(43d) Sandbox (Hura crepitans) Oil Methyl Esters Synthesis: Process Modeling, Optimization, Kinetics and Thermodynamics Studies

In this study, non-edible oil was extracted from underutilized sandbox (Hura crepitans) seeds using microwave-mediated solvent extraction method. The oil was converted into fatty acid methyl esters via transesterification process. The process was modeled and optimized using Taguchi approach. The impact of the pertinent parameters: methanol/oil molar ratio (6:1 – 15:1), KOH loading (0.5 – 1.5 wt.%), reaction temperature (35 – 55 °C) and reaction time (25 – 75 min) together with their mutual interactions on the sandbox oil methyl esters (SOME) yield was established. The reaction kinetic modeling of the transesterification process was carried out by monitoring the pH of the reactions. The SOME produced was characterized by determining its physicochemical properties. The sandbox oil extracted had acid value of 0.673 ± 0.000 mg KOH/g oil, iodine value of 42.463 ± 1.464 g I₂/100 g oil, peroxide value of 3.300 ± 0.100 meq O₂/kg oil, calorific value of 40.826 ± 0.036 MJ/kg and Cetane number of 63.175 ± 0.374. Maximum SOME yield of 97.23 wt.% could be obtained under optimal condition of methanol to sandbox oil molar ratio of 6:1, KOH loading of 0.5 wt.%, reaction temperature of 35 ^oC and reaction time of 25 min. The kinetics of the transesterification process determined at the optimal condition followed a unimolecular pseudo-second-order rate law with reaction rate constants of 0.0016, 0.0018 and 0.0021 L/mol. min at 35, 45 and 55 ^oC, respectively. Thermodynamic properties for the reaction were also determined at the optimal condition. Thus, the activation energy was calculated as 11.40 kJ/mol with frequency factor of 0.1362 min^-1, while the enthalpy and entropy were 8.76 kJ/mol and -270.32 J/mol.K, respectively. The characterization of the SOME produced demonstrates that it could serve as a substitute to fossil diesel since its properties satisfied both ASTM D6751 and EN 14214 standard specifications.