U.S. patent application number 16/349768 was filed with the patent office on 2019-11-21 for organic hydride production apparatus and method for producing organic hydride.
This patent application is currently assigned to National University Corporation YOKOHAMA National University. The applicant listed for this patent is DE NORA PERMELEC LTD, National University Corporation YOKOHAMA National University. Invention is credited to Akihiro KATO, Akiyoshi MANABE, Koji MATSUOKA, Shigenori MITSUSHIMA, Kensaku NAGASAWA, Yoshinori NISHIKI, Setsuro OGATA, Yasushi SATO, Awaludin ZAENAL.
Application Number | 20190352786 16/349768 |
Document ID | / |
Family ID | 62145369 |
Filed Date | 2019-11-21 |
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United States Patent
Application |
20190352786 |
Kind Code |
A1 |
MITSUSHIMA; Shigenori ; et
al. |
November 21, 2019 |
ORGANIC HYDRIDE PRODUCTION APPARATUS AND METHOD FOR PRODUCING
ORGANIC HYDRIDE
Abstract
An organic hydride production apparatus includes: an electrolyte
membrane having proton conductivity; a cathode that includes a
cathode catalyst layer used to hydrogenate a hydrogenation target
substance using protons to produce an organic hydride and also
includes a cathode chamber; an anode that includes an anode
catalyst layer used to oxidize water to produce protons and also
includes an anode chamber; and a gas introduction unit that
introduces, into the anolyte at a certain position, a certain gas
used to remove at least one of the hydrogenation target substance
and the organic hydride that have passed through the electrolyte
membrane and been mixed into the anolyte.
Inventors: |
MITSUSHIMA; Shigenori;
(Yokohama-shi, Kanagawa, JP) ; NAGASAWA; Kensaku;
(Yokohama-shi, Kanagawa, JP) ; NISHIKI; Yoshinori;
(Fujisawa City, Kanagawa, JP) ; KATO; Akihiro;
(Fujisawa City, Kanagawa, JP) ; OGATA; Setsuro;
(Fujisawa City, Kanagawa, JP) ; ZAENAL; Awaludin;
(Fujisawa City, Kanagawa, JP) ; MANABE; Akiyoshi;
(Fujisawa City, Kanagawa, JP) ; MATSUOKA; Koji;
(Chiyoda-ku, Tokyo, JP) ; SATO; Yasushi;
(Chiyoda-ku, Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
National University Corporation YOKOHAMA National University
DE NORA PERMELEC LTD |
Yokohama-shi, Kanagawa
Fujisawa City, Kanagawa |
|
JP
JP |
|
|
Assignee: |
National University Corporation
YOKOHAMA National University
Yokohama-shi, Kanagawa
JP
DE NORA PERMELEC LTD
Fujisawa City, Kanagawa
JP
|
Family ID: |
62145369 |
Appl. No.: |
16/349768 |
Filed: |
October 18, 2017 |
PCT Filed: |
October 18, 2017 |
PCT NO: |
PCT/JP2017/037647 |
371 Date: |
May 14, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25B 9/00 20130101; C25B
1/10 20130101; C25B 9/10 20130101; C25B 9/08 20130101; C25B 3/04
20130101; C25B 15/08 20130101 |
International
Class: |
C25B 9/10 20060101
C25B009/10; C25B 3/04 20060101 C25B003/04; C25B 15/08 20060101
C25B015/08 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 15, 2016 |
JP |
2016-222563 |
Claims
1. An organic hydride production apparatus, comprising: an
electrolyte membrane having proton conductivity; a cathode,
provided on one side of the electrolyte membrane, that comprises a
cathode catalyst layer used to hydrogenate a hydrogenation target
substance using protons to produce an organic hydride and also
comprises a cathode chamber that houses the cathode catalyst layer;
an anode, provided opposite to the one side of the electrolyte
membrane, that comprises an anode catalyst layer used to oxidize
water in an anolyte to produce protons and also comprises an anode
chamber that houses the anode catalyst layer; and a gas
introduction unit that introduces, into the anolyte at a
predetermined position, a predetermined gas used to remove at least
one of the hydrogenation target substance and the organic hydride
that have passed through the electrolyte membrane and been mixed
into the anolyte.
2. The organic hydride production apparatus of claim 1, further
comprising: an anolyte storage tank that stores the anolyte; and a
circulation passage that connects the anolyte storage tank and the
anode, wherein the gas introduction unit introduces the gas into
the anolyte in at least one of the anode chamber, the anolyte
storage tank, and the circulation passage.
3. The organic hydride production apparatus of claim 2, wherein the
gas introduction unit introduces the gas into the anolyte in the
anode chamber.
4. The organic hydride production apparatus of claim 1, wherein the
predetermined gas is at least one selected from a group including
air, nitrogen, argon, and helium.
5. A method for producing an organic hydride, comprising: supplying
an anolyte containing water to an anode catalyst layer and
producing protons by electrolysis of the water; supplying a
hydrogenation target substance to a cathode catalyst layer and
hydrogenating the hydrogenation target substance using the protons
that have passed through an electrolyte membrane, thereby producing
an organic hydride; and introducing a predetermined gas into the
anolyte and removing, from the anolyte, at least one of the
hydrogenation target substance and the organic hydride that have
passed through the electrolyte membrane and been mixed into the
anolyte.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No.
2016-222563, filed on Nov. 15, 2016, and International Patent
Application No. PCT/JP2017/037647, filed on Oct. 18, 2017, the
entire content of each of which is incorporated herein by
reference.
BACKGROUND
Field of the Invention
[0002] The present invention relates to an organic hydride
production apparatus and a method for producing an organic hydride.
The present invention particularly relates to an organic hydride
production apparatus for producing an organic hydride by
electrochemically hydrogenating a hydrogenation target substance,
and to a method for producing an organic hydride using the organic
hydride production apparatus.
Description of the Related Art
[0003] In recent years, widespread use of renewable energy,
obtained by solar power generation, wind power generation,
hydropower generation, geothermal power generation, and the like,
is desired because the renewable energy is considered as new energy
that can be generated with less carbon dioxide emissions, compared
to energy obtained by thermal power generation. However, for such
renewable energy, moderation of output fluctuations, especially the
intermediate and long-period output fluctuations, is required.
Also, large-scale transportation of renewable energy is relatively
difficult. Meanwhile, electric power obtained from renewable energy
can be effectively converted into chemical energy. For processes
for directly converting electric power into chemical energy,
electrochemical systems can be used. Secondary cells, or storage
batteries, are examples of electrochemical systems and are devices
widely used to convert electrical power into chemical energy and
store the chemical energy.
[0004] As an electrochemical system based on renewable energy,
there is a promising system in which large-scale solar power or
wind power generation systems are installed in appropriate
locations around the world, and renewable energy obtained therefrom
is converted into an energy carrier appropriate for transportation,
so as to be transported into a country and consumed domestically.
The energy carrier may be liquid hydrogen, for example. However,
since hydrogen is gaseous at ordinary temperatures and pressures,
special tankers are required for transportation and storage
thereof.
[0005] In such a situation, attention is given to organic hydrides
(organic chemical hydrides) as energy carriers alternative to
liquid hydrogen. Organic hydrides may be cyclic organic compounds,
such as cyclohexane, methylcyclohexane, and decalin. Organic
hydrides are generally liquid at ordinary temperatures and
pressures, and hence can be easily handled. Also, organic hydrides
can be electrochemically hydrogenated and dehydrogenated.
Accordingly, when an organic hydride is used as an energy carrier,
it can be transported and stored more easily than liquid hydrogen.
Particularly, when a liquid organic hydride having properties
similar to those of petroleum is selected, since it has excellent
compatibility with relatively large-scale energy supply systems,
the liquid organic hydride has the advantage of being easily
distributed to ends of such energy supply systems.
[0006] As a method for producing an organic hydride, a method is
conventionally known in which hydrogen is produced by water
electrolysis using renewable energy and is added to a hydrogenation
target substance (dehydrogenated product of an organic hydride) in
a hydrogenation reactor, thereby producing an organic hydride.
[0007] Meanwhile, when an electrolytic synthesis method is used,
since hydrogen can be directly added to a hydrogenation target
substance, the processes for organic hydride production can be
simplified. In addition, the efficiency loss is small regardless of
the production scale, and excellent responsiveness to the start and
stop operations of the organic hydride production apparatus can be
seen. With regard to a technology for such organic hydride
production, for example, Patent Document 1 discloses an
electrolysis cell that includes an oxidizing electrode for
producing protons from water, and a reducing electrode for
hydrogenating an organic compound having an unsaturated bond.
[0008] Patent Document 1: WO 12/091128
[0009] As a result of intensive study regarding the abovementioned
technology for organic hydride production, the inventors have found
that there is room for improving the efficiency of organic hydride
production in the conventional technologies.
SUMMARY OF THE INVENTION
[0010] The present invention has been made in view of such a
situation, and a purpose thereof is to provide a technology for
improving efficiency of organic hydride production.
