U.S. patent application number 11/199050 was filed with the patent office on 2006-10-19 for method and apparatus for making a middle distillate product and lower olefins from a hydrocarbon feedstock.
Invention is credited to Georghios Agamemnonons Hadjigeorge, Frank Hsian Hok Khouw, Weijian Mo.
Application Number | 20060231461 11/199050 |
Document ID | / |
Family ID | 35106982 |
Filed Date | 2006-10-19 |
United States Patent
Application |
20060231461 |
Kind Code |
A1 |
Mo; Weijian ; et
al. |
October 19, 2006 |
Method and apparatus for making a middle distillate product and
lower olefins from a hydrocarbon feedstock
Abstract
Disclosed is a process for making middle distillate and lower
olefins. The process includes catalytically cracking a gas oil
feedstock within a riser reactor zone by contacting under suitable
catalytic cracking conditions within the riser reactor zone the gas
oil feedstock with a middle distillate selective cracking catalyst
that comprises amorphous silica alumina and a zeolite to yield a
cracked gas oil product and a spent cracking catalyst. The spent
cracking catalyst is regenerated to yield a regenerated cracking
catalyst. Within a dense bed reactor zone and under suitable high
severity cracking conditions a gasoline feedstock is contacted with
the regenerated cracking catalyst to yield a cracked gasoline
product and a used regenerated cracking catalyst. The used
regenerated cracking catalyst is utilized as the middle distillate
selective catalyst.
Inventors: |
Mo; Weijian; (Sugar Land,
TX) ; Khouw; Frank Hsian Hok; (Sugar Land, TX)
; Hadjigeorge; Georghios Agamemnonons; (Sugar Land,
TX) |
Correspondence
Address: |
Shell Oil Company
910 Louisiana
Houston
TX
77002
US
|
Family ID: |
35106982 |
Appl. No.: |
11/199050 |
Filed: |
August 8, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60600264 |
Aug 10, 2004 |
|
|
|
Current U.S.
Class: |
208/120.1 ;
422/139; 422/147 |
Current CPC
Class: |
C10G 2400/08 20130101;
C10G 11/05 20130101; C10G 51/026 20130101; C10G 2300/807 20130101;
C10G 2400/04 20130101; C10G 11/182 20130101; C10G 11/18 20130101;
B01J 8/1809 20130101; C10G 2400/20 20130101; C10G 2300/1059
20130101 |
Class at
Publication: |
208/120.1 ;
422/139; 422/147 |
International
Class: |
C10G 11/00 20060101
C10G011/00; B01J 8/18 20060101 B01J008/18 |
Claims
1. A process for making middle distillate and lower olefins, said
process comprises: catalytically cracking a gas oil feedstock
within a riser reactor zone by contacting under suitable catalytic
cracking conditions within said riser reactor zone said gas oil
feedstock with a middle distillate selective cracking catalyst that
comprises amorphous silica alumina and a zeolite to yield a riser
reactor product comprising a cracked gas oil product and a spent
cracking catalyst; regenerating said spent cracking catalyst to
yield a regenerated cracking catalyst; contacing within a dense bed
reactor zone and under suitable high severity cracking conditions a
gasoline feedstock with said regenerated cracking catalyst to yield
a cracked gasoline product and a used regenerated cracking
catalyst; and using said used regenerated cracking catalyst as said
middle distillate selective catalyst.
2. A process as recited in claim 1, further comprising: separating
said riser reactor product into said cracked gas oil product and
said spent cracking catalyst.
3. A process as recited in claim 2, further comprising: adding to
said regenerated cracking cracking catalyst a ZSM-5 additive.
4. A process as recited in claim 3, further comprising: introducing
steam into said dense bed reactor zone.
5. A process as recited in claim 5, wherein said suitable catalytic
cracking conditions are such as to provide for a conversion of said
gas oil feedstock in the range of from 40 to 85 weight percent of
the total gas oil feedstock.
6. A process as recited in claim 5, wherein said used regenerated
cracking catalyst includes a small concentration of carbon.
