U.S. patent number 3,926,778 [Application Number 05/316,632] was granted by the patent office on 1975-12-16 for method and system for controlling the activity of a crystalline zeolite cracking catalyst.
This patent grant is currently assigned to Mobil Oil Corporation. Invention is credited to Edward J. Demmel, Hartley Owen.
United States Patent |
3,926,778 |
Owen , et al. |
December 16, 1975 |
Method and system for controlling the activity of a crystalline
zeolite cracking catalyst
Abstract
A method and system for cracking hydrocarbons and regeneration
of the catalyst is described with particular emphasis directed to
partially restoring the activity of the catalyst after an initial
hydrocarbon conversion use by heat soaking the catalyst at an
elevated temperature before use in a second hydrocarbon conversion
zone.
Inventors: |
Owen; Hartley (Belle Mead,
NJ), Demmel; Edward J. (Pitman, NJ) |
Assignee: |
Mobil Oil Corporation (New
York, NY)
|
Family
ID: |
23229924 |
Appl.
No.: |
05/316,632 |
Filed: |
December 19, 1972 |
Current U.S.
Class: |
208/74; 208/147;
208/159; 502/40; 208/78; 208/151; 208/164; 208/120.15 |
Current CPC
Class: |
B01J
29/90 (20130101); B01J 29/06 (20130101); B01J
29/084 (20130101); C10G 11/18 (20130101); B01J
8/26 (20130101); Y02P 30/40 (20151101); B01J
2229/40 (20130101) |
Current International
Class: |
C10G
11/18 (20060101); C10G 11/00 (20060101); B01J
8/24 (20060101); B01J 8/26 (20060101); B01J
29/08 (20060101); B01J 29/06 (20060101); B01J
29/90 (20060101); B01J 29/00 (20060101); C10G
037/02 (); C10G 011/04 (); B10J 008/24 (); B10J
029/12 () |
Field of
Search: |
;208/74,78,120,146-155,163 ;252/417-419 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gantz; Delbert E.
Assistant Examiner: Schmitkons; G. E.
Attorney, Agent or Firm: Huggett; Charles A. Farnsworth;
Carl D.
Claims
We claim:
1. A method for converting hydrocarbons by cracking in the presence
of a crystalline zeolite containing cracking catalyst which
comprises
a. passing a first hydrocarbon feed in admixture with a crystalline
zeolite cracking catalyst obtained from a catalyst regeneration
zone through a first cracking zone at an elevated cracking
temperature in the range of 1000.degree.F. up to about
1300.degree.F. at a hydrocarbon residence time less than about 10
seconds,
b. separating the first hydrocarbon feed catalyst suspension
product of the first cracking zone into a hydrocarbon phase and a
catalyst phase,
c. combining sufficient hot regeneration catalyst with the
separated catalyst phase to provide a mix catalyst temperature of
at least 1000.degree.F. and heat soaking said mixed catalyst at
said catalyst mix temperature for at least about 5 minutes in the
presence of a gas substantially inert to the environment so as to
substantially improve the used cracking catalyst component
activity,
d. passing catalyst subjected to said heat soaking step through an
additional hydrocarbon conversion step maintained at a temperature
of at least 1000.degree.F., and
e. separating catalyst from said additional hydrocarbon conversion
step for return after stripping thereof to a catalyst regeneration
step.
2. The method of claim 1 wherein the crystalline zeolite containing
cracking catalyst comprises a mixture of faujasite cracking
catalyst particles and ZSM-5 type catalyst particles containing an
oxidation promoter for converting carbon monoxide to carbon
dioxide.
3. In a hydrocarbon conversion process relying upon a catalyst
comprising a crystalline zeolite wherein carbonaceous deposits
deactivate the catalyst during conversion and the deactivated
catalyst is then regenerated with an oxygen containing gas the
improvement which comprises, heat soaking a crystalline zeolite
conversion catalyst contaminated with carbonaceous deposits of
hydrocarbon conversion in the presence of gas substantially inert
to the environment at a temperature of at least 1000.degree.F. for
a period of time of at least 10 minutes and thereafter using the
heat soaked catalyst combined with freshly regenerated catalyst for
further hydrocarbon conversion before passing the catalyst to
regeneration with an oxygen containing regeneration gas.
