Attrition catalysts

FIGURE 10.2 Comparison of the total fines production with process time for different catalysts. (o) Catalyst A, ( ) catalyst B, and (A) catalyst C. (Adapted from Kam, E.K.T. et al., Catal. Today, 64, 297, 2001.) 

Eines produced from catalyst attrition will affect stability of the reactor and modify the process performance, causing problans as those presented when mixing two different catalysts. 

Properties and operating conditions of the catalysts used are shown in Table 10.1. Each catalyst was divided into pellets, scratched pellets, and ground pellets ( 150 jm average particle). The feed was vacuum residue from Jobo-Morichal crude of the Orinoco Belt in Venezuela (8°AP1 gravity), with an initial boiling point of 490°C, and 5.02% sulfur, 0.93% nitrogen, 22% CCR, 21 wt% insolubles in n-Cj, 32.05 wt% insolubles in n-Cs, and 714ppm of vanadium. Reactivity studies were carried out in a CSTR. 

Spent catalyst characterization indicated that the external layer surrounding the catalyst at the beginning is permeable and mainly composed of coke with pregraphitic carbon structure. Continuous piling up of coke and accumulation of metals make the external layer less permeable thus, liquid diffusion, activity, and selectivity decrease. In addition, diffusion of metals and sulfur compounds into the pores is controlled by the reduction of the cross-sectional area and pore blocking. 

Properties of Catalysts Used in Deactivation Studies during Operation of an EBRfor Heavy Residue Hydrocracking 

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The lift pipe design was tapered to a larger diameter at the top. This minimized the effects of erosion and catalyst attrition, and also prevented the instantaneous total collapse of circulations when the saltation concentration, or velocity, of solids is experienced (i.e. the slump veloeity-that velocity helow which particles drop out of the flowing gas stream). In a typical operation, 2 % to 4 % eoke can he deposited on the catalyst in the reactor and burned in the regenerator. Catalyst circulation is generally not sufficient to remove all the heat of eombustion. This facilitated the need for steam or pressurized water coils to be located in the regeneration zone to remove exeess heat. 

Catalyst attrition due to the collision of catalyst particles with the vessel internals and other catalyst particles... 

PSD is an important indicator of the fluidization characteristics of the catalyst, cyclone performance, and the attrition resistance of the catalyst. A drop in fines content indicates the loss of cyclone efficiency. This can be confirmed by the particle size of fines collected downstream of the cyclones. An increase in fines content of the E-cat indicates increased catalyst attrition. This can be due to changes in fresh catalyst binder quality, steam leaks, and/or internal mechanical problems, such as those involving the air distributor or slide vah es. 

An increase in the feed atomizing and/or stripping steam, causing catalyst attrition and generating fines... 

An addition of a large amount of steam to the regenerator, particularly to the torch oil nozzles, again causing catalyst attrition... 

Improperly designed, eroded, or even missing restriction orifices used for steam purge or aeration nozzles could cause catalyst attrition. Catalyst attrition is also caused by broken air and stripping steam distributors. 

The improvements in the catalyst s binder properties will reduce the catalyst attrition rate thus, lowering the flue gas stack opacit This improvement allows refiners to use a harder catalyst without adversely affecting the catalyst s fluidization properties. 

Interesting features of this process include the potential for one-stage methanation to completion without the need for gas recycle. This feature was cited by Chem Systems, but, according to Rheinpruessen-Koppers work on the Fischer-Tropsch (52, 53), gas recycle was necessary with high H2 CO ratios. Drawbacks include such factors as catalyst attrition (48, 50), and low volume productivities of the methanator (less than one-tenth that reported for fixed bed adiabatic reactors) (48, 50, 52, 53, 61). 

Almost all the materials which are being considered as components in automobile exhaust catalyst are somewhat toxic (74)- Most of the compounds considered are low vapor pressure solids which can only escape from the exhaust system as very fine airbone dust particles formed by catalyst attrition. A few compounds, such as the highly toxic metal carbonyls and ruthenium tetroxides, are liquid under ambient conditions and have boiling points less than 100 °C. These compounds are not present in... 

