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Vapor pressure measurements of ethanol–isooctane and 1-butanol–isooctane systems using a new ebulliometer
Fuel 107 (2013) 47–51
Contents lists available at SciVerse ScienceDirect
Fuel journal homepage: www.elsevier.com/locate/fuel
Vapor pressure measurements of ethanol–isooctane and 1-butanol–isooctane systems using a new ebulliometer Rama Oktavian, Vika Amidelsi, Agung Rasmito, Gede Wibawa ⇑ Department of Chemical Engineering, Faculty of Industrial Technology, Sepuluh Nopember Institute of Technology (ITS), Campus ITS Sukolilo, Surabaya 60111, Indonesia
h i g h l i g h t s " A new simple ebulliometer has been developed in this work. " The ebulliometer is reliable to measure vapor pressure of alcohols–isooctane mixture. " The experimental data were well correlated with Wilson, NRTL, and UNIQUAC models.
a r t i c l e
i n f o
Article history: Received 8 November 2011 Received in revised form 31 January 2013 Accepted 2 February 2013 Available online 22 February 2013 Keywords: Ebulliometer Ethanol Isooctane Vapor pressure
a b s t r a c t A new, simpler ebulliometer has been developed to accurately measure the vapor pressure of ethanol– isooctane and 1-butanol–isooctane systems at various mixture compositions. The reliability of the experimental apparatus was validated by comparing the experimental data with published data for pure isooctane and ethanol and ethanol–isooctane system. Our data were in good agreement with the published data, with a deviation of less than 1.9%. The vapor pressure of an ethanol–isooctane mixture was initially elevated by the addition of ethanol until the ethanol concentration reached 0.3 mass fractions, then dropped at concentrations above 0.7 mass fractions. For a 1-butanol–isooctane system, the vapor pressure decreased with increasing 1-butanol concentrations. The experimental data were correlated using the Wilson, Non-Random Two-Liquid (NRTL), and Universal Quasi-Chemical (UNIQUAC) activity coefficient models with an average absolute deviation in the vapor pressures of 3.5%, 3.3%, and 6.1%, respectively. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Fossil fuels, which remain the primary energy resources around the world, cause significant increases in the atmospheric CO2 concentration and have an effect on global warming [1,2]. Fossil fuels combustion contributes 73% of CO2 production [3]. Thus, finding a solution to greenhouse gas emissions is a major research focus for solutions to the global warming problem. Recently, the addition of oxygenates, such as simple alcohols, that are primarily produced from renewable resources has received tremendous attention because these compounds have an ability to reduce pollution and enhance the octane number of gasoline. Nicholas Otto [4] first used ethanol in internal combustion engines. Ethanol–gasoline mixtures have been successfully used in various machines and vehicles that typically run on gasoline [5]. However, the mixture can have a higher vapor pressure than the base gasoline which raises concern regarding the evaporative emission from the fuel mixture. Vapor pressure is one of the most important ⇑ Corresponding author. Tel.: +62 31 5946240; fax: +62 31 5999282. E-mail address: [email protected] (G. Wibawa). 0016-2361/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.fuel.2013.02.005
physical properties of a gasoline mixture because it refers to the volatility of the gasoline and can affect the evaporative emission of the fuel mixture. Therefore, accurate experimental data are important in designing fuel mixtures with specific vapor pressures. The vapor pressures of gasoline mixtures with four alcohols at 37.8 °C (100 °F) of various compositions were measured by Pumphrey et al. [6]. Sun et al. [7] measured the bubble-point vapor pressures for mixtures of an endothermic hydrocarbon fuel with ethanol. The experimental results indicated that the addition of ethanol had a critical effect on the vapor pressure of the fuel. An ethanol-fuel blend with a low ethanol composition can have an increased volatility. The vapor pressures for both pure substances and mixtures are traditionally measured using an ebulliometer, which was first proposed by Cotrell [8] to determine the boiling points of pure substances. Rogalski and Malanowski [9] developed a new ebulliometer in 1980 using Cotrell’s principle for determining vapor–liquid equilibrium data. However, in these ebulliometers analyses of both vapor and liquid-phase compositions are necessary due to a difference between the liquid-phase composition at equilibrium and the feed composition. Therefore, Li et al. [10]
48
R. Oktavian et al. / Fuel 107 (2013) 47–51
developed an inclined ebulliometer that no longer required liquid and vapor-phase composition analysis to measure the bubble point for a chloroform–ethanol–benzene system. Li et al. [10] also noted that they adopted the angle of inclination of 30° for their work to ensure the accuracy of the equilibrium temperature measurement. In this work, a new, simpler ebulliometer is proposed based on the work of Li et al. [10] by removing the inclination and enlarging the volume of the cell. We can ensure that the equilibrium and the feed compositions do not change significantly during the measurements due to the small proportion of vapor formed during equilibrium by enlarging the volume of the cell. Therefore, the present apparatus can be used to accurately measure the vapor pressure of a gasoline mixture. We used isooctane in this work to represent gasoline because it is the main component in gasoline.
simpler ebulliometer by removing the inclined portion from the previous ebulliometer. In addition, a temperature detector was attached at the liquid–vapor interface to ensure the accuracy of equilibrium temperature measurements. The mixtures with varying isooctane and ethanol, isooctane and 1-butanol compositions were prepared by directly weighing the constituent component on an Ohaus balance with a precision of ±0.0001 g. The temperature was measured using an RTD Pt 100 sensor connected to a Shimaden SD 15 temperature display with a measurement accuracy of ±0.1 K. The vapor pressures at various temperatures and compositions were measured using a mercury manometer with an accuracy of ±0.1 mm Hg.
