Extraction and esterification of waste coffee grounds oil as non-edible feedstock for biodiesel production

The potential of waste coffee grounds (WCG) as a non-edible feedstock for biodiesel production was evaluated in term of extraction and esterification of waste coffee grounds oil (WCGO). The effect liquid-solid extraction parameters such as the type and volume of solvent, the extraction time and temperature, and mixing speed were thoroughly investigated. The highest yield of oil extracted from WCGO was 15.47 wt% obtained at a hexane to WCG ratio of 9:1 (v/w) with a mixing speed of 200 rpm and an extraction duration of 5 min at room temperature. An esterification reaction was conducted as a pretreatment step to reduce the concentration of free fatty acid (FFA), optimized by response surface methodology (RSM) combined with a central composite design (CCD). The results indicated that all the parameters including the methanol (MeOH) to FFA molar ratio, quantity of catalyst, reaction time and temperature were significant for %FFA removal. In the esterification step, the FFA conversion was 95% at the predicted optimization condition which corresponded to the experimental data. Therefore, the results of this study support the utilization of WCGO as a source of non-edible oil feedstock for biodiesel production. (C) 2018 Elsevier Ltd. All rights reserved.