(194c) Molecular Modeling of CO2 Adsorption and Transport in Nanoporous Materials

There is a general consensus that new materials are needed to efficiently and cost effectively capture CO2 from fuel or flue gases. Experimental work is critical to progress in developing and testing new materials, but the number of possible candidate materials makes it impractical to use an Edisonian approach to materials discovery. Molecular modeling is a tool that can be used to help guide experiments and screen materials more cost effectively than experiments alone. We present results from both ab initio quantum mechanical calculations and from semi-empirical statistical mechanical models for evaluating the effectiveness of porous sorbent materials for CO2 capture. We have studied adsorption separation using nanoporous materials such as metal organic frameworks and zeolitic imidazolate frameworks. Both pure gas and mixed gas adsorption isotherms are measured. Pure gas adsorption isotherms are compared with experiments where possible. Experimental results for pure gas adsorption are common, but mixed gas adsorption isotherms are extremely difficult to measure. Our calculations therefore complement experimental data by probing conditions that are difficult to measure experimentally. We use equilibrium molecular dynamics to predict diffusion coefficients for pure and mixed gases in nanoporous materials. Measuring pure gas diffusivities is difficult experimentally and there are very few data with which to compare. To the best of our knowledge, there are no experimentally determined mixed gas diffusivities for metal organic frameworks or zeolitic imidazolate frameworks (ZIFs). Our calculations are therefore pure predictions. We have examined adsorption and diffusion of pure and mixed gases in ZIF-68, ZIF-70, and a Ni-pillared material.