Study Of The Supercritical F-T Synthesis Used For Transfer Synthesis Gas Into Light Olefins

Synthesis gas transfer into basic chemical materials via Fischer-Tropsch reaction is a attractive subject. But Fischer-Tropsch (F-T) synthesis is a chemically exothermic reaction. The application of nanosized F-T synthesis catalyst in conventional gas-phase fixed-bed and liquid-phase slurry-bed reactors has been restricted because of many problems. In this paper, the nanosized Fe-Mn-Cu-K catalysts were prepared by the supercritical combined technology, and then the catalyst was used for transfer synthesis gas into light olefin under supercritical F-T synthesis.The research results of catalyst preparation indicates that the catalyst synthesized by the supercritical combined technology has some excellent properties with a diameter of about5-10nm and well dispersed, and the BET surface areas of it is276.6m2/g, additionally, the drying and crystallization of nanosize catalyst could be achieved simultaneously by this supercritical combined technology. And the main phase of catalyst prepared by supercritical fluid drying method was Fe2O3and (Fe, Mn)O. For the catalyst the best precipitator is NaOH, and the catalyst precursor was calcined at550℃for3h. The catalyst have many good characteristic with high activity and high light olefin yield.The effect of Mn, Cu and K promoters on the catalytic performance of FTS catalysts was also studied. The addition of Mn, Cu and K promoters can improve the catalytic performance properties of the catalyst, including lower methane and CO2formation rates, and higher production rates of desired light-olefins. The optimal performance with a95.68%CO conversion and a46.51%light-olefins yield was obtained by using a catalyst component of Fe/Mn/Cu/K=60:25:10:8.5. In order to obtain the best F-T synthesis reaction, the different reaction phase^different supercritical solvent, syngas pressure, reduce time and reaction temperature was studied. And the optimum catalyst testing technological condition is as follows:the supercritical solvent is n-octane, the and the catalyst was online reduced at360℃for4h under H2atmosphere, then continue to react at330℃and1.5MPa under synthesis gas(CO:H2:N2=1:2:1, mol ratio), the partial pressure of supercritical fluid was maintained at3.0MPa. Under this conditions, CO conversion was about97.79%, and olefins yield could reach about50.87%, the selection of CO2was about8.26%. Research about catalyst application finds that the nanosized catalyst and the supercritical phase reaction are an ideal combination.