Conversion of levulinic acid and alkyl levulinates into biofuels and high-value chemicals
Levulinic acid (LA) is one of the most important biomass-derived platform molecules and can be produced from both C5 and C6 carbohydrates via tandem dehydration and hydrolysis reactions. Since LA has different functional groups, it would be converted into various compounds by catalyzed reactions. During the past few decades, it has been proved that the conversion of biomass materials into biofuels and chemicals with LA as intermediate is feasible. Alkyl levulinates derived from LA have similar chemical properties to LA and are also used for the synthesis of LA derived molecules. Herein, this review focuses on the transformation of levulinic acid and alkyl levulinate into biofuels and high-valued chemicals, such as γ-valerolactone, 2-methyltetrahydrofurnan, valeric acid/alkyl valerates, 1,4-pentanediol and N-substituted pyrrolidinones. Different homogeneous and heterogeneous catalysts are reviewed and compared. The ligands and additives exhibit a remarkable impact on the distribution of products in homogeneous catalytic systems. Moreover, the catalytic performances of heterogeneous catalytic systems are influenced by numerous factors, such as the size of the metal particles, surface morphology and acid density. In addition, in order to make this review more complete, the production of LA and alkyl levulinates is also included in the manuscript.