US20150008138A1 - Electrochemical reduction device and method for manufacturing hydride of aromatic hydrocarbon compound or n-containing heterocyclic aromatic compound - Google Patents

Electrochemical reduction device and method for manufacturing hydride of aromatic hydrocarbon compound or n-containing heterocyclic aromatic compound Download PDF

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US20150008138A1
US20150008138A1 US14/493,396 US201414493396A US2015008138A1 US 20150008138 A1 US20150008138 A1 US 20150008138A1 US 201414493396 A US201414493396 A US 201414493396A US 2015008138 A1 US2015008138 A1 US 2015008138A1
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electrode
potential
reduction
control unit
electrolyte membrane
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Yasushi Sato
Kota Miyoshi
Kojiro NAKAGAWA
Yoshihiro Kobori
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Eneos Corp
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JX Nippon Oil and Energy Corp
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B15/00—Operating or servicing cells
    • C25B15/02—Process control or regulation
    • C25B3/04—
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B3/00—Electrolytic production of organic compounds
    • C25B3/20—Processes
    • C25B3/25—Reduction
    • C25B9/06—
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
    • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms
    • C25B9/23—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms comprising ion-exchange membranes in or on which electrode material is embedded

Definitions

  • the present invention relates to a device and a method for electrochemically hydrogenating an aromatic hydrocarbon compound or an N-containing heterocyclic aromatic compound.
  • a purpose of the present invention is to provide a technology capable of electrochemically hydrogenating at least one benzene ring of an aromatic hydrocarbon compound or an N-containing heterocyclic aromatic compound with high efficiency.
  • the electrochemical reduction device includes: an electrode unit including an electrolyte membrane having ionic conductivity, a reduction electrode that is provided on one side of the electrolyte membrane and that contains a reduction catalyst for hydrogenating at least one benzene ring of an aromatic hydrocarbon compound, and an oxygen evolving electrode that is provided on the other side of the electrolyte membrane; a power control unit that applies a voltage Va between the reduction electrode and the oxygen evolving electrode; and a control unit that controls the power control unit such that a relationship, V HER ⁇ arbitrarily-defined acceptable potential ⁇ V CA ⁇ V TRR , can be satisfied when the potential at a reversible hydrogen electrode, the standard redox potential of the aromatic hydrocarbon compound, and the potential of the reduction electrode are expressed as V HER , V TRR , and V CA , respectively.
  • a potential in the present invention means a true electrode potential with respect to a reference potential. Therefore, when there exist, for example, an electrolyte membrane resistance, an electrode catalyst layer resistance, an ohmic loss derived from various electrical connections, and the like, a true electrode potential needs to be calculated and/or corrected in consideration of these as described later.
  • FIG. 1 is a schematic diagram illustrating the configuration of an electrochemical reduction device according to a first embodiment
  • FIG. 2 is a diagram illustrating the configuration of an electrode unit of the electrochemical reduction device according to the first embodiment
  • FIG. 3 is a flowchart illustrating an example of potential control of a reduction electrode by a control unit
  • FIG. 4 is a graph illustrating a relationship between the potential of the reduction electrode and various types of current density
  • FIG. 5 is a schematic diagram illustrating the configuration of an electrochemical reduction device according to a second embodiment.
  • FIG. 6 is a schematic diagram illustrating the configuration of an electrochemical reduction device according to a third embodiment.
  • the electrochemical reduction device includes: an electrode unit including an electrolyte membrane having ionic conductivity, a reduction electrode that is provided on one side of the electrolyte membrane and that contains a reduction catalyst for hydrogenating at least one benzene ring of an aromatic hydrocarbon compound, and an oxygen evolving electrode that is provided on the other side of the electrolyte membrane; a power control unit that applies a voltage Va between the reduction electrode and the oxygen evolving electrode; and a control unit that controls the power control unit such that a relationship, V HER ⁇ arbitrarily-defined acceptable potential ⁇ V CA ⁇ V TRR , can be satisfied when the potential at a reversible hydrogen electrode, the standard redox potential of the aromatic hydrocarbon compound, and the potential of the reduction electrode are expressed as V HER , V TRR , and V CA , respectively.
  • a potential in the present invention means a true electrode potential with respect to a reference potential. Therefore, when there exist, for example, an electrolyte membrane resistance, an electrode catalyst layer resistance, an ohmic loss derived from various electrical connections, and the like, a true electrode potential needs to be calculated and/or corrected in consideration of these as described later.
  • the arbitrarily-defined acceptable potential may be 20 mV.
