Distributed, Integrated Production of Second and Third Generation Biofuels

Abstract

Materials that are burned directly for energy, such as firewood, wood chips, pellets, animal waste, forest and crop residues are considered primary biofuels. First generation biofuels also include bioethanol produced by fermentation of starch (from wheat, barley, corn, or potato) or sugars (from sugarcane or sugar beet), and biodiesel produced by transesterification of oil crops (including rapeseed, soybeans, sunflower, palm, coconut) and animal fats. Second generation biofuels include bioethanol and biodiesel produced from the residual, non-food parts of crops, and from other forms of lignocellulosic biomass such as wood, grasses, and municipal solid wastes (Inderwildi & King, 2009). Third generation biofuels include algae-derived fuels such as biodiesel from microalgae oil, bioethanol from microalgae and seaweeds, and hydrogen from microalgae and microbes (Aylott, 2010; Dragone, et al., 2010). “Drop fuels like green gasoline, green diesel, and green aviation produced from biomass are considered fourth generation biofuels (Kalita, 2008). Efforts are also underway to genetically engineer organisms to secrete these fourth generation hydrocarbon fuels. Today, corn is the major source of first-generation bioethanol, with over 12 billion gallons of fuel ethanol produced in 2010 from approximately 4.6 billion bushels of corn (Anon, 2011b) in 190 operating facilities in 26 states. Most are located in the Midwest, near the site of feedstock production (Figure 1), however some are co-located with dairies or beef cattle feeding operations or dairies outside the Corn Belt. The typical size of corn ethanol plants is 50-100 million gallons per year. Table 1 provides a summary of industry growth in the US over the past decade. Ethanol is also the most important biofuel worldwide in terms of volume and market value (Licht, 2006). In 2007, Congress passed the Renewable Fuels Standard 1 (RFS1), which mandated renewable fuel use of 7.5 billion gallons by 2012. Congress subsequently passed the Energy Independence and Security Act of 2007 (EISA), which made significant changes in the structure and magnitude of the renewable fuel program. The EISA (also called the RFS2) specified use of a total of 15.2 billion gallons/year of renewable fuel by 2012 and 36 billion gallons/year by 2022.1 Also mandated were maximal amounts of corn-based ethanol,