Enhanced α-Terpineol Yield from α-Pinene Hydration via Synergistic Catalysis Using Carbonaceous Solid Acid Catalysts

A carbonaceous solid acid catalyst was prepared from Kraft lignin through the approach of incomplete carbonization and subsequent sulfonation in which Kraft lignin is activated by potassium hydroxide impregnation. The catalyst obtained has a hierarchical porous structure containing micropores, mesopores, and macropores with a moderate specific surface area of 400.6 m(2).g(-1), high total acid density of 4.34 mmol- sulfonic acid density of 0.92 mmol.g(-1), and good amphiphilicity to water and alpha-pinene. The catalyst has an excellent catalytic activity on the synthesis of alpha-terpineol from hydration of alpha-pinene, showing a conversion of 97.8% and a yield of 52.2%, which are much better than those gained by using sulfuric acid or a commercial Amberlyst-15 catalyst under the same conditions. Moreover, it was found that oxygen-containing groups such as carboxyl, hydroxyl, and carbonyl groups functioning as binding sites in the catalyst are significantly enhanced after sulfonation and play an important role in improving the selectivity of the reaction.