Bioethanol: Modeling of Enzymatic Hydrolysis for Lignocellulosic Substrates at High Dry Matter Content

One of the key stages for producing and commercializing second generation bioethanol from lignocellulosic resources is the enzymatic hydrolysis of cellulose into glucose. Indeed this operation is very slow (20-200 h) and requires large quantities of enzymes (10-100 mg/g_cellulose) which are expensive to produce (5-50 US$/kg). The modeling of enzymatic reactions has been the subject of numerous publications. It needs a complex multi-scale approach that takes into account the intrinsic activity of the enzymes, the synergy effects between them, the inhibiting effects of reaction products, the evolution of the substrate morphology (pore size distribution, surface area, crystallinity), the nonproductive adsorption on lignins, etc… These studies are however often performed on pure cellulosic substrates in high diluted conditions.

The objective of this work is to propose a new functional model for predicting the enzymatic hydrolysis at high dry matter content (until 25 wt%) for a real lignocellulosic substrate (pretreated poplar) and enzymatic cocktail (Genencor GC220). This approach is based on a 5-parameter kinetic equation which determines the cellulose conversion rate as function of reaction time, initial dry matter content, enzymes content, and time at which these enzymes are added. The results show an excellent fit between experimental and simulated data for a large range of dry matter [15-25 wt%], enzymes [10-40 mg/g_cellulose] and glucose contents [0-6 wt%]. The effect of adding fresh enzymes during the hydrolysis is also well predicted.