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.

This paper investigates glycerol and glycerides extraction process from fresh and waste sunflower oil biodiesel. Deep eutectic solvent choline-chloride: ethylene-glycol (molar ratio 1:2.5) was used as extraction media in both batch experiments and continuous Karr column. Biodiesel was synthesized in an alkali catalysed chemical transesterification reaction. Three process variables, namely hydrodynamic conditions, solvent to biodiesel ratio and extraction duration were investigated and their impact on the extraction efficiency was found to be largely negligible. Throughout the whole range of process variables the extraction efficiency was relatively high, getting slightly lower only during the continuous experiments. After the extraction, free glycerol content was below the limit for all samples, but the total glycerol and glycerides content was too high to fully comply with biodiesel quality standards. Selected extraction solvent has proved to be efficient for free glycerol removal in the tested range of conditions, but further process modifications and possible raw material and biodiesel processing will be needed to reduce the content of total glycerol and glycerides.

The objective was to determine the content of trace elements (Na, K, Ca, Mg, P, B, Fe) in waste fats and cooking oil and to examine adsorption and extraction as methods for purification of oils and fats for their further use as biodiesel feedstocks. Adsorption was conducted using two bentonite-based adsorbents and extraction was conducted with four deep eutectic solvents. Two were choline chloride based and the other two potassium carbonate based. Extraction with choline chloride-based solvents is recommended for purification of waste fats. For waste cooking oil, a two-step process of extraction followed by adsorption is recommended.

Conventional distillation methods cannot effectively separate the components of an azeotropic mixture since both phases have the same composition, thereby preventing further separation. Additional techniques such as pressure swing distillation or distillation with entrainers are often employed to overcome this limitation and achieve separation. The aim of this investigation was to select the most effective method for separating n-hexane and ethanol. The feasibility of three methods was analyzed: reduced pressure distillation, extractive distillation, and liquid–liquid extraction. The mutual solubility of n-hexane and prepared deep eutectic solvents (DESs) (nine hydrophilic: choline chloride with glycerol, ethylene glycol, or carboxylic acid (malic, citric, glycolic); tetramethylammonium chloride with glycolic acid; lactic acid with glycerol; K₂CO₃ with glycerol or ethylene glycol; two hydrophobic: menthol with decanoic or dodecanoic acid) was experimentally determined. Extraction experiments were conducted to test the solubility of DESs in the feed mixture. The effect of changing DES-to-feed mass ratio was further investigated with choline chloride–glycerol (1:2). The same DES and both hydrophobic DESs were able to increase the relative volatility and enhance the separation of ethanol and n-hexane. Based on the obtained results, extraction was selected as the most effective method for the separation of n-hexane and ethanol.