Improving the enzymatic hydrolysis of Saccharum officinarum L. bagasse by optimizing mixing in a stirred tank reactor: Quantitative analysis of biomass conversion

• Evaluation of the improvements in enzymatic hydrolysis by mixing optimization
• The optimized mixing condition was obtained using stirred tank reactor.
• By improved mixing, the washing step of pretreated biomass can be avoided.
• A higher fermentable sugars yield has been reached.
• A way to energetically and economically improve the bioethanol synthesis is shown.

The enzymatic hydrolysis of sugarcane bagasse, an important source for the second generation bioethanol production, was optimized in a stirred tank reactor and the power of stirring was monitored. A synergistic effect of mixing and enzymatic hydrolysis occurs: the mixing increases the cellulose conversion rate, whilst the increased conversion eases the mixing. The objective was to evaluate the effect of an improved mixing on the efficiency of the enzymatic hydrolysis and the possibility to bypass the washing step carried out before hydrolysis reaction. This step removes the inhibitors of hydrolytic enzymes, but it represents an economical and an energetic cost for bioethanol process. In addition, other monomeric sugars contained in pretreated material as xylose, arabinose and mannose, are removed during the washing step. In this study, the yields of glucose, xylose, arabinose and mannose were evaluated after enzymatic hydrolysis performed under different stirring conditions: at 300 rpm and at 100/150 rpm. At the stirring rate of 300 rpm, the yield increase was 9% for glucose and as high as 90% for the other monosaccharides. These results suggest that the key to optimize the enzymatic hydrolysis reaction is an adequate mixing, proposing a way for an economical optimization of bioethanol synthesis.