Note: Descriptions are shown in the official language in which they were submitted.
:1048434
BACKGROUND OF THE INVENTION
Fluid cracking operations to produce a variety of
useful products have been practiced since early 1940. A prior
art patent of particular interest directed to restricted
conversion operations is +hat of Jewell 2,882,218.
Fluid cracking of distillation products of crude oil
has been practiced sirce early 1940. Naturally occurring clay
- type catalysts were initially employed and subsequently re-
placed ~dth synthetic silica-alumina amorphous type crackin~
catalysts. These catalysts were more active for accomplishing
the desired reactions and thus permitted many processing
variations and equipment changes. The development of crystalline
alurninosilicate conversion catalyst has provided additional
opportunity to develop more efficient conversion operations
as well as substantially improving the equipment irl which
employed. m e present invention is particularly concerned
with processing crude oil distillation products under conditions
to improve the recovery of fuel oil boiling range products of
desired pour point using improved crystalline zeolite conversiGn
catalyst of recent development.
SUMMARY OF THE INVENTION
The present invention relates to the production of
lsght fuel oil and lower boiling products by catalytic cracking.
More particularly, t,he present invention relates to improvin~
~5 the yield of light fuel oil product of a fluid catalyst crackingoperation by conta~ting a fresh gas oil boiling ange feed with
a coked catalyst of reduced activity characteristics in the
--2--
~048434
upper portion of a riser cracking zone at a temperature within
the range of 800 to 900F. and subsequent to contacting freshly
regenerated catalyst passed to a lower inlet of the same riser
cracking zone with a heavy cycle oil product of the cracking
operation at a temperature within the range of 900 to 1000F.
It has been observed from acquired data that the
maximum yield of light fuel oil product obtained by cracking
a gas oil feed in a single pass riser conversion operation
occurs under relatively low severity cracking conditions in
which the fresh gas oil feed is exposed for a contact time
within the range of 2 to 4 seconds to a low activity catalyst
within the range of 20 to 40 FAI at a temperature in the range
of 800F. to about 900F. In`this operational environment
it has also been observed that a coked zeolite cracking catalyst
containing up to lO weight percent REY and comprising from
about 0.5 to about 1.2 weight percent carbon has an activity
within the above identified desired activity level in combi-
nation with good selectivity to particularly promote a maximi-
zation of light fuel oil product. Furthermore, it has been
observed that within the operational parameters herein defined,
that from about 40 to about 60 weight percent of a heavy
distillate material is also produced. This heavy distillate
material so obtained can then be reprocessed or recracked at
much more severe cracking conditions than required by the fresh
gas oil feed to yield additional light fuel oil product. In
fact, the maximum light ~uel oil prcduct yield obtainable from
cracking the heavy distillate results from using a much more
active catalyst at a higher temperature and higher catalyst/oil
1048434
ratio than was found to be ~ptimum for r~aximizing the l ght
f~lel oil from crack~ng the fresh gas oil feed.
Thus, in the concept of this invention, a fresh gas
oil feed preheated to an elevated temperature in the range of
about 700F. to about 800F. is charged to an upper portion
of a riser conversion zone wherein it is brought in contact
with a hydrocarbon-catalyst suspension partially deactivated
by hydrocarbonaceous deposits of recycle oil cracking to form
a second oil-catalyst suspension comprising from about 0.5 to
Io about 1.2 weight percent of carbonaceous deposits identified
as carbon. A mix temperature of the fresh gas oil feed with
the recycle oil product-catalyst suspension above identified
of about ~OO~F. to about 900F. is desirable. In this
environment conversion of the fresh gas oil feed is considerably
restricted not to exceed about 35 vol.% and preferably is
less than about 30 vol.~. The more dilute suspension thus
formed with the fresh gas oil feed traverses the remaining
portion of the riser conversion zone for a li~ited contact
time within the range of 1 to 4 seconds before it is discharged
into suitable separating means such as cyclonic separating
means for separating a hydrocarbon p~ase from a catalyst phase.
m e catalyst phase is stripped with s~ripping gasiform material
such as steam to remove entrained hydrocarbon before it is
passed to a catalyst regeneration zone.
