Ind. Eng. Chem. Res. 2000, 39, 4427-4430
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RESEARCH NOTES High-Pressure Phase Equilibrium Data for Aromatic Components of Wine: Carbon Dioxide/n-Butanal System Marta Va´ zquez da Silva and Domingos Barbosa* Departamento de Engenharia Quı´mica, Faculdade de Engenharia da Universidade do Porto, Po´ lo FEUP do Centro de Biotecnologia e Quı´mica Fina, Rua dos Bragas, 4050-123 Porto, Portugal
Phase equilibrium data, measured in a static-type apparatus, for the system carbon dioxide/ n-butanal at 303.2 and 313.2 K and for pressures up to the critical point are presented. The results are correlated by the Soave-Redlich-Kwong and Peng-Robinson equations of state, and the associated interaction parameters are given. Introduction
Experimental Section
The demand for low-alcohol-content beverages, such as wine, beer, and cider, is increasing because of health issues and more strict driving legislation. The production of these new drinks offers the challenging problem of preserving the organoleptic properties of the original beverage. In this work, we are particularly concerned with the production of low-alcohol-content wine. Many techniques have been suggested for the dealcoholization of wine1, e.g., controlled fermentation, distillation, evaporation, liquid-liquid extraction, reverse osmosis, and dialysis. However, supercritical extraction with carbon dioxide (CO2) seems to be one of the most promising techniques for dealcoholization because of its low operating temperature, which prevents thermal degradation, its capability of producing a final product with no solvent residues, and its energy efficiency. This work is part of a research program that aims to measure the solubility of the most important aromatic compounds of wine in carbon dioxide, the knowledge of which is essential for the correct design of the supercritical fluid extraction (SFE) process of dealcoholization. These aromatics are mainly aldehydes, terpenic alcohols, and esters, and most of them are common to other alcoholic beverages. Therefore, the results of this work are not restricted to the production of low-alcoholcontent wine, but are applicable to the study of other dealcoholization processes by SFE. In a previous work,1 we studied the solubility in carbon dioxide of ethyl acetate and isoamyl acetate, which are two esters that can be found in wine. In this work, we provide experimental data for the solubility of n-butanal, one of the most important aldehydes of wine, in carbon dioxide. The experimental measurements were made in a static-type equilibrium apparatus, and the data were fit by the Soave-Redlich-Kwong (SRK) and PengRobinson (PR) equations of state (EOS).
Apparatus. The experimental equipment used in this work is based on that of Nunes da Ponte and coworkers2 and is described in more detail by Va´zquez da Silva et al.1 The apparatus, which is represented schematically in Figure 1, allows for the measurement of equilibrium phase compositions for temperatures between 295.2 and 353.2 K and pressures up to 30 MPa. The apparatus consists of a cylindrical sapphire cell in a thermostatic air bath, with two sampling systems (one for the liquid and the other for the vapor phase). The use of a sapphire cell has the advantage of allowing the visualization of the phases at equilibrium. The carbon dioxide is compressed using a pressure generator provided by High-Pressure Equipment (model 68-5.75-15). The pressure in the cell is controlled with a Lucas Schaevitz probe (precision (0.1% of the full scale, with a pressure limit of 35 MPa) and at the expansion zone with a Delta Ohm probe (precision (0.05% of the full scale, with a pressure limit of 0.2 MPa). The temperature of the air bath is maintained by a thermo-ventilator connected to an Omrom temperature controller with a Pt100 probe (precision (0.1K). The mixture in the cell is well-stirred (for about 30 min) and allowed to rest for at least 6 h to ensure equilibration. The sampling of the liquid and vapor phases is made through six-way valves. These samples are collected by depressurization and expansion into small glass traps connected to large glass bottles of calibrated volume in a thermostatic air bath. The amount of CO2 in each phase is determined by measuring the corresponding pressure variation in the expansion zone. To ensure that there are no solute losses, the sampling tube is washed with a cleaning solvent (in this study, we used toluene as the washing solvent), which is injected by one of the ports of the six-way valve. The solution obtained in the glass traps is weighed and analyzed with a Hewlett-Packard gas-liquid chromatograph (model HP5880), using an HP20M (Carbowax) column with a TCD (thermal conductivity detector) and a split injector. The carrier gas used was helium. To ensure that only a small amount of sample is
* Author to whom correspondence should be addressed. Phone: 351-22-2041660. Fax: 351-22-2000808. E-mail:
[email protected].
