Note: Descriptions are shown in the official language in which they were submitted.
70~
o~
GASOLINE OCTANE ENHANCEMENT IN FLUID
CATALYTIC CRACKING PROCESS WITH SPLIT
FEED INJECTION TO RISER REACTOR
05
FIELD OF INVENTION
The invention relates generally to catalytic
cracking of hydrocarbons. In one aspect the invention
relates to a change in the method of introduction of the
feed, thereby creating an advantageous increase in the
octane number of the gasoline produced in the process.
Particularly, the invention relates to splitting the
hydrocarbon feed and charging a portion of the total feed
near the bottom of an elongated riser reactor, and the
remaining portions progressively further up the riser.
BACKGROUND OF THE INVENTION
Feedstocks containing higher molecular weight
hydrocarbons are cracked by contacting the feedstocks
under elevated temperatures with a cracking catalyst
whereby light and middle distillates are produced.
Typically, the octane number of the light distillate (gas-
oline) is dependent upon the riser temperature, conversion
level of operation or the catalyst type. Therefore, to
increase the octane number of the gasoline, conversion of
the hydrocarbon feed to lighter products must be increased
by preferably raising the temperature of operation, or by
increasing other operating variables such as catalyst to
oil ratio. ~nfortunately, a limit on the maximum oper-
ating temperature is set by reactor metallurgy, gascompressor constraint or other operating constraints.
Increasing conversion by other means may also result in
poor selectivity to desired products. The octane number
of the gasoline may be increased by switching from a cata-
lyst containing rare earth-exchanged Y zeolite to one
containing ultrastable Y zeolite or ZSM-5, as is well
known in prior art; however, such a switch ~ill generally
involve substantially higher costs, be time consuming, and
above all, lead to significant reductions in the yield of
gasoline.
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Therefore, with the current national emphasis on
lead-free gasoline, and the need for increasing gasoline octane
number by means other than the addition of lead, it is desir-
able to have a modified cracking process available for increas-
ing the octane number of the gasoline while minimizing the
disadvan-tages associated with practices described in the prior
art.
It is thus one object of this invention to provide a
regenerated cracking process, and a further object of this
invention to provide a process for increasing the octane number
of the gasoline from the process. Another object of this
invention is to achieve the increase in octane number of the
gasoline by modifying -the me-thod of introduction of feed to the
! riser reactor in a fluid catalytic cracking process.
SUM~RY OE' THE INVENTIO~
In accordance with this invention, I have found that
a desirable way to advantageously increase the octane number of
the gasoline produced in the process is to charge some of the
fresh hydrocarbon feed to upper injection points along the
length of the riser while charging a majority of the fresh Eeed
to the bottom of the riser.
Thus, according to one aspect, the invention provides
a process for the conversion of hydrocarbon feed in an FCC
riser reactor which comprises:
(a) splittiny the hydrocarbon feed and injecting at a
plurality of positions along a length of said FCC riser re-
actor;
(b) selecting the number of Eeed splits and selecting
said positions along said length of said FCC riser reactor, to
maximize the octane number of the gasoline;
(c) recycling regenerated catalys-t into the bottom of
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- 2a - ~ ~8~7~9 61936-1735
said FCC riser reactor; and
(d) lifting said regenerated catalyst up said FCC riser
reactor to sai~ injection position of said hydrocarbon oil feed
with a flow of catalytically inert gas.
According to another aspect, the invention provides a
process for the conversion of hydrocarbon feed in an FCC riser
reactor which comprises:
(a) injecting said 'hydrocarbon feed at a plurali-ty of
positions along a length of said FCC riser reactor;
(b) apportioning throughput -through said position along
said leng-th of said FCC riser reactor to maximize octane number
of the gasoline;
(c) recycling regenerated catalyst into the bottom of
said FCC riser reactor; and
(d) lifting said regenerated catalyst up said FCC riser
reactor to said injection position of said hydrocarbon oil feed
wit'h a flow of catalytically inert gas.
~ .S. Patent No. 3,617,497 teac'hes segregation o-f
hydrocarbon feeds -to a fluid catalytic cracking process into
low and high boiling -fractions, and charging of the different
fractions at different locations along the lengt'h of the riser
reactor in order to improve the yield of gasoline from the
process. An important aspect of the present invention is that
segregation of'hydrocar'bon feed according to molecular weight,
boiling range or any other criterion is not required to achieve
the gasoline octane improvements associated with the process of
the present invention. In accordance with the process of the
presen-t invention, a typical, full boiling range hydrocar'bon
feed to a fluid catalytic craclcing process can be split into
two or more non-distinct fractions, with one fraction charged
-to the bottom of the riser reactor, and the
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37~3
~1 -3-
remaining fractions charged to upper injection points
along the riser, to achieve the octane improvements.
