Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~2~
F 2909 ' - 1 -
MODIFIED ZSM-5 CATALYST AND
_7 _ _ .
MEil~)D OF PREPARATION AMD USE TE~OF
The invention relates to an improved ZSM-5 zeolite, its method
of preparation, and use of the zeoli~e in hydrocarbon conversion
processes.
Zeolitic materials, both natural and synthetic, have been
demonstrated in the past to have catalytic properties for various
types of hydrocarbon conv~rsions. Certain zeolites are ordered,
porous crystalline aluminosilicat~s having a definite crystalline
structure within which there are a large number of smaller cavities
which may be interconnected by still smaller channels. These
materials are known as molecular sieves.
Many methods have been developed for preparing a variety of
synthetic aluminosilicates. These aluminosilicates have come to be
designated by letter or other symbol, e.g., Zeolite A (U.S. Patent No.
2,882,243), Zeolite X (U.S. Patent No. 2,882,244), Zeolite Y (U.S~
Patent No. 3,130,007), and ZSM-5 (U.S. Patent No. 3,702,886).
ZSM-5 is a particularly interesting zeolite, and much work with
ZSM-5 has been reported in the patent literature on adding an
inter~ediate pore size zeolite, e.g., ZSM-5, to the conventional
cracking catalyst. Use of large pore and small pore crystalline
materials in catalytic cracking is known. Quite a lot of work has
been done adding ZS~-5, and related intermediate pore size zeolites,
to conventional large pore cracking catalyst.
In U.S. Patent No. 3,758,403, from 2.05 to lO~ ZSM-5 catalyst
was added to a conven~ional cracking catalyst containing 10% REY, the
remainder being Georgia clay. Examples were given showing use of 1.5,
2.5, 5 and lO w* ~ ZSM-5 added to the conventional cracking catalyst.
The ZSM-5 catalyst resulted in increased production of dry gas,
some loss of gasoline yield, and an increase in octane number.
ZSM-5 catalyst, especially, virgin catalyst, has exceedingly
high activity. Researchers have attempted to take advantage of the
,
:~2~S25
F-2909 : 2 -
super activity of fresh ZSM-5 catalysts by adding only small amounts
of it to FCC catalyst. Typical of such work is U.S. Patent No.
4,3091280 ~hich taught adding ve~y small amounts of powdered neat
ZS~-5 catalyst, characterized by a particle si~e less than 5 microns.
s This patent taught that adding as little as 0.25 w* % ZSM-5
powder to the circulating catalyst inventory in an FCC unit would
increase dry gas production by 50% (fro~ 3.9 wt % dry gas to 6.0 - see
Example 6 in Table 2).
To summarize the state of the art regards addition of ~SM-5 to
cracking catalyst, the following general statements can be made.
ZSM-5 is exceedingly active, and addition of even small amounts
results in grea~ly augmented production of dry gas, at the expense of
gasoline yield.
So far as is known to applicants, no use has been made on a
commercial or long term scale of ZSM-5 in moving bed catalytic
cracking processes.
Experimental work has shown that ZSM-5 catalyst, in FCC
; processes, loses activity relatively quickly. ZSM-5 is
disproportionately active, compared to conventional PCC catalyst, from
startup up to perhaps as much as a week of operation. After more than
about a week of operation in an FCC unit, and after being subjected to
repeated fluidized bed regenerations, in laboratory or in commercial
units, the ZSM-5 activity becomes much harder to find.
~` These factors, high initial activity of ZSM-5, coupled with
rapid deactivation of ZSM-5, discouraged researchers fro~ adding ZSM-5
to moving bed catalytic cracking units. The high startup activity of
ZSM-5 results in voluminous production of light gases, which
production is difficult to accommodate in downstream processing units
designed to handle the product mix obtained from conventional
catalyst. The rapid deactivation of ZSM 5 meant that its effect would
soon be lost, requiring very expensive turnover of catalyst in the
unit.
The problem of accommodating the initial high activity of ZSM-5
catalyst, has been solvedl and is discussed hereafter.
