U.S. patent application number 16/334132 was filed with the patent office on 2019-09-12 for selective electrochemical hydrogenation of alkynes to alkenes.
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 | 20190276941 16/334132 |
Document ID | / |
Family ID | 59738305 |
Filed Date | 2019-09-12 |
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United States Patent
Application |
20190276941 |
Kind Code |
A1 |
Schmid; Bernhard ; et
al. |
September 12, 2019 |
Selective Electrochemical Hydrogenation of Alkynes to Alkenes
Abstract
Various embodiments include a method for the partial
electrochemical hydrogenation of alkynes of the chemical formula
(I) to alkenes, ##STR00001## wherein R and R' are selected from
inorganic and/or organic radicals, the method comprising:
hydrogenating the compound of the chemical formula (I) on a
copper-containing electrode.
Inventors: |
Schmid; Bernhard; (Erlangen,
DE) ; Schmid; Gunter; (Hemhofen, DE) ; Reller;
Christian; (Minden, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Siemens Aktiengesellschaft |
Munchen |
|
DE |
|
|
Assignee: |
Siemens Aktiengesellschaft
Munchen
DE
|
Family ID: |
59738305 |
Appl. No.: |
16/334132 |
Filed: |
August 16, 2017 |
PCT Filed: |
August 16, 2017 |
PCT NO: |
PCT/EP2017/070699 |
371 Date: |
March 18, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25B 3/04 20130101; C25B
11/035 20130101 |
International
Class: |
C25B 3/04 20060101
C25B003/04; C25B 11/03 20060101 C25B011/03 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 22, 2016 |
DE |
10 2016 218 230.7 |
Claims
1. A method for the partial electrochemical hydrogenation of
alkynes of the chemical formula (I) to alkenes, ##STR00014##
wherein R and R' each comprise at least one inorganic or organic
radicals, the method comprising: hydrogenating the compound of the
chemical formula (I) on a copper-containing electrode.
2. The method as claimed in claim 1, wherein the inorganic and
organic radicals comprise at least one compound selected from the
group consisting of: --H, -D, alkyl, alkenyl, alkynyl and/or aryl
radicals, --OH, --OR*, --SH, --SR*, --NH.sub.2, --NR*R*, --COOH,
--COOR*, --CHO, --COR*, --PH.sub.2, --PR*R*, --F, --Cl, --Br, --I,
--NO, and --NO.sub.2, where R* and R* are organic and/or inorganic
radicals.
3. The method as claimed in claim 1, wherein neither R nor R' are
--H or -D.
4. The method as claimed in claim 1, wherein the alkyne of the
chemical formula (I) comprises no electron-withdrawing
radicals.
5. The method as claimed in claim 4, wherein the
electron-withdrawing radicals comprise a compound selected from the
group consisting of: --COOH, --COOR*, and fluorinated alkyl or aryl
radicals.
6. The method as claimed in claim 1, wherein the alkyne of the
chemical formula (I) comprises no further reducible functional
groups apart from the triple bond.
7. The method as claimed in claim 1, wherein the hydrogenation is
carried out with a proton donor selected from water and alcohols
having 1 to 20 carbon atoms.
8. The method as claimed in claim 1, wherein: the copper-containing
electrode is configured as comprises a gas diffusion electrode; and
the alkyne of the chemical formula (I) is gaseous.
9. (canceled)
10. A device for the partial electrochemical hydrogenation of
alkynes of the chemical formula (I) to alkenes, ##STR00015##
wherein R and R' are selected from inorganic and/or organic
radicals, the device comprising: an electrolysis cell with a
copper-containing electrode configured to reduce the alkyne of the
chemical formula (I) to an alkene; a source of the alkyne of the
chemical formula (I); and a first feeding device configured to feed
the alkyne of the chemical formula (I) from the source of the
alkyne of the chemical formula (I) to the electrolysis cell.
11. The device as claimed in claim 10, wherein: the
copper-containing electrode comprises a gas diffusion electrode;
and the first feeding device for the alkyne of the chemical formula
(I) feeds the alkyne of the chemical formula (I) to the gas
diffusion electrode.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a U.S. National Stage Application of
International Application No. PCT/EP2017/070699 filed Aug. 16,
2017, which designates the United States of America, and claims
priority to DE Application No. 10 2016 218 230.7 filed Sep. 22,
2016, the contents of which are hereby incorporated by reference in
their entirety.
TECHNICAL FIELD
[0002] The present disclosure relates to electrochemistry. Various
embodiments may include methods for the partial electrochemical
hydrogenation of alkynes of the chemical formula (I) to
alkenes,
##STR00002## [0003] wherein R and R' are selected from inorganic
and/or organic radicals.
BACKGROUND
[0004] Alkenes such as ethene and propene are currently produced
mainly by the catalytic cracking of crude oil (naphtha). An
alternative approach is the partial hydrogenation of alkynes (e.g.
ethyne). These may also be prepared from coal or carbides, for
example, and are thus not dependent on crude oil. However, problems
of selectivity occur in classical hydrogenation. Frequently,
over-reduction to alkanes occurs. The hydrogen required for the
hydrogenation is currently also obtained from coal gasification or
steam reforming and is therefore also closely linked with oil
production.
[0005] The catalytic hydrogenation of alkynes has been achieved to
date by specifically poisoned noble metal catalysts. An example of
this is the Lindlar catalyst, which is a palladium catalyst
poisoned with lead and quinoline. Another possibility is the "Birch
analog reduction" which is conducted with a solution of alkali
metals in liquid ammonia. The latter process is very expensive but
selective for E-alkenes.
[0006] Novel approaches for producing hydrocarbons from carbon
dioxide or carbon monoxide for example, are apparent in the context
of the electrification of the chemical industry. Here,
electrification of the chemical industry means carrying out
processes electrochemically which up to now are carried out by
classical thermal methods or are currently not possible. For
instance, the electrochemical hydrogenation of ethyne to ethene is
also known from X. Song, H. Du, Z. Liang, Z. Zhu, D. Duan, S. Liu,
Int. J. Electrochem. Sci., 2013, 8, 6566-6573. However, the authors
here use exclusively electrodes composed of the noble metal
palladium and the substrate choice is also limited to ethyne.
SUMMARY
[0007] The teachings of the present disclosure describe simple and
readily accessible methods for producing alkenes from alkynes which
preferably proceeds without expensive noble metals. For example, a
partial reduction of alkynes can be performed by an electrochemical
method using a Cu electrode in water-based electrolytes. The
electrode can be constructed either as a solid electrode or as a
gas diffusion electrode here. Due to the better substrate
availability of alkynes, the latter is particularly suitable. The
methods exhibit high selectivity and activity here, even in the
case of non-activated alkynes and challenging substrates having
electron donating groups and/or streric hindrance.
[0008] For example, some embodiments include a method for the
partial electrochemical hydrogenation of alkynes of the chemical
formula (I) to alkenes,
##STR00003## [0009] wherein R and R' are selected from inorganic
and/or organic radicals, [0010] wherein the compound of the
chemical formula (I) is hydrogenated on a copper-containing
electrode.
[0011] In some embodiments, the inorganic and/or organic radical is
selected from --H, -D, substituted or unsubstituted alkyl, alkenyl,
alkynyl and/or aryl radicals, --OH, --OR*, --SH, --SR*, --NH.sub.2,
--NR*R*, --COOH, --COOR*, --CHO, --COR*, --PH.sub.2, --PR*R*, --F,
--Cl, --Br, --I, --NO and --NO.sub.2, where R* and R* are organic
and/or inorganic radicals.
