Thermodynamic Properties of Ethanol and Gasoline Blended Fuel

The polynomial equations of Cp and the excess heat capacities ( ), with respect to the thermodynamic temperature, were established through least-squar...
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Energy & Fuels 2005, 19, 2432-2437

Thermodynamic Properties of Ethanol and Gasoline Blended Fuel Zhaodong Nan* Department of Chemistry, Qufu Normal University, Qufu 273165, People’s Republic of China

Zhi-Cheng Tan Thermochemistry Laboratory, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, People’s Republic of China Received May 7, 2005. Revised Manuscript Received July 13, 2005

The heat capacities (Cp) of five types of gasohol (50 wt % ethanol and 50 wt % unleaded gasoline 93# (E50), 60 wt % ethanol and 40 wt % unleaded gasoline 93# (E60), 70 wt % ethanol and 30 wt % unleaded gasoline 93# (E70), 80 wt % ethanol and 20 wt % unleaded gasoline 93# (E80), and 90 wt % ethanol and 10 wt % unleaded gasoline 93# (E90), where the “93” denotes the octane number) were measured by adiabatic calorimetry in the temperature range of 78-320 K. A glass transition was observed at 95.61, 96.14, 96.56, 96.84, and 97.08 K for samples from the E50, E60, E70, E80, and E90 systems, respectively. A liquid-solid phase transition and a solidliquid phase transition were observed in the respective temperature ranges of 118-153 and 155163 K for E50, 117-150 and 151-164 K for E60, 115-154 and 154-166 K for E70, 113-152 and 152-167 K for E80, and 112-151 and 1581-167 K for E90. The polynomial equations of Cp and the excess heat capacities (CEp ), with respect to the thermodynamic temperature, were established through least-squares fitting. Based on the thermodynamic relationship and the equations obtained, the thermodynamic functions and the excess thermodynamic functions of the five gasohol samples were derived.

1. Introduction Nations today often face divergent challenges in the form of climate change, air pollution, energy production, consumption security, and shrinking oil supplies. In response to these challenges, countries around the world have developed programs to support the use of clean fuels, including ethanol.1 Gasohol (which is an ethanolgasoline blend), as a fuel for automobiles, has been studied extensively.2-14 This type of fuel can reduce * Author to whom correspondence should be addressed. E-mail address: [email protected]. (1) Vyas, S. Biomass. In Proceedings for the 4th Biomass Conference of the Americas, Oakland, CA, August 29-September 2, 1999; Overend, R. P., Chornet, E., Eds.; 1999; Elsevier: Oxford, U.K., 1999; Vol. 2, pp 1725-1730. (2) Hsieh, W. D.; Chen, R. H.; Wu, T. L.; Lin, T. H. Atmos. Environ. 2002, 36 (3), 403-410. (3) Masuzo, Y. Baiomasu Enerugi Riyo no Saishin Gijutsu; Yukawa, H., Ed.; Shi Emu Shi: Tokyo, Japan, 2001; pp 287-207. (4) Kremer, F. G.; Fachetti, A. SAE Tech. Pap. Ser. 2001, 1-4. (5) Wang, M.; Saricks, C.; Wu, M. J. Air Waste Manage. Assoc. 1999, 49 (7), 756-772. (6) Whitten, G. Z. Environ. Sci. Technol. 1998, 32 (23), 3840-3841. (7) Tsai, H. H. Shiyou Jikan 1997, 33 (4), 71-82. (8) Jones, B. E.; Ready, K. L.; Karges, M. A.; Willette, P. R. In Proceedings of the 2nd Biomass Conference of the Americas: Energy, Environment, Agriculture, and Industry; National Renewable Energy Laboratory: Golden, CO, 1995; pp 986-995. (9) Kadakia, A. M.; Singh, S. N. CEW, Chem. Eng. World 1997, 32 (1), 71-76. (10) Wyman, C. E. In Proceedings, European Motor Biofuels Forum, 2nd; Joanneum Research Forschungsgesellschaft: Graz, Austria, 1996; pp 81-85. (11) Galbe, M.; Larsson, M.; Stenberg, K.; Tengborg, C.; Zacchi, G. ACS Symp. Ser. 1997, 666, 110-129.

