Fabrication of PP hollow fiber membrane: Via TIPS using environmentally friendly diluents and its CO₂ degassing performance

CO₂ removal is an essential water purification process in many fields, such as petrochemical production and thermal power generation. It is challenging to remove low concentrations of CO₂ from RO effluent water. The core component of the membrane degassing technique is a high-performance hydrophobic microporous membrane. Polypropylene (PP) membranes were prepared with environmentally friendly binary diluents via thermally induced phase separation. Firstly, the effects of PP concentration on the phase diagram, flat sheet membrane structure and mechanical properties were studied to optimize the PP content for a hollow fiber membrane (HFM). The PP HFM showed a sponge-like cross-sectional structure without any dense skin layer, a large loading force and breaking elongation, and a narrow pore size distribution with a mean pore size of 0.16 μm. The as-fabricated PP HFM module was applied for CO₂ removal from RO effluent water from a petrochemical plant. A higher water temperature and vacuum degree facilitated CO₂ removal. Increasing the effective membrane length enhanced degassing efficiency. Increasing the water flow rate increased CO₂ degassing flux, but simultaneously decreased degassing efficiency. When the water flow rate increased from 20 mL min^-1 to 63 mL min^-1, although the effective membrane length increased from 3 m to 4.8 m for the best degassing efficiency of 88%, the amount of treated water increased by 3.15 times. The declined CO₂ concentration in the outlet water was 1.6 mg L^-1.