Characterization of Cellulose Dissolution in Ionic Liquids as Pre-Treatment for Enzymatic Hydrolysis

Abstract:
The cost effective pre-treatment of (ligno)-celluloses is essential for the pro-duction of second and third generation biofuels as well as for the production of affordable and competitive renewable chemicals. A variety of chemical and physical pre-treatment methods are currently applied or closely investi-gated. Most of them come with significant downsides, such as high energy demand, high reaction temperatures and high cost. A very promising alter-native are ionic liquids (ILs) as a new generation of solvents. To characterise the dissolution capability and kinetics of ILs, a high throughput method based on the BioLector technology has been developed1. The change in number and size of suspended particles as a function of time is captured as a change in scattered light intensity and serves as a semi-quantitative measure for cellulose dissolution kinetics. To further character-ize the effect of water on the dissolution kinetics, water adsorption iso-therms for different ILs were determined. The effect of IL content on the activity of a cellulase preparation (Celluclast®, Novozyme) was investi-gated using DNS assay and cellobioside derivatives. A number imidazolium based ILs can effectively dissolve cellulose and wood1. Dissolution capacity and dissolution speed coincide. Water is an anti-solvent for cellulose. Therefore, the effect of water content or activity on the dissolution kinetics is checked. To provide a rationale for the differ-ent dissolution properties, the ILs have been characterised with respect to their water adsorption properties. The ILs currently used for cellulose disso-lution strongly deactivate cellulases. Using the different substrates, it be-comes apparent that this is rather due to enzyme stability in ILs than due to an immediate loss of enzyme activity.