Influence of catalyst deactivation

Figure 6. Influence of Catalysts Deactivation on Product Distribution over SAPO Catalysts (Propylene Inlet Pressure- 16.2 kPA, Temp.= 650 K) (a) SAPO-5 (b) SAPO-34...

Influence of catalyst deactivation on automotive emissions using different cold-start concepts... 

The influence of catalyst deactivation on the cold-start behavior will be discussed with the help of simulation runs for the above cold-start concepts. Figure 9 shows the cold-start with... 

The severity of the conditions can also influence the catalyst deactivation rate. Higher severity or deeper desulfurization can be obtained by operation at higher temperatures for more catalyst activity. As shown in Fig. 54, however, this higher activity is at the expense of useful catalyst life. At higher temperature the metals distribution parameter is lower and coke formation is more rapid because of increased catalyst activity. 

As discussed in Section IV, Agrawal and Wei (1984) and Ware and Wei (1985b) have successfully modeled experimental deposit profiles by using the theory of coupled, multicomponent first-order reaction and diffusion. Wei and Wei (1982) employed this theory to evaluate the influence of catalyst properties on the shape of the deposit profile. Agrawal (1980) developed a model for the deactivation of unimodal and bimodal catalysts based on the consecutive reaction path. These approaches represent a more realistic consideration of the HDM reaction mechanism than first-order kinetics and will, accordingly, be discussed in more detail. 

While most catalyst vendors rely on fixed bed microactivity (MAT) tests, fixed fluid bed (FFB) reactor experiments are widely used within Mobil to characterize FCC catalysts. The amount of catalyst used is constant for each test, and products are collected for a known period of time. In MAT experiments, catalyst bed is fixed while in FFB test the catalyst bed is fluidized. As products are collected over the decay cycle of the catalyst, the resulting conversion and coke yields are strongly influenced by catalyst deactivation. Systematic differences exist between the measured conversion or catalyst activity and coke yields for the MAT and FFB tests. The magnitude of these differences varies depending on the type of catalyst being tested (REY or USY). Experimental data in Figure 1 clearly show that FFB conversion is higher than MAT conversion for USY catalysts. On the other hand, FFB conversion is lower than MAT conversion for REY catalysts. Furthermore, the quantitative... 

Table X. Influence of catalyst ranking by type of deactivation procedure.

As research into gaseous photocatalysis progressed a potential major disadvantage was the possibility of catalyst deactivation. Einaga et al. [208] concluded that the key factors which influenced catalyst deactivation were the formation of carbon deposits on the photocatalyst and their decomposition to CO. The photo oxidation rate of benzene decreased with decreasing humidity due to the increasing amount of carbon deposits on the catalyst, however, photo irradiation in humidified air decomposed the deposits and regenerated the catalyst [208]. 

Coke selectivity directly influences the rate of catalyst deactivation as seen by comparing coke selectivities in Tables VI and VII with observed rate constants in Table V. Our data indicate calcined AFS zeolites show higher coke selectivities than USY zeolites when compared at similar unit cell sizes. This result suggests that distribution of framework acid sites(as reflected by the distribution of framework silicon) has a strong impact on coke selectivity. In addition, coke selectivity has been shown to correlate with the density of strong acid sites in the framework(20). Our data confirm this and show that steaming decreases the density of such sites which, in turn, leads to decreased coke selectivities. 

Influence of Catalyst Pore Size. In the present work, four Ni-Mo/Al203 catalysts with different pore size distributions were used to assess the effect of catalyst pore size on deactivation by coke and metals deposition. Table I summarizes the pore size distribution of the four catalysts used in the present work. The amount of carbon and... 

It is difficult to obtain reliable values for the various adsorption constants since the aluminum alkyl and the donor apparently also influence the catalyst deactivation with reaction time. Nevertheless, it has been found that qualitatively kA < kA for binary catalysts. This result appears to be more reliable than that reported by Keii et al., viz. kA > kA, since this would be in contrast with the greater Lewis acidity which should characterize atactic centers as compared to isotactic ones. This discrepancy is most likely due to the fact that Keii took ternary catalysts into consideration. In that case, the equilibria of complexing between aluminum alkyl, internal base, and active centers are superimposed on organoaluminum adsorption. 

In this review the intrinsic kinetic aspects are dealt with in the first place The progressive coverage of active sites of the catalyst, which affects its activity and the process selectivity, is cast in a mechanistic form. These kinetic aspects are then studied in combination with the influence of the catalyst morphology, first at the pore level, then at the particle level, seen as a network of pores. Next, growth of coke, leading eventually to pore blcx kage and diffusional limitations are introduced The practical application of the models in kinetic studies is given particular attention. Finally, the effect of catalyst deactivation on the behavior of the reactor is discussed. 

The influence of catalyst composition on sulfur tolerance is revealed in Table I and is illustrated in Fig. 2 based on data from the runs of Catalysts 4 and 6. A trend of decreasing deactivation rate during and after H2S pulsing with increasing ZnO content in the catalysts denx>nstnites relatively high sulfur resistance for ZnO-rich catalysts. The results reported here for the influence of Cu/Zn ratio on initial activity arc consistent with previous literature (refs. 8, 9). 

The criteria given by equations 2 and 3 do not take into account citter the influence of other parameters of catalyst deactivation (dc and ds), or the evolution of the deactivating capacity of each cause considered. For this reason, a third indicator is introduced, termed the time-on-stream deactivQtion percentage %TDy defined as ... 

Organometallic compounds in the feed are the primary cause of catalyst deactivation. The deactivation rate is influenced by feedstock characteristics, catalyst characteristics, and operating severity. 

Coke deactivation on Pt/Al203 catalysts have been studied intensively in the literature. Previous works have focused on the kinetics of catalyst deactivation [7] the influence of additives on coke formation [8] the coke deposition on different morphologic surfaces [9] the structure [10] and chemical composition of coke [11]. Deactivation by coke deposition on niobia supported catalysts, or even on other reducible supports which promote SMSI effect has not been studied. 

In this paper we present our results on a study ofthe deactivation and characterisation of FCC catalysts, together with product yields at realistic coke levels (0.5 to 1.0%), that are typically found on FCC catalysts during industrial operation. In particular, the effect of quinoline and phenanthrene as additives to the n-hexadecane feedstock has been studied at two concentration levels and the relative roles ofthese additives as catalyst poison and coke inducer are discussed. A further aspect investigated is the influence of catalyst formulation. Pure zeolites are seldom used as FCC catalysts instead, catalysts comprise a number of components, which apart from the zeolite, may include matrix, binder and clay. In the present work, catalyst formulations ranging fi"om 100% matrix to 100% zeolite have been examined and the influence ofthe various catalyst compositions on product distribution and coke formation is assessed. 

The BHC-concept reduces the cold-start emissions considerably but is most strongly influenced by catalyst deactivation. Due to the short front part of the catalyst which is heated to high temperature levels (Figure 4) the length of an inert front area of an aged catalyst has a strong influence on the HC-emissions. 

The blocking of catalyst pores by polymeric components, especially coke, is another widely encountered cause of catalyst deactivation. In many reactions of hydrocarbons, side reactions lead to formation of polymers. If these are deposited near the pore openings, catalyst activity and selectivity can be influenced due to unpaired mass transport into and out of the pores. 

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