Recycled waste groundnut oil: A potential feedstock for green energy/biodiesel synthesis

Abstract

This work focuses on the recycling of waste groundnut oil as a potential feedstock for biodiesel production using activated coconut husk as a regenerating agent. The coconut husk was functionalized using organic acid. The properties of the functionalized coconut husk were investigated via instrumental analysis. Non-parametric modeling involving 2-degree isotherm models were used. The regeneration/recycling of the waste oil were done in batch mode examining key factors of temperature, time, concentration and dosage. Biodiesel was synthesized from recycled waste groundnut oil using transesterification reaction. The properties of biodiesel were examined using ASTM and AOAC official standards. Brunauer-Emmett-Teller surface analysis revealed the surface area of the adsorbent as 371.88 m²/g and a porosity distribution of 0.567 $\eta$ on the surface at a pH of 6.1. Batch mode analysis revealed that 97.5% of impurities was removed from waste groundnut oil under one batch process at 80 °C after 4 h with 6 g of the activated coconut husk. Langmuir isotherm model provided the best fit to the experimental data with adsorption capacity of 33.5 mg/g at R² of 0.996. Adsorption of waste groundnut oil impurities onto activated coconut husk was endothermic, as evidenced by the calculated ΔH of +2.7914 kJ/mol. A high cetane number of 48.4 obtained after transesterification is an indication of the good ignition quality of the obtained recycled waste groundnut oil methyl ester. Kinematic viscosity and acid value were revealed to be 4.65 mm² S⁻¹ and 0.31 mg KOH/g, while the calorific value stood at 38,053 kJ/kg. GC-MS analysis revealed a complex mixture of fatty acid methyl esters dominated by unsaturated fatty acids (58.78%). Recycling of waste cooking oil in this work using activated coconut husk demonstrated good quality as a regenerating agent. The properties of biodiesel obtained showed that it has all the good qualities comparable to other existing biodiesel based on the ASTM and AOAC official standards. More work on the recycling of other waste cooking oils for green energy synthesis to protect our environment from pollution emanating from the use of conventional petro-diesel and promote energy transition is highly recommended.