Combined liquid hot water and ethanol organosolv treatment of wheat straw for extraction and reaction modeling

Abstract

Lignocellulose feedstock biorefineries produce chemicals, substances, and fuels from agricultural or forestry side products and has the potential to become a cornerstone in a future sustainable economy. The lignocellulosic biomass feedstock has to be fractionated into its main constituents – cellulose, hemicellulose, and lignin – before further processing. The auto-catalyzed liquid hot water (LHW) and ethanol organosolv (EO) treatments are promising, low chemical demand treatments. To overcome their unique limitations, the combined treatment of wheat straw by consecutive LHW prehydrolysis and EO treatment was investigated. A setup of five 45 ml reactors was used to trace carbohydrate and lignin release during the treatments. Delignification and carbohydrate removal were both maximum when harsh EO conditions (200 °C, 20% ethanol) were used after LHW treatment. Both treatments should not exceed severities R0 of 8000 (or approximately 30 min at 180 °C) to limit degradation product formation. Furthermore, two approaches to kinetic modeling of glucan and xylan fractionation were proposed. For EO and LHW treatments, the models estimated either the amount of carbohydrates available for the reactions, or the amount of secondary degradation products. They performed well, but some areas of future improvement were also identified.