Why are certain crops used to make biofuels?

Originally published by the Sustainable, Secure Food Blog

Climate change is one of the top issues of our time. Wind power, solar energy and electric cars grab a lot of headlines as solutions. Biofuels hold promise too, as part of a varied approach to our energy needs.

Biofuels are a low-carbon fuel option that we can use to make a difference right now. Many states are already using ethanol as part of their gasoline supply systems. In California, biodiesel and renewable diesel made up over 25% of the fuel used for diesel engines in 2020. Some crops are better suited than others to be processed into biofuels.

Carbohydrate winners

Corn is used for biofuel generation because of its capacity to make a lot of carbohydrates from sunshine. It’s categorized as a “C4” plant, which means it is very efficient at taking sunlight and creating carbohydrates. Other C4 food plants include sorghum and sugar. Grasses, like miscanthus, are also grown as biofuel sources. When processed into biofuels, carbohydrates become ethanol.

While mainly carbohydrate, the processing of corn to ethanol still provides a significant amount of protein for animal feed and carbon dioxide for a variety of industrial applications.

Oily sources

Soybeans are one crop used to make biodiesel and renewable diesel, particularly from the oil generated by soybeans. Soybeans are also nitrogen fixers, which means they can be beneficial for the soil. In addition, soybeans contain proteins, which can be separated out in processing. Due to the growing demand for protein from soybeans, we produce more vegetable oil than we can consume in the U.S. This extra oil has opened the door for the cost-effective production of biodiesel, and soon, sustainable aviation fuel from soy oil.

Soybeans have become very important in the production of renewable fuels like biodiesel and renewable diesel. These fuels can replace petroleum diesel fuel in regular diesel engines. Like corn, soybeans get much of their value from their high yield. However, unlike corn, soy produces a significant amount of protein for food and animal feed.

Additional products from soy-biodiesel production

Biodiesel is made through a chemical process that removes glycerin from the fat or vegetable oil used. In processing soybeans into biodiesel, glycerin becomes a valuable byproduct. This can be sold as part of animal feed. In addition, glycerin in cosmetics and pharmaceuticals are currently sourced from petroleum, and soy glycerin can be a replacement.

Renewable diesel production

Renewable diesel is a different fuel than biodiesel but is made from the same fats and vegetable oils. Renewable diesel is a hydrocarbon produced through chemical processes such as hydrotreating. This method uses high pressure hydrogen to remove the oxygen, which is converted to water. After more steps, the resulting product is chemically identical to petroleum diesel.

Because a different process is used for processing soy, different byproducts called renewable propane and renewable gasoline are made. These two products can reduce greenhouse gas emissions compared to petroleum.

Finally, biodiesel and renewable diesel have enjoyed success because both convert the fats and oils into finished fuel at a very high rate, meaning there is very little waste.

Today, soybean oil makes up about half of what’s used to produce biodiesel and renewable diesel. Other fats and vegetable oils, including used cooking oil, inedible animal fats and corn oil left over from ethanol production make up the other half. And there are other exciting opportunities ahead. At least one company is commercializing pennycress as a cover crop for farmers. This would help farmers grow a third “cash crop” during the winter, providing soil health benefits to the farm, as well as more meal and oil, all while using the same amount of land. This is just one more way America’s farmers will play a role in helping the industry reach its goal of 6 billion gallons by 2030 and 15 billion gallons by 2050.

The benefits of biofuels

Plant-based fuels have an advantage over petroleum fuels. As the crops are grown, as part of photosynthesis, they pull carbon dioxide from the air. When they are processed and burned as fuel, they release carbon dioxide back in the air. It’s a fairly rapid cycle.

We are often asked, “Why produce biofuels when we will just electrify everything?” There are two simple answers:

  1. Biofuel production complements the protein supply chain. This helps reduce the cost of protein by creating valuable markets for excess fats and carbohydrates.
  2. The rate of electrification across transportation is inconsistent. The rate of electrification in heavy duty trucks, rail, marine and aviation is not able to keep pace with passenger cars, for example.

In short, we need more biofuels now to help us reach our global climate targets! We will need all sustainable options on the table as our nation reduces emissions over the coming decades.

Matt Herman
Matt is an experienced sustainability professional with deep experience using life cycle assessment to measure the environmental attributes of biodiesel, renewable diesel, and the supply chains which support their production. He is passionate about ensuring that policy adequately reflects biodiesel and renewable diesel's contribution in the fight against climate change.
Matt has held positions as the Director of Environmental Science for Clean Fuels Alliance America, Director of Policy of the Industrial and Environmental Section at the Biotechnology Innovation Organization (BIO) and as Manager of Sustainability for Renewable Energy Group, a leading producer of biomass-based diesel. Matt earned his bachelor's degree in History and Political Science and completed graduate studies in Biorenewable Resource Policy at Iowa State University.