2.3. Experimental procedure 2. Experimental 2.1. Materials All materials used in this work (isooctane, ethanol, and 1-butanol) were supplied by Merck, Darmstadt, Germany. These materials were used without further purification. Table 1 lists the properties of all materials used. 2.2. Experimental apparatus A new, simpler ebulliometer based on the principle of the quasistatic method is shown in Fig. 1b. The ebulliometer has a 5.5-cm cell diameter, 14-cm height, and a 332.5-cm3 volume and is connected with a vacuum pump. The ebulliometer cell was turned on via moderate heating, which was controlled using a temperature controller to maintain equilibrium at the desired temperature. The quasi-static method is based on the overall concentration instead of the equilibrium composition of the liquid phase as described by Li et al. [10] and shown in the inclined region in Fig. 1a. The enlargement of the cell volume as shown in Fig. 1b allows for an increase in the amount of substance being tested so that the composition of the fluid hardly changes during the vapor pressure measurement. This can be calculated using the simple mass balance in Eq. (1) as follows:
zi F ¼ xi L þ yi V
ð1Þ
In which, zi is the mole fraction of component i in the initial mixture injected into the ebulliometer, F the total moles of mixture injected into the ebulliometer, xi the mole fraction of component i in the liquid phase at equilibrium, L the number of moles in the liquid phase at equilibrium, yi the mole fraction of component i in the vapor phase at equilibrium, V the number of moles in the vapor phase at equilibrium. We assume, with the same value of V, the same mole fraction for component i in the vapor phase (yi), and the same feed composition (zi), that a smaller ebulliometer means that the amount of mixture injected into the ebulliometer (F) must be smaller, and significant change can occur in the mole fraction of component i in liquid phase at equilibrium (xi). In our work, we developed a new,
A sample containing approximately 220 cm3 of a liquid mixture of known composition was charged in the ebulliometer cell. First, the system was created under vacuum conditions to remove air and impurities from the equilibrium cell. Then, the equilibrium cell was heated to reach the desired equilibrium temperature. The temperature was controlled by a PID controller (Shimaden SR 64). After the ebulliometer reached a constant pressure at a desired equilibrium temperature, the pressure was recorded as the vapor pressure at a desired temperature. The experimental procedure was repeated at different temperatures and compositions.
3. Results and discussion 3.1. Reliability test of the apparatus The proposed ebulliometer was tested for the reliability by comparing the experimental data for the vapor pressures of both pure liquids and mixtures as measured by this apparatus with the published data for pure ethanol, isooctane, and an ethanol–isooctane mixture. The Antoine equation [11] for pure isooctane and the Wagner equation [12] for pure ethanol were used to compare the experimental data. The Antoine and Wagner constants were obtained from Poling et al. [13]. For the ethanol–isooctane mixture, the experimental data were compared with the experimental data from Hull et al. [14]. A comparison of the experimental data obtained in this work with the published data is presented in Tables 2 and 3 and Figs. 2 and 3 along with their deviations. The results indicate that the data were in good agreement with the published data, with a deviation of less than 1.9% calculated as an average absolute deviation (AAD) in the vapor pressures as follows:
AAD ¼
n 1X Plit Pexp 100% n i¼1 Pexp i
ð2Þ
in which Pexp is the vapor pressure obtained in the experiment while P lit is the vapor pressure calculated using both the Antoine [11] and Wagner [12] equations and n is the number of data.
Table 1 Properties of materials used in this work. Property
1-butanol CH3(CH2)3OH
Isooctane C8H18
Ethanol C2H5OH
Molecular weight (g/mol) Purity Density (d 20 °C/20 °C) Boiling range (°C)
74.12 >99.5% 0.809–0.812 116–119
114.23 >99.5% 0.691–0.696 98–100
46.07 99.9% 0.790–0.793 78
49
R. Oktavian et al. / Fuel 107 (2013) 47–51
1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
Condenser tube joint Vacuum jact Inner casing Thermometer well Feed inlet Stirrer Boiler Condenser Vacuum pump Mercury manometer
1. 2. 3. 4. 5. 6.
7.
(a)
Ebulliometer cell Thermocouple Condenser Vacuum unit Mercury manometer Heating system controller Magnetic stirrer
(b)
Fig. 1. Comparison of the ebulliometer apparatus: (a) Ebulliometer developed by Li et al. [10]; (b) new, simpler ebulliometer developed in this work.
Table 2 Comparison of experimentally measured isooctane vapor pressures (Pexp) with the literature data (Plit).
