JPH04354523A - Gas separating membrane - Google Patents

Abstract

PURPOSE:To allow the effective use of the above-mentioned membrane for sepn. of oxygen and nitrogen by forming the polyolefin high-polymer membrane formed by grafting an org. acid having double bonds on a porous membrane of regenerated cellulose and constituting the polyolefin high-polymer membrane of 50 to 200nm particle layers. CONSTITUTION:A cellulosic hydrophilic high-polymer material which has high mechanical strength and is less changed in properties in a specific temp. range is used as a porous or sheet-like base. The graft polymer film consisting of the uniform and specific polymers is securely formed on the cellulosic base by a coating or dipping method, etc., using a graft polymer soln. prepd. by grafting the org. acid having double bonds on a polylelfin high polymer and subjecting the reaction product to a microphase sepn. by addition of a hydrophilic solvent. This membrane can be formed as a thin film consisting of the particles having 50 to 200nm particle sizes and having excellent permeability if the grafting rate is 3 to 15wt.% from the relation between the grafting rate of the org. acid having the double bonds with the olefin high polymer and the particle system constituting the thin film.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a gas separation membrane for the purpose of separating and concentrating a gas mixture, and in particular to a gas separation membrane that selectively separates oxygen in a gas mixture of oxygen and nitrogen. be.

0002

2. Description of the Related Art In recent years, there has been active development of technology for separating and concentrating specific gases from various gas mixtures. In particular, oxygen-enriched air, which has a higher oxygen concentration than air, is expected to have a wide range of uses, including medical use, combustion promotion, and activated sludge treatment.
Membrane separation methods using polymer membranes are strongly desired from the viewpoint of resource and energy conservation.

[0003] Polymer materials such as polysiloxane polymers, polycarbonates, polyvinylpyridine, polysulfones, and methylpentene polymers are used industrially as materials for oxygen enrichment membranes. These materials may be dissolved in a suitable solvent and directly formed into an oxygen-enriched film using a casting method, water surface spreading method, coating method, or melt molding method, but in general, polymeric materials of the same type are used. The oxygen-enriched polymer is typically formed on a support consisting of or other support, and in some cases, the oxygen-enriched polymer is formed on the support by plasma polymerization. When used as an oxygen enrichment membrane, a membrane with good permeation rate and oxygen separation coefficient is desired. The support itself does not have an oxygen concentrating function; it is porous and has mechanical strength so as not to impede the permeability of gas (oxygen) that passes through the oxygen-enriching membrane formed on the support. Superior materials are required. In this respect, among polymeric materials, cellulose-based materials are the best as supports. There is no known gas separation membrane that forms an oxygen-enriched membrane, which is hydrophobic in nature, on top of this, and satisfies concentrating properties and permeability. In general, as the separation coefficient of organic polymer materials increases, the oxygen permeation rate tends to decrease. For this reason, it is generally necessary to form a film as thin as possible, but it is often difficult to do so with ordinary coating or dipping methods.

0004

[Problems to be Solved by the Invention] In order to put organic polymer materials into practical use as polymer membranes, it is necessary to increase the gas permeation rate and reduce the required membrane area by making the membrane thickness as thin as possible. It is necessary to aim for this. In order to prevent damage to a separately formed thin film, methods are known in which a thin film is supported on a porous membrane support, or a thin film is formed by coating or impregnating a dilute solution of a polymer onto a porous membrane support. However, when trying to make a thin film using these methods, the former method can produce a thin film, but depending on the material, it cannot be supported directly on the support, and the latter method has the disadvantage that the affinity between the polymer solution and the support is poor. If it is not good, the thin film may not exhibit sufficient bonding in some parts or the thickness may become uneven.

An object of the present invention is to solve the problems of conventionally known gas separation membranes and to provide a gas separation membrane that is tough and has an excellent gas permeation rate.

[0006]

[Means for Solving the Problems] The gas separation membrane according to the present invention is provided by forming a polyolefin polymer thin film grafted with an organic acid having double bonds on a regenerated cellulose porous membrane. 50~200n
It is characterized by being composed of m particle layers. In the gas separation membrane according to the present invention, the thin film is firmly bonded to the support due to the hydrophilicity of the regenerated cellulose porous membrane as the support, the hydrophilicity of the polymer, and the hydrophilicity of the solvent used.

That is, in the gas separator of the present invention in which a polymeric material having excellent oxygen concentrating property and permeability is supported on a porous polymeric support or a sheet-like support, the porous or sheet-like support In order to provide a gas separation membrane using a cellulose-based hydrophilic polymer material that has high mechanical strength and little change in physical properties in a specific temperature range, it is necessary to use a polyolefin-based polymer that is naturally hydrophobic. An organic acid having a double bond is grafted onto the polyolefin polymer in a suitable solution, and the graft polymer solution is microphase-separated by adding a hydrophilic solvent, and then the grafted polymer is coated uniformly using a relatively simple technique such as coating or dipping. Furthermore, the graft polymer membrane having a specific particle size is firmly formed on a cellulose support, thereby providing a separation membrane with good oxygen concentrating properties and permeability.

[0008] Grafting rate of an organic acid having a double bond to an olefinic polymer (amount of charge relative to the original polymer)
If the grafting rate is 3 wt % or more, it is possible to form a thin film having a particle size with excellent permeability, based on the relationship between the particle size and the particle size constituting the thin film. The grafting rate is preferably 3 wt% to 15 wt%, more preferably 3 wt% to
10wt% is good. At 3wt% or less, the particle size is 50n.
m or less, the separation efficiency of oxygen and nitrogen increases,
Oxygen permeation rate decreases. At 15 wt% or more, a large amount of hydrophilic solvent is required to obtain a homogeneous solution, which tends to penetrate too much into the pores of the porous hydrophilic support and reduce the overall permeability, or Conversely, the particle size constituting the thin film also tends to increase, and the oxygen permeation rate increases, but the separation efficiency decreases.