4. A method for improving the activity of a crystalline zeolite
hydrocarbon conversion catalyst reduced in activity by deposited
carbonaceous material which comprises heat soaking the crystalline
zeolite hydrocarbon conversion catalyst at a temperature of at
least 1100.degree.F. for about 10 minutes in the presence of a gas
substantially inert to the environment.
5. In a hydrocarbon conversion operation using a crystalline
zeolite containing cracking catalyst and regeneration of the
catalyst with an oxygen containing regeneration gas to remove
deposited carbonaceous material the improvement which comprises
passing regenerated catalyst suspended in hydrocarbon material
through a riser cracking zone at a temperature of at least
1000.degree.F. for a hydrocarbon residence time less than 10
seconds, separating the product obtained in said riser cracking
zone into a hydrocarbon phase and a catalyst phase, heat soaking
the catalyst phase thus separated with freshly regenerated catalyst
at a temperature of at least 1000.degree.F. for at least 5 minutes
in the presence of steam stripping gas, passing the heat soaked
catalyst admixed with additional hot regenerated catalyst and
suspended in hydrocarbon feed material through an additional
hydrocarbon conversion zone maintained at a temperature of at least
1000.degree.F. and at a hydrocarbon residence time less than 10
seconds, separating catalyst containing carbonaceous deposits from
hydrocarbon vapors removed from said additional hydrocarbon
conversion zone, stripping the separated catalyst, passing the
stripped catalyst to a fluid bed of catalyst in the lower end of an
elongated riser regeneration zone, raising the temperature of said
fluid bed of catalyst with freshly regenerated catalyst and by
burning deposited carbonaceous material on the catalyst particles
with oxygen containing gas, passing the catalyst particles thus
contacted with gaseous products of carbonaceous material combustion
upwardly through elongated riser regeneration zone, adding
additional oxygen containing gas to said upflowing catalyst
particles to obtain combustion of formed carbon monoxide,
separating hot regenerated catalyst from combustion product gases
at the end of said riser regeneration zone, collecting the
separated catalyst as a dense fluid bed of catalyst at a
temperature in the range of 1000.degree. to 1600.degree.F.
contacting the thus collected dense fluid bed of catalyst with
oxygen containing gas and using the regenerated catalyst in the
hydrocarbon conversion and catalyst regeneration combination as
above recited.
Description
BACKGROUND OF THE INVENTION
The field of catalytic cracking and particularly dense or dilute
fluid phase catalytic operations have been undergoing progressive
development since early 1940. Thus as new experience was gained in
operating and design parameters, new catalyst compositions were
developed which required a further refinement of known operating
and design parameters so as to extract maximum efficiency from the
combination operation. With the advent of high activity crystalline
zeolite cracking catalyst development, we once again find ourselves
in a new area of operation requiring ever further refinements in
order to take advantage of the new catalyst activity, selectivity
and operating sensitivity. The present invention is concerned with
a combination operation which relies upon a combination of catalyst
functions mutually contributing to accomplish upgrading of
available refinery feed material.
SUMMARY OF THE INVENTION
The present invention is concerned with the conversion of
hydrocarbon feed materials in one or more catalytic reaction zones
and maintaining the activity of the catalyst employed therein. More
particularly the present invention is concerned with the removal of
carbonaceous material from the cracking sites of a crystalline
zeolite containing cracking catalyst by the combination of catalyst
regeneration in the presence of oxygen containing gaseous material
and heat soaking of catalyst particles at least partially
inactivated by deposited carbonaceous material. In a more
particular aspect the present invention involves the regeneration
of catalyst comprising crystalline zeolite materials suitable for
cracking hydrocarbon feed materials by the combination of riser
regeneration of a carbon inactivated catalyst composition in the
presence of sufficient oxygen to form combustion products
substantially free of carbon-monoxide. Oxygen regenerated cracking
catalyst is used in a first hydrocarbon conversion zone under
conditions to at least partially deactivate the catalyst by the
deposition of carbonaceous material, the partially deactivated
catalyst is then heat soaked at a temperature preferably in excess
of the temperature of the catalyst as recovered from the first
reaction zone whereby deposited carbonaceous material is
substantially recovered from the active zeolite cracking catalyst
and the zeolite catalyst thus improved in activity is used in a
second hydrocarbon conversion reaction zone under elevated
temperature cracking conditions. Heat soaking of the catalyst is
accomplished in the presence of added freshly regenerated catalyst
provided in an amount to achieve a mixed catalyst temperature of
about 50.degree.F. above the temperature of the catalyst as
recovered from the first reaction zone and preferably 150.degree.F.
above that temperature. The mixed catalyst is heat soaked for a
duration of at least 2 minutes and preferably at least 5 to 10
minutes or more.
