Note: Descriptions are shown in the official language in which they were submitted.
BACI~GROUND OF THE INVl~l~TIO~I
-
In general, gasoline and other liquid hydrocarbon
fuels boil in the range of about 100 -to about 650F. However,
i the crude oil from which these fuels are made contains a diverse
mi.~ture of hydrocarbons and other compounds which vary widely
in molecular weight and therefore boil over a wide range.
For e~ample, crude oils are known in which 30 to 60% or more
of the total volume of oil is composed of compounds boiling
) at temperatures above 650F. Among these are crudes in
which about 10% to about 30% or more of the total volume
consists of compounds so heavy in molecular weight that they
boil above 1025F or at least will not boil below 1025F at
atmospheric pressure.-
Because these relatively abundant high boiling components
of crude oil are unsuitable for inclusion in gasoline and other
liquid hydrocarbon fuels, the petroleum refining industry has
developed processes for cracking or breaking the molecules of
the high molcular weight, high boiling compounds into smaller
molecules which do boil over an appropriate boiling range. The
crac]cing process which is most widely used for this purpose is -
known as fluid catalytic cracking (FCC~. Although the FCC process
has reached a highly advanced state, and many modified forms
and ~riations have been developed, their unifying factor is
that a vaporized hydrocarbon feedstock is caused to crack at an
elevated temperature in contact with a cracking catalyst that
is suspended in the feedstock vapors. Upon attainment of the
desired degree of molecular weight and boiling point reduction
the catalyst is separated from the desired products,
~ru~e oil in the natur~l state contains a variety of
matcrials which tend to have quite troublesome effects on
FCC processes, and only a portion of these troublesome
materials can be economically removed from the crude oil.
Among these troublesome materials are coke precursors (such
as asphaltenes, polynuclear aromatics, etc.), heavy metals
(such as nickel, vanadium, iron, copper, etc.), lighter
metals (such as sodium, potassium, etc.), sulfur, nitrogen
and others. Certain of these, such as the lighter metals, can
be economically removed by desal~ing operations, which are
part of the normal procedure for pretreating crude oil for fluid
catalytic cracking. Other materials, such as coke precursors,
asphaltenes and the like, tend to break down into coke during
the cracking operation, which coke deposits on the catalyst,
impairing contact between the hydrocarbon feedstock and the
catalyst, and generally reducing its potency or activity level.
The heavy metals transfer almost quantitatively from the
feedstock to the catalyst surface.
If the catalyst is reused again and again for process-
ing additional feedstock, which is usually the case, the heavy
metals can accumulate on the catalyst to the point that they
unfavorably alter the composition of the catalyst and/or
the nature of its effect upon the feedstock. For example,
vanadium tends to form flu~es with certain components of
commonly used FCC catalysts, lowering the melting point of
portions of the catalyst particles sufficiently so
that they begin to sinter and become ineffective
cracking catalysts. Accumulations of vanadium and other
-- 2
7~
,
--3--
heavy metals, especially nickel, also "poison" the catalyst. They
tend in varying degrees to promote excessive dehydrogenation and
aromatic condensation, resulting in excessive production of carbon
and gases with consequent impairment of liquid fuel yield. An oil
5 such as a crude or crude fraction or other oil that is par-ticularly
abundant in nickel and/or other metals exhibiting similar behavior,
while containing relatively large quanti-ties of coke precursors, is
referred to herein as a carbo-metallic oil, and represents a
particular challenge to the petroleum refiner.
In general the coke-forming tendency or coke precursor
content of an oil can be ascertained by de-termining the weight
percent of carbon remaining after a sample of that oil has been
pyrolyzed. The industry accepts this value as a measure of the
extent to which a given oil tends to form non-catalytic coke when
employed as feedstock in a catalytic cracker. Two established tests
are recognized, the Conradson Carbon and Ramsbottom Carbon
tests, the latter being described in ASTM Test No. D524-76. In
conventional FCC practice, Ramsbottom carbon values on the order
of about 0.1 to about 1.0 are regarded as indicative of acceptable
feed. The present invention is concerned with the use of
hydrocarbon feedstocks which have higher Ramsbottom carbon
values and thus exhibit substantially greater potential for coke
formation than the usual feeds.
Since the various heavy metals are not of equal catalyst
poisoning activity, it is convenient to express the poisoning activity
of an oil containing a given poisoning metal or metals in terms of
the amount of a single metal which is estimated to have equivalent
poisoning activity. Thus, the heavy metals content of an oil can be
expressed by the following formula (patterned after that of W. L.
Nelson in Oil and Gas Journal, page 143, October 23, 1961) in
which the content of each metal present is expressed in parts per
million of such metal, as metal, on a weigh t basis, based on the
weight of feed:
RI-6049Y
',.~.~
Nickel Equivalents = Ni + 4 ~ + 7 1 + 1 2'
According to conventional FCC practice, the heavy me-tal content
of feedstock for FCC processing is controlled at a ~elatively
low level, e.g. about 0.25 ppm Nickel Equivalents or less.
The present invention is concerned with the processing of feed-
stocks containing metals substantially in e~cess of this value,
and which therefore have a significantly greater potentital
for accumulating on and poisoning catalyst.
The above formula can also be employed as a measure of
the accumulation of heavy metals on cracking catalyst, except
that the quantity of metal employed in the formula is based
on the weight of catalyst (moisture free basis) instead of the
weight of feed. In conventional FCC practice, in which a
circulating inventory of catalyst is used again and again in the
processing of fresh feed, with periodic or continuing minor
addition and withdrawal of fresh and spent catalyst, the metal
content of the catalyst is maintained at a level which may for
e~ample be in the range of about 200 to about 600 ppm Nickel
Equivalents. The process of the present invention is concerned
with the use of catalyst having a substantially larger metals
content, and which therefore has a much greater than normal
tendency to promote dehydrogenation, arornatic condensation,
gas production or coke formation. Therefore, such higher me.als
accumulation is normally regarded as quite undesirable in
FCC processing.
There has been a long standing interest in the conversion
of carbo-metallic oils into gasoline and other liquid fuels. For
e.~am~le, in the l950s it was suggested that a variety of carbo-
mctallic oils could be successfully converted to gasoline and
othcr products in the Houdresid process. Turning from the
FCC mode of o~eration, the Houdrcsid process employed catalyst
_5- ~ r7~
particles of "granular size" (much larger than conventional FCC
catalyst particle size) in a compact gravi-tating bed, rather than
suspending catalyst particles in feed and product vapors in a
fluidized bed.
Although the Houdresid process obviously represented a step
forward in dealing with the effects of metal contamination and coke
formation on catalyst performance, its productivity was limited.
Because its operation was uneconomical, the first Houdresid unit is
no longer operating. Thus, for the 25
. RI - 6049YCA
.~.,
years which have passed since the lloudresid process was first
introduced commercially, the art has continued its arduous
search for suitable modifications or alternatives to the FCC
process which would permit commercially successful operation on
reduced crude and the like. During this period a number of
proposals have been made; some have been used commercially
to a certain extent.
Several proposals involve treating the heavy oil feed
to remove the metal therefrom prior to cracking, such as -by
hydrotreating, solvent extraction and complexing with Friedel-
Crafts catalysts, but these techniques have been criticized as
unjustified economically. Another proposal employs a combination
cracking process having "dirty oil'' and "clean oil" units. Still
another proposal blends residual oil with gas oil and controls
the quantity of residual oil in the mixture in relation to the
equilibrium flash vaporization temperature at the bottom of the
riser type cracker unit employed in the process. Still another
proposal subjects the feed to a mild preliminary hydrocracking
or hydrotreating operation before it is introduced into the crack-
ing unit. It has also been suggested to contact a carbo-metallic
oil such as reduced crude with hot taconite pellets to produce
gasoline. This is a small sampling of the many proposals which
have appeared in the patent literature and technical reports.
Notwithstanding the great effort which has been expended
and the fact that each of these proposals overcomes some
of the difficulties involved, conventional FCC practice today
bears mute testimony to the dearth of carbo-metallic oil-crac~-
ing techniques that are both economical and highly practical in
tcrms o~ technical feasibility. Some crude oils are relatively
frce of co~e precursors or heavy metals or both, and the
troublesome components of crude oil are for the most part
concentrated in the highest boiling fractions. Accordingly.
..
-7~ 5 7 ~(~
it has been possible to largely avoid the problems of coke
precursors and heavy metals by sacrificing the liquid fuel yield
which would be potentially available from the highest boiling
fractions. More par-ticularly, conven-tional FCC practice has
5 employed as feedstock that fraction of crude oil which boils at about
650F to about 1000F, such fractions being relatively free of coke
precursors and heavy metal contamination. Such feedstock, known
as "vacuum gas oil" (VGO) is generally prepared from crude oil by
distilling off the fractions boiling belovv about 650F at a-tmospheric
10 pressure and then separating by further vacuum distillation from
the heavier fractions a cut boiling between about 650F and about
900 to 1025F.
The vacuum gas oil is used as feedstock for conventional FCC
processing. The heavier fractions are normally employed for a
15 variety of other purposes, such as for instance production of
asphalt, residual fuel oil, #6 fuel oil, or marine Bunker C fuel oil,
which represents a great waste of the potential value of this portion
of the crude oil, especially in light of the great effort and expense
which the art has been willing to expend in the attempt to produce
20 generally similar materials from coal and shale oils. The present
invention is aimed at the simultanecus cracking of these heavier
fractions containing substantial quantities of both coke precursors
and heavy metals, and possibly other troublesome components, in
conjunction with the lighter oils, thereby increasing the overall
25 yield of gasoline and other hydrocarbon liquid fuels from a given
quantity of crude. As indicated above, the present invention by
no means constitutes the first attempt to develop such a process,
but the long standing recognition of the desirability of cracking
carbo-metallic feedstocks, along with the slow progress of the
30 industry toward doing so, show the continuing need for such a
process. It is believed that the present process is uniquely
advantageous for dealing with the problem of treating such
carbo-metallic oils in an economically and technically sound manner.
-- RI-6049YCA
7~
SUMMARY OF 'lll~ Irlv~;JTIo~i
The present invelltion is notable in 2roviding a
sim~le, relatively straicJIltforward and hiyhly productive
a~proach to the conversion of carbo-metallic feed such as
rcduced crudc or the like -to various lighter products such as
gasoline. The carbo-metallic feed comprises or is composed of
oil which boils above about 650F. Such oil, or at least the
650F+ portion thereof, is characterized by a heavy metal con-
tent of at least about ~, preferably more than about 5, and
most preferably.at least about S.5 ppm of Nickel Equivalents
by weight and by a caxbon residue on pyrolysis of at least about
1o and more preferably at least about 2% by weight. In accord-
ance with the invention, the carbo-metallic feed, in the form
of a pumpable liquid, is brought into contact with hot conver-
sion cataly,t in a weight ratio of catalyst to feed ln the range
of about 3 to about 18 and preferably more than about 6.
The feed in said mixture undergoes a conversion step
which includes cracking while the mixture of feed and catalyst
is flowing t-hrough a progressive -flow type reactor. The feed,
catalyst, and other materials may be introduced at one or
more points. The reactor includes an elongated reaction
chamber which is at least partly vertical or inclined and in whi-ch
the feed material, resultant products and catalyst are maintained
in contact with one another while flowing as a dilute phase or
stream for a predetermined riser residence time in the range of
about 0.5 to about lO seconds.
The reaction is conducted at a temperature of about 900
to about 1400F, measured at the reaction ch amber exit, under
a total pressure of about 10 to about 50 psia (pounds per square
inch absolute) under conditions sufficiently severe to provide
-- 8 --
r~3
a conversion per pass in the ranye of about 50% or more and
to lay down coke on the catalyst in an amount in the range of
about 0.3 to about 3% by weight and preferably at least about
0.5%. The overall rate of coke production, based on weight of
fresh feed, is in the range of about 4 to about 14% by weight.
~ t the end of the predetermined residence time, the
catalyst is separated from the products, is stripped to remove
high boiling components and other entrained or adsorbed hydro-
carbons and is then regenerated by burning the coke in at least
one regeneration zone with oxygen-containing combustion-supporting
gas under conditions of time, temperature and atmosphere suffi-
cient to reduce the carbon on the regenerated catalyst to about
0.25 percent or less and preferably about 0.05 percent or less
by weight, and wherein at least the major portion of the coke
is burned in a zone wherein the molar ratio of CO:CO2 is main-
tained at a level of at least about 0.25, more preferably at
least about 0.3 and still more preferably at least about 1.
The regenerated catalyst is recycled to the reactor for contact
with fresh feed.
Depending on how the process of the invention is prac-
ticed, one or more of the following advantages may be realized.
If desired, and preferably, the process may be operated without
added hydrogen in the reaction chamber. If desiredl and prefer-
ably, the process may be operated without prior hydrotreating of
the feed and/or without other process of removal of asphaltenes
or metals from the feed, and this is true even where the carbo-
metallic oil as a whole contains more than about 4, or more than
about 5 or even more than about 5.5 ypm ~lickel Equivalents by
weight of heavy metal and has a carbon residue on pyrolysis greater
than about 1%, greater than about 1.4% or greater than about 2%
75~
~y weight ~oreover, all of the converter feed, as above des-
cribed, may be cracked in one and the same conversion chamber.
The crack;ing reaction may be carried out with a catalyst which
has previously been used (recycled, except for such replacement
as required to compensate for normal losses and deactivation) to
crack a carbo-metallic feed under the above described conditions.
Heavy hydrocarbons not cracked to gasoline in a first pass may
be recycled with or without hydrotreating for further cracking
in contact ~ith the same kind of feed in which they were first
subjected to cracking conditions, and under the same ~ind of
conditions; but operation in a substantially once-through or
single pass mode (e.g. less than about 15% by volume of recycle
based on volume of fresh feed) is preferred.
According to one preferred embodiment or aspect of the
invention, at the end of the predetermined residence time referred
to above, the catalyst is projected in a direction established by
the elongated reaction chamber or an extension thereof, while the
products, having lesser momentum, are caused to make an abrupt
change of direction, resulting in an abrupt, substantially in-
stantaneous ballistic separation of products from catalyst. Thethus separated catalyst is then stripped, regenerated and re-
cycled to the reactor as above described.