300.35 302.75 305.95 308.25 310.15 313.15 316.25 318.95 Overall AAD
Plit (kPa) 7.31 8.17 9.46 10.48 11.39 12.97 14.77 16.51
Pexp (kPa) 7.33 8.13 9.47 10.80 11.73 13.07 14.80 16.40
AAD (%) 0.34 0.51 0.08 2.94 2.89 0.76 0.18 0.68 1.05
Pexp Isooctane
30
PLit
Pexp Ethanol
27 24
P (kPa)
T (K)
33
21 18 15 12 9
Table 3 Comparison of experimentally measured ethanol vapor pressure (Pexp) with the literature data (Plit). T (K)
Plit (kPa)
Pexp (kPa)
AAD (%)
301.35 302.55 308.45 314.35 318.95 321.15 323.65 325.85 Overall AAD
8.86 9.50 13.24 18.19 23.07 25.78 29.17 32.46
8.93 9.60 13.60 18.80 23.46 26.26 29.73 33.06
0.86 1.09 2.62 3.23 1.66 1.86 1.89 1.83 1.88
3.2. Vapor pressure measurement The vapor pressures at various temperatures and compositions for the ethanol–isooctane and the 1-butanol–isooctane systems obtained in this work are presented in Tables 4 and 5 and Fig. 4 in which w represents the mass fraction of the ethanol and 1-butanol in the mixtures. For ethanol–isooctane mixture, the vapor pressure was initially elevated by the addition of ethanol until the ethanol concentration reached 0.3 mass fractions. Then, the vapor pressure stabilized as the ethanol concentration increased from 0.3 to 0.6 mass fractions. Finally, the vapor pressure dropped at
6
300
303
306
309
312
315
318
321
324
327
T (K) Fig. 2. Vapor pressure data for isooctane and ethanol.
concentrations above 0.7 mass fractions. For the 1-butanol–isooctane, the vapor pressure of the mixture decreased with increasing 1-butanol concentrations. 3.3. Correlation with the activity coefficient models The experimental data were correlated using the Wilson [15], Non-Random Two-Liquid (NRTL) [16], and Universal Quasi-Chemical (UNIQUAC) [17] activity coefficient models. The best fit correlation of the experimental data for ethanol–isooctane and 1butanol–isooctane mixtures was presented by Wilson activity coefficient model as shown in Fig. 4. Comparisons of the experimental data with the three activity coefficient models are presented in Fig. 5, which depicts one of the mass fractions observed in our work with the parameters obtained from the correlation of all experimental data in this work. The average absolute deviations between the experimental vapor pressures and the calculated vapor pressures with the
50
R. Oktavian et al. / Fuel 107 (2013) 47–51 Table 5 Bubble point vapor pressure data for 1-butanol (1)–isooctane (2) mixture.
20
T (K)
18
w1 = 0.10 302.75 306.15 308.15 309.45 316.65 319.35 w1 = 0.50 304.05 315.05 322.75 325.45 328.15
16
P (kPa)
14 12
Ref [14]
10
Exp Data at T = 308.15 K 8
Overall AAD = 1.23%
6 4 2
0.2
0
0.4
0.6
0.8
P (kPa)
1
ethanol mol fraction
7.73 9.20 10.67 10.80 14.53 15.60 8.53 14.00 19.47 21.33 23.60
w1 = 0.90 305.85 308.15 308.35 320.95 323.45 326.65
T (K) w1 = 0.20 300.95 307.05 308.15 309.35 316.05 322.35 w1 = 0.60 301.95 307.05 308.15 308.75 312.35 316.15
P (kPa) 7.33 9.87 11.33 11.47 15.20 19.33 6.27 8.13 8.93 8.80 10.27 12.67
T (K)
P (kPa)
w1 = 0.30 306.55 308.15 308.95 316.45 320.05 321.65 w1 = 0.70 301.25 308.15 308.85 311.15 319.65 326.45
8.80 10.40 10.27 14.40 16.27 17.47 5.07 7.60 7.47 8.13 12.13 16.00
T (K)
P (kPa)
w1 = 0.40 305.75 308.15 309.05 313.05 316.75 322.35 w1 = 0.80 302.15 308.15 310.95 315.25 318.95 322.25
8.53 9.60 9.65 11.73 14.00 17.47 4.13 6.27 6.80 8.40 9.20 10.53
3.20 4.53 4.00 7.47 8.13 9.20
Fig. 3. Vapor pressure data for the ethanol–isooctane mixture.
