Over the next 10 years, global demand for oil products is
forecast to increase at an average rate of 1.2%/yr through
2020. Demand will be just below 100 million barrels per day of
oil equivalent (MMbdoe). However, this growth will not be
distributed evenly around the world.
In the Organization for Economic Co-operation and
Development (OECD) countries, reductions in automobile fuel
consumption will decrease oil demand at about 0.5%/yr, thus
creating refining overcapacity. The situation
is completely different in nations with growing economies where
the gross domestic product (GDP) is increasing rapidly and the
population aspires to greater mobility. In these (non-OECD)
countries, demand for oil products will rise at 2%/yr and will
comprise 53% of world demand by 2020.
Concerning gasoline demand over the next 10 years, strong
growth is mainly expected in Asia (+2.1 MMbdoe), the Middle
East (+0.3 MMbdoe), the Former Soviet Union States (+0.37
MMbdoe) and Latin America (+0.6 MMbdoe), as shown in
Fig. 1. In these regions of developing and
growing economies, continued strong growth is projected for both gasoline and petrochemical polymers.
Fig. 1. Worldwide
incremental refinery product demand,
Worldwide demand for polymers is growing at a significantly
higher pace than oil and gas production (Fig.
2) and thus initiating large expansions in olefins and aromatics
complexes. Global paraxylene (PX) consumption is forecast to
exceed 40 million tons (MMton) by 2015 compared to 32 MMton in
2011. The additional capacity will be located in the
Asia-Pacific region, where PX demand is the highest, followed
by the Middle East. New aromatic complexes, which include
continuous catalyst regeneration (CCR) reforming units, will be
required to meet the growing demand in polyester used for
bottles and textiles. To meet both aromatics and gasoline
demand, capacity additions for light-oil processing are
expected in these regions at about 1.5 MMbpd in combined
reforming, isomerization and alkylation capacity by 2020.
Fig. 2. Worldwide
growth index in oil, gas
and polymer sectors.
Catalytic reforming of naphtha is central in the production of
both high-octane fuel and aromatics to support both rapidly
growing markets. Accordingly, there is a continued strong
demand for catalytic reforming units and improved catalysts for
new and existing units with a global installed capacity over 13
MMbpd. The present annual worldwide market for reforming
catalyst represents several thousand metric tons for fixed bed,
cyclic and CCR markets.
CATALYTIC REFORMING FUNDAMENTALS
The role of catalytic reforming is fundamental in
transforming low-octane naphtha from crude oil and
hydroprocessing units into high-octane transportation fuels and
aromatics. The process involves transforming or reforming the
paraffinic and naphthenic molecules in the feed into
high-octane aromatics and branched components, and coproducing
hydrogen needed by other refinery units such as hydrotreaters
and hydrocrackers. This is accomplished over a heterogeneous
catalyst at elevated temperature and preferably low pressure
according to Le Chateliers principle.
Reforming catalysts are complex composites of a highly
active precious metal, platinum (Pt), to efficiently perform
dehydrogenation and hydrogenation reactions, and an active
support or carrier to do complementary reactions. The carrier
is a high-purity alumina, with a specific pore structure,
designed to have an acid functionality, which can be moderated
by controlling the amount of chloride added to the support
and/or by the addition of promoters. Together, these
metal and acid components, as shown
schematically in Fig. 3, form a dual-function
catalytic system capable of transforming low-octane paraffins
and naphthenes into high-octane gasoline, aromatics and
Fig. 3. Schematic of
acid and metal sites
on reforming catalyst.
A simplistic representation of the main reactions is shown
in Fig. 4 and is linked to the metallic and
acid functions. The important dehydrogenation reaction to
convert a cyclohexane component into an aromatic is very rapid
and easily accomplished by the metal function of the catalyst.
For many feeds, in particular hydrocracker and coker derived
naphthas, a significant portion of the naphthenic compounds
contain cyclopentane elements that require the acid-catalyzed
reaction of ring extension or conversion into a
cyclohexane-bearing component for subsequent dehydrogenation on
the metallic sites. Ring extension and dehydrocyclization of
paraffins are all difficult, but they are critical functions
that require highly selective catalyst. If the acid and metal
functions are not tuned or properly balanced, undesirable side
reactions do occur, leading mainly to acid cracking and
hydrogenolysis, and, to a lesser extent, dealkylation. In the
reforming unit, these side reactions result in the formation of
light petroleum gas (LPG), light gas and coke; all contribute
to nonselective conversion, catalyst deactivation by coke
deposition, and light-ends handling limitations.
