JPS634639B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a mixed gas containing a relatively low concentration of hydrogen at a predetermined concentration from a mixed gas containing a relatively high concentration of hydrogen, and has the object and The object of the present invention is to provide an efficient and simple method for producing a mixed gas containing hydrogen at a predetermined concentration using an electrochemical method.

In recent years, there has been active research into methods for producing basic chemicals using carbon monoxide and other raw materials, known as "C1 chemistry." An important issue in this "C1 chemistry" is how to achieve a desired mixing ratio of carbon monoxide and hydrogen.

For example, the mixing ratio of carbon monoxide and hydrogen in coke oven gas is 1:10, but how can we produce synthetic natural gas called SNG with a mixing ratio of 1:3? It is extremely important industrially.

Conventionally, the mainstream methods for separating hydrogen from mixed gases containing hydrogen have been membrane separation using non-porous membranes and molecular sieve methods, but these methods are not yet technically mature, and Running costs are also not necessarily cheap.

On the other hand, Langer and Haldeman [Science 142, 225
(1963)] is a gas mixture containing hydrogen, e.g. 24% methane, 3% ethylene, 18% carbon monoxide, 55%
It has been reported that hydrogen can be selectively separated from city gas consisting of hydrogen using an electrochemical method.

This electrochemical method uses a gas diffusion electrode called a hydrogen electrode used in fuel cells as an anode, a hydrogen generating electrode used in water electrolysis as a cathode, and an anode of an electrochemical cell with sulfuric acid as the electrolyte. While supplying a mixed gas containing hydrogen to
When a direct current is passed between the anode and the anode at a current density of about 60mA/cm ² , only hydrogen is selectively ionized at the anode as shown in the following equation (1), H ₂ →2H ⁺ +2e ^- (1) Cathode This method utilizes the principle that hydrogen of considerably high purity can be obtained from the side according to the following equation (2).

2H ⁺ +2e ^- →H ₂ (2) This electrochemical hydrogen separation method has the advantage of superior hydrogen separation selectivity compared to the membrane separation method and molecular sieve method described above.

The present invention attempts to obtain a mixed gas containing hydrogen at a predetermined concentration using this electrochemical hydrogen separation method.

In the electrochemical hydrogen separation method, the hydrogen separation rate is proportional to the applied current, and the power consumption is proportional to the operating voltage. Therefore, in order to downsize the electrochemical hydrogen separation device and reduce power consumption, it is necessary to improve the polarization characteristics. From this point of view,
The performance of the electrochemical hydrogen separation device (current density of 60 mA/cm ² , voltage of 990 mV) seen in the experimental results of Langer et al. cannot be expected to be put to practical use.

In contrast, in recent years, hydrogen ion-transfer type ion exchange resin membranes based on fluorine-containing polymers such as perfluorocarbons and into which cation exchange groups such as sulfonic acid groups and carboxylic acid groups have been introduced have been developed as electrolytes. Fuel cells and water electrolyzers have been developed that exhibit excellent polarization properties. By combining the hydrogen electrode of this type of fuel cell with the hydrogen generating electrode of a water electrolyzer, a practical electrochemical hydrogen separation device can be expected.

The present invention has been made with this point in mind as one of the points of view.

On the other hand, the above-mentioned Langer et al. target high-purity hydrogen generated from the cathode side, and do not pay any consideration to the remaining gas after hydrogen is separated and removed at the anode side. In other words, Langer et al. view electrochemical hydrogen separation devices only as hydrogen concentrators or hydrogen generators.

On the other hand, in the present invention, the hydrogen generated from the cathode side is rather a byproduct, and the main purpose of the present invention is to focus on the reaction on the anode side, and to increase the hydrogen concentration that is industrially valuable. The present invention is intended to obtain a hydrogen-containing mixed gas, and this is a major feature of the present invention.

That is, in the present invention, a mixed gas containing a relatively high concentration of hydrogen is supplied to the anode side of an electrochemical cell in which an ion exchange resin membrane is used as an electrolyte and a cathode and an anode are integrally bonded to this membrane. By passing a direct current through an electrochemical cell, some of the hydrogen in the mixed gas is transferred to the cathode side, and the remaining mixed gas containing a relatively low concentration of hydrogen is obtained from the anode side. be.

The hydrogen concentration of the mixed gas containing relatively low concentration hydrogen as the target gas derived from the anode side is the same as the hydrogen concentration of the mixed gas containing relatively high concentration hydrogen as the primary gas supplied to the anode side. is a function of the feed rate and the operating current. Therefore, in order to make the hydrogen concentration of the target gas derived from the electrode plate a desired value, it is necessary to appropriately control the operating parameters as described above.

