Several concepts have been presented to improve the conversion technology of fuel ethanol from lignocellulose biomass. Thermostable enzymes have clear benefits, potentially reducing processing times and leading to lower investment costs and energy input. Increased thermal stability is usually connected with higher specific activity, reducing the amount of enzymes needed and extending their life-time. Thermostable enzymes would also benefit hydrolysis at higher consistency, which, in turn, would result in additional savings. Distillation costs are sharply reduced as the product concentration is increased.
To improve the overall process economics and to achieve a faster hydrolysis rate by using thermostable enzymes, various modifications of the present process configurations; simultaneous or separate hydrolysis, can be considered. During a partial prehydrolysis at higher temperatures, denoted as liquefaction, the viscosity of the substrate is decreased using a optimal composition of thermostable cellulases. The liquefaction stage significantly improves the mixing properties of the high consistency substrate slurry. After the liquefying step, the saccharification stage using a complete or complementary set of hydrolytic enzymes can be performed either simultaneously or separately with the fermentation. A separate hydrolysis stage can be carried out at elevated temperatures with the complete set of hydrolytic thermostable enzymes needed for a certain substrate. The process concepts were tested using monocomponent preparations of the various classes/families of lignocellulose degrading enzymes (cellobiohydrolases, endoglucanases, xylanases and β glucosidase). New thermostable enzymes are more efficient than traditional enzymes and allow designing more flexible and economical process configurations.