Polyimide-based Hybrid Membranes And CO₂ Facilitated Transport Mechanisms

CO₂ separation is a vital technology for solving the increasingly globle warming as well as for industrial processes such as natural gas and biogas purification. Compared with conventional technologies including absorption and adsorption, CO₂ membrane separation possesses prominent advantages including high energy efficiency, scale-up simplicity and environmental friendliness. Among different CO₂ separation membrane materials, facilitated transport membrane attracts more and more attention since it shows both high permeability and selectivity arising from the reversible interaction between CO₂ and carriers. Preparation of high performance membrane materials and investigation of facilitated transport mechanisms are the key issues.The aim of this dissertation is to obtain high membrane separation performance and probe CO₂ facilitated transport mechanisms. Based on the interactions between CO₂ and carriers, a series of facilitated transport hybrid membranes are designed and prepared, enhanced CO₂ permeability and CO₂/CH4 selectivity are obtained, issues about water microenvironment regulation, the impact of humidified/dry conditions on facilitated transport as well as the relationship between the electronegativity and the facilitated transport ability of metal ions are deeply investigated.Based on nucleophilic addition mechanism, polyzwitterion material（pSBMA） is first utilized to prepare facilitated transport hybrid membrane for CO₂ separation. The quaternary ammonium in repeat unit of pSBMA could serve as CO₂ carrier then introduce nucleophilic addition type facilitated transport mechanism into membrane. Meanwhile, the highly hydrophilic pSBMA could improve water uptake and adjust water state of membrane. These two aspects both contribute to the enhanced membrane separation property. Besides, CO₂ permeability and selectivity of membrane are positively correlated with the water content and the bound water portion in membrane, respectively.Based on nucleophilic addition mechanism and π complexation mechanism, two types of facilitated transport hybrid membranes are prepared for CO₂ separation. Membrane with imidazole group as CO₂ carrier shows facilitated transport behavior based on nucleophilic addition mechanism at humidified state since water participates in the nucleophilic addition reaction. Membrane with Zn²⁺ as as CO₂ carrier shows facilitated tranpsrt behavior based on π complexation mechanism at dry state since water would hinder the π complexation between CO₂ and Zn²⁺.Based on π complexation mechanism, Cu²⁺, Fe²⁺, Ca²⁺ and Mg²⁺ are introduced into CO₂ separation membranes to probe their CO₂ facilitated transport abilities. The result shows that transition metal ions could serve as CO₂ carriers then significantly enhance membrane separation properties. However, main group metal ions show no facilitated transport ability. The CO₂ facilitated transport abilities of metal ions are related to their electronegativities. Zn²⁺ possesses the most suited electronegativity（1.65） for CO₂ facilitated transport and the facilitated transport ability of a metal ion would be poorer when its electronegativity is more deflected from that of Zn²⁺.