Synthesis And Catalytic Properties Of SO₄^2-/ZrO₂-based Solid Acids

As a renewable green energy,biodiesel has the potential to replace some of the traditional fossil fuels.Conversion of triglycerides and fatty acids from animal and vegetable oils or restaurant waste oils to alkane monoesters through Transesterification and esterification is a common method of biodiesel synthesis.Compared with solid base catalyst,solid acid catalyst can catalyze both transesterification and esterification,and has a better catalytic effect for low-order feedstocks with high content of free fatty acids.Among many solid acid catalysts,zirconium sulfate oxide shows more attractive application potential in the synthesis of biodiesel because of its super acid properties,said Transesterification,a professor of chemistry at the University of California,Berkeley.However,the zirconia carrier prepared by traditional method has the disadvantages of poor porosity,low specific surface area and easy to change crystalline phase,as a result,the solid acid materials loaded with sulfuric acid group generally have the problems of low acid content,poor structure stability and easy loss of sulfur components during the reaction,which severely restrict their application in industry.It has been proved by a large number of literatures that the thermal stability and the specific surface area of zirconia support can be improved by the introduction of the mesoporous structure and the homogeneous doping of metal atoms,by changing the coordination state,electronic properties and Zr-OH content of Zr species on the surface,it is expected to enhance the bonding between zirconia carrier and sulfuric acid group and realize the stable immobilization of SO₄^2-in large quantity,type,distribution and strength of acid sites on the surface of modulated materials.In view of this,this thesis aims to synthesize mesoporous zirconia materials with larger surface area and better stability,and improve the structure stability and surface electronic properties of zirconia carrier by high efficient and uniform doping of Al Atom,in order to obtain the Zr O₂ based solid acid materials with better catalytic performance for the synthesis of biodiesel Transesterification.The main research contents are as follows:（1）The ordered mesoporous Zr-Al composite oxide carrier material is prepared by the solvothermal assisted volatilization induced self-assembly method,which is used for a large number of stable immobilization of sulfuric acid groups.XRD,nitrogen adsorption,NH₃-TPD and pyridine infrared characterization results confirmed that the obtained solid acid material SO₄^2-/Zr O₂-Al₂O₃ has a regular and ordered two-dimensional hexagonal mesoporous pore structure,large specific surface area and pore volume,and uniform Mesoporous aperture.The Al atoms in the mesoporous pore walls reach a high degree of uniform doping at the near-atomic level and the formation of skeleton Al-O-Zr bonds,which can effectively adjust the bonding mode between the zirconia carrier and the sulfuric acid group,so that by adjusting the doping of Al atoms The amount of impurities can realize fine control of the amount of surface acid,acid center type and strength of the obtained material.The Zr-Al composite oxide carrier prepared under the optimum Zr/Al feed molar ratio of 1 is loaded with sulfuric acid groups,and the acid content of the obtained solid acid sample,the ratio of B acid and L acid center,and the content of super acid center are significant Enhancement results in the sample showing extremely excellent catalytic performance for the transesterification reaction of synthetic biodiesel.The complete conversion of soybean oil can be achieved at a low temperature of100℃,and the yield of biodiesel is as high as 100%.More importantly,the sample showed extremely excellent catalytic stability,and its yield of biodiesel was only reduced by 15%during the course of 5 repeated uses.（2）Aiming at the key problem that the utilization of zirconium and aluminum in the zirconium-aluminum composite oxide carrier is low,resulting in a small amount of sulfuric acid groups introduced,this paper proposes a preparation of high-performance sulfated ordered mesoporous zirconium-aluminum composite oxide A new method based on solid acid materials.This method is to package organic surfactant micelles and the pore wall surface is rich in Si-OH ordered mesoporous silica material SBA-15 is introduced into the precursor solution in which the aluminum source is dissolved,and subjected to high-temperature hydrothermal treatment at a p H value close to the isoelectric point of silicon oxide to achieve uniform grafting of a large amount of Al onto the mesoporous framework of SBA-15 silicon oxide;The organic surfactant micelles in the Al-SBA-15 pores are subjected to high-temperature carbonization treatment under the atmosphere,resulting in a significant gap between the carbonized and contracted organic surfactant and the mesoporous wall of Al-SBA-15,and then the Al-SBA-15mesoporous pore wall has obvious gaps.The uniform coating of zirconium oxide on the surface of the mesoporous pores of SBA-15 is achieved;finally,high-temperature roasting removes the carbonized surfactant micelles,and promotes the Al-OH species on the surface of the Al-SBA-15 pores and the coating The Zr-OH species on the pore wall undergoes high-temperature polymerization to obtain a Zr O₂/Al-SBA-15 material with a zirconia layer uniformly coated on the surface of the mesoporous pore wall and contains a large number of Zr-O-Al bonds.The carrier is used for efficient and stable immobilization of sulfuric acid groups.Through this method,the utilization rate of zirconium and aluminum species can be effectively improved to improve their bonding ability to sulfuric acid groups and increase the amount of sulfate species introduced,resulting in the obtained ordered mesoporous sulfated Zr O₂/Al-SBA-15 composite solid The acid material not only has a highly regular and ordered mesoporous pore structure,a larger specific surface area and pore volume,and a uniform mesoporous pore size,but also exhibits a significantly increased amount of acid.Compared with various solid acid materials reported in the literature that can be used to synthesize biodiesel transesterification,the samples obtained by this method show significantly improved catalytic activity,stability and reusability,and can realize soybean oil at 140℃It is completely converted into biodiesel,and the yield of biodiesel is only reduced from 100% to 78% in the course of 10 repeated uses.