Performance Of Nickel-based Catalyst For Hydrodeoxygenation Of Fatty Acid Methyl Ester And Consecutive Isomerization Of Products

The shortage of fossil energy and environmental pollution caused by its combustion are particularly prominent.The conversion of oil and ditch oil recovered from kitchen waste into biodiesel is a research hotspot in the field of renewable energy at home and abroad.In this paper,nickel-based bimetallic catalysts were prepared and characterized by trickle-bed reactor using methyl fatty acid ester as a model of waste cooking oil.Hydrodeoxygenation and product isomerization of methyl fatty acid ester were carried out to produce biodiesel with good low temperature fluidity.The conversion rate and product isomerization rate were significantly improved.The structure and catalytic performance of NiCu/SAPO-11 catalyst were probed.From the test of N₂adsorption and desorption,it can be found that the adsorption and desorption isotherms of the catalysts belong to type IV isotherms,indicating that the catalysts were mesoporous materials.The results of NH₃-TPD and Py-IR characterization showed that the acidity still existed even if the acid amounts of the bimetallic NiCu/SAPO-11 catalyst decreased,compared with Ni/SAPO-11 catalysts.It could be concluded from the determination of H₂-TPR that the introduction of copper into nickel-based catalysts could reduce the reduction temperature of NiO phase and might improve the reducibility of mixed oxides.Through TG characterization analysis,it was found that the used and untreated 3Ni1.4Cu/SAPO-11 catalyst exhibited less coke deposition than the catalyst 3Ni/SAPO-11 under the same circumstances,indicating that the introduction of copper in the nickel-based catalyst could inhibit the carbon deposition on the catalyst surface in some extent.The results of catalytic performance test showed that bimetallic NiCu/SAPO-11catalyst displayed higher catalytic activity than single metal Ni/SAPO-11 catalyst,perhaps due to synergistic effect between or among nickel,copper and support.Single factor experimental investigation showed that the bimetallic 3Ni1.4Cu/SAPO-11 catalyst gave better catalytic performance.Under optimal conditions with reaction temperature 400?,pressure 1.5 MPa,space-time velocity 2.6 h^-1,volume ratio of hydrogen to oil 1200,the conversion of fatty acid methyl ester,yield of C_15-18 and isomerization rate of products attained 99.7%,90.17%and 35.99%,respectively.As to NiCo/SAPO-11 catalysts,according to the analysis of N₂ adsorption and desorption the specific surface area and average pore size of the SAPO-11 support decreased with the introduction of nickel and copper metal components.It was also found that the average pore size of the catalyst with higher cobalt loading still maintained relatively large.It was owing to that cobalt could not only improve the dispersion of metal particles,but also help to inhibit the aggregation of metal particles during heat treatment,belonging to the strong interaction between or among Ni and Co components and carrier SAPO-11.The existance of Br?nsted acid in the catalyst NiCo/SAPO-11 was confirmed by Py-IR characterization.The presence of nickel-cobalt solid solution like substances could be speculated from the elemental and EDX spectra of catalyst 3Ni6Co/SAPO-11 by TEM characterization.It was found that 6%cobalt loading catalyst retained relatively better activity.The conversion of fatty acid methyl ester maintained 100%,the yield of C_15-18 93.0%,and the isomerization rate 36.1%as the reaction temperature around 400?.As a contrast,the catalytic performance of NiLa/SAPO-11 catalyst was also investigated.The results showed that the catalytic activity of the catalyst was relatively better when lanthanum loading was 1.5%.Using 3Ni1.5La/SAPO-11 catalyst,while temperature was 400?,the pressure 1.5 MPa,the weight space-time velocity 2.6 h^-1,the volume ratio of hydrogen to oil 1200,the conversion of fatty acid methyl ester,the yield of C_15-18 and the isomerization rate of products were 99.8%,96.62%and 32.77%,respectively.Therefore,nickel-cobalt catalysts exhibited the best catalytic performance among three investigated catalysts for the hydrodeoxygenation of fatty acid methyl esters and consecutive isomerization of products.