JPS63219593A - Hydrogen production - Google Patents

Abstract

PURPOSE:To efficiently produce hydrogen by electrolysis, by using an aqueous solution of sulfuric acid or an aqueous solution containing high-polymer sulfonic acid as an electrolyte, by using an electrolytic cell having a diaphragm, and by supplying a specific reductant into an anode chamber so as to carry out electrolysis. CONSTITUTION:An aqueous solution of sulfuric acid or an aqueous solution containing high-polymer sulfonic acid is poured, as an electrolyte 5, into an electrolytic cell having a diaphragm 10 composed of ion exchange membrane, glass filter, nonwoven fabric, etc., and partitioned into an anode chamber 11 and a cathode chamber 12, and, a substance in which the metallic elements of groups VI, VII, and VIII, such as Pt, Ru, Re, Ir, etc., are dispersed and incorporated into a conductive carbon carrier is used as an anode 1 and, as a cathode 2, a substance in which noble metals such as Pt, Au, Ir, etc., or metals such as Pb, Nb, Ta, etc., or graphite, etc., are dispersed and incorporated into a conductive carbon carrier is used. A reductant composed of liquid fuel of aqueous solution of methanol, ethanol, etc., is added into the anode chamber 11 to carry out electrolysis. Hydrogen due to the decomposition of methanol, etc., is evolved from the surface of the cathode 2, and taken out from an exhaust port 15.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing hydrogen, particularly hydrogen production in which methanol, ethanol, formaldehyde, and formic acid are wet-modified into hydrogen by an electrochemical method. Regarding the method.

[Conventional technology]

From an industrial perspective, hydrogen is generally produced through (1) a water gas reaction between coke and steam ();
2) Reforming reaction of natural gas and methanol (198
1, National Fuel S1l Sesinar, Abstract and JP-A-6O-2
(24166), (3) electrolysis of water (), and on a larger scale, (4) gasification of petroleum and coal.

[Problem that the invention attempts to solve]

Looking at the above-mentioned conventional technology, the water gas reaction between coke and steam is a reaction shown in equation (1) that proceeds at a high temperature of about 1000°C, and hydrogen production under high pressure such as supply of steam. It is. In the methanol reforming reaction, formula (2), methanol and water are supplied as steam, and the reaction usually proceeds over a catalyst such as copper-zinc at a high temperature of 250 to 450°C.

C+H20→CO+Hz...
(1) CHsOH + HzO → CO2 + 3H2- (2) In addition, gasification of petroleum and coal, which is becoming larger in scale, involves reactions at high temperatures and high pressures, and the systems are also becoming more complex.

In the above production method, carbon monoxide and carbon dioxide gas are generated even in the hydrogen production reaction, and it is inevitable that side reactions will proceed in equilibrium, so additional steps are required to obtain highly pure hydrogen. It becomes necessary. In addition, disproportionation reaction (2C○=C
It is necessary to take into account blockages caused by carbon precipitation due to +CO, ).

When looking at relatively small-scale processes such as electronic material processes, or high-purity hydrogen supply sources, cylinders produced by electrolysis of water or reactions between acids and metals are generally used.

In water electrolysis, as shown below, between the positive and negative electrodes,
Negative electrode with electrical energy added through current: 2HzO
→02+ 4 H++ 4 e -(3)(E
o=1. , 23 V) Positive electrode: 4 H++ 4 e −+ 2 H2− (4)
(E o = OV) total 2HzO→Oz+2Hz
It generates hydrogen in the -(5) state. The work (W) of this reaction is the product of the current (i) passed and the voltage (V) between the two poles, and the voltage between the two poles is the theoretical voltage 1.23
By approaching V, W=iXV (6), efficiency is improved.

Currently, high-purity hydrogen sources such as electronic material processes are
The above-mentioned water electrolysis is the main method, but there is a problem in that it consumes a lot of power.

An object of the present invention is to provide a method for producing high-purity hydrogen using electrochemical supplementation, which is relatively low temperature (~60°C), normal pressure, has a simple system, and can reduce electrical work. It is.

