Conversion of cellulose from sweet sorghum (Sorghum bicolor) bagasse to levulinic acid over hierarchical Mn/ZSM-5 heterogeneous catalyst

The non-food biomass, sweet sorghum (Sorghum bicolor) bagasse (SSB), can be a possible source for synthesis of platform chemical such as levulinic acid (LA). It contains high sugar derived from cellulose and hemicellulose. Delignification process of SSB becomes important due to accessibility to those sugars. In this work, the effect of different chemical pretreatments on the delignification process was studied, including alkali pretreatment (NaOH) and oxidative pretreatment (NaOCl₂). The products were characterized by Fourier Transform Infrared (FTIR) and X-Ray Diffraction (XRD). The pretreated SSB was then converted into LA using hierarchical Mn/ZSM-5 heterogeneous catalyst at 100 °C with various concentrations of phosphoric acid and fixed concentration of hydrogen peroxide. The conversion reaction was based on Fenton-like reaction. Quantitative analysis of the products was performed using High Performance Liquid Chromatography (HPLC). The result shows that lignin content was significantly reduced from 28.42 % to 16.81 % using 10 % NaOH. Alkali pretreatment on SSB also produces higher yield of LA than oxidative pretreatment. The optimum % yield of LA 14.37 % was achieved using derived cellulose in alkali pretreatment in reaction condition 30 % of H₃PO₄ (v/v), 30 % H₂O₂ (v/v), and 10 % of Mn/ZSM-5 at 100 °C for 10 h reaction time. The catalyst shows good selectivity to LA due to the absence of HMF as intermediate. Beside LA, formic acid and acetic acid were also found in the conversion products.