Design and Fabrication of Metal-Organic Framework Membranes for Gas Separations

Abstract

Industrial productions need the separation processes, but they are quite energyintensive, which occupy about half of the total energy consumption. Membranetechnology based on a non-thermal route is expected to reduce the associated energy duties by ~90%, but effective membrane materials capable of precisely isolating targeted species from complex mixtures are highly needed. Metal-organic frameworks (MOFs), possessing the tuneable pore size and geometry, are regarded as the promising platform for molecular separations and membrane design. This dissertation illustrates the rational design and the guided fabrication for various MOF membranes. Respectively, different gas separation applications were addressed by using these membranes, such as light hydrocarbon separations, carbon dioxide (CO2) captures and natural gas purifications. A versatile strategy for membrane fabrication is developed based on the electrochemical method. Following this, a family of face-centered cubic (fcu) MOF membranes were obtained, which possess different ligands and different clusters, namely rare-earth hexanuclear or zirconium hexanuclear clusters. Two MOF membranes based on fumarate (fum) linker, Zr-fum-fcu-MOF and Y-fum-fcu-MOF, showed efficient separation for the propylene/propane binary mixture, as well as the butane/isobutane equimolar mixtures, respectively. Further aperture editing applied to Zr-fum-fcu-MOF via mixed-linker approach permits the introduction of shape irregularity to the parent trefoil-shaped apertures, inducing an ideal shape-mismatch with tetrahedral CH4 molecules and blocking their transportation while affecting linear molecules slightly such as nitrogen (N2) and CO2. The resultant Zr-fum67-mesaconate (mes)33-MOF membranes exhibit great promise for natural gas purification, including efficient nitrogen rejection and simultaneous removal of CO2 and N2 from natural gas. In addition, a unique CO2-recognition membrane based on a fluorinated MOF (KAUST-7) is constructed for multipurpose CO2 capture, including CO2/H2, CO2/N2 and CO2/CH4 separation. The specific affinity to CO2 coupling with the molecular sieving capability of KAUST-7 enables the membrane to be nearly only permeable to CO2, excluding both smaller H2 molecule and larger N2 or CH4 molecules. Moreover, in order to be closer to the real applications, the defective Zr-fum-fcu- MOF nanoparticles based mixed-matrix membranes are constructed for natural gas purification under practical conditions