~ ccording to another preferred embodiment or aspect of
the invention, the carbo-metallic feed is not only brought into
contact with the catalyst, but also with one or more additional
materials including particularly liquid water in a weight ratio
relative to feed ranging from about 0.04 to about 0.15, more
preferably about 0.04 to about 0.1 and still more preferably about
0.05 to about 0.1. Such additional materials, including the
liquid water, may be brouyht into admixture with the feed prior
to, during or after mixing the feed with the aforementioned
catalyst, and either after or, preferably, before, vaporization
-- 10 --
of the feed. The feed, catalyst and water (e.y. in the form o~
liquid water or in the form of steam produced by vaporization
of liquid water in contact with the feed) are introduced into
the progressive flow type reactor, which may or may not be a
reactor embodying the above described ballistic separation, at
one or more points along the reactor. ~hile the mixture of feed,
catalyst and steam produced by vaporization of the liquid water
flows through the reactor, the feed undergoes the above mentioned
conversion step which includes crac]cing. The feed material,
catalyst, steam and resultant products are maintained in contact
with one another in the above mentioned elongated reactlon
chamber while flowing as a dilute phase or stream for the above
mentioned pre--determined riser residence time which is in the
range of about 0.5 to about 10 seconds.
The process as -above described may be practiced in
conjunction with other preferred alternatives, refinements or
more commonly encountered conditions, a few of which will be
referred to under the heading l! Description of Various and
Preferred Embodiments" below.
- lOa -
" ` -11-
BRIEF DESCRIPTION OF T~IE DRAWINGS
Figure 1 is a schematic diagram of a firs-t apparatus for
carrying out the invention.
Figure 2 is a schematic diagram of a second apparatus for
5 carrying out the invention.
Figures 3 -through 5 are graphs of data obtained from
operating the process of the invention.
DESCRIPTION OF VARIOUS AND PREFERRED EMBODIMENTS
The present invention provides a process for the continuous
10 catalytic conversion of a wide variety of carbo-metallic oils to lower
molecular weight produc ts, while maximizing production o highly
valuable liquid products, and making it possible, if desired, to
avoid vacuum distillation and other expensive treatments such as
hydrotreating. The term "oils", includes not only those
15 predominantly hydrocarbon compositions which are liquid at room
temperature (i.e., 68F), but also those predominantly hydrocarbon
compositions which are asphalts or tars at ambient temperature but
liquify when heated to temperatures in the range of up to about
800F. The invention is applicable to carbo-metallic oils, whether
20 of pe troleum origin or not . For example, provided they have the
requisite boiling range, carbon residue on pyrolysis and heavy
metals content, the invention may be applied to the processing of
such widely diverse materials as heavy bottoms from crude oil,
heavy hitumen crude oil, those crude oils know as "heavy crude"
25 which approximate the properties of reduced crude, shale oil, tar
sand extract, products from coal liquification and solvated coal,
.~ RI-6049~CA
-12- ~L~t7~
atmospheric and vacuum reduced crude, extracts and/or bo-ttoms
(raffinate) from solvent de-asphalting, aromatic extract from lube
oil refining, tar bottoms, heavy cycle oil, slop oil, other refinery
waste streams and mixtures of the foregoing. Such mixtures can
5 for instance be prepared by mixing available hydrocarbon fractions,
including oils, tars, pitches and the like. Also, powdered coal may
be suspended in the carbo-metallic oil. Persons skilled in the art
are aware of techniques for demetalation of carbo-metallic oils, and
demetalated oils may be converted using the invention; but it is an
10 advantage of the invention that it can employ as feedstock
carbo-metallic oils that have had no prior demetalation treatment.
Likewise, -the invention can be applied to hydrotreated feedstocks;
but it is an advantage of the invention that it can successfully
convert carbo-metallic oils which have had substantially no prior
15 hydrotreatment. However, the preferred application of the process
is to reduced crude, i.e., that fraction of crude oil boiling at and
above 650E', alone or in admixture with virgin gas oils. While the
use of material that has been subjected to prior vacuum distillation
is not excluded, it is an advan tage of the invention that it can
20 satisfactorily process material which has had no prior vacuum
distillation, thus saving on capital investment and operating costs
as compared to conventional FCC processes that require a vacuum
distillation unit.
Table I below provides a comparison between a t~pical vacuum
25 gas oil (VGO~ which has been used heretofore in fluid catalytic
cracking, with various reduced crudes, constituting a few examples
of the many reduced crudes useable in the present invention:
RI-6049YCA
,: ~
E ~ o~
3 ~4Z
77~
o o o C~ o
4 o .~ ~ o o
c~
o ~ ~, P:
~o o
' ~ + ~ ~ o o ~ o ~ ~ n
3 ~1 U) ~ c~ o ~ ~ u
Z ~o ~ 1~ n ~o~ O ~
E~ ~ ~I c~ ,1
In ~ ~ ~C~ 0~ 1
+ ~d 00 r~ o~ ~ ~ ~ ~ ~ ~ c~l co
~Ul o ~ ~~ o ~ C~ o ~ o
3 u~ ~ X
~ a~ o~ ~ ~ ~o r~
P~ ~ Zf~ oo oo~ o ~ ~7 o o~ cr~
Z C~ ~ o~ oo ~~C~i ~ ~~ ~ U~ o ~3
o ~Y ~ ~~ ~ ~ ''
,_ ~ ~ o c~ ~~ ~ ~ ~1 ~ o ^
P; ~,1 ~ ,~
~ ~ ~ o
3 ~ r~ oo o u~ r~ o o o o I o o ~
o ~ ~ ,~ ~ ~ ~ ~ o o ~4 d
C`J~ ~ ~ r~ a~
d
d
E~ c~ o o ~ ~ ~ o~ D C`l O
Z o ~ ~ O; ~ i O
d~1 o~ ~ o o~ ~ o ~ ~1 ~ ~o ~1
e ~ + ~ ~ ~ 0~ 0 ~ ~ ~ +
d o o ~ c~ o
O I Lf)l 0~ 0 ~ ~ 0~ ~ ~ d O ~ A
E! ~ u~ o
R;~ ~OO Oooooooo~S~
. Y
~ ~ ~ o ~ ~u~o~
o o ~ d ~ X 3
~1 ~o s:
1 4~ ~ I ~ o ~ r--I-- o~ o~ d d
O ~r~ O ~ O ~ ~
,o. ~ o Uo~ ~ ~ ~ o
C`l ~ O ~D d
~ ~ o ~ ~ ~ o~ i o r~ V ~1
¢s~ u7 0 ~I ~ ~~' ~ ~ ~1 ~~ ~ ~ ~ a) a~ ~ 3 ~:4
~ ~ ~ ~~ ~ ~o~
C~
~ ~ d
s~ ~ ~ ~ ~ o ~a
O U ~ X r~ e
~ e
o X ~ O ~ ~ O
~ C~ ~ ~ ~ 0 5
~ ~ :~ X ~C ~¢ ~ ~~ ~ 3
D7~q)
-14-
As can be seen from the Table, the heavier or higher boiling
feeds are characterized by relatively lower API Gravity values -than
-the illustrative vacuum gas oil (VGO). In general those catalytic
cracking process feed stocks having lower boiling temperatures
5 and/or higher API Gravity have been considered highly superior to
feedstocks with higher boiling temperatures and/or lower API
Gravity. Comparisons of the gasoline yield of high boiling feeds
compared -to medium boiling eeds at constant coke yield have shown
that the medium boiling feeds provide superior gasoline yield for a
10 given coke yield.
In accordance with the invention one provides a carbo-metallic
oil feedstock, at least about 70%, more preferably at least about 85%
and still more preferably about 100% (by volume) of which boils at
and above abou-t 650F. All boiling temperatures herein are based
15 on standard atmospheric pressure conditions. In carbo-metallic oil
partly or wholly composed of material which boils at and above
about 650F, such material is referred to herein as 650F+ material;
and 650F+ material which is part of or has been separated from an
oil containing components boiling above and below 650F may be
20 referred to as a 650F+ fraction. But the terms "boils above" and
"650F+" are not intended to imply that all of the material
characterized by said ~erms will have the capability of boiling. The
carbo-metallic oils contemplated by the invention may contain
material which may not boil under any conditions; for example,
25 certain asphalts and asphaltenes may crack thermally during
distillation, apparently without boiling. Thus, for example, when it
is said that the feed comprises at least about 70% by volume of
material which boils abs3ve about 650F, it should be understood
that the 70% in question may include some material which will not
30 boil or volatilize at any temperature. These non-boilable materials
when present, may frequently or for the most part be concentrated
RI - 6049Y
~t'~7
-15 -
in portions of the feed which do not boil below about 1000F,
1025F or higher. Thus, when it is said that at least about 10%,
more preferably about 15% and still more preferably at least about
20% (by volume) of the 650F+ frac-tion will not boil below about
51000F or 1025F, it should be understood that all or any part of
the material not boiling below about 1000 or 1025F, may or may
not be volatile at and above the indicated temperatures.
Preferably, -the contemplated feeds, or at least the 650F+
material therein, have a carbon residue on pyrolysis of a-t least
10about 2 or greater . For example, the Ramsbottom carbon con ten t
may be in the range of about 2 to about 12 and most frequently at
least about 4. 1~ particularly common range is about 4 to abou-t 8.
Note that the illustrative VCO in Table 1 has a Ramsbottom carbon
residue value of 0.38, and that the 650 to 1025F fractions of the
15various reduced crudes have Ramsbottom carbon values between
about 0.3 and about 0.5, whereas the various reduced crudes as a
whole (650+ Total) vary upwards in Ramsbottom carbon value from
about 4 to about 16.8, and still higher values are contemplated.
Preferably, the feed has an average cornposition characterized
20by an atomic hydrogen to carbon ratio in the range of about 1.2 to
about 1.9, and preferably about 1.3 to abou-t 1.~.
The carbo-metallic feeds employed in accordance with the
invention, or at least the 650F+ material therein, may contain at
least about 4 parts per million of Nickel Equivalents, as defined
25above, of which at least about 2 parts per million is nickel (as
metal, by weight). Carbo-metallic oils within the above range can
be prepared from mixtures of two or more oils, some of which do
and do not contain I:he quantities of Nickel Equivalents and nickel
set forth above. It should also be noted that the above values
. . ,
RI - 6049Y
~ ., ~.
7~
-16-
for Nickel Equivalents and nickel represent time-weighted averages
for a substantial period of operation of the conversion unit, such as
one month, for example. It should also be noted that the heavy
metals have in certain circums-tances exhibited some lessening of
5 poisoning tendency after repeated oxida-tions and reductions on the
catalyst, and the literature describes criteria for establishing
"effective metal" values. For example, see the article by Cimbalo,
e-t al, entitled "Deposited Metals Poison FCC Catalyst", Oil and Gas
Journal, May 15, 1972, pp 112-122, the contents of which are
10 incorporated herein by reference. If considered necessary or
desirable, the contents of Nickel Equivalents and nickel in the
carbo-metallic oils processed according to the invention may be
expressed in terms of "effective me-tal" values. Notwithstanding the
gradual reduction in poisoning activity noted by Cimbalo, et al, the
15 regeneration of catalyst under normal FCC regeneration conditions
may not, and usually does not, severely impair the
dehydrogenation, deme thanation and aromatic condensation activity
of heavy metals accumulated on cracking catalyst.
It is known that about 0 . 2 to abou-t 5 weight per cent of
~0 "sulfur" in the form of elemental sulfur and/or its compounds (but
reported as elemental sulfur based on -the weight of feed) appears
in FCC feeds and that the sulfur and modified forms of sulfur can
find their way into the resultant gasoline product and, where lead
is added, tend to reduce its susceptibili-ty to octane enhancement.
25 Sulfur in the product gasoline often requires sweetening when
processing high sulfur containing crudes. To the extent that
sulfur is present in the coke, it also represents a potential air
pollutant since the regenerator burns it to SO2 and SO3. However,
we have found that in our process the sulfur in the feed is on -the
30 other
RI-6049Y
.,
-17- ~L~ 7~7~
hand able to inhibit heavy metal activity by maintaining metals such
as Ni, V, Cu, and Fe in the sulfide form in the reactor. These
sulfides are much less active than the metals themselves in
promoting dehydrogenation and coking reactions. Accordingly, it is
acceptable to carry out the invention with a carbo-metallic oil
having at least about 0 . 3%, acceptably more than about 0 . 8% and
more acceptably a-t least about 1. 5% by weight of sulfur in the
650F+ fraction.
The carbo-metallic oils useful in the invention may and usually
do contain significant quantities of compounds containing nitrogen,
a substantial portion of which may be basic nitrogen. For example,
the total nitrogen content of the carbo-metallic oils may be at least
about 0.05% by weight. Since cracking catalyst owe their cracking
activity to acid sites on the catalys-t surface or in its pores, basic
nitrogen-containing compounds may temporarily neutralize these
sites, poisoning the catalyst. However, the catalyst is not
permanently damaged since the nitrogen can be burned off the
catalyst during regeneration, as a result of which the acidity of the
active sites is restored.
The carbo-metallic oils may also include significant quantities
of pentane insolubles, for example at least about 0.5% by weight,
and more typically about 2% or more or even about 4% or more.
These may include for instance asphaltenes and other materials.