[0011] One aspect of the present invention is an organic hydride
production apparatus. The apparatus includes: an electrolyte
membrane having proton conductivity; a cathode, provided on one
side of the electrolyte membrane, that includes a cathode catalyst
layer used to hydrogenate a hydrogenation target substance using
protons to produce an organic hydride and also includes a cathode
chamber that houses the cathode catalyst layer; an anode, provided
opposite to the one side of the electrolyte membrane, that includes
an anode catalyst layer used to oxidize water in an anolyte to
produce protons and also includes an anode chamber that houses the
anode catalyst layer; and a gas introduction unit that introduces,
into the anolyte at a predetermined position, a predetermined gas
used to remove at least one of the hydrogenation target substance
and the organic hydride that have passed through the electrolyte
membrane and been mixed into the anolyte.
[0012] Another aspect of the present invention is a method for
producing an organic hydride. The method includes: supplying an
anolyte containing water to an anode catalyst layer and producing
protons by electrolysis of the water; supplying a hydrogenation
target substance to a cathode catalyst layer and hydrogenating the
hydrogenation target substance using the protons that have passed
through an electrolyte membrane, thereby producing an organic
hydride; and introducing a predetermined gas into the anolyte and
removing, from the anolyte, at least one of the hydrogenation
target substance and the organic hydride that have passed through
the electrolyte membrane and been mixed into the anolyte.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Embodiments will now be described, by way of example only,
with reference to the accompanying drawings which are meant to be
exemplary, not limiting, and wherein like elements are numbered
alike in several Figures, in which:
[0014] FIG. 1 is a schematic diagram of an organic hydride
production apparatus according to an embodiment;
[0015] FIG. 2 is a sectional view that shows a schematic structure
of an electrolysis cell included in the organic hydride production
apparatus according to the embodiment;
[0016] FIG. 3A is a diagram that shows absorption spectra of
anolytes of which bubbling has been performed, and FIG. 3B is a
diagram that shows absorption spectra of anolytes of which bubbling
has not been performed;
[0017] FIG. 4A is a diagram that shows an absorption spectrum of
toluene, FIG. 4B is a diagram that shows an absorption spectrum of
benzyl alcohol, and FIG. 4C is a diagram that shows an absorption
spectrum of benzaldehyde;
[0018] FIG. 5A is a diagram that shows relationships between the
supply rate of air and the remaining percentage of toluene, and
FIG. 5B is a diagram that shows relationships between the duration
of air supply and the remaining percentage of toluene; and
[0019] FIG. 6A is a diagram that shows remaining percentage of
toluene in pure water and remaining percentage of toluene in a
sulfuric acid aqueous solution, and FIG. 6B is a diagram that shows
remaining percentage of various organic substances in a sulfuric
acid aqueous solution.
DETAILED DESCRIPTION OF THE INVENTION
[0020] In the following, the present invention will be described
based on a preferred embodiment with reference to the drawings.
Embodiments of the invention are provided for purposes of
illustration and not limitation, and it should be understood that
not all of the features or combinations thereof described in the
embodiments are necessarily essential to the invention.
[0021] Like reference characters denote like or corresponding
constituting elements, members, and processes in each drawing, and
repetitive description will be omitted as appropriate. Also, the
scale or shape of each component shown in each drawing is set for
the sake of convenience to facilitate the explanation and is not to
be regarded as limitative unless otherwise specified. Further, when
the terms "first", "second", and the likes are used in the present
specification or claims, such terms do not imply any order or
importance and are used to distinguish one configuration from
another, unless otherwise specified.
[0022] FIG. 1 is a schematic diagram of an organic hydride
production apparatus (electrochemical reduction apparatus)
according to an embodiment. In FIG. 1, illustration of separators
included in the electrolysis cell is omitted to simplify the
configuration of the membrane electrode assembly. An organic
hydride production apparatus 10 is an apparatus for hydrogenating a
hydrogenation target substance, which is a dehydrogenated product
of an organic hydride, by an electrochemical reduction reaction,
and the organic hydride production apparatus 10 mainly includes an
electrolysis cell 100 for organic hydride production (hereinafter,
the "electrolysis cell for organic hydride production" may be
simply referred to as the "electrolysis cell" as appropriate), an
electric power controller 20, a catholyte storage tank 30, a
separation tank 36, an anolyte storage tank 40, a control unit 60,
and a gas introduction unit 70.
[0023] The electric power controller 20 may be a DC/DC converter
for converting an output voltage of an electric power source into a
predetermined voltage, for example. The positive output terminal of
the electric power controller 20 is connected to an anode 150
(electrode for oxygen evolution) of the electrolysis cell 100.
Also, the negative output terminal of the electric power controller
20 is connected to a cathode 120 (reduction electrode) of the
electrolysis cell 100. Accordingly, a predetermined voltage is
applied between the anode 150 and the cathode 120 of the
electrolysis cell 100.
[0024] In the electric power controller 20, a reference terminal
may be provided in order to detect the potentials of the positive
and negative electrodes. In this case, the input side of the
reference terminal is connected to a reference electrode (not
illustrated) provided in an electrolyte membrane 110 of the
electrolysis cell 100. The reference electrode is electrically
isolated from the cathode 120 and the anode 150. The reference
electrode is maintained at a reference electrode potential. The
reference electrode potential in the subject application means a
potential with respect to a reversible hydrogen electrode (RHE)
(the reference electrode potential=0 V). Also, the reference
electrode potential may be a potential with respect to an Ag/AgCl
electrode (the reference electrode potential=0.199 V). The current
flowing between the cathode 120 and the anode 150 is detected by a
current detector (not illustrated). The current value detected by
the current detector is input to the control unit 60 and used for
control of the electric power controller 20 by the control unit 60.
The potential difference between the reference electrode and the
cathode 120 is detected by a voltage detector (not illustrated).
The potential difference value detected by the voltage detector is
input to the control unit 60 and used for control of the electric
power controller 20 by the control unit 60.
[0025] The control unit 60 controls outputs at the positive output
terminal and the negative output terminal of the electric power
controller 20 such that the potentials of the anode 150 and the
cathode 120 become desired potentials. The electric power source
may preferably be renewable energy obtained by solar power
generation, wind power generation, hydropower generation,
geothermal power generation, and the like, but is not particularly
limited thereto.
[0026] The catholyte storage tank 30 stores a hydrogenation target
substance to be hydrogenated by an electrochemical reduction
reaction in the electrolysis cell 100. An organic hydride used in
the present embodiment is not particularly limited, as long as it
is an organic compound that can be hydrogenated or dehydrogenated
by a reversible hydrogenation or dehydrogenation reaction.
Accordingly, acetone-isopropanol-based organic hydrides,
benzoquinone-hydroquinone-based organic hydrides, aromatic
hydrocarbon-based organic hydrides, and the likes may be widely
used. Among them, aromatic hydrocarbon-based organic hydrides,
represented by toluene-methylcyclohexane-based organic hydrides,
may be preferable, in terms of transportability during the energy
transportation, toxicity, safety, and storage stability, and also
in terms of the transportable amount of hydrogen per volume or
mass, ease of hydrogenation and dehydrogenation reactions, and
energy conversion efficiency, including the feature by which the
Gibbs free energy does not change significantly.
[0027] An aromatic hydrocarbon compound used as a dehydrogenated
product of an organic hydride is a compound that contains at least
one aromatic ring, such as benzene and an alkylbenzene.
Alkylbenzenes include compounds in which one through four hydrogen
atoms in an aromatic ring is replaced by a linear or branched alkyl
group having one or two carbon atoms, such as toluene and xylene.
Each of the compounds may be used solely or in combination. The
aromatic hydrocarbon compound may preferably be at least one of
toluene and benzene. As the dehydrogenated product, a
nitrogen-containing heterocyclic aromatic compound, such as
pyridine, pyrimidine, and pyrazine, may also be used. The organic
hydride is obtained by hydrogenating a dehydrogenated product as
set forth above and may be methylcyclohexane, dimethylcyclohexane,
or piperidine, for example.
[0028] The dehydrogenated product of an organic hydride, i.e., the
hydrogenation target substance, may preferably be liquid at
ordinary temperatures. When a mixture of a plurality of the
aforementioned aromatic hydrocarbon compounds, of a plurality of
nitrogen-containing heterocyclic aromatic compounds, or of the both
compounds is used, such a mixture may suitably be liquid. When the
hydrogenation target substance is liquid at ordinary temperatures,
such a hydrogenation target substance in the liquid state can be
supplied to the electrolysis cell 100, without performing a process
such as heating and pressurization thereon. Accordingly, the
configuration of the organic hydride production apparatus 10 can be
simplified. In the following, the liquid stored in the catholyte
storage tank 30 may be referred to as the "catholyte", as
needed.