7. A process, comprising: contacting a gas oil feedstock within a
riser reactor zone under suitable catalytic cracking conditions
with a cracking catalyst and yielding a riser reactor product
comprising a cracked gas oil product and a spent cracking catalyst;
separating said riser reactor product into said cracked gas oil
product and said spent cracking catalyst; regenerating said spent
cracking catalyst to yield a regenerated cracking catalyst;
splitting said regenerated cracking catalyst into at least a
portion of said regenerated cracking catalyst and a remaining
portion of said regenerated cracking catalyst; passing said at
least a portion of said spent cracking catalyst to a dense bed
reactor zone wherein said at least a portion of said spent cracking
catalyst is contacted under suitable high severity cracking
conditions with a gasoline feedstock to yield a cracked gasoline
product and a used regenerated cracking catalyst; and using said
remaining portion of said regenerated cracking catalyst and said
used regenerated cracking catalyst as said cracking catalyst.
8. A process as recited in claim 7, further comprising: mixing with
said at least a portion of said spent cracking catalyst a ZSM-5
additive.
9. A process as recited in claim 8, further comprising: introducing
steam into said dense bed reactor zone.
10. A process as recited in claim 9, further comprising: separating
a slurry product from said cracked gas oil product.
11. A process as recited in claim 10, further comprising:
introducing said slurry product to said riser reactor zone.
12. An apparatus, comprising: riser reactor means for contacting a
gas oil feedstock with a catalytic cracking catalyst under
catalytic cracking conditions to yield a riser reactor product
comprising a cracked gas oil product and a spent cracking catalyst;
separator means for separating said riser reactor product into said
cracked gas oil product and said spent cracking catalyst;
regenerator means for regenerating said spent cracking catalyst to
yield a regenerated catalyst; dense bed reactor means for
contacting a gasoline feedstock with said regenerated catalyst
under high severity conditions to yield a cracked gasoline product
and a used regenerated catalyst; and means for providing for the
use of said used regenerated catalyst as said catalytic cracking
catalyst.
Description
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 60/600,264, filed Aug. 10, 2004.
[0002] The invention relates to method and apparatus for the
manufacture of a middle distillate product and lower olefins from a
hydrocarbon feedstock.
BACKGROUND OF THE INVENTION
[0003] The fluidized catalytic cracking (FCC) of heavy hydrocarbons
to produce lower boiling hydrocarbon products such as gasoline is
well known in the art. FCC processes have been around since the
1940's. Typically, an FCC unit or process includes a riser reactor,
a catalyst separator and stripper, and a regenerator. A FCC
feedstock is introduced into the riser reactor wherein it is
contacted with hot FCC catalyst from the regenerator. The mixture
of the feedstock and FCC catalyst passes through the riser reactor
and into the catalyst separator wherein the cracked product is
separated from the FCC catalyst. The separated cracked product
passes from the catalyst separator to a downstream separation
system and the separated catalyst passes to the regenerator where
the coke deposited on the FCC catalyst during the cracking reaction
is burned off the catalyst to provide a regenerated catalyst. The
resulting regenerated catalyst is used as the aforementioned hot
FCC catalyst and is mixed with the FCC feedstock that is introduced
into the riser reactor.
[0004] Many FCC processes and systems are designed so as to provide
for a high conversion of the FCC feedstock to products having
boiling temperatures in the gasoline boiling range. There are
situations, however, when it is desirable to provide for the high
conversion of the FCC feedstock to middle distillate boiling range
products, as opposed to gasoline boiling range products, and to
lower olefins.
SUMMARY OF THE INVENTION
[0005] It is, thus, an object of this invention to provide method
and apparatus for the preferential conversion of a hydrocarbon
feedstock to a middle distillate product and lower olefins.
[0006] Accordingly, a process is provided for making middle
distillate and lower olefins by catalytically cracking a gas oil
feedstock within a riser reactor zone by contacting under suitable
catalytic cracking conditions within the riser reactor zone the gas
oil feedstock with a middle distillate selective cracking catalyst
that comprises amorphous silica alumina and a zeolite to yield a
cracked gas oil product and a spent cracking catalyst. The spent
cracking catalyst is regenerated to yield a regenerated cracking
catalyst. The gasoline feedstock is contacted within a dense bed
reactor zone and under suitable high severity cracking conditions
with the regenerated cracking catalyst to yield a cracked gasoline
product and a used regenerated cracking catalyst. The used
regenerated cracking catalyst is used as the middle distillate
selective catalyst.
