Study On Preparation Of Glucose From Cellulose Hydrolysis In Subcritical Water

Nowdays, with the increasing demand of non-renewable fossil fuels（such as oil and coal）, utilizing cellulose to prepare ethanol is becaming ahot research topic. However, the fiber is one of the most abundantrenewable resources on the Earth, So there is a great significanc to have acomprehensive utilization on its sustainable development. Super/sub-critical water has the advantages of fast reaction rate and good solubility,so it is a good choic to complete cellulose hydrolysis in super/subcriticalwater.In this paper, a system research on the reaction mechanism and ruleof cellulose hydrolysis in super/subcritical water was carried out viacalculating the reaction kinetics parameters, investigating the influence ofdifferent reaction conditions in a batch high-pressure reactor. And apreliminary study on the hydrolysis of rice straw was done.The experimental results showed: the glucose yield graduallyincreased with reaction time when the reaction temperature is200℃.Butthe experimental phenomena was not the same when the reactiontemperature turned to220℃. In this temperature, the glucose yieldgradually increased with reaction time during the initial1h, but decreasedin the time left. There was a small amount of glucose remained after1hreaction when the reaction temperature was240℃, and the glucose yieldturned to zero after1.5hours’reaction. There was no glucose detectedwhen the reaction temperature increased to260℃. It was found that theglucose yield reached the highest point7.71%when the reaction temperature was220℃and reaction time was1h.In this paper the influences of catalysts were also investigated. It wasfound that catalysts such as AlCl₃,CoCl₂,FeCl₃,Fe₂（SO₄）₃,Fe（NO₃）₃andH₂CO₃all could improve the cellulose hydrolysis rate, but made theglucose yield great differences. When the reaction temperature was220℃the catalytic activity order, measured by the glucose yield, was:FeCl₃>CoCl₂>AlCl₃,Fe（NO₃）₃>Fe₂（SO₄）₃>FeCl₃; and the glucose yieldincreased as the raising of partial pressure of carbon dioxide. Themaximum glucose yield reached to21.45%when Fe （NO₃）₃was used ascatalyst and reacted0.5h at200℃.The cellulose reaction rate constant k₁and the glucosedecomposition rate constant k₂at different reaction temperature werecompared. It was found that k₁, k₂were increased as the temperaturerising, and k₂always greater than k₁. It proved that the decomposition rateof glucose is greater than the rate of hydrolysis of cellulose. The cellulosehydrolysis activation energy Ea1=254.24kJ·mol^-1, and the glucosedecomposition activation energy of the E_a2=203.23kJ·mol^-1. Carbondioxide can both promote the cellulose reaction rate and the glucosedecomposition rate, but the glucose decomposition rate decreased whenthe partial pressure increased, which is beneficial for the glucose yield.In this paper the hydrolysis of rice straw in subcritical water wasalso studied. But the glucose yield was relative lower compared tohydrolysis of cellulose. The highest yield of glucose was2.26%when thereaction temperature was260℃and reaction time was0.5h. Although themaximum of the glucose yield happened at260℃, but the yield decreasedwhen reaction time increased.220℃and240℃is relatively suitabletemperature for straw hydrolysis.