U.S. patent application number 09/978180 was filed with the patent office on 2003-05-15 for fcc catalysts for feeds containing nickel and vanadium.
Invention is credited to Dodwell, Glenn W., Harris, David H., Lerner, Bruce, Madon, Rostam, Stockwell, David, Xu, Mingting.
Application Number | 20030089640 09/978180 |
Document ID | / |
Family ID | 25525844 |
Filed Date | 2003-05-15 |
United States Patent
Application |
20030089640 |
Kind Code |
A1 |
Madon, Rostam ; et
al. |
May 15, 2003 |
FCC catalysts for feeds containing nickel and vanadium
Abstract
A fluid catalytic cracking catalyst made from microspheres that
initially contain kaolin, a dispersible boehmite alumina and a
sodium silicate or silica sol binder. The kaolin portion contains
hydrous kaolin and optionally kaolin which has been calcined
through its characteristic exotherm. Calcination of the hydrous
clay to metakaolin and formation of in-situ zeolite by treatment
with sodium silicate yields a catalyst containing Y-faujasite and
transforms the dispersible boehmite into a transitional alumina
which contains a gamma alumina phase. The transitional alumina may
contain a delta alumina phase as well. The catalyst can be used to
crack resid or resid-containing feeds as the alumina phase formed
from the dispersible boehmite passivates nickel and vanadium
contaminants.
Inventors: |
Madon, Rostam; (Flemington,
NJ) ; Harris, David H.; (Mountainside, NJ) ;
Xu, Mingting; (Edison, NJ) ; Stockwell, David;
(Middlesex, NJ) ; Lerner, Bruce; (Princeton
Junction, NJ) ; Dodwell, Glenn W.; (Bartlesville,
OK) |
Correspondence
Address: |
Stuart D. Frenkel, Esq.
Liniak, Berenato, Longacre & White
Ste 240
6550 Rock Spring Drive
Bethesda
MD
20817
US
|
Family ID: |
25525844 |
Appl. No.: |
09/978180 |
Filed: |
October 17, 2001 |
Current U.S.
Class: |
208/122 ; 502/60;
502/63; 502/64; 502/65; 502/68; 502/79 |
Current CPC
Class: |
B01J 2229/64 20130101;
B01J 29/088 20130101; C10G 2300/107 20130101; B01J 2229/42
20130101; B01J 29/084 20130101; B01J 37/0045 20130101 |
Class at
Publication: |
208/122 ; 502/60;
502/63; 502/64; 502/65; 502/68; 502/79 |
International
Class: |
C10G 011/02; B01J
029/04; B01J 029/06 |
Claims
We claim:
1. A zeolitic fluid catalytic cracking catalyst which passivates
nickel and vanadium during catalytic cracking comprising: (a) at
least about 15% by weight Y-faujasite crystallized in-situ from a
metakaolin-containing calcined microsphere; and (b) alumina
obtained by the calcination of a dispersible boehmite contained in
said microsphere.
2. The fluid catalytic cracking catalyst of claim 1, wherein said
alumina comprises a transitional gamma phase.
3. The fluid catalytic cracking catalyst of claim 1, wherein said
alumina comprises a combination of transitional gamma and delta
phases.
4. The fluid catalytic cracking catalyst of claim 1, wherein said
dispersible boehmite is characterized by having at least 90% of
said boehmite disperse into particles less than about 1 micron in
an acidic media of pH less than about 3.5.
5. The fluid catalytic cracking catalyst of claim 1, wherein said
microsphere further contains kaolin calcined through its
characteristic exotherm.
6. The fluid catalytic cracking catalyst of claim 5, wherein said
kaolin calcined through its characteristic exotherm is spinel.
7. The fluid catalytic cracking catalyst of claim 5, wherein said
kaolin calcined through its characteristic exotherm comprises
mullite.
8. The fluid catalytic cracking catalyst of claim 5, wherein said
kaolin calcined through its characteristic exotherm comprises both
spinel and mullite.
9. The fluid catalytic cracking catalyst of claim 1, wherein said
Y-faujasite comprises at least about 40% by weight of said
catalyst.
10. The fluid catalytic cracking catalyst of claim 1, wherein said
Y-faujasite is ion-exchanged to reduce the sodium content of said
catalyst to less than 0.7% by weight Na.sub.2O.
11. The fluid catalytic cracking catalyst of claim 1, wherein said
Y-faujasite is ion-exchanged to reduce the sodium content of said
catalyst to less than 0.5% by weight Na.sub.2O.
12. The fluid catalytic cracking catalyst of claim 10, wherein said
Y-faujasite is the product of ammonium exchange.
13. The fluid catalytic cracking catalyst of claim 10, wherein said
Y-faujasite is exchanged with rare earth cations to provide a rare
earth level as REO of 0.1 to 12 wt. %.
14. The fluid catalytic cracking catalyst of claim 10, comprising
rare earth levels, expressed as rare earth oxide, REO of 0.5 to 9
wt. %.
15. The fluid catalytic cracking catalyst of claim 1, wherein said
Y-faujasite has a crystalline unit cell size of less than 24.7
.ANG..
16. The fluid catalytic cracking catalyst of claim 5, wherein said
calcined microspheres comprise 15 to 85% by weight metakaolin,
5-70% by weight kaolin calcined through its characteristic exotherm
and 10-40% by weight of said alumina.
17. The fluid catalytic cracking catalyst of claim 16, wherein said
alumina comprises a transitional gamma phase.
18. The fluid catalytic cracking catalyst of claim 16, wherein said
alumina comprises a combination of transitional gamma and delta
phases.
