Waste to value - ionic liquid strategies for the valorization of spent coffee grounds

Abstract

This thesis focuses on the development of alternative solvent systems for the improved extraction of pharmaceutically active components from waste coffee. Different types of ionic liquids including conventional ionic liquids based on imidazolium or pyridinium cations, distillable ionic liquids or switchable ionic liquids were successfully synthesized, characterized and applied for spent coffee grounds dissolution. These ionic liquids as well as mixtures of 1-ethyl-3-methylimidazolium acetate ([C2mim]OAc) with conventional solvents such as water or ethanol were used for the extraction of active ingredients including caffeine, chlorogenic acid, phenols and flavonoids. After evaluation of different extraction conditions, caffeine was extracted in the greatest yield with the mixture of [C2mim]OAc/H2O (50 wt%), total phenols and flavonoids could be extracted with the best yields with pure [C2mim]OAc whereas chlorogenic acid could only be extracted with pure water. The last part of this thesis focuses on the membrane separation of solvent mixtures used for the extraction of spent coffee grounds. Analytical strategies to determine the composition of [C2mim]OAc/H2O, [C2mim]OAc/EtOH and EtOH/H2O binary mixtures were developed. The separation of these binary mixtures was investigated using a stirred cell membrane set-up with four different membranes; however no separation could be observed.