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P-2909 ` ~ 3 -
The expected rapid catalyst deactivation~ based on projections
of work using ZSM-5 catalyst in FCC units, did not occur in TCC units.
The properties of the ZSM-5 catalyst changed after repeated
regenerations in a moving bed cracking unit.
It was expected that the catalys~ would lose activity. It did,
but not nearly to the same extent as it did in conventional FCC
catalyst regenerations.
Surprisingly, the ZSM-5 catalyst changed during use, and
behaved differently than it ever had before. It did not just get
older, it got better.
As the feeds are substantially the same in FCC and TCC, it is
postulated that the different reaction/regeneration me~hods used in
these processes might be the cause of the change in the ZSM-5 catalyst.
~here is a difference in the severity and frequency of catalyst
regeneration in TCC and FCC units.
FCC catalyst is frequently regenerated at temperatures of
650-732~C (1200-1350F) in a fluidized bed regenerator. Any hydrogen,
or hydrocarbon, present on the catalyst burns to produce water. The
water, or steam, deactivates the ZSM-5 catalyst fairly rapidly.
In contrast, in Thermofor catalytic cracking regeneration, the
catalyst is regenerated in a moving bed. Hydrogen and hydrocarbon
tend to be burned off the catalyst and swept away from it before coke
on the catalyst is burned, and before very high tenperatures necessary
to burn off coke are reached. In TCC regeneration the catalyst does
not see water vapor for a very long time, and when it does see water
vapor the catalyst is not very hot so the steaning deactivation effect
is not so severe as in FCC.
Even making adjustments for the severity and frequency of FCC
regenerations vs. TCC regenerations, the ZSM-5 catalyst after
regeneration in a TCC unit behaved differently than ZSM-5 catalyst
regenerated in an FCC unit.
After many days of operation in a TCC unit, the Z~M-5 catalyst
became a better catalyst. Some activity was lost, but significant and
unexpected amounts of catalytic activity remained. Most significant,
the aged, TCC regenerated ZSM-5 catalyst retained most of the virtues
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F-29~9 - 4 -
expected of ZSM-5 catalyst ~increased product octans number), while
shedding most of the defects of ZSM-5 catalyst (loss in gasoline
yield, increased dry gas make).
Accordingly, the present invention provides a crystalline
material having the crystal structure of ZSM-5 which, when in contact
with long chain relatively low octane olefins, at hydrocarbon
conversion conditions sufficient to convert at least a portion of the
olefins, exhibits as a primary conversion mechanism the isomerization
of the long chain olefins to higher octane number materials.
In another embodimen~, the present invention provides a
catalytic cracking process operating in the absence of additional
hydrogen, wherein hydrocarbon feedstock is contacted with a catalyst
and the feedstock is cracked to lighter products, characterized by
adding a crystalline material having the crystal structure of ZSM-5
and having a reduced paraffin cracking activity, and exhibiting
substantial olefin isomerization activity, as compared to conventional
ZSM-5 catalyst.
In yet another embodiment, the present invention provides
modified ZSM-5 catalyst characterized by its method of preparation
comprising contacting hydrocarbons with ZSM-5 catalyst initially
having substantial initial paraffin cracking ac~ivity in a catalytic
cracking zone to produce coked catalyst containing minor amounts of
hydrocarbon and coke regenerating the coked catalyst in catalyst
regeneration zone by the steps comprising burning a majority of the
hydrocarbon from the catalyst, while leaving a majority of the coke on
the catalyst removing most of the products of hydrocarbon combustion
fron contact with the catalyst and subsequently burning coke from the
catalyst to produce a regenerated catalyst repeating steps a) and b)
until the initial paraffin cracking ability of the ZSM-5 catalyst has
been reduced by at least 50%~
ZSM-5
ZSM-5 is described in U.S. Patent Nos. 3,702,886 and Re 29,948.
.
.
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F-Z9~9 : 5 -
Quite a lot of work has been done on making material with a
ZSM-5 crystal structure, but with different materials, ranging from
all silica to materials containing silica and some o~her tetravalent
metal such as boron, iron, gallium, etc.
