Controlled Synthesis Of Solid Acid Based On UiO-66（Zr） And Its Catalytic Esterification Performance

Biodiesel is considered as high-quality substitute owing to its great combustion performance,excellent environmental protection,and renewability.At present,the high cost of feedstock oil become the main challenge in restricting biodiesel development in China.The biodiesel production from low-quality cooking waste oils（WCOs）can not only greatly reduce the cost,but also realize the resource utilization of WCOs.Among them,acid catalyst is crucial to complete the efficient conversion of WCOs into biodiesel.While solid acids have advantages of high activity,environmental friendliness,and reusability,etc.However,traditional solid acids have the issues of poor stability caused by the imperfect pore structure and active site’s uneven distribution.Therefore,the development of solid acid catalysts with high stability and high activity has become a research hotspot in the biodiesel field.Metal organic frameworks（MOFs）is a porous crystalline material formed by the coordination of inorganic metal clusters and organic ligands,which has advantages of controllable pore structure and large specific surface area.In this thesis,UiO-66（Zr）was modified via in situ and post-functionalized to control the synthesis of solid acid.With that,the structure-activity relationship between physical and chemical components and catalytic activity was emphatically clarified,and revealing the mechanism of catalytic esterification.The specific research work is as follows:（1）Constructing efficient solid acid based on UiO-66（Zr）via in situ modification strategy:UiO-66-（SH）₂ was pre-synthesize with 2,5-dimercaptoterephthalic acid as organic linker and Zr Cl₄ as metal cluster,then the sulfhydryl group（-SH）was oxidized with H₂O₂ into sulfonic acid group（-SO₃H）to prepare solid acid UiO-66-（SO₃H）₂.With that,the effects of H₂O₂oxidation amount and oxidation time on catalytic activity were investigated,and the catalyst was characterized via TG,XRD,FTIR,SEM,and nitrogen adsorption/desorption.Results found that when-SH was oxidized to-SO₃H,although the specific surface area of UiO-66-（SO₃H）₂was decreased,the catalyst acid amount was increased to 2.28 mol/L.The maximum esterification conversion of 86.21%is achieved via UiO-66-（SO₃H）₂ with catalyst amount of10 wt.%,molar ratio of methanol to oleic acid of 15 at 90℃for 4 h.The conversion only was decreased by 3.54%after four esterification reactions.（2）Constructing efficient solid acid based on UiO-66（Zr）via post-functionalization strategy:Solid acids UiO-66/SFA and UiO-66/SFN were prepared by mixing UiO-66（Zr）and（NH₄）₂SO₄ via impregnation method,and calcining at high temperatures in air and nitrogen,respectively.Meantime,the technical path of‘two-stage calcination’was proposed to enhance catalytic stability.Results indicated that UiO-66/SFN has better catalytic activity and reusability under the same esterification conditions.After secondly calcinated at 500℃（UiO-66/SSN）,the interaction between zirconium and sulfuric acid groups is enhanced.The conversion of95.32%is achieved via UiO-66/SSN with catalyst amount of 8 wt.%,molar ratio of methanol to oleic acid of 8 at 70℃for 2 h,and the conversion decrement of UiO-66/SSN is reduced by16.34%compared with UiO-66/SFN（64.94%）within five cycles.（3）Constructing efficient solid acid based on UiO-66（Zr）via post-functionalization strategy:UiO-66（Zr）and（NH₄）₂SO₄ were fully ground and mixed by mechanical mixing method,and then calcined at high temperature in air atmosphere to prepare solid acid UiO-66@SO₄^2-.Results indicated that calcination at 500℃in the air could enhance the strong electron absorption ability of sulfuric acid groups.This makes the interaction between zirconium with sulfuric acid groups enhanced and improves the catalyst stability.The conversion of 95.36%is achieved by UiO-66@SO₄^2-with catalyst amount of 6 wt.%,molar ratio of methanol to oleic acid of 8 at 70℃for 2 h,and the conversion still reached 83.40%after 4 cycles.The activation energy of UiO-66@SO₄^2-catalyzed esterification was 38.21 k J/mol,and the pre-exponential factor was 1144.76 min^-1.