The Chemistry of Acid Catalyzed Delignification of Sugarcane Bagasse in the Ionic Liquid Trihexyl Tetradecyl Phosphonium Chloride

This article reports on the cleavage of lignin beta-aryl ether bonds in sugarcane bagasse by the ionic liquid (IL) trihexyl tetradecyl phosphonium chloride [P66614] Cl, in the presence of catalytic amounts of mineral acid (ca. 0.4%). The delignification process of bagasse was studied over a range of temperatures (120 degrees C to 150 degrees C) by monitoring the production of beta-ketones (indicative of cleavage of beta-aryl ethers) using FTIR spectroscopy and by compositional analysis of the undissolved fractions. Maximum delignification was obtained at 150 degrees C, with 52% of lignin removed from the original lignin content of bagasse. No delignification was observed in the absence of acid, which suggests that the reaction is acid catalyzed with the IL solubilizing the lignin fragments. The rate of delignification was significantly higher at 150 degrees C, suggesting that crossing the glass transition temperature of lignin effects greater freedom of rotation about the propanoid carbon-carbon bonds and leads to increased cleavage of beta-aryl ethers. An attempt has been made to propose a probable mechanism of delignification of bagasse with the phosphonuim IL.