Enhanced Hydrolysis of Cellulose to Reducing Sugars on Kaolinte Clay Activated by Mineral Acid

Kaolinite, a natural, layered phyllosilicate, has been used as the solid catalyst for the hydrolysis of cellulose in our previous work. In the present study, kaolinite was activated by mineral acid and further evaluated for the hydrolysis of cellulose in water. The acid-activated kaolinite was characterized by XRF, XRD, FT-IR, BET and TG. The effects of reaction temperature, reaction time, mass ratio and water amount were investigated in the system. It was found that the highest total reducing sugars (TRS) yield of 50.2% was obtained on the kaolinite activated by 20% HNO3 with the mass ratio of catalyst to cellulose of 0.2 and water to cellulose of 14 at 205 ℃ for 3 h. Moreover, the catalyst was easily regenerated by calcination and the yield of TRS on the regenerated catalyst changed between 50.2% and 45.2% after four times reuse. The results showed that the acid activation could influence the crystallinity and improve the specific surface area, but the high TRS yield of the activated kaolinite should be ascribed to the increasing of the interlayer Al–OH groups and the formation of inner hydrogen bonds between the octahedral sheets and tetrahedral sheets. Finally, it was suggested that this was the effective way for improving the catalytic performance by increasing the interlayer Al–OH groups on the kaolinite catalyst.