Carbohydrates in Deep Eutectic Solvents: Dissertation

The utilization of renewable biomass and development of greener technologies are in high demand. Especially, cellulose is a desired component in many applications, but the insolubility in most solvents limits its use. The currently used methods have also environmental issues and other concerns. To overcome these problems, ionic liquids were discovered to be able to dissolve cellulose and other renewable biomass fairly effectively. However, ionic liquids cannot be considered as “innocent” solvents, as their synthesis is not green, and they are often toxic and expensive. Deep eutectic solvents are recognized as promising green alternatives for ionic liquids and petroleum-based solvents, and are now widely used in biomass processing. Generally, deep eutectic solvents are binary mixtures formed by mixing cheap components together: a hydrogen bond donor with a hydrogen bond acceptor. The strong hydrogen bonding between the components is believed to be responsible of the reduced melting point of the mixture. As deep eutectic solvents were introduced quite recently, these novel solvents are still lacking the knowledge and understanding of their fundamentals.
In this thesis, the introduction section covers the background on basic carbohydrate chemistry, ionic liquids which are able to dissolve cellulose, and deep eutectic solvents with their applications in biomass treatment. The characteristics of ionic liquids and deep eutectic solvents are compared. Generally, ionic liquids have better dissolution capability towards polysaccharides than deep eutectic solvents, but very little research has been done to explain why.
The aim of this thesis is to understand and explain the fundamentals of deep eutectic solvents. Therefore, the properties affecting carbohydrate solubility, including cellulose (publication I), physicochemical properties of a new DES (publication III), solvent-solute interactions (publication I, II) and phase behavior of different alcoholic solutes in a DES (publication II) are studied in more detail. Furthermore, the unique properties of DESs are utilized in a novel way: as a green binder for Lithium-ion batteries (publication IV).