Design,Synthesis And Synergy Of Reactive Adsorption Desulfurization Catalyst For FCC Gasoline

Green development and environmental protection have become the focus of every field with the development of human society,Cleaner fossil fuels has become one of the main objectives pursued in petroleum refining industry.Over the past ten years,petrol quality standards of many countries made a strict limit on the sulfur content in gasoline,most of them set it lower than 10?g?g^-1.People has developed a variety of gasoline refining technology to process different gasoline for clean gasoline production.Reactive adsorption desulfurization(RADS)technology has many advantages in the field of the fluid catalytic cracking(FCC)gasoline ultra-deep desulfurization,and it has been attracting many attentions in the petroleum refining field.In the process of gasoline ultra-deep desulfurization,saturation of olefin,which leading to a loss of octane number(RON),has been a serious problem for several years.It has been an important focus that reducing the RON loss in the process of FCC ultra-deep desulfurization.Based on the RADS technology,this work studied Ni and ZnO,respectively,which are the main components of RADS catalyst.Some factors,such as reaction feed,reaction conditions and combination type,were studied.On the basis of good desulfurization performance,zeolites were introduced into the RADS catalyst to make a coupling catalytic system.The coupling system was good to directional conversion of hydrocarbons in the FCC gasoline,content of components with high RON was increased.Influencing factors and synergetic mechanism of the coupling system were studied.Hydrogenation performance of the coupling system was modified by the second metal.Computer simulation and performance valuation were carried to study the mechanism of metal modification.This work provided a theoretical foundation for the designation of catalytic system of reactive adsorption desulfurization coupling hydrocarbon directional conversion.Starting from the desulfurization performance of Ni and ZnO,the removal performance of Ni and ZnO on thiophene and propanethiol at different reaction temperatures was investigated.The results showed that ZnO has a good adsorption effect on propanethiol,but has no removal performance on thiophene.H₂ is good to the reaction.Ni can catalyze the decomposition of thiophene in a hydrogen atmosphere,and the products are mainly composed of mercaptans,H₂S and C₄ hydrocarbons.Hydrogen is an important factor in the reaction,for the influence on Ni-based catalyst phase and reaction performance.It plays a role in maintaining the active state of the catalyst while participating in the decomposition reaction of thiophene.Nitrogen is not conducive to the removal of thiophene,because it is easy to deactivate the catalyst due to carbon deposition.The catalytic systems composed of Ni and ZnO by mixed packing and separated packing showed a good desulfurization performance,respectively.The difference in sulfur type distribution of the obtained products in the two states indicated that the reaction adsorption removal process of thiophene is affected to some extent by the diffusion of reactant molecules.The Ni/ZnO catalyst exhibits good desulfurization performance for low-sulfur FCC gasoline.The product sulfur content is less than 10?g?g^-1 in the temperature range of 380°C to 440°C,but the olefin saturation is severe It is necessary to introduce an octane recovery technique to protect the gasoline octane number.After preliminary understanding of the reaction performance and influencing factors of Ni and ZnO,in order to reduce the octane loss caused by saturation of olefin in deep desulfurization process,ZSM-5 with aromatization function was introduced into the RADS catalytic system to form a reactive adsorption desulfurization aromatization coupling catalytic system.The comparison of chemical coupling and physical coupling showed that the combination of Ni and ZSM-5 zeolite at the microscopic level was essentially different from the macroscopic combination.Chemical coupling system had good desulfurization performance and aromatization performance,it gained a desulfurization rate higher than 95%and a 3 percentage point increase in aromatics content.The ZSM-5 zeolite in the chemical coupling system improved the pore structure of the catalyst and promoted the uniform dispersion of Ni,the synergistic system of close contact between the two promoted the desulfurization reaction and the aromatization reaction simultaneously.The combination of reduced Ni and ZSM-5 zeolite promoted the cyclization and dehydrogenation of hydrocarbons,at the same time,the active hydrogen released during the aromatization could act on the thiophene molecule adsorbed on the Ni active site,which promoted the C-S bond breaking and enhanced the desulfurization.Strong acidity of ZSM-5 zeolite could enhance hydrocarbon cracking reaction,it led to reduction of gasoline liquid yield.This could be improved by increasing the space velocity.A good comprehensive performance showed when the space velocity was set between 8 h^-1?12h^-1.In view of the serious cracking reaction caused by the strong acidity of ZSM-5 zeolite,SAPO-11 zeolite with the weaker acidity was coupled with the RADS catalyst to enhance the hydrocarbon isomerization function while reducing the cracking reaction.The addition of SAPO-11 zeolite improved the pore structure of the catalyst,promoted the uniform dispersion of the active metal Ni.Ni and SAPO-11 zeolite formed a synergistic system with good interaction between them.Py-IR and NH₃-TPD analysis indicated that the acid sites in the reactive adsorption desulfurization isomerization coupling system were mainly weak Lewis acids.The FCC gasoline evaluation results showed that the coupling catalyst had the functions of isomerization and aromatization while keeping high desulfurization performance.When reaction temperature was 400°C,the desulfurization rate was higher than 93%,the content of iso-paraffins and aromatics increased by 2.9 percentage points and 1.5 percentage points,respectively,and the liquid yield was 98%.Considering the reaction performance and liquid yield,the content of SAPO-11 zeolite in the coupling catalyst was controlled at about 20%.In order to make further study on improving the performance of the catalyst,the Ni content was increased on the basis of the isomerization coupling catalyst,and the second metal(Co,Cu,Sn,Pb)was introduced to adjust the performance of Ni.TEM-mapping showed that the added second metal was uniformly dispersed,close to the single atom state.XRD,TPR,XPS data showed that the addition of the second metal had a certain influence on the crystal structure and electronic properties of the Ni species in the coupling catalyst,making the Ni species easier to be reduced.Computer simulation showed that the second metal had an electron donating effect on Ni,Co had the weakest effect while Sn had the strongest.The evaluation results showed that the reactivity of the modified coupling catalyst changed significantly.Cu modified catalyst showed the best desulfurization performance,and exhibited good isomerization and aromatization performance.Sn and Pb could inhibit the hydrogenation and dehydrogenation function of Ni,and adversely affected the reaction.