19. The fluid catalytic cracking catalyst of claim 17, wherein said
dispersible boehmite is characterized by having at least 90% of
said boehmite disperse into particles less than about 1 micron in
an acidic media of pH less than about 3.5.
20. A method of making a zeolitic fluid catalytic cracking catalyst
comprising the steps of: (a) forming an aqueous slurry containing
on a dry basis about 15 to 85 parts by weight hydrated kaolin,
metakaolin or mixtures thereof, about 5 to 50 parts by weight
dispersible boehmite, about 0-85 parts by weight kaolin that has
been calcined through its characteristic exotherm, and 5-35%
silicate binder; (b) spray drying the aqueous slurry to obtain
microspheres; (c) calcining the microspheres obtained in step (b)
at a temperature and for a time sufficient to convert the hydrated
kaolin in the microspheres substantially to metakaolin, but
insufficient to cause metakaolin or hydrated kaolin to undergo the
characteristic kaolin exotherm; (d) mixing the microspheres
obtained in step (c) with sodium silicate, sodium hydroxide and
water to obtain an alkaline slurry; and (e) heating the alkaline
slurry of calcined microspheres to a temperature and for a time
sufficient to crystallize at least about 15% by weight Y-faujasite
in the microspheres, said Y-faujasite being in the sodium form.
21. The method of claim 20, wherein at least 40% by weight
Y-faujasite is crystallized in the microspheres in step (e).
22. The method of claim 20, wherein Y-faujasite seeds are added to
the mix of step (d).
23. A method of claim 20 including the steps of: (f) separating the
micropsheres containing at least 15% by weight Y-faujasite from at
least a major portion of its mother liquor; (g) replacing sodium
cations in the microspheres separated in step (e) with ammonium
ions or ammonium ions and thereafter rare earth ions; (h) calcining
the microspheres from step (g) to facilitate release of sodium
ions; (i) further exchanging the microspheres with ammonium ions to
reduce Na.sub.2O content to below 1%; and (j) further calcining the
microspheres to reduce the unit cell size of the zeolite.
24. The method of claim 23 in which the rare earth content
expressed as rare earth oxide, REO, is between 0.1 wt. % and 12 wt.
%.
25. The method of claim 24 in which the rare earth content
expressed as rare earth oxide, REO, is between 0.5 wt. % and 9 wt.
%.
26. The method of claim 23 in which the sodium content expressed as
Na.sub.2O is less than 0.7 wt. %.
27. The method of claim 23 in which the sodium content expressed as
Na.sub.2O is less than 0.4 wt. %.
28. The method of claim 23 in which the sodium content expressed as
Na.sub.2O is less than 0.3 wt. %.
29. The method of claim 20, wherein said dispersible boehmite is
characterized by having at least 90% of said boehmite disperse into
particles less than about 1 micron.
30. The method of claim 20, wherein said aqueous slurry in step (a)
is formed from a first slurry of said kaolin and binder and a
second slurry of said dispersible boehmite.
31. The method of claim 30, wherein said second slurry comprises
said dispersible boehmite peptized in acid.
32. The method of claim 20, wherein said aqueous slurry in step (a)
contains 5-60 wt. % kaolin calcined through the exotherm.
33. The method of claim 20, wherein said binder in step (a) is
sodium silicate.
34. The method of claim 20, wherein said binder in step (a) is
silica sol.
35. A method of cracking a resid containing at least 2000 ppm of Ni
and V metals comprising contacting said resid with the catalyst of
claim 1.
36. A method of cracking a resid containing at least 2000 ppm of Ni
and V metals comprising contacting said resid with the catalyst of
claim 5.
Description
FIELD OF THE INVENTION
[0001] This invention relates to catalysts useful for cracking
heavy hydrocarbon feed stocks, such as resids, that contain high
levels of nickel and vanadium contaminants. In particular, the
invention is directed to improvements in zeolitic fluid cracking
catalysts (FCC) produced by an in-situ reaction wherein preformed
microspheres obtained by calcining microspheres composed of a
mixture of hydrated kaolin, a dispersible boehmite alumina, binder,
and kaolin clay calcined through its characteristic exotherm,
undergo chemical reaction with sodium silicate solution to form
crystals of zeolite and a porous silica/alumina matrix. The
catalyst is metals tolerant, has good catalytic selectivity and is
especially useful as a catalyst for cracking residuum (resid) and
resid-containing feeds.
BACKGROUND OF THE INVENTION
[0002] Since the 1960's, most commercial fluid catalytic cracking
catalysts have contained zeolites as an active component. Such
catalysts have taken the form of small particles, called
microspheres, containing both an active zeolite component and a
non-zeolite component in the form of a high alumina, silica-alumina
matrix. The non-zeolitic component or matrix is known to perform a
number of important functions, relating to both the catalytic and
physical properties of the catalyst. Oblad described those
functions as follows:
[0003] "The matrix is said to act as a sink for sodium in the sieve
thus adding stability to the zeolite particles in the matrix
catalyst. The matrix serves the additional function of: diluting
the zeolite; stabilizing it towards heat and steam and mechanical
attrition; providing high porosity so that the zeolite can be used
to its maximum capacity and regeneration can be made easy; and
finally it provides the bulk properties that are important for heat
transfer during regeneration and cracking and heat storage in
large-scale catalytic cracking." A. G. Oblad Molecular Sieve
Cracking Catalysts, The Oil And Gas Journal, 70, 84 (Mar. 27,
1972).
