JP7726469B2 - Aldehyde production apparatus and aldehyde production method - Google Patents

Description

The present invention relates to an aldehyde production apparatus and an aldehyde production method.

The reaction of oxidizing alcohols to synthesize aldehydes is widely used in the synthesis of organic compounds, such as intermediates for industrial raw materials. However, in conventional reactions like this, it has been difficult to produce aldehydes with high selectivity, as the alcohol is oxidized to produce an aldehyde, which is then further oxidized to form a carboxylic acid.

One known method for producing aldehydes from alcohols is the electrolytic oxidation of alcohols. For example, Patent Document 1 describes the production of benzaldehyde and benzoic acid by electrolytic oxidation of benzyl alcohol in an electrolytic cell equipped with electrodes having a composite plating layer made of a hydrophobic fluorine compound and platinum on the surface of a conductive substrate.

Patent Document 2 describes a method for synthesizing aldehydes by electrolytically oxidizing a primary alcohol together with an N-oxyl compound.

Japanese Patent Application Publication No. 10-280183 Japanese Patent Application Publication No. 02-107790

The electrolytic cell described in Patent Document 1 does not allow for the selective synthesis of aldehydes. The method described in Patent Document 2 requires the use of an N-oxyl compound, which increases production costs.

The present invention was made in light of these circumstances, and one of its objectives is to provide a technology for highly selectively producing aldehydes.

One aspect of the present invention is an apparatus for producing aldehyde. This production apparatus includes a solid polymer electrolysis unit and a supply section that supplies a substrate to the solid polymer electrolysis unit. The solid polymer electrolysis unit electrolytically oxidizes the substrate to produce aldehyde.

Another aspect of the present invention is a method for producing an aldehyde. This method includes electrolytically oxidizing a substrate using a solid polymer electrolysis unit to produce an aldehyde.

In addition, any combination of the above components, or the mutual substitution of the components or expressions of the present invention between methods, devices, programs, temporary or non-temporary storage media on which programs are recorded, systems, etc., are also valid aspects of the present invention.

According to the present invention, aldehydes can be produced with high selectivity.

1 is a schematic diagram showing an aldehyde production apparatus according to an embodiment. FIG. 2 is a cross-sectional view illustrating a schematic configuration of a solid polymer electrolysis unit.

The present invention will be described below with reference to the drawings, based on preferred embodiments. The embodiments are illustrative and do not limit the invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention. Identical or equivalent components, parts, and processes shown in each drawing are designated by the same reference numerals, and redundant description will be omitted where appropriate. The scale and shape of each part shown in each drawing are set for convenience to facilitate explanation and should not be interpreted as limiting unless otherwise specified. Furthermore, when terms such as "first" and "second" are used in this specification or claims, unless otherwise specified, these terms do not indicate any order or importance, but are used to distinguish one configuration from another. Furthermore, some components that are not important for explaining the embodiments are omitted in each drawing. Furthermore, "X to Y" indicating a numerical range means "greater than or equal to X and less than or equal to Y" unless otherwise specified.

Figure 1 is a schematic diagram showing an aldehyde production apparatus according to an embodiment. Note that Figure 1 illustrates a simplified structure of a solid polymer electrolysis unit. The aldehyde production apparatus 10 (aldehyde production apparatus) is an apparatus that produces aldehyde by electrolytically oxidizing a substrate, and is primarily composed of a solid polymer electrolysis unit 100, a power control unit 20, a water storage tank 30, a substrate storage tank 40, and a control unit 60. Hereinafter, the aldehyde production apparatus 10 will be referred to simply as "production apparatus 10" where appropriate.

The power control unit 20 is, for example, a DC/DC converter that converts the output voltage of the power source to a predetermined voltage. The positive output terminal of the power control unit 20 is connected to the anode 130 of the solid polymer electrolysis unit 100. The negative output terminal of the power control unit 20 is connected to the cathode 120 of the solid polymer electrolysis unit 100. As a result, a predetermined voltage is applied between the anode 130 and cathode 120 of the solid polymer electrolysis unit 100.

The power control unit 20 may be provided with a reference electrode for the purpose of detecting the potentials of the anode and cathode. In this case, the reference electrode input terminal is connected to a reference electrode 112 provided on the solid polymer electrolyte membrane 110. The reference electrode 112 is provided in an area of the solid polymer electrolyte membrane 110 separated from the cathode 120 and anode 130 so as to be in contact with the solid polymer electrolyte membrane 110. The reference electrode 112 is electrically isolated from the cathode 120 and anode 130.

The reference electrode 112 is maintained at a reference electrode potential. Unless otherwise specified, the reference electrode potential in this application refers to the potential relative to a reversible hydrogen electrode (RHE) (reference electrode potential = 0 V). The reference electrode potential may also be the potential relative to an Ag/AgCl electrode (reference electrode potential = 0.199 V vs. RHE). Furthermore, the reference electrode 112 is preferably placed on the surface of the solid polymer electrolyte membrane 110 facing the anode 130.