Alkali and alkaline earth metals generally do not tend to
vaporize in large quantities under the distillation conditions
employed in distilling crude oil to prepare the vacuu~n gas oils
normally used as FCC feedstocks. Rather, these metals remain for
the most part in the "bottoms" fraction (the non-vaporized high
boiling portion) which may for instance be used in the production
of asphalt or o ther by-produc-ts . However, reduced crude and
other carbo-metallic oils are in many cases
RI-6049Y
-18~ 0
bottoms products, and therefore may contain significan~ quantities
of alkali and alkaline earth metals such as sodium. These metals
deposit upon the catalyst during cracking. Depending on the
composition of the catalyst and magnitude of the regeneration
temperatures to which it is exposed, -these metals may undergo
interactions and reactions with the catalyst (including the catalyst
support) which are not normally experienced in processing VGO
under conventional FCC processing conditions. If the catalyst
characteristics and regeneration conditions so require, one will of
10 course take the necessary precautions to limit the amounts of alkali
and alkaline earth metal in the feed, which metals may enter the
feed not only as brine associated with the crude oil in its natural
state, but also as components of water or steam which are supplied
to the cracking unit. Thus, careful desalting of the crude used to
prepare the carbo-metallic feed may be important when the catalyst
is particularly susceptible to alkali and alkaline earth metals. In
such circumstances, the content of such metals (hereinafter
collectively referred to as "sodium") in the feed can be maintained
at about 1 ppm or less, based on the weight of the feedstock.
Alternatively, the sodium level of the feed may be keyed to that of
the catalyst, so as to maintain the sodium level of the catalyst
which is in use substan-tially the same as or less than that of the
replacement catalyst which is charged to the unit.
According to a particularly preferred embodiment of the
invention, the carbo-metallic oil feedstock constitutes at least about
70% by volume of material which boils above about 650F, and at
least about 10% of the material which boils above about 650F will
not boil below about 1 025F. The average composition of this
650F+ material may be further charac-terized by: (a) an atomic
30 hydrogen to carbon ratio in the range of about
RI-6049Y
-19~ 7~i ~ 7~
1.3 to about 1.8; ~b) a Ramsbottom carbon value of at least about
2; (c) at least about four parts per million of Nickel Equivalents,
as defined above, of which at least about two parts per million is
nickel (as me-tal, by weight); and (d) at least one of the following:
5 (i) at least abou-t 0.3% by weigh-t of sulfur, (ii) at leas-t about 0.05%
by weight of nitrogen, and (iii) at least about 0 . 5% by weigh-t of
pentane insolubles. Very commonly, the preferred feed will include
all of (i), (ii), and (iii), and other components found in oils of
petroleum and non-petroleum origin may also be present in varying
10 quantities providing they do not prevent operation of the process.
Although -there is no intention of excluding the possibility of
using a feedstock which has previously been subjected to some
cracking, the present invention has the definite advantage that it
can successfully produce large conversions and very substantial
15 yields of liquid hydrocarbon fuels from carbo-metallic oils which
have not been subjected to any substantial amount of cracking.
Thus, for example, and preferably, at least about 85%, more
preferably at least about 90% and most preferably substantially all
of the carbo-metallic feed introduced into the present process is oil
20 which has not previously been contacted with cracking catalyst
under cracking conditions. Moreover, the process of the invention
is suitable for operation in a substantially once-through or single
pass mode. Thus, the volume of recycle, if any, based on the
volume of fresh feed is preferably about 15% or less and more
25 preferably about 10% or less.
, RI - 6049Y
. 7~i7 ~ -
In gencral, thc wcight ratio of catalyst to fresh
fecd (feed whicll has not previously been e~.po~ed to cracking
catalyst under cracking-conditions) used in the process is in
the ran~e of about 3 to about 18. Preferred and more preferred
ratios are about 9 to about 12, more preferably about 5 to
about 10 and still more preferably about 6 to about 10, a
ratio of about 6 to about 8 presently being considered most
nearly optimum. Within the limitations of product quality
requirements, controlling the catalyst to oil ratio at relatively
low levels within the aforesaid ranges tends to reduce the coke
'yield of the process, based on fresh feed. -
In conventional FCC processing of VGO, the ratio between
the number of barrels per day of plant through-put and the total
number of tons of catalyst undergoing circulation throughout
all phases of the process can vary widely. For purposes o~ this
disclosure, daily plant through-put is defined as the number
of barrels of fresh feed boiling above about 650~F which that
plant processes per average day of operation to-liquid products
boiling below about ~30F. For example, in one commercially
successful type of FCC-VGO operation, about 8 to about 12 tons
of catalyst are under circulation in the process per 1000 barrels
per day of plant through-put. In another commercially success-
ful process, this ratio is in the range of about 2 to 3. While
,the ~resent invention may be practiced in the range of about
to about 30 and more typically about 2 to about 12 tons of cata-
lyst inventory per 1000 barrels of daily plant through-put, it
is prcferred to carry out the process of the present invention
with a very small ratio of ca~alyst weight to daily plant through-
put. More specifically, it is preferred to carry out thc process
of the prescnt invention with an inventory of catalyst that is
sufficient to contact the feed for the desired residence time
- 20 -
in the a~ove~indicatcd catalyst to oil ratio while minimizing the
amount of catalyst inventory, relative to pl~nt through-put, ~"hich
is undergoing circulation or being held for treatment in other
phases of the process such as, for example, stripping, regenera-
tion and the like. Thus, more particularly, it is preferred tocarry out the process of the present invention with about 2 to
about 5 and more preferably about 2 tons of catalyst inventory
or less per thousand barrels of daily plant through-put.
In the practice of the invention, catalyst rnay be added
continuously or periodically, such as, for example, to make up
for normal losses of catalyst from the system. Moreover, catalyst-
addition may be conducted in conjunction with withdrawal f -¦
catalyst, such as, for example, to maintain or increase the
average activity level of the eatalyst in the unit. For example,
the rate at which virgin catalyst is added to the unit may be in
the range of about 0.1 to about 3, more preferably about 0.15 to
about 2, and most preferably to about 0.2 to about 1.5 pounds
per barrel of feed. If on the other hand equilibrium eatalyst
from FCC operation is to be utilized, replacement rates as high
as about 5 pounds per barrel ean be practiced Where eireum-
stances are sueh that the catalyst employed in the unit is
below average in resistance to deactivation and/or conditions
prevailing in the unit tend to promote more rapid deactivation,
one may employ rates of addition greater than those stated above;
2~ but in the opposité circumstances, lower rates of aadition may
be employed. - -
Without wishing to be bound by any theory, it appearsthat a number of features of the process to be described in
greater detail below, such as, for instance, the residence
time and optlonal mixing of steam with the feedstock, tend to
restrict the extent to ~hich cracking conditions produce metals
in the reduced state on the catalyst from heavy ~etal sulfide(s),
-- 21
~7~7~
-- .
sulfate(s) or oxide(s) deposited on thc cata1yst particles by
prior e~posures to carbo-metallic feedstock and regen~ration
conditions. Thus, the process appears to afford significant
control over the poisoning effect of heavy metals on the catalyst,
even when the accumulations of such metals are quite substantial.
Accordingly, the process rnay be practiced with catalyst
bearing accumulations of heavy metals which heretofore would
have been considered quite intolerable in conventional FCC-VGO
operations. For these reasons, operation of the process with
catalyst bearing heavy metals accumulations in the range of
about 3,000 to about 70,000 ppm Nickel Equivalents, on the average
is contem~lated. More specifically, the accumulation may be in
the range of about 4,000 to about 50,000 ppm and particularly more
than about 5,000 to about 30,000 ppm. The foregoing ranges are
based on parts per million of Nickel Equivalents, in which the
metals are expressed as metal, by weight, measured on and based on
regenerated equilibrium catalyst. However, in the event that cata-
lyst of adequate activity is available at very low cost, making
feasible very high rates of catalyst replacement, the carbo-metallic
oil could be converted to lower boiling liquid products with
catalyst bearing less than 3,000 ppm Nickel Equivalents of heavy
metals. For example, one might employ equilibrium catalyst from
another unit, for example, an FCC unit which has been used in the
cracking of a feed, e.g. vacuum gas oil, having a carbon residue
on pyrolysis of less than 1 and containing less than about 4 ppm
Nickel Equivalents of heavy metals.
In any event, the equilibrium concentration of heavy
metals in the circulating inventory of catalyst can be controlled
(including maintained or varied as desired or needed) by manipu-
lation of the rate of catalyst addition discussed above. Thus,for e~ample, addition of catalyst may be maintained at a rate
which will control the heavy metals accumulation on the catalyst
in one of the r~n~es set forth above.
- 22 -
~L~7~7~
.. . . . . . .
In gcneral, it is preferrcd to employ a catalyst having- -
a relatively high level of crac~ing activity, providing high
levcls of conversion and productivity at low residence times.
The conversion capabilities of the catalyst may be expressed in
terms of the conversion produced during actual operation of the
process and/or in terms of conversion produced in standard catalyst
activity tests. For example, it is preferred to employ catalyst
which, in the course of extended operation in the process, is
sufficiently active for sustaining a level of conversion of at
least about 50% and more preferably at least about 60~. In this
connection, conversion is expressed in liquid volume percent,
based on fresh feed. Also, for example, the preferred catalyst may
be defined as one which, in its virgin or equilibrium state,
exhibits a specified activity expressed as a volume percentage
derived by the MAT (micro-activity test). For purposes of the
present invention the foregoing percentage is the volume percen-
tage of standard feedstock that is converted to 430F end point
gasoline and lighter pxoducts at 900F, 16 whsv (weight hourly
space velocity), calculated on the basis of catalyst dried at
1100F3 and 3C/0 (catalyst to oil ratio) by tentative ASTM
MAT test D-32, using an appropriate standard feedstock, e.g.
Davison WHPS-12 primary gas oil, having the following analysis
and properties:
API Gravity at 60F, degrees 31.0
Specific Gravity at 60F, g/cc 0.8708
Ramsbottom Carbon, wt. ~0.09
Conradson Carbon, wt. % (est.) 0.04
Carbon, wt. % 84.92
Hydrogen, wt. % 12.94
Sul~ur, wt. ~ 0.68
Nitrogen, ppm 305
- 23 -
.
Viscosity at 100F, centistokes10.36
l~atson K Factor 11.93
Aniline Point~ lB2
Bromine No. 2.2.
Paraffins, Vol. % 31.7
Olefins, Vol. % 1.8
Naphthenes, Vol. % 44.0
Aromatics, Vol.% 22.7
Average Molecular Weight 284
Nickel Trace
Vanadium Trace
Iron Trace
Sodium Trace
Chlorides Trace
B S & W Trace
,
Distillation, F ASTM D-1160
IBP 445
. 10% . 601
30% 664
50% 701
70% 734 --
90~ 787
FBP 834
- 24 -
_ _ . ~ . ....
7t~
The en~ point of the gasôllnc produced in the M~T test is oftcn
.
de~incd as 430F tbp (true boiling point) which is a standard
laboratory distillation, but other end points could serve
equally well for our present purposes. Conversion is calculated
by subtracting from 100 the volume percent (based on fresh feed)
of those products heavier than gasoline which remain in the
recovered product.
The catalyst may be introduced into the process in its
virgin form or, as previously indicated, in other than virgin
form; e.g. one may use equilibrium catalyst withdrawn from
another unit, such as catalyst that has been employed in the
cracking of a different feed. When characterized on the basis
of ~AT activity, the preferred catalysts may be described on the
basis of their MAT activity "as introduced" into the process
of the present invention, or on the basis of their "as withdrawn"
or equilibrium MAT activity in the process of the present inven-
tion, or on both of these bases. A preferred MAT activity
for virgin and non-virgin catalyst "as introduced" into the
process of the present invention is at least about 60%-r but it
will be appreciated that, particularly in the case of non-virgin
catalysts supplied at high addition rates, lower MAT activity
levels may be acceptable. An acceptable "as withdrawn" or
equilibrium MAT activity level of catalyst which has been used
in the process of the present invention is about 20% or more, but
about 40% of more and preferably about 60o or more are preferred
values.
- 25 -
.
~, 7S~
One may employ any hydrocarbon cracking catalyst
having the above indicated conversion capabilities. R parti-
cularly preferred class of catalysts includes those ~hich
have pore structures into which molecules of feed material ma~
enter for adsorption and/or for contact with active catalytic
sites within or adjacent the pores. Various types of catalysts
are available within this classification, including for example
the layered silicates, e.g. smectites. ~lthough the most widely
available catalysts within this classification are the well-
known zeolite-containing catalysts, non-zeolite catalysts are
also contemplated.
The preferred zeolite-containing ca~alysts may
include any zeolite, whether natural, semi-synthetic or
synthetic, alone or in admixture with other materials which
do not significantly impair the suitability of the catalyst,
provided the resultant catalyst has the activity and pore struc-
ture referred to above. For examp~e, if the catalyst is a
mixture, it may include the zeolite component associated with
or dispersed in a porous refractory inorganic oxide carrier; in
such case the catalyst may for example contain about 1% to about
606, more preferably about 1 to about 40% and most typically about
5 to about 25% by weight, based on the total weight of catalyst
(water free basis) of the zeolite, the balance of the catalyst
being the porous refractory inorganic oxide alone or in combination
with any of the k.nown adjuvants for promoting or suppressing various
desired and undesired reactions. For a general explanation of
the genus of zeolite, molecular sieve catalysts useul in
the invention,attention is drawn to the disclosures of the
articles entitled "Refinery Catalysts ~re a Fluid suSiness"
and ''I~laking Cat Crac~ers Work on Varied Diet",
- 2G -
o~
-27-
appearing respec-tively in the July 26, 1978 and September 13, 1978
issues of Chemical Week magazine. The descriptions of the
aforementioned publications are incorporated herein by ref erence .
For the most part, -the zeolite components of the zeolite-
containing catalysts will be those which are know to be useful inFCC cracking processes. In general, these are crystalline
aluminosilicates, typically made up of tetra coordinated aluminum
atoms associated through oxygen atoms with adjacent silicon atoms
in the crystal structure. However, -the term "zeolite" as used in
10 this disclosure contemplates not only aluminosilica-tes, but also
substances in which the aluminum has been partly or wholly
replaced, such as for instance by gallium and/or other metal atoms,
and further includes substances in which all or part of the silicon
has been replaced, such as for ins tance by germanium . Titanium
and zirconium substitution may also be practice.
Most zeolites are prepared or occur naturally in the sodium
form, so that sodium cations are associated with the electro negative
sites in the crystal structure. The sodium cations tend to make
zeolites inactive and much less stable when exposed to hydrocarbon
conversion conditions, particularly high temperatures. Accordingly,
the zeolite may be ion exchanged, and where the zeolite is a
component of a catalyst composition, such ion exchanging may occur
before or after incorporation of the zeolite as a component of the
composition. Suitable cations for replacement of sodium in the
zeolite crystal structure include ammonium ~decomposable l~o
hydrogen), hydrogen, rare earth metals, alkaline earth metals, etc.
