DEVELOPMENT OF HYBRID FACILITATED TRANSPORT MEMBRANES BY PLASMA GRAFT POLYMERIZATION AND THEIR APPLICATION TO HIGHLY SELECTIVE SEPARATIONS

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New types of microporous cation-exchange membranes were prepared by grafting acrylic acid and methacrylic acid onto substrates, such as microporous polyethylene and polytetrafluoroethylene and homogeneous poly[1-(trimethylsilyl)-1-propyne] by the use of the plasma graft polymerization technique. Various monoprotonated amines were immobilized by electrostatic force in the ion exchange membranes as the carrier of CO_2, and the facilitated transport of CO_2 through the grafted membramnes was studied. When CO_2 partial pressure in the feed phase was 0.047 atm, the selectivity for CO_2 over N_2 was 4,700 with a CO_2 permeation rate of 1x10^<-4> cm^3/ (cm^2・s・cmHg). These efficiencies are much higher than those of conventional polymer membranes and are also superior to efficiencies reported previously for ion-exchange membranes containing carriers. These excellent results are probably attributable to the high ion-exchange capacitiy and the high water content of these ion-exchange membranes. The newly prepared membranes were stable if the feed and the sweep gases were presaturated with water vapor upstream of a permeation cell. It was also possible to graft acrylic acid onto a microporous polyethylene hollow fiber membrane, and this membrane containing ethylenediamine showed both high CO_2 permeation rate and selectivity.Membranes having tertiary amine groups as a fixed carrier were also prepared by plasma garfting 2 (N,N-dimethyl) aminoethyl methacrylate to microporous polyethylene membranes. It was suggested that the dry membrane acts as a fixed carrier membrane for CO_2 transport in the dry condition and as a fixed reaction site membrane under the water-containing condition. The carrier transport mechanism is discussed for the dry and wet membranes. The membrane prepared by grafting acrylamide onto a microporous polyethylene membrane also showed the characteristic behavior of CO_2 facilitated transport membrane.