Dr. Raj Shah, Dr. Vikram Mittal and Stanley Zhang
The demand for petroleum-based fuels has escalated in response to the rapid industrialization and motorization of modern society. However, the limited availability and environmental ramifications associated with petroleum have shifted attention toward the implementation of alternative fuels, manufactured from renewable sources.
Biofuels hold several advantages over conventional fossil fuels, including reduced greenhouse gas emissions, increased resource renewability and lessened dependence on unstable foreign suppliers . In contrast, the current disadvantages associated with biofuel use stem from the higher production cost and potential threat to food security. In Part 1 of this two-part series, we look at the main types of biofuels, the current role of biofuels in the modern fuel market and recent developments in the production of advanced biofuels. The benefits and drawbacks of different biofuels will also be explored. In Part 2, we discuss the potential solutions to enhance the outlook of alternative transport fuels.
Biofuels are liquid fuels derived from renewable plant-based organic matter such as trees, crops and agricultural waste. Traditionally, biofuels are manufactured from organic feedstocks composed of edible plants, such as sugarcane, beetroot, wheat, corn, rapeseed, sunflower, soybean and palm . The type of biofuel produced is dependent on the chosen plant-based feedstock and its respective chemical conversion process. Bioethanol and biodiesel are two of the most commercially available types of biofuels on the market today.
Overview of the conversion processes of a wide variety of biofuels from an assortment of feedstocks .
Bioethanol is produced via the fermentation of sugar derived from plants or starch extracted from cereals. The most common feedstocks for ethanol production are made from sugarcane, beetroot, corn and wheat . Ethanol can be used in the form of alcohol, or it is converted into ethyl tert-butyl ether (ETBE), which is then utilized as a gasoline additive. ETBE is manufactured industrially by the acidic etherification of isobutylene with ethanol and functions as an octane number enhancer, while improving combustion .
Ethanol has advantages as a renewable bio-based resource and is oxygenated, providing potential benefits toward the reduction of particulate emissions in compression-ignition (CI) engines. Alcohol can be used as an alternative transportation fuel, as its properties allow for its use in existing engines with only minor modifications . Compared to gasoline, alcohol has higher octane ratings, which allows the fuel to endure higher compression ratios before engine knocking occurs. Additionally, bioalcohol fuel burns cleaner than traditional gasoline and has a higher heat of vaporization, resulting in lower carbon monoxide, hydrocarbon and nitrogen oxide emissions .
Currently, gasoline-ethanol blends containing up to 10% ethanol by volume are readily used by most vehicles. Ethanol content is limited to E10 for most engines in vehicles [manufactured before 2001] due to ethanol’s more aggressive reactivity with materials compared to traditional gasoline. Ethanol can dissolve lubricant layers between metal components, deform elastomers and increase risk of electrolytic or galvanic corrosion . Corrosion inhibitors and other compatible additives are often incorporated into gasoline-ethanol blends to combat these potential issues. Flexible fuel vehicles can utilize E85, which refers to blends with up to 85% ethanol .
Biodiesel is produced from vegetable oils, animal fats and short chain alcohols. The prevailing raw materials used in biodiesel feedstock are rapeseed, soybean, palm and sunflower oils. Oils are reacted with short chain alcohols, typically methanol, and undergo a transesterification process to yield a mixture of fatty acids methyl esters (FAME). Then, this mixture is subjected to successive water washing steps to remove water-soluble remnants of methanol, catalyst and glycerin . The purified product is incorporated in blends with conventional petroleum diesel, such as B2, B5 and B20, which are composed of 2%, 5% and 20% biodiesel, respectively . Sharing multiple similarities with mineral diesels, biodiesel blends below 20% are readily used in modern CI engines without major modifications. However, biodiesel blends above B20 should not be considered as direct replacements for petroleum diesel and may require additional handling precautions, along with fuel system or engine modifications.
High percentage biodiesel blends have comparatively worse cold flow properties, thus further attention may be necessary to ensure that the blend will not gel and clog fuel filters in colder conditions. Material compatibility could become a potential issue as well because fuel system components that contain elastomers and rubbers may soften or degrade when in contact with blends like B100. Additionally, high blend biodiesels may dissolve sediments and deposits left by petroleum diesel, causing clogging in fuel filters and requiring frequent filter changes . With appropriate measures to address these plausible obstacles, biodiesels can have several advantages over conventional petroleum diesels in terms of air quality preservation, engine operation and safety. The use of biodiesel reduces life-cycle emissions, as the carbon dioxide produced from the combustion of biodiesel is offset by the carbon dioxide absorbed from the feedstock plants grown to produce the fuel. Life-cycle analyses have shown that the use of pure, unblended B100 biodiesel over mineral diesel can reduce carbon emissions by up to 74% . Incorporating biodiesel in fuel blends can increase fuel lubricity and raise the cetane number of the fuel, resulting in improved engine performance and enhanced protection against wear. The handling, storage and transport of biodiesel is safer than conventional diesel because it is less combustible and causes far less damage if accidentally released into the environment .