Various suitable ion exchange procedures and cations which may be
exchanged into the zeolite crystal structure are well known to those
skilled in the art.
RI-6049YCA
-` -28- ~ 7~C~
Examples of the naturally occuring crys talline aluminosilicate
zeolites which may be used as or included in the catalyst for the
present invention are faujasite, mordenite, clinoptilote, chabazite,
analci te, erionite, as well as levynite, dachiardite, paulingite,
noselite, ferriorite, heulandite; scolccite, s-tibite, harmotome,
phillipsite, brewsterite, flarite, datolite, gmelinite, caumnite,
leucite, lazuri-te, scaplite, mesolite, ptholite, nepheline, ma trolite,
offretite and sodalite.
Examples of the synthetic crys talline aluminosilicate zeolites
which are useful as or in the catalyst for carrying out the present
invention are Zeolite X, U.S. Pa-tent No. 2,882,244, Zeolite Y, U.S.
Paten-t No. 3,130,007; and Zeolite A, U.S. Patent No. 2,882,243; as
well as Zeolite B, U . S . Patent No . 3,008,803; Zeolite D, Canada
Paten-t No. 661,981; 2eolite E, Canada Patent No. 614,495;
Zeolite F, U.S. Patent No. 2,996,358; Zeolite H, U.S. Patent No.
3,010,789; Zeolite J, U.S. Patent No. 3,001,869; Zeolite L, Belgian
Patent No . 575,177; Zeolite M, U . S . Paten-t No . 2,995,423;
Zeolite O, U.S. Patent No. 3,140,252; Zeolite Q, U.S. Patent No.
2,991,151; Zeolite S, U.S. Patent 3,054,657, Zeolite T, U.S. Patent
No. 2,950,952; Zeolite W, U.S. Patent No. 3,012,853; Zeolite Z,
Canada Patent No. 614,495; and Zeolite Omega, Canada Patent No.
817,915. ~lso, ZK-4HJ, alpha beta and ZSM-type zeolites are
useful . Moreover, the zeolites described in U . S . Patents Nos .
3,140,249, 3,140,253, 3,944,482 and 4,137,151 are also useful, the
disclosures of said patents being incorporated herein by reference.
The crystalline aluminosilicate zeolites having a faujasite-type
crystal structure are particularly preferred for use in the present
invention. This includes particularly natural faujasite and Zeolite X
and Zeolite Y.
RI -6049YCA
-29-
The crystalline aluminosilicate zeolites, such as synthetic
faujasi te, will under normal condi tions crystallize as regularly
shaped, discrete particles of about one to about ten microns in
size, and accordingly, this is the size range frequently found in
5 commercial catalyst which can be used in -the invention.
Preferably, -the particle size of the zeolites is from about 0.5 to
about 10 microns and more preferably is from about 0.1 to about
2 microns or less. For example, zeolites prepared in situ from
calcined kaolin may be characterized by even smaller crystallites.
10 Crys-talline zeoli-tes exhibit both an in terior and an exterior
surface area, which we have defined as "portal" surface area, with
the largest portion of the total surface area being internal. By
portal surface area, we refer to the outer surface of the zeolite
crystal through which reactants are considered to pass in order -to
15 convert to lower boiling products. Blockage of the internal
channels by, for example, coke formation, blockage of en-trance to
the internal channels by deposition of coke in the portal surface
area, and contamination by metals poisoning, will greatly reduce the
total zeolite surface area. Therefore, to minimize the effect of
20 contamination and pore blockage, crystals larger than the normal
size cited above are preferably not used in the catalyst of this
mvenhon .
Commercial zeolite-containing catalysts are available with
carriers containing a variety of metal oxides and combination
25 thereof, including for example silica, alumina, magnesia, and
mixtures thereof and mixtures of such oxides with clays as e . g .
described in U.S. Patent No.
; ~ RI-6049Y
7~;77~
-30-
3,034,948. One may for example select any of the zeolite-containing
molecular sieve fluid cracking catalysts which are suitable for
production of gasoline from vacuum gas oils. However, certain
advantages may be attained by judicious selection of catalysts
5 having marked resis-tance to metals. A metal resistant zeolite
catalyst is, for instance, described in U . S . Patent No. 3,944,482,
in which the catalyst contains 1-40 weight percent of a rare
earth-exchanged zeolite, the balance being a refractory metal oxide
having specified pore volume and size distribution. Other catalysts
10 described as "me-tals-tolerant" are described in the above mentioned
Cimbalo et al article.
In general, it is preferred to employ catalysts having an
over-all particle size in the range of about 5 to about 160, more
preferably about 40 to about 120, and most preferably about 40 to
15 about 80 microns.
The catalyst composition may also include one or more
combustion promoters which are useful in the subsequent step of
regenerating the catalyst. Cracking of carbo-metallic oils results in
substantial deposition of coke on the catalyst, which coke reduces
the activity of the catalyst. Thus, in order to restore the activity
of the catalyst the coke is burne~ off in a regeneration step, in
which the coke is converted to combustion gases including carbon
monoxide and/or carbon dioxide. Various substances are known
which, when incorporated in cracking catalyst in small quantities,
25 tend to promote conversion of the coke to carbon monoxide and/or
carbon dioxide. Promoters of combustion to carbon monoxide tend
to lower the temperature at which a given degree of coke removal
can be attained, thus diminishin~ the potential for thermal
deactivation of the catalyst. Such promoters, normally used in
30 effective amounts ranging from a trace up to about 10 or 20% by
weight of the
-~ RI - 6049YCA
.~
-31-
catalyst, may for example be of any type which generally promotes
combustion of carbon under regenerating conditions to carbon
monoxide in preference to carbon dioxide.
Although a wide variety of other catalysts, including both
5 zeolite-containing and non-zeolite-containing may be employed in the
prac-tice of the invention the following are examples of commercially
available catalysts which have been employed in practicing the
invention:
Table 2
10 Specific Weight Percent
S~rface Zeolite
m /g Content A1203 SiO2 Na20 Fe20 TiO2
AGZ-290 300 11.0 29.5 59.0 0.~l0 0.11 0.59
GRZ-l 162 14.0 23.4 69.0 0.10 0.4 0.9
CCZ-220 129 11.0 ~4.6 60.0 0.60 0.57 1.9
Super DX 155 13.0 31.0 65.0 0.80 0.57 1.6
F-87 240 10.0 44.0 50.0 0.80 0.70 1.6
FOC-90 240 8.0 44.0 52.0 0.65 0.65 1.1
HFZ 20 310 20.0 59.0 40.0 0.47 0.54 2.75
HEZ-55 210 19.0 59.0 35.2 0.60 0.60 2.5
The AGZ-290, GRZ-1, CCZ-220 and Super DX catalysts referred to
above are products of W. R. Grace and Co. F-87 and FOC-90 are
products of Filtrol, while HFZ-20 and HEZ-55 are products of
25 Engelhard/Houdry. The above are properties of virgin catalyst
and, except in the case of zeolite content, are adjusted to a water
free basis, i . e . based on material ignited at 1750F . The zeolite
content is derived by comparison of the X-ray intensities of a
catalyst sample and of a standard material composed of high purity
30 sodium Y zeolite in accordance with draft #6, dated January 9,
1978, of proposed ASTM Standard Method entitled "Determination of
the Faujasite Content of a Catalyst."
RI- 6049YCA
-3z_ 3L~ 7~
It is considered an advantage that the process of the present
invention can be conducted in the substantial absence of tin and/or
antimony or a-t least in the presence of a catalyst which is
slibstantially free of either or both of these metals.
The process of the present invention may be operated with the
above described carbo-me-tallic oil and catalys t as substantially the
sole materials charged -to the reac-tion zone. But the charging of
additional materials is not excluded. The charging of recycled oil
to the reaction zone has already been mentioned. As described in
greater detail below, still other materials fulfilling a variety oE
functions may also be charged. In such case, the carbo-metallic oil
and catalyst usually represent the major proportion by weight of
the total of all materials charged to the reaction zone.
Certain of the additional materials which may be used perform
functions which offer significant advantages over the process as
performed with only the carbo-me tallic oil and catalyst . Among
these functions are: controlling the effects of heavy metals and
other catalyst contaminants; enhancing catalyst activity; absorbing
excess heat in the catalyst as received from the regenera-tor;
disposal of pollutants or conversion thereof to a form or forms in
which they may be more readily separated from products and/or
disposed of; controlling catalyst temperature; diluting the
carbo-metallic oil vapors to reduce their partial pressure and
increase the yield of desired products; adjusting feed/catalyst
contact time; donation of hydrogen -to a hydrogen deficient
carbo-metallic oil feedstock; assisting in the dispersion of the feed;
and possibly also distillation of products. Certain of the metals in
the heavy metals accumulation on the catalyst are more active in
promoting
~, RI-6049YCA
-33 -
undesired reactions when they are in the form of elemental metal,
than they are when in the oxidized form produced by contact with
oxygen in the catalyst regenerator. However, the -time of contact
between catalyst and vapors of feed and product in past
conventional catalytic cracking was suf:Eicient so that hydrogen
released in the cracking reac-tion was able to reconvert a significant
por-tion of the less harmful oxides back to the more harmful
elemental heavy metals. One can take advantage of this situation
through the introduction of additional materials which are in
gaseous (including vaporous) form in the reaction zone in admixture
with the catalyst and vapors of feed and products. The increased
volume of material in the reaction zone resulting from the presence
of such additional materials tends to increase the velocity of flow
through the reaction zone with a corresponding decrease in the
residence time of the catalyst and oxidized heavy metals borne
thereby. Because of this reduced residence time, there is less
opportunity for reduction of the oxidized hea~y metals to elemental
form and therefore less of the harmful elemental metals are available
for contacting the feed and products.
Added materials may be introduced into the process in any
suitable fashion, some examples of which follow. For instance, they
may be admixed with the carbo-metallic oil feedstock prior to
contact of the latter with the catalys t . Alternatively, the added
materials may, if desired, be admixed with the catalyst prior to
contact of the latter with the feedstock. Separate portions of the
added materials may be separately admixed with both catalyst and
carbo-metallic oil. Moreover, the feedstock, catalyst and additional
materials may, if desired, be brought together substantially
simultaneously. A portion of
-~ RI-6049YCA
-34~ 77~
the added materials may be mixed with catalyst and/or carbo-
metallic oil in any of the above described ways, while addi-tional
portions are subsequently brough-t into admixture. For example, a
portion of the added ma-terials may be added to the carbo-metallic
5 oil and/or to the ca-talyst before they reach the reaction zone, while
another portion of the added materials is introduced directly into
the reaction zone. The added materials may be introduced at a
plurality of spaced loca-tions in the reaction zone or along the
length thereof, if elongated.
The amount of additional materials which may be present in the
feed, catalyst or reaction zone for carrying out the above
functions, and others, may be varied as desired; but said amount
will preferably be sufficient to substantially heat balance the
process. These materials may for example be introduced into the
15 reaction zone in a weight ratio relative to feed of up to about 0.4,
preferably in the range of about 0.02 to about 0.4, more preferably
about 0. 03 to about 0. 3 and most preferably about 0~05 to about
0.25.
For example, many or all of the above desirable functions may
20 be attained by introducing H2O to the reaction zone in the form of
steam or of liquid water or a combination thereof in a weight ratio
relative to feed in the range of about o.oa~ or more, or more
prefera~ly about 0.05 to about 0.1 or more. Without wishing to be
bound by any theory, it appears that the use of H2O tends to
25 inhibit reduction of catalyst-borne oxides, sulfites and sulfides to
the free metallic form which is believed to promote condensation-
dehydrogenation with consequent promotion of coke and hydrogen
yield and accompanying loss of product. Moreover, H2O may also,
to some extent, reduce deposition of metals onto the catalyst
30 surface. There may also be some tendency to desorb nitrogen-
containing and other heavy contaminant-containing molecules from
the surface of the catalyst particles, or at leas-t some tendency to
inhibit their absorption by the catalyst. It is also believed that
~- RI-6049YCA
, :,.
7~
added H2O tends to increase the acidity of the catalyst by Bronsted
acid formation which in turn enhances the activity of the catalyst,
Assuming the H2O as supplied is cooler than the regenerated cata-
lyst and/or the temperature of the reaction zone, the sensible
heat involved in raising the temperature of the H2O upon contac-
ting the catalyst in the reaction zone or elsewhere can absorb
excess heat from the catalyst. Preferably, the liquid or vapor
H2O contains less than about 100 ppm of sodium, and less than about
500 ppm each of calcium and magnesium. All or a portion of the
H2O may be and preferably is condensed from the products of a prior
catalytic conversion of a carbo-metallic oil. Where the H2O is or
includes recycled water that contains for example about 500 to
about 5000 ppm of H2S dissolved therein, a number of additional ad-
vantages may accrue. The ecologically unattractive H2S need not
be vented to the atmosphere, the recycled water does not require
further treatment to remove H2S and the H2S may be of assistance
in reducing coking of the catalyst by passivation of the heavy
metals, i.e. by conversion thereof to the sulfide form which has
a lesser tendency than the free metals to enhance coke and hydro-
gen production. In the reaction zone, the presence of H2O candilute the carbo-metallic oil vapors, thus reducing their partial
pressure and tending to increase the yield of the desired products.
It has been reported that H2O is useful in combination with other
materials in generating hydrogen during cracking; thus it may be
able to act as a hydrogen donor for hydrogen deficient carbo-
metallic oil feedstocks. The H2O may also serve certain purely
mechanical functions such as: assisting in the atomizing or dis-
persion of the feed; competing with high molecular weight mole-
cules for adsorption on the surface of the catalyst, thus inter-
rupting coke formation; steam distillation of vaporizable productfrom unvaporized feed material; and disengagement of product from
catalyst upon conclusion of the cracking reaction. It is
- 35 -
-36- ~ V
particularly preferred to bring together H2O catalyst and carbo-
metallic oil substantially simultaneously. For example, one may
admix H2O and feedstock in an atomizing nozzle and immedia-tely
direct the resultant spray into contact wi-th the catalyst at the
downstream end of the reaction zone.
