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

Abstract 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.