S Thus, costly equipment associated with segregation of
hydrocarbon feed into various distinct fractions is
avoided, and simple piping and valving arrangements will
permit practicing of the teachings of the present
invention.
The distribution of feed between lower and upper
injection points can cover a wide range, with between 10
and 90 volume percent of the total feed charged to bottom
injector, and between 90 and 10 volume percent of total
feed charged to upper injection points. Typical yield
shifts associated with the process of the present
invention, as compared to prior art practices of charging
all the feed to the bottom injector in the riser, include:
equivalent or higher conversion of the hydrocarbon feed to
gasoline and lighter components, equivalent or lower yield
~U of gasoline, equivalent or higher yield of C3 and C4
olefins, and equivalent yields of coke and gas make.
Although the yield of gasoline from the process can be
lower, the octane number of the gasoline will be higher,
and the yield of total gasoline (gasoline plus potential
alkylate from alkylation of the C3 and C4 olefins from the
process) will be higher.
Although gasoline octane benefits accrue even
when a majority of the feed is charged to upper injection
points, and a minority to the bottom injector in accord-
ance with the present invention, maximum improvements in
gasoline octane and yields of desirable liquid products
are achieved when a majority of the feed is charged to the
bottom injector. Thus a preferred embodiment of the
present invention is a modified fluid catalytic cracking
; ~S process wherein the hydrocarbon feed is split into several
non-distinct fractions, and a major portion of the feed is
charged to the lowest injection point in a riser reactor,
and the remaining fractions progressively higher up along
the length of the riser reactor. The advantages associ-
~ ated with practicing the teachings of the present
709
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invention will become clearer upon readiny the examples whi~.h
are to follow.
DETAILED DESCRIPTION OF THE IMVENTION
The invention will be ~urther illustrated by way of a
preferred embodiment and with reference to the accompanyincJ
drawinys in which:
Figure 1 represents a suitable reactor and
regenerator system for performing the process accordiny to the
invention.
The cracking occurs with a fluidized æeolitic
catalyst in an elongated reactor tube 10, which is referred to
as a riser. The riser has a lenyth to diameter ratio of above
20, or preferably above 25. Hydrocarbon oil feed in line 2 to
be cracked can be charyed directly into the bottom of the riser
through inlet line 14 or it can be charyed to upper injection
points in the riser through lines 30A, 30B, or 30C or directly
into ~he reactor vessel through line 30D. Steam is introduced
into the lower feed injection point through line 18. Steam is
also introduced independentl~ to the bottom of the riser
through line 22 to help carry upwardly into the riser
regenerated catalyst which flows to the bottom of the riser
through transfer line 26.
Feed to the upper in~ection points Ls introduced at
about a 45 decJree upward angle lnto the riser through lines 30
and 32. Steam can be introduced into the upper feed in~ection
inlet lines throuyh lines 34 and 36. Upper hydrocarbon feed
injection lines 30 and 32 ~ach represent a plurali~y of similar
lines spaced c:Lrcumferentially at the same heiyht of the riser.
Any recycle hydrocarbon can be admitted to the lower section of
the riser through one of the inlet lines designated as 20, or
to the upper section of the riser throu~h one of the lines
designated as 38. The residence time of. hydrocarbon feed in
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09
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the riser can be varied by varying the amoun~s or positions of
introduction of the feed.
The full range oil charge to be cracked in the riser
is a gas oil having a boiling range of about 430F to 1100F.
The feedstock to be cracked can also include appreciable
amounts of virgin or hydrotreated residue having a boiling
range of 900F to 1500F. The steam added to the riser amounts
to about 2 wt% based on the oil
J
~070~3
01 ~5~
charge, but the amount of steam can vary widely. The
catalyst employed may be fluidized zeolitic aluminosili-
05 cate and is preferably added to the bottom only of theriser. The type o$ zeolite in the catalyst can be a rare
earth-exchanged X or Y, hydrogen Y, ultrastable Y, super-
stable Y or ZSM-5 or any other zeolite typically employed
in the cracking of hydrocarbons. The riser temperature
10 range is preferably about 900F to 1100F and is
controlled by measuring the temperature of the product
from the risers and then adjusting the opening of valve 40
by means of temperature controller 42 which regulates the
inflow of hot regenerated catalyst to the bottom of the
riser. The temperature of the regenerator catalyst should
be above the control temperature in the riser so that the
incoming catalyst contributes heat to the cracking
reaction. The riser pressure should be between about 10
and 35 psig. Between about 0 and 10% of the oil charge to
the riser is recycled with the fresh oil feed to the
bottom of the riser.
