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Energy & Fuels 1996, 10, 816-820
Effects of a New Blending Agent on Ethanol-Gasoline Fuels Filiz Karaosmanogˇlu,* Aslı Is¸ ıgˇıgu¨r, and H. Ays¸ e Aksoy Department of Chemical Engineering, Istanbul Technical University, Maslak, Istanbul 80626, Turkey Received July 7, 1995. Revised Manuscript Received February 23, 1996X
Successful use of ethanol-gasoline blends as engine fuel alternatives depends on producing a stable homogeneous liquid fuel. It is crucial to avoid the phase separation phenomenon which occurs due to the hydrophilic character of alcohols and the solubility behavior of gasoline-alcoholwater three-component system. In this study an industrial byproduct is introduced as a new blending agent to ethanol-gasoline fuels, and its effects on the phase separation problem were investigated on samples prepared by blending unleaded gasoline with 5, 10, 15, and 20% (v/v) azeotropic ethanol, respectively.
Introduction Transportation fuels worldwide are almost exclusively derived from petroleum, and 75% of the world’s petroleum reserves belong to the countries of the Middle East. Oil-importing countries around the world are extremely vulnerable both strategically and economically to fuel supply disruptions. In addition, there is a growing global concern about the environmental impacts of using petroleum and other fossil fuels. Therefore, much research has been directed toward biomass energy resources and biofuels. Biofuels such as ethanol, methanol, and biodiesel offer great flexibility in their usage as engine fuels because they can be used in almost any type of current and future vehicle technology. Alcohols (methanol and ethanol) in the form of alcoholgasoline blends are considered as one of the current and near-term transportation fuel options.1 One of the major difficulties encountered with the use of alcohol-gasoline blends is their tendency to phase separation due to the hydrophilic character of alcohols. Phase separation can cause serious operational problems and damage in an engine. Ethanol has been used as an octane booster for gasoline and in the form of 10% anhydrous ethanolgasoline blended fuel (gasohol) since the 1980s. However, using anhydrous ethanol in blended fuels is not economically feasible as producing anhydrous ethanol is a difficult and costly task within the overall alcohol production process.2-4 Industrial ethanol production yields an azeotrope that is 95% ethanol and 5% water by volume. Ethanol in its usual 95% form cannot readily be used in blended fuels due to phase separation, which occurs as the natural result of the solubility behavior of alcohol-water-gasoline three-component Abstract published in Advance ACS Abstracts, April 1, 1996. (1) Biofuels: A Win-Win Strategy; U.S. Department of Energy Biofuels Systems Division: Washington, DC, 1994; pp 6-8. (2) Austin, G. T. Shreve’s Chemical Process Industries; McGrawHill: New York, 1984; pp 581-590. (3) Paul, J. K. Large and Small Scale Ethyl Alcohol Manufacturing Process from Agricultural Raw Materials; Noyes Data Corp.: Parkridge, NJ, 1980; pp 44-111. (4) McKetta, J. J.; Cunningham, W. A. Encyclopedia of Chemical Processing and Design; Dekker: New York, 1984; Vol. 20, pp 40-51. X
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system. The degree of phase separation varies according to the amounts of alcohol and water in the blend, the chemical composition of the gasoline, and the ambient temperature. In lower temperatures, even small quantities of water present in an ethanolgasoline fuel can lead to direct hydrogen bonding between ethanol and water, and phase separation occurs. The upper phase contains paraffinic hydrocarbons and is rich in gasoline; the lower phase is composed of water, ethanol, and the aromatic components of gasoline soluble in ethanol. The usual solution to such a problem is the addition of a blending agent. The water tolerance of an alcohol-gasoline blend or the amount of water that a blend can dissolve before breaking into two phases is dependent upon temperature, the concentration and type of the alcohol (methanol or ethanol), and the characteristics of the gasoline, its aromatic content in particular.4,5 Various blending agents have been proposed to lower the phase separation temperature of the blends below the actual temperatures experienced during winter.6-11 These blending agents can be grouped as aromatic compounds, higher aliphatic alcohols, and aromatic alcohols. In this study molasses fusel oil was introduced as a new blending agent for ethanol-gasoline fuels and its effects on phase separation temperatures were investigated. Molasses fusel oil is a byproduct of the fermentation process for industrial ethanol production. It is an alcohol mixture having a boiling range of 80-132 °C. The amount and composition of fusel oil produced in the fermentation process depend on the raw materials used. A typical fusel oil production ratio during the fermentation process is 0.2-0.7% (wt) on the basis of pure (5) Karaosmanogˇlu, F.; Is¸ igˇigˇu¨r, A.; Aksoy, H. A. SAE Tech Pap. Ser. 1993, No. 932771. (6) Osten, D. W.; Sell, N. J. Fuel 1983, 62, 268-276. (7) Mislavskaya, V. S.; Leonow, V. E.; Mislavskii, N. O.; Ryzhak, I. A. Sov. Chem. Ind. 1982, 14 (3), 270-273. (8) Englin, B. A.; Kyuregyan, S. K.; Levinson, G. I.; Demidenko, K. A.; Golosava, V. F. Zh. Khim. 1978, 20, 106-110. (9) Mu¨eller, H.; Majunke, H. J. Eur. Pat. Appl. EP 171440 A1 (FRG), 1986. (10) Karaosmanogˇlu, F.; Aksoy, H. A.; Civelekogˇlu, H. J. Inst. Energy 1988, 61, 125-128. (11) Karaosmanogˇlu, F.; Is¸ igˇigˇu¨r, A.; Aksoy, H. A. J. Inst. Energy 1993, 66, 9-12.
