Zhang, Jinxuan2025-05-082025-05-082025-05-082025-05-02https://hdl.handle.net/10012/21708Olefins are essential feedstocks for producing a wide range of polymers and chemicals, and their separation from associated paraffins is crucial to obtaining high-purity olefins (>99.5%). However, due to their similar molecular weights and volatilities, olefin/paraffin separation remains a significant challenge. Distillation, the conventional method for this process, is both capital- and energy-intensive. Therefore, the development of alternative technologies that can be effective, sustainable, and energy-efficient for olefin/paraffin separation is a focus. Facilitated transport membranes (FTMs) offer a promising alternative by employing metal ion carriers, typically Ag⁺, to chemically facilitate olefin transport. This work developed a series of FTMs using polymeric matrices with both metal-chelating and hydrogel-like properties, achieving high olefin permeability, selectivity, and stability for olefin/paraffin separation. The first study focused on FTMs based on chitosan and silver nitrate. A large amount of silver was incorporated into the membrane by simply immersing a pre-formed chitosan membrane into an aqueous silver nitrate solution. Through sorption and diffusion, Ag⁺ ions and water were effectively loaded into the membrane, facilitated by the abundant amine groups in chitosan and their chelating interactions with silver ions. The membrane's high-water uptake created an ideal microenvironment for olefin-silver complexation, as well as the migration of both the complexes and silver ions. This study highlights the crucial role of both Ag⁺ and water loading in achieving optimal facilitated olefin transport. To further enhance water retention and membrane performance, a modification using dilute citric acid treatment was proposed. This approach contributes to preserving a small fraction of protonated amine groups, thereby improving the membrane’s water retention capacity and ultimately enhancing its separation efficiency. Next, a poly(vinyl alcohol) (PVA)/poly(vinyl amine) (PVAm)-based membrane was identified as a promising candidate for facilitated olefin transport. These two linear polymers were interpenetrated into a water-insoluble chitosan framework, forming an interpenetrating network (IPN) that achieves membrane insolubility without conventional crosslinking. This approach maximizes the availability of abundant amine and hydroxyl groups within the IPN, enhancing chelating interactions with Ag⁺ and enabling higher Ag⁺ loading compared to crosslinked membranes. The IPN structure allows for a water uptake of up to 2.32 g/g-polymer while maintaining sufficient mechanical strength for facilitated olefin transport, which involves the migration of complexes and silver ions within the membrane. To further optimize the membrane structure, a PVA/PVAm composite FTM with a gradient structure was developed using vapor-solid interfacial crosslinking. Beneath the highly crosslinked outer surface, abundant hydroxyl and primary amine groups were retained to facilitate chelation-based Ag⁺ loading, while the enhanced polymer chain mobility in the interior provided additional free volume for Ag⁺ and water loading. The ultrathin crosslinked surface, formed through interfacial crosslinking, acted as an effective barrier to paraffin molecules while maintaining permeability for olefins, leading to high perm-selectivity in olefin/paraffin separation. Another potential membrane matrix, derived from natural waste cocoons, was investigated for olefin/paraffin separation. Pristine fibroin FTMs exhibited limited performance due to low silver salt and water uptake, attributed to their rigid structure and low swelling capacity. Moreover, their brittleness and mechanical instability prevented them from withstanding the stress induced by Ag⁺ bonding at high concentrations. To address these limitations, fibroin and sericin were blended with chitosan. Both membranes demonstrated increased Ag⁺ and water loading capacities, better film-forming properties, and enhanced olefin permeability and olefin/paraffin selectivity. The β-sheet structure of fibroin in the chitosan/fibroin-Ag⁺ membrane provided greater structural rigidity, reducing paraffin permeability and mitigating competitive effects during mixed-gas permeation, ultimately leading to higher olefin/paraffin selectivity. To further investigate the gas permeation behavior and transport mechanisms in the water-swollen FTMs, the permeability, solubility, and diffusivity of olefins and paraffins were analyzed in four different FTMs. The study demonstrated that the permeability of the FTMs was significantly influenced by Ag⁺ and water content. Sorption tests showed that olefin solubility increased with pressure, deviating from Henry's law due to the combined effects of Ag⁺ complexation and gas condensability. Diffusivity calculations indicated that paraffins generally had higher diffusivity than olefins, primarily governed by molecular size.enDoctoral Thesis