A Broad Introduction to First-, Second-, and Third-Generation Biofuels

The aggregating usage of fossil fuels, rising demand for energy, fluctuating fuel prices, and increasing emissions of greenhouse gases are some of the concerning factors contributing to a shift in the interest from fossil fuels to biofuels. Biofuels are carbon-neutral sources of energy as the CO2 emissions resulting from their combustion is utilized by the plants during photosynthesis leading to no net increase in atmospheric CO2 levels. It is indispensable to focus on the new approaches to the research, development, and production of biofuels and their processing technologies to reshape a sustainable bioeconomy. Biofuels can be categorized into first, second, and third generation depending on the feedstock used for their production. The product range for first-generation biofuels is largely limited to ethanol produced from corn and distillers grains. In contrast, the second-generation biofuels are produced from non-food residues or lignocellulosic biomass such as agricultural biomass and forestry refuse, as well as energy crops. The third-generation biofuels are produced from algae, sewage sludge, and municipal solid wastes. This chapter comprehensively focuses on various first-, second-, and third-generation biofuels with emphasis on their biomass sources, fuel properties, and applications. The fuel products broadly discussed in this chapter are ethanol, butanol, bio-oil, biodiesel, algal oil, hydrogen, biomethane, and aviation fuel.