21 Table 4 Bubble point vapor pressure data for ethanol (1)–isooctane (2) mixture.
18
T (K)
P (kPa)
T (K)
P (kPa)
T (K)
P (kPa)
T (K)
P (kPa)
w1 = 0.10 305.65 308.15 311.95 314.45 316.35
16.13 18.80 21.60 24.00 26.26
w1 = 0.20 302.95 307.05 308.15 310.15 311.75
15.47 19.20 20.00 22.40 23.73
w1 = 0.30 306.75 308.15 313.45 316.15 319.45
19.20 20.27 27.06 30.80 35.46
w1 = 0.40 302.15 302.95 303.65 304.95 308.15
14.13 14.53 15.20 15.87 20.00
15.33 16.67 20.00 22.53 23.06
w1 = 0.60 304.65 305.85 308.15 310.95 313.05
15.20 15.73 19.20 20.93 23.20
w1 = 0.70 308.15 310.75 312.85 313.55 315.15
19.00 20.73 22.46 23.40 24.73
w1 = 0.80 302.55 306.65 308.15 310.85 314.45
12.87 15.67 18.73 19.67 22.73
w1 = 0.90 306.95 308.15 309.25 310.35 313.15
15.87 16.67 17.33 17.73 20.40
interaction parameter pairs of the systems fitted to the experimental data are presented in Table 6. The binary interaction parameters for the mixtures studied in this work were obtained by minimizing the average absolute deviation in the vapor pressures defined in Eq. (2) as the objective function. The experimental data were well correlated with the Wilson, NRTL, and UNIQUAC activity coefficient models with average absolute deviations in the vapor pressures of 3.5%, 3.3%, and 6.1%, respectively.
P (kPa)
12 9 6
Pexp ethanol-isooctane at T = 308.15 K
Pexp 1-butanol-isooctane at T = 308.15 K
3
Wilson eq.
0
0.0
0.2
0.4
0.6
w
0.8
1.0
Fig. 4. Vapor pressures of the ethanol–isooctane and 1-butanol–isooctane mixtures.
24 22 20
Pexp ethanol(1)-isooctane(2) at w1 = 0.5 Pexp 1-butanol(1)-isooctane(2) at w1 = 0.7
18
P (kPa)
w1 = 0.50 303.15 305.45 308.15 311.65 312.15
15
Wilson eq. NRTL eq. UNIQUAC eq.
16 14 12
4. Conclusion The new, simpler ebulliometer proposed in this work is a reliable tool to accurately measure the vapor pressure of both a pure liquid and a mixture. This experimental apparatus was used to measure the vapor pressure of an ethanol–isooctane and a 1-butanol–isooctane mixture with deviations of less than 1.9%. The experimental data were well correlated with the Wilson, NRTL, and UNIQUAC activity coefficient models with average absolute deviations in the vapor pressures of 3.5%, 3.3%, and 6.1%,
10 8 6 4
300
303
306
309
312
315
318
321
324
327
T (K) Fig. 5. Vapor pressure data for the ethanol–isooctane and l-butanol–isooctane mixtures: measured and correlated with three activity coefficient models.
51
R. Oktavian et al. / Fuel 107 (2013) 47–51 Table 6 Summary of models comparison and models parameter calculated for the studied mixtures. Mixture
Ethanol(1)–isooctane(2) Overall AAD (%) 1-butanol(1)–isooctane(2) Overall AAD (%)
Wilson
NRTL
UNIQUAC
a12
a21
a
b12
b21
u12
u21
1630 3.48 1952 4.19
231
0.29 3.29 0.18 4.74
8475
1231
1470
8537
1314
364 6.09 214 4.82
163
respectively. For further research, the new ebulliometer developed in our work will be employed to measure and generate vapor pressures or vapor–liquid equilibrium data for various mixtures. Acknowledgments This work was supported by the Directorate Research and Public Services, Directorate General of Higher Education, Department of National Education, in the Republic of Indonesia (Contract No: 10473/I2.7/PM/2009 April 1, 2009) and Institute of Research and Public Services ITS. References [1] Yu J, Corripo AB, Harrison OP, Copeland RJ. Analysis of the sorbent energy transfer system (SETS) for power generation and CO2 capture. Adv Environ 2003;7:335–45. [2] Demirbas F, Bosbas K, Balat M. Carbon dioxide emiision trends and environmental problems in Turkey. Energy Explor Exploit 2004;22:335–65. [3] Wildenborg T, Lokhorst A. Introduction on CO2 Geological storageclassification of storage options. Oil Gas Sci Technol Rev IFP 2005;44:93–108. [4] Rothman H, Greenshields R, Calle FR. The alcohol economy: fuel ethanol and Brazilian experience. London: Francis Printer; 1983. [5] Balat M. Current alternative engine fuels. Energy Sources 2005;27:569–77. [6] Pumphrey JA, Brand JI, Scheller WA. Vapour pressure measurements and predictions for alcohol–gasoline blends. Fuel 2000;79:1405–11.
