Synthesis and characterization of bio-lubricant from Citrullus colocynthis L. (Bitter Apple) seed oil: A two-step transesterification approach

The growing demand for sustainable and biodegradable lubricants has intensified research on bio-lubricants derived from renewable feedstocks. Citrullus colocynthis L. seed oil, an underutilized, and non-edible source, holds significant potential for industrial applications due to its high oil yield, and favorable fatty acid composition. This study aimed to synthesize ethyl glycol methyl ester-based bio-lubricants using Citrullus colocynthis L. seed oil and to evaluate the influence of key reaction parameters, including catalyst concentration (0.5 %, 1 % and 2 % w/w), reaction temperature (160°C, 170°C and 180°C), and molar ratio of ethyl glycol to Fatty Acid Methyl Esters (FAMEs) (1:1, 2:1 and 3:1). The synthesized bio-lubricants were characterized using thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) spectroscopy. The obtained bio-lubricant exhibited a density of 0.947 g/cm³ , a surface roughness of 1.49 μm, and viscosities of 408.45 cSt and 66.62 cSt at 40°C and 100°C, respectively. Additionally, it demonstrated a viscosity index of 239 and a flash point of 272°C. These findings indicate that Citrullus colocynthis L. seed oil is a promising raw material for bio-lubricant production, offering desirable physicochemical properties and high surface roughness. The results suggest that Citrullus colocynthis L. bio-lubricants can serve as a viable, eco-friendly and sustainable alternative to conventional petroleum-based lubricants, making them suitable for industrial applications. • Two-step transesterification using ethylene glycol as a di-alcohol highlights eco-friendliness and biodegradability • Optimum conditions: 170°C, 3:1 glycol:FAME ratio, 1% catalyst yield high bio-lubricant output. • Produced bio-lubricant showed decomposition temperature at 445°C • Achieved surface roughness of 1.49 μm, better than water (2.05 μm) and mineral oil (1.83 μm). • Bio-lubricants had 239 viscosity index, 272°C flash point, and −6°C pour point, ideal for safe and cold temperature use.