Deactivation model of Fischer-Tropsch synthesis over an Fe-Cu-K commercial catalyst

The effects of COS in synthesis gas on the Fischer-Tropsch (F-T) synthesis over a commercial Fe-Cu-K catalyst in a fixed-bed reactor under 2.31 MPa and at 524 K were investigated. Activity of catalyst decreased rapidly within the first few hours, and then slowly when COS in the syngas was in the range of 51.4-245.6 ppm, while the activity changed little during 72 h when the COS concentration was 4.8 ppm. Prepoisoning of the catalyst was more serious than poisoning in situ. The sulfur resistance of larger catalyst particles was stronger than that of smaller particles and the water-gas shift (WGS) reaction was faster on smaller pellets. A deactivation model in a fixed-bed reactor for F-T synthesis was developed in this paper. Deactivation rate constants obtained from nonlinear regression with the model decrease with the increase of COS concentration, suggesting that the deactivation of catalyst is faster at lower COS concentrations than at higher COS concentrations. The calculated results from the model fitted well with the experimental data. The selectivities of methane and gaseous C-2-C-4 hydrocarbons increased when the catalyst was poisoned by COS. The C-5(+) content in product decreased significantly with increase of sulfur fed to the catalyst. The alkene to alkane ratio in gaseous hydrocarbons decreased over the poisoned catalyst, but C-2(=)-C-4(=) in total C-2-C-4 hydrocarbons changed only slightly. XPS, XRD and TEM studies showed that sulfide compounds were formed on the poisoned catalysts, but the structures were different with variation of COS concentrations, due to the formation of monolayer or mutilayer sulfides on catalysts. (C) 1997 Elsevier Science B.V.