662
[7] Sun H, Fang W, Guo Y, Lin R. Investigation of bubble-point vapor pressures for mixtures of an endothermic hydrocarbon fuel with ethanol. Fuel 2005;84:825–31. [8] Cottrell FG. On the determination of boiling points of solutions. J Am Chem Soc 1919;41:721–9. [9] Rogalski M, Malanowski S. Ebulliometer modified for the accurate determination of vapor liquid equilibrium. Fluid Phase Equilib 1980;5:97–112. [10] Li H, Han S, Teng Y. Bubble points measurement for system chloroform– ethanol–benzene by inclined ebulliometer. Fluid Phase Equilib 1995;113:185–95. [11] Antoine CCR. Tensions des vapeurs; nouvelle relation entre les tensions et les températures. Comptes Rendus des Séances de l’Académie des Sciences 1888;107:681–4.778-80.836-7. [12] Wagner W. New vapour pressure measurements for argon and nitrogen and a new method for establishing rational vapour pressure equations. Cryogenics 1973;13:470–82. [13] Poling BE, Prausnitz JM, O’Connell JP. The properties of gases and liquids. 5th ed. Singapore: McGraw-Hill International Editions; 2001. [14] Hull A, Golubkov I, Kronberg B, Van Stam J. Alternative fuel for conventional spark ignition engines based on a standard gasoline, ethanol and other oxygenates. Int J Engine Res 2005;7:203–14. [15] Wilson GM. Vapor–liquid equilibrium. XI. A new expression for the excess free energy of mixing. J Am Chem Soc 1964;86:127–30. [16] Renon H, Prausnitz JM. Local compositions in thermodynamic excess functions for liquid mixtures. AIChE J 1968;14:135–44. [17] Abrams DS, Prausnitz JM. Statistical thermodynamic of liquid mixture: a new expression for the excess gibbs energy of partly or completely miscible system. AIChE J 1975;21:116–28.
Contents lists available at SciVerse ScienceDirect
Fuel journal homepage: www.elsevier.com/locate/fuel
Vapor pressure measurements of ethanol–isooctane and 1-butanol–isooctane systems using a new ebulliometer Rama Oktavian, Vika Amidelsi, Agung Rasmito, Gede Wibawa ⇑ Department of Chemical Engineering, Faculty of Industrial Technology, Sepuluh Nopember Institute of Technology (ITS), Campus ITS Sukolilo, Surabaya 60111, Indonesia
h i g h l i g h t s " A new simple ebulliometer has been developed in this work. " The ebulliometer is reliable to measure vapor pressure of alcohols–isooctane mixture. " The experimental data were well correlated with Wilson, NRTL, and UNIQUAC models.
a r t i c l e
i n f o
Article history: Received 8 November 2011 Received in revised form 31 January 2013 Accepted 2 February 2013 Available online 22 February 2013 Keywords: Ebulliometer Ethanol Isooctane Vapor pressure
a b s t r a c t A new, simpler ebulliometer has been developed to accurately measure the vapor pressure of ethanol– isooctane and 1-butanol–isooctane systems at various mixture compositions. The reliability of the experimental apparatus was validated by comparing the experimental data with published data for pure isooctane and ethanol and ethanol–isooctane system. Our data were in good agreement with the published data, with a deviation of less than 1.9%. The vapor pressure of an ethanol–isooctane mixture was initially elevated by the addition of ethanol until the ethanol concentration reached 0.3 mass fractions, then dropped at concentrations above 0.7 mass fractions. For a 1-butanol–isooctane system, the vapor pressure decreased with increasing 1-butanol concentrations. The experimental data were correlated using the Wilson, Non-Random Two-Liquid (NRTL), and Universal Quasi-Chemical (UNIQUAC) activity coefficient models with an average absolute deviation in the vapor pressures of 3.5%, 3.3%, and 6.1%, respectively. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Fossil fuels, which remain the primary energy resources around the world, cause significant increases in the atmospheric CO2 concentration and have an effect on global warming [1,2]. Fossil fuels combustion contributes 73% of CO2 production [3]. Thus, finding a solution to greenhouse gas emissions is a major research focus for solutions to the global warming problem. Recently, the addition of oxygenates, such as simple alcohols, that are primarily produced from renewable resources has received tremendous attention because these compounds have an ability to reduce pollution and enhance the octane number of gasoline. Nicholas Otto [4] first used ethanol in internal combustion engines. Ethanol–gasoline mixtures have been successfully used in various machines and vehicles that typically run on gasoline [5]. However, the mixture can have a higher vapor pressure than the base gasoline which raises concern regarding the evaporative emission from the fuel mixture. Vapor pressure is one of the most important ⇑ Corresponding author. Tel.: +62 31 5946240; fax: +62 31 5999282. E-mail address: [email protected] (G. Wibawa). 0016-2361/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.fuel.2013.02.005
physical properties of a gasoline mixture because it refers to the volatility of the gasoline and can affect the evaporative emission of the fuel mixture. Therefore, accurate experimental data are important in designing fuel mixtures with specific vapor pressures. The vapor pressures of gasoline mixtures with four alcohols at 37.8 °C (100 °F) of various compositions were measured by Pumphrey et al. [6]. Sun et al. [7] measured the bubble-point vapor pressures for mixtures of an endothermic hydrocarbon fuel with ethanol. The experimental results indicated that the addition of ethanol had a critical effect on the vapor pressure of the fuel. An ethanol-fuel blend with a low ethanol composition can have an increased volatility. The vapor pressures for both pure substances and mixtures are traditionally measured using an ebulliometer, which was first proposed by Cotrell [8] to determine the boiling points of pure substances. Rogalski and Malanowski [9] developed a new ebulliometer in 1980 using Cotrell’s principle for determining vapor–liquid equilibrium data. However, in these ebulliometers analyses of both vapor and liquid-phase compositions are necessary due to a difference between the liquid-phase composition at equilibrium and the feed composition. Therefore, Li et al. [10]
48
R. Oktavian et al. / Fuel 107 (2013) 47–51
developed an inclined ebulliometer that no longer required liquid and vapor-phase composition analysis to measure the bubble point for a chloroform–ethanol–benzene system. Li et al. [10] also noted that they adopted the angle of inclination of 30° for their work to ensure the accuracy of the equilibrium temperature measurement. In this work, a new, simpler ebulliometer is proposed based on the work of Li et al. [10] by removing the inclination and enlarging the volume of the cell. We can ensure that the equilibrium and the feed compositions do not change significantly during the measurements due to the small proportion of vapor formed during equilibrium by enlarging the volume of the cell. Therefore, the present apparatus can be used to accurately measure the vapor pressure of a gasoline mixture. We used isooctane in this work to represent gasoline because it is the main component in gasoline.
