Morphological design of alumina hollow fiber membranes for desalination by air gap membrane distillation

Abstract

Alumina hollow fiber membranes were prepared by the phase inversion technique under different spinning conditions in order to induce various types of structural morphologies. In the membrane fabrication process, the studied parameters were the polymer concentration in the inorganic suspension and its flow rate, the gap distance, the bore liquid, the outer coagulant composition and their flow rates. After sintering, the hollow fibers were chemically modified by grafting (1H,1H,2H,2H-perfluorodecyltriethoxysilane) rendering them hydrophobic for their use in membrane distillation (MD) process. The effects of the membrane morphology on the obtained MD membrane characteristics and on air gap membrane distillation (AGMD) desalination performance were studied in order to figure out the most promising structure for MD. The suitability of alumina hollow fibers for AGMD was confirmed by various membrane characterization techniques. In general, the membranes prepared with lower polymer concentration in the inorganic suspension exhibited higher AGMD performance (i.e. higher permeate flux with a smaller flux reduction factor and a good salt rejection factor). Among all prepared hollow fiber membranes prepared in this study, the one with the largest micro-channel structure exhibited the best AGMD performance, even better than all hydrophobic ceramic membranes used so far in desalination by AGMD and DCMD.