Effect of membrane structure on gas absorption performance and long-term stability of membrane contactors

The effects of membrane porosity and pore size on CO₂ absorption performance and long-term stability were investigated using asymmetric poly(vinylidene fluoride) hollow fiber membrane contactors, prepared with differing inner surface structures by thermally induced phase separation. Membranes prepared using nitrogen gas as the bore fluid had lower inner surface porosity than membranes prepared with solvent. Monoethanolamine (MEA) solutions were used as absorbents on the tube side, while pure CO₂ was supplied to the shell side. Gas absorption performance and long-term stability of the synthesized membranes were compared with those of a commercial poly(tetrafluoroethylene) membrane. The effect of surface properties on gas absorption performance depended on MEA concentration. A membrane with lower porosity and small pore diameter at the inner surface was stable for 200 h, while a membrane with high porosity and larger pore size was completely wetted within 100 h and flux rate decreased sharply. A mathematical model for pure CO₂ absorption was developed by considering partial wetting of the membrane. The simulation results were discussed in light of the results from long-term stability tests of membranes.