The method and system of this invention is concerned with the
finding that heating of a crystalline aluminosilicate cracking
catalyst containing fresh deposits of carbonaceous material of
cracking will substantially restore the cracking activity of the
catalyst. This discovery is of particular interest in, for example,
a process design wherein catalyst separated from a first riser
reactor with deposited carbonaceous material is combined with
freshly regenerated catalyst, heat soaked for a duration of time of
at least 5 minutes at a temperature of at least 1100.degree.F. and
then using the catalyst mixture in a separate second riser reactor.
However, in a single riser reactor conversion system wherein
seperated catalyst is collected, stripped of entrained hydrocarbons
and then recycled to a regeneration operation, it is contemplated
recycling heat soaked catalyst mixture at least in part to the
inlet of the single riser system. The concepts of the present
invention are widely applicable to crystalline zeolite cracking
catalyst compositions and particularly those employing "X" and "Y"
crystalline zeolites when alone or in combination with crystalline
zeolites of the ZSM-5 and ZSM-8 type of materials. Another suitable
catalyst composition is known as Alderey.
The processing concepts of the present invention are particularly
amenable to modern-day low coke producing crystalline
aluminosilicate catalyst compositions and such catalyst may be used
to advantage in both the hydrocarbon conversion operation of the
process and the catalyst regeneration operation by developing a
greater accumulation of carbonaceous deposits on the total mass of
catalyst than heretofore obtained before regeneration thereof. The
reasons for this observed phenomenon is not readily explained and
most unexpected. Furthermore, it has been found that the concepts
going to the very essence of the present invention are applicable
to other zeolite catalyst mixtures and particularly those
comprising a mixture of a crystalline faujasite cracking component
with a ZSM-5 type of crystalline material.
The catalyst mixture and/or compositions suitable for use in this
invention comprise a mixture of small pore and large pore
crystalline aluminosilicate in combination with one another as
separate discrete particles and these may be composited from
substantially any high activity large pore crystalline zeolite
cracking component in admixture with, for example, a ZSM-5 type of
catalyst composition. The ZSM-5 type catalyst composition is a
relatively small average pore diameter material smaller than, for
example, a rare earth exchanged X or Y crystalline zeolite.
The large and small pore crystalline zeolites above discussed may
be dispersed within a separate or a common matrix material suitable
for encountering relatively high temperatures contemplated in the
fluid cracking operation of this invention with its attendant
catalyst regeneration operation. The catalyst mixture or
composition contemplated for use in this invention will catalyze
the conversion of the various components comprising the hydrocarbon
feed including normal paraffins to produce for example gasoline as
well as LPG types of gaseous materials. Thus the catalysts suitable
for this invention have activity for cracking several different
kinds and types of hydrocarbons found in gas oil boiling range
materials in combination with a very selective cracking of normal
paraffins and singly branched hydrocarbons which are restructured
and/or upgraded to desired higher boiling components.
The novel process combination of this invention using a catalyst
system comprising a mixture of separate catalyst particles or a
homogeneous composition of one or more crystalline zeolite
components dispersed in an amorphous matrix material wherein the
zeolite component or components acts substantially independently as
herein defined upon given hydrocarbon components and each catalyst
component is relied upon substantially to support the function of
the other. Thus it is contemplated employing in the catalyst system
of this invention, a large pore crystalline aluminosilicate having
a pore size in excess of about 9 Angstroms as a major component
with the minor component being a small pore crystalline component
having a maximum pore size not exceeding about 9 Angstroms and
preferably being less than about 7 Angstroms. On the other hand,
the large and small pore zeolites may be used in substantially
equal amounts or the smaller pore crystalline zeolite may be in a
minor or major proportion. On the other hand, either crystalline
zeolite component may be used alone and dispersed in a suitable
matrix material as herein defined. The small pore crystalline
zeolite is preferably a ZSM-5 type of crystalline material such as
that described in U.S. Pat. No. 3,702,886, issued Nov. 14, 1972 or
copending application Ser. No. 257,983 a continuation of Ser. No.
