FCC Equilibrium Catalyst Analysis (RMSE)

Rocky Mountain Salvage and Equipment
FCC Toolkit
Module # 4
FCC Equilibrium Catalyst Analysis
Routine analysis of Equilibrium Catalyst (ECAT), is another critical tool in monitoring the
performance of an FCCU. The chemical and physical analyses performed by catalyst suppliers allow
personnel to ascertain whether mechanical or feed quality issues are impacting unit performance and
help in troubleshooting.
The following items can readily be determined from a typical ECAT report.
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Conversion issues – A change in conversion with a corresponding change in surface area
(matrix/zeolite) can be a result of multiple items such as:
◦ Increased levels of contaminant metals brought about through either a:
▪ Feed quality shift (new crude or issues with a crude distillation column)
▪ Catalyst loader malfunction
◦ Accelerated deactivation – Average bulk density (ABD), pore volume (PV), and pore
diameter (PD) can shed light on whether a severe hydrothermal or thermal deactivation
event is ongoing
Mechanical issues – The particle size distribution (PSD) will help to identify whether there are
cyclone problems or attrition sources
Catalyst Conversion
ECAT conversion is determined using a laboratory scale fixed bed fluidized reactor system. Prior to
testing, the ECAT sample will be placed in a furnace to “burn off” any residual carbon that remains on
the surface. A small catalyst sample will than be contacted with a standard feedstock at very controlled
reactor conditions (fixed Cat/Oil, reactor temperature, and contact time). Catalyst suppliers will utilize
their own standard feedstock, operating conditions, and lab reactor design. Because of this, there will be
conversion variations if an identical catalyst sample is sent to multiple vendors.
After the feedstock has contacted the ECAT, the cracked products will be collected for analysis.
Individual component yields from H2S through C4's are measured. Liquid products will be broken
down into Gasoline (C5-430 F), LCO (430 – 650 F), and Bottoms (650+ F) boiling ranges. The residual
carbon from the cracking process will be measured to determine a coke yield.
The ECAT conversion is defined as either:
Conversion wt % = 100 - LCO wt % - Bottoms wt %
Conversion wt% = Dry Gas wt% + LPG wt% + Gasoline wt% + Coke wt%
The product yield structure generated for each ECAT sample is typically stored in a database. Since
the testing conditions are held constant for each sample tested, this provides an opportunity to track
yield shifts that are due to a catalyst reformulation or a change to a different catalyst supplier. The
ECAT product selectivity can be trended to verify the effectiveness of the change.
It is important to remember that the conversion test is performed on a coke free basis. Residual carbon
will block access of oil molecules from cracking on the active sites of the catalyst. Depending on the
mode of regeneration in a commercial FCCU (full or partial CO burn), combustion kinetics, and
mechanical issues, carbon levels can vary greatly. A full burn unit can typically have a carbon residue
on catalyst (CRC) of 0.05 wt %. At this level, the CRC will have a smaller effect on the catalyst
conversion. A partial burn operation can have CRC levels in the 0.15 to 0.4 wt % range. At these
levels, for every 0.1 wt% carbon, catalyst conversion is reduced by 1.5 to 2.0 wt %.
A significant drop in catalyst conversion can usually be attributed to some type of deactivation
mechanism. This can either be from:
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Increased feed oil contaminants (vanadium and alkaline metals) which destroy the active
cracking sites
Higher regenerator temperatures from feed quality shifts or poorer stripper operation
Catalyst loader malfunction
Physical Analyses
The typical ECAT physical properties reported are:
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Surface area, m2/gm (matrix and zeolite)
Average bulk density, gm/cc
Pore volume, cc/gm
Average pore diameter, angstroms
Particle size distribution
• 0/20 microns, wt%
• 0/40 microns, wt %
• 080 microns, wt%
• Average particle size, microns
Surface Area
Surface area can be used as an indirect measure of catalyst activity. Generally speaking, as ECAT
surface area increases/decreases, its corresponding conversion will also increase/decrease. This
statement is valid when comparing catalysts of the same manufacturing platform from a given supplier.
Surface area measurement is very accurate and reproducible, and at times is a preferred method to
gauge unit activity rather than rely on ECAT conversion measurements.
