Molecular based models for estimation of critical properties of pure refrigerants: Quantitative structure property relationship (QSPR) approach Mohammad Amin Sobati *, Danial Abooali School of Chemical Engineering, Iran University of Science and Technology (IUST), Postal Box 16765-163, Tehran, Iran A R T I C L E I N F O Article history: Received 11 October 2014 Received in revised form 29 November 2014 Accepted 10 January 2015 Available online 13 January 2015 Keywords: QSPR Critical properties Refrigerant Enhanced replacement method (ERM) Molecular descriptor A B S T R A C T In the present survey, new quantitative structure–property relationships (QSPR) have been proposed to estimate critical properties of pure refrigerants. For developing these models, the experimental data of T C for 198 pure compounds, the experimental data of V C for 194 pure compounds, and the experimental data of P C for 197 pure compounds were applied. For each compound, 1650 molecular descriptors were determined. Enhanced replacement method (ERM), as an effectual tool for subset variable selection, was utilized. The proposed models are simple multivariate linear equations with six variables for estimation of T C , five variables for estimation of V C , and six variables for estimation of P C . The variables of models are computed from the molecular structure of refrigerants. The average absolute relative deviation (AARD, %) of the proposed models over all experimental data are 2.65%, 3.76%, and 4.65% for estimation of T C , V C , and P C , respectively. ã 2015 Elsevier B.V. All rights reserved. 1. Introduction Proper design of refrigeration cycles is dependent on the accessibility of physical properties of refrigerants. Although physical properties of some refrigerants have been already published in the literature [1,2] but there are no data available on physical properties of new-designed refrigerants. Vapor–liquid critical temperature, volume, and pressure are three widely used pure component constants. The term critical point is used to specifically denote the vapor–liquid critical point of a component, above which distinct liquid and gas phases do not exist. According to the corresponding states law proposed by van der Waals in 1873, equilibrium properties which depend on intermolecular forces are related to the critical properties in a universal way [3]. In this context, many corresponding state correlations are proposed for estimation of volumetric, thermody- namic, and transport properties of gases and liquids [4]. Therefore, knowledge about critical properties is vital in different chemical processes such as supercritical extraction, design of refrigeration cycles, high pressure phase equilibrium processes, and etc. Besides, knowing critical properties are important in the application of different equation of states. The experimental determination of critical properties is preferred but such measurements are usually expensive, time-consuming, and often involving uncertainty due to the impurities and decomposition [5]. Therefore, different methods, providing an accurate estimation of critical properties are required. The proposed models for estimation of critical properties can be categorized as group contribution based models, and quantity structure property relationship (QSPR) models. The main group contribution based methods for estimation of critical properties are Ambrose method [6], Lydersen method [7], and Joback modification of Lydersen’s method [8,9]. Knowledge of the boiling point is essential for calculation of critical properties by Ambrose and Lydersen methods [10]. More details about group contribution based methods can be found elsewhere [3,4,10]. The group contribution based methods are suffering from some important disadvantageous such as limited applicability for isomers as well as the molecules with new groups [11]. Quantitative structure–property relationship (QSPR) is another approach for estimation of physical properties [5,11–13]. In this approach, the selected physical property is estimated as a function of parameters relate solely to the molecular structure. These structure-based parameters are called molecular descriptors. Molecular descriptors are calculated from the molecular structure of components by application of certain mathematical algorithms. The proposed model can be applied to estimate the property of new designed compounds solely from their molecular structure. Katritizky et al. reviewed the QSPR models proposed for estimation * Corresponding author. Tel.: +98 21 77240496; fax: +98 21 77240495. E-mail address: Sobati@iust.ac.ir (M.A. Sobati). http://dx.doi.org/10.1016/j.tca.2015.01.006 0040-6031/ ã 2015 Elsevier B.V. All rights reserved. Thermochimica Acta 602 (2015) 53–62 Contents lists available at ScienceDirect Thermochimica Acta journa l home page : www.e lsevier.com/loca te/tca