A comparative study on the structure and performance of porous polyvinylidene fluoride and polysulfone hollow fiber membranes for CO2 absorption

Porous polyvinylidene fluoride (PVDF) and polysulfone (PSF) hollow fiber membranes were prepared via a wet spinning method. Glycerol was used as phase-inversion promoter additive in the spinning dopes. Cloud point diagrams of polymer/solvent–glycerol/water were obtained to study precipitation rate of the polymers solution. The membrane structure was compared in terms of morphology, gas permeation, critical water entry pressure, collapsing pressure, overall porosity, contact angle and mass transfer resistance. The cloud point diagrams confirmed a significant increase in the precipitation rate of the spinning dopes with addition of glycerol. The PSF membranes indicated more open cross-section structure with smaller pore sizes. However, the PVDF membranes illustrated an ultra thin outer skin layer with high permeability which resulted in significantly lower mass transfer resistance. Physical CO2 absorption with distilled water was conducted through the gas–liquid membrane contactors. With addition of glycerol, the PVDF membrane demonstrated a structure with significantly higher CO2 flux compared to the commercial asymmetric PVDF membrane. The CO2 flux of 8.20 × 10−4 mol/m2 s was achieved by using the absorbent flow rate of 310 mL/min in the shell side of the membrane module. Therefore, using an improved hollow fiber membrane structure can be a promising alternative for CO2 absorption and separation through membrane contactors.

Research highlights▶ Glycerol significantly improved phase-inversion rate of the PVDF and PSF solutions. ▶ PVDF membranes showed higher surface porosity and wetting resistance. ▶ PSF membranes showed denser outer skin layer with smaller mean pore size. ▶ Among the prepared membranes PVDF/glycerol showed the highest CO2 absorption flux.