Cellulose dissolution in ionic liquids and characterization of the enzymatic hydrolysis in the presence of ionic liquids

Abstract:
For the production of second and third generation biofuels one of the most important process steps is the production of platform chemicals from biomass. Currently, chemical and enzymatic hydrolysis are used for the conversion of cellulose to glucose, but both systems still face major challenges with respect to an efficient commercial application. The selectivity and physiological reaction conditions are advantages of the enzymatic hydrolysis. Unfortunately, the recalcitrant cellulose structure and its insolubility in aqueous systems are challenging. Additionally, strong inhibitory effects of the products and intermediates as well as the different enzyme activities, working together synergistically, make the enzymatic hydrolysis of cellulose a very complex reaction system. To overcome the challenges of enzymatic cellulose hydrolysis in aqueous systems, ionic liquids are applied as a new generation of solvents. We have tested a variety of ionic liquids to assess their ability to dissolve cellulose with a scattered light method [Zavrel et al. 2009]. During the dissolution process of cellulose, the water activity plays an essential role. To characterize this, water adsorption isotherms of different ionic liquids have been determined. The effect of water activity on the cellulose solubility in ionic liquids is investigated using high throughput light scattering technology. For the enzymatic hydrolysis of cellulose in ionic liquids there are no reports of an effective hydrolysis so far [Turner 2003]. Here, the effect of ionic liquids on cellulases is investigated as a function of water activity. To characterize the cellulose hydrolysis, high throughput experiments were performed. Online measurement techniques in small scale are used to measure the enzymatic activity under different conditions. These high throughput methods can also be applied for further characterization of cellulases and the screening of cellulase activities in ionic liquids. The influence of ionic liquids on the enzyme activity and stability of cellulases is shown. Observations of enzyme activity changes at different water activities are correlated to changes in the pH and process stability of the enzymes. This information contributes to further improvements of the enzymatic cellulose hydrolysis with respect to reaction engineering as well as molecular engineering.

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