Preparation Of Aminopropyl Siloxane Block Copolymer Composites Based On H₃PW₁₂O₄₀ And Their Acid Catalytic Performance

Energy is the foundation of human survival and green development is a necessary condition for sustainable development,and the environmental problems caused by excessive use of fossil energy are becoming increasingly severe.As a green and renewable energy source,biodiesel is an ideal substitute for fossil diesel.The traditional methods of preparing biodiesel use strong inorganic acids and bases or Lewis acids as catalysts,but due to the formation of by-product,difficulty in product separation,and difficulty in recycling,which make it impossible to be used in industrial production.Heteropolyacids are very strong Br?nsted acid,among which phosphotungstic acid(H₃PW₁₂O₄₀·x H₂O,hereinafter abbreviated as HPW)has the strongest acidity,the best acid catalytic activity,and has almost no impact on the environment.However,since the above are all homogeneous catalysts,in view of their existing problems,scholars have discovered a variety of supported heterogeneous catalysts,among which polymer-supported heteropolyacid catalysts solve the problems of being soluble in polar solvents and easy to agglomerate when HPW is used as a homogeneous catalyst,and make it possess a series of advantages of polymer-supported catalysts,and the polymer-supported heteropolyacid catalysts exhibit good acid catalytic activity in the esterification reaction of oleic acid and methanol.The specific research contents are as follows:（1）Using octamethylcyclotetrasiloxane（D₄）,3-aminopropylmethyldiethoxysilane（APDES）and hexamethyldisiloxane（MM）as raw materials,tetramethylhydrogen ammonium oxide（TMAH）was used as a catalyst to synthesize an aminopropyl siloxane block copolymer（ASBC）.A series of characterization instruments were used to characterize the physical and chemical properties of the copolymer:the molecular structure of the copolymer were characterized by Proton Nuclear Magnetic Resonance Spectroscopy（¹H-NMR）,Carbon Nuclear Magnetic Resonance Spectroscopy(¹³C-NMR)and Fourier Transform Infrared Spectroscopy（FT-IR）;rotational viscometer,Gel Permeation Chromatography（GPC）and hydrochloric acid titration were used to test the viscosity,molecular weight and amine value of the copolymer.（2）Using self-synthesized ASBC as the carrier and HPW as the active site,a series of polymer-supported heterogeneous composites named xHPW/ASBC are prepared through the acid-base,coordination and hydrogen bonding of the chemical bonding method.A series of characterization instruments were used to characterize the physical and chemical properties of the composites:the structure of the composites were characterized by Fourier Transform Infrared Spectroscopy（FT-IR）,Ultraviolet-visible Absorption Spectroscopy（UV-vis）and Raman Spectroscopy（Raman）;Wide-angle X-ray Powder Diffraction（XRD）was used to test the crystalline form of the composites;the thermal stability of the composites were characterized by Thermogravimetric analysis（TGA）;the surface elements type and atomic valence state of 0.5HPW/ASBC composite material were obtained by the X-ray Photoelectron Spectroscopy（XPS）test;the Contact Angle test（CAs）was used to analyze the hydrophobicity of the composites;the ultra-high resolution thermal field emission Scanning Electron Microscope（SEM）was used to observe and compare the surface morphology of pure HPW and 0.5HPW/ASBC composite material.（3）Taking the esterification reaction of oleic acid and methanol as a model reaction,the effects on catalytic performance were tested respectively through single factor experiments,for example,the type of catalyst,the molar ratio of alcohol to acid,the amount of HPW addition,the amount of catalyst,the reaction temperature,the reaction time,the stirring rate,and the catalyst cycles.The catalytic yields were obtained by the method of characterizing the ¹H-NMR and calculating the peak area.Finally,the physical and chemical properties of the 0.5HPW/ASBC composite material were tested after 3cycles of use.