Cyclic deactivation method

As described by Gerritsen et al [23] in the Cyclic Deactivation method the catalyst is deactivated by several Reaction and Regeneration (coke burning) cycles. As we will discuss in the next section of this paper, this is essential for the realistic aging of the metals. 

A possible explanation for this is that while dealumination in a commercial unit is fastt migration of non-framework alumina from the zeolite structure will be a function of temperature and steam partial pressure [24], This is an area in which the Cyclic Deactivation method approaches the commercial conditions much closer than traditional steaming methods. 

The foregoing combined with the observations made in 3.2 lead us to conclude that we need to try to simulate the deactivated catalyst as close as possible, preferably using the Cyclic Deactivation method. 

Here the Cyclic Deactivation method approaches the commercial conditions much more closely than traditional steaming methods. 

The catalysts were impregnated with 5000 ppm V by the traditional Mitchel pore volume impregnation method and by the cyclic deactivation method. With the pore volume method (PV) the vanadium is distributed homogeneously over the catalyst. With the cyclic deactivation method (CD), the vanadium profile over the particle is as in commercial practice. 

Figure 11 shows that a high-accessibility system will give the best zeolite protection when evaluated by the realistic cyclic deactivation method. This has been confirmed in commercial operations (Figure 12). The FCC catalyst ability to rapidly deactivate the deposited metals will be an important factor in resid cracking.

The route of catalyst deactivation via a cyclic metal impregnation and deactivation method has produced significant improvements in approaching realistic vanadium and nickel profiles over the catalyst particles. From electron microprobe analyses of Ni and V loaded catalyst it has been established that after pore volume saturation, Ni and V are rather homogeneously distributed over the catalyst. 

In cyclic impregnated catalysts, Ni is mainly present on the catalyst surface. In contrast a vanadium profile over the particle is found. In the case that no steam is applied in the regeneration stage of the cyclic deactivation procedure, the V remains mainly concentrated at the surface of the catalyst particles. Other methods as imaging SIMS (19) and Luminescence (20) are also being applied to monitor and compare the Ni and V distribution of deactivated... 

Hence to investigate nickel effects as realistically as possible, Cyclic Deactivation (CD) methods are recommended. 

Figure 6 demonstrates the same point by con aring the MgO based trap to the Barium Titanate lab prototype. Again loss of performance in the presence of sulfur is observed. For these experiments SO2 gas was used to effect the sulfation during the regeneration mode of cyclic deactivation. SO2 gas may also be bled into the system dxiring the Transfer Method experiment allowing sulfur to directly con ete with trap sites as in the above two studies. 

Vanadium interacts with nickel in a manner which inhibits the deactivation behavior of nickel. Metals-resistant catalysts must therefore be evaluated in the presence of both nickel and vanadium. Also, the mobility of vanadium is reduced in the presence of nickel. In general, cyclic deactivation will be the preferred deactivation method in order to simulate the actual metal distribution and interactions on the catalyst and the correct metal age distribution. 

Reaction progress kinetic analysis offers a reliable alternative method to assess the stability of the active catalyst concentration, again based on our concept of excess [e]. In contrast to our different excess experiments described above, now we carry out a set of experiments at the same value of excess [ej. We consider again the proline-mediated aldol reaction shown in Scheme 50.1. Under reaction conditions, the proline catalyst can undergo side reactions with aldehydes to form inactive cyclic species called oxazolidinones, effectively decreasing the active catalyst concentration. It has recently been shown that addition of small amounts of water to the reaction mixture can eliminate this catalyst deactivation. Reaction progress kinetic analysis of experiments carried out at the same excess [e] can be used to confirm the deactivation of proline in the absence of added water as well to demonstrate that the proline concentration remains constant when water is present. 

Various stable radicals such as nitroxide, triazolinyl, trityl, and dithiocarbamate have been used as the mediating or persistent radical (deactivator) for SFRP. Nitroxides are generally more efficient than the others. Cyclic nitroxide radicals such as 2,2,6,6-tetramethyl-l-piper-idinoxyl (TEMPO) have been extensively studied. SFRP with nitroxides is called nitroxide-mediated polymerization (NMP). Polymerization is carried out by two methods that parallel those used in ATRP [Bertin et al., 1998 Georges, 1993 Flawker, 1997 Flawker et al., 2001], One method involves the thermal decomposition of an alkoxyamine such as... 

We have been using the CPS method since it was published by Grace Davison. The method is simple, and consists of a volumetric impregnation of the catalyst followed by a cyclic ReDox deactivation in 50% steam at constant temperature. 

FCC catalyst, supplied by Grace Davison, at three different cat-to-oil ratios, 4,6, and 8. The feed was injected at a constant rate of 3 g/min for 30 seconds. The catalyst to oil ratio was adjusted by varying the amonnt of catalyst in the reactor. Two catalysts used for this evaluation were laboratory deactivated using the cyclic propylene steaming (CPS) method [6]. Properties of these catalysts after deactivation are listed in Table 12.3. 

Since the method of metal impregnation will also have a large impact on the profile of vanadium deposition of the catalyst, we clearly need to review this aspect of catalyst testing. Via cyclic metal impregnation and catalyst deactivation, we can approach "Real-World" conditions far better. (Table VII.)... 

There is only a limited amount of information on the deactivation mechanisms and rates of vanadium and nickel migration. The formation of metal silicates and/or aluminates has been proposed, as they seem to form more easily by reduction and oxidation cycles. Rajagopalan et al. [8] confirm that methods involving cyclic redox aging of metals in the presence of sulfiir are needed for screening metals-tolerant catalyst. They propose a cyclic test (the cyclic propylene steam method), which addresses the redox aging of the metal, but not the nonuniform laydown and age distribution of metals on the catalyst. 

Notice the use of a cyclic anhydride in the first Friedel-Crafts acylation. It doesn t matter where the acylation occurs and the reaction stops there as the ring is deactivated by the ketone and the carboxylic acid released in the reaction is much less electrophilic than the anhydride. The ketone is then reduced to a CH2 group by the Clemmensen method (see Chapter 23) and polyphosphoric acid is used to carry out the intramolecular acylation step. 

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