JPH0363412B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a gas selective separation membrane. More specifically, the present invention relates to a gas separation membrane suitable for separating olefin compounds, in which a liquid hydrocarbon is supported on a plasma polymerized membrane of bistrimethylsilylacetylene formed on a porous substrate during gas separation. Various types of polymer membranes have been known as separation membranes for gas mixtures, but such solid membranes have a drawback in that their gas permeability coefficients are relatively small. In order to increase the gas permeability coefficient, it is desirable that the membrane be in a liquid state. In the case of such a membrane, the gas diffusion coefficient becomes large, and therefore the permeation coefficient can be increased. In addition, the selective performance of a membrane is given by the difference in solubility of gas in the membrane and the difference in the diffusion rate of gas in the membrane. It is possible to enhance the selectivity by increasing the solubility of a certain gas in the membrane by utilizing the interaction with this substance. BACKGROUND ART Conventionally, as an example of separating gas mixtures using a liquid membrane, membranes for separating carbon dioxide gas, carbon monoxide, olefins, etc. using an aqueous solution of a metal salt are known. (For example, special public service in 1977-
1176, Japanese Patent Publication No. 53-31842) Also, as an example of a liquid membrane for organic compounds, a membrane for separating nitric oxide using a formamide solution of ferrous chloride is known (AICh E
Journal Vol 16 No. 3 405 pages, 1970). Homogeneous membranes and porous membranes are used as supports for these liquid membranes, but in the case of homogeneous membranes, the gas permeation coefficient is extremely large so that this support does not become the rate-determining step for permeation. It is necessary to use a very thin film of the material. In addition, when a porous membrane is used as a liquid support, the permeation rate is large and this part does not become the rate-determining step for permeation.
If the pressure difference between the next side (inflow side) and the secondary side (outflow side) is large, there is a possibility that the liquid film will leak as a droplet. Therefore, it is used by flowing another gas or liquid to the secondary side of the membrane to maintain a balance with the pressure on the primary side. As mentioned above, an important issue for liquid films is how to support them, but especially when the liquid is an organic compound, the support film may or may not dissolve in the organic compound. It swells or undergoes some kind of change, and there is no good way to do it. However, among the substances that selectively and reversibly interact with gases, there are many substances such as various complexes that are insoluble in water but soluble in organic solvents, making it possible to use liquid organic compounds as liquid films. A method is desired. The present invention provides a gas separation membrane that includes such a liquid hydrocarbon as a constituent component and can be used even in the presence of a pressure difference between the two surfaces of the membrane. Specifically, the present invention relates to a gas separation membrane in which a thin film layer having many crosslinked structures is formed on a porous substrate by a plasma polymerization method, and a liquid hydrocarbon is retained on the thin film layer. Films with many cross-linked structures are suitable for not being immersed in organic compounds such as organic solvents, and the film is desired to be as thin as possible, so plasma polymerization using glow discharge is the preferred method for forming such films. This led to the realization that the present invention is suitable for the purpose of the present invention. Next, the present invention will be explained in detail. The present invention is a gas separation membrane for olefin compounds in which a liquid hydrocarbon is supported on a plasma polymerized membrane of bistrimethylsilylacetylene formed on a porous substrate. Hydrocarbons that can be used in the present invention are not particularly limited, but non-volatile compounds with a high boiling point are preferred since they are less likely to be lost through evaporation. On the other hand, in the case of highly viscous hydrocarbons with high boiling points and close to solids, the diffusion rate of gases passing through them decreases, and the rate of gas permeation decreases accordingly, so the volatility of organic solvents and gas The optimal compound is selected by considering the permeation rate. Examples of such hydrocarbons include hexane,
Aliphatic saturated hydrocarbons such as heptane, octane, isooctane, nonane, decane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, toluene, xylene, paracymene, indene, styrene, alpha-methylstyrene, mesitylene,
Aromatic compounds such as p-diethylbenzene, prenitene, isodiylene, n-butylbenzene, diphenylmethane, and diphenylethylene; condensed polycyclic hydrocarbons such as indene and methylnaphthalene;
Liquid baraffin, α-olefin, α-olefin oligomer, liquid polypropylene, low molecular weight polybutene, polyisobutylene, liquid polybutadiene, hydrogenated liquid polybutadiene, liquid polybutadiene copolymer, hydrogenated liquid polybutadiene copolymer, Examples include liquid polypentadiene, liquid polystyrene, liquid polystyrene copolymer, and liquid polypentadiene. Under the conditions of use of the present invention, a plasma polymerized membrane of bistrimethylsilylacetylene formed on a porous substrate is used to support liquid hydrocarbons.
The method of forming a plasma polymerized film is to excite a substance to a plasma state and proceed with a chemical reaction.
A low-temperature plasma method is particularly preferred, and among them, a thin film manufacturing technique that mainly utilizes blow discharge can be used. The thickness of the plasma polymerized membrane formed on the surface of the porous membrane substrate is in the range of 0.001 to 100μ, preferably 0.01 to 10μ, and more preferably 0.1 to 1μ. The porous substrate on which the plasma polymerized film is formed can be made of various materials having pores of 100 μm or less. It is desirable that the surface of these porous substrates on which the plasma polymerized film is formed has pores with a pore size of 0.1μ or less, and if the pore size of the surface on which the plasma polymerized film is formed is large, It is necessary to form a thick plasma polymerized layer to cover the holes. A thick plasma polymerized layer has the disadvantage of acting as a barrier to gas permeation. The thickness of the plasma polymerized layer formed on the surface of the porous substrate is preferably thin enough to retain the liquid organic compound even under pressure. The pore size of the substrate is required to be sufficiently small. If the gas permeation rate is high, it is preferable to have no pores, and therefore, the porous substrate as used in the present invention includes an asymmetric membrane having a dense layer on the surface. The types of materials constituting the porous substrate are not particularly limited, but include regenerated cellulose, cellulose ester, polycarbonate, polyester, Teflon, nylon, acetyl cellulose, polyacrylonitrile, polyvinyl alcohol, polymethyl methacrylate, polysulfone, polyethylene, polypropylene, Polyvinylpyridine, polyphenylene oxide, polyphenylene oxide sulfonic acid, polybenzimidazole, polyimidazopyrrolone, polypiperazine amide, polystyrene, polyamino acid, polyurethane, polyamino acid polyurethane copolymer, polysiloxane, polysiloxane polycarbonate copolymer , polyvinyltrimethylsilane, collagen, polyion complex, polyurea polyamide, polyimide, polyamideimide, sulfonated polyfurfuryl alcohol, polyvinyl chloride, and other organic polymers; glass, alumina, silica, silica alumina, carbon, and inorganic materials such as metals. can be given. These porous substrates can be used in any of the shapes of a flat plate, a tube, a spiral, and a hollow fiber. The thickness of the porous substrate is not particularly limited, but is preferably in the range of 100μ to 1000μ. These porous substrates can also be used by being further supported by another support. The gas separation membrane of the present invention is formed by supporting a liquid hydrocarbon on the surface of a porous substrate on which a plasma polymerized layer is formed. Ethylene, propylene, etc. are used as petrochemical raw materials in the production of many products, and the gas separation membrane of the present invention is useful for recovering and utilizing unreacted raw materials contained in waste gas. The content of the present invention will be illustrated below with examples; however, these examples are merely for illustrative purposes, and should not be construed as limiting the present invention to the specific materials, methods, etc. shown therein. No. Example 1 and Comparative Example 1 Porous membrane Millipore Filter VSWP (trademark, manufactured by Nippon Millipore Limited. Average pore diameter)
0.025 μ) was placed on the substrate in a Bergier-type plasma polymerization reactor, the reactor was evacuated, and bistrimethylsilylacetylene was fed into the reactor while being discharged, and the RF power was 50 W and the pressure was 0.2 mbar.
A composite membrane was formed by reacting for 40 minutes and forming a polymerized thin film of bistrimethylsilylacetylene on a Millipore filter. This membrane was attached to a membrane attachment cell (effective membrane area: 12.6 cm ² ), and 8 ml of toluene was placed on the membrane. On the other hand, helium gas or ethylene gas was adjusted to a pressure accumulator and flowed onto the above toluene liquid film (primary side) at 1.2 kg/cm ² (slightly higher pressure than normal pressure) on the secondary side of the membrane. A vacuum was applied and the permeation rate of helium or ethylene permeated over a certain period of time was measured. The measurement results are shown in Table-1.

