Membrane distillation using surface modified multi-layer porous ceramics

•Porous ceramics can be treated into hydrophobic by iCVD.•The multi-layer structures can significantly enhance the liquid entry pressure.•The mass transfer mechanism in the porous ceramics is transition diffusion. Generally, the ideal materials for the membrane distillation are required highly porous with lowest thermal conduction and highly hydrophobic to avoid the pore wetting. Ceramic materials exhibit some excellent intrinsic properties, but cannot be directly used in membrane distillation due to the hydrophilic surface with rich hydroxyl groups. Changing the surface of ceramic to hydrophobic would open up its applications in membrane distillation. In this study, initiated chemical vapor deposition technique was applied to transfer the hydrophilic porous ceramic tubes with various inner structures into hydrophobic. The surface modified multi-layer porous ceramic tubes were applied in membrane distillation. The pore diameter of the porous ceramic plays a predominant role. They should have a reasonably large pore diameter to achieve better membrane distillation performance in terms of permeate flux, and also should have small pore diameter and narrow pore diameter distribution to limit the risk of membrane wetting. An important issue of this work was to find the proper inner structures of the porous ceramic tubes to enhance the liquid entry pressure without decreasing the permeate flux in membrane distillation application.