| Because of the unrestrained exploitation of the limited fossil resources, people now meet the unprecedented challenges of the global energy and environmental crisis. The exploitation of new green processes as well as developing new renewable energy has been a hot issue to the researchers. As an environmental friendly green solvent, supercritical carbon dioxide has superior salvation ability and mass transfer characteristics hence become the first choice in green process development. The relevant basical research and application have attracted more attention of international academic arena.Aiming at the advantages of the SCFs, experiments of oxidation of benzyl alcohol and cellulose hydrogenation of ethylene glycol were carried out in scCO2, and established the appropriate analytical methods. The conditions and feasibilities of the two processes were investigated respectively with catalysts Au-Cu/SiO2-APTS and W2C/AC. The thermodynamic was calculated, and some Mechanisms and optimization of experimental possibilities were proposed. Some main conclusions are obtained as follows:1. Effects of reaction time, reaction temperature, total system pressure and oxygen partial pressure on the oxidization of benzyl alcohol were investigated. The result showed that the yield of benzaldehyde was 82.7% and the selectivity was 100% at the optimal condition of 80℃, oxygen partial pressure of 1.5MPa, system pressure of 13.5MPa and 4h. It was confirmed that the effect of system pressure on the oxidation was induced by the change of phase. The moderate oxygen partial pressure could be helpful to the reaction, but higher amount of oxygen could deactivate the metal oxide catalyst. The high yield and selectivity could be both achieved under high temperature and short time. However the temperature should be controlled because benzaldehyde would be over oxidation under higher temperature.2. Effect of water in the cellulose catalytic hydrogenation reaction had been studied. The results that pure scCO2 and ethanol as solvent didn't effect the reaction indicated that the water, not only as a co-solvent, provided H+ at high temperature to created the hydrolysis condition, and the yield of ethylene glycol increased as soon as increasing the amount of water. In the case of a fixed H2 partial pressure, adding CO2 could enhance the solubility property of system, provide the acid environment and thus promote the yield of ethylene glycol. It found that after changing the ratio of CO2 to H2 the amount of water or H2 was reduced in certain extent at a fixed total pressure, which could decrease the cost, reduce the pollution and increase the safety of production.3. Binary interaction parameters had been obtained by fitting the two systems calculated with PR-BM thermodynamics model. The results showed the solubility of benzyl alcohol as well as benzaldehyde in CO2 was affected by temperature and pressure by calculating the phase behavior and component distribution of initial materials. In addition, the experimental results of hydrotreating cellulose showed that the critical temperature and pressure of the system could be reduced in the mix system, but the poor experimental results showed that the mass diffusivity of the solution was not the main factor for the reaction.The results displayed above can supply experimental data and theoretic reference for the further investigation of the oxidation and hydrogenation reaction in supercritical carbon dioxide. |
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