U.S. patent application number 09/800202 was filed with the patent office on 2001-10-25 for fcc process.
Invention is credited to Mon, Eduardo, Swan, George A. III.
Application Number | 20010032803 09/800202 |
Document ID | / |
Family ID | 27392908 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010032803 |
Kind Code |
A1 |
Mon, Eduardo ; et
al. |
October 25, 2001 |
FCC process
Abstract
The present invention is a fluidized catalytic cracking process
that incorporates a zoned riser reactor. The process provides an
in-situ method for feed upgrading in a riser reactor. The process
assists in the removal of undesirable contaminants, such as
nitrogen, from FCC feedstocks.
Inventors: |
Mon, Eduardo; (Baton Rouge,
LA) ; Swan, George A. III; (Baton Rouge, LA) |
Correspondence
Address: |
EXXONMOBIL RESEARCH AND ENGINEERING COMPANY
P.O. BOX 900
1545 ROUTE 22 EAST
ANNANDALE
NJ
08801-0900
US
|
Family ID: |
27392908 |
Appl. No.: |
09/800202 |
Filed: |
March 6, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60191579 |
Mar 23, 2000 |
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60191530 |
Mar 23, 2000 |
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60246317 |
Nov 6, 2000 |
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Current U.S.
Class: |
208/74 ; 208/113;
208/120.01; 208/130; 208/72; 208/73 |
Current CPC
Class: |
C10G 51/00 20130101;
C10G 51/026 20130101; C10G 11/18 20130101 |
Class at
Publication: |
208/74 ; 208/113;
208/120.01; 208/130; 208/72; 208/73 |
International
Class: |
C10G 051/04 |
Claims
1. A catalytic cracking process comprising: (a) passing a first
portion of regenerated catalyst to a FCC reactor configured to have
a plurality of zones; (b) in a first upstream zone, contacting the
first portion of regenerated catalyst with a secondary FCC feed,
the secondary feed comprising steam and hydrocarbons boiling in the
range of about 25.degree. C. to about 250.degree. C. wherein the
residence time of the secondary feed in the first upstream zone is
less than about 1.5 seconds; (c) in a first primary feed conversion
zone downstream from the first upstream zone, contacting the
effluent from the first upstream zone with a primary FCC feed,
wherein the effluent of the first upstream zone has sufficient
enthalpy to vaporize at least 50 wt% of the FCC primary feed, the
primary FCC feed comprising hydrocarbons boiling in the range of
between about 250.degree. C. and about 575.degree. C., wherein the
residence time within the first conversion zone is between about
0.2 and about 2 seconds and the catalyst to oil weight ratio is
between about 2:1 and about 5:1; (d) contacting a second portion of
regenerated catalyst with a secondary FCC feed, the second portion
of regenerated catalyst comprising a catalytic cracking catalyst,
the secondary feed comprising steam and hydrocarbons boiling in the
range of about 25.degree. C. to about 250.degree. C. and then
passing the second portion of regenerated catalyst and partially
converted secondary FCC feed to a second primary feed conversion
zone; (e) in the second primary feed conversion zone, positioned
downstream from the first primary feed conversion zone, contacting
the effluent of the first primary feed conversion zone with the
second portion of regenerated catalyst wherein the residence time
within the second primary feed conversion zone is less than about
10 seconds; (f) contacting a third portion of regenerated catalyst
with a secondary FCC feed, the third portion of regenerated
catalyst comprising a catalytic cracking catalyst, the secondary
feed comprising steam and hydrocarbons boiling in the range of
about 25.degree. C. to about 250.degree. C. and then passing the
third portion of regenerated catalyst and partially converted
secondary FCC feed to a third primary feed conversion zone; and,
(g) in the third primary feed conversion zone downstream from the
second primary feed conversion zone, contacting the effluent of the
second primary feed conversion zone with the third portion of
regenerated catalyst wherein the residence time in the third
primary feed conversion zone is between about 0.2 and about 1
second.
2. The process of claim 1 wherein the secondary feed comprises
light cat naphtha.
3. The process of claim 2 wherein the secondary feed further
comprises between about 2 and about 50 wt% steam.
4. The process of claim 2 wherein the catalyst to secondary feed
weight ratio in the first upstream zone is between about 30:1 and
about 150:1.
5. The process of claim 1 wherein the residence time within the
first upstream zone is between about 0.1 and about 1 seconds.
6. The process of claim 1 wherein the residence time within the
first primary feed conversion zone is between about 0.2 and about
0.5 seconds.
7. The process of claim 6 wherein the residence time within the
second primary feed conversion zone is less than about 2
seconds.
8. The process of claim 1 wherein the weight ratio of the first
portion of catalyst to the sum of the weights of the second and
third portions of catalyst is between about 1:1 and about 1:2.
9. The process of claim 1 wherein the weight ratio of the second
portion of catalyst to the third portion of catalyst is between
about 1:2 and about 1:1.
10. The process of claim 1 wherein the effluent of the first
upstream zone has sufficient enthalpy to vaporize at least 80 wt%
of the FCC primary feed.
11. A catalytic cracking process comprising: (a) passing a first
portion of regenerated catalyst to a FCC reactor configured to have
a plurality of zones; (b) in a first upstream zone, contacting the
first portion of regenerated catalyst with a secondary FCC feed,
the secondary feed comprising between about 2 and about 50 wt%
steam based on the total weight of the secondary feed and light cat
naphtha, wherein the residence time of the secondary feed in the
first upstream zone is less than about 1.5 seconds and wherein the
catalyst to secondary feed ratio is between about 30:1 and about
150:1; (c) in a first primary feed conversion zone downstream from
the first upstream zone, contacting the effluent from the first
upstream zone with a primary FCC feed, wherein the effluent of the
first upstream zone has sufficient enthalpy to vaporize at least 50
wt% of the FCC primary feed, the primary FCC feed comprising
hydrocarbons boiling in the range of between about 250.degree. C.
