Laboratory catalyst deactivation

Despite the increase in zeolite content, catalyst B deactivated faster than A requiring only four and a half hours to reach 66 FAI activity. Using our catalyst deactivation model which allows us to accurately translate laboratory catalyst deactivation to commercial make-up predictions (10), we estimate a much higher makeup rate is required for catalyst B to achieve the same activity as catalyst A (see Table I). 

Figure 5. Effect of Sodium on Laboratory Catalyst Deactivation...

Recent work on laboratory catalyst deactivation in the presence of Ni and V by cyclic propylene steaming (CPS) has shown that a number of conditions affect the dehydrogenation activity and zeolite destruction activity of the individual metals. These conditions include find metal oxidation state, overall exposure of the metal to oxidation, the catalyst composition, the total metal concentration and the NiA ratio. Microactivity data, which show dramatic changes in coke and hydrogen production, and surface area results, which show changes in zeolite stability, are presented that illustrate the effect each of these conditions has on the laboratory deactivation of metals. The CPS conditions which are adjustable, namely final metal oxidation state and overall exposure of the metal to oxidation are used as variables which can control the metal deactivation procedure and improve the simulation of commercial catalyst deactivation. In particular, the CPS procedure can be modified to simulate both full combustion and partial combustion regeneration. 

Two types of laboratory tests were conducted to evaluate contaminant tests, a catalyst stability test and a high-conversion bromine product test. For catalyst stability testing, only a small amount of catalyst was used (1.5 g) to ensure incomplete conversion of the HBr. If a feed contaminant causes catalyst deactivation, it is apparent as an immediate decrease in conversion. If an excess of catalyst was used instead, even if deactivation occurred at the inlet of the bed, it may not be detected until the region of deactivation moves considerably downstream. This could take many hours or days. 

Stability tests of catalyst. All catalysts deactivate during their life by various causes (see Chapter 3). The aim of stability tests is to examine the cause and rate of deactivation. These experiments are usually performed at conditions similar to those planned for the commercial unit. In some cases, accelerated tests are carried out using a feedstock with an elevated level of impurities or at a temperature significantly higher than that anticipated for the full-scale reactor. A laboratory reactor used for such tests is usually a down-scaled reactor or a part of the full-scale-reactor. Standard analytical equipment is used. 

The other major issue in reactor design concerns catalyst deactivation and membrane fouling. Both contribute to loss of reactor productivity. Development of commercially viable processes using inorganic membrane reactors will only be possible if such barriers are overcome. These subjects will receive greater attention as current R D efforts expand beyond laboratory scale evaluations into field demonstrations. 

These results on commercially-aged samples show that silica is transported from the cracking catalyst particles to the Additive R particles during commercial-unit aging, just as it is during a laboratory steam deactivation. More Importantly, the data show that silica deactivates Additive R in a commercial unit (loss of SOx capability) just as it does in a laboratory deactivation. 

Properties of Two Commercial Catalysts Deactivated in the Laboratory by CPS Method... 

Industrially relevant consecutive-competitive reaction schemes on metal catalysts were considered hydrogenation of citral, xylose and lactose. The first case study is relevant for perfumery industry, while the latter ones are used for the production of sweeteners. The catalysts deactivate during the process. The yields of the desired products are steered by mass transfer conditions and the concentration fronts move inside the particles due to catalyst deactivation. The reaction-deactivation-diffusion model was solved and the model was used to predict the behaviours of semi-batch reactors. Depending on the hydrogen concentration level on the catalyst surface, the product distribution can be steered towards isomerization or hydrogenation products. The tool developed in this work can be used for simulation and optimization of stirred tanks in laboratory and industrial scale. 

An earlier report from this laboratory (7) noted that in a series of mildly extracted mordenites, the hexane cracking activity in a continuous-flow test went through a marked maximum with increasing severity of extraction, while the f-butane to n-butane ratio continuously increased. The activity and product distribution were measured after 10 min on stream. Since catalyst deactivation was rapid, it was not possible to... 

Recent evaluations of S02 oxidation over noble metal catalysts (Pt, Pd, and Rh) have given some information on one particular secondary reaction. It was observed in car tests that S03 formation under the conditions of automobile exhaust is highly vulnerable to catalyst deactivation either by thermal sintering or by poisoning (78, 79). At the same time, the data indicated a lesser sensitivity of CO and hydrocarbon oxidation to catalyst aging. The results were confirmed in laboratory experiments (80). This is one example of preferential suppression of an undesirable side reaction. Obviously, the importance of a given poison on the different secondary reactions will vary widely with catalyst formulation and operating conditions. 