The current flowing between the cathode 120 and the anode 130 is detected by the current detection unit 113. The current detection unit 113 is configured, for example, by a conventionally known ammeter. The current value detected by the current detection unit 113 is input to the control unit 60 and used by the control unit 60 to control the power control unit 20. The potential difference between the reference electrode 112 and the anode 130 is detected by the voltage detection unit 114. The voltage detection unit 114 is configured, for example, by a conventionally known voltmeter. The value of the potential difference detected by the voltage detection unit 114 is input to the control unit 60 and used by the control unit 60 to control the power control unit 20. If necessary, the voltage detection unit 114 may also detect the potential difference between the reference electrode 112 and the cathode 120.

The control unit 60 controls the potential of the solid polymer electrolysis unit 100. That is, the control unit 60 adjusts the potential of the cathode 120 and/or anode 130 to a predetermined potential. The control unit 60 is realized as a hardware configuration by elements and circuits such as a computer CPU and memory, and as a software configuration by a computer program, etc. This is naturally understood by those skilled in the art. The control unit 60 controls the output of the positive output terminal and negative output terminal of the power control unit 20 so that the potential of the cathode 120 and/or anode 130 becomes a predetermined potential.

The water storage tank 30 stores, for example, ion-exchanged water, pure water (distilled water, membrane permeation water, etc.), or an aqueous solution of these with an acid such as sulfuric acid, nitric acid, or hydrochloric acid, or an alkali metal salt such as potassium hydroxide or sodium hydroxide (hereinafter referred to as "cathode solution" as appropriate). The cathode solution stored in the water storage tank 30 is supplied to the cathode 120 of the solid polymer electrolysis unit 100 by a first supply device 32. The first supply device 32 can be, for example, a gear pump, a cylinder pump, or any other pump, or a gravity flow device.

A circulation path 34 is provided between the water storage tank 30 and the cathode 120. The circulation path 34 includes an outward path section 34a that connects the water storage tank 30 and the cathode 120 upstream of the cathode 120 in the flow of the cathode fluid, and a return path section 34b that connects the cathode 120 and the water storage tank 30 downstream of the cathode 120 in the flow of the cathode fluid. A first supply device 32 is provided midway along the outward path section 34a.

The cathode fluid is supplied to the cathode 120 via the outward path 34a. Unreacted cathode fluid at the cathode 120, hydrogen gas produced by the electrode reaction at the cathode 120, and other by-product gases are returned to the water storage tank 30 via the return path 34b. A gas-liquid separator (not shown) is provided midway along the return path 34b, and the hydrogen gas and by-product gases are separated by the gas-liquid separator. The return path 34b can also be omitted.

The substrate is stored in the substrate storage tank 40. Substrates used in this embodiment include alcohols, particularly primary alcohols, benzyl alcohol, and benzyl alcohol derivatives. Specific examples of primary alcohols include ethanol, 1-propanol, 1-hexanol, and 3-methyl-2-buten-1-ol. Aldehydes obtained from these substrates include acetaldehyde, propionaldehyde, hexanal, and 3-methyl-2-butenal. The aldehyde obtained from benzyl alcohol is benzaldehyde. A benzyl alcohol derivative refers to a compound in which the hydrogen atom on the benzene ring of benzyl alcohol is replaced with a functional group or an aliphatic group. Specific examples of benzyl alcohol derivatives include 2-methylbenzyl alcohol, 4-methylbenzyl alcohol, 4-(dimethylamino)benzyl alcohol, and cinnamyl alcohol. The aldehydes obtained using these substrates are 2-methylbenzaldehyde, 4-methylbenzaldehyde, 4-(dimethylamino)benzaldehyde, and cinnamaldehyde.

The substrate stored in the substrate storage tank 40 is supplied to the anode 130 of the solid polymer electrolysis unit 100 by the second supply device 42. The substrate storage tank 40 and the second supply device 42 constitute a supply section 44 that supplies the substrate to the solid polymer electrolysis unit 100.

A circulation path 46 is provided between the substrate storage tank 40 and the anode 130. The circulation path 46 includes an outward path section 46a that connects the substrate storage tank 40 and the anode 130 upstream of the anode 130 in the substrate flow, and a return path section 46b that connects the anode 130 and the substrate storage tank 40 downstream of the anode 130 in the substrate flow. A second supply device 42 is provided midway along the outward path section 46a.

The substrate is supplied to the anode 130 via the outgoing path 46a. The aldehyde produced by electrolytic oxidation of the substrate at the anode 130 and the unreacted substrate are returned to the substrate storage tank 40 via the return path 46b. Note that the return path 46b can be omitted.

