5404
Ind. Eng. Chem. Res. 2006, 45, 5404-5410
Solubilities and Densities of Capsaicin in Supercritical Carbon Dioxide at Temperatures from 313 to 333 K Octavio Elizalde-Solis and Luis A. Galicia-Luna* Instituto Polite´ cnico Nacional, ESIQIE, Laboratorio de Termodina´ mica, UPALM Zacatenco, Edif. Z, Secc. 6, 1ER piso, LindaVista, C. P. 07738, Me´ xico, D. F., Mexico
Solubilities of capsaicin in supercritical carbon dioxide were measured at 313, 318, 323, 328, and 333 K in the range of (5-20) × 10-5 (mole fraction of capsaicin). Measurements were performed in an apparatus based on the static-synthetic method. Good agreement was found between the obtained experimental data and those available in the literature, except for at 333 K. Volumetric properties for the carbon dioxide + capsaicin system were also obtained via a vibrating tube densitometer coupled to the measurement cell in the same range of temperatures and at pressures up to 25 MPa. Densities for this system have not been previously reported. The solubilities of capsaicin in carbon dioxide were correlated with the density-based model proposed by Me´ndez-Santiago and Teja (Fluid Phase Equilib. 1999, 158-160, 501). The results from the correlation show that the reported data are self-consistent. Introduction
Table 1. Chemical Structure of Capsaicin
Capsaicin (8-methyl-N-vanillyl-6-noneamid) is the main component of capsaicinoids and the principal cause of the pungency in the Capsicum annuum species. A wide variety of Capsicum annuum species are cultivated in Mexico. They represent an extensive natural source of colorants in the food industry. Capsaicin is also used in the food industry as an ingredient for its hot flavor. In medicine, it is used in pain therapies as well as for its stimulation effect. It is also an active ingredient in the pepper spray.1,2 Information about the solubility data of capsaicin in supercritical fluids is important for the extraction of capsaicin from Capsicum annuum. The most common supercritical fluid used for the extraction of natural products is carbon dioxide due to its advantages and physical properties. Carbon dioxide reduces problems caused by the use of organic solvents in the extraction of oleoresins.3,4 Organic solvents are not completely removed from the extract, and the operation process temperature produces a thermal degradation of capsaicin and oleoresins. Equilibrium solubilities of capsaicin in supercritical carbon dioxide have been published by some authors. Sˇ kerget et al.5 reported solubilities at 298.15, 313.15, and 333.15 K and pressures up to 36 MPa. Hansen et al.6 measured solubilities of capsaicin in carbon dioxide at 308.15, 318.15, and 328.15 K in the range of 12-25 MPa. de la Fuente et al.7 obtained solubilities in the range of 298-318 K and pressures up to 40 MPa. All these sets of experimental data were measured based on the static-analytic method. The prediction of solubilities of solids in supercritical fluids using thermodynamic models presents some difficulties. Semiempirical correlations such as the density-based models proposed by Chrastil8 and Me´ndez-Santiago and Teja9 are commonly used to interpolate solubilities of solids in supercritical fluids. In this work, solubilities of capsaicin in supercritical carbon dioxide were measured in a static-synthetic setup from 313 to 333 K in the composition range of (5.83-20.19) × 10-5 mole fraction of capsaicin. This method avoids using analytical * To whom correspondence should be addressed. E-mail: lgalicial@ ipn.mx. Phone: (52) 55 5729-6000, ext 55133. Fax: (52) 55 55862728.
molecular weight molecular formula chemical structure
305.41 C18H27NO3
equipment like high-performance liquid chromatography (HPLC), because its maintenance cost is high. Volumetric properties for the carbon dioxide + capsaicin mixtures were quasi-simultaneously determined via a vibrating-tube densitometer at pressures up to 25 MPa. Density data for this system have not been reported previously. For the Me´ndez-Santiago and Teja9 cor-
Figure 1. Experimental apparatus: AB air bath, CA cathetometer, DMA 60 period meter, DPI 145 digital indicator of pressure, EC sapphire tube equilibrium cell, GC gas compressor, PI Isco pump, LB liquid bath, VTD vibrating tube densitometer, MC measurement cell, MR magnetic rod, PT pressure transducer, M multimeter, PTPi platinum probe i, TD digital indicator of temperature F250, Vi shut-off valve i, VSE variable speed engine, VP vacuum pump, FV feeding valve, P piston, ST sapphire tube, B cylindrical support, C cap, PC pressurization circuit, O window.
