Abstract
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.
Highlights
A Scopus search on the term “waste coffee grounds” (WCGs) uncovers an interesting trend.Since 2000, research interest has grown significantly, with 490 papers published on the topic, over half of them in the last four years and the trend is expected to continue in 2020
The quantity of oil ranged from 11.28 to 14.85% in dried waste coffee ground oil (WCGO) and 16.22% in fresh coffee ground oil (FCGO), which was in concordance with the previously published data [23]
Since the TAN of all extracted oils was higher than 2 mg KOH/g oil, the concentration of free fatty acid (FFA) needed to be reduced
Summary
A Scopus search on the term “waste coffee grounds” (WCGs) uncovers an interesting trend. Concerning waste coffee grounds, deep eutectic solvents have been investigated for ultrasound-assisted extraction of bioactive compounds such as chlorogenic acids and flavonoids [26,27] and for pretreatment for enzymatic sugar production due to their ability to solubilize the lignin and increase the availability of the cellulose [28]. The goal of this work was to utilize deep eutectic solvents in the process of biodiesel production from waste coffee grounds. Feedstock pretreatment via extractive deacidification and utilization of deep eutectic solvents for this purpose is a novelty Successful purification of both feedstock and crude biodiesel proved that the application of DESs in the processing of waste coffee grounds has exciting prospects
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