[0012] In some embodiments, neither R nor R' are --H or -D.
[0013] In some embodiments, the alkyne of the chemical formula (I)
comprises no electron-withdrawing radicals.
[0014] In some embodiments, the electron-withdrawing radicals are
selected from --COOH, --COOR* and fluorinated alkyl and/or aryl
radicals.
[0015] In some embodiments, the alkyne of the chemical formula (I)
comprises no further reducible functional groups apart from the
triple bond.
[0016] In some embodiments, the hydrogenation is carried out with a
proton donor selected from water and alcohols having 1 to 20 carbon
atoms.
[0017] In some embodiments, the copper-containing electrode is
configured as a gas diffusion electrode, wherein the alkyne of the
chemical formula (I) is gaseous.
[0018] Some embodiments include the use of a copper-containing
electrode for the partial electrochemical hydrogenation of alkynes
of the chemical formula (I) to alkenes,
##STR00004## [0019] wherein R and R' are selected from inorganic
and/or organic radicals.
[0020] As another example, some embodiments include a device for
the partial electrochemical hydrogenation of alkynes of the
chemical formula (I) to alkenes,
##STR00005## [0021] wherein R and R' are selected from inorganic
and/or organic radicals, comprising: an electrolysis cell (1)
comprising a copper-containing electrode, which is configured to
reduce the alkyne of the chemical formula (I) to alkene; a source
of the alkyne of the chemical formula (I) (3) which is configured
to provide the alkyne of the chemical formula (I); and a first
feeding device (2) for the alkyne of the chemical formula (I) which
is configured to feed the alkyne of the chemical formula (I) from
the source of the alkyne of the chemical formula (I) to the
electrolysis cell.
[0022] In some embodiments, the copper-containing electrode is
configured as a gas diffusion electrode, wherein the first feeding
device (2) for the alkyne of the chemical formula (I) feeds the
alkyne of the chemical formula (I) to the gas diffusion
electrode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The attached drawings are intended to elucidate embodiments
of the present teachings, and to provide further understanding
thereof. In combination with the description, they serve to explain
concepts and principles of the teachings herein. Other embodiments
and many of the advantages specified are apparent in relation to
the drawings. The elements of the drawings are not necessarily
drawn to scale with respect to one another. Identical, functionally
identical, and equivalent elements, features, and components are
each provided with the same reference symbols in the figures of the
drawings, unless otherwise stated.
[0024] The FIGURE shows a schematic representation of a device
incorporating teachings of the present disclosure.
DETAILED DESCRIPTION
[0025] Some embodiments include a method for the partial
electrochemical hydrogenation of alkynes of the chemical formula
(I) to alkenes,
##STR00006## [0026] wherein R and R' are selected from inorganic
and/or organic radicals, wherein the compound of the chemical
formula (I) is hydrogenated on a copper-containing electrode.
[0027] Some embodiments include the use of a copper-containing
electrode for the partial electrochemical hydrogenation of alkynes
of the chemical formula (I) to alkenes,
##STR00007## [0028] wherein R and R' are selected from inorganic
and/or organic radicals.
[0029] Some embodiments include a device for the partial
electrochemical hydrogenation of alkynes of the chemical formula
(I) to alkenes,
##STR00008## [0030] wherein R and R' are selected from inorganic
and/or organic radicals, comprising: an electrolysis cell (1)
comprising a copper-containing electrode, which is configured to
reduce the alkyne of the chemical formula (I) to alkene; a source
of the alkyne of the chemical formula (I) (3) which is configured
to provide the alkyne of the chemical formula (I); and a first
feeding device (2) for the alkyne of the chemical formula (I) which
is configured to feed the alkyne of the chemical formula (I) from
the source of the alkyne of the chemical formula (I) to the
electrolysis cell.
[0031] Some embodiments include a method for the partial
electrochemical hydrogenation of alkynes of the chemical formula
(I) to alkenes,
##STR00009## [0032] wherein R and R' are selected from inorganic
and/or organic radicals, wherein the compound of the chemical
formula (I) is hydrogenated on a copper-containing electrode.
[0033] All chemical compounds comprising a triple bond between 2
carbon atoms are referred to as alkynes. The teachings herein
therefore are not limited to ethyne but can be applied to other
alkynes. A general scheme of the electrochemical reaction of
alkynes of the chemical formula I is as follows:
##STR00010##
wherein the H.sup.+ ions depicted can instead also be D.sup.+ ions
for example.
[0034] The good selectivity arises in this case due to the low
reactivity of the alkenes forming to electrohydrogenation with Cu
electrodes. In particular, electronically deactivated internal
alkenes such as crotyl alcohol (trans-2-butenol) appeared inert to
over-reduction.
[0035] The copper-containing electrode is not especially limited
and may comprise copper in addition to other constituents, for
example other metals and/or ceramics as substrate, but may also
consist of copper. It may also be chemically treated, for example
for oxide formation. It can also be configured as a solid electrode
or as a gas diffusion electrode. Due to the greater substrate
availability of alkynes, the latter, i.e. the gas diffusion
electrode, is particularly suitable, especially for gaseous alkynes
such as ethyne, propyne, 1-butyne or 2-butyne. In contrast to
palladium electrodes, the present copper-containing electrodes are
much more cost effective.
[0036] For example, a copper-containing electrode can be formed by
depositing a layer containing a Cu.sup.+/Cu-comprising catalyst on
a non-copper substrate, as described in DE 10 2015 203 245, or also
by depositing the layer on a copper substrate. The
Cu.sup.+/Cu-comprising catalyst is also referred to below as
copper/copper ion catalyst, copper catalyst or similar and also
simply as catalyst, unless it appears otherwise from the text, such
that these terms are to be understood to be synonymous in the
context of the present disclosure.
[0037] The non-copper substrate is also referred to simply as
substrate, unless it appears otherwise from the text. It is also
not excluded here that the non-copper substrate comprises copper,
as long as it does not consist substantially only of copper. For
instance, the substrate may also consist of brass or comprise brass
for example. For instance, the non-copper substrate comprises, for
example, less than 60% by weight copper, based on the total weight
of the substrate, less than 50% by weight, or less than 40% by
weight and even less than 20% by weight, for example no copper at
all.
[0038] In some embodiments, in the production of an electrode of
this kind, all conductive substrates can be used. In some
embodiments, the substrate comprises at least one metal such as
silver, gold, platinum, nickel, lead, titanium, nickel, iron,
manganese or chromium or alloys thereof such as stainless steels
and/or at least one non-metal such as carbon, Si, boron nitride
(BN), boron-doped diamond, etc., and/or at least one conductive
oxide such as indium tin oxide (ITO), aluminum zinc oxide (AZO) or
fluorinated tin oxide (FTO), for the production of photoelectrodes
for example, and/or at least one polymer based on polyacetylene,
polyethoxythiophene, polyaniline, or polypyrrole for the production
of polymer-based electrodes.
[0039] The Cu.sup.+/Cu-comprising catalyst can be produced in
various ways and is not particularly limited, wherein the various
production methods of the Cu.sup.+/Cu-comprising catalyst can also
be effected on copper substrates. In some embodiments,
electroreduction catalysts can be obtained if the catalyst is
deposited in situ on the electrode substrate. An ex situ deposition
in accordance with the invention is not excluded however. The
substrate must not necessarily comprise copper or be copper in this
case, but can be any conductive material, especially also including
conductive oxides. Particular preference is given to porous
configurations of such an electrode in order to obtain gas
diffusion electrodes.
