U.S. patent application number 13/817333 was filed with the patent office on 2014-05-29 for device for manufacturing organic hydride.
This patent application is currently assigned to Hitachi, Ltd.. The applicant listed for this patent is Takayuki Hirashige, Takao Ishikawa. Invention is credited to Takayuki Hirashige, Takao Ishikawa.
Application Number | 20140144774 13/817333 |
Document ID | / |
Family ID | 45892561 |
Filed Date | 2014-05-29 |
United States Patent
Application |
20140144774 |
Kind Code |
A1 |
Hirashige; Takayuki ; et
al. |
May 29, 2014 |
DEVICE FOR MANUFACTURING ORGANIC HYDRIDE
Abstract
The device for electrochemically manufacturing an organic
hydride of the present invention is characterized by the electrode
structure thereof being a structure that forms a matrix in which a
metal-catalyst supporting carbon or a metal catalyst is suitably
intermingled with a proton-conductive solid polymer electrolyte as
catalyst layers, and the catalyst layers are formed on the front
and back of a proton-conductive solid polymer electrolyte membrane
on which a layer that blocks water from passing through is formed.
When water or water vapor is supplied to the anode side of this
electrode and a substance to be hydrogenated is supplied to the
cathode side, application of a voltage between the anode and the
cathode causes an electrolysis reaction to the water to occur at
the anode and a hydrogenation reaction to the substance to be
hydrogenated to occur at the cathode, producing the organic
hydride.
Inventors: |
Hirashige; Takayuki;
(Hitachi-shi, JP) ; Ishikawa; Takao; (Hitachi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hirashige; Takayuki
Ishikawa; Takao |
Hitachi-shi
Hitachi |
|
JP
JP |
|
|
Assignee: |
Hitachi, Ltd.
|
Family ID: |
45892561 |
Appl. No.: |
13/817333 |
Filed: |
August 18, 2011 |
PCT Filed: |
August 18, 2011 |
PCT NO: |
PCT/JP2011/068660 |
371 Date: |
April 29, 2013 |
Current U.S.
Class: |
204/252 |
Current CPC
Class: |
C25B 3/04 20130101; C25B
9/10 20130101; C25B 3/00 20130101 |
Class at
Publication: |
204/252 |
International
Class: |
C25B 9/10 20060101
C25B009/10; C25B 3/00 20060101 C25B003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2010 |
JP |
2010-220254 |
Claims
1. A device for manufacturing an organic hydride comprising: a
membrane electrode assembly including a cathode catalyst layer that
reduces a substance to be hydrogenated, an anode catalyst layer
that oxidizes water, and a proton-conductive solid polymer
electrolyte membrane disposed between the cathode catalyst layer
and the anode catalyst layer; a member that supplies the substance
to be hydrogenated to the cathode catalyst layer; and a member that
supplies water or water vapor to the anode catalyst layer; wherein
a layer that blocks water is formed on a surface or inside of the
solid polymer electrolyte membrane.
2. The device for manufacturing an organic hydride according to
claim 1, wherein the layer that blocks water includes palladium or
a palladium alloy.
3. The device for manufacturing an organic hydride according to
claim 1, wherein the layer that blocks water includes an organic
polymer having an amount of ion exchange of 0.75 meq/g or less per
dry weight.
4. The device for manufacturing an organic hydride according to
claim 1, wherein the cathode catalyst layer includes a catalytic
metal and a supporter that supports the catalytic metal, and
wherein the anode catalyst layer includes only a catalytic metal or
includes a catalytic metal and a non-carbon supporter that supports
the catalytic metal.
5. The device for manufacturing an organic hydride according to
claim 1, wherein the substance to be hydrogenated is selected from
the group consisting of benzene, toluene, xylene, mesitylene,
naphthalene, methylnaphthalene, and anthracene.
6. The device for manufacturing an organic hydride according to
claim 1, wherein the cathode catalyst layer includes a catalytic
metal and a supporter that supports the catalytic metal, and
wherein the catalytic metal includes platinum, ruthenium, rhodium,
palladium, iridium, molybdenum, rhenium, tungsten, and an alloy
including at least one of these metals.
7. A device for manufacturing an organic hydride comprising: a
membrane electrode assembly including a cathode catalyst layer that
reduces a substance to be hydrogenated, an anode catalyst layer
that oxidizes water, and a proton-conductive solid polymer
electrolyte membrane disposed between the cathode catalyst layer
and the anode catalyst layer; gas diffusion layers disposed on a
surface of the cathode catalyst layer and a surface of the anode
catalyst layer; and separators, each of which is disposed on a
surface of each of the gas diffusion layers and includes a channel
formed on a surface of the separator that contacts the gas
diffusion layer; wherein a layer that blocks water is formed on a
surface or inside of the solid polymer electrolyte membrane.