greenhouse gas emissions and enhance the octane number of gasoline. In our previous papers, the thermodynamic properties of unleaded gasoline 93# and gasohol that consisted of 10 wt % ethanol and 90 wt % unleaded gasoline 93#, 20 wt % ethanol and 80 wt % unleaded gasoline 93#, 30 wt % ethanol and 70 wt % unleaded gasoline 93#, and 40 wt % ethanol and 60 wt % unleaded gasoline 93# were investigated.15,16 In this paper, the heat capacities (Cp) of five gasohol systems, which consist of 50 wt % ethanol and 50 wt % unleaded gasoline 93# (abbreviated as E50), 60 wt % ethanol and 40 wt % unleaded gasoline 93# (abbreviated as E60), 70 wt % ethanol and 30 wt % unleaded gasoline 93# (abbreviated as E70), 80 wt % ethanol and 20 wt % unleaded gasoline 93# (abbreviated as E80), and 90 wt % ethanol and 10 wt % unleaded gasoline 93# (abbreviated as E90), have been measured using an adiabatic calorimeter. The glass-transition temperature (Tg) and the phase-transition temperature of the five systems have been determined. At the same time, the thermodynamic functions and the excess thermodynamic functions of the five systems have been derived. (12) Kremer, F. G.; Jardim, J. L. F.; Maia, D. M. Soc. Automot. Eng. [Spec. Publ.] SP 1996, SP-1208, 415-422. (13) Allsup, J. R.; Eccleston, D. B. Third International Symposium, Alcohol Fuels Technology, May 28-31, 1979; pp 1-7. (14) Allsup, J. R.; Eccleston, D. B. Energy Res. Abstr. 1979, 4 (14), 2-17. (15) Nan, Z.; Tan, Z. C.; Sun L. X. Energy Fuels 2004, 18, 84-89. (16) Nan, Z.; Tan, Z. C. Energy Fuels 2004, 18, 1032-1037.

10.1021/ef050137g CCC: $30.25 © 2005 American Chemical Society Published on Web 08/27/2005

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Energy & Fuels, Vol. 19, No. 6, 2005 2433

Figure 1. Experimental heat capacities (Cp) of samples from (a) the E50 system, (b) the E60 system, (c) the E70 system, (d) the E80 system, and (e) the E90 system.

2. Experimental Section The ethanol, which had a purity of >99.8 wt %, was purchased from Shenyang Chemical Agent Factory. Unleaded gasoline 93#, which was used for calorimetric study, was purchased from the Dalian Branched Company of SINOPEC. Cp measurements were performed in a high-precision automatic adiabatic calorimeter; the structure and procedure of the apparatus have been described in detail elsewhere.15-17 The average cooling rate was determined to be 5.2 K/min in the temperature range of 300-78 K, and 2.4 K/min in the temperature range of 150-78 K, respectively. (17) Tan, Z. C.; Sun, G. Y.; Sun, Y.; Yin, A. X.; Wang, W. B.; Ye, J. C.; Zhou L. X. J. Therm. Anal. 1995, 45, 59-67.

The masses of the samples from the E50, E60, E70, E80, and E90 systems used for Cp measurements were 13.0819, 13.2073, 13.4176, 12.9718, and 13.1894 g, respectively.

3. Results and Discussion 3.1. Determination of Heat Capacity. The Cp values of the E50, E60, E70, E80, and E90 samples were determined using an adiabatic calorimeter in the temperature range of 78-320 K. The results of the Cp measurements of the sample from the E50 system, as well as those from the E60, E70, E80, and E90 systems, are shown in Figure 1; the data for the five systems are listed in Table 1. Figure 1 shows the variation in the

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Table 1. Experimental Heat Capacities of the Five Gasohol Systems T (K)

Cp (J K-1 g-1)

T (K)

Cp (J K-1 g-1)

T (K)