[0040] In some embodiments, a charge compensation in the
Cu.sup.+/Cu-comprising catalyst can be effected by incorporating
anions present in solution during production, for example hydroxide
ions (OH.sup.-), O.sub.2.sup.-, halide ions (halogen-), for example
fluoride, chloride, bromide, iodide, sulfate, hydrogencarbonate,
carbonate or phosphate, etc.
[0041] In some embodiments, the layer comprising copper can also be
deposited on the surface of the electrode from a solution
comprising copper ions. In some embodiments, dendritic structures
from solution can be applied in the coating, wherein complete
coating of the substrate does not have to be achieved here, i.e.
parts of the substrate may still be visible. The coating of the
substrate, also like the structures of the catalyst, can be
analyzed in this case by scanning electron microscopy (SEM) or
transmission electron microsocopy (TEM) for example.
[0042] In the electrodes, the substrate is not necessarily
completely covered by the coating. In some embodiments, the
coverage of the coating in terms of surface area can be, for
example, 10 to 99.9%, based on the surface area of the substrate,
or 50 to 95%, or even 70 to 90%. For example, the substrate is only
covered such that the growth of the catalyst takes place
dendritically.
[0043] Crystalline micro- to nanoporous systems for the
Cu.sup.+/Cu-comprising catalyst can be obtained and/or those having
a particularly high surface area of, for example, more than 100
m.sup.2/g, or equal to or more than 500 m.sup.2/g, or even equal to
or more than 1000 m.sup.2/g, wherein addition of substances such as
brighteners is not excluded. The Cu.sup.+/Cu-comprising catalyst
may comprise pores in this case of a size from 10 nm to 100 .mu.m,
or from 50 nm to 50 .mu.m, or even from 100 nm to 10 .mu.m. The
Cu.sup.+/Cu-comprising catalyst may also comprise dendritic
structures having a fine structure, for example the gap between two
dendrites having a dimension of 1 to 100 nm, or 2 to 20 nm, or even
3 to 10 nm. The coating may be porous for example. The
Cu.sup.+/Cu-comprising catalyst can be crystalline to an extent of
at least 40% by weight, based on the catalyst, or to an extent of
at least 70% by weight, or even to an extent of at least 80% by
weight, wherein the Cu.sup.+/Cu-comprising catalyst and/or the
coating may be crystalline.
[0044] The substrate may be porous, for example to be able to
produce gas diffusion electrodes. The substrate may have pore sizes
from 10 nm to 100 .mu.m, or from 50 nm to 50 .mu.m, or even from
100 nm to 10 .mu.m. By means of the porous configuration of the
non-copper substrate, or even of a copper substrate, such as a gas
diffusion electrode for example, good transport of a gaseous alkyne
to the Cu.sup.+/Cu-comprising catalyst can be ensured and the
efficiency of the electrolysis can be further improved. Especially
by means of a suitable pore size, specific directing to particular
sections of the catalyst can be ensured.
[0045] The concentration of Cu.sup.+ in the porous copper catalyst
layer/the coating comprising the Cu.sup.+/Cu-comprising catalyst
is, for example, greater than 1 mol %, or greater than 5 mol %, or
more than 10 mol %, or even greater than 20 mol %, and for example
up to 99.9 mol %, based on the coating.
[0046] In the copper-containing electrode the substrate may be
porous. The substrate can, in this case, have pores of a size from
10 nm to 100 .mu.m, or from 50 nm to 50 .mu.m, or even from 100 nm
to 10 .mu.m. This may be appropriate for embodiments, for example,
in which the electrode is a gas diffusion electrode.
[0047] In some embodiments, the substrate in the copper-containing
electrode comprises, for example, at least one metal such as
silver, platinum, nickel, lead, titanium, nickel, iron, manganese
or chromium or alloys thereof such as stainless steels, and/or at
least one non-metal such as carbon, Si, boron nitride (BN),
boron-doped diamond etc., and/or at least one conductive oxide such
as indium tin oxide (ITO), aluminum zinc oxide (AZO) or fluorinated
tin oxide (FTO)--for example for the production of photoelectrodes,
and/or at least one polymer based on polyacetylene,
polyethoxythiophene, polyaniline, or polypyrrole, such as in
polymer-based electrodes for example. Copper alloys or mixtures of
the materials mentioned with copper as well as also substrates of
copper or copper oxide are also possible.
[0048] In some embodiments, the coating is at least partially
crystalline. In some embodiments, the Cu.sup.+/Cu-comprising
catalyst is crystalline to an extent of at least 40% by weight,
based on the catalyst, or to an extent of at least 70% by weight,
or even to an extent of at least 80% by weight. In accordance with
particular embodiments, the Cu.sup.+/Cu-comprising catalyst and/or
the coating is/are crystalline.
[0049] In some embodiments, the coating of the copper-containing
electrode is micro- to nanoporous and/or has a particularly high
surface area of, for example, more than 500 m.sup.2/g, or equal to
or more than 800 m.sup.2/g, or even equal to or more than 1000
m.sup.2/g. In some embodiments, the coating is therefore porous.
The Cu.sup.+/Cu-comprising catalyst can have pores of a size from
10 nm to 100 .mu.m, or from 50 nm to 50 .mu.m, or even from 100 nm
to 10 .mu.m. The Cu.sup.+/Cu-comprising catalyst may also comprise
dendritic structures having a fine structure, for example the gap
between two dendrites having a dimension of 1 to 100 nm, or 2 to 20
nm, or even 3 to 10 nm.
[0050] In some embodiments, the concentration of Cu.sup.+ in the
porous copper catalyst layer is, for example, greater than 1 mol %,
or greater than 5 mol %, or more than 10 mol %, or even greater
than 20 mol %, and up to 99.9 mol %, based on the coating.
[0051] In some embodiments, the coverage of the coating in terms of
surface area in the copper-containing electrode can be, for example
10 to 99.9%, based on the surface area of the substrate, or 50 to
95%, or even 70 to 90%. In some embodiments, the substrate is
covered such that the growth of the catalyst takes place
dendritically.
[0052] In some embodiments, the following features are useful in
forming the copper-containing electrode as a gas diffusion
electrode (GDE), as for the gas diffusion electrode described in
102015215309.6. In some embodiments, a gas diffusion electrode as
copper-containing electrode comprises, for example, a support,
maybe containing copper, e.g. in the form of a fabric, and a first
layer comprising at least copper and at least one binder, wherein
the (first) layer comprises hydrophilic and hydrophobic pores
and/or channels, further comprising a second layer comprising
copper and at least one binder, wherein the second layer is located
on the support and the first layer on the second layer, wherein the
content of binder in the first layer is less than in the second
layer.
[0053] In this case, hydrophobic is understood to mean
water-repellent. Hydrophobic pores and/or channels are therefore
those which repel water. In particular, hydrophobic properties are
associated with substances or molecules having non-polar groups. In
contrast thereto, hydrophilic is understood to mean the ability to
interact with water and other polar substances. The second layer,
exactly like the first layer, can comprise hydrophilic and/or
hydrophobic pores and/or channels.
[0054] In some embodiments, there is a gas diffusion electrode
comprising a support, maybe containing copper, e.g. in the form of
a fabric, and a first layer comprising at least copper and at least
one binder, wherein the layer comprises hydrophilic and hydrophobic
pores and/or channels.
