Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to a catalytic cracking process using a
crystalline zeolite of extremely small particle size as cracking
catalyst.
Crystalline zeolites are extensively employed in commercial
operations as catalysts for the production of gasoline. In practice
they are combined with a suitable matrix, such as an inorganic oxide,
to form either a bead suitable ~or use in moving-bed installations or a
1~ fluidizable catalyst particle suitable for use in FCC installations.
Gas oil feed is contacte~ with the catalyst in a reactor until the
catalyst is deactivated by deposition of coke. The catalyst is then
passed through a regenerator in which the coke is burned off. Hot
regenerated catalyst is then re-introduced into the reactor to contact
the -feed again. The cycle repeats continuously.
Such operations enjoy great commercial success and result in
significant econûmic advantages. Nevertheless they do require a
relatively large amount of catalyst in order to effect a satisfactory
conversion of feed with satisfactory selectivity to gasoline. Curren-t
fluid riser cracking processes use catalyst-to-oil weight ratios of
more than 5:1. The possibility of discarding such large amounts of
catalyst when coke-contaminated could certainly not be contemplated,
particularly since the cracking reaction is endothermic and at least
part of the heat necessary to conduct it must be obtained from
~5 combustion of coke in the regenerator and the subsequent introduction of the hot catalyst into the reactor.
Disclosures of catalytic cracking of gas oil with crystalline
zeolites include U.S. Patent Nos. 3,140,249, 3,140,251 and 3,140,253,
in which the particle size of the catalyst composite employed is either
in the range of about û.08 to 0.25 inches (for moving-bed operation) or
the range of 10 to 150 microns (for FCC operation). The matrices
employed include both catalytically active materials, such as
silica-alumina, and catalytically inactive materials, such as silica~
36~3
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The circulation rate of such a catalyst composite is tied to its
catalytic cracking function. Thus, for example, in a typical FCC
operation, circulation rate of a matrix and circulation rate of a
catalyst are inherently tied together and this rate is dependent on
catalyst activity. The extent to which coke is removed in regeneration
is directly tied to the restoration of the catalytic activity of the
catalyst composite which, in turn, controls the rate of circulation of
the catalyst into the cracking unit in order to maintain a stable
operation.
U.S. Patent No. 4,2~3,126 discloses the use as catalyst of a
powdered crystalline aluminosilicate zeolite alone or in a matrix in
order to aid in physical removal of the catalyst from the product or
products.
According to the present invention a cracking process in which
a hydrocarbon feed is contacted with a crystalline zeolite catalyst is
characterized by the fact that said feed contacts both said catalyst,
in the form of particlec 0.01 to 5~ m in size and of an alpha activity
of at least 500, and a hot, substantially catalytically inert solid in
the form of particles 3û to 300~ m in size, whereafter said solid is
separated and calcined and the resulting hot calcined solid
recirculated to contact the feed, the weight ratio of zeolite catalyst
to feed during the contacting being no greater than 0.1, preferably 40
to 2000 ppm. Preferred zeolites are zeolite X, Y, L, ZSM~5, ZSM-ll,
ZSM-12 and/or beta; preferred solids comprise sand, clay, dolomite,
glass and/or metal, advantaseously processing a surface area of at
least 10 m /9. In one embodiment the hot solid contacts unheated
feed in which the zeolite catalyst is already dispersed; and at least
part of the zeolite catalyst may, after contact with the feed, be
separated tnerefrom, calcined and recirculated to contact the feed.
Contact between catalyst, solids and feed usually occurs at a
temperature of 3ûO to 650C, with a residence time of 2 to 10 seconds
at a solids:oil ratio o-f 5:1 to 12:1. It is preferred that the
particle size of the zeolite be no greater than 2~ m.
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The powdered zeolite can thus either be discarded or a portion
of the same entering an air calciner with the heat carrier solids can
be recovered from the flue gas via conventional means, such as by using
an electrostatic precipitator and/or bag filters, and recycled if
desired. As can be seen, a key aspect of the invention is the
separation of the catalytic cracking function from the circulating
solids. Thus, the circulation rate of the solids is not tied to the
catalytic activity but can be varied to the limit of the particular
catalytic cracking unit being utilized, taking full advantage of its
~ mechanical and material design. Thus, neither the circulating solids
themselves or the rate at which they are recirculated are determined by
properties of the crystalline zeolite, which need not be recycled at
all or can be recycled at a rate which is different from the rate at
which the solids are recirculated.
