U of Minnesota team develops zeolite nanosheets; resulting molecular sieve membranes could make fuel and plastics production more energy-efficient and cost-effective
After more than a decade of research, a University of Minnesota team of researchers has devised a means for developing free-standing, highly crystalline zeolite nanosheets that could make the production of gasoline, plastics and various chemicals more cost-effective and energy-efficient.
The research, led by chemical engineering and materials science professor Michael Tsapatsis (earlier post) in the university’s College of Science and Engineering, is published in the most recent issue of the journal Science. The purity and morphological integrity of these nanosheets allow them to pack well on porous supports, facilitating the fabrication of molecular sieve membranes, the team notes in the paper. The team has a provisional patent and hopes to commercialize the technology.
Separating mixed substances can demand considerable amounts of energy—currently estimated to be approximately 15% of the total energy consumption—part of which is wasted due to process inefficiencies. In days of abundant and inexpensive fuel, this was not a major consideration when designing industrial separation processes such as distillation for purifying gasoline and polymer precursors. But as energy prices rise and policies promote efficiency, the need for more energy-efficient alternatives has grown.
One promising option for more energy-efficient separations is high-resolution molecular separation with membranes. They are based on preferential adsorption and/or sieving of molecules with minute size and shape differences. Among the candidates for selective separation membranes, zeolite materials (crystals with molecular-sized pores) show particular promise.
High-aspect-ratio zeolite single crystals with thickness in the nanometer range (zeolite nanosheets) are desirable for applications including building blocks for heterogeneous catalysts and the fabrication of thin molecular sieve films and nanocomposites for energy-efficient separations. They could also be of fundamental importance in probing the mechanical, electronic, transport, and catalytic properties of microporous networks at the nanoscale. Despite steady advances in the preparation and characterization of layered materials containing microporous layers and of their pillared and swollen analogs, the synthesis of suspensions containing discrete, intact, nonaggregated zeolite nanosheets has proven elusive because of structural deterioration and/or aggregation of the lamellae upon exfoliation.
Here, we report the isolation and structure determination of highly crystalline zeolite nanosheets of the MWW and MFI structure types, and we demonstrated the use of their suspensions in the fabrication of zeolite membranes.—Varoon et al.
While zeolites have been used as adsorbents and catalysts for several decades, there have been substantial challenges in processing zeolitic materials into extended sheets that remain intact. To enable energy-savings technology, scientists needed to develop cost-effective, reliable and scalable deposition methods for thin film zeolite formation.
The University of Minnesota team used sound waves in a specialized centrifuge process to develop “carpets” of flaky crystal-type nanosheets that are not only flat, but have just the right amount of thickness. The resulting product can be used to separate molecules as a sieve or as a membrane barrier in both research and industrial applications.
Members of the research team include Ph.D. candidates Kumar Varoon and Xueyi Zhang; postdoctoral fellows Bahman Elyassi and Cgun-Yi Sung; former students and Ph.D. graduates Damien Brewer, Sandeep Kumar, J. Alex Lee and Sudeep Maheshwari, graduate student Anudha Mittal; former undergraduate student Melissa Gettel; and faculty members Matteo Cococcioni, Lorraine Francis, Alon McCormick, K. Andre Mkhoyan and Michael Tsapatsis.
This research is being funded by the United States Department of Energy (including the Carbon Sequestration Program and the Catalysis Center for Energy Innovation – An Energy Frontier Center), the National Science Foundation and a variety of University of Minnesota partners.
Kumar Varoon, Xueyi Zhang, Bahman Elyassi, Damien D. Brewer, Melissa Gettel, Sandeep Kumar, J. Alex Lee, Sudeep Maheshwari, Anudha Mittal, Chun-Yi Sung, Matteo Cococcioni, Lorraine F. Francis, Alon V. McCormick, K. Andre Mkhoyan, and Michael Tsapatsis (2011) Dispersible Exfoliated Zeolite Nanosheets and Their Application as a Selective Membrane. Science 334 (6052), 72-75. DOI: 10.1126/science.1208891