The addi tion of s team to the reac tion zone in frequently
mentioned in the literature of fluid catalytic cracking. Addition of
liquid water to the feed is discussed relatively infrequently,
compared to the introduction of s-team directly into the reaction
zone. However, in accordance with the present invention it is
particularly preferred that liquid water be brought into intimate
admixture with the carbo-metallic oil in a weight ration of about 0.4
to about 0.15 at or prior to the time of introduction of the oil into
the reaction zone, whereby the water (e . g ., in the form of liquid
water or in the form of steam produced by vaporization of liquid
water in contact with the oil) en-ters the reaction zone as part of
the flow of feedstock which enters such zone. Although not
wishing to be bound by any theory, it is believed that the
foregoing is advantageous in promoting dispersion of the feedstock.
Also, the hea-t of vaporization of the water, which heat is absorbed
from the catalyst, from the feedstock, or from both, causes the
water to be a more efficient heat sink than steam alone. Preferably
the weight ratio of liquid water t.o feed is about 0.04 to about 0.1,
more preferably about 0.05 to about 0.1.
Of course, the liquid water may be introduced into the process
in the above described manner or in other ways, and in either
event the introduction of liquid water may be accompanied by the
introduction of additional amounts of water as steam into the same
or different portions of the reaction zone or into the catalyst
and/or feedstock. For example, the amount of additional steam may
be in a weight ratio relative to feed in the range of about 0.01 to
about 0.25, with the weight ra-tio
RI-6049Y
.~
~37~ ~L~L7~7 ~
of total H2O (as steam and liquid water) to feedstock being about
0 . 3 or less . The charging weight ratio of liquid water relative to
steam in such combined use of liquid water and steam may thus
range from about 5 to about 0.2. Such ratio may be maintained at
5 a predetermined level wi-thin such range or varied as necessary or
desired to adjust or maintain the heat balance of the reaction.
Other materials may be added to the reaction zone to perform
one or more of the above described functions. For example, the
dehydrogena-tion-condensation activity of heavy metals may be
10 inhibited by introducing hydrogen sulfide gas into the reaction
zone. Hydrogen may be made available for hydrogen deficien-t
carbo- metallic oil feedstocks by introducing into the reaction zone
either a conventional hydrogen donor diluent such as a heavy
naphtha or relatively low molecular weight carbo-hydrogen fragment
15 contributors, including for example: light paraffins; low molecular
weight alcohols and other compounds which permit or favor
intermolecular hydrogen trans Eer; and compounds that chemically
combine to generate hydrogen in the reaction zone such as by
reaction of carbon monoxide with water, or with alcohols, or with
20 olefins, or with other materials or mixtures of the foregoing.
All of the above mentioned additional materials (including
water), alone or in conjunction with each other or in conjunction
with other materials, such as nitrogen or other inert gases, light
hydrocarbons, and others, may perform any of the above described
25 functions for which they are suitable, including without limitation,
acting as diluents to reduce feed partial pressure and/or as heat
sinks to absorb excess heat present in -the catalyst as received from
the regeneration step.
RI - 6049YCA
~ a~s~
Tllo forcgolng is a discussion of some of the functions which
can bc performed by materials other than catal~lst and carbo-
metallic oil feedstock introduced into the reaction zone,
and it should be understood that other materials may be added
or other functions'performed without departing from the spirit
'of the invention.
The invention may be practiced in a wide variety of
apparatus. However, the preferred apparatus includes means for
rapidly vaporizing as much feed as possible and efficiently
,10 admixing feed and catalyst (although not necessarily in that
order), for causing the resultant mixture to flow as a dilute
suspension in a progressive flow mode, and for separating the
catalyst from cracked products and any uncracked or only
partially cracked feed at the end of a predeter,mined residence
time or times, it being preferred that all or at least a substantial
portion of the product should be abruptly separated from at least
a portion of the catalyst.
For example, the apparatus may include, along its
elongated reaction chamber, one or more points for introduction
of carbo-metallic feed, one or more points for introduction of
catalyst, one or more points for introduction of additional
material, one or more points for withdrawal of products and
one or more points for withdrawal of catalyst. The means
for introducing feed, catalyst and other material may range
from open pipes to sophisticated jets or spray nozzles, it being
preferred to use means capable of breaking up the liquid feed
into fine droplets.
- 38 -
i7t7~
It is preferred that thc reaction chamber, or at
least thc major portion thereof, be more nearly vertical than
horizontal and have a length to diameter ratio of at least
a~out 10, more preferably about 20 or 25 or more. Use of a
vertical riser tyFe reactor is preferred. If tubular, the
reactor can be of uniform diameter throughout or may be
provided with a continuous or step-wise increase in diameter
along the reaction path to maintain or vary the velocity
along the flow path.
In general, the charging means (for catalyst and
feed) and the reactor confiquration are such as to provide a
relatively high velocity of flow and dilute suspension of catalyst.
For example, the vapor or catalyst velocity in the riser will be
usually at least about 25 and more typically at least about 35
feet per second. This velocity may range up to about 55 or- about
75 feet per second or higher. The velocity capabilities of the
reactor will in general be sufficient to prevent substantial
build-up of a catalyst bed in the bottom or other portions of
the riser, whereby the catalyst loading in the riser can be
maintained below about 4 or 5 pounds and below about 2 pounds
per cubic foot, respectively, at the upstream (e.g. bottom) and
downstream (e.g. top) ends of the riser.
The progressive flow mode involves, for example,
flowing of catalyst, feed and products as a stream in a positive-
ly controlled and maintained direction established by the elon-
gated nature of the reaction zone. This is not to suggest
however that there must be strictly linear flow. As is well
known, turbulent flow and "slippage" of catalyst may occur to
some e~tent especially in certain ranges of vapor velocity
and sor,le catalyst loadings, although it has been reported
- 3~-
~L~IL7~'7~
adviseable to employ sufficiently low catalyst loadinys
to restrict slippage and back-mixing.
Most preferably the reactor is one which abruptly
separates a substantial portion or all of the vaporized
cracked products from the catalyst at one or more points
along the riser, and preferably separates substantially
all of the vaporized cracked products from -the catalyst
at the downstream end of the riser. A preferred type of
reactor embodies ballistic separation of catalyst and products;
that is, catalyst is projected in a direction established
by the riser tube, and is caused to continue its motion
in the general direction so established, while the products
having lesser momentum, are caused to make an abrupt change
of direction, resulting in an abrupt, substantially instantaneous
separation of product from catalyst. In a preferred embodiment
referred to as a vented riser, the riser tube is provided
with a substantially unobstructeddischarge opening at its
-
downstream end for discharge of catalyst. An exit port
in the side of the tube adjacent the downstream end received
the products. The discharge opening communicates with a
catalyst flow path which extends to the usual stripper and
regenerator, while the exit port communicates with a product
flow path which is substantially or entirely separated from
the catalyst flow path and leads to separation means for
separating the products from the relatively small portion
of catalyst, if any, which manages to gain entry to the
product exit port. Examples of a ballistic separation
apparatus and technique as above descrlbed, are found in
U.S. Patents 9,066,533 and 4,070,159 to Myers et al.
- 40 -
Preferred conditions Eor operation of thc proccss are
dcscri~ed below. ~mong thcse ar~ feed, catalyst and reaction
tempcraturcs, rcaction and feed pressures, residence tim~ ~nd
levels o~ conversion, coke production and coke laydown on
catalyst.
In conventional FCC opera-tions with VGO, the feed-
stock is customarily preheated, often to temperatures signifi-
cantly higher than are required to make the feed su~ficiently
fluid for pumping and for introduction into the reactor~ For
e~ample, preheat temperatures as high as about 700or 800F
have been reported. But in our process as presently practiced
it is preferred to restrict preheating of the feed, so that the
feed is capable of absorbing a larger amount of heat from the
catalyst while the catalyst raises the feed to conversion
temperature, at the ~ame time minimizing utilization of external
fuels to heat the feedstock. Thus, where the nature of the feed-
stock permits, it may be fed at ambient temperature. Heavier
stocks may be fed at preheat temperatures of up to about
600F, typically about 200F to about 500F, but higher preheat
zo temperatures are not necessarily excluded.
The catalyst fed to the reactor may vary widely in
temperature, for example from about 1100to about 1600F, more
preferably about 1200to about 1500F and most preferably
about 1300to about 1400F, with about 1325 to about 1375
being considered optimum at present.
As indicated previously, the conversion of the
carbo-mctallic oil to lower molecular weight products may be
conducted at a temperature of about 900to about 1~00F,
measured at the reaction chamber outlet. The reaction tempera-
turc as measurcd at said outlet is more pre~erably maintainedin the range of about 975 to about 1300F, still more preferably
about 9aso to about 1200F, and most preferably about 1000
7'~(~
-42 -
to about 1150F. Depending upon the temperature selected and the
properties of the feed, all of the feed may or may not vaporize in
the riser.
Al-though the pressure in -the reactor may, as indica-ted above,
5 range from about 5 to abou-t 50 psia, preferred and more preferred
pressure ranges are about 10 to about 35 and about 20 -to about 35.
In general, the partial (or total) pressure of the feed may be in
the range of about 3 to about 30, more preferably about 7 to about
25 and most preferably about 10 to about 17 psia. The feed partial
10 pressure may be controlled or suppressed by the introduction of
gaseous (including vaporous) materials into the reactor, such as for
instance the steam, wa-ter, and other additional materials described
above. The process has for example been operated with the ratio
of feed partial pressure relative to total pressure in the riser in
the range of about 0 . 2 -to about 0 . 8, more typically about 0 . 3 to
about 0.7 and still more typically about 0.4 to about 0.6, with the
ratio of added gaseous material (which may include recycled gases
and/or steam resulting from introduction of H2O to the riser in the
form of steam and/or liquid water) relative to total pressure in the
riser correspondingly ranging from about 0 . ~ to about 0 . 2, more
typically about 0.7 to about 0.3 and still more typically about 0.6 to
about 0 . 4 . In the illustrative operations just described, the ratio
of the partial pressure of the added gaseous material relative to the
partial pressure of the feed has been in the range of about 0.25 to
about 2.5, more typically about 0 . 4 to abou t 2 and still more
typically about 0.7 to about 1.7.
Although the residence time of feed and product vapors in the
riser may be in the range of about 0. 5 to about 10 seconds, as
described above, preferred and more preferred values are about 0.5
to about 6 and about 1 to about 4 seconds, with
RI-6049Y
i77~
about l.S to about 3.0 seconds currently being considered
about optimum. For example, thc proccss has been o~eratcd with
a riser vapor residence time of about 2.5 seconds or less by
introduction of copious amounts of gaseous materials into the
riser, such amounts being sufficient to provide for example a
partial pressure ratio of added gaseous materials relative to
hydrocarbon feed of about 0.8 or more. sy way of further illus-
tration, the process has been operated with said residence time
being about two seconds or less, with the aforesaid ratio being
in the range of about 1 to about 2. The combination of low
feed partial pressure, very low residence time and ballistic
separation of products from catalyst are considered especially :-
beneficial for the conversion of carbo-metallic oils. Additional
benefits may be obtained in the foregoing combination when there is
a substantial partial pressure of added gaseous material, especially
H2O, as described above.
Depending upon whether there is slippage between
the catalyst and hydrocarbon vapors in the riser, the catalyst
riser residence time may or may not be the same as that of the
vapors. Thus, the ratio of average catalyst reactor residence
time versus vapor reactor residence time, i.e. slippage, may be
in the range of about 1 to about 5, more preferably about 1 to about
4 and most preferably about 1.2 to about 3, with about 1.2 to about
2 currently being considered optimum.
In certain types of known FCC units, there is a riser
which discharges catalyst and product vapors together into an
enlarged chamber, usually considered to be part of the reactor,
in which the catalyst is disengaged from product and collected.
Continued contact of catalyst, uncracked feed (if any) and cracked
products in such enlarged cham~er results in an overall
cata1~st fced contact time appreciably exceeding the riser tube
- ~3 -
_44_ ~
residence times of the vapors and catalysts. When practicing the
process of the present invention with ballistic separation of catalyst
and vapors at the downs-tream (e . g . upper) extremity of the riser,
such as is taught in the above men-tioned Myers et al patents, the
5 riser residence time and the catalyst contact time are substantially
the same for a major portion of the feed and product vapors. It is
considered advantageous if the vapor riser residence time and vapor
catalyst contact time are substantially the same for a-t least about
80%, more preferably at least about 90% and most preferably at least
10 about 95% by volume of the total feed and product vapors passing
through the riser. By denying such vapors continued contact with
catalyst in a catalyst disengagement and collection chamber one may
avoid a tendency toward re-cracking and diminished selectivity.
In general, the combination of catalyst to oil ratio,
15 temperatures, pressures and residence times should be such as to
effect a substantial conversion of the carbo-metallic oil feedstock.
It is an advantage of the process that very high levels of
conversion can be attained in a single pass; for example the
conversion may be in excess of 50% and may range to about 90% or
20 higher. Preferably, the aforementioned conditions are maintained at
levels sufficient to maintain conversion levels in the range of about
60 to about 90% and more preferably about 70 to about 85%. The
foregoing conversion levels are calculated by subtrac-ting from 100%
the percentage obtained by dividing the liquid volume of fresh feed
25 in-to 100 times the volume of liquid product boiling at and above
430F (tbp, standard atmospheric pressure).
These substantial levels of conversion may and usually do
result in relatively large yields of coke, such as for example about
4 to about 14% by weight based on fresh feed, more commonly about
30 6 to about 12% and most frequently about 6 to
RI-6049YCA
_45_
about 10%. The coke yield can more or less quantitatively deposit
upon the catalyst . At contemplated ca talyst to oil ra-tios, the
resultant coke laydown may be in excess of about 0 . 3, more
commonly in excess of about 0 . 5 and very frequently in excess of
5 about 1% of coke by weight, based on -the weight of moisture free
regenera ted catalys-t . Such coke laydown may range as high as
about 2%, or about 3%, or even higher.
