Prediction of the Solubility of Cholesterol and its Esters in Supercritical Carbon Dioxide

Abstract

The ability to predict the solubility of solids in supercritical fluids is important in many applications, including the food and pharmaceutical industries, chemical processing, and separations. In the present work, the solubility of cholesterol and its esters in supercritical carbon dioxide are investigated by applying equations of state. The equations of state used are: (a) the modified Peng-Robinson equation of state (Gasem et al.), and (b) the modified Peng-Robinson equation of state (Boston and Mathias). These equations of state have an exponential alpha function and it is found that they give better results than those resulting from the Peng-Robinson equation of state which has a linear alpha function. The interaction parameters are also obtained for the systems studied and the percentage of average absolute relative deviation (%AARD) is displayed for each calculation. IntroductionSupercritical fluids (SCF) are widely applied to the extraction, separation and purification of pharmaceuticals, as well as the detoxification of hazardous wastes. Carbon dioxide is the most commonly used fluid for supercritical extraction, since it is nontoxic, nonflammable, easy to handle and has relatively low critical temperature and pressure [1].By using supercritical carbon dioxide, it is possible to extract thermally labile compounds, especially with pharmaceutical and food products. As an example, cholesterol can be removed from food products using supercritical solvent, resulting in minimal protein degradation [2]. Cholesterol, an integral component of membranes in Eucaryota, is a modifier of membrane properties. In vivo studies, have demonstrated that cholesterol can also modulate the activities of some G proteincoupled receptors, which are integral membrane proteins [3].Knowledge of the solubility of solids in SCF is essential to evaluate their extraction feasibility and to establish optimum operating conditions. However, solubility data of solids and their mixtures in SCF is limited and the accurate measurement of the solubility of solids in SCF is also difficult and time consuming. In efforts to widen the range of application, thermodynamic models capable of predicting phase equilibria become particularly important.Equations of state in combination with mixing rules are currently the most widely used models for the calculation of the solubility of components in SCF [4]. Some of the work reported in this area includes Gonzalo et al. [5], Valderrama and Alvarez [6], and Higashi et al. [7].In the present study, two modified versions of PR EOS are used to calculate the solubility of cholesterol and its esters in supercritical carbon dioxide. They are the modified PR EOS by Gasem et al. [8] and the modified PR EOS by Boston and Mathias [9], MPR1 and MPR2, respectively. The values of the interaction parameters in the binary systems studied in this work are presented and the percentage of average absolute relative deviation (%AARD) is displayed for each calculation. MethodsThe solubility of solids in SCF is given by 1):In ...

Application of supercritical fluids in cholesterol extraction from foodstuffs: a review

“…The ability to predict the solubility of cholesterol in supercritical fluids is important in the food industry. For this purpose, Peng-Robinson equation (Babaei et al 2006;Bozorgmehr and Housaindokht 2006), density-based correlation (Huang et al 2004), statistical association fluid theory (SAFT) equation (Aghamiri and Nickmand 2010) and Van Der Waals mixing rules (Ksibi and Moussa 2007) have been employed.…”