ESTIMATING DIFFUSION-COEFFICIENTS OF DENSE FLUIDS

A simple and generalized correlation in terms of viscosity and molar d ensity is proposed to estimate diffusion coefficients for hydrocarbon systems. The correlation can be used for both gases and liquids up to a pressure of about 400 bar (6000 psia). It has been shown that the pr oposed method may also be used to estimate effective diffusion coeffic ients in multicomponent systems with a reasonable degree of accuracy. Although the proposed correlation is based on experimental data in hyd rocarbon; systems, preliminary evaluations have shown that it is also satisfactory for nonhydrocarbon systems as well. The proposed equation predicts diffusion coefficients in gases with an absolute-average dev iation of 8% and in liquid systems with an absolute average deviation of 15%. The input parameters for the correlation are molecular weight, critical properties, and acentric factor of components in the system; mixture molar density; low-pressure gas viscosity; and actual viscosi ty. The last three properties may be predicted from appropriate correl ations.