Species Selection, Scale-Up Cultivation, and Oil Characterization of Microalgae for Sustainable Biolubricant Production

This study provides new insights into the development of microalgae-derived oil for biolubricant production through integrated species selection, nutrient-based cultivation optimization, and comprehensive oil characterization. Among the investigated species, Chlorella vulgaris exhibited the highest lipid content (15.5%, dry weight basis) along with a favorable fatty acid methyl ester (FAME) profile, predominantly composed of C16:0 (methyl palmitate) and C18:1 (cis-9-oleic acid methyl ester), making it the prime candidate for scale-up cultivation. Cultivation in Cell-Hi HP medium achieved a high growth rate (μ = 0.6 d–1) while simultaneously elevating lipid accumulation (27.2%), overcoming the conventional trade-off between productivity and oil quality. The extracted oil is compatible for lubricant production, being enriched in long-chain fatty acyl groups and ester functionalities that govern film formation, load-carrying capacity, and oxidative stability. Its balanced fatty acid composition, comprising 47.5% saturated fatty acids (SFAs), 34.5% monounsaturated fatty acids (MUFAs), and 18.0% polyunsaturated fatty acids (PUFAs), closely matches the compositional window required for a durable biolubricant. The oil extracted from microalgae meets ISO VG 15–22 viscosity specifications (17.7 mm2·s–1 at 40 °C) and demonstrates high thermal stability (236 °C), supporting suitability for light- to medium-duty lubrication under elevated temperatures. Further, the microalgae oil exhibits a high calorific value (36.1 MJ kg–1), underscoring its molecular robustness and thermal resilience. Although the acid value exceeded limits for finished lubricants, this represents a routine upgrading step rather than an intrinsic limitation. Tribological assessment via four-ball testing confirmed effective boundary lubrication, with a coefficient of friction of 0.08 and a wear scar diameter of 664 μm. These results position microalgae oil as a scalable, performance-competitive alternative to petroleum- and plant-derived lubricant base oils, with clear implications for sustainable lubrication technologies.