[0007] According to another invention, provided is an apparatus
that comprises riser reactor means for contacting a gas oil
feedstock with a catalytic cracking catalyst under catalytic
cracking conditions to yield a riser reactor product comprising a
cracked gas oil product and a spent cracking catalyst; separator
means for separating the riser reactor product into the cracked gas
oil product and the spent cracking catalyst; regenerator means for
regenerating the spent cracking catalyst to yield a regenerated
catalyst; dense bed reactor means for contacting a gasoline
feedstock with the regenerated catalyst under high severity
conditions to yield a cracked gasoline product and a used
regenerated catalyst; and means for providing for the use of the
used regenerated catalyst as the catalytic cracking catalyst.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a process flow schematic representing certain
aspects of the inventive process.
DETAILED DESCRIPTION OF THE INVENTION
[0009] The invention is a process and apparatus that provides for
the processing of a heavy hydrocarbon feedstock to selectively
produce middle distillate boiling range products and lower olefins.
It has been discovered that the use of a dense phase reactor, or
fixed fluidized bed reactor, between the catalyst regenerator and
riser reactor of a conventional FCC process or unit can provide for
an improved middle distillate yield and for enhanced selectivity
toward the production of lower olefins. The inventive process
utilizes the dense phase reactor to provide for the cracking of a
gasoline feedstock that preferably boils in the gasoline
temperature range to yield lower olefins and for the conditioning
of the catalyst so that when it is used in the cracking of the FCC
feedstock in the riser reactor the reactor conditions are more
suitable for the production of a middle distillate product.
[0010] In the inventive process, a gas oil feedstock is introduced
into the bottom of a riser reactor where it is mixed with hot
cracking catalyst such as a regenerated cracking catalyst or a used
regenerated cracking catalyst or a combination of both catalysts.
The starting catalytic cracking catalyst used in the inventive
process and regenerated to ultimately become the regenerated
cracking catalyst can be any suitable cracking catalyst known in
the art to have cracking activity at the elevated temperatures
contemplated by the invention.
[0011] Preferred catalytic cracking catalysts for use in the
inventive process include fluidizable cracking catalysts comprised
of a molecular sieve having cracking activity dispersed in a
porous, inorganic refractory oxide matrix or binder. The term
"molecular sieve" as used herein refers to any material capable of
separating atoms or molecules based on their respective dimensions.
Molecular sieves suitable for use as a component of the cracking
catalyst include pillared clays, delaminated clays, and crystalline
aluminosilicates. Normally, it is preferred to use a cracking
catalyst that contains a crystalline aluminosilicate. Examples of
such aluminosilicates include Y zeolites, ultrastable Y zeolites, X
zeolites, zeolite beta, zeolite L, offretite, mordenite, faujasite,
and zeolite omega. The preferred crystalline aluminosilicates for
use in the cracking catalyst are X and Y zeolites with Y zeolites
being the most preferred.
[0012] U.S. Pat. No. 3,130,007, the disclosure of which is hereby
incorporated by reference in its entirety, describes Y-type
zeolites having an overall silica-to-alumina mole ratio between
about 3.0 and about 6.0, with a typical Y zeolite having an overall
silica-to-alumina mole ratio of about 5.0. It is also known that
Y-type zeolites can be produced, normally by dealumination, having
an overall silica-to-alumina mole ratio above about 6.0. Thus, for
purposes of this invention, a Y zeolite is one having the
characteristic crystal structure of a Y zeolite, as indicated by
the essential X-ray powder diffraction pattern of Y zeolite, and an
overall silica-to-alumina mole ratio above 3.0, and includes Y-type
zeolites having an overall silica-to-alumina mole ratio above about
6.0.
[0013] The stability and/or acidity of a zeolite used as a
component of the cracking catalyst may be increased by exchanging
the zeolite with hydrogen ions, ammonium ions, polyvalent metal
cations, such as rare earth-containing cations, magnesium cations
or calcium cations, or a combination of hydrogen ions, ammonium
ions and polyvalent metal cations, thereby lowering the sodium
content until it is less than about 0.8 weight percent, preferably
less than about 0.5 weight percent and most preferably less than
about 0.3 weight percent, calculated as Na.sub.2O. Methods of
carrying out the ion exchange are well known in the art.
