Deactivation Parameters

The ODE-model was solved numerically during the estimation of the kinetic, adsorption, and deactivation parameters. 

The deactivation parameters aij are determined by integrating the kinetic deactivation equations ... 

The selectivity and equilibrium parameters for the C6 system are given in Table IX, the activity parameters in Table X, and the deactivation parameters in Table XI. 

E, F deactivation parameters defined by equations I) and (2) k] reaction rate constant, s 1... 

Deactivation parameters obtained by plotting ln[(l — a) a)] versus time are listed in Table XIX for a number of nickel and nickel bimetallic catalysts. The fact that these plots were generally linear confirms that these data are fitted well by this deactivation model. These data, which include initial site densities for sulfur adsorption, deactivation rate constants, and breakthrough times for poisoning by 1-ppm H2S at a space velocity of 3000 hr-1 provide meaningful comparisons of sulfur resistance and catalyst life for both unsupported and supported catalysts. Table XIX shows that the... 

Av = —2 rate constant we assumed that the A av=-2/A av=-i ratio determined from the low temperature data (0.3) was also valid for 300 K. With this modification the deactivation rate constants for He were predicted to be a factor of two greater than those listed in Table 3 (for both the slow and fast deactivation parameters). 

The Constant—Parameter Arrhenius Plot (CPAP) technique uses in addition the effect of temperature. The observed rate constants are plotted in an Arrhenius form at a constant value of the deactivation parameter, r i.e., one curve for points lepieseuting the fresh catalyst (t = 0), etc. For each curve, a low—temperature asymptote and a high-temperature asymptote can be drawn, and these can be extrapolated to intersect at a point with coordinates 1/T ( r), ta k (ir). Then, as shown in ref. (1), the values of k.. ... 

The effect of SO-j on tlie rate of the selective catalytic rcductiori(SCR) of NO by NH3 over a mordenile type ztiolUe catalyst has been examined in a flotv reactor system. The deactivation of the catalyst is strongly dependent on the I eaction temperature and independent of the SO2 feed concentration. The sulfur content of the catalyst and its surface area appear to be dominant deactivation parameters. The catalytic activity is inversely related to the sulfur content of the catalyst. 

Table 1 shows both the initial propane conversion (Xg) and the selectivity to propylene (Sg), measured 4 min after the reaction started, and the deactivation parameter (X/Xg obtained in flow reaction experiments). This parameter is defined as the difference between the initial propane conversion (Xg) and the final conversion (X,) measured at 80 min of the reaction time, referred to the initial propane conversion for the different catalysts. 

Values of initial conversion (Xg), initial selectivity to propylene (Sg) and deactivation parameter (X/Xg) for the different mono and bimetallic catalysts. 

Pt/AljOj, but a much higher selectivity to propylene (95%) and a lower deactivation parameter (Table 1). This effect is also reflected in a lower coke deposition (1.95 wt% C for Pt/AljOjand 0.94 wt% for Pt/ZnAljO ), as is observed in TPO profiles (Figure 1). The different behavior of these two catalysts cannot be related to the metal dispersion, since the... 

Values taken from ref. 10. Activity computed from deactivation parameters. 

Nam et al.l studied the deactivation of a commercial catalyst, 10% V2O5 on alumina, by SO2 in the reduction of NO by NH3. The feed gas was the flue gas from the combustion of No.2 fuel oil in a laboratory furnace, doped with NO and NH3. The physico-chemical properties of the deactivating catalysts were correlated with its activity and accumulating sulfur content, and the deactivation was modeled. The activation energies of fresh and deactivated catalysts were similar. The sulfur content of the catalyst, as well as the surface area, appeared to be a dominant deactivation parameter, analogous to coke-induced deactivation. Pore size distribution changes indicated that... 

In spite of this feet, and as previously described, the initial deactivation parameters can be obtained from the ln(a)-vs-time plot. These values were reported in Table 2. 

The rate constants, the adsorption equilibrium constants, and the deactivation parameters a, and oto were determined from the measurement of Pa and pj, as a function of time and position (i.e., W/F o) in the bed, through a special sampling device. In addition, the coke profile was measured at the end of the run. The parameters were found to be statistically significant, and the rate coefficients obeyed the Arrhenius temperature dependence. 

The form of the deactivation function and the numerical value of the deactivation parameter were determined by means of an electrobalance. The deactivation constant is essentially identical for the three reactions in this case. The total rate of coke formation, rc = reg + rco has been given in Chapter 5 as Eq. (i) of Ex. 5.3.e-l. 

Next the activity of the catalyst has to be related to the amount of deactivating agent. This is done by means of exponential deactivation functions. Three deactivating functions were selected one for the effect of alkylation, one for the monomolecular steps and one for the bimolecular steps, as illustrated in Fig. 5.3.3.D-2. The deactivation parameter in the exponentials was derived from the experimental data. The evolution of the deactivating functions with the coke content is also shown. 

The work done by Weekman (1968), Nace (1970), Nace et al. (1971), Gross et al. (1974), Paraskos et al. (1976) and Shah et al. (1977) using the same decay function based on the time-onstream theory obtained different values for the deactivation parameters. Corella et al. (1985)... 

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