Direct Assessment of Transport Properties of Supercritical Fluids Confined to Nanopores

Supercritical fluids are an essential constitute of the modern chemical industry. However, their optimal use in processes involving porous solids is rather limited owing to poor knowledge of their transport properties under confinement. By using the noninvasive pulsed field gradient (PFG) NMR method, we directly assessed molecular diffusivities of n-pentane in mesopores of model Vycor porous glass at sub- and supercritical temperatures. The obtained results ultimately point out that criticality in pores occurs at lower temperatures than in the bulk liquid surrounding the porous solid. Surprisingly, the data on molecular diffusivities and the pore density may be self-consistently quantified using simple gas−kinetic arguments.