Most zeolite membranes used in industrial processes are selective for water over organic compounds. Due to their good chemical stability, unique framework, and intermediate pore sizes, the hydrophobic MFI-type zeolite membranes have been extensively considered for a wide range of separation processes, particularly for pervaporation separation of organics from organic/water mixtures. Such membranes, if prepared on hollow fiber supports with high packing density (membrane surface area/volume ratio >1000 m2/m3), are attractive for industrial pervaporation separation of organic/water, such as ethanol/water separation involved in bio-fermentation ethanol production. However, reproducible synthesis of MFI zeolite membranes with high organic selectivity remains a challenge.
Researchers at Arizona State University have developed a new synthesis method consisting of dual-layer seeding and varying-temperature secondary growth for the synthesis of hydrophobic MFI zeolite membranes on alumina hollow fiber supports. The effects of seeding method, seed particle size, seed size ratio, and variable temperature/time profile on the microstructure, hydrophobicity and gas perm-selectivity of the membranes are investigated leading to identification of optimum seed structure and secondary growth conditions for synthesis of MFI zeolite membranes with high ethanol/water separation performance. The high-performance MFI zeolite membrane has a microstructure consisting of a thin, fully inter-grown, and dense top zeolite layer responsible for high selectivity, and a porous low inter-grown bottom zeolite layer minimizing resistance and retarding aluminum transfer from the support to zeolite. The best hollow fiber supported MFI zeolite membrane with a Si/Al ratio of 187 exhibits ethanol/water pervaporation separation factor of 160 with total flux of 3 kg m-2 h-1.
These MFI zeolite membranes offer highest ethanol to water selectivity.
• Separation of organics from water mixtures
• Ethanol/water or methanol/water separation
• Membrane reactors for production of ethanol and methanol
Scanning electron microscopy (SEM) images of surface and cross section of hollow fiber α-alumina support.