U.S. patent application number 09/811166 was filed with the patent office on 2001-11-22 for cycle oil conversion process.
Invention is credited to Daage, Michel, Klein, Darryl P., Stuntz, Gordon F., Swan, George A. III, Touvelle, Michele S., Winter, William E..
Application Number | 20010042701 09/811166 |
Document ID | / |
Family ID | 26892963 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010042701 |
Kind Code |
A1 |
Stuntz, Gordon F. ; et
al. |
November 22, 2001 |
Cycle oil conversion process
Abstract
The invention relates to a process for converting cycle oils
produced in catalytic cracking reactions into light olefin and
naphtha. More particularly, the invention relates to a process for
hydroprocessing a catalytically cracked light cycle oil in order to
form a hydroprocessed cycle oil containing a significant amount of
tetralins. The hydroprocessed cycle oil is then re-cracked in an
upstream zone of the primary FCC riser reactor.
Inventors: |
Stuntz, Gordon F.; (Baton
Rouge, LA) ; Swan, George A. III; (Baton Rouge,
LA) ; Winter, William E.; (Baton Rouge, LA) ;
Daage, Michel; (Baton Rouge, LA) ; Touvelle, Michele
S.; (Baton Rouge, LA) ; Klein, Darryl P.;
(Ellicott City, MD) |
Correspondence
Address: |
EXXONMOBIL RESEARCH AND ENGINEERING COMPANY
P.O. BOX 900
1545 ROUTE 22 EAST
ANNANDALE
NJ
08801-0900
US
|
Family ID: |
26892963 |
Appl. No.: |
09/811166 |
Filed: |
March 16, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60197567 |
Apr 17, 2000 |
|
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Current U.S.
Class: |
208/68 ; 208/113;
208/120.01; 208/130; 208/67; 208/72; 208/73 |
Current CPC
Class: |
C10G 69/04 20130101 |
Class at
Publication: |
208/68 ; 208/67;
208/113; 208/120.01; 208/130; 208/72; 208/73 |
International
Class: |
C10G 069/04 |
Claims
What is claimed is:
1. A method for catalytically cracking a primary feed comprising
the continuous steps of: (a) injecting the primary feed into an FCC
riser reactor having at least a first reaction zone and a second
reaction zone upstream of the first reaction zone, the primary feed
being injected into the first reaction zone; (b) cracking the
primary feed in the first reaction zone under catalytic cracking
conditions in the presence of a catalytically effective amount of a
regenerated, zeolite-containing, catalytic cracking catalyst in
order to form at least partially spent catalyst and a cracked
product; (c) separating at least a cycle oil from the cracked
product and then hydroprocessing at least a portion of the cycle
oil in the presence of a catalytically effective amount of a
hydroprocessing catalyst under hydroprocessing conditions in order
to form a hydroprocessed cycle oil having an increased
concentration of tetralins; (d) injecting the hydroprocessed cycle
oil into the second reaction zone; and (e) cracking the
hydroprocessed cycle oil under cycle oil catalytic cracking
conditions in the presence of the catalytic cracking catalyst.
2. The method of claim 1 wherein the primary feed is at least one
of hydrocarbonaceous oils boiling in the range of about 220.degree.
C. to about 565.degree. C.; naphtha; gas oil; heavy
hydrocarbonaceous oils boiling above 565.degree. C.; heavy and
reduced petroleum crude oil; petroleum atmospheric distillation
bottoms; petroleum vacuum distillation bottoms; pitch; asphalt;
bitumen; tar sand oils; shale oil; and liquid products derived from
coal and natural gas.
3. The method of claim 1 wherein conditions in the first reaction
zone include temperatures from about 450.degree. C. to about
650.degree. C., hydrocarbon partial pressures from about 10 to 40
psia, a primary feed residence time of less than about 20 seconds,
and a catalyst to primary feed (wt/wt) ratio from about 3 to 12,
where catalyst weight is total weight of the catalyst
composite.
4. The method of claim 3 wherein steam is concurrently introduced
with the primary feed into the first reaction zone.
5. The method of claim 1 wherein conditions in the riser reactor's
second reaction zone include temperatures from about 550.degree. C.
to about 700.degree. C., hydrocarbon partial pressures from about
10 to 40 psia, a cycle oil residence time of less than about 10
seconds, and a catalyst to cycle oil (wt/wt) ratio from about 5 to
100, where catalyst weight is total weight of the catalyst
composite.
6. The method of claim 5 wherein steam is concurrently introduced
with the cycle oil feed into the second reaction zone.
7. The method of claim 1 wherein the hydroprocessing is performed
at a temperature ranging from about 200.degree. C. to about
500.degree. C., a pressure ranging from about 100 to about 2500
psig, a space velocity ranging from about 0.1 to 6 V/V/Hr, and at a
hydrogen charge rate ranging from about 500 to about 10,000
standard cubic feet per barrel (SCF/B).
