Mutual interaction in mixed gas permeation through zeolite membranes

The gas permeation through zeolite membranes is strongly affected by the mixture concentration and the operating conditions used. In this work, we experimentally investigated the separation performance of a DDR membrane for separation of CO2 from H2 and N2 in the temperature range 25-75°C and up to 700 kPa [1]. Single gas measurements showed that CO2 is the most permeable species, followed by H2 and N2. In mixture, the preferential adsorption of CO2 significantly hinders the permeation of weakly adsorbed species. At the same time, CO2 is itself influenced by the presence of H2 and N2, increasing its permeation when the composition of the other species is higher. The difference between single and mixed gas permeation is emphasized by the low temperature, reflecting in a high selectivity in this region (Figure 1). The highest CO2 selectivity values are 28 and 17 in presence of N2 and H2, respectively, whereas the CO2 permeance exceeds 1.5 times the single gas value (i.e., 18 nmol m-2 Pa-1 s-1) for a CO2:H2 mixture = 40:60. We found that diffusion of CO2 is promoted more by H2 than by N2. Similarly, the hindering effect exerted by CO2 is more important on H2 than on N2. These behaviors are confirmed in other zeolite membranes [2]. The choice of appropriate operating conditions makes DD3R particularly suitable for CO2 separation. The permeance variations with the mixture composition reflected directly on selectivity, which can be five times higher than that in single gas in presence of H2.