Analysis of carbon deposition behavior in methane reforming in order to evaluate the catalyst life

在甲烷重整反应中，最严重的问题之一是反应过程中的碳沉积。然而，对碳的生成途径和碳的结构的研究还不够深入。尤其是在长寿命催化剂的研制中，信息是非常重要的。本论文的研究目的是阐明催化剂寿命与积炭行为之间的关系。考察了不同催化剂上CO2、水蒸气和CO2+水蒸气催化甲烷重整反应。考察了活性测试、反应温度依赖性、空速依赖性和总压依赖性。结果表明，NiO-MgO固溶体催化剂表现出优异的催化性能。尤其是低比表面积的固溶体催化剂比高比表面积的固溶体催化剂表现出更强的抗积碳性能。通过对催化剂床层不同位置的积炭情况的分析，发现催化剂床层入口的积炭受到抑制。这表明甲烷分解生成的碳受到了抑制。此外，还考察了其他金属添加剂的影响。目前，锡的添加抑制了碳的沉积，优良的催化剂也被应用于甲烷内供氧甲烷重整的流态化反应系统。流态化反应系统提高了甲烷的转化率，发现在高压条件下根本没有观察到积碳。这是由于反应器中活性催化剂的原位复制造成的。

In methane reforming, one of the most serious problems is carbon deposition during the reaction. However the investigation of the route of carbon formation and the structure of formed carbon is not enough. Especially, in the development for the long-life catalyst, the information is very important. The research of the purpose is the elucidation of the relation between the catalyst life and carbon deposition behavior.I investigated the methane reforming with CO_2, steam and CO_2+steam over various catalysts. The activity test, reaction temperature dependence, space velocity dependence, and total pressure dependence have been investigated. As a result, NiO-MgO solid solution catalysts showed excellent performance. Especially, the solid solution catalyst with low surface area exhibited much higher resistance to carbon deposition that that with high surface area. From the analysis ol the carbon deposition at various position of the catalyst bed, it is found that the carbon deposition at the inlet of the catalyst bed was inhibited. This indicates that the carbon formation from the methane decomposition is inhibited. Furthermore, the effect of other metal addition is also investigated. At present, the addition of Sn inhibited the carbon deposition.The excellent catalyst is also applied to the fluidized reactor system for the methane reforming with internal heat supply using oxygen introduction with the reforming agents. Fluidization reaction system enhanced the methane conversion and it is found that the carbon deposition is not observed at all under highly pressurized condition. This is caused by the in-situ reproduction ol the active catalyst in the reactor.