and about 575.degree. C., wherein the residence time within the
first conversion zone is between about 0.2 and about 2 seconds and
the catalyst to oil weight ratio is between about 2:1 and about
5:1; (d) contacting a second portion of regenerated catalyst with a
secondary FCC feed, the second portion of regenerated catalyst
comprising a catalytic cracking catalyst, the secondary feed
comprising steam and hydrocarbons boiling in the range of about
25.degree. C. to about 250.degree. C. and then passing the second
portion of regenerated catalyst and partially converted secondary
FCC feed to a second primary feed conversion zone; (e) in the
second primary feed conversion zone, positioned downstream from the
first primary feed conversion zone, contacting the effluent of the
first primary feed conversion zone with the second portion of
regenerated catalyst wherein the residence time within the second
primary feed conversion zone is less than about 10 seconds; (f)
contacting a third portion of regenerated catalyst with a secondary
FCC feed, the third portion of regenerated catalyst comprising a
catalytic cracking catalyst, the secondary feed comprising steam
and hydrocarbons boiling in the range of about 25.degree. C. to
about 250.degree. C. and then passing the third portion of
regenerated catalyst and partially converted secondary FCC feed to
a third primary feed conversion zone; and, (g) in the third primary
feed conversion zone downstream from the second primary feed
conversion zone, contacting the effluent of the second primary feed
conversion zone with the third portion of regenerated catalyst
wherein the residence time in the third primary feed conversion
zone is between about 0.2 and about 1 second, wherein the weight
ratio of the first portion of catalyst to the sum of the weights of
the second and third portions of catalyst is between about 1:1 and
about 1:2 and wherein the weight ratio of the second portion of
catalyst to the third portion of catalyst is between about 1:2 and
about 1:1.
12. A catalytic cracking process comprising: (a) passing a first
portion of catalyst to a FCC reactor configured to have a plurality
of zones, the first portion of catalyst comprising a regenerated
catalyst and an at least partially coked catalyst; (b) in a first
primary feed conversion zone, contacting the first portion of
catalyst with a primary FCC feed, wherein the first portion of
catalyst has sufficient enthalpy to vaporize at least 50 wt% of the
FCC primary feed, the primary FCC feed comprising hydrocarbons
boiling in the range of between about 250.degree. C. and about
575.degree. C., wherein the residence time within the first primary
feed conversion zone is between about 0.2 and about 2 seconds and
the catalyst to oil weight ratio is between about 2:1 and about
5:1; (c) in a second primary feed conversion zone, positioned
downstream from the first primary feed conversion zone, contacting
the effluent of the first primary feed conversion zone with a
second portion of catalyst wherein the residence time within the
second primary feed conversion zone is less than about 10 seconds;
and, (d) in a third primary feed conversion zone downstream from
the second primary feed conversion zone, contacting the effluent of
the second primary feed conversion zone with a third portion of
catalyst wherein the residence time in the third primary feed
conversion zone is between about 0.2 and about 1 seconds.
13. The process according to claim 12 wherein the second portion of
catalyst is selected from the group consisting of a regenerated
catalyst, an at least partially coked catalyst, a pre-coked
catalyst and combinations thereof.
14. The process according to claim 13 wherein the third portion of
catalyst is selected from the group consisting of a regenerated
catalyst, an at least partially coked catalyst, a pre-coked
catalyst and combinations thereof.
15. A catalytic cracking process comprising: (a) passing a first
portion of regenerated catalyst to a FCC reactor configured to have
a plurality of zones; (b) in a first upstream zone, contacting the
first portion of regenerated catalyst with a secondary FCC feed,
the secondary feed comprising steam and hydrocarbons boiling in the
range of about 25.degree. C. to about 250.degree. C. wherein the
residence time of the secondary feed in the first upstream zone is
less than about 1.5 seconds; and, (c) in a first primary feed
conversion zone downstream from the first upstream zone, contacting
the effluent from the first upstream zone with a primary FCC feed,
wherein the effluent of the first upstream zone has sufficient
enthalpy to vaporize at least 50 wt% of the FCC primary feed, the
primary FCC feed comprising hydrocarbons boiling in the range of
between about 250.degree. C. and about 575.degree. C.
16. The method of claim 15 wherein the secondary feed contains
light cat naphtha.
17. The method of claim 16 wherein the steam is present in an
amount ranging from about 2 to about 50 wt.%, based on total weight
of the light cat naphtha.
18. The method of claim 15 wherein the secondary feed vapor
residence time ranges from about 0.1 to about 1 second.
19. The method of claim 15 wherein the catalyst to secondary feed
weight ratio in the upstream zone ranges from about 30:1 to about
150:1.
20. The method of claim 19 wherein the temperature in the
downstream zone ranges from about 450.degree. C. to about
550.degree. C.
21. The method of claim 20 wherein the primary feed vapor residence
time ranges from about 0.2 to about 1 second.
22. The method of claim 21 wherein the catalyst to primary feed
weight ratio in the downstream reaction zone ranges from about 2:1
to about 5:1.
23. The process of claim 1 wherein the effluent of the first
upstream zone has sufficient enthalpy to vaporize at least 90 wt%
of the FCC primary feed.
24. The process of claim 15 wherein the effluent of the first
upstream zone has sufficient enthalpy to vaporize at least 80 wt%
of the FCC primary feed.
25. The process of claim 15 wherein the effluent of the first
upstream zone has sufficient enthalpy to vaporize at least 90 wt%
of the FCC primary feed.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application claims benefit of U.S. provisional
patent applications Ser. No. 60/191,579 filed Mar, 23, 2000, Ser.
No. 60/191,530 filed Mar. 23, 2000, and Ser. No. 60/246,317 filed
Nov. 6, 2000.
BACKGROUND
[0002] The present invention relates to a fluidized catalytic
cracking process that incorporates a zoned riser reactor.
[0003] Catalytic cracking is an established and widely used process
in the petroleum refining industry for converting relatively high
boiling products to more valuable lower boiling products including
gasoline and middle distillates, such as kerosene, jet fuel and
heating oil. The pre-eminent catalytic cracking process is the
fluid catalytic cracking process (FCC) wherein a pre-heated feed
contacts a hot cracking catalyst. During the cracking reactions,
coke and hydrocarbons deposit on the catalyst particles, resulting
in a loss of catalytic activity and selectivity. The coked catalyst
particles, and associated hydrocarbon material, are stripped,
usually with steam, to remove as much of the hydrocarbon material
as technically and economically feasible. The stripped particles,
containing non-strippable coke, pass from the stripper and to a
regenerator. In the regenerator, the coked catalyst particles are
regenerated by contacting them with air, or a mixture of air and
oxygen, at elevated temperatures, resulting in the combustion of
the coke-an exothermic reaction. The coke combustion removes the
coke and heats the catalyst to the temperatures appropriate for the
endothermic cracking reactions.
[0004] The process occurs in an integrated unit comprising the
cracking reactor, the stripper, the regenerator, and the
appropriate ancillary equipment. The catalyst is continuously
circulated from the reactor or reaction zone, to the stripper and
then to the regenerator and back to the reactor. The circulation
rate is typically adjusted relative to the feed rate of the oil to
maintain a heat balanced operation in which the heat produced in
the regenerator is sufficient for maintaining the cracking reaction
with the circulating, regenerated catalyst being used as the heat
transfer medium.
