Monday, May 2, 2011
Grand Ballroom C-D, 2nd fl (Sheraton Seattle)
Conventional biotechnical conversion of lignocellulose biomass to fermentable sugars is usually based on mesophilic enzymes at about 45°C in separate hydrolysis and 35°C in simultaneous saccharification and fermentation. In order to reach the technological minimum of about 4% ethanol concentration in the broth required for an economically feasible distillation increased initial biomass content is needed. In conventional processes this could, however, lead to poor enzymatic conversion due to e.g. diffusion limitations. An approach to overcome this problem is to liquefy the feedstock first - preferably at increased temperatures where viscosities are inherently lower - to achieve better flowability of the high-solids substrate and thus guarantee improved mass transfer conditions for the enzymatic hydrolysis. After a high-temperature liquefaction using thermostable enyzmes the hydrolysis can be continued at conventional temperatures using mesophilic enzymes. This two-step process concept has been in the focus of the present work using novel thermostable enzymes in the pre-hydrolysis (55°C) and a commercial cellulase mixture in the secondary hydrolysis (35°C, 45°C) of hydrothermally pretreated wheat straw. A thermostable enzyme mixture, tailored to efficiently reduce the viscosity of the high-solids substrate, was used for the liquefaction. Various pre-hydrolysis times, temperature profiles, and enzyme loadings in the two-step process were investigated in detail. The obtained conversions were evaluated in comparison with commercial preparations. The use of thermostable enzymes for liquefaction combined with traditional saccharification or SSF offers several advantages and allows more flexible process design.