Preparation and application of RTIL membranes

Abstract

The massive emission of CO2 makes it extremely important to improve technology relating to CO2 capture and usage (CCU). Among the numerous CO2 capture methods, membrane technology is one of the most attractive, because of its easy operation, low price, low energy consumption and small footprint. Room temperature ionic liquids (RTILs), as outstanding CO2 absorbents, were combined in this thesis with membrane technology, including mixed matrix membranes (MMMs), poly(RTIL) modified commercial PSf membranes and free-standing cross-linked poly(vinylimidazole-co-butyl acrylate) (poly(VIm-co-BuA)) membranes. First, magnetic porous particles, ZIF-8@SiO2@Fe3O4, were prepared to form MMMs under magnetic field conditions. It was expected that the ordered porosity and space between the polymer and particles would induce an improvement in CO2 separation performance. Meanwhile, neat polyvinylidene fluorid (PVDF) membranes were cast with different methods, and RTIL monomers were synthesised in order to prepare poly(RTIL) membranes. However, both PVDF and poly(RTIL) membranes could not be formed, so free-standing poly(RTIL) membranes were prepared thereafter and used for CO2 separation in this thesis. Second, the commercially available polysulfone (PSf) ultrafiltration membrane was modified with poly(RTILs) via surface initiated atom transfer radical polymerisation (SI-ATRP), which gave a range of membranes used for CO2 separation and water treatment. The water flux of a series of modified membranes was tested instead of CO2 separation, since the modified membranes were unsuitable for gas separation. The results showed that the water flux of PSf membranes increased 1.8-3.5 times after modification, which made them great candidates for water treatment. The protein rejection performance of modified PSf membranes was investigated, which showed that the modified PSf membrane showed good potential for use as a protein rejection membrane. Third, in order to prepare a free-standing poly(RTIL) membrane, vinylimidazole and butyl acrylate were copolymerised as a poly(VIm-co-BuA) series with different VIm and BuA ratios of 63:37, 48:52 and 24:76. Free-standing poly(RTIL) membranes were formed by cross- linking poly(VIm-co-BuA) (24:76) with 1, 6-dibromohexane in one-pot reactions. Additionally, the poly(RTIL) membranes with different cross- linking degrees were obtained by ranging the ratio of cross- linker 1, 6-dibromohexane and blocking agent 1-bromobutane. The CO2 separation performance of the series of poly(VIm-co-BuA)-based poly(RTIL) membranes was measured with a single gas setup and showed improvement compared to analogous neat poly(RTIL) membranes. Finally, since poly(RTILs) are used in many fields, it was attempted to extend the application of poly(VIm-co-BuA)-based poly(RTIL) membranes to catalytic systems for CO2 conversion. The swelling property and CO2 affinity of cross-linked poly(VIm-co-BuA) membranes made them excellent heterogeneous catalysts for CO2 insertion to epoxides. The catalytic activity of these novel catalysts was therefore evaluated, and the reaction conditions were optimised in the last part of the thesis.