8. The device for manufacturing an organic hydride according to
claim 7, wherein the layer that blocks water includes palladium or
a palladium alloy.
9. The device for manufacturing an organic hydride according to
claim 7, wherein the layer that blocks water includes an organic
polymer having an amount of ion exchange of 0.75 meq/g or less per
dry weight.
10. The device for manufacturing an organic hydride according to
claim 7, wherein the substance to be hydrogenated is supplied into
the channel of the separator at the cathode catalyst layer side,
and wherein water or water vapor is supplied into the channel of
the separator at the anode catalyst layer side.
11. The device for manufacturing an organic hydride according to
claim 7, wherein the substance to be hydrogenated is selected from
the group consisting of benzene, toluene, xylene, mesitylene,
naphthalene, methylnaphthalene, and anthracene.
12. The device for manufacturing an organic hydride according to
claim 7, wherein the cathode catalyst layer includes a catalytic
metal and a supporter that supports the catalytic metal, and
wherein the catalytic metal includes platinum, ruthenium, rhodium,
palladium, iridium, molybdenum, rhenium, tungsten, and an alloy
including at least one of these metals.
Description
TECHNICAL FIELD
[0001] The present invention relates to a device for
electrochemically manufacturing an organic hydride.
BACKGROUND ART
[0002] Global warming by carbon dioxide and others has been
becoming serious. Under this situation, attention is paid to
hydrogen as an energy source for the next generation instead of
fossil fuels. Hydrogen fuel does not impose a large burden on the
environment since a substance discharged when the fuel is consumed
is only water and no carbon dioxide is discharged. Unfortunately,
hydrogen, which is a gas at a normal temperature and a normal
pressure, has disadvantages about transporting, storing and
supplying systems thereof.
[0003] In recent years, attention has been paid to organic hydride
systems using hydrocarbons such as cyclohexane, methylcyclohexane
and decalin as a hydrogen-storing method excellent in safety,
transporting performance, and storing capacity. These hydrocarbons
are liquid at a normal temperature and excellent in
transportability. For example, toluene and methylcyclohexane are
cyclic hydrocarbons having carbon atoms in the same number.
However, toluene is an unsaturated hydrocarbon in which bonds
between hydrocarbon atoms are double bonds while methylcyclohexane
is a saturated hydrocarbon having no double bond. The hydrogenation
reaction of toluene gives methylcyclohexane, while the
dehydrogenation reaction of methylcyclohexane gives toluene. In
other words, the use of the hydrogenation reaction and
dehydrogenation reaction of these hydrocarbons enables storage and
supply of hydrogen.
[0004] In order to manufacture an organic hydride such as
methylcyclohexane, it is necessary to produce hydrogen and react
the hydrogen with toluene on a catalyst. Specifically, the present
process has two steps of generating hydrogen in, for example, a
water electrolysis device, and then reacting the hydrogen with
toluene in a hydrogenation reaction device to generate an organic
hydride.
[0005] Thus, plural devices are necessary for producing the organic
hydride, causing a problem that the system is complicated. Also,
the hydrogen is in a gas form from the production of hydrogen to
the hydrogenation reaction, causing problems about the storage and
transportation thereof. When a hydrogen producing device and a
hydrogenation device are built up to be adjacent to each other,
these problems will be solved. However, another problem is caused
about building and running costs, and total energy efficiency will
be lowered. Furthermore, the devices are made large in size, so
that a place where the devices are installed is restricted.
[0006] In recent year, techniques are disclosed which use a single
device to manufacture an organic hydride at a single step (for
example, in Patent Document 1). These techniques are for
electrochemically manufacturing an organic hydride. For example,
according to Patent Document 1, an organic hydride is manufactured
by arranging metal catalysts onto both sides of a
hydrogen-ion-permeable solid polymer electrolyte membrane, through
which hydrogen ions are selectively permeated, supplying water or
water vapor to one of the sides, supplying a substance to be
hydrogenated to the other side, and using hydrogen ions generated
by electrolysis of the water or water vapor on the anode side to
cause hydrogenation reaction with the substance to be hydrogenated
on the cathode side to manufacture an organic hydride.