© 1996 American Chemical Society
Ethanol-Gasoline Fuels
Energy & Fuels, Vol. 10, No. 3, 1996 817 Table 1. Fuel Properties of Unleaded Gasoline Samples gasoline
property color density @ 15 °C (kg/m3) composition (wt %) saturated hydrocarbons aromatic hydrocarbons olefinic hydrocarbons water (% v/v) sulfur (kg/m3) distillation test (°C) 10% distillate 50% distillate 90% distillate residue (%) loss (%) Reid vapor pressure (kPa) octane number research method motor method corrosion, copper, 50 °C, 3 h
ASTM test method
G1
G2
G3
G4
yellow 734.6
yellow 742.1
yellow 762.5
yellow 795.2
72.20 27.20 0.60 0.1227 28 × 10-3
60.01 39.02 0.97 0.3700 8 × 10-3
49.70 48.80 1.50 0.2504 4 × 10-3
38.96 59.94 1.10 0.1508 6 × 10-3
D 323
57 99 155 1.0 1.0 56.7
50 89 143 0.5 0.5 63.8
52 121 159 0.5 1.0 77.0
78 132 162 0.5 1.0 48.6
D 2699 D 2700 D 130
82.0 76.0 No. 1a
85.0 74.5 No. 1a
96.6 86.5 No. 1a
97.5 86.6 No. 1a
D 1298 D 1319
D 1744 D 381 D 86
ethanol.12 Although 50 different compounds were identified using the gas-liquid chromatography method, the major components of fusel oil are fermentation amyl alcohols such as 2-methyl-1-butanol and 3-methyl-1butanol.13 Experimental Section Materials. The ethanol-gasoline blends used in the experiments were prepared by adding 5, 10, 15, and 20% (v/v) azeotropic ethanol to unleaded gasoline. Ethanol was distilled under normal pressure prior to blending due to its hygroscopic character. The freshly distilled ethanol used in the blends is the ethyl alcohol-water azeotrope (EtOH) having a boiling point of 78.15 °C and containing 4.4 wt % water. Twenty percent ethanol in gasoline is considered to be the maximum amount that today’s engines can tolerate without any modifications, so this figure was the upper limit in the fuels tested.14,15 Unleaded gasolines were obtained from Turkish Petroleum Refineries Inc. and were refinery assured. Table 1 shows the chemical compositions and physical properties of the four unleaded gasoline samples (G1, G2, G3, and G4) determined according to ASTM methods. The fuel blends formed using these gasoline samples will be referred to as B1, B2, B3, and B4, respectively, throughout the text. Methods. Experimental work was performed in four steps: 1, fractionation and characterization of the molasses fusel oil; 2, investigation of the fusel oil fraction as a blending agent; 3, determination of the relationship between the phase separation temperatures and the chemical compositions of gasolines used in fuel blends; and 4, water tolerances of the fuel blends.
