This research centers on the development of a membrane-based method for the downstream separation of ethylene (C₂H₄) from a mixture of carbon monoxide (CO) and carbon dioxide (CO₂), which are byproducts of the electrochemical reduction of CO₂ to C₂H₄. Achieving high-purity C₂H₄ requires the effective removal of both unreacted CO₂ and intermediate impurity CO. However, separating CO from C₂H₄ poses a significant challenge due to their identical molecular sizes (0.375 nm), which hinders the performance of conventional diffusion-based separation methods. To overcome this limitation, we investigate a sorption-driven separation method using carbon molecular sieve (CMS) membranes. These membranes are produced by pyrolyzing rigid polymers at temperatures exceeding 500°C and highly tunable. The research aims to examine how gases partition into different sorption domains within the CMS—specifically the Langmuir and continuous domains. We conduct permeation and sorption measurements across a range of temperatures to extract intrinsic temperature dependence parameters, which are critical for predicting CMS performance and guiding the design of new materials and optimal testing conditions. Additionally, corrected diffusion values are obtained through Maxwell-Stefan diffusivity analysis to improve understanding of gas-material interactions. Mixed gas experiments were also performed to observe how the presence of other gases influences individual gas behavior. The overarching goal of this work is to inform the design of CMS membranes with high selectivity for ethylene separation processes.