[0055] The hydrophilic and hydrophobic regions of the GDE can
achieve a good triphasic relationship between liquid, solid and
gas. In the electrode, for example, hydrophobic channels or regions
and hydrophilic channels or regions are found on the electrolyte
side wherein, in the hydrophilic regions, catalyst centers of lower
activity are located. In addition, inactive catalyst centers are
located on the gas sides. Particularly active catalyst centers are
in the triple phase region of liquid, solid and gas. An ideal GDE
therefore has maximum penetration of the bulk material with
hydrophilic and hydrophobic channels in order to obtain as many
triple phase regions as possible for active catalyst centers. In
some embodiments, the first layer comprises hydrophilic and
hydrophobic pores and/or channels. By means of suitably adjusting
the first layer, it can be achieved that as many active catalyst
centers as possible are present in the gas diffusion electrode.
[0056] The support is not particularly limited to the above, as
long as it is suitable for a gas diffusion electrode and, in some
cases, contains copper. In the extreme case, for example, parallel
wires can also form a support. In some embodiments, the support is
a fabric, e.g. a mesh, or even a copper mesh. As a result, both a
sufficient mechanical stability and functionality as a gas
diffusion electrode can be ensured, for example with respect to
high electrical conductivity. By using copper in the support,
suitable conductivity can be provided and the risk of infiltration
by undesirable foreign metals can be prevented. In some
embodiments, the support therefore consists of copper. In some
embodiments, a copper-containing support is a copper mesh having a
mesh size w of 0.3 mm<w<2.0 mm, or 0.5 mm<w<1.4 mm and
a wire diameter x of 0.05 mm<x<0.5 mm, or 0.1
mm<x.ltoreq.0.25 mm.
[0057] In some embodiments, the first layer comprises copper, also
high electrical conductivity of the catalyst and also, particularly
in connection with a copper mesh, a homogeneous potential
distribution across the whole electrode surface
(potential-dependent product selectivity) can be assured.
[0058] In some embodiments, the binder comprises a polymer, for
example a hydrophilic and/or hydrophobic polymer, for example, a
hydrophobic polymer, especially PTFE. As a result, a suitable
adjustment of the hydrophobic pores or channels can be
achieved.
[0059] In particular, to produce the first layer, PTFE particles
having a particle diameter between 5 and 95 .mu.m, preferably
between 8 and 70 .mu.m are used. Suitable PTFE powders include, for
example, Dyneon.RTM. TF 9205 and Dyneon TF 1750. Suitable binder
particles, PTFE particles for example, can be for example
approximately spherical, for example spherical, and can be
produced, for example, by emulsion polymerization. In some
embodiments, the binder particles are free of surface-active
substances. The particle size in this case can be determined for
example in accordance with ISO 13321 or D4894-98a and can, for
example, correspond to the manufacturers' specifications (e.g. TF
9205: mean particle size 8 .mu.m according to ISO 13321; TF 1750:
mean particle size 25 .mu.m according to ASTM D4894-98a).
[0060] In some embodiments, the first layer comprises at least
copper, which can be present, for example, in the form of metallic
copper and/or copper oxide, and which functions as catalyst center.
In this case, the first layer preferably comprises metallic copper
in oxidation state 0.
[0061] In some embodiments, the first layer may also comprise, for
example, copper oxide, especially Cu.sub.2O. The oxide in this case
can contribute to stabilizing the copper oxidation states of +1 and
thus maintaining the long-term stability with respect to
selectivity for ethylene. Under the electrolysis conditions, it can
be reduced to copper. In some embodiments, the first layer
comprises at least 40 atom %, or at least 50 atom %, or even at
least 60 atom % copper, based on the layer.
[0062] In some embodiments, the first layer can also comprise
further promoters which, in combination with the copper, improve
the catalytic activity of the GDE. For example, the first layer
comprises at least one metal oxide, e.g. ZrO.sub.2,
Al.sub.2O.sub.3, CeO.sub.2, Ce.sub.2O.sub.3, ZnO.sub.2, MgO; and/or
at least one copper-rich intermetallic phase, at least one Cu-rich
phase selected from the group of the binary systems comprising
Cu--Al, Cu--Zr, Cu--Y, Cu--Hf, CuCe, Cu--Mg and the ternary systems
comprising Cu--Y--Al, Cu--Hf--Al, Cu--Zr--Al, Cu--Al--Mg,
Cu--Al--Ce having Cu contents >60 atom %; and/or
copper-containing perovskite and/or defective perovskite and/or
compounds related to perovskite, e.g.
YBa.sub.2Cu.sub.3O.sub.7-.delta., wherein 0.ltoreq..delta..ltoreq.1
(corresponding to YBa.sub.2Cu.sub.3O.sub.7-5X.sub..sigma.),
CaCu.sub.3Ti.sub.4O.sub.12,
La.sub.1.85Sr.sub.015CuO.sub.3.930Cl.sub.0.053,
(La,Sr).sub.2CuO.sub.4. Viable promoters in this case are the metal
oxides.
[0063] In some embodiments, the metal oxide used may be insoluble
in water so that aqueous electrolytes can be used in an
electrolysis using the gas diffusion electrode. The metal oxides
may not be inert, but may be hydrophilic reaction centers which can
serve to provide protons.
[0064] The promoters, especially the metal oxide, can in this way
support the function and production of electrocatalysts that are
stable long-term, by stabilizing catalytically active Cu
nanostructures. As a result, the structural promoters can reduce
the high surface mobilities of the Cu nanostructures and therefore
their tendency to sinter. The concept originates from heterogeneous
catalysis and is used successfully within high temperature
processes. In some embodiments, the promoters used for the
electrochemical reduction can be the following metal oxides which
cannot be reduced to metals in the electrochemical window:
ZrO.sub.2 (E=-2.3V), Al.sub.2O.sub.3 (E=-2.4V), CeO.sub.2
(E=-2.3V), MgO (E=-2.5V). It should be noted here that the oxides
specified are not added as additives but are part of the catalyst
itself. In addition to its function as promoter, the oxide also
fulfils the feature of stabilizing copper in the oxidation stage of
I.
[0065] In some embodiments, the gas diffusion electrodes are metal
oxide-copper catalyst structures which are produced as follows. For
the production of the metal oxides, the precipitation according to
particular embodiments cannot be effected, as frequently described,
in a pH regime between pH=5.5-6.5, but in a region between 8.0-8.5,
such that hydroxide-carbonates similar to malachite
(Cu.sub.2[(OH).sub.2|CO.sub.3]), azurite
(Cu.sub.3(CO.sub.3).sub.2(OH).sub.2) or aurichalcite
(Zn,Cu).sub.5[(OH).sub.6|(CO.sub.3).sub.2]) are not formed as
precursor, but hydrotalcite (Cu.sub.6Al.sub.2CO.sub.3(OH).sub.16.4
(H.sub.2O)), which can be obtained in greater yield. Likewise,
layered double hydroxides (LDHs) are suitable, having a composition
M.sup.z.sub.1-xM.sup.3+.sub.x(OH).sub.2].sup.q+(X.sup.n-).sub.q/n.yH.sub.-
2O, where M.sup.1+=Li.sup.+, Na.sup.+, K.sup.+, M.sup.2+=Ca.sup.2+,
Mg.sup.2+, Cu.sup.2+ and M.sup.3+=Al, Y, Ti, Hf, Ga. The
corresponding precursors can be precipitated by co-addition of a
metal salt solution and a basic carbonate solution in a
pH-controlled manner. A particular feature of these materials is
the presence of particularly fine copper crystallites having a size
of 4-10 nm, which are stabilized structurally by the oxide
present.