Results and Discussion Fractionation and Characterization of the Molasses Fusel Oil. Fusel oil (FO) used in the experiments was obtained from Turkish Sugar Factories Inc. It had a high (8.6% v/v) water content, and its density at 20 °C is 853.6 kg/m3. Using straight fusel oil as a blending agent for the ethanol-gasoline blends will (12) Ullmanns Encykl. Tech. Chem., 4 1974. (13) Thorpe, J. F.; Whiteley, M. A. Thorpe’s Dictionary of Applied Chemistry; Longmans: London, 1962; Vol. 5, pp 403-408. (14) Use of Alcohol in Motor GasolinesA Review; API Publication 4082; American Petroleum Institute: Washington, DC, 1971. (15) Alcohols, A Technical Assessment of Their Application as Fuels; API Publication 4261; American Petroleum Institute: Washington, DC, 1976.
Figure 1. ASTM distillation curve of FOF.
increase the water content of the blend even further. Increasing water content will increase the phase separation temperature of the blend.14-18 Therefore, fusel oil was distilled in a Normschliff Gera¨tebau fractional distillation unit, and the higher boiling fraction (above 120 °C and 75% v/v of FO) of fusel oil (FOF) containing 0.1% (v/v) water was used as the blending agent in the experiments. Figure 1 shows the ASTM distillation curve of the FOF which was formed according to the results of the ASTM D 86 method. Chemical compositions of FO and FOF were determined using the gasliquid chromatography technique. The instrument used was United Technologies Packard Model 437 A gas chromatograph fitted with a flame ionization detector operating at 200 °C and a stainless steel column (2 m × 5 mm) packed with 80-100 mesh Propak Q. The injection block temperature was 200 °C, and the flow rate of the carrier gas, nitrogen, was 40 mL/min. Results of the gas chromatographic analysis of FO and FOF are given in Table 2. Use of Molasses Fusel Oil Fraction as a Blending Agent. Solubility diagrams of gasoline-ethanol-waterFOF blends at various temperatures were investigated (16) Keller, J. I.; Hydrocarbon Process. 1979, 2, 127-138. (17) Terzoni, G.; Pea, R.; Ancillotti, F. Proceedings of the IV International Symposium on Alcohol Fuels Technology; ISAF: Brazil, 1980; Vol. 1, pp 331-335. (18) McKetta, J. J.; Cunningham, W. A. Encyclopedia of Chemical Processing and Design; Dekker: New York, 1984; Vol. 20, pp 1-40.
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Figure 4. PST of ethanol-gasoline blends (B1) containing various amounts of FOF.
Figure 2. Solubility diagram of ethanol/water-gasoline-FOF (B1) at various temperatures.
Figure 3. Solubility of ethanol in gasoline at 25 °C in the presence of water. Table 2. Chemical Compositions (Weight Percent) of FO and FOF alcohol
FO
FOF
ethanol 2-propanol 1-propanol 1-butanol fermentation amyl alcohols
1.45 0.15 1.76 21.94 74.70
0.06 0.41 13.03 86.50
to determine the boundaries of the zone in which the four-component system formed a consistent single homogeneous phase. For reasons of simplicity ethanol and water were considered as one component, and solubility diagrams of G1-(ethanol/water)-FOF three-component systems at -20, 0, and 25 °C were formed. The amount of FOF required to obtain a homogeneous phase was determined by using a micropipet. Figure 2 shows the solubility diagram of an ethanol/water-gasoline-FOF (B1) system at -20, 0, and 25 °C. Figure 3 is the solubility diagram of the ethanol-water-gasoline system at 25 °C without the FOF.11,15 In the ethanolgasoline-water system the heterogeneous zone is quite
large, whereas introduction of FOF narrows this zone significantly. Blends containing 20% or more ethanol form a single homogeneous phase at 25 °C. At lower temperatures a blend containing 10% EtOH required the addition of 0.1% FOF to form a single homogeneous phase. Blends containing more than 30% ethanol were always in a single homogeneous phase at 0 °C without using the blending agent. Blends containing 40% or more ethanol were homogeneous at -20 °C. At this temperature the 9.6% ethanol blend required the most blending agent, which was 3.5% FOF. Using the FOF in amounts ranging from 0.1 to 3.5% resulted in homogeneous blends at temperatures of -20, 0, and 25 °C, and the effect of FOF in the prevention of phase separation was significant. Phase separation