JPH0566322B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for removing hydrogen gas, and more particularly to a method for selectively removing hydrogen gas from a hydrogen-containing gas using electrochemical means. Selective removal of hydrogen gas from hydrogen-containing gas requires a wide range of techniques, including gas purification and separation, control of reaction conditions, atmospheric gas control, and improvement of analytical sensitivity.
It can be used in the industrial field.

[Prior art and problems to be solved by the invention] Conventionally, a typical method for separating and removing hydrogen gas from a mixed gas is to adsorb or absorb hydrogen gas on a metal that absorbs hydrogen. , a method using a polymer membrane or a ceramic membrane having fine pores, and a method using a palladium or palladium alloy membrane are known.

Methods of separating hydrogen gas using hydrogen storage metals include not only single metals such as titanium, zirconium, and niobium, but also alloys such as titanium iron, lanthanum nickel, titanium manganese, magnesium nickel, lanthanum cobalt, and zirconium manganese titanium molybdenum. In this method, a mixed gas containing hydrogen gas is brought into contact with the hydrogen gas, and only hydrogen gas is absorbed and separated. However, this method cannot store hydrogen above the equilibrium concentration determined between the hydrogen concentration absorbed in the hydrogen storage metal and the hydrogen gas partial pressure in the gas.
When the hydrogen concentration in the hydrogen storage metal reaches a value close to the equilibrium concentration, it is necessary to discharge the previously stored hydrogen by heating or reducing pressure, and regenerate it.
Additionally, if oxygen, carbon dioxide, carbon monoxide, water, etc. are contained in a gas containing hydrogen gas, these components may react with the hydrogen storage metal, causing problems such as deterioration of the storage metal. ing. Furthermore, this method has the problem that it is not possible to continuously separate hydrogen gas because it requires periodic replacement or regeneration of the hydrogen storage metal.

On the other hand, as a method for separating hydrogen gas using a polymer membrane, hydrogen gas is separated from a hydrogen-containing gas by utilizing the difference in permeation rate for various gases of polymer membranes such as polysulfone, polyvinyl fluoride, and polyimide. It has been known. However, when a polymer membrane is used, the selectivity of membrane permeation is low, and there is a problem that only hydrogen gas cannot be selectively separated and removed.

In addition, filter-like materials made of ceramics with micropores are being investigated in the same way as polymer membranes, but these are not capable of selectively separating and removing only hydrogen gas, and there are also differences in operating temperature and gas concentration. There were restrictions.

On the other hand, since palladium or palladium alloy has the property of selectively permeating only hydrogen,
By using a thin film of these metals, only hydrogen gas can be separated or removed from hydrogen-containing gas. Industrial methods are being used to utilize this property to make hydrogen gas ultra-high purity.

However, membranes made of palladium or palladium alloys have low hydrogen permeability at low temperatures, so they are usually used at temperatures of 300 to 500°C. Furthermore, even in these temperature ranges, the amount of hydrogen permeation varies depending on the difference in hydrogen partial pressure between both sides of the membrane, so hydrogen gas must be removed in systems with low hydrogen partial pressure or under low temperature conditions. I couldn't do it.

[Means and actions for solving problems]

The present inventors solved the problems of these conventional techniques and selectively and continuously removed only hydrogen gas from a hydrogen-containing gas at a practical speed even at a relatively low temperature and low hydrogen partial pressure. As a result of intensive research in order to find a method, it was discovered that these objects could be achieved by using a thin film of palladium or palladium alloy as an anode of a water electrolyzer, and the present invention was completed.

That is, the present invention uses a water electrolysis device that uses a thin film of palladium or palladium alloy as an anode and is filled with a 0.1 to 20% aqueous solution of an alkali metal hydroxide as a water electrolyte, and heats the water electrolyte at 40 to 100°C. While maintaining a predetermined temperature in the range of
A hydrogen gas removal method characterized in that hydrogen gas is selectively removed from the hydrogen-containing gas by applying a set voltage selected from a range of 0.2 to 10 volts so as to achieve ~2A/ ^cm2 . . In practical terms, the thickness is usually 0.001 to 5 mm, preferably 0.01 to 1 mm, from the viewpoint of mechanical strength. Further, the material for the thin film may be palladium alone or a palladium alloy, but a palladium alloy that does not easily cause plastic deformation of the thin film is preferable. As these alloys, alloys of palladium and silver, gold, rhodium, ruthenium, yttrium, etc. are preferable, such as alloys of palladium and 5 to 50% silver, palladium and 5 to 50% silver, etc.
An alloy consisting of 40% gold and 1 to 20% gold, and an alloy consisting of palladium and 5 to 40% silver, and 2 to 10% rhodium or yttrium are preferably used. These thin films may be used as they are, but they may be coated with palladium black or platinum black on the side where hydrogen-containing gas flows, or activated with molten alkali such as caustic soda or caustic potash. Preferably.