Since extremely small amounts of catalyst may be employed it
is essential that the crystalline zeolite be highly active. As will be
demonstrated in the examples, a zeolite having an alpha actiYity of 40
did not function in the process of this invention. The alpha test is
described in The Journal of CatalYsis~ Vol. 4, pp. 52~-529, August 1965.
Because the use of small particle size catalysts permits
intimate contact of the catalyst with the feeds-tock, the amount of
catalyst needed is greatly decreased. In the preferred practice of
this invention, the catalyst-to-oil ratio is reduced from the
conventional commercial operation of about 5:1 down to ~0-2000 ppm per
weight of oil -- a reduction of more than 125,000-fold. Larger
quantities of catalyst may be used but there is no particular added
advantage to using more catalyst than is necessary effectively to
catalyze the cracking of gas oil to gasoline.
The hot solids which are circulated to provide the necessary
heat for the cracking reaction are not narrowly critical in nature, and
since their circulation rate is divorced from the catalytic cracking
activity of the powdered zeolite catalyst they can include such
relatively low-cost substances as sand, dolomite, clay minerals, glass
and metal particles. Thus, the prefrred solid materials which are used
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as circulating heat carriers are materials wnich have substantially no
catalytic crackiny activity and their function would be merely to
provide the necessary heat for the catalytic cracking reaction.
However, it is to be understood that catalytically active materials,
though not preferred, can also be used. Such materials include silica
alumina, silica-zirconia, silica-titania, acid treated clays, etc.
Although these materials do have catalytic cracking activity it is not
as great as that of the powdered crystalline aluminosilicate zeolite so
that, in effect, the heat transfer function and the catalytic function
have still been separated although not to the extent that they would be
were the heat carrier inert.
In one embodiment of this invention, it is preferred that the
circulating solid have a high surface area, particularly when normally
bothersome feeds such as heavy oils, resids or high metal containing
feeds are used. The circulating solid of high surface area serves to
trap out metal and coke. The preferred surface area should be greater
than about lO sq. meters/gm.
In another embodiment of this invention coke particles can
serve as the circulating solids. Thus, the powdered superactive
crystalline aluminosilicate zeolite may be dispersed in a coke gas oil
or vacuum resid and introduced into a fluid coker.
Crystalline aluminosilicate zeolites which are useful in the
novel process of this invention are extremely well known in the art and
include zeolite X, Y, Beta, L, as well as mixtures of the above with
smaller pore zeolites such as erionite, mordenite, ZSM-5, ZSM-8, ZSM-ll
and ZSM-12 - providing they possess the appropriate alpha activity.
The preferred crystalline aluminosilicate zeolites may include zeolite
X and Y, particularly in their rare earth, acid, or rare earth acid
form. A mixture of zeolites can be used. One may commence the process
with one zeolite then change it to another in order to meet product
demand. Thus, for example, due to the fact that changes in catalyst
composition can be made readily, it is possible to start with a maximum
gasoline producing catalyst, such as rare earth Y and to quickly change
to a maximum distillate catalyst such as dealuminized Y or to a
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dewaxing catalyst~ such as zeolite ZSM-5 or to the use of a mixture of
these catalysts in order to accommodate available charge stocks and
market demand o-f the products.
In order to carry out the novel process of this invention, it
is necessary that the heat carrier solid be of a particle size which is
substantially in excess of the micron size of the powdered crystalline
aluminosilicate zeolite. Since it is desired to separate the heat
transfer function from the catalytic function, it is also necessary to
be able to separate the heat circulating solids from the powdered
crystalline aluminosilicate zeolite. To the extent that the heat
circulating solids have a particle size greater than the powdered
crystalline aluminosilicate zeolite, separation is easier. Thus, the
expression "heat circulating solid" as used throughout the
specification and claims is intended to mean a solid material which is
preferably catalytically inert and which has a particle size of from 30
to 3~0 microns and even more desirably from 45 to 200 microns.
