Combined liquid hot water and sulfonation pretreatment of sugarcane bagasse to maximize fermentable sugars production

Abstract

Sugarcane bagasse (SCB) is a widely available biomass feedstock currently used for ethanol production in various parts of the world. Here, we carried out a combined liquid hot water and neutral/alkaline sulfonation pretreatments of SCB at relatively low temperatures to maximize enzymatic hydrolysis yields. To describe multi-step pretreatments severities, analytical equations for modified combind severity factors (CSF´m) were introduced. Although the chemical composition of SCB after the liquid hot water pretreatment alone has not been significantly changed under tested conditions, this pretreatment led to an increase in the efficiency of its enzymatic hydrolysis. Furthermore, a combination of liquid hot water pretreatment (at 120 °C for 1 h) and sulfonation of SCB (at 120 °C for 2 h) resulted in excellent enzymatic hydrolysis yields. After alkaline sulfonation, glucose yields reached 99.6 ± 0.21% for autoclaved and alkaline sulfonated bagasse (AASB) and 97.47 ± 0.75% for boiled and alkaline sulfonated bagasse (BASB), whereas xylose yields were 86.9 ± 1.9% and 88.0 ± 1.8% for AASB and BASB, respectively. High enzymatic hydrolysis yields are in line with elevated CSF´m of the latter pretreatments. X-ray diffraction, confocal laser scanning microscopy, and solid-state 13C NMR spectroscopy analyses showed that the structural desorganization of bagasse after liquid hot water pretreatment associated to chemical modifications of lignin and its massive removal promoted by alkaline sulfonation led to efficient separation of carbohydrates and lignin, revealing underlying structural reasons of the observed efficient enzymatic hydrolysis.