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.