PTQ Q3 2025 Issue

Combating iron poisoning in FCC catalysts

Effective iron poisoning mitigation strategies using a metals trap additive

Yali Tang, Luis Murillo, Antoinette Bates, Jeremy Mayol, Jarred Drewry, Xunhua Mo, Marie Goret-Rana, and Mehdi Allahverdi Johnson Matthey

T he increasing availability of lower-value feedstocks is creating opportunities for oil refiners to boost profita - bility. In the past 15 years, oil production from uncon- ventional sources like oil sands and shale has surged. 1 , 2 However, these feedstocks often contain a higher metals content, especially iron (Fe), posing processing challenges. As a result, iron contamination is becoming an increasing problem for refiners globally. Feed iron is particularly an issue in the fluid catalytic cracking (FCC) unit as it depos - its on the base catalyst, reducing the catalytic activity. This leads to increased usage of base catalyst, lower process efficiency, and increased costs. With the correct strategy, refineries can take advantage of opportunity high-iron crudes, turning them into valua- ble products and boosting their profitability. Leveraging on cutting-edge R&D capabilities, the newly understood mech- anisms by which a metals trap additive can mitigate iron poisoning will be described. Against this backdrop, a refin - ery case study demonstrating how this mitigation strategy can be deployed at commercial scale will be shared. Impact of Fe poisoning on FCC catalyst and operations The two main sources of iron can usually be identified in FCC units as organic iron from the feed (such as those found in porphyrins and naphthenates) and inorganic iron from equipment corrosion. Rust particles from corrosion are known to have minimal impact on FCC catalyst perfor - mance, whereas feed iron can be very detrimental. 2 Feed iron can be deposited on the catalyst external surface, lead- ing to deactivation of cracking sites, increased coke and hydrogen production, and reduction in fluidisation. Due to their larger molecular size and steric hindrance, iron-containing compounds are unable to diffuse into the internal structure of FCC catalyst particles. Instead, they preferentially deposit and accumulate on the cata- lyst surface, forming low-melting-point eutectic nodules. This alters the surface of the catalyst particles from being smooth with open pores to being covered with a thick, rough coating called iron nodules. These iron nodules lead to a drop in catalyst apparent bulk density (ABD), which can cause catalyst circulation rates to become erratic. These iron-rich deposits, which can be up to several microns thick, further accelerate catalyst

deactivation. 3 They form a barrier that inhibits the move- ment of both feed into the catalyst and products out of the catalyst particle. The inability of feed compounds to enter the catalyst particle prevents cracking, which reduces the activity, resulting in lower conversion. The restricted ability of cracked products leaving the catalyst particle can lead to secondary reactions occurring within the particle. A nega- tive impact of this is reduced liquefied petroleum gas (LPG) olefinicity. Moreover, iron itself catalyses dehydrogenation reactions, leading to increased coke and hydrogen. Finally, iron-poisoned catalysts often behave as inverse sulphur oxide (SOx) reduction additives, capturing hydrogen sul- phide (H₂S) in the riser as iron sulphide (FeS) and releasing it in the regenerator as sulphur dioxide (SO₂). This can be effectively countered by using SOx reduction additives. Iron poisoning is known to start having significant negative impacts at levels over ~0.2 wt% added iron. 4 , 5 Usual mitigation strategies include increasing the catalyst make-up rate or adding substantial quantities of purchased equilibrium catalyst (Ecat) to dilute the iron by flushing it out of the unit. Both strategies lead to increased Opex. Additionally, added Ecat can present different properties than the base catalyst chosen for the unit and lead to dif- ferent product selectivities that may not be optimal. An alternative strategy can be to reformulate the base catalyst to a more metals-tolerant one (for example, high matrix content) or include iron-trapping functionality. This solution can soften the impact of iron poisoning. However, this will not completely prevent it, and typically higher cat- alyst addition rates or Ecat additions will still be required. 2 , 6 Another solution is the use of a metals trap additive, 7 , 8 a solution that will be detailed in the next section. Mitigating Fe poisoning: characterisation techniques Johnson Matthey’s prior study found that iron is deposited on the surface of FCC base catalyst particles as highly dis - persed organic iron or iron salts. 6 This is consistent with the literature that the distribution of added iron is enriched at the exterior of the FCC catalysts particles and highly localised. 8 To further probe the local structure and chemis- try of the iron nodules, high-resolution transmission elec- tron microscopy (HR-TEM) coupled with energy dispersive spectroscopy (EDS) was employed to analyse cross-sec- tions of Ecat particles obtained from commercial FCC units.

PTQ Q3 2025