simpler ebulliometer by removing the inclined portion from the previous ebulliometer. In addition, a temperature detector was attached at the liquid–vapor interface to ensure the accuracy of equilibrium temperature measurements. The mixtures with varying isooctane and ethanol, isooctane and 1-butanol compositions were prepared by directly weighing the constituent component on an Ohaus balance with a precision of ±0.0001 g. The temperature was measured using an RTD Pt 100 sensor connected to a Shimaden SD 15 temperature display with a measurement accuracy of ±0.1 K. The vapor pressures at various temperatures and compositions were measured using a mercury manometer with an accuracy of ±0.1 mm Hg.
2.3. Experimental procedure 2. Experimental 2.1. Materials All materials used in this work (isooctane, ethanol, and 1-butanol) were supplied by Merck, Darmstadt, Germany. These materials were used without further purification. Table 1 lists the properties of all materials used. 2.2. Experimental apparatus A new, simpler ebulliometer based on the principle of the quasistatic method is shown in Fig. 1b. The ebulliometer has a 5.5-cm cell diameter, 14-cm height, and a 332.5-cm3 volume and is connected with a vacuum pump. The ebulliometer cell was turned on via moderate heating, which was controlled using a temperature controller to maintain equilibrium at the desired temperature. The quasi-static method is based on the overall concentration instead of the equilibrium composition of the liquid phase as described by Li et al. [10] and shown in the inclined region in Fig. 1a. The enlargement of the cell volume as shown in Fig. 1b allows for an increase in the amount of substance being tested so that the composition of the fluid hardly changes during the vapor pressure measurement. This can be calculated using the simple mass balance in Eq. (1) as follows:
zi F ¼ xi L þ yi V
ð1Þ
In which, zi is the mole fraction of component i in the initial mixture injected into the ebulliometer, F the total moles of mixture injected into the ebulliometer, xi the mole fraction of component i in the liquid phase at equilibrium, L the number of moles in the liquid phase at equilibrium, yi the mole fraction of component i in the vapor phase at equilibrium, V the number of moles in the vapor phase at equilibrium. We assume, with the same value of V, the same mole fraction for component i in the vapor phase (yi), and the same feed composition (zi), that a smaller ebulliometer means that the amount of mixture injected into the ebulliometer (F) must be smaller, and significant change can occur in the mole fraction of component i in liquid phase at equilibrium (xi). In our work, we developed a new,
A sample containing approximately 220 cm3 of a liquid mixture of known composition was charged in the ebulliometer cell. First, the system was created under vacuum conditions to remove air and impurities from the equilibrium cell. Then, the equilibrium cell was heated to reach the desired equilibrium temperature. The temperature was controlled by a PID controller (Shimaden SR 64). After the ebulliometer reached a constant pressure at a desired equilibrium temperature, the pressure was recorded as the vapor pressure at a desired temperature. The experimental procedure was repeated at different temperatures and compositions.
3. Results and discussion 3.1. Reliability test of the apparatus The proposed ebulliometer was tested for the reliability by comparing the experimental data for the vapor pressures of both pure liquids and mixtures as measured by this apparatus with the published data for pure ethanol, isooctane, and an ethanol–isooctane mixture. The Antoine equation [11] for pure isooctane and the Wagner equation [12] for pure ethanol were used to compare the experimental data. The Antoine and Wagner constants were obtained from Poling et al. [13]. For the ethanol–isooctane mixture, the experimental data were compared with the experimental data from Hull et al. [14]. A comparison of the experimental data obtained in this work with the published data is presented in Tables 2 and 3 and Figs. 2 and 3 along with their deviations. The results indicate that the data were in good agreement with the published data, with a deviation of less than 1.9% calculated as an average absolute deviation (AAD) in the vapor pressures as follows:
AAD ¼
n 1X Plit Pexp 100% n i¼1 Pexp i
ð2Þ
in which Pexp is the vapor pressure obtained in the experiment while P lit is the vapor pressure calculated using both the Antoine [11] and Wagner [12] equations and n is the number of data.
