Vapor–Liquid Equilibria for Hydrocarbon/Water Systems Using Thermodynamic Perturbation Theory

Abstract

Complex phase equilibrium prediction for hydrocarbon systems containing polar compounds such as water and alcohols is essential in oil and gas industry. Conventional thermodynamic model such as cubic equation of state (EoS) provides quick and often reliable phase equilibrium predictions in many inert compound systems. However, cubic EoS often cannot be satisfactorily extended to predict multicomponent systems that contain polar compound. In this work, the well-known cubic EoS and association EoS are applied to predict hydrocarbon/water systems. The association EoS, cubic plus association equation of state (CPA EoS), and statistical associating fluid theory equation of state (SAFT EoS) are based on advanced molecular theory. Vapor–liquid equilibria (VLE) data for ethane/water system, n-hexane/water system, and n-decane/water system at various temperatures have been collected and modeled. Based on the results, association models are capable of predicting near critical points and yield very satisfactory predictions for aqueous systems. Among the selected EoS, CPA EoS yields much better predictions with average absolute relative error (AARE) 10.88 % for ethane/water system, 7.39 % for n-hexane/water system, and 10.41 % for n-decane/water water system.