[0014] The zeolite or other molecular sieve component of the
cracking catalyst is combined with a porous, inorganic refractory
oxide matrix or binder to form a finished catalyst prior to use.
The refractory oxide component in the finished catalyst may be
silica-alumina, silica, alumina, natural or synthetic clays,
pillared or delaminated clays, mixtures of one or more of these
components and the like. Preferably, the inorganic refractory oxide
matrix will comprise a mixture of silica-alumina and a clay such as
kaolin, hectorite, sepiolite and attapulgite. A preferred finished
catalyst will typically contain between about 5 weight percent to
about 40 weight percent zeolite or other molecular sieve and
greater than about 20 weight percent inorganic, refractory oxide.
In general, the finished catalyst may contain between about 10 to
about 35 weight percent zeolite or other molecular sieve, between
about 10 to about 30 weight percent inorganic, refractory oxide,
and between about 30 to about 70 weight percent clay.
[0015] The crystalline aluminosilicate or other molecular sieve
component of the cracking catalyst may be combined with the porous,
inorganic refractory oxide component or a precursor thereof by any
suitable technique known in the art including mixing, mulling,
blending or homogenization. Examples of precursors that may be used
include alumina, alumina sols, silica sols, zirconia, alumina
hydrogels, polyoxycations of aluminum and zirconium, and peptized
alumina. In a preferred method of preparing the cracking catalyst,
the zeolite is combined with an alumino-silicate gel or sol or
other inorganic, refractory oxide component, and the resultant
mixture is spray dried to produce finished catalyst particles
normally ranging in diameter between about 40 and about 80 microns.
If desired, however, the zeolite or other molecular sieve may be
mulled or otherwise mixed with the refractory oxide component or
precursor thereof, extruded and then ground into the desired
particle size range. Normally, the finished catalyst will have an
average bulk density between about 0.30 and about 0.90 gram per
cubic centimeter and a pore volume between about 0.10 and about
0.90 cubic centimeter per gram.
[0016] In the case of the use in the inventive process of a riser
reactor that is vertically arranged, lift gas or lift steam may
also be introduced into the bottom of the riser reactor along with
the gas oil feedstock and the hot cracking catalyst. The
regenerated cracking catalyst that is yielded from the catalyst
regenerator has a higher temperature than the used regenerated
cracking catalyst that is yielded from the dense phase reactor.
Also, the used regenerated cracking catalyst has deposited thereon
as a result of its use in the dense phase reactor a certain amount
of coke. As will be discussed more fully elsewhere herein, a
particular catalyst or combination of catalysts may be used to help
control the conditions within the riser reactor to provide for
certain desired cracking conditions required to provide a desired
product or mix of products.
[0017] The mixture of gas oil feedstock and hot cracking catalyst,
and, optionally, lift gas or steam, passes through the riser
reactor wherein cracking takes place. The riser reactor defines a
catalytic cracking zone and provides means for providing a
contacting time to allow the cracking reactions to occur. The
average residence time of the hydrocarbons in the riser reactor
generally can be in the range of upwardly to about 5 to 10 seconds,
but usually is in the range of from 0.1 to 5 seconds. The weight
ratio of catalyst to hydrocarbon feed (catalyst/oil ratio)
generally can be in the range of from about 2 to about 100 and even
as high as 150. More typically, the catalyst-to-oil ratio can be in
the range of from 5 to 100. The temperature in the riser reactor
generally can be in the range of from about 400.degree. C.
(752.degree. F.) to about 600.degree. C. (1112.degree. F.). More
typically, the riser reactor temperature can be in the range of
from 450.degree. C. (842.degree. F.) to 550.degree. C.
(1022.degree. F.). The riser reactor temperatures of the inventive
process will tend to be lower than those of typical conventional
fluidized catalytic cracking processes; because, the inventive
process is to provide for a high yield of middle distillates as
opposed to the production of gasoline as is often sought with
conventional fluidized catalytic cracking processes.