78.89 81.25 84.35 87.47 91.06 93.25 95.61 98.03 100.14 102.26 104.37 106.48 108.59 112.55 115.24 118.03 136.97 153.95

1.099 1.109 1.153 1.208 1.317 1.481 1.929 2.166 2.172 2.173 2.193 2.198 2.197 2.196 2.181 4.423 -1.014 2.591

154.57 155.15 155.46 155.95 156.26 156.53 157.42 158.16 160.15 163.03 166.01 170.42 173.42 175.87 178.42 180.97 183.52 185.97

3.443 4.763 7.524 10.285 16.928 12.959 9.476 6.735 5.251 3.215 2.154 2.147 2.116 2.121 2.124 2.127 2.132 2.137

188.53 191.52 194.41 197.09 200.82 202.96 205.64 208.52 211.39 213.98 216.86 219.71 222.46 225.39 227.86 230.63 233.55 235.86

78.50 81.28 84.50 87.65 91.16 93.57 96.14 98.35 100.50 102.63 104.77 106.88 108.98 111.07 113.16 115.24 117.31 135.73 150.54

1.028 1.037 1.078 1.130 1.231 1.385 1.804 2.025 2.032 2.032 2.051 2.055 2.055 2.056 2.054 2.040 4.137 -0.949 2.423

151.08 151.55 151.96 152.35 152.68 153.00 153.36 154.29 156.06 157.55 160.05 162.05 164.03 166.01 168.26 170.77 173.28 175.78 178.28

3.220 4.454 6.100 7.748 9.284 10.599 11.822 13.061 14.166 15.672 14.377 10.762 3.007 2.014 2.019 2.026 2.030 2.034 2.037

180.75 183.24 185.71 188.39 191.26 194.12 196.98 199.83 202.66 205.48 208.29 211.09 213.87 216.65 219.42 222.17 224.90 227.63 230.30

78.42 81.99 84.61 87.19 92.36 93.04 96.56 99.11 101.69 104.59 107.45 110.29 113.48 115.70 136.15

1.061 1.077 1.098 1.144 1.205 1.274 1.472 1.990 2.063 2.071 2.079 2.070 2.064 5.104 -0.873

154.11 154.90 155.69 156.27 156.89 157.37 157.74 157.98 158.09 162.74 166.84 170.02 173.82 176.50 178.12

5.272 7.462 9.817 12.302 14.610 16.058 17.536 20.314 22.743 12.951 2.020 2.021 2.022 2.022 2.023

181.85 184.27 186.90 189.26 191.26 193.99 196.60 200.24 203.87 206.70 209.44 211.07 214.63 217.00 219.40

78.52 82.19 84.79 87.41 92.63 94.32 96.84 99.39 101.89 103.45 105.97 107.65 110.49 113.68 113.94 135.86 152.17

1.058 1.074 1.094 1.140 1.202 1.270 1.467 1.983 2.056 2.061 2.069 2.072 2.064 2.058 4.887 -0.788 7.438

153.89 154.47 154.99 155.75 158.47 162.94 167.04 170.82 173.25 176.09 178.32 180.68 183.47 185.76 188.02 190.47 193.14

9.785 12.262 14.562 17.480 26.705 12.909 2.055 2.000 2.010 2.010 2.020 2.020 2.022 2.022 2.022 2.024 2.026

196.80 200.44 203.07 205.85 208.24 211.27 214.83 217.20 219.60 221.29 223.98 226.10 229.37 231.83 233.99 236.38 238.79

Cp (J K-1 g-1)

T (K)

Cp (J K-1 g-1)

T (K)

Cp (J K-1 g-1)

E50 2.141 2.144 2.149 2.156 2.167 2.171 2.176 2.182 2.191 2.200 2.209 2.219 2.230 2.239 2.249 2.266 2.275 2.286

238.63 241.39 243.78 246.49 248.97 251.65 254.29 256.77 259.69 262.49 265.62 268.51 271.73 274.84 277.97 280.85 284.72 285.87

