JPS6245319A - Gas separation membrane - Google Patents

Abstract

PURPOSE:To obtain a gas separation membrane excellent in heat resistance, chemical resistance and mechanical strength and having high transmission coefficient of hydrogen gas without damaging gas separation capacity, by setting the thickness of a dense layer comprising a polyparabanic acid type polymer to 20mum or less. CONSTITUTION:A polyparabanic acid type polymer having a repeating unit shown by formula (wherein R is a divalent org. group) is used. Both of a homopolymer and a copolymer may be used but one with intrinsic viscosity (DMF 25 deg.C) of 0.4-4 is pref. Further, one having diphenylether-4,4'-diyl is excellent in heat resistance. A membrane is formed from a dope solution so as to set the thickness of a dense layer substantially having no fine pore to 20mum or less. After the solvent of the dope solution is evaporated at ambient temp.-140 deg.C, the membrane is heated to 150-200 deg.C to further evaporate the residual solvent or the solvent is evaporated at 50 deg.C-the b.p. of the solvent or less and the resulting membrane is immersed in water at 0-40 deg.C and gelled to obtain an anisotropic membrane.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to gas separation membranes made of heterocyclic polymers.

BACKGROUND OF THE INVENTION In recent years, gas separation membranes made of organic polymers have been attracting attention from the viewpoint of resource and energy conservation. However, membrane materials with a large gas permeability coefficient have a small separation coefficient;
Membrane materials with large Tj ratios have a mutually contradictory relationship, such as low gas permeability coefficients, and it has been difficult to perform separation on an industrial scale using gas separation membranes. For example, polydimethylsiloxane, which is known as a membrane material with a high gas permeability coefficient, has an oxygen permeability coefficient of 6.
．． OX 10-'c11? (s'rp)-, , /, p
*The permeability coefficient of θeC-6nHg1 water cable is 6.5X10
-”crI(STP)・Return/cW?・sec'ffiH
Although it is large, the separation coefficient for oxygen and nitrogen is 2.0 and the separation coefficient for hydrogen and nitrogen is low at 2.3, making it economical as multi-stage processing is required to obtain high concentration oxygen or hydrogen. Therefore, it is not practical.

Furthermore, membrane materials with a large gas permeability coefficient generally have low mechanical strength, making it difficult to form a thin film, and there is a drawback that the substantial permeation rate, which is calculated by dividing the gas permeability coefficient by the film thickness, cannot be increased. f! for the advancement and diversification of membrane separation processes. Therefore, there is a demand for a ζ1 film that has excellent heat resistance, chemical resistance, and mechanical strength.

For this reason, for example, a gas separation membrane made of an aromatic polyimide obtained from pyromellitic acid, aromatic diami/yabiphenyltetracarboxylic acid, and aromatic diamine (Japanese Unexamined Patent Publication No. 49
-45152, JP-A-56-157455), a separation membrane of a specific aromatic copolyimide (JP-A-60-1986),
22902) have been proposed.

Invention: 4 points (-However, the gas separation membrane made of known aromatic polyimide has the following problems: heat resistance, heat resistance, mechanical properties, and gas Although the separation ability was improved, the gas permeability coefficient, especially the hydrogen gas permeation coefficient a, could not be titrated.

The present invention provides a gas separation membrane that maintains excellent gas separation ability, has a particularly low hydrogen gas permeation coefficient, and has excellent heat resistance, chemical resistance, and mechanical strength. The purpose is to provide.

Means to Solve the Problems The present inventors have conducted intensive research to solve the above problems, and have found that a membrane made of polyparabanic acid polymer, which is a heterocyclic polymer, has a high gas separation ability. The present invention was completed based on the discovery that the material has high hydrogen gas permeability and excellent heat resistance, chemical resistance, strength, etc.

That is, the present invention consists of a homopolymer or copolymer having the general formula [wherein R is a divalent organic group] as a repeating unit, and the thickness of the dense layer effective for separation is 20 μm or less. The main topic is gas separation membranes.