Figure 2 is a cross-sectional view showing the schematic configuration of a solid polymer electrolysis unit 100. The solid polymer electrolysis unit 100 of this embodiment is a solid polymer electrolytic cell having an anode chamber on one side of a film-shaped electrolyte membrane and a cathode chamber on the other side. More specifically, the solid polymer electrolysis unit 100 includes a membrane electrode assembly 102 and a pair of separators 150a and 150b that sandwich the membrane electrode assembly 102. The membrane electrode assembly 102 includes a solid polymer electrolyte membrane 110, a cathode 120, and an anode 130.

The solid polymer electrolyte membrane 110 is disposed between the anode 130 and the cathode 120. Types of solid polymer electrolyte membranes 110 include proton exchange membranes (PEMs) and anion exchange membranes (AEMs). The solid polymer electrolyte membrane 110 selectively conducts protons or anions while suppressing the mixing or diffusion of substances between the cathode 120 and the anode 130. The solid polymer electrolyte membrane 110 also allows water from the cathode to pass through.

The thickness of the solid polymer electrolyte membrane 110 is, for example, 5 to 300 μm. By making the thickness of the solid polymer electrolyte membrane 110 5 μm or more, the barrier properties of the solid polymer electrolyte membrane 110 can be ensured and the occurrence of crossover of substrates and the like can be more reliably suppressed. Furthermore, by making the thickness of the solid polymer electrolyte membrane 110 300 μm or less, excessive ion migration resistance can be suppressed.

The proton exchange electrolyte membrane (PEM) preferably contains perfluorosulfonic acid. For example, the solid polymer electrolyte membrane 110 is composed of a perfluorosulfonic acid polymer. Examples of such polymers include Nafion® and Flemion®. The anion exchange electrolyte membrane (AEM) preferably contains a polymer having a strong basic group such as a quaternary ammonium salt. Examples of anion exchange electrolyte membranes include fumapem® FAA-3 and Neosepta® AHA. The solid polymer electrolyte membrane 110 is preferably an AEM. This enables aldehyde to be produced with higher current efficiency. The solid polymer electrolyte membrane 110 may be mixed with a reinforcing material such as porous PTFE (polytetrafluoroethylene). The introduction of a reinforcing material can improve the dimensional stability of the solid polymer electrolyte membrane 110, thereby improving the durability of the solid polymer electrolyte membrane 110. It also suppresses crossover of substrates, etc.

The cathode 120 is an electrode that reduces water to produce hydrogen, and is arranged on one side of the solid polymer electrolyte membrane 110. In this embodiment, the cathode 120 is arranged so as to be in contact with one main surface of the solid polymer electrolyte membrane 110. The cathode 120 has a structure in which a cathode catalyst layer 122 and a diffusion layer 124 are laminated. The cathode catalyst layer 122 is arranged closer to the solid polymer electrolyte membrane 110 than the diffusion layer 124.

The cathode catalyst layer 122 is in contact with one main surface of the solid polymer electrolyte membrane 110. The cathode catalyst layer 122 contains a catalytic metal for reducing water. For example, the cathode catalyst layer 122 contains at least one catalytic metal selected from the group consisting of Pt, Au, Ag, Pd, Rh, Ru, Fe, and Ni. Preferably, the cathode catalyst layer 122 contains Pt. The catalytic metal is supported by a catalyst support made of an electron-conductive material. Supporting the catalytic metal on the catalyst support increases the surface area of the cathode catalyst layer 122. Furthermore, aggregation of the catalytic metal can be suppressed. The electron conductivity of the electron-conductive material used for the catalyst support is preferably 1.0×10 ⁻² S/cm or higher. By ensuring that the electron conductivity of the electron-conductive material is 1.0×10 ⁻² S/cm or higher, electron conductivity can be more reliably imparted to the cathode catalyst layer 122.

Examples of catalyst supports include electron-conductive materials containing porous carbon, porous metal, or porous metal oxide as a primary component. Examples of porous carbon include carbon black, such as Ketjen Black (registered trademark), acetylene black, furnace black, and Vulcan (registered trademark). Examples of porous metals include Pt black, Pd black, and fractal-like precipitated Pt metal. Examples of porous metal oxides include oxides of Ti, Zr, Nb, Mo, Hf, Ta, and W. Catalyst supports can also be made of porous metal compounds, such as nitrides, carbides, oxynitrides, carbonitrides, and partially oxidized carbonitrides of metals such as Ti, Zr, Nb, Mo, Hf, Ta, and W.

Preferably, the catalyst support carrying the catalytic metal is coated with an ionomer. This improves the ionic conductivity of the cathode 120. When the solid polymer electrolyte membrane 110 is a PEM, a proton-conductive ionomer is used. When the solid polymer electrolyte membrane 110 is an AEM, an anion-conductive ionomer is used. Examples of proton-conductive ionomers include perfluorosulfonic acid polymers such as Nafion (registered trademark) and Flemion (registered trademark). Examples of anion-conductive ionomers include polymers with strong basic groups (quaternary ammonium groups, imidazolium groups, etc.), such as Fumion (trademark) FAA-3. The thickness of the cathode catalyst layer 122 is, for example, 1 to 100 μm. By keeping the thickness of the cathode catalyst layer 122 within the above range, an increase in proton transfer resistance can be suppressed.