[0066] After precipitation, drying may include subsequent
calcination in an O.sub.2/Ar gas stream. The oxide precursors
generated can then also be reduced directly in an H.sub.2/Ar gas
stream, in which only the Cu.sub.2O or CuO is reduced to Cu and the
oxide promoter is retained. The activation step can also be carried
out electrochemically afterwards. In order to improve the
electrical conductivity of the applied layer prior to
electrochemical activation, some oxide precursors and activated
precursors can also be mixed. In order to be able to increase the
basic conductivity, 0-10% by weight copper powder of a similar
particle size can also be mixed in.
[0067] In some embodiments, the finished calendered gas diffusion
electrode is subjected to subsequent calcination/thermal treatment
before the electrochemical activation is carried out.
[0068] A further production possibility of suitable
electrocatalysts is based on the approach of producing copper-rich
intermetallic phases such as CusZr, Cu.sub.10Zr.sub.7,
Cu.sub.51Zr.sub.14, which can be produced from the melt.
Corresponding ingots can be milled and fully or partially calcined
retrospectively in the O.sub.2/argon gas stream and be converted
into the oxide form. Of particular interest are the Cu-rich phases
of the binary systems Cu--Al, Cu--Zr, Cu--Y, Cu--Hf, CuCe, Cu--Mg
and the corresponding ternary systems having Cu contents >60
atom %: CuYAl, ChHfAl, CuZrAl, CuAl Mg, CuAl Ce.
[0069] Copper-rich phases are known, for example, from E. Kneller,
Y. Khan, U. Gorres, The Alloy System Copper-Zirconium, Part I.
Phase Diagram and Structural Relations, Zeitschrift ftir
Metallkunde [Journal of metallurgy] 77 (1), pp. 43-48, 1986 for
Cu--Zr phases, from Braunovic, M.; Konchits, V. V.; Myshkin, N. K.:
Electrical contacts, fundamentals, applications and technology; CRC
Press 2007 for Cu--Al phases, from Petzoldt, F.; Bergmann, J. P.;
Schtrer, R.; Schneider, 2013, 67 Metall, 504-507 (see Table 1 for
example) for Cu--Al phases, from Landolt-Bornstein--Group IV
Physical Chemistry Volume 5d, 1994, pp. 1-8 for Cu--Ga phases, and
from P. R. Subramanian, D. E. Laughlin, Bulletin of Alloy Phase
Diagrams, 1988, 9, 1, 51-56 for Cu--Hf phases.
TABLE-US-00001 TABLE 1 Copper-aluminum phases (taken from Petzoldt,
F.; Bergmann, J. P.; Schurer, R.; Schneider, 2013, 67 Metall,
504-507) Specific elec. Cu Al Hardness resistance Phase [wt %] [wt
%] [HV] [.mu..OMEGA.cm] Cu 100 0 100 1.75 .GAMMA..sub.1 80 20 1050
14.2 Cu.sub.9Al.sub.4 .DELTA. 78 22 180 13.4 Cu.sub.3Al.sub.2
.zeta..sub.2 75 25 624 12.2 Cu.sub.4Al.sub.3 .eta..sub.2 CuAl 70 30
648 11.4 .theta. CuAl.sub.2 55 45 413 8.0 Al 0 100 60 2.9
[0070] In some embodiments, these copper-rich intermetallic phases
may include a proportion of copper greater than 40 atom %, or
greater than 50 atom %, or even greater than 60 atom %. However, in
some embodiments, the intermetallic phases also comprise
non-metallic elements such as oxygen, nitrogen, sulfur, selenium
and/or phosphorus, i.e. for example oxides, sulfides, selenides,
nitrides and/or phosphides are present. The intermetallic phases
are partially oxidized for example.
[0071] In some embodiments, the following copper-containing
perovskite structures and/or defective perovskite and/or compounds
related to perovskite can be used for electrocatalysts:
YBa.sub.2Cu.sub.3O.sub.7-.delta., wherein
0.ltoreq..delta..ltoreq.1, CaCu.sub.3Ti.sub.4O.sub.12,
La.sub.1.85Sr.sub.0.15, CuO.sub.3.930Cl.sub.0.053,
(La,Sr).sub.2CuO.sub.4. In some embodiments, mixtures of these
materials can be used for electrode preparation or that subsequent
calcination or activation steps are carried out as required.
[0072] In some embodiments, the catalyst particles comprise or
consist of copper, for example copper particles which are used for
producing the GDE, have a uniform particle size between 5 and 80
.mu.m, or 10 to 50 .mu.m, or even between 30 and 50 .mu.m.
Furthermore, the catalyst particles may have a high purity without
traces of foreign metals.
[0073] By means of suitable structuring, optionally with the aid of
promoters, high selectivity and long-term stability can be
achieved.
[0074] In some embodiments, the promoters, for example the metal
oxides, can also have a corresponding particle size in the
production.
[0075] In order to further adjust the porosity of the electrode, Cu
powder supplements having a particle diameter of 50 to 600 .mu.m,
or 100 to 450 .mu.m, or even 100-200 .mu.m, can be added. The
particle diameter of these supplements is, for example, 1/3- 1/10
of the total layer thickness of the layer. Instead of Cu, the
supplement can also be an inert material such as a metal oxide. In
this manner, an improved formation of pores and channels can be
achieved.
[0076] In some embodiments, the first layer comprises less than 5%
by weight, or less than 1% by weight, or even no carbon- and/or
carbon black-based or carbon- or carbon black-like, for example
conductive, fillers, based on the layer. In some embodiments, the
first layer comprises no surface-active substances. In some
embodiments, the first and/or second layer also do not comprise any
sacrificial material, for example a sacrificial material with a
release temperature of below approximately 275.degree. C., e.g. of
below 300.degree. C. or below 350.degree. C., in particular no pore
former which typically can remain at least partially in the
electrode when using such a material in the production of
electrodes. For instance, if only a (first) layer is present in the
GDE, the content or proportion of binder, for example PTFE, can be
for example 3-30% by weight, or 3-20% by weight, or 3-10% by
weight, or even 3-7% by weight, based on the one (first) layer.
[0077] The GDE described above further comprises a second layer
comprising copper and at least one binder, wherein the second layer
is located on the support and the first layer on the second layer,
wherein the content of binder in the first layer is less than in
the second layer. In addition, the second layer may comprise
coarser Cu or inert material particles, for example having particle
diameters of 50 to 700 .mu.m, or 100-450 .mu.m, in order to provide
a suitable channel or pore structure.
[0078] In some embodiments, the second layer in this case comprises
3-30% by weight binder, or 10-30% by weight binder, or 10-20% by
weight binder, or >10% by weight binder, or even >10% by
weight and up to 20% by weight binder, based on the second layer,
and the first layer comprises 0-10% by weight binder, e.g. 0.1-10%
by weight binder, or 1-10% by weight binder, or 1-7% by weight, or
even 3-7% by weight binder, based on the first layer. Here, the
binder can be the same as in the first layer, for example PTFE. In
some embodiments, the particles for producing the second layer may
correspond to those of the first layer, but may also be different
therefrom. The second layer in this case is a metal particle layer
(MPL), which is below the catalyst layer (CL). By means of such
layering, specifically strongly hydrophobic regions can be
established in the MPL and a catalyst layer having hydrophilic
properties can be generated. Owing to the strongly hydrophobic
character of the MPL, an undesirable penetration of the electrolyte
into the gas transport channels, i.e. a stream thereof, can
likewise be prevented.
[0079] In some embodiments, the second layer partially penetrates
the first layer. This enables a good transfer between the layers
with respect to diffusion. In addition to the second layer, the GDE
may comprise further layers still, for example on the first layer
and/or on the other side of the support.