Furthermore, olefinic polymer solvents do not dissolve at all in hydrophilic solvents. Therefore, when coating an olefin-based polymer on a regenerated cellulose porous membrane, which is a hydrophilic material, it is necessary to coat it uniformly and firmly, not only because of the affinity between the two, but also because the solvent used has a poor affinity with the regenerated cellulose porous membrane. There is a problem that coating cannot be performed while bonded to the surface. However, as in the present invention, by grafting an organic acid having a double bond onto an olefinic polymer, it has become possible to make the olefinic polymer have affinity with regenerated cellulose. Furthermore, this is facilitated by the use of hydrophilic solvents in the coating and dipping solutions.

As the hydrophilic porous support used in the present invention, so-called paper or regenerated cellulose porous membrane, which is mainly composed of natural cellulose fibers, can be used. Cellulose porous membranes are preferred. In addition, the regenerated cellulose porous membrane is manufactured using a microphase separation method to ensure a high permeation rate.
Average pore diameter is 0.02 μm to 10 μm, porosity is 50 to 8
0% is usually used. Furthermore, since the regenerated cellulose porous membrane is excellent in terms of mechanical strength, it is effective when incorporated according to the shape when modularizing. Generally, the mechanical strength of a porous membrane decreases when it becomes porous, but in the regenerated cellulose porous membrane used in the present invention, by increasing the molecular weight of cellulose in the cellulose cupric ammonia solution. , the mechanical strength of the obtained porous membrane can be increased. In addition, since the porous membrane is manufactured using a microphase separation method, the membrane itself is composed of particles of a concentrated cellulose phase, and the particles are tightly connected to each other, resulting in excellent mechanical strength.

[0011] Depending on the final purpose, the hydrophilic porous support may be formed using porous glass beads, ceramics, or the like.

[0012] As the olefinic polymer material, polyethylene, polypropylene, poly-3-methyl-butene-
1, poly-4-methylpentene-1, and the like. Poly-4-methylpentene-1 is preferred in terms of oxygen concentrating properties. Further, examples of the organic acid having a double bond include maleic anhydride, fumaric acid, itaconic acid, crotonic acid, and maleamic acid.

[0013]

EXAMPLE A toluene or xylene solution in which maleic acid was dissolved and a toluene solution of benzoyl peroxide were added to a cyclohexane solution of poly-4-methylpentene-1 and reacted in a reflux state. The 1 wt % poly-4-methylpentene-1-maleic acid/cyclohexane/ethanol solution prepared in this way was kept at around 60° C. to obtain a solution with a slight loss of transparency. In the solution, an average pore size of 35 nm was added.
, porosity 51.2%, inner diameter 345.5 μm, film thickness 30
．． A 2 μm regenerated cellulose hollow fiber was immersed to coat the outer wall surface of the hollow fiber. In the grafting reaction, the amount of maleic anhydride used relative to poly-4-methylpentene-1 is regarded as the grafting ratio, and these solutions are used to coat cellulose porous hollow fibers for a predetermined number of coatings. Ten hollow fibers obtained in step 1 were bundled to form a module, and air was allowed to permeate without pre-filtering. Table 1
shows the results and the particle diameter and appearance observation results of the graft polymer observed using an electron microscope. Table 1 shows that hollow fibers with anhydrous maleic grafting ratio of 0 wt% do not achieve oxygen concentrating properties even after being coated four times, and seven or more coatings are required to form a membrane that concentrates oxygen on cellulose. be. However, the oxygen permeation rate in that case becomes extremely low. This is because, as is clear from electron microscopy, the graft polymer formed on cellulose forms a so-called dense film. In addition, coating spots occur very frequently, making it impossible to put it to practical use. Furthermore, the durability of the module performance was poor, and when the gas permeability test was conducted several times, the oxygen concentrating performance decreased, but on the other hand, the gas permeation performance increased, and when air was allowed to pass through it, almost all of the air passed through it. This is due to poor adhesion (bond state) between the regenerated cellulose porous membrane and poly-4-methylpentene-1.

[0014]

[Table 1]

The coated hollow fibers of the present invention had excellent oxygen concentrating properties and oxygen permeability, and showed no problems with coating unevenness or durability in gas permeability tests. FIG. 1 shows the infrared absorption spectra of the graft polymer and the original polymer obtained by this method. -CO at 1700 cm-1
A characteristic peak of OH is observed in the grafted polymer.

[0016]

Effects of the Invention In the separation membrane of the present invention, a thin film can be formed on a regenerated cellulose porous membrane by grafting an organic acid having a double bond to an olefinic polymer, and the resulting separation membrane Thin films are composed of particles,
By controlling the particle size, a gas separation membrane with excellent permselectivity can be obtained, and it can be effectively used as a highly practical oxygen-enriching membrane for the separation of oxygen and nitrogen.

[Brief explanation of drawings]

FIG. 1 shows infrared absorption spectra of the graft polymer obtained by this method and the original polymer. In Figure 1, (a) is the original polymer, (b) is the 3wt% graft polymer, and (c) is the 6wt%
% grafted polymer, (d) shows the infrared absorption spectrum of 10 wt% grafted polymer.

Claims (1)

[Claims] 1. A polyolefin polymer thin film grafted with an organic acid having double bonds is formed on a regenerated cellulose porous membrane, and the polyolefin polymer thin film is
A gas separation membrane comprising a particle layer of 0 to 200 nm.