[0005] There is a growing need to process heavier feeds containing
contaminants such as nitrogen in FCC operations. Therefore, a need
exists for a process that can perform in-situ upgrading of
nitrogen-containing feeds that can effectively and efficiently
minimize the problems caused by nitrogen-containing FCC feeds.
[0006] Additionally, an increased demand for high octane, low
emissions fuels and hydrocarbons useful for olefin production has
led to a desire to increase the light (C.sub.2 - C.sub.4) olefin
content is riser reactor products. Typical heavy oil, gas oil, or
resid feeds for riser reactor processes generally contain at most
small amounts of light olefins, if any. Catalytic cracking in the
riser reactor produces light olefins; however, these products may
be thermally cracked into undesirable products such as catalyst
coke, diolefins, and dry gas (including methane). These products
may also be saturated via hydrogen transfer reactions before they
reach the end of the riser. Both activities reduce the
concentrations of high-octane naphtha and light olefins.
SUMMARY
[0007] One embodiment of the present invention is a catalytic
cracking process comprising (a) contacting a first portion of
catalyst with a secondary feed in a first upstream zone wherein the
secondary feed has a boiling range between about 25.degree. C. and
about 250.degree. C.; (b) in a first primary feed conversion zone,
contacting a primary feed comprising nitrogen contaminants with the
first portion of catalyst passed from the first upstream zone,
wherein the temperature in the first primary feed conversion zone
is greater than about 450.degree. C, thereby vaporizing a
substantial portion of the primary feed; (c) passing the effluent
from the first primary feed conversion zone to a secondary primary
feed conversion zone and contacting the effluent from the first
primary feed conversion zone with a second portion of catalyst
under catalytic cracking conditions.
[0008] Another embodiment comprises a catalytic cracking process
comprising (a) passing a first portion of regenerated catalyst to a
FCC reactor configured to have a plurality of zones; (b) in a first
upstream zone, contacting the first portion of regenerated catalyst
with a secondary FCC feed, the secondary feed comprising steam and
hydrocarbons boiling in the range of about 25.degree. C. to about
250.degree. C. wherein the residence time of the secondary feed in
the first upstream zone is less than about 1.5 seconds; (c) in a
first primary feed conversion zone downstream from the first
upstream zone, contacting the effluent from the first upstream zone
with a primary FCC feed, wherein the effluent of the first upstream
zone has sufficient enthalpy to vaporize at least 50 wt% of the FCC
primary feed, the primary FCC feed comprising hydrocarbons boiling
in the range of between about 250.degree. C. and about 575.degree.
C., wherein the residence time within the first primary feed
conversion zone is between about 0.2 and about 2 seconds and the
catalyst to oil weight ratio is between about 2:1 and about 5:1;
(d) contacting a second portion of regenerated catalyst with a
secondary FCC feed, the second portion of regenerated catalyst
comprising a catalytic cracking catalyst, the secondary feed
comprising steam and hydrocarbons boiling in the range of about
25.degree. C. to about 250.degree. C. and then passing the second
portion of regenerated catalyst and partially converted secondary
FCC feed to a second primary feed conversion zone positioned
downstream from the first primary feed conversion zone; and, (e) in
the second primary feed conversion zone, contacting the effluent of
the first primary feed conversion zone with the second portion of
regenerated catalyst wherein the residence time within the second
primary feed conversion zone is less than about 10 seconds.
[0009] Another embodiment of the present invention comprises a
catalytic cracking process comprising (a) passing a first portion
of regenerated catalyst to a FCC reactor configured to have a
plurality of zones; (b) in a first upstream zone, contacting the
first portion of regenerated catalyst with a secondary FCC feed,
the secondary feed comprising steam and hydrocarbons boiling in the
range of about 25.degree. C. to about 250.degree. C. wherein the
residence time of the secondary feed in the first upstream zone is
less than about 1.5 seconds; (c) in a first primary feed conversion
zone downstream from the first upstream zone, contacting the
effluent from the first upstream zone with a primary FCC feed,
wherein the effluent of the first upstream zone has sufficient
enthalpy to vaporize at least 50 wt% of the FCC primary feed, the
primary FCC feed comprising hydrocarbons boiling in the range of
between about 250.degree. C. and about 575.degree. C., wherein the
residence time within the first conversion zone is between about
0.2 and about 2 seconds and the catalyst to oil weight ratio is
between about 2:1 and about 5:1; (d) in a second primary feed
conversion zone downstream from the first primary feed conversion
zone, contacting the effluent of the first primary feed conversion
zone with a second portion of regenerated catalyst passed into the
second conversion zone, the regenerated catalyst passed into the
second conversion zone comprising a catalytic cracking catalyst
wherein the residence time within the second primary feed
conversion zone is less than about 10 seconds; and (e) in a third
primary feed conversion zone downstream from the second primary
feed conversion zone, contacting the effluent of the second primary
feed conversion zone with a third portion of regenerated catalyst
passed into the third conversion zone, the regenerated lo catalyst
comprising a catalytic cracking catalyst, wherein the residence
time in the third primary feed conversion zone is between about 0.2
and 1 second.
[0010] Another embodiment is a catalytic cracking process
comprising (a) passing a first portion of regenerated catalyst to a
FCC reactor configured to have a plurality of zones; (b) in a first
upstream zone, contacting the first portion of regenerated catalyst
with a secondary FCC feed, the secondary feed comprising steam and
hydrocarbons boiling in the range of about 25.degree. C. to about
250.degree. C. wherein the residence time of the secondary feed in
the first upstream zone is less than about 1.5 seconds; (c) in a
first primary feed conversion zone downstream from the first
upstream zone, contacting the effluent from the first upstream zone
with a primary FCC feed, wherein the effluent of the first upstream
zone has sufficient enthalpy to vaporize at least 50 wt% of the FCC
primary feed, the primary FCC feed comprising hydrocarbons boiling
in the range of between about 250.degree. C. and about 575.degree.
