The Fundamental Study On Supported Transition Metal Oxides Catalyst For Seawater Flue Gas Desulfurization Application

Coal is the largest source of energy in China. However, most coal was combusted without cleaning, which would emit a large amount of SO₂ to atmosphere if not post-processed. Thus desulfurization after combustion (flue gas desulfurization) becomes the most effective method to reduce SO₂ emission in China. The seawater flue gas defulfurization (FGD) has a range of application in the coastal power plant in China. However, the application of this process is limited by the excessive use of water, and the large demand on land area for aeration tank.In this thesis, the FGD process was optimized by adding supported transition metal oxide catalysts to the system. The optimization enhanced the SO₂ removal performance under low temperature and low pH environment. It can be used in the seawater FGD process for the coastal power plants whose fuel is high sulfur coal.A series of ceramic and natural clinoptilolite catalysts supported by Fe₂O₃ and MnO₂ have been prepared. This paper investigates the types of supporters, supporting methods, calcination temperatures and the reaction temperature conditions, which may impact the effect of desulfurization. The catalysts are characterized by SEM-EDS, TEM, XPS, XRD and H₂-TPR to determine the properties and structures which may impact the catalytic activity. The catalysts have a high SO₂ removal efficiency in the whole temperature range investigated (50℃, 60℃, 70℃, 80℃and 90℃). Different dynamic models have been used to calculate the dynamics of ceramic and natural clinoptilolite catalysts before and after supported. The conclusions as following:(1) The active components of ceramic supported catalysts were Fe₂O₃ and MnO₂, which were determined by XPS. Ceramic supported Fe₂O₃ catalyst which was prepared by sol-gel method has better catalytic activity than the ceramic supported MnO₂ catalyst. The SEM images show that the sol-gel ceramic supported Fe₂O₃ catalyst has a larger amount of supported Fe₂O₃ and better degree of dispersion. Ceramic supported Fe₂O₃ catalyst has the highest catalytic activity at 70℃. The rate ratio of SO₂ removal is 43.45%. After the injection of seawater, the SO₂ concentration rapidly reduces and then recovers slowly.(2) The paper investigates the impact of impregnation methods and calcination temperatures to the catalytic activity of clinoptilolite supported catalysts. For the clinoptilolite supported MnO₂ catalysts, the catalytic activity below 70℃is Mn-24h-350> Mn-24h-250> Mn-24h-500, and that of above 70℃is Mn-24h-500> Mn-24h-250. Mn-24h-350 has the highest desulfurization ratio at 60℃, which is 52.63%. For the clinoptilolite supported Fe₂O₃ catalysts, the activity of Fe-24h-250 is stable throughout the whole temperature range. Fe-24h has the highest desulfurization ratio at 70℃, which is 44.45%, but has no significant improvement over the natural clinoptilolite. The desulfurization activity of Mn-clinoptilolite is higher than Fe-clinoptilolite.(3) Because the natural clinoptilolite has more uniform channels than ceramic, it can be combined with the metal oxides more easily. The clinoptilolite supported catalysts in the whole temperature range have much higher activity of SO₂ removal.(4) The external diffusion control model and oxygen activation control model have been used to calculate the dynamics of seawater FGD process with catalysts. The calculation reveals that the reaction orders of the catalysts by either of the two supporters are both approximately to 1. And the ceramic supported catalysts behave much closer to the external diffusion control model. The clinoptilolite supported catalyst (Mn-24h-350) behaves closer to the other one. The temperature dependence of the reaction rate in this paper complies with the Arrhenius equation of ceramic supported catalysts and clinoptilolite supported catalyst (Mn-24h-350). Whereas the dependence of reaction rate of natural clinoptilolite does not comply the commonly used Arrhenius equation, due to the fact that the natural clinoptilolite adsorbs SO₂ with some extent.