2.301 2.315 2.329 2.338 2.349 2.364 2.374 2.389 2.406 2.420 2.438 2.456 2.477 2.499 2.529 2.554 2.587 2.605

288.57 291.38 293.97 295.86 297.28 299.39 301.46 303.51 305.72 307.58 309.18 311.27 313.18 316.27 319.76

2.639 2.669 2.692 2.714 2.729 2.750 2.774 2.795 2.831 2.860 2.882 2.914 2.941 3.002 3.071

E60 2.040 2.044 2.048 2.053 2.055 2.058 2.062 2.068 2.072 2.077 2.083 2.091 2.100 2.104 2.111 2.120 2.130 2.139 2.152

233.02 235.69 238.34 240.92 243.48 246.12 248.74 251.35 253.99 256.58 259.47 261.99 264.93 268.05 271.27 274.46 277.72 280.60 284.20

2.164 2.177 2.191 2.202 2.212 2.222 2.232 2.245 2.259 2.274 2.287 2.299 2.316 2.337 2.356 2.378 2.407 2.437 2.468

285.66 288.18 291.20 293.70 295.60 296.86 298.99 301.11 303.20 305.28 307.34 309.38 311.41 313.42 315.43 317.41 319.80

2.498 2.520 2.549 2.572 2.593 2.608 2.627 2.651 2.683 2.709 2.734 2.770 2.802 2.838 2.873 2.918 2.958

222.54 225.90 229.17 232.52 236.18 239.62 243.19 246.80 250.28 253.62 257.01 260.50 263.99 267.62 271.39

2.089 2.101 2.114 2.128 2.145 2.162 2.181 2.202 2.222 2.243 2.266 2.290 2.316 2.343 2.373

274.87 278.20 281.70 285.11 288.90 292.32 294.60 297.60 301.00 303.49 306.81 309.47 313.03 316.42 319.73

2.402 2.431 2.462 2.494 2.530 2.564 2.588 2.619 2.656 2.683 2.721 2.752 2.795 2.836 2.878

240.86 243.39 247.00 249.54 251.76 253.82 257.21 260.70 264.19 267.82 271.59 274.02 276.38 278.40 281.90 285.31 288.05

2.170 2.184 2.204 2.219 2.232 2.245 2.267 2.291 2.316 2.343 2.372 2.391 2.411 2.428 2.459 2.489 2.515

290.47 292.55 294.82 297.80 299.83 301.84 303.69 306.18 308.92 311.01 313.23 315.81 317.93 319.93

2.537 2.558 2.581 2.611 2.632 2.654 2.673 2.701 2.731 2.755 2.781 2.812 2.837 2.861

E70 2.023 2.024 2.024 2.025 2.026 2.028 2.030 2.034 2.040 2.045 2.051 2.055 2.064 2.071 2.078 E80 2.030 2.035 2.039 2.044 2.049 2.056 2.066 2.073 2.081 2.086 2.096 2.104 2.117 2.127 2.137 2.148 2.160

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Table 1 (continued) T (K)

Cp (J K-1 g-1)

T (K)

Cp (J K-1 g-1)

T (K)

78.72 82.41 85.03 87.59 92.83 94.58 97.08 99.59 102.09 106.17 107.85 110.69 112.14 134.57 151.08 153.37 154.09

1.057 1.072 1.093 1.139 1.200 1.269 1.466 1.981 2.054 2.067 2.070 2.062 5.407 -0.592 5.249 7.431 9.775

154.67 155.19 155.95 158.66 160.97 163.14 167.24 169.94 171.02 173.87 176.29 178.58 180.89 183.47 185.96 188.39 190.67

12.250 14.548 17.463 24.301 18.903 12.896 2.053 2.027 2.018 2.019 2.020 2.021 2.022 2.023 2.023 2.024 2.026

193.03 196.99 200.64 203.97 206.05 208.94 211.46 215.09 217.33 219.82 222.37 224.18 225.74 229.04 231.85 234.47 236.79