Current State of Biofuel Applications
The modern biofuels market is dominated by the United States and Brazil, with the combined shares of both countries accounting for 87% of the 2,616 thousand barrels produced per day in 2018. The United States is the leading producer of biogasoline and biodiesel, with production shares of 55.4% and 19.4% respectively . Corn is the primary feedstock for ethanol production in the U.S., while soybeans are the predominant choice for biodiesel production. Similarly, Brazil mainly produces biodiesel with soybean feedstocks, but utilizes sugarcane for ethanol fuel. Brazil is the second-largest contributor to the worldwide production of biofuels, having a 31.5% share in biogasoline and a 14.1% share in biodiesel . Germany, Argentina and China rank third, fourth and fifth, respectively, in the global production of biofuels. According to the International Energy Agency (IEA), global biofuel production experienced a record 7% increase from 2017 to 2018, and a forecasted 24% growth is expected to occur from 2019-2024 .
The success of biofuels has largely been attributed to the advantages that they provide over traditional fossil fuels. As an exhaustible resource, fossil fuels are heavily limited in regard to long-term sustainability. In contrast, biofuels are produced from renewable feedstocks and could theoretically be sustained indefinitely, as long as feedstock crops are consistently grown. In addition, feedstock crops can be domestically cultivated, which allows for the domestic production of biofuels. If the use of biofuels reduces the consumption of mineral oils, this could lower U.S. dependence on foreign petroleum imports and decrease vulnerability to supply disruptions . Due to the cleaner combustion of biofuels, fewer greenhouse gases (GHGs) are emitted, and the growth of the plants used in biofuel feedstock can mitigate the pollutant emissions that are produced. However, it is important to note that peak benefits only occur in circumstances where fossil fuel consumption and use are reduced in favor of biofuels .
Currently, biofuels have a few disadvantages that are hindering their development as the premier transport fuel over petroleum products. According to the U.S. Energy Information Administration (EIA), petroleum products account for about 91% of the total U.S. transportation sector use, while biofuels have contributed to a comparatively measly 5% . A major factor limiting the prevailing use of biofuels resides in their potential risk to food security. Biofuels produced from edible plant-based feedstocks depend on the same crops commonly used for food production. This shared pool of edible plant resources is limited by the amount of arable land available for agriculture. Consequently, increased production of conventional biofuels would cause the price of food to rapidly surge in response to escalating crop demand for both food and fuel production . This would result in increased risk of hunger for individuals in developing countries and raise the production cost of biofuels, reducing the economic feasibility of large-scale manufacturing. However, recent developments have been made addressing the “food versus fuel” dilemma.
Dr. Raj Shah is a director at Koehler Instrument Company, a leading manufacturer of petroleum testing instruments, and an active ASTM member for the past 25 years. He has held numerous leadership positions within various ASTM committees and is a three-time recipient of the ASTM award of Excellence. Contact him at email@example.com.
Dr. Vikram Mittal is an assistant professor at the United States Military Academy in the Department of Systems Engineering. He earned his doctorate in Mechanical Engineering at the Massachusetts Institute of Technology, where he researched the relevancy of the octane number in modern engines.
Stanley Zhang is a chemical engineering student at Stony brook University, where Dr. Shah is the chair of the Advisory board of directors and Zhang is also a part of a thriving internship program at Koehler instrument company
 “Economics Biofuels.” EPA, United States Environmental Protection Agency.
 “What future for biofuels?” IFPEN. IFP Energies nouvelles.
 Agarwal, Avinash K. “Biofuels (alcohols and biodiesel) applications as fuels for internal combustion engines.” Progress in Energy and Combustion Science, vol. 33, no. 3, 2007, pp. 233-271.
 de Menezes, Eliana W., and Cataluña, Renato. “Optimization of ETBE (ethyl tert-butyl ether) production process.” Fuel Processing Technology, vol. 89, no. 11, 2008, pp. 1148-1152.
 “E10 compatibility issues.” Advanced Motor Fuels.
 “Biofuels Basics.” US Office of Energy Efficiency & Renewable Energy.
 Romano, Silvia D., and Sorichetti, Patricio A. “Introduction to Biodiesel Production.” Dielectric Spectroscopy in Biodiesel Production and Characterization. Springer, 2011, pp. 7-24.
 “Biofuels explained.” EIA. US Energy Information Administration. 26 Aug. 2020.
 “Guidance on Blends Above B20.” National Biodiesel Board. Nov. 2007
 “Biodiesel Benefits and Considerations.” AFDC. US Office of Energy Efficiency & Renewable Energy.
 Besta, Shankar. “Top five countries for biofuel production across the globe.” NS Energy. 15 Nov. 2019.
 “Transport.” Renewables 2019. IEA. Oct. 2019.
 “Advantages of Biofuels.” Biofuel UK.
 “Use of energy explained.” EIA. US Energy Information Adminstration. 2 Jun. 2020.
 “Disadvantages of Biofuels.” Biofuel UK.