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Energy & Fuels 2004, 18, 334-337
Water Tolerance and Ethanol Concentration in Ethanol-Gasoline Fuels at Three Temperatures Mo´nica B. Gramajo de Doz, Carlos M. Bonatti, and Horacio N. So´limo* Departamento de Fı´sica, Facultad de Ciencias Exactas y Tecnologı´a, Universidad Nacional de Tucuma´ n, Av. Independencia 1800, 4000 Tucuma´ n, Argentina Received July 31, 2003. Revised Manuscript Received October 17, 2003
Several gasoline-ethanol-water multicomponent systems at temperatures of 283.15, 293.15, and 313.15 K were studied, to obtain water tolerances and ethanol concentrations at equilibrium in the upper gasoline-rich phase. The lower aqueous phase was not studied, because of its very small volume. The ethanol and water concentrations were determined by a chromatographic method, using the external standard method for quantification, whereas no other gasoline component was determined. Moreover, the influence of the gasoline volume in the tank was simulated and studied in the laboratory. From experimental results, we conclude that the ethanol concentration decreases as the tank becomes more empty, whereas it is only slightly affected by the temperature within the studied temperature range. A similar behavior was observed for the water tolerance, when the water volume inside the tank corresponds to 0.5 vol % of water. In addition, the loss of ethanol that is drawn into the aqueous phase diminishes dramatically when the water volume in the tank diminishes, and the loss of ethanol becomes negligible when this volume corresponds to e0.05 vol % of water.
Introduction Presently, there is an increasing interest in adding oxygenated compounds to gasoline, because of their octane-enhancing and pollution-reducing capabilities. In the last several years, many interesting works have been published on ternary, quaternary, or quinary systems that contain a synthetic reformate (hydrocarbon mixtures), an oxygenated compound (ethers or alcohols), and water, at approximately ambient temperature;1-11 however, studies of multicomponent systems that contain gasoline, an oxygenated compound, and water are rarely found in the literature.12 Within the oxygenated compounds, ethers and alcohols are the most important, and among these compounds, ethanol has been receiving much current attention.13,14 * Author to whom correspondence should be addressed. E-mail:
[email protected]. (1) Peschke, N.; Sandler, S. I. J. Chem. Eng. Data 1995, 40, 315320. (2) Hellinger, S.; Sandler, S. I. J. Chem. Eng. Data 1995, 40, 321325. (3) Gramajo de Doz, M. B.; Bonatti, C. M.; Barnes, N.; So´limo, H. N. J. Chem. Thermodyn. 2001, 33, 1663-1677. (4) Gramajo de Doz, M. B.; Bonatti, C. M.; Barnes, N.; So´limo, H. N. Sep. Sci. Technol. 2002, 37, 245-260. (5) Gramajo de Doz, M. B.; Bonatti, C. M.; So´limo, H. N. Fluid Phase Equilib. 2003, 205, 53-67. (6) Gramajo de Doz, M. B.; Bonatti, C. M.; So´limo, H. N. J. Chem. Thermodyn. 2003, 35, 825-837. (7) Alkandary, J. A.; Aljimaz, A. S.; Fandary, M. S.; Fahim, M. A. Fluid Phase Equilib. 2001, 187-188, 131-138. (8) Arce, A.; Blanco, M.; Soto, A. Fluid Phase Equilib. 1999, 158160, 949-960. (9) Chen, J.; Duan, L.-P.; Mi, J.-G.; Fei, W.-Y.; Li, Z.-C. Fluid Phase Equilib. 2000, 173, 109-119. (10) Garcı´a-Flores, B. E.; Galicia-Aguilar, G.; Eustaquio-Rinco´n, R.; Trejo, A. Fluid Phase Equilib. 2001, 185, 275-293. (11) Aiouache, F.; Goto, S. Fluid Phase Equilib. 2001, 187-188, 415-424. (12) Karaosmanogˇlu, F.; Is¸ igˇigu¨r, A.; Ays¸ e Aksoy, H. Energy Fuels 1996, 10, 816-820.
