FCC Catalyst Evaluation 1.0 Introduction Catalyst management is a very important aspect of the FCC process. Selection and management of the catalyst, as well as how the unit is operated, are largely responsible for achieving the desired products. Proper choice of a catalyst will go along way toward achieving a successful cat cracker operation. Catalyst change-out is a relatively simple process and allows a refiner to select the catalyst that maximizes the profit margin. Although catalyst change-out is physically simple, it requires a lot of homework. As many catalyst formulations are available, catalyst evaluation should be an ongoing process; however, it is not an easy task to evaluate the performance of an FCC catalyst in a commercial unit because of continual changes in feedstocks and operating conditions in addition to inaccuracies in measurements. Because of these limitations, refiners sometimes switch catalysts without identifying the objectives and limitations of their cat crackers. To ensure that a proper catalyst is selected, each refiner should establish a methodology that allows identification of ‘real’ objectives and constraints and 1
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FCC Catalyst Evaluation
1.0 Introduction
Catalyst management is a very important aspect of the FCC process.
Selection and management of the catalyst, as well as how the unit is
operated, are largely responsible for achieving the desired products.
Proper choice of a catalyst will go along way toward achieving a
successful cat cracker operation.
Catalyst change-out is a relatively simple process and allows a
refiner to select the catalyst that maximizes the profit margin.
Although catalyst change-out is physically simple, it requires a lot of
homework.
As many catalyst formulations are available, catalyst evaluation
should be an ongoing process; however, it is not an easy task to
evaluate the performance of an FCC catalyst in a commercial unit
because of continual changes in feedstocks and operating conditions
in addition to inaccuracies in measurements. Because of these
limitations, refiners sometimes switch catalysts without identifying
the objectives and limitations of their cat crackers. To ensure that a
proper catalyst is selected, each refiner should establish a
methodology that allows identification of ‘real’ objectives and
constraints and ensures that the choice of the catalyst is based on
well-thought-out technical and business merits.
In today’s market, there are over 120 different formulations of FCC
catalysts. Refiners should evaluate catalysts mianly to maximize
profit opportunity and to minimize risk. The right catalyst for one
refiner may not necessarily be right for another.
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2.0 Catalyst Selection Methodology
One of the most important parameters that specify the
competitiveness of a refinery FCC unit is the proper selection of
catalyst, since the catalyst type determines both quantity and quality
of the catalytic cracking products. Laboratory of Environmental Fuels
and Hydrocarbons evaluates FCC catalysts, through MAT tests,
specifying each catalyst activity and selectivity.
For the above purpose a Short Contact Time Microactivity Test
unit (SCT-MAT) was constructed in CPERI, at the beginning of 1999, in
order to replace the conventional MAT unit, as an attempt to follow
the worldwide inclination of short residence times during the FCC
reaction. The unit's excellent performance along with the compatible
results derived by comparing it with the FCC pilot plant soon lead to
the construction of an identical unit (January, 2001).
Catalysts are evaluated following a standard FCC evaluation
protocol. Initially the catalysts are deactivated; either by metal
deposition or by steaming sieved and finally tested in one of CPERI's
MAT units. At least eight different tests are carried out for a specific
catalyst and for each test detailed experimental and normalised mass
balances are quoted. The individual product yields are plotted vs.
conversion and catalysts evaluation is completed by comparing their
product yields at a constant conversion level (65%wt).
The microactivity test (MAT) unit was originally designed to
determine the activity and selectivity of either equilibrium or
Currently, the MAT unit is accepted as a tool to perform general
laboratory scale FCC research and testing because of its simple
operation and cost effectiveness. The unit only requires small
quantities of catalyst and gas oil for each MAT test, compared with
barrels of materials needed for a pilot-scale riser run.
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A comprehensive catalyst selection methodology will have the
following elements:
1. Optimize unit operation with current catalyst and vendor. a. Conduct test run. b. Incorporate the test run results into an FCC kinetic model. c. Identify opportunities for operational improvements. d. Identify unit’s constraints. e. Optimize incumbent catalyst with vendor.
2. Issue technical inquiry to catalyst vendors. a. Provide Test run results. b. Provide E-cat sample. c. Provide Processing objectives. d. Provide Unit Limitations.
3. Obtain vendor responses. a. Obtain catalyst recommendation. b. Obtain alternate recommendation. c. Obtain comparative yield projections.
