Studies On Improvement Of Permselectivity Of Membranes For CO₂Separation

Efficient CO₂separation processes play key roles for clean energy supply andgreenhouse gas reduction. Membrane technology for CO₂separation has attractedincreasing attention for fuel gas purification and flue gas CO₂capture. However, themembrane technology has not been widely applied in practical processes due to thelack of high-performance membranes.The separation between CO₂and other gases is based on the permselectivity ofmembranes, including diffusivity-selectivity, solubility-selectivity and reactivity-selectivity. The effective way to improve the membrane performance is to improvethe permselectivity of membranes. In this work, we explored the methods to improvethe reactivity-selectivity and solubility-selectivity of membranes, respectively.Firstly, membranes with reactivity-selectivity were developed by interfacialpolymerization （IP） with hexane-soluble trimesoyl chloride （TMC） and water-solublediamines with tertiary amino groups. The effects of the content of tertiary aminogroups and the reaction rate constant between CO₂and tertiary amino groups on themembrane performance have been investigated by using1,4-bis （3-aminopropyl）piperazine （DAPP）, N-aminoethylpiperazine （EAP） or3,3’-diamino-N-methyldipropylamine （DNMDAm） as the monomer in the aqueous phase. Resultsindicate that the membrane containing cyclic tertiary amino groups developed withDAPP possesses high separation performance due to the high content of carriers andthe high reaction rate constant between CO₂and carriers. Moreover, the membranedeveloped with DAPP shows high plasticization resistance at high pressure due to theappropriately rigid polymer chains consisting of covalent crosslinking structure andcyclic structure.After that, membranes with solubility-selectivity were developed by IP withhexane-soluble TMC and water-soluble binary or ternary amines with propyleneoxide （PO） groups. The effects of PO group content and crosslinked density on themembrane performance have been investigated by using D400, D230or T403as themonomer in the aqueous phase. Results indicate that the membrane developed withD400exhibits the highest separation performance due to its high PO group contentand low crosslinked density. Moreover, the effects of monomer concentration, acid acceptor, pH of aqueous solution and temperature of polymerization reaction on theseparation performance of membranes have been investigated. The high-performancemembrane containing PO groups has been developed by optimizing these preparationconditions.