Phase behavior of (CO 2 + methanol + lauric acid) system Franciele M. Ferreira a , Luiz P. Ramos b , Papa M. Ndiaye a , Marcos L. Corazza a,⇑ a Department of Chemical Engineering, Federal University of Paraná, CEP 81531-990, Curitiba, PR, Brazil b Department of Chemistry, Federal University of Paraná, CEP 81531-990, Curitiba, PR, Brazil article info Article history: Received 6 September 2010 Received in revised form 16 February 2011 Accepted 17 February 2011 Available online 25 February 2011 Keywords: Phase equilibrium Lauric acid Supercritical CO 2 Methanol SF equilibrium PR-EoS abstract In this study the phase equilibrium behaviors of the binary system (CO 2 + lauric acid) and the ternary system (CO 2 + methanol + lauric acid) were determined. The static synthetic method, using a variable- volume view cell, was employed to obtain the experimental data in the temperature range of (293 to 343) K and pressures up to 24 MPa. The mole fractions of carbon dioxide were varied according to the systems as follows: (0.7524 to 0.9955) for the binary system (CO 2 + lauric acid); (0.4616 to 0.9895) for the ternary system (CO 2 + methanol + lauric acid) with a methanol to lauric acid molar ratio of (2:1); and (0.3414 to 0.9182) for the system (CO 2 + methanol + lauric acid) with a methanol to lauric acid molar ratio of (6:1). For these systems (vapor + liquid), (liquid + liquid), (vapor + liquid + liquid), and (solid + fluid) transitions were observed. The phase equilibrium data obtained for the systems were modeled using the Peng–Robinson equation of state with the classical van der Waals mixing rule with a satisfac- tory correlation between experimental and calculated values. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction In last decade, there has been a great interest in finding alterna- tive routes for production and purification of biodiesel. The use of heterogeneous catalysts for biodiesel production gained particular attention due the advantages related to costs reduction and simpli- fication of products purification. Recent investigations have shown that esterification and transesterification reactions can be carried out with relative success using layered (lamellar) carboxylates cat- alysts, such as zinc laurate in the presence of methanol. In partic- ular promising results for esterification of lauric acid to biodiesel production were reported [1,2]. However, relative low yields were obtained even at high molar ratio methanol to oil. A common explanation given in the literature is that the catalyst is not effec- tive for triacylglycerols systems. These reactions are commonly carried out at high temperature and high molar ratio of methanol to oil and pressures closes to the methanol vapor pressure [1]. From kinetics point of view, coexisting two phase systems, can lead to mass transfer limitation of reactants and a subsequent termina- tion of the reaction. To perform the mass transfer in the reaction media, an alternative way is the use of supercritical dioxide carbon as diluents or solvent. There are a great variety of potential appli- cations of supercritical carbon dioxide in the industry processing of fat oils and derivatives, and this subject has been extensively stud- ied over the last three decades [3–6]. On the other hand, supercrit- ical fluid extraction is an interesting separation process, because the removal of the solvent is accomplished without exposing the triacylglycerols and fatty acids to high temperatures, avoiding the thermal degradation of these compounds [6,7]. In this case, the use of supercritical CO 2 is attractive because it is inexpensive, nontoxic, nonflammable, inert, naturally abundant and has a rela- tively low critical temperature (304.1 K) [8–11]. Several studies report the phase behavior of systems involving triacylglycerols, fatty acids and carbon dioxide [11–19]. These studies showed that triacylglycerols and fatty acids are poorly sol- uble in CO 2 , due to its non-polarity. However, the addition of third component commonly known as cossolvent can improve this solu- bility [20,21]. Knowledge of the phase behavior is of great importance for the modeling, design and optimization of separation processes con- trolled by equilibrium [9]. However, a lack of experimental data and reliable thermodynamic models which can aid the technical- economic evaluation of processes has limited the industrial use of supercritical fluids [10]. Some studies reporting the phase behavior of such systems in the presence of cosolvents are available in the literature [21–28]. However, none of these studies reported phase equilibrium data for systems with methanol as the co-solvent. The use of methanol instead ethanol is mainly due to the fact that in the methanol pro- cess, reaction are faster and purification is easier, especially when water is used, so that most of the actual biodiesel plant are designed for methanol use. Understanding phase behavior of these systems in the presence of methanol is the first and fundamental step for development and optimization of esterification process using the lamellar catalysts. 0021-9614/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2011.02.017 ⇑ Corresponding author. Tel.: +55 41 3361 3178. E-mail address: corazza@ufpr.br (M.L. Corazza). J. Chem. Thermodynamics 43 (2011) 1074–1082 Contents lists available at ScienceDirect J. Chem. Thermodynamics journal homepage: www.elsevier.com/locate/jct