Examples of the homopolymer or copolymer having the above general formula as a repeating unit in the present invention include a polyparabanic acid polymer (hereinafter abbreviated as PPA). This PPA is disclosed in, for example, U.S. Pat. In the above general formula, (diphenylmethane-a,a'-diyl) and its polymer or copolymer have an intrinsic viscosity (at DMF of 25°C) of [14 to 4.0], and are highly flexible. In order to obtain a film with good properties, α6 to 2.0 is particularly desirable. Further, in order to improve the heat resistance more than the heat resistance, it is desirable to have diphenyl ether-4,/-diyl as R.

When the intrinsic viscosity is too low, self-supporting properties are poor when a film is formed, while when it is too high, it becomes difficult to prepare a uniform dope for forming a polymer or copolymer into a film. Therefore, it becomes difficult to form the entire gas separation membrane uniformly.

By using PPA, which is an aromatic heterocyclic polymer or copolymer having the above-mentioned 5i:L repeating units, it is possible to impart heat-resistant and chemical-resistant functions to the gas separation membrane, as well as provide mechanical resistance. In particular, due to the large intermolecular force of aromatic polymers, it is possible to obtain a dense structure that is essential for improving separation characteristics.

Further, the gas content 1IILF membrane of the present invention has a dense layer having substantially no pores with a thickness of 20 μm or less, preferably α01 to 20 μm, more preferably α05 to 10 μm.
It's poisonous. If the thickness of the dense layer of the gas separation membrane exceeds 20 μm, the gas permeation rate will be insufficient. In order to increase the gas permeation rate, the thinner the film is, the better; however, from the point of view of mechanical strength, the thicker the film is, the better, and from these points of view, the thickness of the dense layer is preferably within the above range.

Note that the gas separation membrane may be a homogeneous membrane in which the entire membrane is composed of only dense layers as described above, or it may be an anisotropic membrane in which a dense layer is laminated and supported on a porous layer. , or K may be an anisotropic film in which a dense layer and a porous layer are integrated.

The method for producing the gas separation membrane in the present invention is not particularly limited, and it can be made into a flat membrane shape, hollow fiber shape, tubular shape, etc. by a known method.
A uniform film-forming dope is prepared by using an organic solvent (hereinafter referred to as a polymer), and this is cast onto an appropriate support base material, and then heated at room temperature or under normal pressure or reduced pressure. It can be obtained by processing to remove the solvent by evaporation, or by gelling the membrane in which a part of the solvent has been evaporated in a coagulation bath. Here, dope liquid for film formation? The state of aggregation of the dope varies depending on the type of organic solvent used, and therefore has a large effect on the gas permeation performance of the membrane formed from the dope. Therefore, the selection of organic solvent is important. Examples of the organic f8m for dope 11j73 in the present invention include dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, N-methyl-2-piperidone, and dimethylsulfoxide.
Among these, dimethylformamide is particularly preferred.

In addition, should the polymer solution be filtered through an appropriate filter? It is preferable to remove the solid matter using the dope, or to defoam it to light by vacuum degassing or the like to obtain a dope solution for production.

As a method for forming a liquid thin film from a film-forming dope, a known casting film-forming method can be employed. For example, a method of casting a dope onto the surface of a support substrate with a smooth surface (glass plate, stainless steel plate, aluminum plate, copper plate, synthetic resin plate, etc.) and uniformly forming a liquid thin film using a doctor blade, or using a smooth roll. Alternatively, a method may be used in which a dope solution is supplied to the surface of the belt and cast to a uniform thickness using a doctor knife to form a thin film. Furthermore, a method of forming a thin film by extruding the polymer through a die can also be adopted.

The thin film of the film-forming dope solution cast onto the support substrate is removed by evaporation of the solvent by heat treatment at room temperature or under normal pressure or reduced pressure. Here, the heat treatment depends on the solvent of the dope group, but usually, most of the solvent is evaporated in the range from room temperature to 140°C, and then the remaining solvent is further evaporated by heating to 150 to 200°C. This results in a homogeneous film having a uniform and dense layer throughout.

In addition, a part of the solvent, usually only the surface layer, is removed from the doped thin film on the support substrate at a temperature of 50°C to below the boiling point of the solvent.
After evaporation, preferably in the range from 80°C to the boiling point of the solvent -40°C, the thin film together with the supporting substrate is placed in a coagulation bath such as water or a mixture of water and solvent at a temperature of 0 to 40°C for 5 minutes. By immersing for ~2 hours to effect gelation, an anisotropic film in which a dense layer and a porous layer are integrated can be obtained.

