FeZnNa/Zeolite Two-stage Catalyst Catalyzed Synthesis Of Light Olefins From Synthesis Gas

Lower olefins(O2-4-)are important chemical raw feedstocks,which traditionally produced from the cracking of naphtha in industry.With the increasing diminishing of petroleum reserves,to develop alternative production pathway based on non-oil resources has gradually attracted attention.Using syngas(a mixture of CO and H2)derived from coal,natural gas and biomass,to produce lower olefins is a very promising non petroleum synthesis route.The syngas can be converted to olefins by Fischer-Tropsch synthesis.However,the distribution of products is complex and obeys Anderson-Schulz-Flory(ASF)distribution.The selectivity limit of C2-4 hydrocarbons is 58%.Therefore,the key factor of producing lower olefins from syngas by Fischer-Tropsch synthesis route is to adjust the distribution of Fischer-Tropsch synthesis products,break through the distribution of ASF products and improve the selectivity of lower olefins.In this paper,Zn and Na modified Fe-based FTS catalyst was loaded in the upper section of the reaction tube,and various porous solid acid catalyst zeolites with hydro cracking effect in the lower section of the reaction tube.In this way,FeZnNa/N??dual-bed catalysts were successfully developed.The catalytic performance between FeZnNa and nine kinds of zeolites(HY,NaY,ZSM-5,SAPO-34,H?,Li?,Na?,K?,and Rb?)in dual-bed catalysts were explored in detail.The coupling manners,ratio and reaction parameters of two active components in FTO process were optimized.Several characterization methods such as BET,XRD,XRF,ICP,SEM,NH3-TPD-MS,MES and Raman are employed on FeZnNa and zeolites to investigate the organization,structure,morphology,acidity and carbon deposition of catalysts.We found that the fresh FeZnNa catalyst was mainly composed of ZnFe2O4 spinel and ZnO species.After reduction,the oxidized Fe was reduced to elemental Fe,besides,Fe mainly exists in the form of iron carbide,the proportion of FexC species increased with the reaction time prolonged.The acid and pore structure of zeolites were modified by NaOH solution soaking-hydrothermal post-treatment.The process didn't destroy the skeleton structure of zeolite,and the modified zeolite catalyst was more eligible in FTO reaction.The integration behavior,mass ratios of the two active components and reaction parameters of the FTO process make an enormous impact on catalytic performance either.The highest selectivity of C2-4= up to 50.5%and a high CO conversion of 92.9%were achieved for the FeZnNa/Na? dual-bed catalyst.Importantly,the FeZnNa/Na?catalyst had outstanding long-term stability with no obvious deactivation over 100 h of testing,making it a potential catalyst for industrial applications.The acidity and pore structure of the zeolite were found to be key factors for improving the yields of lower olefins from these dual-bed catalysts.The excellent catalytic performance of FeZnNa/Na? is attributed to the suitable acidity and hierarchical pore structure of Na?.