Effects of aluminum chloride-catalyzed hydrothermal pretreatment on the structural characteristics of lignin and enzymatic hydrolysis.

Abstract In this study, Eucalyptus camaldulensis was pretreated with 0.02 M aluminum chloride (AlCl 3 ) at 140–180 °C to obtain digestible substrates for glucose and lignin. The effects of AlCl 3 -catalyzed hydrothermal pretreatment on the degradation of carbohydrates, structural changes of lignin, crystallinity, morphologic changes, and cellulose conversion of the pretreated biomass have been investigated by HAPEC, HPLC, FT-IR, XRD, CP/MAS NMR, SEM, and 2D-HSQC NMR. Results showed that the pretreatment significantly removed hemicelluloses and cleaved β- O -4 linkages of lignin at high temperatures. Under an optimum condition (at 170 °C for 1 h), almost all of hemicelluloses were removed and most of β- O -4 linkages in lignin were cleaved, and 77.8% cellulose conversion of the pretreated biomass was achieved, which was 7.3-fold higher than that of the original biomass. In short, this process was regarded as a promising approach to achieve an efficient conversion of lignocellulosic biomass to fermentable glucose and residual lignin.