JPS60251101A - Production of hydrogen - Google Patents

Abstract

PURPOSE:To produce hydrogen of high purity with a short process and reduced cost effectively by passing steam through a diaphragm constituted of an O<->- electroconductive solid electrolyte composed of Sm, Nd, F and O as constituting components to transfer the oxygen in the steam to an O2 accepting substance selectively. CONSTITUTION:An O<->-electroconductive solid electrolyte expressed by the formula is prepd. as the material for the diaphragm, by mixing pulverized neodymium oxide with samarium fluoride or samarium oxide with neodymium fluoride, and treating the mixture at 1,200-1,400 deg.C in an inert gaseous atmosphere. Suitable thickness of the obtd. soild electrolyte is generally 1mu-5mm.. A gas-permeable material, such as Au for the anode, Pt for the cathode is used in this invention. The electrodes are provided by screen printing on the solid electrolyte to prepare a diaphragm, and steam is allowed to contact one side of the diaphragm. Oxygen which has passed through the diaphragm selectively is absorbed by an O2-accepting substance (e.g. CO). H2 is separated by the diaphragm and recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing hydrogen, particularly a method for producing hydrogen using a novel oxygen ion conductive solid electrolyte having high permselective properties for oxygen.

Reflecting the energy situation in recent years, various methods have been proposed for obtaining hydrogen, such as methods for obtaining it by electrolyzing the inexhaustible water, and methods for obtaining hydrogen by decomposing hydrocarbons and the like using various methods.

However, in many of these methods, the step (b) is complicated, the equipment cost is high, and it cannot necessarily be said that it is a means for efficiently obtaining high-purity hydrogen.

Recently, stabilized zirconia doped with calcium oxide or yttrium oxide, which has the property of selectively permeating oxygen, has been used for partition walls, carbon oxide or methane gas has been used as an oxygen acceptor, and high temperature (approximately 700°C) A method to obtain high purity hydrogen by decomposing water vapor has been proposed.

This method is attracting attention as a means of shortening the process, reducing costs, and efficiently obtaining high-purity hydrogen compared to conventional methods, but the conductivity of the stabilized zirconia used as the partition wall is not necessarily sufficient. In addition, in practical use, 70
It has the property of not being able to transfer oxygen sufficiently unless it is placed at a high temperature of 0° C. or higher, and there are considerable problems in practical use, such as the fact that there are considerable restrictions on the materials, especially when electrodes are used.

In order to eliminate such problems, the inventors of the present invention have conducted various studies and found that the object can be achieved by using a fluorinated oxide having a specific composition in place of stabilized zirconia.

Thus, the present invention provides a method in which a substance capable of accepting water vapor is present on one side of the diaphragm and a substance capable of accepting oxygen is present on the other side, and oxygen in water molecules is transferred to the oxygen-accepting substance through the membrane.
In the method of decomposing water vapor to obtain hydrogen, the general formula % a+ b = 12. The present invention provides a method for producing hydrogen characterized by using an oxygen ion conductive solid electrolyte represented by c+2d=38). Examples of the oxygen-accepting substance used in the present invention include carbon oxide and hydrocarbons such as methane and ethane, and one or more of these can be used as appropriate.

The amount of these substances to be used is strictly determined by the difficulty of the substance in accepting oxygen, the amount of hydrogen to be obtained, the reactivity per unit time, etc., but in general, it is 0.1% of the amount of water vapor supplied. It is appropriate to adopt approximately -10 times.

The solid electrolyte used in the present invention has a ratio of cations and anions of Sm/N.
d=0.222-4.5, Flo=1-9.

In the composition range of these solid electrolytes, a=4 to 8,
b=4~B, c=18~24. d=8~9, and a+b
=12 and c+2d=38 is particularly preferred since it exhibits particularly high conductivity. Also, when this is expressed as the ion ratio of cations and anions, Sm/Nd
= 0.5-2, which corresponds to F/0 = 2-4.

These solid electrolytes have the advantage of having sufficiently higher conductivity at low temperatures than those conventionally proposed.

