Energy Fuels 2010, 24, 2683–2691 Published on Web 03/15/2010
: DOI:10.1021/ef9014795
Distillation Curves for Alcohol-Gasoline Blends V. F. Andersen,† J. E. Anderson,*,‡ T. J. Wallington,*,‡ S. A. Mueller,‡ and O. J. Nielsen† †
Copenhagen Center for Atmospheric Research, Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denmark, and ‡Systems Analytics and Environmental Sciences Department, Research and Advanced Engineering, Ford Motor Company, Mail Drop RIC-2122, Dearborn, Michigan 48121-2053 Received December 3, 2009. Revised Manuscript Received February 5, 2010
Distillation curves are presented for single-alcohol blends in gasoline, containing 5-85% by volume of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, i-butanol (2-methyl-1-propanol), and t-butanol (2methyl-2-propanol). Most alcohols are shown to form mixtures with gasoline exhibiting near-azeotropic behavior that significantly affect the shape of the distillation curves. The results are compared to literature data available for some alcohols. In addition, distillation curves for a variety of dual-alcohol blends are presented, containing 10% of each of two alcohols. We show that such dual-alcohol blends have distillation curves closer to that of the base gasoline than single-alcohol blends with 20% of either alcohol individually. At present, ethanol is the only biofuel alcohol available in scale. As other alcohol biofuels become available in the future, it may be advantageous to use them in dual- or multialcohol blends to minimize their impact on fuel volatility.
lifecycle greenhouse gas emissions) there is a large ongoing research effort to develop second-generation biofuels derived from nonfood crops (e.g., wood, straw, agricultural, and municipal wastes). There are a variety of potential second-generation biofuels under consideration; many are alcohols. Alcohols can be produced from biomass via either biotic routes (e.g., pretreatment of cellulose and hemicellulose to release sugars that can be fermented to give ethanol,6 butanol, or higher alcohols7) or abiotic routes (e.g., gasification followed by thermochemical synthesis giving a mixture [typically C1-C4] of alcohols). Alcohols are typically blended with gasoline for use in LDVs. In general, alcohol blend percentages in gasoline are commonly expressed as volumetric percentages;unless otherwise specified, this convention is used here. In the US, gasoline blends with 10% ethanol by volume (E10) are common, and blends nominally with 85% denatured ethanol (commercial E85) are available. The denaturant is typically gasoline and the resulting ethanol content in summer-grade commercial E85 can be as little as 79%.8 To improve cold starting, winter-grade commercial E85 has a lower denatured ethanol content (75%) and thus may contain as little as 70% ethanol. To minimize the risk of water-induced phase separation of ethanol-gasoline blends,9 anhydrous ethanol is blended into gasoline at the terminal prior to shipping to retail gas stations rather than distributing it through pipelines. Due to the recent mandate in the US calling for greater biofuel use, there is investigation underway into the feasibility of using “mid-level” blends, which are defined here as blends containing more than 10% and less than 70% v/v alcohol. The use of ethanol blends greater than 10% requires some engine and fuel system modifications. Flexible fuel
1. Introduction Growing recognition of the importance of climate change and energy security issues has led to increased interest in the use of automotive fuels derived from biomass.1 In the United States, the Energy Independence and Security Act of 2007 established a new Renewable Fuel Standard that requires increased biofuel use (through 2022) and greater fuel economy (through 2020) for the US light-duty vehicle (LDV) fleet. The Renewable Fuel Standard mandates the use of 36 billion gallons (136 billion liters) of renewable fuel by 2022, which corresponds to replacement of approximately 17% of projected gasoline use for LDVs in 2022.2 In Europe, the Renewable Energy Directive calls for 10% use of renewable energy in the transportation sector by 2020.3 In Brazil, the production of ethanol reached 6.5 billion gallons (25 billion liters) in 2008,4 corresponding to 37% of global ethanol fuel demand4 and is projected to grow in the future. First-generation biofuels made from food crops (e.g., ethanol from sugar cane, corn, or sugar beet; biodiesel from oil seeds such as soy or rapeseed) are the primary type of biofuels used today. Ethanol produced from the fermentation of sugars accounted for approximately 85% of the total global volume of biofuels produced in 2007.5 To increase the yield, minimize direct competition with food crops, and increase the environmental benefits (i.e., reduce *To whom correspondence should be addressed. E-mail: jander63@ ford.com (J.E.A.),
[email protected] (T.J.W.). (1) International Energy Agency, Biofuels for Transport - An International Perspective; Organisation for Economic Co-Operation and Development: 2004. (2) Anderson, J. E; Baker, R. E.; Hardigan, P. J.; Ginder, J. M.; Wallington, T. J. Technical Paper Series, 09FFL-0302; Society of Automotive Engineers: 2009. (3) Directive 2009/28/EC of the European Parliament and of the Council; Official Journal of the European Union; 2009; L140/16. (4) Renewable Fuels Association, Industry Statistics: 2008 World Fuel Ethanol Production; 2010 (http://www.ethanolrfa.org/industry/statistics/#E). (5) Organisation for Economic Co-Operation and Development, Economic Assessment of Biofuel Support Policies, Directorate for Trade and Agriculture: 2008. r 2010 American Chemical Society
(6) Farrell, A. E.; Plevin, R. J.; Turner, B. T.; Jones, A. D.; O’Hare, M.; Kammen, D. M. Science 2006, 311, 506–508. (7) Atsumi, S.; Hanai, T.; Liao, J. C. Nature 2008, 451, 86–89. (8) ASTM D5798-07, Standard Specification for Fuel Ethanol (Ed75Ed85) for Automotive Spark-Ignition Engines; ASTM: 2007. (9) Mueller, S. A.; Anderson, J. E.; Wallington, T. J. J. Chem. Educ. 2009, 86, 1045–1048.
