Study On Decomposition Of Cellulose To Levulinic Acid Under Subcritical H₂O-CO₂ Conditions

Nowadays, the fossil resource is severely exhausted. The biomass is a kind of renewable resource, and is being studied by more and more people. The decomposition of cellulose, which is the largest kind of biomass, to levulinic acid which is called"green platform chemical"is going to be studied in this paper.In this study, subcritical H₂O-CO₂ system was used as the reaction media. The technologcial conditions for preparation of levulinic acid were studied. The quantitative analysis method of levulinic acid by HPLC was established. The relationship between reaction rate and product yield was studied. Combined with the pyrolysis of cellulose, the mechanism of cellulose hydrothermal decomposition was discussed.The mass yield of levulinic acid was used as the research target. The optimum technologcial conditions were determined: mass feed ratio of water and cellulose 1:0.0135, temperature 290℃, CO₂ molar fraction 7.5%, pressure 17.2MPa and time 15min. Under above conditions, the mass yield of levulinic acid was up to 34.99%, and accounted for 49% of theory mass yield (71.4%).Another experiment was set by substituting N₂ for CO₂. And the results showed that high pressure was helpful for the improvement of mass yield of levulinic acid. The addition of CO₂ to subcritical water could increase the pressure; on the other hand, it could enhance the acidity of the system. This promoted the decomposition of cellulose, and improved the mass yield of levulinic acid.Through the qualitative analysis of products in cellulose pyrolysis and hydrothermal decomposition by GC-MS, it could be concluded that the hydrothermal decomposition of cellulose was a complex process which included hydrolysis, pyrolysis, dehydration, and so on. The reaction contains several stages: cellulose→levoglucosan→5-hydroxymethyl-furaldehyde→levulinic acid. After the mechanism for the preparation of levulinic acid was analyzed, the networks for the decomposition of cellulose under subcritical H₂O-CO₂ conditions werre obtained.The research of reaction rate showed that the system was a first-order reaction under the conditions which were 250℃～310℃, 7.5%CO₂, and 17.2MPa. The apparent activation energy of the reaction (E_a) is 141.52kJ/mol. The relationship between reaction rate and product yield is as follows:...