Biodiesel is a proven fuel. The conversion of vege­table oil to biodiesel was first described as early as 1853 by Patrick Duffy, many years before the first diesel engine became functional (Duffy, 1853). Rudolf Diesel’s engine was built several years later, running for the first time on August 10, 1893 using nothing but peanut oil feedstock. In a 1912 speech, Diesel said, "the use of vege­table oils for engine fuels may seem insignificant today but such oils may become, in the course of time, as important as petroleum and the coal-tar products of the present time."

Fossil fuel-derived petrodiesel is produced from the fractional distillation of fossil fuel crude oil. It contains ~75% saturated hydrocarbons and 25% aromatic hy­drocarbons (including naphthalenes and alkylben — zenes). Compared to petrodiesel, biodiesel molecules are comprised almost entirely FAME saturated, or monosaturated, hydrocarbons and ~ 5% aromatic com­pounds. Table 10.2 shows a comparison between the properties of biodiesel to petrodiesel. Biodiesel has a higher lubricity and thus better lubricating properties

than fossil diesel, which reduces wear on fuel systems and engine components. Biodiesel likewise has higher cetane ratings than today’s lower sulfur diesel fuels. The cetane number is a measure of a fuel’s ignition delay, or the time period between the start of injection and the first identifiable pressure increase during com­bustion of the fuel; the higher the cetane number the more easily the fuel will combust. Therefore higher ce­tane biodiesel should cause an engine to run more smoothly and quietly. Biodiesel’s higher flash point makes biofuel vehicles much safer in accidents than those powered by petrodiesel or gasoline. Biodiesel is biodegradable and nontoxic and also contains little to no sulfur, which makes it a much cleaner burning fuel compared to petrodiesel (Hai et al., 2000; Anderson et al., 2002; Hoekema et al., 2002; Choi et al., 2003; Grima et al., 2003; Zijffers et al., 2008; Brindley et al., 2011).

Biodiesel has higher oxygen content than petrodie — sel, which can also reduce pollution emissions. How­ever, this benefit is offset by the fact that biodiesel is more likely to oxidize (react with oxygen), producing contaminants (gumming/sludge) that will plug fuel filters, leave deposits on injectors and cause injector pump problems. Further, continuous oxidization leads to the fuel becoming more acidic, which in turn causes corrosion on the components in the injection system. It will also dissolve fossil-diesel sludge built up over time and send it through fuel lines, plugging fuel fil­ters. Biodiesel cloud or gel point is higher than pump diesel, meaning that it tends to gel at low tem­peratures more readily which can lead to poor cold starting. Clearly, there are both benefits and draw­backs for using biodiesel in today’s automobile engines.

BIOETHANOL

First-generation bioethanol is usually produced by alcoholic fermentation of starch (e. g. corn and wheat) or sugar (e. g. sugarcane, sugar beet and sweet sorghum). Second-generation bioethanol feedstocks include ligno- cellulosic grasses, woody biomass, and algae. Bioethanol is an already well-established fuel in Brazil and the USA (Goldemberg, 2007). Owing to mandates enacted by the Brazilian government in 1976, all light-duty fleet vehi­cles are required to operate using a blend of gasoline and bioethanol fluctuating between 10% and 25%, or E10—E25. In 2003, the Brazilian car manufacturing in­dustry introduced flexible-fuel vehicles that can run on any proportion of gasoline (E20—E25 blend) and hy­drous ethanol (E100) (Horta Nogueira, 2004). Sales reached an impressive 92.3% share of all new cars and light-vehicle sales for 2009, and overall bioethanol pro­duction reached 5.5 billion U. S. liquid gallons.

Although the vast majority of bioethanol is produced by fermentation of corn glucose in the United States or sugarcane sucrose in Brazil (Rosillo-Calle and Cortez, 1998), bioethanol can be derived from any material that contains sugars, including microalgae. Unlike land-based food crops, the production of bioethanol from microalgae does not divert agricultural foods away from grocer’s shelves. This is especially true for corn and corn products, which serve as base ingredients of many processed foods. Further, microalgae can be cultivated in areas nonsuitable for traditional agricul­tural crops and can be harvested many times a year. Therefore, in the U. S., microalgae are generally thought to be the only practical alternative to current bioethanol crops such as corn and soybean (Chisti, 2007; Hu et al., 2008; Singh and Gu, 2010).

Matsumoto et al. (2003) screened several strains of marine microalgae with high-carbohydrate content and identified a total of 76 strains with a carbohydrate con­tent ranging from 33% to 53% . It has been estimated that approximately 46—140 kl of ethanol/ha year can be produced from microalgae (Mussatto, 2010). This yield is several orders of magnitude higher than yields obtained from other bioethanol feedstocks (Table 10.3).