Because the application of Pd catalysts to the treatment of contaminated water is relatively new, only one major field study (at Lawrence Livermore National Laboratories) has been conducted and published thus far. (McNab et al. 2000) Other studies, such as that in Bitterfeld, Germany, are currently underway. The Bitterfeld site operates at a residence time of 15 minutes, with a flow of approximately 100 pore volumes/day and uses a zeolite-supported Pd catalyst, which was optimized in laboratory experiments. In the initial tests in the field, the catalyst was deactivated, apparently by sulfide-producing bacteria. Treating the column with 10 g/L of hydrogen peroxide for 2 hours each week (approximately 8 pore volumes of peroxide solution per 700 pore volumes of water treated) resulted in column operation for 15 weeks with 90-99% removal of chlorobenzene and without any apparent catalyst deactivation. (Weiss et al. 1999) As the Pd technology develops further, more field tests are expected. 

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. 

Comparison with Lab Steam Deactivations. Catalyst fractions which exhibit 50% or greater loss in micropore volume/crystallinity comprise less than 15% of equilibrium catalyst. The major portion of this particular equilibrium catalyst is remarkably similar to the material which results from increasingly severe laboratory steam deactivations at 815°C or less (Tables VI and VII). Dealumination is rapid, the associated crystallinity loss is small, and the matrix surface area shows little change. Crystallinity retention falls below 70% only after dealumination is complete. 

The comparison of physical properties of laboratory-steamed catalyst with those of equilibrium catalyst fractions given in Table VII indicates that a wide range of steaming temperatures is necessary to reproduce the equilibrium catalyst deactivation profile for lab steaming times of one day or less. These results indicate that an improved catalyst aging procedure for simulating... 

A theory has been developed which translates observed coke-conversion selectivity, or dynamic activity, from widely-used MAT or fixed fluidized bed laboratory catalyst characterization tests to steady state risers. The analysis accounts for nonsteady state reactor operation and poor gas-phase hydrodynamics typical of small fluid bed reactors as well as the nonisothermal nature of the MAT test. Variations in catalyst type (e.g. REY versus USY) are accounted for by postulating different coke deactivation rates, activation energies and heats of reaction. For accurate translation, these parameters must be determined from independent experiments. 

A model for the riser reactor of commercial fluid catalytic cracking units (FCCU) and pilot plants is developed This model is for real reactors and feedstocks and for commercial FCC catalysts. It is based on hydrodynamic considerations and on the kinetics of cracking and deactivation. The microkinetic model used has five lumps with eight kinetic constants for cracking and two for the catalyst deactivation. These 10 kinetic constants have to be previously determined in laboratory tests for the feedstock-catalyst considered. The model predicts quite well the product distribution at the riser exit. It allows the study of the effect of several operational parameters and of riser revampings. 

Surface vanadium appears to be most stable (to reduction) at low (<1%) V concentration when present as monomeric vanadyl units. Its stability decreases with increasing V levels. It is least stable (to reduction) at high (5%) V levels when present as a supported Vanadia phase. This difference in reactivity with V concentrations is believed responsible for the rapid decline in cracking activity observed in dual function cracking catalysts containing alumina when V start to exceed the 1.0-1.25 wt.% level (4). Further details of the mechanism of catalyst deactivation by V age the subject of continuing investigations 1n our laboratories by 31V solid state NMR, XPS, and Raman spectroscopy. 

The catalyst and oil are in plug flow and the contact time is short so that secondary reactions are avoided and catalyst deactivation by coke formation is properly simulated. The resulting product selectivity, then, is similar to commercial units. Experimental results from a laboratory scale unit can thus be translated to commercial units. 

Due to the strong interaction between the physical and chemical mechanisms, particularly when catalyst deactivation is present, the parameter estimation becomes very difficult. The kinetic parameters are normally obtained from laboratory scale reactors and when used in pilot plant studies, have to be tuned (1, 2) or even re-evaluated (3, 4) to obtain reasonable predictions. The transport parameters are estimated... 

The hydrogenation of THEAQ is a zero-order reaction with respect to hydrogen and a first order reaction with respect anthraquinone [2]. The kinetics of the catalyst deactivation has been studied in a laboratory continuous reactor. Two deactivation mechanisms have been recognized, a reversible and fast one due to the presence of water a d a permanent and slow one probably due to the formation of... 

This value was verified in a continuous laboratory reactor used to study the catalyst deactivation in long time kinetic runs[2]. On the basis of experimental observations, we recognized that the palladium catalyst is subjected to both reversible and irreversible poisoning. Water beiing responsible for reversible poisoning of the catalyst. Thus, we suggested, the following mechanism ... 

The gum phenomenon was studied in detail 10-25 years ago. The composition of "gum deposits" was studied by extracts of deactivated catalysts. Jackson et al, 10) found that the chemical structure of gum deposits on catalysts deactivated in laboratory tests was independent of the reacting hydrocarbons and consisted of -CH2-polymers, whereas Bhatta and Dixon (77) found aromatics in extracts from... 

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