Evaluation of Deep Eutectic Solvents for Xylan-Based Furfural Synthesis

This study investigated the catalytic conversion of corncob-derived xylan to furfural (furan-2-carbaldehyde) using deep eutectic solvents (DESs). An improved method for recovering furfural from xylan and xylose in agricultural waste streams was developed using a cost-effective chloride-based DES and ferric chloride (FeCl3) as catalyst. The solvents were synthesized using choline chloride (ChCl) as a hydrogen bond acceptor and malic acid (MA) as a hydrogen bond donor. Additionally, sodium chloride (NaCl) and ferric chloride (FeCl3) were explored as a cheaper substitute for ChCl, while the FeCl3 + MA DES was also investigated as an alternative system. DESs were prepared with a 1:1 molar ratio of components at 80 °C. The physical properties of the synthesized DES were evaluated using differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), rheology, and thermogravimetric analysis (TGA). The effects of temperature, reaction time, catalyst, and solvent composition on furfural yield were investigated. Compared to NaCl + MA DES and FeCl3 + MA DES, the ChCl + MA DES appeared as a moderately viscous transparent liquid and exhibited favorable solvent properties. The highest furfural yields were achieved at 160 °C and a reaction time of 30 min at 87% for xylose in ChCl + MA + FeCl3 DES and 82% for xylan in ChCl + MA DES, while FeCl3 + MA DES showed significantly lower yields at 7% and 2% for xylose and xylan, respectively. This newly improved method using a NaCl-ChCl DES represents the most cost-effective and efficient approach for furfural production.