| Due to the increase in oil consumption,exhaust emission has become a serious problem of environmental.Producing ultra-low-sulfur diesel fuel is necessary in order to prevent air pollution.It is well known that hydrodesulfurization(HDS)is an effective desulfurization technology in industrial process.Therefore,it is very important to improve the performance of the current HDS catalysts.However,it would be consume a lot of resources(human,time,financial)to develop a new catalyst or improve the original catalyst.Therefore,it is necessary to propose a model approach to increase the HDS activities by controlling the main physicochemical properties of the catalysts and optimizing the process parameters.Mathematical modeling is an efficient and lowcost method which can lay the foundation for HDS catalysts technological service platform.Hence,this thesis proposed and developed a mathematical model that could be used to quantitatively analyze the effect of different variables on the HDS activity.Otherwise,the model benefits to understand the influence rule of a certain variable on HDS performance in the case as those variables are dependent on each other.The results indicate that the model has a good expansibility.Firstly,a series of Al2O3 with different textural properties and acidity were obtained by hydrothermal method with acetic acid solution.The NiMo/Al2O3 catalyst which prepared by wet co-impregnation method has been shown that the textural properties and acidity are strongly dependent on the support.In addition,the support properties can influence the reducibility and the dispersion of active phase.Accordingly,a quantitative relationship model between the support properties(surface area,average pore size and surface acidity)and the conversion of dibenzothiophene(DBT)HDS was established by building the correlation between "property index" and apparent rate coefficient.So we get the equation as follows:XM=1-exp(-4.319g2.84)=1-exp(-4.319· Sr1.824 · Dr0.674·br0.346)It shows that the total average relative deviation for the proposed model is 1.43%and the prediction deviation is 2.21%.The effects of the property variables on the catalyst activity follow the order as surface area>average pore size>surface acidity properties of the supports.Moreover,an analysis method for the contribution rate of the property variables to the catalytic activity was provided and ?XM will be determined by ?g.Next,a series of NiMo/Al2O3 catalysts with different metal loading were prepared to revise the model.The metal loading can influence the reducibility and the dispersion of the catalysts.NiO loading,MoO3 loading and the MoS2 dispersion of the catalysts will be considered and a "dynamic super geometric average" was applied to replace describe catalyst property index.So we get a quantitative relationship equation between the catalyst properties and the HDS conversion as follows:XM =1-exp(-1.95·Nr1.45-2.83Nr·Mr1.35-2.06Mr·fr0.65)The average relative deviation is only 1.13%.The results indicate that NiO loading has a higher influence degree than MoO3 loading on the HDS activity.The optimum MoO3 loading and NiO loading are 12 wt.%and 3 wt,%respectively.The revised model suggests that this approach also can be worked for wide range of variables.Finally,a series of NiMo/Al2O3 catalysts with different calcination temperature were prepared in order to research the selectivity of model variables and expand the application of the model.High calcination temperature will cause a great loss of specific surface area,pore volume and increases average pore size.Moreover,with the calcination temperature increasing,the reducibility and dispersion of the active components decrease.The calcination temperature is regarded as a property variable,so an equation between calcination temperature and the HDS conversion can be obtained as follows:XM?1-exp(-0.19·Tr5.43-17.1Tr)The average relative deviation is 2.68%and the fitting curve is good match with experimental results.The results indicate that the model variables can extend to preparation conditions of catalysts.In addition,the optimum calcination temperature is 450?500? according to the fitting results.Moreover,the model was verified by different type of variables.The NiO loading,M0O3 loading and calcination temperature of the catalysts will be considered within a certain range.We can obtainXM?1-exp(-0.27·Tr-5.82 · Nr1.78·Mr0.59)The average relative deviation is 2.68%.The results are consistent with the research of separate variable. |
PDF Full Text Request