Dagang vacuum residue was fractionated into sixteen narrow fractions and an end-cut by supercritical fluid extraction and fractionation.The effective diffusion coefficients of five chosen fractions and the end-cut through 15

50

80 and 1000 nm polycarbonate membranes were measured at 308 K by a diaphragm cell.The results showed that diffusivities of residue fractions and end-cut decreased gradually as the experiment proceeded.It indicated that residue cuts were all composed of various molecules with different sizes.The effective diffusion coefficients of residue cuts decreased with increasing molecular weight and decreasing membrane pore size.The degree of hindered diffusion of five fractions and the end-cut diffusing through 15 nm membranes was more significant

when compared with 50 nm and 80 nm membranes.Comparisons between fractions and end-cuts sufficiently showed that the diffusion of end-cut was more severely hindered in these three types of membranes.The difference of molecular configuration might contribute to different degrees of hindered diffusion between fractions and end-cut.