Hydrothermal deactivation

This type of coke depends exclnsively on the FCC cracking activity. In order to have samples with different activity and little inflnence of contaminant coke, the fresh catalyst was deactivated hydrothermally at different severity conditions withont metals. MAT test for these deactivated samples was performed with VGO as a feedstock to diminish coke yields. 

The introduction of zeolites in cracking catalysts combined with various non-zeolite matrix types (a.o. higher stability silica-alumina types) certainly complicates the picture of FCC hydrothermal deactivation. Letzsch et al [7] have shown that like amorphous catalysts the zeolite is more strongly deactivated hydrothermally than purely thermally. 

Letzsch et al [7] have shown that like amorphous catalysts the zeolite is more strongly deactivated hydrothermally than purely thermally. 

More irreversible deactivation (hydrothermal, metals), if the feed is not hydrotreated. 

The activity of catalyst degrades with time. The loss of activity is primarily due to impurities in the FCC feed, such as nickel, vanadium, and sodium, and to thermal and hydrothermal deactivation mechanisms. To maintain the desired activity, fresh catalyst is continually added to the unit. Fresh catalyst is stored in a fresh catalyst hopper and, in most units, is added automatically to the regenerator via a catalyst loader. 

Pore volume is an indication of the quantity of voids in the catalyst particles and can be a clue in detecting the type of catalyst deactivation that takes place in a commercial unit. Hydrothermal deactivation has very little effect on pore volume, whereas thermal deactivation decreases pore volume. 

Catalyst residence time in the stripper is determined by catalyst circulation rate and the amount of catalyst in the stripper. This amount usually corresponds to the quantity of the catalyst from the centerline of a normal bed level to the centerline of the lower steam distributor. A higher catalyst residence time, though it increases hydrothermal deactivation of the catalyst, will improve stripping efficiency. 

The regenerator design, either single-stage or two-stage, should provide uniform catalyst regeneration, increase flexibility for processing a variety of feedstocks, and minimize thermal and hydrothermal deactivation of the catalyst. 

There are also different hypotheses on the reaction mechanism, as will be discussed in the following chapters. This is still an open area of research and a further understanding will certainly lead to the development of improved catalysts. There are, in particular, three main areas in which further development is necessary (1) improve the low-temperature activity, e.g. below 250°C, (2) improve resistance by deactivation by sulphur and (3) improve the hydrothermal stability. Hydrotalcite-based materials [3la,97] offer interesting opportunities in this direction. 

Kiss, G., KJiewer, C. E., DeMartin, G. J., Culross, C. C., and Baumgartner, J. E. 2003. Hydrothermal deactivation of silica-supported cobalt catalysts in Fischer-Tropsch synthesis. J. Catal. 217 127-40. 

Steam is invariably present in a real exhaust gas of motor vehieles in relatively high concentration due to the fuel combustion. The influence of water vapor on catalytic performances should not be ignored when dealing with the aim to develop a practical TWCs. Cu/ZSM-5 catalysts once were regarded as suitable substitutes to precious metal catalysts for NO elimination[78], nevertheless, they are susceptible to hydrothermal dealumination leading to a permanent loss of activity[79], Perovskites have a higher hydrothermal stability than zeolites[35]. Although perovskites were expected to be potential autocatalysts in the presence of water[80], few reports related to the influence of water on the reactants adsorption, the perovskite physicochemical properties, and the catalytic performance in NO-SCR were previously documented. The H2O deactivation mechanism is also far from well established. 

Fast deactivation rates due to coking and the limited hydrothermal stability of pillared clays have probably retarded the commercial development of these new type of catalysts and prevented (to date) their acceptance by chemical producers and refiners. However, there is a large economic incentive justifying efforts to convert inexpensive (i.e. 40-100/ton) smectites into commercially viable (pillared clay) catalysts (56). Therefore, it is believed that work on the chemical modification of natural (and synthetic) clays, and work on the preparation and characterization of new pillared clays with improved hydrothermal stability are, and will remain, areas of interest to the academic community, as well as to researchers in industrial laboratories (56). 

Different procedures can be used in practice to activate the zeolite, and the choice of a particular method will depend on the catalytic characteristics desired. If the main objective is to prepare a very active cracking catalyst, then a considerable percentage of the sodium is exchanged by rare earth cations. On the other hand, if the main purpose is to obtain gasoline with a high RON, ultrastable Y zeolites (USY) with very low Na content are prepared. Then a small amount of rare earth cations is exchanged, but a controlled steam deactivation step has to be introduced in the activation procedure to obtain a controlled dealumination of the zeolite. This procedure achieves a high thermal and hydrothermal stability of the zeolite, provided that silicon is inserted in the vacancies left by extraction of A1 from the framework (1). The commercial catalysts so obtained have framework Si/Al ratios in the... 

CATALYST PREPARATION AND TESTING. The Y-containing catalysts examined in this study were prepared either by 1) a microunit accelerated metals laydown technique or 2) by a simulated deactivation procedure involving hydrothermal treatment of Y-doped catalysts. 

Vanadium Deactivation of FCC Catalyst Effect of Thermal/Hydrothermal Treatment and V Source... 

