Study On Sulfur Reduction Additives For FCC Process

With development of the society, the environment which humankind lived in is required cleanner. Air pollution, caused by gasoline engine exhaust gas (SOX), is one of the most serious problems in the world, and much attention has been focused on the deeping desulfurization of gasoline. Sulfur in gasoline is not only a direct contributor to SOX emissions, it is also a poison affecting the low-temperature activity of automobile catalytic converters. Therefore, it influences volatile organic compounds, NOX, and total toxic emissions. Consequently, every country limits the content of sulfur in gasoline stringently. Sulfur content has been lower than 10μg/g in some states of the United States. In China it is reduced to 150μg/g from 300μg/g in 2008. About 90% of sulfur in gasoline originates from FCC (fluid catalytic cracking) gasoline, so reducing the sufur content of FCC gasoline is main target of sufer removal.Several different routes to reduce the content of sulfur can be considered, but using additives for sulfur removal to reduce sulfur content of FCC gasoline during the in situ FCC process is the most economical route to desulfurization. The USY/ZnO/Al2O3 additive we developed can reduce more than 30% of sulfur in gasoline. However, the hydrothermal treatment at high temperature may cause deactivation of the additive. After the fresh additive is aged at 800℃with 100% steam, the micro-activity and sulfur removal activity drop significantly. These changes may be caused by the strong interactions between USY and ZnO. ZnO can capture the framework Al of USY to form inert ZnAl2O4 spinel and cause the collapse of the framework. When the content of ZnO in the samples is enough, ZnO can react with the Si in the collapsed framework to form Zn2SiO4 willemite. Here, we introduce a porous mass to isolate ZnO and USY, in order to depress the interactions between them. In this paper, additives for desulfurization of FCC gasoline during FCC process have been evaluated in a Confined-Fluidized-Bed reaction apparatus with Lanzhou VGO as feedstock. The results were as follows: the hydrothermal stability of additives can be improved by introducing the porous mass, but there is a optimum adding amount of porous mass in additives; The optimum mass of additive in equilibrium catalyst is 25%, and the sulfur content of gasoline can be reduced by more than 30 %,compared with only using equilibrium catalyst, while products distribution do not change obviously. Another additive sample Al2O3/USY/A/porous mass has a higher desulfurization ratio, yet products distribution change obviously.