As used herein, the term ZSM-5 refers to a material which has
substantially the same crystal struc~ure as shown in U.S. Patent No.
3,702,886. Substitution of different cations, or changing the
silicajalumina, or silica/boron ratio, may result in minor
modifications of the X-ray diffraction patterns of the crystalline
material so produced, but it is still ZSM-5, and contemplated for use
herein.
MOVING BED CATALYTIC CRACKING
This process was introduced in the early 1940's and a detailed
description thereof is not believed necessary.
Brie1y, the prccess uses a moving bed of catalytic cracking
catalyst. Catalyst moves from the catalytic cracking reactor to a
moving bed regenerator, and from there back to the reactor.
The oil chargestock to the process, usually without added
hydrogen, is passed over the moving bed of catalyst and is
catalytically cracked tu lighter products. During catalytic cracking,
the catalyst is deactivated by coke deposition. Coke deposition is
removed from the catalyst in a moving bed regenerator associated with
the moving bed cracking unit.
MOVING BED REGENERATI~N
_
Moving bed catalytic cracking units have moving bed catalyst
regeneration units associated therewith. The catalyst is generally
maintained as a downflowing moving bed of catalyst. The catalyst may
be disposed as an annular bed, with radial in or out gas flow. The
moving catalyst bed may have the cross-section of a circle or a
rectangle with gas flow from the lower portion of the catalyst bed to
the upper, or the reverse. Alternatively5 gas flow may be across the
moving bed of catalyst, or some combination of cross-flow, downflow
and upflow.
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F-2909 : 6 -
It is preferred to have a moving bed of catalyst going down,with gas flow generally in an upward direction.
Although the catalyst from the moving bed catalytic cracking
unit is usually stripped before being sent to the regenerator, there
S is usually a small amount of hydrocarbon, and hydrog~n containing
coke, contained on the catalyst. m is material is relatively easy to
burn, and is usually burned from the catalyst in the top 5-10% of the
moving bed catalyst regeneration unit. Usually-more severe conditions
are necessary to completely remove the more refractive, relatively
hydrogen free coke that remains on the catalyst after hydrocarbons are
burned off, so progressively more severe operating conditions are
experienced in the lower portions of the moving bed. These conditions
may be in the form of increased temperature, increased oxygen
concentration~ or both.
Much, if not all, of the heat required for catalyst
regeneration is obtained by burning coke, and to a lesser extent, the
light hydrocarbons that happen to be present on the catalyst. For
start-up, or to adjust temperatures in the regenerator, an air
preheater may be used. It is also possible to provide various heat
exchange arrangements, e.g., incoming cool gas against hot exhaust
gases, using hot exhaust gases to preheat catalyst, using hot
regenerated catalyst as a source of incoming cool regeneration gas,
etc. The conditions used in the moving bed catalyst regeneration
units are highly conventional -- whatever temperatures, pressures,
oxygen partial pressures have been found satisfactory in the past are
believed to be satisfactory for use in the present invention.
In very general terms~ regeneration conditions in the moving
bed regeneration should be adjusted so that at least half of the H20
precursors are burned off and at least the top half of the bed, and
preferably in the top 5-10% of the moving bed o catalyst in the
catalyst regeneration zone. Conditions should not be severe enough to
remove more than 50% of the coke from the catalyst in the top one half
of the moving bed regeneration zone, and prefsrably 60 to 90% of the
coke remains on the catalyst after the H20 precursors have been
burned away.
~2~2S
F-29~9 ~ 7 ~
Suitable regeneration conditions inclu~e temperatures of about
204-760C (400-1400F), preferably 427-649C (800-1200~F).
Regeneration pressure may range from subatmospheric to 10
atmospheres or higher if desired. Usually regeneration is conducted
at pressures slightly above atmospheric. Oxygen concentration may
range from about 1/2 mole % oxygen to the oxygen content of air, or
even higher if desired. Very high oxygen concentrations should be
avoided as ~hey lead to high cataIyst regeneration temperatures which
tend to deactivate the catalyst. Regeneration with 1 to 20 mole %
oxygen is preferred~
No way is known today to duplicate this regeneration procedure
in existing FCC units, although it may be possible to modify FCC
regeneration procedures to achieve this, i.e., staged regeneration
where most of the water precursors are burned off at low temperatures,
before coke combustion.
