Hydrocarbon Processing - December 2021 - 23

Special Focus Catalysts
D. FOOTE, CHS, Laurel, Montana; A. SHACKLEFORD,
BASF, Detroit, Michigan; and A. VJUNOV, BASF,
New York City, New York
Choosing an FCCU CO promoter is no longer
driven by NOx
emissions
Fluidized catalytic cracking units (FCCUs)
form coke during the reaction that
combusts in the regenerator and supplies
heat for the process. The reactions can
be full combustion to carbon dioxide
(CO2
) and water or partial combustion to
carbon monoxide (CO) and water emissions.
CO can further combust to CO2
An FCCU may utilize CO promoter additives
to catalyze these reactions to:
* Meet environmental regulations
on CO emissions
* Reduce afterburn, which occurs
when CO and oxygen react in the
dilute phase (or less commonly the
flue gas line) of the regenerator.
In the dilute phase, there is less
catalyst to absorb the heat of
combustion, potentially causing
significant temperature increases
above metallurgical limits.
Beyond the desired oxidation reactions,
promoters also catalyze the unwanted
reaction of nitrogen in the coke to form
nitrogen oxides (NOx
) (vs. N2
ing on NOx restrictions, there are
types of platinum group metals (PGM):
1. Platinum promoters that allow
higher degrees of CO promotion
but generate substantial NOx
2. Non-platinum promoters, which
typically use palladium that
generate comparably less NOx
but
are less effective in CO oxidation.
In early 2018, platinum and palladium
both cost approximately $1,000/
troy ounce (oz t). At present, palladium is
more than double the price of platinum.
As palladium-based catalysts tend to require
more metal to achieve equivalent
CO promotion, a palladium-based CO
promoter is around $25/lb more expensive
than a platinum-based CO promoter
). Dependtwo
.
due
to metals cost alone. For example,
an average unit uses 2 lb-5 lb of CO promoter
additive per sT catalyst. At 5 sT/d,
that could be more than $200,000/yr
higher costs to use a palladium promoter
vs. a platinum promoter. Note: The metals
are generally not considered recoverable.
Given this, FCCUs will preferably
use platinum-based CO promoters. Palladium
is used by units that either have
an environmental consent decree and/
or cannot meet NOx
num-based promoters.
emissions with platiNovel
promoters. Conventional promoters
also have a short half-life (around
a few days) due to metal sintering under
high-temperature conditions in the
FCCU. To mitigate these issues, a new
generation of CO promoters has been
developed. These novel promoters use
a tuned PGM-support interaction, hindering
sintering by anchoring PGM on
the support. The resulting morphology
modification (FIG. 1) improves promoter
durability. Anchoring enables the ability
to control PGM-oxygen interaction
through oxygen on-demand shuttling.
The products are designed to have optimized
attrition, density and particle size
distribution for use in the FCCU.
The co-authors' company has designed
a novel, proprietary, durable platinum-based
CO promotera
CO conversion, %
NOx conversion, %
, 700°C.
Palladium-based
50
75
that generates
significantly less NOx
vs. traditional platinum
promoters. In laboratory testing, the
proprietary CO promoter was compared
to the latest generation of palladium and
platinum promoters (TABLE 1). The proprietary
promoter matched palladium
promoter activity at 15% lower addition.
The NOx
generation increases about 10%
when using palladium-in comparison,
the platinum promoter generated 160%
more NOx
vs. the proprietary design.
For most units, the proprietary CO promotera
dium
vs. platinum to no longer be driven
by NOx
allows the choice between pallaemissions
constraints, but rather
based on PGM pricing.
The first commercial adoption of the
proprietary CO promoter was at CHS's
Laurel refinery outside Billings, MonFIG.
1. The image, using a scanning electron
microscope, shows the customized surface
morphology of the CO promoter.
TABLE 1. Lab testing results for commercial palladium- and platinum-based promoters
vs. the proprietary promotera
Platinum-based
50
200
Proprietary promotera
50
82
Note: Samples were aged and normalized on CO conversion (%) basis. Aging: 12h, Tmax = 780°C; fl ow-through reactor:
10 min air, 10 min N2, 10 min H2, 10 min N2, constant 10% H2O-steam. Test: 99% spent catalyst + 1% promoter, 1 l/min,
2 vol% O2/N2
Hydrocarbon Processing | DECEMBER 2021 23

Hydrocarbon Processing - December 2021

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