Conversion of Cellulose to Levulinic Acid/Ester over an Acid Catalyst: Impacts of Dispersion of Hydrogen Ions on Polymerization Reactions

Abstract

Polymerization is a major challenge in the conversion of cellulose to platform chemicals, such as levulinic acid. In this study, the distinct dispersion patterns of hydrogen ions in a solid acidic resin catalyst (D008 catalyst) and H2SO4 catalyst on the polymerization reactions during conversion of cellulose to levulinic acid/ester were investigated in water and in alcohol medium. The results showed that the distinct patterns for dispersion of hydrogen ions impacted both the efficiency for conversion of cellulose and the tendency for the polymerization reactions. The hydrogen ion in D008 concentrated in pores or the local area of the catalyst, creating steric hindrance for cellulose to access the hydrogen ions but facilitated polymerization of glucose. The homogeneous dispersion of the hydrogen ion in H2SO4 facilitated conversion of cellulose and minimized the polymerization reactions, especially in alcohol medium. When alcohol is used as a reaction medium, the polymerization reaction could be effectively suppressed. Furthermore, alcoholysis was more efficient than the hydrolysis for converting cellulose to levulinic acid/ester. The reaction medium also affected properties of the coke formed. In water, the coke formed contained abundant carbonyl functionalities with a higher thermal stability. In alcohol, the coke formed had less carbonyl functionalities but the thermal stability was lower.