  • the electrochemical reduction device may further include: a reference electrode that is arranged to be in contact with the electrolyte membrane and to be electrically isolated from the reduction electrode and the oxygen evolving electrode and that is held at a reference electrode potential V Ref ; and a voltage detection unit that detects a potential difference ⁇ V CA between the reference electrode and the reduction electrode, and the control unit may acquire the potential V CA of the reduction electrode based on the potential difference ⁇ V CA and the reference electrode potential V Ref .
  • the control unit may control the potential V CA of the reduction electrode to be in a predetermined range by changing the voltage Va.
  • the control unit controls the power control unit such that an expression, Va ⁇ (V OER ⁇ V CA ), is satisfied.
  • the reference electrode may be arranged on the side of the electrolyte membrane on which the reduction electrode is provided.
  • the electrochemical reduction device includes: an electrode unit assembly in which a plurality of electrode units are electrically connected to one another in series, the electrode units each including an electrolyte membrane having ionic conductivity, a reduction electrode that is provided on one side of the electrolyte membrane and that contains a reduction catalyst for hydrogenating at least one benzene ring of an aromatic hydrocarbon compound, and an oxygen evolving electrode that is provided on the other side of the electrolyte membrane; a power control unit that applies a voltage VA between a positive electrode terminal and a negative electrode terminal of the electrode unit assembly; and a control unit that controls the power control unit such that a relationship, V HER ⁇ arbitrarily-defined acceptable potential ⁇ V CA ⁇ V TRR , can be satisfied when the potential at a reversible hydrogen electrode, the standard redox potential of the aromatic hydrocarbon compound, and the potential of the reduction electrode of each electrode unit are expressed as V HER , V TRR , and V CA , respectively
  • the arbitrarily-defined acceptable potential may be 20 mV.
  • the electrochemical reduction device may further include: a reference electrode that is arranged to be in contact with an electrolyte membrane of any one of electrolytic layers contained in the electrode unit assembly and to be electrically isolated from the reduction electrode and the oxygen evolving electrode; and a voltage detection unit that detects a potential difference ⁇ V CA between the reference electrode and the reduction electrode, and the control unit may acquire the potential V CA of the reduction electrode based on the potential difference ⁇ V CA and the reference electrode potential V Ref .
  • the control unit may control the potential V CA of the reduction electrode of each electrode unit to be in a predetermined range by changing the voltage VA.
  • the control unit may control the power control unit such that an expression, VA ⁇ (V OER ⁇ V CA ) ⁇ N, is satisfied where N (two or greater) is the number of serially-concatenated electrode units.
  • the reference electrode may be arranged on the side of the electrolyte membrane on which the reduction electrode is provided.
  • the reference electrode may be arranged on the side of the electrolyte membrane on which the reduction electrode is provided.
  • Another embodiment of the present invention relates to a method for manufacturing a hydride of an aromatic hydrocarbon compound or an N-containing heterocyclic aromatic compound.
  • the method for manufacturing a hydride of an aromatic hydrocarbon compound or an N-containing heterocyclic aromatic compound includes introducing an aromatic hydrocarbon compound or an N-containing heterocyclic aromatic compound to the reduction electrode side of the electrode unit, circulating water or a humidified gas to the oxygen evolving electrode side, and hydrogenating at least one benzene ring of the aromatic hydrocarbon compound or the N-containing heterocyclic aromatic compound introduced to the reduction electrode side, by using the electrochemical reduction device according to any one of above-stated embodiments.
  • the aromatic hydrocarbon compound or the N-containing heterocyclic aromatic compound to be introduced to the reduction electrode side may be introduced to the reduction electrode side in a liquid state at a reaction temperature.
  • At least one benzene ring of an aromatic hydrocarbon compound or an N-containing heterocyclic aromatic compound can be electrochemically hydrogenated with high efficiency.
  • FIG. 1 is a schematic diagram illustrating the configuration of an electrochemical reduction device 10 according to an embodiment.
  • FIG. 2 is a diagram illustrating the configuration of an electrode unit of the electrochemical reduction device 10 according to the embodiment.
  • the electrochemical reduction device 10 has an electrode unit 100 , a power control unit 20 , an organic material storage tank 30 , a water storage tank 40 , a gas-liquid separator 50 , and a control unit 60 .
  • the power control unit 20 is, for example, a DC/DC converter for converting the output voltage of a power source into a predetermined voltage.
  • the positive electrode output terminal of the power control unit 20 is connected to the positive electrode of the electrode unit 100 .
  • the negative electrode output terminal of the power control unit 20 is connected to the negative electrode of the electrode unit 100 . With this, a predetermined voltage is applied between an oxygen evolving electrode (positive electrode) 130 of the electrode unit 100 and a reduction electrode (negative electrode) 120 .
  • a reference electrode input terminal of the power control unit 20 is connected to a reference electrode 112 provided on an electrolyte membrane 110 , which will be described later, and the potential of the positive electrode output terminal and the potential of the negative electrode output terminal are determined based on the potential of the reference electrode 112 in accordance with an instruction from the control unit 60 .
