The diffusion coefficient of paraffin molecules is of importance in the wax deposition prediction models. In this work

an instrument based on the principle of Taylor dispersion method was built in order to measure the diffusion coefficient of paraffin molecules in the model crude oil. The newly developed apparatus was carefully calibrated and adequate operating conditions were summarized. Measured with this apparatus

the diffusion coefficients (DAB) of methanol in water

acetone in water

and hexane in heptane agree with those in literature

with an absolute deviation 1.13%. Using heptane as the solvent

six binary solutions were prepared with n-C18

n-C20

n-C22

n-C24 and n-C26 as solute. DAB of a solute in a solvent was measured at the temperature from 30℃ to 50℃. It is found that the diffusion coefficient of paraffin molecules increases linearly with temperature. As solute concentration increases

diffusion coefficients decrease exponentially. In the same solvent

paraffin molecules with longer chain present higher diffusion coefficient. The measured DAB is compared to that obtained by empirical equation. The calculated DAB by Hayduck-Minhas correlation are 50% lower than measured values. Obviously

the wax deposition prediction models employing Hayduck-Minhas correlation will underestimate the mass flux of wax molecules from the main flow to the pipe wall.