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Oct-2012

FCC catalysts and additives for cost and emissions control

A rare earth-free catalyst enabled a refinery to reduce its FCC catalyst costs and a non-platinum combustion promoter helped control NOx emissions

KENNETH HINDLE and MARIA LUISA SARGENTI Grace Catalysts Technologies
JUAN VARGAS Coryton Refinery
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Article Summary
In 2011, Grace Catalysts Technologies commercialised the REpLaCeR series of low and zero rare earth catalysts for both hydrotreated and resid feed applications. REpLaCeR catalysts utilise proprietary zeolites (Z-21 and Z-22) and state-of-the-art stabilisation methods to deliver similar, or even improved, performance compared to more traditional rare earth-based FCC technologies. They received market acceptance and offered significantly reduced catalyst costs for refiners when rare earth prices were at their highest levels. These catalysts continue to be used in more than 50 FCC units globally, even in an environment where rare earth prices have dropped from their peak in mid-2011.

Based on the Z-21 and Z-22 technologies, there have been a total of 69 applications to date, which includes 27 applications of zero rare earth catalysts for low-metal hydrotreated feed and VGO applications. For resid applications, the development of rare earth-free catalysts is much more challenging due to the additional demands placed on zeolite stability. However, significant advances in combining metals resistance functionality with the rare earth-free Z-21 and Z-22 zeolites resulted in the development of the REduceR catalyst for resid applications. This rare earth-free catalyst can be blended with rare earth-based resid FCC catalysts, thus reducing the overall rare earth requirement and the costs associated without sacrificing performance.

One example of an application of REduceR catalyst is at an FCC unit in a UK refinery. The FCC unit is a UOP high-efficiency design with a catalyst inventory of 290 tonnes and a fresh catalyst addition rate of 13-15 t/d. The FCC unit operates in full burn; the regenerator temperature is typically in the vicinity of 740°C with an excess oxygen content of between 0.7 and 1.3 vol%. This is a resid unit that processes 60-100% atmospheric resid, with a feed concarbon of 3.5 wt%. The e-cat metal levels are approximately 3500 ppm V and 2500 ppm Ni. The refinery began the catalyst trial in August 2011 by blending 30% of the REduceR catalyst with its previous Nektor catalyst. The objective of the trial was simply to maintain the performance of the Nektor catalyst while reducing overall rare earth content from 3.1 to 2.2 wt%.

Table 1 shows the feed properties and specific catalyst addition rate (SCAR) for the 100% Nektor catalyst as well as the subsequent period when 30% of the REduceR catalyst was blended. It can be seen that feed properties and SCAR were very similar for both periods. The very slight increase in SCAR (by 5%) can be attributed to an increase in feed vanadium content by 14%. Vanadium deactivates FCC catalysts, causing product yields to deteriorate.

Microactivity was not affected by the use of 30% REduceR catalyst (see Figure 1). Furthermore, the FCC test run data shown in Figure 2 demonstrate the performance obtained using the REduceR catalyst. It can clearly be seen that dry gas, LPG, gasoline and LCO yields remained similar with the use of 30% of this catalyst, while bottoms yield was slightly reduced. To summarise the performance of the REduceR catalyst, rare earth content of the catalyst was reduced from 3.1 to 2.2 wt% while maintaining, and even improving, catalyst performance. The refinery estimated that the new catalyst provided cost savings in the region of $500 000 per month.

Case study:  a non-platinum
low-NOx combustion promoter

Increasing environmental legislation is forcing refiners to reduce their emissions of nitrogen oxides (NOx). The FCC unit regenerator is typically the single largest source of NOx within a refinery and can account for as much as 40-50% of total refinery NOx emissions. These emissions are the result of nitrogen impurities in the feed depositing on the catalyst during the cracking reaction. When the coke is burned off in the regenerator, a portion of the nitrogen is converted to NOx. Since NOx emissions contribute to acid rain, to the formation of ground level ozone, as well as to respiratory health impacts, various environmental agencies have been tightening NOx emission standards over the last decade. There are a variety of NOx reduction options, both catalytic and hardware oriented, available to help refiners comply with limits on NOx content emitted from the FCC unit regenerator flue gas stream. However, NOx-reducing additives are becoming an increasingly popular option among refiners, as they require no additional infrastructure or chemical reactants. Indeed, NOx-reducing additives are now considered to be the best available technique from the Integrated Pollution Prevention and Control (IPPC) Directive. Grace Catalysts Technologies has developed a series of NOx-reducing additives, including XNOX W, which is a non-platinum low-NOx combustion promoter.

Traditional platinum-based combustion promoters are effective at reducing carbon monoxide (CO), but unfortunately also dramatically increase NOx emissions due to the fact that platinum catalyses the oxidation of intermediate nitrogen species, such as ammonia and cyanide gases. Low-NOx combustion promoters were introduced to alleviate this problem by retaining the CO oxidation function while controlling the sharp increase in NOx. XNOX W is a non-platinum-based, low-NOx combustion promoter, which with a dual functionality actually reduces NOx levels at the same time as retaining the CO oxidation function.

The UK refinery discussed above has also recently trialled this low-NOx combustion promoter. Before the use of the promoter, the refinery previously used the high-activity Grace CP 3 platinum-based combustion promoter on a regular basis. Platinum is known to catalyse NOx formation from intermediate nitrogen species. The basic nitrogen in the FCC feedstock was typically 500 to 600 ppm, which led to uncontrolled NOx emissions of around 20 mg/Nm3. In late 2010, the refinery started antimony injections to help passivate nickel from the feedstock. The use of antimony is also known to increase NOx formation from the regenerator, and the combined use of the platinum-based combustion promoter with antimony resulted in a sharp increase in NOx formation. Due to this sharp increase in NOx formation, the injection of antimony had to be stopped. Grace 
recommended switching from 
the platinum-based combustion promoter to the non-platinum low-NOx combustion promoter to reduce NOx emissions. Generally, a replacement ratio of between 1.5-2.0: 1 is required for XNOX W to provide the same combustion promotion as CP 3. As Figure 3 shows, the use of XNOX W allowed the refinery to reinitiate its additions of antimony while still keeping NOx emissions under control.

An excess of oxygen in the regenerator is also known to increase NOx emissions. As Figure 4 shows, the use of the non-platinum low-NOx combustion promoter provided NOx reduction even at a high oxygen excess. In addition, its use had no effect on afterburning performance (see Figure 5). The overall performance comparison of CP 3 versus XNOX W is shown in Table 2, where it can be seen that the latter resulted in a 65% reduction in NOx emissions.
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