Making Thin Film Composite Membranes for Nanofiltration: Selecting Appropriate Substrates for Aqueous and Organic Systems

Separation processes play a significant role in chemical industry and account for 45 % to 55 % of industrial energy use. Methods to separate chemicals in more energy efficient way are in urgent demand to reduce the energy consumption, carbon dioxide emission, and financial cost. Pressure-driven membrane process, starting in the late 1960s, has been extensively used for industry separation given the remarkable economic and environmental benefits over conventional thermally-driven separation techniques. Nanofiltration (NF) is one such process that encompasses selective properties that lie between ultrafiltration and reverse osmosis. NF can be used to separate molecules with molecular weights from 200 to 1000 g/mol. NF has been widely applied for water-related separation applications since it was first introduced during the late 1980s, though more recently has been extended to organic liquids, referred to as organic solvent nanofiltration (OSN). This newly established process allows the separation of organic solvent mixtures down to molecular level, and has been considered a feasible alternative to current thermally-driven organic solvent separation and purification techniques, such as distillation. In this dissertation, the history and current status of NF membranes for aqueous system and organic systems are summarized and technical areas of need are identified. In particular, I propose the development of new types of thin film composite NF membranes that are fabricated using specially chosen substrates that enable their use in various NF applications.