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Research of a New Kind of Catalyst for FT Synthesis

Author: GuoMeng
Tutor: ChenYi
School: Zhengzhou University
Course: Industrial Catalysis
Keywords: layered clay catalyst additive Co metal FT synthesis SF distribution carbon number distribution slurry reactor
CLC: TQ529.2
Type: Master's thesis
Year: 2009
Downloads: 49
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Abstract

Fischer-Tropsch synthesis（F-T synthesis） is an important way to transform coal or natural gas into high-quality liquid fuels and high value-added chemicals,the purpose of which is to obtain a highly selective product of C₅₊ through the optimal choice of catalyst, reactor and process conditions.F-T synthesis reaction is a reaction typically with the Fe-based or Co-based catalyst,which consists of a series of parallel reactions and consecutive reaction.The product distribution comply with the traditional distribution of SF:In addition to methanol,methane,low-carbon hydrocarbons and above C₃₅ high-carbon hydrocarbons selectivity can be higher than 90%,the C₅～C₁₁ gasoline and diesel fraction hydrocarbon C₉～C₂₅ hydrocarbon selectivity does not exceed 50%,and low-carbon gas are abundant.In practice in order to get fuel C₉～C₂₅ hydrocarbon oil,deep processing of the FT synthesis products is necessary,which will increase the cost of F-T synthesis.With the active metals,iron and cobalt,the study developed a new catalyst with the layered clay structure.The main feature of the catalyst is:vector by the Si-O tetrahedron and Fe（or Co）-O octahedral structure,with 2-8 surface-type layered montmorillonite clay body configuration,channel uniformity,iron（or cobalt） in the skeleton catalyst and the layer,the layer of cobalt iron reduction after the activation phase to become a major source of activity,different layer spacing to provide gasoline,diesel molecular chain growth of the appropriate space,the catalyst for F-T synthesis of synthetic fuel oil can be highly selective,with its good heat transfer capacity,easy to operate,to the advantages of online replacement of catalyst,as a direction of development of F-T synthesis reaction. Thus,the experiments use continuous stirred tank reactor to simulate the slurry F-T synthesis.The main contribution of this study is shown in the following section:Firstly,we investigated the influence of promoters on the structure of iron-based catalyst and the selectivity of reaction products,and optimized the preparation conditions of the layered clay catalyst.Based on the different additive content,more than ten kinds of catalysts were prepared.Catalyst phase was determined by XRD,SEM,BET.The catalytic performance of the catalysts in F-T synthesis was investigated through the slurry reactor.XRD results showed that the catalysts have a layered structure except Cu-007 and Cu-008.Catalysts have obvious characteristic peaks.BET analysis showed that the preparation of the layered clay structure of the catalyst specific surface area increased with the additive showed a certain regularity of diminishing.On this stage,the optimal catalyst preparation conditions are:Fe³⁺ as raw materials,NaOH as the precipitating agent,pH value between 6.8～8.7,the dynamic hydrothermal synthesis,the mass ratio of Cu/Fe is 4%.Under these conditions the catalyst for F-T synthesis was prepared.The results show that the content of liquid hydrocarbons product C₉～C₂₅ up to 90%.Secondly,we optimized the preparation conditions of layered clay cobalt-based catalysts, and studied the performance of the catalyst through the F-T synthesis slurry reactor.The catalyst was characterized and XRD results show that the catalyst prepared with the layered structure,the characteristic peaks are obvious.BET analysis showed that the layered clay catalyst has a large surface area,and the highest specific surface area up to 391.63m²/g.On this stage,the preferred experimental conditions are:CoCl₂ as raw materials,NaOH as precipitant,the preparation is additive,pH value between 6.8～8.7, the dynamic hydrothermal synthesis.Under these conditions the catalyst for F-T synthesis was prepared.,The results show that the content of liquid products C₉～C₂₅ hydrocarbon up to 90%the same,and oil and water are relatively high.Thirdly,we studied the vector structure of the F-T synthesis reaction selectivity. Compared different cobalt-based catalyst carrier liquid product carbon number distribution.The results are as follows:carbon number distribution of layered clay supported catalyst reaction products mainly concentrated in the C₁₂-C₃₆,which is very similar to 0# diesel oil.While that of HZSM-5 zeolite supported cobalt catalysts and cobalt-loaded zeolite L catalyst concentrated in the C₁₂-C₃₆,the C₁₂-C₁₉ hydrocarbon substances were abundant.Modified silica gel supported cobalt catalysts and silica supported cobalt catalyst liquid product carbon number distribution is almost exactly the same,and the carbon number distribution of the relative concentration of nearly 80%of the product are concentrated in the C₁₂-C₁₉.The difference of liquid product obtained from several different carriers treated under the same condition is closely related to the selectivity of catalyst support.In this study,we report for the first time the synthesis of a montmorillonite clay layered catalyst for FT synthesis under hydrothermal conditions,which can synthesize the C₉～C₂₅ mixed gasoline and diesel distillates.The results show that the Cu additives in favor of a catalyst for selective hydrocarbon chain transfer to the carbon;Vector of the FT synthesis of different studies have shown that the performance of carrier structure has a great impact on the selectivity of the catalyst.

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