Vacuum membrane distillation of liquid desiccants utilizing hollow fiber membranes
R. Lefers, N.M. S. Bettahalli, N. Fedoroff, S. P. Nunes, T. Leiknes
Sep. Pur. Tech. 199, 57-63 (2018)
This paper documents the testing of a vacuum membrane distillation system intended for use with liquid desiccants.
Liquid desiccants offer the possibility for low-energy, ambient temperature dehumidification. Effective
desalination and purification of diluted desiccants outputs two important products: a concentrated desiccant for
reuse in dehumidification and fresh water. In this study, vacuum membrane distillation was used in the laboratory
to purify diluted liquid desiccants. Calcium chloride and magnesium chloride were the desiccants
selected for testing. Desiccant solutions were pumped through the lumens of poly(vinylidene fluoride) (PVDF)
hollow fiber membranes at varying feed inlet temperatures, solution velocity rates and vacuum set points during
membrane distillation. An average flux of 8 kgm−2 h−1 was obtained using 30 wt% magnesium chloride solution
at a temperature of 50 °C while applying vacuum to achieve 25 mbar absolute pressure on the air side of the
membrane. The results are promising for the development of a full-scale vacuum membrane distillation process
for desiccant solution regeneration and fresh water recovery. In addition, the recovered condensate was of
sufficient quality for use in agricultural irrigation or drinking water.