Blending of feedstock and catalyst may be carried out before the
feedstock is introduced into the reactor. In such a mode oF operation,
it is preferred to bypass or to eliminate the feed preheater in order
to avoid catalyst deactivation. However, if it becomes necessary to
use a feed preheater, another mode of operation is to disperse the
catalyst in a separate cold hydrocarbon stream and inject it directly
into the catalytic cracker whilst the remaining portion of the
hydrocarbon feed, e.g. gas oil, is passed through the feed preheater.
Another advantage of the invention is that it is possible to
incorporate additional functions into the circulating solids, such as
Sû2 emission control by the use of antimony compounds or carbon
monoxide combustion catalysts such as trace amounts of platinum or
other well known materials which ha~e an oxidation function.
The single figure of the Drawing is a schematic diagram of a
process in accordance with the invention. A powdered crystalline
aluminosilicate is dispersed into a hydrocarbon feed and the mixture is
fed into mixing zone 1 wherein it contacts hot solids such as sand,
which enter into mixing zone 1 through line 3. In mixing zone 1, the
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hot solids and the relatively cold catalyst-oil mixture are
equilibrated and en-ter into reactor 2 wherein the hydrocarbon oil is
catalytically cracked into lower molecular weight products such as gas
oil. In general, the catalyst oil mixture moves rapidly through the
reactor at a rate faster than that of the heat carrier solids. The
products from reactor 2 pass to a separator 4 where a gas liquid
product is separated. This liquid product contains some of the micron
or sub-micron size crystalline aluminosilicate zeolite, but the
presence of these materials in the oil does not present any technical
problems. The remaining portion of the powdered material, together
with the solids~ passes through line 5 into an air calciner 6 to which
air is introduced through line 7. The powdered crystalline alumino
silicate zeolite passes through line 8 into filter 9 where it is
recovered and either discarded or a portion recirculated back to
reactor 3 through line 10. The hot solids from the air calciner 6 are
recirculated to the mixing zone 1 through line 3.
The following examples illustrate the invention.
FEED F~EPARATION
In all the examples which follow, a waxy, high pour point
2U Gippsland crude was used~ Table 1 summarizes the properties of the
crude oil. The oil was fractionated into a 420F minus fraction, and a
420F+ reduced crude fraction which included the residuum. The reduced
crude was used as the feed without further purification or separation.
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TaDle 1
,:~[g~
Gravity, API 46.9
Sulfur, % Wt. 0.11
Carbon residue, ~/0 wto 0~23
Viscosity, cs ~100F 2~09
Pour Point, F 60
Ni, ppm ~ 0.1
V, ppm 0.16
Nitrogen, ppm 77
Hydrogen, ~ wt. 14.2
Boiling Range, Vol. %
IBP-120F 5.0
120-380F 34.7
380-650F 32.8
650F+ 26.6
GENERAL TE5T PROCEDURE
The reduced crude either neat or containing 400 to 2000 ppm of
a dispersed aciri cracking catalyst was charged into a fluidized bed
reactor maintained at 510C, at a rate of 1.1~ gm/min. The reactor
contained SO ml (19 grams) of y-alumina particles which served as the
heat transfer solids. The particles were fluidized by flowing 20
ml/min to 850 ml/min of helium depending on the activity of the
dispersed catalyst and the oil residence time desired. Material
balances were made at 10-minute intervals. To o~tain a value of coke
for the material balance, the oil was momentarily stopped and the
reactor flushed with helium, after which the coke deposit on the heat
transfer solids was burnt with a stream of 40~0 oxygen in nitrogen
flowing at 400 ml/min and the combustion gas monitored with an IR
detector for Cû and C02 until all the coke was burnt. At the end of
the burn, the reactor was flushed with helium be~ore restarting the
crude oil/dispersed catalyst feed pump.
.
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EX~MPLES 1 3
In the following examples, the reactor was filled with 19 gms
of fluid particles of ~-alumina (60-120 mesh) 9 a thermal background
run was first made without any added dispersed catalystO After the
thermal run, the feed was changed to the one containing the dispersed
catalyst. To prepare the dispersed catalyst, a 4û/1 SiO2/A1203
ZSM-5 was steam activated according to U.S. Patent No. 4,326,994 ~o an
alpha value of 1600. The zeolite was in powdered form comprising
submicron particles. It was dispersed in the oil at a concentration of
40û ppm.
In a second series of experiments, a superactive rare earth Y
was prepared according to U.S. Patent No. 3,49~,519 from a REY to an
alpha value of 10,20û.