[0029] The hydrogenation target substance stored in the catholyte
storage tank 30 is supplied to the cathode 120 of the electrolysis
cell 100 by a first liquid supply device 32. As the first liquid
supply device 32, each of various pumps, such as a gear pump and a
cylinder pump, or a gravity flow type device can be used, for
example. Between the cathode 120 and the catholyte storage tank 30,
a circulation passage 34 is provided. The circulation passage 34
includes an outward part 34a that connects the catholyte storage
tank 30 and the cathode 120 on the upstream side of the cathode 120
in the catholyte flow direction, and a return part 34b that
connects the cathode 120 and the catholyte storage tank 30 on the
downstream side of the cathode 120 in the catholyte flow direction.
On the outward part 34a, the first liquid supply device 32 is
provided. Also, on the return part 34b, the separation tank 36 is
provided.
[0030] The hydrogenation target substance hydrogenated in the
electrolysis cell 100, i.e., an organic hydride, and the unreacted
hydrogenation target substance flow through the return part 34b of
the circulation passage 34 to reach the separation tank 36. In the
separation tank 36, hydrogen gas as a by-product, the anolyte
flowing into the cathode 120 side via the electrolyte membrane 110,
or the like is separated from the mixture of the organic hydride
and the hydrogenation target substance. The separated gas is
processed in a decomposition unit 38 containing a decomposition
catalyst or the like. The separated anolyte is reused. The organic
hydride and the hydrogenation target substance are then returned
into the catholyte storage tank 30.
[0031] The anolyte storage tank 40 stores ion exchanged water, pure
water, or an aqueous solution obtained by adding acid, such as
sulfuric acid, phosphoric acid, nitric acid, and hydrochloric acid,
to ion exchanged water or pure water, for example (hereinafter,
referred to as the "anolyte", as needed). The ion conductivity of
the anolyte measured at 20 degrees C. may preferably be 0.01 S/cm
or greater. By setting the ion conductivity of the anolyte to 0.01
S/cm or greater, industrially sufficient electrochemical reactions
can be induced.
[0032] The anolyte stored in the anolyte storage tank 40 is
supplied to the anode 150 of the electrolysis cell 100 by a second
liquid supply device 42. As the second liquid supply device 42,
each of various pumps, such as a gear pump and a cylinder pump, or
a gravity flow type device can be used, for example. Between the
anode 150 and the anolyte storage tank 40, a circulation passage 44
that connects the anode 150 and the anolyte storage tank 40 is
provided. The circulation passage 44 includes an outward part 44a
that connects the anolyte storage tank 40 and the anode 150 on the
upstream side of the anode 150 in the anolyte flow direction, and a
return part 44b that connects the anode 150 and the anolyte storage
tank 40 on the downstream side of the anode 150 in the anolyte flow
direction. On the outward part 44a, the second liquid supply device
42 is provided. In other words, the organic hydride production
apparatus 10 includes an anolyte supply line, constituted by the
anolyte storage tank 40 and the circulation passage 44, for
supplying an anolyte containing water to the anode 150.
[0033] The unreacted anolyte in the electrolysis cell 100 is
returned to the anolyte storage tank 40 via the return part 44b of
the circulation passage 44. In the anolyte storage tank 40, a
gas-liquid separation unit (not illustrated) is provided, so that
oxygen produced by electrolysis of the anolyte in the electrolysis
cell 100, and gases, such as the gasified hydrogenation target
substance and organic hydride, mixed into the anolyte via the
electrolyte membrane 110 are separated from the anolyte in the
gas-liquid separation unit and then processed in a decomposition
unit 46 containing a decomposition catalyst or an adsorbent, for
example. When a sulfuric acid aqueous solution or the like is used
as the anolyte, the material of the anolyte storage tank 40 may
preferably be polyvinyl chloride, polyethylene, polypropylene, or
fiber-reinforced plastic, for example. Also, the component parts of
the drive unit of the second liquid supply device 42 may preferably
be coated with ceramics, fluororesin, or the like.
[0034] The electrolysis cell 100 includes the electrolyte membrane
110, the cathode 120, and the anode 150. FIG. 2 is a sectional view
that shows a schematic structure of the electrolysis cell included
in the organic hydride production apparatus according to the
embodiment. As shown in FIG. 2, the electrolysis cell 100 includes
a membrane electrode assembly 102 and a pair of separators 170a and
170b between which the membrane electrode assembly 102 is disposed.
The membrane electrode assembly 102 includes the electrolyte
membrane 110, the cathode 120, and the anode 150.
[Electrolyte Membrane]
[0035] The electrolyte membrane 110 is formed of a
proton-conducting material (an ionomer). The electrolyte membrane
110 selectively conducts protons while restraining mixture and
diffusion of substances between the cathode 120 and the anode 150.
The proton-conducting material may be a perfluorosulfonic acid
polymer, such as Nafion (registered trademark) and Flemion
(registered trademark). The thickness of the electrolyte membrane
110 is not particularly limited, but may preferably be 5-300 .mu.m,
more preferably be 10-200 .mu.m, and further preferably be 20-100
.mu.m. By setting the thickness of the electrolyte membrane 110 to
5 .mu.m or greater, the barrier performance of the electrolyte
membrane 110 can be ensured, so that cross leakage of the
hydrogenation target substance, organic hydride, oxygen, and the
like can be restrained more certainly. Also, setting the thickness
of the electrolyte membrane 110 to 300 .mu.m or less can prevent
excessive increase of ion transfer resistance.
[0036] The area resistance, i.e., ion transfer resistance per
geometric area, of the electrolyte membrane 110 is not particularly
limited, but may preferably be 2000 m.OMEGA.cm.sup.2 or less, more
preferably be 1000 m.OMEGA.cm.sup.2 or less, and further preferably
be 500 m.OMEGA.cm.sup.2 or less. By setting the area resistance of
the electrolyte membrane 110 to 2000 m.OMEGA.cm.sup.2 or less, lack
of proton conductivity can be prevented more certainly. The ion
exchange capacity (IEC) of the cation-exchange ionomer is not
particularly limited, but may preferably be 0.7-2 meq/g, and more
preferably be 1-1.3 meq/g. By setting the ion exchange capacity of
the cation-exchange ionomer to 0.7 meq/g or greater, insufficiency
of ion conductivity can be prevented more certainly. Also, setting
the ion exchange capacity to 2 meq/g or less can more certainly
prevent insufficiency of the strength of the electrolyte membrane
110 caused by increase of solubility of the ionomer in the anolyte,
hydrogenation target substance, or organic hydride.
[0037] The electrolyte membrane 110 may be mixed with a
reinforcement material, such as porous polytetrafluoroethylene
(PTFE). Adding a reinforcement material can restrain deterioration
of dimension stability of the electrolyte membrane 110 caused by
increase of the ion exchange capacity. Accordingly, durability of
the electrolyte membrane 110 can be improved. Also, crossover of
the hydrogenation target substance, organic hydride, oxygen, and
the like can be restrained. A surface of the electrolyte membrane
110 may be made hydrophilic by providing asperities on the surface,
coating the surface with a predetermined inorganic layer, or the
combination thereof.
[Cathode]
[0038] The cathode 120 is provided on one side of the electrolyte
membrane 110. In the present embodiment, the cathode 120 is
provided to be in contact with one main surface of the electrolyte
membrane 110. The cathode 120 includes a cathode catalyst layer
122, and a cathode chamber 124 that houses the cathode catalyst
layer 122. The cathode 120 also includes a spacer 126, a
microporous layer 128, a diffusion layer 130, a flow passage part
132, a cathode chamber inlet 134, and a cathode chamber outlet
136.
[0039] The cathode catalyst layer 122 is in contact with one main
surface of the electrolyte membrane 110 in the cathode chamber 124.
The cathode catalyst layer 122 contains a reduction catalyst used
to hydrogenate a hydrogenation target substance using protons to
produce an organic hydride. As the reduction catalyst, metal
particles of a substance selected from a group including Pt, Ru,
Pd, Ir, and an alloy containing at least one of them may be used.
The reduction catalyst may be a commercially available product, or
may be synthesized according to a publicly-known method. Also, the
reduction catalyst may be constituted by a metal composition that
contains a first catalyst metal (noble metal) including at least
one of Pt, Ru, Pd, and Ir, and one or more kinds of second catalyst
metals selected from among Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Sn,
W, Re, Pb, and Bi. In this case, the form of the metal composition
may be an alloy of the first catalyst metal and the second catalyst
metal(s), or an intermetallic compound constituted by the first
catalyst metal and the second catalyst metal(s), for example.
[0040] The average particle size of the reduction catalyst may
preferably be 1 nm-1 .mu.m, and more preferably be 1-5 nm. By
setting the average particle size of the reduction catalyst to 1
.mu.m or less, the surface area per weight (reactive area) of the
catalyst can be increased. Also, setting the average particle size
of the reduction catalyst to 1 nm or greater can more certainly
restrain deterioration of the durability caused by the proceeding
of catalyst particle cohesion.
