Application of fluoroalkylsilanes (FAS) grafted ceramic membranes in membrane distillation process of NaCl solutions

Novel fluorosilanes grafted ceramic membranes were prepared and characterized in the air-gap membrane distillation (AGMD) process. The hydrophobic active layer was created by grafting 1H,1H,2H,2H-perfluorodecyltriethoxysilane (C8 compound) on the commercial ceramic membrane (zirconia layer on the microporous alumina support). Two kinds of commercial membranes were used with average pore diameter of the zirconia layer equal to 50 or 200 nm. Four hydrophobic membranes were prepared using different grafting conditions. The efficiency of grafting process was characterized by TGA, contact angle and liquid water entry pressure (LEP) measurements. These new kinds of hydrophobic ceramic membranes were applied in the membrane distillation (MD) process. The influence of NaCl concentration and feed/permeate temperature difference on the efficiency of MD process were determined. The rejection of NaCl was found to be close 100%, indicating good hydrophobic behaviour of the FAS grafted ceramic membranes. The permeate fluxes were dependent of the NaCl concentration, pore diameter of the zirconia layer and the temperature difference between feed and permeate side of the membrane. The average flux of about 6.67 L/(m2 h) was found for M1 and M2 membranes in contact with pure water and at feed/permeate temperatures equal 95 and 5 °C, respectively. The flux of about 5.42 L/(m2 h) was found for M3 membrane in contact with 1 M NaCl solution and feed/permeate temperatures equal 99 and 5 °C, respectively. This is the first broader study of the use of modified ceramic membranes in MD process.