Promoting acid gas separations via strategic alkoxysilyl substitution of vinyl-added poly (norbornene)s

The development of membranes for the concurrent removal of CO2 and H2S from natural gas continues to elude researchers and frustrate industrial adoption of membrane technologies. A long-observed performance trade-off exists where glassy polymers generally lend themselves to diffusion-controlled CO2/CH4 separations, while rubbery polymers excel in solubility-controlled H2S/CH4 separations. These orthogonal separation preferences complicate materials development in pursuit of a membrane capable of simultaneous acid gas removal from concentrated sour gas feeds with high efficiency. Herein, we report our examination of alkoxysilyl-substituted vinyl-added poly (norbornene)s (VAPNBs) for the removal of CO2 and H2S from simulated natural gas feeds. This study investigates the sour gas separation performance of ten distinct VAPNBs that systematically vary in alkoxysilyl substitution to evaluate their ability to perform this challenging separation. High-pressure mixed gas permeation testing highlights structure-property relationships stemming from previously observed design principles related to side chain polarity and sterics that lead to high H2S/CH4 selectivities, exceptional CO2 and H2S permeabilities, and notable improvements in CO2/CH4 permeation properties compared to a well-studied alkylsilyl VAPNB derivative. By combining permeation analysis and pure gas sorption measurements, changes in the Langmuir contributions were found to be influential on acid gas separation performance. These results provide insight and opportunity to further expand this work in order to bring to market membranes capable of simultaneously removing CO2 and H2S from natural gas.