Study On Hydrogenation Of Olefins And Its Kinetics In Heavy Fraction Of FCC Gasoline

Catalytic hydrodesulfurization?HDS?is the most widely used desulfurated technology in refining industries,and this technology could produce gasoline which is coincident with the commercial gasoline standard.However,part of olefins are inevitable to be hydrogenated to paraffins in the deep HDS process,leading to a large octane number loss of gasoline.Therefore,the improvement for HDS technology is conducted,which separates FCC gasoline into light and heavy fractions,and only the heavy fraction is sent to the hydrogenation process.The octane number loss is reduced,because olefins in light fraction are prevented from hydrogenation.The primary olefins in heavy fraction are C7⁺olefins,and the content of C7^C9 olefins is larger than 85 wt%in the total content of olefins in heavy fraction.Hence,the study on C7^C9 olefins hydrogenation is meaningful to understand the law of olefins hydrogenation and octane number loss in the HDS of heavy fraction,the improvement of HDS technology parameter and the reduction of octane number loss.The heavy fraction in FCC gasoline was fractionated to 80¹00 ^oC distillate fraction,100¹30 ^oC distillate fraction and 130¹60 ^oC distillate fraction according to the distribution of olefins with different carbon number,and C7^C9 olefins were gathered in three distillate fractions respectively.The influence of reaction temperature?220²70 ^oC?,reaction pressure?1.5³.0 MPa?,space velocity(1⁴ h^-1)and the ratio of hydrogen to feed?100⁴00?on C7^C9 olefins hydrogenation was studied.Reaction temperature and space velocity have larger effect on olefins hydrogenation than reaction pressure and the ratio of hydrogen to feed.The saturated percentage of C7^C9 olefins is:C7>C9>C8.This study finds that the position of C=C double bond plays more important role than the steric hindrance on the saturated percentage of olefins.C=C double bond is shifted from internal position to terminal position,leading to the larger saturated percentage of internal olefins than terminal olefins and the influence of steric hindrance on olefins hydrogenation is changed.Besides,the research on hydrogenation of olefins with different structures finds that the hydrogenated law of olefins with different structures in the heavy fraction is different.The hydrogenated law of olefins with different structures is:C7 normal olefins>C7 iso-olefins,and C8,C9 normal olefins<C8,C9 iso-olefins.The reason is that Co exerts strong suppressive effect on normal olefins hydrogenation,and this effect is weak on iso-olefins hydrogenation in the condition of weak influence of steric hindrance,leading to the larger saturated percentage of C8,C9iso-olefins.The reason for the smaller saturated percentage of C7 iso-olefins is that the content of 2,3-dimethyl-1-pentene is large in C7 iso-olefins,and the saturated percentage of 2,3-dimethyl-1-pentene is small,leading to the small saturated percentage of C7 iso-olefins.Besides,the influence of olefins hydrogenation on octane number is decreased with the increase of carbon number.The reason is that the primary part of olefins hydrogenation is turned from normal olefins to iso-olefins with the increase of carbon number.The octane number loss of iso-olefins hydrogenation is smaller than normal olefins.Based on above study,the kinetics of C8 olefins hydrogenation was studied,using power functional kinetic model,which is applicable in the kinetics study of gasoline.The reaction order of C8 olefins hydrogenation is 1.21,and the reaction activation energy is59.83 kJ/mol.The law of C7^C9 olefins hydrogenation and related change of octane number makes abundant data support and theoretical basis on the design of HDS process scheme.