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08.09

Biofuel Review: Part 1 — Biofuel Basics

By Patrick E. MEyer

Introduction

A biofuel is any type of liquid or gaseous fuel that can be produced from biomass and that can be used as a full or partial substitute for fossil fuels (Giampietro et al., 1997). There are two basic biofuel types used in the United States — namely, biodiesel and ethanol — and a handful of other fuels which classify as having a biological feedstock. Both biodiesel and ethanol have numerous specific incarnations, dependent on production, type of feedstock, and fuel blend.

Despite all the hype, biofuel usage has been quite limited. In 2000, only 44 million gasoline gallon equivalent (gge) of ethanol (E85) and biodiesel were consumed, excluding ethanol in gasohol. The number rose nearly seven fold to over 304 million gge in 2006 (most recent reliable data), but petroleum consumption still accounted for over 94 percent of all transportation energy consumption (Davis et al., 2009).

Biofuel usage has become a heated debate, with numerous critical issues surrounding its production, transportation, and consumption. Over the next year, Today's Engineer will review ten of the most critical issues encompassing the biofuel debate, in six bi-monthly articles. This article, the first in the series, is an introductory article which discusses the basics of each major biofuel type: biodiesel, ethanol, and other fuels. The second article will focus on the carbon emissions impacts of biofuels, and the transportation, distribution, and infrastructure of biofuel systems. Future articles will focus on land availability, and deforestation and land conversion; the food versus fuel and profit versus hunger arguments; impacts on water usage and biodiversity; and impacts on jobs and government spending.

Biodiesel

Biodiesel is a domestically produced, renewable fuel that can be manufactured from soybeans and similar vegetables, vegetable oils, animal fats, or recycled restaurant greases. The interest in biodiesel as an alternative transportation fuel stems mainly from its renewable, domestic production; its safe, clean-burning properties; and its compatibility with existing diesel engines (EERE, 2009d). The EERE (2009e) argues that biodiesel is safe and biodegradable, and its use significantly reduces greenhouse gas emissions and serious toxic air pollutants.

Specifically, biodiesel is a liquid fuel made up of fatty acid alkyl esters, fatty acid methyl esters (FAME), or long-chain mono alkyl esters. Like petroleum diesel, biodiesel is used to fuel compression-ignition (diesel) engines and thus is a suitable replacement for petroleum-based diesel fuel (EERE, 2009e).

Biodiesel can be legally blended with petroleum diesel in any percentage. The percentages are designated as B20 for a blend containing 20 percent biodiesel and 80 percent petroleum diesel, B100 for 100 percent biodiesel, and so forth (EERE, 2009d). B100 contains no petroleum, but is not compatible with most automobile engines. Thus, B20, a fuel blend, is the most common type of biodiesel used in the United States.

The United States makes its biodiesel primarily from soybean oil, whereas Europe uses rapeseed and sunflower oil, and other countries, like Malaysia use palm oil. Biodiesel can also be produced from vegetable oils, tallow and animal fats, and restaurant waste and trap grease (EERE, 2009c). Although biodiesel can be made from raw vegetable oil, the biodiesel available for sale at refueling stations is not of the same makeup as vegetable oil. Fuel-grade biodiesel must be produced to strict industry specifications (ASTM D6751) in order to insure proper performance (NBB, 2009).

According to the National Biodiesel Board, biodiesel is the only alternative fuel to have fully completed the health effects testing requirements of the 1990 Clean Air Act Amendments. Biodiesel that meets ASTM D6751 and is legally registered with the Environmental Protection Agency is a legal motor fuel for sale and distribution. Raw vegetable oil cannot meet biodiesel fuel specifications, it is not registered with the EPA, and it is not a legal motor fuel.

In 2006 (most recent reliable data), about 260 million gge of biodiesel were consumed by the transportation sector. While this amount may seem noteworthy an accomplishment for the biodiesel sector, in the grand scheme the amount is miniscule when compared to total highway fuel use, which reached 175 billion gallons in 2006 (Davis et al., 2009).

Ethanol

Ethanol is a renewable fuel made from various plant materials, which collectively are called "biomass." Ethanol contains the same chemical compound (C2H5OH) found in alcoholic beverages. Nearly half of U.S. gasoline contains ethanol in a low-level blend to oxygenate the fuel and reduce air pollution. Ethanol used in gasoline results in a cleaner-burning fuel with higher octane (ethanolfacts.com, 2007). This blend is referred to E10 or gasohol and contains 10 percent ethanol and 90 percent gasoline; almost 5 billion gge of ethanol were consumed in 2007 in the United States as part of a gasohol mix (Davis et al., 2009). Ethanol is also increasingly available in E85, an alternative fuel that can be used in flexible fuel vehicles (EERE, 2009f).

