The effect of hexane treatment on the permeation of silicone‐coated polyethersulfone membranes

Abstract

SynopsisThe polyethersulfone membranes were cast from casting solutions including poly (vinyl pyrrolidone) additive. The membranes were further dried, silicone-coated, and used for the permeation study with hydrogen and nitrogen gases. It has been found that solvent hexane which was included in the silicone rubber solution for surface coating increased the pore size on the membrane surface when poly(viny1 pyrrolidone) was present in the membrane. The above effect counteracted the pore size decrease by silicone coating, and, as a result, an H2/Nz permeability ratio of only 8.9 was achieved as compared with 28, which was obtained when the base polyethersulfone membrane was prepared from a casting solution without poly( vinyl pyrrolidone) additive. INTRODUCTIONIn contrast to most of the fundamental works on gas permeation, in which dense homogeneous membranes are used, all of commercially important membranes possess asymmetric structures. This is natural because the combination of high flux and sufficiently high separation factor for the components of gas mixtures can be achieved by the asymmetric membrane structure. It is well known that the performance of the membrane depends largely on the condition of the formation of such asymmetric structures. There is, however, only limited work in the literature in which the effect of membrane preparation variables on the membrane performance for the gas separation has been systematically studied.'-?The objective of this work is to cIarify the cause and etfect relationship between variables involved in the membrane preparation and the membrane performance. More specifically, this is one of a series of investigations which have been conducted to clarify the etfect of the pore size of the polyethersulfone base membrane and the number of the silicone coatings on t,he performance of the silicone rubber coated polyethersulfone membrane for gas separation. In our previous work,8 we have found that the maximum in the permeation rate ratio of hydrogen/ nitrogen gas system achieved by silicone-coated membranes increased with a decrease in the average pore size of the base polyethersulfone film. The natural consequence of the previous work, therefore, is to decrease the average pore size of the polyethersulfone membrane further to achieve an even higher maximum permeation rate ratio. It has to be noted that all poly-' T o whom correspondence should be addressed.,Journal of Applied Polymer Science, Vol. 41, 2169-2176 (1990) Published with permission by tJohn Wiley & Sons, Inc.Copyright owned by the Crown in right of Canada.CCC 002 1-8995/90/9-102 169-08$04.00 2170 CHEN ET AL.ethersulfone films used in the previous work were prepared from the casting solution including polyethersulfone polymer and dimethylsulfoxide solvent alone. From a separate investigation on the preparation of polyethersulfone ultrafiltration membranes, it has been known that the average pore radii of membranes prepared from casting solutions without any additives were larger than those of membranes prepared from...