Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED METAL PASSIVATOR/TRAP FOR FCC PROCESSES
FIELD OF THE INVENTION
The present invention provides a metal passivator/trap and methods to
mitigate the deleterious effect of metals on catalytic cracking of hydrocarbon
feedstocks. This objective is achieved through the use of a mixed metal
additive
as a passivator and a trap for metal contaminants.
BACKGROUND OF THE INVENTION
Catalytic cracking is a petroleum refining process that is applied
commercially on a very large scale. About 50% of the refinery gasoline
blending
pool in the United States is produced by this process, with almost ail being
produced using the fluid catalytic cracking (FCC) process. In the FCC process,
heavy hydrocarbon fractions are converted into lighter products by reactions
taking place at high temperatures in the presence of a catalyst, with the
majority
of the conversion or cracking occurring in the gas phase. The FCC hydrocarbon
feedstock (feedstock) is thereby converted into gasoline and other liquid
cracking
products as well as lighter gaseous cracking products of four or fewer carbon
atoms per molecule. These products, liquid and gas, consist of saturated and
unsaturated hydrocarbons.
In FCC processes, feedstock is injected into the riser section of a FCC
reactor, where the feedstock is cracked into lighter, more valuable products
upon
contacting hot catalyst circulated to the riser-reactor from a catalyst
regenerator.
As the endothermic cracking reactions take place, carbon is deposited onto the
catalyst. This carbon, known as coke, reduces the activity of the catalyst and
the
catalyst must be regenerated to revive its activity. The catalyst and
hydrocarbon
vapors are carried up the riser to the disengagement section of the FCC
reactor,
where they are separated. Subsequently, the catalyst flows into a stripping
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section, where the hydrocarbon vapors entrained with the catalyst are stripped
by
steam injection. Following removal of occluded hydrocarbons from the spent
cracking catalyst, the stripped catalyst flows through a spent catalyst
standpipe
and into a catalyst regenerator.
Typically, catalyst is regenerated by introducing air into the regenerator
and burning off the coke to restore catalyst activity. These coke combustion
reactions are highly exothermic and as a result, heat the catalyst. The hot,
reactivated catalyst flows through the regenerated catalyst standpipe back to
the
riser to complete the catalyst cycle. The coke combustion exhaust gas stream
rises to the top of the regenerator and leaves the regenerator through the
regenerator flue. The exhaust gas generally contains nitrogen oxides (N0x),
sulfur oxides (S0x), carbon monoxide (CO), oxygen (02), HCN or ammonia,
nitrogen and carbon dioxide (CO2).
The three characteristic steps of the FCC process that the cracking
catalyst undergoes can therefore be distinguished: 1) a cracking step in which
feedstock is converted into lighter products, 2) a stripping step to remove
hydrocarbons adsorbed on the catalyst, and 3) a regeneration step to burn off
coke deposited on the catalyst. The regenerated catalyst is then reused in the
cracking step.
A major breakthrough in FCC catalysts came in the early 1960s, with the
introduction of molecular sieves or zeolites. These materials were
incorporated
into the matrix of amorphous and/or amorphous/kaolin materials constituting
the
FCC catalysts of that time. These new zeolitic catalysts, containing a
crystalline
aluminosilicate zeolite in an amorphous or amorphous/kaolin matrix of silica,
alumina, silica-alumina, kaolin, clay or the like were at least 1,000-10,000
times
more active for cracking hydrocarbons than the earlier amorphous or
amorphous/kaolin containing silica-alumina catalysts. This introduction of
zeolitic
cracking catalysts revolutionized the fluid catalytic cracking process. New
processes were developed to handle these high activities, such as riser
cracking,
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shortened contact times, new regeneration processes, new improved zeolitic
catalyst developments, and the like.
The new catalyst developments revolved around the development of
various zeolites such as synthetic types X and Y and naturally occurring
faujasites; increased thermal-steam (hydrothermal) stability of zeolites
through
the inclusion of rare earth ions or ammonium ions via ion-exchange techniques;
and the development of more attrition resistant matrices for supporting the
zeolites. The zeolitic catalyst developments gave the petroleum industry the
capability of greatly increasing throughput of feedstock with increased
conversion
and selectivity while employing the same units without expansion and without
requiring new unit construction.
After the introduction of zeolite containing catalysts the petroleum industry
began to suffer from a lack of crude availability as to quantity and quality
accompanied by increasing demand for gasoline with increasing octane values.
The world crude supply picture changed dramatically in the late 1960's and
early
1970's. From a surplus of light-sweet crudes the supply situation changed to a
tighter supply with an ever-increasing amount of heavier crudes, such as
petroleum residues, having a higher sulfur content.
Petroleum resid(ue) is the heavy fraction remaining after distillation of
petroleum crudes at atmospheric pressure (atmospheric resid) or at reduced
pressure (vacuum resid). Resids have a high molecular weight and most often
contain polycyclic aromatic hydrocarbons (PAH's). These molecules have more
than 3-4 aromatic rings and provide the greatest limitation to the conversion
of
the resids into the desired products. This is because of their high stability
and the
lack of sufficient hydrogen in the ring structures to be converted to smaller
more
useful molecules. Moreover, the desired products, e.g. transportation fuels,
are
limited to alkylated single aromatic rings. No matter which type of resid
conversion process is applied, a substantial fraction of resid molecules have
fragments, which can be cracked off to become liquids (or gas) in the
transportation fuels and vacuum oil boiling range. The aromatic cores cannot
be
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cracked under FCC cracking conditions (in order to also remove these species
hydrocracking must be considered). Therefore, one should not try to overly
convert resids because then the selectivity will shift to the
thermodynamically
favored, but lower valued products: coke and gaseous hydrocarbons. As a
result,
gasoline yields are lower in resid FCC processing. These heavier and high
sulfur
crudes and resides present processing problems to the petroleum refiner in
that
these heavier crudes invariably also contain much higher metals with
accompanying significantly increased asphaltic content. Typical contaminant
metals are nickel, vanadium, and iron.
