Contaminant coke

At high metals levels, the coking characteristics of a cracking catalyst can be greatly increased that is, the ratio of contaminant coke to catalytic coke can be quite high. The effect of the contaminant metals on the coke response is affected not only by the level of metals but also by the type of catalyst and the use of a metals passivator. Catalysts, which contain effective metals traps to inhibit the contaminant effects, do produce much less contaminant coke than catalyst without metal traps. 

Additive inhibitors have been developed to reduce the contaminant coke produced through nickel-cataly2ed reactions. These inhibitors are injected into the feed stream going to the catalytic cracker. The additive forms a nickel complex that deposits the nickel on the catalyst in a less catalyticaHy active state. The first such additive was an antimony compound developed and first used in 1976 by Phillips Petroleum. The use of the antimony additive reportedly reduced coke yields by 15% in a commercial trial (17). 

Contaminant coke is produced by catalytic activity of metals such as nickel, vanadium, and by deactivation of the catalyst caused by organic nitrogen. 

Furthermore, the restrictions on operating voltage that apply to titanium in a marine enviroment are not always relevant to titanium in soils free of chloride contamination. Coke breeze is, however, an integral part of the groundbed construction and ensures a lower platinum consumption rate. However, for some borehole groundbeds, platinised niobium is preferred, particularly in the absence of carbonaceous backfill or in situations where the water chemistry within a borehole can be complex and may, in certain circumstances, contain contaminants which favour breakdown of the anodic Ti02 film on titanium. In particular, the pH of a chloride solution in a confined space will tend to decrease owing to the formation of HOCl and HCl, and this will result in an increase in the corrosion rate of the platinum. 

Containment building, for nuclear power facilities, 77 538 Containment landfills, 25 877 Contaminant coke, 77 705 Contaminant concentration, measurements of, 74 214 Contaminant deposition, from steam in turbines, 23 228-228 Contaminant effects, on magnesium and magnesium alloys, 75 370-373 Contaminant metals... 

Effects of Ni and V in Catalysts on Contaminant Coke and Hydrogen Yields... 

Figure 1. Contaminant hydrogen (a) and contaminant coke (b) yields as weight percent of feed from non-zeolitic particles 2000 ppm Ni (+) 2000 ppm V (x), at constant conversion (70%).

On non-zeolitic particles in the absence of a vanadium passivator, vanadium (when present at the 0.4 wt% level) makes a greater contribution to contaminant coke and hydrogen yields than nickel at constant surface area and metals loading. Incorporation of a vanadium passivator into the catalyst matrix can greatly alter the selectivity effects of vanadium, and can essentially negate its effect on non-zeolitic particles as in the case of magnesium. 

This observation was not so obvious on coke yields because the coke production is a contribution of mnltiple mechanisms and reactions. Thus, the coke yields are quite similar, probably because the catalytic coke is decreased while the contaminant coke is increased. The coke remarks are also observed on the CPS samples taking into account that the dehydrogenation degree is not strongly affected by the extended ReDox cycles, becanse the lower catalysts decay is limiting the effect of the required mass of catalyst (C/0 ratio). Thus, the small decrement of the coke yield on the CPS samples is possibly related to the descent of the catalyst (less specific area) leaving less available space for coke adsorption and less activity for catalytic coke production. It is clear that prolonging the deactivation procednres is not beneficial as far as the metal effects are concerned. 

The TPO profiles obtained were analyzed by deconvoluting them using Gaussian peaks and GRAMS 32 software. The peaks obtained were assumed to represent the four different types of coke in the spent catalyst catalytic coke, contaminant coke, occluded coke, and additional coke (Conradson carbon). 

This type of coke depends exclnsively on the FCC cracking activity. In order to have samples with different activity and little inflnence of contaminant coke, the fresh catalyst was deactivated hydrothermally at different severity conditions withont metals. MAT test for these deactivated samples was performed with VGO as a feedstock to diminish coke yields. 

The Figures 10.1 and 10.3 present the TPO spectra of the samples with and without metals. For the sample impregnated with 4100 ppm vanadium, it was observed the appearance of a shoulder around 680°C that translates in a 10% increase in peak C area, compared to the metal-free catalyst as illustrated in Figure 10.3. Then, the signal C located around 61TC apparently corresponds to the contaminant coke produced by the hydro-dehydrogenation properties of vanadium. 

Table 10.6 summarizes data from the TPO profiles for the three samples with and without metals. This table clearly shows how the signal C increase as the concentration of nickel and vanadium increases and supports the hypothesis that this peak corresponds to contaminant coke. It is possible to support the theory that a higher content of vanadium in the catalyst results in a loss of activity because the peak area B, previously attributed to catalytic coke, decreases strongly with vanadium levels. 

In Figure 10.4 was plotted the contaminant coke yield as a function of Ni equivalent. In this graph it is observed that the signal C, expressed as grams of contaminant coke, is almost a linear function of Ni equivalent. When the vanadium factor is changed to 0.38 the ratio is completely linear. Then with this technique it is possible to find the real dehydrogenation factor of vanadium with respect to nickel. 

The peak related with the contaminant coke is located between 665 and 677°C, and is a direct function of the nickel equivalents in the catalyst. This type of coke decreases the catalytic activity. Activity losses are mainly attributed to the presence of vanadium on the catalyst surface. 

Overall, evaluation of catalysts on resid feedstocks requires sophisticated and well integrated catalyst deactivation, catalyst stripping and cracking systems. It is important to determine not only the coke yield, but each of its components (Catalytic coke, contaminant coke, CCR coke and stripper (soft) coke). This paper provides details on how each of the components of the coke yield may be experimentally determined using catalyst metallation by cyclic deactivation, catalyst strippability measurements and modified catalytic cracking techniques. 

Contaminant Coke The use of a low matrix surface area to lower the dispersion of nickel and therefore its dehydrogenation activity is a possible option which, however, is associated with poor intrinsic bottoms upgrading capability. 

Contaminant coke - from the catalytic action of metal poisons such as nickel and vanadium... 

Consequently, there are significant differences in FCC unit operation when residue is added to normal feed. Conversion falls and less gasoline is produced, as shown in Table 5.2, and the catalyst-to-oil ratio must rise as coke yields increase. The coke also has a different composition relative to that produced from normal feed not only because of the higher Conradson carbon levels and high-boiling compounds, which are absoibed by the catalyst particles, but also from the dehydrogenation activity of the metal impurities, which leads to polymerization reactions and contaminant coke formation. 

Contaminant coke forms as a result of the dehydrogenation and polymerization reactions catalyzed by metal impurities in the feed. 

---