The cathode catalyst layer 122 can be produced, for example, by mixing catalyst component powder, a catalyst carrier, and a solvent such as water to prepare a catalyst ink, mixing the resulting catalyst ink with a conductive filler such as carbon nanotubes and a binder to prepare a catalyst paste, and then forming this catalyst paste into a sheet. Alternatively, the cathode catalyst layer 122 can be produced by applying the catalyst ink to the diffusion layer 124, drying it, and then hot pressing it. The cathode catalyst layer 122 may also be formed on the solid polymer electrolyte membrane 110.

The diffusion layer 124 functions to uniformly diffuse the cathode fluid supplied from the separator 150a into the cathode catalyst layer 122. Examples of materials that can be used to form the diffusion layer 124 include woven carbon fabric (carbon cloth), nonwoven carbon fabric, and carbon paper. Carbon cloth is made by bundling hundreds of thin carbon fibers with diameters of a few microns into a woven fabric. Carbon paper is made by using a papermaking method to turn raw carbon fiber into a thin film precursor, which is then sintered. The thickness of the diffusion layer 124 is preferably 50 to 1000 μm.

The separator 150a is laminated on the main surface of the cathode 120 opposite the solid polymer electrolyte membrane 110. The separator 150a can be formed, for example, from carbon resin or a corrosion-resistant alloy such as a Cr-Ni-Fe, Cr-Ni-Mo-Fe, Cr-Mo-Nb-Ni, Cr-Mo-Fe-W-Ni, or Ti alloy. One or more groove-shaped flow paths 152a are provided on the surface of the separator 150a facing the diffusion layer 124. The forward path section 34a and the return path section 34b are connected to the flow path 152a. The separator 150a, the solid polymer electrolyte membrane 110, and the frame-shaped spacer 126 disposed therebetween define a cathode chamber, which houses the cathode catalyst layer 122 and the diffusion layer 124.

Cathode fluid flows into the flow path 152a in the cathode chamber via the outward path section 34a. The cathode fluid permeates the diffusion layer 124 from the flow path 152a. The cathode fluid then flows into the cathode catalyst layer 122. Unreacted cathode fluid flows out of the cathode chamber via the return path section 34b and is returned to the water storage tank 30. The shape of the flow path 152a is not particularly limited, but may be, for example, a linear flow path or a serpentine flow path. Alternatively, the separator 150a may have a porous layer, and the flow path 152a may be formed by the voids in the porous layer.

The anode 130 is an electrode for electrolytically oxidizing a substrate to produce aldehyde, and is arranged on the other side of the solid polymer electrolyte membrane 110, i.e., the side opposite the side on which the cathode 120 is arranged. In this embodiment, the anode 130 is arranged so as to contact the other main surface of the solid polymer electrolyte membrane 110. The anode 130 has a structure in which an anode catalyst layer 132 and a diffusion layer 134 are laminated. The anode catalyst layer 132 is arranged closer to the solid polymer electrolyte membrane 110 than the diffusion layer 134.

The anode catalyst layer 132 is in contact with the other main surface of the solid polymer electrolyte membrane 110. The anode catalyst layer 132 contains a catalytic metal for oxidizing the substrate. Preferably, the anode catalyst layer 132 contains at least one catalytic metal selected from the group consisting of Ru, Rh, Pd, Ir, Pt, and Au. More preferably, the anode catalyst layer 132 contains Au. When the anode catalyst layer 132 contains one of these catalytic metals, aldehyde can be produced highly selectively. Here, "highly selective" means that more aldehyde than carboxylic acid is produced by the electrolytic oxidation of the substrate. The selectivity of aldehyde is greater than 50%, preferably 70% or more, more preferably 90% or more, and most preferably 99% or more, of the total amount of "aldehyde + carboxylic acid."

The catalytic metal may be supported by a catalyst support made of an electron-conductive material. Furthermore, when the anode catalyst layer 132 contains Au, metal particles containing Au are preferably supported on the catalyst support. This allows aldehyde to be produced with higher current efficiency. From the perspective of further increasing current efficiency, the average particle diameter of the metal particles is preferably 0.2 nm or more and 50 nm or less.

