Gas separation – Means within gas stream for conducting concentrate to collector
Patent
1987-06-08
1988-05-24
Foelak, Morton
Gas separation
Means within gas stream for conducting concentrate to collector
55 16, 521 61, 521 64, 521154, 521140, 525105, 525106, B01D 1300
Patent
active
047463341
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a novel poly(disubstituted acetylene)/polyorganosiloxane graft copolymer, where the main chain is composed of poly(disubstituted acetylene) and the side chain is composed of polyorganosiloxane, and a membrane prepared from the copolymer useful for separation of a gaseous mixture. More particularly, the membrane to which the present invention relates is a gas separation membrane which has high membrane strength and sufficient permeability and excellent selectivity for oxygen suitable enough to concentrate oxygen in the air.
BACKGROUND ART
Gas separation techniques using a membrane are rapidly developing their applications because of economy of energy, high safety and simpleness in handling. Among them, the technique with which oxygen is separated from other members in a mixture of gases is useful, particularly when the mixture of gases is the air and the technique is employed to concentrate oxygen. If an oxygen-enriched air could be produced from air in a simple and economical way, a large contribution is expected in many fields of industry, for example, a variety of combustion engines, medical instruments, food industry, and disposal of industrial exhausts.
Membranes which are employed for these purposes should desirably bear the characteristics; a large ratio of the permeability coefficients of oxygen gas upon nitrogen gas and a large permeability for oxygen gas. Especially the latter is more important, because a larger amount of oxygen per unit time permits the separation apparatus to be smaller and the amount of treated gas to be increased. A large permeation of oxygen gas can be obtained by choosing a material of a high permeability coefficient P.sub.O2 for oxygen and making the thickness of the membrane as thin as possible. Thus, the material of the membrane should have sufficient strength enough to sustain the gaseous pressure when formed in a thin film.
Among the polymer membranes ever known, polydimethylsiloxane membranes typically represent those having the largest permeability coefficient P for gases (if not otherwise specified, unit of the permeability coefficient is expressed hereinafter in cm.sup.3 (STP).cm/cm.sup.2.sec cmHg). Although the permeability coefficient P.sub.O2 for oxygen is as high as 6.times.10.sup.-8, the separation coefficient .alpha. between oxygen and nitrogen gases (the permeability coefficient P.sub.O2 for oxygen gas divided by the permeability coefficient P.sub.N2 for nitrogen gas) is as low as 2.0. Further, a membrane of polydimethylsiloxane is low in the mechanical strength and therefore a membrane not more than several ten .mu.m thick can not be employed for practical uses. Thus, polydimethylsiloxane does not provide a membrane of sufficient high permeability for oxygen in the practical sense. For improving the membrane characteristics of polydimethylsiloxane, copolymers of polydimethylsiloxane with polymers of high mechanical strength such as polycarbonate and poly-.alpha.-methylstyrene have been developed (for example, as disclosed in U.S. Pat. No. 3,980,456, U.S. Pat. No. 3,874,986 and in Japanese Laid-Open Patent Application No. Sho 56-26504). But result was not always satisfactory because of the lowered permeability coefficient P.sub.O2 for oxygen or the insufficient separation coefficient .alpha..
On the other hand, as a material having a higher permeability coefficient for gases than polydimethylsiloxane is known poly(disubstituted acetylene) represented by polytrimethylsilylpropyne (J. Am. Chem. Soc., 1983, 105, p. 7473 and J. Appl. Polym. Sci., 1985, 30, p. 1605). Membranes prepared from polytrimethylsilylpropyne have a permeability coefficient P.sub.O2 for oxygen 4-7.times.10.sup.-7 and a separation coefficient .alpha. 1.7-2.0. This material can be processed in the form of membrane due to its excellent film strength. However, if used as separation membrane for oxygen, sufficiently high oxygen concentration is not obtained owing to the small separation coefficient .alpha. and a further defect is that the perm
REFERENCES:
patent: 4261876 (1981-04-01), Reusser
patent: 4526922 (1985-07-01), Pickwell et al.
patent: 4526930 (1985-07-01), Keogh
patent: 4535126 (1985-08-01), Iida
Matsui Kiyohide
Nagase Yu
Uchikura Masaki
Foelak Morton
Sagami Chemical Research Center
Tosoh Corporation
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