Solid-acid and ionic-liquid catalyzed one-pot transformation of biorenewable substrates into a platform chemical and a promising biofuel

Abstract

A wide variety of polymeric carbohydrate-rich weed species were directly converted to a platform chemical, 5-hydroxymethylfurfural (HMF), and a promising next-generation biofuel, 5-ethoxymethyl-2-furfural (EMF), with homogeneous and heterogeneous catalysts under mild reaction conditions. Brønsted acidic IL catalysts, [DMA]⁺[CH₃SO₃]⁻ and [NMP]⁺[CH₃SO₃]⁻, were found to be effective enabling maximum 58 and 52 wt% HMF yields, respectively, from foxtail weed. Strong Lewis acidic silica supported heteropolyacid (HPA-SiO₂) catalyst was also effective producing a maximum 32 wt% HMF from the same weed substrate. Both IL catalysts were effective for high-purity EMF production from HMF and weeds. HMF was quantitatively converted to EMF in 2 h. In the case of weed substrates, EMF was formed as the major product. The ratio of EMF and ethyl levulinate (EL) in the isolated product was 7 : 1. To address the sustainability issue and potential industrial application opportunity of the current method, a larger scale experiment under conventional heating demonstrated to produce 55 wt% HMF in 4 h. Most importantly, the spent catalyst and the solvent system were efficiently recycled for four consecutive catalytic cycles without a significant loss in yield.