Study On Improving The Octane Number Of FCC Gasoline In Reactive Adsorption Desulfurization

With the increasingly strict environmental regulations,the production of clean oil products has become a major demand for the development of the national economy.More than 70%of the commercial gasoline blending components come from fluid catalytic cracking gasoline in China.Catalytic cracking gasoline has the characteristics of high sulfur content and high olefin content,so the refining of catalytic cracking gasoline has become one of the major challenges in our gasoline production.Reactive adsorption desulfurization（RADS）which has the advantages of high desulfurization activity and low hydrogen consumption plays an important role in the refining of catalytic cracking gasoline in China.However,industrial application data show that there still exist olefin saturation in the reactive adsorption desulfurization process,resulting in the loss of octane number of the product gasoline.In order to further optimize the process and reduce the loss of octane number of the product gasoline,in this paper the author firstly analyzes the change tendency of hydrocarbon composition during the reactive adsorption desulfurization process on Ni-based adsorbents.It is found that the change of hydrocarbon composition in FCC gasoline is mainly caused by the direct saturation reaction of olefins,and the cracking,isomerization and aromatization reactions of hydrocarbons basically do not occur.In view of the characteristics of the conversion characteristic of hydrocarbon during the RADS process,in this paper the author firstly explored the preparation of bimetallic adsorbents with low hydrogenation activity and high desulfurization activity.The use of bimetallic adsorbents with low hydrogenation activity can reduce the saturation reaction of olefin in the RADS process as much as possible.On this basis,some modified catalysts with isomerization and aromatization functions were added to the adsorbent to make the remaining olefin undergo isomerization and aromatization reactions on the modified catalyst as much as possible.By converting olefin into iso-alkanes and aromatics with the same high octane number,high-quality gasoline with low sulfur,low olefin content and high octane number can be produced in this way.For this purpose,the author in this paper firstly tried to optimize the composition of the adsorbent used in the traditional RADS process.Considering the excellent desulfurization activity of metal Ni,Ni was retained as the main desulfurization active component of the adsorbent.The S atoms in organic sulfide compounds are mainly adsorbed on the active Ni site by the S-M bond,while the olefins are adsorbed byπcomplexation.Different from the adsorption method of the S-M bond,the adsorption force ofπcomplexation is relatively weak and easily affected by the electronic structure of Ni.Using the interaction between metals to adjust the electronic structure of Ni is a feasible scheme to weaken theπcomplexation adsorption between Ni and olefin.A Ni-based adsorbent with added metal Fe was designed and prepared.The experimental results show that the adsorbent can greatly reduce the saturation reaction of olefin and increase the breakthrough sulfur capacity.The addition amount of metal Fe was optimized,and the optimal loading content of Fe was determined.The Ni-based adsorbent modified by Fe was used for multi-cycle reaction experiments,and the result show that the optimized adsorbent possess excellent desulfurization activity,olefin retention ability and good regeneration performance.In order to prepare olefin modification catalyst suitable for RADS process,this paper studied the olefin conversion performance of molecular sieves with different structures under the condition of RADS with the 1-hexene as raw material.By comparing the conversion rate,liquid yield and reaction product distribution of olefin on molecular sieves with different structures,ZSM-5 molecular sieves was determined as the suitable catalyst for RADS process.The effects of Si O₂/Al₂O₃ ratio,hydrothermal treatment,alkali treatment modification and metal loading modification on the physicochemical properties,product selectivity and liquid yield of ZSM-5 molecular sieve were investigated and the modification method of ZSM-5 was determined.The feasibility in the process of RADS coupling olefin conversion were studied and discussed,and it was found that the sulfur-containing compounds in FCC gasoline basically did not have a significant effect on the reaction of olefin upgrading catalyst.Raman spectrum analysis shows that the ratio of carbon to hydrogen deposited on upgrading catalyst are lower than that of the adsorbent;the thermogravimetric analysis shows that the regeneration temperature of carbon burning on the upgrading catalyst is higher than that of the adsorbent,indicating that the regeneration condition of the RADS process is not suitable for the regeneration of the upgrading catalyst.In this paper,we try to reduce the regeneration temperature of the modified catalyst by loading some combustion-supporting metal on the upgrading catalyst.By examining the regeneration performance of upgrading catalyst supported by Ag,Pt,Pd respectively,the scheme of upgrading catalyst supported by 0.05 wt%Pt was finally selected to reduce the regeneration temperature of the catalyst and make it suitable for the regeneration condition used in the RADS process.The effect of adding proportion of upgrading catalyst on desulfurization activity and hydrocarbon composition of the product was investigated in the process of Ni-based adsorbent that modified by Fe mixed with upgrading catalyst.The experimental results show that the higher the proportion of upgrading catalyst,the higher the content of iso-alkanes,aromatics and octane number of the product will be,but the breakthrough time will be shortened accordingly.Taking into account the desulfurization performance and the hydrocarbon composition of the product,the optimal addition ratio of upgrading catalyst was determined.Finally,the influence of process conditions on the desulfurization efficiency of the new process and the hydrocarbon composition of gasoline was investigated at this ratio.After comprehensive consideration,the optimum reaction conditions were determined as follows:reaction temperature 420°C,reaction pressure 2 MPa,molar ratio of hydrogen to oil 0.3 and weight hourly space velocity 5 h^-1.