Effect of AlCl₃ and Choline Chloride Catalysts on Levulinic Acid Production from Cellulose

Efficient production of levulinic acid (LA) from cellulose typically requires strong mineral acids, posing challenges in terms of catalyst recovery, corrosion, and environmental burden. In this study, we demonstrate a one-pot, fully aqueous conversion of cellulose to LA using aluminum chloride (AlCl₃) as a Lewis acid and choline chloride (ChCl) as a benign, low-toxicity cocatalyst. Systematic batch experiments at 160-180 °C revealed that the addition of ChCl significantly enhances LA formation despite a minimal decrease in solution pH, highlighting a clear synergistic catalytic effect. The optimum condition was obtained at 170 °C with 20 wt % ChCl, achieving an LA yield of 34.4 mol % at 180 min and a maximum yield of 35.6 mol % at 240 minboth distinctly higher than those obtained with AlCl₃ alone. The kinetic trends of glucose, fructose, and hydroxymethylfurfural further indicated that ChCl accelerated cellulose hydrolysis and moderated lactic acid formation, thereby improving the conversion of carbon to LA. Although the reaction is accelerated at elevated temperature (180 °C), humins become the dominant product, suppressing the LA yield. These results demonstrate that the AlCl₃-ChCl aqueous system is a practical alternative to mineral acids for cellulose valorization and offer new insights into the cocatalytic control of reaction pathways in biomass conversion.