[0018] The mixture of hydrocarbons and catalyst from the riser
reactor pass as a riser reactor product comprising cracked gas oil
product and spent cracking catalyst to a stripper system that
provides means for separating hydrocarbons from catalyst and
defines a stripper separation zone wherein the cracked gas oil
product is separated from the spent cracking catalyst. The stripper
system can be any system or means known to those skilled in the art
for separating FCC catalyst from a hydrocarbon product. In a
typical stripper operation, the riser reactor product, which is a
mixture of cracked gas oil product and spent cracking catalyst
passes to the stripper system that includes cyclones for separating
the spent cracking catalyst from the vaporous cracked gas oil
product. The separated spent cracking catalyst enters the stripper
vessel from the cyclones where it is contacted with steam to
further remove cracked gas oil product from the spent cracking
catalyst. The coke content on the separated spent cracking catalyst
is, generally, in the range of from about 0.5 to about 5 weight
percent (wt. %), based on the total weight of the catalyst and the
carbon. Typically, the coke content on the separated spent cracking
catalyst is in the range of from or about 0.5 wt. % to or about 1.5
wt. %.
[0019] The separated spent cracking catalyst is then passed to a
catalyst regenerator that provides means for regenerating the
separated spent cracking catalyst and defines a regeneration zone
into which the separated spent cracking catalyst is introduced and
wherein carbon that is deposited on the separated spent cracking
catalyst is burned in order to remove the carbon to provide a
regenerated cracking catalyst having a reduced carbon content. The
catalyst regenerator typically is a vertical cylindrical vessel
that defines the regeneration zone and wherein the spent cracking
catalyst is maintained as a fluidized bed by the upward passage of
an oxygen-containing regeneration gas, such as air.
[0020] The temperature within the regeneration zone is, in general,
maintained in the range of from about 621.degree. C. (1150.degree.
F.) to 760.degree. C. (1400.degree. F.), and more, typically, in
the range of from 677.degree. C. (1250.degree. F.) to 715.degree.
C. (1320.degree. F.). The pressure within the regeneration zone
typically is in the range of from about atmospheric to about 345
kPa (50 psig), and, preferably, from about 34 to 345 kPa (5 to 50
psig). The residence time of the separated spent cracking catalyst
within the regeneration zone is in the range of from about 1 to
about 6 minutes, and, typically, from or about 2 to or about 4
minutes. The coke content on the regenerated cracking catalyst is
less than the coke content on the separated spent cracking catalyst
and, generally, is less than 0.5 wt. %. The coke content of the
regenerated cracking catalyst will, thus, generally, be in the
range of from or about 0.01 wt. % to or about 0.5 wt. %. It is
preferred for the coke concentration on the regenerated cracking
catalyst to be less than 0.1 wt. % and, it will thus preferably be
in the range of from 0.01 wt. % to 0.1 wt. %.
[0021] The regenerated cracking catalyst from the catalyst
regenerator is passed to the dense phase reactor, or fixed
fluidized bed reactor, that provides means for contacting a
gasoline feedstock with the regenerated cracking catalyst and which
defines a dense phase reaction zone wherein the gasoline feedstock
is contacted with the regenerated cracking catalyst under suitable
high severity cracking conditions.
[0022] The dense phase reactor can be a vessel that defines the
dense phase reaction zone. Contained within the vessel is
regenerated cracking catalyst that is fluidized by the introduction
of the gasoline feedstock and, optionally, steam. The dense phase
reaction zone is operated under such reaction conditions as to
provide for a cracked gasoline product and, preferably, to provide
for a high cracking yield of lower olefins. The high severity
cracking conditions can include a temperature within the dense
phase reaction zone that is in the range from about 482.degree. C.
(900.degree. F.) to about 871.degree. C. (1600.degree. F.), but,
preferably, the temperature is in the range of from 510.degree. C.
(950.degree. F.) to 871.degree. C. (1600.degree. F.), and, most
preferably, from 538.degree. C. (1000.degree. F.) to 732.degree. C.
(1350.degree. F.). The pressure within the dense phase reaction
zone can be in the range of from about atmospheric to about 345 kPa
(50 psig), and, preferably, from about 34 to 345 kPa (5 to 50
psig).