C., wherein the residence time within the first conversion zone is
between about 0.2 and about 2 seconds and the catalyst to oil
weight ratio is between about 2:1 and about 5:1; (d) contacting a
second portion of regenerated catalyst with a secondary FCC feed,
the second portion of regenerated catalyst comprising a catalytic
cracking catalyst, the secondary feed comprising steam and
hydrocarbons boiling in the range of about 25.degree. C. to about
250.degree. C. and then passing the second portion of regenerated
catalyst and partially converted secondary FCC feed to a second
primary feed conversion zone; (e)in the second primary feed
conversion zone, positioned downstream from the first primary feed
conversion zone, contacting the effluent of the first primary feed
conversion zone with the second portion of regenerated catalyst
wherein the residence time within the second primary feed
conversion zone is less than about 10 seconds; (f) contacting a
third portion of regenerated catalyst with a secondary FCC feed,
the third portion of regenerated catalyst comprising a catalytic
cracking catalyst, the secondary feed comprising steam and
hydrocarbons boiling in the range of about 25.degree. C. to about
250.degree. C. and then passing the third portion of regenerated
catalyst and partially converted secondary FCC feed to a third
primary feed conversion zone; and, (g) in the third primary feed
conversion zone downstream from the second primary feed conversion
zone, contacting the effluent of the second primary feed conversion
zone with the third portion of regenerated catalyst wherein the
residence time in the third primary feed conversion zone is between
about 0.2 and about 1 second.
[0011] Another embodiment is a catalytic cracking process
comprising (a) passing a first portion of catalyst to a FCC reactor
configured to have a plurality of zones, the first portion of
catalyst comprising a regenerated catalyst and an at least
partially coked catalyst; (b) in a first primary feed conversion
zone, contacting the first portion of catalyst with a primary FCC
feed, wherein the first portion of catalyst has sufficient enthalpy
to vaporize at least 50 wt% of the FCC primary feed, the primary
FCC feed comprising hydrocarbons boiling in the range of between
about 250.degree. C. and about 575.degree. C., wherein the
residence time within the first primary feed conversion zone is
between about 0.2 and about 2 seconds and the catalyst to oil
weight ratio is between about 2:1 and about 5:1; (c) in a second
primary feed conversion zone, positioned downstream from the first
primary feed conversion zone, contacting the effluent of the first
primary feed conversion zone with a second portion of catalyst
wherein the residence time within the second primary feed
conversion zone is less than about 10 seconds; and, (d) in a third
primary feed conversion zone downstream from the second primary
feed conversion zone, contacting the effluent of the second primary
feed conversion zone with a third portion of catalyst wherein the
residence time in the third primary feed conversion zone is between
about 0.2 and about 1 seconds.
[0012] Another embodiment is catalytic cracking process comprising
(a) passing a first portion of regenerated catalyst to a FCC
reactor configured to have a plurality of zones; (b) in a first
upstream zone, contacting the first portion of regenerated catalyst
with a secondary FCC feed, the secondary feed comprising steam and
hydrocarbons boiling in the range of about 25.degree. C. to about
250.degree. C. wherein the residence time of the secondary feed in
the first upstream zone is less than about 1.5 seconds; and, (c) in
a first primary feed conversion zone downstream from the first
upstream zone, contacting the effluent from the first upstream zone
with a primary FCC feed, wherein the effluent of the first upstream
zone has sufficient enthalpy to vaporize at least 80 wt% of the FCC
primary feed, the primary FCC feed comprising hydrocarbons boiling
in the range of between about 250.degree. C. and about 575.degree.
C.
[0013] Another embodiment is a process comprising: (a) passing a
vacuum resid having boiling range greater than about 565.degree. C.
(about 1050.degree. F.) to a resid processing unit; (b) separating
a light resid fraction having boiling range between about
565.degree. C. and about 650.degree. C. (about 1200.degree. F.)
from the vacuum resid; (c) combining the light resid fraction with
a FCC feed; (d) passing the combined FCC feed to a FCC unit
configured to have a plurality of reaction zones; (e) in the FCC
unit: (i) contacting a first portion of catalyst with a secondary
feed in a first upstream zone, the secondary feed having a boiling
range between about 25.degree. C. and about 250.degree. C.; (ii) in
a first primary feed conversion zone, contacting the combined feed
comprising nitrogen contaminants with the first portion of catalyst
passed from the first upstream zone, wherein the temperature in the
first primary feed conversion zone is greater than about
450.degree. C., thereby vaporizing a substantial portion of the
combined feed; and, (iii) passing the effluent from the first
primary feed conversion zone to a secondary primary feed conversion
zone and contacting the effluent from the first primary feed
conversion zone with a second portion of catalyst under catalytic
cracking conditions.
[0014] Another embodiment is a process comprising: (a) passing a
atmospheric pipe still bottoms stream to a vacuum pipe still; (b)
separating a vacuum gas oil having a boiling range between about
340.degree. C. and about 565.degree. C. from the bottoms stream,
the remainder comprising a vacuum resid fraction; (c) passing at
least a portion of the vacuum resid fraction to a short-path
distillation unit; (d) in the short-path distillation unit,
separating a lighter resid fraction having a boiling range between
about 565.degree. C. and about 650.degree. C. (about 1200.degree.
F.); (e) combining the lighter resid fraction with the vacuum gas
oil to form a FCC feed; (f) passing the FCC feed to a FCC unit
configured to have a plurality of reaction zones; and, (e) in the
FCC unit: (i) contacting a first portion of catalyst with a
secondary feed in a first upstream zone, the secondary feed having
a boiling range between about 25.degree. C. and about 250.degree.
C.; (ii) in a first primary feed conversion zone, contacting the
FCC feed comprising nitrogen contaminants with the first portion of
catalyst passed from the first upstream zone, wherein the
temperature in the first primary feed conversion zone is greater
than about 450.degree. C., thereby vaporizing a substantial portion
of the FCC feed; and ,(iii) passing the effluent from the first
primary feed conversion zone to a secondary primary feed conversion
zone and contacting the effluent from the first primary feed
conversion zone with a second portion of catalyst under catalytic
cracking conditions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 illustrates an embodiment of a riser used with the
present process wherein the riser has three zones.
[0016] FIG. 2 illustrates an embodiment of a riser used with the
present process wherein the riser has four zones.
[0017] FIG. 3 illustrates another embodiment of a riser used with
the present process wherein the riser has four zones.
[0018] FIG. 4 illustrates an embodiment of a riser used with the
present process wherein the riser has five zones.
DETAILED DESCRIPTION
[0019] Suitable FCC feeds for the process of the present invention
include hydrocarbon oils boiling in the range of about 430.degree.
F. to about 1050.degree. F. (220.degree. C.-565.degree. C.), such
as gas oil, heavy hydrocarbon 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 liquefaction processes, and mixtures thereof.
Small amounts (less than about 15 wt.%) of higher boiling fractions
such as vacuum resids may be added to the feedstocks.
