Removal of Non-Hydrocarbon Natural Gas Impurities over Gas Hydrate Membranes

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Every year close to 100 trillion standard cubic feet of natural gas are used worldwide, making natural gas processing the largest industrial gas separation technology. Natural gas consists primarily of methane, carbon dioxide, nitrogen, hydrogen sulfide, and other hydrocarbon fuels. It is highly desirable to remove non-fuel impurities from natural gas to improve its heat content. These impurities may be removed with selective membranes, which allow one component to pass while retaining other components. Membranes can save energy relative to separation techniques that require compression or liquefaction of the gas at cryogenic temperatures. The main objective of this work is the rational design of novel gas hydrate membranes for natural gas purification. This research may result in a viable energy-saving approach to potentially reduce the costs associated with natural gas purification. The central thrust of this proposal is the rational design of a novel family of membranes, composed of gas hydrates which offer the possibility of demonstrating high separation performance for natural gas purification. The specific objectives of this work include: (i) Development of gas hydrate membranes for the separation of CO2, N2, and mercaptans from methane; (ii) Understanding and tuning the kinetics of hydrate formation and dissociation; (iii) Demonstration of gas hydrate membrane performance for the separation of CO2, N2, and mercaptans from methane, and (iv) Establish the basic structure/separation relationships of gas hydrates membranes for the separation of CH4 from non-hydrocarbon natural gas impurities. Specifically, we propose a separation process in which gas hydrate membranes will be employed to capture natural gas impurities, such as CO2, N2, and mercaptans as H2S substitutes. Fundamentally, it is expected that the proposed separation may be promoted or favored by a dynamic replacement in which there will be an exchange of natural gas impurity molecules from the feed gas with the guest molecules in the initially formed natural gas hydrate. This separation mechanism would be very distinctive from traditional mechanisms observed in polymeric or inorganic membrane materials. Finally, this proposal aims at understanding fundamental questions related to gas hydrate membrane, kinetics of formation and dissociation, and stability, which are key aspects for developing robust gas hydrate membranes. The ability to fabricate gas hydrate membranes for industrially relevant gas separations constitutes a new and distinctive direction in membrane science, with the ultimate goal of achieving higher combinations of permeability and selectivity for natural gas purification. The educational outreach of the proposed plan spans from summer workshops and REU programs, inclusion of underrepresented groups in undergraduate education, and recruitment of minorities for graduate studies.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.