Water desalination using ceramic membrane distillation

In order to avoid hydrophilic behaviour of ceramic membranes prepared with metal oxides, alumina and zirconia membranes with 200 and 50 nm pore diameters were grafted with fluoroalkylsilanes. The grafting was controlled by TGA, and the hydrophobicity was characterised by water contact angle and permeability measurements. Results show that surfaces have hydrophobic behaviour with high values of contact angle. Grafted membranes were characterised by measuring the outlet pressure. The hydrophobic membranes were tested in a membrane distillation process. NaCl solution was used as the salt solution. This is the first example of membrane distillation using ceramic membranes.

Z1 membrane Fluxes increased when the temperature difference increased. This corresponds to a well-known result. The values of the fluxes are about the same for 0.001, 0.01 and 0.1 M solutions for each type This work demonstrates that it is possible to perform membrane distillation using grafted ceramic membranes. These membranes are hydrophobic, and transport of water through the membrane is only by transport of vapour. The salt rejection in this process is close to 100%. Values of water flux through the membrane in the membrane distillation process depend strongly on temperature differences. Values of water flux do not depend on the salt concentration when it is lower or equal to 0.1 M. Solar energy could very much help this process in countries which are very sunny due to the reduction of energy costs; and thus membrane distillation could become competitive relative to other processes — reverse osmosis or distillation, for instance. It would be also interesting for these countries to prepare ceramic membranes from clay at a low cost, as found in the literature [12,13]. The use of ceramic hollow fibers would be also very interesting for developing modules with high surface/volume ratio. This research is in progress in our laboratory.