Table 1 Properties of materials used in this work. Property
1-butanol CH3(CH2)3OH
Isooctane C8H18
Ethanol C2H5OH
Molecular weight (g/mol) Purity Density (d 20 °C/20 °C) Boiling range (°C)
74.12 >99.5% 0.809–0.812 116–119
114.23 >99.5% 0.691–0.696 98–100
46.07 99.9% 0.790–0.793 78
49
R. Oktavian et al. / Fuel 107 (2013) 47–51
1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
Condenser tube joint Vacuum jact Inner casing Thermometer well Feed inlet Stirrer Boiler Condenser Vacuum pump Mercury manometer
1. 2. 3. 4. 5. 6.
7.
(a)
Ebulliometer cell Thermocouple Condenser Vacuum unit Mercury manometer Heating system controller Magnetic stirrer
(b)
Fig. 1. Comparison of the ebulliometer apparatus: (a) Ebulliometer developed by Li et al. [10]; (b) new, simpler ebulliometer developed in this work.
Table 2 Comparison of experimentally measured isooctane vapor pressures (Pexp) with the literature data (Plit).
300.35 302.75 305.95 308.25 310.15 313.15 316.25 318.95 Overall AAD
Plit (kPa) 7.31 8.17 9.46 10.48 11.39 12.97 14.77 16.51
Pexp (kPa) 7.33 8.13 9.47 10.80 11.73 13.07 14.80 16.40
AAD (%) 0.34 0.51 0.08 2.94 2.89 0.76 0.18 0.68 1.05
Pexp Isooctane
30
PLit
Pexp Ethanol
27 24
P (kPa)
T (K)
33
21 18 15 12 9
Table 3 Comparison of experimentally measured ethanol vapor pressure (Pexp) with the literature data (Plit). T (K)
Plit (kPa)
Pexp (kPa)
AAD (%)
301.35 302.55 308.45 314.35 318.95 321.15 323.65 325.85 Overall AAD
8.86 9.50 13.24 18.19 23.07 25.78 29.17 32.46
8.93 9.60 13.60 18.80 23.46 26.26 29.73 33.06
0.86 1.09 2.62 3.23 1.66 1.86 1.89 1.83 1.88
3.2. Vapor pressure measurement The vapor pressures at various temperatures and compositions for the ethanol–isooctane and the 1-butanol–isooctane systems obtained in this work are presented in Tables 4 and 5 and Fig. 4 in which w represents the mass fraction of the ethanol and 1-butanol in the mixtures. For ethanol–isooctane mixture, the vapor pressure was initially elevated by the addition of ethanol until the ethanol concentration reached 0.3 mass fractions. Then, the vapor pressure stabilized as the ethanol concentration increased from 0.3 to 0.6 mass fractions. Finally, the vapor pressure dropped at
6
300
303
306
309
312
315
318
321
324
327
T (K) Fig. 2. Vapor pressure data for isooctane and ethanol.
concentrations above 0.7 mass fractions. For the 1-butanol–isooctane, the vapor pressure of the mixture decreased with increasing 1-butanol concentrations. 3.3. Correlation with the activity coefficient models The experimental data were correlated using the Wilson [15], Non-Random Two-Liquid (NRTL) [16], and Universal Quasi-Chemical (UNIQUAC) [17] activity coefficient models. The best fit correlation of the experimental data for ethanol–isooctane and 1butanol–isooctane mixtures was presented by Wilson activity coefficient model as shown in Fig. 4. Comparisons of the experimental data with the three activity coefficient models are presented in Fig. 5, which depicts one of the mass fractions observed in our work with the parameters obtained from the correlation of all experimental data in this work. The average absolute deviations between the experimental vapor pressures and the calculated vapor pressures with the
50
R. Oktavian et al. / Fuel 107 (2013) 47–51 Table 5 Bubble point vapor pressure data for 1-butanol (1)–isooctane (2) mixture.
20
T (K)
18
w1 = 0.10 302.75 306.15 308.15 309.45 316.65 319.35 w1 = 0.50 304.05 315.05 322.75 325.45 328.15
16
P (kPa)
14 12
Ref [14]
10
Exp Data at T = 308.15 K 8
Overall AAD = 1.23%
6 4 2
0.2
0
0.4
0.6
0.8
P (kPa)
1
ethanol mol fraction
7.73 9.20 10.67 10.80 14.53 15.60 8.53 14.00 19.47 21.33 23.60
w1 = 0.90 305.85 308.15 308.35 320.95 323.45 326.65
T (K) w1 = 0.20 300.95 307.05 308.15 309.35 316.05 322.35 w1 = 0.60 301.95 307.05 308.15 308.75 312.35 316.15
P (kPa) 7.33 9.87 11.33 11.47 15.20 19.33 6.27 8.13 8.93 8.80 10.27 12.67
T (K)
P (kPa)
w1 = 0.30 306.55 308.15 308.95 316.45 320.05 321.65 w1 = 0.70 301.25 308.15 308.85 311.15 319.65 326.45
8.80 10.40 10.27 14.40 16.27 17.47 5.07 7.60 7.47 8.13 12.13 16.00
T (K)
P (kPa)
w1 = 0.40 305.75 308.15 309.05 313.05 316.75 322.35 w1 = 0.80 302.15 308.15 310.95 315.25 318.95 322.25
8.53 9.60 9.65 11.73 14.00 17.47 4.13 6.27 6.80 8.40 9.20 10.53
3.20 4.53 4.00 7.47 8.13 9.20
Fig. 3. Vapor pressure data for the ethanol–isooctane mixture.
