Hong Kong: VPS seminar discusses Cashew Nut Shell Liquid properties in bunker fuel blends

Cashew Nut Shell Liquid (CNSL) as a bunker fuel presents a complex profile with both promising attributes and significant challenges, states the President of Strategic Partnerships at VPS.

“While the concept of utilising CNSL as a marine fuel aligns with the broader trend for biofuels, its practical application in the shipping industry has yielded mixed results,” noted Captain Rahul Choudhuri during the Hong Kong leg of the global VPS seminar Fuel Quality, New Fuels Challenges & Decarbonisation Challenges.

According to Captain Choudhuri, CNSL naturally exhibits good resistance to microbial growth and possesses favorable cold flow properties. These characteristics make it an attractive option for using the material as a bunker fuel.

However, its inherent acidity and high reactivity pose considerable hurdles for marine use. Experience in the shipping industry has shown that using CNSL as fuel can lead to problems such as fuel sludging and injector failure.

The primary culprit behind its instability is Cardol, a dihydroxyl phenolic component that makes the product unstable when exposed to temperatures above 200 degrees Celsius giving rise to polymerisation forming gums and fuel deposits, but can occur at lower storage temperatures though ongoing research aims to reduce or remove this element to enhance stability.

A notable concern arises when CNSL is used as an undeclared or cheaper blend stock. One case involved a vessel that received what was supposed to be B100 biofuel but bunkered a blend containing only 40% FAME, 10% FAME bottoms, and 50% CNSL.

This misrepresentation led to operational problems, including significant difficulties with blocked filters, delayed ignition and abnormal exhaust temperatures, underscoring the critical need for thorough fuel analysis.

“Know your fuel, it’s components and bio-source,” advised Captain Choudhuri.

“To mitigate risks, it is recommended CNSL is blended to a maximum of 20% with a fuel combustion analysis test performed, particularly for blends involving MGO or VLSFO, to assess combustion characteristics.

“Furthermore, Gas Chromatography-Mass Spectrometry (GCMS) screening and analysis are essential to accurately detect CNSL as a component in fuel, ensuring transparency and preventing issues arising from undeclared blending.”

Related: Singapore: VPS seminar presents global 2024/2025 marine fuel consumption & off-spec trends
Related: Singapore: Experts discuss maritime decarbonisation, biofuel bunker transition at VPS seminar

Photo credit: Manifold Times
Published: 19 November 2025