Study On Ni₂P Catalysts For Hydrotreating-isodewaxing Of Distillate

To produce clean raw material and improve the economic benefit have attracted increasing attention in oil refining industry.Environmental protection and the needs of the market demand for clean fuels provide new opportunities to the development of hydrogenation catalysts.Currently,noble metal catalysts are widely used in hydro-isodewaxing processes,but they are expensive and vulnerable to be poisoned by sulfur,nitrogen and other impurities.To solve these problems,in this thesis,non-noble metal Ni₂P catalysts supported on?-Al₂O₃/SAPO-11 composite supports were designed and prepared.Isomerization reaction mechanism of the catalysts and synergistic reaction mechanism of acid center and Ni₂P metal active center were deeply investigated,which provide theoretical guidance for the design of the high-performance non-noble metal isomerization catalysts.On this basis,efforts were made to put forward the straight run diesel heterogeneous flow both deep desulfurization and denitrogenation technology.The?-Al₂O₃/SAPO-11 composites supported non-noble metal Ni₂P catalysts were prepared by the saturated impregnation method.The isomerization performance of n-dodecane was performed in a high pressure fixed-bed reactor with continuous flow system.The results indicate that dodecanoic conversion rate increases with the increase of adding amount of SAPO-11 in the isomerization reaction.Isomerization yield first increased and then decreased,while the isomerization selectivity decreased gradually.Based on the relationship between reaction conditions and isomerization performance,the optimum reaction conditions were determined as follows:temperature 360?,2.5MPa pressure,hydrogen to oil ratio500:1,space velocity1.0h^-1.The pore structures of composite supports were modified by using carbon black.The synergetic effect of the nickel phosphide metal components and the acid center of supports was optimized.The results show that pore-enlarging agents contribute to producing more large pores,increasing pore diameter and mesoporous pore volume of catalysts,enhancing the mass transfer performance of the catalyst,suppressing the cracking reaction and clogging of the pores,and further significantly improving the isomerization performance of catalysts.With the increase of Ni₂P loading,the isomerization activity and selectivity of catalysts were improved.The synergistic effect of metal activity centers and acid centers reached optimal performance with 10%Ni₂P loading.The yield of dodecanoic isomerization over the catalyst was 71.8%and the isomerization selectivity of that was up to 91.3%.By using the optimized Ni₂P/Al₂O₃-SAPO-11catalyst and straight run diesel oil as feed,single reactor hydrotreating-isodewaxing integrated process and double reactors hydrotreating-isodewaxing combined process were designed.The results indicate that the single reactor hydrotreating-isodewaxing integrated process simultaneously contains dual functions of isomerization and hydrotreating.The developed catalysts were resistant to sulfur andnitrogen poisoning,But the isodewaxing performance was restrained by the competition reaction.For the hydrotreating-isodewaxing combined process,the refining agent deeply desorbed sulfur and nitrogen compounds from straight run diesel and eliminated the inhibiting effect of isodewaxing reaction.The combined process of hydrodesulfurization and hydrodenitrogenation are superior to the integrated process.Meanwhile the combined process showed good isodewaxing performance.