Structured Catalysts for Continuous Biphasic Furfural Synthesis from Biorefinery Feedstock

Sustainable chemicals from lignocellulosic biomass can accelerate material transition. Heterogeneous catalysts provide a superior alternative to homogeneous catalysts for xylose dehydration to furfural, a promising platform chemical. This work uses 3D open-cell aluminum foam structures as catalyst support for the biphasic furfural synthesis from biorefinery hydrolysate (obtained via birch pretreatment). 3D open-cell aluminum foams were coated with commercial TiO₂. The foams were dip-coated in a solid slurry consisting of TiO₂ dispersed in water and binders. Coatings were found to be reproducible and mechanically stable. Catalytic activity testing of the TiO₂ foams showed ∼60-70% furfural selectivity at near-complete xylose conversion in the range of 170-190 °C. The enhanced mass transport properties of foams minimized the formation of insoluble humin species in the aqueous phase. Employing <i>sec</i>-butylphenol (SBP) as the organic extractant enables long-term operation for at least 36 h. This is due to the coextraction of furfural and 5-hydroxymethylfurfural (obtained from glucose in the feed). Varying foam thickness while maintaining constant mass of washcoat showed absence of both external and internal mass transfer limitations. Finally, performing xylose dehydration at 190 °C using TiO₂-coated foams enabled a remarkably high furfural productivity of 5.8 × 10^-2 g_furfural g_cat ^-1 min^-1, over an order of magnitude greater than the highest reported in the literature.