Study On The Iron Catalysts For Fischer-tropsch Synthesis

Light olefins(ethylene,propylene,butene)have been always regarded as vital chemical raw materials.While the sustainability of traditional light olefin production processes,which rely on petroleum resources,is challenged by the depletion of petroleum resources.The research and development for new light olefin production processes has gathered much concern in industrial R&D and academic research.Fischer-Tropsch synthesis to light olefins(FTO)process possesses the advantages of simplicity in process flow and industrial facility requirements.For the FTO process,Fe-based catalysts have the advantages of strong adaptability to reaction conditions and easier adjustment of product distribution to light olefins,which make it an ideal type of catalyst for this process.In this paper,the froth powder iron(FPI)catalyst was investigated in detail.The catalyst was prepared by the loading method and the chemical surface treatment method,respectively.The optimal preparation method of the FPI catalyst was optimized and determined.As a result,an FPI catalyst with high light olefin selectivity and high olefin to paraffin ratio of lower carbon products was obtained.In this study,we first studied the supported froth powder iron catalyst prepared by the impregnation method,including the studies about the effects of different types and different loading amounts of promoters on the performance of the supported froth powder iron catalyst for Fischer-Tropsch synthesis.Through N2 adsorption and desorption,XRD,SEM and Mapping characterization,the structural and surface characteristics of the supported froth powder catalyst were investigated.Results have shown that the 1K-1Mn/FPI catalyst with a combined loading of 1.00 wt%K and 1.00 wt%Mn is the catalyst with the best performance for Fischer-Tropsch synthesis to light olefins in this series,which the selectivity of light olefins can reach 39.8%and the C2-C4 olefin to paraffin ratio can reach 9.8.To obtain a froth powder iron catalyst with higher light olefin selectivity and higher C2-C4 olefin to paraffin ratio,this study used acidic KMnO4 solution to perform a surface treatment on the foamed.iron powder.This treatment could cause the surface of the froth powder iron to be oxidized and load an amount of K and Mn as promoters in the meantime.Through this method,a surface-treated froth powder iron catalyst with excellent FTO reaction performance is prepared.The catalyst preparation conditions with the best FTO reaction performance under this preparation method were investigated,including the c(KMnO4)was 0.30 mol·L-1,the pH level was 1.69,and the treatment time was 15 h.By this preparation method,the FPI catalyst had reached its best FTO performance,which the light olefin selectivity is 55.4%,and C2-C4 olefin to paraffin ratio is 10.8,which could be ranked as a high O/P ratio.Through SEM-Mapping characterization,it was found that the surface of the froth powder iron treated by acidic KMnO4 solution was oxidized to a certain degree,and the load of K and Mn elements was also found,which met the expectations of the preparation method.After the preparation method was determined,a long-term reaction with 40 h of TOS was carried out to evaluate the long-term stability of the CO conversion and the selectivity of light olefins.This paper also did research in the influence of reaction pressure and reduction temperature of the fresh catalyst on the performance of Fischer-Tropsch synthesis,through which the optimum reaction condition was determined.