Objetivo
It has been found that naptha sulfur is reduced through formation of H2S. One key factor for improving sulphur reduction is the availability of hydrogen for formation of H2S.
The availability of hydrogen can be increased by several means:
use of a FCC catalyst with higher transfer activity
addition of small amounts of a hydrogen transfer promotor to the additive , such as platinum
addition of small amounts of a hydrogen donating liquid to the FCC feed
If benzothiophene is included in the naptha, the best results obtained in MAT are slightly lower than the target value of 40%
Pilot plant results have not shown such important sulphur reduction in the gasoline fraction as the MAT unit permitted. It was concluded that the most probable reason for the small sulphur reduction at plant level are the specific operating of this unit compared to the MAT system. The small testing unit works at very high contact time and lower temperature than the circulating unit.
It is likely to believe that sulfur reduction additives will suffer from deactivation in a commercial unit. This statement is based on results obtained in the project. When the FCC catalyst and an additive are steamed together, ie when the FCC regenerator conditions are imitated, the additive loses most of its sulfur reduction capability. This additive deactivation is supposed to be due to silicon poisoning from the FCC catalyst. Due to the fact the steaming conditions are harder than commercial FCC regenerator conditions, it is likely to believe that deactivation of the additive will not be important in commercial FCC unit.
In order to know the impact of the silica sol binder on the active additives, the evaluation of a particle with no added silica and steaming seperately from other FCC components could provide the partners with an answer for this poisoning phenomena. This may be accomplished by using an alumina binder or perhaps no binder at all if a pure sepiolite particle has sufficient integrity to withstand process handling.
BE95-1172 Sulfur Removal from FCC Gasoline
Western countries have to meet in the coming years a strong reduction in the sulfur content of the gasoline. FCC gasoline is by far the most important source of sulfur in the final gasoline pool, and a reduction in its content will become necessary.
The objective of this project is to obtain cracking catalysts or additives which can reduce the sulfur content in the FCC gasoline produced by at least 40%, without increasing the production of coke and gases. If this is accomplished, a relatively expensive post-treatment of the gasoline could be avoided, as well as the reduction in gasoline production if the heavy end has to be removed in order to decrease the total sulfur content. The problem is attacked here, from a knowledge of the kinetic data on the formation and cracking of sulfur compounds present in the FCC gasoline. Thus, catalysts are intended to work either by avoiding the occurrence of secondary reactions leading to gasoline sulfur compounds, and/or increasing the rate of adsorption-cracking of those compounds when formed. To carry out the project a first approximation includes the modification of actual catalysts by the appropriate introduction of Lewis acid sites, which when in an adequate ratio and proximity with the Br"nsted acid sites of the catalysts, and when induced in medium pore molecular sieves, should be able to allow diffusion, adsorption, and reaction of the sulfur containing compounds while avoiding the formation of coke owing to geometrical constrains.
A second approximation consists in preparing additives based on metal oxides which very quickly react with sulfur containing compounds present in the gasoline by cracking them and giving the corresponding oxysulfur complexes which decompose in the reducing atmosphere of the riser, as well as hydrolyze in the stripper zone to give H2S as product.
Ámbito científico
- engineering and technologyenvironmental engineeringenergy and fuelsliquid fuels
- natural scienceschemical sciencesinorganic chemistryinorganic compounds
- natural scienceschemical sciencesinorganic chemistrytransition metals
- natural scienceschemical sciencescatalysis
- natural scienceschemical sciencesinorganic chemistrymetalloids
Convocatoria de propuestas
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