  • the power source electrical power derived from natural energy such as sunlight, wind power, and the like can be used. The mode of the potential control of the positive electrode output terminal and the negative electrode output terminal by the control unit 60 will be described later.
  • the organic material storage tank 30 stores an aromatic compound.
  • An aromatic compound used in the present embodiment is an aromatic hydrocarbon compound or an N-containing heterocyclic aromatic compound containing at least one aromatic ring and includes benzene, naphthalene, anthracene, diphenylethane, pyridine, pyrimidine, pyrazine, quinoline, isoquinoline, N-alkylpyrrole, N-alkylindole, N-alkyldibenzopyrrole and the like.
  • One through four hydrogen atoms of the aromatic ring of the aromatic hydrocarbon compound or the N-containing heterocyclic aromatic compound may be substituted by alkyl groups.
  • alkyl of the above aromatic compounds is a linear or branched alkyl group with one through six carbons.
  • alkylbenzene includes toluene, ethyl benzene, and the like
  • dialkylbenzene includes xylene, diethylbenzene, and the like
  • trialkylbenzene includes mesitylene and the like.
  • alkylnaphthalene includes methylnaphthalene.
  • the above-stated aromatic ring of the aromatic hydrocarbon compound or the N-containing heterocyclic aromatic compound may have one through three substituents.
  • aromatic hydrocarbon compound and an N-containing heterocyclic aromatic compound used in the present invention are often referred to as “aromatic compounds”.
  • the aromatic compound is a liquid at room temperature.
  • the aromatic compounds need to be a liquid as the mixture.
  • the aromatic compound can be supplied to the electrode unit 100 in a liquid state without performing processes such as heating, pressurizing, and the like.
  • the concentration of the aromatic hydrocarbon compound in a liquid state is 0.1 percent or greater, preferably 0.3 percent or greater, and more preferably 0.5 percent or greater.
  • the aromatic compound stored in the organic material storage tank 30 is supplied to the reduction electrode 120 of the electrode unit 100 by a first liquid supply device 32 .
  • a first liquid supply device 32 for example, various types of pumps such as a gear pump, a cylinder pump, or the like or a gravity flow device or the like can be used.
  • an N-substitution product of the above-stated aromatic compound may be used.
  • a circulation pathway is provided between the organic material storage tank 30 and the reduction electrode of the electrode unit 100 .
  • An aromatic compound in which at least one benzene ring is hydrogenated by the electrode unit 100 and an unreacted aromatic compound are stored in the organic material storage tank 30 via the circulation pathway. No gas is generated by a major reaction that progresses at the reduction electrode 120 of the electrode unit 100 .
  • a gas-liquid separation device may be provided in the middle of the circulation pathway.
  • the water storage tank 40 stores ion-exchanged water, purified water, and the like (hereinafter, simply referred to as “water”). Water stored in the water storage tank 40 is supplied to the oxygen evolving electrode 130 of the electrode unit 100 by a second liquid supply device 42 . As in the case of the first liquid supply device 32 , for example, various types of pumps such as a gear pump, a cylinder pump, or the like or a gravity flow device or the like can be used for the second liquid supply device 42 . A circulation pathway is provided between the water storage tank 40 and the oxygen evolving electrode of the electrode unit 100 . Water that is unreacted in the electrode unit 100 is stored in the water storage tank 40 via the circulation pathway.
  • the gas-liquid separator 50 is provided in the middle of a pathway where unreacted water is sent back to the water storage tank 40 from the electrode unit 100 .
  • the gas-liquid separator 50 separates oxygen evolved by the electrolysis of water in the electrode unit 100 from water and discharges the oxygen outside the system.
  • the electrode unit 100 has an electrolyte membrane 110 , a reduction electrode 120 , an oxygen evolving electrode 130 , liquid diffusion layers 140 a and 140 b , and separators 150 a and 150 b .
  • the electrode unit 100 is simplified for illustration, and the liquid diffusion layers 140 a and 140 b and the separators 150 a and 150 are omitted.
  • the electrolyte membrane 110 is formed of a material (ionomer) having protonic conductivity. While selectively conducting protons, the electrolyte membrane 110 is required to prevent substances from getting mixed or being diffused between the reduction electrode 120 and the oxygen evolving electrode 130 .
  • the thickness of the electrolyte membrane 110 is preferably from 5 to 300 ⁇ m, more preferably from 10 to 150 ⁇ m, and most preferably from 20 to 100 ⁇ m. If the thickness of the electrolyte membrane 110 is less than 5 ⁇ m, the barrier property of the electrolyte membrane 110 is lowered, and the amount of cross-leaking substances is more likely to increase. If the thickness of the electrolyte membrane 110 is more than 300 ⁇ m, ion transfer resistance becomes too large. Thus, the thickness of more than 300 ⁇ m is not preferred.
