Molecular perspective for CO2 storage and capture in nanoporous adsorbents and polymeric membranes

Abstract

With the rapid increase of population and energy consumption, a huge amount of CO2 has been released into the atmosphere and caused severe impact on global warming. Development of cost-effective process for CO2 storage is one of the pressing issues in environmental protection. In last decade, meta-organic frameworks (MOFs) have emerged as a special class of hybrid nanoporous materials and been considered as versatile candidates for storage. Using molecular simulations, we have examined CO2 storage in a series of MOFs by varying metal center, organic linker, functional group and framework topology. The affinity with CO2 is enhanced by the addition of functional groups and the formation of constricted pores; both lead to a stronger adsorption at low pressures. The organic linker plays a critical role in tuning the free volume and accessible surface area, and thus largely determines CO2 adsorption at high pressures. The capacities correlate well with framework density, free volume, porosity and accessible surface area of MOFs. These molecular-based structure-function correlations are useful for a priori prediction of CO2 capacity and for rational screening of MOFs toward the high-efficacy CO2 storage. An equally important issue is CO2 capture from mixtures such as syngas, natural gas, and flue gas in chemical industry. We have investigated CO2 capture in a unique rho zeolite-like MOF (ZMOF) with anionic framework and charge-balancing extraframework ions. At ambient temperature and pressure, the selectivities are 1800 for CO2/H2 mixture, 80 for CO2/CH4 mixture, and 500 for CO2/N2 mixture. Compared with other MOFs and nanoporous materials reported to date, rho-ZMOF exhibits unprecedentedly high selective adsorption for these gas mixtures. The simulation results reveal that rho-ZMOF is a promising candidate for the separation of syngas, natural gas, and flue gas. Finally, simulation studies for CO2 separation in polymeric membranes will be also discussed.