A molecular simulation study of commensurate–incommensurate adsorption of n-alkanes in cobalt formate frameworks

Abstract

The channels of the cobalt formate frameworks consist of one-dimensional channels that have a zig-zag configuration. Propane (C3) has a length that commensurates with the channel segment length; longer n-alkanes such as n-butane (nC4), n-pentane (nC5) and n-hexane (nC6) have conformations that straddle two channel segments. Configurational-bias Monte Carlo (CBMC) simulations show that the adsorption strength of C3 is higher than that of n-butane (nC4) and n-pentane (nC5); this unusual hierarchy is a direct consequence of the commensurate–incommensurate adsorption. CBMC simulations also reveal the possibility of separating C3–nC6, C3–nC4, nC4–nC6 and nC4–nC5 liquid mixtures for which the adsorbed phase contains predominantly the shorter alkane. Molecular dynamics simulations show that the hierarchy of self-diffusivities is non-monotonic and is the mirror image of the hierarchy of adsorption strengths.