It has long been known that topped crudes, residual oils and reduced
crudes with high contaminating metals levels present serious problems, as
reducing the selectivity to valuable transportation fuels and as deactivating
FCC
catalysts at relatively high metal concentrations, e.g., 5,000-10,000 ppm in
combination with elevated regenerator temperatures. It has also been
particularly
recognized that, when reduced crude containing feeds with high vanadium and
nickel levels are processed over a crystalline zeolite containing catalyst,
and
especially at high vanadium levels on the catalyst, rapid deactivation of the
zeolite can occur. This deactivation manifests itself in substantial measure
as a
loss of the crystalline zeolitic structure. This loss has been observed at
vanadium
levels of 1,000 ppm or less. The loss in the crystalline zeolitic structure
becomes
more rapid and severe with increasing levels of vanadium and at vanadium
levels
about 5,000 ppm, particularly at levels approaching 10,000 ppm complete
destruction of the zeolite structure may occur. The effects of vanadium
deactivation at vanadium levels of less than 10,000 ppm can be reduced by
increasing the addition rate of virgin catalyst, but it is financially costly
to do so.
As previously noted, vanadium poisons the cracking catalyst and reduces its
activity. The literature in this field has reported that vanadium compounds
present in feedstock become incorporated in the coke which is deposited on the
cracking catalyst and is then oxidized to vanadium pentoxide in the
regenerator
as the coke is burned off (M. Xu et al. J. Catal. V. 207 (2), 237-246). At 700-
830
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C in the presence of air and steam, V will be in a surface mobile state in an
acidic form. This V species reacts with cationic sodium, facilitating its
release
from the Y exchange site. The sodium metavanadate thus formed hydrolyzes in
steam to form NaOH and metavanadic acid, which may again react with Na+
cations. V thus catalyzes the formation of the destructive NaOH.
Iron and nickel on the other hand are not mobile. The nickel containing
hydrocarbons deposits on the catalyst and forms nickel oxide in the
regenerator.
in the riser section it may be reduced to metallic nickel, which, like
metallic iron,
catalyzes the dehydrogenation of hydrocarbons to form undesired hydrogen and
coke. High hydrogen yields are undesirable because it can lead to limitations
in
the FCC downstream operations (the wet gas compressor is volume limited).
High amounts of coke can otherwise lead to regenerator air blower constraints,
which may result reduced feed throughput.
Because compounds containing vanadium and other metals cannot, in
general, be readily removed from the cracking unit as volatile compounds, the
usual approach has been to trap and/or passivate these compounds under
conditions encountered during the cracking process. Trapping or passivation
may
involve incorporating additives into the cracking catalyst or adding separate
additive particles along with the cracking catalyst. These additives combine
with
the metals and therefore either act as "traps" or "sinks" for mobile V species
so
that the active component of the cracking catalyst is protected, or
passivators for
immobile Ni and Fe. The metal contaminants are then removed along with the
catalyst withdrawn from the system during its normal operation and fresh metal
trap is added with makeup catalyst so as to affect a continuous withdrawal of
the
detrimental metal contaminants during operation. Depending upon the level of
the harmful metals in the feedstock, the quantity of additive may be varied
relative to the makeup catalyst in order to achieve the desired degree of
metals
trapping and/or passivation.
It is known to incorporate various types of alumina in the FCC catalyst
particle for trapping vanadium and nickel. Examples of this can be found in
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commonly assigned U.S. Pat. Nos. 6,716,338 and 6,673,235, which add a
dispersible boehmite to the cracking catalysts. Upon calcination, the boehmite
is
converted to a transitional alumina phase, which has been found useful in
passivation of nickel and vanadium contaminants in the hydrocarbon feedstock.
Meanwhile, high surface area aluminas may also serve to trap vanadium,
protecting the zeolite, but not to passivate vanadium , so that the level of
contaminant hydrogen and coke remains high.
Vanadium can also be trapped and effectively passivated by using alkaline
earth metal containing traps (Ca, Mg, Ba) and/or Rare earth based traps, see
the
commonly assigned and co-pending application 12/572,777; U.S. Patent
Numbers 4,465779; 4549,548; 5300,496; 7,361,264; W082/00105; GB 218314;
EP A020151 and EP A 0189267. However, these traps are sensitive to sulfur,
and sulfur could block to active sites for vanadium trapping to make them less
effective.
Usage of antimony and antimony compounds as passivators are also well
known in the patent literature including U.S. Pat. Nos. 3,711,422; 4,025,458;
4,031,002; 4,111,845; 4,148,714; 4,153,536; 4,166,806; 4,190,552; 4,198,317;
4,238,362 and 4,255,287. Reportedly, the antimony reacts with nickel to form a
NiSb alloy, which is difficult to reduce under riser conditions thus
deactivting
nickel for catalyzing the formation of hydrogen and coke. This process is
commonly referred to as passivation.
