Direct contact membrane distillation for desalination: Membrane characteristics approach

Membrane distillation process is an emerging technology for separation purposes traditionally accomplished by conventional distillation or reverse osmosis. This process is based on the hydrophobic characteristics of microporous membranes solely allowing the vapor to pass through the pores of the membrane. Because specific membranes for membrane distillation have not been developed yet, microfiltration membranes made of hydrophobic polymers are usuallyused. In this work, twelve flat sheet commercial membranes made of PTFE were used and their characteristics were investigated under different operating conditions contain three feed temperatures (40, 60 and 80oC), four hot feed flow rates (200, 400, 600 and 800mL/min), fourcold stream flow rates (100, 200, 300 and 400mL/min), two feed concentrations (35 and 45g/L). Membranes properties contain pore size, thickness, support layer and salt rejection investigated.Long term performance for all membranes investigated to evaluation of direct contact membranedistillation as stand-alone desalination process. Results shown that feed temperature has the major effect on the permeate flux. Increase of hot feed flow rate led to reduction of polarizations effect and increased the permeate flux, while cold stream flow rate had negligible effect.Membranes with pore sizes of 0.45 and 1.0μm achieved higher flux while membrane with pore size of 0.22μm achieved higher salt rejection. Increase of membrane thickness led to decrease of the permeate flux due to increase of mass transfer resistance. Support layers had negligible effect on the permeate flux and salt rejection

Keywords:

direct contact membrane distillation , desalination , PTFE membrane , membrane characteristics