21 Table 4 Bubble point vapor pressure data for ethanol (1)–isooctane (2) mixture.
18
T (K)
P (kPa)
T (K)
P (kPa)
T (K)
P (kPa)
T (K)
P (kPa)
w1 = 0.10 305.65 308.15 311.95 314.45 316.35
16.13 18.80 21.60 24.00 26.26
w1 = 0.20 302.95 307.05 308.15 310.15 311.75
15.47 19.20 20.00 22.40 23.73
w1 = 0.30 306.75 308.15 313.45 316.15 319.45
19.20 20.27 27.06 30.80 35.46
w1 = 0.40 302.15 302.95 303.65 304.95 308.15
14.13 14.53 15.20 15.87 20.00
15.33 16.67 20.00 22.53 23.06
w1 = 0.60 304.65 305.85 308.15 310.95 313.05
15.20 15.73 19.20 20.93 23.20
w1 = 0.70 308.15 310.75 312.85 313.55 315.15
19.00 20.73 22.46 23.40 24.73
w1 = 0.80 302.55 306.65 308.15 310.85 314.45
12.87 15.67 18.73 19.67 22.73
w1 = 0.90 306.95 308.15 309.25 310.35 313.15
15.87 16.67 17.33 17.73 20.40
interaction parameter pairs of the systems fitted to the experimental data are presented in Table 6. The binary interaction parameters for the mixtures studied in this work were obtained by minimizing the average absolute deviation in the vapor pressures defined in Eq. (2) as the objective function. The experimental data were well correlated with the Wilson, NRTL, and UNIQUAC activity coefficient models with average absolute deviations in the vapor pressures of 3.5%, 3.3%, and 6.1%, respectively.
P (kPa)
12 9 6
Pexp ethanol-isooctane at T = 308.15 K
Pexp 1-butanol-isooctane at T = 308.15 K
3
Wilson eq.
0
0.0
0.2
0.4
0.6
w
0.8
1.0
Fig. 4. Vapor pressures of the ethanol–isooctane and 1-butanol–isooctane mixtures.
24 22 20
Pexp ethanol(1)-isooctane(2) at w1 = 0.5 Pexp 1-butanol(1)-isooctane(2) at w1 = 0.7
18
P (kPa)
w1 = 0.50 303.15 305.45 308.15 311.65 312.15
15
Wilson eq. NRTL eq. UNIQUAC eq.
16 14 12
4. Conclusion The new, simpler ebulliometer proposed in this work is a reliable tool to accurately measure the vapor pressure of both a pure liquid and a mixture. This experimental apparatus was used to measure the vapor pressure of an ethanol–isooctane and a 1-butanol–isooctane mixture with deviations of less than 1.9%. The experimental data were well correlated with the Wilson, NRTL, and UNIQUAC activity coefficient models with average absolute deviations in the vapor pressures of 3.5%, 3.3%, and 6.1%,
10 8 6 4
300
303
306
309
312
315
318
321
324
327
T (K) Fig. 5. Vapor pressure data for the ethanol–isooctane and l-butanol–isooctane mixtures: measured and correlated with three activity coefficient models.
51
R. Oktavian et al. / Fuel 107 (2013) 47–51 Table 6 Summary of models comparison and models parameter calculated for the studied mixtures. Mixture
Ethanol(1)–isooctane(2) Overall AAD (%) 1-butanol(1)–isooctane(2) Overall AAD (%)
Wilson
NRTL
UNIQUAC
a12
a21
a
b12
b21
u12
u21
1630 3.48 1952 4.19
231
0.29 3.29 0.18 4.74
8475
1231
1470
8537
1314
364 6.09 214 4.82
163
respectively. For further research, the new ebulliometer developed in our work will be employed to measure and generate vapor pressures or vapor–liquid equilibrium data for various mixtures. Acknowledgments This work was supported by the Directorate Research and Public Services, Directorate General of Higher Education, Department of National Education, in the Republic of Indonesia (Contract No: 10473/I2.7/PM/2009 April 1, 2009) and Institute of Research and Public Services ITS. References [1] Yu J, Corripo AB, Harrison OP, Copeland RJ. Analysis of the sorbent energy transfer system (SETS) for power generation and CO2 capture. Adv Environ 2003;7:335–45. [2] Demirbas F, Bosbas K, Balat M. Carbon dioxide emiision trends and environmental problems in Turkey. Energy Explor Exploit 2004;22:335–65. [3] Wildenborg T, Lokhorst A. Introduction on CO2 Geological storageclassification of storage options. Oil Gas Sci Technol Rev IFP 2005;44:93–108. [4] Rothman H, Greenshields R, Calle FR. The alcohol economy: fuel ethanol and Brazilian experience. London: Francis Printer; 1983. [5] Balat M. Current alternative engine fuels. Energy Sources 2005;27:569–77. [6] Pumphrey JA, Brand JI, Scheller WA. Vapour pressure measurements and predictions for alcohol–gasoline blends. Fuel 2000;79:1405–11.
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