  • the area specific resistance, i.e., ion transfer resistance per geometric area, of the electrolyte membrane 110 is preferably 2000 m ⁇ cm 2 or less, more preferably 1000 m ⁇ cm 2 or less, and most preferably 500 m ⁇ cm 2 or less. If the area specific resistance of the electrolyte membrane 110 is 2000 m ⁇ cm 2 or greater, protonic conductivity becomes insufficient.
  • An example of a material having protonic conductivity (which is a cation-exchanging ionomer) includes a perfluorosulfonic acid polymer such as Nafion (registered trademark), Flemion (registered trademark), etc.
  • the ion exchange capacity (IEC) of the cation-exchanging ionomer is preferably from 0.7 to 2 meq/g and more preferably from 1 to 1.2 meq/g. If the ion exchange capacity of the cation-exchanging ionomer is less than 0.7 meq/g, ionic conductivity becomes insufficient. On the other hand, if the ion exchange capacity of the cation-exchanging ionomer is greater than 2 meq/g, the solubility of the ionomer in water becomes increased, and the strength of the electrolyte membrane 110 thus becomes insufficient.
  • a reference electrode 112 is provided in an area spaced apart from the reduction electrode 120 and the oxygen evolving electrode 130 in such a manner that the reference electrode 112 is in contact with the electrolyte membrane 110 .
  • the reference electrode 112 is electrically isolated from the reduction electrode 120 and the oxygen evolving electrode 130 .
  • the reference electrode 112 is held at a reference electrode potential V Ref .
  • the reference electrode 112 is preferably provided on the surface of the electrolyte membrane 110 on the side of the reduction electrode 120 .
  • a potential difference ⁇ V CA between the reference electrode 112 and the reduction electrode 120 is detected by a voltage detection unit 114 .
  • the value of the potential difference ⁇ V CA detected by the voltage detection unit 114 is input to the control unit 60 .
  • the reduction electrode 120 is provided on one side of the electrolyte membrane 110 .
  • the reduction electrode 120 is a reduction electrode catalyst layer containing a reduction catalyst for hydrogenating at least one benzene ring of an aromatic compound.
  • a reduction catalyst used for the reduction electrode 120 is not particularly limited but is composed of, for example, a composition containing a first catalyst metal (noble metal) that contains at least one of Pt and Pd and containing 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.
  • the form of the composition is an alloy of the first catalyst metal and the second catalyst metal or an intermetallic compound composed of the first catalyst metal and the second catalyst metal.
  • the ratio of the first catalyst metal to the total mass of the first catalyst metal and the second catalyst metal is preferably from 10 to 95 wt %, and more preferably from 20 to 90 wt %, and most preferably from 25 to 80 wt %.
  • the ratio of the first catalyst metal of less than 10 wt % may result in deterioration in durability from the perspective of resistance to dissolving or the like.
  • the ratio of the first catalyst metal is greater than 95 wt %, the properties of the reduction catalyst become similar to the properties of a noble metal alone, and the electrode activity thus becomes insufficient.
  • a first catalyst metal and a second catalyst metal are often collectively referred to as “catalyst metals”.
  • the above-described catalyst metals may be supported by a conductive material (support).
  • the electrical conductivity of the conductive material is preferably 1.0 ⁇ 10 ⁇ 2 S/cm or greater, more preferably 3.0 ⁇ 10 ⁇ 2 S/cm or greater, and most preferably 1.0 ⁇ 10 ⁇ 1 S/cm or greater. If the electrical conductivity of the conductive material is less than 1.0 ⁇ 10 ⁇ 2 S/cm, sufficient conductivity cannot be provided.
  • the conductive material include a conductive material containing any one of a porous carbon, a porous metal, and a porous metal oxide as a major component.
  • the porous carbon includes carbon black such as Ketjenblack (registered trademark), acetylene black, Vulcan (registered trademark), or the like.
  • the BET specific surface area of the porous carbon measured by a nitrogen adsorption method is preferably 100 m 2 /g or greater, more preferably 150 m 2 /g or greater, and most preferably 200 m 2 /g or greater. If the BET specific surface area of the porous carbon is less than 100 m 2 /g, it is difficult to uniformly support the catalyst metals. Therefore, the rate of utilization of a catalyst metal surface is lowered, causing the catalyst performance to be lowered.
  • porous metal examples include, for example, Pt black, Pd black, a Pt metal deposited in a fractal shape, and the like.
  • a porous metal oxide examples include an oxide of Ti, an oxide of Zr, an oxide of Nb, an oxide of Mo, an oxide of Hf, an oxide of Ta, and an oxide of W.
