Lignosulfonate-based sulfonated polymers for highly efficient one-pot conversion of fructose into 5-ethoxymethylfurfural in ethanol

A renewable lignin-derived sulfonated polymer solid acid (LFS) was fabricated by sulfonating the polymerization material of industrial waste sodium lignosulfonate and bio-based furfural. The prepared bio-based LFS was first reported as a cost-effective catalyst for the one-pot selective dehydration-etherification of fructose in ethanol to produce green bio-fuel 5-ethoxymethylfurfural. Compared to conventional cation-exchange resins, LFS had multiple acidic sites with diverse strengths. Moreover, the hydrophobic property of LFS was retained even after grafting adequate -SO3H groups into the polymer framework. The LFS displayed a satisfactory catalytic activity, and a highest 5-EMF yield of 68.4 % was gained from fructose one-pot dehydration-etherification in ethanol at 120 °C within 40 min, which was more effective than the homogeneous acid catalysts, conventional acid resin Amberlyst-15, and some mesoporous solid acids in 5-EMF production from fructose. This superior catalytic ability of the LFS catalyst was resulted from its multiple acidic sites with diverse strengths dispersed around the hydrophobic catalyst skeleton. More significantly, the leaching and recyclability tests suggested that the as-prepared LFS exhibited notable stability and reusability with only a slight drop in 5-EMF yield from 68.4 % to 60.8 % after five cycles.