Apart from that, there is no further restriction in the
first organic material that is soluble in or miscible with a first
nonpolar solvent.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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 Bu.sub.3MeP.sup.+
((CF.sub.3)SO.sub.2)N.sup.-, 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.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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 H.sub.2SO.sub.4, 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.
[0048] 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.degree. 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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.sup.- in the case of use of
water in the polar electrolyte.
[0053] The pore size here is not particularly restricted, but in
particular embodiments is in the range from 0.1 to 500 .mu.m, for
example in the range from 0.2 to 100 .mu.m, e.g. 0.5 to 10 .mu.m.
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.
[0054] 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.
[0055] 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.
[0056] 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.
[0057] 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.
[0058] 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.
[0059] 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.
[0060] 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.
[0061] 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.
[0062] 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).
[0063] It is also possible to introduce hydrophilic additives, e.g.
metal oxides, for example Al.sub.2O.sub.3, TiO.sub.2, ZnO,
Y.sub.2O.sub.3, etc., into the second hydrophilic layer. In
particular embodiments, the second hydrophilic layer thus comprises
first hydrophilic additives, especially metal oxides.
[0064] 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.
[0065] As well as the first lipophilic layer and the second
hydrophilic layer, the first electrode may also comprise further
"layers".
[0066] 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.
[0067] 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.
[0068] 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.
[0069] 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.
[0070] 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.
[0071] 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.
[0072] 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 H.sub.2 or O.sub.2 at the second
electrode, for example in the case of an aqueous first polar
electrolyte.
[0073] 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.
[0074] 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.
[0075] 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.
[0076] 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.
[0077] 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).
[0078] 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.
[0079] 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.
[0080] 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.
[0081] 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.
[0082] 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.
[0083] 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.
[0084] 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.
[0085] 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.
[0086] 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
.ltoreq.30%, preferably .ltoreq.25%, further preferably
.ltoreq.20%, based on the pores of the hydrophilic layer.
[0087] 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.
[0088] 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.
[0089] 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.
[0090] 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.
[0091] 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.
[0092] 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.
[0093] 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.
[0094] 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.
[0095] 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.
[0096] 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.
[0097] 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.
[0098] 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.
[0099] In particular embodiments, the first lipophilic layer
comprises hydrophobic, preferably conductive, first particles
and/or at least one first hydrophobic binder.
[0100] 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.
[0101] 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.
[0102] 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.
[0103] 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.
[0104] 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.
[0105] 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.
[0106] 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.
[0107] 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.
[0108] 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.
[0109] 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.
[0110] 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.
[0111] 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.
[0112] 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.
[0113] 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.
[0114] 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.
[0115] 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.
[0116] 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.
[0117] 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.
[0118] A first illustrative embodiment of an electrolysis cell with
an amphiphilic electrode is shown in schematic form in FIG. 1.
[0119] 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.
[0120] 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 H.sub.2 or
O.sub.2.
[0121] 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.sup.+,
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.
[0122] 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)
[0123] Non-water-consuming or water-generating processes: in these
processes, water is converted locally into OH.sup.- or H.sup.+, 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.sup.-+2H.sub.2O.fwdarw.R--CH.sub.2--O +2OH.sup.- OX:
2EtO.sub.2C--(CH.sub.2).sub.4--CO.sub.2H.fwdarw.EtO.sub.2C--(CH.sub.2).su-
b.8--CO.sub.2Et+2e.sup.-+2H.sup.++2CO.sub.2 Electrolyte:
-2H.sub.2O+2OH.sup.-+2H.sup.+=0 REDOX:
R--COH+2EtO.sub.2C--(CH.sub.2).sub.4--CO.sub.2H.fwdarw.R--CH.sub.2--OH+2C-
O.sub.2+EtO.sub.2C--(CH.sub.2).sub.8--CO.sub.2Et
[0124] 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.sup.-+2H.sub.2O.fwdarw.R--CH.sub.2--OH+2OH.sup.-I.times.2
OX: R--CH.sub.2--OH+H.sub.2O.fwdarw.R--COOH+4e.sup.-+4H.sup.+
Electrolyte: -2H.sub.2O+2OH.sup.---H.sub.2O+2H.sup.+=-H2O REDOX:
2R--COH+R--CH.sub.2--OH+H.sub.2O.fwdarw.2R--CH.sub.2--OH+R--COOH
[0125] 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--NO.sub.2+6e.sup.-+4H.sub.2O.fwdarw.R--NH.sub.2+6OH.sup.- OX:
2R--CCH.fwdarw.R--CC--CC--R+2e.sup.-+2H.sup.+I.times.3 Electrolyte:
-4H.sub.2O+6OH.sup.-+6H.sup.+=+2H.sub.2O REDOX:
R--NO.sub.2+6R--CCH.fwdarw.R--NH.sub.2+3R--CC--CC--R+2H.sub.2O
[0126] 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.
[0127] The present invention is notable here for the use of
specific electrodes for performance of the electroorganic redox
processes at a phase boundary.
[0128] 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.
[0129] 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
[0130] An illustrative cell construction was realized according to
FIG. 1.
[0131] In this case, the electroreduction of nitrobenzene to
aniline was demonstrated. The first polar electrolyte was realized
by an aqueous 0.5 M K.sub.2SO.sub.4 solution. The counterelectrode,
an IrO.sub.2-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 CO.sub.2 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
[0132] FIG. 7 shows the working electrode potential E.sub.WE versus
a silver-silver chloride electrode in nitrobenzene bulk
electrolysis.
[0133] 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.
[0134] 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.
[0135] 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.
* * * * *