Fig. 4. Bi-functional
reactions. The desired reactions are labeled
in blue, with undesirable side-reactions
labeled in red.
The carrier and highly dispersed Pt metal interact in a
complex way to accomplish the desired reforming reactions.
Performance of the catalyst is described in terms of activity,
selectivity and stability.
Activity is commonly defined in terms of
temperature required to achieve a given objective; it is very
similar to the definition used to describe hydrotreating
catalysts. A more active catalyst is able to achieve the same
product yield or severity (gasoline octane or aromatics yield)
at a lower reactor temperature. For fixed-bed units, this means
longer cycle lengths, and, for CCR units, it means greater
operating flexibility within unit constraints.
Selectivity. The selectivity of the
catalyst refers to the relative yield of desired product, such
as C5+ reformate gasoline or aromatics,
compared to another catalyst operating with the same severity
target (RONc) under similar process parameters (pressure, WHSV,
H2/HC). As with most reaction systems, high
selectivity is desired, as long as the performance can be
Stability is a measure of how long a
desired performance can be maintained, and it usually reflects
the coking tendency of the catalyst as
it affects both activity and selectivity. Higher stability in a
fixed-bed catalyst translates into a longer cycle length while
meeting process severity targetsi.e., more profitable
onstream time. For reforming units equipped with CCR, higher
stability means lower coking tendencies and slower
regeneration cycles, thereby adding operational flexibility.
Such operating flexibility provides opportunities to process
more demanding feed, such as higher endpoint feed or increased
amounts of coker naphtha, or an increased catalyst life
resulting from a reduced regeneration frequency. Higher
catalyst stability can also allow reducing the recycle gas
requirement, thus lowering operating costs.
Carrier. The carrier formulation and method
of metal impregnation have a significant impact on the
activity, selectivity and stability of reforming catalysts. But
this is only the beginning of catalyst design and production
PROMOTERS AND ENHANCED PERFORMANCE
In addition to the essential alumina carrier and Pt metal,
other elements known as promoters are introduced to influence,
moderate or otherwise change the catalyst activity, selectivity
and stability. When combined effectively, the catalyst system
allows the refinery to optimize gasoline yield
and cycle-length or regeneration frequency to improve
profitability and operability within unit constraints.
In fixed-bed reformers, promoters have been used for a long
time to increase the stability (onstream time) of the catalyst
by moderating the coke formation rate. Platinum-Rhenium (Pt-Re)
catalysts allow for longer cycles or more severe operation at
thermodynamically favored lower pressure where the coking tendency is greater.
Additional promoters are often added to fine-tune the
selectivity and stability of the catalyst. There are trade-offs
in performance and response to feed contaminants, such as
sulfur, with these promoted catalyst systems. The challenge in
catalyst development is to prepare the right catalyst
formulation to achieve the best performance with the least
degree of compromise. Traditionally, this results in trading
selectivity and introduces a selectivity-stability barrier, as
shown in Fig. 5.
Fig. 5. Selectivity
stability trade-off or barrier.
Metallic and acid functions
The interaction between the metallic and acid functions is
complex, and optimizing the relative importance of each
function is fundamental to obtain the desired balance of
selectivity, activity and stability. With the addition of other
promoters, the permutations of interactions increases, and the
relative affinity of molecules to either the metal or acid
sites can be tuned for the desired effect, as in the case of
Pt-Re. Fig. 6 is a catalyst system with
multiple metals and varying chloride content.
Fig. 6. Schematic of
Identification of promising promoter combinations requires
extensive laboratory work and pilot testing. The exact
formulation, impregnation method and manufacture are highly
proprietary. Ultimately, the active site density and location
are critical to achieving both the desired metal and acid
functions. Moderating the acid site strength on the carrier is
one important way to limit cracking reactions, but this is only
possible if uniform deposition of the promoter(s) is achieved.