10.1021/ie060284h CCC: $33.50 © 2006 American Chemical Society Published on Web 06/27/2006
Ind. Eng. Chem. Res., Vol. 45, No. 15, 2006 5405 Table 2. Experimental Mole Fraction Solubilities of Capsaicin (2) in Supercritical Carbon Dioxide (1) T ) 312.86 K
T ) 317.82 K
T ) 322.91 K
T ) 328.01 K
T ) 332.92 K
P/(MPa)
y2/(mol/mol)
P/(MPa)
y2/(mol/mol)
P/(MPa)
y2/(mol/mol)
P/(MPa)
y2/(mol/mol)
P/(MPa)
y2/(mol/mol)
11.508 13.771 13.432 13.832 15.197 17.890 19.130 19.787 19.925 21.228 22.907
5.83 × 10-5 8.19 × 10-5 9.66 × 10-5 9.72 × 10-5 10.19 × 10-5 13.32 × 10-5 15.44 × 10-5 16.35 × 10-5 16.46 × 10-5 17.24 × 10-5 18.17 × 10-5
10.865 11.961 12.030 12.543 12.932 16.211 17.878 18.219 19.301 20.203
5.83 × 10-5 8.19 × 10-5 9.66 × 10-5 9.72 × 10-5 10.19 × 10-5 13.32 × 10-5 16.35 × 10-5 17.24 × 10-5 18.17 × 10-5 20.19 × 10-5
10.678 13.506 13.719 15.700 17.555 18.035 18.233 18.401
5.83 × 10-5 8.19 × 10-5 9.72 × 10-5 13.32 × 10-5 16.35 × 10-5 17.24 × 10-5 18.17 × 10-5 20.19 × 10-5
10.444 14.519 15.258 16.836 17.218 17.618 16.814
5.83 × 10-5 9.72 × 10-5 13.32 × 10-5 16.35 × 10-5 17.24 × 10-5 18.17 × 10-5 20.19 × 10-5
10.787 16.421 15.932 17.670 15.809 17.014 15.604
5.83 × 10-5 9.72 × 10-5 13.32 × 10-5 16.35 × 10-5 17.24 × 10-5 18.17 × 10-5 20.19 × 10-5
Table 3. Densities for the Carbon Dioxide (1) + Capsaicin (2) System at y2 ) 5.83 × 10-5 T ) 318.01 K
T) 313.07 K P/(MPa)
F/(kg‚m-3)
11.508 11.598 11.690 11.811 12.012 12.232 12.526 12.995 14.070 15.011 15.890 17.034 18.026 19.024 19.992 21.625
706.64a
a
T ) 323.04 K
P/(MPa)
F/(kg‚m-3)
10.865 10.942 11.028 11.236 11.543 11.995 13.035 14.017 15.016 16.003 17.020 18.027 19.039 20.054 21.020 22.013 23.157
602.97a
709.46 712.34 715.97 721.89 727.55 734.95 745.75 766.92 782.41 795.31 809.89 821.11 831.55 841.07 855.10
608.72 614.14 627.46 643.56 663.38 698.64 724.33 745.04 762.07 777.58 791.33 803.44 814.64 824.33 833.63 843.50
P/(MPa) 10.678 10.791 10.933 11.276 11.877 13.001 13.991 15.023 15.996 17.009 17.999 19.010 20.003 21.033 22.042 23.116
481.29a 493.76 509.23 540.66 585.59 642.00 675.77 703.59 724.43 743.11 759.08 773.42 785.71 797.77 808.41 818.62
T ) 332.93 K
P/(MPa)
F/(kg‚m-3)
P/(MPa)
F/(kg‚m-3)
10.444 10.575 10.680 10.856 11.004 12.007 13.018 14.074 15.049 16.007 16.998 18.029 19.001 20.000 20.957 21.964 23.158
372.30a
10.787 10.861 11.044 12.065 13.053 14.024 15.000 16.030 17.000 18.018 19.095 20.008 21.016 21.998 23.109
349.21a 354.87 370.10 448.64 516.66 568.09 608.84 642.59 667.60 689.89 710.17 725.58 740.17 753.27 766.76
384.93 395.07 412.06 427.76 515.09 579.66 627.18 658.89 684.91 706.90 725.85 741.81 755.91 768.49 780.61 793.43
Saturation density.
