Study On Cobalt Based Catalysts For Fischer-Tropsch Synthesis

The Fischer-Tropsch synthesis (FTS) offers the potential of converting syngas into high value chemicals. China has rich natural gas resources, but mostly in remote areas, leading to transportation difficulties. Through the F-T synthesis into liquid fuel, it makes it easy to transport. Zhejiang Province has rich natural gas resources and biomass resources in The East China Sea oilfield. F-T synthesis can solute the problem of oil resources shortage in Zhejiang Province. From energy and economic sense, or the F-T synthesis as a new industry terms, the F-T synthesis has important practical and theoretical significance in Zhejiang province with natural gas and bio-based raw materials.The type and pretreatment of SiO₂ supports, cobalt loading content, calcination and reduction temperature, reduction time, solvents, dry condition and promoters were studied in this paper. F-T synthesis was carried out on a fixed bed reactor. Several characterization technologies, such as XRD,TPR,IR and so on, were used in order to understand the relationship between the above factors and F-T synthesis activity of cobalt catalysts. Main results of this work are listed bellow:The supports' pore size, pore volume, stability of Si-O bond and crystal morphology are very important factors. The suitable pore diameter range is between 4-8nm. Catalysts reduction ability is affected significantly by the Si-O bond stability. In the case of the Si-O bond is weak, CoSiOx can be formed by Co and part of SiO-, which leads to decrease reduction ability. On the contrary, if the Si-0 bond is strong, only weak SiO-Co bond can be formed, which can be reduced easily. Catalysts supported on amorphous SiO₂ have a better reduction performance than that with crystal SiO₂The optimum coalt loading content depends on support SiO₂. Six hours are the best time period for reduction. If the reduction time is not enough, the catalysts can not be reduced well, however, if the time is too long, the catalysts will be sintered and crashed easily. The catalysts calcined at 350℃have a high reaction activity, lower CO₂ and CH₄ selectivity than that of 400℃. Reduction is not complete if the temperature is 250℃or below. No sintering appeared in the catalysts which were calcined at 450℃. The best prepare condition is to vacuum supports before impregnation, use dehydrated alcohol as solvent, and utilize microwave to dry and calcine catalysts.Catalysts' antioxidant properties can be improved by the addition of Zr. Zr also can inhibit the reaction between Co and SiO₂ to some extent and form new Co-Zr specie which can be easily reduced. the reactivity difference of Co catalysts added with Zr were not caused by crystal size.