Separating membrane of polyion complex

Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...

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21050037, 21050043, B01D 6136

Patent

active

053934326

DESCRIPTION:

BRIEF SUMMARY
SPECIFICATION

1. Field of Industrial Application
The present invention relates to a permselective membrane for water having a broad spectrum of applications. The permselective membrane for water according to the present invention is useful as those which are used in pervaporation and vapor permeation, and futher is used in reverse osmosis and dehumidification of air utilizing the hydrophilicity of the membrane.
2. Related Art
Reverse osmosis has been put into practical use to concentrate an aqueous solution of an organic substance having a low concentration with a membrane. However, the reverse osmosis is inapplicable to an aqueous solution having a high concentration and hence exhibiting a high osmotic pressure, because a pressure not lower than the osmotic pressure of a fluid fed for separation (namely, fluid to be treated) must be applied to a separating membrane. That is, there is a limit in the concentration of a solution to which the reverse osmosis is applicable. In contrast, pervaporation and vapor permeation are now drawing attention as novel separation methods, because these methods are separation methods which are not affected by osmotic pressure. Pervaporation is a method comprising reducing the pressure or passing a carrier gas on the secondary side (permeate side) of a membrane while feeding a fluid for separation to the primary side of the membrane so as to cause a substance to be separated to permeate the membrane in gaseous form. Vapor permeation is a similar method to the pervaporation, except that a vapor mixture is fed to the primary side of the membrane. A membrane-permeating substance (a substance to be separated) can be collected by cooling vaporous permeate to effect condensation thereof.
With respect to pervaporation, various researches have been reported. For example, one in which a mixture of an organic substance and water was separated using a membrane of a polymer having active anion groups and another one in which a mixture of ethanol and water was separated using a membrane of cellulose acetate or polyvinyl alcohol have been reported. Further, a crosslinked polyvinyl alcohol membrane, a cellulose triacetate membrane and a crosslinked membrane based on a polyethyleneimine have been reported as a separating membrane for use in pervaporation. However, it can be stated that the membranes described in these research reports have such a low permeation rate that their practical value is poor.
On the other hand, a membrane of an anionic polysaccharide or a polysaccharide derivative may be mentioned as a membrane having excellent separating performance. However, the use of such membranes involves latent problems inevitable for natural polymers, such as depolymerization caused by an acid or alkali and bacterial decomposition. Therefore, desirable durability and chemical resistance cannot be expected from these membranes.
A separating membrane of a polyion complex of a carboxylated polymer, such as polyacrylic acid (see, for example, U.S. Pat. No. 4,871,461), may be mentioned as a membrane which is excellent in both permeation rate and separation factor. However, it is difficult to use this separating membrane at high temperatures. For example, when a 99 wt. % aqueous ethanol solution is used as a fluid feed (fluid to be treated), the employment of a temperature as high as 70.degree. C. or above to increase the permeation rate is likely to cause the separation factor to decrease.
The object of the present invention is to provide a membrane exhibiting stable separation factor and permeation rate irrespective of the employment of high temperatures (e.g., 70.degree. C. or above) for a fluid feed.
The term "permeation rate" used in the present invention means the amount of permeation of a substance fed for treatment (fluid or vapor feed) per unit membrane area and per unit time, which is expressed in kg/m.sup.2 .multidot.hr. On the other hand, the separation factor (.alpha.) is the ratio of the ratio of water to an organic substance in a gaseous permeate {(X/Y).sub.p } to that of water to

REFERENCES:
patent: 4871461 (1989-10-01), Karakane et al.
patent: 5032282 (1991-07-01), Linder et al.

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