The use of DSC in the determination of the Vapor–Liquid Equilibrium data for fatty acids
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Laboratório de EXtração, TeRmodinâmica Aplicada e Equilíbrio The use of DSC in the determination of the Vapor–Liquid Equilibrium data for fatty acids Matricarde Falleiro, R. M. 1 , Meirelles, A. J. A. 2 , Krähenbühl, M. A. 1, * 1 Laboratory 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: [email protected] OBJECTIVES 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). METHODOLOGY Lauric acid, myristic acid, ethyl myristate and ethyl palmitate with 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 (x 1 = 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. 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. The data were modelated using the NRTL and UNIQUAC Equations (Table 1). Both models were able to describe the experimental data with low deviations. 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) Figure 1 – (a) General view of experimental apparatus room; (b) Expanded perspective of the DSC furnace; (c) Tungsten ball being placed on the pinhole; (d) Perspective in more details of some accessories under of the bench; (e) Differential thermal curve obtained by DSC (b) (c) (a) (d) onset temperature baselin e boiling endotherm (e) x 1 ≈ 0.1 x 1 ≈ 0.3 x 1 ≈ 0.5 x 1 ≈ 0.7 x 1 ≈ 0.9 Sistemas g E Model A 12 / cal.mol - 1 A 21 / cal.mol -1 a 12 * Mean Deviation / ºC Ethyl Myristate + Myristic Acid NRTL 1529.5500 -782.9940 0.2987 0.14 UNIQUAC 637.3379 -447.0392 - 0.14 Lauric Acid + Ethyl Palmitate NRTL -865.8260 1339.6447 0.3181 0.17 UNIQUAC -341.7366 437.2044 - 0.18 Ethyl Palmitate + Oleic Acid NRTL 844.9378 -927.5403 0.3054 0.38 UNIQUAC 283.2647 -275.0970 - 0.38 11 N , N 1 T T C º / deviation Mean N 1 i model g al experiment * E Table 1 – Binary interaction parameters of NRTL and UNIQUAC models. 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. 0.0 0.2 0.4 0.6 0.8 1.0 188 192 196 200 204 208 T his w o rk NRTL U N IQ U AC Tem p eratu re / ºC x 1 ,y 1 0.0 0.2 0.4 0.6 0.8 1.0 188 192 196 200 204 208 T his w ork NRTL U N IQ U AC Tem p eratu re / ºC x 1 ,y 1 0.0 0.2 0.4 0.6 0.8 1.0 212 216 220 224 228 232 236 240 T h is w o rk NRTL U N IQ U AC Tem p eratu re / ºC x 1 ,y 1 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. 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) (a) (a) (b) (b) (b)
description
The use of DSC in the determination of the Vapor–Liquid Equilibrium data for fatty acids. x 1 ≈ 0.1. x 1 ≈ 0.3. x 1 ≈ 0.5. o nset temperature. x 1 ≈ 0.7. x 1 ≈ 0.9. Matricarde Falleiro, R. M. 1 , Meirelles, A. J. A. 2 , Krähenbühl, M. A. 1, * - PowerPoint PPT Presentation
Transcript of The use of DSC in the determination of the Vapor–Liquid Equilibrium data for fatty acids
Laboratório de EXtração, TeRmodinâmica Aplicada e Equilíbrio
The use of DSC in the determination of the
Vapor–Liquid Equilibrium data for fatty acids Matricarde Falleiro, R. M. 1, Meirelles, A. J. A. 2, Krähenbühl, M. A. 1, *
1 Laboratory of Thermodynamic Properties, LPT, School of Chemical Engineering, University of Campinas, Brazil2 Laboratory of Extraction, Applied Thermodynamics and Equilibrium, ExTrAE, School of Food Engineering, University of Campinas, Brazil
* Corresponding author e-mail: [email protected]
OBJECTIVESVapor-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).
METHODOLOGY Lauric acid, myristic acid, ethyl myristate and ethyl palmitate with 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.
RESULTS AND DISCUSSIONFor every analyzed sample (Figure 2, 3 and 4), the boiling temperature was determined by the onset temperature measured as shown in Figure 1-d.
The data were modelated using the NRTL and UNIQUAC Equations (Table 1). Both models were able to describe the experimental data with low deviations.
CONCLUSIONThe 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) Figure 1 – (a) General view of experimental apparatus room; (b) Expanded perspective of the
DSC furnace; (c) Tungsten ball being placed on the pinhole; (d) Perspective in more details of some accessories under of the bench; (e) Differential thermal curve obtained by DSC
(b)
(c)
(a)
(d)onset temperature
baseline
boilingendotherm
(e)
x1 ≈ 0.1
x1 ≈ 0.3
x1 ≈ 0.5
x1 ≈ 0.7
x1 ≈ 0.9
Sistemas gE Model A12 / cal.mol-
1A21 /
cal.mol-1a12
* Mean Deviation / ºC
Ethyl Myristate + Myristic Acid
NRTL 1529.5500 -782.9940 0.2987 0.14UNIQUAC 637.3379 -447.0392 - 0.14
Lauric Acid + Ethyl Palmitate
NRTL -865.8260 1339.6447 0.3181 0.17UNIQUAC -341.7366 437.2044 - 0.18
Ethyl Palmitate + Oleic Acid
NRTL 844.9378 -927.5403 0.3054 0.38UNIQUAC 283.2647 -275.0970 - 0.38
11N,N1TT Cº/ deviation Mean
N
1 imodelgalexperiment
*E
Table 1 – Binary interaction parameters of NRTL and UNIQUAC models.
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.
0.0 0.2 0.4 0.6 0.8 1.0
188
192
196
200
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208 This work NRTL UNIQUAC
Tem
pera
ture
/ ºC
x1, y1
0.0 0.2 0.4 0.6 0.8 1.0
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208 This work NRTL UNIQUAC
Tem
pera
ture
/ ºC
x1, y1
0.0 0.2 0.4 0.6 0.8 1.0
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240 This work NRTL UNIQUAC
Tem
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/ ºC
x1, y1
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.
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)
(a)
(a)
(b)
(b)
(b)