Ethanol is made of the same chemical compound whether it is produced from starch- and sugar-based feedstocks such as corn grain (as it primarily is in the United States) and sugar cane (as it primarily is in Brazil) or from cellulosic feedstocks (EERE, 2009g). Making ethanol from cellulosic feedstocks — such as grass, wood, crop residues, or old newspapers — is more challenging than using starch or sugars. These materials must first be broken down into their component sugars for subsequent fermentation to ethanol in a process called biochemical conversion (EERE, 2009g).

A primary concern with ethanol production is its reliance on corn as a feedstock. According to the U.S. Congressional Research Service (CRS):

Current U.S. biofuel supply relies almost exclusively on ethanol produced from Midwest corn. In 2006, 17% of the U.S. corn crop was used for ethanol production. To meet some of the higher ethanol production goals would require more corn than the United States currently produces, if all of the envisioned ethanol was made from corn. … a significant increase in U.S. biofuels would likely require a movement away from food and grain crops. Other biofuel feedstock sources, including cellulosic biomass, are promising, but technological barriers make their future uncertain (Yacobucci and Schnepf, 2007).

Because of complications associated with the widespread production of both biodiesel and ethanol, many experts have argued that the transportation sector is in need of a diverse portfolio of biofuel options and automotive technologies that are flexible enough to accommodate a range of fuels. In this case, biodiesel and ethanol may serve as base fuels, but there would be a number of other supplemental fuels, which are discussed as follows.

Other Fuels: Biobutanol, Biogas, and Hydrogenation-Derived Renewable Diesel

Dürre (2007) argues that biodiesel and ethanol have inherent limitations due to their reliance on fossil fuel blending and a limited feedstock, and that these limitations can be overcome by alternative native biofuels such as biobutanol. Regular butanol is a four-carbon alcohol (butyl alcohol). Biobutanol, on the other hand, is butanol produced from biomass feedstocks. Like ethanol, biobutanol is a liquid alcohol fuel that can be used in today's gasoline-powered internal combustion engines. The properties of biobutanol make it highly amenable to blending with gasoline. It is also compatible with ethanol blending and can improve the blending of ethanol with gasoline. Biobutanol proponents claim that today's vehicles can be fueled with high concentrations of biobutanol — up to 100 percent - with minor or no vehicle modifications, although testing of this claim has been limited (EERE, 2009a).

Biogas is the gaseous product of the anaerobic digestion (decomposition without oxygen) of organic matter. It is typically made up of 50-80 percent methane, 20-50 percent carbon dioxide, and traces of gases such as hydrogen, carbon monoxide, and nitrogen. Biogas is sometimes called swamp gas, landfill gas, or digester gas. When its composition is upgraded to a higher standard of purity, it can be called renewable natural gas (EERE, 2009b). It has been shown that compared with other biomass-based vehicle fuels available today, biogas often has several advantages from an environmental and resource-efficiency perspective (Börjesson and Mattiasson, 2008).

In rural communities, small-scale digesters provide biogas for single-household cooking and lighting. China alone is estimated to have 8—17 million of these systems. A 2007 report estimated that 12,000 vehicles are being fueled with upgraded biogas worldwide, with 70,000 biogas-fueled vehicles predicted by 2010. Europe has most of these vehicles. Sweden alone reports that more than half of the gas used in its 11,500 natural gas vehicles is biogas. Germany and Austria have established targets of 20 percent biogas in natural gas vehicle fuel (EERE, 2009b).

Hydrogenation-derived renewable diesel (HDRD) is the product of fats or vegetable oils — alone or blended with petroleum — that have been refined in an oil refinery. This involves hydrogenation of triglycerides using existing refinery infrastructure (IEA, 2008). HDRD produced in this manner is sometimes called a "second-generation biodiesel." Although largely unproven, it is expected that HDRD will substitute directly for or blend in any proportion with petroleum-based diesel, without modification to vehicle engines or fueling infrastructure. HDRD is not widely available at present, but it is likely to become fully commercialized in the near future. A number of producers have commercial trials underway (EERE, 2009c).