[Means for solving problems]

The present inventors have proposed that in an electrolytic cell consisting of an anode that performs an oxidation reaction, a cathode that performs a reduction reaction, and an electrolyte located between the two, a reductant is supplied to the anode, and an oxidant is made non-coexisting with the cathode. This is achieved by electrochemically generating hydrogen from the cathode.

[Effect]

The present invention will now be described in detail, particularly in comparison to the reforming reaction of methanol and the electrolysis of water.

In the electrochemical methanol oxidation reaction, the following reaction proceeds at the anode (negative electrode).

Anode: CHsOH+HzO-+COx+6 old+6
e.=(7) (Standard potential Eo=0.04V) If current is applied without supplying an oxidant (eg, oxygen) to the cathode, the following reaction will occur.

Anode: CHaOH+ )120→C(h+6 old+
6e - (7) Cathode: 61N++6e→3Hz
...(8) (Standard potential E o =
OV) total CHaolI + H2,O→CO
z+3Hz ''・(2) This total equation is the methanol reforming reaction mentioned above, which is usually a catalytic reaction at 300℃ and is proceeded at high temperature.
), By electrochemically reacting with formula (8), methanol can be reformed wet and at low temperatures, which has great merits.

In addition, the electrolysis of water, which is an electrochemical reaction, proceeds as follows: anode: 2H20→Oz+411++4e (Eo=1,2
3 V) -(3) Cathode: 4H++4e-+2Hz (Eo=OV) -(4
)2H20→Oz+2Hz The standard potential of the anode 1 (negative electrode) reaction is 1.23V, and the standard potential of the cathode 2 (positive electrode) is Ov. Figure 1 shows a model when current is passed through these two electrodes. As shown in Figure 1, oxygen is generated from the anode,
Hydrogen is generated from the cathode. (3), (4)
As shown in the formula, the amount of hydrogen generated is controlled by the amount of current, but as shown in Figure 1, when the current is increased, the anode becomes more polarized to the positive side and the cathode to the negative side.
The applied voltage increases.

On the other hand, looking at the oxidation of methanol, which is the subject of the present invention, the standard voltage is 0.04 from equations (7) and (8).
The voltage is lower than the standard voltage for water electrolysis, which is 1.23V, and the efficiency is higher. Fig. 2 shows an example of the experiment, and Fig. 3 shows a model diagram when current is applied.

In Figure 2, an anode 1 and a cathode 2 are placed in an electrolytic cell at a distance of 1 m through a gas filter (4G), and a 1.5 mol/Q sulfuric acid aqueous solution is used as an electrolytic solution in the cell. Contains 4% methanol. When an electric current is passed from outside, carbon dioxide gas 3 (Co
w) , hydrogen 4 is produced at the cathode. From Figure 3,
When a current is passed through the anode and cathode, the polarization increases. However, it can be seen that the applied voltage is reduced compared to water electrolysis due to the lower standard potential in equation (7). This gives electricity from the outside. In other words, the efficiency is good because the electrochemical work amount (W=iXV) is low (V (voltage between electrodes)), and the merits of the present invention are obvious.

As an electrode in the present invention, it can be used as long as it is chemically stable with respect to the electrolyte and conductive, and as an anode, it has excellent methanol oxidation activity (the anode shown in Figure 3 has small polarization). containing one or more metals such as platinum, ruthenium, rhenium, tin, iridium, etc., or to increase the reaction area.
The above-mentioned metal may be dispersed and contained in a conductive carbon carrier. The cathode may contain one or more of noble metals such as platinum, gold, iridium, rhodium, ruthenium, and osmium, base metals such as lead, niobium, tantalum, zirconium, and hafnium, and carbon materials such as graphite, or conductive carbon. Dispersion and inclusion in a carrier can be applied. The method of containing the catalyst may be any of the usual catalyst preparation methods such as a deposition method, an impregnation method, an intercurrent method, and a kneading method.