Table 4. Densities for the Carbon Dioxide (1) + Capsaicin (2) System at y2 ) 8.19 × 10-5 T ) 318.01 K
T) 313.06 K P/(MPa)
F/(kg‚m-3)
13.771 13.906 14.055 14.258 14.551 15.023 16.002 17.029 18.066 19.137 19.972 21.095 21.834
761.98a
a
T ) 328.01 K
F/(kg‚m-3)
764.4 767.06 770.61 775.53 782.98 797.07 810.12 821.97 833.05 841.04 850.68 857.18
P/(MPa)
F/(kg‚m-3)
11.961 12.361 12.527 13.039 13.528 14.03 14.529 15.033 16.013 17.011 18.174 19.041 20.066 21.081 22.003 23.293
662.45a 676.62 682.11 699.36 712.69 725.01 735.57 745.66 763.15 778.36 793.6 803.93 815.07 825.32 833.84 844.95
Table 5. Densities for the Carbon Dioxide (1) + Capsaicin (2) System at y2 ) 9.66 × 10-5
T ) 323.04 K P/(MPa)
F/(kg‚m-3)
13.506 13.595 13.771 13.871 14.035 15.026 16.015 17.007 18.147 19.036 19.987 21.114 22.047 23.31
660.92a
T) 313.12 K P/(MPa)
P/(MPa)
F/(kg‚m-3)
13.432 13.701 13.904 14.009 14.210 14.436 14.609 14.828 15.047 15.229 15.411 15.615 15.817 16.032 16.281 16.639 16.983 17.555 18.020 19.059 19.999 21.125 22.037 23.115 23.948 24.520
753.63a
12.030 13.046 14.069 14.997 16.048 17.023 18.094 19.066 20.004 21.045 22.069 23.026 23.838 24.999
662.74a 697.43 723.97 743.32 761.94 776.96 791.36 803.16 813.52 824.04 833.58 842.01 848.69 856.69
663.87 669.5 672.87 678.13 703.99 725.42 743.53 761.48 773.84 785.91 797.44 808.67 820.68
Saturation density.
relation, we compare the use of the solvent density and the mixture density. Similar deviations confirm that, in this correlation, we can use the solvent density when the mixture density is not available. Experimental Section a
Materials. Carbon dioxide and nitrogen with a stated purity of 99.995 mol % were purchased from Air Products-Infra (Me´xico). Aldrich Chemical Co., Inc., supplied capsaicin natural grade, with a purity of ∼65% capsaicin and 35% dihydrocapsaicin. The chemical structure of capsaicin is given in Table 1.
T ) 318.06 K
F/(kg‚m-3) 758.93 762.70 764.43 768.17 772.07 775.00 778.47 781.92 784.68 787.40 790.37 793.21 796.16 799.48 804.10 808.34 815.14 820.37 831.30 840.37 850.44 858.05 866.42 872.57 876.61
Saturation density.
Water (HPLC grade) was also purchased from Aldrich Chemical Co., Inc. No additional purification was carried out for these compounds. Capsaicin and water were carefully degassed while stirring and under vacuum before they were used.
5406
Ind. Eng. Chem. Res., Vol. 45, No. 15, 2006
Table 6. Densities for the Carbon Dioxide (1) + Capsaicin (2) System at y2 ) 9.72 × 10-5 T ) 318.01 K
T) 313.07 K P/(MPa)
F/(kg‚m-3)
13.832 13.932 14.038 14.530 15.031 16.026 17.032 18.017 19.030 20.033 21.037 21.990 23.001 23.846
762.33a
a
764.27 766.22 774.74 782.72 796.93 809.69 820.98 831.54 841.24 850.18 858.06 866.01 872.19
P/(MPa)
F/(kg‚m-3)
12.543 12.625 12.749 12.880 13.032 13.487 14.033 14.542 15.079 16.013 17.026 18.063 19.053 20.044 21.026 22.082 23.054 23.703
683.04a
T ) 323.05 K
685.93 688.81 693.86 698.36 710.98 724.07 735.23 745.85 762.10 777.70 791.63 803.55 814.46 824.30 834.16 842.55 847.92
P/(MPa)
F/(kg‚m-3)
13.719 13.828 13.962 14.072 15.003 16.000 17.025 18.039 19.001 20.087 21.080 22.022 23.059 23.560
667.26a 670.51 674.64 678.65 698.56 724.49 743.42 759.54 773.10 786.88 798.07 807.97 818.04 822.64
T ) 328.01 K
T ) 332.90 K
P/(MPa)
F/(kg‚m-3)
P/(MPa)
F/(kg‚m-3)
14.519 14.698 14.808 14.921 15.026 16.010 17.003 18.008 19.023 20.043 20.988 21.979 23.057 23.655
641.86a
16.421 16.623 16.837 17.028 18.027 19.031 20.044 21.041 22.032 23.022 23.323
652.57a 657.97 663.39 667.97 690.15 709.12 725.94 740.73 753.96 766.03 769.43
646.55 652.21 654.48 658.43 684.40 706.05 725.03 741.68 756.52 768.85 780.75 792.48 798.55
Saturation density.
