The potential of hybrid membranes as a CO 2 capture technology for integrated gasification combined cycle applications was evaluated. Commercial γ-alumina supports were modified with a variety of trichlorosilanes intended to enhance the surface adsorption of CO 2 . The resulting hybrids were characterized using X-ray photoelectric spectroscopy and Fourier transform infrared spectroscopy and tested for performance in the separation of He and CO 2 . The silanization temperature was determined to be important because membranes fabricated at 273 K had substantially different performance properties than those fabricated at room temperature. Specifically, the permeances of membranes modified with alkyltrichlorosilanes at reduced temperatures were 1−2 orders of magnitude higher than those of membranes fabricated at room temperature, and the selectivities of these low-temperature silanized membranes were relatively similar to those expected from Knudsen diffusion. Supports modified with silanes containing one of a variety of functionalities were tested for CO 2 /He selectivity. Membranes modified with 2-acetoxyethyl, 2-carbomethoxyethyl, and 3-aminopropyl groups exhibited CO 2 selectivity, with the highest values approaching 7 for 2-carbomethoxyethyl-silated membranes at 50 °C. Temperature dependences resulted in selectivity maxima for the 2-acetoxyethyl and 2-carbomethoxyethyl membranes. Mixed-gas selectivities were slightly higher than pure-gas selectivities because of a decrease in He permeance with a relatively minor reduction in CO 2 permeance. Transport in the selective membranes is believed to occur by a combination of activated and solution diffusion for He and a combination of activated and surface diffusion for CO 2 .
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Luebke et al. (2006) studied this question.