Catalytic hydrolysis of microcrystalline and rice straw-derived cellulose over a chlorine-doped magnetic carbonaceous solid acid

Abstract

A magnetic carbonaceous solid acid containing chlorine (Cl) groups as cellulose-binding sites and sulfonic (SO3H) groups as cellulose-hydrolyzing sites was designed and synthesized as a novel cellulase-mimetic catalyst (CMC-SO3H) for the hydrolysis of microcrystalline cellulose (MCC). In comparison to carboxylic (COOH) and phenolic hydroxyl (OH) groups, Cl groups with a stronger electronegativity could not only improve the adsorbability to MCC but also enhance the acidity of SO3H groups, which results in a satisfactory yield of total reducing sugars (TRS) with 78.5% in the presence of ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) at a moderate reaction temperature of 130°C for 4h, indicating that CMC-SO3H showed an excellent catalytic activity. Furthermore, CMC-SO3H could be easily separated from the reaction mixture by using an outer magnet, and when it was reused 5 successive reaction runs, an obvious decrease in the yield of TRS was not observed, demonstrating that CMC-SO3H possessed a good catalytic stability. More gratifyingly, under the same catalytic system of CMC-SO3H and [BMIM]Cl, rice straw-derived cellulose (RSDC) could also be directly hydrolyzed into TRS with a good yield of 73.2%, which is very beneficial for the comprehensive utilization of rice straw.