Hydrothermal Decomposition of Carbohydrates to Levulinic Acid with Catalysis by Ionic Liquids

The hydrothermal decomposition reactions of cellulose, glucose, and fructose were catalyzed by ionic liquids (ILs) to produce levulinic acid (LA). Among 18 types of ionic liquids with different anions, the ionic liquids containing haloids and hydrogen sulfates exhibited a universal activity for the conversion of fructose, glucose, and cellulose to produce LA. Reusability tests for [PrSO3HMIm]­Cl and [BSO3HMIm]­HSO4 were carried out and revealed that [BSO3HMIm]­HSO4 can be used over four cycles without a loss of activity. The effects of reactant loading, ionic liquid loading, reaction temperature, and time on the decomposition of glucose and cellulose were investigated with [BSO3HMIm]­HSO4. The optimum reaction conditions were obtained as a [BSO3HMIm]­HSO4 loading of 0.5 g, a reactant loading of 0.05 g, a temperature of 180 °C, and a reaction time of 1 h. Yields of 60.8% from glucose and of 54.5% from cellulose were obtained for the catalysis with [BSO3HMIm]­HSO4. Kinetics studies of the decomposition of glucose and cellulose were conducted. The rate constants at each temperature were obtained. For the decomposition of glucose, the activation energies for the conversion of glucose to LA and conversion of glucose to humins were determined as 121.1 ± 4.7 kJ/mol and 114.6 ± 6.1 kJ/mol, respectively. For the decomposition of cellulose, the activation energies for the conversion of cellulose to glucose, conversion of glucose to LA, and conversion of glucose to humins were determined as 186.8 ± 7.4 kJ/mol, 114.0 ± 2.7 kJ/mol, and 148.3 ± 11.2 kJ/mol, respectively.