State of the Art and Perspectives in Membranes for Membrane Distillation/Membrane Crystallization

Membrane distillation (MD) and membrane crystallization (MCr) are receiving more attention because of process intensification. MD is a promising separation technology that can result in water recovery higher than 90%, while MCr is a complementary process that creates the opportunity to extract valuable components from an aqueous solution. Using temperature gradient as a driving force allows utilization of waste heat and/or alternative energy sources, such as solar and geothermal energy, to obtain water with high purity while nonvolatile components are retained. Typical applications of MD are seawater and brackish water desalination, wastewater treatment, and solution concentration. MCr is employed in the crystallization of valuable products in biopharmaceutical, chemical, electronics, and mineral fields. Applications of MCr in desalination and wastewater treatment provide the opportunity to simultaneously recover freshwater and minerals. The main issue for these membrane-based technologies is the design and preparation of improved membranes with suitable characteristics to improve water vapor transport, mitigate fouling and scaling, and prevent wetting issues. This chapter provides a critical overview of different approaches to membrane distillation and MCr processes. Special emphasis is given to membrane development, including recent improvements in manufacturing, progress in module fabrication, innovative technique,s and application of materials to prepare membranes suitable for membrane contactors (MCs), but with a low environmental impact.