8. The method of claim 1 further comprising conducting the
partially spent catalyst to a stripping zone and removing
strippable hydrocarbons in order to form stripped, spent catalyst,
and then conducting the stripped spent catalyst to a regeneration
zone for regenerating the spent catalyst under FCC catalyst
regeneration conditions in order to form the regenerated,
zeolite-containing, catalytic cracking catalyst.
9. The method of claim 8 further comprising separating propylene
from the cracked product and then polymerizing the propylene in
order to form polypropylene.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application claims benefit of U.S. provisional
patent application 60/197,567 filed Apr. 17, 2000.
FIELD OF THE INVENTION
[0002] The present invention relates to a process for converting
cycle oils produced in catalytic cracking reactions into olefin and
naphtha. More particularly, the invention relates to a process for
converting a catalytically cracked cycle oil such as heavy cycle
oil ("HCO" or "HCCO"), light cycle oil ("LCO" or "LCCO"), and
mixtures thereof into olefins and naphthas using a zeolite
catalyst.
BACKGROUND OF THE INVENTION
[0003] Cycle oils such as HCCO and LCCO produced in fluidized
catalytic cracking ("FCC") reactions contain two-ring aromatic
species such as naphthalene. The need for blendstocks for forming
low emissions fuels has created an increased demand for FCC
products that contain a diminished concentration of multi-ring
aromatics. There is also an increased demand for FCC products
containing light olefins that may be separated for use in
alkylation, oligomerization, polymerization, and MTBE and ETBE
synthesis processes. There is a particular need for low emissions,
high octane FCC products having an increased concentration of
C.sub.2 to C.sub.4 olefins and a reduced concentration of
multi-ring aromatics and olefins of higher molecular weight.
[0004] A high octane gasoline may be formed conventionally by
hydrotreating an FCC cycle oil and then re-cracking hydrotreated
cycle oil. The hydrotreated cycle oil may be recycled to the FCC
unit from which it was derived, or it may be re-cracked in an
additional catalytic cracking unit.
[0005] In such conventional processes, hydrotreating a cycle oil
such as LCCO partially saturates bicyclic aromatics such as
naphthalene to produce, for example, tetrahydronaphthalene and
alkyl-substituted derivatives thereof (collectively referred to
herein as ("tetralins"). Hydrotreatment and subsequent cycle oil
re-cracking may occur in the primary FCC reactor. Hydrotreated
cycle oil may also be injected into the FCC feed riser upstream or
downstream of primary feed injection. In another conventional
process, hydrotreated cycle oil is recycled with a hydrotreated
naphtha, and both are injected into the primary riser reactor at a
point upstream of primary feed injection.
[0006] Unfortunately, such re-cracking of hydrotreated LCCO results
in undesirable hydrogen transfer reactions that convert species
such as tetralins into polynuclear aromatics such as
naphthalene.
[0007] There remains a need, therefore, for new processes for
forming naphtha and olefin from hydrotreated cycle oils.
SUMMARY OF THE INVENTION
[0008] In one embodiment, the invention is a method for
catalytically cracking a primary feed comprising:
[0009] (a) injecting the primary feed into an FCC riser reactor
having at least a first reaction zone and a second reaction zone
upstream of the first reaction zone, the primary feed being
injected into the first reaction zone;
[0010] (b) cracking the primary feed in the first reaction zone
under primary feed catalytic cracking conditions in the presence of
a catalytically effective amount of a zeolite-containing catalytic
cracking catalyst in order to form a cracked product;
[0011] (c) separating at least a cycle oil from the cracked product
and then processing the cycle oil in the presence of a
catalytically effective amount of a hydroprocessing catalyst under
hydroprocessing conditions in order to form a hydroprocessed cycle
oil having an increased concentration of tetralins;
[0012] (d) injecting the hydroprocessed cycle oil into the second
reaction zone; and
[0013] (e) cracking the hydroprocessed cycle oil under cycle oil
catalytic cracking conditions in the presence of the catalytic
cracking catalyst.
[0014] In another embodiment, the invention is a cracked product
formed in accordance with such a process.
DETAILED DESCRIPTION OF THE INVENTION
[0015] The invention is based on the discovery that recycling a
hydrotreated cycle oil such as HCCO and LCCO to an FCC reaction
zone in the presence of a catalytically effective amount of an
appropriate FCC catalyst results in increased propylene production
when the cycle oil injection is along the feed riser at a point
upstream of gas oil or residual oil feed injection. It is believed
that injecting the cycle oil into the FCC reaction zone in the
presence of an appropriate FCC catalyst and at a point upstream of
gas oil or residual oil injection suppresses undesirable hydrogen
transfer reactions by re-cracking potential hydrogen donors present
in the cycle oil before such donors can contact the primary
feed.
[0016] Preferred hydrocarbonaceous feeds (i.e. the primary feed)
for the catalytic cracking process described herein include
naphtha, hydrocarbonaceous oils boiling in the range of about
430.degree. F. (220.degree. C.) to about 1050.degree. F.
