(351v) Improved Synthesis of Sterically Hindered Poly(N-methyl-N-vinylamine) Membrane for Post-Combustion Carbon Capture
Commercial polyvinylamine (PVAm) was mono-methylated into SH-PVAm using the stepwise reductive amination with a highly polar fluorinated alcohol as solvent to enhance the equilibrium shift to the imine formation. The method was found to prevent the over-alkylation, resulting in the increased yield of the target product. The synthesized SH-PVAm was characterized and confirmed by FTIR and 1H NMR. The SH-PVAm solution retained a sufficiently high viscosity after incorporating the aminoacid salt, 2-(1-piperazinyl)ethylamine sarcosinate, as the mobile carrier for the membrane coating without any penetration issue. The SH-PVAm exhibited a significantly enhanced performance in the blended membrane of about 170 nm thickness over the unmodified PVAm for CO2/N2 separation at 57oC. The former membrane demonstrated a CO2 permeance of 1071 GPU and a CO2/N2 selectivity of 183 whereas the latter showed 975 GPU CO2 permeance and 163 selectivity. The improved membrane performance corresponded well with our computational results on the reaction chemistry of CO2 between the sterically hindered vinylamine monomer (SH-VAm) and the pristine vinylamine monomer (VAm) by density functional theory (DFT). SH-VAm showed a preference for the more efficient bicarbonate formation pathway and contributed to a higher CO2 loading capacity. Therefore, the steric hindrance effect of SH-PVAm enhanced the solubility of CO2 in the polymer matrix and resulted in the higher CO2 permeance.