Alkali-catalyzed Transesterification of Hibiscus sabdariffa (Roselle) Seed Oil for Biodiesel Production

Abstract

The need of energy never comes to an end so; the challenge is to procure power source sufficient to offer for our energy needs. Besides, this energy source must be dependable, renewable, recurring and non-contributing to climate change. Aims: This study was aimed to produce biodiesel from Roselle seed oil and to investigate its quality.  Methodology: The Roselle seeds were clean from dirt, milled to proper size and the oil was extracted using soxhlet with n-hexane as solvent. The extracted oil was subjected to physiochemical analysis tests and then transesterified using methanol and potassium hydroxide as catalyst; with ratio of oil to alcohol 1:8 at 65°C. The quality of produced biodiesel was investigated and compared to international standards. The fatty acid composition of the produced biodiesel was determined by GC-MS. Results: Based on the experimental results, the yellow with characteristic odor oil was obtained from the seeds had the following physicochemical properties: yield, 12.65%; refractive index (25°C), 1.467 m ; free fatty acids, 5.5%; saponification value, 252 mg KOH/g of oil; density, 0.915 g/mL and ester value, 241 mgKOH/g. Also the biodiesel yield achieved was 96%, with density, 0.80 g/mL; API, 44.63; Kinematics viscosity @ 40˚C, 0.742; Pour point, < -51˚C; and Micro Carbon Residual (MCR), 0.65%; which conformed to the range of ASTM D6751 and EN 14214 standard specifications. However, the GC-MS analysis result revealed that the biodiesel produced was methyl ester and free other undesired products such as linoleic acid (33%), elaidic acid (29%) and palmitic acid (17%) and other biomolecules. Conclusion: Based on the obtained results, Roselle seed oil had potential for biodiesel production due to its high contains of free fatty acids. Therefore, in the future, more investigations in alcohol: oil ratio and the concentration of catalyst may be warranted to increase the yield much more.