Structural features influential to enzymatic hydrolysis of cellulose-solvent-based pretreated pinewood and elmwood for ethanol production.

Dissolution of lignocelluloses in N-methylmorpholine-N-oxide (NMMO or NMO) at moderate conditions, e.g., 120 °C for 3 h under atmospheric pressure, and regeneration with water, is among the most effective nonderivatization pretreatment for the improvement of enzymatic hydrolysis and ethanol production. The effects of the pretreatment on two different types of wood, hardwood elm and softwood pine, were compared via physicochemical structural analyses, i.e., FTIR, XRD, SEM, TGA, and enzyme adsorption techniques, to relate their properties to the extent of enzymatic conversion. After the pretreatment, cellulose was highly recovered and characterized to be mainly cellulose II and amorphous cellulose, with lower cellulose crystallinity index, higher thermal stability, and more favorable surface features for hydrolysis, compared to native woods. Moreover, the strength of enzyme binding onto the lignocelluloses, which was directly related to the enzymatic hydrolysis rate, increased by 57% and 164% for pinewood and elmwood, respectively. The highest total reducing sugars yield for untreated pinewood was 9.8% (74 mg/g-substrate) and improved to 58.5% (330 mg/g-substrate) after the pretreatment, whereas the corresponding values for elmwood were 14.7% (104 mg/g-substrate) vs. 51.4% (274 mg/g-substrate). Furthermore, maximum ethanol theoretical yields of 63.5 and 41.4% were obtained from pinewood and elmwood by Saccharomyces cerevisiae and Mucor indicus, respectively.