[0020] The invention is useful for riser reactor processes such as
fluidized catalytic cracking (FCC) processes. The FCC process
preferably occurs in an integrated unit comprising a riser reactor
500, a stripper, a regenerator, and appropriate ancillary
equipment. The cracking catalyst continuously circulates from the
reactor 500 to the stripper to the regenerator and back to the
reactor 500.
[0021] In a conventional FCC process, a pre-heated feed contacts
the regenerated cracking catalyst that cracks the heavier
hydrocarbon components into more valuable products having a lower
boiling point. During the cracking reactions, coke and hydrocarbons
deposit on the catalyst particles, resulting in a loss of catalytic
activity. The catalyst particles then separate from the vapor
products in a solid/gas separator, such as a cyclone. The coked
catalyst particles, and any associated hydrocarbon material, are
stripped, usually with steam, to remove the strippable (volatile)
components. The stripped components pass with the cracked products
to a fractionator.
[0022] The stripped particles, containing non-strippable coke, pass
from the stripper to the regenerator where the coked catalyst
particles are regenerated by contacting air, or a mixture of air
and oxygen, at elevated temperatures. Suitable regeneration
conditions include a temperature from about 1100 to about
1500.degree. F. (593.degree. C.-816.degree. C.), and a pressure
ranging from about 0 to about 150 psig (101-1136 kPa). Regeneration
bums at least a portion of the coke off the catalyst and heats the
catalyst to the temperatures necessary for the endothermic cracking
conditions in the reactor 500.
[0023] The catalytic cracking catalyst used in the present process
may be any conventional FCC catalyst. Suitable catalysts include
(a) amorphous solid acids, such as alumina, silica-alumina,
silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia,
silica-titania, and the like, and (b) zeolite catalysts containing
faujasite. Silica-alumina materials suitable for use in the present
invention are amorphous materials containing about 10 to 40 wt. %
alumina. Other promoters may or may not be added.
[0024] The catalyst may also comprise zeolite materials that are
iso-structural to zeolite Y, including the ion-exchanged forms such
as the rare-earth hydrogen and ultra stable (USY) form. The
particle size of the zeolite may range from about 0.1 to 10
microns, preferably from about 0.3 to 3 microns. The zeolite is
mixed with a suitable porous matrix material when used as a
catalyst for fluid catalytic cracking. The catalyst may contain at
least one crystalline aluminosilicate, also referred to herein as a
large-pore zeolite, having an average pore diameter greater than
about 0.7 nanometers (nm). The pore diameter, also sometimes
referred to as effective pore diameter, is 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 second catalytic
cracking catalyst 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.
[0025] The large-pore zeolites may 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.
The crystalline admixtures are themselves medium-pore-size,
shape-selective 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.
[0026] The catalytic cracking 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. In addition,
individual catalyst particles may contain large-pore zeolite,
amorphous species, other components described herein, and mixtures
thereof.
[0027] Non-limiting porous matrix materials that may be used
include alumina, silica-alumina, silica-magnesia, silica-zirconia,
silica-thoria, silica-beryllia, silica-titania, and 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 matrix itself
may possess acidic catalytic properties and may be an amorphous
material. The inorganic oxide matrix component binds the particle
components together so that the catalyst particle product is hard
enough to survive inter-particle and reactor wall collisions. The
inorganic oxide matrix may be made according to conventional
processes from an inorganic oxide sol or gel that is dried to bind
the catalyst particle components together. Preferably, the
inorganic oxide matrix is not catalytically active and comprises
oxides of silicon and aluminum. Preferably, separate alumina phases
may be incorporated into the inorganic oxide matrix. Species of
aluminum oxyhydroxides, boehmite, diaspore, and transitional
aluminas such as .alpha.-alumina, .beta.-alumina, .gamma.-alumina,
.delta.-alumina, .epsilon.-alumina, .kappa.-alumina, and
.rho.-alumina can be employed. The alumina species may be an
aluminum trihydroxide such as gibbsite, bayerite, nordstrandite, or
doyelite. The matrix material may also contain phosphorous or
aluminum phosphate.
[0028] The catalyst of the present invention may also comprise one
or more known nitrogen scavenger catalysts, including, but not
limited to, amorphous aluminosilicates, acid clays, hydrogen or
ammonium exchanged mordenite, clinoptilolite, chabazite, erionite,
mineral acids or mineral acid precursors supported on a previously
described matrix material, and Catapal alumina. Acid clays include
kaolin, halloysite, sepiolite, and vermiculite. Mineral acids may
include phosphoric acid, sulfuric acid, and boric acid. Mineral
acid precursor refers to a compound that will form a mineral acid
when subjected to FCC conditions.
[0029] Preferably, the nitrogen scavenger has a relatively low
catalytic activity. If desired, in one embodiment, the nitrogen
scavenger catalyst is less dense than the conventional FCC catalyst
previously described. The difference in density provides at least
two advantages. First, the lower density of the nitrogen scavenger
catalyst decreases the lift gas 300 (steam) requirements for
passing the catalyst up the riser. Second, by using a less dense
nitrogen scavenger catalyst, selective catalyst separation may
occur in the regenerator. Because the nitrogen scavenger is less
dense, the fluidization of the regenerator bed causes: (a) the
nitrogen scavenger to migrate to the top of the regenerator
catalyst bed; and, (b) the conventional catalyst to migrate to the
bottom of the regenerator catalyst bed. Accordingly, the nitrogen
scavenger may be withdrawn at or near the top of the regenerator
catalyst bed, and the conventional FCC catalyst may be withdrawn at
or near the bottom of the regenerator catalyst bed. Of course,
other suitable separation techniques may be employed if catalyst
separation is desired.
[0030] When a nitrogen scavenger catalyst is incorporated into the
present process, the nitrogen scavenger comprises all or a portion
of the regenerated catalyst 400 passed into zone I if separation
techniques are used. If no separation is used, the catalyst 400
passed to the upstream end of the reactor 500 comprises both the
nitrogen scavenger and the conventional FCC catalyst.
[0031] Viewing FIG. 1, the present process incorporates a riser
reactor 500 having one or more, preferably three zones I, II,
III-although in some embodiments, the riser reactor may be
configured to have four or five zones (zones IV and V). A first
portion of the catalyst 400 from the regenerator (not shown) passes
through a standpipe and enters the base of the riser reactor 500 by
any conventional means. For example, FIG. 1 illustrates one
configuration employing a J-bend where a lift gas 300, preferably
steam, provides some of the lift necessary to flow the catalyst 400
up through reactor 500.
