Effect of Resid Addition to Fluid Catalytic Cracking Feedstocks – Assessment in the Laboratory Table 1: Properties of the Residual Feedstock
Distillation (% volume) Initial point 5
10 20 30 40
Final point Yield
Density
Viscosity at 50°C Iron
Nickel
Vanadium Nitrogen Sulphur CCR
CCR = Conradson carbon residue.
Table 2: Distribution of Products from Resid Conversion, 550ºC, Reaction Time 15 Seconds
Hydrocarbon group Dry gas
Liquified petroleum gas Gasoline
Light cycle oil Coke
Yield (%) 3.5
23.0 45.5 8.5
13.3
Table 3: Selectivity to Gasoline and Coke from the Resid, Light Cycle Oil and Their Mixture, 550 ºC, Reaction Time 15 Seconds
Feedstock
Conventional Catalyst LCO LCO– Resid resid
Gasoline selectivity (%) 65.9 64.0 53.3 Coke selectivity (%) 9.8
LCO = light cycle oil. Figure 2: Conversion as a Function of Reaction Time 10.5 15.6 Resid Catalyst
LCO LCO– Resid resid
73.2 68.5 57.2 7.9
8.1 12.8
be convenient if the selectivity of gasoline is to be maximised in the refinery when this particular residual cut is to be processed and added to the standard feedstock.
Following this approach, the benefits and problems with the addition of resid were pre-evaluated in the laboratory. Ten per cent of resid was then mixed with a typical VGO (see properties in Table 4) and subjected to the same conversion experiments on the conventional and resid catalysts tested.9
The conversion profiles as a function of
contact time in the CREC Riser Simulator reactor can be observed in Figure 2. The conversions achieved are in the range of usual commercial values.
0 5 10 Time (s) VGO VGO-resid
Over conventional Resid catalyst
VGO = vacuum gas oil.
The results were similar to those observed with the resid–LCO mixtures. The yields of the main hydrocarbon groups obtained with both catalysts in the conversion of the VGO, the resid–VGO mixture and the resid
10 HYDROCARBON WORLD – VOLUME 6 ISSUE 1 15 20 25
It is obvious that whatever the feedstock, the conventional catalyst is more active than the resid catalyst. When the resid is included, however, the response of each catalyst is significantly different: the resid catalyst shows the same or slightly lower conversion compared to the VGO alone. By contrast, the conventional catalyst increased conversion by about five points. This could be due to the higher reactivity of a fraction in the resid compared with VGO. This is because some hydrocarbon molecules with high molecular weight could have long aliphatic chains attached to aromatic rings and behave similarly to a more paraffinic, lighter feedstock in FCC. The activity of the resid catalyst would not be enough to show this behaviour with the mixture.
°C °C °C °C °C °C °C %
g/cm3 sSU
ppm ppm ppm ppm % %
294.8 385.2 411.7 448.8 473.1 500.2 513.9 45.6 0.95 350 28
15.6 38.2 3336 1.4
8.11
(LCO), which can represent more complex hydrocarbon mixtures, was used with 10% resid added. This resid proportion, which should not significantly alter the FCC operation, can be considered typical of commercial practice and is aimed at reducing the magnitude of residual streams.
It was observed that the yields of the most important hydrocarbon groups from the resid, the LCO, and their mixture, followed a very similar trend as a function of conversion on a given catalyst. Indeed, at least with this particular set of feeds, the yields seemed to depend on the conversion level alone.
However, some differences in the yields were observed between catalysts as a result of their different formulations (see Table 3). Under the same conditions, the resid catalyst yielded more gasoline than the conventional catalyst when cracking the resid alone, which moderately translated into conversion of the resid–LCO mixture.
The better coke selectivity of the resid catalyst can also be observed. As an example, it can be concluded that the resid catalyst would
Resids differ from conventional vacuum gas oil feedstocks as they have a higher proportion of catalyst contaminant metals
Conversion (%)
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