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Energy Fuels 2010, 24, 2683–2691
: DOI:10.1021/ef9014795
Andersen et al.
vehicles (FFVs) are currently the only vehicles available in the US that are designed to utilize blends greater than E10 and up to E85. In Brazil, the ProAlcool program in 1975 made it mandatory to blend 20-25% anhydrous ethanol into gasoline and vehicles were designed for compatibility with those blends.10 In addition, dedicated vehicles were developed and sold that ran only on pure hydrous ethanol (containing 5-7% water11). Recently, most new vehicles in Brazil are flexible fuel vehicles that can run on any blend containing 0% (E0) to 100% ethanol (E100), including hydrous ethanol, and thus can take advantage of the most cost-effective fuel available.11 In 2007, 86% of new cars manufactured in Brazil were FFVs.12 In Europe, low concentration blends of methanol with gasoline were sold during the 1980s and early-1990s. Flexible fuel vehicles capable of running on methanol blends with gasoline were introduced into the US in the early 1990s. The advantages of methanol included its availability and low cost. By the late 1990s, ethanol had emerged as the predominant alcohol for blending with gasoline, and flexible fuel vehicles were designed instead for ethanol blends. As of 2008, there were approximately 7 million flexible fuel vehicles on US roadways.13 With the development of second-generation biofuels it is possible that alcohols other than ethanol will enter the market. In addition, there is increasing interest in gasoline that contains alcohol concentrations different from current practice. Prior to such an introduction, a detailed knowledge of the physical and chemical properties of alcohol-gasoline blends is required and their performance in engines and impact on emissions needs to be tested. Volatility is a critical property of fuels. When ethanol and methanol are blended with gasoline, a positive azeotropic mixture is formed.14-19 At certain concentrations of ethanol this results in a blend that has a higher volatility than either the alcohol or the gasoline.20 This can make evaporative emissions more difficult to control.21 The American Society for Testing and Materials (ASTM) D86 distillation curve is a convenient and widely used standard test that describes the volatility of fuel mixtures. Limitations of the D86 method have been discussed by others previously, including the inappropriateness of its use in fluid theory applications.16 The D86 distillation curve is a plot of the temperature of the fuel vapor versus the volumetric fraction of the fuel sample distilled. In a mixture, an azeotrope
would manifest itself as a flat portion of the distillation curve at the boiling temperature of the azeotrope.17,22 While this is a necessary condition to verify that an azeotrope is present, it should be noted that a flattening of the curve can also be observed for a zeotropic mixture dominated by one component. The distillation curve provides insight into the boiling range of the fuel and can be used to predict its operation in engines. The low temperature region of the curve (up to 70 °C) can be related to ease of engine starting, engine warm-up, evaporative emissions, and vapor lock (for carbureted vehicles). The middle range of the curve (70-100 °C) can be related to warm-up, acceleration, and cold-weather performance,23 while the top range of the curve (above 150 °C) relates to propensity for combustion deposits and oil dilution.24 Although there is substantial interest in the potential use of different alcohols in blends with gasoline, the published database concerning distillation curves for alcohol-gasoline mixtures is incomplete. Distillation curves for mixtures of methanol,16 ethanol,17,25-28 and butanol23 blended with gasoline have been reported. However, to the best of our knowledge, distillation curves of propanol blends have not been reported. Also, there is little available data concerning the behavior of mixtures of two or more alcohols (e.g., ethanol and butanol) with gasoline. To better understand the volatility of alcohol-gasoline blends and their utility as motor vehicle fuels, distillation curves for gasoline and blends of 5-85% methanol, ethanol, 1- and 2-propanol, and the four butanol isomers with gasoline were determined (see Table 1). In addition, we present distillation curves for dual-alcohol blends containing 10% ethanol and 10% methanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, i-butanol, or t-butanol in gasoline as well as blends containing 10% each of methanol and 2-propanol, methanol and 1-butanol, and 2-propanol and 1-butanol (see Table 2). The results are discussed with respect to the available literature data and the use of alcohol-gasoline blends in LDVs. 2. Experimental Section The base gasoline used was Haltermann EEE gasoline (Channelview, TX). EEE gasoline is similar to “Indolene” from Amoco/BP, both of which are standard gasolines without additives used in the US Federal Test Procedure (FTP) to certify vehicles for compliance with emissions regulations. EEE gasoline has a Reid vapor pressure of 60-63 kPa (8.7-9.1 psi). The alcohols used were methanol (99.8% purity,