In commonly assigned U.S. 7,678,735, the addition of an ammoxidation
catalyst to the FCC regenerator is described as reducing the emissions of NOx
and NOx precursors during FCC catalyst regeneration. A particular useful
ammoxidation catalyst is a mixed oxide of iron antimony and an additional
metal,
such as Mg, Mn, Mo, Ni, Sn, V or Cu. There is no mention in the patent of the
specific utility of an ammoxidation catalyst in cracking of resids, and in
particular,
in the trapping and/or passivation of nickel and vanadium contaminants which
can poision and/or deactivate the zeolite cracking catalyst.
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SUMMARY OF THE INVENTION
The invention is directed towards an improved metal passivator/trap
comprising a mixed metal oxide of antimony, at least one redox element and an
optional promoter, and use thereof in trapping metal contaminants during the
catalytic cracking of hydrocarbon feedstocks.
BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the nature and advantages of the present
invention, reference should be made to the following detailed description read
in
the conjunction with the accompanying drawings.
Figure I illustrates a reduction of H2 yield in wt% resulted from a FCC
catalyst containing iron/antimony additive and Flex-Teo metallated with 3000
ppm of Ni at various conversion rates.
Figure II illustrates a reduction of H2 yield in wt% resulted from a FCC
catalyst containing iron/antimony additive and Flex-Tec metallated with 3000
ppm of V at various conversion rates.
Figure III illustrate a reduction of H2 yield in wt% with an increase in
amounts of an iron/antimony additive, used as a metal passivator/trap with a
FCC catalyst contaminated with 3000 ppm of Ni and 3000 ppm of V.
DETAILED DESCRIPTION OF THE INVENTION
This invention is directed towards an improved metal passivator/trap and
its use in conjunction with a FCC catalyst to catalyze petroleum oil feeds
containing significant levels of metals contaminants (i.e. Ni and/or V).
Specifically, the metals passivator/trap comprises a mixture of metal oxides
to
immobilize vanadium and nickel, such that the deactivation effect of the FCC
catalyst by the metal contaminants in the hydrocarbon oil feeds is reduced
and/or
the selectivity towards transportation fuels is increased (of all types
utilized in
FCC operations). The invention is particularly useful in the processing of
carbo-
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metallic oil components found in whole crudes, topped crude, residual oil and
reduced crude feeds in a modern fluid catalytic cracking unit.
The process of the present invention comprises the catalytic cracking of
hydrocarbonaceous feedstock using a catalyst mixture which comprises a first
component of which is a cracking catalyst preferably contained within a matrix
material, and a second component of which comprises a mixed metal oxide alloy
as described above having an effectiveness for metals passivation and metals
trapping. The improvement of the present invention resides in the ability of
the
catalyst system to function well even when the feedstock contains high levels
of
metals.
It must be noted that "passivator" and "trap" are not used interchangeably,
and that the mixture of metal oxides of the present invention contains
components that either passivate or trap the metal contaminants. "Passivator"
is
defined as a composition that reduces the activity of unwanted metals, i.e.
nickel
and vanadium to produce contaminant H2 and coke during the FCC process.
While a "trap" is a composition that immobilizes contaminant metals that are
otherwise free to migrate within or between microspheres in the FCC catalyst
mixture, i.e. V and Na. A passivator may not necessarily immobilize V and a
trap
certainly may not passivate V.
Cracking Catalyst
The cracking catalyst component employed in the process of the present
invention can be any cracking catalyst of any desired type having a
significant
activity. Preferably, the catalyst used herein is a catalyst containing a
crystalline
aluminosilicate, preferably ammonium exchanged and at least partially
exchanged with rare earth metal cations, and sometimes referred to as "rare
earth-exchanged crystalline aluminum silicate," i.e. REY, CREY, or REUSY; or
one of the stabilized ammonium or hydrogen zeolites.
Typical zeolites or molecular sieves having cracking activity are used
herein as a catalytic cracking catalyst are well known in the art.
Synthetically
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prepared zeolites are initially in the form of alkali metal aluminosilicates.
The
alkali metal ions are typically exchanged with rare earth metal and/or
ammonium
ions to impart cracking characteristics to the zeolites. The zeolites are
crystalline,
three-dimensional, stable structures containing a large number of uniform
openings or cavities interconnected by smaller, relatively uniform holes or
channels. The effective pore size of synthetic zeolites is suitably between,
but not
limited to, 6 and 15 A in diameter.
Zeolites that can be employed herein include both natural and synthetic
zeolites. These zeolites include gmelinite, chabazite, dachiardite,
clinoptilolite,
faujasite, heulandite, analcite, levynite, erionite, socialite, cancrinite,
nepheline,
[azurite, scolecite, natrolite, offretite, mesolite, mordenite, brewsterite,
ferrierite,
and the like. The faujasites are preferred. Suitable synthetic zeolites which
can
be treated in accordance with this invention include zeolites X, Y, including
chemically or hydrothenmally dealumintated high silica-alumina Y, A, L, ZK-4,
beta, ZSM-types or pentasil, boralite and omega. The term "zeolites" as used
herein contemplates not only aluminosilicates but also substances in which the
aluminum is replaced by gallium or boron and substances in which the silicon
is
replaced by germanium. The preferred zeolites for this invention are the
synthetic
faujasites of the types Y and X or mixtures thereof. Alternatively, a
catalytic
catalyst known as Flex-Tec0 from BASF Corporation is also useful. The amount
of catalytic catalyst used for the present invention is of about 30 to about
95 wt%
of the catalyst mixture. An amount of about 50% to about %90 is also useful.
