Development Of Diesel Hydrodesulfurization Catalysts And The Study On Catalyst Stacking Techenology

Diesel deep hydrodesulfurization is one of the effective measures to solve the SOx and other pollutants. Some reshearches show that when the sulfur contents in diesel decrease from500μg/g down to lOug/g, it could reduce the SOx emissions obviously, and PM2.5reduced by30%. Automotive diesel sulfur contents in the developed countries have been limited less than10μg/g, which also is the development trend of Chinese diesel specification.Most of the sulfides can be removed by conventional technology. The study of molecular structure of different sulfides and their desulfurization reaction mechanism shows that4,6-DMDBT species are the hardest sulfides to remove, because the two alkyl substituent on the beta site has strong steric hindrance. In order to producing low sulfur diesel product, the key is the efficient removal of such sulfides.At present, it is an effective way to remove the sulfur of4,6-DMDBT species by promoting aromatics hydrogenation saturation in abroad, but there are some disadvantages. Firstly, the highly hydrogen consumptions and processing costs will rise caused by excessive aromatics saturation, secondly, operation cycle of industrial plant will be shorten because of the operation temperature range becoming narrow leading to response for the thermodynamic equilibrium limit.Through systematic analysis of diesel deep desulfurization reaction mechanism, this article thinks that alkyl transfer is a more scientific and economic desulfurization way to eliminate steric hindrance before hydrogen desulfurization reaction. At the same time, the systematic research on the commercial application has been carried out.In order to achieve the alkyl transfer desulfurization, firstly, designed new catalytic material from the aspect of molecular with large volume diameter and effective pore size distribution concentration, and comparing with the old one, Bronsted acid contents of new alumina materials increase to2.3times. These new catalytic materials can meet the special acidity requirements of alkyl transfer reaction for4,6-DMDBT sulfide desulfurization reaction. Secondly, gradient impregnation and dispersion technology of active metal research have been carried out which can make the metal-support interaction weakensupport, improve the degree of sulfidation of active metal and control active sites microstructures. On this basis, two type new diesel deep hydrodesulfurization catalystshave been developed. One is FHUDS-6Mo-Ni type catalyst with higher HDN and polycyclic aromatic satuation activity, which could deeply desulfur for coking diesel containing higher nitrogen contents and higher polycyclic aromatic hydrocarbons contents. Another is FHUDS-5Mo-Co type catalyst with good alkyl transfer function under high reaction temperature condition which has the advantage of lower hydrogen consumptions in view of straight run gas oil with lower nitrogen and aromatic hydrocarbon contents. Thirdly, through further research into the dynamics of new deep desulfurization catalyst reaction, seven lumped kinetics equations containing alkyl transfer reaction mechanism are established. Fourthly, depending on the studying of deep hydrosulfurization reaction kinetics, the changing of hydrogenation reactor macroscopic environment, the influencing of feedstocks properties in bottom bed of reactor, the stacking technology of different type catalysts has been developed. A suitable catalyst grading technology for promoting alkyl transfer desulfurization reaction and reduce the consumption of hydrogention has been achieved. In order to remove4,6-DMDBT sulfides species, Mo-Ni catalyst with high HDN and hydrogenation activity should be used in the upper bed, effectively reduce the organic nitrides inhibitory effect of alkyl transfer and establish for alkyl transfer reaction environment. Mo-Co catalyst with high DDS, good alkyl transfer activity, lower hydrogen consumption and strong hydrogen sulfide tolerance should be loaded in the bottom bed, to mitigate the effect of thermodynamic equilibrium limitations under high reaction temperature. The research results have been applied in3.3MT/a of Shanghai petrochemical company and Paramo refinery in the Czech Republic device. Up to now,these catalysts and the grading technology have been applied in more than20hydrogenation industrial units to meet the requirements of long period producing clean diesel of national IV and Europeon V.This study developed the theory of alkyl transfer desulfurization reaction, and achieved the industrial application. On this basis, a set of7level total reaction kinetics model for diesel deep hydrodesulfurization reaction was established, which contains alkyl transfer reaction path. The calculated values and measured values of product sulfur content coincide well, which enhances the theory of diesel deep hydrodesulfurization application.