Conversion of rice husks cellulose to levulinic acid on hierarchical Mn₃O₄/ZSM-5 catalyst from natural aluminosilicate

Rice husks contain many compounds, one of them is cellulose that can be converted to levulinic acid (4-oxopentanoic acid). Rice husks need to be pretreated to get larger amount of cellulose so that the yield of levulinic acid is higher. Prior to pre-treatment, rice husks were grinded and sieved, followed by dewax. In this study, rice husks were pretreated using chemical method, namely delignification using NaOH 10%, and mechanical method using ball milling and ultrasonication. The pretreated rice husks were then converted to levulinic acid using Mn₃O₄/ZSM-5 catalyst (2% of Mn loading) that was synthesized using natural aluminosilicate. The XRD pattern of the catalyst confirmed the structure of MFI, while XRF data gave the Si/Al ratio of 9.31. The pretreated rice husks were characterized using FTIR, and the conversion result were characterized using HPLC. FTIR spectra show that both methods successfully reduced lignin and hemicellulose. Based on HPLC results, the reaction of rice husks pretreated with chemical method gave the highest yield of levulinic acid (14%), followed by mechanical method using ultrasonication (8%) and ball milling (6%). These results show that besides chemical method, mechanical method can also be used as pre-treatment method on biomass in order to get higher yield of levulinic acid in this conversion reaction.