Study On Carbon Deposit Deactivation And Performance Optimization Of FeMo/Al₂O₃ Hydrodesulfurization Catalyst In Coke Oven Gas

Coke oven gas is rich in constant components H₂,CH₄,CO,CO₂,C₂H₄,C₂H₆,O₂,N₂ and other gases.The existence of these components makes coke oven gas have great application value.However,there are many harmful impurities in the coke oven gas,including H₂S,COS,CS₂,thiophene,mercaptan,thioether,benzene,naphthalene,tar,etc.Which will cause poisoning and damage of various catalysts in the subsequent utilization,resulting in serious consequences.Therefore,the desulfurization of coke oven gas is an important process for the purification and utilization of coke oven gas.The thiophene organic sulfide has a stable structure and is difficult to be remove,so it is necessary to carry out deep hydrogenation conversion.In industry,it is generally removed by two-stage hydrogenation process.FeMo/Al₂O₃ catalyst as a common pre-hydrogenation and primary hydrodesulfurization catalyst in the secondary hydrodesulfurization process of coke oven gas,has been forced to stop and replace the catalyst due to its short service life in industrial use.At present,there are many researches on the desulfurization performance of this kind of catalyst,but there are very few researches on catalyst deactivation.If this kind of catalyst’s deactivation mechanism can be studied and analyzed,so as to make the targeted improvements and prolong the service life of the catalyst,the economic performance of this process will be greatly improved.Therefore,this paper studies the service life of such catalysts,characterizes and analyzes the industrial fresh and deactivated catalysts to determine their internal changes,and studies the activity,selectivity and carbon deposition of catalysts with different pore structures and different atmospheres on the fixed bed microreactor.The specific research contents and conclusions are as follows:（1）A series of analyses such as BET,XRD,Raman,SEM-EDS,thermogravimetry,UV Vis and carbon sulfur content were carried out for fresh samples,deactivated samples,carbon powder and burnt carbon samples of five industrial catalysts in the coke oven gas hydrodesulfurization section,to compare and analyze the structure,morphology,internal causes of deactivation.It was found that serious carbon deposition occurred during the deactivation of the catalyst,which would cause pore plugging and cover the active sites,which was the main reason for the deactivation of the catalyst;The form of carbon deposition on the catalyst is complex,but it is mainly graphite carbon,and the deactivation of carbon deposition mainly occurs on the surface of the catalyst;The deactivation of the catalyst is accompanied by the loss of metal.It is judged that this is another important reason for the deactivation of the catalyst.In particular,the loss of active metal Mo leads to the destruction of the active center,which makes the catalyst inactive.（2）The hydrodesulfurization reaction and the degree of catalyst carbon deposition of various carbon-containing atmospheres（nitrogen,methane,ethylene,ethane,carbon monoxide,carbon dioxide）in coke oven gas were studied in the same catalyst and the same sulfur-containing reaction gas.It is found that the atmosphere effect has a great influence on the hydrodesulfurization activity of COS,and has little effect on the hydrodesulfurization activity of CS₂ and thiophene.The conversion rate of CS₂ is high,all above 99%,and the conversion rate of thiophene is not high,which affects the stability of high temperature reaction also smaller.The atmosphere effect has a great influence on the reaction selectivity,and different influence sulfides will be produced in different atmospheres.Ethylene is the most important atmosphere influence that leads to the deactivation of catalyst coke deposition,because ethylene easily undergoes self-condensation on the catalyst surface,and then further dehydrogenation,condensation and coking.Therefore,the carbon deposition of the catalyst can be reduced and the life of the catalyst can be prolonged by regulating the ethylene reaction.（3）Activity and selectivity analysis of catalysts prepared by Al₂O₃ carriers with five different pore structures was carried out in a comprehensive atmosphere of sulfur-containing reaction gas（COS,CS₂,C₄H₄S and H₂ mixture）and C₂H₄.The samples before and after reaction were subjected to a series of analyses such as BET,XRD,Raman,XPS,HRTEM,and infrared high-frequency carbon-sulfur to explore the relationship between the pore structure of the carrier and the hydrodesulfurization activity,selectivity,and coke resistance of the catalyst.It is found that the pore structure of the carrier has a great influence on the activity,selectivity and anti-coking performance of the catalyst.The active components in the fresh catalyst are Mo O₃ and Fe₂（Mo O₄）₃.After the reaction,there are Mo S₂ active groups formed after vulcanization.the catalyst’s activity is still high after the reaction,and the amount of carbon deposition is small,but carbon deposition does exist.There is a general rule between the pore structure of the carrier and the presents performance of the catalyst.The catalyst prepared by the carrier with the larger pore volume has the stronger the anti-carbon deposition ability.