Preparation And Catalytic Performance Of Catalysts For Hydrodeoxygenation Of Fatty Acid Methyl Ester

The wide use of fossil fuels brought about the accumulation of greenhouse gases in the atmosphere. Depletion of oil reserves due to the increasing demands for energy compel to find replacement of fossil fuels from renewable energy sources. Triglycerides-based biomass such as plant oils, animal fats, waste cooking and micro-algal oils can be upgraded by transesterification,cracking/hydro-cracking, hydrodeoxygenation?HDO? and selective deoxygenating?SDO?,respectively, to provide biodiesel?mixture of fatty acid methyl esters?, and green diesel?hydrocarbons in the diesel range?. The most promising process for green diesel?the second generation of biodiesel? production is believed to be SDO or HDO of natural triglycerides.A series of Ni-Mo/?-Al₂O₃ catalysts were prepared by stepwise impregnation and co-impregnation methods. Those catalysts were characterized by X-ray powder diffraction?XRD?,temperature programmed reduction?H2-TPR?, automatic specific surface area and porosity analyzer?BET?, inductively coupled plasma atomic emission spectroscopy?ICP–OES?, et al. An high-pressure fixed bed reactor test installation was built and the catalytic performances were tested using refined the mixture of fatty acid methyl ester?the first generation biodiesel? as feed.The correlations of catalyst physical structure and catalytic performances with Ni/Mo loading,carrier particle shape, the nature of immersion solution and added La₂O₃ were investigated. The main results are as follows:?i? GC analysis results showed that the main components of the mixture of fatty acid methyl esters are methyl palmitate, methyl linoleate, methyl oleate and methyl stearate, as well as small amounts of methyl myristate and palm methyl oleate. Thereinto, using eicosane as the internal standard substance, standard curves of components in feed and product were established.?ii? Within stepwise impregnation processes, it was found that the supersaturated impregnation method can effectively retain the loading of active components. Bimetallic Ni and Mo catalyst showed excellent catalytic activity for hydrogenation decarbonylation or decarboxylation in the hydrodeoxygenation of fatty acid methyl ester due to the synergy between the two active components. Results confirmed that Ni species contributed to decarburization routine, forming the CO or CO2. Meanwhile, Mo species tended to the deoxygenating routine,producing H2 O in the products. Within the ingredient investigated of supported catalysts, when the loaded Ni and Mo species were respectively 15.0wt.% and 5.0wt.%, active components were better dispersed on the surface of support. At the same time, the conversion of fatty acid methyl ester and selectivity of n-alkanes?C15^C18? were relatively higher, the interactions relatively stronger between active components and carrier components also. The optimal ratio of Ni to Mo species in supported catalyst was found to be 14.9Ni4.8Mo/?-Al₂O₃.?iii? For support ?-Al₂O₃, the p H value of impregnation solution adjusting to use ammonia water can impact the load quality of active components. The introduce of ammonia can enhance the dispersion of active components in catalyst. As a result, the conversion of fatty acid methyl ester and alkanes?C15^C18? yield increased significantly. Meanwhile, introduced La₂O₃ further promoted the catalytic activity of Ni-Mo/?-Al₂O₃. For Ni-Mo/La₂O₃-?-Al₂O₃ catalyst, the conversion of fatty acid methyl ester continues to improve with increasing reaction temperature,the yield of n-alkanes?C15^C18? was raised from 40.2% under 300? to 79.2% under 350?, when the pressure is 2.9 MPa, the conversion of long chain fatty acid methyl ester and yield of n-alkanes?C15^C18? were increased to 95.8% and 90.2%, respectively, the influence of reaction temperature on the catalytic performance is more significant with respect to the reaction pressure, which were the optimal reaction temperature of 350? and reaction pressure of 2.9 MPa.?iv? The stability of Ni-Mo/La₂O₃-?-Al₂O₃ catalyst was also investigated under the conditions of temperature 350?, pressure 2.9 MPa, ratio of hydrogen to oil 1000 m L/m L, and weight hourly space velocity 2.0 h-1. Within the progress of catalytic reaction, the average conversion of raw material and yield of n-alkanes were maintained respectively about 80% and65% for 37 h. Then, the catalytic activity began to decrease. XRD spectra of Ni-Mo/La₂O₃-?-Al₂O₃ catalyst in before and after the catalytic reaction was compared. It was found that support phase did not change, while the part of diffraction peaks of Ni O disappears, it was suggests that the active component losing of catalyst is the main reason for the catalyst deactivation.