[0004] In prior art fluid catalytic cracking catalysts, the active
zeolitic component is incorporated into the microspheres of the
catalyst by one of two general techniques. In one technique, the
zeolitic component is crystallized and then incorporated into
microspheres in a separate step. In the second technique, the
in-situ technique, microspheres are first formed and the zeolitic
component is then crystallized in the microspheres themselves to
provide microspheres containing both zeolitic and non-zeolitic
components.
[0005] For many years a significant proportion of commercial FCC
catalysts used throughout the world have been made by in-situ
synthesis from precursor microspheres containing kaolin that had
been calcined at different severities prior to formation into
microspheres by spray drying.
[0006] 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
metakaolin, i.e., kaolin clay calcined to undergo the
characteristic kaolin exothermic reaction, sometimes referred to as
the spinel 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.
[0007] 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
(Al.sub.2O.sub.3:2SiO.sub.2:2H.sub.2O) and powdered calcined kaolin
clay that has undergone the exotherm together with a small 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
results 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.
[0008] 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.
[0009] The aforementioned technology has met widespread commercial
success. Because of the availability of high zeolite content
microspheres which are also attrition-resistant, custom designed
catalysts are now available to oil refineries with specific
performance goals, such as improved activity and/or selectivity
without incurring costly mechanical redesigns. A significant
portion of the FCC catalysts presently supplied to domestic and
foreign oil refiners is based on this technology.
[0010] U.S. Pat. Nos. 5,023,220 and 5,395,809, assigned to the
present assignee are further examples of patents which teach the
formation of catalytic FCC microspheres from mixtures of hydrous
kaolin, metakaolin and kaolin that has been calcined through the
characteristic exotherm. These mentioned patents are herein
incorporated by reference in their entirety.
[0011] Improvements in cracking activity and gasoline selectivity
of cracking catalysts do not necessarily go hand in hand. Thus, a
cracking catalyst can have outstandingly high cracking activity,
but if the activity results in a high level of conversion to coke
and/or gas at the expense of gasoline the catalyst will have
limited utility. Catalytic cracking activity in present day FCC
catalysts is attributable to both the zeolite and non-zeolite
(e.g., matrix) components. Zeolite cracking tends to be gasoline
selective. Matrix cracking tends to be less gasoline selective.
After appropriate ion-exchange treatments with rare earth cations,
high zeolite content microspheres produced by the in situ procedure
described in the '902 patent are both highly active and highly
gasoline selective. As zeolite content of these unblended
microspheres is increased, both activity and selectivity tend to
increase. This may be explained by the decrease in matrix content
with increase in zeolite content and the decreasingly prominent
role of nonselective matrix cracking.
[0012] In recent years the oil refining industry has shifted to
processing a larger quantity of resid due to the changing product
slate and price structure of crude oil. Since the early 1980's many
refiners have been processing at least a portion of residual oil as
a feedback in their units and several now run a full residual oil
cracking program. Processing resid can drastically alter yields of
valuable products in a negative direction relative to a light
feed.
[0013] Several factors are important to resid catalyst design. It
is highly favorable if the catalyst can upgrade bottoms, minimize
coke and gas formation, maximize catalyst stability, and minimize
deleterious contaminant selectivity due to metal contaminants in
resid feedstocks such as nickel and vanadium. While in-situ
catalysts are commercially valuable, none of these in-situ
catalysts possessed such a combination of properties when used to
crack resid feedstocks.
[0014] Following the inception of catalytic cracking by Houdry in
the early 1900's where an acid treated clay was used, the first
revolution in the art of catalyst technology was the use of
synthetic silica-alumina. The use of silica-alumina which had much
more acidic Bronsted and Lewis acid sites increased the cracking
activity and selectivity of the process over the clays. The second
revolution came with the advent of zeolites and the discovery that
they could be applied to cracking. The clear advantage of the
zeolite was that the non-selective cracking to coke and gas was
greatly reduced owing to the discrete pore structure of the
crystalline zeolite and the shape selective chemistry which they
provided. With the thrust in modern refining to limit the amount of
coke and gas so as to maximize gasoline production the designed use
of silica-alumina in cracking catalysts has decreased (see A. A.
Avidan in: Fluid Catalytic Cracking: Science and Technology.
Studies in Surface Science and Catalysis, Vol. 76. Magee, J. S. and
Mitchell, M. M. Eds.; Elsevier, Amsterdam; 1993). The use of added
aluminas has also found merit in helping to boost a catalyst's
activity since pure aluminas also posses acidic sites. The relative
activity of a catalyst is roughly proportional to the total
quantity of acid sites present. Unfortunately alumina
characteristically contains a large fraction of Lewis acid sites
relative to Bronsted type sites. Lewis sites have been shown to be
largely involved in the chemistry of hydride abstraction and coke
formation (see Mizuno, et al. in Bulletin of the Chemical Society
of Japan, Vol. 49, 1976, pp. 1788-1793).
[0015] Fluid cracking catalysts which contain silica-alumina or
alumina matrices are termed catalysts with "active matrix".
Catalysts of this type can be compared with those containing
untreated clay or a large quantity of silica and which are termed
"inactive matrix" catalysts. Work done by Otterstedt, et al.
(Applied Catalysts, Vol. 38, 1988, pp. 143-155.) clearly shows the
disadvantage of active matrices for coke and gas production
sometimes producing twice as much as the inactive formulation.
