Separation performance of PVAm composite membrane for CO₂ capture at various pH levels

Polyvinyamine (PVAm) Fixed-Site-Carrier (FSC) composite membrane has been reported to have a good potential to be applied for large scale for CO₂ capture applications with respect to high permeance and high selectivity. In this study, the membrane was investigated with respect to pH of the casting solution as a step for optimization of the membrane. It was found out that the pH of the PVAm casting solution could be easily controlled with a simple agent. The degree of protonation of the functional groups depends on the pH of the casting solution and influenced the reaction of carriers with CO₂ and the solubility of CO₂ in the FSC membrane swollen by water vapor in the feed flue gas. So it was expected that the pH could affect greatly the membrane’s CO₂ capture performance. Membranes from casting solutions of different pH have been prepared, characterized and tested in a permeation set-up for CO₂ separation from humidified flue gas. Permeation tests have shown that the performance of the PVAm FSC membrane for CO₂ capture could be enhanced remarkably by pH control. This is explained by the increased number of free amine groups available for facilitated transport of CO₂ with increasing pH. At low pH, it is assumed that the decreased number of free amines and the increased viscosity of casting solution have resulted in the decreased membrane performance.