DOCUMENTS ON PRIOR ARTS
Patent Documents
[0007] Patent Document 1: JP 2003-45449 A
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0008] Unfortunately, these methods for manufacturing an organic
hydride have difficulty in giving high energy efficiencies. The
reason thereof would be an effect of passed water. Specifically, it
is considered that water used in the anode reaction passes through
the hydrogen-ion-permeable solid polymer electrolyte membrane to
reach the cathode, so that the passed water causes a bad effect
onto the cathode reaction. Water and a substance to be
hydrogenated, such as toluene, are insoluble into each other and
not mixed with each other. Thus, when water is present in the
cathode catalyst layer, the water hinders toluene from being
supplied into the catalyst. As a result, hydrogen will be generated
on the catalyst to which the substance to be hydrogenated, such as
toluene, is not supplied. Thus, no hydrogenation reaction is caused
to the substance to be hydrogenated and no organic hydride is
generated, decreasing the energy efficiency. Moreover, when the
passed water is mixed with the organic hydride after the
hydrogenation reaction, another process for removing the water is
required. This is undesired when the simplification of the system
is considered.
[0009] An object of the present invention is to provide a
small-scale and highly-efficient device for electrochemically
manufacturing an organic hydride.
Means for Solving the Problem
[0010] In light of such a situation, the inventors have made eager
researches to find out that highly-efficient electrodes can be
obtained by forming a layer for blocking water from passing from
the anode to the cathode on a surface of a solid polymer
electrolyte membrane or inside the solid polymer electrolyte
membrane. The electrodes in the present invention are characterized
in that catalyst layers have a matrix structure in which
metal-catalyst supporting carbon or a metal catalyst is suitably
intermingled with a proton-conductive solid polymer electrolyte,
and the catalyst layers are formed on the front and back of a
proton-conductive solid polymer electrolyte membrane which includes
a water-blocking layer.
[0011] The device for manufacturing an organic hydride of the
present invention includes a membrane electrode assembly including
a cathode catalyst layer that reduces a substance to be
hydrogenated, an anode catalyst layer that oxidizes water, and a
proton-conductive solid polymer electrolyte membrane disposed
between the cathode catalyst layer and the anode catalyst layer,
the membrane including a water-blocking layer from passing through,
a member that supplies the substance to be hydrogenated to the
cathode catalyst layer, and a member that supplies water or water
vapor to the anode catalyst layer. The cathode catalyst layer
includes a catalytic metal that reduces the substance to be
hydrogenated to react into a hydride, a supporter supporting the
catalytic metal, and a proton-conductive solid polymer electrolyte.
The anode catalyst layer includes a catalytic metal that oxidizes
water to react into protons, a supporter supporting the catalytic
metal, and a proton-conductive solid polymer.
Advantageous Effects of the Invention
[0012] According to the present invention, a small-scale and
highly-efficient device for electrochemically manufacturing an
organic hydride can be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a view illustrating a device for manufacturing an
organic hydride or a fuel cell in accordance with an embodiment of
the present invention;
[0014] FIG. 2 is a view illustrating a membrane electrode assembly
in the present invention;
[0015] FIG. 3 is a view illustrating a membrane electrode assembly
in a conventional technique;
[0016] FIG. 4 is a view showing an embodiment of the device for
manufacturing an organic hydride of the present invention;
[0017] FIG. 5 is a view showing an embodiment of the device for
manufacturing an organic hydride of the present invention;
[0018] FIG. 6 is a view showing an example of the device for
manufacturing an organic hydride according to a conventional
technique; and
[0019] FIG. 7 is a view showing an example of the device for
manufacturing an organic hydride according to a conventional
technique.
DESCRIPTION OF EMBODIMENTS
[0020] A device for electrochemically manufacturing an organic
hydride of the present invention has an electrode structure that a
catalyst layer, the layer having a matrix structure in which a
proton-conductive solid polymer electrolyte and a metal-catalyst
supporting carbon or metal catalyst are suitably intermingled with
each other, is formed on the front and back of a proton-conductive
solid polymer electrolyte membrane, the membrane including a
water-blocking layer. In the electrodes, water or water vapor is
supplied to the anode side, and a substance to be hydrogenated is
supplied to the cathode. In this state, a voltage is applied to
between the anode and the cathode to cause the electrolysis
reaction of water in the anode and hydrogenation reaction of the
substance to be hydrogenated in the cathode, thus manufacturing an
organic hydride.
[0021] Embodiments of the present invention will be described in
detail, referring to the drawings.
[0022] FIG. 1 illustrates a device for manufacturing an organic
hydride in accordance with an embodiment of the present invention.
