pH-Controlled Efficient Conversion of Hemicellulose to Furfural Using Choline-Based Deep Eutectic Solvents as Catalysts

The valorization of hemicellulose isolated from lignocellulosic biomass (wheat straw, rice husk, and bagasse) to furfural was achieved by pH-controlled acid catalysis using choline-based Bronsted acidic (BA) and natural acidic (NA) deep eutectic solvents (DES) serving both as catalyst and solvent. The effect of pH variation on the catalytic activity of various BADES and NADES prepared in 1:1 molar ratio was observed, and choline chloride/p-toluene sulfonic acid (ChCl/p-TSA) was found to be the best with lower pH value of 1.0. The yield of furfural decreased from 85 to 51% with increase in pH from 1.0 to 3.0. The molar ratio of hydrogen bond donor to acceptor components was varied from 1:1 to 1:9 to achieve the lowest possible pH values of the DESs and to increase the furfural yield. Further optimization of reaction conditions was also done in terms of DES loading, time of reaction, and temperature using the model DES to achieve higher furfural yield. The best results were obtained using 5 mmol DES at pH 1.0 in 1.5 h at 120 degrees C. ChCl/p-TSA and ChCl/oxalic acid among BADES and ChCl/levulinic acid among NADES investigated in this work yielding 85% furfural were found to be most efficient. The reported methodology is advantageous in terms of using bio-based green solvents, mild reaction conditions, and efficient scale-up of the reaction. The DESs were found to be efficiently recyclable up to five consecutive runs for the process.

Automated summary

In this study, valorization of hemicellulose isolated from lignocellulosic biomass to furfural was achieved through pH-controlled acid catalysis using choline-based Bronsted acidic and natural acidic deep eutectic solvents. The optimal deep eutectic solvents were found to be ChCl/p-TSA and ChCl/levulinic acid, yielding 85% furfural. The reported methodology offers advantages such as using bio-based green solvents, mild reaction conditions, and efficient scale-up of the reaction.