In the present invention, the water electrolytic cell itself may be used as a cathode, and in addition, a metal rod or plate may be provided inside the tank and both may be used as a cathode, or the water electrolytic cell itself may not be used as a cathode. Only the metal rod or plate provided therein may serve as the cathode. Further, it is preferable that the anode and the cathode be arranged so that the distance between the water electrolytic surface of the anode and the opposing surface of the cathode is as equal as possible.

The material of the cathode is not particularly limited, but metals that are electrochemically resistant to corrosion and have low overvoltage during hydrogen generation are preferred, such as nickel, nickel alloys, and nickel chrome steel.

The aqueous electrolyte solution must have a high conductivity and a composition that allows water electrolysis to occur selectively, and sodium hydroxide and hydroxide are solutions that have low electrochemical corrosive effects on the electrode materials and the constituent materials of the electrolytic device. A 0.1-20% aqueous solution of an alkali metal hydroxide such as potassium is used. In the present invention, the aqueous solution in the water electrolyzer is maintained at a predetermined temperature in the range of 40 to 100°C,
Also, the pressure inside the water electrolyzer is usually normal pressure to 5 kg/cm ² G.
It is said that

In the present invention, a hydrogen-containing gas is caused to flow and a voltage is applied. The voltage applied here is the voltage required for current to flow in a state where hydrogen-containing gas is flowing. In the present invention, even if a voltage slightly lower than the voltage at which water electrolysis occurs without flowing hydrogen-containing gas is applied, no current is generated, and therefore neither hydrogen gas nor oxygen gas is generated.

On the other hand, by flowing a hydrogen-containing gas under this voltage in contact with the back side of the electrolytic surface of the thin film (anode), a current is generated and the hydrogen in the hydrogen-containing gas is removed by diffusing and passing through the thin film. At this time, a corresponding amount of hydrogen gas is generated from the cathode, but almost no oxygen gas is generated from the anode. Electricity is therefore consumed only when there is hydrogen gas to be removed, in which case an amount of electricity corresponding to the electrochemical equivalent of hydrogen removed, ie approximately 1 faraday for the removal of 1 gram equivalent of hydrogen. (96500 clones) of electricity is consumed. In addition, when a voltage that causes normal water electrolysis is applied while flowing hydrogen-containing gas, water electrolysis occurs and at the same time hydrogen in the hydrogen-containing gas is preferentially removed, and the consumed electricity is removed from the cathode. An electrochemical equivalent of hydrogen gas corresponding to the amount of hydrogen gas is generated, and only oxygen gas of an electrochemical equivalent equivalent to the amount of electricity obtained by subtracting the amount of electricity required to remove hydrogen from the hydrogen-containing gas is generated from the anode.

The voltage applied between the anode and the cathode is set in the range of 0.2 to 10 volts depending on the material of the electrode, the concentration of the electrolyte, the temperature, the distance between the two electrodes, the current density, etc.

Regarding the current density on the anode surface, if the current density is too low, the amount of hydrogen removed per unit area of the anode is too small to be practical, and if it is too high, the applied voltage must be increased, so the power The current density is 0.01 because efficiency decreases.
The applied voltage is set within the above range so that it is ~2 A/cm ² . The distance between the anode and cathode also varies depending on the voltage, current density, shape and size of the electrolytic cell, etc., but is usually 0.5 to 100 mm, preferably 0.5 to 50 mm.
It is assumed to be mm.

Next, the present invention will be specifically explained with reference to the drawings.

FIG. 1 is a longitudinal sectional end view showing an example of a water electrolysis device used in the present invention.

