Effective Production of Levulinic Acid from Biomass through Pretreatment Using Phosphoric Acid, Hydrochloric Acid, or Ionic Liquid

Levulinic acid is one of the top value-added chemicals. It can be obtained through the hydrolysis of some types of saccharides such as glucose, the constituent unit of cellulose. Cellulose is the most abundant natural resource on this planet; however, its rigid structure prevents the easy utilization of cellulose. In this study, an efficient method for the conversion of cellulose to levulinic acid was sought by reforming the structure of cellulose through several types of pretreatment. Pretreatment with highly concentrated acid was found to enhance the conversion efficiency of the subsequent acidic hydrothermal treatment. Through pretreatment with highly concentrated acid at 50 °C and acidic hydrothermal treatment in the range of 200–210 °C, cellulose was converted into levulinic acid by 40.1 C-% (48.2 mol %) and 49.2 C-% (59.1 mol %) when phosphoric acid and hydrochloric acid, respectively, were used as the reagent. When ionic liquid was used as the reagent for pretreatment, 60.7 C-% (72.9 mol %) of cellulose was successfully converted into levulinic acid. In addition, the key factors for the conversion were clarified to be the decrease of crystallinity; the solubilization of cellulose; and in the case of treatment using ionic liquid, an appropriate interaction between the ionic liquid and cellulose.