Ethanol as Oxygenated and Renewable Fuel

Oxygenated fuel is conventional gasoline that has been blended with an oxygenated hydrocarbon to achieve a certain desired concentration level of oxygen in the blended fuel. Oxygenated fuel is required by the Clean Air Act Amendments of 1990 for areas that do not meet federal air quality standards, especially those for carbon monoxide. The oxygen present in the blended fuel helps the engine to burn the fuel more completely, thus emitting less carbon monoxide. Extra oxygen already present in situ in the oxygenated fuel formulation helps efficient conversion into carbon dioxide rather than carbon monoxide. Gasoline blends of at least 85% ethanol are considered alternative fuels under the Energy Policy Act of 1992 (EPAct). E85 is used in flexible fuel vehicles (FFVs) that are currently offered by most major automobile manufacturers. FFVs can run on 100% gasoline, E85, or any combination of the two and qualify as alternative fuel vehicles under EPAct regulations.

Reformulated gasoline is a formulation of gasoline that has lower controlled amounts of certain chemical compounds that are known to contribute to the formation of ozone (O3) and toxic air pollutants. It is less evaporative than conventional gasoline during the summer months, thus reducing evaporative fuel emission and leading to reduced volatile organic compound emission. It also contains oxygenates, which increase the combustion efficiency of the fuel and reduce carbon monoxide emission. The Clean Air Act Amendments of 1990 require RFG to contain oxygenates and have a minimum oxygen con­tent of 2.0% oxygen by weight. RFG is required in the most severe ozone nonattainment areas of the United States. Other areas with ozone problems have voluntarily opted into the program. The U. S. EPA has implemented the RFG program in two phases: Phase I for 1995 to 1999 and Phase II having begun in 2000.

To be more specific, the Clean Air Act Amendments mandated the sale of reformulated gasoline in the nine worst ozone nonattainment areas beginning January 1, 1995. Initially, the U. S. EPA determined the nine regulated areas to be the metropolitan areas of Baltimore, Chicago, Hartford, Houston, Los Angeles, Milwaukee, New York City, Philadelphia, and San Diego. The impor­tant parameters for RFG by the Clean Air Act Amendments of 1990 were

1. At least 2% oxygen by weight

2. A maximum benzene content of 1% by volume

3. A maximum of 25% by volume of aromatic hydrocarbons

As of 2011 in the United States, RFG is required in cities with high smog levels and is optional elsewhere. RFG is currently used in 17 states and the District of Columbia. About 30% of gasoline sold in the United States as of 2011 is reformulated.

Methyl tertiary-butyl ether was one of the most commonly used oxygen­ated blend fuels until recent claims arose of health and environmental prob­lems associated with MTBE used as a blending fuel. Tertiary-amyl methyl ether (TAME), ethyl tertiary-butyl ether, and ethanol have also been used in oxygenated and reformulated fuels. Responding to the rapid phase-out of MTBE in the United States, ethanol has gained the most popularity as a blending fuel, based on its clean burning, relatively low Reid vapor pres­sure, the renewable nature of the fuel, minimal or no health concerns, and relatively low cost.

The RFG should have no adverse effects on vehicle performance or the durability of engine and fuel system components. However, there may be a slight decrease in fuel mileage (1 to 3% or 0.2-0.5 mile/gallon) in the case with well-tuned automobiles due to the higher concentrations of oxygenates that inherently have lower heating values. However, RFG burns more com­pletely, thereby reducing formation of engine deposits and often boosting the actual gas mileage, particularly for older engines.

The Reid vapor pressure is crucially important information for blended gasoline from practical and regulatory standpoints. Evaporated gasoline compounds combine with other pollutants on hot summer days to form ground-level ozone, commonly referred to as smog. Ozone pollution is of particular concern because of its harmful effects on lung tissue and breath­ing passages. Therefore, the government, both federal and state, imposes an upper limit as a requirement, which limits the maximum level reformu­lated gasoline can have as its Reid vapor pressure. By such regulations, the government not only controls the carbon monoxide emission level, but also limits the evaporative emission of the fuel. Due to this limit, certain oxygen­ates may not qualify as a gasoline blending fuel even if they may possess excellent combustion efficiency and high octane rating. One such example is methanol. Furthermore, the legal limits for the Reid vapor pressure depend
upon many factors including current environmental conditions, geographi­cal regions, climates, time of the year (such as summer months vs. winter months), and the like. It should also be noted that ground-level ozone is harmful to humans, whereas stratospheric ozone is essential and beneficial for global environmental safety.

The oxygenated fuel program (OFP) is a winter-time program for areas with problems of carbon monoxide air pollution. The oxygenated winter fuel program uses normal gasoline with oxygenates added. On the other hand, the reformulated gasoline program is for year-round use to help reduce ozone, CO, and air toxins. Although both programs use oxygenates to reduce CO, RFG builds on the benefit of oxygenated fuel and uses improvements in the actual formulation of gasoline to reduce pollutants including volatile organic compounds [35].

Although methyl-tertiary-butyl ether was once credited with significantly improving the nation’s air quality, it has been found to be a major contributor to groundwater pollution. Publicity about the leaking of MTBE from gasoline storage tanks into aquifers as well as its adverse health effects has prompted legislators from the midwestern United States to push for a federal endorse­ment of corn-derived ethanol as a substitute oxygenate. Many U. S. states including California and New York mandated their own schedules of MTBE phase-outs and bans. This MTBE phase-out has served as an incentive for corn ethanol industries for marketing their products as being environmen­tally more acceptable than other alternatives and at the same time renewable.

The Energy Policy Act of 2005 (EPAct 2005, P. L. 110-58), established the first-ever renewable fuels standard (RFS) in federal law, requiring increas­ing volumes of ethanol and biodiesel to be blended with the U. S. fuel sup­ply between 2006 and 2012. The Energy Independence and Security Act of 2007 (P. L. 110-140, H. R. 6) amended and increased the RFS, requiring 9 billion

Подпись: New RFS Schedule FIGURE 3.8 New renewable fuels standard (RFS) indicating the total amount of renewable fuel use for 2008 through 2022. (Courtesy of the American Coalition for Ethanol. 2010. All About Ethanol (October). Available at: http://www.ethanol.org/.) 40

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gallons of renewable fuel use in 2008, stepping up to 36 billion gallons by 2022, as shown in Figure 3.8. A major portion of the increase is expected to come from cellulosic ethanol.

Considering the annual gasoline consumption in the United States to be approximately 140 billion gallons and also assuming that all gasoline sold in the United States is blended with ethanol up to 10% (i. e., E10), the total annual demand for ethanol by E10 in the United States would be about 15.5 million gallons. One can readily notice that this estimated saturation point for etha­nol demand in the United States for E10 blend is not far from the 2010 total U. S. ethanol production from corn, which was 13.2 million gallons. Thus, it is evident that the RFS numbers for future years are based on (a) expanded use of nonethanol renewable fuels such as biodiesel, (b) increased availability of cellulosic ethanol, (c) expanded adoption of alternative fuel vehicles (AFVs) and flexible fuel vehicles (FFVs), and more.