Jul-2014

Reversing catalyst poisoning

Residue and shale oil feeds often contain high levels of contaminants that can create a number of challenges for refiners today.

Bart de Graaf
Johnson Matthey

Article Summary

In recent commercial applications, Johnson Matthey’s Intercat_JM catalyst enhancement additive Cat-Aid has been found to be able to reverse the effects of iron poisoning of the FCC catalyst.

By breaking down the nodular iron-rich shell on the surface of the catalyst, Cat-Aid opens up access to the inner core of the catalyst, allowing it to become available for cracking once more. This significantly increases the profitability of the FCC operation by relieving operating constraints, improving product yields, and reducing fresh and flushing equilibrium catalyst consumption.

Metal contaminants such as vanadium, nickel, iron, calcium, sodium and potassium can limit the refiner’s ability to process residue and shale oil feeds and significantly impact the profitability of the FCC.  Iron poisoning, specifically, can have a devastating effect on FCC performance; iron typically lowers conversion, increases slurry, coke, dry gas selectivity and increased regenerator flue gas SOx emissions. In addition, unit constraints such as impaired fluidisation may lead to operational difficulties.

Most fresh catalysts are capable of handling up to +0.3 wt% add-on Fe2O3 before detrimental effects are observed. When the iron content is high enough it ‘seals off’ the catalyst interior by forming a nodular shell-like layer at the catalyst surface that inhibits hydrocarbon diffusion into and out of the catalyst particle interior.  Zeolite and matrix active components at the core of the catalyst particle are unaffected by iron, but are no longer readily accessible due to the barrier formed on the outer surface. Often refiners will try to tackle iron poisoning with an increased fresh catalyst make-up rate or use of added equilibrium catalyst to dilute the iron by flushing it out of the FCC unit.

Cat-Aid is an effective trap for vanadium and other contaminants such as iron. Vanadium is a permanent poison that accumulates on the catalyst where it causes catalyst deactivation by increasing the rate of destruction of the zeolite component, and promotes undesirable dehydrogenation reactions, leading to increased coke and gas make. Cat-Aid was originally designed to capture vanadium thereby protecting the base catalyst and greatly improving its performance.

For more information: Bart.deGraaf@Matthey.com