[0041] The reduction catalyst is supported by a catalyst support
made of an electron-conductive material. When the reduction
catalyst is supported by a catalyst support, the surface area of
the cathode catalyst layer 122 can be increased. Also, cohesion of
the reduction catalyst can be restrained. The electron conductivity
of the electron-conductive material used for the catalyst support
may preferably be 1.0.times.10.sup.-2 S/cm or greater, more
preferably be 3.0.times.10.sup.-2 S/cm or greater, and further
preferably be 1.0.times.10.sup.-1 S/cm or grater. By setting the
electron conductivity of the electron-conductive material to
1.0.times.10.sup.-2 S/cm or greater, the electron conductive
properties can be more certainly imparted to the cathode catalyst
layer 122.
[0042] For the catalyst support, an electron-conductive material
containing, as a major component, one of porous carbon (such as
mesoporous carbon), porous metal, and a porous metal oxide may be
used, for example. The porous carbon may be carbon black, for
example, including Ketjenblack (registered trademark), acetylene
black, furnace black, and Vulcan (registered trademark).
[0043] The BET specific surface area of the porous carbon measured
by a nitrogen adsorption method may preferably be 50-1500
m.sup.2/g, more preferably be 500-1300 m.sup.2/g, and further
preferably be 700-1000 m.sup.2/g. By setting the BET specific
surface area of the porous carbon to 50 m.sup.2/g or greater, the
reduction catalyst can be evenly supported more easily. Also, the
diffusivity of the hydrogenation target substance or organic
hydride can be ensured more certainly. Also, setting the BET
specific surface area of the porous carbon to 1500 m.sup.2/g or
less can prevent the catalyst support becoming likely to
deteriorate during a reaction of the hydrogenation target substance
or when the organic hydride production apparatus 10 is started or
stopped. Accordingly, sufficient durability can be imparted to the
catalyst support. The average particle size of carbon particulates,
such as carbon black, used as the catalyst support may preferably
be 0.01-1 .mu.m.
[0044] The porous metal may be Pt black, Pd black, or Pt metal
deposited in a fractal form, for example. The porous metal oxide
may be an oxide of Ti, Zr, Nb, Mo, Hf, Ta, or W, for example. Also,
for the catalyst support, a porous metal compound, such as a
nitride, a carbide, an oxynitride, a carbonitride, or a
partially-oxidized carbonitride of metal, such as Ti, Zr, Nb, Mo,
Hf, Ta, and W, may also be used (hereinafter, such a porous metal
compound may be referred to as a "porous metal carbonitride or the
like" as appropriate). The BET specific surface area of the porous
metal, the porous metal oxide, and the porous metal carbonitride or
the like measured by a nitrogen adsorption method may preferably be
1 m.sup.2/g or greater, more preferably be 3 m.sup.2/g or greater,
and further preferably be 10 m.sup.2/g or greater. By setting the
BET specific surface area of the porous metal, the porous metal
oxide, and the porous metal carbonitride or the like to 1 m.sup.2/g
or greater, the reduction catalyst can be evenly supported more
easily.
[0045] The catalyst support supporting the reduction catalyst is
coated with an ionomer. Accordingly, the ion conductivity of the
cathode 120 can be improved. The ionomer may be a perfluorosulfonic
acid polymer, for example, including Nafion (registered trademark)
and Flemion (registered trademark). The ion exchange capacity (IEC)
of the ionomer may preferably be 0.7-3 meq/g, more preferably be
1-2.5 meq/g, and further preferably be 1.2-2 meq/g. When the
catalyst support is porous carbon, a mass ratio I/C of the ionomer
(I) to the catalyst support (C) may preferably be 0.1-2, more
preferably be 0.2-1.5, and further preferably be 0.3-1.1. By
setting the mass ratio I/C to 0.1 or greater, sufficient ion
conductivity can be obtained more certainly. Also, setting the mass
ratio I/C to 2 or less can prevent excessive thickening of the
ionomer coating for the reduction catalyst, so that the situation
can be avoided in which the hydrogenation target substance is
inhibited from coming into contact with a catalytic active
site.
[0046] Preferably, the reduction catalyst may be partially coated
with the ionomer included in the cathode catalyst layer 122. This
enables efficient supply of three elements (a hydrogenation target
substance, protons, and electrons) necessary for the
electrochemical reaction in the cathode catalyst layer 122, to a
reaction field.
[0047] The thickness of the cathode catalyst layer 122 may
preferably be 1-100 .mu.m, and more preferably be 5-30 .mu.m. If
the thickness of the cathode catalyst layer 122 is increased, the
proton transfer resistance will be increased, and, in addition, the
diffusivity of the hydrogenation target substance or organic
hydride will be reduced. Therefore, adjusting the thickness of the
cathode catalyst layer 122 within the abovementioned range would be
desirable.
[0048] The cathode catalyst layer 122 may be prepared by the
following method, for example. First, catalyst component powder,
hydrophobic resin (fluorine component) of a gas-permeable material,
water, a solvent such as naphtha, and an ionomer {such as Nafion
(registered trademark) Dispersion Solution DE521 (made by E. I. du
Pont de Nemours and Company)} are mixed together. The amount of the
ionomer added may preferably be set such that the ratio of the mass
of the ionomer after drying to the mass of carbon in the catalyst
component powder is 1:10-10:1. The hydrophobic resin is powdery,
and the particle size thereof may preferably be 0.005-10 .mu.m. To
the obtained mixture, a solvent is added as appropriate, so as to
prepare catalyst ink.
[0049] Thereafter, the catalyst ink thus obtained is applied to the
microporous layer 128, and drying and hot pressing is performed
such that the cathode catalyst layer 122 is fixed to the
microporous layer 128. Preferably, applying the catalyst ink and
drying as stated above may be performed divisionally in multiple
times before hot pressing is performed. This can make the cathode
catalyst layer 122 to be obtained more homogenous. Through the
process set forth above, the cathode catalyst layer 122 can be
prepared. The cathode catalyst layer 122 may be formed on the
electrolyte membrane 110. For example, by applying the catalyst ink
to one main surface of the electrolyte membrane 110 using a bar
coater, a complex of the cathode catalyst layer 122 and the
electrolyte membrane 110 can be prepared. Also, by applying the
catalyst ink to one main surface of the electrolyte membrane 110 by
spray coating and drying the solvent component in the catalyst ink,
a complex of the cathode catalyst layer 122 and the electrolyte
membrane 110 can be prepared. The catalyst ink may be preferably
applied such that the mass of the reduction catalyst in the cathode
catalyst layer 122 per electrode area is 0.5 mg/cm.sup.2.
[0050] The cathode chamber 124 is defined by the electrolyte
membrane 110, the separator 170a, and the spacer 126 of a frame
shape disposed between the electrolyte membrane 110 and the
separator 170a. The cathode chamber 124 houses the microporous
layer 128, the diffusion layer 130, and the flow passage part 132,
besides the cathode catalyst layer 122. In the spacer 126, the
cathode chamber inlet 134 and the cathode chamber outlet 136, which
each communicate with the inside and the outside of the cathode
chamber 124, are disposed.
[0051] The microporous layer 128 is disposed adjacent to the
cathode catalyst layer 122. More specifically, the microporous
layer 128 is provided to be in contact with a main surface of the
cathode catalyst layer 122 opposite to the electrolyte membrane 110
side. The diffusion layer 130 is disposed adjacent to the
microporous layer 128. More specifically, the diffusion layer 130
is provided to be in contact with a main surface of the microporous
layer 128 opposite to the cathode catalyst layer 122 side.
[0052] The diffusion layer 130 has a function to evenly diffuse, in
the cathode catalyst layer 122, the hydrogenation target substance
in a liquid state supplied from the flow passage part 132. A
constituent material of the diffusion layer 130 may preferably have
high compatibility with the hydrogenation target substance and
organic hydride. The constituent material of the diffusion layer
130 may be a porous conductive base material or a fiber sintered
body, for example. Porous conductive base materials and fiber
sintered bodies are preferable because they have porosity suitable
for supply and removal of gas and liquid and are capable of
maintaining sufficient conductivity. The diffusion layer 130 may
preferably have a thickness of 10-5000 .mu.m, percentage of voids
of 30-95%, and representative pore size of 1-1000 .mu.m. Also, the
electron conductivity of the constituent material of the diffusion
layer 130 may preferably be 10.sup.-2 S/cm or greater.
[0053] More specific examples of the constituent material of the
diffusion layer 130 include carbon woven fabric (carbon cloth),
carbon non-woven fabric, and carbon paper. Carbon cloth is woven
fabric made with bundles of hundreds of thin carbon fibers of which
the diameter is a few micrometers. Also, carbon paper is obtained
by making a thin film precursor from carbon material fiber using a
papermaking method and then sintering the thin film precursor.