  • a porous conductive material for supporting a catalyst metal examples include a nitride, a carbide, an oxynitride, a carbonitride, a partially-oxidized carbonitride of a metal such as Ti, Zr, Nb, Mo, Hf, Ta, W, or the like (hereinafter, these are collectively referred to as porous metal carbonitrides and the like).
  • the respective BET specific surface areas of the porous metal, the porous metal oxide, the porous metal carbonitrides, and the like measured by a nitrogen adsorption method are preferably 1 m 2 /g or greater, more preferably 3 m 2 /g or greater, and most preferably 10 m 2 /g or greater. If the respective BET specific surface areas of the porous metal, the porous metal oxide, the porous metal carbonitrides, and the like are less than 1 m 2 /g, it is difficult to uniformly support the catalyst metals. Therefore, the rate of utilization of a catalyst metal surface is lowered, causing the catalyst performance to be lowered.
  • a simultaneous impregnation method or a sequential impregnation method can be employed as a method for supporting the catalyst metals on the support.
  • the first catalyst metal and the second catalyst metal are simultaneously impregnated into the support in the simultaneous impregnation method, and the second catalyst metal is impregnated into the support after the first catalyst metal is impregnated into the support in the sequential impregnation method.
  • a heat treatment or the like may be performed once, and the second catalyst metal may be then loaded onto the support.
  • the alloying of the first catalyst metal and the second catalyst metal or the formation of an intermetallic compound composed of the first catalyst metal and the second catalyst metal is performed by a heat treatment process.
  • a material having conductivity such as the previously-stated conductive oxide, carbon black, or the like may be added to the reduction electrode 120 in addition to a conductive compound on which a catalyst metal is supported. With this, the number of electron-conducting paths among reduction catalyst particles can be increased. Thus, resistance per geometric area of a reduction catalyst layer can be lowered in some cases.
  • a fluorine-based resin such as polytetrafluoroethylene (PTFE) may be contained in the reduction electrode 120 .
  • PTFE polytetrafluoroethylene
  • the reduction electrode 120 may contain an ionomer having protonic conductivity.
  • the reduction electrode 120 contains ionically conducting materials (ionomers) having a structure that is identical or similar to that of the above-stated electrolyte membrane 110 in a predetermined mass ratio. This allows the ionic conductivity of the reduction electrode 120 to be improved.
  • the reduction electrode 120 makes a significant contribution to the improvement of the ionic conductivity by containing an ionomer that has protonic conductivity.
  • An example of an ionomer having protonic conductivity includes a perfluorosulfonic acid polymer such as Nafion (registered trademark), Flemion (registered trademark), etc.
  • the ion exchange capacity (IEC) of the cation-exchanging ionomer is preferably from 0.7 to 3 meq/g, more preferably from 1 to 2.5 meq/g, and most preferably from 1.2 to 2 meq/g.
  • a mass ratio I/C of the cation-exchanging ionomer (I) to the carbon support (C) is preferably from 0.1 to 2, more preferably from 0.2 to 1.5, and most preferably from 0.3 to 1.1. It is difficult to obtain sufficient ionic conductivity if the mass ratio I/C is less than 0.1. On the other hand, if the mass ratio I/C is 2 or greater, an increase in the thickness of an ionomer coating for the catalyst metal inhibits an aromatic compound, which is a reactant, from touching a catalytic site, or a decrease in the electron conductivity lowers the electrode activity.
  • the ionomers contained in the reduction electrode 120 partially coat a reduction catalyst. This allows three elements (an aromatic compound, a proton, and an electron) that are necessary for an electrochemical reaction at the reduction electrode 120 to be efficiently supplied to a reaction field.
  • the liquid diffusion layer 140 a is laminated on the surface of the reduction electrode 120 on the opposite side of the electrolyte membrane 110 .
  • the liquid diffusion layer 140 a plays a function of uniformly diffusing, to the reduction electrode 120 , a liquid aromatic compound supplied from the separator 150 a that is described later.
  • As the liquid diffusion layer 140 a for example, carbon paper and carbon cloth are used.
  • the separator 150 a is laminated on the surface of the liquid diffusion layer 140 a on the side opposite to the electrolyte membrane 110 .
  • the separator 150 a is formed of a carbon resin, an anticorrosion alloy of Cr—Ni—Fe, Cr—Ni—Mo—Fe, Cr—Mo—Nb—Ni, Cr—Mo—Fe—W—Ni, or the like.
  • a single or a plurality of groove-like flow channels 152 a is/are provided on the surface of the separator 150 a on the side of the liquid diffusion layer 140 a .
  • the liquid aromatic compound supplied from the organic material storage tank 30 circulates through the flow channel 152 a .
  • the liquid aromatic compound soaks into the liquid diffusion layer 140 a from the flow channel 152 a .