To obtain a good cracking activity the zeolites have to be in a proper form.
in most cases this involves reducing the alkali metal content of the zeolite
to as
low a level as possible. Further, high alkali metal content reduces the
thermal
structural stability, and the effective lifetime of the catalyst will be
impaired as a
consequence thereof. Procedures for removing alkali metals and putting the
zeolite in the proper form are well known in the art, for example, as
described in
U.S. Pat. No. 3,537,816.
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The zeolite can be incorporated into a matrix. Suitable matrix materials
include the naturally occurring clays, such as kaolin, halloysite and
montmorillonite and inorganic oxide gels comprising amorphous catalytic
inorganic oxides such as silica, silica-alumina, silica-zirconia, silica-
magnesia,
alumina-boria, alumina-titania, and the like, and mixtures thereof. Preferably
the
inorganic oxide gel is a silica-containing gel, more preferably the inorganic
oxide
gel is an amorphous silica-alumina component, such as a conventional silica-
alumina cracking catalyst, several types and compositions of which are
commercially available. These materials are generally prepared as a co-gel of
silica and alumina, co-precipitated silica-alumina, or as alumina precipitated
on a
pre-formed and pre-aged hydrogel. In general, silica is present as the major
component in the catalytic solids present in such gels, being present in
amounts
ranging between about 55 and 100 weight percent. Most often however, active
commercial FCC catalyst matrix are derived from pseudo-boehmites, boehmites,
and granular hydrated or rehydrateable aluminas such as bayerite, gibbsite and
flash calcined gibbsite, and bound with peptizable pseudoboehmite and/or
colloidal silica, or with aluminum chlorohydrol. The matrix component may
suitably be present in the catalyst of the present invention in an amount
ranging
from about 25 to about 92 weight percent, preferably from about 30 to about 80
weight percent of the FCC catalyst.
U.S. Pat. No. 4,493,902, the teachings of which are incorporated herein by
cross-reference, discloses novel fluid cracking catalysts comprising attrition-
resistant, high zeolitic content, catalytically active microspheres containing
more
than about 40%, preferably 50-70% by weight Y faujasite and methods for
making such catalysts by crystallizing more than about 40% sodium Y zeolite in
porous microspheres composed of a mixture of two different forms of chemically
reactive calcined clay, namely, metakaolin (kaolin calcined to undergo a
strong
endothermic reaction associated with dehydroxylation) and kaolin clay calcined
under conditions more severe than those used to convert kaolin to rnetakaolin,
i.e., kaolin clay calcined to undergo the characteristic kaolin exothermic
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sometimes referred to as the spinet form of calcined kaolin. In a preferred
embodiment, the microspheres containing the two forms of calcined kaolin clay
are immersed in an alkaline sodium silicate solution, which is heated,
preferably
until the maximum obtainable amount of Y faujasite is crystallized in the
microspheres.
In practice of the '902 technology, the porous microspheres in which the
zeolite is crystallized are preferably prepared by forming an aqueous slurry
of
powdered raw (hydrated) kaolin clay (A1203: 2Si02: 2H20) and powdered
calcined kaolin clay that has undergone the exotherm together with a minor
amount of sodium silicate which acts as fluidizing agent for the slurry that
is
charged to a spray dryer to form microspheres and then functions to provide
physical integrity to the components of the spray dried microspheres. The
spray
dried microspheres containing a mixture of hydrated kaolin clay and kaolin
calcined to undergo the exotherm are then calcined under controlled
conditions,
less severe than those required to cause kaolin to undergo the exotherm, in
order to dehydrate the hydrated kaolin clay portion of the microspheres and to
effect its conversion into metakaolin, this resulting in microspheres
containing the
desired mixture of metakaolin, kaolin calcined to undergo the exotherm and
sodium silicate binder. In illustrative examples of the '902 patent, about
equal
weights of hydrated clay and spinel are present in the spray dryer feed and
the
resulting calcined microspheres contain somewhat more clay that has undergone
the exotherm than metakaolin. The '902 patent teaches that the calcined
microspheres comprise about 30-60% by weight metakaolin and about 40-70%
by weight kaolin characterized through its characteristic exotherm. A less
preferred method described in the patent, involves spray drying a slurry
containing a mixture of kaolin clay previously calcined to metakaolin
condition
and kaolin calcined to undergo the exotherm but without including any hydrated
kaolin in the slurry, thus providing microspheres containing both metakaolin
and
kaolin calcined to undergo the exotherm directly, without calcining to convert
hydrated kaolin to metakaolin.
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In carrying out the invention described in the '902 patent, the
microspheres composed of kaolin calcined to undergo the exotherm and
metakaolin are reacted with a caustic enriched sodium silicate solution in the
presence of a crystallization initiator (seeds) to convert silica and alumina
in the
microspheres into synthetic sodium faujasite (zeolite Y). The microspheres are
separated from the sodium silicate mother liquor, ion-exchanged with rare
earth,
ammonium ions or both to form rare earth or various known stabilized forms of
catalysts. The technology of the '902 patent provides means for achieving a
desirable and unique combination of high zeolite content associated with high
activity, good selectivity and thermal stability, as well as attrition-
resistance.
