Study On Fused Iron Catalysts For Improving The Selectivity Of Light Olefins

Light olefins(ethylene,propylene and butene,etc.)is important organic chemical raw materials,they play an extremely important role in the national economy.It is significant to convert syngas directly into light olefins by Fischer-Tropsch(F-T)synthesis.The fused iron catalyst have the advantages of low price,simple to be prepared and high selectivity of light olefins.The precursors and promoters have great impaction on improving the selectivity of light olefins of fused iron catalyst,so the precursors,promoters and reaction conditions were evaluated on the selectivity of light olefins of fused iron catalyst in this paper.The catalysts were characterized by means of XRD,TPD,TG-DTG and SEM-EDS and so on to provide better insight into the relationship of each promoter and the interaction of the promoters.Main results from this work are as follows.It is found that different precursors have significant effect on the conversion and the selectivity of light olefins.The experiment results show that the catalyst which n(Fe2+)/n(Fe3+)in the iron oxide precursors is about 1.0 had the highest selectivity of low olefins in C2?C4,which reaches 50.59%.The catalyst which n(Fe2+)/n(Fe3+)is about 1.0 has the most basic on the surface according to CO2-TPD.The addition of K can greatly improve the selectivity of light olefins.However,the experiments indicate that the optimum content of K is 2%.If K content exceeds 2%,the CO conversion and selectivity of light olefins decrease with reaction time prolongs.The effect of the content of Sm2O3 and mixed rare earth RE on the selectivity of light olefins are also obvious.For the iron catalyst which n(Fe2+)/n(Fe3+)is about 1.0,the optimum content of Sm and RE are 1.5%,0.5%,respectively.According to the L8(27)experimental,it showes that the selectivity of the light olefins increase when ZnO and TiO2 added,but decrease when V2O5 and MoO3 added.At the optimal combination of orthogonal,the CO conversion is 73.5%and the n(O1efin):n(Paraffin)in C2-4 is 5.31 at the condition of 583 K,2.0 MPa,11400 h-1 and H2/CO 1.6.The study of reaction conditions indicates that space velocity,pressure,temperature,and the ratio of H2/CO have a great impact on the the selectivity of light olefins.For the synthesis of light olefins,the optimal reaction conditions are:space velocity of 11400 h-1,pressure of 1.0 MPa,temperature of 583 K,the ratio of H2/CO 1.6.