The use of DSC in the determination of the Vapor–Liquid Equilibrium data for fatty acids

1. The use of DSC in the determination of the Vapor–Liquid Equilibrium data for fatty acids x1 ≈ 0.1 x1 ≈ 0.3 x1 ≈ 0.5 onset temperature x1 ≈ 0.7 x1 ≈ 0.9 Matricarde Falleiro, R. M. 1, Meirelles, A. J. A. 2, Krähenbühl, M. A. 1, * 1Laboratory of Thermodynamic Properties, LPT, School of Chemical Engineering, University of Campinas, Brazil 2 Laboratory of Extraction, Applied Thermodynamics and Equilibrium, ExTrAE, School of Food Engineering, University of Campinas, Brazil * Corresponding author e-mail: mak@feq.unicamp.br OBJECTIVES RESULTS AND DISCUSSION For every analyzed sample (Figure 2, 3 and 4), the boiling temperature was determined by the onset temperature measured as shown in Figure 1-d. Vapor-liquid equilibrium (VLE) data of mixtures involving fatty acids and ethyl esters are practically nonexistent in literature. The great importance of such data for the biodiesel industry is related to the quality of the biofuel. Generally, its quality can be influenced by several factors, such as presence of Free Fatty Acids (FFA). These, depending on concentration, inhibit phase separation of ethyl esters and glycerol, which compromises the quality standards of biodiesel. Therefore, the present work aims to determine VLE data for fatty mixtures of acids and esters by Differential Scanning Calorimetry (DSC). (a) (b) Figure 2 – (a) Boiling endotherms to system: ethyl myristate (1) + myristic acid (2) obtained by DSC; (b) liquid-vapor equilibria: ethyl myristate (1) + myristic acid (2) at 2.67 kPa. METHODOLOGY Lauric acid, myristic acid, ethyl myristate and ethyl palmitatewith purity greater than 99% were acquired from Sigma, and oleic acid, with 99% purity, was acquired from Fluka. The experimental apparatus (Figure 1-a) consists of a DSC (Model 2920) with a vacuum system fitted to it. For the DSC analysis, binary mixtures of ethyl myristate + myristic acid; lauric acid + ethyl palmitate and ethyl palmitate + oleic acid was evaluated at 2.67 kPa, covering the entire phase diagram (x1 = 0, 0.1, 0.2 ... to 1.0). Samples of 4 to 8 mg were used in the study, with a heating rate of 25 °C.min−1 and a small ball placed over the pinhole (Figure 1-c), in order to avoid the pre-vaporization of the sample, since it behaves as an exhaust valve, releasing the vapor phase in a controlled manner. (a) (b) Figure 3 – (a) Boiling endotherms to system: lauric acid (1) + ethyl palmitate (2) obtained by DSC; (b) liquid-vapor equilibria: lauric acid (1) + ethyl palmitate (2) at 2.67 kPa. (b) (a) Figure 4 – (a) Boiling endotherms to system: ethyl palmitate (1) + oleic acid (2) obtained by DSC; (b) liquid-vapor equilibria: ethyl palmitate (1) + oleic acid (2) at 2.67 kPa. (a) The data were modelated using the NRTL and UNIQUAC Equations (Table 1). Both models were able to describe the experimental data with low deviations. (b) Table 1 – Binary interaction parameters of NRTL and UNIQUAC models. (c) (e) (d) CONCLUSION The results obtained have shown that the applied method is an accurate experimental technique that uses a shorter operation time and small amount of sample. This study also improved the thermodynamic modeling by determining the binary interaction parameters of models used to describe non-ideality of the liquid phase needed for the development of equipment for fuel production (biodiesel) baseline boiling endotherm Figure 1 – (a) General viewof experimental apparatus room; (b) Expanded perspective ofthe DSC furnace; (c) Tungstenballbeing placed on thepinhole; (d) Perspective in more details of some accessoriesunderofthebench; (e) Differential thermal curve obtainedby DSC