Metal cassivator/trap
The metal passivator/trap of the present invention reduces vanadium
attack and nickel dehydrogenation of the cracking catalyst during FCC cracking
of gas oil and resids.
Successful mixed metal oxide catalysts for passivation/trapping in this
invention is compromised of mixtures known as RSbM, wherein R is at least one
redox element selected from Fe2+13+, Ce3114+, Cr2+/3+, U5+/6+,Sn, or Mn, whose
role
is to make lattice oxygen from 02 and then replenish the Sb3.45+ active sites
with
this lattice oxygen, each of which can be further improved by the addition of
at
least one optional promoter, M, selected from oxides of Na, Zn, W, Te, Ca, Ba,
Mo, Mg, Mn, Sn, or Cu.
In particular, the current invention is directed towards using iron-antimony
(FeSb) on a carrier to passivate and/or trap Ni and V, wherein the reaction
with
nickel will take place in the reductive atmosphere of the riser, while the
pick-up of
vanadium will happen in the oxidative environment of the regenerator. The
following equation illustrates this reaction:
Fe2Sb208 + NiO + V205 -) 2FeVO4 + NiSb206
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Although iron is known to be a catalyst poison and leads to formation of
hydrogen and coke, it was surprisingly found that the combination of Fe and Sb
reduces the yield in hydrogen and coke.
The FeSb is prepared with a low surface area to limit H2 formation. The
Sb is mobile such that the Sb can find and passivate the Ni on the catalyst.
Since Sb and V are similar in chemistry (V is also mobile), Fe0xcan react with
V
to form FeV0x. FeV0), is stable as nonsulfating vanadate in the SOx containing
regenerator gas. Without wishing to be bound by any theory of operation, we
believe the FeSb structure faciliates the V to get inside or exchange into the
iron
oxide structure.
The ratio of R:Sb:M is also significant to the catalytic results. The atomic
ratio of R:Sb:M may be in the range of 0.1-10 to 0.1-10 to 0-10, preferably
0.5-3
to 0,5-3 to 0-5.
The metal passivator/trap may be blended with separate zeolite catalyst
particles before being introduced to an FCC unit. Alternatively, the
passivator/trap particles can be charged separately to the circulating
catalyst
inventory in the cracking unit. Typically the metal passivation particles are
present in amounts within the range of 1 to 50% by weight, preferably 2 to 30%
by weight, and most preferably 5 to 25% by weight of the catalyst mixture.
When
used in insufficient amounts, improvements in vanadium and nickel passivation
may not be sufficient. When employed in excessive amounts, cracking activity
and/or selectivity may be impaired, and the operation becomes costly. Optimum
proportions vary with the level of metal contaminants within oil feeds.
Accordingly, with the metal trapping component acts as a scavenger for the
mobile metal contaminants, preventing such contaminants from reaching the
cracking centers of the catalytically active component, the concentration of
the
passivator/trap in the catalyst mixture can be adjusted so as to maintain a
desired catalyst activity and conversion rate, preferably a conversion rate of
at
least 55 percent. The passivator/trap of this invention is particularly useful
for
cracking oil feed containing a level of metal contaminants (i.e. Ni and/or V),
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,
having concentrations in the range of about 0.1ppm of nickel and/or 0.1ppm of
vanadium, to about 200ppm of metal contaminants comprising Nickel, Vanadium,
and/or mixture thereof. However, it must be noted that during the FCC
cracking,
the amount of metal contaminants accumulated on the FCC catalyst can be as
minimally as 300ppm to as high as 40,000ppm of metal contaminants comprising
Nickel, Vanadium, and/or mixture thereof.
Carrier
Inert carrier support material may be used to carry the metal
passivator/trap. The carrier support material is selected from, but not
limited to:
(i) in situ FCC containing zeolites, (ii) calcined kaolins (iii) alumina or
(iv) silica. If
silica is used, zirconium can be added to provide thermal stability. Alumina
such
as Puralox produced by Sasol is useful. Calcined kaolins in the forms of
microspheres are preferred. The method of making carriers used for the current
invention can be found in the commonly assigned U.S. Patent Number
7,678,735, which is incorporated herein by reference. The amount of carrier
used is from about 1% to 99 wt%, preferably 5% to 95 wt% of the catalyst
mixture. The carrier preferably has a surface area of about 5 to 200 m2/g.
Preparation of the Composition of the Present Invention (impreqnation)
The RSbM metal passivator/trap is generally prepared by 1) impregnating
a carrier with an antimony solution; 2) impregnating the processed carrier
from 1)
with a solution of the redox element, such that only a portion of the pore
volume
of the carrier microsphere is filled, and 3) filling the remaining portion of
the pore
volume with a concentrated ammonium hydroxide solution. Accordingly,
antimony chloride or antimony trioxide can be used to prepare the antimony
solution.