The device for manufacturing an organic hydride of the present
embodiment includes a membrane electrode assembly (MEA), a pair of
gas diffusion layers 15 and a pair of separators 11 which are
disposed to sandwich the membrane electrode assembly. The membrane
electrode assembly (MEA) includes a solid polymer electrolyte
membrane 12 having a water-blocking layer, an anode catalyst layer
13 on one surface of the sol id polymer electrolyte membrane 12,
and a cathode catalyst layer 14 on the other surface of the
membrane 12, the anode catalyst layer 13, the membrane 12 and the
cathode catalyst layer 14 being joined and integrated. Each of the
separators 11 includes a gas channel. A gasket 16 for gas seal is
inserted into between the pair of separators 11.
[0023] Each of the separators 11 has electroconductivity, and the
material thereof is desirably a dense graphite plate, a carbon
plate obtained by shaping a carbon material such as graphite or
carbon black by aid of a resin, or a metal material excellent in
corrosion resistance, such as stainless steel or titanium. It is
also desired to plate surfaces of the separators 11 with a noble
metal, or apply a conductive paint excellent in corrosion
resistance and heat resistance to the surfaces to subject the
separators 11 to the surface-treatment. A groove which is a channel
for a reactive gas or liquid is formed on each of the surfaces of
the separators 11 that face the anode catalyst layer 13 and the
cathode catalyst layer 14, respectively. Water or water vapor is
supplied into the channel of the separator 11 at the anode side.
The water or water vapor flowing through the channel is supplied to
the anode catalyst layer through one of the gas diffusion layers
15. A substance to be hydrogenated is supplied to the separator 11
at the cathode side. The substance to be hydrogenated flowing
through the other channel is supplied to the cathode catalyst
through the other gas diffusion layer 15. The method for supplying
the substance to be hydrogenated includes a method of supplying the
substance to be hydrogenated which is a liquid substance as it is
or supplying the substance to be hydrogenated which is a vapor-form
substance using He gas or N.sub.2 gas as a carrier.
[0024] Each of the gas diffusion layers 15 is provided for
supplying uniformly a reactive substance (gas or a liquid), which
has been supplied to the channel of the separator 11, over the
plane of the catalyst layer. A substrate having permeability to
gases is used for the gas diffusion layers 15, such as carbon paper
or carbon cloth. Particularly, a water-repellent substrate is
preferable.
[0025] The gasket 16 has an electrically-insulating property,
resistant particularly against hydrogen or the substance to be
hydrogenated, and the organic hydride, and made of a material which
passes through small amount of these components and has
airtightness. Examples of such materials include butyl rubber,
Viton rubber, and EPDM rubber.
[0026] When a voltage is applied to between the anode and the
cathode in the state of supplying water or water vapor to the anode
side and supplying toluene as the substance to be hydrogenated to
the cathode side, electrolysis reaction of water is caused in the
anode according to a formula (1) illustrated below. Protons
generated by the electrolysis reaction according to the formula (1)
moves through the solid polymer electrolyte membrane 12 to the
cathode 14 to cause hydrogenation reaction according to a formula
(2) illustrated below in the cathode. Thus, methylcyclohexane,
which is an organic hydride, is manufactured.
H.sub.2O.fwdarw.2H.sup.++1/2O.sub.2+2e.sup.- (1)
C.sub.7H.sub.8+6H.sup.++6e.sup.-.fwdarw.C.sub.7H.sub.14 (2)
[0027] In the device for manufacturing an organic hydride of the
present embodiment, the water-blocking layer is formed on the solid
polymer electrolyte membrane, so that the water in the anode does
not pass to the cathode. Thus, the organic hydride can be
manufactured with a high efficiency.
[0028] FIG. 2 illustrates an electrode part of the device for
manufacturing an organic hydride of the present embodiment. FIG. 2
shows a plan view of the MEA viewed from the cathode side, a cross
sectional view taken from line D-E in the plan view, and an
enlarged view. The MEA includes a solid polymer electrolyte
membrane 21 on which a water-blocking layer 27 is formed, a cathode
catalyst layer 22 and an anode catalyst layer 23 which are formed
on the front and back of the solid polymer electrolyte membrane
21.
[0029] As illustrated in the cross sectional view taken from line
D-E, in the MEA, the cathode and the anode are formed on the upper
and lower sides of the solid polymer electrolyte membrane 21,
respectively, as dense catalyst layers, the water-bloc layer 27
formed on the membrane 21. As illustrated in the enlarged view of
F, in the cathode catalyst layer 22, a catalytic metal 24 is
supported on a catalyst supporter 25. The catalyst supporters 25
are bonded to each other by a solid polymer electrolyte 26. The
catalytic metal 24 has a network structure in which its portions
are connected to each other through the catalyst supporter 25, and
forms a passing way for electrons necessary for the reaction (2).