As a method of controlling the hydrogen concentration of the target gas,
A simple method is to detect the hydrogen concentration of the target gas with a hydrogen concentration meter and control the current value to be applied or the current value to be applied so that the hydrogen concentration becomes a desired value. For example, if the hydrogen concentration in the target derived gas is too high than the desired value, you can reduce the current value or lower the applied voltage; on the other hand, if it is too low, either increase the current value or All you have to do is increase the applied voltage. Such a method of controlling hydrogen concentration is also one of the important features of the present invention.

The heart of the electrochemical hydrogen separation device of the present invention is a bonded body in which a cathode and an anode are integrally bonded to an ion exchange resin membrane. The ion exchange resin membrane is made of a fluorine-containing polymer, preferably perfluorocarbon,
A cationic group, preferably a sulfonic acid group or a carboxylic acid group, or a combination of both is used. The cathode is preferably formed by bonding platinum to the ion exchange resin membrane by electroless plating, or by bonding a mixture of platinum black and polytetrafluoroethylene to the ion exchange resin membrane by hot pressing. The anode is preferably made of a mixture of catalyst metal and polytetrafluoroethylene and bonded to the ion exchange resin membrane by hot pressing. A platinum group metal is used as the catalyst metal. It is important to use a material that is not easily poisoned by carbon monoxide. Further, it may be effective to further form a mixture layer of carbon powder and polytetrafluoroethylene on the mixture layer of catalyst metal and polytetrafluoroethylene.

When bonding the electrode to the ion exchange resin membrane using the hot press method, ion exchange resin powder based on perfluorocarbon with cation exchange groups introduced or sulfonic acid groups added to the styrene-divinylbenzene copolymer may be used. It is also an effective method to mix ion exchange resin powder into the electrode layer. When such a method is employed, the contact area between the electrode and the ion exchange resin serving as the electrolyte becomes larger, so that the polarization characteristics of the electrode are generally improved.

When an electrochemical hydrogen separation device using such a conjugate is operated, hydrogen ions (H ⁺ ) generated at the anode according to the above equation (1) pass through the ion exchange resin membrane from the anode side to the cathode side. Move to the side, but at that time,
Because hydrogen ions are accompanied by several moles of water molecules,
Water becomes insufficient at the interface between the anode and the ion exchange resin, and the polarization characteristics of the electrochemical hydrogen separator deteriorate. In order to prevent this phenomenon, it is advantageous to sufficiently humidify the mixed glass containing hydrogen with a relatively high hydrogen concentration to be supplied to the anode. Such humidification operation is also one of the important features of the present invention.

On the other hand, the ion exchange resin membrane used in the present invention functions as an electrolyte only when it contains water, and it is important that the water for this purpose be as pure as possible. If it contains metal ions, the hydrogen ions in the ion exchange resin will be replaced with metal ions, causing the above-mentioned problem.
The reactions according to equations (1) and (2) slow down rapidly. Therefore, if metal is mixed in the supplied gas, it is necessary to remove it as much as possible.

An electrochemical hydrogen separation device is typically constructed from a plurality of electrochemical cells, but the feed gas may be supplied to the plurality of electrochemical cells in parallel;
Although it is possible to adopt a method in which the hydrogen concentration is reduced sequentially in series, or in other words, in a multi-stage manner, the former method is preferable because it allows each electrochemical cell to operate equally. .

An embodiment of the present invention will be described in detail below.

FIG. 1 is a schematic cross-sectional diagram of a unit electrochemical cell that constitutes a part of an electrochemical hydrogen separation device according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of a unit electrochemical cell for producing synthetic natural gas from coke oven gas. The system diagram is shown below.

In Fig. 1, 1 is an ion exchange resin membrane based on perfluorocarbon with sulfonic acid groups introduced, 2 is a cathode made of platinum, and 3 is a platinum black powder and styrene-divinylbenzene copolymer with sulfonic acid groups. This anode is made of a mixture layer of ion exchange resin powder into which acid groups have been introduced and polytetrafluoroethylene. The cathode 2 is bonded to the ion exchange resin membrane 1 by electroless plating, and the anode 3 is bonded to the ion exchange resin membrane 1 by hot pressing.
4 is a cathode current collector made of expanded titanium metal plated with platinum, and 5 is an anode current collector made of expanded titanium metal plated with platinum. A cathode gas chamber is formed in the gap between the anode current collectors 5 and an anode gas chamber. 6 is a cathode terminal plate made of titanium plate,
7 is an anode terminal plate made of a titanium plate. 8 is a cell frame made of polypropylene.

