Hydrophobic alumina hollow fiber membranes for sucrose concentration by vacuum membrane distillation

Abstract

Hydrophobic alumina hollow fiber membranes were first used for sucrose concentration in a vacuum membrane distillation (VMD) system. The alumina hollow fiber membranes were prepared using the combined phase inversion and sintering method and then grafted with FAS to impart hydrophobicity. The as-prepared hydrophobic alumina hollow fiber membrane had a high mechanical strength of 191 MPa, a high water contact angle of 140° and a high liquid entry pressure of water of 5.0 bar. Fifty-two hydrophobic alumina hollow fibers were packed into a shell-and-tube module. To evaluate the sucrose concentration performance of the prepared membrane module, the effects of various parameters on the permeate flux, such as the feed flow rate, temperature, vacuum pressure and concentration, were investigated in the VMD system. In the batch sucrose concentration tests, an 8 L 10°Brix sucrose solution was successfully concentrated to 50°Brix by removing 6.4 L of water using the VMD system. At a feed flow rate of 5 L/min and temperature of 70 °C, the permeate flux remained as high as 35.1 and 19.0 kg/m2 h when the sucrose solution was concentrated to 10°Brix and 50°Brix. Furthermore, the permeate flux could be recovered in a new concentration cycle after the membrane module was washed with pure water. The results revealed that the hydrophobic alumina hollow fiber membranes are promising and feasible for concentration processes in a VMD system.