Bio-diesel

The feedstocks for bio-diesels (fatty acid methyl esters, FAME, and hydro-treated vegetable oils, HVO) are fats, oils, and greases. These feedstocks can undergo either transesterification to produce FAME, or hydroprocessing to produce HVO.

Feedstock availability for bio-diesels is affected by regional and international regulations. The FuelEU Maritime regulation accepts only non-food/non-feed feedstocks (e.g., used cooking oils) as valid feedstock for emissions reduction compliance, in order to minimize land-use change. Conversely, the International Maritime Organization (IMO) does not preclude the use of biofuels from food and feed biomass for international shipping. However, the IMO does add a risk factor associated with land use change when undertaking life-cycle assessments (LCA) of this biomass. These IMO LCA risk factors are still under negotiation at time of writing.

FAME biodiesels are already commercial products, but the availability of non-food/non-feed biomass is low, with intense competition from aviation and road transport. Therefore, we do not expect these products to contribute significantly to the energy transition of the shipping sector in Europe. To understand bio-diesels' potential contribution to maritime decarbonization outside Europe, we must await the results of the IMO negotiations on the default values in their LCA.

There are two main types of bio-diesels, namely fatty acid methyl esters (FAME) and hydro-treated vegetable oil (HVO, also known as ‘renewable diesel’). FAME and HVO are produced by transesterification and hydroprocessing, respectively. Both fuels are technologically mature and already commercially available.

Of the two, FAME will likely be more relevant for shipping. This is because HVO is an expensive product, primarily due to the high level of hydro-treating required for its production, which is not necessary for marine engines. Neither FAME nor HVO is currently widely available, and we do not expect this to change significantly.

Fuel supply logistics and bunkering are well-established for conventional fossil-based diesel - very low-sulfur fuel oil, VLSFO). Given that the molecular composition of bio-diesel is similar to that of - VLSFO, its use does not represent any fundamentally new challenges in fuel storage, logistics, and bunkering. Existing port infrastructure is technically adequate for bunkering and storage of bio-diesel, but bio-diesel is currently not widely used due to a lack of regulatory clarity. Standardization and certification are required as for conventional fuels.

Several successful trials with drop-in and pure bio-diesels ranging from B24 to B100 have been conducted. NOx emissions from combustion of bio-diesels can be managed with engine tuning and appropriate design of selective catalytic reduction systems.

Compatibility issues between the fuel and motor occur when there are asphaltenes in the fuel. Another issue is the potential for microbial growth in bio-diesels during long-term storage, especially for fatty acid methyl esters (FAME). Prevention of such growth should be considered in fuel preparation system design, especially fuel filtration.

Bio-diesel has properties that resemble those of conventional maritime fuels in many ways. Technology and safe operations are mature and not considered a challenge.

When bio-diesels are produced with waste biomass, the well-to-wake emissions associated with this fuel can reach close to net-zero. This is because the CO₂ emitted during onboard combustion is offset by the CO₂ that was absorbed by the regenerating biomass during its growth (see also the tiles for feedstock availability and fuel production for bio-diesels).

Vessel propulsion through combustion of bio-diesels emits some local air pollutants, including nitrogen oxides (NO_X) and particulate matter (PM). However, the levels of sulfur oxides (SO_X) and PM are significantly lower than those from conventional diesel, due to bio-diesel’s low sulfur content and high oxygenation.

Variations in the quality and feedstock sources of bio-diesels can lead to differences in emissions profiles. For fatty acid methyl ester (FAME) bio-diesel, it is generally expected that NO_X emissions will be comparable to or slightly higher than those from conventional diesel, depending on specific engine conditions and fuel formulation.

Bio-diesels are already being used as shipping fuel. The International Maritime Organization (IMO) has provided further clarification on the application of safety regulations to bio-diesels, allowing the use of a large variety of blends. The International Organization for Standardization (ISO) has also progressed in developing standards for bio-diesels. However, some issues with physical properties and engine compatibility persist. In addition, fuel quality standards and their associated certification procedures need to be further developed. This task may be complex, as bio-diesels’ characteristics can vary based on the feedstock and how the fuel is made.

The IMO is advancing its development of well-to-wake-based regulations to promote the use of sustainable fuels, including bio-diesels. Regulating the climate impact of fuel use from a life-cycle (well-to-wake) perspective offers the industry the opportunity to establish sustainable fuel production and consumption patterns. Such regulation can help mitigate the risk of shifting climate impact from the downstream (tank-to-wake) segment of the value chain to the upstream (well-to-tank). This is a crucial consideration for alternative marine fuels, as a significant portion of their climate impact is associated with upstream activities (see also tiles for feedstock availability and fuel production). However, many elements of these regulations remain to be discussed and finalized, including certification, sustainability criteria, and implementation in the IMO mid-term measures.

The European Union (EU) has made progress with the introduction of the EU Emissions Trading Scheme (ETS) and the FuelEU Maritime regulation, which will promote the uptake of bio-diesels. Certification procedures for this fuel are in place and operational in the EU. We expect to see bio-diesels being widely used to comply with FuelEU Maritime and for reducing compliance costs with the EU ETS.

As such, despite the ongoing need for international greenhouse gas regulations from the IMO, there are no immediate regulatory barriers to the uptake of bio-diesels as maritime fuel.