As with the catalyst support of the cathode catalyst layer 122, examples of the catalyst support include porous carbon, porous metal, and porous metal oxide. From the perspective of further increasing current efficiency, the catalyst support is preferably porous carbon, and more preferably acetylene black. The catalyst metal is preferably coated with an ionomer, thereby improving the ionic conductivity of the anode 130. When the solid polymer electrolyte membrane 110 is a PEM, a proton-conductive ionomer is used. When the solid polymer electrolyte membrane 110 is an AEM, an anion-conductive ionomer is used. Examples of proton-conductive ionomers include perfluorosulfonic acid polymers such as Nafion (registered trademark) and Flemion (registered trademark). Examples of anion-conductive ionomers include polymers with strongly basic groups (quaternary ammonium groups, imidazolium groups, etc.), such as Fumion (trademark) FAA-3. The thickness of the anode catalyst layer 132 is, for example, 1 to 100 μm.

The anode catalyst layer 132 can be produced, for example, by mixing catalyst component powder with a binder to prepare a catalyst paste and then forming this catalyst paste into a sheet. It can also be produced by applying catalyst ink to the diffusion layer 134, drying it, and then hot pressing it. The anode catalyst layer 132 may also be formed on the solid polymer electrolyte membrane 110.

The diffusion layer 134 functions to uniformly diffuse the substrate supplied from the separator 150b into the anode catalyst layer 132. It is preferable that the material constituting the diffusion layer 134 has a high affinity for the substrate. Examples of materials constituting the diffusion layer 134 include woven carbon fabric (carbon cloth), nonwoven carbon fabric, and carbon paper. The thickness of the diffusion layer 134 is preferably 50 to 1000 μm.

Separator 150b is laminated on the main surface of the anode 130 opposite the solid polymer electrolyte membrane 110. Separator 150b can be made of the same material as separator 150a. One or more groove-shaped flow paths 152b are provided on the surface of separator 150b facing the diffusion layer 134. The outgoing path section 46a and the returning path section 46b are connected to the flow path 152b. The separator 150b, the solid polymer electrolyte membrane 110, and the frame-shaped spacer 136 disposed between them define an anode chamber, which houses the anode catalyst layer 132 and the diffusion layer 134.

The substrate flows into the flow path 152b of the anode chamber via the outward flow path 46a. The substrate permeates the diffusion layer 134 from the flow path 152b. The products of the electrolytic oxidation reaction in the anode catalyst layer 132 and the unreacted substrate flow out of the anode chamber via the return flow path 46b and are returned to the substrate storage tank 40. The configuration of the flow path 152b is the same as that of the flow path 152a.

The solid polymer electrolysis unit 100 produces aldehyde by electrolytically oxidizing a substrate. When the solid polymer electrolyte membrane 110 is an AEM and benzyl alcohol is used as the substrate, the reaction in the solid polymer electrolysis unit 100 is as follows:
<Electrode Reaction at the Anode 130>
OH ^- →O ^* +e ^-
C ₇ H ₈ O+O ^* →C ₇ H ₆ O+H ₂ O
<Electrode Reaction at Cathode 120>
2H ₂ O+2e ^- →2OH ^- +H ₂
<Total response>
2C ₇ H ₈ O→2C ₇ H ₆ O+H ₂

That is, first, water receives electrons from an external circuit at the cathode 120, generating hydrogen, and at the same time, hydroxide ions (OH ⁻ ) are generated. These hydroxide ions are conducted through the AEM and supplied to the anode side.

In the anode catalyst layer 132, active oxygen species (O ^* ) and electrons (e ⁻ ) are generated from hydroxide ions (OH ⁻ ) that have been conducted through the membrane. The generated active oxygen species react with benzyl alcohol as a substrate supplied to the anode catalyst layer 132 by the supply unit 44, generating benzaldehyde as an aldehyde and water (H ₂ O). The electrode reactions at the anode 130 and the cathode 120 proceed in parallel.

During the electrolytic oxidation of a substrate using the solid polymer electrolysis unit 100, the control unit 60 controls the potential of the anode 130 based on the reference electrode potential or the cathode 120. When a Pt-containing electrode is used as the cathode, the hydrogen generation overvoltage at the cathode can be considered to be essentially zero. Therefore, controlling the anode potential based on the cathode potential is essentially equivalent to controlling it to the reversible hydrogen electrode (RHE) reference potential. The control range of the anode potential relative to the RHE is preferably 0.6 V or higher and 1.8 V or lower, more preferably 0.8 V or higher and 1.6 V or lower. This allows for more efficient production of aldehyde. When controlling the anode potential based on the reference electrode potential, the RHE-equivalent potential is controlled to be within the above range, taking into account the temperature and the pH of the electrolyte. For example, when an electrolyte with a pH of 14 at 25°C is used with an Ag/AgCl reference electrode potential as the standard, the reference electrode potential is -0.059 x 14 - 0.199 = -1.025 V. Therefore, the preferred range for the anode potential relative to this reference electrode potential is -0.425 V or more and 0.775 V or less, and a more preferred range is -0.225 V or more and 0.575 V or less (reference: https://pubs.acs.org/doi/10.1021/acscatal.0c02046).