Surface area is determined using nitrogen (N2) absorption. N2 is absorbed in a mono layer over the
entire exposed surface of the catalyst filling the pores (micro and mesopores). The surface area is
calculated from the amount of N2 absorbed in relationship with its pressure at the boiling temperature
of liquid N2 under normal atmospheric pressure.
Typically, total ECAT SA will be reported along with the breakdown of zeolite and matrix
contributions. There will be differences in the surface areas measured by various suppliers on identical
test specimens. This is due to variations in the test conditions for the absorption equipment. While the
absolute measurements may vary, the direction of SA change should be consistent amongst suppliers.
The total SA reported does not reflect that which is available to feed molecules in the cracking process.
The molecular diameter of N2 used in the absorption test is 4.4 angstroms. It's small size guarantees
that it can reach any pore structure within the catalyst particle. Depending on feed quality, an average
oil molecule can be several hundred angstroms large. The sheer size prevents access to the smaller
pores (and significant SA) in a catalyst particle.
Apparent Bulk Density (ABD)
The ABD represents the ratio of a known catalyst mass and its volume. Fresh catalyst ABD is typically
in the 0.7 to 0.8 gm/cc range. Density is affected by the composition of the catalyst and the
manufacturing style utilized. ECAT ABD will always be higher than that of fresh catalyst. An increase
of 0.1 to 0.2 gm/cc from the fresh starting point is typical. In a normal FCCU operation, the high
regenerator temperature essentially calcines the particles causing some collapse of its structure. Another
factor that will impact ECAT ABD is the turnover ratio from fresh additions.
Turnover Ratio = Catalyst additions (tons/day)/unit inventory (tons)
If the turnover ratio is high, catalyst will remain in the circulating inventory for a shorter time period. It
will have less opportunity for its structure to be calcined and will have a lower ABD when compared to
an operation at a lower turnover rate.
If there is an extreme thermal deactivation event, it is possible to observe ECAT ABD in excess of
1gm/cc. In this situation, the catalyst will have suffered massive losses of surface area and conversion.
Contaminant iron levels can affect ABD. As iron concentration builds on the catalyst, it begins to form
nodules, which protrude from the surface. When there is sufficient point-to-point contact of these
nodules, a given mass of catalyst will now occupy a larger volume and the ABD will begin to decrease.
Some units experience fluidization and circulation issues as iron concentration increases (> 0.9 wt%
total).
Generally speaking, ABD can be used as a qualitative guide in predicting circulation problems. A lower
ABD catalyst is easier to circulate than a heavier one (for constant particle size distribution). Lower
ABD systems can lead to higher catalyst losses as the Transport Disengaging Height (TDH) will
increase and lead to higher solids loading to cyclones.
Two fluidization terms are typically provided in a catalyst report. They are the Fluidization Property
(F-Prop) and the Ratio of the Minimum Bubbling Velocity to Minimum Fluidization Velocity
(Umb/Umf). These take into account, ABD, the mean particle size, and the amount of 0/45 micron.
Fprop = exp^(0.508*F45)/(dp^0.568*ABD^0.663)
Umb/Umf = exp^(0.176*F45)/(dp^0.568*ABD^0..663)
where
F45 = weight fraction of 0/45 micron
dp = catalyst mean diameter, m
ABD = kg/m3
Generally, the higher the Fprop or Umb/Umf ratio, the less likely a unit will experience circulation
issues.
Pore Volume (PV) and Average Pore Diameter (APD)
Water Porosimetry is the standard method used to measure the total void volume in the catalyst
structure. The test is useful mainly when there is a significant change in PV. This could occur during a
period when a severe thermal deactivation event is ongoing.
Mercury Porosimetry is a non standard ECAT test that is used to determine pore size distribution. This
information is useful in studying pore plugging in a catalyst particle
Average Pore Diameter (° A) is defined as:
APD (° A) = 40000*PV/Total SA
APD increases as catalyst activity declines. This is primarily due to the destruction of the zeolite
component of the catalyst, which contributes large quantities of small diameter structures. The
remaining meso structures will have large openings that raise the APD. Units not undergoing severe
thermal deactivation will typically have an APD in the 100 – 120 ° A. When a severe thermal event
occurs, APD can exceed 150 ° A.
