Extension of the CPA equation of state with dipolar theories to improve vapour–liquid-equilibria predictions

• Published in: Fluid phase equilibria 2011-12, Vol.312, p.66-78
• Main Authors: de Villiers, A.J., Schwarz, C.E., Burger, A.J.
• Format: Article
• Language: English
• Subjects: Chemistry; Computational fluid dynamics; CPA-GV; CPA-JC; Density; Dipolar; Equations of state; Esters; Ethers; Exact sciences and technology; General and physical chemistry; Interaction parameters; Liquid-vapor equilibria; Liquids; Mathematical models; Phase equilibria; Vapour–liquid-equilibria
• ISSN: 0378-3812; 1879-0224
• DOI: 10.1016/j.fluid.2011.09.007

► CPA extended with dipolar terms of Jog and Chapman (JC) and Gross and Vrabec (GV). ► New model parameters for selected compounds are determined for these EOSs. ► Accurate VLE predictions of polar/alkane and polar/polar systems. ► Good predictions of ternary VLE. ► Similar performance for JC and GV models with improvement compared to CPA. The Cubic-Plus-Association (CPA) equation of state (EOS) is extended with the dipolar theories of Jog and Chapman (JC) and Gross and Vrabec (GV). These new extended models are termed CPA-JC and CPA-GV and each require four pure component model parameters for non-associating polar compounds and six parameters for associating compounds. Model parameters for selected ketones, aldehydes, esters, ethers and alcohols are presented for these two EOSs and were determined by including saturated vapour–pressure, liquid density and binary vapour–liquid-equilibria (VLE) data in the objective function. Furthermore, it is necessary to explicitly account for cross-association in binary mixtures where one component cross-associates, but does not self-associate. Major improvement in VLE predictions of polar/alkane and polar/polar systems are obtained with both CPA-GV and CPA-JC compared to normal CPA. In the majority of cases investigated, CPA-GV and CPA-JC require no or very small binary interaction parameters ( k ij ) to accurately represent VLE. The VLE of ternary mixtures is also predicted with good accuracy by both CPA-GV and CPA-JC. For the systems under investigation, no significant difference is observed between the performance of the CPA-JC and CPA-GV EOS models.