Catalytic solvent delignification of agricultural residues: organic catalysts

The effects of moderate‐temperature aqueous butanol pretreatment of rice straw on several organic catalysts have been studied. Maximum delignification was obtained with an aromatic organic acid catalyst. Presoaking of straw in aqueous improved delignification, particularly in high solid–liquid rations. However, due to the difficulty of penetration of lignin into the solvent phase, an increase in the solid‐liquid ratio appears to affect delignification. A two‐stage catalytic solvent process involving presoaking at 80°C followed by delignification at 120°C resulted in 83% removal of lignin in aqueous‐butanol, whereas 75% lignin removal was possible in ethanol. Higher reduction in the crystallinity was possible with etanol. Lignin produced by the solvent process offers desirable physical properties for polymer applications compared to Kraft lignin.