Study On Promoted Ni-based Hydrodesulfurization Catalyst For The Claus Tail Gas

In petroleum refineries,depurating of natural gas and other industrial off-gas,there are plenty of hydrogen sulfide,which is often treated by Claus process. Various sulfur compounds presented in the Claus tail gas which can not meet the national environmental regulations until it is treated.Nowadays,SCOT process is employed most widely to treat the gas,CoMo/γ-Al₂O₃ are usually used as the commercial catalyst in the processes mentioned above.Currently,study on new type catalysts such as iron(nickel)-containing materials showed higher activities at low temperature.The present work is based on the previous study,the object of this work is firstly to discuss the reaction mechanism for the hydrogenation of SO₂ on Ni-based catalysts and find the reason for water poison.And then improve the catalysts by dopting other elements or promoting support.Relationship between structure and performance(under dry feed or wet feed) of these catalysts were explained via XRD,XPS,H₂-TPR,BET as well.The following conclusions were obtained through aboving experiments:(1) There is little effect of water on perfrmance of Ni/Al₂O₃ catalyst unless the water content is higher than 10%.Both conversion of sulfur dioxide and the hydrogen sulfide selectivity are decreased as the water content increased,the activities can restore when H₂O is removed.Deactivation by water is probably caused by the sulfite formed from H₂O and SO₂ adsorpting on the surface,which inhibit regenerating of sulfur vacancies.When the water is removed,under in situ state,these unstable sulfide species would Release the sulfur vacancies.(2)In the absence of water,the catalytic activities of Mo-doped Ni/Al₂O₃ catalysts for hydrogenation of SO₂ at low temperatures is better,among which MoNiAl-3(Mo/Ni=0.1)has the highest activity.However,addition of W reduces the catalytic activity at low-temperature,and the reduction becomes stronger when W content increases.Under the gas feed containing 30%water vapor,activities of NiAlMo catalysts enhance the activity greatiy.NiAlMo-3 with the best water resistance can still maintain the yield of 93.1%at 220℃.Further characterization showed,addition of Mo can effectively inhibit the the formation of the sulfite.(3)In La-doped Ni/Al₂O₃catalysts,La are included in the NiO Crystal lattice and improve the hydrogen absorption capacity of the catalyst,but adding too much will lead to reduction of sulfide to reduce the hydrogenation activity of catalyst.In Ce-doped Catalysts,Ce are not included in the NiO Crystal lattice,and adding Ce to catalysts lead to lower activities.Under the gas feed containing 30%water vapor,La improve the water resistance capacity,but Ce doesn't work.(4) Adding Al₂O₃ to NiTi and NiZr catalysts can modify the interaction between supports and active phases,improve the surface areas so as to enhance the catalyst activity.After reaction under 30%water vapor,sulfite was formed on the surface of NiAlTi,which lead a sharp decreasing of catalytic activity,while water vapor has little effect to the yield of NiAlZr catalyst,the presence of water does not change its active phase,but resulted in the forward reaction in the Claus reaction.