In the catalyst regeneration zone, the deposited
carbonaceous material is substantially completely removed
from the catalyst by burning with an oxygen containing gas
thereby heating the catalyst to ar. elevated temperature within
~048434
the range of 1~00F. up to about 1400F. The carbonaceous
deposits substantially completely removed from the c~talyst
during regeneration and remaining as residual coke, is reduced
to at least about 0.2 weight percent.
The hydrocarbon phase separated as above provided
or by any other suitæble separating arrangement, is passed
to the product fractionator wherein a separation is made for
the separate recovery of a naphtha stream and lower boiling
gasiform materials, a light fuel oil stream and a heavy cycle
oil ~trea~. A clarified slurry stream may also be recovered
from the lower portion of the fractionator. m e heavy cycle
oil comprising an initial boiling point within the range of
650 to 720F. is passed as charge to the bottom portion of a
riser reactor or conversion zone for admixture with hot
15- freshly regenerated catalyst to form a suspension. The heavy
cycle oil at a relatively low temperature n the range of
about 350F. up to about 500F. is combined with the hot
freshly regenerated catalyst to form a suspension at a mix
temperature less than about 1000F. and more usually above
about 850F. but not above about g5ooF~ The conversion
conditions maintained in the lower portion of the riser
conversion zone are selected to provide a conversion of the
heavy cycle oil to lower boiling products including gasoline
and particularly a light fuel oil product. During conversion
of the heavy cycle oil in the .ower portion of the riser
conversion zone, carbonaceous deposits are formed on the
catalyst in an a~ount of at least 0.5 ~-eight percent. Also,
conversion of the heavy cycle oil to gasoline and lower
- 1048~34
boiling products is restricted usually not to exceed about
65 vol.%. For example, conversion of the heavy cycle oil
may be restricted to produce about 10 weight percent (wt.~)
gas, 35 wt.% gasoline, 20 wt.% light fuel oil, 5 wt.% coke and
30 wt.% of unconverted 650F. plus material.
The combination operation of tne present invention
is unique in several respects and particularly unique in
that fresh gas oil feed contacts a process generated catalyst
of reduced activity at a lower catalyst to oil ratio than that
used for converting heavy cycle oil product of the combina~ion
operation. Furthermore, the overall conversion of the hydro-
carbon feeds can be maintained at a selected high level with
a low steady state concentration of heavy cycle oil and the
light fuel oil product thereof will be maximized because of
the particularly selected low severity conditions that it
encounters as a result of its first pass contact with the
catalyst of reduced activity particularly employed in the
operation.
The catalyst employed in the combination operation
of this invention may be substantially any cracking catalyst
known in the art provided its activity is selectively reduced
with hydrocarbonaceous material to within the range of 20-40
FAI during conversion of a heavy cycle oil and prior to contact
with a fresh gas oil feed. Thus, the catalyst may be an
amorphous silica-alumina cracking catalyst, a crystalline
zeolite cracking catalyst, or a combination thereof. A
preferred catalyst is a rare earth exchanged "Y" type crystalline
faujasitF- in an amount up to about 15 weight percent and more
1048434
usually within the range of 2 to 10 weight percent dispersed
in a suitable matrix material. For example, a more preferred
catalyst comprises as much as about 10 weight percent of a
rare earth exch~ged "Y" faujasite crystalline zeolite
dispersed in a silica clay matrix and provided with a small
amount of zirconia. Such preferred catalysts are more
completely defined in U.S. Pætent 3~556,988 issued January
17, 1971.
DISCUSSION OF SPECIFIC EMBODI~ENTS
The yield data obtained by passing a Durban fresh
gas oil feed over cracking catalyst compositions deac'ivated
by carbon deposits is presented in Table I.
1048434
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1048434
The data obtained by con~erting a hea~y cycle oil
product of the Durban gas oil cracking in the presence of a
more active regenerated catalyst composition, clean burned
and containing a small amount of residual carbon thereon is
presented in Table II.