4. Obtain current product price projections. a. For present and future four quarters.
5. Perform economic evaluations for vendor yields. a. Select catalyst for MAT evaluations.
6. Conduct MAT of selected list. a. Perform physical and chemical analyses. b. Determine steam deactivation conditions. c. Deactivate incumbent fresh catalysts to match incumbent E-cat d. Use same deactivation steps for each candidate catalyst.
7. Perform economic analysis of alternatives. a. Estimate commercial yield from MAT evaluations.
8. Request commercial proposals. a. Consult at least two vendors. b. Obtain references. c. Check references.
9. Test the selected catalyst in a pilot plant. a. Calibrate the pilot plant steaming conditions using incumbent E-cat.
b. Deactivate the incumbent and other candidate catalysts.c. Collect at least two or three data points on each by
varying catalyst-to-oil ratio.
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10. Evaluate pilot plant results.a. Translate the pilot data.b. Use the kinetic model to heat-balance the data.c. Identify limitations and constraints.
11. Make the catalyst selection.a. Perform economic evaluation.b. Consider intangibles-research, quality control, price,
steady supply, manufacturing location.c. Make the recommendations.
12. Post selection.a. Monitoring transitions-% changeover.b. Post transition test run.c. Confirm computer model.
13. Issue the final report.a. Analyze benefits.b. Evaluate selection methodology.
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3.0 Reactors Used for FCC Studies
Catalytic cracking catalyst development requires the adequate
evaluation of catalyst performance. Different kinds of laboratory
reactors are available to evaluate catalyst performance. These
reactors include fixed bed, fluidized bed, stirred batch, differential,
recycle, and pulse reactors (Weekman, 1974: Sunderland, 1976).
The testing of catalyst at the laboratory scale can serve many
purposes. One possibility is the need of improving catalyst
formulation or altogether to develop a new catalyst (Mooreheed et
al., 1993). However, a common task for a bench scale unit is to
compare the relative performance of two or more catalysts
(Mooreheed et al., 1993).
Regarding the specific approach used for FCC catalysts, very
frequently catalyst evaluations are done on the basis of a
microactivity test (MAT). MAT studies are hindered by mismatching of
industrial operating conditions. Thus, MAT studies with long catalyst
time-on-stream, low hydrocarbon partial pressures, and cumulative
coke content do not represent industrial operation.
It is our view that to represent, in a laboratory scale unit, the
reaction environment of a commercial riser, the operation of this unit
has to be carefully controlled. The present dissertation considers in
this respect, a novel CREC Riser Simulator invented by de Lasa
(1992) at the University of Western Ontario.
3.1-Microactivity Test (MAT)
The Micro Activity Test (MAT) has been a main tool for basic
FCC research, and this includes catalyst selection and feedstock
evaluation (O’Connor and Hartkamp, 1988; Campagna et al., 1986).
This test was developed due to its simplicity, reproducibility, and
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quickness of evaluation in comparison to tests in a continuous pilot
plant.
The MAT technique is an ASTM procedure (ASTM D-3907-88)
which was developed on the basis of using a fixed bed of 4 grams of
catalyst, operated with a continuous oil vapour feed for 75 seconds at
a temperature range of 480-550oC and using an average catalyst/oil
ratio of about 3. The standard MAT has had limited success predicting
commercial unit performance and has provided limiting information
about product selectivity (Mauleon and Courcelle, 1985; O’Connor
and Hartkamp, 1988; Mooreheed et al, 1993). There are important
warnings in the technical literature about the value of the data
obtained in the MAT for catalyst selection. Some authors claim,
without fundamentally based arguments, that the MAT could provide
some kind of relative comparison on catalyst activity and coke make
selectivity (Humphries and Wilcox, 1990).
Although the MAT unit can provide some data for catalyst
screening, several important differences exist between MAT and the
commercial FCC unit (Mooreheed et al, 1993) as follows;
a-) The MAT reactor is based on a cylindrical (ASTM design) catalyst
fixed bed with a flow of feedstock flowing through a bed of catalyst. A
commercial riser uses instead an upflow of oil and catalyst circulating
together (Mooreheed et al, 1993).
b-) The MAT uses a cumulative catalyst time on stream of 75 second
while a commercial riser uses a short contact time of 3-5 second.
c-) The MAT employs a reactant partial pressure much lower than the
one of the commercial riser: 0.05 atm for MAT and 1.5 atm for the
commercial riser.
d-) Coke profiles develop in the 150 mm long catalyst bed of the MAT
and the catalyst deactivates at different rates. On the other hand, in
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the riser all catalyst particles experience the same feed exposure
having at the riser outlet uniform coke concentration.
e-) The operation of the MAT provides average results over a 75
second period. These results are by nature different than those taken
after 3-5 seconds contact time in the riser. For instance, this
difference explains the low olefinicity of the MAT products
(Mooreheed et al, 1993).
f-) The MAT cannot provide information about catalyst attrition since
it is a fixed bed unit.