Table 2. Fitting Coefficients ai and Standard Deviations δ system E50 E60 E70 E80 E90

a4

a3

a2

a1

a0

0.3237 -2.9198 10.107 -15.501 10.914 0.1891 -1.5493 4.9657 -7.1069 5.789 -0.0428 0.4376 -1.1868 1.0107 1.944 -0.0757 0.7755 -2.4983 3.2760 0.483 -0.0237 0.2424 -0.4897 -0.0232 2.483

δ (J K-1g-1) 0.005 0.006 0.002 0.003 0.001

heat capacity (Cp) of the five systems, relative to increasing temperature T. The plot of Cp versus T presents smooth curves in the temperature range of 170-320 K for the five systems. In other words, no thermal anomalies were observed in this temperature range. The Cp values of the five systems were fitted to the following polynomial expressions by the least-squares method:

Cp(J K-1 g-1) )

i

∑ i)0

ai

( ) T

100

i

(1)

The fitting results are given in Table 2. 3.2. Glass Transition. Figure 1 shows that the Cp values of the five systems clearly increase as T increases in the region of 78-100 K. The Cp value clearly changes before and after the glass-transition temperature (Tg).18 Glass transitions then occur in the five systems in the temperature range of 78-100 K. By analyzing the curves of dCp/dT, with respect to T, the Tg values of the five systems were determined and are listed in Table 3. These temperatures correspond to those at which the values of dCp/dT reach the maximum. Table 3 shows that the Tg value increases as the content of ethanol increases in the systems. This is in agreement with the results from the literature.16 The reason may be that the Tg can be affected by the structure change of the system. The amount of polar group (hydroxyl, -OH) of the system increases as ethanol is added into the gasoline. Thus, the hydrogen bond was formed because of the addition of ethanol into gasoline in the system. The Tg value increases when the (18) Liu, Z. H.; Hatakeyama, T. Handbook of Analytical Chemistry, 2nd Edition; Chemical Industry Press: Beijing, 2000; p 64. (19) Masson, J.-F.; Polomark, G. M.; Collins, P. Energy Fuels 2002, 16, 470-476.

Cp (J K-1 g-1) E90 2.026 2.033 2.039 2.045 2.049 2.058 2.062 2.072 2.079 2.087 2.096 2.103 2.106 2.121 2.134 2.147 2.158

T (K)

Cp (J K-1 g-1)

T (K)

Cp (J K-1 g-1)

238.94 241.16 243.04 247.22 249.77 252.16 254.19 257.44 261.02 264.39 268.13 271.94 273.88 276.58 278.74 282.33 285.54

2.167 2.178 2.189 2.211 2.226 2.240 2.252 2.274 2.298 2.322 2.349 2.378 2.395 2.417 2.433 2.463 2.494

288.37 290.61 292.72 295.00 298.00 300.14 302.04 303.89 306.69 309.14 311.21 313.45 316.27 318.16 319.74

2.520 2.541 2.561 2.583 2.613 2.635 2.655 2.674 2.704 2.731 2.754 2.779 2.812 2.834 2.853

molecular structure becomes more rigid, which is due to the increased number of polar groups.20 3.3. Phase Transition. The Cp values reach the maxima in the temperature range of 100-170 K, as observed in Figure 1. The unusual phenomenon is that the systems first absorbed energy and then released energy. Heating through the glass transition results in a deeply undercooled liquid, which starts to crystallize within the noted temperature range, so that the liquidsolid phase transition of the sample occurs in the systems and the energy is released. This phenomenon is more complex and will be further investigated. A similar phenomenon was observed when a binary system of ethanol and benzene was studied.21 The range of the phase-transition temperature (Tl-s) was determined and is listed in Table 3. A solid-liquid phase transition occurs, and the corresponding temperature range (Ts-l) was determined, which also is given in Table 3. 3.4. Thermodynamic Function. The thermodynamic function data of the five systems, based on a reference temperature of 298.15 K, in the temperature range of 170-320 K, were derived, according to the relationship of heat capacity Cp with thermodynamic functions.22 The results of the thermodynamic functions (H(T) - H(298.15K) and S(T) - S(298.15K)) are listed in Table 4. The values of S(T) - S(298.15K) increase as the temperature T increases for the five systems. These values show that the molecules of liquid become more active at higher temperature. 3.5. Excess Thermodynamic Function. Excess thermodynamic properties can be used to investigate the interaction between the compositions in the mixture. The excess heat capacity (CEp ) for the five systems in the liquid was calculated using the following equation: id id CEp ) Cexp p - xCp,1 - (1 - x)Cp,2