The amount of the ammonium used is generally equal to the equivalents
of the nitrates plus chlorides. This provides a neutral pH and the
precipitation of
the dissolved metals inside the microspheres at incipient wetness volume. The
entrained ammonium nitrate salts can be explosive if dried. Therefore, the
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impregnated microspheres should be allowed to react for about 30 minutes, then
slurried with deionized water, filtered and washed to remove the salts,
leaving the
RSbM hydrogels in the microspheres. The hydroxide mixture can then be
calcined. If a promoter (M) is used, the promoter can be combined with the
redox
element in the second impregnation, or the ammonium solution in the third
impregnation, such that each of the solutions remain fully dissolved and that
the
overall equivalents are being adjusted to provide neutrality after both the
acidic
and basic solutions are impregnated.
Alternatively, the redox element can be added directly to the antimony
prior to impregnation onto the inert carrier. In particular, the incorporation
of
metal cations in the antimony structure is carried out in a second synthesis
step
by addition of one or more metal salts (i.e. nitrates, chlorides or acetates)
of the
redox element:
Fe(0Ac)2 + 2 Sb+5(OH)30 + 2 H20 --> Fe+2[Sb+5(OH)40]2 + 2 HOAc
The passivator/trap can also be prepared by introducing the metal salts in
the production process (spray drying of kaolin clay, followed by calcination)
or by
co precipitation of Fe and Sb salts without carrier support, see Allen et al.,
Appl.
Catal. A. Gen., 217 (2001), 31.
Application
The reaction temperature in accordance with the above-described process
is at least about 900 F (482 C). The upper limit can be about 1100 F (593.3 C)
or more. The preferred temperature range is about 950 F to about 1050 F
(510 C to 565.6 C). The reaction total pressure can vary widely and can be,
for
example, about 5 to about 50 psig (0.34 to 3.4 atmospheres), or preferably,
about 20 to about 30 psig (1.36 to 2.04 atmospheres). The maximum riser
residence time is about 5 seconds, and for most charge stocks the residence
time will be about 1.0 to about 2.5 seconds or less. For high molecular weight
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charge stocks, which are rich in aromatics, residence times of about 0.5 to
about
1.5 seconds are suitable in order to crack mono- and di-aromatics and
naphthenes which are the aromatics which crack most easily and which produce
the highest gasoline yield, but to terminate the operation before appreciable
cracking of polyaromatics occurs because these materials produce high yields
of
coke and C2 and lighter gases. The length to diameter ratio of the reactor can
vary widely, but the reactor should be elongated to provide a high linear
velocity,
such as about 25 to about 75 feet per second; and to this end a length to
diameter ratio above about 20 to about 25 is suitable. The reactor can have a
uniform diameter or can be provided with a continuous taper or a stepwise
increase in diameter along the reaction path to maintain a nearly constant
velocity along the flow path.
The weight ratio of catalyst to hydrocarbon in the feed is varied to affect
variations in reactor temperature. Furthermore, the higher the temperature of
the
regenerated catalyst, the less catalyst is required to achieve a given
reaction
temperature. Therefore, a high regenerated catalyst temperature will permit
the
very low reactor density level set forth below and thereby help to avoid back
mixing in the reactor. Generally catalyst regeneration can occur at an
elevated
temperature of about 1250 F (676.6 C) or more. Carbon-on-catalyst of the
regenerated catalyst is reduced from about 0.6 to about 1.5, to a level of
about
0.3 percent by weight. At usual catalyst to oil ratios, the quantity of
catalyst is
more than ample to achieve the desired catalytic effect and therefore if the
temperature of the catalyst is high, the ratio can be safely decreased without
impairing conversion. Since zeolitic catalysts, for example, are particularly
sensitive to the carbon level on the catalyst, regeneration advantageously
occurs
at elevated temperatures in order to lower the carbon level on the catalyst to
the
stated range or lower. Moreover, since a prime function of the catalyst is to
contribute heat to the reactor, for any given desired reactor temperature the
higher the temperature of the catalyst charge, the less catalyst is required.
The
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lower the catalyst charge rate, the lower the density of the material in the
reactor.
As stated, low reactor densities help to avoid back mixing.
It is to be understood that the catalyst mixture described above can be
used in the catalytic cracking of any hydrocarbon charge stock containing
metals,
but is particularly useful for the treatment of high metals content charge
stocks.
Typical feedstocks are heavy gas oils or the heavier fractions of crude oil in
which the metal contaminants are concentrated. Particularly preferred charge
stocks for treatment using the catalyst mixture of the present invention
include
deasphalted oils boiling above about 900 F (482 C) at atmospheric pressure;
heavy gas oils boiling from about 600 F to about 1100 F (343 C to 593 C) at
atmospheric pressure; atmospheric or vacuum tower bottoms boiling above
about 650 F.
The metal passivator/trap may be added to the FCC unit via an additive
loader in the same manner as CO promoters and other additives. Alternatively,
the metal passivator/trap may be pre-blended with the fresh FCC catalyst being
supplied to the FCC unit.
Example 1
Preparing a passivator/trap comprising a mixture of Fe/Sb
1. Antimony Solution:
Weighed an appropriated amount of Sb203 in a 50 ml beaker, filled the beaker
with water up to 30 ml, and then heated mixture up to 70 C. Added H202 and
maintained the mixture at 70 C for 1 hour. Following reaction took place:
Sb203 + 2 H202 + H20 ---> 2 Sb(OH)30
The mixing and heating resulted in a milky white colloidal solution.
2. Impregnating Sb oxide-hydroxide onto an inert support:
Placed a calcined kaolin support in a bowl and drizzled about one third of the
solution from step 1. Wisped the support and repeated the process with the
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remaining two thirds of solution from step 1. Placed the impregnated support
in a Pyrex bowl and dried the support overnight in a vented 100 C oven.