865,418 filed Oct. 10, 1969 both now abandoned. The large pore
crystalline zeolite may be any of the now known crystalline
aluminosilicates which are suitable for cracking hydrocarbons and
providing a pore size in excess of 8 Angstroms. Such a composition
has the structure and capability to act upon substantially all the
components usually found in a gas oil feed boiling in the range of
500.degree. up to 950.degree. or 1100.degree.F. Large pore zeolites
of this type are well known and include materials or synthetic
faujasite of both the X and Y type as well as zeolite L. Of these
materials zeolite Y is particularly preferred.
The crystalline zeolites above identified may be exchanged,
combined, dispersed or otherwise intimately admixed with a porous
matrix. By porous matrix it is intended to include inorganic and
organic compositions with which the crystalline aluminosilicates
may be affixed. The matrix may be active or substantially inactive
to the hydrocarbon conversion reactions encountered. The preferred
porous matrix may be selected from the group comprising inorganic
oxides such as clay, acid treated clay, silica-alumina etc. A more
complete description of a catalyst composition comprising ZSM-5
type materials which may be used with advantage in this invention
and their method of preparation may be found in the application and
patent above identified.
In the combination of this invention the small pore crystalline
zeolite component of the catalyst is relied upon for promoting new
ring formations and/or alkylation thereof in a manner which may be
made to increase with reaction severity either by increasing
temperatures or by increasing residence time thus encountering a
corresponding decrease in alkylation reaction with the ZSM-5
crystalline component.
In yet a further embodiment it is contemplated combining the ZSM-5
type catalyst with a porous matrix as suggested above and an
oxidation catalyst suitable for converting carbon monoxide to
carbon dioxide. Thus separate particles of catalyst, one comprising
ZSM-5 and the oxidation catalyst dispersed in a suitable material
are provided with the other comprising catalytically active X or Y
faujasite dispersed in a suitable matrix material from a mixture of
catalyst particles which are circulated in the system herein
discussed for the reasons discussed.
A significant observation contributing to the operational concepts
of this invention is the finding that high temperature cracking of
the gas oil feed above about 1000.degree.F. does not significantly
deactivate the activity and selectivity of a smaller pore ZSM-5
crystalline component combined with the larger pore size cracking
component. Furthermore, it has been observed that combining a
carbon monoxide oxidation promoter such as chromium oxide with the
ZSM-5 catalyst component is not significantly deactivated by coke
depositors and thus each component of the catalyst particle can
function to independently perform its desired reaction mechanism,
the ZSM-5 component for olefin cyclization and the oxidation
promoter for conversion of carbon monoxide to carbon dioxide in the
regeneration steps of the overall combination herein described.
Furthermore, the total mass of catalyst circulated in the system
desirably is a heat sink for promoting desired endothermic
conversion reactions encountered in the operation. When the
oxidation component such as copper, nickel, chromium, manganese
oxide or copper chromite is combined with the catalyst as above
described a significant heat benefit is realized by virtue of the
exothermic conversion of CO to CO.sub.2 during regeneration of the
catalyst and every opportunity for recovering this heat supply is
taken advantage of in the processing concepts herein described. The
oxidation component may comprise from one tenth to three weight
percent of the catalyst inventory.
The small pore size crystalline zeolite catalyst material preferred
in the combination of this invention is preferably of the ZSM-5
type and as such the small pore has a uniform pore size varying
because of its elliptical shape from about 5.5 Angstroms up to
about 6 and about 9 Angstrom units.
One embodiment of this invention resides in the use of a single
porous matrix material as the sole support for the two different
pore size crystalline zeolites herein defined. Thus the catalyst
may comprise an aluminosilicate of the ZSM-5 type blended with an
aluminosilicate having a pore size generally larger than that of
ZSM-5 and more usually greater activity 8 Angstrom units in a
porous matrix as a homogenous mixture in such proportions that the
resulting product contains from about 1 up to about 95% by weight
and preferably from about 10 to 50% by weight of total crystalline
aluminosilicates in the final composite.
