Reactive Inorganic Membranes for CO$_{2}$/N$_{2}$ separations: Ab-initio Density Functional Theory Calculations

POSTER

Abstract

The selectivity (CO$_{2}$/N$_{2})$ of mesoporous silica membranes can be enhanced by surface modification using APTS (3-aminopropyl-triethoxy silane). The hypothesized transport mechanism in such materialsis the reaction of CO$_{2}$ with surface amine groups to form a carbamate species and subsequent surface ``hopping'' of CO$_{2}$. DFT calculations were performed in order to elucidate the mechanism of CO$_{2}$ transport in APTS modified membranes, to compute the CO$_{2}$ diffusivity through the membrane, and to calculate its binding energy on an amine strand. The computed binding energy for docking one CO$_{2}$ molecule to an amine was calculated to be 15.5 kcal/mol (0.67 eV). The activation/barrier energy for a CO$_{2}$ molecule to hop from one amine strand (in form of carbamate) to another computed using Transition State Theory (TST) was 7.2 kcal/mol (0.31 eV) and compares well with our experimental data ($\sim $ 8kcal/mol; 0.35 eV). In the configuration studied, CO$_{2}$ hops from one strand to another in a zigzag fashion due to thermal motion of the strands; a strand with the CO$_{2}$ molecule undulates and eventually moves so that the CO$_{2}$ can be attracted by an adjacent strand. The CO$_{2}$ diffusivity calculated using the computed activation energy ranged from 1.1 X 10$^{-11}$m$^{2}$/sec (@ 25 C) to 5.7 X 10$^{-10}$m$^{2}$/sec (@100 C).

Authors

  • M. Ostwal

    Colorado School of Mines

  • John Poate

    Brigham Young University, Los Alamos National Laboratory, Department of Physics and Astronomy, University of Utah, USA, MV Systems, Inc., USA, Helmholtz-Zentrum Berlin fuer Materialien und Energie, Abteilung Silizium-Photovoltaik, Germany, Colorado School of Mines, Department of Physics, USA, Georgia Institute of Technology, Arizona State University, Physics Department of Babolsar University, Iran, Physics Department, New Mexico State University, Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ, 85287-1604, USA, Department of Electrical Engineering, University of Arkansas, Fayetteville, AR 72701, USA, Department of Physics, Arizona State University, Tempe, AZ, 85287-1504, USA, Colorado State University, University of Wisconsin, NSF ERC for Extreme Ultraviolet Science and Technology, Colorado State University, BYU-Provo, Michigan Technical University and Pierre Auger Collaboration, University of Colorado, Colorado School of Mines, Department of Physics, Colorado State University, Department of Physics, Cornell University, NASA, University of Massachusetts at Amherst, University of Massachusetss at Amherst, APS President, Harvard University, Society of Physics Students, Duke University, Computer Science, Brigham Young University, Chemistry \& Biochemistry, Brigham Young University, University of Arizona, University of Utah, Kansas State Univ., Bethel University, University of New Mexico, Stanford University, JILA, University of Colorado at Boulder, NIST, JILA, University of Colorado at Boulder, National Renewable Energy Laboratory, University of Denver, University of Colorado, Boulder, NREL, Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ, 85287- 1604, USA, DU, ERI, Eleanor Roosevelt Institute (ERI), Cerro Tololo Interamerican Observatory, Utah State University, Center for Atmospheric and Space Sciences, Sciprint.org, University of Colorado at Boulder, JILA and University of Colorado, Kirchhoff Institute for Physics, University of Heidelberg, Utah Valley University, University of New South Wales, San Francisco State University, Weber State University, Cambridge University, Department of Physics and Astronomy, University of Utah, Kansas State University, Columbia University, NY, University of Colorado/JILA, Vice-President for Research and Technology Transfer, Colorado School of Mines

  • John Poate

    Brigham Young University, Los Alamos National Laboratory, Department of Physics and Astronomy, University of Utah, USA, MV Systems, Inc., USA, Helmholtz-Zentrum Berlin fuer Materialien und Energie, Abteilung Silizium-Photovoltaik, Germany, Colorado School of Mines, Department of Physics, USA, Georgia Institute of Technology, Arizona State University, Physics Department of Babolsar University, Iran, Physics Department, New Mexico State University, Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ, 85287-1604, USA, Department of Electrical Engineering, University of Arkansas, Fayetteville, AR 72701, USA, Department of Physics, Arizona State University, Tempe, AZ, 85287-1504, USA, Colorado State University, University of Wisconsin, NSF ERC for Extreme Ultraviolet Science and Technology, Colorado State University, BYU-Provo, Michigan Technical University and Pierre Auger Collaboration, University of Colorado, Colorado School of Mines, Department of Physics, Colorado State University, Department of Physics, Cornell University, NASA, University of Massachusetts at Amherst, University of Massachusetss at Amherst, APS President, Harvard University, Society of Physics Students, Duke University, Computer Science, Brigham Young University, Chemistry \& Biochemistry, Brigham Young University, University of Arizona, University of Utah, Kansas State Univ., Bethel University, University of New Mexico, Stanford University, JILA, University of Colorado at Boulder, NIST, JILA, University of Colorado at Boulder, National Renewable Energy Laboratory, University of Denver, University of Colorado, Boulder, NREL, Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ, 85287- 1604, USA, DU, ERI, Eleanor Roosevelt Institute (ERI), Cerro Tololo Interamerican Observatory, Utah State University, Center for Atmospheric and Space Sciences, Sciprint.org, University of Colorado at Boulder, JILA and University of Colorado, Kirchhoff Institute for Physics, University of Heidelberg, Utah Valley University, University of New South Wales, San Francisco State University, Weber State University, Cambridge University, Department of Physics and Astronomy, University of Utah, Kansas State University, Columbia University, NY, University of Colorado/JILA, Vice-President for Research and Technology Transfer, Colorado School of Mines