3. Iron Solution:
Weighed Fe(NO3)3.9H20 in a 50 ml beaker, filled the beaker with water up to
22 ml, then mixed the components until Fe(NO3)3.9H20 was dissolved.
4. Impregnate the processed inert support from step 2 with the iron solution
from
step 3, using procedure listed in step 2. The impregnated support was left at
room temperature to allow the components to react for about 30 minutes,
followed by slurried with deionized water, filtered and washed to remove
unincorporated particles or salts. Placed the impregnated support (now
containing both Fe and Sb) in a Pyrex bowl and dry overnight in a vented
100 C oven. Cooled the support to room temperature, then calcined the
support at 400 C for 3hrs in a vented oven.
Example 2
Following the steps from Example 1, passivators/traps of various ratio of
Fe:Sb
were made:
Table 1
Sample A
Constituents Fe/Sb Fe/Sb Fe/Sb
Atomic Ratio 1:2 1:1 2:1
Support Puralox Puralox Puralox
g of Support 100 100 100
Total Mox wt % 5 5 5
Wt% Sb204 target 3,97 3.29 2.45
g of Sb203 3.76 3.12 2.33
g of H202 8.44 7.00 5.23
Wt0/0 Fe203 target 1,03 1.71 2.55
g of Fe(NO3)3 9H20 5.49 9.1 13.57
g of Water 45.5 45.5 45.5
% Distribution after calcination
at 400C for 3 hours
Fe203 1.03 1.71 2.46
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Sb204 3.30 2.84 2.32
Table 2
Sample D E F
Constituents Fe/Sb Fe/Sb Fe/Sb
Atomic Ratio 1:2 1:1 2:1
Calcined Calcined Calcined
Support Kaolin Kaolin Kaolin
g of Support 100 100 100
Total Mox wt % 5 5 5
Wt% Sb204 target 3.97 3.29 2,45
g of Sb203 4,14 3.43 2.56
g of H202 8.44 7.00 5.23
Wt% Fe203 target 1.03 1.71 2.55
g of Fe(NO3)3 9H20 5.49 9.1 13.57
g of Water 45.5 45.5 45.5
, 0/0 Distribution after calcination at 400C for 3 hours
Fe203 1.71 2.43 3,15
Sb204 3,08 1.95 1,35
Table 3
Sample G H I
Constituents Fe/Sb Fe Sb
Atornic Ratio 1:1 N/A N/A
Calcined Calcined Calcined
Support Kaolin Kaolin Kaolin
g of Support 100 100 100
Total Mox wt % 5 5 5
Sb204 target wt% 3.29 N/A 5.00
Sb203 9 3.12 N/A 4.74
H202 9 6.99 N/A 10,62
Fe203 target wt% 1.71 5.00 N/A
Fe(NO3)3 9H20 g 9.10 26.63 N/A
Water g 22 22 22
Analysis (wt%)
Sb204 2.99 N/A 3.68
Fe203 2.45 5.59 N/A
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The passivators/traps were then incorporated within pre-metallated FCC
catalysts. The combinations were the steamed at 1450 F for 4 hours in a flow
of
90% steam / 10% air prior to testing:
Table 4
Sample 3 K L M
FCC Flex-Tec/3000 Flex-Tee/3000 Flex-Tec/3000 Flex-Tec/3000
Catalyst ppm Ni ppm Ni ppm V ppm V
wt% 35 35 35 35
Inert Calcined Kaolin Calcined Kaolin Calcined Kaolin Calcined
Kaolin
wt% 65 50 50 50
Passivator Not Added Sample G Not Added Sample G
wt% N/A 15 N/A 15
Table 5
Sample N 0 P Q R
Flex-Tec/
Flex-Tec/ Flex-Tec/ 3000 Flex-Tec/ Flex-Tec/
3000 ppm 3000 ppm ppm Ni + 3000 ppm 3000 ppm
FCC Ni + 3000 Ni + 3000 3000 Ni + 3000 Ni + 3000
Catalyst ppm V ppm V ppm V ppm V ppm V
wt% 60 60 60 60 60
Calcined Calcined Calcined Calcined
Calcined
Inert Kaolin Kaolin Kaolin Kaolin Kaolin
wt% 25 30 35 39 40
Passivator Sample G Sample G Sample G Sample G Sample G
wt% 15 10 5 1 0
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Example 3
Metal passivators/traps comprising promoters were made:
1. Impregnation of 2.5% Sb203: 2.5% Fe203: 1% Mn02 on calcined kaolin:
Dissolved first 3.91g of SbCI3 in 25m1 deionized H20 and 15m1 of HCI (37%),
then
mixed in 12.62g Fe(NO3)3.9H20 and 3.53g of Mn(NO3)3.4H20 . Applied 40m1 of
the mixture onto 100g of calcined kaolin, mixed well, dried the calcined
kaolin at
100 C overnight (16 hours). Calcined the impregnated carrier further at 400 C
for 3 hours in air. The % yield was: 3.0862% of Fe203, 1.0944% of Mn02, and
2.2779% Sb203.