[0054] The microporous layer 128 has a function to promote
diffusion of the hydrogenation target substance and organic hydride
in liquid states in a surface direction of the cathode catalyst
layer 122. The microporous layer 128 may be formed by applying, to
a surface of the diffusion layer 130, paste-like kneaded matter
obtained by mixing and kneading conductive powder and a water
repellent, and then drying the kneaded matter, for example. As the
conductive powder, conductive carbon such as Vulcan (registered
trademark) may be used, for example. As the water repellent,
fluororesin such as polytetrafluoroethylene (PTFE) resin may be
used, for example. The ratio between the conductive powder and
water repellent may be appropriately determined within a range such
that desired conductivity and water repellency can be obtained. As
an example, when Vulcan (registered trademark) is used as the
conductive powder and PTFE is used as the water repellent, the mass
ratio (Vulcan:PTFE) may be 4:1-1:1, for example. As with the
diffusion layer 130, the microporous layer 128 may also be formed
of carbon cloth, carbon paper, or the like.
[0055] The mean flow pore size (dm) of the microporous layer 128
after hot pressing may preferably be 100 nm-20 .mu.m, and more
preferably be 500 nm-5 .mu.m. The mean flow pore size of the
microporous layer 128 can be measured using a mercury porosimeter,
for example. Setting the mean flow pore size to 100 nm or greater
can more certainly restrain increase of the diffusion resistance
caused by excessive increase of the contact area between the wall
surface of each pore and the liquid hydrogenation target substance
or liquid organic hydride. Also, setting the mean flow pore size to
20 .mu.m or less can more certainly restrain decrease of the
fluidity caused by decrease of suction by capillary action for the
liquid hydrogenation target substance and liquid organic hydride.
Also, by setting the mean flow pore size to 100 nm-20 .mu.m, the
liquid hydrogenation target substance and liquid organic hydride
can be smoothly suctioned or discharged by capillary action.
[0056] The thickness of the microporous layer 128 may preferably be
1-50 .mu.m, and more preferably be 2-20 .mu.m. When the microporous
layer 128 is formed such as to be recessed inward from the surface
of the diffusion layer 130, an average thickness of the microporous
layer 128, including the recessed portion in the diffusion layer
130, is defined as the thickness of the microporous layer 128. A
metal component may be coexistent on a surface of the microporous
layer 128. This can improve the electron conductivity of the
microporous layer 128 and make the current uniform.
[0057] The microporous layer 128 and the diffusion layer 130 are
used in a state where pressure is applied thereto in the respective
thickness directions. Accordingly, it will be unfavorable if such
pressurization in the thickness directions during use changes the
conductivity in the thickness directions. Therefore, the
microporous layer 128 and the diffusion layer 130 may preferably be
subjected to press working in advance. This can compress a carbon
material in each layer, thereby improving and stabilizing the
conductivity in a thickness direction in each layer. Also, the
cathode 120 with a stable filling rate of 20-50% can be
obtained.
[0058] Further, improving the degree of bonding between the cathode
catalyst layer 122 and the microporous layer 128 also contributes
to improvement of the conductivity of the cathode 120. Such
improvement of the degree of bonding also improves the capability
of supplying a raw material and the capability of removing a
product. As a press-working apparatus, a publicly-known apparatus,
such as a hot press and a hot roller, may be used. Also, the
pressing conditions may preferably be the temperature of room
temperature -360 degrees C., and the pressure of 0.1-5 MPa.
[0059] The flow passage part 132 is disposed adjacent to the
diffusion layer 130. More specifically, the flow passage part 132
is provided to be in contact with a main surface of the diffusion
layer 130 opposite to the microporous layer 128 side. The flow
passage part 132 has a structure in which grooves 132b are provided
on a main surface of a body part 132a of a plate shape. The grooves
132b constitute a flow passage for the hydrogenation target
substance. The body part 132a is made of a conductive material. The
flow passage part 132 also functions as a cathode support for
positioning the cathode catalyst layer 122, microporous layer 128,
and diffusion layer 130 within the cathode chamber 124.
[0060] The cathode chamber inlet 134 is disposed below the cathode
chamber 124 in the vertical direction. One end of the cathode
chamber inlet 134 is connected to the flow passage of the flow
passage part 132, and the other end thereof is connected to the
first liquid supply device 32 via the outward part 34a of the
circulation passage 34. The hydrogenation target substance supplied
from outside the cathode chamber 124 is introduced into the cathode
chamber 124 through the cathode chamber inlet 134. The
hydrogenation target substance introduced into the cathode chamber
124 is supplied to the cathode catalyst layer 122 via the grooves
132b of the flow passage part 132, the diffusion layer 130, and the
microporous layer 128.
[0061] The cathode chamber outlet 136 is disposed above the cathode
chamber 124 in the vertical direction. One end of the cathode
chamber outlet 136 is connected to the flow passage of the flow
passage part 132, and the other end thereof is connected to the
return part 34b of the circulation passage 34. The organic hydride
and the unreacted hydrogenation target substance within the cathode
chamber 124 are discharged outside the cathode chamber 124 through
the cathode chamber outlet 136.
[0062] The separator 170a is disposed on the cathode 120 side in
the electrolysis cell 100. In the present embodiment, the separator
170a is laminated to a main surface of the flow passage part 132
opposite to the diffusion layer 130 side.
[Anode]
[0063] The anode 150 is provided opposite to the one side of the
electrolyte membrane 110, i.e., opposite to the cathode 120. In the
present embodiment, the anode 150 is provided to be in contact with
the other main surface of the electrolyte membrane 110. The anode
150 includes an anode catalyst layer 152, and an anode chamber 154
that houses the anode catalyst layer 152. The anode 150 also
includes a spacer 156, a supporting elastic body 158, an anode
chamber inlet 160, and an anode chamber outlet 162.
[0064] The anode catalyst layer 152 is in contact with the other
main surface of the electrolyte membrane 110 in the anode chamber
154. The anode catalyst layer 152 is a layer containing a catalyst
used to oxidize water in an anolyte to produce protons. As the
catalyst included in the anode catalyst layer 152, metal particles
of a substance selected from a group including Ru, Rh, Pd, Ir, Pt,
and an alloy containing at least one of them may be used.
[0065] The catalyst may be dispersedly supported by a metallic base
material having electron conductivity, or such a metallic base
material may be coated with the catalyst.
[0066] Such a metallic base material may be metal fiber (the fiber
diameter may be 10-30 .mu.m, for example), a mesh (the mesh size
may be 500-1000 .mu.m, for example), a sintered metal porous body,
a foam molded body (foam), expanded metal, or the like, made of
metal, such as Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ta, and W,
or an alloy composed primarily of such metal.
[0067] In consideration of the necessity of electrical conductivity
sufficient to conduct current required for electrolysis, and the
necessity of mechanical strength of the electrolysis cell 100, the
base material used for the anode catalyst layer 152 may preferably
be a plate-like material having a thickness of 0.1-2 mm. Also, in
order to promote the supply of an anolyte without increase of
resistance caused by bubbles, the base material may preferably be a
porous body and have excellent corrosion resistance to the anolyte.
As such a base material, titanium expanded mesh is widely used. The
expanded mesh may preferably have short way of mesh of 0.1-4 mm,
long way of mesh of 0.1-4 mm, and an aperture ratio of about
30-70%.
[0068] The anode chamber 154 is defined by the electrolyte membrane
110, the separator 170b, and the spacer 156 of a frame shape
disposed between the electrolyte membrane 110 and the separator
170b. The anode chamber 154 houses the supporting elastic body 158,
besides the anode catalyst layer 152. In the spacer 156, the anode
chamber inlet 160 and the anode chamber outlet 162, which each
communicate with the inside and the outside of the anode chamber
154, are disposed.
[0069] The supporting elastic body 158 is disposed adjacent to the
anode catalyst layer 152. More specifically, the supporting elastic
body 158 is provided to be in contact with a main surface of the
anode catalyst layer 152 opposite to the electrolyte membrane 110
side. The supporting elastic body 158 has a function to bias the
anode catalyst layer 152 toward the electrolyte membrane 110. By
pressing the anode catalyst layer 152 onto the electrolyte membrane
110 using the supporting elastic body 158, the electrolytic
properties of the electrolysis cell 100 can be improved. The
supporting elastic body 158 may be constituted by, for example, a
conductive member having an elastic body structure, such as a leaf
spring structure and a coil structure. The supporting elastic body
158 may preferably have acid resistance. The constituent material
of the supporting elastic body 158 may be titanium or a titanium
alloy, for example. Specific examples of the elastic body structure
include a V-shaped spring, a cross spring, a cushion coil spring,
and a chatter fiber aggregation.
[0070] The anode chamber inlet 160 is disposed below the anode
chamber 154 in the vertical direction. One end of the anode chamber
inlet 160 is connected to the inside of the anode chamber 154, and
the other end thereof is connected to the second liquid supply
device 42 via the outward part 44a of the circulation passage 44.