Particle Size Distribution (PSD)
Measurement of catalyst PSD can provide invaluable information that is helpful in diagnosing
mechanical problems on the reactor or regenerator side of the FCCU. Most PSD testing today is
performed on MALVERN equipment.
The PSD results will provide an indication of how well the catalyst will fluidize and whether
reactor/regenerator cyclones are operating efficiently. The Fprop and Umb/Umf ratio are both very
dependent on the 0/45 micron fraction and the mean particle diameter of the catalyst. Generally
speaking, if the 0/45 fraction is high then the mean diameter will be low. Units that have these
characteristics are usually not prone to having circulation issues. Some FCCU designs require higher
amounts.
There are many factors that ultimately influence the PSD of a FCCU’s ECAT. Some of these are:
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Fresh catalyst characteristics – Fine, normal, or coarse grade. A fine catalyst grade will have
significantly more 0/40 micron material than a coarse. Its APS will be also lower. Catalyst
suppliers each have their own shipping specifications for the various grades being offered. If an
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FCCU has poor catalyst retention but not necessarily issues with circulation, quite often a
coarse grade of catalyst will be used to help reduce reactor and stack losses. This also helps
reduce operating costs.
Fresh catalyst additions – Fresh additions are the primary source of the lower diameter particles
in the circulating inventory. If fresh additions decline, the 0/40 fraction will decline and APS
increase. There is some generation of 0/40 material due to catalyst attrition as catalyst
circulates in the unit.
Cyclone operation – As charge rate to the FCCU is raised, this will impact cyclone operations.
On the regenerator side, more air is required to satisfy heat demand on the reactor side.
Superficial velocity will increase (constant pressure) along with the minimum transport
disengaging height. This may cause increased catalyst loading to the cyclones and a reduction in
efficiency. On the reactor side, cyclone loading can also increase along with more catalyst
breakage due to higher feed nozzle velocities. More catalyst will be lost to the main fractionator.
Catalyst attrition resistance – As attrition index worsens, this would lead to the generation of
smaller particles due to breakage. If the unit has very good cyclones, the 0/40 will increase and
APS will be reduced.
There are two additional analyses that are critical in further understanding the mechanical integrity of
the FCCU. These are:
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Slurry solids and PSD – The test helps determine the amount of catalyst that is lost from the
reactor to the main fractionator. A sample of slurry is filtered and any carbonaceous material is
burned off leaving only catalyst. The weight of this material determines the wt % solids in the
slurry. The reactor losses can than be calculated by:
Reactor losses (tpd) = 0.01*wt% slurry solids*Slurry BPD*Slurry density (Lbs/BBL)
The solids collected are analyzed for PSD. The analysis of these fines will generate a very
detailed breakdown from sub to several hundred microns sized particles. This will be used to
generate a plot of micron size versus the amount of catalyst in each PSD range. An example of a
commercial unit slurry sample is shown in Figure 1. In this example, a peak will be
observed at a very low particle diameter. This indicates there is an attrition source present. As
the particle diameter increases, there is a second peak that represents the average PSD of the
slurry solids. It is recommended that routine analyses of slurry be taken to establish a baseline
for reactor cyclone operations.
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Regenerator fines – Tertiary cyclones, electrostatic precipitator (ESP), or a wet flue gas scrubber
(WGS) may be employed for stack emissions control. PSD analysis of fines collected from these
sources can help determine trouble spots in the regenerator. A plot generated from the detailed
PSD analysis of regenerator fines is shown in Figure 2. The blue curve represents an operation
with no serious issues with regenerator cyclones. The red curve shown on the same plot
represents a scenario where the efficiency of the secondary cyclones has been reduced. One can
see that the curve has shifted to the right indicating larger particles are leaving the secondary
cyclones. The shift could be due to operational issues (higher air rates from increased feed) or
could be from a degradation of the cyclone itself.
Figure 1 Slurry Fines Differential PSD )
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wt % capture d
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m icrons
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Figure 2 Regenerator Fines PSD
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wt % Captured
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Microns
Chemical Analyses
ECAT chemical properties are determined using X-Ray Flourescence Spectrometry (XRF). The
following elements that can be measured are:
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Al, Bi, Ba, Ca, Cu, Fe, K, Mg, Na, Ni, P, Pb, Rare Earth (La, Ce, Pr, Nd), Sb, Si, Sn,V, Ti, Zn,
Zr
Trending of these elements (and associated oxides) helps to better understand the impact on unit
operations. It also provides a means to estimate the % changeover when a catalyst reformulation is
made, or a switch to another suppliers product, or when a supplemental additive is utilized.