[0023] While, as previously mentioned, the introduction of steam
along with the gasoline feedstock into the dense phase reaction
zone is optional, a preferred aspect of the invention, however, is
for both steam and gasoline feedstock to be introduced into the
dense phase reaction zone and to be contacted with the regenerated
cracking catalyst contained therein. The use of the steam is
particularly desirable; because, it can provide in the cracking of
the gasoline feedstock for an improved selectivity toward lower
olefin yield. Thus, when steam is used, the weight ratio of steam
to gasoline feedstock introduced into the dense phase reaction zone
can be in the range of upwardly to or about 15:1, but, preferably,
the range is from 0.1:1 to 10:1. More preferably, the weight ratio
of steam to gasoline feedstock is in the range of from 0.2:1 to
9:1, and, most preferably, from 0.5:1 to 8:1.
[0024] Used regenerated cracking catalyst is removed from the dense
phase reaction zone and utilized as hot cracking catalyst mixed
with the gas oil feedstock that is introduced into the riser
reactor. One beneficial aspect of the inventive process, in
addition to its high yield of lower olefins, is that it provides
for the partial deactivation of the regenerated catalyst prior to
its use as hot cracking catalyst in the riser reactor. What is
meant by partial deactivation is that the used regenerated cracking
catalyst will contain a slightly higher concentration of carbon
than the concentration of carbon that is on the regenerated
cracking catalyst. This partial deactivation of the regenerated
cracking catalyst helps provides for a preferred product yield when
the gas oil feedstock is cracked within the riser reactor zone. The
coke concentration on the used regenerated cracking catalyst is
greater than the coke concentration on the regenerated cracking
catalyst, but it is less than that of the separated spent cracking
catalyst. Thus, the coke content of the used regenerated catalyst
can be greater than 0.1 wt. % and even greater than 0.5 wt. %.
Preferably, the coke content of the used regenerated catalyst is in
the range of from about 0.1 wt. % to about 1 wt. %, and, most
preferably, from 0.1 wt. % to 0.6 wt. %.
[0025] Another benefit provided by the use of the dense phase
reaction zone is associated with the used regenerated cracking
catalyst having a temperature that is lower than the temperature of
the regenerated cracking catalyst. This lower temperature of the
used regenerated cracking catalyst in combination with the partial
deactivation, as discussed above, provides further benefits in a
preferential product yield from the cracking of the gas oil
feedstock.
[0026] To assist in providing for the control of the process
conditions within the riser reactor of the inventive process and to
provide for a desired product mix, the regenerated cracking
catalyst can be divided into at least a portion that is passed to
the dense phase reaction zone and a remaining portion of the
regenerated cracking catalyst that is mixed with the gas oil
feedstock to be introduced into the riser reactor. The at least a
portion of the regenerated cracking catalyst introduced into the
dense phase reaction zone can be in the range of upwardly to 100
percent (%) of the regenerated cracking catalyst yielded from the
catalyst regenerator depending upon the requirements of the process
and the desired product yields. Specifically, however, the at least
a portion of regenerated cracking catalyst will represent from
about 10% to 100% of the separated regenerated catalyst withdrawn
from the catalyst regenerator. Also, the at least a portion of
regenerated cracking catalyst can be from about 50% to about 90% of
the separated regenerated catalyst that is withdrawn from the
catalyst regenerator.
[0027] Another method by which the process conditions within the
riser reactor are controlled and a desired product mix is provided
is through the addition of a ZSM-5 additive to the dense phase
reaction zone. The ZSM-5 additive is a molecular sieve additive
selected from the family of medium pore size crystalline
aluminosilicates or zeolites.
[0028] Molecular sieves that can be used as the ZSM-5 additive of
the present invention include medium pore zeolites as described in
"Atlas of Zeolite Structure Types," eds. W. H. Meier and D. H.
Olson, Butterworth-Heineman, Third Edition, 1992, which is hereby
incorporated by reference. The medium pore size zeolites generally
have a pore size from about 0.5 nm, to about 0.7 nm and include,
for example, MFI, MFS, MEL, MTW, EUO, MTT, HEU, FER, and TON
structure type zeolites (IUPAC Commission of Zeolite Nomenclature).
