Kinetics and thermodynamic studies on Moringa oleifera oil extraction for biodiesel production via transesterification

Abstract

Moringa oleifera produces oil which can be extracted and converted to biodiesel. However, the kinetics and thermodynamics of this viable fuel have been seldomly investigated. We examine the kinetics and thermodynamics of the oil extraction for biodiesel production. The biodiesel kinematic viscosity (3.75 ± 0.04 mm²/s), cetane number (67.12), oxidative stability (15.2 ± 0.5), acid value (0.012 mg/KOH), pour point (−9$°\mathrm{C}$) and carbon residue (0.020 $\pm$ 0.001) satisfy the American Society for Testing and Materials (ASTM) limits. Fourier transform infrared spectroscopy distinguishes the biodiesel and the base oil at 1435.77 cm⁻¹ (-CH₃ stretch), 1195.74 cm⁻¹ (O-CH₃) and 1377.67 cm⁻¹ (O-CH₂) because -CH₃ and O-CH₃ stretches are absent in the oil whereas the biodiesel lacks O-CH₂ stretch. The highly negative activation entropy (−214.11 $\pm$ 0.16 J mol⁻¹ K⁻¹) and greater activation enthalpy (30.39 $\pm$ 0.05 kJ/mol) indicate a slower extraction rate due to the higher energy requirement and stiffer transition of the extraction, respectively. The slower extraction rate agrees with the lower mass transfer coefficients (0.0119–0.0210 min⁻¹). The equilibrium constant (K) is positive whilst the Gibbs free energy (ΔG) is negative, indicating a forward and spontaneous process. This investigation of kinetics, thermodynamics and transesterification essentially provides in-depth knowledge on oil extraction and biodiesel production.

Keywords:

• Kinetics
• thermodynamics
• transesterification
• biodiesel
• Moringa oleifera
• cetane number
• extraction

Acknowledgements

We are grateful to the University of Cape Coast-Ghana for the availability of their laboratories. We also thank Ayensu Akwasi Oware, Ernest Yirenkyi, Titus William Monney and Kofigah Mensah Prosper for their assistance in performing the experiments.

Disclosure statement

No potential conflict of interest was reported by the authors.