The residence time of both hydrocarbon and
catalyst in the riser is very small and preferably ranges
from 0.5 to 5 seconds. The velocity throughout the riser
is about 35 to 65 feet per second and is sufficiently high
so that there is little or no slippage between the hydro-
carbon and catalyst flowing through the riser. Therefore,
no bed of catalyst is permitted to build up within the
riser, whereby the density within the riser is very low.
The density within the riser ranges from a maximum of
about 4 pounds per cubic foot at the bottom of the riser
and decreases to about 2 pounds per cubic foot at the top
of the riser. Since no dense bed of catalyst is
ordinarily permitted to build up within the riser, the
space velocity through the riser is usually high and
ranges between 100 or 120 and 600 weight of hydrocarbon
per hour per instantaneous weight of catalyst in the
reactor. No significant catalyst buildup within the
reactor should be permitted to occur and the instantaneous
catalyst inventory within the riser is due to a flowing
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Ol -6-
catalyst to oil weight ratio between about 4:1 and 15:1,
the weight ratio corresponding to the feed ratio.
05 The hydrocarbon and catalyst exiting from the
top of each riser is passed into a disengaging vessel
44. The top of the riser is capped at ~6 so that
discharge occurs through lateral slots 50 for proper
dispersion. An instantaneous separation between hydro-
carbon and catalyst occurs in the disengaging vessel. The
hydrocarbon which separates Erom the catalyst is primarily
gasoline together with middle distillate and heavier
components and some lighter gaseous components~ The
hydrocarbon effluent passes through cyclone system 54 to
separate catalyst fines contained therein and is
discharged to a fractionator through line 56. The cata-
lyst separated from hydrocarbon in disengager 44 immedi-
ately drops below the outlets o~ the riser so that there
is no catalyst level in the disengager but only in a lower
stripper section 58. Steam is introduced into catalyst
stripper section 58 through sparger 60 to remove any
entrained hydrocarbon in the catalyst.
Catalyst leaving stripper 58 passes through
transfer line 62 to a regenerator 64. This catalyst
contains carbon deposits which tend to lower its cracking
activity and as much carbon as possible must be burned
from the surface of the catalyst. The bùrning is
accomplished by introduction to the regenerator through
line 66 of approxirnately the stoichiometrically required
amount of air for combustion of the carbon deposits. The
catalyst Erom the stripper enters the bottom section of
the regenerator in a radial and downward direction througl
trans~er line 62. Flue gas leaving the dense catalyst bed
in regenerator 6~ flows through cyclones 72 wherein cata-
lyst fines are separated rom flue gas permitting the fluegas to leave the regenerator through line 7~ and pass
through a turbine 76 before leaving for a waste heat
boiler, wherein any carbon monoxide contained in the flue
gas is burned to carbon dioxide to accomplish heat
recovery. Turbine 76 compresses atmospheric air in air
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compressor 78 and this air is charged to the bottom of the
regenerator through line 66.
05 The temperature throughout the dense catalyst
bed in the regenerator is about 1250F. The temperature
of the flue gas leaving the top of the catalyst bed in the
regenerator can rise due to afterburning of carbon
monoxide to carbon dioxide. Approximately a stoichio-
metric amount of oxygen is charged to the regenerator in
order to minimize afterburning of carbon monoxide to
carbon dioxide above the catalyst bed, thereby avoiding
injury to the equipment, since at the temperature of the
regenerator flue gas some afterburning does occur. In
order to prevent excessively high temperatures in the
regenerator flue gas due to afterburning, the temperature
of the regenerator flue gas is controlled by measuring the
temperature of the flue gas entering the cyclones and then
venting some of the pressurized air otherwise destined to
be charged to the bottom of the regenerator through vent
line 80 in response to this measurement. Alternatively,
CO oxidation promoters can be employed, as is now well
known in the art, to oxidize the CO completely to CO2 in
the regenerator dense bed thereby eliminating any problems
due to afterburning in the dilute phase. With complete CO
combustion, regenerator temperatures can be in excess of
1250F up to 1500F. The regenerator reduces the carbon
content of the catalyst from about 1.0 wt~ to 0.2 wt~, or
less for the maximum gasoline mode of operation. If
3~ required, steam is available through line 82 for cooling
the reyenerator. Makeup catalyst may be added to the
bottom of the regenerator through line 84. Hopper 86 i9
disposed at the bottom of the regenerator for receiving
regenerated catalyst to be passed to the bottom of the
reactor riser through transfer line 26.