In the same manner, the solid polymer electrolyte 26 in the
catalyst layer also has a network structure in which its portions
are connected to each other, and forms a passing way for protons
necessary for the reaction (2).
[0030] The electrode reaction is conducted on three-phase
interfaces in which the metal catalyst 24 on the catalyst supporter
25, the electrolyte and the reactive substance contact each other.
In the electrode of the present embodiment, the solid polymer
electrolyte membrane 26 forms the passing way for protons, so that
the three-phase interfaces are formed also in the metal catalyst
24, which does not directly contact the solid polymer electrolyte
membrane 21. Accordingly, the electrode has a structure in which a
large volume of the metal catalyst can contribute to the electrode
reaction.
[0031] In the electrodes of the device for manufacturing an organic
hydride of the present embodiment, the water-blocking layer 27 is
formed on the solid polymer electrolyte membrane, so that the water
in the anode can be prevented from passing to the cathode. Thus, an
organic hydride can be manufactured with a high efficiency.
[0032] FIG. 3 illustrates a structure of electrodes in a
conventional technique. In the electrodes illustrated in FIG. 3, a
catalyst supporter 35 supporting a metal catalyst 34 is directly
formed on each surface of a solid polymer electrolyte membrane 31.
In the electrode structure in a conventional technique, a portion
of the metal catalyst 34 which contributes to the electrode
reaction is present only in its region directly contacting the
electrolyte membrane. The metal catalyst 34 has small quantity of
three-phase interface, so that the catalyst quantity contributing
to the reaction is limited. Moreover, it is considered that the
formation of the network structure of the catalyst is small in
quantity, leading to high resistance.
[0033] In FIG. 3, the electrode structure in a conventional
technique has been illustrated. The electrodes illustrated in FIG.
3 have a structure in which the catalyst supporter 35 supporting
the catalytic metal 34 is mixed with a solid polymer electrolyte 36
on each surface of the solid polymer electrolyte membrane 31. In a
conventional technique, passed water 37 is present in the cathode
catalyst layer, the passed water 37 being water which has passed
through the solid polymer electrolyte membrane 31 from the anode.
Water and a substance to be hydrogenated, such as toluene, are
insoluble into each other, not miscible with each other. Thus, when
water is present in the cathode catalyst layer 32, the water
hinders the supply of toluene into the catalyst. As a result, on
the catalytic metal 38 to which no substance to be hydrogenated,
such as toluene, is supplied, it considered that hydrogen is
generated according to a formula (3) illustrated below, without
hydrogenation reaction.
2H.sup.++2e.sup.-H.sub.2 (3)
[0034] Thus, the electrodes in a conventional technique include the
catalyst causing no reaction of hydrogenation onto the substance to
be hydrogenated, so that the manufacture of any organic hydride is
restricted. As a result, it is considered that energy efficiency is
low in a conventional technique.
[0035] The MEA of the present invention can be produced by the
following method. First, a cathode catalyst paste and an anode
catalyst paste are produced. The cathode catalyst paste is obtained
by sufficiently mixing a supporter supporting a catalytic metal, a
solid polymer electrolyte, and a solvent in which the solid polymer
electrolyte is soluble. The anode catalyst paste is obtained by
sufficiently mixing a catalytic metal, a solid polymer electrolyte,
and a solvent in which the solid polymer electrolyte is soluble.
These pastes are each sprayed onto a peelable film, such as a
polyfluoroethylene (PTFE) film, by a spray drying method, for
example. The resultants are dried at 80.degree. C. to vaporize the
respective solvents to form a cathode catalyst layer and an anode
catalyst layer. Next, a hot press method is used to join the
cathode and anode catalyst layers sandwiching a solid polymer
electrolyte membrane including a water-blocking layer therebetween.
The peelable film (PTFE) is then peeled. Thus, the MEA of the
invention can be produced.
[0036] In another example of the production of the MEA of the
invention, a spray-dry method is used to spray a cathode catalyst
paste and an anode catalyst paste directly onto a solid polymer
electrolyte membrane including a water-blocking layer. The cathode
catalyst paste is obtained by sufficiently mixing a supporter
supporting a catalytic metal, a solid polymer electrolyte, and a
solvent in which the solid polymer electrolyte is soluble. The
anode catalyst paste is obtained by sufficiently mixing a catalytic
metal and a solid polymer electrolyte, and a solvent in which the
solid polymer electrolyte is soluble.
