Liquid Biofuels: Ethanol and Biodiesel

Liquid biofuels are transportation fuels including such fuels as ethanol, biodiesel, renewable diesel, and sustainable aviation fuels. The federal government promotes biofuels as transportation fuels to help reduce oil imports and CO2 emissions. In 2007, the U.S. government set a target to use 36 billion gallons of biofuels by 2022. As a result, nearly all gasoline now sold in the United States contains some ethanol. Traditional biodiesel and ethanol are a part of the four generations of biofuels currently existing.  These “generations” are characterized by the feedstocks used, their limitations as a renewable source of energy, and their technological progress.

The product range for first-generation biofuels is largely limited to ethanol produced from corn and distillers grains. In contrast, 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. The new “fourth-generation” biofuels are the result of recent developments in plant biology and biotechnology (metabolic engineering) in the field of carbon capture and storage techniques.

Historically, first-generation liquid biofuels (ethanol in particular) faced two major criticisms: (1) competition with food resources (the food versus fuel debate); and (2) that ethanol production from corn grain required significant consumption of fossil resources, in such a way that there was arguably minimum benefits from a “carbon emissions” perspective.  As we progressed to second-generation biofuels (cellulosic-ethanol), we utilized supportable, nonfood feedstocks like waste vegetable oil, forest residue, industry residue, and sustainable biomass, eliminating the food v. fuel debate. The third-generation biofuels are often known as “algae fuel” as they are produced from the algae.  Algae can be used to produce all types of biofuels, like biodiesel, gasoline, butanol, propanol, and ethanol with yields often 10 times higher than the second-generation biofuels. Cultivation of third-generation biofuel biomass also assists in maintaining environmental balance by consuming the CO₂ present in the atmosphere. The difficulty here has been to do this cost-effectively.  The newer fourth generation biofuels require an advanced method for production, but certainly hold great promise as these bio-engineered plants, trees & algae serve as carbon capture machines.

World governments support efforts to develop alternative sources of biomass that do not compete with food crops and use less fertilizer and pesticides than traditional corn and sugar cane. They also support biofuels production methods that require less energy than conventional fermentation. As advanced continue, we should see more of these renewable fuels being made from waste, creating a “win-win” situation worldwide.

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