As the electrolyte in the method of the present invention, an electrolytic solution and/or a diaphragm containing an electrolytic solution are used, and specific examples of the electrolytic solution include an aqueous sulfuric acid solution and/or an aqueous solution containing a polymeric sulfonic acid.

As for the reaction conditions, the sulfuric acid concentration in the electrolyte is set to the oxidation potential of the anode (current density 60 mA/ad) as shown in Figure 4.
) of 0.5 to 3.0 Ilol/Q (4% methanol) is suitable. The reaction temperature is based on the 7-node characteristic shown in Figure 5 (in 4% methanol-1,5n+ol/Q sulfuric acid aqueous solution)
The higher the temperature, the lower the oxidation potential, but the decomposition temperature of methanol is 64 ° C (100% methanol),
Room temperature to 60°C is desirable from the utilization rate.

Moreover, the methanol purity does not need to be 100%, and although it is related to the amount of hydrogen production, there is an advantage that it can be applied from about a few percent.

In addition to methanol, substances mixed with formic acid, formaldehyde, ethanol, etc. can also be used.

〔Example〕

EXAMPLES The present invention will be illustrated in more detail by examples below, but the present invention is not limited to the following examples.

Example 1 This example describes the production of an electrode used in a method of electrochemically reforming hydrogen into hydrogen using particularly methanol and ethanol as reductants.

(1) Take 4.5 g of catalyst powder carrying 30v and % of platinum on an anode carbon carrier (Furnace Black: Cabot), add water, mix, and add Polyflon dispersion (D-1: Daikin) to Polyflon dispersion (D-1: Daikin). 30v as tetrafluoroethylene
t%, and then carbon paper (E-7
15: Kureha Kagakusha) Coated on 250x300, after air drying,
Anode A was obtained by burning in an air electrode at 300°C for 30 minutes.

Anode B was prepared using the same specifications as anode A by taking 6.7 g of a catalyst in which 5C++t% of platinum and ruthenium were supported on a carbon carrier.

6.7 g of a catalyst in which 50 tzt% of platinum and tin were supported on a carbon carrier was taken, and anode C was produced with the same specifications as anode A.

(2) Catalyst powder with 20 wt% platinum supported on cathode carbon carrier
After mixing by adding water, polytetrafluoroethylene was added in an amount of 50 wt %, and cathode A was produced in the same manner as anode A.

A 40a+esh platinum mesh was used as cathode B.

Example-2 1.5 mol/
12 Add sulfuric acid and 5wt% methanol, and place anode A (50x50am) on the anode and cathode A (50x50am) on the cathode.
0x501111) at a current density of 6 at 60°C.
Hydrogen was produced by passing a current of 0 mA/d. At this time,
When the voltage between the two electrodes was measured, it was 30.69V.

Example-3 Same as Example-2 except that Anode B is used as the anode. The voltage between the electrodes was measured.

The result was 0.43V.

Example-4 The voltage between both electrodes was measured in the same manner as in Example-2 except that Anode C was used as the anode.

The result was 0.45V.

Example-5 Anode B is used as the anode, and cathode B is used as the cathode.
The same test as in Example 2 was conducted using the following. The voltage between both electrodes was 0.44V.

Comparative Example-1 Anode A was used as the anode, cathode A was used as the cathode, and a sulfuric acid electrolyte of 1.5 mol/Q was used.
Voltage decomposition of water was carried out under the same conditions as in Example 2. At this time,
When the voltage between the two electrodes was measured, it was 2.33V.

Comparative Example-2 The same electrode as in Example-3 was used, and the same test as in Comparative Example-1 was conducted. The voltage between the two poles was 2.32V.

Comparative Example-3 Using the same electrode as in Example-4, the same test as in Comparative Example-1 was conducted. The voltage between the two poles was 2.33V.

Comparative Example-4 Using the same electrode as in Example-5, the same test as in Comparative Example-1 was conducted. The voltage between the two poles was oOv.