[0037] The organic polymer included in the solid polymer
electrolyte membrane can be perfluorocarbon sulfonic acid, or a
polymer yielded by incorporating a dopant of a proton donor, such
as a sulfonate, phosphonate or carboxylate group, or bonding/fixing
the donor chemically into polystyrene, polyetherketone,
polyetheretherketone, polysulfone, polyethersulfone or some other
engineering plastic. It is desired to make the material into a
crosslinked structure, or fluoridate the material partially to make
the material high in stability. Moreover, a composite electrolyte
membrane may be used which is composed of an organic polymer and,
e.g., a metal oxide hydrate.
[0038] The layer that blocks water from passing through is a layer
which can pass through hydrogen ions and blocks water. The layer
includes inorganic substance such as palladium and any palladium
alloy, for example. Examples of metals which form the alloy with
palladium include transition metals such as Rh, Cu, Co, Ir, and Ag.
Furthermore, as the metal to be combined with palladium to make the
alloy, various metals are conceivable, examples thereof including
alkaline earth metals such as Mg and Ca, and rare earth metals such
as La and Nd. For the layer that blocks water from passing through,
a hydrogen storage alloy may be used. Examples of the hydrogen
storage alloy include Ti--Fe based metals, V based metals, Mg based
alloys, and Ca based alloys. Other examples thereof include
AB.sub.2 type metals, each of which contains, as a base, a
transition metal such as Ti, Mn, Zr or Ni; and LaNi.sub.5,
ReNi.sub.5, and other AB.sub.5 type metals, each of which contains,
as a base, an alloy containing a rare earth metal, Nb or Zr, and 5
atoms of a transition metal having a catalytic effect (such as Ni,
Co or Al) per atom of the rare earth metal, Nb or Zr. Furthermore,
it is allowable to use an organic polymer small in quantity of
proton donors contained therein, such as sulfonate, phosphonate and
carboxylate groups. The organic polymer small in the proton donor
quantity is desirably an organic polymer having an amount of ion
exchange of 0.75 meq/g or less per dry weight.
[0039] The water-blocking layer may be formed on the surface of the
solid polymer electrolyte membrane or the inside of the solid
polymer electrolyte membrane. In the invention, a layer that blocks
water from passing through is formed to restrict the amount of
water passing through. The water moves following the movement of
protons. Then, the amount of the water passing through is varied in
accordance with the value of the flowing current. The membrane
electrode assembly including the water-blocking layer in the
invention desirably has an amount of water passing through of 30
.mu.g/cm.sup.2sec or less when the current density value is 60
mA/cm.sup.2. A water-blocking layer described above is used to
satisfy this requirement.
[0040] In the solid polymer electrolyte included in each of the
catalyst layers, a polymer material exhibiting proton conductivity
is used. Examples thereof include sulfonated or alkylenesulfonated
fluorine-contained polymers and polystyrenes, typical examples
thereof including perfluorocarbon based sulfonic acid resins, and
polyperfluorostyrene based sulfonic acid resins. Other examples
thereof include polysulfones, polyethersulfones,
polyetherethersulfones, polyetheretherketones, and materials in
which a proton donor such as a sulfonate group is introduced in a
hydrocarbon based polymer.
[0041] The catalytic metal used in the invention can be a catalytic
material having a hydrogenating effect. The material may be, for
example, a metal such as Ni, Pd, Pt, Rh, Ir, Re, Ru, Mo, W, V, Os,
Cr, Co or Fe, or a catalyst of an alloy of any of these metals. The
hydrogenating catalyst is preferably made into fine particles to
decrease costs by a reduction in the catalytic metal and increase
the reaction surface area. In order to prevent reduction of the
specific surface area of the catalyst by the aggregation of the
fine particles, the catalyst may be supported on a supporter. The
method for producing the catalyst may be a co-precipitation method,
a thermal decomposition method or an electroless plating method,
and is not particularly limited.
[0042] The material of the supporter for the cathode catalyst may
be, for example, a carbon material such as activated carbon, carbon
nanotube or graphite, silica, alumina, or an alumina silicate such
as zeolite. However, when a carbon material is present in the
anode, the carbon may be unfavorably oxidized. Thus, the material
of the supporter for the anode catalyst may be a non-carbon
material such as silica, alumina, or an alumina silicate such as
zeolite. Alternatively, in the anode, only the catalytic metal may
be used without using any supporting material.
[0043] The substance to be hydrogenated may be anyone of benzene,
toluene, xylene, mesitylene, naphthalene, methylnaphthalene,
anthracene, biphenyl and phenanthroline, and alkyl-substituted
compounds thereof, or a mixture of two or more of these compounds.
When hydrogen is added to carbon-carbon double bonds of these
compounds, the compounds can store the hydrogen.
