REY catalysts

Thus, the dominant contributor of cracking selectivity of Super D is expected to be the REY zeolite present in the catalyst. Yields of Cs to C paraffin isomers measured during the cracking of the gas oil at 500 C by the steam treated REY catalyst are shown in Table III. The yield of branched paraffins was generally five to ten times higher than the yield of normal paraffins and the major (>50%) portion of the branched paraffin yield consisted of monomethyl paraffins. 

A - Laboratory prepared catalyst using commercial USY B - Commercial REY catalyst... 

This work provides conclusive evidence that transient catalyst characterization tests can result in erroneous catalyst ranking. For example, USY catalysts show higher activity than REY catalysts in the laboratory tests but lower activity in a steady state riser. Although emphasis in this paper is placed mainly on the coke-conversion selectivity, the analysis is also extended to yields of other FCC products. 

While most catalyst vendors rely on fixed bed microactivity (MAT) tests, fixed fluid bed (FFB) reactor experiments are widely used within Mobil to characterize FCC catalysts. The amount of catalyst used is constant for each test, and products are collected for a known period of time. In MAT experiments, catalyst bed is fixed while in FFB test the catalyst bed is fluidized. As products are collected over the decay cycle of the catalyst, the resulting conversion and coke yields are strongly influenced by catalyst deactivation. Systematic differences exist between the measured conversion or catalyst activity and coke yields for the MAT and FFB tests. The magnitude of these differences varies depending on the type of catalyst being tested (REY or USY). Experimental data in Figure 1 clearly show that FFB conversion is higher than MAT conversion for USY catalysts. On the other hand, FFB conversion is lower than MAT conversion for REY catalysts. Furthermore, the quantitative... 

Table V. Estimated Relative Rate Constants and Parameters For REY Catalysts (Catalyst D)...

REY Catalysts. REY catalysts always give lower FFB conversions than MAT conversions (Figure 1). To simulate the observed conversion differences in the MAT and FFB units for REY catalysts, the intrinsic cracking activity kj is increased at constant coking activity Aj. This choice of parameters is a first order approximation for the activity and coke-conversion selectivity variation of equilibrium catalysts. Parameters summarized in Table V are used as the initial starting point. 

The results of the simulation are shown by the curve marked REY in Figure 1, and the curves of Figure 2. The results of Figure 1 agree with our experimental observations, showing that the MAT conversion is always higher than the FFB conversion for REY catalysts. 

Figure 2 Predicted coke-conversion selectivity as a function of catalyst activity (crackability) for REY catalysts.

In Figure 6, we show the results of a simulation in which the cracking activity kj was varied while keeping the coking activity Aj constant (similar to the simulation above for REY catalysts). It is interesting to note that for the choice of the parameters noted above, kg values in MAT and riser closely trace each other. On the other hand, FFB coke-conversion selectivity, kg, has somewhat lower slope. 

The coke deactivation exponent n, is typically estimated from riser pilot plant experiments at varying catalyst contact time for different catalyst types. A value of n of 0.2 was found for REY catalyst data base. For USY and RE-USY catalysts n was estimated to be 0.4. 

Heats of reactions were estimated from heats of formations and chemical compositions of feed and product using standard procedures. For REY catalysts, we estimated approximately 130 Btu/lb heat of reaction. The heat of reaction was close to 200 Btu/lb for USY catalysts. These values are in close agreement with reported data (21)- The activation energies for different catalyst types were estimated from our extensive pilot plant data base, and found to be a weak function of catalyst type. The adsorption constants and other kinetic parameters used in these simulations were fitted to a large in-house data base. Typical parameter values are reported in Tables III and V. The kinetic parameters (k-, and Aj) are a strong function of catalyst used, whereas the adsorption parameters were found to be relatively insensitive. One could estimate these parameters even from a limited data base as illustrated below for Catalyst D. 

These parameters are summarized in Table V. These parameter values were in close agreement with other REY catalysts, for example Catalyst A in Table III. 

For example, the gasoline, IPG and dry gas selectivities obtained with 4B do not differentiate between the REY (catalyst A) and the USY/REY (catalyst B) as well as the other methods. The reason for this is not fully understood but may be related to the relatively mild steaming (1400°F, 4 hours) which does not severely deactivate the catalysts. 

T. Masuda, H. Kuwahara, S. Mukai, and K. Hashimoto, Production of high quality gasoline from waste polyethylene derived heavy oil over Ni-REY catalyst in steam atmosphere, Chem. Eng. Set, 54, 2773-2779 (1999). 

Figure 6.23 Changes in the catalytic activity of the MFl-type zeolite, Ni-REY, and REY catalysts during the repetition of a sequence of reaction and regeneration (T = 400"C, W/F = 1 h), carrier gas in the reaction nitrogen for MFI, steam for REY and Ni-REY. (Reproduced with permission from Elsevier)...

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