(565.degree. C.), such as gas oil; heavy hydrocarbonaceous oils
comprising materials boiling above 1050.degree. F. (565.degree.
C.); heavy and reduced petroleum crude oil; petroleum atmospheric
distillation bottoms; petroleum vacuum distillation bottoms; pitch,
asphalt, bitumen, other heavy hydrocarbon residues; tar sand oils;
shale oil; liquid products derived from coal and natural gas, and
mixtures thereof.
[0017] The preferred cracking process may be performed in one or
more conventional FCC process units. Each unit comprises a riser
reactor having a first reaction zone and a second reaction zone
upstream of the first reaction zone, a stripping zone, a catalyst
regeneration zone, and at least one separation zone.
[0018] The primary feed is conducted to the riser reactor where it
is injected into the first reaction zone wherein the primary feed
contacts a flowing source of hot, regenerated catalyst. The hot
catalyst vaporizes and cracks the feed at a temperature from about
450.degree. C. to 650.degree. C., preferably from about 500.degree.
C. to 600.degree. C. The cracking reaction deposits carbonaceous
hydrocarbons, or coke, on the catalyst, thereby deactivating the
catalyst. The cracked products may be separated from the coked
catalyst and a portion of the cracked products may be conducted to
a separator such as a fractionator. At least a cycle oil fraction,
preferably an LCCO fraction, is separated from the cracked products
in the separation zone. Other fractions that may be separated from
the cracked products include light olefin fractions and naphtha
fractions.
[0019] Light olefins separated from the process may be used as
feeds for processes such as oligimerization, polymerization,
co-polymerization, ter-polymerization, and related processes
(hereinafter "polymerization") in order to form macromolecules.
Such light olefins may be polymerized both alone and in combination
with other species, in accordance with polymerization methods known
in the art. In some cases it may be desirable to separate,
concentrate, purify, upgrade, or otherwise process the light
olefins prior to polymerization. Propylene and ethylene are
preferred polymerization feeds. Polypropylene and polyethylene are
preferred polymerization products made therefrom.
[0020] Preferably, the coked catalyst flows through the stripping
zone where volatiles are stripped from the catalyst particles with
a stripping material such as steam. The stripping may be preformed
under low severity conditions in order to retain a greater fraction
of adsorbed hydrocarbons for heat balance. The stripped catalyst is
then conducted to the regeneration zone where it is regenerated by
burning coke on the catalyst in the presence of an oxygen
containing gas, preferably air. Decoking restores catalyst activity
and simultaneously heats the catalyst to, e.g., 650.degree. C. to
800.degree. C. The hot catalyst is then recycled to the riser
reactor at a point near or just upstream of the second reaction
zone. Flue gas formed by burning coke in the regenerator may be
treated for removal of particulates and for conversion of carbon
monoxide, after which the flue gas is normally discharged into the
atmosphere.
[0021] Preferably, at least a portion of the cycle oil is
hydroprocessed in the presence of a hydroprocessing catalyst under
hydroprocessing conditions in order to form a cycle oil having a
significant amount of tetralins. At least a portion of the
hydroprocessed cycle oil is conducted to the riser reactor and
injected into the second reaction zone. The hydroprocessing may
occur in one or more hydroprocessing reactors. It should be noted
that such hydroprocessing conditions may also result in the
formation of substantial amounts of other species such as indans
and functionalized indans. The presence of such species is not
detrimental to the practice of the invention.
[0022] Preferred process conditions in the riser reactor's first
reaction zone include temperatures from about 450.degree. C. to
about 650.degree. C., preferably from about 525.degree. C. to
600.degree. C., hydrocarbon partial pressures from about 10 to 40
psia, preferably from about 20 to 35 psia; and a catalyst to
primary feed (wt/wt) ratio from about 3 to 12, preferably from
about 4 to 10, where catalyst weight is total weight of the
catalyst composite. Though not required, it is also preferred that
steam be concurrently introduced with the primary feed into the
reaction zone, with the steam comprising up to about 10 wt. %,
preferably about 2 to about 3 wt. % of the primary feed. Also, it
is preferred that the primary feed's residence time in the reaction
zone be less than about 20 seconds, preferably from about 1 to 20
seconds, and more preferably from about 1 to about 6 seconds.
[0023] Preferred process conditions in the riser reactor's second
reaction zone include temperatures from about 550.degree. C. to
about 700.degree. C., preferably from about 525.degree. C. to
650.degree. C., hydrocarbon partial pressures from about 10 to 40
psia, preferably from about 20 to 35 psia; and a catalyst to cycle
oil (wt/wt) ratio from about 5 to 100, preferably from about 10 to
100, where catalyst weight is total weight of the catalyst
composite. Though not required, it is also preferred that steam be
concurrently introduced with the cycle oil feed into the reaction
zone, with the steam comprising up to about 10 wt. %, preferably 1
to 5 wt. % of the primary feed. Also, it is preferred that the
cycle oil's residence time in the reaction zone be less than about
10 seconds, preferably from about 0.1 to about 10 seconds, and more
preferably from about 0.1 seconds to about 1.0 seconds.