It is believed that other methods will be developed to quickly
produce ZSM-5 with the properties obtainable now only after weeks and
months of aging and regeneration in a moving bed catalytic cracking
unit.
GATALYST PREPARATION ~Y REGæNeRA~IOn
Modified ZSM-5 cataIyst can be obtained by periodically
replacing some of the circulating inventory of ~oving bed catalytic
cracking catalyst, and processing the catalyst to recover the ZSM-5
catalyst, or simply using the extrudate catalyst (with or without
additional modifiers, hydrogenation/ dehydrogenation co~ponents) for
the desired catalytic use.
Preferably the aged ZSM-5 catalyst is obtained downstream of
the moving bed catalyst regeneration process, where it is essentially
coke free. It is also acceptable to obtain the ZSM-5 containing
catalyst downstream of the reactor and upstream of the moving bed
regeneration zone. If this is done, because of the presence of
relatively large amounts of coke on the catalyst in such circumstance,
it will usually be necessary to subject the catalyst to conventional
regeneration techniques prior to use.
~ 2~ 5
F-2909 - 8 -
If TGC units are run to produce improved ZSM-5 catalyst, rather
than improve TCC operati~n, some modifications to T~C operation may be
perrnitted. Reiatively high concentrations of ZSM-5 may be added,
e.g., 10 to 100%, preferably 20 to 80, wt ~ ZSM-5 catalyst content may
be used. The 7SM-5 catalyst added ~ay have a smaller or larger
particle size than the conventional catalyst, or a dlfferent L/D. The
binder, or amorphous material used to give the catalyst strength and
attrition resistance may be modified to optimize end use of the
catalyst in some process other than TCC. Thus the binder may be
inert, or all alumina, or some o~her material compatible with future
catalytic use of the modified Z5M-5.
HYDROGARBON OONVERSION PROCESS~S
The ZSM-5 catalyst produced by the method of the present
invention may continue to be used in moving bed catalytic cracking
units with very good results.
The catalyst may also be used in any other hydrocarbon
conversion process using catalyst. The ZSM-5 catalyst should be
especially useful in-catalytic dewaxing processes designed to r~duce
the pour point of fuel oils, or reduce the ~ax content of lubricating
oil base stock.
The ZSM-5 catalyst of the present invention will also be very
useful in hydrocracking, though in such service it is usually
preferred to add a conventional hydrogenation/ dehydrogenation
component.
HYDROGENATION/DEHYDROGENATION QOMPONENTS
Any of the conventional hydrogenation/dehydrogenation
; components heretofore added to zeolite or amorphous catalyst can be
~added to the ZSM-5 catalyst produced by the method of the present
invention.
Suitable hydrogenation/dehydrogenation components include noble
and base metals. Especially preferred among the noble metals are the
Group VIII noble metals, especially platinum, palladium, and
irridium. The noble metals may be present in an amount equal to 0.01
2~;i
.. , . ~
F-2909 - 9 -
to lO wt %, preferably O.l to 2 wt %, of the finished catalyst, on an
elemental metal basis.
Base metal promoters may be used instead of noble metal
promoters, or in conjunction with noble metal promoters. Base metal
promoters consist of one or more elements selected from the metals of
Group rVA and the base metals of Group VIII. Especially preferred are
nickel, molybdenum, tungsten, nickel-moly, cobalt, and cobalt-moly.
Base metal promoters may be present in an amount e~ual to l to
25 wt ~, and preferably 4 to 20 wt %, of the finished catalyst,
calculated on an elemental metal basis.
CATALYTIC PROPERTIES OF MODIFIED ZSM-5
ZSM-5 catalyst which has been modified by the process of the
present invention is indistinguishable by any known X-ray or elemental
analysis from conventional ZSM-5 catalyst.
