Preparation Of Chitosan Composite Membranes For CO₂/N₂Separation

Global warming caused by CO2makes capture and separation of CO2important research topic in the energy and environment area. Compared with the traditional separation methods such as absorption, adsorption and low temperature separation, membrane separation has advantages of no phase transition, low energy consumption, simple investment for equipment, small investment and environmentally friendly. So it is widely used in CO2separation area. Traditional polymers are based on solution-diffusion mechanism and can hardly breakthrough "Robeson up limit", so they are difficult to obtain high CO2permeation rate and selectivity. However, facilitated transport membrane can break this limitation and get good permeation selectivity because of carriers in molecules. As one kind of facilitated transport membranes, fixed carrier membrane attracts widespread attention because of its carrier stability. In this thesis, chitosan containing amino group as carrier is selected to be membrane material. And three kinds of composite membrane CS/PP, TEA-CS/PP and PEI-CS/PP are prepared.CS/PP composite membrane was prepared with chitosan (CS) as separating coating layer and polypropylene (PP) as supporting layer. Effects of chitosan molecular weight, concentration, solvent evaporation temperature and relative humidity on gas separation performance were investigated. Optimized membrane preparation conditions were determined with1wt.%of CS200000under solvent evaporation temperature of30℃and relative humidity of20%. The permeability of CO2is201.8GPU and selectivity for CO2/N2is46.9at the pressure of0.3MPa under the optimized preparation conditions.In order to improve the CO2separation performance and mechanical property of chitosan membrane, triethanolamine was used as blending additives to prepare TEA-CS/PP blending composite membrane. TEA can destroy the intra-molecular and intermolecular hydrogen bond interaction of chitosan so as to reduce the crystallinity of the membrane. And TEA can also improve the facilitated transportation of CO2by providing carriers. TEA can improve mechanical property and CO2separation performance of chitosan membrane in certain concentrations. When the concentration of TEA is15%, CO2permeation rate of the composite membrane is240GPU under0.3MPa which is1.2times of chitosan membrane. And CO2/N2selectivity is63.4which increased35%than CS/PP composite membrane.In order to improve the CO2permeation rate, TEA-CS/PP blending composite membrane is prepared with macromolecular polyethyleneimine (PEI) as blending additives. Primary amine, secondary amine and tertiary amine in PEI molecular are used to improve content of carrier in membrane, so as to improve CO2permeation rate and CO2/N2selectivity. FTIR and DSC showed good compatibility between PEI and CS. XRD showed that PEI can make blending membrane form new diffraction peaks, which implied improvement of crystallinity of blending membrane. When the concentration of PEI is10%, the blending membrane obtains its best CO2separation performance with permeation rate of249.2GPU and CO2/N2selectivity of49.8under0.3MPa.For all the three kinds of composite membrane above, CO2permeation rate and CO2/N2selectivity decrease as the pressure decreases, as meets up with facilitated transport principle. Experimental data of this thesis are compared to results reported in the literatures. Chitosan composite membrane of this work has excellent competitive advantages.