Conversion of saccharides in enteromorpha prolifera to furfurals in the presence of FeCl3

[Display omitted] •The promotion effect of FeCl3 for the conversion of carbohydrates in E. prolifera.•45.0 wt% yield of furfurals were obtained at 190 °C in FeCl3-H2O-THF-NaCl system.•Fe-polysaccharides complex formed in situ was catalytically active to HMF production.•The rehydration of HMF was suppressed by Fe-polysaccharides complex.•THF extracted and protected HMF from the reaction system. In this work, the conversion of saccharides in Enteromorpha prolifera (E. prolifera) in the presence of a series of metal chloride was studied. FeCl3, was found the best precursor of catalyst for obtaining furfural products, with 8.9 wt% 5-hydroxymethylfurfural (HMF), 14.9 wt% 5-methylfurfural (5-MF), and 4.2 wt% 2-formylfuran (FF) without levulinic acid (LA) formation, under the optimized reaction conditions (190 °C, 60 min and 0.0125 mol/L FeCl3 loading). In H2O-THF-NaCl bi-solvent system catalyzed by FeCl3 derived species, the highest yields of furfurals (20.0 wt% HMF, 19.8 wt% 5-MF, and 5.2 wt% FF) could be obtained when 2 wt% NaCl was added. With the help of THF by in situ extraction, nearly 90 % of the furfural products was enriched in the THF phase, while H2O had a great contribution to the dissolution and hydrolysis of polysaccharides. The catalytic activity and product selectivity of FeCl3 for the conversion of other saccharide model compounds were also studied comparatively. In the presence of FeCl3, the hexose model compounds were converted to LA, whereas those in E. prolifera to HMF. It was found that FeCl3 might interact with the saccharides from E. prolifera to form new species, which could catalyze the conversion of hexose to HMF without LA generation. The new species was considered as a kind of complexes containing Fe(II), which suppressed the rehydration decomposition of HMF. This work provided an effective method for the production of value-added chemicals from E. prolifera.