1048434
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1048~34
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12
1048434
Table III combines two comparisons cf products
obtained when processing a fresh gas oil feed over a coke
containing catalyst and the heavy fuel oil trecycle) product
thereof over regenerated catalyst at two different conversion
levels. From the data presented in Table III, it will be
observed that the combination of I, II and III produced higher
yields of light fuel oil than the combinatlon of I, IV ~nd V.
The data presented in Tables I, II and III above
have been developed to form Figures I through VI discussed
below.
BRIEF DESCRIPTION OF THE FIGURES
Figure I graphically presents the response of
conversion to catalyst/oil ratio in cracking a 650F. heavy
cycle oil and a Durban fresh feed with a 55~57 FAI catalyst
- 15 comprising a rare earth exchanged "Y" crystalline faujasite cracking catalyst.
- Figure II graphically presents the product se~ectively
from cracking 650F.~ heavy cycle oil and Durbæn fresh feed
over a 55 FAI REY type crystalline zeolite cracking catalyst.
Figure III graphically presents the effect of 650F.
heavy recycle on the overall yield of products on a fresh feed
baæis.
Figure IV graphically presents a comparison of the
Cs+ gasoline products octane number.
Figure V graphically presents the pour point and
API gravity of the 430-650F. light fuel oil (IFO) fraction
~ade from cracking Durban fresh feed and from 650F.+ hea-~y
cycle oil.
-13-
104843~ -
Figure VI graphically presents a yield and pour
point comparison of the 690F. end point light fuel oil (LFG)
obtained from Durban fresh feed and from a 550F.+ heavy
cycle oil (HCO) by cracking with coked and clean REY type
zeolite cracking catalysts.
Figure VII is a diagrammatic sketch in elevation
of one arrangement of ~pparatus comprising a riser crackir.g
zone and a catalyst regeneration zone interconnected by
suitable catalyst transfer conduit means and a product
recovery zone for separation, recovery and recycle of desired
hydrocarbon product material to the cracking operation.
DISCUSSIO~J OF SPECIFIC E~ODII~ENTS
Figures I through VI herein presented are essentially
self-explanatory and clearly represent the processing advantages
of the concept of the present invention with respect to product
yield and quality.
In Figure I, for example, it is shown that the fresh
feed hydrocarbon charge is more conversion responsive than
the 650F. plus heavy cycle oil feed to catalyst to oil ratio
and temperature variations for a given activity crystalline
zeolite cracking catalyst.
In Figure II it is graphically shown that the fresh
feed converted at 1000F. produced greater yields than the
650F.+ heavy cycle oil processed at 850F. and ~50F. Also
the gasoline yield was generally higher from the fresh feed
cracking operation. Ve~y little difference, if any, is noted
in the yields of dry gas and C4 hydrGcarbons. Variations in
~14-
1048434
the coke yields for different conversion levels is readily
observed.
In Figure III the data of Table III is graphically
presented. In this figure it is shown that the 850F, single
pass operation combined with the 850F, recycle operation
produced similar levels of light fuel oil product at conversion
levels in the range of 45 to 55 and was much better than the
single pass operations graphically depicted. Also at conversion
levels less than 50 weight percent the yields of C4 hydro-
carbons, dry gas and coke are not materially different.
In Figure IV the first pass gasoline octane number
(O,N,) processing fresh feed at 950F, with a coked catalyst
was much higher than that obtained at 850F. and at either
- temperature with the heavy cycle oil feed, On the other hand,
the blended gasoline octane number obtained at the 850F,
single pass fresh feed operation combined with the gasoline
product of the 950F, recycle operation provided an octane
number (R+O) in excess of 85.
- In Figure V it is graphically shown that the pour
point of the light fuel oil (430-650F) and obtained fro~
the fresh feed and the heavy cycle oil is satisfactory and
relatively stable at conversion levels up to about 55 weight
percent. ~ne gravity of the oil steadily drops off, however,
Figure VI graphically shows the influence of tempera-
ture and conversion on cracking the fresh feed and recracking
a heavy cycle oil product thereof on the yield of a light
fuel oil product therefrom, The curves plotted and attached
identifications clearly support the improved cracking combination
-15-
10~843~
- of the presen~ invention.