The particular proportions of one aluminosilicate component to the
other in the catalyst system or composition herein defined is not
narrowly critical and even though it can vary over an extremely
wide range it has been found that the weight ratio of the ZSM-5
type aluminosilicate to the large pore size aluminosilicate can
range from 1:10 up to 3:1 and preferably should be from about 1:3
to 1:1.
Hydrocarbon charge stocks which may be converted by the combination
and method of this invention comprise petroleum fractions having an
initial boiling point of at least 400.degree.F. and an end point of
at least 600.degree.F. and as high as 950 to 1100.degree.F. The
present invention also contemplates the cracking of naphtha boiling
in the range of C.sub.5 hydrocarbons up to about 400.degree.F. to
improve its octane rating in combination with producing significant
quantities of LPG type materials which then can be used as part of
the charge to the ZSM-5 contact stage of the combination.
Hydrocarbons boiling above 400.degree.F. include gas oils, residual
oils, cycle stocks, whole topped crudes and heavy hydrocarbon
fractions derived by destructive hydogenation processes. These may
be used alone or in combination as the first riser reactor
hydrocarbon charge.
BRIEF DESCRIPTION OF THE DRAWING
The drawing diagrammatically depicts a processing scheme and
arrangements of vessels for effecting hydrocarbon conversion in a
combination of riser reactor stages, regeneration of catalyst under
dense and dispersed phase conditions and heat soaking of used
catalyst between the hydrocarbon conversion stages.
DISCUSSION OF SPECIFIC EMBODIMENTS
Referring now to the drawing, a cracking catalyst comprising a
crystalline aluminosilicate such as a faujasite cracking component
either alone or in admixture with a ZSM-5 type material dispersed
in matrix material of relatively low cracking activity is caused to
circulate in a system of hydrocarbon conversion and catalyst
regeneration shown in the drawing and herein defined. In the
process of the drawing a catalyst contaminated with deposited
carbonaceous material of cracking and obtained as hereinafter
defined is passed by conduit 2 provided with flow control valve 4
at a temperature within the range of 800.degree. up to about
1000.degree.F. and more usually about 950.degree.F. into a vessel 6
which tapers inwardly and upwardly to form a riser regenerator 8 of
restricted cross section in the upper portion. In the lower bulb
portion 6 of riser 8 the catalyst is retained as a relatively dense
fluid bed of catalyst 10 to which hot freshly regenerated catalyst
at a temperature in the range of 1200.degree. to 1400.degree.F. may
be added by conduit 12 provided with valve 14 to form a heated
catalyst mixture to be regenerated. Oxygen containing regeneration
gas is introduced by conduit 16 to a bottom portion of the dense
fluid mass of catalyst 10 under conditions of temperature, pressure
and space velocity to initiate combustion of carbonaceous material
and raise the temperature of the mass of catalyst sufficient to
substantially complete burning of deposited carbonaceous materials.
The mixing of hot regenerated catalyst with spent catalyst to raise
the temperature of the spent catalyst can be further assisted by
the addition of a combustion supporting fuel as by conduit 18 along
with the oxygen containing regeneration gas. The catalyst being
regenerated in bed 10 in a relatively dense fluid condition is
caused to move upwardly from the bed by combustion gases and
carried into the restricted riser section with gaseous products of
combustion for discharge from the end of the riser 8 into a
combination of cyclone separators 24 and 26 arranged in parallel
flow arrangement for separating regenerated catalyst from
regeneration flue gases. The regeneration system of this invention
is particularly useful and desirable since additional oxygen
containing regeneration gas is added to the suspension in riser 8
by one or more spaced apart conduits represented by conduits 20 and
22. The additional oxygen rich gas causes further burning of
carbonaceous deposits to be accomplished along with promoting the
combustion of formed carbon monoxide (CO) so that the restricted
riser section is an effective heat exchange zone of considerable
magnitude between catalyst particles and combustion product gases
passing therethrough. Thus a more selective temperature control
increasing in the direction of flow of the catalyst passing
upwardly through the riser from about 900.degree. up to about
1200.degree.F. and as high as 1400.degree.F. may be realized by the
combination operation above described. The suspension in riser 8 is
discharged by a "T" connecting conduit into cyclone separators 24
and 26 on each end thereof. The cyclonic separators are provided
with diplegs 28 and 30 for passing separated hot catalyst
sequentially to fluid catalyst bed 32 therebelow. Gaseous products
of combustion pass overhead from cyclone separator 24 and 26 by
open end conduits 34 and 36 discharging into a dispersed phase
above a fluid bed of catalyst 32 and thence into cyclone separators
38 and 40 provided with diplegs 42 and 44. Fluidizing gas and/or
oxygen containing regeneration gas may be added by conduit 46 to
the lower portion of catalyst bed 32 to effect a final burning of
carbonaceous material if such is required and desired to further
elevate the temperature of the catalyst. Gaseous products of
regeneration or flue gases are passed from cyclone separators 38
and 40 to chamber 48 from which they are withdrawn by conduit 50.
