Abstract
The present study assessed the recycling of spent coffee grounds (SCG) as a perspective source of oil which can be used as a feedstock for the production of fuel-grade hydrocarbons or Fatty Acid Methyl Esters (FAME). Traditionally, hexane is used for the recovery of lipids from lipids bearing seeds. The challenge is finding novel solvent/solvents which are derived from renewable materials but with the same or improved oil extraction efficiency than the traditional solvents such as hexane. One such solvent is 2-methyltetrahydrofuran (2-MeTHF), which is produced from renewable lignocellulosic materials. This investigation aimed to assess the capability of 2-MeTHF as a novel green solvent for the recovery of lipids from SCG employing a Soxhlet extraction system and to investigate the effectiveness of the lipid extraction process. Hexane was used as a reference solvent to measure the oil extraction capability of 2-MeTHF. The effect of the solvent-to-SCG ratio and the effect of oil recovery time on the oil yield were investigated. The SCG were characterised with regard to moisture content and particle size, and they were found to contain 66.23 wt% water, on average and a particle size of 481.22 µm on average. The lipid extraction process was carried out for 8 h using both hexane and 2-MeTHF, at a solvent-to-SCG ratio of 15:1 (% w/v), producing an oil yield of 18.99 wt% for hexane and 27.95 wt% for 2-MeTHF on average. The density of the oil extracted using 2-MeTHF was 1162.83 kg/m3 and kinematic viscosity of 37.67 mm2/s on average. The average free fatty acid content (FFA) of the oil extracted using 2-MeTHF was found to be 4.54 wt% and the saponification value (SV) of the oil was found to be 170.22 mg KOH/g. These values were relatively higher than those obtained for the oil extracted using hexane.
