Bio-oils

Feedstocks for bio-oils are waste biomass streams such as agricultural waste, wet waste, forestry residues, manure, and digestate. These wastes can be converted to bio-fuels via processes including hydrothermal liquefaction, pyrolysis, oil extraction processes, and solvothermal liquefaction. The resulting bio-crudes can then be upgraded to bio-oils.

We currently estimate that the biogenic feedstocks for bio-oils are abundant, but their availability will be challenged by high demand across multiple industries, such as road transport and chemical manufacturers.

Manufacturing bio-oils from waste improves waste management practices and avoids methane emissions from spontaneous rotting of waste. However, not all regulatory frameworks allow the accounting of carbon credits for improved waste management practices. The ability to account for such credits could boost the bio-energy industry further.

The two main production pathways for bio-oils are based on pyrolysis and hydro-thermal liquefaction (HTL), both of which comprise various subcategories. Other production pathways include oil extraction processes and solvothermal liquefaction. Bio-crudes from pyrolysis and HTL must be upgraded to bio-oils to be fit for purpose as a fuel.

A few small plants producing bio-crudes from fast pyrolysis are now operating. In addition, projects to upgrade oils from both fast pyrolysis and HTL are currently at the pilot scale.

While conventional (slow) pyrolysis technology is well-known, optimizing the technology to maximize the production of biofuels with suitable properties requires further development. Given the multiple demonstration facilities now set up, we expect that fast pyrolysis, flash pyrolysis, catalytic pyrolysis, and HTL will become available for producing bio-crudes by the end of this decade.

These bio-crudes may be co-processed in existing refineries at a low blending ratio with fossil oil (1-5%). Bio-oils obtained by this route are suited to be used as a fuel for shipping. As an alternative to refinery co-processing, bio-oil producers are exploring whether bio-oils upgraded by less extensive and cheaper means are suitable as marine fuels.

There are various bottlenecks for short-term impact of bio-oils on maritime decarbonization. The characterization of these fuels’ physical and chemical properties is not fully established. Due to extensive approval procedures, we may not see a “bio-oil” category reaching the market, but rather individual well-defined bio-oil types. Once a new bio-oil type is understood and approved, the rate of construction of new production plants per year and, in the long term, the availability of suitable biomass feedstock, will define an upper limit of impact.

Logistics and bunkering need to be established for bio-oils. Here, bio-oils that are fully upgraded or blended into established fuel could benefit from the existing infrastructure for conventional maritime fuels such as low-sulfur fuel oil (LSFO) and liquefied natural gas (LNG).

There are several remaining hurdles to wide-scale implementation of bio-oils as shipping fuels. Managing a variety of bio-oil specifications in the supply chain, including potential mixing of different bio-oils, can prove to be challenging. The stability of bio-oils during storage is also currently uncertain. Low oxidative stability of bio-oils can lead to fuel degradation and the formation of harmful components, potentially resulting in corrosion and filter blockages. Additionally, controlling bacterial growth at the interface between the oil/fuel and water presents another challenge.

To our knowledge, bio-oils have not yet been tested on board vessels, due to limited supply.

Bio-oils can have different characteristics depending on their production method and feedstock. Some grades of bio-oils have undesirable properties, such as heterogeneous composition and acidity, which may present challenges (see also fuel storage, logistics & bunkering tile for bio-oils).

Bio-oils are high-flashpoint fuels that resemble conventional maritime fuels in many ways. Technology and safe operations are mature and not considered a challenge.

When bio-oils are produced with waste biomass, the well-to-wake emissions associated with these fuels can be close to net-zero. This is because the CO₂ emitted during onboard fuel 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-oils).

Emissions of local air pollutants, including sulfur oxides (SO_x) and particulate matter (PM), are generally lower when using bio-oils compared to conventional fossil fuels. This reduction is due to bio-oils’ low sulfur content and high oxygenation.

However, the varying quality and feedstock sources of bio-oils can result in different emission profiles, especially emissions of nitrogen oxides (NO_X). Higher NO_X emissions from some bio-oil types may lead to challenges in meeting compliance requirements under MARPOL Annex VI Regulation 13, which sets limits on NO_X emissions. However, mature NO_X reduction technologies, such as selective catalytic reduction, are available to help manage these emissions.

Current engine certifications are primarily based on fuels derived from petroleum refining, meaning that bio-oil use may require adjustments or additional certification for compliance.

‘Bio-oils’ is a collective term for different oils of biogenic origin. As such, their properties vary according to feedstock and processing, and the development of standards and certification is therefore complex. Further standardization for bio-oils is still required, including rules regarding emissions for comparable, but not identical, bio-products.

The International Maritime Organization (IMO) has progressed in accepting a wide range of bio-blends, albeit mostly focused on bio-diesels, in marine applications. 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.

At the same time, the IMO is advancing its development of well-to-wake-based regulations to promote the use of sustainable fuels, including bio-oils. 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, the consideration of life-cycle perspectives in the IMO mid-term measures regulations is a missing element that must be addressed, particularly regarding certification and sustainability criteria.

The European Union (EU) has made progress with the introduction of the EU Emissions Trading Scheme and the FuelEU Maritime regulation, which may promote the uptake of bio-oils. Certification procedures are in place and operational for these fuels in the EU.