Abstract
HMF synthesis typically requires high temperature and is carried out in aqueous solutions. In this work, the low-temperature dehydration of fructose to HMF in different deep eutectic solvents (DES) was investigated. We found a very active and selective reaction system consisting of the DES tetraethyl ammonium chloride as hydrogen bond acceptor (HBA) and levulinic acid as hydrogen bond donor (HBD) in a molar ratio of 1:2 leading to a maximum HMF yield of 68% after 120 h at 323 K. The DES still contained a low amount of water at the initial reaction, and water was also produced during the reaction. Considering the DES properties, neither the molar ratio in the DES nor the reaction temperature had a significant influence on the overall performance of the reaction system. However, the nature of the HBA as well as the acidity of the HBD play an important role for the maximum achievable HMF yield. This was validated by measured yields in a DES with different combinations of HBD (levulinic acid and lactic acid) and HBA (choline chloride and tetra-n-alkyl ammonium chlorides). Moreover, addition of vanadium containing catalysts, especially the polyoxometalate HPA-5 (H8PV5Mo7O40) leads to drastically increased reaction kinetics. Using HPA-5 and the DES tetraethyl ammonium chloride—levulinic acid we could reach a maximum HMF yield of 57% after only 5 h reaction time without decreasing the very high product selectivity.
Highlights
The chemical industry of the future will have to move from decades of fossil energy sources, such as coal and oil, to more sustainable organic resources
Furan dicarboxylic acid (FDCA) and levulinic acid (LA), which are included in the list of top 12 biomass-based chemicals with high-added-value published by the U.S Department of Energy (Bozell and Petersen, 2010)
In order to define a meaningful temperature for fructose dehydration in deep eutectic solvents (DES), the influence of the reaction temperature on the HMF yield was measured in the DES choline chloride (ChCl):LA
Summary
The chemical industry of the future will have to move from decades of fossil energy sources, such as coal and oil, to more sustainable organic resources. Biomass has the greatest substitution potential for fossil raw materials among renewable energy sources. 5-Hydroxymethylfurfural (HMF) is a biomass-based key component in the biological pathways of a variety of high-value platform chemicals. Due to its high functionality, HMF represents an ideal building block in the interface between carbohydrate and petrochemicals. Both the Fructose Dehydration Using DES+POMs hydroxymethyl group and the aldehyde group open up the possibility of various subsequent reactions to important platform chemicals (Bozell and Petersen, 2010). Furan dicarboxylic acid (FDCA) and levulinic acid (LA), which are included in the list of top 12 biomass-based chemicals with high-added-value published by the U.S Department of Energy (Bozell and Petersen, 2010). In addition to the normal market for polyethylene terephthalate (PET, 1.8 · 109 tons per year), this substitution potential is gaining in importance with regard to increasing research activities in the direction of “bio-PET” (Werpy and Petersen, 2004; Iwata, 2015)
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