Irreversible Deactivation of Zeolite Fluid Cracking Catalyst. 2. Hydrothermal Stability of Catalysts Containing NH₄Y and Rare Earth Y

Abstract

that since the fraction of the bed exposed to the high temperature is small, the activity of the catalyst, as measured by the gas oil test, did not reflect this compositional change.The top part of unstabilized samples after 133 cycles showed a reduction of cell parameter from 24.67 to 24.44 Á, which is close to 24.35 Á found for the stabilized sample. Its crystallinity also compared favorably with that obtained by the standard stabilization procedure. Comparison with the crystallinity of the unstabilized sample indicated that the unit cell shrinkage was not accompanied by further loss of crystallinity. However, the stabilization reaction is apparently slower than the crystal destruction reaction at >1300 °F. As a result, the unstabilized sample at the bottom of the bed was substantially destroyed by the high temperatures. ConclusionsThe most significant finding of this study is the failure to simulate the commercial deactivation experience in the laboratory. It is clear that at temperatures typical of normal commercial operation, little hydrothermal deactivation occurred; only at substantially higher temperature did deactivation become significant. It is possible that gas-phase temperatures in regenerator cyclones sometimes could exceed 1400 °F and, during upsets, the dilute phase regenerator temperature can also reach such levels. These results would suggest that the catalyst deactivation rate could be significantly improved if these high-temperature excursions could be avoided.In commercial practice, the make-up catalyst in its ammonium form is added directly to the dense phase of the fluidized regenerator. Although the x-ray data indicate that the zeolite in the equilibrium catalyst is in its stabilized form, it is believed that additional resistance to deactivation could be achieved if the make-up catalyst were prestabilized.Literature Cited

Role of Nanoporous Al₂O₃ as Matrix for Catalytic Cracking

“…Research on FCC catalysts in the 1980s and earlier was focused on the role of active sites in the zeolite crystal lattice 1) . Recently, discussion on the role of active sites has been given over to the role of extralattice or non-framework aluminum atoms.…”

Cracking and Hydrocracking

“…As mentioned, and perhaps surprisingly, this is not evident from available experimental data -rather, at least for vacuum gasoil 2) Needless to say this is only a first-order approximation as many catalyst vendors claim various approaches to break this trade-off. cracking, equilibrium catalyst activity correlates to resulting zeolite content only, and unit-cell size, while determining selectivity, has a much smaller effect on activity (see Figure 18.9, and also Figure 18.8 above) [42]. This is still an unsolved puzzle in the understanding of FCC catalysis.…”

“…Setting rare-earth content of the fresh catalyst, and indirectly thereby steering its equilibrium zeolite unit-cell size, therefore allows for a trade-off between higher activity and higher gasoline selectivity on the one hand, and higher gasoline octane number and lower coke make on the other hand [41]. 2) The higher activity of the high unit-cell size materials is sufficiently explained by a better crystallinity retention of the zeolite [42] but generally assumed to be due to a higher density of acid sites also [43]. 3) The yield and selectivity effects are more complicated.…”

“…VGO cracking activity (expressed as pseudo second-order rate constant) depends on equilibrium catalyst (residual) zeolite content with little dependence on unit-cell size[42].…”

Synthesis of Hierarchical MgO-Containing Silicalite-1 Zeolites with High Hydrothermal Stability

“…Zeolite catalysts are widely used in industry, [1][2][3][4][5] however, the catalysts slowly deactivate during catalytic reaction and regeneration due to the poor stability under the steam condition 6,7 and the presence of coke. [8][9][10][11][12][13] The zeolite catalyst with a high hydrothermal stability is therefore highly important for more regeneration cycles and extending the catalyst life.…”