Prediction of the critical properties of n-alkanes and their mixtures with two versions of SAFT equation of state

Abstract

industry. Hence, the study of their thermodynamic behavior, especially their critical properties, is noteworthy.Since there is some particular behavior in the critical region, the study of this property is a challenge from any modeling and experimental approach, so in many cases reliable EoSs are needed to predict these kinds of properties. Among all of the proposed EoSs, some of the equations which have a theoretical basis show a good performance as well as reliable experimental ones. Two of the fundamental theories of these EoSs, prevalently used in science and chemical engineering (especially for n-alkanes), are the simplified perturbed hard chain theory (SPHCT) [1] and the statistical associating fluid theory (SAFT).The SAFT approach is based on the Wertheim's firstorder perturbation theory [2, 3] and has been developed by Chapman et al. [4,5] and Huang and Radosz [6,7] and the attained equation is called original SAFT. Up to now, several versions of the SAFT EoSs have been proposed and it has been shown that they have a good performance in predicting the thermodynamic properties of pure compounds and mixtures. As the most commonly used SAFT EoSs, we can mention the Lennard-Jones (SAFT-LJ) [8], the soft-SAFT [9], the variable range (SAFT-VR) [10], the hard-sphere (SAFT-HS) [11], the Boublik-Alder-ChenKreglewski (BACK), the perturbed-chain (PC-SAFT) [12], the SAFT + cubic EoS [13], etc.The most prominent characteristics of the SAFT theory is that it explicitly takes into account the effects of the molecular shape (non-sphericity) and association interactions. This feature has turned SAFT EoS into a good predictive tool in calculating the thermodynamic properties.The BACK equation is one of the SAFT EoSs which is a successful inaccurate description of the PVT behavior of simple, non-associating molecular systems and their mixtures in a wide range, especially near and above fluids' Abstract Two versions of statistical associating fluid theory (SAFT) equation of state (EoS), namely modified SAFT-BACK and original SAFT, were used to calculate the critical temperatures and pressures of 10 n-alkanes (from c 1 to c 10 ). The obtained results were compared with the available experimental data to assess the predictive power of these EoSs in the critical region. The absolute average percentage deviation (AAD %) of the results obtained from the modified SAFT-BACK model indicated that this EoS had a good performance in the prediction of the critical points of the n-alkanes, but the deviation resulting from the original SAFT EoS reflected the limitations of the latter EoS in representing the critical region. Moreover, the critical temperatures for binary mixtures of n-alkane were calculated using both the original SAFT and the modified SAFT-BACK models and the results were compared with the data predicted by the correlation relations. The modified SAFT-BACK model showed a very good performance, while the original SAFT model did not yield an appropriate prediction of the critical temperatures of n-alkane binary mixtures.