[Method for producing aldehyde]
The method for producing an aldehyde according to the present embodiment includes producing an aldehyde by electrolytically oxidizing a substrate using the solid polymer electrolysis unit 100. More specifically, a substrate is supplied to the anode 130, and a catholyte is supplied to the cathode 120. A predetermined voltage is then applied between the anode 130 and the cathode 120 of the solid polymer electrolysis unit 100 by the power control unit 20. At that time, the potential of the anode 130 relative to the reversible hydrogen electrode (RHE) is controlled preferably to be 0.6 V or more and 1.8 V or less, more preferably 0.8 V or more and 1.6 V or less.

As a result, in the anode catalyst layer 132, active oxygen species and electrons are generated from the hydroxide ions that have migrated from the cathode 120 side. The generated active oxygen species then react with the substrate to generate aldehyde and water. The generated water passes through the solid polymer electrolyte membrane 110 and migrates to the cathode 120 side. Then, in the cathode catalyst layer 122, hydroxide ions and hydrogen are generated from the water.

As described above, the aldehyde production apparatus 10 according to the present embodiment includes a solid polymer electrolysis unit 100 and a supply unit 44 that supplies a substrate to the solid polymer electrolysis unit 100. The solid polymer electrolysis unit 100 has an anode 130 including an anode catalyst layer 132, a cathode 120 including a cathode catalyst layer 122, and a solid polymer electrolyte membrane 110 disposed between the anode 130 and the cathode 120. The supply unit 44 supplies the substrate to the anode 130. The solid polymer electrolysis unit 100 then electrolytically oxidizes the substrate to produce aldehyde. The aldehyde production method according to the present embodiment also includes producing aldehyde by electrolytically oxidizing a substrate using the solid polymer electrolysis unit 100.

In this way, in this embodiment, by using the solid polymer electrolysis unit 100, aldehyde can be highly selectively synthesized from the substrate. Furthermore, because the electrode reaction at the anode 130 and the electrode reaction at the cathode 120 occur in parallel, aldehyde can be synthesized through a simpler process.

The anode catalyst layer 132 preferably contains at least one catalytic metal selected from the group consisting of Ru, Rh, Pd, Ir, Pt, and Au, and more preferably contains Au. This allows for more reliable production of aldehyde.

Furthermore, when the anode catalyst layer 132 contains Au, the anode catalyst layer 132 further contains a catalyst support, in which metal particles containing at least Au are supported on the catalyst support, and the average particle size of the metal particles is 0.2 nm or more and 50 nm or less. This can improve the efficiency of aldehyde production.

The aldehyde production apparatus 10 also includes a control unit 60 that controls the potential of the solid polymer electrolysis unit 100. The control unit 60 controls the potential of the anode 130 relative to the reversible hydrogen electrode (RHE) to be 0.6 V or higher and 1.8 V or lower. This increases the efficiency of aldehyde production.

The following describes examples of the present invention, but these examples are merely illustrative examples for the purpose of explaining the present invention and are not intended to limit the present invention in any way.

Example 1
<Preparation of solid polymer electrolyte membrane>
An anion exchange membrane (AEM) Fumapem™ FAA-3 was prepared. This AEM membrane was Br ^- type. The AEM was cut to a predetermined size, immersed in a 1 M KOH aqueous solution at room temperature for 24 hours, and then thoroughly washed with ion-exchanged water. This ion ^- exchanged the Br- of the AEM with ^OH- , removing impurities. The treated AEM membrane was stored in ion-exchanged water.

<Preparation of cathode>
Pt/C (product number: TEC10E50E, manufactured by Tanaka Kikinzoku Co., Ltd.) was mixed with 10 wt % Fumion™ FAA-3 NMP (N-methyl-2-pyrrolidone) solution, pure water, and 1-propanol (1-PrOH) in a mass ratio of 4:18:18:60. The resulting mixture was pulverized in a ball mill to obtain a catalyst composition for the reduced electrode catalyst layer. This catalyst composition was spray-coated onto one main surface of an electrolyte membrane (product name: Fumapem™ FAA-3, manufactured by FumaTech) to form a reduced electrode catalyst layer. The catalyst loading was 0.5 mg/ ^cm² per geometric area of Pt metal.

<Preparation of anode>
Au/C (manufactured by Hartagold Co., Ltd.), 10 wt % Fumion™ FAA-3 NMP (N-methyl-2-pyrrolidone) solution, pure water, and 1-propanol (1-PrOH) were mixed in a mass ratio of 4:18:18:60. The resulting mixture was pulverized in a ball mill to obtain a catalyst composition for an oxidizing electrode catalyst layer. This catalyst composition was spray-applied to the side of an electrolyte membrane (trade name: Fumapem™ FAA-3, manufactured by FumaTech Co., Ltd.) opposite the cathode side to form an oxidizing electrode catalyst layer. The catalyst loading was 0.5 mg/ ^cm² per geometric area of Au metal. A membrane electrode assembly (MEA) was obtained through the above process.

