Study On Pt/Zeolite Hydroisomerization Catalysts For N-hexane

Alkane isomerized gasoline is a high-octane clean gasoline blending component that is substantially free of sulfur and nitrogen and contains no olefins and aromatics.The molecular sieve isomerization catalyst has the advantages of raw material impurity tolerance,high activity,high octane number of isomerization products and good stability.So,the molecular sieve alkane isomerization technology has been widely concerned.The carriers was prepared by extrusion molding using HZSM-5 molecular sieve and aluminum hydroxide dry glue as raw materials.After the phosphorus modification,the Pt-P/HZSM-5 catalysts were loaded with Pt.The Pt-P/HZSM-5 catalysts were characterized by N₂ adsorption-desorption,XRD,Py-IR and NH₃-TPD.And the effects of phosphorus content on the isomerization performance of Pt/HZSM-5 catalysts was evaluated using n-hexane as a raw material.The results showed that the specific surface area and pore volume of the modified Pt-P/HZSM-5 catalyst decrease with the increase of phosphorus content.The addition of a small amount of phosphorus can significantly change the acid amount and acid strength distribution of Pt/HZSM-5.The strong acid sites decrease and the weak acid and Br?nsted acid sites increase.Pt-P/HZSM-5 catalyst significantly inhibite the cracking reaction and improve the isomerization rate and dimethylbutane selectivity.The Pt-P/HZSM-5 catalyst with 1 wt%phosphorus gives the best isomerization results.The n-hexane conversion was 75.78%,the yield of isomerization was 75.36%,the cracking rate was 3.69%,and the selectivity of DMB?dimethylbutane?was 6.65%.The carriers were prepared by extrusion molding,using H?molecular sieves and aluminum hydroxide dry glue as raw materials,and the Pt/H?-Al₂O₃ isomerization catalysts were prepared by loading noble metal Pt.The Pt/H?-Al₂O₃ catalysts with different molecular sieves Si/Al and content were characterized by BET,XRD,Py-IR and NH₃-TPD.The effects of different H?molecular sieves Si/Al and content on the isomerization performance of Pt/H?-Al₂O₃ catalyst was evaluated using n-hexane as a raw material.The results showed that With the Si/Al of H?increased,the surface area,pore volume and total acid sites of Pt/H?-Al₂O₃ catalyst decreased,while strong acid sites increased.The conversion and cracking of n-hexane increased,the yield of isomerization and selectivity of DMB decreased.With the content of H?molecular sieves increased,the specific surface area,pore volume,total acid and strong acid sites of Pt/H?-Al₂O₃ catalyst increased.The conversion,yield of isomerization and selectivity of DMB increased,and the cracking increased slightly.The optimum Si/Al of H?is 25,and the optimum content is?10+X?%.The n-hexane conversion was 77.24%,the yield of isomerization was 80.10%,the cracking rate was 0.93%,and the selectivity of DMB?dimethylbutane?was 18.25%.Based on the reduction and isomerization conditions of the Pt/H?-Al₂O₃ catalyst,it is found that the reduction conditions and reaction conditions have important effects on the isomerization performance of the Pt/H?-Al₂O₃ catalyst.Under the reduction conditions of temperature 350?,pressure 0.75 MPa and hydrogen flow rate 90 mL/min,the reaction conditions were temperature 280?,pressure 1.5 MPa,LHSV 1 h^-1 and H₂/oil volume ratio500:1,the best performance was obtained.The n-hexane conversion was 81.16%,the yield of isomerization was 82.89%,and the selectivity of DMB?dimethylbutane?was 25.58%.