(397c) Polymerization of High-Molecular-Weight Polyvinylamine for CO2-Selective Membranes with High Separation Performance

Polymer membranes for CO2 separation from flue gas has been believed to be one of the most important solutions to greenhouse gas driven climate change. Facilitated transport membranes containing amines show a much higher CO2/N2 selectivity compared to solution-diffusion membranes. The polyamine membrane has to be thin enough to show a high CO2 permeance. Polyvinylamine (PVAm) with high molecular weights (MWs) was successfully synthesized for the preparation of thin CO2 separation membranes for CO2 capture from flue gas. PVAm was synthesized through free radical polymerization using 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AIBA) as the initiator. The synthesis process takes six steps: polymerization, acidic hydrolysis, precipitation, redissolution, hydroxide ion exchange, and vacuum filtration. PVAm polymers with different MWs were synthesized by adjusting the monomer concentration and initiator amount. The weight average MW of the synthesized PVAm was characterized by dynamic light scattering (DLS). The highest MW obtained was around 1,200,000. The effects of monomer concentration and initiator amount on the MW of the synthesized polymer will be discussed. The high MW PVAm synthesized in this work has shown a much higher viscosity than the commercially available PVAm (Lupamin® 9095, from BASF Corporation). The high MW PVAm solution with 3 wt.% polymer concentration showed a viscosity of 400 – 1400 cp, while Lupamin® 9095 solution with 3 wt.% polymer concentration showed a viscosity of only 50 cp. The high viscosity of the PVAm solution at a low concentration allowed the preparation of much thinner
membranes. It could also help to reduce the penetration of polymer solution into the pores of the substrate, and further reduce the mass transfer resistance. Consequently, a much higher CO2 permeance could be obtained from such a thin membrane with the thickness of 100 – 200 nm. Moreover, Lupamin® was obtained by basic hydrolysis using sodium hydroxide (NaOH), therefore the byproduct (sodium formate salt) was formed in the polymer product. The large amount of the non-reactive salt with CO2 not only did not contribute to the facilitated transport of CO2, but also could hamper the stability of the membrane due to the salting-out problem. In contrast, acidic hydrolysis was used in this work, and no byproduct was formed. Overall, the high MW PVAm synthesized in this work was advantageous to the membrane transport performance compared to the commercial available Lupamin® product. After the incorporation of mobile carriers (aminoacid salts) to the high MW polyvinylamine, the resulting membranes showed a high separation performance with a CO2 permeance of about 1000 GPU and a CO2/N2 selectivity of more than 200 at 57 ºC. The promising CO2 separation performance from the amine-containing polymer membrane shows great potential for the application of CO2 capture from flue gas.