[0024] A preferred fluidized catalytic cracking catalyst ("FCC
catalyst" herein) is a composition of catalyst particles and other
reactive and non-reactive components. More than one type of
catalyst particle may be present in the catalyst. A preferred FCC
catalyst particle useful in the invention contains at least one
crystalline aluminosilicate, also referred to as zeolite, of
average pore diameter greater than about 0.7 nanometers (nm), i.e.,
large pore zeolite cracking catalyst. The pore diameter also
sometimes referred to as effective pore diameter can be measured
using standard adsorption techniques and hydrocarbons of known
minimum kinetic diameters. See Breck, Zeolite Molecular Sieves,
1974 and Anderson et al., J. Catalysis 58, 114 (1979), both of
which are incorporated herein by reference. Zeolites useful in the
invention are described in the "Atlas of Zeolite Structure Types,"
eds. W. H. Meier and D. H. Olson, Butterworth-Heineman, Third
Edition, 1992, which is hereby incorporated by reference. As
discussed, the FCC catalyst may be in the form of particles
containing zeolite. The catalyst may also include fines, inert
particles, particles containing a metallic species, and mixtures
thereof. Particles containing metallic species include platinum
compounds, platinum metal, and mixtures thereof.
[0025] FCC catalyst particles may contain metals such as platinum,
promoter species such as phosphorous-containing species, clay
filler, and species for imparting additional catalytic
functionality such as bottoms cracking and metals passivation. Such
an additional catalytic functionality may be provided, for example,
by aluminum-containing species. More than one type of catalyst
particle may be present in the FCC catalyst. For example,
individual catalyst particles may contain large pore zeolite, shape
selective zeolite, and mixtures thereof.
[0026] The FCC catalyst particle may be bound together with an
inorganic oxide matrix component. The inorganic oxide matrix
component binds the particle's components together so that the FCC
catalyst particle is hard enough to survive interparticle and
reactor wall collisions. The inorganic oxide matrix may be made
according to conventional methods from an inorganic oxide sol or
gel which is dried to "glue" the catalyst particle's components
together. Preferably, the inorganic oxide matrix is not
catalytically active and comprises oxides of silicon and aluminum.
It is also preferred that separate alumina phases be incorporated
into the inorganic oxide matrix. Species of aluminum
oxyhydroxides--alumin a, boehmite, diaspore, and transitional
aluminas such as -alumina, -alumina, -alumina, -alumina, -alumina,
-alumina, and -alumina can be employed. Preferably, the alumina
species is an aluminum trihydroxide such as gibbsite, bayerite,
nordstrandite, or doyelite. The matrix material may also contain
phosphorous or aluminum phosphate.
[0027] Preferred FCC catalyst particles in the present invention
contain at least one of:
[0028] (a) amorphous solid acids, such as alumina, silica-alumina,
silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia,
silica-titania, and the like; and
[0029] (b) zeolite catalysts containing faujasite.
[0030] Silica-alumina materials suitable for use in the present
invention are amorphous materials containing about 10 to 40 wt. %
alumina and to which other promoters may or may not be added.
[0031] Suitable zeolite in such catalyst particles include zeolites
which are iso-structural to zeolite Y. These include the
ion-exchanged forms such as the rare-earth hydrogen and ultra
stable (USY) form. The zeolite may range in size from about 0.1 to
10 microns, preferably from about 0.3 to 3 microns. The zeolite
will be mixed with a suitable porous matrix material in order to
form the fluid catalytic cracking catalyst. Non-limiting porous
matrix materials which may be used in the practice of the present
invention include alumina, silica-alumina, silica-magnesia,
silica-zirconia, silica-thoria, silica-beryllia, silica-titania, as
well as ternary compositions, such as silica-alumina-thoria,
silica-alumina-zirconia, magnesia and silica-magnesia-zirconia. The
matrix may also be in the form of a cogel. The relative proportions
of zeolite component and inorganic oxide gel matrix on an anhydrous
basis may vary widely with the zeolite content, ranging from about
10 to 99, more usually from about 10 to 80, percent by weight of
the dry composite. The matrix itself may possess catalytic
properties, generally of an acidic nature.
[0032] The amount of zeolite component in the catalyst particle
will generally range from about 1 to about 60 wt. %, preferably
from about 1 to about 40 wt. %, and more preferably from about 5 to
about 40 wt. %, based on the total weight of the catalyst.
Generally, the catalyst particle size will range from about 10 to
300 microns in diameter, with an average particle diameter of about
60 microns. The surface area of the matrix material will be less
than or equal to about 350 m.sup.2/g, preferably 50 to 200
m.sup.2/g, more preferably from about 50 to 100 m.sup.2/g. While
the surface area of the final catalysts will be dependent on such
things as type and amount of zeolite material used, it will usually
be less than about 500 m.sup.2/g, preferably from about 50 to 300
m.sup.2/g, more preferably from about 50 to 250 m.sup.2/g, and most
preferably from about 100 to 250 m.sup.2/g.
