Process Intensification using Ionic Liquids for dissolving cellulose
Ionic liquids are substances totally formed by ions that are liquid at room temperature. In the last decades they have been intensely studied as green solvents due to their special properties mainly their non-volatility, high solvation power and capacity for stabilizing different catalyst including enzymes. In addition their properties can be tuned by appropriate modification of cations and anions costituting the ionic liquid.
It is known that carbon dioxide can be dissolved in concentrations as high as 70% in mol at moderated pressures. In addition it is known that carbon dioxide is able to decrease high viscosities and melting points of ionic liquids even at very low concentrations.
This behaviour has lead to the study of the application of ionic liquids for some applications as CO2 capture, absorbent in refrigeration absorbent cycles, combined extraction/reaction process etc.
In the High Pressure Process Group we work in the intensification of process by the application of ionic liquids, ionic liquids+CO2 mixtures, and in determining and modeling gas solubilities and melting points of mixtures CO2 + ionic liquids.
Recently some ionic liquids have proved to be able to dissolve cellulose and other natural polymers in high concentrations. These natural polymers can be easily recovered just by addition of water. Anions and cations of ionic liquids able to dissolve cellulose are shown in the figure.
This cellulose solvation capacity opens the possibility of creating new efficient processes for biomass pretreatment, hydrolysis and synthesis of cellulose derivatives. Main drawback of these processes is the high viscosity of ionic liquids and the solutions of natural polymers in ionic liquids, that can be solved by adding co-solvents such as carbon dioxide.
The High Pressure Process Group of the University of Valladolid is studying cellulose processing in ionic liquid media and the influence of carbon dioxide in these processes: substitution reactions, hydrolysis etc.