CO₂-catalyzed Hydrolysis Of Cotton Cellulose To Glucose In High-temperature Liquid Water

Hydrolysis of cellulose to glucose and further fermentation to ethanol is a promising way in exploiting biomass resources from the viewpoint of energy shortage and environment pollution. Utilizing the low corrosiveness and the weak acidity of CO2 and the less severity of high-temperature liquid water, it is expected to hydrolyze cellulose to glucose in high yield and avoid the corrosiveness in the traditional strong acid catalyzed hydrolysis process of cellulose. Using degreased cotton fiber as model cellulose and CO2 as an acid catalyst, the hydrolysis of cellulose to glucose under high-temperature conditions was studied thoroughly in this dissertation.To better understand the glucose degradation behavior, the stability of glucose in super(sub)critical water and in super(sub)critical methanol were investigated respectively. The experimental results showed that temperature had an important effect on the stability of glucose. Glucose stability decreased with rising temperature both in water and in methanol. The effect of pressure on stability of glucose in the super(sub)critical water was unnoticeable, while the stability of glucose decreased with the increase of pressure and leveled off after reaching critical pressure in methanol. The longer the residence time was, the lower the stability of glucose would be. In addition, it was found that glucose in super(sub)critical methanol was more stable than in super(sub)critical water.CO2-catalyzed hydrolysis of cellulose to glucose was systematically studied in high-temperature liquid water in a batch-reactor. The glucose yield depends on the difference between the hydrolysis rate of cellulose and the decomposition rate of glucose. The experimental results indicated that the best yield of glucose presented at the vicinity of 200℃, and glucose decomposed rapidly at the temperature higher than 200℃. The acidity is stronger at high CO2 pressure than that at low CO2 pressure. The selectivity of glucose increased with the pressurization at low pressure and then decreased after reaching a maximum at 10 MPa, indicating that high CO2 pressure not only accelerated the hydrolysis of cellulose, but also decreased the stability of glucose. Excess reaction time decreased the stability and the selectivity of glucose. Kinetics of hydrolysis of cellulose to glucose was also studied. An isothermal kinetic model and an isobaric kinetic model were established, respectively. The relative standard deviations between the model calculated values and the experimental results were both less than±15%. The kinetics analysis showed that increasing temperature appropriately was beneficial to the increase of glucose yield. However,too high temperature would decrease the selectivity of glucose. High CO2 pressure not only accelerated the glucose formation but also the decomposition of glucose.