Conclusion

It is estimated that biofuels will continue to constitute a greater percentage of total liquid fuel consumption in the United States and around the globe. The Energy Information Administration estimates that domestic production of ethanol and biodiesel will increase 88 and 156 percent from 2010 to 2030, respectively. So called second generation biofuels, or liquids from biomass, will increase from essentially zero to 330 thousand barrels per day by 2030 [EIA, 2009].

Yet, numerous concerns remain unresolved, such as: the carbon and emissions impacts of biofuels; the transportation, distribution, and infrastructure systems; land availability, deforestation, and conversion; the food versus fuel and profit versus hunger debates; impacts on water use and biodiversity; and impacts on jobs and government spending. Over the next year, I will discuss these issues in-depth, providing research and analysis on each topic with the goal of educating the readership and fostering discussion on biofuel issues. 

References

1. Börjesson, P., & Mattiasson, B. (2008). Biogas as a resource-efficient vehicle fuel. Trends in Biotechnology 26(1), 7-13.

2. Davis, S., Diegel, S., & Boundy, R. (2009). Transportation Energy Data Book: Edition 28. Oak Ridge, TN: Oak Ridge National Laboratory.

3. Dürre, P. (2007). Biobutanol: An attractive biofuel. Biotechnology Journal, 2(12), 1525-1534.

4. EERE. (2009a). Alternative & Advanced Fuels: What is biobutanol. Retrieved 29 July 2009, from http://www.eere.energy.gov/afdc/fuels/emerging_biobutanol_what_is.html

5. EERE. (2009b). Alternative & Advanced Fuels: What is biogas. Retrieved 29 July 2009, from http://www.eere.energy.gov/afdc/fuels/emerging_biogas_what_is.html

6. EERE. (2009c). Alternative & Advanced Fuels: What is Hydrogenation-Derived Renewable Diesel? Retrieved 29 July 2009, from http://www.eere.energy.gov/afdc/fuels/emerging_green_what_is.html

7. EERE. (2009d). Alternative and Advanced Fuels: B20 and B100: Alternative Fuels. Retrieved 29 July 2009, from http://www.eere.energy.gov/afdc/fuels/biodiesel_alternative.html

8. EERE. (2009e). Alternative and Advanced Fuels: Biodiesel Basics. Retrieved 29 July 2009, from http://www.eere.energy.gov/afdc/fuels/biodiesel_basics.html

9. EERE. (2009f). Fuels: Ethanol: Ethanol Basics. Retrieved 29 July 2009, from http://www.eere.energy.gov/afdc/ethanol/basics.html

10. EERE. (2009g). Fuels: Ethanol: What is Ethanol? Retrieved 29 July 2009, from http://www.eere.energy.gov/afdc/ethanol/what_is.html

11. EIA. (2009). Annual Energy Outlook 2009 with Projections to 2030, Updated Annual Energy Outlook 2009 Reference Case with ARRA: Table 11, Liquid Fuels Supply and Disposition. Washington, DC: Energy Information Administration.

12. ethanolfacts.com. (2007). Ethanol Basics: What ethanol is and what it does. Retrieved 29 July 2009, from http://www.ethanolfacts.com/ETHL2007/ebasics.html

13. Giampietro, M., Ulgiati, S., & Pimentel, D. (1997). Feasibility of Large-Scale Biofuel Production: American Institute of Biological Sciences.

14. IEA. (2008). Analysis and Identification of Gaps in Research for the Production of Second-Generation Liquid Transportation Biofuels: IEA Bioenergy, U.S. Department of Energy, and Purdue University.

15. NBB. (2009). Biodiesel Basics. Retrieved 29 July 2009, from http://www.biodiesel.org/resources/biodiesel_basics/

16. Yacobucci, B., & Schnepf, R. (2007). Ethanol and Biofuels: Agriculture, Infrastructure, and Market Constraints Related to Expanded Production. Washington, DC: U.S. Congressional Research Service.

Patrick E. Meyer is a doctoral student and research associate at the University of Delaware’s Center for Energy and Environmental Policy and is also a research associate with Energy and Environmental Research Associates, LLC., Pittsford, New York, specializing in energy and environmental life-cycle analysis. Meyer also serves on the IEEE-USA Communications Committee and is IEEE-USA Today’s Engineer Energy, Environment & Sustainability Editor.

Comments may be submitted to todaysengineer@ieee.org.