JPH02261513A - Method for controlling gas permeability - Google Patents

Abstract

PURPOSE:To easily control the velocity of permeation of gas through a membrane and the selectivity of permeation with electricity at about room temp. by bringing electrodes into contact with both sides of the membrane made of an electrically conductive polymer and impressing voltage between the electrodes. CONSTITUTION:Electrodes are brought into contact with both sides of a membrane made of an electrically conductive polymer, e.g., a polymer of a heterocyclic arom. compd. such as pyrrole or its deriv. and voltage is impressed between the electrodes. The velocity of permeation of gas and the selectivity of permeation can easily be controlled with electricity at about room temp. The gas is not especially limited and may be oxygen, hydrogen, CO2, CO, gaseous halogen such as chlorine or org. gas.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a gas permeability control method using a conductive polymer membrane. The method of the present invention is useful for concentrating or separating gases such as oxygen or adjusting the flow rate of gases.

[Prior Art] Many studies have been conducted on methods of separating gases such as oxygen from other gases using membranes. For example, in order to improve the permselectivity of a specific gas or the gas permeation rate, various polymer membranes have been developed and modified through physical treatment or chemical modification. (Literature examples, Manabu Seno,
Co-authored with Naofumi Kimura, “New Functional Material “Membrane””, Kogyo Kenkyukai, 1
983; co-authored by Shimizu, Saito, and Nakako, "New Functional Membrane",
(Kodansha, 1984) Gas separation using these conventional polymer membranes was based on molecular diffusion using the gas concentration difference (pressure difference) between the two sides of the membrane as a driving force.

On the other hand, a method of separating oxygen from air using a liquid electrolyte has been proposed (U, S, 3,888.749
). In this case, the separation is carried out by pumping a liquid electrolyte, and the oxygen is said to be transferred in the form of ions. Furthermore, using a solid electrolyte membrane, hydrogen separation (Prepr.
ints, Fuel Div, A, C, S
,, Vol, 20°No, 2. , Ap r i
1. 1975) and oxygen separation (U, S, 4,
131,514) is known. In these cases, separation is carried out by using an inorganic membrane and passing electricity through it, but this must be carried out at a temperature of several hundred to 1,000 degrees Celsius, which limits the locations and conditions under which it can be used.

[Problems to be Solved by the Present Invention] An object of the present invention is to provide an inexpensive and easy method for controlling gas permeability at a temperature close to room temperature.

[Means for Solving the Problems] The present inventors utilized the property of a conductive polymer membrane to conduct electric current to improve the permeability of gases such as oxygen by applying a voltage in a direction perpendicular to the membrane surface. The inventors have discovered that this can be easily controlled, and have arrived at the present invention.

That is, the present invention provides a method for controlling gas permeability of a conductive polymer membrane by bringing electrodes into contact with both sides of the conductive polymer membrane and applying a voltage to the electrodes.

[Effect] The present invention will be explained in more detail below.

The conductive polymer film used in the present invention refers to a film made of a heterocyclic aromatic compound such as pyrrole, thiophene, furan, indole, selenophene, tellurophene or a polymer of a derivative thereof, polyacetylene or poly(1,6-
membranes made of polyacetylene-based polymers such as hebutadiin) or their derivatives, polyvaraphenylene,
Membranes made of polyphenylene-based polymers such as polyphenylene vinylene and polyphenylene sulfide; membranes made of ionic polymers obtained by polymerizing aromatic amines such as aniline and aminopyrene; and membranes made of ionic polymers such as polyacene and polyphenanthrene, which are generally called ladder polymers. (Reference, Susumu Yoshimura, “Conductive Polymer”)
, Polymer Science Society of Japan, Kyoritsu Publishing). These polymers can be produced by chemical polymerization (catalytic polymerization) or electrolytic polymerization (electrochemical polymerization).
Alternatively, polymerization can be carried out by a known method such as gas phase polymerization or solid phase reaction.

These conductive polymers may be used after being given high conductivity by doping, or may be used without doping.

The above-mentioned conductive polymers can be used alone in the form of a membrane, but in order to improve mechanical strength and functionality, they are used in combination with various supports.

Supports in this case include ion exchange membranes, various natural and synthetic polymer membranes, porous glasses, porous ceramics, and the like.

Chemical oxidative polymerization, which is one of the chemical polymerization methods, uses Lewis acids, simple halogens, peroxides,
This is carried out by bringing an oxidizing agent such as a metal acid into contact with the above monomer using a diaphragm method using a porous support. Alternatively, a conductive polymer film can also be obtained by bringing monomer vapor into contact with a support containing these oxidizing agents.

On the other hand, in electrolytic oxidative polymerization, a conductive polymer film is obtained by bringing the above monomer into contact with electricity through an electrode covered with a polymer film.