The preparation was carried out contacting 52 grams of rare
earth exchanged Y with 398.7 grams of 2.0 molar NH4N03 for 96C for
one hour. The material was then steamed for one hour at lû00F with
saturated steam followed by treatment with ethylene diaminetetraacetic
acid (neutralized with ammonium hydroxide to a pH of 6.7). The treated
2~ material was then calcined at 1000F for one hour followed by exchange
with 2 molar hot NH4N03. The material was again calcined for one
hour, exchanged with boiling NH~N03 for one hour and washed with
boiling water. The washed material was again exchanged with boiling
NH4N03 (2 molar) for one hour, washed with boiling water and dried
2~ overnight at 130F.
The zeolite was in the powdered form, comprising particles of
2~m or smaller. It was dispersed in the oil at a concentration of
2000 ppm.
8Oth the thermal run and the catalytic runs were made at 510O
and 1.13 gm oil/min and about 20 ml/min of helium as the fluidizing
gas. From the results shown in Table 2, high activity ZSM-5 and
superactive REY are clearly effective catalysts for the dispersed
cracking system.
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TABLE 2
High Activity
HZSM-5 REY
Feed Thermal o~ = 1600 ~ - 10,200
Example 1 2
Conversion, wt. %
420F -- 14.5 40.6 29.6
650F -- 31.7 63.9 54.0
Products, wt. %
Cl's -- 0.2 1.2 1.0
C2's -- 1.1 2.1 1.7
C3's -- 0.2 12.0 3.1
C iS -- 0.5 8.2 1.7
C5 - 420~F 4.3 16.2 19.3 25.1
420-650F 54.2 56.0 41.9 48.3
650F~ 41.5 25.8 15.0 19.1
Coke - ~0.1 0.3 ~ 0.1
EXAMPLES 4-6
In order to reduce thermal cracking, the following experiments
were carried out at shorter vapor residence times by increasing the
flow rate of the fluidizing gas from about 20 ml/min to about 850
ml/min. In addition to the thermal run, two catalytic runs were ~ade
under otherwise identical conditions with two high activity zeolite
catalysts dispersed in the oil prepared as described previously. The
results, as shown in Table 3, demonstrate that the conversion due to
thermal reactions was greatly reduced and both high activity dispersed
catalysts effected significant conversion of th feedstock to 420F
minus cracked products.
~2~
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TABLE 3
400 ppm HZSM-5 2000 ppm HY
FeedThermal ~ _ 1600
Example 4 5 6
Conversion, wt. Y0
420f -- 6.~ 24.1 28.5
Products, wt. ~
Cl ~ C2 s . 1.4 0.9
C3 + C4's -- 0.3 12.7 9.8
C5 - 420~F 4.3 9.9 13.0 20.7
420-650~F 54.2 54.8 38.2 41.0
650F+ 41.5 34.6 34.5 27.4
Coke -- 0.1 0.2 0.2
EXA~PLES 7-9
lS In the last series of experiments, two commercial acid
catalysts were used as the dispersed catalysts: a HZSM-5 steamed to an
alpha value of 40, and a steam stabilized rare earth Y cracking
catalyst (oC= 0.5). Thes~ catalysts were evaluated in the presence of
another batch of freshly prepared ~'-alumina which was more thermally
2~ active than the batch used in previous experiments, as indicated by its
high methane yield. Results of the tests together with the thermal
background run as presented in Table 4 show that these commercial acid
catalysts were not effective when used in low concentration in the
dispersed form. These experiments serve to demonstrate the importance
of using catalysts possessing high intrinsic acid activity.
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TABLE 4
2000 ppm 400 pprn
Stearned Steamed
REY/SiAl HZSM-5
Feed Thermal = 0.5 = 40
Example - - 7 8 9
Conversion, wt. ~
420F -- 22. 3 22. 8 24.1
Products, wt. ~
1 0 Cl's -- 1.4 1.1 1.2
C2's -- 2.6 2.3 1.8
C3's -- 3.1 3.3 4.5
C4's -- ~.1 2.2 3.8
C5 - 420f 4.3 16.4 16.9 15.7
42n-650F 54.2 51.9 48.6 47.9
650F~ 41.5 22.5 25.3 24.8
Coke -- 0.2 0.3 0.3