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TABLE I
FEEDSTOCK INSPECTIONS
05
Description Feed 1 Feed 2
API Gravity 22.8 26.7
Sulfur: Wt% 1.89 0.71
Nitrogen: Wt% 0.085 0.12
Hydrogen: Wt% 11.98
Carbon Residue: Wt% 0.39 1.74
Aniline Point: F 172.4 198.4
Viscosity @ 210F 45.2
Pour Point: ~F +95
15 Nickel: ppm 0.3 4.9
Vanadium: ppm 0.5 l.0
Distillation: D1160
10% 666 573
30% 740 717
50% 791 811
70% 856 928
90~ 943 1101
EP
Hydrocarbon Types: Mass Spec.
Aromatics 49.3
Mono 21.6
Di 14.8
Tri+ 7 0
Saturates 49.5
Alkanes 18.5
Cycloalkanes 31.0
Polar Compounds 1.2
Insolubles - -
Volatiles
EXAMPLES
To demonstrate the efficacy of my invention, a
number of tests were conducted on a circulating pilot
plant of the fluid catalytic cracking process using
feedstocks described in Table I.
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Example I
Table II presents pilot plant data on cracking
05 of a gas oil feed using a conventional rare earth-
exchanged Y zeolitic cracking catalyst in the pilotplant. Run No. 1 involved char~ing of all the fresh
hydrocarbon feed to the bottom injector in the pilot
plant. In Run No. 2, 75 volume percent of the fresh feed
was charyed to the bottom injector and the remaining 25
volume percent was charged to an injection point higher up
in the riser reactor. Comparing the results from Run
No. 1 and Run No. 2, it is evident that the yield of total
gasoline plus alkylate, and the octane numbers (both
lS research and motor octane numbers) of the gasoline are
significantly higher with Run No. 2 which practiced the
teachings of the present invention. In Run No. 3, only 25
volume percent of the fresh feed was charged to the bottom
injector, with the remaining 75 volume percent was charged
to the upper injection point. Comparing the results of
Run Nos. 1, 2 and 3, it is obvious that while research
octane number benefits are associated with both Run Nos. 2
and 3 compared to Run No. 1, the total yield of gasoline,
and the motor octane number of the gasoline are highest
for Run No. 2. Thus, while research octane numbers
increase by apparently the same extent for both Run Nos. 2
and 3 compared to Run No. 1, best results are achieved
when a majority of the feed is charged to the bottom
injector, as in the case of Run No. 2. While the research
octane number increase is the same for the two cases
involving split feed injection shown in Table III (Run
Nos. 2 and 3), it is important to note that mechanisms
involved in achieving the increase are different in the
two cases. As shown in Table II, the increase in research
J~ octane number for Run No. 2, over Run No. 1, comes from an
increase in the aromatic content of the gasoline; this
explains why the motor octane number is also higher for
Run No. 2 over Run No. 1. However, comparing the results
of Run Nos. 1 and 3, it is obvious that the higher research
octane number of the gasoline for Run No. 3 is due to the
3 2~3~)709
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01
increase in the olefinic content of the gasoline, not the
aromatic content. For those skilled in prior art, this
05 will also explain why the motor octane number of the gaso-
line from Run No. 3 is not higher than that from Run
No. l~
Example II
Table III shows pilot plant data on a high
octane-producing catalyst containing the rare earth-
exchanged Y zeolite and the ZSM-5 zeolite. Run No. 4
corresponds to a conventional fluid catalytic cracking
process wherein all the fresh feed is charged to the
bottom of the riser reactor. In Run No. 5, 60 volume
percent of the fresh feed is charged to the bottom of the
riser, and the remaining 40 volume percent to an upper
injection point along the length of the riser. Comparing
- the results from the two runs, the higher octane numbers
and higher total gasoline yield advantages associated with
Run No. 5, in accordance with the present invention, are
obvious.
