Abstract
Spent coffee grounds (SCGs) and roasted defective coffee beans (RDCBs), are a potentially sustainable source for biofuel production if the processing of these residues, and the recovery of energy-dense lipids, can be undertaken in an energy efficient way. A necessary step in solvent extraction of lipids is prior drying of the feedstock, and this can incur a significant energy cost in the case of SCGs. This study investigates solvent extraction strategies for crude lipid recovery from wet or partially dried SCG samples, with mechanical pressing used as pre-treatment and alternative to thermal drying. Dewatering of SCGs by application of pressures up to 550 bars removed 42% of the moisture present, while lipid expression from whole RDCBs was achieved, with a maximum crude lipid recovery of 77.1% relative to available oil obtained. Crude extracts removal from partially wet pressed SCGs through accelerated solvent extraction (ASE) with ethanol was not impeded by moisture presence, and the obtained extracts had high energy density (∼39 MJ/kg) comparable to hexane-extracted crude lipids. SCG and RDCB crude oil removed through solvent extraction and mechanical pressing respectively had similar fatty acid (FA) compositions, but a higher proportion of free fatty acids (FFAs) in solvent-extracted oil.
Highlights
The majority of worldwide energy consumption continues to come from fossil sources [1]
Solvent extraction of oil from wet and partially wet pressed Spent coffee grounds (SCG) at elevated temperature was investigated through accelerated solvent extraction (ASE) for the first time, and in addition, crude coffee lipids recovered through mechanical pressing and solvent extraction were compared in terms of fatty acid (FA) profile and Free fatty acid (FFA) content so as to determine the effect of the extraction method on the composition of the oil obtained, and evaluate the potential suitability of these crude lipids for biodiesel production
Any water or oil removed from the SCGs and Roasted defective coffee bean (RDCB) was collected in a petri dish positioned below the perforated supporting plate and in the case of wet SCGs, the pressed cake was subjected to prolonged drying at 100 °C in an oven so as to determine by mass difference the amount of moisture remaining within the grounds
Summary
The majority of worldwide energy consumption continues to come from fossil sources [1]. Solvent extraction of oil from wet and partially wet pressed SCGs at elevated temperature was investigated through ASE for the first time, and in addition, crude coffee lipids recovered through mechanical pressing and solvent extraction were compared in terms of FA profile and FFA content so as to determine the effect of the extraction method on the composition of the oil obtained, and evaluate the potential suitability of these crude lipids for biodiesel production
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