Optimizing ammonia pressurization/depressurization processing conditions to enhance enzymatic susceptibility of dwarf elephant grass

Corn stover pretreatment by metal oxides for improving lignin removal and reducing sugar degradation and water usage

Five metal oxides, Fe₂O₃, CuO, NiO, ZnO, and MgO, were investigated as catalysts to improve lignin removal and reduce sugar degradation during corn stover pretreatment. Liquid hot water (LHW) pretreatment was used as control. Among the five metal oxides, MgO was the most suitable for biomass pretreatmen. The optimal pretreatment condition was the solid/liquid ratio of 1/10 with 0.10 mol/L MgO at 190 °C for 40 min. The fermentable xylose (85%) and glucose (97%) from MgO pretreatment were equivalent to those (89 and 95%) from LHW pretreatment, and lignin removal was 1.5-fold more than that from LHW pretreatment. The pH of the resulting biomass slurry was close to 7.0 and without furfural and 5-hydroxymethylfurfural formation. Thus, the water-washing step for inhibitor removal can be omitted. The biomass liquor can be used directly for downstream hydrolysis and fermentation. Acid-resistant equipment is not required due to the absence of acids.

A review on alkaline pretreatment technology for bioconversion of lignocellulosic biomass

The native form of lignocellulosic biomass is resistant to enzymatic breakdown. A well-designed pretreatment that can promote enzymatic hydrolysis of biomass with reasonable processing cost is therefore necessary. To this end, a number of different types of pretreatment technologies have been developed with a common goal of making biomass more susceptible to enzymatic saccharification. Among those, a pretreatment method using alkaline reagent has emerged as one of the most viable process options due primarily to its strong pretreatment effect and relatively simple process scheme. The main features of alkaline pretreatment are that it selectively removes lignin without degrading carbohydrates, and increases porosity and surface area, thereby enhancing enzymatic hydrolysis. In this review, the leading alkaline pretreatment technologies are described and their features and comparative performances are discussed from a process viewpoint. Attempts were also made to give insights into the chemical and physical changes of biomass brought about by pretreatment.

Coordinated development of leading biomass pretreatment technologies

For the first time, a single source of cellulosic biomass was pretreated by leading technologies using identical analytical methods to provide comparative performance data. In particular, ammonia explosion, aqueous ammonia recycle, controlled pH, dilute acid, flowthrough, and lime approaches were applied to prepare corn stover for subsequent biological conversion to sugars through a Biomass Refining Consortium for Applied Fundamentals and Innovation (CAFI) among Auburn University, Dartmouth College, Michigan State University, the National Renewable Energy Laboratory, Purdue University, and Texas A&M University. An Agricultural and Industrial Advisory Board provided guidance to the project. Pretreatment conditions were selected based on the extensive experience of the team with each of the technologies, and the resulting fluid and solid streams were characterized using standard methods. The data were used to close material balances, and energy balances were estimated for all processes. The digestibilities of the solids by a controlled supply of cellulase enzyme and the fermentability of the liquids were also assessed and used to guide selection of optimum pretreatment conditions. Economic assessments were applied based on the performance data to estimate each pretreatment cost on a consistent basis. Through this approach, comparative data were developed on sugar recovery from hemicellulose and cellulose by the combined pretreatment and enzymatic hydrolysis operations when applied to corn stover. This paper introduces the project and summarizes the shared methods for papers reporting results of this research in this special edition of Bioresource Technology.