SAPO-11 Supported Catalyst For Preparing Of Biofuels Via Hydroisomerization Of Long Chain Normal Paraffins

Due to the increasing energy crisis and environmental pollution,the development and application of higher-quality biofuels is essential to improve combustion efficiency and reduce pollutant emissions such as PM 2.5 and photochemical smog.As one of the important steps in catalytic reforming technology,n-paraffin hydroisomerization technology can increase the octane number of gasoline fractions,reduce the cloud point of diesel fractions,and improve the low temperature performance of paraffin products.In this paper,the SAPO-11 supported catalyst was modified in both support and metal components,and the physical and chemical properties of the catalyst were investigated using X-ray diffractomer,N₂ adsorption-desorption,scanning electron microscope,transmission electron microscope and NH₃ temperature-programmed desorption.Taking n-hexadecane as a model compound,the influence of catalyst modification on the hydroisomerization performance of the catalyst was investigated.The mechanism of the hydroisomerization reaction of the catalyst was studied and the conditions of the hydroisomerization process were optimized.Using hydrothermal synthesis with MCM-41 as the silicon source,micro-mesoporous SAPO-11-M molecular sieve with hollow structures and spherical columnar aggregates could be synthesized.And SAPO-11 synthesized with traditional hydrothermal and MCM-41/SAPO-11 molecular sieve prepared by mechanical mixing method were compared.The characterization results and experimental data showed that SAPO-11-M has a larger specific surface area and a higher amount of B acid,and showed the best hydroisomerization performance.Under the optimal process conditions of 330?,1.5 MPa,WHSV=1.5 h^-1,V?H₂?:V?n-hexadecane?=1000:1,the conversion of n-hexadecane reached 95.5%,the selectivity of i-C₁₆ was 98.9%.The results showed that the introduction of mesoporous material MCM-41 into SAPO-11 molecular sieve could provide greater specific surface area and pore channels,reduce mass transfer resistance,shorten the residence time of isomeric olefin intermediates in the pore channels,and improve the yield of target products.A series of bimetal 3.0Nix Cu/SAPO-11?x was the amount of copper loaded,x=0,1.0,1.5,2.0,wt%?catalysts were prepared by co-impregnation technology.Characterization analysis showed that the loading of the metal reduced the crystallinity of SAPO-11,but hardly damaged its structure.At the same time,after the introduction of the metal component,the BET surface area and total volume decreased,indicating that the metal component interacted with the support and was supported on the pores and the outer surface of the SAPO-11 molecular sieve.With the increase of copper loading,the number of acid sites of 3Nix Cu/SAPO-11 catalyst gradually decreased.The results of n-hexadecane hydroisomerization experiments showed that the bimetallic3Ni1.5Cu/SAPO-11 catalyst not only showed high catalytic activity,but also suppressed the hydrogenolysis reaction and improved the selectivity of i-C₁₆.Under the optimal optimization conditions of 3.0Ni1.5Cu/SAPO-11 catalyst at T=380?,P=1.5MPa,WHSV=1.0 h^-1,V?H₂?/V(n-C₁₆)=1000,the conversion of n-C₁₆ was 97.3%,the selectivity of i-C₁₆ was 87.3%,and the yield of i-C₁₆ was 84.9%.Therefore we could conclude that copper metal played an important role in the reaction process.Adding copper to a nickel-based catalyst formed a Ni-Cu alloy.Copper in Ni-Cu alloy not only diluted the overall size of nickel,made nickel more uniformly dispersed on the surface of the molecular sieve,but also effectively suppressed the hydrogenolysis reaction and improved the selectivity of i-C₁₆.A series of Ni Cu/SAPO-11-y?y was the molar ratio of CA/Ni,y=0,1.0,1.5,2.0?catalysts were prepared by citric acid complex impregnation method.The addition of citric acid increased the BET surface area and pore volume of the catalyst,thereby exposing more acidic sites and increasing the number of acidic sites.Due to the addition of citric acid,the metal component also improved the dispersion on the surface of the molecular sieve.The results of n-hexadecane hydroisomerization experiments showed that the Ni Cu/SAPO-11-1.5 catalyst showed the best catalytic activity,at T=340?,P=1.5 MPa,WHSV=1.5 h^-1,V?H₂?/V(n-C₁₆)=1000,the conversion of n-hexadecane is95.6%,the selectivity of i-C₁₆ is 94.8%,and the yield of i-C₁₆ is 90.7%.The pore expansion effect of citric acid enabled n-hexadecane and intermediates to be transferred to metal sites and acidic sites more quickly,shortened the residence time of isomeric olefin intermediates in the pores,thereby improved the selectivity of i-C₁₆.