Preparation Of Solid Acid Catalyst And Its Catalytic Esterification Of Oleic Acid And Methanol For Biodiesel

Biodiesel,as a kind of green and renewable energy,is one of the most potential energy sources to replace petrochemical diesel.In recent years,solid acid catalysts have become one of the research hotspots in the synthesis of biodiesel by esterification because of their advantages such as easy separation,high catalytic activity,good stability and reusability.Based on the summary and analysis of domestic and foreign biodiesel preparation and solid acid catalyst design research status,this paper designed and prepared four different solid acid catalysts and applied them in the esterification of oleic acid and methanol to prepare biodiesel.Meanwhile,the microstructure?stability and catalytic activity of the four catalysts were studied.First,a series of glycerol-derived sulfonic carbon-based solid acid catalysts SCG-(x)-(y)(Where x represents temperature(°C)and y represents sulfonation time(h))were prepared by in-situ carbonization and sulfonation using glycerol as raw material.The results showed that the amount of acid on the surface of the catalyst increased with the increase of sulfonation time and temperature during the preparation of the catalyst.Considering energy consumption and thermal stability of the catalyst,the SCG-(180)-(10)was selected as the best catalyst.Under the reaction conditions that the alcohol-to-oil molar ratio was 12:1,the reaction temperature was80°C,and the amount of catalyst was 5 wt.%,the catalyst can make oleic acid conversion rate up to 98.40%.The catalyst exhibited excellent stability and could still maintain an oleic acid conversion rate of 83%when used repeatedly for 7 times.Secondly,the x HPW/Fe-Z magnetic solid acid catalyst was prepared by using environmentally friendly phosphotungstic acid as the acid active center,using the co-precipitation method and the static-impregnation method.Through the single factor method,the best esterification reaction conditions of oleic acid and methanol were explored as the molar ratio of alcohol to oil was 12:1,the amount of catalyst was 3 wt.%,the reaction was at 80°C for 4 h,and the highest conversion of oleic acid was 98.1%.The catalyst had strong magnetism,which effectively solved the problem that the catalysts were difficult to separate from the reaction system.The 30HPW/Fe-Z catalyst still maintained an oleic acid conversion rate of81%,exhibiting the least loss of activity after repeated use for 5 times,30HPW/Fe-Z catalyst.In addition,the deactivation analysis of the used catalyst showed that the residual organic matter in the pore structure of the catalyst was a major cause of the loss of catalyst activity,which provides a reference for the pore design of the catalyst in the future.Third,in order to improve the reusability of the catalyst and increase its specific surface area,the HPW/Fe₃O₄@Si O₂ catalyst was prepared by the co-precipitation method and the improved stirring impregnation method.TEM characterization showed that the catalyst had a core-shell structure,in which the core was nano-Fe₃O₄,which made the catalyst strong magnetic and helped the catalyst to achieve rapid recovery and reuse under the action of an external magnet.The shell layer was Si O₂,which could not only protect the internal Fe₃O₄ from the acidic environment,but also provide the catalyst with a mesoporous structure and a larger specific surface area.The results showed that the improved stirring impregnation method made the active center more firmly loaded.Compared with the catalyst prepared by the traditional impregnation method in the previous chapter,the catalyst stability had been effectively improved.In the esterification reaction of catalyzing oleic acid and methanol to prepare biodiesel,a 98.3%oleic acid conversion rate could be obtained.After the catalyst was repeatedly used for 5 times,the oleic acid conversion rate could still be maintained at 85%.Finally,considering that the multi-level pore structure material has more advantages than the single pore size material,solid Si O₂ spheres were synthesized by the St(?)ber method,and then selectively etched by cationic surfactants to prepare hollow mesoporous silica nanospheres(HMSN),through the improved impregnation method to introduce phosphotungstic acid as the active center to prepare the nano-solid acid catalyst HPW/HMSN with multistage pore structure.Research on the structure and performance of the catalyst found that the hollow structure of the catalyst and the shorter pore structure of the shell were beneficial to the transmission of reactants and products.The worm-like mesoporous structure of the catalyst made the phosphotungstic acid highly dispersed in the pores,which can avoid reunions.BET characterization results showed that the specific surface area of the catalyst was as high as 481m²/g,and the catalyst also had a relatively high acid density.Applying the catalyst into the esterification reaction of oleic acid and methanol,the conversion rate of oleic acid could be as high as 98.7%.The stability test of the catalyst showed that it also had good repeated use performance.