[0032] In an embodiment of the present process incorporating a
riser reactor 500 with three zones-a first zone I, a second zone II
downstream from zone I, and a third zone III downstream from zone
II-a primary feed 100 passes into zone II and a secondary feed 200
passes upstream into zone I, also referred to herein as the first
upstream zone.
[0033] The secondary feed 200 preferably comprises hydrocarbons
having boiling point between 25.degree. C. and 250.degree. C. and
includes, but is not limited to, light cat naphtha (LCN), heavy cat
naphtha, light cycle oil, virgin naphtha, hydrocracked naphtha,
coker naphtha, and/or combinations thereof. Secondary feed 200
preferably comprises LCN and additional steam. Secondary feed 200
passes into zone I of the riser reactor 500. LCN is a hydrocarbon
stream having a final boiling point less than about 140.degree. C.
(300.degree. F.) and comprises olefins in the C.sub.5-C.sub.9
range, single ring aromatics (C.sub.6-C.sub.9) and paraffins in the
C.sub.5-C.sub.9 range. LCN passes into zone I together with about 2
to about 50 wt.% steam based on the total weight of LCN. Zone I is
configured so that the LCN and steam passed into zone I have a
vapor residence time less than about 1.5 sec., preferably less than
about 1.0 sec. and more preferably between about 0.1 and about 1
sec. Cat/oil ratios range between about 30:1 and about 150:1
(wt.:wt.), pressures range between about 100 and about 400 kPa, and
catalyst temperatures range from about 620.degree. C. to about
775.degree. C.
[0034] The injection of steam and LCN into zone I results in (a)
increased C.sub.3 and C.sub.4 olefin yields by cracking
C.sub.5-C.sub.9 olefins in the LCN, and (b) a reduced volume of
naphtha that has an increased octane value. At least about 5 wt.%
of the C.sub.5-C.sub.9 olefins are converted to C.sub.3 and C.sub.4
olefins. While not wanting to be bound by any theory, applicants
believe that adjusting the LCN feed rate into zone I regulates the
amount of coke formed on the zeolite component of the catalyst.
Regulating the amount of coke on the zeolite enables a degree of
control over the amount of catalytic conversion that occurs in the
subsequent, downstream zone(s). Moreover, regulating the secondary
feed 200 rate into zone I regulates the temperature and
consequently, the conversion and adsorption of nitrogen-containing
species in the subsequent downstream zone(s).
[0035] The effluent from zone I flows to a second zone II, also
referred to herein as the first primary feed conversion zone. In
zone II, a primary FCC feed 100 passes into the riser reactor 500
and contacts the up-flowing catalyst 400. Reaction conditions in
zone II include initial catalyst temperature of from about
570.degree. C. to about 725.degree. C. at pressures of from about
100 to about 400 kPa and cat:oil ratios of about 2:1 to about 5:1
(wt.:wt.). Zone II is configured so that vapor residence times
range from about 0.2 to about 2 seconds, preferably from about 0.2
to about 1 second, and more preferably from about 0.2 to about 0.5
seconds. Average temperatures in zone II largely depend on the
boiling range of the primary FCC feed 100. Typically, the average
temperature ranges from greater than about 450.degree. C. to about
550.degree. C., and preferably from about 480.degree. C. to about
500.degree. C. In one embodiment using a conventional heavy oil
feed having a gravity of 20.degree. API and a Watson
characterization factor ("K.sub.w") of about 11.6, the catalyst
exiting zone I has a temperature of at least 480.degree. C., and
preferably ranging from about 480.degree. C. to about 500.degree.
C.
[0036] The effluent from zone I should have sufficient enthalpy to
vaporize at least about 50 wt.% of the primary FCC feed 100, more
preferably at least 80 wt.%, and more preferably at least about 90
wt.%, based on the total weight of the primary FCC feed 100. While
not wishing to be bound by any theory or model, it is believed that
when at least 80 wt.% of the primary FCC feed 100 is vaporized in
zone II, a substantial portion of the nitrogen-containing
impurities in the primary FCC feed 100 are irreversibly adsorbed
onto the catalyst and converted to coke, thus removing at least a
portion of the impurities from the primary FCC feed 100. This
effect should increase as the molecular weight and basicity of the
nitrogen-containing species increases. The bulk of the nitrogen
removed leaves the reactor in the form of coke on catalyst, while a
smaller fraction may yield ammonia.
[0037] Controlling the enthalpy of the effluent from zone I so that
at least 80 wt.% of the primary FCC feed 100 is vaporized but so
that there is not significant primary FCC conversion, leads to a
relatively low catalyst to primary FCC feed ratio and a lower
average temperature in zone II. Applicants 25 believe that the
lower average temperature in zone II favors adsorption by the
catalyst of undesirable nitrogen-containing species in the primary
FCC feed 100. Additionally, lower average temperatures result in
reduced thermal cracking and consequently, improved selectivity to
naphtha and light olefins.
[0038] Effluent from zone II may be further converted
(catalytically cracked) in subsequent reaction zones in the riser
500 and passed to the cyclones and stripper as previously
described.
[0039] In one embodiment of the present invention, the riser
reactor 500 is configured to have a third zone III between zone II
and riser reactor outlet. The conditions in zone III may be
regulated to take advantage of the in-situ feed upgrading process
previously described.
[0040] In zone III, also referred to herein as the second primary
feed conversion zone, fresh regenerated catalyst 401, preferably
comprising a conventional FCC catalyst, passes into the riser
reactor 500 through one or more ports 250 in zone III to contact
the upgraded primary FCC feed effluent from zone II, which includes
catalyst 400. Catalyst 401 may pass into the reactor 500 in any
conventional manner. Contacting the upgraded FCC feed with fresh
regenerated catalyst 401 leads to substantially less coke and
nitrogen deposition on the regenerated catalyst 401 passed into
zone III, which leads to an effective increase in catalyst
activity.
[0041] Catalyst to oil ratio in zone III may be adjusted by
regulating the feed rates of the catalyst(s) passed into the first
zone I and third zone III. Preferably, the amount of regenerated
catalyst passed 401 into zone III (R.sub.3) exceeds the amount of
catalyst 400 passed into zone I (R.sub.1). More preferably, the
ratio of R.sub.3 to R.sub.1 ranges from about 1:2 to about 2:1.
[0042] Conditions in zone III are similar to those in a
conventional FCC operation and include (i) temperatures from about
500.degree. C. to about 650.degree. C., preferably from about
500.degree. C. to about 600.degree. C.; (ii) hydrocarbon partial
pressures from about 10 to about 40 psia (70-280 kPa), preferably
from about 20 to about 35 psia (140-245 kPa); and, (iii) a catalyst
to oil (wt:wt) ratio from about 3:1 to about 12:1, preferably from
about 4:1 to about 10:1.
