(662e) Crosslinked Polyvinylalcohol-Polysiloxane/Fumed Silica Composite Membranes Containing Amines for CO2/H2 Separation

CO2-selective facilitated transport membranes containing both amine carriers and fumed silica in either the crosslinked polyvinylalcohol-polysiloxane (PVA-POS) or the crosslinked PVA matrix were successfully prepared for CO2/H2 separation. The effects of operating temperature, feed pressure, gas relative humidities, crosslinking degree of PVA, and membrane compositions (including type of aminosilane, type of fixed carrier and fumed silica (FS) nanoparticle addition) on the transport properties of membranes, including CO2 permeability, CO2/H2 selectivity, CO2 and H2 flux, were studied with a feed gas containing 20% CO2 and 80% H2. The results showed that the optimal operating temperature of the membranes was 107°C, and both CO2/H2 selectivity and CO2 permeability decreased as feed pressure increased from 70 to 220 psia, which can be explained by the carrier saturation phenomena. Increasing the crosslinking degree of PVA from 30 to 100 mol% could slightly decrease CO2 permeability but had insignificant effect on CO2/H2 selectivity. There were no obvious improvements found by replacing the monoaminosilane, i.e., 3-aminopropyltriethyoxysilane (APTEOS) with triaminosilane, i.e., N1-(3-Trimethoxysilylpropyl)diethylenetriamine (DETA) in membrane compositions, indicating the unfavorable PVA/DETA interactions leading to the formation of larger silica agglomerates causing some amine groups from silane-derived silica to be inactive. An increase in the total amine concentration (AC) value generally enhanced both CO2/H2 selectivity and CO2 permeability. Comparisons of the relative contributions of two fixed carriers, poly(allylamine) (PAA) and silane-derived aminosilica, to membrane performance indicated that PAA facilitated more CO2 transport through membranes than aminosilica. Increasing FS nanoparticle addition from 12 to 22 wt% could significantly increase CO2/H2 selectivity by a factor of ~ 20 while keeping a CO2 permeance as high as 41 GPU, presumably due to the silica-induced polymer packing effects leading to the increase of polymer free volume. Further increasing FS content caused both CO2/H2 selectivity and CO2 permeability to decrease due to the significant decrease of total carriers inside the membranes. The optimized membrane with about 22 wt% fumed silica showed simultaneously a high CO2 permeability of ~1300 Barrers and a high CO2/H2 selectivity of 87 at the feed pressure of 220 psia and the temperature of 107°C.