As another method of conjugation, it is also possible to graft polymerize the same heterocyclic aromatic compound to a polymer such as polystyrene having the above-mentioned heterocyclic aromatic compound in its side chain by electrolytic oxidation.

In the present invention, gases whose permeability can be controlled include oxygen,
Examples include nitrogen, hydrogen, carbon dioxide, carbon oxide, halogen gas such as chlorine, organic gas, and are not particularly limited.

In the present invention, in order to control gas permeability using a conductive polymer membrane, it is sufficient to adjust the voltage applied through porous electrodes placed in contact with both surfaces of the membrane. This operation may be performed in a state where there is a gas pressure difference between the two sides of the membrane, or may be performed in a state where there is no pressure difference.

The electrodes used here include copper, platinum, gold, nickel, stainless steel, and metals coated with metal oxides.

The gas permeation rate and permeation selectivity change rapidly with voltage loading and return to their original values when the load is removed. The degree of change increases as the voltage increases, and the degree of change increases as the conductivity of the membrane used increases. Furthermore, at the same voltage, the smaller the gas pressure difference between the two sides of the membrane, the greater the rate of change in gas permeability.

In the present invention, such gas permeability control can be performed at a temperature around room temperature, but may also be performed at a temperature other than room temperature.

[Examples] Examples are shown below to explain the present invention in more detail, but the present invention is not particularly limited to the following examples.

Example 1 Using water as a solvent, pyrrole (0°LM) and iron(III) chloride (0.4M), which is an oxidizing agent for pyrrole, were
Nucleobore's micro filter (pore size, 0.05μ
m; porosity, 1.2%) by the diaphragm method at 4°C.
A polypyrrole film was prepared by chronochemical oxidative polymerization. The obtained membrane was washed in distilled water for 24 hours to remove unreacted substances such as pyrrole monomer, and then dried under vacuum and subjected to measurement. The conductivity of this film is approximately 73/c
It was m.

A gas permeation experimental device was assembled by pressing copper mesh onto both sides of the polypyrrole membrane to fix the membrane. Here, oxygen was used as the gas. After oxygen permeation through the membrane reached a steady state under a constant oxygen pressure (the low pressure side was almost a vacuum), the change in gas permeation caused by applying a voltage (3V) was measured using a Baratron pressure gauge. . At this time, the side with higher oxygen pressure was used as the anode, and the side with lower oxygen pressure was used as the cathode. For the gas permeation rate, a value corrected by the porosity (1, 2%) of the support membrane was used.

The oxygen permeation rate increased rapidly with voltage loading and returned to its original value when the loading was stopped. The rate of this change was greater when the gas pressure was low than when it was high. In Figure 1,
The oxygen permeability coefficient before and after voltage loading and the ratio of the permeability coefficient before and after voltage loading were plotted against the gas pressure. When the pressure is low, the ratio of the permeability coefficient before and after the voltage load is approximately 3, indicating that the oxygen permeation rate changes significantly by 1 degree due to the voltage load.

Example 2 Using the same polypyrrole membrane as used in Example 1, the oxygen pressure was fixed at 10 cmHg, the voltage was varied, and changes in the permeability coefficient before and after voltage loading were observed. Figure 2 shows the results. It can be seen that the ratio of the transmission coefficients before and after voltage loading increases as the voltage increases.

Example 3 Several polypyrrole films with different conductivities were obtained by adjusting the polymerization temperature. Using these, the oxygen pressure was fixed at 10 cmHg and the voltage was fixed at 3 V, and changes in the permeability coefficient before and after voltage loading were observed.

Figure 3 shows the results. It can be seen that the ratio of permeability coefficients before and after voltage loading increases as the conductivity of the membrane increases.

Example 4 Using the same polypyrrole film as that used in Example 1, 3
When a voltage of V was applied, the ratio of oxygen and nitrogen permeability coefficients before and after the voltage was applied was measured. Figure 4 shows the results. It can be seen that the ratio of oxygen and nitrogen permeability coefficients increased significantly with voltage loading.

[Effects of the Invention] As explained above, according to the present invention, it has become possible to easily control gas permeation rate and permeation selectivity near room temperature using electricity.

1 to 4 show data for each embodiment of the invention.

P: Gas permeability coefficient under standard conditions (ecsTPcM/cm2 seccmHg
)p: Pressure of gas (co+Hg) P: Permeability coefficient n when voltage is applied P: Permeability coefficient of'f when no voltage is applied V: Applied voltage (volt) Pv: When applied voltage V Permeability coefficient P: Permeability coefficient when no voltage is applied -O P: Permeability coefficient when a voltage of 3V is applied -3 σ: Conductivity of membrane (S/0m) P: Oxygen permeability coefficient P: Nitrogen transmission coefficient of

Claims (1)

[Claims] A method for controlling gas permeability of a conductive polymer membrane by bringing electrodes into contact with both sides of the conductive polymer membrane and applying voltage to the electrodes.