As a result of the above described inadequacies, some
modifications have been suggested to the MAT to provide a more
reliable method for catalyst testing (O’Connor and Hartkamp, 1988;
McElhiney, 1988, Mott, 1987; Tasi et al., 1989). However, and despite
the proposed modifications the MAT still allows coke profiles and
temperature differences. Consequently, the kinetic modeling of
catalytic cracking reactions using the standard MAT test is rather
unreliable, and a number of strong approximations are needed
(Froissier and Bernard, 1989).
Corma et al., (1994) highlighted the limitations and the
inadequacies of MAT unit to compare different FCC catalysts made
from different materials. These authors pointed out that when two
different FCC catalysts, one made from ultrastable Y-zeolite and the
other was made of SAPO-37, which had a faujasite structure with
different framework composition, were used in the MAT, the tests
performed were not reliable. It was recommended, by these authors,
to use different tools with short contact times and based on mini-
fluidized beds.
3.2- Pilot plant unit.
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A successful scale up procedure is essential for further
advancement of any chemical technology. Usually, if the tested
catalyst passes the bench scale reactor test (like the MAT), the
following level of demonstration is the pilot plant unit. In this respect,
it is extremely important to bridge the differences between the lab-
scale and commercial FCC units. According to Carter and McElhiney
(1989), circulating riser pilot plants can provide the best small-scale
simulation of commercial FCC yields.
Several pilot plants are available for the FCC process, with the
favored ones being those with a riser reactor and continuous catalyst
regeneration (Yang and Weatherbee, 1989). Davison Circulating Riser
(DCR) unit is one of the most effective FCC pilot plants. It includes an
adiabatic riser reactor where the reactor temperature is maintained
by controlling the circulating rate of the hot regenerated catalyst.
This process is identical to the commercial unit. This unit can work in
the isothermal mode for certain kinetic studies. It is reported that this
unit can be used to process heavy oils and it can be also used for
catalyst studies. The DCR unit is 12 feet in height and it has a
catalyst and vapor residence time of about 6 and 3 sec respectively
(Yang and Weatherbee, 1989).
While, these pilot plant units provide, in principle, good
simulation for commercial FCC units, they are expensive, difficult and
costly to operate, and they are not suited to test large number of
catalyst samples. Furthermore, there is an intrinsic difficulty to
operate these pilot plants isothermally, showing some limitations in
catalyst/oil ratios and contact times (Corella et al., 1986).
3.3- CREC Riser Simulator
As stated, one of the most important challenges for FCC
catalyst development has been the one of simulating catalyst
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performance under commercial conditions and in this respect, a
laboratory scale unit is needed (Book and Zhao, 1997).
The Riser Simulator is a novel unit invented by de Lasa (1987)
to overcome the technical difficulties of MAT units. This unit can be
used for several purposes: a) to test industrial catalysts at
commercial conditions (Kraemer, 1990), b) to carry out kinetic and
modeling studies for certain reactions, c) to develop adsorption
studies (Pruski, 1996). d) to use the data of this unit for assessing the
enthalpy of cracking reactions.
The different characteristics and advantages of the CREC Riser
Simulator can be summarized as follows:
a-) Temperature, reaction time, cat/oil can be varied in a wide range,
b-) Different feedstocks (VGO, gas oil, and model compounds) can be
tested,
c-) Different chemical reactions such as alkylation, hydrogen transfer,
transalkylation, and coke formation can be investigated,
d-) Catalyst regeneration is simple and can be conducted at typical
regeneration conditions,
e-) For testing a catalyst, only a small catalyst sample (0.8 g) can be
used throughout many runs at different temperatures, contact times,
and cat/oil ratios,
f-) For testing a feedstock, only a small amount of feed (0.16 g) is
needed,
g-) The Riser Simulator can be operated in a broad range of total
pressures,
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h-) The Riser Simulator can be used in the fluidized bed mode with
active mixing of catalyst particles. In this respect, perfect mixing with
the absence of coke profiles and gas channeling can be obtained with
all catalyst particles being exposed to the same reaction
environment.
In conclusion, and in order to obtain reliable cracking results,
the appropriate tools have to be used in conducting reaction runs. For
example, it is well known that to measure catalyst activity and
selectivity of FCC catalysts a number of conditions have to be met: a)
a short contact time, b) fluidized bed conditions, c) appropriate