(351v) Improved Synthesis of Sterically Hindered Poly(N-methyl-N-vinylamine) Membrane for Post-Combustion Carbon Capture

Membrane separation technology requires highly CO₂-selective and permeable membranes for a cost-effective post-combustion CO₂ capture from flue gas. Amine-containing facilitated transport membranes are able to realize an increased permeability due to the reversible reaction between CO₂ and amino groups. Here, we have developed an improved method for the synthesis of a high-molecular-weight sterically hindered polyvinylamine (SH-PVAm) as the new fixed-site carrier in our ultra-thin CO₂ selective membranes.

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 57^oC. 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.