The efficient production of primary renewable building blocks from biomass-derived carbohydrates must be achieved to develop economically viable biorefineries. Lactic acid (LA) and 5-(Hydroxymethyl)furfural (HMF) are two examples of primary renewable building blocks that can be obtained from fructose as starting feedstock. LA is currently used industrially for the production of green solvents and biodegradable polymers and is extensively used in the food industry. HMF is used as a building block for the manufacturing of solvents, polymers and fuel precursors. The heterogeneous catalytic conversion of fructose in water is limited, in most cases, by low selectivities, especially towards the production of these two platform molecules. Dumesic and coworkers  found that polar aprotic organic solvents such as g-valerolactone (GVL) and tetrahydrofural (THF) cause significant increases in reaction rates compared to water in addition to increased product selectivity for Brønsted acid-catalyzed reactions like conversion of xylose into furfural, dehydration of 1,2-propanediol to propanal and for the hydrolysis of cellobiose to glucose. Here we report a similar effect for the Lewis and Brønsted acid-catalyzed reaction of fructose to lactic acid or HMF, respectively. Sn-Beta catalyst was employed as catalyst for the Lewis acid-catalyzed reaction and a sulfonic acid-based CMK-3 catalyst was used for the Brønsted acid-catalyzed reactions. We demonstrate that the employment of aprotic polar solvents, especially GVL, in addition of the aforementioned catalysts is an effective combination for the selective catalytic conversion of fructose to LA or HMF.
The catalysts were characterized using nitrogen adsorption, X-ray Diffraction, X-ray Photoelectron Spectroscopy, Fourier Transform Infrared Spectroscopy and Inductively Coupled Plasma Atomic Emission Spectroscopy. Characterization of the modified materials shows that the desired physical and chemical properties of the catalysts were attained. Catalytic performance studies were performed in 10 mL batch reactors. The solvent effects on the catalytic performances were assessed at 160°C for the conversion of fructose to LA and at 130°C for the conversion of fructose to HMF. The results demonstrate that using aprotic polar solvents, especially GVL, as a reaction solvent significantly increases the fructose conversion turnover frequency to both, LA and HMF.
- Mellmer, M. A., Sener, C., Gallo, J. M. R., Luterbacher, J. S., Alonso, D. M., and Dumesic, J. A. Angew. Chem. Int. Ed. 53, 11872 (2014).