(152o) Separation of Similar-Sized Gas Molecules (CO, C2H4) Using Carbon Molecular Sieve (CMS) Membranes

In this poster, I will describe my ongoing efforts to design membranes for the downstream separation of C₂H₄ from a mixture of CO, CO₂ following the electrochemical conversion of CO₂ to C₂H₄. To produce high purity C₂H₄, unconverted CO₂ and residual CO must be removed from the product stream. CO (d = 3.76 Å) and C₂H₄ (d = 3.75 Å) are particularly difficult to separate based on their relative diffusion coefficients; therefore, we hypothesize that a sorption-based separation mechanism could be leveraged to achieve this separation. This project intends to make metal-embedded carbon molecular sieve membranes to separate CO and C₂H₄ . CMS membranes, which are pyrolyzed end-products of rigid polymers, have demonstrated precise separations for several similar-sized gas-pairs.

The addition of metal functionalities, especially Cu⁺/Cu²⁺ is hypothesized to enhance the sorption-based selectivity of these membranes, as has been demonstrated in Cu-based metal organic frameworks in prior research. I will also describe some novel techniques that we are developing to characterize metal-incorporated membranes.

Furthermore , I will highlight an alternate entropic diffusion selectivity mechanism to separate these similar-sized, yet differently-shaped molecules. Enthalpic diffusion selectivity would have lower separation but by looking at entropic diffusion selectivity, CMS membranes could be tightened or loosened to adjust to the degrees of freedom of the gas molecules. For this purpose, pyrolysis conditions will be tuned to achieve the perfect balance between restricting C₂H₄ degrees of freedom, while still retaining most of the degree of freedom for CO.