[Table] Ethylene permeated with high selectivity due to the difference in solubility of helium and ethylene in toluene. Also, the secondary side (outflow side) of the membrane is evacuated and 1 kg/kg is passed through the membrane.
Even with a pressure difference of more than ^cm2 , toluene droplets did not leak through the membrane. Example 2 Same as Example 1 except that a mixed gas containing 36% helium and 64% ethylene was adjusted to the pressure accumulator instead of helium or ethylene alone as the supply gas, and flowed over the toluene liquid film (primary side). It was carried out in The results are shown in Table-2.

[Table] Ethylene permeates with high selectivity, and no toluene droplets pass through the membrane and leak to the secondary side of the membrane. Example 3 α-methylnaphthalene was used instead of toluene as the liquid film, and helium 67.3% was used as the supply gas.
The same procedure as in Example 1 was carried out except that a mixed gas containing 32.7% ethylene was adjusted to a pressure accumulator and flowed over the α-methylnaphthalene liquid film (primary side). The results are shown in Table-3.

[Table] Ethylene permeated with high selectivity, and droplets of α-methylnaphthalene did not leak to the secondary side of the membrane when current was passed through the membrane. Example 4 Liquid paraffin was used instead of toluene as the liquid film, and a mixed gas containing 61.2% helium and 38.8% ethylene was adjusted to the pressure accumulator as the supply gas, and the mixture was flowed over the liquid paraffin liquid film (primary side). was carried out in the same manner as in Example 1. The results are shown in Table 4.

[Table] Droplets of liquid paraffin through which ethylene permeated with high selectivity did not pass through the membrane and leak to the secondary side. Comparative Example 2 Porous membrane Millipore Filter VSWP (trademark, manufactured by Nippon Millipore Limited, average pore diameter
The procedure was carried out in the same manner as in Example 1, except that a membrane (effective membrane area: 12.6 cm ² ) was attached to the cell (effective membrane area: 12.6 cm 2 ). I couldn't do it.

Claims (1)

[Claims] 1. A gas separation membrane for olefin compounds, comprising a plasma polymerized membrane of bistrimethylsilylacetylene formed on a porous substrate and supporting a liquid hydrocarbon thereon.