Aging rate

Catalytic upgrading of short contact time products allows catalysts to be used in more optimal conditions selectivities are improved and aging rates decreased. 

The aging constant, or aging rate, is defined as the percentage loss of capacitance due to the aging process of the dielectric occurring over a decade of time (a tenfold increase in age). This means that in a capacitor with an aging rate of 1% per decade of time, the capacitance will decrease at a rate of ... 

A positive property of the most active reactivators of the second generation lies in their ability to reduce 2 to 2.5 times aging rate of AChE inhibited with soman. 

Deactivation could be modeled by using first-order irreversible aging rates. 

In addition, based on pure component studies, the aging rates were found to depend on time and also on the local temperature, pressure, and composition in the vicinity of the catalytic site. Thus, aging rates for each reaction vary axially along the reactor length. 

The same criteria were used for start-of-cycle and deactivation lumping. Start-of-cycle lumping was based on thermodynamics and molecular-reaction similarity. The deactivation kinetic lumps contain the start-of-cycle lumps as a subset. The additional deactivation lumps were required to properly describe the effect of carbon number on aging rate. 

Effect of Aromatic Carbon Number on Rino-Closure Aging Rates... 

Aromatic carbon number Contribution to ring closure aging rate ... 

Despite the same start-of-cycle temperature, the aging rate is significantly reduced due to the higher-pressure operation. KINPTR predicts that doubling the pressure will triple the cycle length and reduce start-of-cycle C5 + yield to 83.8 vol %. The yield shift results from less favorable aromatization equilibrium. Over the cycle, the C5+ yield drops by 4 vol %. This example clearly illustrates the trade-off between cycle length and yields discussed in Section II. 

The last column in the table shows a decrease in space velocity to 0.7 hour 1 at the higher octane, 98 R + 0. The model results show that the inlet temperature decreases to 768 K owing to the increased catalyst volume. Because of the lower space velocity and temperature, the aging rate is significantly reduced so that the cycle length is 250 days. The C5 start-of-cycle yield is 79.5% with a 5.8 vol % yield loss over the cycle. 

We have evaluated and developed new process modifications using the model. The concept of staggering the reactor inlet temperatures to equalize the aging rates in all three reactors (15) was evaluated with the model. Model simulations, to quantify the benefits of this modification, could be carried out in a day. Corresponding experiments showing similar effects would have required months to complete. With minimal modifications to the model, the benefits for splitting the reformer feed among the three reactors (16) were also determined. 

Properties and Aging Rates for Commercial Reforming Catalysts... 

Kerr, Plank, and Rosinski reported the preparation and catalytic properties of aluminum-deficient zeolite Y materials 35). Topchieva and co-workers studied the catalytic properties of cationic forms of aluminum-deficient Y zeolites, the aluminum deficiency being effected by the H4EDTA method 36-40). They found that up to 50% aluminum removal increased both stability and cumene cracking activity maximum activity was observed at the 50% removal level. Increased catalytic cracking activity was observed by Eberly and Kimberlin for mordenites from which about 80% aluminum had been removed (. 1). Weiss et al. removed over 99% of the aluminum from a hydrogen mordenite and found the zeolite retained catalytic activity of the type induced by Bronsted acids 42). Although the initial activity of this material was lower than that of more aluminum-rich mordenites, the aging rate was markedly reduced, and in a relatively short time the aluminum-deficient catalyst was the most active. 

Another outstanding characteristic of the platinum-rhenium catalyst is its low aging rate with respect to activity. Typical comparisons with conventional catalysts are shown in Figure 5 where operating conditions were essentially constant for the two types of catalysts. The comparisons obtained to date indicate that the catalyst life for the platinum—rhenium catalyst when operated to a given activity decline or temperature rise is about four times that of the conventional catalysts. Under these conditions the yield loss from the rhenium containing catalyst is considerably less than from the platinum catalyst. If the platinum—rhenium catalyst were allowed to operate to the same yield loss as the rhenium-free catalyst, the life would be considerably greater than the four times indicated above. 

The aging rate, Aay/At, is reduced if the crosslink density increases (Cook et al., 1999). This effect could be erased by rejuvenating the sample by heating above Tg or applying large deformations above ey (Oyanguren et al., 1994). 

In summary, piezoelectric coefficients are complex numbers that depend on the measurement frequency, excitation field, temperature, and time (e. g. time after poling in samples that show finite aging rates). Consequently, in reporting piezoelectric data, it is important to specify how the property was measured. 

Figure4.4 Effect of thickness on aging rate of glassy polymer films determined by change in oxygen permeability at 35 °C [46]. Reproduced with permission of Elsevier.

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