In common with conventional FCC operations on VGO, the
present process includes stripping of spent catalyst after
10 disengagement of the catalyst from product vapors. Persons skilled
in the art are ac~uainted with appropriate stripping agents and
conditions for stripping spent catalyst, but in some cases the
present process may require somewhat more severe conditions than
are commonly employed. This may result, for example, from the
15 use of a carbo-metallic oil having constituents which do not
volatilize under the conditions prevailing in the reactor, which
constituents deposit themselves at least in part on the catalyst.
Such adsorbed, unvaporized material can be troublesome from at
least two standpoints. First, if the gases (including vapors) used
20 to strip the catalyst can gain admission to a catalyst disengagement
or collection chamber connected to the downstream end of the riser,
and if there is an accumulation of catalyst in such chamber,
vaporization of these unvaporized hydrocarbons in the stripper can
be followed by adsorption on the bed of catalyst in -the chamber.
25 More particularly, as the catalyst in the stripper is stripped of
adsorbed feed material, the resultant feed material vapors pass
through the bed of catalyst accumulated in the catalys t collection
and/or disengagement chamber and may deposit coke and/or
condensed material on the catalyst in said bed. As the catalyst
30 bearing such deposits moves from the bed and into the stripper and
from
RI -6049YCA
'~
-46~
thence to the regenerator, the condensed products can create a
demand for more stripping capacity, while the coke can tend .o
increase regeneration temperatures and/or demand greater
regeneration capacity. For the foregoing reasons, it is preferred
to prevent or restrict contact between stripping vapors and catalyst
accumulations in the catalyst disengagemen-t or collection chamber.
This may be done for example by preventing such accumulations
from forming, e . g . with the exception of a quantity of catalyst
which essen-tially drops out of circulation and may remain at the
bot-tom of the disengagement~and/or collection chamber, the catalyst
that is in circulation may be removed from said chamber promptly
upon settling to the bottom of the chamber. Also, to minimize
regeneration tempera tures and demand for regenera tion capacity, it
may be desirable to employ conditions of time, temperature and
atmosphere in the stripper which are sufficient to reduce potentially
volatile hydrocarbon material borne by the stripped catalyst to
about 10% or less by weight of the total carbon loading on the
catalyst. Such stripping may for example include reheating of the
catalyst, extensive stripping wi-th steam, -the use of gases having a
temperature considered higher than normal for FCC/VGO operations,
such as for instance flue gas from the regenerator, as well as other
refinery stream gases such as hydro~reater off-gas (H2S
containing), hydrogen and others. For example, the stripper may
be operated at a temperature of about 1025F or higher.
Substantial conversion of carbo-metallic oils to lighter products
in accordance with the invention tends to produce sufficiently large
coke yields and coke laydown on catalyst to require some care in
catalyst regeneration. In order to maintain adequate activity in
zeolite and non-zeolite catalysts, it is desirable to regenerate the
catalyst under conditions of time, temperature and atmosphere
sufficient to reduce the percent
-~ RI-6049YCA
-
~47~ ~ S~7~
by weigh-t of carbon remaining on -the ca-talyst to about 0.25% or
less, whether the catalyst bears a large heavy metals accumulation
or not. Preferably this weight percentage is about 0.1% or less and
more preferably about 0.05% or less, especially with zeolite
5 catalysts. The amoun-ts of coke which must -therefore be burned off
of the catalysts when processing carbo-metallic oils are usually
subs-tantially greater than would be the case when cracking VGO.
The term coke when used to describe the present invention, should
be understood to include any residual unvaporized feed or cracking
product, if any such material is present on the catalyst after
stripping .
Regeneration of catalyst, burning away of coke deposited on
the catalyst during the conversion of the feed, may be performed at
any suitable temperature in the range of about 1100 to about
1600F, measured at the regenerator catalyst outlet. This
temperature is preferably in the range of about 1200 to about
1500F, more preferably about 1275 to about 1425F and optimally
about 1325 to about 1375F. The process has been operated, for
example, with a fluidized regenerator with the temperature of the
catalys t dense phase in the range of about 1300 to about 1400F .
When regenerating catalyst employed in the cracking of carbo-
metallic oils, it has heretofore been suggested that the success of
the cracking operation depended upon the burning of the coke in
contact with combustion producing gases containing excess oxygen.
By excess oxygen is meant an amount in excess of the
stoichiometric require-
. RI-6049YCA
-48- ~7~7~
ment for burning all of the hydrogen, all of the carbon and all of
the other combustihle components, if any, which are present in the
above-mentioned selec-ted portion of the coke immediately prior to
regeneration. The gaseous produc-ts of combustion conducted in the
presence oE excess oxygen will normally include an appreciable
amount of free oxygen. Such free oxygen, unless removed from
the by-product gases or converted to some other form by a means
or process other than regeneration, will normally manifest itself as
free oxygen in the flue gas from the regenerator unit. In order to
provide sufficient driving force to complete the combustion of coke
to low levels, when burning all or a major portion of the coke with
excess oyxgen, the amount of free oxygen will normally be not
merely appreciable but substantial, i . e . there will be a
concentration of at least about 2 mole percent of free oxygen in the
total regeneration flue gas recovered from the entire, completed
regeneration operation. While such technique is effective in
attaining the desired low levels of carbon on regenerated ca talyst,
it has its limitations and difficulties as will become apparent from
the discuss below.
As conventionally practiced, the burning of coke during
regeneration produces some H2O because of the small amount of
hydrogen normally found in coke; but carbon monoxide and carbon
dioxide are generally regarded as the principal products. The
conversion of the carbon content of coke to carbon monoxide and
carbon dioxide are highly exothermic reactions. For instance the
reaction of oxygen with coke to produce carbon dioxide produced
14,108 BTUs per pound of coke, while the reaction of oxygen with
coke or carbon to form carbon monoxide produces approximately
3 ,967 BTUs per pound of coke . The larger the amount of coke
which must be burned from a given weight of catalyst, -the greater
the amount of heat released during cornbustion in the regenerator.
-~ RI-6049YCA
_49_ ~7~
Heat released by combustion of coke in the regenerator is
absorbed by the catalyst and can be readily retained thereby until
the regenerated catalyst is brought into con-tact with fresh feed.
When processing carbo-metallic oils to the relatively high levels of
5 conversion involved in the present invention, -the amount of
regenerator heat which is transmitted -to fresh feed by way of
recycling regenerated ca-talyst can substan-tially exceed the level of
heat input which is appropriate in the riser for heating and
vaporizing the feed and other materials, for supplying the
10 endothermic hea-t of reaction for cracking, for making up the heat
losses of the unit and so forth. Thus, in accordance with the
invention, the amount o regenerator heat -transmitted to fresh feed
may be controlled, or restricted where necessary, within certain
approximate ranges. The amount of heat so transmitted may for
example be in the range of about 500 to about 1200, more
particularly about 600 to about 900, and more particularly abo~-t 650
to about 850 BTUs per pound of fresh feed. The aforesaid ranges
refer to the combined heat, in BTUs per pound of fresh feed,
which is transmitted by the catalyst to the feed and reaction
20 products (between the contacting of feed with catalyst and the
separation of product from catalyst) for supplying the heat of
reaction ~e.g. for cracking) and the difference in enthalpy between
the products and the fresh feed. Not included in the foregoing are
the heat made available in the reactor by the adsorption of coke on
25 the catalyst, nor the heat consumed by heating, vaporizing or
reacting recycle streams and such added materials as water, steam,
naphtha and other hydrogen donors, flue gases and inert gases, or
by radiation and other losses.
One or a combination of techniques may be utilized in this
30 invention for controlling or restricting the amount of regeneration
heat transmitted via catalyst to fresh feed.
6049YCA
7~
. . . ~ . . _ : .
,
For example, one may'add a combustion promotor to the cracking
catalyst in order to reducc the temperature of combustion of
co~e to carbon dioxide and/or carbon monoxide in the regenerator.
~loreover, one may remove heat from the catalyst through
heat exchange means, including for example heat exchangers
(e.g. steam coils) built into the regenerator itsell, whereby
one may extract heat from the catalyst during regeneration. Heat
exchangers can be built into catalyst transfer lines, such as
for instance the catalyst return line from the regenerator to
the reactor, whereby heat may be removed from the catalyst after
t is regenerated. The amount of heat imparted to the catalyst
in the regenerator may be restricted by reducing the amount of
insulation on the regenerator to permit some heat loss to the
'surrounding atmosphere, especially if feeds of exceedingly high
coking potential are pIanned for processing; in general, such
loss of heat to the atmosphere is considered economically less
desirable than certain of the other alternatives set forth
herein. One may also inject cooling fluids into the regenerator,
for example water and/or steam, whereby the amount of inert gas
available in the regenerator ~or heat absorption and removal is
increased.
Whether practiced with the foregoing techni~ues or not,
the present invention includes the technique of
controlling or restricting the heat transmltted to fresh feed
via recycled regenerated catalyst while maintaining a specified'
ratio between the carbon dioxide and carbon monoxïde'formëd'in
the regenerator while such gases are in heat exchange contact
or relationship with catalyst undergoing regeneration. In
general, all or a major portion by weight of the coke present on the
catalyst immediately prior to regeneration is r~moved in atleast one
- 50 -
7577~ .
, .
'combustion zonc in which thc aforcsaid ratio is controlled as
described below. More particularly, at least the major portion
more preferably at least about 65% and more preferably at least
about 80" by weight of the coke on the catalyst is removed in a
combustion zone in which the molar ratio o CO2 to CO is main-
,tained at a level substantially below 5, e.g. about 4 or less.Looking at the CO2/CO relationship from the inverse stand~oint,
it is preferred that the CO/CO2 molar ratio should be at least
' about 0.25 and preferably at least about 0.3 and still more'prefer-
ably about 1 or more or even 1.5 or more. While persons skilled
in the art are aware of techniques for inhibiting the burning
of CO to CO2, it has been suggested that the mole ratio of CO:CO2
should be kept,less than 0.2 when regenerating catalyst with
large heavy metal accumulations resulting from the processing
of carbo-metallic oils; in this connection see for example
U. S. Patent 4,162,213 to Zrinscak, Sr. et al. In this invention
however, maximizing CO productionwhile regenerating catalyst to
about 0.1% carbon or less, and preferably about 0.05% carbon or
less, is a particularly preferred embodiment of this invention.
Moreover, according to a preferred method of carrying out the
invention the sub-process of regeneration, as a whole, may be
carried out to the above-mentioned low levels of carbon on --
regenerated catalyst with a deficiency of oxygen; more specifi-
,cally, the total oxygen supplied to the one or more stages of
reg~neration can be and preferably is less than the stoichiometric
amount which would be required to burn all hydrogen in the coke
to II2O and to burn all carbon in the coke to CO2. If the coke
includes other combustibles, the aforementioned stoichiometric
amount can be adjusted to include the amount of oxygen required
to burn them.
. _ _
7~)
.
Still anothcr ~articularly ~rcferred techniquc
for controlling or restricting thc regcneration heat im?artcd
to fresh feed via recycled catalyst involves the diversion of a
portion of the heat borne by recycled catalyst to added materials
introduced into the reactor, such as the water, steam, naphtha,
otller hydrogen donors, flue gases, inert ga~es, and other gaseous
or vaporizable materials which may be introduced into the reactor.
The larqer the amount of coke which must be burned
from a given weight of catalyst, the greater the potential for
exposing the catalyst to excessive temperatures. Many otherwise
desirable and useful cracking catalysts are particularly susceptible
to deactivation at high temperatures, and among th~se are quite
a few of the costly molecular sieve or zeolite types of catalyst.
The crystal structures of zeolites and the pore structures of
the catalyst carriers generally are somewhat susceptible to
thermal and/or hydrothermal degradation. The use of such
catalysts in catalytic conversion processes for carbo-metallic
feeds creates a need for regeneration techniques which will not
destroy the catalyst by exposure to highly severe temperatures
and steaming. Such need can be met by a multi-
stage regeneration process which includes conveying spent catalyst
into a first regeneration zone and introducing oxidizing gas
thereto. The amount of oxidizing gas that enters said first zone
and the concentra~ion of oxygen or oxygen bearing gas therein are
Z5 sufficient for only partially effecting the desired conversion
of co~e on the catalyst to carbon oxide gases. The partially
regenerated catalyst is then removed from the first regeneration
zone and i~ conveyed to a second regeneration zone. O~idizing
gas is introduced into the second regeneration zone to provide
a highcr concentration of oxygen or oxygcn-containing gas
tlan in the first zone, to com21ete the removal of carbon
~o the dcsired leve~. The regenerated catalvst may then be
- 52 -
t;~r3
removed from the second zone and recycled to the reactor for
contact with fresh feed. An ex~le of such multi-stage re-
generation process is described in U.S. Patent 2,938,739.
Multi-stage regeneration offers the possibility
of combining oxygen deficient regeneration with the control of the
CO:CO~ molar ratio. Thus, about 50% or more, more preferably
about 65% to about 956, and more preferably about 80~ to about
95~ by weight of the coke on the catalyst immediately prior
to regeneration may be removed in one or more stages of regenera-
tion in which the molar ratio of CO:CO2 is controlled in the
manner described above. In combination with the foregoing, the
last 5% or more, or 10% or more by weight of the co]~e originally
present! up to the entire amount of coke remaining after the
preceding stage or stages, can be removed in a subsequent stage
of regeneration ln which more oxygen is present. Such process
is susceptible of operation in such a manner that the total flue
gas recovered from the entire, completed regeneration operation
contains little or no excess oxygen, i.e. on the order of about
~0.2 mole percent or less, or as low as about O.l mole percent or
less, which is substantially less than the 2 mole percent
~,thich has been suygested elsewhere. Thus, multi-stage regeneration
is particularly bene~icial in that it provides another convenient
techniyue for restricting regeneration heat transmitted to
fresh feed via re~enerated catalyst and/or reducing the potential
for thermal deactivation, while simultaneously affording an oppor-
tunity to reduce the carbon level on regenerated catalyst to those
vcry low percentages (e.g. about 0.1~ or less) which particularly
-54~ ~ 7~77~
enhance catalyst activity. Moreover, where the regeneration
conditions, e. g . temperature or atmosphere, are substantially less
severe in the second zone than in the first zone (e.g. by at least
about 10 and preferably at least about 20F), tha-t part of the
5 regeneration sequence which involves the mos-t severe conditions is
performed while there is still an appreciable amount of coke on the
catalyst. Such operation may provide some protection of the
catalyst from the more severe conditions. A particularly preferred
embodiment of the invention is two-stage fluidized regeneration at a
10 maximum temperature of about 1500F with a reduced temperature of
at least about 10 or 20F in the dense phase of the second stage as
compared to the dense phase of the first stage, and with reduction
of carbon on catalys-t to about 0.05% or less or even about 0.025% or
less by weight in the second zone. In fact, catalyst can readily be
15 regenerated to carbon levels as low as 0 . 01% by this technique,
even though the carbon on catalyst prior to regeneration is as much
as about 1%.
