A New Cubic Equation of State for Improved Liquid Density Prediction

Hydrocarbon fluid phase behaviours have numerous implications in natural gas and petroleum engineering and are often predictable from equations of state (EOSs). Equations of state methods are far less expensive (in terms of material cost and time) than laboratory or experimental forages and the results are interestingly within acceptable limits of accuracy. Several cubic EOSS have been presented in literature, most of Fluid PVT and phase behavior properties to good degrees of accuracy. However, most fail in predicting liquid phase densities accurately enough. A new three parameter cubic EOS was developed based on a modification of the van der Waals (vdW) attraction term contribution to pressure. The success of the new EOS was derived from recognizing that the attraction term of previous EOSs has been inadequate in capturing the dense fluid properties especially liquid densities and PVT properties at or near the critical region. The primary goal was to minimize the gap between experimentally derived-, and equation of state (EOS)- calculated PVT or fluid phase behavior data especially, liquid densities, for pure components and mixtures. Volumetric and phase equilibria calculations were carried out with the new EOS for pure components, binary ternary and multicomponent mixtures and results compared to experimental data (available in literature) and results obtained from industry-popular cubic EOSs, in particular, the two parameter, Peng-Robinson's (PR) and the three parameter PatelTeja's (PT) EOs. The results indicate that the new EOS predicts the liquid densities of pure hydrocarbon components and mixtures more accurately than the Peng Robinson's (PR) and Patel-Teja's (PT) EOS. The new EOS predicted liquid phase densities of pure components and mixtures with a grand average percent absolute deviation (AAPD) of 1.60% as opposed to 3.01% and 11.17% for PT and PR EOSs respectively.