However, one of the major difficulties encountered with the use of alcohol-gasoline blends is their tendency to phase-separate on contact with small amounts of water, yielding an upper gasoline-rich phase than mainly contains paraffinic hydrocarbons and a lower dilute aqueous ethanol-rich phase that contains some aromatic hydrocarbons that are soluble in ethanol. This is very important, because phase separation can have very undesirable effects, because the lower phase has a greater volume and a lower density than the original water and, therefore, is more apt to be suspended and delivered to vehicles along with the upper fuel phase. Experience shows that most tanks in the commercial gasoline distribution system contain a water volume that corresponds to concentrations varying from 0.05% up to 0.5% of the complete-filled tank volume. Therefore, the aim of this work was (i) to measure water tolerances and ethanol concentrations at equilibrium in the upper gasoline-rich phase for three typical ethanol-gasoline blends, each one containing these two extreme water overall concentrations at 283.15, 293.15, and 313.15 K, because this range of temperature is typically found in tropical and subtropical climates; and (ii) to analyze the influence of the gasoline volume in the tank on the water tolerances and ethanol concentrations. The water tolerance in blends is the amount of water (volume percent) that a blend can dissolve before separating into two phases at equilibrium. This value (13) Oge, M. T. Presented to the United States Environment Protection Agency (USEPA) before the Subcommittee on Energy and Environment of the Committee on Science, U.S. House of Representatives, Washington, DC, September 14, 1999. (Available via the Internet at http://www.epa.gov/oms/speeches/mto99rfg.htm.) (14) Browner, C. M. Presented at the Press Conference of the EPA Administrator. Remarks Available from USEPA, Office of Communications, Education and Public Affairs, Washington, DC, March 20, 2000.
10.1021/ef034040a CCC: $27.50 © 2004 American Chemical Society Published on Web 12/06/2003
Water and Ethanol Content in Ethanol-Gasoline
Energy & Fuels, Vol. 18, No. 2, 2004 335
Table 1. Fuel-Blend Compositions of Unleaded Gasolines A, B, and C Used in the Experiments composition (vol %) ASTM test method paraffinic hydrocarbons aromatic hydrocarbons olefinic hydrocarbons naphthenic hydrocarbons ethanola watera total
D-5134 D-5134 D-5134 D-5134 11.70 0.060
benzene
D-5134
a
A
B
Experimental Section
C
43.05 48.19 53.67 37.67 40.08 29.64 5.22 3.67 8.61 2.35 2.87 3.48 5.17 4.59 0.063 0.038 100.05 100.043 100.028 2.67
2.66
1.97
Determined by gas chromatography using a TCD detector.
Table 2. Gasoline/Water Ratios for Multicomponent Equilibrium Data for Two Volumes of Water water volume, 0.5 vol %
water volume, 0.05 vol %
tank filled gasoline water gasoline water up to volume (mL) volume (µL) volume (mL) volume (µL) full /4 full 5 /8 full 1 /2 full 3 /8 full 1 /4 full
3
7.96 7.95 7.94 7.92 7.89 7.84
40a 53 63.5 79.2 105.2 156.8
8.0 8.0 8.0 7.99 7.99 7.98
particularity was taken into consideration and simulated in our laboratory, to study different blend/water ratios.
4.0b 5.3 6.4 8.0 10.7 16.0
a Original water composition: 0.5% of the completely filled tank volume. We assume that this is the highest percentage of water found in commercial gasoline distribution systems. b Original water composition: 0.05% of the completely filled tank volume.
is dependent upon temperature, the ethanol concentration, the concentration and type of ingredients that are added as cosolvents, and the gasoline characteristics (particularly, the aromatic content). The commercial gasoline distribution system has an important particularity. If phase separation occurs, the volume of water is practically constant in the storage tanks while the volume of the upper gasoline-rich phase is variable, because vehicles load only from the upper fuel phase, leaving the lower phase unaltered. This
Materials. Table 1 lists the chemical composition of three typical unleaded ethanol-gasoline blends used in the experiments, which will be called A, B, and C throughout the text. Methods. Multicomponent equilibrium data were obtained by preparing six (fuel blend + water) mixtures at each temperature, to obtain a total volume of 8 mL for each mixture with the gasoline/water ratios listed in Table 2. These ratios were selected to simulate typical situations in the filling stations when phase separation occurs, because the volume of the upper gasoline-rich phase in the storage tanks changes continuously every time an automobile loads fuel; however, the volume of the aqueous phase remains practically constant and it is equal to or less than the tank’s drainage volume. However, in this work, we assume that the water volume is always equal to the drainage volume of the tank, which corresponds to 0.05 or 0.5 vol % of water, as previously indicated. All