  • the form of the flow channel 152 a is not particularly limited. For example, a straight flow channel or a serpentine flow channel can be used.
  • the separator 150 a may be a structure in which ball-like or pellet-like metal fine powder is sintered.
  • the oxygen evolving electrode 130 is provided on the other side of the electrolyte membrane 110 .
  • the oxygen evolving electrode 130 that contains catalysts of noble metal oxides such as RuO 2 , IrO 2 , and the like is preferably used. These catalysts may be supported in a dispersed manner or coated by a metal substrate such as a metal wire or mesh of metals such as Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ta, W, and the like or of alloys composed primarily of these metals.
  • a metal substrate such as a metal wire or mesh of metals such as Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ta, W, and the like or of alloys composed primarily of these metals.
  • IrO 2 is high-priced, manufacturing costs can be lowered by performing thin film coating on a metal substrate when IrO 2 is used as a catalyst.
  • the liquid diffusion layer 140 b is laminated on the surface of the oxygen evolving electrode 130 on the side opposite to the electrolyte membrane 110 .
  • the liquid diffusion layer 140 b plays a function of uniformly diffusing, to the oxygen evolving electrode 130 , water supplied from the separator 150 b that is described later.
  • As the liquid diffusion layer 140 b for example, carbon paper and carbon cloth are used.
  • the separator 150 b is laminated on the surface of the liquid diffusion layer 140 b on the side opposite to the electrolyte membrane 110 .
  • the separator 150 b is formed of an anticorrosion alloy of Cr—Ni—Fe, Cr—Ni—Mo—Fe, Cr—Mo—Nb—Ni, Cr—Mo—Fe—W—Ni, or the like or of a material in which the surfaces of these metals are coated by an oxide layer.
  • a single or a plurality of groove-like flow channels 152 b is/are provided on the surface of the separator 150 b on the side of the liquid diffusion layer 140 b .
  • the water supplied from the water storage tank 40 circulates through the flow channel 152 b .
  • the water soaks into the liquid diffusion layer 140 b from the flow channel 152 b .
  • the form of the flow channel 152 b is not particularly limited. For example, a straight flow channel or a serpentine flow channel can be used.
  • the separator 150 b may be a structure in which ball-like or pellet-like metal fine powder is sintered.
  • liquid water is supplied to the oxygen evolving electrode 130 .
  • a humidified gas e.g., air
  • the dew-point temperature of the humidified gas is preferably from room temperature to 100° C. and more preferably from 50 to 100° C.
  • the electrode reaction at the oxygen evolving electrode and the electrode reaction at the reduction electrode progress in parallel, and protons evolved by electrolysis of water are supplied to the reduction electrode via the electrolyte membrane 110 by the electrode reaction at the oxygen evolving electrode and used for hydrogenation of at least one benzene ring of the aromatic compound in the electrode reaction at the reduction electrode.
  • the control unit 60 controls the power control unit 20 such that a relationship, V HER ⁇ 20 mV ⁇ V CA ⁇ V TRR , can be satisfied when the potential at a reversible hydrogen electrode, the standard redox potential of the aromatic compound, and the potential of the reduction electrode 120 are expressed as V HER , V TRR , and V CA , respectively. If the potential V CA is below V HER ⁇ 20 mV, competition with a hydrogen generation reaction will occur, and the reduction selectivity of the aromatic compound will become insufficient. Thus, the potential V CA of below V HER ⁇ 20 mV is not preferred.
  • the potential V CA of higher than the standard redox potential V TRR is not preferred since the hydrogenation of at least one benzene ring of the aromatic compound will not progress at a practically sufficient reaction speed.
  • the potential V CA by setting the potential V CA to be in a range that satisfies the above-stated relational expression, an electrochemical reaction can be progressed at the both electrodes, and the hydrogenation of at least one benzene ring of the aromatic compound can thus be industrially practiced.
  • the temperature of the electrode unit 100 is preferably from room temperature to 100° C. and more preferably from 40 to 80° C.
  • the temperature of the electrode unit 100 of below the room temperature is not preferred since there is a possibility that the progress of an electrolytic reaction is slowed down or an enormous amount of energy is required to remove heat generated as the reaction progresses.
  • the reduction electrode potential V CA is a true electrode potential
  • the reduction electrode potential V CA may be different from a potential V CA — actual that is actually measured. If there are resistance components, among various resistance components that exist in an electrolytic cell used in the present invention, that result in ohmic resistance, a resistance value per electrode area of the entirety of these components is set to be the entire ohmic resistance R ohmic , and the true electrode potential V CA is calculated using the following expression.
  • V CA V CA — actual +R ohmic ⁇ J (current density)
  • Examples of the resistance components that result in ohmic resistance are proton transfer resistance of the electrolyte membrane, electron transfer resistance of the electrode catalyst layer, and, furthermore, contact resistance on an electric circuit.
