Effect of Resid Addition to Fluid Catalytic Cracking Feedstocks – Assessment in the Laboratory
alone showed that, at least under these conditions and catalysts, they followed the same variation as a function of conversion (see Figure 3 for the example of the resid catalyst).
The characteristics resulting from the different catalyst formulations are revealed in the comparison of various product selectivities. In effect, with both feedstocks (VGO and resid–VGO) the conventional catalyst (more active) produces more dry gas and LPG and less gasoline than the resid catalyst (see Table 5). The catalyst designed specifically to convert residual feedstocks shows better coke selectivity, which is crucial.
A very important effect of the addition of this resid to VGO can be observed in the comparison of the gasolines compositions. Changes were more perceptible on the resid catalyst. At typical conversions, when resid was added to VGO, the content of olefins in gasoline increased significantly (from 23.3 to 28.0%), while that of aromatics (from 36.9 to 35.1%) and isoparaffins (from 28.0 to 25.2%) decreased. This was coincident with observations in commercial and fluidised bed laboratory ACE units.10
Changes in the gasoline composition after
adding resid to the VGO followed the same trends on the conventional catalyst, but were only significant at low conversion levels – far from usual refinery values.
These results are consistent with the catalyst properties, because the resid catalyst has a higher accessibility and would adsorb components from the resid more extensively than the conventional catalyst. As a consequence, the higher olefin yields in gasoline would result from the more significant reduction in density of paired sites. This would have a more significant impact on hydrogen transfer, given its dependence on that surface property.11
This method is also useful to determine the yields of particular hydrocarbons such as, for example, isobutane or C4–C5 olefins that can be used as raw materials for other processes. It can be seen in Table 5 that the resid yields more light olefins than the VGO over the two catalysts; however, this fact is again reflected in the conversion of the mixture with the resid catalyst alone.
Conclusion
The observations about yields, selectivities and group compositions in the experiments with resid or VGO alone, as well as with their mixture, strongly suggest that the impact of resid addition cannot be evaluated with information from the base reactants only. The intended mixture must be analysed.
The application of this approach to the evaluation of the performance of commercial and prototype FCC catalysts has produced very satisfactory results. n
1. Andersson S, Myrstad T, Evaluation of residue FCC catalysts, Appl Catal Gen, 1998;170:59–71.
2. Harding R, Peters A, Nace J, New developments in FCC catalyst technology, Appl Catal Gen, 2001;221:389–96.
3. de Lasa H, Riser Simulator, US Patent 5102628, registered 1992.
4. de la Puente G, Sedran U, Recycling polystyrene into fuels by means of FCC: performance of various acidic catalysts, Appl Catal B Environ, 1998;19:305–11.
5. Hakuli A, Imhof P, Kuehler C, Understandig FCC Catalyst VGO = vacuum gas oil.
Table 5: Selectivities from the Resid, Vacuum Gas Oil and their Mixture, 550°c
Conventional Catalyst Feedstock
Gasoline selectivity (%) 52.4 49.3 Coke selectivity (%) 13.1 14.7 C4 olefinicity
VGO = vacuum gas oil. Resid Catalyst 0.33 0.34
VGO VGO–resid Resid VGO VGO–resid Resid 53.3 57.6 57.2 15.6 13.1 11.6 0.45 0.48 0.51
57.2 12.8 0.53
Table 4: Vacuum Gas Oil Properties
Distillation (% volume) 10 30 50 70 90
Density ° API Iron
Nickel
Vanadium Nitrogen Sulphur CCR
CCR = Conradson carbon residue. Figure 3: Yields as a Function of Conversion Over Resid Catalyst: 550ºC
°C °C °C °C °C
g/cm3
ppm ppm ppm ppm % %
361 408 432 456 494
0.916 22.3 2.4 0.1 0.7
1,441 2.03 0.11
020406080100 VGO
Conversion (%) VGO-resid Resid
Architecture and Accessibility, Paper F-4, Akzo Nobel ECO-MAGIC Catalysts Symposium, 2001, Noordwijk, the Netherlands.
6. de la Puente G, Devard A, Sedran U, Conversion of residual feedstocks in FCC. Evaluation of feedstock reactivity and product distributions in the laboratory, Energ Fuel, 2007;21:3090–94.
7. Xu C, Gao J, Zhao S, et al., Correlation between feedstock SARA components and FCC product yields, Fuel, 2005;84:669–74.
8. Devard A, de la Puente G, Sedran U, Laboratory evaluation of HYDROCARBON WORLD – VOLUME 6 ISSUE 1
the impact of the addition of resid in FCC, Fuel Process Tech, 2009;90:51–55.
9. Devard A, de la Puente G, Passamonti F, et al., Processing of resid–VGO mixtures in FCC: Laboratory approach, Appl Catal Gen, 2009;353:223–27.
10. Gilbert W, Baptista C, Pinho A, Exploring FCC flexibility to produce mid-distillates and petrochemicals, Stud Surf Sci Catal, 2007;166:31–39.
11. de la Puente G, Sedran U, Evaluation of hydrogen transfer in FCC catalysts. A new approach for cyclohexene as a test reactant, Chem Eng Sci, 2000;55:759–65.
11
Yield (%)
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