mixtures were prepared simultaneously, by introducing each one in 16-mL screw sample vials (Hewlett Packard, model HP 5183-4535) equipped with a cap, septa, and a Teflon-coated magnetic bar (to provide an intense stirring for at least 7 days), which simulates the filling station tank. A water bath that was thermostated at a temperature of 283.15, 293.15, or 313.15 K ((0.05 K) was connected in series with a set of acrylic boxes that each have six holes with O-ring seals, where the sample vials were inserted, as described earlier.4 The uniformity of temperature within the vials was maintained by continuous agitation of the mixture samples with a multipoint magnetically coupled stirrer (SBS, model A-04) that was placed under the boxes. After phase equilibrium was reached, the magnetic stirrers were turned off and both liquid phases were allowed to settle for 24 h. At the end of each experiment, samples were taken from the upper gasoline-rich phase with hypodermic syringes and analyzed by means of gas chromatography. The liquid that wet the needle externally was eliminated with a soft paper tissue before the sample was introduced into the 2-mL analysis vial (Hewlett Packard, model HP 5182-0714). A gas chromatograph
Table 3. Water Tolerances and Ethanol Concentration at Equilibrium for the Upper Gasoline-Rich Phase with 0.5 vol % of Water at Different Temperatures Gasoline A tank filled up to
Gasoline B
water tolerance (vol %)
ethanol (vol %)
full 4 full 5/ full 8 1/ full 2 3/ full 8 1/ full 4
0.38 0.32 0.28 0.22 0.16 0.11
10.78 9.65 9.07 8.14 7.10 5.77
full 3/ full 4 5/ full 8 1/ full 2 3/ full 8 1/ full 4
0.39 0.36 0.30 0.25 0.19 0.15
full 3/ full 4 5/ full 8 1/ full 2 3/ full 8 1/ full 4
0.45 0.40 0.35 0.30 0.23 0.18
3/
water tolerance (vol %)
Gasoline C ethanol (vol %)
water tolerance (vol %)
ethanol (vol %)
T ) 283.15 K 0.08 0.08 0.07 0.06 0.05 0.05
4.13 3.90 3.89 3.57 3.23 2.60
0.10 0.09 0.08 0.07 0.06 0.05
4.83 4.33 4.15 3.90 3.34 2.71
11.00 10.45 9.38 8.61 7.45 6.40
T ) 293.15 K 0.07 0.07 0.07 0.06 0.06 0.05
4.16 3.93 3.76 3.50 3.17 2.68
0.10 0.09 0.08 0.08 0.07 0.06
5.04 4.62 4.25 3.94 3.58 3.11
10.36 10.09 9.65 8.80 8.04 6.94
T ) 313.15 K 0.08 0.07 0.06 0.06 0.05 0.04
4.39 4.24 3.95 3.65 3.33 2.96
0.11 0.10 0.09 0.09 0.07 0.06
5.04 4.89 4.44 4.26 3.94 3.31
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Gramajo de Doz et al.
Table 4. Water Tolerances and Ethanol Concentrations at Equilibrium for the Upper Gasoline-Rich Phase with 0.05 vol % of Water at Different Temperatures Gasoline A tank filled up to
Gasoline B
water tolerance (vol %)
ethanol (vol %)
full 4 full 5/ full 8 1/ full 2 3/ full 8 1/ full 4
0.08 0.08 0.08 0.08 0.08 0.08
11.35 11.30 11.31 11.27 11.26 11.25
full 3/ full 4 5/ full 8 1/ full 2 3/ full 8 1/ full 4
0.08 0.08 0.08 0.08 0.08 0.08
full 3/ full 4 5/ full 8 1/ full 2 3/ full 8 1/ full 4
0.08 0.08 0.08 0.08 0.08 0.08
3/
water tolerance (vol %)
Gasoline C ethanol (vol %)
water tolerance (vol %)
ethanol (vol %)
T ) 283.15 K 0.07 0.07 0.07 0.07 0.07 0.07
5.28 5.26 5.20 5.16 5.14 4.96
0.07 0.07 0.07 0.07 0.07 0.07
5.93 5.82 5.79 5.74 5.73 5.62
11.36 11.29 11.27 11.25 11.10 11.12
T ) 293.15 K 0.07 0.07 0.07 0.07 0.07 0.07
5.30 5.28 5.20 5.17 5.02 4.76
0.07 0.07 0.07 0.07 0.07 0.07
5.99 5.91 5.69 5.45 5.58 5.33
11.44 11.43 11.44 11.45 11.46 11.47
T ) 313.15 K 0.07 0.07 0.07 0.07 0.07 0.07
5.48 5.26 5.20 5.11 4.93 4.72
0.07 0.07 0.07 0.07 0.07 0.07
6.02 5.95 5.90 5.70 5.36 5.34
Figure 1. Ethanol concentration (presented as a volume percentage), as a function of temperature and the gasoline volume in the tank for 0.5 vol % of water. Legend regarding the filling of the tank is as follows: ([) full; (9) 3/4 full; (2) 5/8 full; (4) 1/2 full; (×) 3/8 full; and (b) 1/4 full. (Hewlett-Packard, model 6890) that was directly connected to a ChemStation (Hewlett Packard, model HP G2070AA) was used, as well as a 7683 Series Agilent injector, and the external standard method was applied to obtain quantitative results. Unfortunately, the lower phase could not be analyzed, because its small volume did not allow withdrawal of the samples. Good separation for ethanol and water from hydrocarbons was obtained on a 30 m × 0.25 mm × 0.5 µm capillary column (INNOWax, which is cross-linked poly(ethylene glycol); Hewlett Packard, HP 19091N-233). The temperature program was as follows: heating at an initial temperature of 343 K for 2 min, a ramp at 15 K min-1, and heating at a final temperature of 373 K for another 2 min. The nitrogen carrier gas flow rate was electronically kept constant, working with a split ratio of 20:1 and the injector was fitted at 453 K. Detection was performed by a thermal conductivity detector at 523 K. Three or four analysis were performed for each sample, to obtain a mean volume percent value with a repeatability of better than 1%. Only ethanol and water were quantified; no other component received attention in this work.
