Do Residual Solvent Molecules Always Hinder Gas Sorption in Metal-Organic Frameworks?

The nature and magnitude of effects of residual solvent on gas uptake and selectivity in metal-organic frameworks (MOFs) have been systematically studied using high-throughput Monte Carlo simulations in the Grand Canonical ensemble. We focus on the uptake and separation of the essential CO2 and CH4 gases, which are pertinent to biogas upgrading and other common industrial processes and represent distinct types of interaction with the host MOF structures. We demonstrate that in circumstances where the residual solvent has a significant effect, CO2 uptake and selectivity in a curated data set of MOFs are likely to be affected negatively by its presence, while CH4 uptake may be affected either positively or negatively with a preference for positive effects. Both negative and positive residual solvent effects become greater at a higher pressure. Chemical, physical, and geometrical origins of the residual solvent effect have also been discussed. The relationship between various geometrical properties of MOFs and the extent of the residual solvent effect has been assessed, showing the greatest impact on MOFs with a pore diameter of around 5 & Aring;. These results inform whether the presence of residual solvent is likely to be useful or detrimental in a MOF for a given application.