[0016] Aluminas have long been used in hydrotreating and reforming
catalyst technology (see P. Grange in Catalysis Reviews-Science and
Engineering, Vol. 21, 1980, p. 135). Aluminas, and particularly
transition aluminas, in addition to displaying acidic character
also posses high surface areas typically on the order of several
hundred meters squared per gram. They may be well suited for
catalyst applications such as those mentioned where a metallic
component is to be supported on the substrate surface (alumina in
this case). The high surface area of the host material above allows
for a more uniform, dispersed arrangement of the metal. This leads
to smaller metal crystallites and helps to minimize metal
agglomeration. Metal agglomeration or sintering is a leading cause
of loss of activity since the activity for metal catalyzed reaction
is proportional to the exposed metal surface area. When the metal
"balls up" metallic surface area is lost and so is activity. In
relation to catalytic cracking, despite the apparent disadvantage
in selectivity, the inclusion of aluminas or silica-alumina has
been beneficial in certain circumstances. For instance when
processing a hydrotreated/demetallated vaccum gas oil (hydrotreated
VGO) the penalty in non-selective cracking is offset by the benefit
of cracking or "upgrading" the larger feed molecules which are
initially too large to fit within the rigorous confines of the
zeolite pores. Once "precracked" on the alumina or silica-alumina
surface, the smaller molecules may then be selectively cracked
further to gasoline material over the zeolite portion of the
catalyst. While one would expect that this precracking scenario
might be advantageous for resid feeds they are unfortunately
characterized for the most part as being heavily contaminated with
metals such as nickel and vanadium and to a lesser extent, iron.
When a metal such as nickel deposits on a high surface area alumina
such as those found in typical FCC catalysts, it is dispersed and
participates as highly active centers for the catalytic reactions
which result in the formation of contaminant coke (contaminant coke
refers to the coke produced discretely from reactions catalyzed by
contaminant metals). This additional cokes exceeds that which is
acceptable by refiners.
[0017] Loss of activity or selectivity of the catalyst may also
occur if the metal contaminants such as nickel, vanadium, from the
hydrocarbon feedstock, deposit onto the catalyst. These metal
contaminants are not removed by standard regeneration (burning) and
contribute markedly to undesirably high levels of hydrogen, dry gas
and coke and reduce significantly the amount of gasoline that can
be made. Contaminant metal levels are particularly high in certain
feedstocks, especially the more abundant heavier crudes. As oil
supplies dwindle, successful economic refining of these heavier
crudes becomes more urgent. In addition to reduced amounts of
gasoline, these contaminant metals contribute to much shorter life
cycles for the catalyst and an unbearably high load on the vapor
recovery system. Deposited nickel and vanadium species have an
intrinsic dehydrogenation activity which leads to the formation of
coke and gas, two undesirable products. Furthermore, vanadium
assists in destroying the crystallinity of the sieve. This leads to
a loss of catalytic activity and to the formation of certain
silica-alumina species which tend to promote the formation of coke
and gas. The increased expense of refining metal-contaminated
feedstocks due to the aforementioned factors lays a heavy economic
burden on the refiner. Therefore, much effort has been spent in
finding means to modify the catalyst or feedstock in such a way as
to passivate the aforementioned undesirable effects of the metal
contaminants.
[0018] Commonly assigned U.S. Pat. No. 5,559,067 addresses the
problem of providing a resid FCC catalyst made by the in-situ route
which can upgrade bottoms, minimize coke and gas formation,
maximize catalyst stability and minimize deleterious contaminant
selectivity due to contaminant metals. The resid FCC catalyst of
the patent achieves metal tolerance in a manner considered to be
relatively inexpensive to practice and does not result in the use
of environmentally toxic additives such as the use of prior art
technologies for achieving metals tolerance such as those involving
the use of antimony. In accordance with the patent, microspheres
comprising hydrous kaolin clay, gibbsite (alumina trihydrate),
spinel, and a silica sol binder are prepared, the microspheres
calcined to convert the hydrous kaolin component to metakaolin and
the calcined microspheres reacted with an alkaline sodium solution
into crystallized zeolite Y and ion exchanged.
[0019] During the conversion of hydrous kaolin to metakaolin,
gibbsite also undergoes transformation to a transition alumina.
Transition alumina may be defined as any alumina which is
intermediate between the thermodynamically stable phases of
gibbsite, bayerite, boehmite, and nordstandite on one end of the
spectrum and alpha alumina or corrundum on the other. Such
transition aluminas may be viewed as metastable phases. A scheme of
the transformation sequence can be found in the text: Oxides and
Hydroxides of Aluminum by K. Wefers and C. Misra; Alcoa Technical
Paper No. 19, revised; copyright Aluminum Company of America
Laboratories, 1987.
SUMMARY OF THE INVENTION
[0020] A novel, in-situ fluid cracking catalyst is provided which
is useful in cracking feeds that contain nickel and vanadiaum. The
FCC catalyst of this invention is made from microspheres which
initially contain kaolin, binder, and a dispersible boehmite
alumina. The microsphere is subsequently converted using standard
in-situ Y zeolite growing procedures to make a Y-containing
catalyst. Exchanges with ammonium and rare earth cations with
appropriate calcinations provides an FCC catalyst that contains a
transitional alumina obtained from the boehmite. This transitional
alumina contains the gamma phase although delta alumina may also be
present.
[0021] Preparation of the novel fluid cracking catalyst, in
accordance with an aspect of this invention, involves an initial
step of preparing microspheres comprising hydrous kaolin clay
and/or metakaolin, a dispersible boehmite (Al.sub.2O.sub.3,
H.sub.2O), optionally spinel and/or mullite, and a sodium silicate
or silica sol binder. The microspheres are calcined to convert any
hydrous kaolin component to metakaolin. The calcination process
transforms the dispersible boehmite into a transitional gamma-delta
alumina phase. The calcined microspheres are reacted with an
alkaline sodium silicate solution to crystallize zeolite Y and
ion-exchanged. The transitional alumina, gamma-delta phase that
results from the dispersible boehmite during the preparative
procedure and which forms the matrix of the final catalyst,
passivates the Ni and V that are deposited on to the catalyst
during the cracking process, especially during cracking of heavy
residuum feeds. This results in a substantial reduction in
contaminant coke and hydrogen yields. Contaminant coke and hydrogen
arise due to the presence of Ni and V and reduction of these
byproducts significantly improves FCC operation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a graph comparing the hydrogen make of cracking
catalysts of the present invention and control catalysts upon
cracking a heavy aromatic feed.