[0044] Hereinafter, the embodiments of the invention will be
described in detail. The invention is not limited to the following
embodiments.
Embodiment 1
[0045] As a solid polymer electrolyte membrane, a membrane was used
which was obtained by physically bonding a palladium membrane
having a thickness of 25 .mu.m onto a surface of a Nafion
(manufactured by Du Pont). The palladium membrane was bonded to the
surface on the anode side.
[0046] A spray coater was used to apply a catalyst slurry directly
onto the solid polymer electrolyte membrane to form a cathode
catalyst layer. In the following steps, the cathode catalyst layer
was formed by the application onto the solid polymer electrolyte
membrane.
[0047] The Nafion onto which the palladium membrane was bonded was
put on a hot plate of a substrate, and then sucked to be fixed
thereon. The temperature of the hot plate was set to 50.degree.
C.
[0048] Next, a mask was put thereto, and a spray coater
(manufactured by Nordson Corp.) was used to apply a cathode
catalyst slurry thereon. The used cathode catalyst slurry was a
slurry obtained by mixing a platinum supporting carbon catalyst
TEC10E70TPM (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.),
water, a 5% by weight Nafion solution, and a 221 solution
(1-propanol:2-propanol:water=2:2:1) with each other at a ratio by
weight of 2:1.2:5.4:10.6. Conditions for the application were as
follows. The solution pressure was set to 0.01 MPa. The swirl
pressure was set to 0.15 MPa. The spraying pressure was set to 0.15
MPa. The distance from the gun to the substrate was set to 60 mm.
The temperature of the substrate was set to 50.degree. C. The
amount of the cathode catalyst was set to 0.4 mgPtcm.sup.-2.
[0049] The cathode catalyst layer was formed on the surface of the
Nafion on which the palladium membrane was bonded. An anode
catalytic slayer was formed on the back surface of the Nafion. The
anode catalyst layer was formed by a transferring method. First, an
anode catalyst slurry was prepared. The used anode catalyst slurry
was obtained by mixing a platinum black HiSPEC1000 (manufactured by
Johnson Matthey PLC), a 5% by weight Nafion solution, and a 221
solution with each other at a ratio by weight of 1:1.11:2.22. An
applicator was used to apply this slurry onto a sheet made of
Teflon (registered trademark). The anode catalyst layer applied on
the sheet of Teflon (registered trademark) was formed on the
surface of the Nafion on which the palladium membrane was bonded by
thermal transfer using a hot press (SA-401-M manufactured by Tester
Sangyo Co., Ltd.). The hot press pressure was set to 37.2
kgfcm.sup.-2, the hot press temperature to 120.degree. C., and the
hot press time to 2 minutes. The amount of the anode catalyst was
set to 4.8 mgPtcm.sup.-2.
[0050] The produced MEA was integrated into the device for
manufacturing an organic hydride illustrated in FIG. 1. The cell
resistance thereof was 200 m.OMEGA..
[0051] Toluene was supplied as a substance to be hydrogenated to
the cathode at each of flow rates of 0.03 mL/min and 0.1 mL/min.
Pure water was supplied to the anode at a flow rate of 5 mL/min. In
these states, a voltage of 2.2 V was applied to between the anode
and the cathode. The temperature of the cell was set to each of 25,
40, 60 and 80.degree. C.
[0052] FIG. 4 shows the current values relative to the temperatures
of the cell. As the cell temperature was made higher, the current
densities became larger. The reason of this is considered that as
the temperature became higher, the reaction activity of the
electrode catalysts for the reaction became higher. In the case of
supplying toluene in the amounts of 0.03 mL/min and 0.1 mL/min, the
result was that the current flowed at substantially the same
level.
[0053] After the hydrogenation reaction under each of the
conditions, the cathode solution was collected and analyzed by gas
chromatography to find a generation of methylcyclohexane, which is
an organic hydride. This suggests that the hydrogenation reaction
of toluene yielded methylcyclohexane with the electrodes in the
invention. The solution collected from the cathode contained no
water. It is believed that the palladium membrane formed on the
surface of the Nafion was able to prevent the water from passing
through from the anode.
[0054] FIG. 5 shows the conversion ratios from toluene to
methylcyclohexane in the hydrogenation reaction. The conversion
ratios were calculated from peak areas of the gas chromatograph
according to the following equation:
Conversion ratio="the peak area of methylcyclohexane"/("the peak
area of toluene"+"the peak area of methylcyclohexane").times.100.
