Measurement of the diffusivity of benzene in microporous silica by quasi-elastic neutron scattering and NMR pulsed-field gradient technique

The diffusivity of benzene in a microporous silica powder has been measured by neutron scattering and NMR techniques. The measurements have been performed on un-supported silica but the powder has the same characteristics as the active layer of a real membrane. Self-diffusion coefficients of the order of 10-(10) m(2)s(-1) are found at 300 K by both techniques so that the model of Knudsen diffusion is not valid for benzene in this microporous material. Due to the presence of small pores, the diffusion of benzene in the membrane-material approaches the diffusion regime usually observed in zeolites. Furthermore, the diffusivity of benzene follows an Arrhenius law with an activation energy of 11 kJ mol(-1).