7~;)9
0 1
TABLE II
05 Run Number 1 2 3
Chargestock <--------- Feed 1 ----------->
Catalyst ContainingConventional Rare Earth
<--- Exchanged Y Zeolite ---->
lO Operating Conditions
Riser Outlet Temp., F <----------- 980 ----------->
Riser Inlet Temp., F <----------- 1200 ----------->
Volume % Feed to Bottom
Injector 100 75 25
Volume % Feed to Upper
Injector 0 25 75
Conversion: Vol% FF81.9 81.6 78.7
Product Yields: Vol% FF
Total C3 12.0 13.9 12.4
C3= 10.1 11.7 10.5
tal C4 196 19 26 6 15 3
C4= 12.5 13.7 12.8
C5-430F Gasoline63.1 59.9 59.6
430-650F Light
Catalytic Gas Oil 11.5 11.6 12.7
650F~ Decanted Oil6.6 6.8 8.6
2S C3~ Liquid 113.2 114.0 112.7
Total Gasoline
+ Alkylate 103.1 104.8 100.7
Product Yields: Wt% FF
C2 and Lighter 2.8 3.0 2.8
Coke 5.6 5.6 5.3
Gasoline
API 57.1 55.7 56.6
Aromatics: Vol~ 27.5 31.1 26.5
Olefins: Vol~ 36.9 30.7 40.2
Saturates: Vol~35.5 38.3 33.3
Motor Octane Clear80.7 Bl.4 80.2
Research Octane Clear 93.9 95.1 95.2
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01 -12-
TABLE III
05
Run Number 4 _ 5
Chargestock <-~ -- Feed 1 -------->
Catalyst Containing <---- ZSM-5 Zeolite ----->
Operating Conditions
Riser Outlet Temp., F <--------- 980 --------->
Riser Inlet Temp., F<--------- 1200 ~ -->
Volume % Feed to Bottom
Injector 100 60
Volume % Feed to Upper
Injector 0 40
Conversion: Vol% FF 72.8 75.4
Product Yields: Vol% FF
Total C3 10.5 11.6
C3= 8.0 8.8
Total C4 15.6 17.5
iC4 5.8 6.4
C4= 8.3 9.3
C5-430F Gasoline 52.6 51.5
430-650F Light Catalytic
Gas Oil 11.2 10.5
650F~ Decanted Oil 15.2 13.3
C3+ Liquid 105.9 105.2
Total Gasoline + Alkylate 99.4 101.4
Product Yields: Wt% FF
C2 and Lighter 3.4 3.7
Coke 6.0 5.9
Gasoline
Motor Octane Clear 79.5 80.7
Research Octane Clear90.8 93.3
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Example III
In this example, a feedstock containing a high
~5 boiling residual cornponent (boiling above 1000F) was
cracked over conventional rare earth-exchanged Y zeolite
containing catalyst in the fluid catalytic crac~ing pilot
plant. Again, Run No. 6 corresponds to a conventional
fluid catalytic cracking process wherein all the fresh
feed is charged to the bottom of the riser reactor. In
Run No. 7, 40 volume percent o~ the fresh feed was charged
to the bottom of the riser, and the remaining 60 volume
percent to an upper injection point in the riser. In ~un
No. 8, 60 volume percent of the fresh feed was charged to
the bottom of the riser while the remaining 40 volume
percent was charged to the upper injection point. It is
important to note that in all of the cases described in
Table IV, the various feed fractions were identical in
quality, in other words, the lower and upper injection
feeds were not segregated according to molecular weight or
boiling range or any other criterion. Comparing the
results in the three columns in Table IV, the advantages
associated with the teachings of the present invention,
and in particular, charging a majority of the fresh feed
to the bottom injector as in the case of Run No. 8, are
obvious.
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TABLE IV
05 Run Number 6 7 8
Chargestock <------- - Feed 2 ~ ---->
Catalyst Containing Rare Earth
<--- Exchanged Y Zeolite ---->
Operating Conditions
Riser Outlet Temp., F <----------- 980 ----------->
l Riser Inlet Temp., F <----------- 1250 ----------->
Volume % Feed to Bottom
lnjector 100 40 60
Volume % Feed to Upper
Injector 0 60 40
lS Conversion: Vol% FF70.7 72.8 74.9
Product Yields: Vol% FF
Total C3 9.0 11.2 10.4
c3= 7.6 9.4 9.1
Total C4 13.8 16.0 16.7
iC~ 2.6 3.3 301
C4= 10.4 11.7 12.6
C5-430F Gasoline 56.6 55.2 58.5
430-650F Light
Catalytic Gas Oil18.0 16.8 15.0
650F+ Decanted Oil11.3 10.4 10.2
C3+ Liquid
Total Gasoline
+ Alkylate 88.4 92.5 97.0
Product Yields: Wt% FF
C2 and Lighter 3.1 3.6 3.0
Coke 4.2 4.3 4.2
Gasoline
API 57.1 56.4 56.3
Aromatics: Vol~ 23.5 24.7 24.4
Olefins: Vol% 51.1 51.0 48.0
Saturates: Vol% 25.3 24.3 27.6
Motor Octane Clear77.4 77.5 78.8
Research Octane Clear 91.4 92.4 92.4
~10