2. Impregnation of 2.5%Sb203: 2.5% Fe203: 1% W03 on calcined kaolin:
Dissolved first 3.91g of SbCI3 in 10m1 of 1-1C1 (37%) and 20m1 of deionized
H20,
secondly 1.52g of Ammonium Metatungstate with 5m1fo HCI, then 12.65g of
Fe(NO3)3.9H20. Applied 30m1 of the mixture onto 100g of calcined kaolin, mixed
well, dried the calcined kaolin at 100 C overnight (16 hours). Calcined the
impregnated carrier further at 400 C for 3 hours in air. The % yield was 3.37%
of
Fe203, 1.22% of W03, and 2.68% of Sb203.
3. Impregnation of 2.5%Sb203: 2.5% Fe203: 1% ZnO on calcined kaolin:
Dissolved 3.91g SbCI3 in 20m1 of HC1(37%) and 15m1 deionize H20, then added
12.62g of Fe(NO3)3.9H20 and 3.62g of Zn(NO3)2. Applied 35m1 of the mixture
onto 100g of calcined kaolin, mixed well, dried the calcined kaolin at 100 C
overnight (16 hours). Calcined the impregnated carrier further at 400 C for 3
hours in air, The % yield was 3.18% of Fe203, 0.843% of ZnO, and 2.63% of
Sb203.
4. Impregnation of 2.5%Sb203: 2.5% Fe203: 1% SnO on calcined kaolin:
Dissolved first 3.91g of SbCI3 inlOml HCI(37%) then added 12.65g of
Fe(NO3)3.9H20 and 1.675g of SnC12=2H20, balanced with 20m1 of deionized H20.
Applied 30m1 of the mixture onto 100g of calcined kaolin, mixed well, dried
the
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calcined kaolin at 100 C overnight (16 hours). Calcined the impregnated
carrier
further at 400 C for 3 hours in air. The % yield was 2.78% of Fe203, 0.743% of
SnO, and 2.65% of Sb203.
5. Impregnation of 2.5% Sb203: 2.5% Fe203: 1% Mo03 on calcined kaolin:
Dissolved first 3.91g of SbC13 in 20m1 deionized 1-120 and 10m1 of HC1(37%),
then
12.65g Fe(NO3)3-9H20, and 1.43g of (NH4)2Mo04. Applied 30m1of the mixture
onto 100g of calcined kaolin, mixed well, dried the calcined kaolin at 100 C
overnight (16 hours). Calcined the impregnated carrier further at 400 C for 3
hours in air. The % yield was: 3.03% of Fe203, 1.36% of Mo03, and 2.59%
Sb203.
Example 4
Flex-Tec in samples J and K was metallated to 3000 ppm of nickel, by adding an
appropriated amount of nickel and cyclohexane, mixed and poured onto a
cordierite tray to air dry, then burned at 315 C and calcined at 593 C. The
passivators/traps were then incorporated within pre-metallated FCC catalysts.
The combinations were the steamed at 1450 F for 4 hours at 90% steam 110%
air prior to testing.
The hydrogen yield was measured on an ACE fluid-bed hydrocarbon
cracking unit using a hydrocarbon oil feed. It can be shown in Figure 1 that
at
various conversion rates of the catalyst, the hydrogen yield in wt% for sample
K
was 15% lower than sample J, the control sample.
Flex-Tec in samples L and M was metallated to contain 3000 ppm of vanadium,
by adding an appropriated amount of vanadium and cyclohexane, mixed and
poured onto a cordierite tray to air dry, then burned at 315 C and calcined at
593 C. The passivators/traps were then incorporated within pre-metallated FCC
catalysts. The combinations were the steamed at 1450 F for 4 hours at 90%
steam / 10% air prior to testing.
The hydrogen yield was measured on an ACE fluid-bed hydrocarbon
cracking unit using a hydrocarbon oil feed. It can be shown in Figure 2 that
at
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various conversion rates of the catalyst, the hydrogen yield in wt% for sample
M
was 20% lower than sample J, the control sample.
Flex-Tec in samples N, 0, P, Q and R was metallated to 3000 ppm of
nickel and 3000 ppm of vanadium, by adding an appropriated amount of
vanadium, nickel, and cyclohexane, mixed and poured onto a cordierite tray to
air
dry, then burned at 315 C and calcined at 593 C. The rate of hydrocarbons
being stripped and the amounts of hydrocarbon yields were measured on an
ACE fluid-bed hydrocarbon cracking unit using a hydrocarbon oil feed. Table 6
shows the hydrocarbon yields for samples P and T at 75% of conversion rate:
Table 6
FCC cracking for zeolite catalyst vs. zeolite catalyst+Fe/Sb passivator/trap
No passivator/trap added Fe/Sb passivator/trap added
(Sample R) (Sample N)
Conversion 75.0 75.0
Cat/Oil 11.3 8.8
Acty C/0=5 1.7 1.9
Yields in wt%
H2 1.49 0.88
Total C4- 20.3 21.8
Gasoline 42.4 45.7
LCO 15.3 13.7
HCO 9.7 11.3
Coke 12.3 7.5
it can be shown that H2 and coke were significantly reduced (>30%), while
the desirable products (gasoline and LPG) were increased in yield. Figure 3
was
plotted based on a 70% conversion rate of Samples R, Q, P, 0, and N vs. the
amount of H2 yielded in wt%. It can be shown in Figure 3 that as the amount of
Fe/Sb passivator/trap increased (Samples N, 0, P and Q), the amount of H2
yield
ultimately decreased about 28% from the control (Sample R).
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