Oct-2024

Enabling high iron feed processing in the FCC with in-situ catalyst technology (TiA)

A thorough understanding of deactivation mechanisms related to processing high iron (Fe) feeds through the FCC is required for effective catalyst design, such as extremely open pore architecture.

Kevin Yao
BASF Refinery Catalysts

Article Summary

High Fe feeds (often from the Permian region) are consistently sourced with significant discounts relative to conventional vacuum gasoil (VGO) and thus present reliable lucrative opportunities for refiners. Experience has shown that feed Fe can present challenges to FCC operation. However, when high Fe opportunity feeds are suitably processed, product values can rival those from a conventional low-sulphur VGO with minimal impact on FCC operability.

Those who have experienced Fe-related catalyst poisoning episodes can relate to how dramatic it is to deal with an impactful, sudden loss in conversion followed by a difficult time trying to recover normal activity. It is well understood that Fe forms a layer on catalysts, which can be observed as nodules present on particle surfaces. The nodules themselves can reduce catalyst apparent bulk density (ABD), which can cause catalyst circulation instability for units that are sensitive to changes in fluidisation characteristics.

Binders used to improve the mechanical strength of finished catalyst particles are known to interact with Fe, thus worsening this catalyst surface layer. As this layer grows enough to inhibit mass transfer, catalytic reaction rates can slow dramatically even as surface area remains high. Experience has shown steady-state Fe can affect activity, but Fe transients (high steady-state equivalent Ecat concentrations) produce the most dramatic and debilitating effects. Thus, it is important to monitor not just Fe levels, but also how quickly they are changing.

It is important to have a thorough understanding of deactivation mechanisms related to Fe and how critical it is to utilise the correct FCC catalyst design when processing high Fe feeds. BASF’s catalyst production does not require the use of binders for mechanical strength, thus minimising the formation of mass transfer limiting layers. Additionally, BASF catalysts exhibit extremely open pore architectures, which limit the impact of Fe-associated layers on particles. These two catalyst features enable unmatched Fe tolerance for BASF catalysts, as will be shown in a case study below. Key factors to successfully processing Fe on a routine basis include:

Leveraging in-situ FCC catalyst:
· High surface porosity increases resistance to mass transfer inhibition.
· Binder-free framework prevents formation of diffusion barrier.
· High ABD provides larger fluidisation operability range:
   - ABD shown to stabilise at 0.65 g/cc with >0.35 wt% added Fe.

FCC unit operations:
· Monitor steady-state Fe equivalent in addition to instantaneous concentration.
· Be mindful of Ca, Na, V, and Ni effects since they are often associated with feed Fe.
· Ensure spare fresh catalyst addition capability to respond to metals excursions.
   -On an equivalent steady-state basis, Fe has less than half the impact of vanadium (V) on fluidised activity test (FACT) – demonstrated as high as 8,000 ppm Fe.

Figure 1 shows that by using BASF catalyst, a refiner operates comfortably at steady-state Fe levels of up to 8,000 ppm, where the limiting factor for Fe is feed availability. Additionally, this figure highlights the value and importance of starting with a high ABD. A high ABD offers a larger window of operability as added Fe inevitably begins to impact ABD. As added Fe approaches 5,000 ppm, ABD stabilises at 0.65 g/cc with no further deterioration out to 8,000 ppm added Fe.

Case study
A refiner using a BASF catalyst is able to operate comfortably at steady-state Fe levels of around 8,000 ppm and is able to handle a rapid rise in Fe levels as high as 12,000 ppm steady-state equivalent. Figure 1 shows how ABD decreases. As Ecat added Fe increases from 0 to 3,000 ppm, the ABD drop is a linear function of Fe level. However, above ~4,000 ppm added Fe, ABD reaches a new steady level and stops changing (at least up to 8,000 ppm added Fe).

Figure 2 shows how catalyst activity (FACT) changes with Fe. In the orange highlighted region, Fe rises very rapidly (nearly 12,000 ppm steady state equivalent) and it can be seen that activity is strongly affected (-4 to -6 FACT) even though instantaneous Ecat Fe levels are only in the 6,000-8,000 ppm range. It can be seen that activity starts to recover immediately after Fe levels start to drop, and there is no delay in activity recovery.

Contrast these dynamics with the grey highlighted region where Fe rises more slowly with a steady-state Ecat Fe equivalent of only 9,000-10,000 ppm. In this case, catalyst activity is not affected outside of the normal variability baseline. Thus, by keeping steady-state Fe equivalent below 10,000 ppm, there is minimal catalyst activity impact beyond effects from other associated contaminants such as V. Even when Fe levels rise quickly, catalyst activity can still be maintained by increasing the catalyst addition rate to keep steady-state equivalent Fe to below 10,000 ppm.

Controlled activity and operation are key to the future of operating residual feedstocks. The yield objectives for this case study, such as coke, delta coke, slurry, and other unit yields, were achieved while processing this high Fe feedstock.

This short case study originally appeared in PTQ's Technology In Action Feature - Q4 2024 Issue

For more information: kevin.yao@basf.com