Influence of hydrophobization conditions and ceramic membranes pore size on their properties in vacuum membrane distillation of water-organic solvent mixtures

The initially hydrophilic micro-and macroporous ceramic membranes were successfully hydrophobized by grafting with fluoroalkylsilane (FAS) molecules. The influence of diverse parameters (e.g. type of molecule, duration of grafting, concentration of FAS solution, type of solvent) on the resulting hydrophobic surface was investigated. The liquid entry pressure of water (LEPw) was used as a measure of the hydrophobization efficiency. The prepared membranes were subsequently investigated in vacuum membrane distillation (VMD) process using pure water and water-organic solvent solutions as feed mixtures. It was found that permeate flux of pure water is strictly correlated with LEPw value. The selectivity of membranes in contact with water-organic mixtures depends strongly on the pore size of the hydrophobized membrane. Microporous membrane are much less efficient in the separation of organics from water (separation factor of ethyl acetate - EtAc in the range 1.3-30) comparing with macroporous ones (separation factor of EtAc in the range 32-60). The results were also discussed assuming the various mechanism of transports through porous ceramic membranes. These latter results were additionally compared with the results obtained for hydrophobic polymeric membranes (separation factor of EtAc in the range 25-450). (C) 2015 Elsevier B.V. All rights reserved.