Title：Active Adsorbents for Molecular Separation
Speaker：Dr. Jin SHANG(Assitant Professor, City University of Hong Kong)
Time：Oct 27, 2016 ( Thursday ), 15:00-16:00
Location：Room 120, Chemistry Building
Molecular separation plays a key role in energy and environmental technologies. Notable examples are H2 and CH4 purifications, CO2 capture, volatile organic compounds (VOCs) removal, CO removal for fuel cell technology, flue-gas purification, desulfurization from natural gas and transported fuels etc. Molecular separation is an important unit operation in chemical industry, accounting for more than 60% of the total cost in some processes. Of the adsorption-based molecular separations, molecular sieving is the most desirable separation mechanism because it affords unparalleled high-selectivity.
In this talk, I will present our recent discovery of a new “active” molecular sieving mechanism – “molecular trapdoor” – in a class of chabazite zeolites through combined experimental and atomistic simulation works [1-7]. These trapdoor chabazite absorbents have their eight-membered-ring (8MR) aperture (the only possible gas passage) blocked by some extraframework cations. Some specific gas molecules can interact with the aperture-keeping cations to induce temporary and reversible cation deviation from the center of 8MR aperture, allowing for the gas admission. The different chemical/physical interaction capability of various gas molecules with the aperture-keeping cations endows a selective gas admission, which is in striking contrast to conventional sieving mechanism where the molecular size plays a decisive role. A novel absorption model is developed to quantitatively describe the isobar adsorption curves (i.e., adsorption amount as a function of temperature) for our “active” trapdoor chabazites. Several key physical quantities are identified, laying a ground for rational design of novel molecular sieving materials based on the trapdoor mechanism. Several unique applications based on our trapdoor mechanism will be presented as well, including counter-intuitive “size-inverse” sieving where the larger sized CO is admitted but smaller sized N2 is rejected, separation of H2 and D2 with the same size, temperature-controlled invertible selective adsorption of N2 and CH4, record high selectivity of CO2 over CH4 and N2, and appreciable H2 storage without sustained pressure. These examples have important implications in energy and environmental fields, which are not attainable by using conventional “passive” adsorbents.
In the end of my talk, I will present my perspectives on further development of “active” trapdoor adsorbents. It includes development of membrane for temperature-regulated permeation to enhance the uptake kinetics, core-shell zeolite adsorbents to improve the guest capacity, electric-field regulated adsorbents to enable fast admission/release of guests, and metal-organic frameworks based trapdoor adsorbents to enrich the design possibilities.
1) G. Li, J. Shang, Q. Gu, A. Grant, N. Jensen, X. Zhang, J.Z. Liu, P.A. Webley, and E. May, Nature Chemistry 2016, in review.
2) J. Shang, G. Li, P.A. Webley, and J.Z. Liu, Computational Materials Science 2016, 122, 307-313.
3) J. Shang, G. Li, Q. Gu, R. Singh, P. Xiao, J.Z. Liu, and P.A. Webley, Chemical Communications 2014, 50 (35), 4544-4546.
4) J. Shang, G. Li, R. Singh, P. Xiao, D. Danaci, J.Z. Liu, The Journal of Chemical Physics 2014, 140, 084705.
5) J. Shang, G. Li, R. Singh, P. Xiao, J.Z. Liu, and P.A. Webley, The Journal of Physical Chemistry C 2013, 117, 12841-12847.
6) J. Shang, G. Li, R. Singh, Q. Gu, K. Nairn, T. Bastow, N. Medhekar, C. Doherty, A. Hill, J.Z. Liu, and P.A. Webley, Journal of the American Chemical Society 2012, 134, 19246-19253.
7) J. Shang, G. Li, R. Singh, P. Xiao, J.Z. Liu, and P.A. Webley, The Journal of Physical Chemistry C 2010, 114, 22025-22031.