Influence of fluorocarbon flat-membrane hydrophobicity on carbon dioxide recovery

The influence of hydrophobicity in flat-plate porous poly(vinylidene fluoride) (PVDF) and expended polytetrafluoroethylene (PTFE) membranes on CO2 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 CO2 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 CH4 plasma (100 W). Increases in the CO2 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, km, 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 CF4 plasma treatment (100 W/5 min) and comparable to that of PTFE membranes.