The method for producing the oxygen ion conductive solid electrolyte used in the present invention involves pulverizing and mixing neodymium oxide and resonance samarium fluoride or samarium oxide and neodymium fluoride, and holding the mixture at 1200 to 1400°C for about 2 to 8 hours in an inert gas atmosphere. It can be obtained by forcing. For example, Sm6 Nd6
To obtain F1@09, 1 mol of Nd2O3 and 2
Pulverize and mix mol of S■F3 or 1 mol of 511203 and 2 mol of NdF3, and 1 mol of NdF3 in an argon gas atmosphere.
It can be easily obtained by firing at 350°C for about 3 to 4 hours.

In addition, the shape of these solid electrolytes can be imparted by, for example, plasma spraying, vacuum evaporation, sputtering, etc. when obtaining a thin film-like material, and hot-breathing, rubber-pressing, hot isostatic sintering when obtaining a relatively thick shape. Closing methods, etc. may be adopted as appropriate.

The thickness of the solid electrolyte used in the present invention is generally Ig~5
A value of about mm is appropriate. If the thickness is less than the above range, it will be non-uniform and gas leakage will easily occur, whereas if it exceeds the above range, there is a risk that the resistance loss will become significantly large, which is not preferable.

Further, the material for the anode used in the present invention includes, for example, perovskite materials such as platinum, silver, cobalt, or LaCoO3, and the material for the cathode includes, for example, metallic materials such as platinum, silver, and nickel. A perovskite-based oxide material or the like can be appropriately employed.

In addition, gas must be able to pass through both of these anodes and anodes, and for this reason, it is recommended that these electrodes have physical properties that are porous, difficult to semi-melt, and have good adhesion to the solid electrolyte. Appropriate.

The thickness of these electrodes is generally about several thousand to about 100 μl.

These electrodes can be provided on the solid electrolyte by means such as screen printing or sputtering.

Next, the present invention will be explained by examples.

Example 1 1 mole of 5II203 and 2 moles of NdF3 were pulverized and mixed using a ball mill, and then milled to a diameter of 20 mm by bar press method.
It was molded into pellets with a thickness of 2Il11 mm. 3. The pellets were heated at 1350°C in an argon gas atmosphere.
It was baked for 5 hours. The result of subjecting this pellet to X-ray diffraction is as shown in Figure 1, and the composition is Sm6Nd6F
It was 1809. A PT wire was attached to both sides of the pellet by baking coarse PT powder, and the entire pellet was attached to one end of a sintered alumina tube with alumina cement to prepare a steam electrolysis cell.

This cell was inserted into an electric furnace and heated to 600° C., and CO gas was supplied to the inside at a flow rate of 50 mJL/min, and water vapor-saturated Ar gas was supplied to the outside at a flow rate of 25 m1/min. After 1 hour, the amount of hydrogen gas produced was measured and found to be 0.6 exchanges/min (calculated at room temperature).

Example 2 0.25 mol 5l1203 and 0.75 mol NdF3
The powder was mixed, shaped and fired in the same manner as in Example 1.

The results of X-ray diffraction of this sintered body are shown in Figure 2, and the composition is Sm4.8Nd7.2 F21.607
．． It was 2. The amount of hydrogen produced was measured under the same conditions as in Example 1, and the result was 0.4 h/min.

Example 3 0.3 mol of 511203 and 0.7 mol of NdF3 were mixed, molded, and fired in the same manner as in Example 1. The results of subjecting this sintered body to X-ray diffraction are as shown in Figure 3, and the composition was S''5.5.Nd6.5 F19.4 os3. A steam electrolysis cell was made using this. Example 1
The hydrogen production amount was measured under the same conditions as 0.5m/min.

[Brief explanation of the drawing]

1 to 3 are X-ray diffraction patterns of the compositions used in the present invention shown in Examples.

Claims (1)

[Claims] 1. A method for decomposing water vapor to obtain hydrogen by allowing a substance capable of accepting water vapor to exist on one side of a diaphragm and oxygen in the other, and transferring oxygen in the water vapor to the oxygen-accepting substance through the membrane, General formula SmaN as a diaphragm
dbFoOd (however, a= 2.18~9.82.b
= 2.18~9.82°c = 12-29.45.
d=3.25-12, and a+b=12. C+ 2
A method for producing hydrogen, characterized by using an oxygen ion conductive solid electrolyte represented by d=36).