(2)

id id where C p,1 and C p,2 are the heat capacities for the ethanol and the unleaded gasoline 93#, respectively,

(20) Haida, O.; Suga, H.; Seki, S. J. Chem. Thermodynam. 1977, 9, 1133-1148. (21) Nan, Z.; Jiao, Q. Z.; Tan, Z. C.; Sun, L. X. Thermochim. Acta 2003, 406, 151-159. (22) Tan, Z. C.; Xue, B.; Lu, S. W.; Meng, S. H.; Yuan, X. H.; Song, Y. J. J. Therm. Anal. Calorim. 2001, 63, 297-308.

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Table 3. Glass-Transition Temperatures and Phase-Transition Temperatures of the Five Gasohol Systems Phase-Transition Temp (K)

a

sample

Glass-Transition Temp, Tg (K)

unleaded gasolinea 10 wt % ethanol/90 wt % gasolinea 20 wt % ethanol/80 wt % gasolineb 30 wt % ethanol/70 wt % gasolineb 40 wt % ethanol/60 wt % gasolineb E50 E60 E70 E80 E90 ethanolc

92.42 93.17 94.24 95.15 95.44 95.61 96.14 96.56 96.84 97.08 97.46

Tl-s

Ts-l

135.18 131.82 121.29 118-153 117-150 115-154 113-152 112-151

151.30 152.10 155.09 155-163 151-164 154-166 152-167 151-167 159.00

Data taken from ref 15. b Data taken from ref 16. c Data taken from ref 19. Table 4. Thermodynamic Functions of the Five Gasohol Systems

T (K)

∆Ha (kJ/g)

Cp (J K-1 g-1)

∆Sb (J K-1 g-1)

Cp (J K-1 g-1)

E50 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 298.15

2.130 2.129 2.140 2.161 2.189 2.223 2.261 2.304 2.353 2.409 2.474 2.551 2.645 2.759 2.900 3.073 2.736

-0.2976 -0.2763 -0.255 -0.2335 -0.2118 -0.1897 -0.1673 -0.1445 -0.1212 -0.0974 -0.073 -0.0479 -0.0219 0.0051 0.0334 0.0632 0

170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 298.15

2.011 2.015 2.023 2.036 2.057 2.085 2.122 2.167 2.222 2.287 2.362 2.446 2.539 2.640 2.750 2.866 2.621

-0.281 -0.261 -0.241 -0.221 -0.200 -0.180 -0.159 -0.137 -0.115 -0.093 -0.070 -0.046 -0.021 0.005 0.032 0.060 0

∆H ) H(T) - H(298.15

K).

b

-1.290 -1.168 -1.053 -0.943 -0.837 -0.734 -0.635 -0.537 -0.442 -0.349 -0.257 -0.166 -0.075 0.017 0.110 0.204 0

2.026 2.035 2.050 2.069 2.093 2.121 2.153 2.191 2.236 2.290 2.355 2.434 2.529 2.646 2.787 2.957 2.622

-0.284 -0.264 -0.243 -0.223 -0.202 -0.181 -0.159 -0.138 -0.116 -0.093 -0.070 -0.046 -0.021 0.005 0.032 0.061 0

-1.219 -1.104 -0.995 -0.891 -0.792 -0.695 -0.602 -0.511 -0.421 -0.333 -0.246 -0.159 -0.071 0.016 0.104 0.193 0

2.021 2.019 2.025 2.038 2.059 2.088 2.125 2.171 2.226 2.290 2.362 2.443 2.533 2.631 2.738 2.852 2.612

