(720b) Challenges and Opportunities in the Production of Dimethylfuran from Sugars By Performing Tandem Catalysis

The conversion of biomass-derived carbohydrates to fuels and fine chemicals has experienced a large interest over the last decade. The platform molecule hydroxymethylfurfural (HMF) has been envisioned as the cornerstone of a new decentralized industry able to take on the challenges inherent in a decrease in availability of fossil fuels. Especially the interest in the hydrodeoxygenation (HDO) product of HMF, dimethylfuran (DMF) has been high due to its high energy density as an attractive fuel replacement,¹ but also due its diene character making it an interesting candidate for the production of commodity chemicals such as p-xylene (subsequently used for PET production) via [4+2] cycloaddition.² Integration of the processes into a single reactor remains challenging due to reaction conditions, the complexity of solvents (partitioning of products in desired phases and stability of catalysts in solvents), supplying the reduction potential necessary for the HDO reaction, as well as a plethora of side reactions due to reactivity of the substrates and products. However, in an effort of process intensification, the use of microreactors significantly improves heat and mass transport while shortening residence times, which limits the potential for side reactions.

As such, this contribution will discuss the challenges associated with matching the glucose dehydration with the HDO reaction of HMF to DMF in H₂ donating alcohol solvents

The dehydration of Glucose can be effectively achieved by a combination of Lewis acid sites and Brønsted acid sites in either heterogeneous or homogeneous catalyst systems. This takes place at mild temperatures in the aqueous phase. At the same time, the HDO reaction of HMF on carbon supported ruthenium catalysts in the presence of secondary alcohols can be effectively separated into two parts, the facile Lewis acid catalyzed hydrogenation of the aldehyde function of HMF followed by the slow hydrogenolysis of the alcohol intermediates via a reverse Mars-van Krevelen mechanism.³ Ru/RuOx/C has been shown to be one of the most effective catalysts with a DMF yield up to 80% in 6h.

One of the biggest challenges arises from the rate of sugar dehydration being significantly faster than the corresponding rate of HDO to DMF. While the development of superior HDO catalysts poses one pathway towards succeeding, another pathway can be the deliberate poisoning of the dehydration reaction to match the HDO reaction. Both pathways will be discussed. In addition, the reactivity of the intermediates will need to be considered, requiring the optimization of the reaction conditions.

Finally, the impact of the HDO catalyst on the sugar dehydration as well as the impact of water on the HDO catalyst and the HDO reaction itself will be discussed.

1. Román-Leshkov, Y.; Barrett, C. J.; Liu, Z. Y.; Dumesic, J. A. Nature 447, 982 (2007).
2. Chang, C.-C.; Je Cho, H.; Yu, J.; Gorte, R. J.; Gulbinski, J.; Dauenhauer, P.; Fan, W. Green Chem. 18, 1368 (2016).
3. Mironenko, A. V.; Vlachos, D. G. Conjugation-Driven “Reverse Mars–van Krevelen”-Type Radical Mechanism for Low-Temperature C–O Bond Activation. Am. Chem. Soc. 138, 8104 (2016).