[0023] FIG. 2 is a graph comparing the coke make of cracking
catalysts of the present invention and control catalysts upon
cracking a heavy aromatic feed.
DETAILED DESCRIPTION OF THE INVENTION
[0024] Catalysts of the invention are made by spray drying a feed
mixture of hydrated kaolin, boehmite alumina and silica sol or
sodium silicate binder. The spray dried microspheres are washed and
then calcined to form precursor porous microspheres in which any of
the hydrous kaolin is converted to metakaolin. It is preferred that
calcination be conducted at temperatures below that which would
cause any kaolin present to undergo the characteristic kaolin
exothermic reaction to spinel or mullite. Optionally, the feed
mixture to the spray drier may include spinel or mullite, most of
which along with the boehmite will form the non-zeolite matrix of
the catalyst. The addition of spinel or mullite to the microsphere
results in an FCC catalyst that contains multiple matrix
components; i.e., the alumina and the spinel or mullite. The spinel
is useful for improving the upgrading of the heaviest fraction, in
a feed, referred to as bottoms. The ratio of alumina to spinel or
mullite is important, since as this ratio decreases, there is less
efective passivation on Ni and V. Any binder which is used should
contain only sodium, expressed as Na.sub.2O, which is easily
exchangeable.
[0025] The precursor microspheres are reacted with zeolite seeds
and an alkaline sodium silicate solution, substantially as
described in U.S. Pat. No. 5,395,809, the teachings of which are
incorporated herein by cross-reference. The microspheres are
crystallized to a desired zeolite content (typically ca. 50-65%),
filtered, washed, ammonium exchanged, exchanged with rare-earth
cations if required, calcined, exchanged a second time with
ammonium ions, and calcined a second time if required.
[0026] Especially preferred compositions of the solids in the
slurries that are spray dried to form porous microspheres, and
later calcined to prepare precursor microspheres, are expressed
hereinafter below in table form as the weight percent of hydrated
kaolin, boehmite and kaolin calcined through the exotherm (spinel
or mullite) on a binder-free basis; weight % SiO.sub.2 binder is
based on the total weight of dry microspheres and provided by
sodium silicate.
1 Ingredients Broad Preferred Hydrated Kaolin 0-90 15-85 Metakaolin
0-60 0-30 Boehmite Alumina 5-50 10-40 Kaolin calcined 0-85 5-70
through the exotherm Binder 5-35 5-25
[0027] The reactive kaolin of the slurry to form the microspheres
can be formed of hydrated kaolin or calcined hydrous kaolin
(metakaolin) or mixtures thereof. The hydrous kaolin of the feed
slurry can suitably be either one or a mixture of ASP.RTM. 600 or
ASP.RTM. 400 kaolin, derived from coarse white kaolin crudes. Finer
particle size hydrous kaolins can also be used, including those
derived from gray clay deposits, such as LHT pigment. Purified
water-processed kaolin clays from Middle Georgia have been used
with success. Calcined products of these hydrous kaolins can be
used as the metakaolin component of the feed slurry.
[0028] Silicate for the binder is preferably provided by sodium
silicates with SiO.sub.2 to Na.sub.2O ratios of from 1.5 to 3.5 and
especially preferred ratios of from 2.00 to 3.22.
[0029] A commercial source of powdered kaolin calcined through the
exotherm, e.g., Ansilex.RTM. 93 calcined kaolin, may be used as the
spinel component. Preferably, hydrated kaolin clay is converted to
this state by calcining the kaolin at least substantially
completely through its characteristic exotherm. (The exotherm is
detectable by conventional differential thermal analysis, DTA.) For
example, a one inch bed of hydrated kaolin clay may be calcined for
about 1-2 hours in a muffle furnace at a chamber temperature of
about 1800.degree.-1900.degree. F. to produce clay that has been
calcined through its characteristic exotherm, preferably without
any substantial formation of mullite. During calcination, some of
the finely divided clay agglomerate into larger particles. After
completion of calcination, the agglomerated calcined clay is
pulverized into finely divided particles before being introduced
into the slurry that is fed to a spray dryer. The spray dried
product is repulverized. The surface area (BET) of typical spinel
form kaolin is low, e.g., 5-10 m.sup.2/g; however, when this
material is placed in a caustic environment such as that used for
crystallization, silica is leached, leaving an alumina-rich residue
having a high surface area, e.g. 100-200 m.sup.2/g (BET).
[0030] It is preferred that the alumina used to prepare the
microsphere is a highly dispersible boehmite. Other aluminas such
as pseudo-boehmite with low dispersiblity, and gibbsite are not as
effective. Dispersibility of the hydrated alumina is the property
of the alumina to disperse effectively in an acidic media such as
formic acid of pH less than about 3.5. Such acid treatment is known
as peptizing the alumina. High dispersion is when 90% or more of
the alumina disperses into particles less than about 1 micron. When
this dispersed alumina solution is spray dried with the kaolin and
binder, the resulting microsphere contains uniformly distributed
alumina throughout the microsphere.
