Coke poisoning

Various mechanisms of coke poisoning active site coverage, pore filling as well as pore blockage have been observed in FCC [18, 19, 43] and Percolation theory concepts have been proposed for the modelling here of [45, 46, 47, 48]. This approach provides a framework for describing diffusion and accessibility properties of randomly disordered structures. 

Now we still have to specify a relationship between the coke (poison) on the catalyst and the catalyst activity. Several relationships were considered in the original work our illustration is based on an exponential relationship between activity and coke concentration... 

In the system studied, the duration of the run is limited by coke poisoning which is related to the high temperature of the second reactor. There was not found a clear relationship between temperature and extent of the deposits, through the techniques used so it seems that quality more than quantity of the coke deposited determine the catalyst activity lost which must be associated to the temperature under which the reactions are carried out. 

Apparently there is not a clear relationship between the catalyst nature and the coke poisoning susceptibility but the tendency to retain and withstand higher metal poisoning of some catalysts over others is clear. Catalysts with pore size near to 120 A present the maximum metals retention for this type of feeds, but a better definition of the texture needs more information and is the reason of further research at ICP. 

In Fig. 7, the do values obtained for MgO, AI2O3 and MgyAlOx oxides were plotted as a function of the density of basic sites, nb (Table 1). It is observed that the initial deactivation correlates linearly with the density of basic sites. No correlation was found between the NH3 site density (n,. Table 1) and do. These results show that although Mg AlOx oxides promote the selfcondensation of acetone by both acid- and base-catalyzed pathways (Fig. 2), the initial deactivation rate is essentially related to the surface basic properties. This dependence of do with nb for MgyAlOx oxides probably reflects the fact that the acetone oligomerization rate decline is significantly higher when coke poisons very active basic Mg-0 pairs than when eliminates moderately active acidic Al-0 pairs. 

Third, by using these techniques, determine the conditimis for the decomposition of the precursors during the preparation of the catalyst and the identification of coke, poisons, or impurities after reaction, in addition to the possibility of removing these compounds. 

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