Hindered Diffusion of Residue Narrow Cuts Through Polycarbonate Membranes

Hindered diffusion plays an important role in catalytic processing of residue and heavy oil because of large size molecules in these feedstocks. Vacuum residue of Athabasca oil sand bitumen was fractionated into 13 narrow fractions and an end-cut by supercritical fluid extraction and fractionation (SFEF). Diffusion transport of five SFEF cuts through four polycarbonate membranes was investigated using a diaphragm cell at 308 K. The results showed that diffusion coefficients of the five SFEF cuts decreased as the experiment proceeded, which illustrates that these cuts are polydisperse in size. The effective diffusion coefficients varied with molecular size and pore size. Hindered diffusion of the five SFEF cuts is significant in the membranes with nominal pore diameter of 15 nm, which is around the average pore size of typical hydrotreating catalyst. Comparisons between experimental data and theoretical prediction revealed that the actual hindered degree for diffusion of the five SFEF cuts is higher than that calculated by the Renkin equation. There were slight differences in diffusivity among saturate, aromatic, and resin constituents. (C) 2010 American Institute of Chemical Engineers AlChE J, 56: 2030-2038,2010