Equally important is the production trials where proprietary
techniques are applied to produce commercial product meeting
both the target process chemistry and particle mechanical
properties. Detailed particle analysis is performed to ensure
that the manufacturing method is effective, as shown in
Fig. 7. CCR catalyst
particle composition profile.
Uniform distribution of the carrier and metallic
components is important to ensure accessibility to these
precious constituents and proper function. When the promoter is
mainly on the shell of the particle, the metal-to-acid function
ratio is not constant along the diameter. Thus, hydrocarbons
diffusing into the particle encounter a higher acid-to-metal
ratio leading to undesired cracking reactions. This reduces the
intrinsic catalyst selectivity and increases coke make.
Moreover, when the promoter is preferentially on the surface,
it is more sensitive to contamination, and its elution
increases over time.
When the promoters are properly introduced, they remain
effective for the service life of the catalyst, even under
harsh operating conditions found in cyclic and CCR units.
Earlier work on promoted systems demonstrates that the
promoters are robust and do not elute from the catalyst over
many regeneration cycles. Fig. 8 demonstrates
excellent promoter retention, within the analytical accuracy of
the test, for various CCR catalysts.
Fig. 8. Commercial
promoter retention on CCR reformer catalysts.
BREAKING THE SELECTIVITY-STABILITY BARRIER
When targeting specific catalyst performance, there are many
choices of promoters, method of impregnation and design of the
carrier. Two fundamentally different catalyst lines using
unique design approaches were recently compared leading to a
new family of catalysts that break the selectivity-stability
barrier commonly encountered in catalyst design.
At the macroscopic level, the two lines of catalyst produced
similar results, but at the micro level, one exhibited better
carrier production technique and the other better promoter
characteristics. There were clearly opportunities to optimize
the systems at the micro level to provide better performance.
The first products to be explored were the CCR catalysts as
used in severe, high-profit-margin aromatics units.
CCR catalyst formulations are built around a platinum-tin
(Pt-Sn) base system. This provides significantly greater
selectivity over Pt-only catalyst, but requires low pressure
for best results and continuous regeneration to overcome the
greater coke formation tendency. Additional metals, other than
Pt and Sn, can be added as promoters to further optimize the
catalyst systems. The importance of promoter selection can be
demonstrated in Fig. 9.
Pilot-plant testing results are shown in Fig.
9A of the C5+ reformate yield
selectivity over time for four catalyst systems: Pt+Sn
(bimetallic), tri-metallic 1, tri-metallic 2 and optimized
Quad-metallic. In this batch pilot testing strategy, the unit
is operated at a constant RON target to reflect either a
constant conversion toward aromatics for aromatics application
or a constant octane in the case of gasoline application. As
the test progresses, catalyst selectivity is measured by the
reformate yield and stability by the rate of reformate-yield
decay over time as the fixed batch of catalyst age.
During the test, coke is progressively deposited on the
catalyst and the required temperature to maintain the target
RON increases (Fig. 9B). Low coke formation
and catalyst deactivation is indicated by a slow increase in
reactor temperature to maintain the target RON. A small slope
of the temperature curve indicates high catalyst stability,
while the duration of the C5+ plateau and
the slow rate of yield decay is the complementary indicator of
the C5+ stability of the catalyst. From a
commercial unit perspective, the latter part of the test, where
temperature increases sharply to maintain severity, defines the
ultimate catalyst stability (cycle life) within unit
Looking more closely at Fig. 9, the two
tri-metallic systems show initial selectivity performance
higher than the base Pt-Sn, but the performance falls over time
as a result of the lower stability (higher coke yield), shown
in Fig. 9B, for these systems. When a fourth
metal is properly introduced, the quad metallic or simply Quad
system, a superior yield selectivity and equal stability is
attained relative to the Pt-Sn system. In this case, the
selectivity-stability barrier is broken, and stability does not
suffer to attain superior selectivity. Significantly, this
improvement was obtained while reducing the Pt loading on the
catalyst by 20%, thereby offering a substantial cost reduction
for our customers.
Fig. 9A. Reformate
yield vs. promoter system,
and 9B. Stability and coke yield
When the optimized carrier and promoter system were applied to
the low-density CCR catalyst platform, a new Quad catalyst was
developed. Fig. 10 shows the performance of
this new system. The reformate yield is increased by 0.8 wt%;
hydrogen increased by 0.1 wt% (50 scf/bbl), while the activity
and stability are slightly improved.
