Biofuel

Biofuel is any liquid fuel made from “biomass”—that is, plants and other biological matter like animal waste and leftover cooking fat. Biofuels can be used as replacements for petroleum-based fuels like gasoline and diesel.

As we search for fuels that won’t contribute to the greenhouse effect and climate change, biofuels are a promising option because the carbon dioxide (CO₂) they emit is recycled through the atmosphere. When the plants used to make biofuels grow, they absorb CO₂ from the air, and it’s that same CO₂ that goes back into the atmosphere when the fuels are burned. In theory, biofuels can be a “carbon-neutral” or even “carbon-negative” way to power cars, trucks and planes, meaning they take at least as much CO₂ out of the atmosphere as they put back in.

A major promise of biofuels is that they can lower overall CO₂ emissions without changing a lot of our infrastructure. They can work with existing vehicles, and they can be mass-produced from biomass in the same way as other biotechnology products, like chemicals and pharmaceuticals, which are already made on a large scale. In the future, we may also be able to move large amounts of biofuels through existing pipelines.

Toward advanced biofuels

Today, many different biofuels are in production, made in many different ways. The most common process is to use bacteria and yeast to ferment starchy foods like corn into ethanol, a partial replacement for gasoline. Most gasoline sold in the U.S. is mixed with 10% ethanol.

Newer research in biofuels aims to produce higher-grade fuels like jet fuel; to create cleaner-burning fuels that are better for the environment and human health; or to use less valuable biomass like algae, grasses, woody shrubs, or waste from cooking, logging and farming. While some of these “advanced biofuels” are already in production, none are being used in nearly the amounts of “first-generation” ethanol and biodiesel.

Climate challenges

There are many challenges to making biofuels that are truly carbon neutral. That’s because many steps used to create biofuels—fermentation, the energy for processing, transportation, even the fertilizers used to grow plants—may emit CO₂ and other greenhouse gases even before the fuels are burned. The farmland used to grow biomass can also have its own climate impacts, especially if it takes the place of CO₂-storing forests. This means that the details of how biofuels are made and used are very important for their potential as a climate solution.

Published September 3, 2020.