서강대학교

초록

On a daily basis, we see many different chemical products and their main ingradients are hydrocarbons which are obtained by energy-intensive separation processes. The chemical separation processes, largely relying on thermally-driven separation processes, consume a significant amount of energy, corresponding to 10-15% of the world’s total energy consumption. Membrane separation technology is considered an attractive alternative to the conventional energy-intensive separation processes due to its high energy efficiency and small footprint. Among various membrane materials, polymeric membranes have been most widely accepted in various gas separation applications because of their high processability and low material cost. However, they are suffering from some drawbacks, including the separation performance limit, physical aging-induced permeability loss, and plasticization-induced selectivity loss. Mixed matrix membranes (MMMs) are hybrid membranes consisting of polymeric membranes and molecular sieves, offering dual advantages of high processability and excellent gas-separation performance. Zeolitic imidazolate frameworks are porous crystalline materials that are made by coordinating zinc or cobalt metal ions with imidazole organic ligands. They are considered a subclass of metal organic frameworks (MOFs) that are topologically isomorphic with zeolites. Although MMMs may possibly address the above mentioned shortcomings of conventional polymeric membranes, several technical challenges still exist: refinement of pore structures at a sub-angstrom precision, suppression of interfacial voids between polymer and molecular sieve, and incorporation of high concentrations of molecular sieves into the polymeric matrix without the formation of non-selective voids. In this study, the structural engineering of ZIF-8 nanoparticles was demonstrated for propylene/propane (C3H6/C3H8) separation by either the substitution of metal ions (Chapter 3) or the formation of new defective sites (Chapter 5). Also, the significance of interfacial morphology between polymer and ZIFs in MMMs was elucidated by incorporating ZIF-8 nanoparticles into the flexible polyethylene glycol methyl ethyl methacrylate moieties grafted polysulfone matrix (Chapter 4). Furthermore, post-synthetic modification of ZIF-8 allowed for the formation of multivariate ZIF-8 nanoparticles by using a solution-based approach. The multivariate ligands of our newly developed ZIF-8 made both pore structures and textural properties suitable for carbon dioxide (CO2) separation (Chapter 6). Lastly, mixed matrix hollow fiber membranes were prepared by dip coating 6FDA-DAM/multivariate ZIF-8 (60/40 w/w) hybrid matrix on top of the outer surface of alumina hollow fiber supports for CO2 separation (Chapter 7).