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Over three billion cups of coffee are consumed daily, making waste coffee grounds readily available throughout the world. Containing approximately 10–15 wt% of oil, they have great potential for biodiesel production. The goal of this work was to produce high quality biodiesel from waste coffee grounds. One fresh and four different types of waste coffee grounds were collected. Oil was extracted by the Soxhlet method with n-hexane and then purified via extractive deacidification with a potassium carbonate-based deep eutectic solvent. Biodiesels were synthesized by means of alkali catalyzed transesterification at different catalyst:methanol:oil mass ratios and reaction times. Impurities present in crude biodiesels were extracted with a choline chloride-based deep eutectic solvent. All batch extraction experiments were performed at room conditions in a small scale extractor. Optimal conditions for synthesis and purification were defined in order to assure high quality of the produced biodiesel. Additionally, continuous column extraction with the choline chloride-based solvent was tested as a purification method for crude biodiesel. Stabilization time and optimal biodiesel to solvent mass ratio were determined. The potassium carbonate-based solvent efficiently reduced the total acid number of the feedstock (deacidification efficiency ranged from 86.18 to 94.15%), while the one based on choline chloride removed free glycerol and glycerides from crude biodiesels. After continuous purification, the purified biodiesel was of excellent quality with glycerol and glyceride contents below the EN 14214 limit.

From Coffee to Biodiesel—Deep Eutectic Solvents for Feedstock and Biodiesel Purification