Surface diffusion of hydrocarbon in activated carbon

This paper considers the surface diffusion of propane, and n-butane in activated carbon. The flux measurements were obtained using a differential permeation apparatus, and the surface diffusion flux, and hence surface permeability, was obtained. The surface diffusivity and permeability increase very fast with loading. The increase in the permeability is not due to the surface heterogeneity. All theories in the literature exhibit a surface diffusivity increase with loading, but they all predict a decrease in the surface diffusion permeability, while experimental surface permeability shows an increase. In the light of failure of all models in the literature, we propose a new model here, where we follow the traditional approach of Darken, but anew for the activation energy for surface diffusion to be a function of loading.