Facilitated transport membranes (FTMs) make use of a reversible reaction between the target solute and chemical sites in the membrane, termed “carriers”, to improve the permselectivity for the solute. Polyvinylamine (PVAm) is the most studied polymeric amine for CO2 separation FTMs due to its high density of amine carriers and excellent film forming properties. PVAm prepared by partial hydrolysis of poly(N-vinylformamide) (PNVf) is a random copolymer of vinylamine and N-vinylformamide repeat units. Since CO2 transport through the membrane is enhanced by reaction with the amine carriers, a higher concentration of carrier sites should lead to improved CO2 permeability, but this is not the case. PVAm with a range of amine contents was prepared from a single batch of PNVf. Bulk films of these PVAm’s were then permeation tested under the following conditions: 14/86 CO2/N2 mixed gas, 95% relative humidity, 60 °C. The PVAm with 52 mol% amine content had the highest CO2 permeability and selectivity, while further increasing amine content reduced CO2 permeability while retaining selectivity. Contrary to prior reports which attribute such trends to increases in PVAm crystallinity, XRD and DMA experiments showed the PVAm films were amorphous across the composition range. Instead, our rheology experiments strongly suggest that the CO2-amine reaction products lead to a reduction in polymer chain mobility, which in turn reduces gas diffusivity in the film. This effect becomes more significant as amine content in the polymer increases.

Effect of amine content on the carbon dioxide separation performance of polyvinylamine membranes for flue gas carbon capture

ACS Fall 2021

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