The anolyte supplied from outside the anode chamber 154 is
introduced into the anode chamber 154 through the anode chamber
inlet 160. The anolyte introduced into the anode chamber 154 is
supplied to the anode catalyst layer 152 directly or via the
supporting elastic body 158.
[0071] The anode chamber outlet 162 is disposed above the anode
chamber 154 in the vertical direction. One end of the anode chamber
outlet 162 is connected to the inside of the anode chamber 154, and
the other end thereof is connected to the return part 44b of the
circulation passage 44. Oxygen gas and the unreacted anolyte within
the anode chamber 154 is discharged outside the anode chamber 154
through the anode chamber outlet 162.
[0072] The separator 170b is disposed on the anode 150 side in the
electrolysis cell 100. In the present embodiment, the separator
170b is laminated to a main surface of the supporting elastic body
158 opposite to the anode catalyst layer 152 side.
[0073] In the electrolysis cell 100 having the structure set forth
above, reactions that occur when toluene (TL) is used as the
hydrogenation target substance are as follows. When toluene is used
as the hydrogenation target substance, the organic hydride to be
obtained is methylcyclohexane (MCH).
<Electrode Reaction at the Anode>
[0074] 2H.sub.2O.fwdarw.O.sub.2+4H.sup.++4e.sup.-,
E.sub.0=1.23V
<Electrode Reaction at the Cathode>
[0075] TL+6H.sup.++6e.sup.-.fwdarw.MCH, E.sub.0=0.15V
<Total Reaction>
[0076] 2TL+6H.sub.2O.fwdarw.2MCH+3O.sub.2
[0077] Thus, the electrode reaction at the anode 150 and the
electrode reaction at the cathode 120 proceed in parallel. Protons
(H.sup.+) produced by electrolysis of water at the anode 150 are
supplied to the cathode 120 via the electrolyte membrane 110. The
protons supplied to the cathode 120 are used for hydrogenation of
the hydrogenation target substance at the cathode 120. Accordingly,
toluene is hydrogenated, so that methylcyclohexane is produced.
Therefore, with the organic hydride production apparatus 10
according to the present embodiment, the electrolysis of water and
the hydrogenation of the hydrogenation target substance can be
performed in one step.
[0078] In the organic hydride production apparatus 10, the
hydrogenation target substance and the organic hydride (organic
compound) supplied to the cathode 120 are inhibited from moving to
the anode 150 side by the electrolyte membrane 110. However, it is
difficult to perfectly prevent the move of the hydrogenation target
substance and organic hydride with the electrolyte membrane 110, so
that part of the hydrogenation target substance and organic hydride
pass through the electrolyte membrane 110 to reach the anode 150
and are mixed into the anolyte. The hydrogenation target substance
and organic hydride mixed into the anolyte may be adsorbed by the
anode catalyst layer 152. Also, such hydrogenation target substance
and organic hydride may become oxides by electrolytic oxidation in
the anode catalyst layer 152, which may promote corrosion of the
anode catalyst layer 152. Accordingly, the hydrogenation target
substance and organic hydride mixed into the anolyte would
deteriorate the function of the anode catalyst layer 152, which may
increase the cell voltage in the organic hydride production
apparatus 10, for example. Thus, the efficiency of organic hydride
production would be reduced.
[0079] Meanwhile, the organic hydride production apparatus 10
according to the present embodiment includes the gas introduction
unit 70, as shown in FIGS. 1 and 2, for introducing a predetermined
gas into the anolyte so as to remove at least one of the
hydrogenation target substance and the organic hydride mixed in the
anolyte. In the following, a configuration for removing both the
hydrogenation target substance and the organic hydride using a gas
will be described as a preferable example, but configurations for
removing only one of the hydrogenation target substance and the
organic hydride are also included in the present embodiment. For
example, the gas introduction unit 70 introduces, as a
predetermined gas, at least one selected from a group including
air, nitrogen, argon, and helium, into the anolyte. More
specifically, the gas introduction unit 70 causes bubbling of the
anolyte using the predetermined gas. The gas introduction unit 70
includes a pump or an ejector, for example, as a mechanism for
introducing a gas into the anolyte.
[0080] Introduction of a gas into the anolyte by the gas
introduction unit 70 promotes gasification of the hydrogenation
target substance and the organic hydride in the anolyte, thereby
removing the hydrogenation target substance and the organic hydride
from the anolyte. This can restrain the adsorption of the
hydrogenation target substance and the organic hydride by the anode
catalyst layer 152, and the corrosion of the anode catalyst layer
152 caused by oxides of the hydrogenation target substance and the
organic hydride. The gasified hydrogenation target substance and
organic hydride are discharged outside the system via the
decomposition unit 46.
[0081] The gasification of the hydrogenation target substance and
the organic hydride is also promoted partway by oxygen gas produced
in the electrode reaction at the anode 150. However, the
introduction of a gas by the gas introduction unit 70 can further
promote the gasification of the hydrogenation target substance and
the organic hydride, thereby removing more hydrogenation target
substance and organic hydride from the anolyte more promptly. This
can reduce the amount of oxides produced, thereby further
restraining the deterioration of the anode catalyst layer 152.
[0082] As the hydrogenation target substance, toluene may be used,
for example, as described previously. The solubility of toluene in
the anolyte is up to about 500 mg/L. Toluene has a boiling point of
110.6 degrees C. and is relatively likely to gasify. However, when
toluene is mixed into the anolyte, not a little toluene is
electrolyzed and oxidized in the anode catalyst layer 152.
Compounds produced by the electrolytic oxidation of toluene include
benzyl alcohol, benzaldehyde, and benzoic acid. The boiling points
of benzyl alcohol, benzaldehyde, and benzoic acid are 205 degrees
C., 178.1 degrees C., and 249.2 degrees C., respectively, and, with
the introduction of a gas by the gas introduction unit 70, it is
difficult to remove such compounds from the anolyte.
[0083] However, by providing the gas introduction unit 70, more
toluene can be promptly removed from the anolyte. Accordingly, the
amount of toluene removed from the anolyte before electrode
oxidation can be increased. As a result, the produced amount of
oxides of toluene is reduced, thereby further restraining the
deterioration of the anode catalyst layer 152. Other hydrogenation
target substances and organic hydrides thought to be used in the
organic hydride production apparatus 10 can also be removed from
the anolyte using the gas introduction unit 70, by adjusting the
temperature, humidity, and the like of the gas to be introduced, as
needed. When adjusting the temperature and humidity of the gas, it
is desirable to provide adjustment such as to allow a greater
amount of hydrogenation target substance and organic hydride to
dissolve in the gas rather than in the anode electrolyte.
[0084] At a predetermined position in the route for the anolyte, a
gas is introduced from the gas introduction unit 70 into the
anolyte. In the present embodiment, the gas introduction unit 70 is
disposed such as to introduce the gas into the anode chamber 154.
However, the configuration is not particularly limited thereto, and
the gas introduction unit 70 may be connected to another position
in the route for the anolyte instead of the anode chamber 154, such
as the anolyte storage tank 40 and the circulation passage 44.
Also, the gas introduction unit 70 may be connected to only one of
the anode chamber 154, anolyte storage tank 40, and circulation
passage 44, or may be connected to two or more thereof.
[0085] The concentration of the hydrogenation target substance and
the organic hydride in the anolyte is higher in the anode catalyst
layer 152 and the return part 44b than in the anolyte storage tank
40 and the outward part 44a, and is particularly higher in the
anode catalyst layer 152.
[0086] Accordingly, the gas from the gas introduction unit 70 may
preferably be introduced into the anolyte in the anode chamber 154
or the return part 44b, and more preferably be introduced into the
anolyte in the anode chamber 154. This can improve the efficiency
of the removal of the hydrogenation target substance and the
organic hydride from the anolyte.
[0087] When the gas is introduced into the anode chamber 154, the
gas introduction unit 70 may preferably be connected to the
downstream side of the anode catalyst layer 152 in the anolyte flow
direction. This can more certainly avoid the situation in which the
gas supplied from the gas introduction unit 70 inhibits the
electrode reaction in the anode catalyst layer 152. Meanwhile, when
the gas is introduced into the anolyte storage tank 40, the gas
introduction unit 70 may preferably be connected to a bottom part
of the anolyte storage tank 40. When the gas is introduced into the
outward part 44a of the circulation passage 44, the gas
introduction unit 70 may be connected to a suction part of the
second liquid supply device 42.
[0088] The amount of the gas introduced from the gas introduction
unit 70 may be set based on the amount per unit time of the
hydrogenation target substance and the organic hydride shifted to
the anode 150, for example. When the total shift amount of the
hydrogenation target substance and the organic hydride per
electrode area is about 0.01 mmol/(hcm.sup.2), for example, the
introduction amount of the gas may preferably be 60 L/(hcm.sup.2)
or greater. Also, the introduction amount of the gas may be, for
example, equal to or more than the amount of oxygen gas produced in
the electrode reaction at the anode 150, and equal to or less than
200 times the amount of oxygen gas produced. The introduction
amount of the gas may preferably be adjusted such that the
concentration of the hydrogenation target substance and organic
hydride in the gas discharged from the decomposition unit 46 is the
explosive limit concentration or less.