Figure 2. Time dependence of catalyst attrition in a submerged jet test (D, = 0.05 m, uor = 100 ms-1, dor = 2 mm, HA-HPV is a fresh catalyst whereas FCC is a spent cracking catalyst from a commercial unit. (From Werther and Xi, 1993.)...

Kokkoris et al. (1991, 1995) suggested another method to impair catalyst attrition. In a small scale slugging bed they reduced the attrition rate of zeolites by addition of only very small quantities of various fine solid lubricants. In the case of graphite the reduction was up to 30%. The fines were assumed to reduce attrition by forming a protective coating that... 

Weeks, S. A., and Dumbill, P., Method Speeds FCC Catalyst Attrition Resistance Determinations, Oil GasJ., 88 38 (1990)... 

Commissioning of the Oryx GTL facility started in 2006 and production of the first GTL products was announced in February 2007.63 However, overproduction of a fine sediment as a result of catalyst attrition reduced throughput,64 and at the time of this writing sustained full-scale production had not yet been achieved. The syncrude resembles other LTFT syncrudes (Tables 18.2 and 18.8), and the refinery consists of a single conversion unit, namely, a hydrocracker (Figure 18.9). 

Although the results from these methods may correlate to some extent, they simulate different essential requirements of the catalysts. Attrition loss primarily relates to handling, transport, loading and screening whereas the crush tests simulate the forces imposed on the catalyst in a fixed bed. The drop test simulates the risk of catalyst break-up during loading and pneumatic transport. 

Dust explosions (ASTM E789) that can occur during catalytic reactor shutdown and cleaning are due to the production of finely divided solids through attrition. Many catalyst dusts can bum explosively in air. Thus, control of dust generated by catalyst attrition is essential (Mody and Jakhete, 1988). 

Excessive vapor entrainment down the dipleg can increase erosion and possibly catalyst attrition. On the reactor side, excessive entrainment will send more cracked product vapors to the stripper. 

The choice and properties of the aeration gas are important factors for maintaining stable standpipe operation. The condensate source for steam aeration can cause several problems. If the steam is not kept dry, the condensate can lead to stress cracking of the tap piping, plugging of the tap nozzle with mud, erratic aeration rates, orifice erosion, and potentially catalyst attrition. Similar problems can occur with wet fuel gas as an aeration source. When possible, dry air and/or nitrogen are preferred rather than steam as aeration media for standpipes. However, in actual... 

The decomposition of the catalyst beads can cause a secondary air pollution emission consisting of the particulate dust generated by abrasion of the surface of the catalyst. Operating cost for catalyst replacement varies directly with catalyst attrition rate. The system can process waste streams with VOC concentrations of up to 25% of the lower explosive limit (LEL). The proprietary catalyst contains up to 10% chromium, including 4% hexavalent chromium. This could lead to the emission of hexavalent chromium in some applications of the technology. 

The phase transformations in the catalyst play an important role in determining the activity, attrition resistance, and deactivation of this catalyst. Activation of this precipitated catalyst transforms single crystals of hematite to smaller crystallites of carbide. While the transformation from hematite to magnetite is extremely rapid, the magnetite to carbide transition is much slower under the conditions of temperature and pressure employed in this study. As carbon deposits on the carbide particles, it serves to further prise the carbide particles apart. In a commercial slurry phase reactor the carbide particles break away leading to catalyst attrition. The implication of this work for the attrition resistance of iron FT catalysts is explored in detail elsewhere.18... 

This approach minimizes the effects of catalyst attrition phenomena on the vanadium mobility determination. 

Advantages of fluidized beds are temperature uniformity, good heat transfer, and the ability to continuously remove catalyst for regeneration. Disadvantages are solids backmixing, catalyst attrition, and recovery of fines. Baffles have been used often to reduce backmixing. 

The attrition of solid particles is an unavoidable consequence of the intensive solids motion resulting from the presence of bubbles in the fluidized bed. The attrition problem is especially critical in processes where the bed material needs to remain unaltered for the longest possible time, as in fluidized-bed reactors for heterogeneous catalytic gas-phase reactions. Catalyst attrition is important in the economics of such processes and may even become the critical factor. 

A number of sources can be identified for catalyst attrition in industrial fluidized-bed reactors ... 

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