Direct conversion of unsubstituted furan into benzene

The conversion of lignocellulosic biomass to renewable fuels and chemicals has attracted significant attention as a key technology to enable the replacement of petroleum. Lignocellulosic biomass is the most promising renewable carbon energy source, as it is widely available around the world at a relatively low cost. Although it is the most abundant plant material resource, its conversion into chemical faces a range of technological and economic challenges. In order to overcome these challenges, several different processes to obtain chemicals and biofuels from biomass are currently under development. The most promising is the multistep strategy using platform molecules as intermediates. Some platform molecules that can be obtained from biomass at good yields are biomass-derived furans, such as furfural, 5- hydroxymethylfurfural (HMF), 2-methylfuran (MF), unsubstituted furan and 2,5-dimethylfuran (DMF), etc.

In order to overcome the challenges, Giannis Mpourmpakis and their colleagues have shown the direct Catalytic Conversion of Biomass Derived Furan and Ethanol to Ethylbenzene. They have used a synthetic strategy to convert biomass-derived unsubstituted furan to aromatics at high selectivity, especially to ethylbenzene via alkylation/Diels-Alder cycloaddition using ethanol, while greatly reducing the formation of the main side product, benzofuran, over zeolite catalysts. The conversion is based on the DA [4+2] cycloaddition of readily formed ethylfuran intermediate with in-situ produced ethylene from ethanol dehydration (ED) in a ‘onepot’ solvent-free reaction.

They have developed a synchrotron X-ray powder diffraction (SXRD) combined with Rietveld refinement method to elucidate adsorbate structures in zeolites. The alteration in scattering parameters of modified framework atoms by the molecule(s) enables the probing of adsorption geometries and interactions with the Brønsted acid site in terms of atomic distances and angles, within experimental error. They have also applied SXRD and Rietveld refinement technique to study the fundamental molecular interactions of furan/ethylene or furan/ethanol with BA in the zeolite. We further investigated the local concentration of ethanol and/or furan, and their corresponding interactions with the BAS for HUSY (Si/Al=6) loaded with Ethanol/Furan ratios of 3:1 and 10:1 using FTIR spectroscopy. By using first principle calculations they have provided the species adsorption in the HUSY and the detailed reaction energy profiles of the competing catalytic reactions.

In conclusion, they have demonstrated a valuable biomass conversion strategy into useful products. The zeolite catalysts provide unique and geometrically defined active BAS for a cascade ‘onepot’ reactions to form useful aromatics via the DA cycloaddition. The use of ethanol (can also be produced from bio-sources) instead of traditionally used, non-renewable ethylene reduces substantially the formation of the undesired side product – benzofuran. It makes possible for the first time the conversion of the important platform molecule, the unsubstituted furan into aromatics, especially the highly desired ethylbenzene, at high yield and selectivity at mild conditions.

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