Analysis of the effect of amino density and water on amino-containing fixed carrier membranes via computational chemistry

The economic advantage of membrane-based CO2 separation technology is more prominent with the development of high-performance membrane materials. The amino-containing fixed carrier membranes with excellent CO2 separation performance show great potential, especially in post-combustion CO2 capture. However, the reaction and transport mechanism between CO2 and amino groups has rarely been systematically investigated due to the limitation of experimental characterization. In this paper, quantum chemistry computations and molecular dynamic simulations are used to analyze the effect of amino density and water in fixed carrier membranes containing primary amino groups. Research result shows that as the spacing between amino groups increases, bicarbonate plays an increasing role in the facilitated transport mechanism due to the gradual increase of reaction energy barrier in carbamate scheme. In the dry PVAm, the reaction energy barrier is 69 % higher than the bicarbonate mechanism and the diffusion coefficient is two orders of magnitude lower than the humid PVAm, which are the reasons for limiting the facilitated transport mechanism and membrane separation performance. Water molecules can provide a polar environment conducive to reactions, directly participate in the reaction process and form highly mobile continuous water clusters for gas high-speed diffusion. Regulating the nitrogen atom spacing of amino group to be less than 3.1 Å and constructing abundant CO2 transport channels may achieve weakly humidity-dependent facilitated transport membranes.