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Employment of Supercritical C02 in Membrane Preparation Process

Supercritical C02 (SC-CO2) have been extremely used in membrane formation process due to the appropriate properties. Numerous polymeric membranes have been prepared by the phase separation process using SC-CO2 as a non-solvent for the polymer solution. This process exhibit several advantages, mainly membrane properties may bemanupulated by changing process condition; i.e., supercritical C02 can produce very different non-solvent activities using different pressures and temperatures. However the major drawback of this technique is limited affinity between C02 and water at the ordinary process conditions. Consequently, this process cannot be used to produce membranes of water-soluble polymers. In another supplement method, the phase inversion of water-soluble polymers was proposed using liquids expanded by SC-CO2. With this process, it is possible to take advantage of both capabilities of the organic solvents and SC-CO2 at very low temperatures. The next methods are synthesis of composite membranes. In a case study for improving the conductivity of Nation membranes and to inhibit methanol permeation, styrene monomer was radically grafted onto the Nation 115 membrane using SC CO2- In another work; Pd particles Were grafted on Nation 117 by supercritical-impregnation and chemical reduction. Moreover the gas permeation properties of carbon molecular sieve (CMS) membranes dispersed with palladium nano particles via SC-C02 impregnation method were investigated in another work. In this review paper we cite other methods which have successfully used for preparation of membranes namely formation of integrally skinned asymmetric gas separation membranes by SC-C02 and proton conducting membrane preparation using multi-layer acid- base complex formation on porous polymeric film.