Production and Physicochemical Characterization of Biodiesel from Senegalia macrostachya seed oil

Abstract

The search for locally available, non-edible and renewable feedstocks for biodiesel production has increased interest in underutilized oil-bearing plants. This study investigated the physicochemical characteristics of Senegalia macrostachya seed oil before and after refining and evaluated its suitability for biodiesel production. Mature seeds collected from Wanke village, Shagari Local Government Area, Sokoto State, Nigeria, were dried, milled and extracted with n-hexane using Soxhlet extraction. The crude oil was refined by degumming, neutralization and bleaching, and its physicochemical properties and fatty-acid profile were determined. Biodiesel was produced by methanol-based transesterification using a calcium oxide catalyst prepared from mussel shells. The crude oil yield was 32.50 ± 0.20%, while the reported refined-oil recovery was 13.95 ± 0.32%. Refining reduced moisture, viscosity, acid value, free fatty acids and peroxide value from 1.24 ± 0.05 to 0.31 ± 0.02%, 42.65 ± 0.72 to 38.41 ± 0.63 cSt, 5.84 ± 0.16 to 1.92 ± 0.08 mg KOH/g, 2.94 ± 0.08 to 0.96 ± 0.04%, and 6.32 ± 0.21 to 2.14 ± 0.11 meq/kg, respectively. The major fatty acids reported in the oil were 9-hexadecenoic acid, oleic acid, linoleic acid, palmitic acid and stearic acid. Biodiesel yield was 86.34%, with specific gravity of 0.83 ± 0.01, kinematic viscosity of 2.92 ± 0.24 cSt at 40 °C, moisture content of 0.03 ± 0.00%, acid value of 0.48 ± 0.02 mg KOH/g, iodine value of 42.36 ± 0.02 g I₂/100 g, cetane number of 58.12 ± 0.20, copper-strip corrosion rating of 1b and higher heating value of 42.06 ± 0.013 MJ/kg. Sulfated ash was 0.009 ± 0.001%, the results indicate that S. macrostachya seed oil is a promising underutilized feedstock for biodiesel production, although further work should include full ASTM/EN fuel-quality testing, oxidative-stability measurement, FAME purity determination and engine-performance evaluation.