Novel high-precision wax molecular diffusion coefficient correlation based on the diffusion laboratory apparatus coupled with differential scanning calorimeter

Abstract

Wax molecular diffusion coefficient is a crucial factor determining the wax deposition rate of waxy crude oil, but the calculation accuracy of the traditional Hayduk-Minhas and Wilke-Chang relations is unclear. The Couette wax deposition experiments of Changqing crude oil under different operating conditions (oil temperature, wall temperature, rotation speed and deposition duration) were carry out and find the traditional Hayduk-Minhas relationship will underestimate the wax molecular diffusion coefficient. To increase the calculation accuracy of wax molecular diffusion coefficient, a newly-developed diffusion laboratory apparatus coupled with the Differential Scanning Calorimeter (DSC) were utilized to evaluate the diffusion coefficient of C16, C18, C20, C22, C24 in n-alkane solutions at different temperatures (10, 15, 20, 25, 30,35, and 40 °C). Based on the experimental results, a novel high-precision correlation was put forward and the calculated results are in good agreement with the experimental results, the average relative error is within 3.0 %. The applied solvent of the n-alkane solutions is mineral oil and it has a complex composition. Therefore, the developed correlation can be used to evaluate the wax molecular diffusion coefficient in the real crude oil. The application of the new relationship will lead to more accurate wax deposition calculations.