temperatures (PST) of ethanolgasoline blends using FOF as the blending agent were determined by adding FOF to the blends in various ratios and investigating its behavior in accordance with the DIN 51583 method. The water content of each blend was determined according to the Karl-Fischer method (ASTM D 1744). A mixture of acetone and dry ice was used to create low-temperature conditions, and the lowest temperature achievable in this way was -77 °C. Temperature measurements were taken with an alcohol thermometer with a scale ranging from -120 to +40 °C. Blends with PSTs above room temperature were first heated to 39 °C and cooled gradually until separation occurred. Temperatures higher than that were avoided because of gasoline’s low vapor pressure.6 Readings throughout the experiments were taken between -77 and +39 °C. Ethanol-gasoline blends (B1 and B4) were prepared using gasolines G1 (rich in saturated hydrocarbons and having the lowest octane number) and G4 (rich in aromatic hydrocarbons and having the highest octane number). Figures 4 and 5 show the PSTs for blends B1 and B4. Adding 9% FOF to B1 and 6% FOF to B4 dropped the PSTs below -77 °C. A drop in the PSTs was observed when the amount of EtOH increased in blends containing a constant amount of FOF. PSTs also dropped when the amount of EtOH was held constant and the FOF content was increased. Results suggested that there was a close connection between the chemical composition of gasolines used in the blends and the PSTs. Relationship between the Phase Separation Temperatures and the Chemical Compositions of Gasolines Used in Fuel Blends. In this part of the study, the variations in the PSTs of the ethanolgasoline fuel samples (B1, B2, B3, and B4) prepared by
Ethanol-Gasoline Fuels
Energy & Fuels, Vol. 10, No. 3, 1996 819
Figure 5. PST of ethanol-gasoline blends (B4) containing various amounts of FOF. Table 3. PSTs for Ethanol-Gasoline Blends Prepared with Gasolines of Different Compositions FOF (%)
EtOH (%)
H2O (%)
B1
0
5 10 15 20 5 10 15 20 5 10 15 20
0.3 0.5 0.7 0.9 0.3 0.5 0.7 0.9 0.3 0.5 0.7 0.8
>39.0 19.0 11.5 9.0 16.5 5.5 -1.0 -3.0 -12.5 -17.5 -22.0 -26.5
1
3
PST (°C) B2 B3 >39.0 17.5 6.5 2.5 12.5 4.5 -3.0 -8.0 -16.0 -23.5 -28.5 -34.5
>39.0 16.5 1.5 -8.0 10.5 3.0 -5.5 -13.5 -19.5 -27.0 -33.5 -37.5
B4
Figure 6. WTs for B1 fuel blends.
>39.0 15.0 -1.2 -12.5 8.5 2.5 -12.5 -18.2 -22.0 -35.7 -37.5 -40.5
using gasolines with different chemical compositions were investigated. Table 3 shows the PSTs of the blends in the presence of 0, 1, and 3% FOF. In blends that did not contain the FOF the PSTs dropped as the EtOH and water content of the blend increased. This was due to the similar solubility behavior of EtOH in both aromatic and nonaromatic hydrocarbons. Solubility also increases with temperature level.15,19 For a constant amount of FOF and EtOH in a blend, increasing aromatic character of the gasoline corresponded to a decrease in the PSTs. Water Tolerances of the Fuel Blends. Water tolerance (WT) of an alcohol-gasoline blend is defined as the amount of water that can be added to a blend at 20 °C until a haze is formed.20,21 Water tolerances of blends B1 and B4, which were determined at 20 °C, are shown in Figures 6 and 7, respectively. At a constant amount of FOF, increasing the EtOH content of the blend, and at constant EtOH, increasing the FOF of the blend, increased the WT of the blend. When the WT values of B1and B4 were compared with each other, B4, which was prepared using G4 (gasoline rich in aromatic hydrocarbons), had higher WT values than B1. Results showed that the chemical composition of the gasoline was an important parameter for WTs of the blends and the effect of this parameter is shown in Table 4. From Tables 3 and 4 it can be concluded that a high WT value indicates a low PST. However, if a blend contains more water than its WT value, an (19) Goodger, E. M. Alternative Fuels, Chemical Engineering Resources; MacMillan: London, 1980; pp 141-142. (20) Annual Book of ASTM Standards; Information on Document on Gasohol (Motor Fuel Containing 10% Volume of Denatured Ethanol in Gasoline); American Society for Testing and Materials: Philadelphia, PA, 1981; Vol. 25, pp 920-937. (21) MIL G-53006 Appendix Test Method (USA).
