Study On Hydroaromerization Catalysts For Light Gasoline Fraction

With the increasingly stringent environmental protection regulations,the new vehicle gasoline standard has set higher requirements for sulfur content,olefin content and benzene content in gasoline,and the demand for high octane clean gasoline blending components has increased year by year.In addition,with the increasing in the demand for downstream products of aromatics,the demand for aromatic products has grown rapidly.The light gasoline fractions with low octane value are treated with hydrogen aromatization,which can produce high octane gasoline blending components,and can also be produced into benzene,toluene and xylene?BTX?.In this paper,selecting different silica-alumina ratio HZSM-5 zeolite as the main raw material to prepare the catalyst carrier,the Pt/HZSM-5 catalyst was prepared by the equal volume impregnation method,The physical properties of different aromatization catalysts were characterized by BET,XRD,Py-IR,NH₃-TPD and other methods.The aromatization activity of Pt/HZSM-5 catalysts by different Si/Al ratio and Molecular sieve content was evaluated with n-heptane as a raw material.The results showed that the Si/Al ratio of the molecular sieve has little effect on the pore volume and pore size distribution of the support and catalyst,but the surface area and acidity of the surface have a greater influence,and the addition of the molecular sieve has a great influence on the acidity and strength of the support and the catalyst.The catalyst made by HZSM-5 zeolite with Si/Al ratio of 50 and molecular sieve content is 75%have a higher aromatic yield and BTX aromatic selectivity.The Pt/HZSM-5 catalyst was prepared by adding 75%HZSM-5 zeolite with Si/Al ratio of50.The effect of hydrothermal temperature and hydrothermal treatment methods on the physicochemical properties and n-heptane aromatization performance of the catalyst were investigated.The results showed that both the hydrothermally treated molecular sieves and the hydrothermally treated carriers can effectively adjust the surface acidity and pore structure of the HZSM-5 zeolite.The catalysts prepared by the hydrothermal treatment supports are superior to the catalysts prepared by the hydrothermal heat treatment molecular sieves in terms of aromatics yield and aromatic selectivity.The conditions of the hydrothermal treatment supports were as follows:the hydrothermal treatment temperature was 480°C,the mass velocity of the water vapor was 3 h^-1,and the treatment time was 4 h.The Pt/HZSM-5 catalyst was prepared by hydrothermal-citric acid washing treatment.The effect of hydrothermal-citric acid washing treatment carrier conditions on the physicochemical properties and n-heptane aromatization performance of the catalyst.The results showed that the citric acid washing eliminates the non-framework aluminum remaining in the pores during the hydrothermal treatment.The BET specific surface area,microporous specific surface area,external specific surface area,pore volume,mesoporous pore volume and catalyst pore size of the catalyst increase.The acid amount and acid strength increase of catalyst.Compared with the catalyst prepared only by the hydrothermal treatment,the conversion of n-heptane increased,and the liquid yield,aromatic yield,and BTX selectivity increased.The Pt/HZSM-5 catalyst was prepared by hydrothermal treatment at 480°C-citric acid washing treatment.The reaction temperature was 490°C,the reaction pressure was 2.0 Mpa,the space velocity was 1.5 h^-1,and the ratio of hydrogen to oil was 100:1.The heptane conversion was 95.83%,the aromatic yield was 18.42%,and the BTX selectivity was 86.37%.