Fig. 10. Optimized
comparison: A) reformate yield, B) hydrogen
yield, and C) activity/stability.
ENHANCED PHYSICAL PROPERTIES
CCR moving bed catalysts also require careful attention to
the physical properties to ensure mechanical strength and
surface-area stability over many regeneration cycles, which is
indicative of catalyst life and chlorine retention.
Accelerated aging tests have been performed on the new
Quad-metallic catalyst to compare surface area retention to
conventional Pt-Sn bimetallic catalyst. Fig.
11 shows the surface area decline over time following
such test protocols. A conventional Pt/Sn catalyst reaches its
end-of-life surface area (approximately 140 m2/g)
relatively quickly, whereas the new Quad catalyst retains a
higher surface area in the range of 160 m2/g. Higher
surface area is associated with improved regeneration (Pt
redispersion) and better chloride (C1) retention. As a
consequence, the new Quad catalysts will exhibit longer life,
reduced salt deposit in downstream units, and lower chloride
content in the hydrogen-rich gas, resulting in longer chloride
Fig. 11. Catalyst
surface area aging test,
quad metallic vs. bimetallic Pt-Sn.
Put in quantitative terms, the better surface area retention
and intrinsically higher chloride retention resulting from a
new quad catalyst with a proprietary promoter system results in
30% lower chloride injection over the life of the catalyst vs.
The mechanical properties of the catalyst are also important
in CCR applications. Unlike fixed-bed catalysts, which are
mainly concerned about crush strength to endure the static load
forces within a fixed bed, CCR catalysts are spherical and
designed to resist the dynamic forces from slow movement in the
catalyst beds to pneumatic lifting between reactor and
regenerator. These forces lead to particle attrition and fines
production. Although the fines or broken pieces of the catalyst
are captured within the system, they can lead to fouling of
screens and increase pressure drop.
Highly developed CCR catalysts are more robust to ensure
extended service over 79 years. New formulations are
subjected to large-scale circulating test units to accurately
represent commercial conditions and the forces leading to
attrition. The new carrier and multi-promoted catalyst systems
have proven to be as robust as previous-generation catalysts
with an excellent track record of low particle attrition.
As a licensor of catalytic reforming and aromatics chain
technologies, and supplier of catalysts for these units, Axens
is focused on continuous improvement in both process technology and catalyst development.
The recent acquisition of the Criterion catalytic reforming
catalyst business in 2011, including production facilities and know-how, provided a
unique opportunity to compare, contrast and build upon two
different approaches to reforming catalyst development and
production. New proprietary formulations and production
techniques have emerged from this union resulting in
breakthrough catalysts for both fixed-bed and moving-bed CCR
units that provide superior selectivity without compromising
activity and stability. Re-engineered fixed-bed catalysts are
under development and on-track for release in 2013. These new
products promise the benefits of higher selectivity and reduced
cost through promoter selection and loading optimization.
Goff is Axens senior technical manager
for reforming catalysts and project leader for catalyst
development. Dr. Le Goff started his career as a
research engineer at Rhodia, where he specialized in
catalyst support design and process development. Dr. Le
Goff holds an engineering degree from the École
de Chimie de Mulhouse, an MBA from Université de
la Sorbonne in Paris, and a PhD from Université
is a senior technology and marketing
manager for Axens covering the field of transportation
fuels including FCC, catalytic reforming, isomerization
and biodiesel production. He has over 30 years of
experience in the refining and petrochemical industry
including process engineering design, R&D,
licensing and technical assistance. Mr. Ross is a
graduate from Princeton University with a degree in
Lopez is a development and industrialization
engineer in Axens production plant of adsorbents
and catalysts in Salindres, France. He is responsible
for the development and scale-up of reforming supports
and catalysts. He started his professional career as a
research engineer at Rhodia working mainly in the field
of heterogeneous and homogeneous catalysis. Dr. Lopez
holds an engineering degree from the Ecole Nationale
Supérieure de Chimie de Montpellier and a PhD in
catalysis from the Université Claude Bernard of