[0080] To produce such a multi-layered GDE, firstly, for example, a
mixture for an MPL can be sieved, based on a highly conductive Cu
mixture of dendritic Cu having particle sizes between 5-100 .mu.m,
or than 50 .mu.m and coarser Cu or inert material particles having
particle sizes of 100-450 .mu.m, or 100-200 .mu.m, with a PTFE
content of 3-30% by weight, or 20% by weight, in a layer thickness
of 0.5 mm for example on a Cu mesh having a mesh size of 1 mm for
example (thickness e.g. 0.2-0.6 mm, e.g. 0.4 mm) and can be drawn
via a frame or doctor blade. Corresponding dendritic copper may
also be present in the first layer.
[0081] Subsequently, the catalyst/PTFE mixture (CL) can be further
sieved, for example with a PTFE content of 0.1-10% by weight, and
can be smoothed out or drawn over a 1 mm thick frame for example,
such that an overall layer thickness (Hf) of 1 mm can be obtained.
The layer thus prepared can then be supplied to a calender having a
gap width H.sub.0=0.4-0.7 mm, or 0.5-0.6 mm, and be rolled out so
that a multi-layered gas diffusion electrode can be obtained, as
shown schematically in FIG. 3, having a copper mesh 8, an MPL 9 and
a CL 10. By means of the MPL, better mechanical stability, further
prevention of penetration of electrolyte and better conductivity
can be achieved, especially when using meshes as supports. A
stepwise production of the GDE by sieving and rolling out in each
case of each individual layer can result in a lower adhesion
between the layers and is therefore may be less effective.
[0082] The degree of fibrillation of the binder, PTFE for example,
(structural parameter .zeta.) correlates directly with the applied
shear rate since the binder, a polymer for example, behaves as a
shear-thinning (pseudoplastic) fluid on rolling out. After
extrusion, the layer obtained by fibrillation has an elastic
character. This structural modification is irreversible such that
this effect can no longer be subsequently strengthened by further
rolling out, rather the layer is damaged by the elastic behavior on
further exposure to shear forces. A particularly intense
fibrillation may disadvantageously result in rolling up on the
layer side of the electrode such that excessively high contents of
binder should be avoided.
[0083] In some embodiments, the gas diffusion electrode may apply a
copper-PTFE base layer as second layer to improve contact of
nanoscale materials while simultaneously maintaining a high
porosity. The base layer may be characterized by very high
conductivity, for example 7 mOhm/cm or more, and may have a high
porosity, for example of 50-70%, and a hydrophobic character. The
binder content, for example PTFE, can be selected for example
between 3-30% by weight, e.g. 10-30% by weight. The copper
intermediate layer as second layer can itself be catalytically
active as the first layer in the region of the overlapping zone of
the catalyst layer, and particularly serves for better surface
electrical connection of the electrocatalyst. With the aid of this
method, the amount of catalyst required can be reduced by a factor
of 20-30.
[0084] The method of two-layered construction further offers the
possibility of omitting binder materials within the catalyst layer
as first layer, whereby better electrical conductivity can be
achieved. It also allows processing of very ductile or brittle
powder particles. Subsequent electrochemical activation of the
resulting electrode may optionally be carried out, by chemical or
electrochemical activation for example, and is not particularly
restricted. An electrochemical activation procedure may result in
cations of the conducting salt of the electrolyte (e.g. KHCO.sub.3,
K.sub.2SO.sub.4, NaHCO.sub.3, KBr, NaBr) penetrating the
hydrophobic GDE channels and as a result hydrophilic regions are
created.
[0085] The method according to the invention is suitable for the
partial electrochemical hydrogenation of alkynes of the chemical
formula (I) to alkenes,
##STR00011## [0086] wherein R and R' are selected from inorganic
and/or organic radicals.
[0087] In this case, the inorganic and/or organic radicals are not
particularly restricted, and the inorganic radicals may also
comprise organic substructures, for example in adducts or
complexes. According to particular embodiments, organic radicals
comprise 1 to 100 carbon atoms, for example 1 to 40 carbon atoms,
or 1 to 20 carbon atoms, e.g. 1-10, 1 to 6, 1 to 4, 1 to 2 carbon
atoms or even only 1 carbon atom. All inorganic radicals are
possible as inorganic radicals. Derivatives of inorganic radicals
and/or substituted organic radicals are also useful. Feasible as
inorganic and/or organic radicals are, for example, --H, -D, --OH,
--OR*, --SH, --SR*, --NH.sub.2, --NR*R*, --COOH, --COOR*, --CHO,
--COR*, --PH.sub.2, --PR*R*, --F, --Cl, --Br, --I, --NO,
--NO.sub.2, and also substituted or unsubstituted alkyl, alkenyl,
alkynyl and aryl groups, where R* and R* can likewise be in this
case any organic side chains, for example having 1 to 100 carbon
atoms, for example 1 to 40 carbon atoms, preferably 1 to 20 carbon
atoms, e.g. 1-10, 1 to 6, 1 to 4, 1 to 2 carbon atoms or even only
1 carbon atom, or inorganic side chains, such as --H, -D, --OH,
--SH, --NH.sub.2, --COOH, --CHO, --PH.sub.2, --F, --Cl, --Br, --I,
--NO, --NO.sub.2, and also substituted or unsubstituted alkyl,
alkenyl, alkynyl and aryl groups. Therefore, all alkynes are
suitable as reactants of the method. As a consequence, compounds of
the chemical formula (I) having two or more C--C triple bonds can
also be partially hydrogenated. In accordance with particular
embodiments however, the compound of the chemical formula (I) has
only one C--C triple bond, namely the one depicted in the chemical
formula (I).
[0088] In this context, partial hydrogenation is understood to mean
the hydrogenation of an alkyne, i.e. a triple bond, to alkene, i.e.
a double bond. The reaction takes place electrochemically using
electricity, for example in an electrolysis cell.
[0089] In some embodiments, the inorganic and/or organic radicals R
and R' are selected from substituted or unsubstituted alkyl,
alkenyl, alkynyl and/or aryl radicals, preferably alkyl and/or aryl
radicals, having 1 to 40 carbon atoms, or 1 to 20 carbon atoms,
e.g. 1-10, 1 to 6, 1 to 4, 1 to 2 carbon atoms or even only 1
carbon atom, --H, -D, --OH, --OR*, --SH, --SR*, --NH.sub.2,
--NR*R*, --COOH, --COOR*, --CHO, --COR*, --PH.sub.2, --PR*R*, --F,
--Cl, --Br, --I, --NO and --NO.sub.2, where R* and R* are organic
and/or inorganic radicals preferably selected from --H, -D, --OH,
--SH, --NH.sub.2, --COOH, --CHO, --PH.sub.2, --F, --Cl, --Br, --I,
--NO, --NO.sub.2, and also substituted or unsubstituted alkyl,
alkenyl, alkynyl and aryl groups, e.g. alkyl and/or aryl groups,
having 1 to 40 carbon atoms, or 1 to 20 carbon atoms, e.g. 1-10, 1
to 6, 1 to 4, 1 to 2 carbon atoms or even only 1 carbon atom.
[0090] Suitable substituents for the substituted or unsubstituted
alkyl, alkenyl, alkynyl and aryl groups or radicals are, for
example, -D, --OH, --SH, --NH.sub.2, --COOH, --CHO, --PH.sub.2,
--F, --Cl, --Br, --I, --NO, --NO.sub.2. Therefore, functionalized
side chains such as, for example, --CH.sub.2--OH or fluorinated
alkyl and/or aryl radicals such as --CF.sub.3 may result.