Figure 7. WTs for B4 fuel blends. Table 4. WTs for Ethanol-Gasoline Blends Prepared with Gasolines of Different Compositions WT (%) FOF (%)
EtOH (%)
B1
B2
B3
B4
0
5 10 15 20 5 10 15 20 5 10 15 20
0.30 0.50 0.76 1.08 0.31 0.54 0.90 1.30 0.34 0.70 1.20 1.64
0.30 0.50 0.77 1.12 0.31 0.54 0.92 1.34 0.35 0.72 1.23 1.71
0.30 0.50 0.79 1.18 0.31 0.55 0.96 1.38 0.37 0.74 1.28 1.78
0.30 0.50 0.80 1.23 0.32 0.56 1.00 1.40 0.38 0.75 1.31 1.81
1
3
increase in the PST could be expected. This effect was further investigated by increasing the water content of the blend B1 and recording the variation in PSTs. The FOF content of the blend also affected the WT; Table 5 shows the results of the PST readings taken with B1 containing 1 and 6% FOF, respectively. The parameters investigated up to this point are also summarized in Table 5. An increase in the water content of the ethanol-gasoline blends resulted in higher PSTs, whereas increasing the FOF content of the blends increased the WT and decreased the PSTs. The pres-
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Figure 8. Variation of WTs with temperature for B1 fuel blends containing 1% FOF.
Figure 9. Variation of WTs with temperature for B1 fuel blends containing 3% FOF.
Table 5. Change in the PSTs According to the Water Content of B1 Blends Containing 1 and 6% FOF
separation temperatures and increasing the water tolerances of the azeotropic ethanol-unleaded gasoline blends. The essential results concerning the change in the PSTs in FOF-added ethanol-gasoline blends are as follows: 1. Increasing the amount of the fusel oil fraction in the ethanol-gasoline blends of known alcohol and water content increases the WT values and decreases the PSTs of the blends. 2. The chemical composition of the gasoline used is an important factor for the ethanol-gasoline blends. Higher aromatic content of gasoline results in lower PSTs. 3. Environmental temperature is vitally important for the stability of the ethanol-water-gasoline-fusel oil fraction four-component system. An increase in temperature results in an increase in the WT of the blend, whereas the amount of blending agent required for a stable blend decreases. 4. Climatic conditions and seasonal temperature variations differ among regions in Turkey. Although -21 °C is the lowest average temperature observed in winter over the past 5 years, temperatures below -10 °C are not very common. Therefore, 20% ethanolgasoline blends prepared with gasoline rich in aromatics and containing 0.1% FOF can be used safely throughout the year without any phase separation problem, whereas the 20% ethanol-parafinic gasoline blends containing the same amount of FOF may be used anytime except winter. Fuel ethanol production can yield sufficient fusel oil to supply the suggested 0.1% FOF as the blending agent. The results obtained in this study suggest that a byproduct of the ethanol production process may be used effectively in solving the phase separation problem of the ethanol-gasoline fuels otherwise solved by using various pure cosolvents.
FOF (%)
EtOH (%)
WT (%)
H2O (%)
PST (°C)
1
5
0.31
10
0.54
15
0.90
20
1.30
5
0.57
10
1.06
15
1.60
20
2.20
0.3 0.5 0.7 1.0 0.5 0.7 1.0 1.3 0.7 1.0 1.3 1.6 0.9 1.3 1.6 2.0 0.3 0.5 0.7 1.0 0.5 0.7 1.0 1.3 0.7 1.0 1.3 1.6 0.9 1.3 1.6 2.0
16.5 29.0 >39.0 >39.0 10.5 21.0 >39.0 >39.0 18.0 31.0 >39.0 >39.0 -3.0 21.0 >39.0 >39.0 -49.5 -1.0 23.0 >39.0 -55.0 -27.5 1.5 28.0 -58.0 -33.5 -12.2 19.5 -59.0 -40.2 -14.5 7.2
6
ence of water in amounts exceeding the WT values of the blends resulted in very high PSTs. WT is highly dependent on temperature; therefore, WT values for B1 containing 1 and 3% FOF were determined within a temperature range of -20 to +40 °C. Increasing the temperature as well as increasing the EtOH and FOF content of the blend resulted in an increase in the WTs. Figures 8 and 9 show the change in WTs versus increasing temperature. Conclusions The fusel oil fraction is a new blending agent that was found to be highly effective in reducing the phase
Acknowledgment. We thank Turkish Petroleum Refineries Inc. and Istanbul Regional BranchsTurkish Sugar Factories Inc. for their valuable cooperation. EF950131Z
