Vegetable oils as heat transfer fluids: literature review and thermal aging study under inert atmosphere

Heat transfer fluids (HTFs) are key to thermal energy transport and storage in many systems. Their selection depends on their thermophysical performance, chemical and thermal stability, process compatibility, safety constraints, and cost. With rising concerns about decarbonization and sustainability, interest in non-toxic, biosourced and biodegradable fluids is also increasing. Yet most HTFs in use are still mineral, synthetic or silicone-based oils: oils remain the most suitable option, especially for medium temperatures, where water requires pressure and salts solidify. In this context, this work investigates the potential of vegetable oils as HTFs.

An extensive bibliographic and technical screening compared several vegetable oils with more than 40 of the most common commercial HTFs. Results show that vegetable oils are highly sensitive to oxidation and degrade rapidly above 250 ∘^{\circ}C even under inert atmosphere. However, below this threshold, they offer better thermal properties than most commercial oils, high flash points, and low vapor pressures. These features make them promising candidates for operating near atmospheric pressure and under the flash point, in applications under 250∘^{\circ}C and without oxygen.

However, their use at industrial scale is limited by the lack of long-term thermal stability data under various conditions, especially under inert atmospheres. Additionally, standard methods commonly used to assess thermal stability of commercial HTFs are not directly applicable to vegetable oils.

To address this gap, an experimental study was undertaken to evaluate thermal aging under nitrogen. Two vegetable oils (rapeseed and high-oleic sunflower) were aged in autoclaves at temperatures ranging from 150 ∘^{\circ}C to 250 ∘^{\circ}C, for 400, 800, and 1200 hours. The samples were then characterized using standard techniques, with the aim of assessing degradation kinetics under these specific conditions. The study is ongoing, and initial results will be presented.

Work In Progress