In the drawing Figure VII, a fresh gas oil feed
is introduced by conduit 2 to furnace 4 wherein preheating
of the feed to a desired elevated temperature is accomplished.
Preheating of the gas oil feed should be sufficient to form
a suspension mix temperature in the upper portion of the
riser within the range of 800 to 900F. The preheated feed
is then passed by conduit 6 to an upper portion of riser
conversion zone 8 identified at "B". At this point of
fresh feed introduction, a suspension is formed with
previously used catalyst of reduced activity and comprising
from about 0.5 to about l.2 weight percent carbon deposit.
m e suspension thus formed will comprise a catalyst to fresh
feed weight ratio within the range of 3 to 9 to give a fresh
feed conversion to gasoline and lower boiling products within
the range of lO to 40 weight percent. The suspension thus
formed and diluted with the products of heavy cycle oil
recracking obtained as discussed below pass upwardly through
the remaining portion of the riser into a catalyst separation
zone lO. The fresh feed-catalyst-suspension is provided a
hydrocarbon contact time within the range of l to 4 seconds
under the conditions specified above.
In separation zone lO provided with cyclonic
separating means 12, separation of the suspension into a
catalyst phase and a hydrocarbon phase is accomplished. The
hydrocarbon phase is recovered and withdrawn by conduit 14
co~municating with fractionation zone 16. The separated
catalyst pnase is collected and passed down, usually through
an annular stripping zone l~ countercurrent to stripping gas
-15-
1~)48434
introduced to a lower portion thereof by conduit 25.
Catalyst stripped of entrained hydrocarbon vapors but
deactivated with carbonaceous products of cracking is
then passed by conduit 22 to regeneration zone 24. Tn
regeneration ~one 24, the catalyst activity is restored
by burning carbonaceous deposits with, for example, air
introduced to the lower portion of the regeneration zone
by conduit 26. Gaseous products of combustion comprising
flue gas are withdrawn from the regeneration zone by
conduit 28.
The catalyst of restored activity by the re-
generation procedure and heated to an elevated temperature
up to about 1400F. is withdrawn by conduit 30 and passed
to the lower portion of riser 8. In the lower portion of
riser 8, the freshly regenerated catalyst comprising a
small amount of residual carbon is admixed with a heævy
cycle oil product of the cracking operation in conduit 32,
boiling above about 650F. to form a catalyst/oil suspension
at a mix temperature within the range of 900 to about 1000F.
Preheating of the cycle oil product of cracking before forming
- the suspension is contemplated. Also, the catalyst to oil
ratio is preferably selected from within the range of 10 to
20. Under the conditions above defined the cycle oil catalyst
suspension is provided a contact time within the range of 4
to 8 seconds before the suspension is diluted with the fresh
gas oil feed as defined above
In ~he ccmbination operation above described, it is
important that the operat'ng parameters be selected to
1~48434
deposit an amount of carbonaceous material on the catalyst
to reduce its activity within the range of 20 to 40 (~AI)
fluid activity index before contact is made with the fresh
gas oil feed under selected conversion conditions particularly
for the production of light ~uel oil product.
The products of converting heavy cycle oil and
fresh gas oi~ feedstocks under the above recited conversion
conditions are conveyed by conduit 14 to fractionator 16.
In fractionator 16, the hydrocarbon products of
catalytic cracking are separated into a gaseous phase removed
by conduit 34, a naphtha phase removed by conduit -3~., a light
fuel oil phase removed by conduit 38, a heavy cycle oil phase
removed by conduit 32 and a bottom or clarified slurry oil
phase removed by conduit 40.
Having thus generally described the combination
operation of the present invention and discussed specific
embodiments going to the very essence thereof, it is to be
- understood that no undue restrictions are to be imposed by
reason thereof except as defined by the following claims.
-18-
