Abstract
Cracked macadamia nuts, intergrifolia from Limpopo, South Africa were used as a feedstock. The macadamia nut oil was extracted using both mechanical cold press and chemical solvent extraction techniques. The oil physicochemical properties experiments were conducted to determine the free fatty acid content and deduce which biodiesel production method would be suitable. Free fatty acid was found to be within the required ASTM D7651 standard and thus only the transesterification method was required to produce biodiesel. Reactant parameters used for the synthesis of the biofuel viz. oil: alcohol molar ratio, temperature with respect to reaction time and catalyst weight. Both organic Calcined eggshell (CaCO3/CES) and inorganic potassium hydroxide (KOH) catalysts together with methanol alcohol and macadamia nut vegetable oil were deployed in the synthesis of biodiesel. For modeling and optimization, STAT-EASE 360, Design-Expert 13.0.1 V22.0.8, Response Surface Methodology (RMS) tool embedded with Box-Behnken design (BBD), and Central Composite Design (CCD) was used to assess the best optimal conditions for the manufacture of biodiesel from macadamia nut oil. From the results findings, the analysis of variance for biodiesel production using KOH and CaCO3 as a catalyst revealed that the biodiesel yield was influenced enormously by the implemented variables. The experimental study conducted with reaction conditions of oil: alcohol molar ratio of 6:1, the temperature of 60°C and catalyst weight of 1 wt.% resulted in biodiesel percentage yield of 91% for KOH catalyst. For the CaCO3/CES catalyst-based biodiesel the greatest biodiesel percentage output of 96% was achieved at optimal level conditions of oil: alcohol molar ratio of 6:1, temperature of 60.2°C and catalyst weight of 1 wt.%. Even though the biodegradable CaCO3 catalyst showed good catalytic activity in the transesterification of the MNO and resulted in a biodiesel yield of 96% and predicted biodiesel yield of 96.58%, it was however unable to be transesterified at higher ratios of 9:1, 70°C and 5 w/t% catalyst weight whilst KOH was able to be transesterified at those given conditions. The unreacted reactant mixture of 9:1 and 12:1 resulted in a milky-white cloud like soap. The Physicochemical properties of the biodiesel were examined and compared with that of macadamia nut oil to compare if transesterification did take place. Equally so, it was found out that the fuel characteristics of biodiesel were within the specifications of the ASTM D6751 and indeed transesterification did take place. Lastly, the characterization of the produced biodiesel was assessed and examined further with
Gas chromatography-mass Spectrometry (GC-MS) and Fourier transform infrared spectrometry (FTIR). From GC-MS analysis, C18:1, C16:1 and C16:0 was dominant in both macadamia nut oil and biodiesel produced.