Highly selective extraction of lignin and hemicellulose with retained original structure from sugarcane bagasse via low-temperature soaking and acidic precipitation

Low-temperature soaking can be used to extract the majority of the hemicellulose and lignin from bagasse without substantially changing its structure.The effects of temperature, alkali concentration, and treatment duration on the extraction of hemicellulose and lignin from bagasse via low-temperature alkaline soaking were investigated. Acid precipitation provided a solution by separating lignin from black liquor and enabled the categorization of the lignin into different groups based on the reduced pH of the solution. The precipitation of hemicellulose and lignin from black liquor under different pH conditions was investigated. The optimal pretreatment conditions for bagasse were determined to be an alkali concentration of 75 g L–1 at 35 °C for 8 d, achieving a pentose selectivity of 0.97. The main organic components of lignin and carbohydrates precipitated in different pH environments. The highest xylose content in the precipitate was obtained at pH 13.65 (above 85%), whereas the lignin content was above 90% at pH 2. The results of fourier transform infrared (FTIR) spectroscopy and two-dimensional nuclear magnetic resonance (2D NMR) analyses showed that the structure of the water-soluble substances and precipitates slightly changed during alkali pretreatment, which allowed for increased accessibility in subsequent biorefineries, such as in catalytic hydrogenolysis.