Multistage reaction catalyst with advanced metals tolerance

The metal trapping capabilities of a catalyst gave a refiner greater flexibility to upgrade heavy residue feed with increased metals content in its RFCC unit.


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Article Summary

Tamoil’s Collombey refinery in Switzerland operates an R2R design residue fluidised-bed catalytic cracking (RFCC) unit. (The R2R process is offered through the FCC alliance between Axens, IFP Energies Nouvelles and Technip Stone & Webster Process Technology.) It has a two-stage regenerator. The feedstock is 100% atmospheric residue derived from crudes such as Es Sider, El Sharara, Saharan Blend and Brega with a moderate-to-high metals content and a high Conradson carbon residue (CCR) content (typically 4-6 wt%).

Increased flexibility to upgrade heavy residue feed with even higher metals is a key enabler for further improving the profitability of the Collombey refinery.

Base catalyst in use
Collombey changed to BASF’s Aegis catalyst during the first half of 2012. This catalyst combines the benefit of BASF’s DMS and Prox-SMZ technology platforms. It is designed for resid feed applications where moderate-to-high metals tolerance is needed, and it offers the flexibility to improve both diesel and gasoline yields. Compared to the best-proposed solution of a competitor, Aegis delivered improved LPG/gasoline selectivity at a low equilibrium catalyst (e-cat) rare earth level, similar gasoline and coke yields, and better bottoms upgrading, all leading to a profitability increase of $0.40/bbl of fresh feed.

To satisfy changing feed quality and product slate demand, and to continuously maximise the unit’s profitability, the Aegis catalyst was fine-tuned several times during the first year of operation.

Unit operating data are routinely reviewed using BASF’s Technical Support Service (TSS), and this identified that catalyst performance could be further improved through even better feed metals passivation. This triggered a review of catalyst technology options.

Using BASF’s Catalyst Change Management Process, Fortress catalyst, based on the company’s Distributed Matrix Structures (DMS) and Multi-stage Reaction Catalyst (MSRC) technologies, was selected as the best option.2

The changeover to the customised Fortress catalyst proceeded smoothly, and the new catalyst delivered excellent performance. Using typical feed and product values, the profitability has been increased by $0.30/bbl of fresh feed compared to the Aegis catalyst. Thus, this past year, the refinery has improved profitability by approximately $0.70/bbl (Aegis and Fortress).

This article shows how advanced FCC catalysts and value-added technical service are supporting Collombey refinery. This is made possible by Collombey’s good approach to data sharing and collaboration to form the best team.

Impact of feed metals on FCC operation
The contaminant metals in residue feed that need to be controlled by the FCC unit are mainly vanadium (V) and nickel (Ni), with iron (Fe) and calcium (Ca) also high from some crudes. Sodium (Na) is typically reduced to low levels by crude desalting. The potential detrimental effects of these metals on FCC performance are summarised below:
• Ni: dehydrogenation activity leading to increased H2 and coke
• V: catalyst deactivation, with some dehydrogenation activity
• Fe and Ca: surface pore plugging and nodules formation at higher levels, leading to conversion loss, higher dry gas yield and possibly catalyst circulation problems
•  Na: involved in catalyst deactivation (more information below).
This article focuses on mitigating the deactivation/dehydrogenation effects of Ni and V through the application of the appropriate catalyst technology to passivate these metals.

Improving FCC catalyst vanadium tolerance
As previously indicated, V deactivates the catalyst, and increased feed V will require higher catalyst additions to maintain the optimum target e-cat activity. The deactivation steps are:6
• V is deposited onto the catalyst and is oxidised in the FCC regenerator
• The oxidised form undergoes further reactions to form several highly mobile types of vanadic acids
• These vanadic acids remove Na+ from the zeolite exchange sites
• The sodium vanadate hydrolyses to sodium hydroxide (Na+OH-)
• The hydroxyl group (OH-) then attacks the silica-oxygen zeolite framework, leading to zeolite collapse, destruction and catalyst deactivation.

There is residual Na+ on the fresh catalyst from the manufacturing process. In BASF FCC catalysts, the amount of residual Na+ on zeolite is reduced to ultra-low levels by a unique combination of calcination and ion exchange steps, which improves resistance to Na-V zeolite deactivation.

Impact of H2 and coke on FCC operation
Additional production of H2 and coke from processing high metals content and high CCR feeds has a significant impact on FCC unit operation, as most units operate to gas and coke handling limits.

High volumetric flow from the low molecular weight H2 may lead to wet gas compressor and gas concentration unit capacity limits. In addition, at many refineries, H2 in the absorber off-gas from the FCC’s gas concentration unit is routed to the refinery fuel gas system, where it has a low economic value — ample reasons to focus on minimising the formation of H2 in the FCC unit.

Coke is any carbonaceous, high molecular weight, non-volatile resi­due formed from cracking. The maximum tolerable coke yield/production may be constrained by regenerator operating limits; for instance, due to air blower capacity limits or mechanical design temperatures limits. There are four types of contribution to FCC coke: contaminant metals, feed additive, cat-to-oil (strippable) and catalytic.

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