-0.282 -0.262 -0.242 -0.221 -0.201 -0.180 -0.159 -0.138 -0.116 -0.093 -0.070 -0.046 -0.021 0.005 0.032 0.060 0

Cp (J K-1 g-1)

∆Ha (kJ/g)

∆Sb (J K-1 g-1)

E70 -1.231 -1.115 -1.004 -0.899 -0.797 -0.699 -0.604 -0.512 -0.422 -0.333 -0.245 -0.158 -0.071 0.016 0.105 0.196 0

2.025 2.021 2.024 2.034 2.053 2.080 2.117 2.163 2.219 2.284 2.360 2.445 2.540 2.643 2.756 2.877 2.623

-0.282 -0.262 -0.241 -0.221 -0.201 -0.180 -0.159 -0.138 -0.116 -0.093 -0.070 -0.046 -0.021 0.005 0.032 0.060 0

-1.221 -1.105 -0.996 -0.892 -0.792 -0.696 -0.603 -0.512 -0.422 -0.334 -0.246 -0.159 -0.072 0.016 0.105 0.194 0

E90

∆S ) S(T) - S(298.15

i

( ) T

bi ∑ 100 i)0

The fitting results are listed in Table 6.

-1.222 -1.107 -0.997 -0.893 -0.793 -0.697 -0.603 -0.512 -0.422 -0.334 -0.246 -0.159 -0.071 0.016 0.104 0.193 0

K).

Cexp is the experimental heat capacity of the gasohol, p and x represents the content of ethanol in the systems (50% (x ) 0.5), 60% (x ) 0.6), 70% (x ) 0.7), 80% (x ) 0.8), and 90% (x ) 0.9) for the E50, E60, E70, E80, and were E90 systems, respectively). The values of Cexp p determined using the adiabatic calorimeter, and the id id values of C p,1 and C p,2 were cited from ref 15. The E values of Cp are summarized in Table 5. The CEp values were fitted with the following polynomial expression by least-squares fitting:

CEp (J K-1 g-1) )

∆Sb (J K-1 g-1)

E60

E80

a

∆Ha (kJ/g)

i

(3)

The excess thermodynamic functions of the five systems were derived according to the thermodynamic relationships. The data are given in Table 5. This table shows that the CEp values are all positive for the five systems in the temperature range of 170-320 K. PosiE values are indicative of more structure in the tive Cp,m solution.23 This means that the interaction between the molecules in the gasohol becomes stronger than that in unleaded gasoline 93#. This result is in good agreement with the conclusion derived from the differences in the Tg values for the ethanol, the unleaded gasoline, and the different types of gasohol. (23) Cerdeirin˜a, C. A.; Tovar, C. A.; Carballo, E.; Romanı´, L.; Delgado, M. C.; Torres, L. A.; Costas, M. J. Phys. Chem. B 2002, 106, 185-191.

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Table 5. Excess Thermodynamic Functions of the Five Systems T (K)

cpE (J K-1 g-1)

∆Ha (J/g)

170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 298.15

0.268 0.262 0.263 0.269 0.278 0.288 0.298 0.308 0.319 0.332 0.351 0.377 0.414 0.468 0.544 0.647 0.457

-40.33 -37.69 -35.07 -32.42 -29.68 -26.86 -23.93 -20.91 -17.77 -14.52 -11.11 -7.484 -3.541 0.855 5.895 11.82 0

170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 298.15

0.117 0.121 0.122 0.123 0.125 0.128 0.133 0.141 0.152 0.166 0.184 0.205 0.229 0.255 0.283 0.311 0.250

-19.67 -18.48 -17.27 -16.04 -14.80 -13.53 -12.23 -10.86 -9.400 -7.811 -6.061 -4.117 -1.950 0.467 3.153 6.121 0

∆Sb (J K-1 g-1)

cpE (J K-1 g-1)

∆Ha (J/g)

-0.173 -0.158 -0.143 -0.13 -0.116 -0.103 -0.09 -0.077 -0.065 -0.052 -0.039 -0.026 -0.012 0.003 0.019 0.038 0

