A Study On Catalytic Transfer Hydrogenation Of Oleic Acid In Near-critical Isopropanol

The global energy crisis and environmental problems have restricted the sustainable development of modern society.Biomass has been regarded as an ideal substitute for fossil-fuel resources for production of liquid fuels and carbon-based materials.Therefore,the development and utilization of biomass has becoming particularly important nowadays.Natural oils,as high energy density substances composed of C,H,O element,with a wide range of supply sources.However,they cannot be used directly as internal combustion engine fuels due to their high content of oxygen compounds and viscosity.Hence,further refinement and modification of natural oils is required by catalysis before use.The conversion of oils to fatty alcohols and liquid hydrocarbon fuels,especially the second generation biodiesel,has become one of the most attractive technologies and shows great potential for industrial application of biomass energy.This thesis focuses the research area on the reduction of unsaturated fatty acids without external hydrogen.Using oleic acid as a model substance and isopropanol as a hydrogen donor,the catalytic transfer hydrogenation of oleic acid to fatty alcohol and long-chain alkanes in near-critical isopropanol has been systematically studied.It consists of the characterization and evaluation of non-precious metal catalysts,optimization of reaction technological conditions and exploration of reaction mechanism.Finally,a new method for the preparation of fatty alcohol and long-chain alkanes under mild conditions from oleic acid without hydrogen was established.The concrete progress of this paper is as follows:Firstly,a method for the catalytic transfer hydrogenation of oleic acid to produce octadecanol in near-critical isopropanol was established,and the reaction mechanism was also proposed.Then comparing the catalytic activity of Fe,Co,Cu,Ni catalysts,which are prepared by traditional precipitation method.The results show that Co catalyst has excellent catalytic activity in the CTH of oleic acid to octadecanol.The reduction temperature of the catalyst has a significant effect on the catalytic activity of Co-T catalyst.Among the Co-T catalysts,Co-350,which was reduced at 350?,shows the optimum activity.The structure and properties of Co-350 was indicated by H2-TPR,XRD,XPS and TEM.According to the results,the coexisting metal Co(Co0)and CoOx(Co2+/3+)on the surface of Co-350 is the key catalytic active sites,and there is a synergistic catalytic effect between them,which is beneficial for the preparation of octadecanol.The optimum conditions for the preparation of octadecanol from oleic acid CTH in near critical isopropanol are obtained:7 mL isopropanol,70 mg oleic acid,10 mg Co-350,200?,4 h.With the complete conversion of oleic acid,the yield of the target product octadecanol can reach 91.9%.The main reaction pathways in this reaction system are as follows:C=C bond in oleic acid is rapidly saturated to stearic acid,then the carboxyl group of stearic acid is reduced to octadecanol,and octadecanol can be further deoxidized to long-chain alkanes including heptadecane(n-C17)and octadecane(n-C18).Secondly,with heptadecane as the target product,the supported Cu-NiOx/CoOy bimetallic catalysts are prepared by co-precipitation method,and a method of catalytic transfer hydrogenation of oleic acid in near-critical isopropanol to prepare heptadecane was established.The results indicate that the catalytic activity of Cu-NiOx/CoOy was better than CuCo and NiCo catalysts,and the optimum molar ratio of Cu/Ni is 1:1,showing the best activity.The reduction temperature of the catalyst has a significant effect on the catalytic activity of Cu-NiOx/CoOy catalyst.Among these catalysts,Cu-NiOx/CoOy reduced at 150? has the best activity for the selective synthesis of heptadecane from oleic acid.Based on the characterization analysis and reaction results,it was found that the synergetic catalysis among the Cu,Ni,Co trimetallic components was the key to the high activity of Cu-NiOx/CoOy,which is beneficial to the further conversion of octadecanol to heptadecane.The optimum conditions for the preparation of heptadecane from oleic acid CTH in near critical isopropanol are obtained:7 mL isopropanol,70 mg oleic acid,20 mg 30wt%Cu-NiOx/CoOy,240?,8 h.With the complete conversion of oleic acid,the yield of the target product heptadecane can reach 91.3%.Finally,trying to achieve the selective synthesis of octadecane from oleic acid by adjusting the third metal component of Cu-MOx/CoOy catalyst.Besides,the reaction rule of catalytic transfer hydrogenation of oleic acid in near-critical isopropanol is studied under different catalytic systems.Cu-FeOx/CoOy catalysts with different molar ratio of Cu/Fe are prepared by coprecipitation method,comparing their catalytic activity in this reaction system.The results show that the content of Fe component has a great influence on the value of n-C18/n-C17 in product,and the optimum molar ratio of Cu/Fe was 1:1.Similarly,Cu-FeOx/CoOy reduced at 150? show relatively high activity in the selective synthesis of octadecane from oleic acid.The optimum conditions for the preparation of octadecane from oleic acid CTH in near critical isopropanol are obtained:7 mL isopropanol,70 mg oleic acid,20 mg 20wt%Cu-FeOx/CoOy,240?,8 h.With the complete conversion of oleic acid,the yield of the target product octadecane only reach 50.7%.Combined with the characterization analysis of the catalysts,it is inferred that the strong acid site on the surface of Cu-FeOx/CoOy catalyst is the key catalytic site to promote the selective preparation of octadecane from oleic acid,because the acid site can effectively catalyze the dehydration of octadecanol.Based on the contents of the above,it is concluded that the reaction conditions and catalytic system has a decisive effect on the oleic acid CTH reaction.Therefore,selective preparation of different target products(octadecanol,heptadecane,octadecane)from oleic acid can be achieved by controlling the reaction conditions and catalytic systems.