In Figure 1, the upper end is closed and the lower end is open, and around the opening is a flange 1 that also serves as a cathode terminal.
A metal cylindrical container having
The water electrolyzer 2 also serves as a cathode. The upper side wall of the water electrolyzer (cathode) 2 is provided with a discharge pipe 3 for extracting generated hydrogen gas and oxygen gas, and the opening at the lower end of the water electrolyzer (cathode) 2 is disc-shaped and insulated. It is closed with a gasket 4 having a property. A thin film tube (anode) 6 made of palladium alloy, with a flange 5 that also serves as an anode terminal attached around the lower open end, is inserted from the bottom of the water electrolyzer (cathode) 2 through the center of the gasket 4. The upper end is connected to an insulating tube 7 for supplying hydrogen-containing gas, which is provided through the upper part of the water electrolyzer (cathode) 2 . The lower flange 5 of the thin film tube (anode) 6 is further connected to a flange 10 having a gas vent pipe 9 and a flange 1 of the water electrolytic cell (cathode) 2 via a ring-shaped insulating gasket 8 below. They are tightened and fixed by insulating bolts 11, . . . , 11 between them. Flowmeters 12 and 1 are installed in the insulating tube 7 and the gas vent tube 9.
3 are arranged respectively. Water electrolyzer (cathode)
The internal space of 2 is filled with an electrolytic solution 14.
Also, a heater 15 is placed around the water electrolyzer (cathode) 2.
is provided. The positive side of the DC power supply 16 is installed on the flange 5 of the thin film tube (anode) 6, and the negative side is installed on the flange 1 of the water electrolyzer (cathode) 2, and a voltmeter 17 and an ammeter 18 are installed in the middle of the wiring. are arranged respectively.

During the hydrogen gas removal operation, a voltage is applied between the thin film tube (anode) 6 and the flange of the water electrolyzer (cathode) 2 by the DC power supply 16, and hydrogen is transferred from the insulating tube 7 into the thin film tube (anode) 6. By flowing the containing gas, only the hydrogen in the hydrogen-containing gas selectively diffuses and permeates from the inside of the thin film tube (anode) 6 to the outside (the surface in contact with the electrolyte) and is removed, while the hydrogen is removed from the cathode. Gas is generated. When the applied voltage is lower than the voltage at which normal water electrolysis occurs, hydrogen gas in the hydrogen-containing gas is removed and hydrogen gas equivalent to the amount of electricity passed from the surface of the water electrolyzer (cathode) 2 is released. Oxygen gas is not generated from the outer surface of the thin film tube (anode) 6. In addition, when the applied voltage is a voltage that causes normal water electrolysis, hydrogen in the hydrogen-containing gas is preferentially removed, and the electrochemical equivalent equivalent to the amount of electricity flowing from the water electrolyzer (cathode) 2 is of hydrogen gas is generated, and from the outer surface of the thin film tube (anode) 6, oxygen gas with an electrochemical equivalent equivalent to the amount of electricity after subtracting the amount of electricity required to remove hydrogen from the hydrogen-containing gas is generated, and each gas is extracted to the outside through the discharge pipe 3. During this time, the temperature of the electrolytic solution 14 is adjusted appropriately by the heater 15. The amount of hydrogen gas removed from the hydrogen-containing gas is determined from the difference in the flow rates indicated by the flow meters 12 and 13 provided in the insulating tube 7 and the gas extraction tube 9.

〔Effect of the invention〕

The method of the present invention has many excellent effects as follows.

1 Only hydrogen gas in a hydrogen-containing gas stream can be selectively and continuously removed.

2. It can be operated at relatively low temperatures and at low hydrogen partial pressures, and does not require particularly high temperature heating or pressurization.

3. High energy efficiency, as power efficiency can be maintained at nearly 100% when operated at a voltage slightly lower than that at which water electrolysis occurs.

4. It can be carried out using relatively simple equipment, and operation and maintenance of the equipment are also easy.

5. It can be operated regardless of the hydrogen gas concentration, and has a wide range of industrial uses, such as purifying gas by removing hydrogen and adjusting the hydrogen concentration in gas used for reactions and analysis.

〔Example〕

Example 1 In a device similar to that shown in FIG.
A cylindrical nickel electrolytic cell with a length of 260 mm is used as the cathode, and the center part of this electrolytic cell has an outer diameter of 1.6 mm and a wall thickness of 1.6 mm.
0.08mm, length 200mm, 70% palladium, 20% silver,
An alloy thin-film tube made of 10% gold and coated with black palladium on both the inner and outer surfaces was placed as an anode.