Non-limiting examples of such medium pore size zeolites, include
ZSM-5, ZSM-12, ZSM-22, ZSM-23, ZSM-34, ZSM-35, ZSM-38, ZSM-48,
ZSM-50, silicalite, and silicalite 2. The most preferred is ZSM-5,
which is described in U.S. Pat. Nos. 3,702,886 and 3,770,614.
ZSM-11 is described in U.S. Pat. No. 3,709,979; ZSM-12 in U.S. Pat.
No. 3,832,449; ZSM-21 and ZSM-38 in U.S. Pat. No. 3,948,758; ZSM-23
in U.S. Pat. No. 4,076,842; and ZSM-35 in U.S. Pat. No. 4,016,245.
All of the above patents are incorporated herein by reference.
Other suitable molecular sieves include the silicoaluminophosphates
(SAPO), such as SAPO-4 and SAPO-11 which is described in U.S. Pat.
No. 4,440,871; chromosilicates; gallium silicates, iron silicates;
aluminum phosphates (ALPO), such as ALPO-11 described in U.S. Pat.
No. 4,310,440; titanium aluminosilicates (TASO), such as TASO-45
described in EP-A No. 229,295; boron silicates, described in U.S.
Pat. No. 4,254,297; titanium aluminophosphates (TAPO), such as
TAPO-11 described in U.S. Pat. No. 4,500,651; and iron
aluminosilicates.
[0029] The ZSM-5 additive may be held together with a catalytically
inactive inorganic oxide matrix component, in accordance with
conventional methods.
[0030] U.S. Pat. No. 4,368,114 describes in detail the class of
zeolites that can be suitable ZSM-5 additives in the inventive
process, and such patent is incorporated herein by reference.
[0031] The combination of one or more of the above described
process variables and operating conditions allows for the control
of the conversion of the gas oil feedstock. Generally, it is
desired for the gas oil feedstock conversion to be in the range of
from 30 to 90 weight percent, and, preferably, from 40 to 85 weight
percent. What is meant by gas oil feedstock conversion is the
weight amount of hydrocarbons contained in the gas oil feedstock
that has a boiling temperature greater than 221.degree. C.
(430.degree. F.) that is converted in the riser reactor to
hydrocarbons having a boiling temperature less than 221.degree. C.
(430.degree. F.) divided by the weight amount of hydrocarbons
contained in the gas oil feedstock having a boiling temperature
greater than 221.degree. C. (430.degree. F.). As earlier noted, the
inventive process may be operated so as to provide for the
preferential or selective yielding of middle distillate boiling
range products and lower olefins.
[0032] The gas oil feedstock charged to the process of the
invention may be any hydrocarbon feedstock that may be or is
typically charged to a fluidized catalytic cracking unit. In
general terms, hydrocarbon mixtures boiling in the range of from
345.degree. C. (650.degree. F.) to 760.degree. C. (1400.degree. F.)
can make suitable feedstocks for the inventive process. Examples of
the types of refinery feedstreams that can make suitable gas oil
feedstocks include vacuum gas oils, coker gas oil, straight-run
residues, thermally cracked oils and other hydrocarbon streams.
[0033] The gasoline feedstock charged to the dense phase reaction
zone may be any suitable hydrocarbon feedstock having a boiling
temperature that is in the gasoline boiling temperature range.
Generally, the gasoline feedstock comprises hydrocarbons boiling in
the temperature range of from about 32.degree. C. (90.degree. F.)
to about 204.degree. C. (400.degree. F.). Examples of refinery
streams that may be used as the gasoline feedstock of the inventive
process include straight run gasoline, naphtha, catalytically
cracked gasoline, and coker naphtha.
[0034] Now referring to FIG. 1 that presents a process flow
schematic representative of one aspect of the inventive process 10.
In the inventive process 10, a gas oil feedstock passes through
conduit 12 and is introduced into the bottom of riser reactor 14.
Riser reactor 14 defines a riser reactor zone, or cracking reaction
zone, wherein the gas oil feedstock is mixed with a catalytic
cracking catalyst. The catalytic cracking catalyst can be a used
regenerated cracking catalyst or a regenerated cracking catalyst,
or a combination of both catalysts.