[0031] The surface area (BET, nitrogen) of the crystalline boehmite
(as well as the gamma-delta alumina conversion product) is below
150 m.sup.2/g, preferably below 125 m.sup.2/g, and most preferably
below 100 m.sup.2/g, e.g. 30-80 m.sup.2/g.
[0032] Following are typical properties of fully peptizable and
dispersible crystalline boehmites which can be used in practice of
the invention.
2 Al.sub.2O.sub.3 wt % 99.0 min. (ignited) Carbon " 0.5 max.
SiO.sub.2 " 0.015 max. Fe.sub.2O.sub.3 " 0.015 max. Na.sub.2O "
0.005 max. Surface Area (m.sup.2/g) (before calcination) 30-80 Pore
volume, cc/g 70% in pores having radii from 100 to 1,000 .ANG.
units Total volatiles .about.20 wt. % max. Pore size diameter
150-1,000 .ANG.
[0033] Monoprotic acids, preferably formic, can be used to peptize
the crystalline boehmite. Other acids that can be employed to
peptize the alumina are nitric and acetic.
[0034] During production, spray dried microspheres containing
crystalline boehmite in the matrix are calcined. As a result of
calcination, the crystalline boehmite is converted to a porous
gamma phase and to a lesser extent a delta alumina. The BET surface
area of this material only increases marginally, e.g., increases
from 80 m.sup.2/g to 100 m.sup.2/g.
[0035] In preferred embodiment of the invention an aqueous slurry
of finely divided hydrated kaolin, kaolin that has been calcined
through its characteristic exotherm, boehmite and binder is
prepared. More preferably, the finely divided boehmite alumina
peptized with formic acid at pH 2.7 to 3.2 is slurried in water and
is added separately to the aqueous slurry of hydrous koalin and
binder. Thus, the hydrous kaolin, calcined kaolin and binder are
premixed in one tank and fed to the spray drier from one line, and
the aqueous alumina slurry, peptized such as with formic acid is
introduced from a separate line immediately prior to when the whole
mix enters the spray drier. Other mixing and injection protocols
may also be useful. The final slurry solids are about 30-50 wt. %.
The aqueous slurry is then spray dried to obtain microspheres
comprising a silica bonded mixture of hydrated kaolin, boehmite and
kaolin that has been calcined at least substantially through its
characteristic exotherm (spinel or mullite). The microspheres have
average particle diameters that are typical of commercial fluid
catalytic cracking catalysts, e.g., 65-85 microns. Suitable spray
drying conditions are set forth in the '902 patent.
[0036] After spray drying, the microspheres are washed and calcined
at a temperature and for a time (e.g., for two to four hours in a
muffle furnace at a chamber temperature of about
1500.degree.-1550.degree. F.) sufficient to convert the hydrated
clay component of the microspheres to metakaolin, leaving the
spinel component of the microspheres essentially unchanged. Most
preferably the calcined microspheres comprise about 40 to 80% by
weight metakaolin and about 10 to 30% by weight spinel and 20 to
30% by weight transitional phase alumina.
[0037] After crystallization by reaction in a seeded sodium
silicate solution, the microspheres contain crystalline Y-faujasite
in the sodium form. In order to obtain a product having acceptable
catalytic properties, it is necessary to replace sodium cations in
the microspheres with more desirable cations. This may be
accomplished by contacting the microspheres with solutions
containing ammonium or rare earth cations or both. The ion exchange
step or steps are preferably carried out so that the resulting
catalyst contains less than about 0.7%, most preferably less than
about 0.5% and most preferably less than about 0.4%, by weight
Na.sub.2O. After ion exchange, the microspheres are dried to obtain
the microspheres of the present invention. In order to make 0
(zero) wt. % rare earth (REO) catalysts, the Na.sup.+ cations are
exchanged by using only an ammonium salt such as NH.sub.4NO.sub.3
and without using any rare earth salt during exchange. Such 0
(zero) wt. % REO catalysts are especially beneficial as FCC
catalysts that give higher octane gasoline and more olefinic
product. Rare earth versions of catalysts of this invention, post
treated after crystallization by ion-exchange with high levels of
rare earth, e.g., by procedures such as described in the '902
patent, are useful when exceptionally high activity is sought and
the octane rating of the FCC gasoline produce is not of prime
importance. Rare earth levels in the range of 0.1% to 12% usually
between 0.5% and 7% (weight basis) are contemplated. Following
ammonium and rare earth exchange, the catalyst is calcined at
1100.degree.-1200.degree. F. for 1-2 hours and unit cell size of
the Y zeolite is reduced. Preferably, this calcination is done in a
covered tray with 25% free moisture present.
[0038] "Silica Retention" may be practiced to alter porosity. The
teachings of U.S. Pat. No. 4,493,902 at col. 12, 1.3-31, regarding
silica retention are incorporated herein by cross-reference.
[0039] The preferred catalyst of the invention comprises
microspheres containing at least 15% and preferably from 40 to 65%
by weight Y faujasite, expressed on the basis of the
as-crystallized sodium faujasite form zeolite. As used herein, the
term Y faujasite shall include synthetic faujasite zeolites
exhibiting, in the sodium form, an X-ray diffraction pattern of the
type described in Breck, Zeolite Molecular Sieves, p. 369, Table
4.90 (1974), and having a crystalline unit cell size, in the sodium
form (after washing any crystallization mother liquor from the
zeolite), of less than about 24.75 .ANG. as determined by the
technique described in the ASTM standard method of testing titled
"Determination of the Unit Cell Size Dimension of a Faujasite Type
Zeolite" (Designation D3942-80) or by an equivalent technique. The
term Y faujasite shall encompass the zeolite in its sodium form as
well as in the known modified forms, including, e.g., rare earth
and ammonium exchanged forms and stabilized forms. The percentage
of Y faujasite zeolite in the microspheres of the catalyst is
determined when the zeolite is in the sodium form (after it has
been washed to remove any crystallization mother liquor contained
within the microspheres) by the technique described in the ASTM
standard method of testing titled "Relative Zeolite Diffraction
Intensities" (Designation D3906-80) or by an equivalent technique.
