Preparation Of The Second Generation Biodiesel By Hydrodeoxygenation Of Fatty Acid Methyl Esters

Since the beginning of the 21st century,environmental protection and new energy development have attracted the attention of many countries in the world.The development of alternative fuels from biomass can effectively mitigate the problem of energy exhaustion and global warming associated with fossil fuels.Fatty acid methyl esters（FAMEs）,as the main component of the first generation of biodiesel,have the advantages of sufficient raw materials,renewability and clean properties.However,the application of FAMEs has been limited due to its high viscosity,high freezing point and low heating value associated with oxygen atom.Therefore,hydrodeoxygenation of fatty acid methyl esters is of great significance for improving the combustion performance,flow properties and application range of biodiesel.In order to solve the above problems,this paper developed several hydrodeoxygenation catalysts.Then,the acidity,pore size distribution and active components dispersity of catalyst were regulated by the change of acid carrier content,precious metal loading and acidic carrier type,thereby achieving the target of high fatty acid methyl esters conversion rate and high diesel component yield.The physicochemical properties of the catalyst were characterized by XRD,BET,NH₃-TPD,SEM,TEM,STEM,EDX,H₂-TPR techniques.The research in this paper includes the following aspects:（1）Several hydrodeoxygenation catalysts（including different ZSM-5 ratios,Pt loading,and acidic carrier species）were prepared by methods combining kneading extrusion and equal volume impregnation.Subsequently,the series of noble metal catalysts were applied to the hydrodeoxygenation reaction of fatty acid methyl esters,and the results of hydrodeoxygenation were compared.The result indicates that with an increase in content of ZSM-5 decreased pore size,while increasing the acidity and Pt dispersion of the catalyst.The optimized reaction conditions were as follows:T=350°C,P=2 MPa,H₂/Oil=1000,WHSV=0.5 h^-1.Compared with the conventional single-supported Pt/Al₂O₃ and Pt/ZSM-5 catalysts,Pt/ZSM-5-Al₂O₃ catalyst has a significant improvement in the conversion of fatty acid methyl esters（30.7、24.8%to99.3%）and the yield of diesel components（25.3、20.8%to 85.7%）under optimal condition,.（2）This work developed another mixed carrier catalyst Pt/beta（10%）-Al₂O₃.The difference in FAMEs hydrodeoxygenation performance between single carrier and mixed carrier catalyst was investigated;the hydrodeoxygenation process conditions of catalyst also were optimized.The results showed that the addition of beta zeolite could effectively improve the conversion of fatty acid methyl ester and the yield of the product.The hydrodeoxygenation performance of Pt/beta（10%）-Al₂O₃ was significantly superior to Pt/beta and Pt/Al₂O₃.The optimized reaction conditions were as follows:T=350°C,P=2 MPa,H₂/Oil=1000,WHSV=0.5 h^-1.Under this condition,the FAMEs conversion rates and diesel component yield of Pt/beta-Al₂O₃ were reached 99.5 and 88.5%,respectively.（3）The mixed carrier catalysts（Pt/beta-Al₂O₃）with different beta ratios were prepared,and their differences in hydrodeoxygenation performance of FAMEs were compared.It was found that the three catalysts exhibited excellent deoxygenation performance on the hydrodeoxygenation of FAMEs（>99%）,and the yield of diesel components in the products decreased significantly with the increase of beta content.Combined with the results of various characterizations,the reason was that an increase in the content of beta zeolite increased the acid strength and the microporous channels proportion of catalyst,which leads to a sharp increase in the cracking reaction and secondary cracking,thereby reducing the long-chain alkane yield.（4）After comparing the performance of the catalysts,it was founded that the Pt/beta（20%）-Al₂O₃ exhibited better hydrodeoxygenation performance than others.Next,the hydrodeoxygenation results of Pt/beta（20%）-Al₂O₃ catalyst under different process conditions were investigated.Meanwhile,the hydrodeoxygenation products were analyzed.Finally,the stability of Pt/beta（20%）-Al₂O₃ with excellent deoxygenation performance on hydrodeoxygenation of FAMEs was investigated under appropriate reaction conditions.It was found that the Pt/beta（20%）-Al₂O₃catalyst exhibited a nice stability during the whole reaction time.After 160 h,the catalyst still maintained 98.9%conversion rates of FAMEs,and the catalyst is expected to be further industrial application.