10.1021/ie0002273 CCC: $19.00 © 2000 American Chemical Society Published on Web 10/06/2000
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Figure 1. Schematic representation of the apparatus for measuring equilibrium data. Table 1. Pure Component Critical Properties and Acentric Factor6 component
Tc (K)
Pc (MPa)
ω
carbon dioxide n-butanal
304.2 545.4
7.376 5.380
0.239 0.352
collected, it was always verified that the pressure drop in the cell was less then 0.1 MPa after the sampling procedure. The reproducibility of the composition results was verified by several measurements under the same conditions of pressure and temperature, which allowed us to estimate their precision as (0.0015 in mole fraction. Materials. The n-butanal was provided by Merck with a purity greater than 99% (by weight). Riedel-de Hae¨n provided the toluene, used as a washing solvent, with a minimum purity of 99.7% (by weight). The CO2 and helium were obtained from ArLiquido and had a mole fraction purities greater than 0.99998 and 0.99999, respectively. All reagents were used with no further purification.
Table 2. Experimental (xEXP, yEXP) and Correlated Data with SRK EOS (xSRK, ySRK) and PR EOS (xPR, yPR) and Relative Quadratic Deviation Values (RQD) at 303.2K P (MPa)
xEXP
yEXP
5.25 5.10 5.07 4.77 4.56 4.21 4.00 3.71 3.33 2.92
0.994 0.947 0.938 0.896 0.868 0.837 0.824 0.798 0.757 0.718
0.996 0.991 0.998 0.996 0.995 0.988 0.993 0.997 0.994 0.991
xSRK
ySRK
0.895 0.894 0.874 0.859 0.832 0.815 0.789 0.752 0.709
RQD
7.0E-04 1.1E-05 6.1E-04 1.9E-05
0.997 0.996 0.996 0.996 0.995 0.995 0.994 0.993 0.992
xPR
yPR
0.896 0.895 0.876 0.862 0.837 0.821 0.797 0.763 0.722
0.998 0.998 0.998 0.997 0.997 0.997 0.996 0.996 0.995
Data Correlation In this work, the Soave-Redlich-Kwong3 (SRK) and the Peng-Robinson4 (PR) equations of state (EOS), together with the classic mixing rule with two parameters,5 were used to correlate the experimental data. The expressions for these equations are given in the Appendix.
Ind. Eng. Chem. Res., Vol. 39, No. 11, 2000 4429 Table 3. Experimental (xEXP, yEXP) and Correlated Data with SRK EOS (xSRK, ySRK) and PR EOS (xPR, yPR) and Relative Quadratic Deviation Values (RQD) at 313.2K P (MPa)
xEXP
yEXP
7.09 7.03 6.81 6.69 6.61 6.30 5.88 5.57 5.18 4.73 4.56 4.28 3.82 3.43 2.79
0.995 0.985 0.971 0.956 0.951 0.932 0.908 0.888 0.856 0.800 0.789 0.771 0.732 0.692 0.643
0.995 0.997 0.992 0.994 0.994 0.992 0.991 0.995 0.992 0.991 0.991 0.988 0.991 0.990 0.986
xSRK
ySRK
xPR
yPR
0.954 0.940 0.934 0.930 0.914 0.892 0.875 0.851 0.822 0.810 0.790 0.753 0.719 0.652
0.995 0.995 0.995 0.995 0.995 0.995 0.995 0.994 0.994 0.994 0.993 0.992 0.991 0.990
0.922 0.896 0.877 0.852 0.820 0.808 0.786 0.746 0.709 0.637
RQD
3.1E-04 3.7E-06 4.1E-04 6.6E-06
experimental data is only 10 K. To get an idea of the quality of the correlation, the relative quadratic deviation (RQD) was calculated. nres
0.991 0.991 0.991 0.991 0.990 0.990 0.990 0.989 0.988 0.986
∑
RQD )
m)1
(
)
xEXP,m - xCALC,m xEXP,m
2
(1)
nres