In this electrochemical cell, while a saturated, humidified mixed gas containing hydrogen at a relatively high concentration is supplied from the primary gas supply port 9, an external power source is connected between the cathode terminal plate 6 and the anode terminal plate 7. When a direct current is applied, an ionization reaction of hydrogen occurs at the anode 3, a hydrogen generation reaction occurs at the cathode 2, and this hydrogen is transferred to the hydrogen outlet 1.
Derived from 0. On the other hand, the remaining mixed gas containing hydrogen at a relatively low concentration after some of the hydrogen has been consumed at the anode 3 is led out from the secondary gas outlet 11. Next, in FIG. 2, reference numeral 13 denotes an electrochemical hydrogen separation apparatus in which a plurality of electrochemical cells of the unit shown in FIG. 1 are assembled. Coke oven gas with a volume ratio of carbon monoxide and hydrogen of 1:10 is first humidified to saturation in a humidifier 14, distributed in a primary gas manifold 15, supplied to an electrochemical hydrogen separator 13, and then powered by a DC power supply. When a direct current is applied to the electrochemical hydrogen separator 13 from the built-in controller 16, some hydrogen in the coke oven gas is separated, collected in the hydrogen gas manifold 17, and extracted at the same time from the coke oven gas. Hydrogen is consumed and synthetic natural gas having a volume ratio of carbon monoxide to hydrogen of 1:3 is collected in the secondary gas manifold 18 and led out.

The secondary gas manifold 18 has a hydrogen concentration meter 19.
The hydrogen concentration meter 19 detects the hydrogen concentration in the secondary gas manifold 18, and the signal is sent to the controller 16, which detects the carbon monoxide and hydrogen concentration in the secondary gas manifold 18. The current supplied to the electrochemical hydrogen separation device 13 is controlled by the controller 16 so that the volume ratio between the hydrogen separation device 13 and the hydrogen separation device 13 is maintained at 1:3.

Next, an example of specific operating conditions for the system shown in FIG. 2 will be described.

First, the electrochemical hydrogen separation device used was constructed by stacking 16 unit electrochemical cells each having an active area of 1 dm ² . When this electrochemical hydrogen separator was supplied with 10 Nm ³ of coke oven gas per hour with a dew point of 60°C in a humidifier and operated with a direct current of 100 A, the electrochemical hydrogen separator ( The voltage (electrically connected in series) was 4.8V. In addition, the hydrogen gas extracted from the hydrogen outlet was 6.4Nm ³ per hour.
The amount of synthetic natural gas obtained from the secondary gas outlet is 1
It was ^3.6Nm3 per hour.

As detailed above, the present invention provides a very simple method for producing a mixed gas containing a relatively low concentration of hydrogen from a mixed gas containing a relatively high concentration of hydrogen, and its industrial value is Extremely large.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional diagram of a unit electrochemical cell constituting a part of an electrochemical hydrogen separation device according to an embodiment of the present invention, and FIG. A system diagram for producing gas is shown. 1... Ion exchange resin membrane, 2... Cathode, 3... Anode,
4... Cathode current collector, 5... Anode current collector, 6... Cathode terminal plate, 7... Anode terminal plate, 8... Cell frame, 9... Primary gas supply port, 10... Hydrogen outlet, 11... Secondary gas guide Outlet, 13... Electrochemical hydrogen separation device, 14
...Humidifier, 15...Primary gas manifold, 16...
Controller, 17...Hydrogen gas manifold, 1
8...Secondary gas manifold, 19...Hydrogen concentration meter.

Claims (1)

[Scope of Claims] 1 A hydrogen ion transfer type ion exchange resin membrane based on a fluorine-containing polymer and having a cation exchange group introduced therein, a cathode on one side and an anode on the other side are integrally bonded. An electrical system consisting of a cathode gas chamber, an anode gas chamber, a hydrogen outlet, a supply port for a mixed gas containing a relatively high concentration of hydrogen, and an outlet for a mixed gas containing a relatively low concentration of hydrogen. In the chemical hydrogen separation device, a mixed gas containing a relatively high concentration of hydrogen is supplied in a humidified state from the supply port of the mixed gas containing a relatively high concentration of hydrogen, and the electrochemical hydrogen separation device By passing a direct current between the cathode and the anode, a portion of the hydrogen in the mixed gas containing a relatively high concentration of hydrogen is electrochemically transferred from the anode side to the cathode side, and from the hydrogen outlet. A mixed gas containing hydrogen at a constant concentration, characterized in that the remaining mixed gas containing hydrogen at a relatively low concentration is led out from an outlet for the mixed gas containing hydrogen at a relatively low concentration. How to manufacture. 2. Detecting the hydrogen concentration in the mixed gas containing relatively low concentration of hydrogen derived from the outlet of the mixed gas containing relatively low concentration of hydrogen with a hydrogen concentration meter, and determining that the hydrogen concentration of the derived gas is at a predetermined level. A method for producing a mixed gas containing hydrogen at a constant concentration according to claim 1, which comprises controlling the current value to be applied or the voltage value to be applied to an electrochemical hydrogen separation device so that the hydrogen concentration is maintained at a certain concentration. .