Synthesis of a Homogeneous Propyl Sulfobetaine-Tungstophosphoric Acid Catalyst with Tunable Acidic Strength and Its Application to Waste Wood Hydrolysis

The preparation of an ionic liquid (pyridinium propyl sulfobetaine; PPS)-heteropolyacid (tungstophosphoric acid; H3PW12O40; TPA) composite catalyst and its performance during hydrolysis of waste wood powder are reported. The acidic strengths of various aqueous PPS-TPA and sulfuric acid (H2SO4) solutions were assessed by 31P nuclear magnetic resonance (NMR) spectroscopy using the dissolved trimethylphosphine oxide (TMPO) as the probe molecule. Accordingly, an aqueous PPS-TPA catalyst with acidic strength resembling that of a conventional industrial liquid acid, namely 2 wt% aqueous H2SO4 solution, was selected for further studies. The aqueous PPS-TPA catalysts, which exhibited unique physicochemical properties and self-separation characteristics, were found to exhibit superior catalytic performances for hydrolysis of wood powder compared to that of aqueous H2SO4 solutions. In addition, the organic–inorganic PPS-TPA composite catalysts tend to inhibit the formation of inhibitors such as 5-hydroxymethylfurfural (HMF) and furfural during hydrolysis of lignocellulosic biomass, hence, well-suited for the productions of glucose and xylose.