Controlled Synthesis Of Microwave Targeted Catalysts And Catalytic Performance For Biodiesel Production

As a green and renewable energy source,biodiesel has the advantages of high cetane number,non-toxicity and degradability,making it an ideal alternative to traditional fossil diesel.Transesterification with alkaline catalysts as the core driver is the main process for biodiesel production,especially solid alkaline catalysts with high activity,easy separation and reusability,but existing studies have used temperature difference to transfer heat to supply the energy required for the reaction,with low energy utilization,slow reaction rates and long reaction times.Microwave heating has the characteristics of immediacy,integrity,selectivity,efficiency and safety.If microwave energy is targeted at the active site of the catalyst to achieve in situ supply of heat to the reactants,it can accelerate the reaction rate and improve the efficiency of energy use.Metal Organic Frameworks（MOFs）derivatives are carbon/metal composites formed by high temperature carbonization of MOFs in an inert atmosphere,which have the advantages of large specific surface area,high porosity,and adjustable structure.The physical phase components and structural characteristics of MOFs derivatives make them have good microwave absorption ability.Therefore,this study proposes the research idea of synthesizing microwave-targeted catalysts based on MOFs derivatives,exploring the best preparation conditions of catalysts,and optimizing the parameters of microwave heating transesterification conditions.The microwave absorption capacity of the catalysts is analyzed by the vector network analyzer and solid-state source microwave heating system.The physical and chemical properties of the catalysts are analyzed by XRD,FTIR,TG,SEM,TEM,Hammett indicator titration and other characterization methods.To establish the conformational relationships between the physical and chemical properties of catalysts,microwave absorption properties and catalytic activity.（1）MIL-100（Fe）formed carbon/iron composites after high temperature calcination in a nitrogen atmosphere with dielectric and magnetic losses in microwave fields,which makes up for the shortcomings of carbon materials with a single microwave loss mechanism and rapidly converting microwave energy into thermal energy.Therefore,the preparation of magnesium-based microwave-targeted solid alkaline catalysts by MIL-100（Fe）loaded magnesium acetate.The effect of magnesium acetate addition and activation temperature on catalytic activity is studied,and the microwave absorption capacity of the catalyst is analyzed.The effect of catalyst amount,molar ratio of methanol to oil,reaction temperature,reaction time,and other transesterification factors on the conversion of biodiesel is examined.The results showed that the best activity of KF/Mg-MIL with the dielectric loss tangent value of 0.22 and the magnetic loss tangent value of 0.023 is obtained when the magnesium acetate addition is 12 wt.%and the activation temperature is 550℃.With catalyst amount of 6 wt.%,molar ratio of methanol to oil of 12,reaction temperature of 65℃,and microwave power of 300 W,biodiesel conversion of 99.20%is achieved in only 15 min.In addition,the saturated magnetization of KF/Mg-MIL is 21.32 emu/g,which allows the separation of catalyst and product using magnets and reduces the energy consumption for catalyst separation.（2）Ca-BTC is directly carbonized to obtain structurally stable MOFs derivatives（CaO/C）and calcium-based microwave-targeted solid alkaline catalyst is prepared by cobalt doping of CaO/C.The effect of cobalt acetate addition and activation temperature on microwave characteristic parameters and catalytic activity are investigated to examine the effect of transesterification factors on the conversion of biodiesel.The results showed that the optimum catalyst 10Co/CaO/C-750 is obtained at 10 wt.%cobalt acetate addition and 750℃ activation temperature,and the complex permittivity is enhanced from 15.09-11.95j to 20.25-13.47j and the complex permeability from1.00-0.0088j to 1.01-0.0099j compared to CaO/C.The cobalt doping enhanced the conductivity loss,dipole polarization,and interfacial relaxation of the catalysts,resulting in the enhancement of both electrical and magnetic energy storage and dissipation capabilities.10Co/CaO/C-750 showed99.22%biodiesel conversion at catalyst amount of 4 wt.%,molar ratio of methanol to oil of 9,reaction temperature of 65℃,microwave power of 400 W and reaction time of 15 min,and maintained 83.96%biodiesel conversion after 15 consecutive cycles.（3）A kinetic model for the solid-liquid-liquid transesterification reaction is established,and the kinetic parameters such as the average reaction order,activation energy,and frequency factor are compared between the microwave-targeted catalyst KF/Mg-MIL water bath heating and microwave heating conditions by non-linear fitting to obtain the biodiesel conversionηas a function of reaction time t at different temperatures.The results show that the transesterification conversionηand the reaction time t fit the first-order decay exponential model.The average reaction order is 1.43 for water bath heating and 1.78 for microwave heating.The activation energy of the water bath heating reaction is 29.55 kJ/mol and the microwave heating reaction activation energy is reduced to 27.06 kJ/mol.The frequency factor of water bath heating is 104.52 min^-1 and that of microwave heating is increased to 897.85 min^-1.