Influence of fluorocarbon flat-membrane hydrophobicity on carbon dioxide recovery

Abstract

The influence of hydrophobicity in flat-plate porous poly(vinylidene fluoride) (PVDF) and expended polytetrafluoroethylene (PTFE) membranes on CO 2 recovery using aqueous solutions of piperazine (PZ) and alkanolamine is examined. Experiments were conducted at various gas flow rates, liquid flow rates, and absorbent concentrations. The CO 2 absorption flux increased with increasing gas flow rates and absorbent concentrations. When using 2-amino-2-methyl-1-propanol (AMP) or AMP + PZ aqueous solution as absorbent, this process was dominantly governed by gas film layer diffusion and membrane diffusion. The diffusion resistance of the membrane phase was only important when using N-methyldiethanolamine as the sole absorbent. The water contact angle increased initially with increasing plasma working power and reached at steady state value of 155° beyond 100 W. The elemental fluorine-to-carbon ratio (F/C) and water contact angle of the PVDF membrane increased with increasing treatment time and reached a plateau after 5 min of CH 4 plasma (100 W). Increases in the CO 2 absorption fluxes of 7% and 17% were observed for plasma-treated PVDF membranes in comparison to non-treated PVDF and PTFE, respectively, when using 1 M AMP as absorbent. The membrane mass transfer coefficient, k m , for plasma-treated PVDF membranes increased from 2.1 × 10 −4 to 2.5 × 10 −4 m s −1. Membrane durability was greatly improved by CF 4 plasma treatment (100 W/5 min) and comparable to that of PTFE membranes.