[0033] Another preferred FCC catalyst contains a mixture of zeolite
Y and zeolite beta. The Y and beta zeolite may be on the same
catalyst particle, on different particles, or some combination
thereof. Such catalysts are described in U.S. Pat. No. 5,314,612,
incorporated by reference herein. Such catalyst particles consist
of a combination of zeolite Y and zeolite beta combined in a matrix
comprised of silica, silica-alumina, alumina, or any other suitable
matrix material for such catalyst particles. The zeolite portion of
the resulting composite catalyst particle will consist of 25 to 95
wt. % zeolite Y with the balance being zeolite beta.
[0034] Yet another preferred FCC catalyst contains a mixture of
zeolite Y and a shape selective zeolite species such as ZSM-5 or a
mixture of an amorphous acidic material and ZSM-5. The Y zeolite
(or alternatively the amorphous acidic material) and shape
selective zeolite may be on the same catalyst particle, on
different particles, or some combination thereof. Such catalysts
are described in U.S. Pat. No. 5,318,692, incorporated by reference
herein. The zeolite portion of the catalyst particle will typically
contain from about 5 wt. % to 95 wt. % zeolite-Y (or alternatively
the amorphous acidic material) and the balance of the zeolite
portion being ZSM-5.
[0035] Shape selective zeolite species useful in the preferred FCC
catalyst include medium pore size zeolites generally having a pore
size from about 0.5 nm, to about 0.7 nm. Such zeolites 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.
[0036] Other preferred medium pore size zeolites 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.
[0037] The large pore and shape selective zeolites in the catalytic
species can include "crystalline admixtures" which are thought to
be the result of faults occurring within the crystal or crystalline
area during the synthesis of the zeolites. Examples of crystalline
admixtures of ZSM-5 and ZSM-11 are disclosed in U.S. Pat. No.
4,229,424 which is incorporated herein by reference. The
crystalline admixtures are themselves medium pore, i.e., shape
selective, size zeolites and are not to be confused with physical
admixtures of zeolites in which distinct crystals of crystallites
of different zeolites are physically present in the same catalyst
composite or hydrothermal reaction mixtures.
[0038] As set forth above, the process of the invention comprises
cracking a primary feed in the first reaction zone of a riser
reactor in order to form a cracked product. At least a portion of
the cycle oil is separated from the cracked product and then
hydroprocessed prior to injection into an FCC reaction zone. The
hydroprocessed cycle oil is conducted to the riser reactor for
injection into the second reaction zone upstream of the first
(i.e., primary) injection zone. Preferably, the cycle oil
hydroprocessing occurs in a hydroprocessing reactor under
hydroprocessing conditions in the presence of a hydroprocessing
catalyst in order to form a cycle oil having significant amounts of
tetralins.
[0039] The term "hydroprocessing" is used broadly herein, and
includes, for example, hydrogenation such as aromatics saturation,
hydrotreating, hydrofining, and hydrocracking. As is known by those
of skill in the art, the degree of hydroprocessing can be
controlled through proper selection of catalyst as well as by
optimizing operation conditions. It is desirable that the
hydroprocessing convert a significant amount of aromatic species
such as naphthalenes into tetralins using a catalytically effective
amount of a hydrogenation catalyst. Objectionable species can also
be removed by the hydroprocessing reactions. These species include
species that may contain sulfur, nitrogen, oxygen, halides, and
certain metals.
[0040] Cycle oil hydroprocessing may be performed under
hydroprocessing conditions that result in conversion of multi-ring
aromatic species (e.g., naphthalene) to the corresponding one-ring
aromatic species (e.g., tetrahydronaphthalene). Hydroprocessing
conditions can be effectively chosen to minimize conversion of
multi-ring aromatic species to their fully saturated analogs (e.g.
decahydronaphthalenes) in order to reduce hydrogen consumption in
the hydroprocessing reactor. Preferably, the reaction is performed
at a temperature ranging from about 200.degree. C. to about
500.degree. C., more preferably from about 250.degree. C. to about
400.degree. C. The reaction pressure preferably ranges from about
100 to about 2500 psig, more preferably from about 450 to about
1500 psig. The space velocity preferably ranges from about 0.1 to 6
VNV/Hr, more preferably from about 0.5 to about 2 V/V/Hr, where
V/V/Hr is defined as the volume of oil per hour per volume of
catalyst. The hydrogen containing gas is preferably added to
establish a hydrogen charge rate ranging from about 500 to about
10,000 standard cubic feet per barrel (SCF/B), more preferably from
about 500 to about 7,000 SCF/B. Actual conditions employed will
depend on factors such as feed quality and catalyst, but should be
consistent with the objective of maximizing conversion of
multi-ring aromatic species to tetralins.