[0035] The used regenerated cracking catalyst is a regenerated
cracking catalyst that has been used in dense bed reactor 16 in the
high severity cracking of a gasoline feedstock. The used
regenerated cracking catalyst passes from dense bed reactor 16 and
is introduced into riser reactor 14 by way of conduit 18.
Regenerated cracking catalyst may also be mixed with the gas oil
feedstock. The regenerated cracking catalyst passes from
regenerator 20 through conduit 22 and is introduced by way of
conduit 24 into riser reactor 14 wherein it is mixed with the gas
oil feedstock.
[0036] By passing through riser reactor 14 that is operated under
catalytic cracking conditions the mixture of gas oil feedstock and
hot catalytic cracking catalyst forms a riser reactor product that
comprises a mixture of a cracked gas oil product and a spent
cracking catalyst. The riser reactor product passes from riser
reactor 14 and is introduced into stripper system or
separator/stripper 26.
[0037] The separator/stripper 26 can be any conventional system
that defines a separation zone or stripping zone, or both, and
provides means for separating the cracked gas oil product and spent
cracking catalyst. The separated cracked gas oil product passes
from separator/stripper 26 by way of conduit 28 to separation
system 30. The separation system 30 can be any system known to
those skilled in the art for recovering and separating the cracked
gas oil product into the various FCC products, such as, for
example, cracked gas, cracked gasoline, cracked gas oils and cycle
oil. The separation system 36 may include such systems as absorbers
and strippers, fractionators, compressors and separators or any
combination of known systems for providing recovery and separation
of the products that make up the cracked gas oil product.
[0038] The separation system 30, thus, defines a separation zone
and provides means for separating the cracked gas oil product into
cracked products. The cracked gas, cracked gasoline and cracked gas
oils respectively pass from separation system 30 through conduits
32, 34, and 36. The cycle oil passes from separation system 30
through conduit 38 and is introduced into riser reactor 14.
[0039] The separated spent cracking catalyst passes from
separator/stripper 26 through conduit 40 and is introduced into
regenerator 20. Regenerator 20 defines a regeneration zone and
provides means for contacting the spent cracking catalyst with an
oxygen-containing gas, such as air, under carbon burning conditions
to remove carbon from the spent cracking catalyst. The
oxygen-containing gas is introduced into regenerator 20 through
conduit 42 and the combustion gases pass from regenerator 20 by way
of conduit 44.
[0040] The regenerated cracking catalyst passes from regenerator 20
through conduit 22. As an optional feature of the inventive
process, the stream of regenerated cracking catalyst passing
through conduit 22 may be divided into two streams with at least a
portion of the regenerated catalyst passing from regenerator 20
through conduit 22 passing through conduit 46 to the dense bed
reactor 16 and with the remaining portion of the regenerated
catalyst passing from regenerator 20 passing through conduit 24 to
riser reactor 14.
[0041] The dense bed reactor 16 defines a dense bed fluidization
zone and provides means for contacting a gasoline feedstock with
the regenerated cracking catalyst contained within the dense bed
reactor 16. The dense bed fluidization zone is operated under high
severity cracking conditions so as to preferentially crack the
gasoline feedstock to lower olefin compounds, such as ethylene,
propylene, and butylenes, and to yield a cracked gasoline product.
The cracked gasoline product passes from dense bed reactor 16
through conduit 48.
[0042] The used regenerated cracking catalyst passes from dense bed
reactor 16 through conduit 18 and is introduced into riser reactor
14. The gasoline feedstock is introduced into the dense bed reactor
16 through conduit 50 and steam is introduced into the dense bed
reactor 16 by way of conduit 52. The gasoline feedstock and steam
are introduced into the dense bed reactor 16 so as to provide for a
fluidized bed of the regenerated catalyst. A ZSM-5 additive may be
added to the regenerated catalyst of the dense phase reactor 16 or
introduced into the dense bed reactor 16 through conduit 54.
[0043] Reasonable variations, modifications and adaptations can be
made within the scope of the described disclosure and the appended
claims without departing from the scope of the invention.
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