ABSTRACT
Membrane distillation (MD) is an emerging separation technology that operates at the expense of less thermal energy. During this process, warmer feed water flows on one side of the microporous membrane, and cooler distillate collects at the permeate side or in a condenser. The temperature difference on both sides of the membrane creates the vapor pressure difference that facilitates the diffusion of vapors through the pores. Vapors condense at the permeate side, leaving highly concentrated solute at the feed stream; a theoretical 100% rejection of pollutants is one of the most significant advantages of this separation technique. Also, the requirement of lower temperature, utilization of the waste heat energy left during the various industrial processes, and reduced membrane fouling makes this process highly demanding over the traditional reverse osmosis. The primary requirement of the MD is the membrane hydrophobicity, which keeps a nonwetting membrane surface and ameliorates the diffusion of vapors through the pores. Recently, polymeric and two-dimensional nanomaterial (graphene and graphene analogs) membranes are widely used for the MD application. Hence, progress in developing the materials for this separation technology is also an interest of this chapter.
