Cashew Nut Shell Liquid – Background

Introduction to CNSL

Cashew Nut Shell Liquid (CNSL), a by-product of the cashew industry, is a naturally occurring substituted phenol. It is abundantly available and a waste product, with a lower demand than FAME. CNSL is a potential alternative to FAME, as it is abundant and has a lower demand.

Composition and Properties of CNSL

The composition, properties and quality of CNSL depend upon the specific manufacturing production process used to extract the oil from the shell. These vary from, mechanical pressing to solvent extraction, vacuum pyrolysis, vacuum distillation or solvent extraction.

• Cardanol (also known as Ginkgol), Cardol and Anacardic Acid are the three main components of CNSL.
• These substituted phenols exhibit high acid number values (>3mgKOH/g), indicating an elevated level of unsaturation and hence increased degrees of reactivity and instability.
• They also show high iodine values (>300gI2/100g), indicating an elevated level of unsaturation and hence increased degrees of reactivity and instability.
• High potassium levels leading to potential post-combustion deposits and corrosion of turbocharger nozzle rings.

Industrial Applications of CNSL

The industrial applications where CNSL is a key component are wide ranging and include, the production of polymers, plastics, resins, adhesives, surface coatings, insecticides, fungicides, anti-termite products and even pharmaceutical products.

Challenges and Risks of CNSL

As monomers, these chemicals are also prone to polymerisation at temperatures, >200ºC. As a consequence CNSL is potentially a highly reactive, very corrosive material. The levels of acidity and reactivity can be reduced during the production and refining process by converting Cardol and Anacardic Acid to Cardanol. If the CNSL is >98% Cardanol, then the reactivity is significantly reduced.

Testing and Evaluation of CNSL

Over the past 3 years VPS have tested various CNSL compounds and fuel-blends to assess the potential of CNSL to be a viable biofuel.

• Use of CNSL blends can significantly reduce HC, CO/CO2 and smoke emissions, although they can raise NOx emissions slightly.
• However, VPS would advise never to use 100% CNSL as a fuel, as its far too reactive and corrosive.
• Further advice is to always check with the OEM regarding the compatibility of CNSL-based biodiesel blended products, with their machinery.

Fuel Combustion Analysis (FCA) of CNSL/Fossil Fuel Blends

In the recent past, VPS have tested CNSL products, blended with marine gas oil (MGO), very low sulphur fuel oils (VLSFO) and high sulphur fuel oils (HSFO). When undertaking fuel combustion analysis (FCA) of CNSL blended at varying percentages with MGO, VLSFO and HSFO, a wide range of results were produced in relation to, estimated cetane number, ignition delay and rate of heat release (ROHR), examples are given in the table below:

Burning CNSL/Fossil Blends

CNSL-blended fuels with MGO, VLSFO, or HSFO, have shown mixed reactions to vessel operations, where some CNSL-blends have been stored and burnt without issue, whilst, other CNSL-blends have given rise to operational problems such as:

• Fuel sludging
• Fuel injector failure
• Corrosion of engine parts
• Filter clogging
• Fuel system deposits
• Corrosion of turbocharger nozzle rings
• Damage to Selective Catalytic Reactor (SCR) units.

A B100 Case Study

In early 2024, two vessels bunkered a B100 fuel in Flushing. The B100, was assumed to be 100% FAME, however, the first vessel began burning the fuel and experienced significant difficulties with blocked filters, delayed ignition and abnormal exhaust temperatures. Prior to burning the fuel, the second vessel sent samples to VPS for testing and via proprietary GCMS methodology. The fuel was found to consist of 40% FAME, 10% FAME Bottoms and 50% CNSL. So theoretically the fuel was a B100, it just wasn’t the 100% FAME, which had been ordered. This case highlights the need to know your fuel, its components and for biofuels, the need to know if the bio-source is truly sustainable?

Pre-burn Screening for CNSL Contamination

In the final quarter of 2024, a VPS customer experienced numerous operational issues with its vessels when burning VLSFO fuels. These issues included blocked filters, delayed ignition and abnormal exhaust temperatures. On testing the fuel, GCMS analysis detected and identified the presence of 10,000-15,000ppm of CNSL within these fuels. Up to the end of 2024, CNSL, which is a non-volatile chemical species, could only be detected using high-end, GCMS methodology. As CNSL is now more common within the fuel supply chain, it brings an elevated risk of potential contamination to fossil fuel supplies. Therefore, VPS has developed a pre-burn, rapid screening technique, which detects and identifies the presence CNSL and other non-volatile organic chemicals. Whereas previously, only volatile organic chemicals could be detected by GCMS-Headspace Screening, this new and unique development of a qualitative GCMS-Headspace chemical screening method makes it possible, within a single analysis, to detect volatile (VOC), semi-volatile (SVOC) and non-volatile (NVOC) components within HSFO and VLSFO fuels.

Conclusion

CNSL has certainly divided opinion of its applicability to be considered as a bio-component within marine biofuels. Its natural high level of acidity and reactivity, along with its potential to polymerise, certainly raises negative questions. Data would indicate using 100% CNSL as a fuel should be avoided, along with blending CNSL with HSFO fuels. Vessel operational issues, due to the presence of high levels of CNSL have caused fuel system, engine and exhaust damages. For the purposes of ISO 8217:2024 and all preceding versions, CNSL is not recognised as a standard fuel component. Accordingly, its presence in a marine fuel may be considered a contaminant and potentially classified as off-specification when assessed against the ISO 8217 standard. However, in instances where CNSL is intentionally used as a blending component and does not fully conform to any of the defined categories within ISO 8217, the fuel may still be deemed acceptable—provided that its characteristics and specification limits are mutually agreed upon by the buyer and seller. In such cases, the fuel shall be classified under an appropriate category defined in ISO 8217, accompanied by any necessary deviations or additional parameters required to adequately characterise the fuel’s properties. As stated, when the CNSL has a Cardanol content of >98%, with a significant reduction in the presence of Cardol and Anacardic Acid, then the product is a far less reactive component. Therefore, from a fuel purchasers perspective, it will be the choice of the CNSL supplier and the production processes they employ, which will be a significant factor in what is received and the CNSL properties, behaviour and overall quality of the product.