[0089] The gas introduction unit 70 may preferably include a porous
member and introduce a gas into the anolyte via the porous member.
Via such a porous member, the gas can be introduced in a state of
fine bubbles into the anolyte. This can facilitate the gasification
of the hydrogenation target substance and the organic hydride. The
gas introduction unit 70 may also include a conventionally
well-known agitation means, such as a propeller.
[Method for Producing Organic Hydride]
[0090] In a method for producing an organic hydride according to
the present embodiment, an anolyte containing water is supplied to
the anode catalyst layer 152 of the anode 150 described above. In
the anode catalyst layer 152, protons are produced by electrolysis
of water. The protons thus produced then pass through the
electrolyte membrane 110 and move to the cathode 120 side. Also, a
hydrogenation target substance is supplied to the cathode catalyst
layer 122 of the cathode 120. In the cathode catalyst layer 122,
the hydrogenation target substance is hydrogenated by the protons
that have passed through the electrolyte membrane 110, so that an
organic hydride is produced. In parallel with the production of the
organic hydride, a predetermined gas is introduced from the gas
introduction unit 70 into the anolyte, so that the hydrogenation
target substance and the organic hydride that have passed through
the electrolyte membrane 110 and been mixed into the anolyte are
removed from the anolyte. The process of producing protons, the
process of producing the organic hydride by the electrolytic
reduction reaction, and the process of removing the hydrogenation
target substance and the organic hydride from the anolyte occur in
parallel at least at one point in time.
[0091] As described above, the organic hydride production apparatus
10 according to the present embodiment includes the electrolyte
membrane 110, the cathode 120, the anode 150, and the gas
introduction unit 70 for introducing a gas into the anolyte so as
to remove the hydrogenation target substance and the organic
hydride. The removal of the hydrogenation target substance and the
organic hydride from the anolyte using the gas introduction unit 70
can restrain adsorption, by the catalyst, of the hydrogenation
target substance and the organic hydride mixed in the anolyte, and
corrosion of the catalyst caused by oxides of the hydrogenation
target substance and the organic hydride.
[0092] As a result, functional deterioration of the anode catalyst
layer 152 is restrained, so that increase in cell voltage can be
avoided. Accordingly, the reduction reaction of the hydrogenation
target substance in the cathode 120 can be made to proceed for a
long period of time with lower electric power consumption rate.
Therefore, the efficiency of organic hydride production can be
improved. Also, the life of the anode catalyst layer 152 can be
prolonged.
[0093] Meanwhile, the present embodiment includes a configuration
in which the anolyte is circulated between the anolyte storage tank
40 and the anode 150. Accordingly, the hydrogenation target
substance and the organic hydride mixed into the anolyte is likely
to accumulate in the anolyte storage tank 40. Therefore, the
removal of the hydrogenation target substance and the organic
hydride using the gas introduction unit 70 is particularly
effective to improve the efficiency of organic hydride production
and to prolong the life of the anode catalyst layer 152.
[0094] The method for producing an organic hydride according to the
present embodiment includes: the process of supplying an anolyte to
the anode catalyst layer 152 and producing protons by electrolysis
of water in the anolyte; the process of supplying a hydrogenation
target substance to the cathode catalyst layer 122 and
hydrogenating the hydrogenation target substance with protons that
have passed through the electrolyte membrane 110, so as to produce
an organic hydride; and the process of introducing a predetermined
gas into the anolyte to remove, from the anolyte, the hydrogenation
target substance and the organic hydride that have passed through
the electrolyte membrane 110 and been mixed into the anolyte.
Accordingly, the organic hydride can be produced for a longer
period of time, with higher efficiency. Even when only one of the
hydrogenation target substance and the organic hydride is removed
using a gas, the efficiency of organic hydride production can be
improved and the life of the anode catalyst layer 152 can be
prolonged, compared to the case where such removal is not
performed.
[0095] The embodiment stated above is intended to be illustrative
only, and the present invention is not limited thereto. It is to be
understood that various changes and modifications, including design
modifications, may be made based on the knowledge of those skilled
in the art and that embodiments with such changes and modifications
added are also within the scope of the present invention.
EXAMPLE
[0096] An example of the present invention will now be described by
way of example only to suitably describe the present invention and
should not be construed as limiting the scope of the invention.
Example 1
[0097] First, catalyst ink for the cathode catalyst layer was
prepared by adding Nafion (registered trademark) Dispersion
Solution DE2020 (made by E. I. du Pont de Nemours and Company) to
powder of PtRu/C catalyst TEC61E54E (23% Pt by mass, 27% Ru by
mass, made by TANAKA KIKINZOKU KOGYO K.K.) and by using a solvent
as appropriate. An amount of Nafion (registered trademark)
Dispersion Solution was added such that the ratio of the mass of
Nafion after drying to the mass of carbon in the catalyst became
1:1. Also, as the electrolyte membrane, Nafion (registered
trademark) 115 (thickness of 120 .mu.m, made by E. I. du Pont de
Nemours and Company) subjected to hydrophilic treatment was
prepared. The catalyst ink thus obtained was applied to one main
surface of the electrolyte membrane by spray coating. The catalyst
ink was applied such that the total mass of Pt and Ru per electrode
area became 0.5 mg/cm.sup.2. Thereafter, the coated film was dried
at 80 degrees C. to remove the solvent component in the catalyst
ink, obtaining a laminated body of the cathode catalyst layer and
the electrolyte membrane.
[0098] Subsequently, a cathode diffusion layer SGL35BC (made by SGL
Carbon) cut out according to the shape of an electrode surface was
attached to a surface of the cathode catalyst layer. The cathode
catalyst layer and the cathode diffusion layer were then thermally
bonded together for two minutes, at the temperature of 120 degrees
C. and the pressure of 1 MPa. Accordingly, a complex constituted by
the electrolyte membrane, the cathode catalyst layer, and the
cathode diffusion layer was obtained.
[0099] Meanwhile, a carbon-based structure was prepared by molding
with carbon/epoxy resin. The carbon-based structure corresponds to
an assembly of the flow passage part 132, the spacer 126, and the
separator 170a. On a surface of the carbon-based structure on the
side corresponding to the flow passage part 132, multiple flow
passages were formed. Each flow passage was formed into a linear
shape with the width of 1 mm and the depth of 0.5 mm. The distance
between adjacent flow passages was set to 1 mm. One end of each
flow passage was connected to a liquid supply header that
integrates the respective flow passages. The other end of each flow
passage was connected to a liquid discharge header that also
integrates the respective flow passages.
[0100] Also, as an anode base material, expanded mesh having the
thickness of 1.0 mm, the short way of mesh of 3.5 mm, the long way
of mesh of 6.0 mm, the width of 1.1 mm, and the aperture ratio of
42% was prepared. Dry blasting was performed on surfaces of the
anode base material, and a cleaning process in 20 percent sulfuric
acid aqueous solution was performed. Thereafter, using an arc ion
plating apparatus and a titanium-tantalum alloy plate, 2-micrometer
thick coating was formed on the surfaces of the anode base
material, at the base material temperature of 150 degrees C. and
the vacuum of 1.0.times.10.sup.-2 Torr. To the anode base material
with the coating, a mixed aqueous solution of iridium tetrachloride
and tantalum pentachloride was applied. The anode base material was
then placed in an electric furnace and subjected to heat treatment
at 550 degrees C. By repeating the application of the solution and
the heat treatment multiple times, an anode catalyst layer
containing equimolar amounts of iridium oxide and tantalum oxide as
catalysts was formed. The amount of the supported catalyst, in
terms of the amount of Ir metal, per electrode area was 12
g/m.sup.2.
[0101] Also, an elastic body obtained by processing a 0.3-milimeter
thick titanium plate such that flat springs with a pitch of 10 mm
were arranged was prepared as an anode supporting elastic body. On
a surface of each flat spring in contact with the anode catalyst
layer, a layer of a slight amount of platinum was formed. Further,
an anode spacer and an anode separator were also prepared.
[0102] The carbon-based structure, complex, anode spacer, anode
catalyst layer, anode supporting elastic body, and anode separator
thus prepared were laminated in this order. The anode catalyst
layer was fixed to the electrolyte membrane-side surface of the
complex. The carbon-based structure was disposed such that each
flow passage extended in a vertical direction when the organic
hydride production apparatus was installed, and was fixed to the
cathode diffusion layer-side surface of the complex. To one end of
each flow passage, a supply passage for a hydrogenation target
substance (corresponding to the outward part 34a of the circulation
passage 34) was connected via the liquid supply header. Also, to
the other end of each flow passage, a discharge passage for an
organic hydride (corresponding to the return part 34b of the
circulation passage 34) was connected via the liquid discharge
header. Further, a supply passage for an anolyte (corresponding to
the outward part 44a of the circulation passage 44) was connected
to the anode chamber inlet in the anode spacer, and a discharge
passage for the anolyte (corresponding to the return part 44b of
the circulation passage 44) was connected to the anode chamber
outlet in the anode spacer.
