(587c) Development of New Siloxane Terpolymers for Enhanced C3+ Hydrocarbon Recovery from Natural Gas

Natural gas plays a significant role in the global energy mix. Although raw natural gas consists primarily of CH₄, it can contain significant amounts of other gas components, including acid gases (CO₂ & H₂S), N₂, He, and C₃₊ hydrocarbons. These C₃₊ hydrocarbons are valuable chemical feedstocks and can be used as a liquid fuel for power generation and seawater desalination. Commercially available rubbery siloxane membranes are utilized in industry for the rejection of N₂ and for the concentration of C₃₊ hydrocarbons in the membrane permeate stream. However, current state-of-the-art PDMS membranes with (Me₂SiO)_n backbones show lower C₃₊/CH₄ selectivities under industrially relevant feed streams and testing conditions. In this work, modified crosslinked siloxane terpolymer (VinylMeSiO)_p(Me₂SiO)_m(OctMeSiO)_n membranes (Ter-PDMS) were fabricated and evaluated for separations of C₃₊ hydrocarbons from natural gas. Results show that modified crosslinked siloxane Ter-PDMS membranes showed enhanced C₃₊ separation performance compared to conventional PDMS membrane under simulated typical field gas testing conditions (i.e. feed pressures up to 850 psi for multicomponent gas mixture consisting C₁-C₅ hydrocarbons, CO₂, N₂, and BTEX). At 800 psi, Ter-PDMS membranes exhibited C₄/CH₄ mixed gas selectivity and C₄H₁₀ permeability of 17.2 and 15100 Barrers, respectively. These results emphasize the observations that membrane separation performance is strongly related to the testing conditions and feed compositions, highlighting the importance of exploring and designing better modified rubbery siloxane membrane materials for the actual industrial process.