|中文摘要||Fischer-Tropsch (F-T) synthesis is an important means to convert coal, natural gas, biomass and other carbonaceous resources into high quality liquid hydrocarbon fuels free of sulfur and nitrogen and low in aromatics. However, the traditional F-T synthesis is featured by the Anderson-Schultz-Flory (ASF) distribution with the wider carbon number distribution of the products. How to suppress the formation of methane and light hydrocarbons and increase the proportion of middle distillates (gasoline and diesel fractions) is not only one of the most important direction to improve the F-T synthesis technology, but also the most difficult challenges in the F-T synthesis research. Co-based catalyst is considered to be the best F-T synthesis catalyst for middle distillate products due to its high activity, high stability, high selectivity towards alkanes and low water-gas shift reaction.This report focuses on the influences of support properties (SBA-15 and ZSM-5), promoter of Zr and preparation methods on the structure, surface physical and chemical properties of the catalysts and product distribution. The main bodies of the work included the following aspects:The influence of the addition of several zeolites (such as ZSM-5, USY and Hβ) and the incorporation manner of ZSM-5 on the catalytic performance of the Co-based catalysts was studied. The preparation method of the catalyst with Co impregnated on the composite support of SBA-15 and ZSM-5 mechanically mixed was established. And the catalysts prepared by this method showed a moderate size of cobalt particles, favorable cobalt-support interaction and moderate acidity, leading to the maximum selectivity to gasoline and diesel distillate.The effect of the amount of ZSM-5 addition in the composite support on the structure, surface physicochemical properties of the catalyst and the product distribution was subsequently researched. It was found that the catalyst with 20% ZSM-5 in the composite support was shown to have the maximum pore volume and degree of cobalt particle dispersion, as well as the moderate reduction of the catalyst and acidity, which facilitated to the production of the gasoline and diesel fractions. This catalyst also showed well stability during 600 hr continuous run with the CO conversion and C5+ selectivity remaining stable after a 50 hr induction period, and the ratio of n-alkanes in the product was gradually increased.A series of Co-Zr-SBA-15 F-T catalysts were prepared using the co-impregnation method, stepwise-impregnation method and in-situ synthesis method to incorporate Zr as a promoter. It was shown that the CO conversion (80%) and chain growth probability (α=0.78) were lower on the catalysts prepared by in-situ synthesis method due to the stronger interaction between cobalt and zirconium. Conversely, higher selectivity of diesel distillate (C12-C22) and higher chain growth probability (α=0.84) were observed on the catalysts prepared by stepwise-impregnation method, which could be attributed to the larger pores, larger particle size of cobalt, weaker interaction between cobalt and zirconium. While the higher selectivity of gasoline distillate (C5-C11) and moderate chain growth probability (α=0.81) were observed on the catalysts prepared by co-impregnation method.|
李琢. 高馏分油选择性钴基费托合成催化剂的开发及催化工艺研究. 2015.