Thermophysical and Chemical Evaluation of Macaw Palm Almond Oil as a Biobased Heat-Transfer Fluid Candidate for Medium-Temperature Solar Thermal Applications.

Macaw palm (Acrocomia aculeata) almond oil was evaluated as a potential renewable heat-transfer fluid (HTF) candidate for medium-temperature solar thermal applications through thermophysical and chemical characterization. The oil was extracted using Soxhlet extraction and characterized by gas chromatography with flame ionization detection (GC-FID), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-Vis), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The extraction yield was 15.74 ± 2.85% (w/w), with an acid value of 3.44 ± 0.02 mg KOH·g-1, density of 0.917 ± 0.006 g·cm-3 at 20 °C, and kinematic viscosity of 29.75 ± 0.76 mm2·s-1 at 40 °C. Fatty acid composition revealed a predominance of lauric acid (39.36%), followed by oleic (29.99%) and linoleic acids (14.47%), indicating a mixed saturated-unsaturated profile with implications for viscosity behavior and oxidative susceptibility. FTIR and UV-Vis analyses confirmed the triglyceride structure and indicated early oxidation markers associated with unsaturated lipid fractions. Thermal analysis indicated the onset of measurable degradation around 300 °C, suggesting that continuous thermal-fluid operation should be maintained below this temperature. Compared with other vegetable oils previously investigated for thermal-fluid applications, macaw palm almond oil presents favorable density and viscosity characteristics, although oxidative stability and acid value remain engineering concerns requiring pretreatment or formulation improvements. These findings represent a first-stage screening assessment of macaw palm almond oil as a biobased HTF candidate and support further investigation involving oxidative aging, thermal cycling, corrosion compatibility, and pilot-scale validation.