When catalyst meets reactor: continuous biphasic processing of xylan to furfural over GaUSY/Amberlyst-36

The multi-step conversion of xylan hemicellulose and xylose to furfural is investigated in a continuous-flow biphasic fixed-bed reactor over a catalytic bed constituted of a physical mixture of a Lewis acid gallium-containing USY zeolite for xylose isomerisation and a Bronsted acid ion-exchanged resin, Amberlyst-36, for hemicellulose hydrolysis and xylulose dehydration. The water-soluble substrates are converted in the aqueous phase into intermediates which promptly transform into the desired furan product due to the high degree of contact between the solid catalysts. The large interfacial area developed in the reactor through the Taylor flow of liquids enables efficient extraction of furfural to the organic phase, minimising side reactions. The diminished contact of the GaUSY catalyst with water controls its instability against metal leaching, leading to stable operation for 24 h on stream. Optimisation of the variables, including the catalyst ratio, the nature of the extracting phase, the contact time, and the feed concentration, enables to attain furfural yields of 72% from xylose and 69% from xylan. The latter value is the highest reported in the literature for hemicellulose processing over a heterogeneous catalytic system. These results highlight the potential of concerted catalyst and reactor design strategies towards the realisation of more efficient and intensified processes for the sustainable production of bio-based chemicals and fuels.