Homogeneous acetylation of hemicelluloses from soy sauce residue in imidazolium-based ionic liquid

The acetylation of hemicelluloses isolated from deoiled soy sauce residue by a novel process was achieved in a complete homogeneous imidazolium-based ionic liquid system with acetic anhydride for the first time. The key parameters of acetylation reaction were studied, which included the acetic anhydride/hydroxyl functionality in hemicellulose ratio, reaction time and temperature. The degree of substitution (DS) of acetylated hemicelluloses ranged between 0.67 and 1.68 as a function of experiment conditions. Under the optimal reaction conditions (14:1 molar ratio of acetic anhydride to hydroxyl functionality, 20 min reaction time and 100 °C reaction temperature) developed by orthogonal method, over 90 % hydroxyl groups in hemicelluloses were acetylated. The structural features of the acetylated hemicelluloses were characterized by means of SEM, FT-IR, TG and ¹³CNMR. The thermal stability of the acetylated hemicelluloses increased upon chemical modification. At the end of acetylation of hemicelluloses, the ionic liquid could be effectively recovered and reused for at least four times with similar DS values. This study presents a promising approach and green process to make use of soy sauce residue and other similar waste materials.