Using the guidelines discussed hereafter, it is possible to
take a ZSM-5 catalyst, and determine if it has been modified as
disclosed in the present invention.
Conventional ZSM-S catalyst, when added to conventional FCC
catalyst, usually gives about 2 octane no. gain/l LV ~ yield loss. In
contrast, modified ZSM-5 catalyst of the present invention can give an
octane no. gain with little or no yield loss. Conventional ZSM-5
catalyst results in significantly increased dry gas productionJ while
this is not seen with the modified ZSM-5 catalyst of the present
invention.
The modified ZSM-5 catalyst behaves differently from
conventional ZSM-5 catalyst. Much of the ZSM-5's cracking activity is
diminished, leading to reduced gas make and increased yield, at least
in FCC units. It is believed that some paraffin cracking activity is
lost.
Olefin isomerization activity is believed to be present. It is
not exactly understood why ZSM-5 begins to exhibit olefin isomerization
activity as it ages.
.
~2~iS;~5
F-2909 - 10 -
EX~PLE 1 ,
This process was tested in a commercial size TCC unit.
Operating conditions are shown below:
Fresh Feed Rate,m3/S 2.45 x 10-2
Fresh Peed Rate, BPD 13,400
Recycle O
Catalyst Circulation, tons/hr 397
Catalyst Circulation, metric tons/hr 360
Catalyst/Oil 4.44 wt/wt
Reactor Vapor Outlet Temp. 903F/484C
Catalyst Activity (CAT-~) 53.8
This unit had a 315 metric ton (347 ton) catalyst inventory.
The conventional catalyst in the unit had the following
specifications.
.
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;
F-2909 - 11 -
Durabead lOA
.
Wt ~ REY ~ 12.~%
Bead Diameter 0.36-0.70 cm
- The changeover catalyst had the following properties:
Wt % ZSN-5 5%
Wt % REY 7 5%
Bead Diameter 0.36-0.70 cm
~lring normal operation, this unit required makeup catalyst
rates of 1.13 metric tons (1.25 tons) per day. The makeup catalyst
rate is set to satisfy those catalys~ losses due to attrition, and
also to maintain catalyst activity.
Catalyst addition was usually maintained at 1.8 metric tons (2
tons) per day, although there were short pericds of addition rates as
high as 3.6 metric tons ~4 tons) per day.
Results of the test are reported hereafter in Table 1.
Feed properties are reported hereafter. The numbers reported
are approximate because the feed was a blend of different crudes, and
the blend varied somewhat.
!.
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F-2909 - 12 -
: Feed Properties
Test Results
Test Test MethodResults
..
Pour Point, C/F D 97 29/85
Carbon Residue Conradson D 189 0.31
Kinematic Viscosity 40C D 445-3 40.55
Kinematic Viscosity 100C D 445-5 5.922
: AniIine Point D 611 164.5
Bromine No. D1159 6.8
~ 10 Refractive Index Liquids D1218-9 1.49000
: API Gravity D129B-3 23.0
Density, g/cc 0.916
Molecular Weig~t 353
Sulfur by XRFJ 0.002-5% 1.65
: 15 Hydrogen-Micro Pregl. 12.37
Nickel by AA 0.25 ppm
Vanadium by AA 0.70 ppm
Iron by AA ~.15 ppm
Copper by AA 0.10 ppm
Sodium by AA 2.95 ppm
Nitrogen-Microdumas .16%
; REDU~ED PRESSURE DISTILLATION, D1160
~ % (~ol) Over -C/CF @ 760 mm
,
IBP 220/428
~25 5 324/615
352/665
381/718
~:~ 30 399/75
416/781
431/808
446/8~5
463/865
484/903
510/950
: 35 95 528/983
EP 532/990
:
` NOTE: IBP = Initial Boiling Point
EP = End Point
, . .
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F 2909 - 13 -
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F-2909 - 14 -
The circulating catalyst had, on average, slightly less than
2.5 wt % ZSM-5. Although roughly half the catalyst inventory had been
dumped~ incrementally, and replaced with changeover catalyst which was
rich in ZSM-5, so~e of the catalyst that was dumped had ZSM-5 in it
from previous additions.