Table 7. Densities for the Carbon Dioxide (1) + Capsaicin (2) System at y2 ) 10.19 × 10-5 T) 313.08 K
T ) 318.02 K
P/(MPa)
F/(kg‚m-3)
P/(MPa)
F/(kg‚m-3)
15.197 15.397 15.615 15.810 16.200 16.607 16.995 18.011 18.986 20.002 21.010 22.014 22.996 24.128 24.386
785.02a 788.00 791.11 794.52 799.15 804.39 809.18 820.84 831.10 840.86 849.85 858.21 865.90 874.21 876.03
12.932 13.224 13.525 13.893 14.183 14.509 14.813 15.016 15.998 17.015 18.021 19.030 20.025 21.024 21.937 23.029 23.881 24.421
695.51a 704.00 711.90 721.01 727.58 734.55 740.70 744.65 762.10 777.51 791.05 803.24 814.16 824.34 832.82 842.36 849.36 853.59
a
Saturation density.
Apparatus. Experimental solubilities and density measurements were performed in a static-synthetic setup. The schematic flow diagram of the apparatus is illustrated in Figure 1. A complete description of this apparatus has been given by Zu´n˜igaMoreno et al.10 The apparatus consists of a variable-volume sapphire tube equilibrium cell (Armines, France) with an internal volume of ∼10 cm3 and a vibrating U-tube densitometer (DMA 60/512P, Anton Paar), made of hastelloy C-276 with an internal volume of ∼1 cm3. The equilibrium cell can be operated up to 25 MPa and 473 K. The piston is used for increasing or decreasing pressure, and the magnetic rod is used for the sample mixing. A cathetometer equipped with a camera allows an enlarged visualization of the sapphire tube. The equilibrium cell temperature was regulated by an air bath, and the vibrating tube densitometer was thermoregulated by recirculating water with a liquid bath. Two platinum probes, PTP2 and PTP3 (Pt100, Specitec), were immersed in two thermometric wells located at the top and bottom of the cell body to measure the temperature of the cell, and the platinum probe, PTP1, was used to measure the temperature in the vibrating-tube densitometer. These platinum probes were connected to a digital indicator (F250, Automatic Systems Laboratories) to monitor temperature. Pressure measurements were
Figure 2. Comparison between the experimental solubilities of capsaicin (2) in supercritical carbon dioxide (1) reported in this work and those reported in the literature at ∼313 K: (b) Sˇ kerget et al.;5 (9) de la Fuente et al.;7 (3) this work.
made with a pressure transducer (250, Sedeme) placed above the equilibrium cell and connected to a digital multimeter (34401A, HP). Calibration. The calibration for the temperature probes was performed in a calibration system (F300S, Automatic Systems Laboratories) fitted with a 25-Ω reference probe (162CE, (0.005 K certified accuracy, Rosemount). Temperature uncertainty for the platinum probes was estimated to be (0.03 K. A dead weight balance (model 5304 Class S2, (0.005% F. S. precision up to 138 MPa, Desgranges & Huot) was used for the pressure transducer calibration in the range of 313-333 K. The estimated uncertainty for the pressure measurements was within (0.008 MPa. The vibrating-tube densitometer calibration was carried out using water and nitrogen as reference fluids.11 Densities for water and nitrogen were calculated with the equations of state proposed by Wagner and Pruβ12 and Span et al.,13 respectively. The estimated uncertainty of the experimental carbon dioxide + capsaicin densities was (0.20 kg‚m-3 in the reported data range. Experimental Procedure. Solubilities of capsaicin in supercritical carbon dioxide were measured based on the second method described by Zu´n˜iga-Moreno et al.10 where the equilibrium cell is coupled to the vibrating U-tube densitometer. This method has been tested for solid solubilities in supercritical carbon dioxide with naphthalene as the solid compound.