  • R ohmic can be obtained as an actual resistance component on an equivalent circuit by using an alternating-current impedance method or an alternating-current resistance measurement at a fixed frequency.
  • a method is preferably employed where R ohmic is used in the following control while considering R ohmic as an almost stationary value.
  • FIG. 3 is a flowchart illustrating an example of potential control of the reduction electrode 120 by the control unit 60 .
  • a potential V CA (target value) that satisfies the expression, V HER ⁇ 20 mV ⁇ V CA ⁇ V TRR , is set (S 10 ).
  • the potential V CA (target value) is a value that is stored in advance in memory such as ROM.
  • the potential V CA (target value) is set by a user.
  • the potential difference ⁇ V CA between the reference electrode 112 and the reduction electrode 120 is then detected by the voltage detection unit 114 (S 20 ).
  • control unit 60 determined whether the potential V CA (actual measurement value) satisfies the following expressions (1) and (2) (S 40 ).
  • V HER ⁇ 20 mV ⁇ V CA (actual measurement value) ⁇ V TRR (2)
  • the acceptable value is, for example, 1 mV.
  • the step proceeds to “yes” in S 40 , and the process performed at this point is ended. On the other hand, if the potential V CA (actual measurement value) does not satisfy the expressions (1) and (2), the step proceeds to “no” in S 40 , and the control unit 60 adjusts a voltage Va that is applied between the reduction electrode 120 and the oxygen evolving electrode 130 (S 50 ). After the adjustment of the voltage Va, the process goes back to the above-stated process in S 10 .
  • the control unit 60 transmits to the power control unit 20 an instruction to lower the voltage Va by only 1 mV. Even when the expression,
  • a value (adjustment range) for increasing or decreasing the voltage Va is not limited to 1 mV.
  • the adjustment range of the voltage Va may be set to be equal to the above-stated acceptable value in a first adjustment of the voltage Va, and the adjustment range of the voltage Va may be set to be, e.g., one-fourth of the above-stated acceptable value in a second or subsequent adjustment of the voltage Va.
  • the control unit 60 can more promptly adjust the potential V CA (actual measurement value) to be in a range where the expressions (1) and (2) are satisfied.
  • V OER oxygen evolution equilibrium potential in the electrolysis of water
  • the control unit 60 controls the power control unit 20 in such a manner that an expression, Va ⁇ (V OER ⁇ V CA ), is satisfied. This allows a potential V AN of the oxygen evolving electrode 130 to be maintained to be the oxygen evolution equilibrium potential V oER or greater.
  • FIG. 4 is a graph illustrating a relationship between the potential of the reduction electrode and various current density.
  • the mass of reduction catalyst metals is 0.5 mg/cm 2 .
  • a current density A, a current density B, and a current density C that are shown in FIG. 4 are as shown in the following.
  • Current density B current density used for the reduction of toluene that is back-calculated from the evolution amount of methylcyclohexane determined quantitatively by gas chromatography or the like
  • Current density C Current density A ⁇ Current density B (current density that was not used for the reduction of toluene but was mainly used for hydrogen generation)
  • FIG. 5 is a schematic diagram illustrating the configuration of an electrochemical reduction device according to a second embodiment.
  • an electrochemical reduction device 10 comprises an electrode unit assembly 200 , a power control unit 20 , an organic material storage tank 30 , a water storage tank 40 , a gas-liquid separator 50 , and a control unit 60 .
  • the electrode unit assembly 200 has a laminated structure where a plurality of electrode units 100 are connected in series. In the present embodiment, the number N of the electrode units 100 is five.
  • the configuration of each electrode unit 100 is similar to the configuration according to the first embodiment.
  • the electrode units 100 are simplified for illustration, and liquid diffusion layers 140 a and 140 b and separators 150 a and 150 are omitted.
  • the positive electrode output terminal of the power control unit 20 is connected to the positive electrode terminal of the electrode unit assembly 200 .
  • the negative electrode output terminal of the power control unit 20 is connected to the negative electrode terminal of the electrode unit assembly 200 .
  • a predetermined voltage VA is applied between the positive electrode terminal and the negative electrode terminal of the electrode unit assembly 200 .
  • a reference electrode input terminal of the power control unit 20 is connected to a reference electrode 112 provided on an electrolyte membrane 110 of a specific electrode unit 100 , which will be described later, and the potential of the positive electrode output terminal and the potential of the negative electrode output terminal are determined based on the potential of the reference electrode 112 .
  • a first circulation pathway is provided between the organic material storage tank 30 and reduction electrodes 120 of the respective electrode units 100 .