[0041] Accordingly, when cycle oil hydroprocessing is conducted
under conditions that convert polynuclear aromatic species such as
naphthalene into significant amounts of tetralins, catalytically
cracking the hydrotreated cycle oil in accordance with this
invention results in augmented cycle oil conversion to naphtha and
light (i.e., C.sub.2 to C.sub.5) olefin. This beneficial conversion
occurs, it is believed, because undesirable hydrogen transfer
reactions are suppressed compared to conventional FCC cycle oil
recycle processes.
[0042] In one example of such a conventional process, where a
hydrotreated naphtha and a hydrotreated cycle oil are recycled to
the primary FCC reactor, hydrogen transfers from tetralins present
in the hydrotreated cycle oil to the olefin present in the
hydrotreated naphtha before catalytic cracking can occur. Such
hydrogen transfer reactions diminish the concentration of light
olefin in the cracked product because olefin in the naphtha
fraction is saturated and because species such as tetralin are
converted into polynuclear aromatics instead of being cracked into
light olefin and more desirable mononuclear aromatic species.
[0043] In other conventional processes, hydrotreated cycle oil is
recycled to the primary FCC reactor without a hydrotreated naphtha
fraction. Hydrogen transfer reactions prevent cycle oil conversion
to naphtha and light olefin in these reactions because olefin
present in the gas oil/resid feeds are effective hydrogen receptors
for converting tetralins to naphthalene. Moreover, conventional
amorphous cat cracking catalysts have a low activity for cracking
tetralins into species such as xylene and light olefin. When the
rate of hydrogen transfer from the tetralins to the light olefin
exceeds the cracking rate, the tetralins will be preferentially
converted to naphthalene, i.e., an undesirable, toxic, stable
polynuclear aromatic species.
[0044] It is believed that these undesirable hydrogen transfer
reactions are avoided in the present invention by recycling the
hydrotreated cycle oil to a region of the primary riser reactor
that is substantially free of a hydrogen receptor species naturally
present in naphtha, gas oils, and resids. Moreover, the preferred
catalysts of this invention contain a zeolite species, and
consequently are far more active in cracking tetralins into species
such as xylene and light olefin than are the amorphous catalytic
cracking catalysts used in conventional cycle oil re-cracking.
Consequently, the cracking of species such as tetralins into
mononuclear aromatic species and light olefin is believed to
proceed at a much higher rate that olefin hydrogenation in the
practice of the present invention.
[0045] Preferred hydroprocessing conditions can be maintained by
use of any of several types of hydroprocessing reactors. Trickle
bed reactors are most commonly employed in petroleum refining
applications with co-current downflow of liquid and gas phases over
a fixed bed of catalyst particles. It can be advantageous to
utilize alternative reactor technologies. Countercurrentflow
reactors, in which the liquid phase passes down through a fixed bed
of catalyst against upward-moving treat gas, can be employed to
obtain higher reaction rates and to alleviate aromatics
hydrogenation equilibrium limitations inherent in co-current flow
trickle bed reactors. Moving bed reactors can be employed to
increase tolerance for metals and particulates in the
hydroprocessor feed stream. Moving bed reactor types generally
include reactors wherein a captive bed of catalyst particles is
contacted by upward-flowing liquid and treat gas. The catalyst bed
can be slightly expanded by the upward flow or substantially
expanded or fluidized by increasing flow rate, for example, via
liquid recirculation (expanded bed or ebullating bed), use of
smaller size catalyst particles which are more easily fluidized
(slurry bed), or both. In any case, catalyst can be removed from a
moving bed reactor during onstream operation, enabling economic
application when high levels of metals in feed would otherwise lead
to short run lengths in the alternative fixed bed designs.
Furthermore, expanded or slurry bed reactors with upward-flowing
liquid and gas phases would enable economic operation with
feedstocks containing significant levels of particulate solids, by
permitting long run lengths without risk of shutdown due to
fouling. Use of such a reactor would be especially beneficial in
cases where the feedstocks include solids in excess of about 25
micron size, or contain contaminants which increase the propensity
for foulant accumulation, such as olefinic or diolefinic species or
oxygenated species. Moving bed reactors utilizing downward-flowing
liquid and gas can also be applied, as they would enable on-stream
catalyst replacement.
[0046] The catalyst used in the hydroprocessing stages should be a
hydroprocessing catalyst suitable for aromatic saturation,
desulfurization, denitrogenation or any combination thereof.
Preferably, the catalyst is comprised of at least one Group VIII
metal and a Group VI metal on an inorganic refractory support,
which is preferably alumina or alumina-silica. The Group VIII and
Group VI compounds are well known to those of ordinary skill in the
art and are well defined in the Periodic Table of the Elements. For
example, these compounds are listed in the Periodic Table found at
the last page of Advanced Inorganic Chemistry, 2nd Edition 1966,
Interscience Publishers, by Cotton and Wilkenson. The Group VIII
metal is preferably present in an amount ranging from 2-20 wt. %,
preferably 4-12 wt. %. Preferred Group VIII metals include Co, Ni,
and Fe, with Co and Ni being most preferred. The preferred Group VI
metal is Mo which is present in an amount ranging from 5-50 wt. %,
preferably 10-40 wt. %, and more preferably from 20-30 wt. %.
