Can bio-diesels and bio-oils decarbonize the shipping industry?

Published — June 16, 2023

Insights from Roberta Cenni and Sam Nivin

Alternative fuels will play a central role in decarbonizing the shipping industry, and a range of alternative fuels that could reduce emissions from shipping are currently in development. However, the availability of alternative fuels is currently limited and will continue to be so in the coming years. As a result, we must utilize all alternative fuel pathways to decarbonize the industry as quickly and efficiently as possible.

Liquid biofuels are particularly attractive alternative fuels for shipping. We expect they will be compatible with existing onboard equipment, making them 'drop-in' fuels that can directly replace fossil fuels. Liquid biofuels include bio-diesels and bio-oils. These two categories are often lumped together in decarbonization discussions and strategies. However, key differences between their properties, feedstocks, and readiness levels make their potential roles in decarbonizing the shipping industry very different.

To learn more about the differences between bio-diesels and bio-oils, and their expected roles in decarbonizing the shipping industry, we spoke to Roberta Cenni, Head of Biofuels at the Center, and Sam Nivin, Decarbonization Specialist at NORDEN and secondee to the Center.

What are bio-diesels and bio-oils?

"Even though the characteristics of liquid biofuels are similar, and they are often discussed interchangeably, there is a clear distinction between bio-diesels and bio-oils," explains Roberta. Bio-diesels are commonly made from vegetable oils. These oils undergo either simple processing called transesterification, which results in a mixture of molecules called fatty acid methyl esters (FAME), or hydroprocessing, which results in a product closer to standard diesel called hydrogenated vegetable oil (HVO) or renewable diesel.

And what about bio-oils? "Bio-oils are entirely different from bio-diesels," Roberta says. "They are made from different types of biological waste that do not need to be oils in the first place, using processes called pyrolysis or hydrothermal liquefaction." Bio-oils do not require oil feedstocks and can be made from forestry residues, plastics, or sewage sludge, allowing them to use a much broader feedstock pool than bio-diesels.

As bio-diesels and bio-oils have very different origins, they also have different chemical properties. "Bio-diesels are typically well-defined mixtures of molecules and can be very similar to the marine diesel oil widely used in the maritime industry. On the other hand, bio-oils are a pool of many different types of molecules that may need to be upgraded before they can be used as a fuel," Roberta explains. Both fuels can offer significant emissions reductions compared with fossil fuels, depending on their production processes.

Only bio-diesels are ready for onboard use

Using liquid biofuels onboard depends on two factors: whether the fuel is commercially available at major bunkering hubs, and whether the fuel is compatible with vessels and onboard machinery.

Bio-diesels are already commercially available and can be bunkered at some ports, including Amsterdam, Rotterdam, and Singapore. "Bio-diesel use in shipping is at very initial stages," explains Sam. "A lot of ship owners and operators are doing one test or trial to see if the fuel suits their vessels and engines. A few companies, including us at NORDEN, have conducted multiple trials using bio-diesel and now use the fuel to provide carbon-neutral freight to our customers," he says.

Bio-diesels are also well characterized and compatible with existing onboard machinery, making them attractive drop-in fuels. "Using bio-diesel means we can reduce our well-to-wake emissions without having to make any machinery changes to our vessels, although it does require different handling to standard fuel oil," says Sam.

The story for bio-oils is quite different. "There is a lot of research and knowledge about producing bio-oils, but very small amounts are commercially available," explains Roberta. "The feedstocks and production processes for bio-oils are still under optimization, so their composition and properties are still uncertain," she says.

Sam echoes Roberta's conclusions, adding, "Because bio-oils are not commercially available yet, we still need to learn about the best ways to store them on vessels and then eventually use them in engines."

Bio-oils are the better long-term solution for the shipping industry

At first glance, bio-diesels seem like the most promising liquid biofuel, as they are already available for bunkering at some ports and can be used as a drop-in fuel. However, it is unlikely that bio-diesels will contribute significantly to decarbonizing the entire shipping industry. "We can see that there are some ports that can collect a large amount of bio-diesel, thanks in part to regional subsidy schemes," says Roberta. "This could make bio-diesels important locally, but when we look at global availability, the picture changes because of the limited availability of bio-diesel feedstocks."

"At NORDEN, we can't use bio-diesels on all our ships, primarily because of availability," confirms Sam. "The amount of bio-diesel we can source is very small compared to the overall quantity of fuel we bunker annually."

New regulations will also further restrict the availability of bio-diesels. "The new European regulation Fuel EU Maritime will not allow biofuels to use feedstocks suitable for food or feed, or with implications for land usage. As a result, biofuels will only be able to use feedstocks that are wastes or residues," explains Roberta. "Unfortunately, bio-diesel is bound to using vegetable oils, and there is not a lot of waste or residue vegetable oil available." Center calculations estimate that global bio-diesel production will only be able to cover a very small proportion (around 3%) of the shipping industry's fuel demand, without accounting for competition from other industries.

Although bio-oils are not commercially available yet, their long-term outlook is much more promising. "The feedstocks for bio-oils are more varied, so their potential long-term availability is much larger, and a significant amount will be available to the shipping industry. As a result, we believe they will be relevant for the industry when they become commercially available if they are price-competitive with other alternative fuels," says Roberta.

Bio-diesels offer immediate emissions reductions, but they require careful handling

Although bio-diesel supplies are limited, if they are available on your shipping routes, they are one of the few options that offer immediate emissions reductions without major modifications onboard your vessel. However, it is important to note that bio-diesels are not identical to fuel oils, so they require slightly different handling. For example, bio-diesels must be stored at the correct temperature to prevent sedimentation.

"Operators who wish to try bio-diesel must do their due diligence to understand how bio-diesels should be handled onboard their vessels. This includes conducting fuel sample analyses to understand the properties of their fuel," says Sam.

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