The product selectivity was calculated as follows: Productselectivity=[Product][Hydrogenolysisproducts]×100%where [Product] was the concentration of a certain product (g/L), e.g., ethanediol, or 1,2-propanediol in the reaction broth; the [Hydrogenolysis products] was the total products concentration in the reaction broth (g/L). The three key parameters, solids loadings, enzyme dosages, and the reactor scales, were selected for optimization to obtain the minimum cost of stover sugar preparation
as shown in Fig. 2. The data in Fig. 2(a) shows that the production of total sugars (glucose and xylose) increased substantially with increasing solids loading from 5% to 20% (w/w), while learn more the glucose yield and xylose yield decreased slightly. Fig. 2(b) shows that the more cellulase used, the higher sugar concentration and sugar yields were obtained, but only a minor increment of both sugar yield and concentration was obtained when the enzyme dosage was further increased from 15 FPU/g DM to 20 FPU/g DM. Fig. 2(c) shows that glucose
yield and the total sugars in 5 L and 50 L reactors were similar, and both were higher comparing to that this website in 250 mL flasks, indicating that the scale-up effect could be reasonably ignored at least to the 50 L scale. Although the enzymatic hydrolysis conditions were kept the same while conducted at 0.25 L flasks, 5 L and 50 L bioreactors, the mixing and mass transfer demonstrated a better performance in the helical stirring bioreactor than in the flasks . This might be the major reason for the difference in sugars yield between flasks and helical stirring bioreactors. And in the helical agitated bioreactors at different scales, 5 L and 50 L, the different hydrolysis yield should come from the difference of mass transfer in the forms of mixing efficiency, shear stress on enzymes, and fluid velocity distributions originated form the different helical ribbon sizes. The
preliminary cost estimation Sclareol of stover sugars was calculated by considering the costs of feedstock (corn stover), sulfuric acid, cellulase enzyme, steam used in the pretreatment and in the sugar concentrating, the conditioning cost in terms of the sodium hydroxide used, as well as the purification costs. The method and the results are shown in Supplementary Materials. The target concentration of the stover sugars was 400 g/L to meet the requirement of hydrogenolysis by Raney nickel catalyst #12-2. The results show that the minimum cost of producing 1 t of stover sugar hydrolysate at 400 g/L was approximately $255.5 at 7.0 FPU/g DM and 15% solids loading for 72 h hydrolysis. The cost of stover sugars was close to that of the corn-based glucose with the same concentration (400 g/L) around $180–240 per ton .