[0047] All metals weight percents given are on support. The term
"on support" means that the percents are based on the weight of the
support. For example, if a support weighs 100 g, then 20 wt. %
Group VIII metal means that 20 g of the Group VIII metal is on the
support.
[0048] Any suitable inorganic oxide support material may be used
for the hydroprocessing catalyst of the present invention.
Preferred are alumina and silica-alumina, including crystalline
alumino-silicate such as zeolite. More preferred is alumina. The
silica content of the silica-alumina support can be from 2-30 wt.
%, preferably 3-20 wt. %, more preferably 5-19 wt. %. Other
refractory inorganic compounds may also be used, non-limiting
examples of which include zirconia, titania, magnesia, and the
like. The alumina can be any of the aluminas conventionally used
for hydroprocessing catalysts. Such aluminas are generally porous
amorphous alumina having an average pore size from 50-200 A,
preferably, 70-150 A, and a surface area from 50-450 m.sup.2/g.
[0049] Following cycle oil hydroprocessing, the hydroprocessed
cycle oil is conducted to the riser reactor for injection into the
second reaction zone. Accordingly, the cycle oil is cracked into
lower molecular weight cracked products such as light olefin and
undesirable hydrogen transfer reactions are suppressed. In addition
to cycle oil, cracked products formed in the riser reactor include
naphtha in amounts ranging from about 5 wt. % to about 50 wt. %,
butanes in amounts ranging from about 2 wt. % to about 15 wt. %,
butenes in amounts ranging from about 4 wt. % to about 11 wt. %,
propane in amounts ranging from about 0.5 wt. % to about 3.5 wt. %,
and propylene in amounts ranging from about 5 wt. % to about 20 wt.
%. All wt. % are based on the total weight of the cracked product.
In a preferred embodiment, at least 90 wt. % of the cracked
products have boiling points less than 430.degree. F. While not
wishing to be bound by any theory, it is believed that the
substantial concentration of propylene in the cracked product
results from the hydroprocessed cycle oil cracking in the second
reaction zone.
[0050] As used herein, cycle oil includes heavy cycle oil, light
cycle oil, and mixtures thereof. Heavy cycle oil refers to a
hydrocarbon stream boiling in the range of 240.degree. C. to
370.degree. C. (about 465.degree. F. to about 700.degree. F.).
Light cycle oil refers to a hydrocarbon stream boiling in the range
of 190.degree. C. to 240.degree. C. (about 375.degree. F. to about
465.degree. F.). Naphtha includes light cat naphtha and refers to a
hydrocarbon stream having a final boiling point less than about
190.degree. C. (375.degree. F.) and containing olefins in the
C.sub.5 to C.sub.9 range, single ring aromatics (C.sub.6-C.sub.9)
and paraffins in the C.sub.5 to C.sub.9 range.
EXAMPLES
Example 1
[0051] A calculated comparison of cycle oil injection for
re-cracking in an FCC reaction zone is set forth in Table 1. R.O.T.
represents the riser outlet temperature, and the cat to oil ratio
is on a total feed basis.
[0052] Simulations 1, 2, and 3 are compared to a "base case" FCC
process with no cycle oil recycle. In case 1, cycle oil is
separated from the FCC products and recycled to the FCC process via
injection with the primary feed. In case 2, recycled cycle oil is
injected upstream of primary feed injection. In case 3, the cycle
oil is injected upstream of primary feed injection, as in case 2,
and the cycle oil is hydrotreated under conditions to produce
significant amounts of tetralins (Table 2). The hydrotreatment
resulted in improved olefin yield compared to the base case and
cases 1 and 2. Moreover, cycle oil conversion increased, and
coke-make decreased. In all cases, a conventional large pore
zeolite catalytic cracking catalyst was present in the reaction
zone. No shape selective zeolite was employed.
1TABLE 1 R.O.T. = 977.degree. F.(525.degree. C.), Cat/Oil = 6.6 (TF
basis), 26 kB/D FF Rate CASE BASE 1 2 3 HCO Recycle, 0 2.3 2.3 2.3
kB/D Injection Location Main Fd. Pre-Inj. Pre-Inj. Preheat None
None H/T Yields, Wt. % FF C.sub.2-- Dry Gas 2.93 2.99 3.18 3.2
C.sub.3.dbd. 3.94 3.99 4.09 4.09 C.sub.4.dbd. 5.41 5.53 5.67 5.72
LPG 13.46 13.8 14.06 14.2 Naphtha 46.39 48.33 45.5 45.85 LCO 5.93
5.86 6.94 7.02 HCO 16.39 13.59 13.3 12.91 Bottoms 9.37 9.32 11.18
11.08 Coke 4.83 5.41 5.11 5.07 430.degree. F. Conv. 72 74.7 72.2
73.2 % HCO Converted 0 31 34 38
Example 2
[0053] In accordance with a preferred embodiment, this example
describes hydroprocessing a cycle oil stream and then injecting it
at a point in a FCC riser reactor below (upstream of) the normal
VGO feed injectors (i.e., a pre-injection zone). This provides a
high temperature, high cat/oil, short residence time region wherein
the hydrotreated cycle oil may be converted to naphtha and light
olefins. Catalytic cracking conditions in the second reaction zone
include temperatures ranging from about 1000-1350.degree. F.
