The Art of Evaluating Laboratory Fixed Bed Catalytic Cracking Data

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Thus the proper comparison of laboratory data for the two catalysts lies somewhere in-betweenthe conversion required for constant conversion and the conversion required for constant coke, startingfrom the base case conversion and coke.Since the hard coke is typically ~ 75% of the total coke, at a constant total coke yield (as dictatedby the heat balance), the actual change in hard coke would only be ~75% of the coke change required tobring the ACE or MAT result to a constant coke level. Thus the proper conversion for the catalystcomparison is at the conversion that gives that 75% ACE or MAT coke change.This point is also illustrated in the example in Figure 10. The new catalyst at 74% conversion hasa hard coke yield of 3.6%, which is 1.4 wt% lower than the 5.0% hard coke yield of the old basecatalyst. The actual coke yield of the new catalyst, for comparison purposes should then be 3.6 +0.75(1.4) = 4.6. At 4.6 wt% coke yield, the new catalyst conversion is ~ 81 wt% (point 4 in Figure 10),which is the conversion to use to compare product yields of the new catalyst with yields from the basecatalyst at 74 wt% conversion.ConclusionA simple procedure is described, that provides reliable correlations of small scale laboratoryFCC test results, even though there may only be a very limited amount of data and the data may bebadly scattered .The method uses the yield of the individual products at zero conversion as an anchor pointthrough which the regressed data for each product yield must pass. In these regressions, the anchor pointat zero conversion is not necessarily 0 wt%, and techniques are disclosed as to how to position suchanchor points. For the correlation of LCO and HCO yields, an additional anchor point of 0 wt% at 100%conversion is also applied.The coke yield, and all the hydrocarbon yields of the C 4 and lighter products are correlatedagainst second conversion. For many of these products, second order conversion provides a linearcorrelation with product yield.Gasoline yield is obtained by difference, using the relationship:Gasoline = Conversion – (Coke + Σ C 4 -)Since the laboratory tests and commercial unit operations have fundamentally different cokeyields, a new method is proposed to allow for the interpretation of laboratory test results at conditionsrelevant to potential commercial FCC unit operations. This procedure facilitates the accurate comparisonof various catalysts and their potential commercial cracking performance.
References(1) ASTM Standard D 5154-91 “Standard Test Method for Determining the Activity and Selectivity ofFluid Catalytic Cracking (FCC) Catalysts by Microactivity Test”(2) F.G.Ciapetta and D.S.Henderson, O. & G.J., 65, (42), 1967 p.88(3) W.R.Gustafson, ACS Div. Petrol. Chem. 14 (3), 1969 B 56-57(4) D.M.Stockwell, W.S.Wieland, and F.L.Himpsel, “Catalyst Evaluation using Fixed Fluid BedReactors” Paper presented at Spring 1998 AiChE National Meeting, New Orleans, LA, March 3-12(5) J.F.Crocoll and R.D.Jaquay, Petro./Chem.Eng.,C-24, Nov. 1960(6) D.M. Nace, I&EC, Prod Res. & Dev., 8, 24, 1969(7) V.W.Weekman and D.M.Nace, AIChE J, 16, 3, May 1970(8) C.Vergel-Hernandez, Appl. Catalysis A, 220, 2001, pg 265H:\WORD\ Coke\ Catalyst Testing Paper-Short Version - Resized
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Page 3 and 4: ExperimentalThe data used in this p
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