Preparation Ofpolysiloxane Membranes Modiifed By Branched Cross-linking Agents And Their Gas Permeability Perofrmance

Greenhouse effect has now become a matter of human survival and the development ofglobal issues, while most of greenhouse gas “carbon dioxide”（CO₂） was produced by fossilfuels. Therefore it is important to improve the combustion efficiency, separation and captureof carbon dioxide gas from the combustion of gas emission in order to deal with greenhouseeffect. Compared with the traditional separation technology, it brings outstandingadvangtages, like high efficiency, simple equipment, easy operation and low energyconsumption. Increasing attention has been paid in recent years in the field of gas separationmembrane technology.Polydimethyl siloxane （PDMS） is a semi-organic and inorganic polymer silicone rubber.Due to its unique molecular structure, the PDMS film has a high permeation flux, a strongmechanical properties and anti-stretch film performance. However, the molecular structureconstrains the selectivity of PDMS membrane separation. A lot of research work is carriedout in order to improve the selectivity of PDMS membrane separation. PDMS film canimprove the gas separation performance through the PDMS membrane material segmentmodified by manner like PDMS methyl ester copolymer. However, these methods canimprove the selectivity of PDMS membrane gas while also destroy the flexible PDMSmolecules. The gas permeation performance of the PDMS film decreases.A cross-linking agent as an important part of the synthetic PDMS membrane isintroduced in their molecular structure. The PDMS membrane gas selectivity can beimproved with adding functional groups which have specific interactions with carbon dioxideand oxygen while maintaining its high gas permeation properties. This paper includesdesigning crosslinker molecule structure through silicon hydrogen reaction with three newchain molecules cross-linking agent the PMV, PEGMV and HDFPMV in order to obtainhydroxyl-terminated PDMS crosslinked film. PDMS/PMV film, the PDMS/PEGMV film andPDMS/HDFPMV film were synthesized. When certain amount of crosslinker was added, thechanges and amount in the content of the cross-linking agent in functional branched wereinvestigated. The effect of them on PDMS membrane gas separation performance of thecarbon dioxide, oxygen and nitrogen was also studied.The results show that:（1） CO₂and O₂permeation flux and the N₂selectivity of PDMS/PMV membrane weresignificantly increased compared with pure VTES crosslinked PDMS membrane（PDMS/VTES）, permeation fluxes of CO₂and O₂of pure PDMS membrane was2752barrerand1986barrer, CO₂/N₂and O₂/N₂selectivity was2.82and2.03, respectively. Withincreasing content of the cross-linking agent in MMA branched PDMS/PMV membrane,permeation flux of CO₂and O₂increased and selectivity of CO₂/N₂and O₂/N₂first increasedand then reduced; With the growth of PMV cross-linking in the amount of agent which wasadded the PDMS/PMV films, penetration flux of CO₂and O₂increased at first and thenreduced, the selectivity of CO₂/N₂and O₂/N₂been reduced. When the molar ratio ofMMA:VTES was3:7, the amount of added PMV crosslinker was20wt%, the gaspermeability of the membrane of CO₂and O₂flux reached4406barrer and2472barrerrespectively, selectivity of CO₂/N₂and O₂/N₂was4.951and2.78, respectively. （2） The PDMS/PEGMV membrane is introduced in the molecular structure of the PEGgroups, while maintaining the selectivity constantly permeation flux of CO₂/N₂and O₂/N₂was improved further. When the molar ratio of PEGMA:VTES is30%, the amount ofPEGMV cross-linking agent is20wt%, the gas permeation fluxes of CO₂and O₂were5246barrer and2640barrer.（3） Due to the introduction of a fluorine-containing inorganic ion in the molecularstructure, the film PDMS/HDFPMV membrane has both an organic film property and theinorganic film because of some interaction between the fluoride ion and O₂. The permeabilityand selectivity of PDMS/HDFPMV film CO₂/N₂and O₂/N₂increased which could enhancethe O₂permeability. When molar ratio of HDFDMA: VTES was3:7, the added amount ofHDFPMV cross-linking agent was20wt%, CO₂and O₂gas permeation flux reached7023barrer and4245barrer, selectivity of CO₂/N₂and O₂/N₂,6.4and3.36, respectively.