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) synth esis 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 s yngas was in the range of 51.4-245.6 ppm, while the activity changed l ittle during 72 h when the COS concentration was 4.8 ppm. Prepoisoning of the catalyst was more serious than poisoning in situ. The sulfur r esistance of larger catalyst particles was stronger than that of small er particles and the water-gas shift (WGS) reaction was faster on smal ler pellets. A deactivation model in a fixed-bed reactor for F-T synth esis was developed in this paper. Deactivation rate constants obtained from nonlinear regression with the model decrease with the increase o f COS concentration, suggesting that the deactivation of catalyst is f aster at lower COS concentrations than at higher COS concentrations. T he calculated results from the model fitted well with the experimental data. The selectivities of methane and gaseous C-2-C-4 hydrocarbons i ncreased when the catalyst was poisoned by COS. The C-5(+) content in product decreased significantly with increase of sulfur fed to the cat alyst. The alkene to alkane ratio in gaseous hydrocarbons decreased ov er the poisoned catalyst, but C-2(=)-C-4(=) in total C-2-C-4 hydrocarb ons changed only slightly. XPS, XRD and TEM studies showed that sulfid e compounds were formed on the poisoned catalysts, but the structures were different with variation of COS concentrations, due to the format ion of monolayer or mutilayer sulfides on catalysts. (C) 1997 Elsevier Science B.V.