Effect of rice husk pretreatment on the conversion of cellulose to levulinic acid over the Mn₃O₄/ZSM-5 catalyst

A considerable amount of low-cost wasted rice husk that has not been optimally utilized is available in Indonesia. Almost half of the rice husk, which comprises a biomass resource, is composed of cellulose. Cellulose can be converted to platform chemicals such as levulinic acid. However, cellulose is typically bonded strongly to lignin by β-(1,4)-glycosidic linkages. In this study, we examine the use of four rice husk pretreatment methods for the conversion of cellulose to levulinic acid, namely, dewaxing followed by delignification to remove lignin from biomass, dewaxing followed by ultrasonication in an ethanol solution, ultrasonication using a phosphoric acid solution, and only dewaxing. Meanwhile, hierarchical ZSM-5 impregnated by manganese oxide was used as a catalyst in the conversion of cellulose to levulinic acid at 130 °C. The conversion products were characterized using highperformance liquid chromatography. The dewaxing product after delignification afforded the highest yield of 21.71%, followed by the product ultrasonicated using phosphoric acid (8.81% yield). Hence, ultrasonication using phosphoric acid demonstrates promise for producing platform chemicals by the use of low amounts of chemical compounds. The results of this study can provide useful information regarding the utilization of rice husk waste as a substrate for converting biomass to levulinic acid.