[0043] The increased availability of strong catalyst acid sites in
zone III enables the attainment of the required feed conversion at
relatively short contact (residence) times of less than ten
seconds, more preferably between about 2 and about 5 seconds, and
even more preferably less than 2 seconds. As used herein, contact
time and residence time are synonymous and are used to designate
the average residence time of the solids (catalyst) passing through
a particular zone. Applicants believe that contacting freshly
regenerated catalyst in zone III with upgraded feed passing from
zone II leads to substantially less coke and nitrogen deposition on
the catalyst. In turn, this results in an effective increase in
catalyst conversion activity. Coke yields from zone III decrease
due to reduced hydrogen transfer and enhanced primary cracking,
thus allowing the option of constant coke operation via increased
zone III cat to oil ratios.
[0044] FIG. 2 illustrates another embodiment of the present
invention. Riser reactor 500 is configured to have a fourth zone
IV, also referred to herein as a second upstream zone, positioned
upstream from port(s) 250 (or port(s) 350 as described below). In
zone IV, another stream of secondary feed 200, preferably LCN,
contacts catalyst stream 401 before catalyst stream 401 passes
through port(s) 250. The additional LCN injection occurs as
previously described for zone I (and may include steam
co-injection). Incorporating zone IV helps quench the temperature
of the subsequent zones, minimizes thermal cracking and aromatics
formation, and generates additional light olefins by conventional
cracking. Zone IV also provides the option of increasing the cat to
oil ratio without unwanted increases in the subsequent reaction
zone temperatures. Operating conditions for the optional zone IV
lie within those previously described for zone I.
[0045] Viewing FIG. 3, in another embodiment, the riser reactor 500
employs a fifth zone, zone V, also referred to herein as the third
primary feed conversion zone. In an embodiment including zone V,
which may or may not include zone IV, at least one additional
regenerated catalyst inlet port(s) 350 are positioned downstream
from zone III and a portion of regenerated catalyst 402 is directed
through port(s) 350, although catalyst 402 may pass into zone V in
any conventional manner. Port(s) 350 are configured in the same
manner as described for port(s) 250, but port(s) 350 are positioned
downstream from port(s) 250 so that the contact (residence) time of
the catalyst to oil between the injection ports is between about
0.2 and about 1 second, preferably about 0.5 seconds. This
configuration provides an additional stage of feed pretreatment.
The catalyst-to-oil ratio (wt:wt) in zone V is between about 3:1
and about 12:1, and the temperature within zone V is between about
500.degree. C. and about 650.degree. C.
[0046] Zone V may be used in conjunction with an embodiment
incorporating zones I-IV (see FIG. 4), or with an embodiment that
incorporates only zones I-III (see FIG. 3). Regenerated catalyst
402 passing into zone V may also contact a secondary feed stream
200 to provide additional advantages as already set forth for zones
I and IV. The secondary feed 200 may be contacted with a single
catalyst stream that is thereafter separated into catalyst streams
401, 402, or the secondary feed 200 may be contacted with the
catalyst streams 401, 402 separately. In some embodiments, the
combined residence time within zones III and V is less than about 4
seconds.
[0047] In some embodiments, the weight ratio of catalyst stream 401
to catalyst stream 402 ranges between about 1:2 and about 1:1, and
the weight ratio of catalyst stream 400 to the combined weight of
catalyst streams 401 and 402 is between 1:1 and 1:2.
[0048] Coked catalyst particles and cracked hydrocarbon products
exit the riser reactor 500 and pass the cyclones where the cracked
products separate from coked catalyst particles. Coked catalyst
particles from the cyclones pass to a stripping zone. The stripper
removes and recovers the strippable hydrocarbons from coked
catalyst particles. Stripped hydrocarbons pass with cracked
hydrocarbon products for further processing. After the coked
catalyst is stripped, it passes to the regenerator and eventually
back to the riser reactor 500.
[0049] In other embodiments not shown in the Figures, it may be
desirable to eliminate the step of pre-contacting one or more of
the catalyst streams with a secondary feed 200. In such
embodiments, the catalyst streams flowing to the reactor 500 would
comprise an at least partially coked catalyst, preferably having a
coke content of greater than 0.1 wt% based upon the total weight of
the catalyst charge. In some embodiments, the catalyst would also
comprise fully regenerated catalysts. For instance, in one
embodiment, at least partially coked catalyst from the stripper may
pass into the base of the riser reactor 500 alone or in combination
with regenerated catalyst 400. In another embodiment, at least
partially coked catalyst may pass into any of the zones discussed
herein in place of or in combination with catalyst that to be
pre-coked with a secondary feed 200, although applicants prefer
pre-coking with secondary feed 200.
[0050] In yet another embodiment, a two-stage catalyst regenerator
may be employed, and the catalyst 400 passed to the base of the
riser may comprise a first portion of substantially regenerated
catalyst passed from one stage of the regenerator and a second
portion of only partially regenerated and at least partially coked
catalyst that passed from another stage of the regenerator.
Applicants believe that the use of the partially coked catalyst
provides benefits similar to that found by using catalyst pre-coked
by contact with LCN or other secondary feed 200.
[0051] In another embodiment of the present invention, the
embodiments of the multi-zone riser may be used in conjunction with
a resid upgrading unit or process, such as short-path distillation.
In an embodiment employing short path distillation, high vacuum
evaporation of volatile species from a thin liquid film spread on a
heated surface is used. Evolved vapor is rapidly condensed on a
closely adjacent cooled surface. Wiper blades on the heated and
cooled surfaces operate continuously to facilitate heat and mass
transport. Typically, two or more stages are employed. The overhead
vapor is routed through an entrainment separator to minimize
carryover of heavier components. Holdup is minimal and the short
residence time acts to prevent thermal cracking of the overhead and
bottoms streams. Short path distillation is also described in U.S.
Pat. Nos. 5,415,764 and 4,925,558, which are incorporated herein by
reference to the extent they do not conflict with the present
disclosure. Short path distillation offers the potential to boost
the 1050/1200.degree. F. (565/650.degree. C.) fraction of vacuum
resid to the FCC without incurring the typical debits for high feed
metals as well as rejecting the highest Conradson carbon
1200.degree. F.+(650.degree. C.+) fraction.
