Study Of The Fe-Mn-K/AC Nanocatalyst Used For Transfer Synthesis Gas Into Light Olefins

Synthesis gas transfer into basic chemical materials via Fischer-Tropsch reaction is a attractive subject. Based on former works in our lab, the Fe-basis F-T synthesis catalyst, used for the synthesis of light olefins from synthesis gas, was prepared successfully, and the influencing factors during catalyst praparation and application process was researched.The research results of catalyst preparation indicates that ferric nitrate, manganese nitrate and potassium carbonate are optimal materials. Coconut shell active carbon as carrier, water as solvent, fatty alcohol polyoxy divinyl ether (AEO-3) as dispersant and immersion method as preparation method are suitable choice. The best final catalyst makeup are Fe:Mn:K:AC=39:18:3:40(mass ratio).Research about catalyst application finds that the optimum catalyst testing technological condition is as follows:online reduced at360℃for4h under H2atmosphere with space velocity of1800b-1, then continue to react at360℃and1.5MPa under synthesis gas(CO:H2=1:2, mol ratio) atmosphere with space velocity of600h-1. Under this conditions, CO conversion was about95%, hydrocarbons selectivity in gaseous products was70%, olefins content in hydrocarbons was66%-68%, and olefins yield could reach about45%. XRD results indicated that catalyst structure before reaction was a-Fe and (Fe,Mn)O, and new FexCy structure formed after reaction.Anions impurity is inevitable during catalyst preparation and application process, and the addition of anions resulted in the reduction of catalysis activity. Experimental results indicate that when anion content in catalyst was500ppm, the influence of different anions on catalysis activity was as follow:S2->Cl->SO42->NO3-.Influence of N03-and S042-was little. The addition of S2-improved the selectivity of total hydrocarbon in products, and Cl-reduced this selectivity, but increased olefin content in total hydrocarbon at the same time. When the content of S2" and Cl-in catalyst was less that50ppm, their influence could be ignored in a way. The XRD results indicate that the addition of anions reduced the content of a-Fe and Fe3C, which are the active component in catalyst. This result verify the carbonide mechanics of Fischer-Tropsch synthesis.