Bridging the gap between mechanical and chemical engineering

by | May 20, 2023

Last August, VM Industrials presented at the S&P Global Platts Middle Eastern Bunker Fuel Virtual Conference on Aderco’s behalf. The Aderco group had just concluded a number of stability tests from samples collected over the previous six months since the introduction of the new VLSFO 0.5% fuels.

The objective was to decipher those results and explore what might be the cause in a number of cases of instabilities and incompatibilities, and how these might be avoided.

This is a summarised version of the presentation.

As circled in red on this image, with a limited time to present, we only focused on Stability and Compatibility.

There were three key points;

A) To explore the differences between HFO 3.5% S and VLSFO 0.5% S besides an obvious drop in Sulfur.

B) To identify the reasons Total Sediment Potential TSP was at times remaining active with ongoing hydrocarbon and water aggregations resulting in a fuel with a short shelf life.


C) To highlight just how narrow the margins are between an operable, an impaired, and non-operable blend of VLSFO.

Breaking down VLSFO’s into three categories.

The available streams in feedstock to produce a compliant VLSFO are endless, therefore to simplify Aderco created three categories by viscosity.

This enabled us to separate between the more paraffinic blends (Category 1), those blends that were a balance between paraffinic and aromatic hydrocarbons (Category 2) and finally the blends with higher content in aromatics and asphaltene hydrocarbons (Category 3), as shown in this image.

Focusing on the usual suspect.

With 40 years experience in the field and an R&D team of scientists at the Centre Research Industrielle du Quebec CRIQ (the equivalent of our CSIRO in Australia) Aderco’s focus had perviously been on the most problematic of hydrocarbons, the asphaltene.

Asphaltene hydrocarbons are so complex and so varied that even with today’s technology not all is known about their make up, molecular weight* or their intermolecular forces**.

Intermolecular forces are non-chemical bond reactions, they are physical attractions between molecules. When the maltene layer in yellow surrounding the hydrocarbon is damaged the asphaltene’s electronegativity becomes uninhibited and can be so powerful it can aggregate with other hydrocarbons into a solid. A road surface is not exact, but is not a bad example, it can melt and become liquid with extreme heat.

Here is an example of asphaltene aggregation on this heating coil of a ships fuel tank.

When the electronegativity is neutralised these hydrocarbons return to a singular liquid state.

A method to verify between a physical and a chemical bond.

The TSP in this test above is evidence of a physical aggregations still in a liquid form. When we neutralise the activity the TSP drops dramatically.

Unlike a polymer that will have a chemical bond reaction, that is usually irreversible, just like in the production of plastics. These aggregations remain only physically bonded and when those forces are neutralised, the hydrocarbons disperse and return to singular hydrocarbons and a liquid state.

The solution is to neutralise.

Above is a molecule’s physical action neutralising the hydrocarbon activity.

This is why Aderco clients’ fuel tanks remain clean, even when using HFO with a far higher content in asphaltene. When treated the asphaltene’s that are lacking the maltene layer are encased by the molecule and those forces that would otherwise attract other hydrocarbons and water are now inhibited and neutralised.

Our conundrum – VLSFO’s have very few asphaltenes…

After categorising the fuels we were facing a conundrum, what we thought would be the most problematic, therefore, the third category with higher asphaltene (however still far lower than HFO 3.5% as seen on the table above) actually turned out to be the most stable, and the category with least reported problems.

The category with the most reports with an active TSP and water absorption was category 1 with the higher content in paraffinic hydrocarbons.

The only explanation for this would be that some of the paraffinic hydrocarbons are infact olefins. Olefins are incomplete hydrocarbons chains, they are not natural in oil, they are a by-product from fractioning larger hydrocarbon chains and they are used as a reacting agent to make solids when combined with a polymers***.

The same way as asphaltene intermolecular forces work, the olefins will also aggregate, not quite to the extent of mimicking a solid, but enough to effect stability and cause complications such as excessive sludge formations.

With olefins present the TSP will remain active, giving one value one day and a higher value in the following weeks, possibly even eventually becoming off-spec.

The sample drop tests and tight margins.

A drop test indicates whether the fuel is compatible, it is critical to perform a drop test before commingling fuels to avoid incompatibility. A ring formation or separation will generally indicate an unstable or incompatible fuel.

The drop tests above are of three VLSFO’s from the different viscosity categories, before and after being neutralised by the Aderco molecule. After treatment there is a slight improvement in all three. However, in this case the category 2 fuel looks like the least stable before treatment and a ship should expect higher than usual sludge formations.

The drop tests above are of commingled fuels from different categories and in different percentages in volume. After neutralising those forces all of the commingled fuels are more compatible.

However, the margins of error in commingling are tight, with the tests in the top red box where 2A, comprising of 10% C1 & 90% C3 looking compatible, where test 2C comprising of 20% C1 & 80% C3 incompatible.

There is no room for assumptions.

More challenging is a situation above where test 5A with 10% C1 & 90% C3 is compatible and the opposite with the same fuels in test 5B with 90% C1 & 10% C3 is incompatible.

The long and complex supply chain.

The VLSFO supply chain is long an complex. It may be more likely that a larger producer (in green) will have more control over their supply chain and encounter less problems with their fuels, however as the blends differ so widely this does not make them immune.

At the same time it is fair to assume that a smaller blender (in orange) without as much control over their supply chain may encounter a larger share in the proportion of issues.

Bridging the gap between mechanical and chemical engineering.

Training mechanical engineers to understand how to navigate these complex VLSFO should be a priority for the shipowner. As the cases of impaired fuels continue to increase ****, it becomes a lottery on whether a ship encounters a situation.

An important note.

In the event a fuel is contaminated with waste chemicals, such as polymers. When the circumstances perfectly align (or not so perfect), there is a risk of a polymerisation taking place. This is a chemical bond reaction and therefore irreversible.

Further benefits of neutralising the forces.

As with all blended fuels whether, gasolines, distillates or HFO, most VLSFO are far from optimal and stabilising them by neutralising these forces not only will protect against the larger issues that may happen from time to time, but will also deliver considerable OPEX benefits, with tanks remaining clean, engine workloads reduced, scuffing and piston ring wear reduced and reduced emissions emitted, by the improvement in delayed combustion and reduced after-burn.*****

One thing evident is that mechanical engineering alone will not be enough to resolve some of the challenges seen today, and ship owners must consider training engineers in the chemical aspects of fuels or at minimum give them access to specialists in order to help navigate and avoid surprises that may lead to costly delays at best or complete disruption at worst.

Written by Francisco Malta – VM Industrials

Contacts – Via LinkedIn or

Disclaimer; These are VM Industrials’ opinions from the Aderco test findings only. The article intends to prompt discussions on this topic within the bunkering and shipping industry. VM Industrials engage and contract independent chemists and partake in University Of New England relevant chemistry units to verify their research.

VM Industrials is the official distributor for Aderco in Oceania

References –

*Unraveling the Molecular Structures of Asphaltenes by Atomic Force Microscopy


*** Olefins

**** VPS VLSFO Insights #7 &#10 (only available with VPS subscription)

***** VLSFOs Ignition & Combustion – By VISWA

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