Modeling of enzymatic hydrolysis of pretreated wheat straw as a function of hydrolysis time, enzyme concentration, and lignin concentration

Enzymatic hydrolysis is one of the most expensive stages in the production of lignocellulosic ethanol. To optimize reaction conditions, reactor design, and substrate composition and subsequently improve hydrolysis rates and yields and reduce costs, enzymatic hydrolysis models are needed.  A model capable of predicting glucose production during enzymatic hydrolysis of oxygen delignified wheat straw at different enzyme loadings (20 and 40 FPU/g cellulose), lignin content (5 wt% and 9 wt%), solids concentration (5 to 10% w/w dry basis) and hydrolysis time has been developed. In this model, the irreversible adsorption of cellulases on lignin was accounted for through the introduction of a lignin factor.  In addition, since pretreatment conditions determine substrate lignin content, this factor connects enzymatic hydrolysis yields to pretreatment.  Diffusion limitations present at solids concentration ≥ 10% were accounted for with an effectiveness factor. The model requires only five parameters and has a relatively simple mathematic solution therefore it can be implemented in simulation software such as AspenTech.  Using such software, it is possible to evaluate the effects of pretreatment conditions such as time, temperature and chemical loading, and enzymatic hydrolysis conditions such as time, solids loading, and enzyme loading on overall production costs.