[0091] If R and R' are in each case --H or -D, then the compound of
the chemical formula (I) is the special case ethyne. If either R or
R', but not both, is --H or -D, the alkyne is referred to as a
terminal alkyne. In the case of internal alkynes, neither R nor R'
is --H or -D. In the case of terminal alkenes, the amount of charge
used may be precisely controlled, since over-hydrogenation is
possible, albeit with lower efficiency. In accordance with
particular embodiments, neither R nor R' are --H or -D, owing to
this necessary control, i.e. internal alkynes are hydrogenated.
[0092] In some embodiments, electron-poor and therefore activated
alkynes are less suitable for the method since the desired alkenes
are more reactive to electrohydrogenation. Therefore, poorer
selectivities are achieved with electron-poor alkenes. In some
embodiments, alkynes described herein may bear no
electron-withdrawing radicals such as, e.g. --COOH, --COOR*,
--CF.sub.3 (in which R* is as defined above). In some embodiments,
the alkyne of the chemical formula (I) therefore has no
electron-withdrawing radicals. In some embodiments, the
electron-withdrawing radicals are selected from --COOH, --COOR* and
fluorinated alkyl and/or aryl radicals, preferably perfluorinated
alkyl and/or aryl radicals such as --CF.sub.3.
[0093] In some embodiments, alkynes bear no functional groups which
may in turn be converted by electroreduction. Simultaneous
electroreduction of a reducible side chain or a reducible radical
is possible however. Examples of such alkynes having a reducible
side chain or a reducible radical are alkynes bearing functional
groups such as --CHO, --COR*, --NO or --NO.sub.2, or side chains
thereof comprising these radicals. The reduction of aldehydes
(--CHO), ketones (--COR*) and nitro compounds (--NO.sub.2) could be
confirmed experimentally. In this case, alcohols (--CH.sub.2--OH)
or (--CHR*--OH) were obtained from aldehydes (--CHO) and ketones
(--COR*) and amines (--NH.sub.2) from nitro compounds (--NO.sub.2).
In some embodiments, therefore, the alkyne of the chemical formula
(I) comprises no further reducible functional groups apart from the
triple bond.
[0094] In some embodiments, gaseous or water-soluble/water-miscible
alkynes, gaseous alkynes for example, may be used as alkyne of the
chemical formula (I). Examples of such suitable compounds are
ethyne, propyne, 1-butyne or 2-butyne, propargyl alcohol
(2-propyn-1-ol) and 2-butyn-1-ol.
[0095] Good synergy is apparent particularly in the case of using
gaseous alkynes of the chemical formula (I) with a
copper-containing gas diffusion electrode. In some embodiments,
therefore, the copper-containing electrode is configured as a gas
diffusion electrode, wherein the alkyne of the chemical formula (I)
is gaseous.
[0096] In some embodiments, the hydrogenation is carried out with a
proton donor selected from water and alcohols having 1 to 20 carbon
atoms, e.g. water and alcohols having 1 to 12, e.g. 1 to 6 or 1 to
4 carbon atoms. The water in this case may also be fully or
partially deuterated, i.e. comprise HDO or D.sub.2O, or also
tritium, for example in the production of radioactive markers.
[0097] Although an electrolyte that can be used in the method is
not particularly restricted, some embodiments use an aqueous
electrolyte. In addition, any conductive salts and/or ionic liquids
can be used. Mixtures of water with inert organic solvents, such as
1,4-dioxane for example, can be used to improve the substrate
solubility.
[0098] Some embodiments include use of a copper-containing
electrode for the partial electrochemical hydrogenation of alkynes
of the chemical formula (I) to alkenes,
##STR00012## [0099] wherein R and R' are selected from inorganic
and/or organic radicals.
[0100] The copper-containing electrode corresponds in this case to
that which has been described in connection with the methods
above.
[0101] Some embodiments include a device for the partial
electrochemical hydrogenation of alkynes of the chemical formula
(I) to alkenes,
##STR00013## [0102] wherein R and R' are selected from inorganic
and/or organic radicals, comprising an electrolysis cell (1)
comprising a copper-containing electrode, which is configured to
reduce the alkyne of the chemical formula (I) to alkene; a source
of the alkyne of the chemical formula (I) (3) which is configured
to provide the alkyne of the chemical formula (I); and a first
feeding device (2) for the alkyne of the chemical formula (I) which
is configured to feed the alkyne of the chemical formula (I) from
the source of the alkyne of the chemical formula (I) to the
electrolysis cell.
[0103] The electrolysis cell is not particularly restricted in this
case, as long as it comprises the copper-containing electrode which
can correspond to that of the methods described above. In some
embodiments, using the device, the methods can be carried out. In
this case, the copper-containing electrode can function as cathode.
The other constituents of the electrolysis cell such as anode,
optionally membrane, power source etc., are not particularly
restricted, as well as the arrangement thereof.
[0104] Examples of a possible cell arrangement are as follows. A
cathode chamber II can be arranged such that a catholyte is fed
from below and then exits the cathode chamber II from above. In
some embodiments, however, the catholyte can also be fed from
above, as for example in falling film electrodes. At the anode A,
which is electrically linked to the cathode K by means of a power
source for providing the voltage for the electrolysis, the
oxidation of a substance takes place in an anode chamber I, which
substance is fed from below, for example with an anolyte, in which
the anolyte then exits the anode chamber with the product of the
oxidation. The anode chamber and cathode chamber can be separated
by a membrane M. In such a 3-chamber design, as well as in other
designs, a reaction gas, such as an alkyne of the chemical formula
(I) for example, can be conveyed through a gas diffusion electrode
as cathode into the cathode chamber II for the reduction.
Embodiments with porous anodes are also feasible. Chambers I and II
may also be separated by a membrane M as described.
[0105] In contrast thereto, in the PEM (proton or ion exchange
membrane) set-up, a cathode K, a gas diffusion electrode for
example, and an anode A are directly adjacent to the membrane M,
whereby the anode chamber I is separated from the cathode chamber
II.
[0106] Hybrid forms of these cell designs are also feasible, in
which on the catholyte side for example, a set-up with a gas
diffusion electrode can be provided, which is not directly adjacent
to the membrane, whereas on the anolyte side the anode can be
adjacent to the membrane. Obviously, other hybrid forms or other
configurations of the exemplary electrode chambers depicted are
also feasible.
[0107] Also feasible are embodiments without a membrane. In some
embodiments, the electrolyte on the cathode side and the
electrolyte on the anode side may therefore be identical, and the
electrolysis cell/electrolysis unit can be operated without a
membrane. In some embodiments, the electrolysis cell comprises a
membrane, but this may be associated with additional inconvenience
with regard to the membrane as well as the voltage applied.
Catholyte and anolyte can also optionally be mixed again outside
the electrolysis cell.
[0108] The membrane, if present, can also be of multi-layered
design, so that separate feedings of anolyte and catholyte are
enabled. Separation effects are achieved in aqueous electrolytes by
the hydrophobicity of intermediate layers for example. Conductivity
can nevertheless be ensured if conductive groups are integrated
into such separation layers. The membrane can be an ion-conducting
membrane or a separator which only effects a mechanical separation
and is permeable to cations and anions.