It is important to equilibrate the microspheres carefully before
X-ray evaluations are made since equilibration can have a
significant effect on the results.
[0040] It is preferred that the Y faujasite component of the
microspheres, in their sodium form, have a crystalline unit cell
size of less than about 24.73 .ANG. and most preferably less than
about 24.69 .ANG.. Typically, the Y faujasite component of the
microspheres has a crystalline unit cell size range of between
24.64 to 24.73 .ANG., corresponding to a SiO.sub.2/Al.sub.2O.sub.3
molar ratio of the Y faujasite of about 4.1-5.2.
[0041] Table 1 below sets forth ranges for the chemical composition
and surface areas of catalysts formed in accordance with this
invention.
3TABLE 1 Range of surface areas and UCS for invention catalyst
Range Low High SiO.sub.2, wt. % 35 65 Al.sub.2O.sub.3, wt. % 30 60
TSA, m.sup.2/g 300 475 MSA, m.sup.2/g 60 120 ZSA, m.sup.2/g 190 415
UCS, A 24.40 24.57
[0042] Conditions useful in operating FCC units utilizing catalyst
of the invention are well-known in the art and are contemplated in
using the catalysts of the invention. These conditions are
described in numerous publications including Catal. Rev.--Sci.
Eng., 18 (1), 1-150 (1978), which is incorporated herein by
cross-reference. The catalysts of this invention are particularly
useful in cracking residuum and resid-containing feeds having a
Ni+V metals content of at least 2,000 ppm and a Conradson carbon
content greater than 1.0.
EXAMPLE 1
[0043] Preparation of Catalysts
[0044] Below is described the preparation of five catalyst samples
that exemplify the catalyst of the present invention. Each catalyst
was an in-situ catalyst made from microspheres that contained
kaolin in some form, dispersible boehmite alumina that is indicated
as AOH, and sodium silicate binder. Formulations of the
microspheres are described as a combination of kaolins and alumina
and add up to 100%. To this was added sodium silicate binder
written as % SiO.sub.2. Each sample is identified by a ratio x/y
where x is the alumina AOH and y is some form of calcined
kaolin.
[0045] Formulation of Microspheres
4 Sample 1: 30/0 - 70% hydrous kaolin, 30% AOH, 15% silica binder.
Sample 2: 30/10 - 60% hydrous kaolin, 30% AOH, 10% spinel, 15%
silica binder. Sample 3: 20/10 - 70% hydrous kaolin, 20% AOH, 10%
spinel, 15% silica binder. Sample 4: 20/10 - 70% hydrous kaolin,
20% AOH, 10% mullite, 15% silica binder. Sample 5: 20/60 - 15%
hydrous kaolin, 20% AOH, 60% spinel, 5% silica binder.
[0046] To make the microspheres, the hydrous kaolin, spinel, water,
and silicate binder were spray dried together. Kaolins and binder
were premixed together in one tank and fed to the dryer from one
line, and the alumina slurry, peptized with formic acid at pH of
2.7 to 3.2, was introduced to this premix from a separate line just
before the whole mix was directed into the spray drier. All
microspheres were finally calcined at 1500.degree. F. for 4 hours.
The temperature and time of the calcination ensured that all
hydrous kaolin was transformed to a reactive metakaolin clay.
[0047] Zeolite Crystallization and Work Up of Microspheres (MS)
[0048] Samples 1 to 4--Crystallization conditions
[0049] SiO.sub.2/Na.sub.2O=2.70, SiO.sub.2/Al.sub.2O.sub.3=7.0,
H.sub.2O/Na.sub.2O=7.0, Seeds/MS=0.0044
[0050] Reaction temperature: 210.degree. F., Crystallization time:
20 to 30 hours
[0051] Target zeolite index=50 to 70%
[0052] Other formulations may be used; the above described
formulation is a typical example.
[0053] After crystallization a series of base exchanges and
calcinations were done as follows:
[0054] (a) First series of ammonium exchanges were conducted to a
target 2.7% Na.sub.2O
[0055] Three exchanges at 180.degree. F. and pH 3 (15 min. for each
exchange)
[0056] 1 g 54% NH.sub.4NO.sub.3:1 g VF Catalyst:1 g H.sub.2O
[0057] Repeated for second exchange
[0058] 0.5 g 54% NH.sub.4NO.sub.3:1 g VF catalyst:1 g H.sub.2O
[0059] (b) Rare earth nitrate exchanged catalyst to following
target
[0060] One exchange at 180.degree. F. and pH 3.25 for 30 min.
[0061] Target REO 3.0%, Dose to give REO 3.7% (range 2.6 to
3.5)
[0062] (c) Dried the sample
[0063] (d) Shock calcined sample at 1200.degree. F./2 hr./25%
LOI
[0064] (e) Second series of ammonium exchanges were conducted to a
target 0.35% Na.sub.2O
[0065] (Range 0.3-0.55%) Na.sub.2O
[0066] Five exchanges at 180.degree. F. and pH 3 and 15 min
each.
[0067] All were 1 g 54% NH.sub.4NO.sub.3:1 g VF catalyst:1 g
H.sub.2O
[0068] (f) Final shock calcination at 1200.degree. F./2 hr./25%
LOI.
