365 - How fast is gas separation through a nanoporous graphene membrane? The role of surface adsorption, and application to post-combustion CO2 capture
Joshua Schrier, firstname.lastname@example.org, Department of Chemistry, Haverford College, Haverford, PA 19041, United States
Membrane-based methods are potentially an efficient and economical way to separate gases because they avoid the energy cost of liquefying the gases needed for cryogenic distillation, and the large size and high maintenance associated with pressure- and temperature- swing adsorption processes. Nanoporous graphene membranes provide the limiting case of membranes, and high performance separations of small molecules such as H2 and He from larger molecules have been described in the literature. Here I will discuss how strong surface adsorption can lead to enhanced transmission for larger molecules due to the increased dispersion interaction. I will describe two types of models---one based on Langmuir-adsorption which is appropriate when the barrier crossing rate is much slower than adsorption and desorption rates, and a detailed kinetic model which is generally applicable---and show how they can be fit to atomistic molecular dynamics simulations. Using these two models, membrane permeance and selectivity under arbitrary pressure conditions can be computed. The noble gases provide an example in which surface adsorption favors the transmission of Xe atoms rather than Ne atoms, even though the potential energy barrier for the former is higher. Based on this principle, I will describe the design and characterization of a nanoporous graphene membrane for the separation of CO2 from N2 and CH4. The final membrane has a CO2 permeance of 3×105 GPU, CO2/N2 selectivity of 190 and CO2/CH4 selectivity exceeding 1000, thus having applications to post-combustion carbon dioxide capture and utilization of biogenic methane.
Tuesday, August 21, 2012 02:35 PM
1st International Symposium on Graphene for Energy and Fuels (01:30 PM - 05:20 PM)
Location: Pennsylvania Convention Center
Room: 119 A