(4)
[0055] Methylcyclohexane was detected at each of the cell
temperatures of 25, 40, 60 and 80.degree. C., and the conversion
ratios became larger as the cell temperature became higher. The
conversion ratios were higher at the supply amount of toluene of
0.03 mL/min than at that of 0.1 mL/min. The reason of this is
considered that as the supply rate of toluene was smaller, a chance
for toluene to contact the electrode catalysts was increased. The
condition that the cell temperature was 80.degree. C. and the
toluene flow rate was 0.03 mL/min gave the highest conversion ratio
of 68% among the conditions in this embodiment.
Comparative Example 1
[0056] As a solid polymer electrolyte membrane, an MEA was produced
using a Nafion. Other producing conditions were same as described
above.
[0057] The produced MEA was integrated into the device for
manufacturing an organic hydride illustrated in FIG. 1. The cell
resistance thereof was measured to be 250 m.OMEGA..
[0058] Under the same conditions as in embodiment 1, a test of the
hydrogenation reaction to toluene was conducted. At a cell
temperature of each of 25, 40, 60 and 80.degree. C., a voltage of
2.2 V was applied to between the anode and the cathode. FIG. 6
shows the current values relative to the temperatures of the cell.
As the temperature of the cell was made higher, larger currents
flowed. However, at each of the temperatures, the current densities
were lower than in embodiment 1.
[0059] After the hydrogenation reaction under each of the
conditions, the cathode solution was collected and analyzed by gas
chromatography to find a generation of methylcyclohexane, which is
an organic hydride. However, at each of the temperatures, the waste
solution collected from the cathode was separated into two phases.
The upper phase was presumed to be toluene and methylcyclohexane,
and the lower phase was presumed to be water. As the temperature
was higher, the proportion of the water in the lower phase was
larger. It is considered that the water came to the cathode from
the anode passing through the electrolyte membrane. In particular,
it is presumed that as the cell temperature was higher and a larger
current flowed, a larger quantity of protons was moved from the
anode to the cathode and, in accordance with the movement of the
protons, a larger quantity of water was moved.
[0060] FIG. 7 shows the conversion ratios from toluene to
methylcyclohexane. As the cell temperature was made higher, the
conversion ratios became higher. However, the conversion ratios
were smaller than in embodiment 1. The reason of this is considered
that the passed water was present in the cathode catalyst layer and
the water hindered the supply of toluene to the catalyst. As a
result, it is presumed that hydrogen was generated on the catalyst
to which no toluene was supplied, so that methylcyclohexane was not
generated to lower the conversion ratios.
Embodiment 2
[0061] A Nafion was used as an electrolyte membrane, and an S-PES
(sulfonated polyethersulfone) having thickness of 10 .mu.m was
bonded onto the surface of the Nation. S-PES is an organic polymer
obtained by introducing sulfonate groups into polyethersulfone. The
used S-PES had an amount of ion exchange of 0.6 meq/g per dry
weight. Other conditions for producing the MEA were same as in
embodiment 1.
[0062] The produced MEA was integrated into the device for
manufacturing an organic hydride illustrated in FIG. 1. The cell
resistance thereof was measured to be 350 m.OMEGA.. Under the same
conditions as in embodiment 1, a test of the hydrogenation reaction
to toluene was conducted. At a cell temperature of each of 25, 40,
60 and 80.degree. C., a voltage of 2.2 V was applied to between the
anode and the cathode.
[0063] After the hydrogenation reaction under each of the
conditions, the cathode solution was collected and analyzed by gas
chromatography to find a generation of methylcyclohexane, which is
an organic hydride. At each of the temperatures, the waste solution
collected from the cathode was separated into two phases, although
the solution contained smaller amount of water than in comparative
example 1. The reason of this is considered that the S-PES did not
completely prevent the water from passing through. However,
comparing this case with the case where only Nafion was used as the
electrolyte membrane in comparative example 1, higher conversion
ratios were obtained in this case since the amount of the passed
water was reduced. The highest conversion ratio was 58% when the
cell temperature was 80.degree. C. and the toluene flow rate was
0.03 mL/min.
EXPLANATION OF REFERENCE CHARACTERS
[0064] 11: separator [0065] 12, 21 and 31: solid polymer
electrolyte membranes [0066] 13, 23 and 33: anode catalyst layers
[0067] 14: cathode catalyst layer [0068] 15: gas diffusion layer
[0069] 16: gasket [0070] 22 and 32: cathode catalyst layers [0071]
24 and 34: catalytic metals [0072] 25 and 35: catalyst supporters
[0073] 26 and 36: solid polymer electrolytes [0074] 27:
water-blocking layer [0075] 37: passed water [0076] 38: catalytic
metal not contributing to the reaction.
* * * * *