Comprehensive understanding of co-producing fermentable sugar, furfural, and xylo-oligosaccharides through the pretreatment with CTAB-based deep eutectic solvent containing Brønsted and Lewis acid

Abstract

The deep eutectic solvents (DESs) with additional functionalities synthesized using the cationic surfactant cetyltrimethylammonium bromide (CTAB) have gained attention due to their remarkable enzymatic enhancement capability. By combining CTAB, lactic acid, and FeCl3, a DES containing both Brønsted and Lewis acids was synthesized and the pretreatment parameters were optimized using response surface methodology. The results demonstrated the selective and efficient delignification (83.2 %) and xylan removal (76.3 %) from canola straw by CTAB:LA:Fe3+, resulting in an increased saccharification efficiency of 81.8 %. Besides, abundant furfural (3.36 g/L) and xylo-oligosaccharides (3.41 g/L) were co-produced during pretreatment, providing comprehensive insights into the efficient co-production of fermentable sugars, furfural, and xylo-oligosaccharides. A thorough analysis of mass balance and energy flow was conducted to evaluate the entire process. Then, molecular dynamics (MD) simulations and quantum chemical calculations were performed on lignocellulosic biomass models and elucidate the interactions between the biomass and CTAB:LA:Fe3+ at the molecular level through the independent gradient model (IGM), thus explaining the high removal efficiency of hemicellulose and lignin. Furthermore, the physicochemical properties of the DESs were investigated, and molecular-level insights into the mechanism of CTAB:LA:Fe3+ pretreatment of lignocellulosic biomass were proposed in conjunction with biomass characterization such as FT-IR and CLSM, as well as MD simulations.