Composite membrane

Details Composite membrane Composite membrane

1992-01-21

1993-11-09

Sever, Frank

Liquid purification or separation

Filter

Supported, shaped or superimposed formed mediums

21050028, B01D 6700

Patent

active

052599507

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a composite membrane to be used for pervaporation method, which membrane is excellent in solvent resistance, to a composite membrane useful for selective separation of liquid mixtures, especially for the separation of aqueous solutions containing organic solvents or aqueous solutions at high temperatures, and to a composite membrane which may be used for selective separation of mixed gas, which has high gas permeability, high separation ability and high resistance to organic vapors.


BACKGROUND ART

Pervaporation method is a useful method for separating organic liquid mixtures containing volatile components by utilizing a membrane. By this method, separation of liquid mixtures of organic components which are difficult to separate by distillation because the boiling points thereof are close, because the mixture is an azeotrope, or because the organic components are denatured by heating, can be attained. This separation method has an advantage in that the energy cost is lower than separation by distillation or the like. Recently, intensive studies of this method were made especially for the separation of alcohol/water mixtures. A membrane by which water can be removed from a high concentration aqueous alcohol solution is now practically used.
In this method, an organic liquid mixture containing a volatile component is supplied to one side of a membrane and the pressure of the other side of the membrane (secondary side) is reduced with or without flowing an inert gas. By so doing, a component in the mixture having a high affinity with the polymer constituting the membrane preferentially permeates the membrane to the secondary side in gaseous form, and separation is performed. For example, in the case of aqueous ethanol solution, if the membrane has a high affinity for ethanol, ethanol preferentially permeates the membrane, and if the membrane has a high affinity for water, water preferentially permeates the membrane.
Designating the component which preferentially permeates as Component A, and designating the other component as Component B, the performance of a pervaporation method is expressed by the separation coefficient .alpha. defined as follows and by the permeation rate Q. in the secondary side, PB represents the concentration by weight of Component B in the secondary side, FA represents the concentration by weight of Component A in the supplying side, and FB represents the concentration by weight of Component B in the supplying side. Q means the amount of the permeated component per unit area of the membrane per unit time, and the unit is usually kg/m.sup.2.hr.
In the membrane used for the pervaporation method, the thickness of the membrane largely influences the membrane performance, especially the permeation rate. That is, the thinner the membrane, the higher the permeation rate. In order to attain a membrane performance which may be practically employed, it is necessary to make the thickness of the membrane several .mu.m or less. However, it is difficult to produce such a thin membrane. Further, even if such a thin membrane can be produced, it cannot be used in practice because the mechanical strength is poor. To solve this problem, a support may be used. Thus, composite membranes comprising an active layer having the substantial separation ability by pervaporation and a support layer for mechanically reinforcing the active layer are now investigated. Such composite membranes are usually produced by first providing a porous support and then applying the active layer on the surface of the support by coating or the like.
Various membranes for pervaporation have been proposed. For example, Japanese Laid-open Patent Application (Kokai) No. 58-89911 discloses a composite membrane employing polyorganosiloxane as the active layer and polyfluorovinylidene or fluorovinylidene copolymer as the support. Japanese Laid-open patent application (Kokai) No. 60-28803 discloses a composite membrane having an active layer made of a polyethyleneimine modified by a wate

REFERENCES:
patent: 5112487 (1992-05-01), Himeshima et al.

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