An analysis of Tables 2 and 3 and Figure 2 shows that the solubility of n-butanal in the vapor phase is low, almost always less than 1% for the pressures studied, and that the Soave-Redlich-Kwong and Peng-Robinson equations of state fit the experimental results equally well. As the solubility of n-butanal in the vapor phase is low, we may expect that this aromatic compound will tend to stay in the wine during dealcoholization, which means that the organoleptic characteristics of the product are maintained. Acknowledgment The authors acknowledge the financial support provided by the Fundac¸ a˜o para a Cieˆncia e Tecnologia (project PRAXIS XXI BD/9729/96) and by the Centro de Biotecnologia e Quı´mica Fina, and the facilities made available by the Faculdade de Engenharia da Universidade do Porto. Appendix Equations of State and Mixing Rule Soave-Redlich-Kwong3 P)
RT a v - b v(v + b)
Peng-Robinson4 P)
a RT v - b v(v + b) + b(v - b)
R(T,Tc,ω) )
[ ( x )]
a(T) ) R(T,Tc,ω)ac Figure 2. Experimental (b, 303.2K; 2, 313.2K) and correlated data with SRK (- - -) and PR EOS (s). Table 4. Interaction Parameters for the SRK and PR EOS EOS
T (K)
P (MPa)
ka
kb
SRK PR
303-313 303-313
2-9 2-9
-0.2094 -0.2326
-0.7095 -0.5824
ac ) 0.427 47
R2Tc2 Pc
ac ) 0.457 27
m) 0.485 08 + 1.551 71ω 0.156 13ω2 b ) 0.086 64
The critical properties and the acentric factor for the pure components, necessary for the application of the equations of state, are summarized in Table 1.
T Tc
2
R2Tc2 Pc
m) 0.374 64 + 1.542 26ω 0.269 92ω2
RTc Pc
b ) 0.077 80
RTc Pc
mixing rule5 nc
a)
Results and Discussion
nc
∑∑x x a
i j ij
aij ) xaiaj(1 - ka)
i)1 j)1 nc
The experimental procedure described previously was used to determine the phase equilibrium compositions for the system carbon dioxide/n-butanal. The equilibrium compositions for this system at 303.2 and 313.2 K are given in Tables 2 and 3, respectively, and shown graphically in Figure 2. In these tables and figure, the experimental values are compared with the data correlated by the SRK EOS and PR EOS. The interaction parameters associated to the equations of state are presented in Table 4. These parameters were obtained by fitting the all of the data together, because the temperature difference for the
1+m 1-
b)
nc
∑∑x x b
i j ij
bij )
b i + bj (1 - kb) 2
i)1 j)1
Literature Cited (1) Va´zquez da Silva, M.; Barbosa, D.; Ferreira, P. O.; Mendonc¸ a, J. High-Pressure Phase Equilibrium Data for the Systems Carbon Dioxide/Ethyl Acetate and Carbon Dioxide/Isoamyl Acetate at 295.2, 303.2 and 313.3 K. Fluid Phase Equilib. 2000, in press. (2) Pereira, P. J.; Gomes de Azevedo, E. J. S.; Nunes da Ponte, M. Phase Equilibria for {2,3-Epoxypropanol (Glycidol) + Carbon Dioxide} from T ) 292 K to T ) 343 K at Pressures up to 27 MPa. J. Chem. Thermodyn. 1997, 29, 197.
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(3) Graboski, M. S.; Daubert, T. E. A Modified Soave Equation of State for Phase Equilibrium Calculations. 1. Hydrocarbon Systems. Ind. Eng. Chem. Process Des. Dev. 1978, 17, 443. (4) Peng, D. Y.; Robinson, D. B. A New Two-Constant Equation of State. Ind. Eng. Chem. Fundam.1976, 15, 59. (5) Solo´rzano-Zavala, M.; Barra´gan-Aroche, F.; Bazu´a, E. R. Comparative Study of Mixing Rules for Cubic Equations of State in the Prediction of Multicomponent Vapor-Liquid Equilibria. Fluid Phase Equilib. 1996, 122, 99.
(6) Yaws, C. L.; Chen, D.; Yang, H. C.; Tan, L.; Nico, D. Critical Properties of Chemicals. Hydrocarbon Process. 1989, 68, 61.
Received for review February 14, 2000 Revised manuscript received August 21, 2000 Accepted August 29, 2000 IE0002273