<Electrolysis experiment>
The fabricated MEA was sandwiched between the anode and cathode compartments to form a two-compartment electrolytic cell. Using this electrolytic cell, a substrate (anolyte) was supplied from the anode inlet, and constant-potential electrolysis was performed (one-pass system) until 5 mL of electrolyte was collected from the anode outlet (20 minutes). The reaction conditions were as follows:
Catholyte: 1 M potassium hydroxide (KOH) aqueous solution Anolyte: 25 mM benzyl alcohol in a water/acetonitrile (6:4) mixture Substrate flow rate: 0.25 mL/min Reference electrode: Ag/AgCl
Potential: 0 V, 0.2 V, 0.4 V relative to the reference electrode
Temperature: room temperature

<Analysis of Electrolyte>
After the completion of the constant-potential electrolysis, the components of the recovered electrolyte were analyzed by high-performance liquid chromatography (HPLC). Specifically, benzaldehyde was quantified as a molar concentration based on the peak area corresponding to the obtained product and a calibration curve prepared from the measurement results of samples prepared in advance with the substance at a known concentration. From the HPLC analysis results, the current efficiency of the target product, benzaldehyde, was calculated using the following formula:
Current efficiency = (molar concentration of product by HPLC) x (volume of reaction liquid) x (number of reaction electrons) x (Faraday constant 96,480) / (accumulated amount of current) x 100

Example 2
The MEA was fabricated, and the electrolysis experiment and analysis were carried out in the same manner as in Example 1, except that Pt was used instead of Au as the anode metal catalyst.

(Comparative Example 1)
The MEA was fabricated, and the electrolysis experiment and analysis were carried out in the same manner as in Example 1, except that Ketjen black containing no metal catalyst was used as the anode.

(Reference example 1)
The MEA was fabricated, and the electrolysis experiment and analysis were carried out in the same manner as in Example 1, except that Ru was used instead of Au as the anode metal catalyst.

Example 3
MEA fabrication and electrolysis experiments were carried out in the same manner as in Example 1, except that the potential relative to the reference electrode was set to 0.2 V, the anolyte was a 0.5 M 1-propanol aqueous solution, and constant-potential electrolysis was performed in a cyclic manner instead of a single-pass manner. The cyclic manner refers to the circulation of the anolyte. The components of the recovered electrolyte were analyzed by gas chromatography (GC). Specifically, propionaldehyde was quantified as a molar concentration based on the peak area corresponding to the obtained product and a calibration curve created from the measurement results of samples in which the substance was previously prepared at a known concentration. From the GC analysis results, the current efficiency of the target product, propionaldehyde, was determined in the same manner as in Example 1.

Example 4
Except for the potential relative to the reference electrode being 0.2 V and for cyclic constant-potential electrolysis being performed instead of one-pass, MEA fabrication, electrolysis experiments, and analysis were carried out in the same manner as in Example 1. The amount of the converted substrate (benzyl alcohol) (amount of substrate conversion, mmol) and the amount of the target product (benzaldehyde) (amount of product, mmol) were quantified by HPLC, and the conversion yield (amount of product/amount of substrate conversion x 100) was calculated.

Example 5
Except for the fact that the anolyte in the electrolysis experiment was a 1 M aqueous 1-propanol solution, MEA fabrication, electrolysis experiment, and analysis were carried out in the same manner as in Example 3. The amounts of substrate conversion and product were quantified by GC, and the conversion yield was calculated.

Example 6
MEA fabrication, electrolysis experiments and analysis were carried out in the same manner as in Example 5, except that the anolyte in the electrolysis experiments was a mixed solution of 1 M 3-methyl-2-buten-1-ol in water/acetonitrile (6:4).

Example 7
MEA fabrication, electrolysis experiments and analysis were carried out in the same manner as in Example 4, except that the anolyte in the electrolysis experiments was a mixed solution of 25 mM cinnamyl alcohol in water/acetonitrile (6:4).

The type of anode catalyst, potential, and current efficiency for Example 1, Example 2, Comparative Example 1, and Reference Example 1 are shown in Table 1.

As shown in Table 1, in Examples 1 and 2, benzaldehyde was selectively obtained from benzyl alcohol. Examples 1 and 2 confirmed that using Au as the catalytic metal enabled benzaldehyde to be obtained with high current efficiency. Furthermore, HPLC analysis results showed that no benzoic acid or other by-products were detected in Examples 1 and 2. In other words, aldehyde was obtained with 100% selectivity in Examples 1 and 2. In Reference Example 1, benzoic acid was obtained with a current efficiency of 1% at a potential of 0.2 V and 3% at 0.4 V. In addition to benzoic acid, product peaks (unidentified) of similar magnitude were also observed.

