An efficient method to calculate multisolid-(wax) precipitation

• An efficient method to calculate multisolid (wax) precipitation in liquid and vapor–liquid petroleum mixtures is described.
• A monotonic equation is proposed for the calculation of liquid and multisolid equilibria.
• The liquid multisolid phase calculations can be extended to vapor–liquid multisolid phase calculations by means of the Rachford–Rice equation.
• Numerical cases of study are presented to illustrate the applicability and efficiency of the proposed iterative scheme.

Based on the multisolid-wax precipitation assumption for petroleum mixtures, a monotonic equation is proposed for the calculation of liquid and multisolid equilibria. Owing to the fact that the number of precipitating species can be determined instantly at fixed temperature and pressure through a stability analysis, the computation is fast and reliable. Although the developed iteration procedure is focus to liquid mixtures it is shown that can be easily incorporate into existing vapor–liquid iteration procedures based on the Rachford–Rice equation to get a vapor–liquid–multisolid-(wax) flash calculations. Numerical experimentations are shown and even more the proposed iteration method is used in the construction of phase boundaries without any problem.