A hybrid strategy for efficient valorization of bulrush into furoic acid in water–ChCl-based deep eutectic solvent

Abstract

Furoic acid, an important biobased furan chemical, was synthesized from available, inexpensive and renewable bulrushes (Phragmites communis) via chemoenzymatic route in aqueous media containing DES (deep eutectic solvent) as an additive. Organic carboxylic acid as HBD (hydrogen-bond-donor) was used to prepare ChCl-based DES for transforming bulrushes to furfural. By studying the relationship between pKa value of different organic acids in DESs and furfural yield, ChCl-based DES with citric acid (pKa = 3.13) as HBD could obtain higher furfural yield. ChCl:Citric acid (20.0 vol% dose) yielded furfural (75.5 mM) at 47.64% yield from AS-bulrush (NaOH-soaked bulrush) at 180 °C in 30 min. Characteristics of untreated and pretreated bulrushes were captured with XRD (X-ray diffraction), FT-IR (Fourier transform infrare spectra), and SEM (scanning electron microscope). AS-bulrush-valorized furfural was sequentially biotransformed into furoic acid with HMFOMUT (Recombinant E. coli HMFOMUT) whole-cells at 30 °C in ChCl:Citric acid–H2O (pH 7.0). The yield of furoic acid reached 42.51% after 56 h. This study developed an environmentally friendly strategy for chemoenzymatic cascade catalysis of lignocellulosic biomass into furoic acid via tandem chemocatalysis and biocatalysis in ChCl:Citric acid–H2O. It was feasible to produce value-added furan-based chemicals from the renewable sources.