A Study On Preparation Of Long-chain Hydrocarbons By Low-temperature Deoxygenation Of Saturated Fatty Acids

Energy is the material basis of social development.With the depletion of fossil resources and the intensification of caused environmental problems,exploring green,renewable and alternative resources has become an important strategy for the development of all countries.As a widespread renewable resource,biomass can be converted into fuels and high value-added chemicals through a series of catalytic means.Biomass-derived lipids,which are of highly concerned,have great advantage in preparation of long-chain alkanes and linear alpha-olefins due to their long carbon chain.At present,the main method for preparing long-chain alkanes from fats and oils is hydrodeoxygenation technique,which can be accomplished over Ru-based catalysts at relatively lower temperatures.However,the whole reaction mechanism is still unclear and needs to be further investigated.Homogeneous catalysis is used as a main tool to prepare linear alpha-olefins from fatty acids.The limited heterogeneous catalysts are focusing on noble metals,which have some obvious disadvantages such as high catalyst cost and high reaction temperature.Therefore,this thesis using stearic acid as a model substance to study the preparation of long-chain alkanes and linear alpha-olefins under mild conditions.Firstly,the hydrodeoxygenation of stearic acid over commercial Ru/C catalyst in different solvents was carried out and the reaction conditions was also optimized in this thesis.The difference of catalytic activity in n-hexane,dodecane,isopropanol,water and solvent-free systems was evaluated while using Ru/C to catalyze the hydrodeoxygenation of stearic acid.The effect of different reaction conditions such as solvents,hydrogen,catalyst and stearic acid and the reusability of Ru/C catalyst was then evaluated.The conversion of stearic acid at different reaction time and reaction temperatures was also investigated.It was found that the conversion of stearic acid and yield of heptadecane could reach up to 99.1%and 89.3%respectively with octadecane yield of 4.8%under optimized reaction conditions(50 mg stearic acid,30 mg Ru/C,200?,90 min,3 mL n-hexane,3 MPa H2,1000 rpm magnetic stirring).Subsequently,the reaction was fitted according to the first-stage reaction kinetics model,and the obtained apparent activation energy(Ea)of the reaction was 58.6 kJ/mol.Next,linear alpha-olefin was used as target product to explore the catalytic performance of decarbonylation/dehydration of stearic acid over different catalysts by adding acetic anhydride and bis(2-diphenylphosphinophenyl)ether.Fe/C,FeNi/C and Ni/C catalyts were all prepared by the traditional impregnation method with activated carbon as the carrier,and it was found that reaction activity was significantly improved over FeNi/C bimetallic catalyst compare with the corresponding Fe/C and Ni/C catalysts.Subsequently,the characterization result of these catalysts such as XRD,H2-TPR,CO-TPD,ICP,TEM,EDS-Mapping,XPS and BET indicate that FeNi alloy does exist in FeNi/C and is the key active site for catalyzing the whole reaction process.Then,by optimizing the reaction conditions,the yield of olefin and selectivity to alpha-olefin could reach up to 66.3%and 91.7 respectively under optimum reaction conditions(50 mg stearic acid,190?,16 h,30 ?L acetic anhydride,30 mg bis(2-diphenylphosphinophenyl)ether,30 mg catalyst).Finally,in order to further increase the yield of linear alpha-olefins,we continue to explore other highly efficient catalytic systems for the preparation of linear alpha-olefins from stearic acid.A series of MoOx catalysts were prepared by reducing MoO3 under hydrogen atmosphere at different temperature.It was found that the MoOx reduced at 600? displayed the best catalytic performance,and the yield of olefin and selectivity to alpha-olefin could reach up to 66.3%and 91.7 respectively under optimized reaction conditions(50 mg stearic acid,190?,16 h,30 ?L acetic anhydride,30 mg bis(2-diphenylphosphinophenyl)ether,30 mg catalyst).Subsequently,in order to exploring the effects of reduction temperature on the composition of the catalyst,all catalysts were characterized by XRD,TEM,H2-TPR and XPS,it was found that MoO2 is the key active component combined with the reaction results.