Techno-economic analysis of a liquid hot water pretreated switchgrass biorefinery: Effect of solids loading and enzyme dosage on enzymatic hydrolysis

Material and energy results were used in a techno-economic model to analyze the effect of different parameters and configurations on the economics of the process of a liquid hot water pretreated switchgrass (Panicum virgatum L.) biorefinery. Previous experimental results for switchgrass composition and its cellulose enzymatic hydrolysis at different high solids content and enzyme dosages were used in order to obtain a more realistic analysis. The minimum ethanol selling price (MESP) obtained for a facility that produces only ethanol and electricity was within the expected price range for advanced alcohol fuels and could compete with oil prices above $100 per barrel. The MESP was lower for a biorefinery scenario that produces furfural, acetic acid, and formic acid as high-value co-products. The MESP was sensitive to plant size and to switchgrass composition. Enzyme dosage, solids content, and hydrolysis and fermentation efficiencies were the operating parameters with a higher impact on the MESP. Experimental results were combined with the techno-economic models to find correlations between the MESP, and solids content and enzyme dosage. The conditions necessary for a high efficiency of hydrolysis and glucose concentration are not necessarily those that produce an economic optimum (lower cost). The enzyme dosage that minimizes MESP is not always associated with the optimal hydrolysis efficiency (e.g., 95%). The best conditions identified through optimization were an enzyme dosage of 37 mg(protein) g(glucan)(-1) and a solids content of 21%, leading to the lowest MESP of $0.84 L-1 (for an enzyme cost of $4.5 kg(protein)(-1)).