[0052] Combining the short path distillation or other suitable
process to capture a 1050/1200.degree. F. (565/650.degree. C.)
fraction of vacuum resid with the multi-zone FCC riser results in a
synergy to capture additional advantage from the lower coke
selectivity of the multi-zone process. A particular benefit from
the multi-zone riser is improved coke/bottoms selectivity, which
can be exploited by increasing the final boiling point of the
primary feed to the riser. Vacuum pipe still bottoms have an
initial boiling point >1050.degree. F. (.degree. 565.degree.
C.), and small increments of that stream elevate nickel and
vanadium concentrations in the primary feed, resulting in higher
coke and dry gas yields. The nickel and vanadium content of the
primary feed is comparable to that of typical gas oil FCC feeds
because the lighter vacuum resid fraction is typically low in
metals. The nitrogen content and Conradson carbon content are
greater than typical gas oil FCC feeds but well suited for the
multi-zone FCC riser. The multi-zone riser can tolerate increased
nitrogen concentrations, but the metals contamination debits
remain. Short-path distillation of vacuum pipe still bottoms and
blending the 1050/1200.degree. F. (565/650.degree. C.) fraction
from the short-path distillation unit with the primary feed permits
processing of the lower boiling fraction of the vacuum resid.
[0053] In a particular embodiment, a bottoms stream from an
atmospheric pipe still is passed to a vacuum pipe still where a gas
oil stream boiling in the about 650/1050.degree. F. (about
340/565.degree. C.) range is derived from a vacuum pipe still
(distillation column). A vacuum resid fraction boiling above
1050.degree. F. (565.degree. C.) passes from the vacuum pipe still
to a short-path distillation unit such as the VRSD process offered
by Buss AG, or other suitable resid unit. Overhead streams,
referred to herein as a lighter resid stream, having a boiling
range of 1050/1200.degree. F. (565/650.degree. C.) taken from the
resid unit are then combined with the 650/1050.degree. F.
(340/565.degree. C.) gas oil fraction obtained from the vacuum pipe
still (or other suitable FCC feed stream) and may be preheated for
injection into the multi-zone riser as the primary FCC feed. Other
suitable process(es), such as solvent deasphalting, may also be
used to obtain a lower final boiling point cut of lighter vacuum
resid.
[0054] Boiling ranges of various streams are measured by
conventional methods, preferably ASTM distillation.
EXAMPLES 1-3
[0055] Examples 1-3 illustrate the nitrogen removal capabilities of
the present invention. Examples 1-3 were conducted using a
conventional FCC catalyst and a vacuum gas oil feed containing
about 925 wppm total nitrogen. The catalyst was not lightly coked
by cracking a secondary light feed. Results are therefore deemed
conservative, in the sense that lightly coked catalyst would have
been expected to further suppress conversion, without adversely
affecting nitrogen removal efficiency.
[0056] Example 1 represents a base case at typical cat to oil ratio
and reactor temperature. Operation at these conditions results in
relatively high (430.degree. F.-/221.degree. C.-) conversion of 80
wt.%. The nitrogen removal from the collected liquid product was
83.3 wt.%.
[0057] Example 2 shows that reducing reactor temperature to about
944.degree. F. (507.degree. C.) and using a cat to oil of 3.15
(conditions that are within the range of operation of the zone II
of the present invention) lowered conversion to 50.6 wt.%. However,
a large percentage (62.1 wt.%) of the total feed nitrogen was
removed. This is about 75% of the amount of nitrogen removed in
Example 1, but only 41% of the catalyst was used.
[0058] Example 3 data was obtained by reducing contact time to 0.33
seconds, which is close to the lower end of the preferred contact
times of the present invention for the conversion zone(s).
Conditions otherwise were roughly comparable to those in Example 1.
Lower contact time significantly reduced conversion to 65.5 wt.%,
but nitrogen was still high at 71.7 wt.%. Table 1 illustrates the
results from Examples 1-3.
1TABLE 1 Total N Contact Reactor Wt. % Removal, Time, Temp. Cat to
Oil (430.degree. F.-) wt. % of Feed Example sec. .degree. C. Ratio
Conversion N 1 1.8 541 7.73 80.0 83.3 2 2.0 507 3.15 50.6 62.1 3
0.33 541 7.02 65.6 71.7
EXAMPLES 4-5
[0059] Examples 4-5 were conducted with a conventional FCC catalyst
and a vacuum gas oil containing about 1900 wppm total nitrogen.
Reactor temperature was 557.degree. C. in both cases.
[0060] Example 4 represents base case FCC operation with a captive
fluid bed employing a typical FCC catalyst to oil ratio.
[0061] Example 5 is the combined result of two sequential steps
performed in the captive fluid bed simulating the second and third
zone of the present invention. The presence of a first zone was
simulated by using a lightly coked (0.16 wt% coke) version of the
base case catalyst in the second zone simulation by coking it with
the base vacuum gas oil feed instead of a secondary light feed due
to equipment constraints. Equipment constraints also mandated a
reactor temperature of 557.degree. C. Therefore, the results are
conservative because the pre-coking with a lighter feed and lower
reactor temperature would have been expected to increase the amount
of nitrogen removed.
[0062] In the first step of Example 5, the vacuum gas oil feed was
cracked at 2.5 catalyst to oil ratio over the lightly coked
catalyst.
[0063] The lower nitrogen content liquid product as well as the
more highly coked, but stripped catalyst produced in the first
step, were collected for use in the second step. Nitrogen removal
was about 46%.
[0064] Stripping of second zone catalyst would not occur in the
actual process, but was required to fully material balance the
stage-wise simulation. In the second step, the reactor was charged
with a 1:1 weight ratio blend of regenerated catalyst with the same
coke on regenerated catalyst as the base case (Example 4) and
coked, stripped catalyst collected in step 1, for an overall
catalyst to original base vacuum gas oil feed ratio of 4.9. Liquid
product from the first step served as feed. Overall process yields
were obtained by combining results of the two steps.
[0065] The results shown in Table 2 illustrate than despite the
lower catalyst to oil ratio, the process of Example 5 resulted in a
2.9 wt% higher 430.degree. F.-(221.degree. C.-) conversion and
significant improvement in selectivity as shown by the lower
650.degree. F.+(343.degree. C.+) bottoms/coke yield ratio.
2TABLE 2 Wt % 430.degree. F.- 650.degree. F.+(343.degree. C.)
650.degree. F.+(343.degree. C.+) Catalyst to (221.degree. C.) Coke
Yield, Bottoms Yield, Bottoms/Coke Example Oil Ratio Conversion wt
% wt % Yield Ratio 4 6.1 71.5 7.4 11.7 1.6 5 4.9 74.4 7.4 8.9
1.2
* * * * *