Study On Two Reaction Processes Of Diesel Hydrodesulfurization Based On In-Situ Infrared Experiments

As fuel cleanliness standards increase,the requirements for petroleum refining technology are becoming higher and higher.The paper taked the direct desulfurization pathway of Co-Mo catalyst and hydrogenation pathway of Ni-Mo-W catalyst used in industrial plants as the research object,and used in-situ infrared technology to investigate the adsorption and desorption behavior of sulfides on the two hydrodesulfurization catalysts,in order to clarify the difference of two hydrodesulfurization pathway including the hydrogenation pathway and the direct desulfurization pathway on the two catalysts.The paper first examines the physicochemical properties of the two hydrodesulfurization catalysts.The results show that there is a weak force between active metal Mo in Ni-Mo-W/γAl₂O₃ and the γ-Al₂O₃ support,and Ni-Mo-W/γ-Al₂O₃ has higher activity and is easy to sulfide;The pore size of Ni-Mo-W/γ-Al₂O₃ is about 25%higher than that of Co-Mo/γ-Al₂O₃ which is beneficial to the diffusion of large molecular sulfides and the hydrogenation（HYD）pathway activity of Ni-Mo-W/γ-Al₂O₃ is better.The analysis results of sulfides in hydrogenated diesel show that as the severity of the reaction conditions increases,it is difficult to remove dibenzothiophene and its derivatives in the hydrodesulfurization reaction.Secondly,the adsorption capacity of thiophene and its derivatives on two hydrodesulfurization catalysts was investigated.The desorption temperature of thiophene compounds on Co-Mo/γ-Al₂O₃ at about 300℃ was about 10-70℃ higher than that of Ni-Mo-W/γ-Al₂O₃,it indicates that S atoms on Co-Mo/γ-Al₂O₃ have strong adsorption strength and direct desulfurization（DDS）pathway activity of Co-Mo/γ-Al₂O₃ is better.Next,the paper used in-situ infrared experiments to investigate the sulfidation behavior of two hydrodesulfurization catalysts and the adsorption and desorption behavior of thiophene.The starting sulfided temperature of Ni-Mo-W/γ-Al₂O₃ at about 60℃ was 20℃ lower than CoMo/γ-Al₂O₃,indicating that Ni-Mo-Wγ-Al₂O₃ has a higher activity and is easier to sulfide.The infrared characteristic peak types of thiophene adsorption on the two catalysts are basically the same.The C=C vibration peak（1679,1575 cm-1）and C-H vibration peak（1396 cm-1）of thiophene adsorption on sulfide Co-Mo/γ-Al₂O₃ are stronger than those of thiophene adsorption on sulfided Ni-Mo-W/γ-Al₂O₃;the C=C vibration peak（1537,1513 cm-1）and C-H vibration peak（1340 cm-1）of thiophene adsorbed on the sulfided Ni-Mo-W/γ-Al₂O₃ are stronger than those of thiophene adsorption on the sulfided Co-Mo/γ-Al₂O₃.Finally,the in-situ infrared experiments and molecular simulation were used to explore the similarities and differences of the two desulfurization pathways on the two hydrodesulfurization catalysts.The more π complex adsorption modes with strong adsorption strength of thiophene on the sulfided Ni-Mo-W/γ-Al₂O₃,the higher hydrogenation（HYD）pathway activity of NiMo-W/γ-Al₂O₃;The more M-S adsorption modes on the sulfided Co-Mo/γ-Al₂O₃,the more higher direct desulfurization（DDS）pathway activity of Co-Mo/γ-Al₂O₃.