[0103] Pressing each layer using the anode supporting elastic body
could create a state in which the layers are in close contact with
each other. The distance between the electrolyte membrane and the
anode catalyst layer was set to 0.05 mm. Through the processes set
forth above, the organic hydride production apparatus of Example 1
was obtained. The active electrode area of the electrolysis cell
was 12.3 cm.sup.2.
[0104] In this organic hydride production apparatus, toluene as the
catholyte was made to flow through the cathode chamber. Also, 100
g/L sulfuric acid aqueous solution as the anolyte was made to flow
through the anode chamber. The flow rate of the catholyte was set
to 0.6 mL/minute. Also, the flow rate of the anolyte was set to 5
mL/minute. At the temperature of 60 degrees C. and the current
density of 40 A/dm.sup.2, the electrolytic reaction was caused. The
anolyte was supplied from the anolyte storage tank to the anode
chamber using a pump, and then returned from the anode chamber to
the anolyte storage tank to be circulated (batch operation). The
anolyte was supplied through a lower part of the electrolysis cell
to the anode chamber. Also, the anolyte was circulated while an
amount of water reduced by electrolysis was supplemented.
[0105] Also, to the anolyte storage tank, a gas introduction unit
including a glass filter was connected. Through the glass filter,
air was supplied to the anolyte storage tank for bubbling of the
anolyte. The supply rate of air was set to 2.8 L/minute. After 24,
48, and 72 hours from the initiation of the electrolytic reaction,
the anolyte was analyzed using an ultraviolet absorbance detector
(from SHIMADZU CORPORATION). FIG. 3A shows the results.
Comparative Example 1
[0106] Except that the gas introduction unit was not connected to
the anolyte storage tank, an organic hydride production apparatus
similar to that of Example 1 was obtained. Also, except that air
was not supplied into the anolyte and bubbling was not performed,
the electrolytic reaction was caused under the conditions same as
those in Example 1. After 24, 51, and 72 hours from the initiation
of the electrolytic reaction, the anolyte was analyzed using an
ultraviolet-visible spectrophotometer (from SHIMADZU CORPORATION).
FIG. 3B shows the results.
[0107] FIG. 3A shows absorption spectra of the anolyte of which
bubbling was performed. FIG. 3B shows absorption spectra of the
anolyte of which bubbling was not performed. As shown in FIGS. 3A
and 3B, regardless of whether or not bubbling was performed, an
absorption spectrum corresponding to that of toluene (see FIG. 4A)
was not detected. Meanwhile, absorption spectra considered to
correspond to those of benzyl alcohol (see FIG. 4B) and
benzaldehyde (see FIG. 4C), which are oxides of toluene, were
detected.
[0108] When the absorption spectra considered to be derived from
benzyl alcohol and benzaldehyde are compared in terms of whether or
not bubbling was performed, the absorbance is higher when bubbling
of the anolyte was not performed (FIG. 3B) than when bubbling of
the anolyte was performed (FIG. 3A). This comparison shows that the
amount of oxides of toluene included in the anolyte was larger when
the bubbling was not performed than when the bubbling was
performed. This means that the bubbling of the anolyte promptly
removed toluene from the anolyte, thereby restraining production
and accumulation of the oxides of toluene.
[0109] Meanwhile, in each of Example 1 and Comparative Example 1,
the anolyte was extracted also after one hour from the initiation
of the electrolytic reaction. Thereafter, the concentration of
toluene included in the gas discharged from the anolyte was
measured using detector tubes (No. 122, from GASTEC CORPORATION).
The results were 2.8 ppm in Example 1 and 410 ppm in Comparative
Example 1. This suggests that the bubbling of the anolyte promptly
removed toluene. In terms of the cell voltage, any change according
to whether or not bubbling was performed was not observed (2.2 V on
average). Also, the electrolysis cell was operated for a long time
in each of Example 1 and Comparative Example 1, and the consumption
rate of iridium in the anode catalyst was measured using an X-ray
fluorescence instrument (from Rigaku Corporation). The results were
that, when the operation time was 1000-2000 hours, the consumption
rate was 3% in Example 1 and 6% in Comparative Example 1. Thus, the
catalyst consumption behavior improved by the bubbling can be
ascertained.
[0110] Further, except that the mole ratio of iridium oxide to
tantalum oxide included in the anode catalyst layer was set to 2:1,
an organic hydride production apparatus similar to that of Example
1 or Comparative Example 1 was obtained. In the apparatus, an
electrolytic reaction similar to that in Example 1 or Comparative
Example 1 was caused. Also in this case, results similar to those
in Example 1 and Comparative Example 1 were obtained.
[0111] Also, the effect of the bubbling of the anolyte on removal
of toluene and oxides of toluene was tested. Multiple beakers
containing pure water or 100 g/L sulfuric acid aqueous solution as
the anolyte were prepared. The amount of the anolyte in each beaker
was one liter. To each beaker, one of toluene, benzyl alcohol,
benzaldehyde, and benzoic acid was added. The concentration of each
organic substance was set to 500 ppm. Agitation was performed for
five minutes to evenly disperse the organic substance. Also, as the
gas introduction unit, an air pump including a porous silica-glass
tube (with a tube inner diameter of 10 mm) was prepared, and the
tip of the tube was inserted into a beaker. The temperature of the
anolyte was set to 25 degrees C.
[0112] On an anolyte containing one liter of pure water with a
toluene concentration of 500 ppm, bubbling was performed at
multiple different air supply rates. The air supply rates were 0.1
L/minute, 0.8 L/minute, 1.7 L/minute, 2.8 L/minute, and 3.8
L/minute. At each air supply rate, bubbling was performed for five
minutes. The concentration of residual toluene in the anolyte after
bubbling in each case was measured using an ultraviolet-visible
spectrophotometer (from SHIMADZU CORPORATION). Accordingly, the
remaining percentage of toluene after bubbling was calculated. The
remaining percentage is proportion of the amount of toluene after
bubbling to the amount of toluene before bubbling. FIG. 5A shows
the results. FIG. 5A shows relationships between the supply rate of
air (unit: L/minute) and the remaining percentage of toluene (unit:
%).
[0113] Meanwhile, on an anolyte containing one liter of pure water
with a toluene concentration of 500 ppm, bubbling was performed at
an air supply rate of 2.8 L/minute. After 1, 2, 3, 5, and 10
minutes from the initiation of the bubbling, the concentration of
residual toluene in the anolyte was measured using an
ultraviolet-visible spectrophotometer (from SHIMADZU CORPORATION).
Accordingly, the remaining percentage of toluene after bubbling was
calculated. FIG. 5B shows the results. FIG. 5B shows relationships
between the duration of air supply (unit: minutes) and the
remaining percentage of toluene (unit: %).
[0114] As shown in FIG. 5A, the remaining percentage of toluene
tends to decrease when the supply rate of air is increased. Also,
as shown in FIG. 5B, the remaining percentage of toluene tends to
decrease also when the duration of bubbling is increased. It is
ascertained that, with the bubbling for five minutes at 2.8
L/minute, 95% or more of toluene can be removed.
[0115] Meanwhile, on an anolyte containing one liter of 100 g/L
sulfuric acid aqueous solution with a toluene concentration of 500
ppm, bubbling was performed for five minutes at 2.8 L/minute, and
the remaining percentage of toluene was calculated. FIG. 6A shows
the result. FIG. 6A also shows the result of the anolyte containing
one liter of pure water with a toluene concentration of 500 ppm.
FIG. 6A shows the remaining percentage of toluene in pure water and
the remaining percentage of toluene in sulfuric acid aqueous
solution.
[0116] Also, on anolytes that each contain one liter of 100 g/L
sulfuric acid aqueous solution with a concentration of one of
benzyl alcohol, benzaldehyde, and benzoic acid of 500 ppm, bubbling
was performed for five minutes at 2.8 L/minute, and the remaining
percentage of each organic substance was calculated. FIG. 6B shows
the results. FIG. 6B also shows the result of the anolyte with a
toluene concentration of 500 ppm. FIG. 6B shows the remaining
percentage of various organic substances in sulfuric acid aqueous
solution.
[0117] As shown in FIG. 6A, a greater amount of toluene could be
removed by bubbling from sulfuric acid aqueous solution, compared
to the case of pure water. However, as shown in FIG. 6B, benzyl
alcohol, benzaldehyde, and benzoic acid, i.e., oxides of toluene,
could scarcely be removed by bubbling. This shows that removing
toluene before it becomes an oxide by electrolytic oxidation is
effective.
* * * * *