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Similarity coefficient and prediction of critical properties of fluids
Mehdi Ghanbari, Sayed Mostafa Hosseini and Mohammad Mehdi Alavianmehr

Recently, a new parameter named “similarity coefficient (SC)” has been proposed (Ghanbari and Tahery, Fluid Phase Equilib., 310, 82, 2011) to show the new regularity of the organic compounds based on the group-contribution (GC) method. This parameter provides the relation between the co-volume of the fluids and their heat capacities. In the present study, two new methods on the basis of SC were proposed for predicting critical properties of fluids. To achieve this goal, Peng-Robinson (PR) equation of state and GC method of Ambrose were employed to develop SC-PR and SC-Ambrose methods. The performance of the proposed methods was assessed by predicting the critical properties of 150 hydrocarbons, including: alkanes, alkenes, alkynes, aromatics and cyclic compounds at vapor liquid equilibrium condition; the average absolute deviations (AAD in %) of the predicted critical temperatures and critical pressures using SC -PR were found to be 1.28% and 3.26%, respectively. The critical pressures of studied hydrocarbons have also been predicted from SC-Ambrose with AAD equal to 2.56%. The predicted results were also compared with those obtained by the well-known Ambrose’s GC method. Results showed that the harmony between our method and Ambrose’s method was quite satisfactory. Furthermore, the surface tensions of long-chained hydrocarbon fluids have been predicted using the molecular-based model proposed by Chunsheng-Chongli (Y. Chunsheng, Z. Chongli, Chinese. J. Chem. Eng., 12; 85, 2004), in which the required critical temperatures were predicted accurately from the proposed SC -PR method. From 460 data point examined, the AAD of the predicted surface tensions of the above hydrocarbon fluids using SC -PR-CC was found to be 4.45%.

Keywords: similarity coefficient, critical property, regularity, Surface tension

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