The current efficiency in Example 3 is shown in Table 2.

As shown in Table 2, in Example 3, no carboxylic acid was detected, and propionaldehyde was produced, albeit at a low current efficiency. In addition, one by-product (unidentified) with a peak similar to that of propionaldehyde was detected.

The current efficiency and conversion yield for Examples 4, 5, 6, and 7 are shown in Table 3.

As shown in Table 3, in Example 4, aldehyde was obtained in high yield. In Example 5, products other than aldehyde and carboxylic acid were also confirmed, and the conversion yield of the target product was 23%. For 1-propanol in Example 5, a decrease in conversion yield may have been due to volatilization of the substrate. In Example 6, no carboxylic acid was detected, and only aldehyde was selectively obtained. In Example 7, the current efficiency was low at 23%, but only aldehyde was detected in the HPLC analysis, and no peaks derived from other by-products, including carboxylic acid, were detected. Note that cinnamyl alcohol, the substrate in Example 7, is highly sensitive to UV light, and excessive peaks were detected, making it impossible to calculate the conversion yield.

The above provides a detailed description of the embodiments of the present invention. The above-described embodiments merely illustrate specific examples of how the present invention may be implemented. The content of the embodiments does not limit the technical scope of the present invention, and many design changes, such as modifications, additions, and deletions of components, are possible within the scope of the inventive concept defined in the claims. In the above-described embodiments, content for which such design changes are possible is emphasized by using notations such as "in this embodiment" or "in this embodiment," but design changes are also permitted even in content without such notation. Any combination of the above-described components is also valid as an aspect of the present invention. Hatching in cross sections in the drawings does not limit the material of the hatched objects.

10: Aldehyde production apparatus, 44: Supply unit, 60: Control unit, 100: Solid polymer electrolysis unit, 110: Solid polymer electrolyte membrane, 120: Cathode, 122: Cathode catalyst layer, 130: Anode, 132: Anode catalyst layer.

Claims (14)

a solid polymer electrolysis unit;
a supply unit that supplies a substrate to the solid polymer electrolysis unit,
the solid polymer electrolysis unit electrolytically oxidizes the substrate to produce an aldehyde;
the substrate is a primary alcohol and is not 5-hydroxymethylfurfural;
The solid polymer electrolysis unit comprises:
an anode including an anode catalyst layer;
a cathode including a cathode catalyst layer;
a solid polymer electrolyte membrane provided between the anode and the cathode;
the supply unit supplies the substrate to the anode;
the cathode catalyst layer is in contact with one main surface of the solid polymer electrolyte membrane,
The anode catalyst layer is in contact with the other main surface of the solid polymer electrolyte membrane . The aldehyde production apparatus according to claim 1, wherein the substrate is benzyl alcohol or a derivative thereof. 3. The apparatus for producing aldehyde according to claim 2 , wherein water is supplied to the cathode to carry out a hydrogen generation reaction. The apparatus for producing aldehyde according to claim 1 , wherein the cathode catalyst layer contains Pt. 5. The apparatus for producing aldehyde according to claim 1 , wherein the anode catalyst layer contains at least one catalytic metal selected from the group consisting of Ru, Rh, Pd, Ir, Pt, and Au. The apparatus for producing aldehyde according to claim 5 , wherein the anode catalyst layer contains Au. 7. The apparatus for producing aldehyde according to claim 6 , wherein the anode catalyst layer further includes a catalyst support, metal particles containing Au are supported on the catalyst support, and the average particle diameter of the metal particles is 0.2 nm or more and 50 nm or less. 8. The apparatus for producing aldehyde according to claim 7 , wherein the catalyst support is porous carbon. 9. The apparatus for producing aldehyde according to claim 8 , wherein the catalyst carrier is acetylene black. The apparatus for producing aldehyde according to claim 1 , wherein the solid polymer electrolyte membrane contains perfluorosulfonic acid. 10. The apparatus for producing aldehyde according to claim 1, wherein the solid polymer electrolyte membrane is an anion exchange type electrolyte membrane. a solid polymer electrolysis unit including an anode including an anode catalyst layer, a cathode including a cathode catalyst layer, and a solid polymer electrolyte membrane provided between the anode and the cathode, wherein the cathode catalyst layer is in contact with one main surface of the solid polymer electrolyte membrane and the anode catalyst layer is in contact with the other main surface of the solid polymer electrolyte membrane; and the substrate is a primary alcohol , and is not 5-hydroxymethylfurfural . The method for producing an aldehyde according to claim 12 , wherein the anode catalyst layer contains Au, the cathode catalyst layer contains Pt, and the substrate is a solution containing a primary alcohol. 14. The method for producing an aldehyde according to claim 13 , wherein water is supplied to the cathode to generate hydrogen, and the potential of the anode relative to a reversible hydrogen electrode (RHE) is controlled to be 0.6 V or more and 1.8 V or less.