Q&A with Dr Prapisala THEPSITHAR on the significance of trialling a prescribed B100 bio-blend comprising two types of biodiesels

An interview with Dr Prapisala THEPSITHAR on our latest trial with BHP!

This trial intentionally combines two types of biodiesel at prescribed amounts: one made from used cooking oil and one made from tallow, a waste animal fat.

But why does the exact blend ratio matter?

Biodiesels derived from different feedstocks can vary in cost, life cycle GHG emissions intensity and chemical properties.

That is why it is important to understand not only that a fuel is a bio-blend, but also how much of each biodiesel is in the final blend.

In this Q&A, Dr Prapisala THEPSITHAR explains:

• how the blend ratio affects GHG emissions reporting
• what it means for onboard operations
• how we are verifying what is in the blend
• why this trial matters for shipowners and operators
• why trialling through an existing supply chain is important

Read the full Q&A here

Question 1: This trial intentionally combines two types of biodiesel at prescribed amounts: one made from used cooking oil and one made from tallow. Why does the exact proportion of each biodiesel matter?

It matters because not all biodiesels are the same.

Biodiesel from used cooking oil and tallow can differ in costs, life cycle GHG intensities and chemical properties.

This means that the proportion of each component in the blend can affect the commercial value of the blend, the emissions claims associated with it and how ship operators should handle it onboard.

In other words, it is important to know not only that the fuel is a bio-blend, but also how much of each biodiesel has gone into the final B100 fuel.


Question 2: Can you explain how the blend ratio affects GHG emissions reporting?

In this trial, the B100 bio-blend combines two FAME^*-based biodiesels: tallow-derived FAME, produced from waste animal fats, and UCOME, or used cooking oil methyl ester, produced from recycled used cooking oil.

Approximately 1,000 MT of the B100 bio-blend was prepared as a 50:50 blend of tallow-derived FAME and UCOME. Accordingly, the final fuel’s life cycle GHG emissions intensity should reflect the contributions of both biofuels.

Tallow-derived FAME is estimated to have a life cycle GHG emissions intensity of 13.6-21.0 gCO₂e/MJ, compared with 9.3-14.9 gCO₂e/MJ for UCOME.

While both are significantly lower than conventional heavy fuel oil, estimated at around 92.8-95.5 gCO₂e/MJ, the difference between the two biodiesels still matters for GHG accounting and emissions-reduction reporting.

In practical terms, the emissions profile should reflect what is actually in the fuel supplied and consumed.

^* FAME, or fatty acid methyl ester, is a type of biodiesel.


Question 3: And how does the blend ratio affect onboard operations?

FAME-based biodiesels from different feedstocks can have different chemical compositions and properties.

For example, tallow-derived FAME generally contains a higher proportion of saturated fatty acid methyl esters. These molecules are straight-chain hydrocarbons that can pack together easily. As a result, they tend to solidify before UCOME does on cooling from room temperature, increasing the risk of clouding, wax formation or reduced fluidity under cooler storage and handling conditions.

Operationally, this matters because wax formation or sludge can contribute to filter blockage or fuel system clogging.

However, it does not mean tallow-derived FAME cannot be used; rather, it means ship operators need to understand the blend’s properties so they can take preventive measures, such as managing storage and transfer temperatures, monitoring filters more closely, and checking fuel condition during use.


Question 4: It seems like more work. Why not just keep using used cooking oil?

Used cooking oil is already one of the most widely used feedstocks for marine biofuels, but its availability is limited. Demand is also growing from other sectors, including road transport sectors and aviation.

If shipping wants to use biofuels at a larger scale, we need to broaden the feedstock base. Waste animal fats, including tallow, could help supplement used cooking oil to expand the feedstock pool and improve biofuel supply resilience. In a market where sustainable feedstocks are increasingly constrained, every eligible waste-based feedstock matters.


Question 5: How do you verify what is in the blend?

One tool we are using is chemical fingerprinting.

Just as a human fingerprint can help identify a person, biodiesel has a chemical fingerprint that can indicate which oils or fats it was made from.

By analysing the bio-blend’s chemical fingerprints, we can determine whether the label of the fuel is consistent with its feedstock origin.

For blends, chemical fingerprinting can also help quantify how much of each biofuel component is present.

It does not replace sustainability certification but it can complement it with physical evidence from the fuel itself.


Question 6: You mentioned that this trial uses an existing supply chain. Why is that important?

It is important because the industry does not have the luxury of building a completely new fuel supply chain for every biofuel feedstock.

Used cooking oil-based biodiesel is already more established in marine fuel markets, so this trial asks a very practical question: can we bring in another biodiesel, such as tallow-derived FAME, by blending it into an existing FAME-based marine biofuel supply chain without requiring the development and buildout of new infrastructure for every new pathway.

Ultimately, this is about making biofuels more available for the maritime sector.  


Question 7: What does this mean for shipowners and operators?

It gives shipowners and fuel users greater optionality in their procurement strategies.

By assessing the compatibility of tallow-derived FAME and UCOME, and tracking the quality of the resulting B100 bio-blend across an existing supply chain, the trial helps demonstrate whether multiple waste-based feedstocks can be integrated credibly into marine biofuel supply chains.

The trial also demonstrates how quality and quantity assurance can be applied across that supply chain, giving users confidence that the fuel delivered matches the agreed specification.

The more we can integrate eligible waste-based feedstocks into existing marine fuel supply chains, the more flexibility shipowners have to optimise fuel procurement based on availability, cost and life cycle emissions performance.


Question 8: I understand GCMD plans to publish a report after the trial. What kind of findings can the industry expect?

The report will focus on practical, real-world learnings.

That includes whether the blend remains stable, whether it can be traced and verified, and whether it raises any operational considerations for shipowners, such as filter blockage, injector deposits, corrosion, leakage, material compatibility or changes to lubricating oils.

We will also look at emissions performance, including NO_x and non-CO₂ greenhouse gases such as N₂O.

The aim is to give the industry a clearer picture of what it takes to safely, reliably and traceably integrate a prescribed blend of biodiesels derived from different feedstocks into existing marine fuel supply chains.