Insights into adsorption behaviour of binary liquid mixtures in porous media using fast field cycling NMR

Abstract

Fast field cycling, FFC, NMR relaxometry experiments are reported in the frequency range of 10 kHz–40 MHz to characterise the adsorption behaviour of cyclohexane:THF (non-polar:polar) and THF:methanol (polar:polar) binary liquid mixtures adsorbed on a γ-alumina surface of catalytic interest. Laplace inversion of the relaxation rate data is employed to identify the chemical species in the binary mixture. In both systems studied, the more polar molecule preferentially interacts with the surface compared to the co-imbibed species. The relaxation rate data were analysed to explore the relative influences of surface dynamics and surface accessibility on the observed relaxation rates. For both binary systems, the change in relaxation behaviour with composition is interpreted as a change in the surface accessibility of each species caused by a micro-phase separation at the pore surface.