Tubular hydrophobic ceramic membrane with asymmetric structure for water desalination via vacuum membrane distillation process

A porous ceramic membrane without water wetting is essential for the application of water desalination in membrane distillation. In this study, we report a hydrophobic tubular asymmetric alumina membrane that was modified by grafting hexadecyltrimethoxysilane (C16) molecules. The grafting efficiency and hydrophobicity of the grafted membrane were characterized by its morphology, contact angle and FTIR spectrum, as well as the changes in terms of nitrogen permeance and pure water flux over various pressures. Four kinds of tubular asymmetric alumina membranes were employed in the vacuum membrane distillation (VMD) process. The effects of membrane thickness and pore size on the water flux or salt retention were investigated. The mass transport resistance in substrate was non-negligible and sometimes could be the main contributor to the total mass transport resistance. The membrane with a top layer thickness of 20 μm, pore size of 150 nm and support pore size of 3.2 μm was appropriate in the VMD process. After >1000 min desalination, the permeate flux and salt rejection were maintained as high as at the beginning, i.e., approximately 30 kg·m⁻²·h⁻¹ and 99.9%, respectively.