(538-732.degree. C.), cat/oil ratios of 25-150 (wt/wt), and vapor
residence times of 0.1-1.0 seconds in the pre-injection zone.
Conventional catalytic cracking conditions were used in the first
reaction zone, with temperature ranging from about 950.degree. F.
(510.degree. C.) to about 1050.degree. F. (566.degree. C.) and the
cat:oil ratio ranging from about 4 to about 10.
[0054] In this example, the cycle oil was hydrogenated under the
conditions set forth in Table 2, prior to upstream injection into
an FCC riser reactor's upstream injection zone. The hydrotreatment
resulted in a combined concentration of tetralins and indans of
32.6 wt. % compared to a concentration of less than 10 wt. % in the
cycle oil before hydroprocessing.
2 TABLE 2 H/T LCCO Conditions Catalyst NiMo/Al.sub.2O.sub.3
Temperature .degree. F./.degree. C. 700/371 Pressure (psig) 1200
LHSV 0.7 H.sub.2 Treat Gas Rate (SCF/B) 5500 Product Properties
Boiling Point Distribution 0.5 wt. % .degree. F./.degree. C.
224.6/107 50.0 wt. % .degree. F./.degree. C. 513.4/267 99.5 wt. %
.degree. F./.degree. C. 720.4/382 Gravity (.degree.API) 26.2 Total
Aromatics (wt. %) 57.6 One-Ring Aromatics (wt. %) 43.1 Feedstock
Properties Boiling Point Distribution 0.5 wt. % .degree.
F./.degree. C. 299.8/149 50.0 wt. % .degree. F./.degree. C.
564.9/296 99.5 wt. % .degree. F./.degree. C. 727.8/387 Gravity
(.degree.API) 13.8 Total Aromatics (wt. %) 83.5 One-Ring Aromatics
(wt. %) 9.7
[0055] A Microactivity Test Unit ("MAT") using a large pore zeolite
cracking catalyst was employed for cracking the hydroprocessed
cycle oil. Cracking conditions are set forth in Table 3.
[0056] MAT tests and associated hardware are described in Oil and
Gas 64, 7, 84, 85, 1966, and Oil and Gas, Nov. 22, 1971, 60-68.
Conditions used herein included temperature 550.degree. C., run
time 0.5 sec., catalyst charge 4.0 g, feed volume 0.95-1.0
cm.sup.3, and cat:oil ratio 4.0-4.2.
[0057] Catalyst A is a commercially available, conventional, large
pore FCC catalysts containing Y-zeolite. As can be seen in the
table, significant conversion to propylene can be achieved by
cracking hydrotreated cycle oil over the FCC catalyst.
3 TABLE 3 Feedstock H/T LCCO Catalyst (steamed) A Temp., .degree.
F./.degree. C. 1020/550 Cat Oil 3.96 Conversion 81.2 Yields, Wt. %
C.sub.2-- Dry Gas 3.5 Propylene 5.4 Propane 1.9 Butenes 4.2 Butanes
8.8 Naphtha 53.2 430.degree. F.+ 18.8 Coke 4.3
[0058] The 81.2 total conversion, 9.6 wt. % light olefin yield, and
the 18.8 wt. % yield of products boiling above 430.degree. F., all
compare favorably with conventional processes.
[0059] For example, in U.S. Pat. No. 3,479,279, a hydrotreated
cycle oil containing a significant amount of tetralins (J=8) is
recycled to the primary FCC unit and injected into a common
cracking zone with the primary feed. The resulting FCC product
contained 45 volume percent aromatics with the most numerous
aromatic species being naphthalenes (J=12). This abundance of
naphthalene strongly suggests the prevalence of undesirable
hydrogen transfer reactions in addition to cracking.
[0060] In U.S. Pat. No. 3,065,166, a cycle oil is hydrotreated
under conditions sufficient to result in partial saturation of the
aromatic species, i.e., species such as naphthalenes are converted
to species such as tetralins. The hydrotreated cycle oil is then
injected into an upstream reaction zone of the primary FCC rector
together with a hydrotreated naphtha. That the same amount of cycle
oil is present in the cracked products independent of whether the
recycled cycle oil is hydroprocessed, strongly suggests the
prevalence of undesirable hydrogen transfer reactions resulting in
the conversion of species such as tetralins into the more difficult
to crack polynuclear aromatic species such as naphthalene.
* * * * *