Coupling of metal halides with a co-solvent to enhance and consolidate co-production of furfural and 5-HMF from lignocellulosic biomass

We recently developed a novel co-solvent system using THF and dilute sulphuric acid to enhance the delignification, hydrolysis, and cyclodehydration  reactions from raw maple wood to produce furfural at very high yields (87%) and a highly digestible glucan-rich material suitable for conversion into 5-HMF, LA, or ethanol.¹ However, mineral acids typically used are highly corrosive and are not easily recyclable. In addition, sulphuric acid promotes 5-HMF hydrolysis to LA and rapid furfural degradation, thus requiring a two-stage reaction to obtain the high LA yields (75%) we reported. In this study, we exploit the Lewis acid activities of metal halide acid catalysts in our THF co-solvent system to achieve even higher yields of furfural and 5-HMF from raw maple wood and corn stover in a one-pot reaction. At moderate solvent-to-water ratios, we obtained product yields of 95% for furfural and 51% for 5-HMF (of theoretical) in a clean organic phase that can then be delivered directly to a catalytic reactor for upgrading into fuel components. We also demonstrate how the catalyst can be recycled in the aqueous stream. Furthermore, similar to our previous study, after vacuum recovery of the solvent, over 93% of the K-lignin initially present in biomass was recovered as a highly oxidized powder suitable for conversion into valuable chemicals. These exciting results enable a new pathway for the integrated catalytic production of hydrocarbon fuels from both the hemicellulose and cellulose fractions of lignocellulosic biomass.

1. Cai CM, TZ, RK, CEW. 2013. Green Chemistry. DOI: 10.1039/C3GC41214H.