Combination of ionic liquids with membrane technology: a new approach for CO2 separation
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The objective of this PhD study is to combine the advantages of membrane and ILs technologies to develop high-performance IL-based membrane contactors and membranes for CO2 separation from various sources. First of all, membrane contactors employing ILs as absorbents for pre-combustion CO2 capture at elevated temperatures and pressures have been developed. Proper membrane materials suitable for pre-combustion CO2 separation condition were selected based on their chemical and thermal stability contact angle, pore size, and so on. Porous glass membranes and PTFE membranes, as well as Teflon-PP thin-film composite (TFC) membranes, were selected out of seven membrane candidates. Meanwhile, a suitable IL absorbent was selected from the ones available on the market in view of its CO2 solubility and CO2/H2 selectivity, viscosity and thermal stability. In particular, butyl-3-methlyimidazolium tricyanomethanide ([Bmim][TCM]) was chosen as the absorbent. According to the selected materials, different membrane contactor modules have been prepared using hollow fibre membranes, and the separation performances were tested using a CO2/He (45%/55% volume) gas mixture at elevated temperatures and pressures. In addition to the investigation on membrane contactors for CO2/H2 separation, high-performance CO2 separation membranes have also been developed by blending or cross-linking polymeric materials with ILs for CO2/N2 and CO2/CH4 separation. Defect-free TFC membranes with different ILs content were fabricated and characterized in terms of SEM, TGA, DSC, and FT-IR spectroscopy. The gas separation performance of the polymer/IL TFC blend membrane was investigated using a CO2/N2 (10%/90% volume) gaseous mixture under various feed pressures and relative humidities at room temperature. The experimental results show that the incorporation of IL into the Pebax TM 2533 matrix can significantly increase both the CO2 permeance and CO2/N2 selectivity. The second approach to develop CO2 separation membranes employed an IL ([TETA][Tfa]) as a cross-linker in PEG diglycidyl ether to fabricate self-standing membranes with a stable cross-linked polymeric matrix. The cross-linking reaction mechanism, the thermal stability of the resulting membranes, as well as the water uptake of the formed membranes were systematically investigated. The CO2, N2, and CH4 gas transport properties of these new membranes were studied by single-gas permeation tests. Free PEG dimethyl ether was added to the polymeric matrix to enhance the gas transport. The gas permeation results showed that the free PEGDME additive acts as plasticizer in the polymeric matrix. Excellent CO2/N2 and CO2/CH4 separation properties over the 2008 Robeson upper bound were obtained.