Example 6 A unit cell schematically shown in FIG. 6 is constructed. This is 10
0 x 128m (7) 7/-do B and 1.5mol/Q
Using cathode A holding sulfuric acid, 1,
Ion exchange membrane (CM) containing 5 mol/Q sulfuric acid
V:M glass) to bring them into close contact with each other. Into the anode chamber of this cell, add 1, , 5 mol/Q methanol and 1.5 mol/Q sulfuric acid at 200 mQ/1 lin.
The temperature of the cell was kept constant at 60°C. A current of 7.7 A was applied to this cell from the outside, and the cell voltage at that time was measured.

As a result, the voltage was 0.42V.

Comparative Example-5 In the anode chamber of the unit cell of Example-6, ■, 5 mol/
The cell voltage was measured in the same manner as in Example 6, except that 12 sulfuric acid aqueous solution was supplied. The result was 2.30V.

〔Effect of the invention〕

As described above, the method of electrochemically reforming a reductant such as methanol into hydrogen according to the present invention can (a) operate at a lower temperature and normal pressure than conventional hydrogen production methods.

(b) High purity hydrogen can be produced.

(c) Reduce electrochemical workload.

・V of work W=iXV: Voltage can be lowered.

・115 of water electrolysis while satisfying (a) and (b)
The following was possible.

It has the advantage of

Further, by stacking a plurality of unit cells as shown in Example 6, it is possible to make the device compact.

As described above, the present invention has superior effects compared to other hydrogen production methods.

[Brief explanation of the drawing]

Figure 1 is a current density-potential characteristic model diagram for water electrolysis.
Figure 2 is a schematic diagram of a methanol reformer to hydrogen, Figure 3 is a current density-potential characteristic model diagram for methanol reforming, and Figure 4 is a diagram of a current density-potential characteristic model diagram for methanol reforming.
The figure shows the sulfuric acid concentration in the electrolytic solution and the anode performance diagram, Figure 5 shows the operating temperature and anode performance diagram, and Figure 6 shows the schematic diagram of the methanol reformer to hydrogen. 1... Anode, 2... Cathode, 3... Carbon dioxide gas, 4... Hydrogen, 5... Sulfuric acid + methanol aqueous solution,
6...Power supply, 7...Voltmeter, 8...Ammeter, 9.
...Glass filter, 10...Ion exchange membrane, 11.
...Anode chamber, 12...Cathode chamber, 13°゛°Ad'-terminal, 14°°　Power y+,... Do terminal, 15.
...Hydrogen outlet.

Claims (1)

[Scope of Claims] 1. In an electrolytic cell consisting of an anode that undergoes an oxidation reaction, a cathode that undergoes a reduction reaction, and an electrolyte located between the two, a reductant is supplied to the anode, and an oxidant does not coexist with the anode. A hydrogen production method characterized by electrochemically generating hydrogen from a cathode by. 2. The hydrogen production method according to claim 1, wherein the anode contains one or more types of group VI, VII, or VIII elements and/or coexists with a conductive carbon material. 3. The method for producing hydrogen according to claim 1, characterized in that the cathode contains platinum and/or a conductive carbon material. 4. The hydrogen production method according to claim 1, wherein the electrolyte is an electrolytic solution and/or a diaphragm containing an electrolytic solution. 5. The hydrogen production method according to claim 4, wherein the electrolyte comprises an aqueous sulfuric acid solution and/or an aqueous solution containing a polymeric sulfonic acid. 6. The diaphragm is an ion exchange membrane, a glass filter, or a nonwoven fabric.
5. The method for producing hydrogen according to claim 4, wherein the hydrogen production method is characterized in that the hydrogen production method comprises at least one species. 7. The method for producing hydrogen according to claim 1, wherein the reductant is a liquid fuel. 8. The hydrogen production method according to claim 7, wherein the liquid fuel consists of methanol and/or ethanol aqueous solution. 9. Liquid fuel is formaldehyde, formic acid, methanol,
8. The hydrogen production method according to claim 7, wherein the hydrogen production method is one or more types of ethanol. 10. The method for producing hydrogen according to claim 8, wherein the liquid fuel is composed of an aqueous methanol solution, and 1 mole or more of water is mixed with 1 mole of methanol.