Hydrodeoxygenation reactivity of the carbonyl group and carboxyl group and their interaction: taking 2-pentanone, valeric acid, and levulinic acid as examples

Abstract

Varieties of complex oxygen-containing compounds in bio-oil precursors strongly affect the properties of biofuels. Hydrodeoxygenation (HDO) is an effective way for biofuel upgrading. In this work, levulinic acid (LA) which bears both a ketone carbonyl group and a carboxyl group was selected as a model compound to help understand the HDO reactivity of the complex oxygen-containing precursors. Furthermore, two reference model compounds (2-pentanone and valeric acid), which have the same carbon number as LA and bear respectively a ketone carbonyl group and a carboxyl group, were employed to help elucidate the HDO reactivity of LA and the interaction of the carboxyl group with the ketone carbonyl group. The Ru/HZSM-5 catalyst was used to investigate the HDO reactivity of 2-pentanone, valeric acid, a mixture of 2-pentanone and valeric acid (molar ratio 1 : 1), and LA. The liquid products of the HDO reaction of the mixture and LA were identified by GC-MS analysis. Subsequently, the reactions for the formation of each product in the system were speculated and a reaction network was established separately for the HDO reaction of the mixture and LA. On this basis, the power law model was adopted to analyze the HDO reaction kinetics of 2-pentanone, valeric acid, the mixture, and LA. By comparing the HDO reaction activation energies, the HDO reactivity of the ketone carbonyl group and carboxyl group and their mutual influence were discussed. The results showed that the ketone carbonyl group promotes the transformation of the carboxyl group while the carboxyl group inhibits the conversion of the ketone carbonyl group in the HDO reaction.