Catalysts attrition index

For glass beads, the values of Ka were found to be about V12 those for FCC catalyst. For other materials, one should obtain a relative attrition index with respect to either FCC or glass beads and then obtain a value of Ka based on that index. 

Of the various mechanical properties of a formed catalyst containing zeolite, attrition resistance is probably the most critical. This is particularly the case for FCC catalysts because of the impact on the addihon rate of fresh catalyst, particulate emissions of fines and overall catalyst flow in the reactor and regenerator. Most attrition methods are a relative determination by means of air jet attrition with samples in the 10 to 180 xm size range. For example the ASTM D5757 method attrites a humidified sample of powder with three high velocity jets of humidified air. The fines are continuously removed from the attrition zone by elucidation into a fines collection assembly. The relative attrition index is calculated from the elutriated fines removed at a specific time interval. 

The data in Figure 5 can be examined from three viewpoints. First, the curves of the Reference and CP-2 samples resemble that of a commercial material (Catalyst I) that has a low Attrition Index (5.3). Second, the CP-2 curve rises at a slower rate than the Reference. This indicates more attrition resistance in the CP-2 alumina formula. Finally, the pseudoboehmite formula produced fines much more rapidly than the CP-2 product. These findings suggest that the rehydratable alumina is a superior binder for some FCC formulations. 

The effect of catalyst slurry and sol age time on the Attrition Indexes of the CP-formulated samples is seen in Table III. There is a trend toward greater attrition as the batch holding time increases for both CP-2 products. Concomitantly, the viscosity range becomes higher, as was observed previously. CP-5 also appears to lose attrition resistance as the age and viscosity of the slurry advance. On the other hand, the holding time does not impact the CP-25 Attrition Index. The CP-2(4) material, made with a sol aged 4 hours, exhibits lower AI values, and, perhaps, a longer useful batch lifetime. 

Attrition index (AI, wt%). A fresh catalyst sample is subjected to high-velocity fluidization for a long time. In this process, wear on the particles occurs as they are... 

Equilibrium catalyst attrition index and average particle size distribution (APS) indicate changes in the rate of catalyst attrition. Further analysis of APS for any catalyst that is carried forward into the fractionator, present in the slurry, or which leaves the unit via the regenerator stack can identify problems associated with catalyst quality or cyclone operation. Problems include operation at greater than design feed, catalyst rates or cyclone maloperation. APS is also important in predicting the fluidization properties of the catalyst inventory. 

As well as the need for routine analyses of equilibrium catalyst, regular checks on all batches of fresh catalyst are carried out to check the consistency of particle size, the attrition index, and the activity of the catalyst added to a unit. Excess steam deactivates the catalyst and causes abnormal attrition. High air velocity or maldistribution of air in the regenerator increases catalyst attrition and leads to variations in the carbon content of the equilibrium catalyst. 

Much effort has been made by catalyst manufacturers to improve catalyst atttition resistance and thus reduce the formation of fines (see Catalysts, supported). In the 10-year petiod from 1980 to 1990, most catalyst manufacturers improved the atttition resistance of their catalyst by a factor of at least 3—4. This improvement was achieved even though the catalyst zeoHte content duting this petiod was continually increasing, a factor that makes achieving catalyst hardness more difficult. As an example of the type of atttition improvement that has been achieved, the catalyst atttition index, which is directiy related to catalyst loss rate in a laboratory attrition test, decreased from 1.0 to 0.35 for one constant catalyst grade during 1989—1990 (37). 

Hardness and attrition of particles and extrudates can be measured according to the ASTM hardness test or by measuring of the abrasion index. For activated carbons as catalyst carrier bulk and particle crushing strength tests have been developed. In Table 4 the hardness, the abrasion index and crushing strength are given. Extrudated carbons are extremely hard. 

The attrition of the composite FCC particles was measured using the Davison Attrition Test. Higher values of the index indicate weaker particles that attrit easier. A series of catalysts were prepared by spray drying the USY zeolites with one of the two sols and the attrition of the composite was measured. The results are shown in Figure 4. 

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