Clean sandbox (Hura crepitans) oil methyl esters synthesis: A kinetic and thermodynamic study through pH monitoring approach

Abstract

Abstract In this study, oil was extracted from underutilized sandbox seeds and converted into biodiesel via transesterification process using KOH as a base catalyst. The impact and optimum values of the essential process variables (methanol-to-sandbox seed oil (SSO) ratio, KOH loading, reaction temperature and reaction time) on the sandbox oil methyl esters (SBOME) yield were established via Taguchi orthogonal array design method. Kinetic modeling of the transesterification process was carried out by monitoring the pH of the reaction. Maximum SBOME yield of 97.10 ± 0.03 wt% could be achieved under optimal condition of methanol-to-SSO molar ratio of 6:1, KOH loading of 0.5 wt%, reaction temperature of 35 °C and reaction time of 25 min. The kinetics of the process followed a unimolecular pseudo-second order rate law with reaction rate of 0.0016 L/mol.min at 35 °C. The activation energy and frequency factor of the reaction were calculated to be 11.40 kJ/mol and 0.1362 L/mol.s, respectively. The ΔH‡, ΔS‡ and ΔG‡ for the process were determined as 8.76 kJ/mol, – 0.270 kJ/mol.K and 92.02 kJ/mol, respectively. The quality of the SBOME demonstrates that it could serve as a replacement for diesel as its properties complied with standard specifications for biodiesel. The kinetic data obtained in this study could be used in reactor design for the process.