The gas flowmeter used in this example was a precision membrane flowmeter SF-11 [L] manufactured by Estec Co., Ltd., the voltmeter was a digital voltmeter TR-6320 manufactured by Takeda Riken, and the ammeter was manufactured by Yokogawa Hokushin Co., Ltd. Precision ammeter TYPE 2012. In addition, a DC power supply with a slide regulator manufactured by Kyoritsu Riko was used. A 4% aqueous sodium hydroxide solution was placed inside the water electrolytic cell as an electrolyte.
The outer surface of the water electrolyzer was heated to maintain it at 65°C using a heater.

At a room temperature of 24°C, hydrogen gas was flowed at 17.40 ml per minute at normal pressure from the top to the bottom inside the thin film tube, and a DC voltage was applied so that a current of 1A would flow between the electrode terminals, with the thin film tube as the anode and the electrolytic cell as the cathode. When the application was adjusted, hydrogen gas was continuously generated from the cathode surface. On the other hand, no generation of oxygen from the anode was observed. The terminal voltage at this time was 0.84 Volt.
In addition, the outlet gas flow rate from the bottom of the thin film tube is 9.80ml per minute.
This was a decrease of 7.6ml per minute compared to the inlet gas flow rate. Calculating the amount of hydrogen removed relative to the amount of electricity from this reduction in gas flow rate and current value, it means that 1 gram equivalent of hydrogen was removed per Fara day (96500 clones), which means that hydrogen was removed with 100% current efficiency. I found out that

Comparative example When the gas flowing inside the thin film tube was changed to nitrogen gas instead of the hydrogen gas in Example 1, a
Even when a voltage of 0.84 Volt was applied, a current of only 0.0001 A flowed, and no water electrolysis reaction was observed.

Example 2 Using the same water electrolysis device as in Example 1, the room temperature was 20°C,
Using the same method at a water electrolyzer temperature of 65°C, 121.0 ml of nitrogen gas containing 24.9% hydrogen gas by volume was produced per minute.
At the same time, the current value between the two pole terminals is
The voltage was applied while adjusting it to be 2.0A.
The voltage at this time was 0.88 to 0.91 Volt. In this case as well, hydrogen gas was generated from the cathode, but almost no oxygen gas was observed from the anode.
At this time, the gas flow rate at the outlet of the thin film tube was 106.1 ml per minute, and if we calculated that all of the reduced gas amount was due to the removal of hydrogen, it would have been removed with a current efficiency of 99.6%.

Example 3 Using the same water electrolysis device as in Example 1, the room temperature was 20°C,
The terminal voltage was adjusted so that the current was 1.0 A while flowing nitrogen gas containing 10% hydrogen by volume at a rate of 51.70 ml per minute at a water electrolyzer temperature of 65°C. The terminal voltage at this time was 1.83 Volt. Furthermore, the gas flow rate at the outlet of the thin film tube was 46.5 ml per minute, and no hydrogen gas was observed in this gas, indicating that it was almost completely removed. In addition, in the case of this example, hydrogen gas was generated from the cathode, and oxygen gas was also generated from the electrolytic surface of the thin film tube (anode).

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional end view showing an example of a water electrolysis device used in the present invention. In the figure, 1, 5 and 10... flange,
2...Water electrolyzer (cathode), 3...Discharge tube, 4 and 8...Gasket, 6...Thin film tube (anode), 7
...Insulation tube, 9...Gas vent pipe, 11...
Volts, 12 and 13...flow meter, 14...electrolyte, 15...heater, 16...DC power supply, 1
7... voltmeter and 18... ammeter.

Claims (1)

[Claims] 1 A thin film of palladium or palladium alloy is used as the anode, and alkali metal hydroxide is used as the water electrolyte.
Using a water electrolyzer filled with a 0.1-20% aqueous solution, the aqueous electrolyte is kept at a predetermined temperature in the range of 40-100°C while contacting the back side of the electrolytic surface of the palladium or palladium alloy thin film. Selectively removing hydrogen gas from the hydrogen-containing gas by flowing the hydrogen-containing gas and applying a set voltage selected from the range of 0.2 to 10 volts so that the current density is 0.01 to ² A/cm2. A method for removing hydrogen gas, characterized by: