Biodiesel from Queensland bush nut (Macadamia integrifolia)

Macadamia, an oil-enriched Queensland bush nut, is one of the Australian native species. In this study, crude vegetable oil was extracted from Macadamia nuts by the n-hexane (98%) method and converted to biodiesel by a transesterification reaction. The reaction utilized potassium methoxide as a catalyst with a reaction temperature of 60°C for 60 min. The physiochemical fuel properties of the crude vegetable oil and converted biodiesel were tested under the ASTM and EN standards and compared with ultra-low sulfur diesel (ULSD). The fatty acid methyl esters (FAMEs) were analyzed by gas chromatography (GC) using the AOCS Ce 1a-13 standard method. The physical behavior of the biodiesel at different temperatures was analyzed and compared with ULSD. The mass and energy balances were studied for both the oil extraction and biodiesel conversion processes to calculate the total process loss of the conversion system. The study found about 73% oil yield for macadamia nut by n-hexane extraction and a 98.21% conversion efficiency utilizing the designated reaction. The GC test identified 21 FAMEs in the biodiesel that contains mainly 15.39%vol. palmitoleic acid (C16:1) and 61.09%vol. oleic acid (C18:0). Other fuel properties, such as calorific value (39.88 MJ/kg), flash point (137°C), and cetane number (56.9) were measured and compared with ULSD values. In the biodiesel conversion process, 58.71% of total mass was recovered as a final product (biodiesel) and 12.51% as by-product (glycerin), respectively, which means that 84% energy was recovered by biodiesel and 10% by glycerin with a 6% energy loss during the conversion process. © 2017 Elsevier Inc. All rights reserved.