Results Tables 3 and 4 report the experimental water tolerances and ethanol concentrations at equilibrium for the three fuel blends listed in Table 1 at temperatures of 283.15, 293.15, and 313.15 K, for the upper gasoline-
Figure 2. Ethanol concentration (presented as a volume percentage), as a function of temperature and the gasoline volume in the tank for 0.05 vol % of water. Legend regarding the filling of the tank is as follows: ([) full; (9) 3/4 full; (2) 5/8 full; (4) 1/2 full; (×) 3/8 full; and (b) 1/4 full.
Figure 3. Water tolerance (presented as a volume percentage), as a function of temperature and the gasoline volume in the tank for 0.5 vol % of water. Legend regarding the filling of the tank is as follows: ([) full; (9) 3/4 full; (2) 5/8 full; (4) 1/2 full; (×) 3/8 full; and (b) 1/4 full.
rich phase and for both water concentrations (0.5 and 0.05 vol %), respectively. Figure 1 illustrates both the filling of the tank and the temperature effects on the ethanol concentration for 0.5 vol % of water. Figure 2 shows the same, but for 0.05 vol% of water, whereas Figure 3 shows the water tolerance for 0.5 vol % of water. These plots were constructed with data from Tables 3 and 4 for the fuel
Water and Ethanol Content in Ethanol-Gasoline
blend called gasoline A. Similar plots were obtained for the other blends and concentrations of water, which are not shown, because the water tolerances and ethanol concentrations are practically constant for 0.05 vol % of water. Neither temperature nor the filling volume of the tank have any influence on the results for this water concentration, as can be seen from Table 4.
Energy & Fuels, Vol. 18, No. 2, 2004 337 Table 5. Loss of Ethanol Drawn into the Aqueous Phase at Equilibrium, Comparing a Full Tank with a Tank Filled to One-Fourth of Its Volumea for the Three Gasolines Listed in Table 1 with a Water Content of 0.5 vol % at Temperatures of 283.15, 293.15, and 313.15 K Loss of Ethanol (vol%) temp (K)
gasoline A
gasoline B
gasoline C
283.15 293.15 313.15
46.5 41.8 33.0
37.1 35.6 32.6
43.9 38.3 34.3
Discussion Figure 1 shows that the ethanol concentration decreases as the tank empties for 0.5 vol % of water, whereas temperature has only a minor effect on its concentration for both water concentrations, as can be seen from Figures 1 and 2. On the other hand, the water tolerance presents a similar behavior for both variables and for 0.5 vol % of water, as can be shown from Figure 3. From this last statement, we conclude that phase separation will be facilitated by the emptying of the tank, because the multicomponent system needs a smaller water content for separation into two phases to occur. From the experimental results, we also conclude that the loss of ethanol drawn into the aqueous phase diminishes dramatically when the water volume diminishes in the tank, and the loss of ethanol is negligible if this volume corresponds to e0.05 vol % of water. This means that avoiding phase separation is a very important premise; however, if it does occur,one way to minimize its consequences is to reduce the content of water below this value, which could be achieved by draining the lower phase periodically and, in addition, not permitting the tank to empty, so that a more favorable blend/water ratio can be obtained. This drainage is not a serious pollution problem, because the aqueous phase presents a very low concentration of hydrocarbons.4-6,10
a
Data from Table 3.
Tables 3 and 4 show that small water tolerances are observed for the three types of gasoline, particularly for gasolines B and C, the water tolerances for which are of the same order of magnitude as the water concentration of the original gasolines (see Table 1). However, for gasoline A, this water tolerance is considerably larger than its original water content, because of its higher ethanol concentration. The dependence of the losses of ethanol drawn into the aqueous phase on the volume of the tank and the temperature can be calculated from the results listed in Table 3, and they are shown in Table 5 for the three gasolines. Moreover, Table 4 shows that the loss of ethanol is negligible when the water content is 0.05 vol %. In practice, the situation in the laboratory (this work) is different from that in the filling stations, because equilibrium conditions between both phases cannot be reached in these latter environments, mainly because of a lack of stirring, which produces an ethanol loss that is probably less than that indicated in Table 5. Acknowledgment. Financial support from the Consejo de Investigaciones de la Universidad Nacional de Tucuma´n, Argentina (CIUNT, Grant 26/E236) and Refinor S.A.-Argentina is gratefully acknowledged. EF034040A
