Towards the use of eco-friendly solvents as adjuvants in remediation processes

Testing Thymol-Based DES for the Elimination of 11 Textile Dyes from Water

Textile industries release dangerous wastewater that contain dyes into the environment. Due to their toxic, carcinogenic and mutagenic nature, they must be removed before the discharge. Liquid–liquid extraction has proven to be an efficient method for the removal of these dyes. As extractants, deep eutectic solvents (DESs) have shown excellent results in recent years, as well as presenting several green properties. Therefore, four different hydrophobic DESs based on natural components were prepared thymol:decanoic acid (T:D (1:1)), thymol:DL-menthol (T:M (1:1)), thymol:DL-menthol (T:M (1:2)) and thymol:coumarin (T:C (2:1)) for the extraction of Malachite Green (MG), Brilliant Blue G (BBG), Acid Yellow 73 (AY73), Reactive Red 29 (RR29), Acid Blue 113 (AB113), Reactive Black 5 (RB5), Remazol Brilliant Blue (RBB), Direct Yellow 27 (DY27), Acid Blue 80 (AB80), Direct Blue 15 (DB15) and Acid Violet 43 (AV43) dyes from water. The operational parameters of the liquid–liquid extraction were selected in order to save time and materials, resulting in 30 min of stirring, 15 min of centrifugation and an aqueous:organic ratio of 5:1. In these conditions, the highest values of extraction obtained were 99% for MG, 89% for BBG and 94% for AY73. Based on these results, the influence of the aqueous:organic phase ratio and the number of necessary stages to achieve water decolorization was studied.

A Review of the Use of Eutectic Solvents, Terpenes and Terpenoids in Liquid–liquid Extraction Processes

Diverse and abundant applications of the eutectic solvents have appeared in the last years. Their promising tunable properties, eco-friendly character and the possibility of being prepared from numerous compounds have led to the publication of numerous papers addressing their use in different areas. Terpenes and terpenoids have been employed in the formulation of eutectic solvents, though they also have been applied as solvents in extraction processes. For their hydrophobic nature, renewable character, low environmental impact, cost and being non-hazardous, they have also been proposed as possible substitutes of conventional solvents in the separation of organic compounds from aqueous streams, similarly to hydrophobic eutectic solvents. The present work reviews the application of eutectic solvents in liquid–liquid extraction and terpenes and terpenoids in extraction processes. It has been made a research in the current state-of-the-art in these fields, describing the proposed applications of the solvents. It has been highlighted the scale-up feasibility, solvent regeneration and reuse procedures and the comparison of the performance of eutectic solvents, terpenes and terpenoids in extraction with conventional organic solvents or ionic liquids. Ultimately, it has been also discussed the employ of predictive methods in extraction, the reliability of thermodynamic models in correlation of liquid–liquid equilibria and simulation of liquid–liquid extraction processes.