[0109] By using a gas diffusion electrode, it is possible to
construct a three-phase electrode. For example, a gas can be fed
from behind to the electrically active front side of the electrode
in order to carry out an electrochemical reaction there. In
accordance with particular embodiments, the gas diffusion electrode
can only be supplied in countercurrent, i.e. a gas such as the
alkyne of the chemical formula (I) is fed past the reverse side of
the gas diffusion electrode in relation to the electrolytes,
wherein the gas can penetrate through the pores of the gas
diffusion electrode and the product can be discharged from the
rear. The gas flow may be reversed during countercurrent to the
flow of the electrolyte, so that potential liquid pressed through
can be transported away.
[0110] By means of adequate porosity of the gas diffusion
electrode, two operating modes are thus possible: one cell variant
enables a direct active perfusion of the GDE with a gas. The
products formed are removed from the electrolysis cell through the
catholyte outlet and can be separated from the liquid electrolyte
in a downstream phase separator. The second cell variant describes
an operating mode in which the gas flows in the rear region of the
GDE by an applied gas pressure. The gas pressure should be selected
in this case such that it is identical to the hydrostatic pressure
of the electrolyte in the cell so that no electrolyte permeates
through.
[0111] In order to further prevent penetration of electrolyte
through the gas diffusion electrode, a film can be applied to the
side of the gas diffusion electrode facing away from the
electrolyte in order to prevent the electrolyte crossing over to
the gas. The film can be provided so as to be suitable for this
purpose, and is hydrophobic for example.
[0112] In some embodiments, the electrolysis cell comprises a
membrane which separates the cathode chamber and the anode chamber
of the electrolysis cell in order to prevent mixing of the
electrolytes. The membrane is not particularly restricted in this
case, as long as it separates the cathode chamber and the anode
chamber. In particular, the membrane substantially prevents a
cross-over of the gases arising at the cathode and/or anode to the
anode and cathode chambers. In some embodiments, the membrane is an
ion exchange membrane, for example based on polymer. In addition to
polymer membranes, ceramic membranes can also be used.
[0113] The anode material is likewise not particularly restricted
and primarily depends on the desired reaction. Exemplary anode
materials include platinum or platinum alloys, palladium or
palladium alloys, and glassy carbon. Other anode materials are also
conductive oxides such as doped or non-doped TiO.sub.2, indium tin
oxide (ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc
oxide (AZO), iridium oxide, etc. Optionally, these catalytically
active compounds can also be applied superficially only in thin
film technology, for example on a titanium support.
[0114] In addition, the source of the alkyne of the chemical
formula (I) and a first feeding device (2) for the alkyne of the
chemical formula (I) are not particularly restricted. The alkyne of
the chemical formula (I) can for example originate as source from a
reservoir or other container as well as from a separate reactor,
etc. For example, tubes, hoses etc. may serve as first feeding
device. In particular, the source of the alkyne of the chemical
formula (I) and the first feeding device (2) for the alkyne of the
chemical formula (I) are adjusted to the particular alkyne in
regard to the materials used so that they are not attacked by the
alkyne of the chemical formula (I).
[0115] In some embodiments, there are further feeding devices, e.g.
for electrolyte, discharge devices, pumps, heating and/or cooling
devices etc.
[0116] In some embodiments, the copper-containing electrode is
configured as a gas diffusion electrode, wherein the first feeding
device (2) for the alkyne of the chemical formula (I) feeds the
alkyne of the chemical formula (I) to the gas diffusion
electrode.
[0117] The aforementioned embodiments, configurations, and other
developments can be combined with one another as desired, where
appropriate. Further possible configurations, developments and
implementations of the invention also include combinations not
explicitly specified above or in the following in relation to the
features of the invention described in the working examples. In
particular, a person skilled in the art will also add individual
aspects as improvements or supplements to the respective basic form
of the present invention.
[0118] The handful of exemplary embodiments described below may
illuminate the teachings of the present disclosure but do not limit
the scope of the teachings thereto.
EXAMPLES
[0119] The four following working examples were carried out in an
H-cell. Here, a 2 cm.sup.2 large solid Cu electrode was used which
had been coated with high-purity Cu from a CuSO.sub.4 solution. A
constant current of 30 mA was applied. 0.1M aqueous KBr was used as
electrolyte. In order to avoid influences from the anode, the anode
chamber was separated off by a Nafion N 117 membrane.
Example 1: Reduction of Ethyne
[0120] After a 10 minute run-in phase, in which the cell was purged
with argon, a flow of 7.7 ml/min of ethyne was passed through the
cell. This resulted in a current yield of 60% for the reduction of
ethyne to ethene. Over-reduction to ethane occurred at a maximum
current yield of 1.5%. The current residue resulted in formation of
hydrogen. The total conversion of the gas stream was around
1.5%.
Example 2: Reduction of Propargyl Alcohol
[0121] The cell was purged with argon during the whole experiment.
After a 10 minute run-in phase, propargyl alcohol (32 .mu.l, 0.55
mmol) was added to the electrolyte. On the basis of this sample
weight, a charge equivalent of 3.7 F/mol (2 F/mol required) is
apparent. Despite the significant charge excess, only traces of
propanol occurred. Conversely, the conversion of propargyl alcohol
to allyl alcohol was complete. At the starting concentration of
0.1M propargyl alcohol, also no more hydrogen evolution occurred.
Electricity efficiency for the conversion of propargyl alcohol to
allyl alcohol at high concentrations is therefore significantly
above 90%.
Example 3: Reduction of 1-butyn-1-ol
[0122] The cell was purged with argon during the whole experiment.
After a 10 minute run-in phase, butyn-1-ol (32 .mu.l, 0.43 mmol)
was added to the electrolyte. The conversion of butyn-1-ol to
crotyl alcohol was complete. The initial electricity yield is over
90%. Despite a charge equivalent of 4.8 F/mol used (2 F/mol
required), no over-reduction to n-butanol could be observed.
Comparative Example 1: Reduction of Allyl Alcohol
[0123] The cell was purged with argon during the whole experiment.
After a 10 minute run-in phase, allyl alcohol (32 .mu.l, 0.47 mmol)
was added. In contrast to the alkynes, neither high electricity
yields nor high conversion could be observed. After a charge
equivalent of 4.4 F/mol, a conversion of only 34% could be
observed.
Comparative Example 2: Reduction of Potassium Fumarate
[0124] The cell was purged with argon during the whole experiment.
After a 10 minute run-in phase, fumaric acid (58.7 mg, 0.51 mmol)
and KOH (200 .mu.l 5M, 1 mmol) were added. The conversion to
potassium succinate after a charge equivalent of 4.1 F/mol was
complete. The initial electricity yield was over 90%.
[0125] Using a gas diffusion electrode, the results of
electrohydrogenation of ethyne over a solid Cu electrode and 15
mA/cm.sup.2 at a current density of 170 mA/cm.sup.2 could be
readjusted.
[0126] The reactions arising from the examples are therefore as
follows:
[0127] Good selectivity, as shown here, is achieved by the low
reactivity with respect to electrohydrogenation with Cu electrodes.
Electronically deactivated internal alkenes such as crotyl alcohol
appeared inert to over-reduction.
[0128] It has been shown in the experiments that the method
according to the invention exhibits high selectivity and
activity.
[0129] Ethyne, propargyl alcohol and 2-butyn-1-ol were evaluated as
substrates. None of the 3 substrates is to be considered as
activated, which underlines the high activity of the catalytic
process. Propargyl alcohol and 2-butyn-1-ol are to be considered as
difficult substrates since both bear electron donating
substituents. 2-butyn-1-ol is also an internal alkyne which is also
sterically hindered.
[0130] The alkyne hydrogenation described here, in addition to the
high-volume compounds, can also be used for the electroorganic
synthesis of specialty chemicals such as active ingredients or
feedstuff additives.
* * * * *