Study On Fused Iron Catalysts For Fischer-Tropsch Synthesis In Fixed-bed Reactor

The conversion of syngas to hydrocarbon products via Fischer-Tropsch synthesis（FTS） reaction has long been an important topic in both catalysis and chemical engineering field.Due to a stringent pressure of enviromental protection and the lack of petroleum resources,FTS reaction attracts people’s concern again.This paper uesd high temperature fusion method to prepare the fused iron catalysts。The effect of promoters and reaction conditions for FTS performances were studied in a fixed bed reactor.Catalysts were characterized by means of low temperature N₂ physisorption、SEM、XRD and TPH-MS to provide better insight into the relationship of each promoters and the interaction of the promoters.Main results from this work are as follows:1.The effect of Promoters on fused iron catalysts for FTS reaction:（1） The results showed that Al₂O₃ was the most significant promoter in FTS reaction,when the contents of Al₂O₃ increased,the FTS reactivity enhanced,C₂₊ yields increased too.The optimal catalysts combination of orthogonal experiment was Al3/K3/B1/Ca2.5/Fe100,and synthesis gas conversion was 74.5%,CH₄ selectivity was 5.9%,C₂₊ yield was 145.0 g/m³.（2） The second group test results showed that:B was the most significant promoters in FTS reaction.With the increase of B content,the FTS reactivity enhanced,C₅～C₁₁,C₁₉₊selectivity and C₂₊ yields increased too,while the by-product CO₂ and CH₄ selectivity decreased.The optimal catalysts combination of orthogonal experiment was Al3/K3/B1/Ca2.5/Fe 100,and synthesis gas conversion was 74.5%,CH₄ selectivity was 5.9%, C₂₊ yield was 161.3g/m³.（3） With the increase of K content,the catalyst BET surface area decreased.The adsorption of CO was enhanced,with a corresponding improvement in FTS activity which showed by the FTS performance test results.The increase of K content enchanced the WGS reaction,restrained the CH₄ formation and shifted the product to heavy hydrocarbon,increased the olefins and oxygenates selectivities.2.Fused iron catalyst at FTS reaction had a good stability.In nearly 2400 hours stability experiment,CO conversion remained in about 80%. Hydrocarbon distribution of the active ingredient in the C₂₊ selectivity maintained in a high level（91%）;but the catalysts at 548 K is more stable than at 523 K. 3.The results of the reaction conditions indicated that:Temperature was the most significant conditions in FTS reaction.The optimal reaction conditions of orthogonal experiment were P=2.0 Mpa,H₂/CO=1.6, GHSV=5000 h^-1.The optimal temperature is from 523K to 573K.4.From the catalysts surface carbon deposition,it was found that the FTS catalysts surface main carbon species were carbideγ₁ andγ₂,α-carbon （the most reactive carbon form） and iron carbideγ₁,γ₂ content increased, whileβ,δ₁ andδ₂ contens decreased with the addition of Al₂O₃,Al₂O₃ can promote the most livelyαcarbon’s formation after FTS reaction.