The effects of sequential hydrothermal-mechanical refining pretreatment on cellulose structure changes and sugar recoveries

Authors: CHENG, MING-HSUN - University Of Illinois; MAITRA, SHRADDHA - University Of Illinois; CARR CLENNON, AIDAN - University Of Illinois; Appell, Michael; Dien, Bruce; SINGH, VIJAY - University Of Illinois

Submitted to: Biomass Conversion and Biorefinery
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2022
Publication Date: 10/12/2022
Citation: Cheng, M.H., Maitra, S., Carr Clennon, A.N., Appell, M., Dien, B.S., Singh, V. 2022. The effects of sequential hydrothermal-mechanical refining pretreatment on cellulose structure changes and sugar recoveries. Biomass Conversion and Biorefinery. https://doi.org/10.1007/s13399-022-03359-3.
DOI: https://doi.org/10.1007/s13399-022-03359-3

Interpretive Summary: ARS research and collaborators are developing a commercial friendly process to produce biomass sugars from plant leaves and stems. The process is named sequential hydrothermal-mechanical refining pretreatment (HMR). It is particularly favorable because the biomass is processed by only adding water and steam. While the process has been successfully demonstrated using various crops, it was unknown why the process worked so well. In this study, two different crops were processed by HMR and the molecular properties of the resulting biomass analyzed. These properties were correlated with the sugar yields following enzymatic digestion of the biomass samples. It was determined that a critical aspect of the treatment was what it did to the cellulose fibers woven throughout the plant material. Sugars yields were correlated with the degree to which these fibers were disrupted at the molecular scale. This result will provide insight into how to improve the process. More generally, if the process can be commercialized, it will provide a new market for farmers interested in selling their corn stover, wheat straw, and new low-input dedicated bioenergy crops.

Technical Abstract: Recalcitrance of lignocellulosic biomass necessitates an efficient pretreatment for operating a successful cellulosic biorefinery. It is critical to increase cellulose accessibility for hydrolysis and fermentation by altering the plant cell wall's physical structure and chemical composition. The sequential hydrothermal-mechanical refining pretreatment (HMR) allows good cellulosic sugar recovery without adding chemicals. HMR has been successfully applied to Liberty switchgrass, a bioenergy cultivar released by the USDA. It is now being applied to oilcane, a recently developed transgenic sugarcane plant engineered to accumulate lipids in its vegetative tissues. Sugar yields of oilcane bagasse (OCB) and switchgrass (SG) treated with HMR are 96.4% and 75.4%, respectively. This study sought to correlate cellulosic sugar yields with structural changes within the cell wall caused by HMR. Simon’s staining technique was used to measure the specific surface area. In addition, ATR-FTIR was performed to determine the effects of HMR on physical structures based on total crystallinity index (TCI) and hydrogen bonding intensity (HBI). HMR increased the biomass specific surface area by 80-112%, decreased beginning crystalline cellulose contents by 3.5%, and reduced TCI and HBI by 7-13%. Sugar yields were negatively correlated to reducing values of HBI, crystalline cellulose content, and TCI.