16 EFFECT OF DIFFERENT ADDITIVES ON THE PROPERTIES AND PERFORMANCE OF POROUS POLYSULFONE HOLLOW FIBER MEMBRANES FOR CO_2 ABSORPTION

摘要

Recently, porous membranes have attracted considerable attention in the area of membrane gas absorption [1-6]. The high hydrophobicity, low membrane transfer resistance, and excellent chemical resistance to various chemical-feed streams are the essential properties of these membranes. Polypropylene (PP), polyethylene (PE), polytetrafluourethylene (PTFE) and poly(vinylidene fluoride) (PVDF) are the most popular hydrophobic polymeric materials. However, since PE, PP, and PTFE cannot be dissolved in solvents, and the membranes are usually fabricated using stretching and thermal methods that give symmetric structure with relatively low porosity. On the other hand, because of critical surface tension of PVDF, the rate of exchange between solvent and nonsolvent is very low, and it is difficult to spin hollow fibers, particularly when using high percentage of solvent for the bore fluid. Asymmetric hollow fiber membranes with low mass transfer resistance could be fabricated by increasing the outer surface porosity (high permeability) and removing the inner skin layer during spinning process. Moreover, for the membrane wetting pressure, despite depending on the property of the membrane material, it could also be adjusted by the membrane pore size, as suggested by the Laplace-Young equation.