Mechanism of the Concentrated Acid Hydrolysis
A generally accepted explanation of dissolution of cellulose in acid involves the penetration of concentrated acids into the cellulose structure by disrupting hydrogen bonding network, which leads to cellulose swelling and glycosidic bond breakage. The
first account on a systematic study on dissolution of cellulose in concentrated acid was reported by Saeman et al. in 1945, where they reported that cellulose swells at atmospheric pressure and room temperature when sulfuric acid concentration is higher than 50%. Furthermore, they found that as the concentration is increased further to above 62% (or 39% hydrochloric acid), cellulose changes from a limited swollen state into a soluble state [11]. Later, Rovenskii et al. [12, 13] and Camacho et al. [14] also studied the effect of sulfuric acid concentration in the 31-70% (w/v) range on the solubilization rate of microcrystalline cellulose at temperatures in the 25-40°C range. This study also showed that total solubilization of the cellulose is possible in concentrations above 62% (w/v) within 4 h. These solubilizations are shown to follow zero — order kinetics [14].