Ind. Eng. Chem. Res., Vol. 45, No. 15, 2006 5407 Table 8. Densities for the Carbon Dioxide (1) + Capsaicin (2) System at y2 ) 13.32 × 10-5 T ) 313.07 K P/(MPa)
F/(kg‚m-3)
17.890 18.082 18.233 18.447 18.678 18.856 18.995 20.047 21.038 22.020 22.973 24.234
819.39a
a
821.49 823.12 825.39 827.80 829.63 831.17 841.19 850.10 858.20 865.59 874.86
T ) 318.02 K P/(MPa)
F/(kg‚m-3)
16.211 16.424 16.673 16.884 17.050 17.230 17.463 18.002 19.010 19.995 21.026 22.002 23.072 24.509
765.17a 768.53 772.27 775.40 777.82 780.31 783.51 790.63 802.86 813.71 824.20 833.28 842.60 854.17
T ) 323.04 K P/(MPa)
F/(kg‚m-3)
15.700 15.867 15.956 17.036 18.044 19.027 20.028 20.994 22.012 22.995 24.158
718.24a 721.71 724.77 743.46 759.42 773.29 785.98 797.07 807.84 817.44 827.97
T ) 328.00 K
T ) 332.93 K
P/(MPa)
F/(kg‚m-3)
P/(MPa)
F/(kg‚m-3)
15.258 15.378 15.482 15.597 15.755 15.886 16.048 16.982 17.963 19.028 20.025 21.006 22.020 22.991 23.956
664.63a
15.932 16.105 16.287 16.472 16.619 16.779 16.899 17.001 18.040 18.973 19.983 21.014 21.984 22.951 23.963
639.24a 644.17 649.32 654.33 658.17 662.22 665.22 667.68 690.63 708.54 725.42 740.75 753.78 765.69 777.03
667.97 670.91 673.81 677.98 681.20 685.10 705.84 724.55 741.96 756.44 769.46 781.52 792.05 801.79
Saturation density.
Table 9. Densities for the Carbon Dioxide (1) + Capsaicin (2) System at y2 ) 16.35 × 10-5 T) 313.07 K
T ) 318.01 K
T ) 323.03 K
T ) 328.01 K
T ) 332.92 K
P/(MPa)
F (kg‚m-3)
P/(MPa)
F/(kg‚m-3)
P/(MPa)
F/(kg‚m-3)
P/(MPa)
F/(kg‚m-3)
P/(MPa)
F/(kg‚m-3)
19.787 19.844 19.902 20.022 21.001 22.176
838.46a 839.14 839.96 841.35 849.81 859.74
17.878 17.947 18.029 18.200 18.612 19.001 19.988 20.975 22.042 22.994 24.294
789.47a 790.40 791.35 793.66 798.62 803.30 814.10 824.10 834.09 842.31 852.86
17.555 17.717 17.955 18.014 19.018 20.028 21.002 22.006 22.993 24.244
752.54a 755.42 758.71 759.47 773.52 786.34 797.63 808.19 817.80 829.08
16.836 16.903 17.007 18.030 19.025 20.036 21.026 22.024 23.018 23.995
703.24a 704.63 706.80 726.09 742.38 757.08 769.98 781.83 792.70 802.55
17.670 17.831 17.920 18.028 19.013 20.025 21.023 21.954 23.009 23.860
683.46a 687.29 689.19 691.01 709.64 726.55 741.30 753.78 766.64 776.27
a
Saturation density.
The equilibrium cell was loaded with the desired composition of solid capsaicin and carbon dioxide by successive loadings of pure compounds. First, the empty cell without air was weighed. Then, ∼7 mg of capsaicin was added in the cell and degassed by a vacuum pump. The cell was again weighed. Finally, carbon dioxide was compressed by means of a syringe pump (100 DM, Isco), and ∼8 g of it was loaded into the cell. A third weighing was carried out to know the quantity of carbon dioxide. Weightings were performed in a comparator balance (MCA 1200, Sartorius) within an uncertainty of (1 × 10-7 kg. Mole fraction uncertainties for the carbon dioxide + capsaicin mixtures reported in this work were lower than (3 × 10-6. The equilibrium cell with the known composition for the capsaicin and carbon dioxide mixture was placed in the air bath and then connected to the vibrating-tube densitometer. They were set to the same temperature. The vibrating-tube densitometer was degassed, and the feeding valve was closed to avoid the flow of the mixture. The temperature for the densitometer was ∼0.4 K higher than that measured for the equilibrium cell. With constant temperatures, the equilibrium cell was carefully pressurized up to 25 MPa by means of a gas compressor, which uses nitrogen as a pressuring fluid. The magnetic rod was used for mixing purposes. Once capsaicin was completely dissolved in the supercritical carbon dioxide, the feeding valve was opened to feed the mixture into the vibrating-tube densitometer. Pressure was again increased because of the expansion of the mixture. The system was in equilibrium when the temperature and pressure in the cell and the signal of the densitometer were constant. The equilibrium conditions were reached in a lower time (3 h) compared with the 12 h reported by de la Fuente et al.7
Afterward, decrements in pressure