Contaminant Metals
Contaminant metals have three primary effects on FCC catalyst. These are:
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Facilitate accelerated deactivation of the catalyst or additive
Contribute to non-selective cracking reactions
Restrict access of oil molecules to the active cracking sites
The alkali metals (sodium, potassium and calcium) neutralize acid sites and will form a low melting
point eutectic with vanadium that causes zeolite destruction. It is important to note that vanadium has
mobility in the regenerator (full CO burn) until it finds a zeolite to destroy. Generally speaking,
vanadium and sodium are fairly equivalent in their ability to deactivate zeolites. A rule of thumb is a
loss of 1 wt% ECAT conversion for every 350 wppm add on of the contaminants. Each FCCU will
have its own characteristics for deactivation, and is highly dependent on the catalyst formulation and
the actual unit severity. Catalysts formulated with high levels of rare earth oxides will fare better in
contaminated environments as the zeolites have much greater stability.
One must be careful when looking at catalyst contaminants and the possible effects on activity. If a SOx
additive is utilized, it will inflate the final ECAT vanadium level. Vanadium is an integral part along
with the rare earth (CeO) in the additive. The vanadium concentration in the pure additive is quite
high and will inflate the vanadium level observed on the ECAT. This vanadium is chemically tied to
the additive, is not mobile, and does not contribute to any catalyst deactivation. One should work with
their additive supplier to obtain a correction factor to reflect the actual contaminant level of vanadium
on their ECAT. MgO levels of the ECAT will also be affected as this is an integral component of the
additive substrate.
At times, a separate vanadium trap may be used to maintain activity. These materials utilize CaO and
MgO as the trapping components. Again the CaO is bound within the particle structure and will not
cause any zeolite neutralization.
Metals that can cause non-selective reactions are nickel, copper, vanadium and iron. These metals
promote dehydrogenation reactions that increase hydrogen yields and increase the formation of ring
structures that can condense and elevate unit delta coke. As far as rankings of these contaminants,
nickel and copper are roughly equivalent in terms of the ability to generate hydrogen. Vanadium has
approximately 25 % the activity of nickel, and iron is roughly 10 – 15 %.
Antimony passivation is the industry standard for controlling the effects of nickel. It forms an alloy with
nickel and can reduce hydrogen yields by up to 40 %. One should work with their chemical supplier to
determine the appropriate level of antimony injection (25 - 40% of nickel loading). It is important not
to overdose the amount of antimony as it can lead to fouling of the slurry heat exchange circuit. It is
recommended that the slurry be periodically tested for antimony as a means of determining whether
overdosing is occurring. Antimony will also cause the effectiveness of CO promoters to be reduced.
Lead will also lead to the poisoning of CO promoters.
The final role that contaminants can play is interfering with the access of oil molecules to the cracking
sites (zeolite and matrix) in the catalyst. The primary offender is iron that deposits on the surface of the
catalyst during the cracking process. Depending on the catalyst type being used, relatively low levels of
“add-on” iron (0.3 to 0.4 wt%) can result in a loss of conversion. The conversion that is lost primarily
goes to increased slurry production. Most catalyst technologies will all suffer once the “add-on” iron is
over 0.7 wt%. The accepted method of controlling iron is to utilize catalysts with very open pore
architecture and increasing the amount of catalyst additions (a combination of fresh and good quality
ECAT).
As mentioned earlier in this section, monitoring of certain chemical properties can be used to determine
the concentrations of a new or reformulated catalyst that has been introduced to the FCCU. Al2O3,
TiO2, or rare earth level can be used to calculate the changeover, as there usually are sufficient
differences between various suppliers’ products.
The equation used to calculate changeover using TiO2:
Changeover fraction = 1 – (TiO2 new catalyst - TiO2 ECAT)/(TiO2 new catalyst - TiO2
old catalyst)
Methods of determining catalyst changeover can be found on the Rocky Mountain
Salvage and Equipment website in Module 2.