Toward an efficient wax precipitation model: Application of multi-solid framework and PC-SAFT with focus on heavy end characterization for different crude types

Several studies have investigated the wax precipitation process, focusing on the equations of state, correlations for fusion properties, and calibration of parameters. In most of them, the impact of the fluid characterization on the wax properties has not been addressed widely. In this study, we show that a single characterization scheme is not applicable to all crudes with wax precipitation. However, it is possible to categorize the crudes based on the compositional data and wax parameters to have a primary understanding of the fluid description for modeling. We employed the PC-SAFT equation of state for modeling of liquid phase behavior and the multi-solid framework to describe solid phase. The heptane plus fraction of the studied fluids is defined by the three-parameter gamma distribution of Whitson, et al. [1], and the continuous description of the plus fraction is discretized by the pseudoization method of Whitson, et al. [2]. We also show the significance of binary interaction parameters on calculating wax appearance temperature and wax weights. The critical volumes of the precipitating hydrocarbons are adjusted to find the best binary interaction parameters values for the WAT and wax weight determination. The WAT and wax weight of eleven crude oil samples are calculated and compared to experimental and modeling results of previous studies. Our model shows considerable improvements in estimating fluid description, WAT, and wax weight compared to other available models. Moreover, we demonstrated that the number of pseudo-components and the heaviest molecular weight in the description of plus fraction highly depend on the compositional data of the heavy end and wax properties. According to our results, 15 pseudo-components with the highest molecular weight of 1200 g/mol would result in the accurate presentation of WAT and wax weight for crudes with WAT higher than 310 K and high wax weights.