Effects of the Invention The gas separation membrane of the present invention has excellent heat resistance, chemical resistance, mechanical strength, etc., and has a lower permeability coefficient, especially for hydrogen gas, without impairing the gas fraction 1iiiIi ability compared to conventional gas separation membranes. is large, and the separation performance between hydrogen gas and nitrogen gas or methane gas is improved. It is also characterized by a small decrease in gas separation coefficient even at high temperatures.

Therefore, it is useful not only for oxygen enrichment but also for the preparation of synthesis gas that requires gas separation at high temperatures, gas separation in processes that require gas separation at high temperatures, recovery of hydrogen gas from waste gas in oil refining and petrochemical processes, and even biogas. It can be suitably used in fields such as separation of methane gas from.

Example The present invention will be described in detail below with reference to Examples.

Example 1 P with a solid viscosity of 1.0 having a diphenylmethane-4,4'-diyl group as R in the general formula of the above polymer
PA i was uniformly dissolved in dimethylformamide to prepare an 8% by weight solution, which was filtered once and defoamed to obtain a dope solution for film formation. After casting the film-forming dope onto a glass plate, the film-forming dope was cast in a nitrogen stream at room temperature for 30 hours, and then I C1
The mixture was dried at 70° C. for 12 hours under a reduced pressure of mH17 and then at 150° C. for 2 hours to remove the solvent by evaporation to obtain a film having a homogeneous dense layer with a thickness of 10 μm.

The method for measuring gas permeation rate using this membrane is to create a vacuum on the downstream side of the membrane, and then inject a specified gas from the upstream side of the membrane for 1 k
Gas permeability measurement bag C'Z (manufactured by Qi1 headquarters, GTR
-3a).

The permeability coefficient of this film for various gases at 30°C and the permeability coefficient ratio (separation coefficient) for nitrogen gas (light -1
It was shown to.

Table 1 Table 2 also shows the permeability coefficients for various gases and the permeability coefficient ratio (separation coefficient) for nitrogen gas at 100°C for the above membranes.

Table 2 Example 2 A film was formed in the same manner as Example 1 except that N-methyl-2-pyrrolidone was used instead of dimethylformamide as the solvent for PPA in Example 1.

The permeability coefficient L of this membrane for various gases at 50°C
Table 3 shows the permeability coefficient ratio (separation coefficient) for and nitrogen gas.
It shows.

Table-3 Example 3 Used in Example 1* ppAl 2. The dope family was prepared by dissolving sy in dimethylformamide 87.57, filtered and defoamed. This dope solution was cast onto a smooth glass plate, and a thin film with a thickness of 200 μm was formed using a doctor blade. After holding the thin film at 90°C for 8 minutes, water and dimethylformamide were mixed in equal volumes. It was immersed in a solvent-based coagulation bath at 6° C. for 2 hours. Next, the film was immersed in a methanol bath for 3 hours and then dried with hot air at 100° C. for 3 hours to obtain an anisotropic film with a dense layer having a thickness of 1/1 m.

The table below shows the 33B velocity for various gases and the permeation velocity ratio (separation coefficient) for nitrogen gas at 30°C for this membrane.
4.

Table 4 Comparative Example 1 21 Anhydride 272, a, 4'
--) 7minodiphenyl ether 259 and N,N-
576 g of dimethylacetamide was charged, and a polymerization reaction was carried out at room temperature for 2 hours while stirring under nitrogen gas flow.

The obtained reaction solution containing polyamic acid with a rolling viscosity of 05 was cast onto a smooth glass plate using a doctor blade, dried at 100°C for 1 hour, and then dried at 200°C for 2 hours. By heating and imide cyclizing polyamic acid, 15
A polyimide film of μγrt19 was obtained. 30℃V of this film
The permeability coefficients for various gases and permeability coefficient ratios (separation coefficients) for nitrogen gas are shown in Table 5.

Table-5 that's all

Claims (1)

[Claims] Consisting of a homopolymer or copolymer having the general formula ▲numerical formula, chemical formula, table, etc.▼ [However, R represents a divalent organic group] as a repeating unit, and effective for separation. A gas separation membrane in which the thickness of the dense layer is 20 μm or less.