Oil extracted from spent coffee grounds as a renewable source for fatty acid methyl ester manufacturing

The effect of different extraction solvents (polar and non-polar) on yield, chemical and physical properties, including free fatty acid content (FFA) or acid value (AV), saponification value (SV), density, viscosity, elemental composition and heating values of oil extracted from spent coffee grounds (SCG) is investigated. The Soxhlet extraction method is utilized for the extraction of oil from spent coffee grounds. Iso-propanol, ethanol, and acetone as polar solvents and toluene, chloroform, hexane and n-pentane as nonpolar solvents are used. For each solvent, the oil yield is recorded for different time spans. The results show that the highest oil yield (15.3%) is achieved using hexane as an extraction solvent after 30 min of extraction time. The AV and SV of the extracted oils vary depending on the extraction solvent. The results indicate that AV of SCG oil extracted with hexane is 3.65% (7.3 mg(KOH)/g). This value is lower than the values for spent coffee oil extracted with the other solvents (ethanol 3.85%, isopropanol 6.4%, chloroform 4.55%, and toluene 4.15%). Free fatty acids (FFA) of the extracted oil are converted into fatty acid methyl ester (FAME) by base-catalyzed esterification. Effects of temperature, the ratio of FFA to the methanol-KOH solution and the reaction time are investigated. With one step alkali-catalyzed transesterification, oil conversion to methyl ester can be enhanced from approx. 55-85% by increasing the reaction time, the reaction temperature and the MeOH-KOH/FFA ratio. However, a complete oil conversion could only be achieved by utilizing a two-steps transesterification process. (C) 2012 Elsevier Ltd. All rights reserved.