0.154 0.159 0.165 0.170 0.175 0.178 0.181 0.184 0.19 0.198 0.213 0.236 0.271 0.321 0.391 0.485 0.311

-24.95 -23.39 -21.77 -20.09 -18.36 -16.6 -14.8 -12.97 -11.11 -9.172 -7.122 -4.886 -2.362 0.584 4.128 8.486 0

-0.083 -0.077 -0.070 -0.064 -0.058 -0.052 -0.046 -0.040 -0.034 -0.028 -0.021 -0.014 -0.007 0.002 0.010 0.020 0

0.105 0.115 0.123 0.130 0.135 0.139 0.142 0.145 0.149 0.154 0.162 0.174 0.192 0.216 0.250 0.294 0.211

-18.80 -17.70 -16.51 -15.24 -13.91 -12.54 -11.14 -9.700 -8.231 -6.718 -5.140 -3.463 -1.638 0.395 2.717 5.425 0

E50

∆Ha (J/g)

E60

E80

a

cpE (J K-1 g-1)

∆Sb (J K-1 g-1)

∆Sb (J K-1 g-1)

E70 -0.107 -0.098 -0.089 -0.080 -0.072 -0.064 -0.056 -0.048 -0.040 -0.033 -0.025 -0.017 -0.008 0.002 0.014 0.027 0

-21.26 -19.87 -18.54 -17.24 -15.96 -14.66 -13.32 -11.90 -10.36 -8.658 -6.759 -4.620 -2.202 0.531 3.614 7.077 0

0.142 0.136 0.131 0.129 0.128 0.131 0.137 0.147 0.161 0.179 0.201 0.227 0.257 0.290 0.327 0.366 0.284

-0.090 -0.082 -0.075 -0.068 -0.062 -0.056 -0.050 -0.044 -0.038 -0.031 -0.024 -0.016 -0.007 0.002 0.012 0.023 0

E90 -0.080 -0.074 -0.068 -0.061 -0.055 -0.048 -0.042 -0.036 -0.030 -0.024 -0.018 -0.012 -0.006 0.001 0.009 0.018 0

E E E E ∆H ) H (T) - H (298.15K) . b ∆S ) S (T) - S (298.15K) .

Table 6. Coefficients bi and Standard Deviations δ system E50 E60 E70 E80 E90

b4

b3

b2

b1

b0

0.3233 -2.9152 9.8585 -14.7190 8.422 0.1885 -1.5446 4.6939 -6.2237 3.183 -0.0396 0.4071 -1.3658 1.8298 0.691 -0.0767 0.7856 -2.8481 4.4311 -2.404 0.0677 -0.5046 1.3263 -1.3583 0.495

δ (J K-1 g-1) 0.001 0.002 0.001 0.003 0.004

CEp (x) curves change only slightly when x increases in the systems. The CEp values reach the maxima as the content of ethanol reaches a value of ∼50% in the systems. 4. Conclusion

Figure 2. Excess heat capacities (CEp ) of the systems from 10 wt % ethanol to 90 wt % ethanol, at intervals of 10 wt %, at different temperatures. (Plotted lines represent temperatures of 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 298.15, 300, 310, and 320 K, from low to high.)

The curve of CEp , with respect to x, is given in Figure 2. To compare the change of the CEp data with the content of ethanol (x), the CEp values for x ) 0.1 (10%), 0.2 (20%), 0.3 (30%), and 0.4 (40%) were cited from the literature.15,16 Figure 2 shows that the shapes of the

The glass transitions in five gasohol systems (E50, E60, E70, E80, and E90) have been observed to occur at temperatures of 95.61, 96.14, 96.56, 96.84, and 97.08 K, respectively. A liquid-solid-phase transition and a solid-liquid-phase transition are observed in the five systems. The interaction between the molecules in the gasohol becomes stronger than that in the unleaded gasoline. Acknowledgment. This work was financially supported by the National Natural Science Foundation of China (under Contract No. NSFC No. 20073047) and Doctorial Foundation of Shandong Province (under Contract No. 2004BS04021). EF050137G