Solid-liquid equilibrium of n-alkanes using Global-TPT2 equation of state

Abstract

An equation of state (EOS) in the framework of thermodynamic perturbation theory (TPT) is applied to the systems containing n-alkanes and the wax deposition phenomena. The EOS used is derived by Alavi and Feyzi (J. Chem. Phys. 2013, vol.139, 074104) and is comprised of a perturbed-chain reference term based on second-order thermodynamic perturbation theory (TPT2), followed by a square-well perturbation contribution. Since the EOS is developed without any phase related assumptions, it can describe vapor, liquid and solid phases. For this reason we have called the EOS Global-TPT2. The pure component parameters are adjusted to pure n-alkane compounds performing linear optimization algorithm. Solubility temperature of some heavy n-alkanes in the n-hexane and n-heptane solvents is evaluated. Good agreement with the experimental data is observed with Average Absolute Relative Percent Deviation (%AAD) of lower than 2 by adjusting only one binary interaction parameter. In addition, the wax appearance temperature and the amount of precipitated wax are predicted using the Global-TPT2 EOS for two North Sea oil samples and also samples composed of methane plus ternary waxy systems. In all these calculations the same EOS is used for both liquid and solid phases. Even though some simplifying assumptions are applied, the model is proved to be capable of adequately describing the systems containing solid phase.