Effect of the Type of Bean, Processing, and Geographical Location on the Biodiesel Produced from Waste Coffee Grounds

Abstract

Waste coffee grounds offer a viable waste feedstock for biodiesel production. Approximately 8 million tonnes of coffee are produced globally each year and contain up to 15 wt % lipid, of which the glyceride portion is predominantly made up of palmitic, stearic, oleic, and linoleic acids. In this investigation, the variation in the oil content, saponifiable lipids, and lipid profile according to the regional location and processing or brewing techniques was assessed. A number of key fuel properties were also investigated. The oil content for fresh coffee grounds (FCGs) ranged from 11 to 15% across the range of coffees examined. Spent coffee grounds (SCGs) had slightly reduced levels of lipid, between 7 and 13 wt %, for the coffees under investigation. The lipids contained between 0 and 40% unsaponifiable material, which could not be processed to fatty acid methyl ester (FAME). For all samples, with the exception of Vietnamese coffee, the FAME profile of the resulting biodiesel was consistent; the oils contained between 35 and 40% palmitic acid, between 7 and 8% oleic acid, between 44 and 50% linolenic acid, and between 7 and 8% stearic acid, although the fuel properties were reasonably variable across the data set. The kinematic viscosity ranged between 4.0 and 5.5 mm2 s–1; the density ranged between 841 and 927 kg m–3; and the pour point ranged between −1 and 16 °C. This variation was also observed in previous reports, suggesting that these fuel properties are not solely determined by the FAME profile but other lipid-soluble biomolecules present in the coffee biodiesel.