Study Of The Selective Hydrogenation Catalysts For The Removal Of Diolefins In Cracking C9 Fraction

Cracking C9 fraction is an important by-product in ethylene production.The aromatics content is above 90%in C9 fraction,and it has a high octane number.By hydrorefining to reduce sulfur content of C9 fraction to meet the requirements of the national VI gasoline standard,cracking C9 fraction can be a good blending component for gasoline.The purpose of this paper was to develop an excellent selective hydrogenation catalyst to remove diolefins for the C9 fraction one-stage hydrogenation process,and to determine the optimal catalyst pretreatment conditions and hydrogenation process conditions.A series of NiO/Al₂O₃catalysts with different NiO loadings were prepared by equivalent-volume impregnation using nickel nitrate and nickel acetate as nickel sources in this paper.The results of low-temperature nitrogen adsorption,XRD,Py-IR and other characterization methods showed that the NiO loading had a great influence on the properties of crystal phase structure and pore structure of the catalysts.With the increase of NiO loading,the size of NiO grains on the catalyst surface increased,and the specific surface area,pore volume and pore size of the catalyst showed a decreasing trend.The catalyst prepared by nickel acetate had larger specific surface area,smaller pore size,more uniform NiO grains with the same NiO loading,but easier to form Ni Al₂O₄structure.The research results of pretreatment conditions indicated that the reduction degree of NiO increased on the surface of catalyst with the increase of reduction temperature.At the reduction temperature of 350?,the NiO on the surface of catalyst was reduced partially and the reduced Ni⁰distributed evenly.The optimum reduction temperature of NiO/Al₂O₃catalyst was 350?.For the catalyst with wet sulfurization treatment,in the range of 280?-320?,with the increase of sulfurization temperature,the sulfidity increased first and then decreased,and the grain size of nickel sulfide decreased first and then increased.The optimum sulfurization temperature of catalyst was 300?For the catalyst with dry sulfurization treatment,in the range of 250?-300?,the sulfidity and the grain size of nickel sulfide increased with the increase of sulfidation temperature,and the agglomeration phenomenon of nickel sulfide grain occurred at 300?.The optimum sulfidation temperature of catalyst was280?.Compared with several pretreatment methods,the reduced catalyst showed better hydrogenation activity at lower temperature,but its selectivity was poor.The sulfided catalyst needed a higher reaction temperature to catalyse reaction,the selectivity of the monoolefin was better.The hydrogenation activity and selectivity of wet sulfided catalyst was better than that of dry sulfided catalyst.The research results of the hydrogenation reaction process conditions showed that For the hydrogenation process of the reduced catalyst,the optimum conditions for selective hydrogenation of cracking C9 were as follows:reaction pressure was 3.0 MPa,reaction temperature range was 120-150?,liquid hourly space velocity was 1.5-2.0 h^-1.For the hydrogenation process of the sulfided catalyst,the optimum conditions for selective hydrogenation of cracking C9 were as follows:reaction pressure was 3.0 MPa,reaction temperature was 165-180?,and the liquid hourly space velocity was 3.0-3.5 h^-1.