In most circumstances, it will be important to insure that no
adsorbed oxygen containing gases are carried into the riser by
recycled catalyst. Thus, whenever such action is considered
necessary, the catalyst discharged from the regenerator may be
stripped wi th appropriate stripping gases to remove oxygen
containing gases. Such stripping may for instance be conducted at
relatively high temperatures, for example about 1350 to about
1370F, using s team, nitrogen or other inert gas as the stripping
gas(es). The use of nitrogen and other inert gases is beneficial
from the standpoint of avoiding a tendency toward hydro-thermal
catalyst deactivation which may result from the use of steam.
'X
RI-6049YCA
7~
,
The following comments and discussion relating to
metals managcment, carbon management and heat management may be
of assist~nce in obtaining best results when operating the inven-
tion. Since these remarks are for the most part directed to what
is considered the bes-t mode of operation, it should be apparent
that the invention is no-t limited to the particular modes of
operation discussed below. Moreover, since certain of these
comments are necessarily based on theoretical considerations,
there is no intention to be bound by any such theory, whether
expressed herein or implicit in the operating suggestions set
forth hereinaEter.
Although discussed separately below, it is readily
apparent that metals management, carbon management and heat mange-
ment are inter-related and interdependent subjects both in theory
and practice. While coke yield and coke laydown on catalyst are
primarily the result of the re`latively large quantities of coke
precursors found in carbo-metallic oils, the production of coke is
exacerbated by high metals accumulations, which can also signifi-
cantly affect catalyst performance. Moreover, the degree of
success experienced in metals management and carbon management
will have a direct influence on the extent to which heat manage-
ment is necessary. Moreover, some of the steps taken in support of
metals management have proved very helpful in respect to carbon
and heat management.
As noted previously the presence of a large heavy
metals accumulation on the catalyst tends to aggravate the problem
of dehydrogenation and aromatic condensation, resulting in increased
production of gases and coke for a feedstock of a given Ramsbottom
carbon value. The introduction of substantial quantities of H2O
into the reactor, either in the form of steam or liquid water,
- 55 -
56- ~7~
appears highly beneficial from the standpoint of keeping the heavy
metals in a less harmful form, i . e . the oxide rather than metallic
form. This is of assistance in maintaining the desired selectivity.
Also, a unit design in which sys-tem components and residence
5 -times are selected to reduce the ratio of catalyst reactor residence
time relative to ca-talyst regenerator residence time will tend to
reduce the ratio of the times during which the catalyst is
respectively under reduction conditions and oxidation conditions.
This too can assist in maini:aining desired levels of selectivity.
Whether the metals content of the catalys-t is being manage
successfully may be observed by monitoring the total hydrogen plus
methane produced in the reactor and/or the ratio of hydrogen to
methane thus produced. In general, it is considered that the
hydrogen to methane mole ratio should be less than about 1 and
15 preferably about 0 . 6 or less, with about 0 . 4 or less being
considered about optimum.
Careful carbon management can improve both selectivity, ~the
ability to maximize production of valuable products ) and heat
productivity. In general, the techni~ues of metals control
20 described above are also of assistance in carbon management. The
usefulness of water addition in respect to carbon management has
already been spelled out in considerable detail in that part of the
specification which relates to added materials for introduction into
the reaction zone. In general, those techniques which improve
25 dispersion of the feed in the reaction zone should also prove
helpful; these include for instance the use of fogging or misting
devices to assist in dispersing the feed.
RI - 6049YCA
,~
-57-
Catalyst to oil ratio is also a fac-tor in heat management. In
common with prior FCC prac tice on VGO, the reactor temperature
may be controlled in the practice of the present invention by
respectively increasing or decreasing the flow of hot regenerated
5 catalyst to the reac-tor in response to decreases and increases in
reactor temperature, typically the outlet temperature in the case of
a riser type reactor. Where the automatic controller for catalys-t
in-troduction is set to maintain an excessive catalyst to oil ratio, one
can expect unnecessarily large rates of carbon production and heat
10 release, relative to the weight of fresh feed charged to the reaction
zone .
Relatively high reactor temperatures are also beneficial from
the standpoint of carbon management. Such higher temperatures
foster more complete vaporization of feed and disengagement of
15 product from catalyst.
Carbon management can also be facilitated by suitable
restriction of the total pressure in the reactor and the partial
pressure of the feed. In general, at a given level of conversion,
relatively small decreases in the aforementioned pressures can
20 substantially reduce coke production. This may be due to the fact
that restricting total pressure tends to enhance vaporization of high
boiling components of the feed, encourage cracl~ing and facilitate
disengagement of both unconverted feed and higher boiling cracked
products from the catalyst. It may be of assistance in this regard
25 to restrict the pressure drop of equipment downstream of and in
communication with the reactor. But if it is desired or necessary
to operate the system at higher total pressure, such as for
instance because of operating limitations (e . g . pressure drop in
downstream equipment) the above described benefits may be
30 obtained by restricting the feed partial pressure. Suitable ranges
for total reactor pressure and feed partial pressure have been set
forth above, and in general it is desirable to attempt to minimize
the pressures within these ranges.
~r ~I-6049Y
7~
-58-
The abrupt separation of ca-talyst from product vapors and
unconverted feed (if any) is also of great assistance. It is for this
reason that the so-called vented riser apparatus and technique
disclosed in U.S. Patents 4,070,159 and 4,066,533 to George D.
Myers et al is the preferred type of apparatus for conducting this
process. For similar reasons, it is beneficial to reduce insofar as
possible the elapsed time between separation of catalyst from
product vapors and the commencement of stripping. The vented
riser and prompt stripping tend to reduce the opportunity for
10 coking of unconverted feed and higher boiling cracked products
adsorbed on the catalyst.
A particularly desirable mode of operation from the standpoint
of carbon management is to operate the process in the vented riser
using a hydrogen donor if necessary, while maintaining the feed
partial pressure and total reactor pressure as low as possible, and
incorporating relatively large amounts of water, steam and if
desired, other diluents, which provide the numerous benefits
discussed in greater detail above. Moreover, when liquid water,
steam, hydrogen donors, hydrogen and other gaseous or
20 vaporizable ma-terials are fed to the reaction zone, the feed of these
materials provides an opportunity for exercising additional control
over catalyst to oil ratio. Thus, for example, the practice of
increasing or decreasing the catalyst to oil ratio for a given amount
of decrease or increase in reactor temperature may be reduced or
25 eliminated by substituting either appropriate reduction or increase
in the charging ratios of the water, steam and other gaseous or
vaporizable material, or an appropriate reduction or increase in the
ratio of water to steam and/or other gaseous materials introduced
into the reaction zone.
;~``' RI-6049YCA
,, .
59~ 7~
Heat management includes measures taken to control the amount
of heat released in various parts of the process and/or for dealing
successfully with such heat as may be released. Unlike
conventional FCC practice using VGO, wherein it is usually a
5 problem -to generate sufficient heat during regeneration to heat
balance the reactor, the processing of carbo-metallic oils generally
produces so much heat as to require careful management thereof.
Heat management can be facili tated by various techniques
associated with the materials introcluced into the reactor. Thus,
10 heat adsorption by feed can be maximized by minimum preheating of
feed, it being necessary only that the feed temperature be high
enough so that it is sufficiently fluid for successful pumping and
dispersion in the reactor. When the catalyst is maintained in a
highly active state with the suppression of coking (metals control),
15 so as to achieve higher conversion, the resultant higher conversion
and greater selectivity can increase the heat adsorption of the
reaction. In general, higher reactor temperatures promote catalyst
conversion activity in the face of more refractory and higher boiling
constituents with high coking potentials. While the rate of catalyst
20 deactivation may thus be increased, the higher temperature of
operation tends to offse-t this loss in activity. Higher temperatures
in the reactor also contribute to enhancement of octane number,
thus off-setting the octane depressant effect of high carbon lay
down. Other techniques for absorbing heat have also been
25 discussed above in connection with the introduction of water,
steam, and other gaseous or vaporizable materials into the reactor.
~ RI - 6049YCA
-60~ ~7~
The severe stripping and various regeneration techniques
discussed above are useful in controlling heat release in the
regenerator. While removal of heat from catalyst in or downstream
of the regenerator by means of heat exchangers (including steam
5 coils) has been suggested as a means for controlling heat release,
the above described techniques of multi-stage regeneration and
control over the CO/CO2 ratio (in either single or multi-stage
regeneration) are considered more advantageous. The use of steam
coils is considered to be partly selE-defeating, in that a steam coil
10 or heat exchanger in the regenerator or catalyst return line will
generally cause an increase in the catalyst to oil ratio with a
resultant increase in the rates of carbon production in the reactor
and heat release in the regenerator.
As noted above, the invention can be practiced in the above
15 described modes and many others. Two illustrative, non-limiting
examples are described by the accompanying schematic diagrams in
Figures 1 and 2 and by the descriptions of -those figures which
follow .
Figure 1 is a schematic diagram of an apparatus for carrying
20 out the process of the present invention. The carbo-metallic oil
feed (which may have been heated in a feed preheater not shown)
and water (when used) supplied through delivery pipe 9, are fed
by feed supply pipe 10 having a control valve 11 to a wye 12 in
which they mix with a flow of catalyst delivered through supply
25 pipe 13 and controlled by valve 14. Of course a variety of mixing
arrangements may be employed, and provisions may be made for
introducing the other added materials discussed above. The
mixture of catalyst and feed, with or without such additional
materials, is then introduced into riser 18.
RI - 6049YCA
-61~ 7g~
Although riser 18 appears vertical in the drawing, persons
skilled in the art will recognize that the riser need not be vertical,
as riser type reactors are known in which an appreciable portion of
the riser pipe in non-vertical. Thus, riser pipes having an upward
5 component of direction are contemplated, and usually the upward
component of their upwardly flowing inclined portions is substantial,
i. e. at least abou-t 30 . It is also known to provide risers which
have downwardly flowing inclined or vertical portions, as well as
horizontal portions. Folded risers are also know, in which -there
10 are both upwardly extending and downwardly extending segments.
Moreover, it is entirely feasible to practice the process of the
invention in an inclined and/or vertical pipe in which the feed and
catalyst are in-troduced at an upper elevation and in which the feed
and catalyst moves under the influence of gravity and the down
15 flow of the Eeed to a lower elevation. Thus, in general, the
invention contemplates the use of reaction chambers having a long
L/D ratio and having a significant deviation from horizontal.
At the upper end of the riser 18 is a chamber 19 which
receives the catalyst from the riser. While chamber 19 may be a
20 conventional disengagement and collection chamber, it is preferred
that means be provided for causing product vapors to undergo a
sufficient change of direction relative to the direction traveled by
the catalyst particles, whereby the vapors are suddenly and
effectively separated from the catalyst. Preferably, there is
25 "ballistic" separation of catalyst particles and product vapors as
described above.
In the present schematic diagram, the disengagement chamber
19 includes an upward extension 20 of riser pipe 18 having an open
top 21 through which the catalyst particles are discharged. This
30 embodiment makes use of the so-called vented riser described in the
above-mentioned Myers et al patents.
~ RI-6049YCA
-62~ 7~7~7~
Because of the refractory nature of carbo-metallic fractions,
relatively high severity is required, but -the rapid disengagement of
catalys-t from lighter cracked products in the vented riser prevents
overcracking of desirable liquid products such as gasoline to
5 gaseous products. The product vapors are caused to undergo a
sudden change of direction into lateral port 22 in the side of riser
extension 20, the catalyst particles being, for the most part, unable
to follow the product vapors into port 22.
The vapors and those few particles which do manage to follow
10 them into port 22 are transferred by cross pipe 23 to a cyclone
separator 24. It is an advantage of the vented riser system shown
that it can function satisfactorily with a single stage cyclone
separator. However, in the present embodiment the cyclone
separator 24 is employed as a first stage cyclone separator which is
15 connected via -transfer pipe 17 with optional secondary cyclone
separator 25. The cyclone separator means, whether of the single-
or multi-stage type, separates from the product vapors those small
amounts of catalyst which do enter the lateral port 22. Product
vapors are discharged from disengagement chamber 19 through
20 product discharge pipe 26.
The catalyst particles which discharge from open top 21 of
riser pipe extension 20, and those catalyst particles which are
discharged from the discharge legs 27 and 28 of primary and
secondary cyclones 24 and 25 drop to the bottom of disengagement
RI-6049YCA
-63~ 7~771D
chamber 19. The inventory and residence time of catalyst in
chamber 19 are preferably minimized. During startup those catalyst
particles which are present may be kept in suspension by fluffing
jets 30 supplied wi-th s team -through s team supply pipe 29. Spent
catalyst spilling over from the bottom of disengagement chamber 19
passes via drop leg 31 to a stripper chamber 32 equipped with
baffles 33 and steam jet 34. Any of the other stripping ~ases
referred to above may be employed with or in place of the steam.