Pt on alumina and activated carbon also show high activity, whereas Pt supported on Si02-Al203 and Zr02 show moderate catalytic activity for H2 production. Lower activity has been observed for Pt supported on Ce02 and ZnO, mainly due to the deactivation caused by hydrothermal degradation of the supports. 

Catalyst hydrothermal deactivation was carried out in two different equipments a lOOg capacity fixed bed steamer was used for the advanced cracking evaluation (ACE) unit tests and a 5 kg capacity fluidized bed steamer was used for the other testing protocols. Steaming conditions in the two cases were the same 788°C for 5 hours under 100% steam flow. Although conditions were similar, higher pressure buildup in the fixed bed steamer led to lower surface area retentions. 

The application of the two protocols without the presence of the contaminant metals was carried out in order to investigate their contribution to the overall deactivation mechanism. The comparison of the acidities deltas between the two deactivation protocols for both cases (with or without metals) is presented in Table 9.2. As is obvious, the deltas in the presence of the metals are positive, while in the absence of the metals the deltas are negative. Thus, the sample deactivated with the ADV-CPS protocol without metals ends up with less acidity than the sample deactivated with the corresponding CPS. This was expected due to more severe hydrothermal deactivation conditions during the ADV-CPS application. The higher loss of specific areas verifies the more intense hydrothermal deactivation. 

In general, although proper metal aging is still an open issue, it seems that severe hydrothermal conditions during ReDox cycles with an emphasized reducing step is the direction to optimization of the artificial deactivation methods. The development of such a simulative lab-deactivation protocol will undoubtedly be very essential and a major contribution in the FCC research field. 

The catalyst used in this study corresponds to a fresh commercial catalyst used in one FCC unit of ECOPETROL S.A. This solid is hydrothermal deactivated at the laboratory in cycles of oxidation-reduction (air-mixture N2/Propylene) at different temperatures, different times of deactivation, with and without metals (V and Ni), and different steam partial pressures. Spent catalysts (with coke) are obtained by using microactivity test unit (MAT) with different feedstocks, which are described in Table 10.1. 

The catalysts with metals are previously impregnated with solutions of vanadyl and nickel naphtenates based on the Mitchell method [4], Before hydrothermal deactivation the samples were calcined in air at 600°C. The activity was performed in the conventional MAT test using 5 grams of catalyst, ratio cat/oil 5, stripping time 35 seconds, and reaction temperature 515°C. Elemental analyses to determine the total amount of carbon in the spent catalysts were done by the combustion method using a LECO analyzer. 

Hydrothermal Deactivation of Catalyst Impregnated with Different Levels of Metal... 

ECC catalyst is subject to hydrothermal deactivation. This occurs when the A1 atom in the zeolitic cage is removed in the presence of water vapor and temperature. The result is a loss of activity and unit conversion. The effect of temperature on this process is nonlinear. The deactivation rate increases exponentially with temperature. Units that experience high afterburn have attributed high rates of catalyst deactivation on the higher dilute phase temperatures. This phenomenon is more apparent on units with high combustion air superficial velocities. The high velocity not only increases afterburn, but also increases catalyst entrainment to the cyclones and dilute area. COP is used to decrease afterburn and minimize catalyst deactivation. 

This loop is, however, affected by the availability of the reactant oxygen, which in surplus destroys the precursor VPO. Further, oxygen is positively needed to activate and re-oxidize the VxOy sites but leads also to more water formation that in turn hydrothermally deactivates the active mass. Likewise, water is needed to separate, via hydrolysis, the vanadium phosphate into VxOy and mobile phosphate. The multiplicity of the feedback loops is at first puzzling but explains the apparent stable steady state that can be reached with a catalyst undergoing so many chemical and microstructural transformations the multiplicity of controls prevents one single factor becoming dominant and thus potentially destabilizing the whole process. 

Laboratory steam deactivations represent a significant compromise in the effort to simulate equilibrium catalyst. Since hydrothermal deactivation of FCC catalysts is not rapid in commercial practice, deactivation of the fresh catalyst in the laboratory requires accelerated techniques. The associated temperatures and steam partial pressures are often in substantial excess of those encountered in commercial units. In some instances, the effect of contaminant metals is measured by an independent test not affiliated with steam deactivation. In subsequent yields testing, interactions between different modes of deactivation may be overlooked. Finally, single mode deactivation procedures can not reproduce the complex profile of ages and levels of deactivation present in equilibrium catalyst. 

E - Severe Hydrothermal Conditions - Catalyst deactivation/ stability problems - High Activity and Stability Catalysts... 

Careful selection of the deactivation conditions (metals per cycle, regenerator tempeature, % wt steam in can also allow us to distinguish between catalyst deactivation by metals and by hydrothermal effects. (Table VIII.)... 

It is clear that the zeolite delta coke will have a strong effect on the regenerator temperature and hence on the catalyst deactivation. Depending on the trend in FCC regenerator temperatures, the aspect of hydrothermal stability might become of greater importance. 

The complexity of the inter-relations between catalyst deactivation by aging, poisoning and fouling and the effect on heat balance and catalyst circulation rate are described. For catalyst poisoning at high metal contents as well as for hydrothermal aging with low metals, cyclic deactivation of the catalyst in various age fractions is the preferred route for a realistic simufation and quantification of these phenomena. 

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