  • Aromatic compounds stored in the organic material storage tank 30 is supplied to the reduction electrodes 120 of the respective electrode units 100 by a first liquid supply device 32 . More specifically, a pipeline that forms the first circulation pathway is branched on the downstream side of the first liquid supply device 32 , and the aromatic compounds are supplied to the reduction electrodes 120 of the respective electrode units 100 in a distributed manner.
  • Aromatic compounds in which at least one benzene ring are hydrogenated by the electrode units 100 and unreacted aromatic compounds merge into a pipeline that communicates with the organic material storage tank 30 and are then stored in the organic material storage tank 30 via the pipeline.
  • a second circulation pathway is provided between the water storage tank 40 and oxygen evolving electrodes 130 of the respective electrode units 100 .
  • Water stored in the water storage tank 40 is supplied to the oxygen evolving electrodes 130 of the respective electrode units 100 by a second liquid supply device 42 .
  • a pipeline that forms the second circulation pathway is branched on the downstream side of the second liquid supply device 42 , and the water is supplied to the oxygen evolving electrodes 130 of the respective electrode units 100 in a distributed manner. Unreacted water merges into a pipeline that communicates with the water storage tank 40 and is then stored in the water storage tank 30 via the pipeline.
  • a reference electrode 112 is provided on an electrolyte membrane 110 of a specific electrode unit 100 in an area spaced apart from the reduction electrode 120 and the oxygen evolving electrode 130 in such a manner that the reference electrode 112 is in contact with the electrolyte membrane 110 in the same way as in the first embodiment.
  • the specific electrode unit 100 needs to be any one of the plurality of electrode units 100 .
  • a potential difference ⁇ V CA between the reference electrode 112 and the reduction electrodes 120 is detected by a voltage detection unit 114 .
  • the value of the potential difference ⁇ V CA detected by the voltage detection unit 114 is input to the control unit 60 .
  • the control unit 60 controls the power control unit 20 such that a relationship, V HER ⁇ 20 mV ⁇ V CA ⁇ V TRR , can be satisfied when the potential at a reversible hydrogen electrode, the standard redox potential of an aromatic compound, and the potential of the reduction electrodes 120 of the respective electrode units 100 are expressed as V HER , V TRR , and V CA , respectively.
  • the mode of the potential control of the reduction electrode 120 by the control unit 60 is similar to the mode according to the first embodiment. Note that while an applied voltage Va is adjusted by the control unit 60 in the first embodiment, a voltage VA applied between the positive electrode terminal and the negative electrode terminal of the electrode unit assembly 200 is adjusted by the control unit 60 in the present embodiment.
  • the control unit 60 controls the power control unit 20 in such a manner that an expression, VA ⁇ (V OER ⁇ V CA ) ⁇ N, is satisfied where N (two or greater) is the number of electrode units and is five in the present embodiment. This allows the potential V AN to be maintained to be the oxygen evolution equilibrium potential V oER or greater.
  • the hydrogenation of an aromatic compound can be progressed in parallel in a plurality of electrode units.
  • the amount of hydrogenation of at least one benzene ring of aromatic compounds per unit time can be dramatically increased. Therefore, the hydrogenation of at least one benzene ring of aromatic compounds can be industrially practiced.
  • FIG. 6 is a schematic diagram illustrating the configuration of an electrochemical reduction device according to a third embodiment.
  • the basic configuration of an electrochemical reduction device 10 according to the present embodiment is similar to the basic configuration according to the second embodiment.
  • an electrode unit assembly 200 is held in an electrolytic tank 300 .
  • a second circulation pathway is provided between the electrolytic tank 300 and a water storage tank 40 , and the electrolytic tank 300 is filled with water supplied from the water storage tank 40 . Water that fills the electrolytic tank 300 can circulate in oxygen evolving electrodes 130 of the respective electrode units 100 .
  • the electrochemical reduction device 10 has an advantage of decreasing an in-plane temperature difference of the oxygen evolving electrodes 130 , a temperature difference among electrode units, and an interelectrode temperature difference from reduction electrodes 120 by increasing the heat capacity of a water tank in the electrolytic tank.
  • a reduction electrode 120 contains an ionomer having protonic conductivity.
  • a reduction electrode 120 may contain an ionomer having hydroxy ion conductivity.
  • a reference electrode 112 is provided on an electrolyte membrane 110 of a single electrode unit.
  • a reference electrode 112 may be provided on respective electrolyte membranes 110 of a plurality of electrode units 100 .
  • the voltage detection unit 114 a potential difference ⁇ V CA between each reference electrode 112 and a corresponding reduction electrode 120 is detected, and a potential V CA is calculated by using an average value of a plurality of potential differences ⁇ V CA that are detected. With this, a voltage VA can be adjusted to be in a more appropriate range when variation in potential is caused among the electrode units 100 .

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