Carbon is burned from the surface of the catalyst in the
combustor 38 which receives stripped catalyst via downcomer pipe
39 and control valve 40. Blowers 41 and 42, in association with a
valve and piping arrangement generally indicated by 44, supply air
to combustion air jets 48 at the bottom of the combustor and to
fluffing jets 49 at an elevated position. Air preheater 43, although
usually unused when processing heavy hydrocarbons in accordance
with the invention, may be employed when starting up the unit on
VGO; then, when the unit is switched over to the carbo-metallic
feed, preheater operation may be discontinued (or at least
reduced). Supplemental fuel means may be provided to supply fuel
¢~hrough the combustion air jets 48; but such is usually unnecessary
since the carbon lay down on the catalyst supplies more than
enough fuel to maintain the requisite temperatures in the
regeneration section. Regenerated catalyst, with most of the
carbon burned off, departs the combustor through an upper outlet
50 and cross pipe 51 to a secondary chamber 52, where i-t is
deflected into the lower portion of the chamber by a baffle 53.
Although the use of two stage regeneration is contemplated, and
preferred, in this particular embodiment the secondary chamber 52
was operated primarily as a separator chamber, although it can be
used to remove additional carbon down to about 0.01% or less in the
final stages of regeneration.
~7'
j ¢ RI - 6049YCA
_~4_ ~7S~7~
Catalyst moves in up to three differen-t directions from the
secondary chamber 52. A portion of the catalyst may be circulated
back to combustor 38 via catalyst recirculation loop 55 and control
valve 56 -Eor heat control in -the combustor. Some of the catalyst is
en-trained in the product gases, such as CO and/or CO2 produced
by burning the carbon on the catalys t in -the combustor, and the
entrained catalys-t fines pass upwardly in chamber 52 to two sets of
primary and secondary cyclones generally indicated by 57 and 58
which separate these catalyst fines from the combustion gases.
Catalyst collected in the cyclones 57, 58 and discharged through
their drop legs is directed to the bottom of chamber 52 where
catalyst is kep-t in suspension by inert gas and/or steam jets 59 and
by a baffle arrangement 54, the latter facilitating discharge of
regenerated catalyst through outlet 69 to catalyst supply pipe 13
through which it is recirculated for contact with fresh feed at wyte
12, as previously described.
Combustion product gases produced by regenera-tion of the
catalyst and separated from entrained catalyst fines by the sets 57,
58 of primary and secondary cyclones in chamber 52, discharge
through effluent pipes 61, 62 and heat exchangers 60, 63. As such
gases contain significant amounts of CO, they may be sent via gas
supply pipe 64 to an optional furnace 65 in which the CO is burned
to hea t heating coil 66 connected with steam boiler 67. Additional
heat may be supplied to the contents of the boilers through conduit
loop 68, which circulates fluid from the boiler 67 to heat exchangers
60, 63 and hack to the boiler. This is of course only one example
of many possible regeneration arrangements which may be employed.
The amount of heat passed from the regenerator back to the riser
via regenerated catalyst may be controlled in any of the other ways
described above; but the present invention controls the relative
proportions
RI-6049YCA
65 ~3~7~77~
of carbon monoxide and carbon dioxide produced while the catalyst
is in heat exchange relationship with the combus-tion gases resulting
from regeneration. This same technique is also involved in the
particularly preferred embodiment described in Figure 2.
In Figure 2 reference numeral 80 identifies a feed con-trol
valve in feedstock supply pipe 82. Supply pipe 83 (when used)
introduces liquid water into the feed. Heat exchanger 81 in supply
pipe 82 acts as a feed preheater, whereby preheated feed material
may be delivered to the bot-tom of riser type reactor 91. Catalyst
is delivered to the reactor through catalyst standpipe 86, the flow
of catalyst being regulated by a control valve 87 and suitable
automatic control equipment (not shown) with which persons skilled
in the art of designing and operating riser type crackers are
familiar .
The riser 91 may optionally include provision for injection of
water, steam and, if desired, other gaseous and/or vaporizable
material for the purpose described above. The reactor is equipped
with a disen~agement chamber 92 similar to the disengagement
chamber 19 of the reactor shown in Figure 1, and the Figure 2
embodiment thus includes means for causing product vapors to
undergo a change of direction for sudden and effective separation
from the catalyst as in the previous embodiment. Catalys-t departs
disengagement chamber 92 -through stripper 94 which operates in a
manner similar to stripper 32 of Figure 1. Spent catalyst passes
from stripper g4 to regenerator 101 via spent catalys-t transfer pipe
97 having a slide valve 9û for controlling the flow.
Regenerator 101 is divided into upper chamber 102 and lower
chamber 103 by a divider panel 104 intermediate the upper and
lower ends of the regenerator. The spent catalyst from -transfer
pipe 97 enters upper chamber 102 in which -the
'~
~ RI-6049Y
66 ~ ;77~
catalyst is partially regenerated. A funnel-like collector 106 having
a bias-cut upper edge receives partially regenerated catalyst from
the upper surface of the dense phase of catalyst in upper chamber
102 and delivers it via drop leg 107 having an outlet 110 beneath
5 the upper surface of the dense phase of catalyst in lower
regeneration chamber 103. Instead of -the internal catalys-t drop leg
107, one may use an e~ternal drop leg. Valve means in such
external drop leg can control the catalyst residence time and flow
rate in and between the upper and lower chambers.
Air is supplied to the regenerator through an air supply pipe
113. A portion of the air travels through a branch supply pipe 114
to bayonet 115 extending upwardly in the interior of plenum 111
along its central axis. Catalyst in chamber 103 has access to the
space wi-thin plenum 111 between its walls and -the bayonet 115. A
15 small bayonet (not shown~ in the aforementioned space fluffs the
catalyst and urges it upwardly toward a horizontally arranged ring
distributor (not shown) where the open top of plenum 111 opens
into chamber 103. The remainder of the air passing through air
supply pipe 113 may be heated in air heater 117 (at least during
20 start-up with VGO) and is then introduced into the inlet 118 of the
aforementioned ring distributor, which may be provided with holes,
nozzles or other apertures which produce an upward flow of gas to
fluidize the partially regenerated catalyst in chamber 103.
The air introduced in the manner described above completes in
25 chamber 103 the regeneration of the partially regenerated catalyst
received via drop let 107. The amount of air that is supplied is
sufficient so that the air and/or the resultant combustion gases are
still able to support combustion
~^~ RI-6049YCA
-67- ~ t77~
upon reaching the top of chamber 103. The aforementioned drop
leg 107 extends through an enlarged aperture in panel 104, to
which is secured a gas distributor 120 which is concentric with and
surrounds the drop leg. Via gas distributor 120, combustion
5 supporting gases, which have now been partially depleted of
combustion support gas, are introduced into the upper regenerator
chamber 102 where they contact for purposes of partial oxidation
the incoming spent catalyst from spent catalyst transfer pipe 97.
Apertured probes 121 or other suitable means in gas distributor 120
10 assist in achieving a uniform distribution of the partially depleted
combustion supporting gas in upper chamber 102. Supplemental air
or other fluids may be introduced into upper chamber 102, if
desired through supply pipe 122, which discharges into or through
gas distributor 120.
~ully regenerated catalyst with less than about 0.25% carbon,
preferably less than about 0.1% and more preferably less than about
0.05%, is discharged from lower regenerator chamber 103 through a
regenerated catalyst stripper 128, whose outlet feeds into the
catalyst standpipe 86 mentioned above. Thus, regenerated catalyst
20 is returned to riser 91 for contact with additional fresh feed from
feed supply pipe 82. Whatever heat is introduced into the recycled
catalyst in the regenerator 101 is available for heat transfer with
the fresh feed in the riser.
The division of the regenerator into upper and lower
25 regeneration chambers 102 and 103 not only smooths out variations
in catalyst reyenerator residence time but is also uniquely of
assistance in restricting the quantity of regeneration heat which is
imparted to the fresh feed while yielding a regenerated catalyst
with low levels of residual carbon for return to the reactor.
... .
- ` RI-6049YCA
-68~
Because of the arrangement of the regenerator, the spent catalyst
from transfer line 97, with its high loading of carbon, contacts in
chamber 102 combustion supporting gases which have already been
at least partially depleted of oxygen by the burning of carbon from
partially regenerated catalyst in lower regenera-tor chamber 102.
Because of this, it is possible -to control both -the combustion and
the quantity of carbon dioxide produced in upper regenerator
chamber 102. Although the air or other regenerating gas
introduced through air supply pipe 113 and branch conduit 114 may
contain a relatively large quantity of oxygen, the partially
regenerated catalyst which they contact in lower regenerator
chamber 103 has already had part of its carbon removed. The high
concentration of oxygen and the temperature of the partially
regenerated catalyst combine to rapidly remove the remaining carbon
in the catalyst, thereby achieving a clean regenerated catalyst with
a minimum of heat release. Thus, here again, the combustion
temperature and the CO:CO2 ratio in the lower regeneration
chamber are therefore readily controlled. The regeneration off
gases are discharged from upper regenerator chamber 102 via off
gas pipe 123, regulator valve 124, catalyst fines trap 125 and outlet
126.
The vapor products from disengagement chamber 92 may be
processed in any convenient manner such as for example, by
discharge through vapor discharge line 131 to the inlet of
fractionator 132. Said fractionator includes a bottoms outlet 133,
side outlet 134, flush oil stripper 135, and stripper bottom outlet
and discharge line 136 connected to pump 137 for discharging flush
oil. The overhead product from stripper 135 is routed via stripper
overhead return line 138 to the fractionator 132.
~, RI-6049YCA
-6g- ~ 7~3
The main overhead discharge line 139 of the fractionator is
connected to overhead receiver 142 having a bottoms discharge line
143 feeding into pump 144 for discharging gasoline product. If
desired, a portion of this product may be sent via recirculation
line 145, the flow being con trolled by recircula tion valve 146,
back to the fractionator 132. The overhead receiver also includes
a water receiver 147 and a water discharge line 148. The gas
outlet 150 of the overhead receiver discharges a stream which
is mainly below C5, but containing some C5, C6 and C7 material
If desired, the C5 and above material in this gas stream may be
separated by compression, cooling and fractionation and recycled to
the overhead receiver with a compressor, cooler and fractionator
~not shown).
RI-6049Y
,
~7~7~
-70-
EXAMPLES
The following examples are given only by way of illustration
and not for limiting the invention. Data on the catalysts employed
herein is provided in Table 2 above.
Heretofore commercial practice in some refineries has included
the blending of relatively small quantities of carbo-metallic oils with
the vacuum gas oils commonly used as feedstock for fluid cataly-tic
cracking. It should be emphasized however -that the usual prac-tice
was to restrict the quantities of carbo-metallic oil in such blends in
order -to provide a feedstock which was characterized by relatively
low levels of nickel equivalents of heavy metals and by relatively
low levels of carbon residue on pyrolosis. Quite unexpectedly
however, it appears that the level of conversion of the
carbo-metallic oils is grea-ter when such oils are employed in
sufficient amounts so that the nickel equivalents of heavy metals
and the carbon residue are at the relatively higher levels taught
herein, such as for example when the quantity of carbo-metallic oil
ranges from a major weight proportion up to substan~:ially all of -the
hydrocarbon cracking reactant in the feedstock.
EXAMPLES lA - lD
These examples employ the unit substantially as depic ted in
Figure 1 and as described in the accompanying text. Examples lA
- 1 C illustrate operation with blends containing different relative
amounts of vacuum gas oils (VGO) and reduced crudes. Examples
25 lC and lD compare operation with a blend versus operation with
100% reduced crude. For analyses of the vacuum gas oils and
red-uced crudes, refer to Table 3 which follows. For the unit
operating conditions and tabula-tion of results refer to Table 4
below .
-~ RI-6049YCA
Comparison of Results of Examples lA and lB
At a -temperature in the range of about 975-980F, the unit
employed herein is known to produce a conversion level of about
78% when operating with equivalent catalyst on VGO similar to the
vacuum gas oils illus trated in Table 3 . A comparison of the data
from Examples lA and lB will show that if the vacuum gas oil in
each blend is assumed to have converted at the previously
established rate of 78%, the reduced crude which was present in a
lower proportion (about 40%) in the run of Example lA was
converted to the extent of only about 44%, whereas in the
processing of the blend containing a higher proportion of reduced
crude (about 66%) shown in Example lD, a 63% conversion of the
reduced crude was achieved. Note also the increase in volume
yield. Thus, the invention can ~e operated to produce higher
conversion of the reduced crude and/or higher volume yield at very
adequate octane levels when the reduced crude is charged in
blends, as compared to blends having substantially larger amounts
of VGO and substantiaily smaller amounts of reduced crude.
Comparison of Results of Examples lC and lD
A comparison of the data from Example lC and lD will show
that if the VGO in the blend of 5 :xamples lC is assumed to have
converted at the previously established rate of 78%, then the
reduced crude was converted to the extent of only about 58% when
it constituted about 42% of the feedstock, whereas it was converted
to a level of about 64% when it represented 100% of the feedstock.
Note again the increase in volume percent yield. Thus, the
invention can be operated in such a manner as to provide higher
conversion of reduced crude and/or increased volume percent yield
of liquid products at very adequate octane levels when the reduced
crude is charged alone as compared to a blend of reduced crude
with VGO.
RI-6049YCA
-72-
EXAMPLES 2 & 3
Using as feedstock the reduced crude of Example lD, shown in
Table 3, a unit constructed in accordance with Figure 1 was
operated in accordance wi-th the portion o the text relating to
5 Figure 1 and in accordance with the conditions set forth in Table 4,
giving the results indicated in Table 4.
EXAMPLES 4 - 6
These examples were conducted with a unit constructed in
accordance with the teachings of Figure 7! and the related text.
10 Upon operating the unit in accordance with said text and the
conditions set forth in Table 4, employing regeneration in two
stages, results were obtained as reported in Table 4.
EX~MPLES 7 - 10
These examples were conducted in a pilot scale unit using
15 feedstock, catalyst and operating conditions as shown in Tables 1,
2 and 4. Figures 3-5 o the drawings show the yield in volume
percent of (3) C3 olefins, (4) C4 saturates and olefins, and (5)
gasoline, respectively versus volume percent conversion, obtained
through use of the feeds and catalysts of Examples 7-10 repeated a-t
20 various levels.
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