Hydrocarbon Processing - December 2022 - 35

Special Focus Catalysts
N. PONGBOOT, Avantium, Amsterdam, the Netherlands; and
T. UPIENPONG, PTT Global Chemical, Rayong, Thailand
Refinery catalyst selection: Facts and fictions
every refiner should know
Most refiners carefully evaluate their
refining catalysts to ensure maximum benefits
over the catalyst cycle length. Without
a doubt, pilot plant testing is the best method
to evaluate true catalyst performance.
Often, the incremental catalyst cost is trivial
compared with the economic benefits
from improved catalyst performance.
To the authors' surprise, many refiners
only consider testing some refining
catalysts, such hydrocracking, fluid catalytic
cracking (FCC) or naphtha reforming
units. This seems a reasonable line of
thought, as these refining units are the
critical profit makers of a typical refinery.
So, why risk not testing?
Conversely, these refiners somehow
believe testing other refining catalysts
(e.g., diesel hydrotreating catalysts) is unnecessary.
They argue that other refining
catalysts are less critical and a paper-based
evaluation is usually sufficient. This notion
seems sensible on the surface, and
many refiners follow this practice. However,
is this really the case? Should refiners
consider an 86,000-bpd diesel hydrotreater
(like the one shown in FIG. 1)
as not critical? Where is the line defining
the criticality? Is a paper-based evaluation
even a valid method? This article will answer
these questions and emphasize why
refiners should remain skeptical about
skipping refinery catalyst testing.
Reliance on a paper-based catalyst
evaluation. Many refiners think that
comparing catalyst proposals from different
catalyst vendors is a completely valid
evaluation technique. However, this is
flawed approach.
A typical catalyst proposal is the result
of a proprietary kinetic model developed
by an individual catalyst vendor. Although
most (if not all) kinetic models share the
same core principles (e.g., Langmuir-Hinshelwood
kinetics), each of them is unique
if you look further into the assumptions
and the details. Also, these kinetic models
are not 100% accurate, so they are likely
to yield different results despite the same
feed properties.
Secondly, the feed properties provided
by the refiner in the catalyst tender documents
are mostly incomplete, inconsistent
with each other or even over-specified. In
the authors' experience, a set of feed properties
is often a mix of data from various
sources (e.g., original design data plus past
operating data), as shown in TABLE 1.
It is not uncommon to see catalyst
vendors making certain feed assumptions
(typically based on institutional knowledge)
during the feed characterization
step (e.g., nitrogen, sulfur or aromatics
distribution). A catalyst vendor might
assume 35% of total nitrogen is basic nitrogen
for Middle Eastern crudes while
another uses 1/3 as an assumption. Which
number is more accurate? How can we
know if all catalyst vendors are adopting
the same assumptions? Additionally, a
typical crude diet is often a mix of various
crudes from all around the world, and
not only from a specific region. What if
South American or West African crudes
are dominant in the crude slate?
To add to the challenges, some catalyst
vendors are more aggressive than others
with their yield estimates. It must be remembered
that a catalyst vendor's priority
is to secure the sale. The authors have experienced
cases where it became apparent
that a catalyst vendor " tuned " its kinetic
model to produce yields for its proposal
that were more attractive. For example, a
diesel hydrotreating catalyst vendor once
proposed an almost nil offgas yield to a refiner
without justifying or explaining this
anomaly. When challenged, the catalyst
vendor just stated that it was the result of
the kinetic model. To add insult to injury,
the same catalyst vendor also proposed
a suspiciously aggressive diesel product
density (e.g., a much lower than usual diesel
density). Although the same catalyst
vendor later revised the new diesel density
because the refinery expressed strong disbelief
in the performance predictions, the
vendor did not make any changes in aromatic
contents in the diesel product and
overall hydrogen consumption. The illogical
revision was clear proof that this catalyst
vendor deliberately tuned the catalyst
performances presented in its proposal.
Without a reasonable explanation from
the catalyst vendor regarding the " too
good to be true " catalyst performance, the
refiner decided to negatively weigh the
results from the abovementioned catalyst
vendor due to the uncertainty over the
FIG. 1. The diesel hydrotreater is one of the
most important-yet-ignored refining units
when it comes to refinery catalyst testing.
Hydrocarbon Processing | DECEMBER 2022 35
Hydrocarbon Processing - December 2022

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