The hot regenerated catalyst comprising bed 32 being at an elevated
temperature in excess of about 1000.degree.F. and as high as
1400.degree. or 1600.degree.F. is withdrawn from a lower portion
thereof for distribution and use as discussed above and below.
A stream of hot regenerated catalyst is withdrawn from catalyst bed
32 by conduit 52 provided with flow control valve 54 and passed to
the bottom portion of riser reactor 56 to which a suitable
hydrocarbon feed is introduced by conduit 58. A suspension is
formed with the catalyst and hydrocarbon introduced to the riser
providing a catalyst to oil ratio sufficient to obtain a suspension
temperature of at least 1000.degree.F. The hydrocarbon feed may be
preheated by means not shown up to about 800.degree.F. before
admixture with the catalyst. In riser reactor 56, hydrocarbon
conversion conditions of temperature in the range of 1000.degree.
up to about 1200.degree.F. or 1300.degree.F. are maintained and
space velocity conditions sufficient to provide a hydrocarbon
residence time with the range of a fraction of a second up to
several seconds such as 5 to 10 seconds or as high as about 15
seconds. More usually the hydrocarbon residence time within riser
56 will be in the range of 1 to 5 seconds. The hydrocarbon-catalyst
suspension passed through riser 56 discharges at the upper end
thereof into one or more suitably arranged cyclone separator 60
provided with catalyst dipleg 62. Gasiform hydrocarbon material
separated in cyclone 60 is carried overhead by conduit 64 into
chamber 66 and thence by conduit 68 to a product fractionation zone
not shown.
The catalyst separated by cyclone 60 is conveyed by dipleg 62 to a
dense fluid bed of catalyst 70 therebelow. In accordance with this
invention hot freshly regenerated catalyst is added to fluid bed 70
by riser conduit 72 in an amount sufficient to achieve a desired
temperature increase of at least 50.degree.F. and sufficient to
provide a catalyst mix temperature of at least 1000.degree.F. The
regenerated catalyst is supplied to riser 72 by conduit 74 provided
with flow control valve 76. Lift gas, substantially inert to the
environment contacted is introduced to the base of riser 72 by
conduit 78. In the dense fluid catalyst bed 70, the catalyst is
maintained at a temperature of at least 1000.degree.F. under
agitated conditions to provide a heat soaking of used catalyst
discharged by dipleg 62 with freshly regenerated catalyst for a
time duration of at least about 2 minutes and as high as 15
minutes. During heat soaking of the cracking catalyst it has been
found that carbonaceous material deposited on the catalyst is
removed or displaced in such amounts to substantially restore the
activity of the cracking catalyst to that expected from the
crystalline zeolite cracking component of the catalyst. This
unexpected and unusual finding is particularly useful when using
low coke producing crystalline zeolite cracking catalysts since it
has been found that a much greater accumulation of carbonaceous
material may be collected on the catalyst before regeneration
thereof without undesirably influencing the useful activity of the
catalyst for cracking hydrocarbon materials. A stripping and/or
fluidizing gas is introduced to the lower portion of bed 70 by
steam conduit 80 to maintain the catalyst during its head soaking
operation in a fluidized condition. The heat soaked catalyst is
then withdrawn at an elevated temperature in the range of
1000.degree. to about 1300.degree.F. from the bottom of the bed by
conduit 82 provided with a flow control valve 84 for passage to the
bottom portion of a second riser reactor 86 to which a second
hydrocarbon feed is introduced by conduit 88. Additional hot
regenerated catalyst may also be withdrawn by conduit 90 provided
with flow control valve 92 and mixed with the catalyst in conduit
82 passed to riser 86.
