| Biodiesel is a kind of "safe, clean and high combustion efficiency" energy, it has received much attention in recent years. However, large surplus of crude glycerol is produced as the main by-product in the production of biodiesel with the rapid development of biodiesel industry. According to recent estimates, the world-wide production of glycerol could have reached 2 million tons in 2010 and it is expected to grow in the near future due to the increasing demand for biodiesel. Consequently, new applications for glycerol, as a low-cost raw material, need to be developed. On the other hand, CO2 is recognized as main green house gas and most abundant Cl building block, the conversion of CO2 to useful compounds has attracted much attention recently.The synthesis of glycerol carbonate from glycerol and CO2 has been considered as an attractive process because it has a variety of applications due to its low toxicity, high boiling point, biodegradability and two active functional groups. It can be used as a new component of gas separation membranes, polyurethane foams and surfactant as well as the component in coatings, paints and detergents, etc. Oxidative carbonylation reaction is the best way to prepare glycerol carbonate due to its high atom efficiency among many approaches. However, the reaction route suffers from difficulty in harsh reaction conditions such as high temperature and high pressure.and thermodynamic limitations. It has great importance to prepare glycerol carbonate through the method of oxidative carbonylation.The synthesis of glycerol carbonate from glycerol and CO2 catalyzed by Co3O4 has been investigated in the third part. Glycerol and CO2 can be activated by Co3O4 for p-type semiconductor can transfer electrons. Various parameters such as reaction temperature, the mass of catalyst, reaction time and the initial filled pressure have been investigated in detail. Under initial pressure 5.5 MPa,170℃ for 6 h, and acetonitrile was used as solvent and dehydrant, the conversion of glycerol, the yield of glycerol carbonate and the specific reaction rate were 45.3%,7.3% and 1.314 h-1, respectively. Moreover, a reaction mechanism was proposed for oxidative carbonylation of glycerol to glycerol carbonate related with a metal chelate with five-membered ring which was considered as active species. Then CO2 was activated by the active species and glycerol carbonate was produced last.In the forth chapter of this paper, the CNx and Al2O3 were prepared by thermal decomposition at high temperature with melamine and AlOOH as the precursors. ZnO-bascd catalysts supported on different supports (ZnO/CNx, ZnO/Al2O3, ZnO/CNx-Al2O3) were prepared by an impregnation method with the precursor of Zn(OAC)2·2H2O. Also, the different loading of ZnO on the CNx-Al2O3 (mmelamine:mAlOOH=3:1) support was studied. The prepared catalysts were characterized by N2-sorption, SEM and CO2-TPD. And we try to establish the relationships between reaction activity and acid-base properties of the catalysts. Some conclusions can be reached as follows:(1) A better catalytic activity can be obtained with the sample 3.6 wt% ZnO/CNx-Al2O3 (mmelamine:mAlOOH=3:1). Under initial filled pressure 5.5 MPa,160℃ for 12 h, and acetonitrile was used as solvent and dehydrant, the conversion of glycerol, the yield of glycerol carbonate and the specific reaction rate were 48.5%,14.0% and 0.274 h-1, respectively.(2) ZnO species have a strong ability for glycerol activity and the amount of ZnO loading has significant impacts on the catalytic performance.(3) CO2 can be activated by CNx contained Lewis base and CNx is essential for a better catalytic activity. We propose that there is synergistic effect of CNx and Al2O3 on the performance of the ZnO complex catalyst. And the medium strength basic sites may play an important role in the carbonylation of glycerol and CO2. |
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