[0069] Target UCS=24.50 A.
[0070] See Table 2 for a summary of the chemical composition and
surface area properties of the catalyst samples.
[0071] Sample 5--Crystallization conditions
[0072] SiO.sub.2/Na.sub.2O=3.15, SiO.sub.2/Al.sub.2O.sub.3=7.50,
H.sub.2O/Na.sub.2O=10.75, Seeds/MS=0.0044
[0073] Reaction temperature: 210.degree. F., Crystallization time:
22-28 h, Target Zeolite Index: 40-55%
[0074] Steps (a) to (b) as shown above were conducted to obtain
final catalyst.
[0075] See Table 2 for a summary of the chemical compositions and
surface area properties of the catalyst samples.
5TABLE 2 Catalyst Sample 1 2 3 4 5 Microsphere 30/0 30/10 20/10 (1)
20/10 (2) 20/60 Na.sub.2O, wt. % 0.39 0.36 0.38 0.48 0.16% REO, wt.
% 3.30 3.34 3.56 2.57 4.44% SiO.sub.2, wt. % 53.53 52.3 58.2 57.46
40.98% Al.sub.2O.sub.3, wt. % 40.44 41.8 36.6 37.94 52.07% TSA,
m.sup.2/g 409.10 404.7 446 435.6 341.6 MSA, m.sup.2/g 77.0 77.0 80
77.4 102.3 ZSA, m.sup.2/g 332.1 327.7 366 358.2 239.3 UCS 24.510
24.505 24.558 24.487 24.535
EXAMPLE 2
[0076] Control Sample Preparation
[0077] The five samples above were tested versus two in-situ FCC
catalysts that did not contain AOH in the formulation. These
controls are identified as Samples A and B.
[0078] Sample A had a starting microsphere formulation of 70%
hydrous kaolin, 30% spinel, ca. 12% silica binder and is therefore
designated as 0/30.
[0079] Sample B had a starting microsphere formulation of 70%
hydrous kaolin, 15% gibbsite alumina, 15% spinel, 15% silica binder
(as silica sol instead of sodium silicate). Note here the alumina
used was gibbsite which is not dispersible like AOH.
[0080] Both catalysts were crystallized and worked up using the
same approach as that used for Samples 1 to 4.
EXAMPLE 3
[0081] Tests and Evaluation
[0082] Microactivity tests (MAT) were carried out using a heavy
aromatic feed. The MAT conditions were 970.degree. F. reactor
temperature, 1.2 g of feed delivered in 30 s, catalyst weight was
varied to vary space time (inverse space velocity) . Space time is
defined as catalyst weight/feed flow rate.
[0083] In order to note behavior with Ni and V, all catalysts were
first steamed at 1350.degree. F. for 2 hours in 100% flowing steam.
Then 3000 ppm Ni and 3000 ppm V were added as naphthanate or oleate
solutions in cyclohexane via the Mitchell method. The organic
compound was burned away, and the metal-containing catalysts were
steamed again at 1450.degree. F. for 4 hours in a flowing mixture
of 90% steam and 10% air. In order to evaluate catalysts without
metals all samples were steamed at 1450.degree. F. for 4 hours in
100% flowing steam.
[0084] Metals Ni and V on the catalysts give rise to excess
hydrogen formation and contaminant coke. In order to measure the
contaminant coke, the total coke was first obtained with a
metallated sample then subtracted from this was the catalytic coke
obtained at the corresponding activity with the same sample but not
containing metals. For hydrogen, the results from the metallated
samples were used since clean samples give very low amounts of
hydrogen.
[0085] The best comparison for ability to passivate Ni and V is
made by plotting hydrogen and contaminant coke yields versus space
time. See FIGS. 1 and 2. Table 3 compares hydrogen yields and
contaminant coke yields at a space time of 80 s.
6TABLE 3 Compared at a space time of 80 s Catalyst Hydrogen yield,
wt. % Contaminant coke yield, wt. % Sample A 1.18 8.32 Sample B
1.17 7.48 Sample 1 0.76 4.28 Sample 2 0.77 3.89 Sample 3 0.84 4.01
Sample 4 0.98 5.50 Sample 5 1.03 5.87
[0086] From Table 3 and the figures it can be seen that the
inventive catalysts, Samples 1 to 5, that contained dispersible
boehmite alumina (AOH) gave substantially less hydrogen and
contaminant coke than the comparative samples A and B that did not
contain AOH.
[0087] Table 4 compares Sample A, Sample 1, and Sample 3 at
constant 70% conversion. Comparisons are for metallated samples.
Only samples with identical activities are thus comparable at
constant conversion. Note the higher gasoline yields and low coke
yields obtained for the AOH-containing samples.
7 TABLE 4 Sample A Sample 1 Sample 3 Ratio (1) 0/30 30/0 20/10
Hydrogen 1.31 0.84 0.91 Methane 0.94 0.86 0.88 Ethane 0.56 0.62
0.58 Ethylene 0.77 0.83 0.80 Total Dry Gas 3.58 3.14 3.18 LPG 11.54
11.73 11.43 Gasoline 40.94 45.72 45.33 LCO 18.73 18.51 19.21 HCO
11.27 11.49 10.79 Coke 13.94 9.40 10.06 % Conversion 70 70 70 space
time, s 90 89 89 (1) Ratio = AOH/calcined clay
[0088] Once given the above disclosure, many other features,
modifications, and improvements will become apparent to the skilled
artisan. Such other features, modifications, and improvements are,
therefore, considered to be a part of this invention, the scope of
which is to be determined by the following claims.
* * * * *