To make biomass more accessible for enzymatic hydrolysis, lime pretreatment of Miscanthus giganteus with oxidants was explored from 100 to 150 °C. Composition data for the recovered solid were obtained to determine the effects of the reaction time, lime dosage, oxidant loading, and temperature on sugar production efficiency. Under selected conditions (0.2 g of lime/g of biomass, 200 psig O2, and 150 °C for 1 h), delignification was 64.7%. The pretreated biomass was then followed by enzymatic hydrolysis. The yield of cellulose in the recovered solid to glucose was 91.7% and hemicellulose to xylose was 67.3%, 7.1 and 18.2 times larger than those obtained from raw biomass, respectively. Pretreatment with oxidants substantially raised delignification of raw M. giganteus, thereby enhancing enzymatic hydrolysis to sugars, while results were not improved when pretreatment included ammonium molybdate.

Miscanthus giganteus (M. giganteus) is a promising feedstock for the production of bioethanol or biochemicals. Using only dilute nitric acid, this work describes a two-step process for hydrolyzing hemicellulose and cellulose to fermentable sugars. Primary variables were temperature and reaction time. The solid-to-liquid mass ratio was 1:8. No enzymes were used. In the first step, M. giganteus was contacted with 0.5 wt.% nitric acid at temperatures between 120 and 160°C for 5 to 40 min. The second step used 0.5 or 0.75 wt.% nitric acid at temperatures between 180 and 210°C for less than 6 min. Under selected conditions, almost all hemicellulose and 58% cellulose were transferred to the liquid phase. Small amounts of degradation products were observed. The xylose solution obtained from the nitric-acid hydrolysis was fermented for 96 h and the glucose solution for 48 h to yield 0.41 g ethanol/g xylose and 0.46 g ethanol/g glucose. To characterize residual solids and the liquor from both steps, nuclear-magneticresonance (NMR) spectroscopy was performed for each fraction. The analytical data indicate that the liquid phase from Steps 1 and 2 contain little lignin or lignin derivatives.

Pretreatment of miscanthus is essential for enzymatic production of sugars to yield bioethanol. A two-step process using 10 wt % aqueous ammonia in the first step is followed by 1 wt % sodium hydroxide (with or without oxygen or 1 wt % hydrogen peroxide) in the second step. The first step retains about 90% of the cellulose and about 67% of the hemicellulose in the solid while removing about 62% of the lignin. Both steps together achieve 83-90% delignification. Subsequent enzymatic conversion to fermentable sugars is close to 90% after 96 h. While an oxidant does not significantly increase delignification, it has a favorable effect on saccharification of the recovered solid. Infrared spectroscopy, X-ray diffraction, and two-dimensional nuclear magnetic resonance spectroscopy provide data concerning the chemical composition of the recovered solid. Inclusion of an oxidant to the pretreatment breaks β-O-4′- linked aryl ether bonds of the remaining lignin in the recovered solid. © 2013 American Chemical Society.

BACKGROUND: Miscanthus×giganteus (M.×giganteus) is a potential source for bioethanol or other useful products. Pretreatment of lignocellulosic biomass is an essential step prior to enzymatic hydrolysis to sugars and fermentation to bioethanol. RESULTS: In this work, a one-step process uses aqueous ammonia with or without hydrogen peroxide; a proposed two-step process uses aqueous ammonia in the first step and hydrogen peroxide in the second step. In the two-step process, overall 89.5% lignin is removed. The pretreated biomass is followed by using cellulase and β-glucosidase to convert cellulose and hemicellulose from the recovered solid to fermentable sugars. The conversion of cellulose to glucose is 90.2% and to xylose is 73.4%. Characterization data are obtained for the recovered solid using scanning electron microscopy (SEM), attenuated total reflection-infrared spectroscopy (ATR-IR), and X-ray diffraction (XRD) for better understanding of the two-step process. CONCLUSION: Results from the two-step process using aqueous ammonia and hydrogen peroxide separately are much better than those from the one-step process for removing lignin and for enhancing conversion to sugars by enzymatic hydrolysis. © 2013 Society of Chemical Industry.