서강대학교

초록 (요약문)

Chemical separation processes consume a significant amount of energy, accounting for 10-15% of the world’s total energy consumption. Pressure-driven membrane separation processes are considered a promising alternative to conventional energy-intensive separation processes. Polymers are the most widely used commercial membrane materials for gas separations due to high processability and low material cost. However, commercial polymeric membranes are limited in their low separation efficiency and plasticization-resistance under high-pressure condensable feed. Moreover, separation of N2 from CH4 in natural gas is a challenging task due to their small kinetic diameters and high critical temperature of CH4. Ladder-structured polysilsesquioxanes (LPSQ) are a subclass of polysilsesquioxanes with rigid double-stranded backbones which enhance the mechanical properties in polymer blends at high temperatures. Furthermore, their organic side-chains can be engineered so that highly compatible blends with polyimides (PI) can be prepared. The first part of this research describes gas transport in thermally cross-linked polyimide/ladder-structured polysilsesquioxane (PI/LPSQ) membranes. The formation of larger, or more interconnected free volume elements in the membrane caused improvements in the permeability with plasticization resistance. PI/LPSQ membranes are further transformed into carbon molecular sieve (CMS) membranes through pyrolysis for the development of N2 selective membranes. CMS PI/LPSQ membranes show enhanced N2/CH4 selectivity compared to CMS PI membranes from increased CH4 diffusion barrier caused by electron accumulation at SiOx phases. Lastly, plasticization-resistant polyimide membranes in the commercially viable hollow fiber configuration were fabricated by dip-coating a polyamic acid layer on the thermally cross-linked PI/LPSQ support.