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  • Writer's pictureSarah Whiteford

Biofuel: a renewable, drop-in fuel for shipping?

80% of international trade is handled by merchant shipping, transporting goods worth approximately $7 trillion every year, according to IEA Bioenergy. As the world becomes more globalized, these numbers will continue to grow as they have since the late 1800s, increasing the need for energy to power the shipping industry. More goods are shipped by water than by land or air, and shipping is the most reliable and economic method of transportation. It also accounts for 2-3% of global CO2, 4-9% of SOx, and 10-15% of NOx emissions. So how can arguably the most important transportation methods for goods needed around the world decarbonize? Land-based transportation is quickly moving toward electrification due to the benefits of quiet, emissions-free operation and a fast-growing network of charging stations. But, air and shipping face a similar problem: the size and distance travelled of planes and ships are too great to rely solely on electric power with current technology. This is where alternative fuels come in, and today we’ll take a look at biofuels and how they can help shipping decarbonize while keeping the world’s goods flowing.

“Merchant shipping routes around the world”. Image from IEA Bioenergy.

What is biofuel?

Since diesel engines became popular on ships in the early 1900s, heavy fuel oil, also called bunker fuel, has been the common fuel for shipping. With growing interest in renewable fuels and pollution reduction, the goal is to make fuels that can be used now, without a lot of conversions and cost. Bioethanol and biodiesel are the two most common types of fuels that have been used on road. Biodiesel is compatible with ship engines currently, while bioethanol is not yet compatible, but may be in the future. So what are biofuels? They are simply biomass converted into a liquid fuel. For example, ethanol can be made from various plant materials like starches and sugars, with scientists working to use other parts of plants as well. Biodiesel is made from new or used vegetable oils and animal fats combined with alcohol to create a biodegradable, nontoxic diesel fuel. The resulting fuel is especially flexible as it can be blended with petroleum based diesel in any percentage, resulting in a B rating. The most common is B20 which is 20% biodiesel and 80% petroleum diesel, but it can be used in ratios all the way up to B100, pure biodiesel. Since biofuels are replacing petroleum fuels already in production with existing infrastructure and powertrains, they are created to be almost identical to traditional fuels, meaning they can “drop-in” to most applications.

“The shipping industry is one of the biggest consumers of petroleum fuel. Using biofuels instead could lower greenhouse gas emissions from the sector. (Image by Shutterstock/GreenOak.)” Image from Argonne National Laboratory.

How is biofuel made?

According to, creating advanced biofuels is a multistep process. The first step is breaking down the tough cell wall structure of the plant through high or low temperature destruction. In high temperature deconstruction, heat and pressure break down solid biomass into liquids and gases through pyrolysis, gasification, or hydrothermal liquefaction. Pyrolysis heats biomass to 500-700 degree Celsius in an oxygen-free environment to break everything down, then it can be cooled into liquid “bio-crude” oil. Gasification is similar but uses temperatures over 700 degrees with oxygen to produce syngas, made of mostly carbon monoxide and hydrogen. Hydrothermal liquefaction uses lower temperatures of 200-350 degrees Celsius with high pressure to produce a liquid bio-crude oil; this process works well with algae and other wet feedstocks. Low temperature deconstruction uses biological catalysts such as enzymes or chemicals to break down feedstocks. They are pretreated to break down the physical structure, then broken down further into simple sugars with hydrolysis. After any of the deconstruction processes, the chemical building blocks are upgraded to produce the final product. “Microorganisms, such as bacteria, yeast, and cyanobacteria, can ferment sugar or gaseous intermediates into fuel blendstocks and chemicals” ( The products are then finished and ready for commercial use. In summary, the plant structures have to be broken down through heat or biological catalysts, then upgraded into fuels that are ready to be used.

“NREL Post Doc Brenna Black draws samples from a tubular bag photobioreactor, to inoculate new growth media, at the Algal Research Lab at the National Renewable Energy Laboratory (NREL) in Golden, CO. Photo by Dennis Schroeder, NREL”. Image from

Is biodiesel safe?

Biodiesel is safe for engines as it is almost identical to the fuels it replaces, but made from different sources. As emissions standards have become stricter, the lubricity of traditional diesel fuels has gone down, necessitating additional lubrication measures. Biodiesel has better fuel lubricity and can help increase lubrication even at a 1% blend. It also raises the cetane number for fuel, providing a shorter ignition delay. Unblended biodiesel also causes less environmental damage if spilled and is less combustible. According to, petroleum diesel has a flashpoint of only 52 degrees Celsius, while biodiesel has a flashpoint of 130 degrees, making it safer to store and transport.

Generations of biofuel processes. Image from Science Direct.

Biodiesel emissions

Carbon emissions from ships went up almost 10% from 2012 to 2018 and biofuel could help reduce some of those emissions. The U.S. Department of Energy (DOE) and the Department of Transportation did a study that compared heavy fuel oil with biomass-based fuel and found it could reduce greenhouse gas emissions by 40 to 93%. Without changes to current fuels, emissions numbers are likely to increase 40% more by 2050 from where they are now, but the International Maritime Organization (IMO) wants to cut those in half, along with other standards for soot and sulfur oxides. According to Argonne National Laboratory, “biofuels analyzed reduced sulfur oxides emissions by 97% or more; particulate matter emissions came down between 84 and 90%.”

Biofuel - the panacea?

There is approximately 160 years of infrastructure in the United States built around oil, while biofuel is just in its infancy. Organizations like the IMO and governments around the world support and set standards for renewable fuels, but it will take time to scale up production. Biofuels are working well so far, but existing infrastructure will have to be modified and new infrastructure built to support new types of fuels and new methods of creating them. They can provide a great addition to petroleum-based fuels and can even be blended with no issues, all positives that will improve adoption. Over time, they will provide another source of energy for shipping and transportation around the world and help shipping to decarbonize as the maritime industry continues to be the backbone of global trade.

Check out 10 Promising Alternative Shipping Fuels to learn more about other methods for powering large vessels.

Happy Fun Fact Friday!


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