The catalyst and oil introduced to the lower portion of riser 86 is
adjusted to form a suspension providing a temperature within the
range of 1000.degree. to 1250.degree.F. which then moves upwardly
through the riser during the conversion of the hydrocarbon charge.
The operating conditions in riser 86 may be the same as that
employed in riser 56 or more severe by relying upon an increased
catalyst to oil ratio within the range of 3 to 20 and a hydrocarbon
residence time within the range of 0.5 to 15 or more seconds. For
example, a more dense catalyst phase suspension may be employed in
riser reactor 86 than employed in riser reactor 56. The suspension
passed through riser 86 is separated in cyclone 94 provided with
dipleg 96. Separated gasiform hydrocarbon material is removed from
separator 94 by conduit 98 and passed to chamber 66 wherein it is
combined with hydrocarbons separated by cyclone 60. Catalyst
separated in cyclone 94 is passed by dipleg 96 to a separate dense
fluid bed of catalyst 100 separated from catalyst bed 70 by a
common baffle member 102. It is contemplated maintaining catalyst
bed 100 and 70 as concentric cylindrical and annular beds within
the lower portion of the vessel with bed 70 being retained
preferably as the concentric cylindrical bed of catalyst. Catalyst
bed 100 is stripped with stripping gas such as steam introduced by
conduit 104. Stripped catalyst is withdrawn from catalyst bed 100
and conveyed by conduit 2 to catalyst regeneration as defined
above.
A further embodiment of this invention is concerned with utilizing
a dual function catalyst such as a Y faujasite crystalline zeolite
in conjunction with a ZSM-5 type of crystalline material to provide
the capability of internally controlling to some considerable
degree the activity level of each of the separate zeolite
components. For example, varying the temperature and time of heat
soaking the catalyst apparently yields a higher activity for the Y
faujasite component. On the other hand, since the ZSM-5 type
component lays down very little coke by comparison it inherently
retains much more of its initial cracking activity. Thus using no
heat soaking between stages or after the first stage will maximize
the activity of the ZSM-5 component in the second riser. The amount
of activity would be proportional to the ratio of recycled to
freshly regenerated catalyst. Reheating the catalyst after a first
stage of cracking to a very high temperature such as about
1300.degree.F. before or concurrent with stripping will operate to
reactivate the Y faujasite component more and thus result in a
higher activity in relation to the ZSM-5 type component.
EXAMPLE
A Y faujasite crystalline zeolite containing cracking catalyst was
coked for one minute at 925.degree.F., at a 6 weight hourly space
velocity using a 10 catalyst to oil ratio with a gas oil feed
boiling from 460.degree. to 900.degree.F. of 22 API gravity. The
catalyst thus coked had a cracking activity of about 27.9.
Determination of the catalyst cracking acitvity was obtained by
contacting the catalyst with a Light East Texas Gas Oil (LETGO) at
850.degree.F., 2 catalyst/oil ratio, 6 weight hourly space
velocity.
The spent catalyst of 27.9 activity was stripped with nitrogen at
925.degree.F. resulting in a catalyst with an activity of 34.3 as
determined by LETGO test above defined.
The stripped catalyst was then heat soaked for 10 minutes at
1100.degree.F. and tested for activity. The activity determined by
the above recited LETGO test was 38.9. It is clear from the above
that heat soaking of a crystalline zeolite containing catalyst used
for cracking gas oil can restore its activity far beyond that
obtained by high temperature stripping of the catalyst above. The
activity of a stabilized Y sieve cracking catalyst after
regeneration is usually in the range of 40 to 45.
Having thus provided a general discussion of the invention and
provided specific examples in support thereof, it is to be
understood that no undue limitations are to be imposed by reason
thereof except as defined in the following claims.
* * * * *