Conventional catalyst addition continued after a 2.5 wt ~ ZSM-5
level had been obtained. This was primarily to make up for normal
attrition losses. This catalyst addition averaged roughly about 0.5
per day of catalyst inventory. This make-up catalyst added had no
ZSM-5 added. The reason for this was that no more ZSM-5 containing
catalyst happened to be available at that site.
Example 2 - Laboratory E aluation
A laboratory test was conducted using a ZSM-5 catalyst in a
standard laboratory test apparatus designed to simulate a moving bed
cracking operation.
Feedstock Properties
The feedstock was a gas oil fraction having the approximate
properties reported earlier.
~hangeover Catalyst
The changeover catalyst used in the laboratory test was
essentially the same as the changeover catalyst used in the commercial
test.
The catalyst addition scheme used was designed to rapidly bring
the ZSM-5 content of the circulating or equilibrium catalyst to the
desired level well before 72 days of operation~
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F-2909 - 15
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F-2909 - 16 -
A POSSIBLE EXPLANATION - OLEFIN ISOMERIZATION
It is believed that this modified ZSM-5 catalyst has acquired
- the ability to isomerize olefins. The theory can be stated as follows:
In order to fully explain these test results the chemistry of
octane enhancement being promoted by the ZSM-5 catalyst must first be
understood. ZSM-5 increàses gasoline octane in catalytic cracking by
cracking linear low octane components in the heavy end of the gasoline
to lighter and more branched components. Such a mechanism is adequate
to explain the performance during the addition of fresh ZSM-5 catalyst.
Nevertheless we must also consider the residual octane enhancement
observed after fresh catalyst addition has been ended. Based upon
gasoline compositional data obtained independent of this commercial
test ZSM-5 is now known to isomerize low octane linear olefins to more
highly branched and higher octane olefins.
We believe the activity enhancement catalyzed by fresh ZSM-5
catalyst addition is dominated by the first reaction, paraffin
cracking. As the catalyst a~es in the unit and equilibrates the
latter reaction mechanism, olefin isomerization, dominates as the
cracking activity decreases, hence the residual octane enhancement
activity observed.
Our test on a commercially sized unit of ZSM-5 addition gave
initial octane gains (3.5-4.5 RON+O and 2.0-2.5 MONfO) with
corresponding gasoline losses of 2.0-2.5% vol and C3 I C4
increases of 3.0-4.0% vol. Thère were no substantial increases in
coke make observed. The increase in C3 I C4 together with
additional outside i-C4 can be translated into increases in alkylate
yield of 3.0-3.5% vol. The octane enhancement decayed at a relatively
slow rate after ZSM-S addition has been terminated indicating that
ZSM-5 octane enhancement shifted from paraffin cracking to olefin
isomerization. The cracking of low octane components in the heavy
gasoline end is dominant with fresh catalyst while olefin isomerization
dominates as the catalyst ages in the TCC units.
~ 3~2~652~ii
F-2909 - 17 -
If we wanted to improve the operation of a moving bed catalyticcracking unit by the addition of ZSM-5 to it, we would replace 1-2%
per day of the circulating catalyst inventory with a ZSM-5 rich
catalyst containing 1-10 wt ~ ZSM-5. ZSM-5 catalyst addition would
continue until the circulating catalyst inventory contained the
desired ZSM-5 content.
To obtain modified ZSM-5 catalyst for use in other units, we
would add a ZSM-5 makeup catalyst that had much higher levels of
ZSM-5, typically 10 to 100 wt ~, preferably 20-50 wt ~ ZSM-5. This
may not be the optimal addition scheme as far as the moving bed
catalytic cracking unit is concerned, but it would be the best way of
making modified ZSM-5 catalyst in a moving bed cracking unit that had
to keep running.
The ZSM-5 rich catalyst added to a TCC may be made with a
slightly different particle size, or L/D, or geometry, permitting
eventual separation and recovery of modified ZSM-5 catalyst from
circulating catalyst inventory.
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