Note: Descriptions are shown in the official language in which they were submitted.
1 BACKGROUND OF THE INVENTION
The invention is concerned wi~h increasing the portion
of heavy petroleum crudes which can be utilized as catal-ytic
cracking feedstock to produce premium petroleum products, particularly
motor gasoline of high octane number. The heavy ends of many crudes
are high in Conradson Carbon and metals which are undesirable in
catalytic cracking feedstocks. The present invention provides an
economically attractive method for utilizing the residues of
atmospheric and vacuum distillations, commonly called atmospheric
and vacuum residua or "resids." The undesirable CC (for Conradson
Carbon) and metal bearing compounds present in the crude tend to be
concentrated i~ the resids because most of them are o~ high boiling
point.
When catalytic cracking was first introduced to the
petroleum industry in the 1930's, the process constituted a major
advance in its advantages over the previous technique for increasing
the yield of motor gasoline from petroleum to meet a fast-growing
demand for that premium product. The catalytic process produces
abundant yields of high octane naphtha from petroleutn fractions boilLng
above the gasoline range, upwards of about ~}00F. Catalytic cracking
has been greatly improved by intensive research and development efforts
and plant capacity has expanded rapidly to a present-day status
:ln which the catalytic cracker is the dominant unit, the workhorse"
oE a petrole~lm reflnery.
25~8 Lnstalled cayaci~y oE catalytic crackLng has Lncreasecl,
there has been Lncreaslng pressure to charge to those unlts greater
proportlons oE the crude enterlng the refinery. 'L~o very efEectlve
restraLnts oppose that pressure, name:Ly Conradson Carbon and metals
content of the feed. ~s these values rlse, capaclty and eEflciency
of the catalytic cracker have been adversely affected.
i
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, - 2 -
::'
1 The effect of higher Conradson Carbon is to increase the
portion of the charge converted to "coke" deposited on the catalyst.
As coke builds up on the catalyst, the active surface of the
catalyst is masked and rendered inactive ~or the desired conversion.
It has been conventional to burn off the inactivating coke with air
to "regenerate" the active surfaces, after which the catalyst is
returned in cyclic fashion to the reaction stage for contact with
and conversion of additional charge. The heat generated in -the
burning regeneration stage is recovered and used, at least in part,
to supply heat of vaporization of the charge and endothermic heat
of the cracking reaction. The regeneration stage operates under a
maximum temperature limitation to avoid heat damage of the catalyst.
Since the rate of coke burning is a function of temperature, it
follows that any regeneration stage has a limit of coke which can
be burned in unit time. As CC of the charge stock is increased,
coke burning capacity becomes a bottleneck which forces reduction
in the rate of charging feed to the unit. This is in addition to
the disadvantage that part of the charge has been diverted to an
undesirable reaction product.
~etal bearing fractions contain, inter alia, nickel and
- vanadium which are potent catalysts for production of coke and hydrogen.
These metals, when present in the charge, are deposited on the
catalyst as the mo:Lecule6 ln w~llch they occur are crackecl and tencl
to buL:Lcl up to leve:ls whlch become very trouble60tne. The adver~e
efeects O.e increa~ed coke are as revlewed above. The lighter
end~ o~ the cracked product, butcme and llghter, are processed through
fractlonatlon equlpment to separate components of value greater
than fuel to furnaces, prlmarily propane, butane and the olefins
of llke carbon number. ~Iydrogen, being incondensible in the "gas
plant", occupies ~pace as a gas in the compression and fractionation
1 train and can easily overload the system when excessive amounts are
produced by high metal content catalyst, causing reduction in charge
rate to maintain the FCC unit and auxiliaries operative.
These problems have long been recognized in the art and
many expedients have been proposed. Thermal conversions of resids
produce large quantities of solid fuel (coke) and the pertinent
processes are characterized as coking, of ~hich two varieties are
presently practiced commercially. In delayed colcing, the feed is
heated in a furnace and passed to large drums maintained at 780 to
840F. During the long residence time at this temperature, the
charge is converted to coke and distillate products taken off the
top of the drum for recovery of "coker gasoline", "coker gas oil"
and gas. The other coking process now in use employs a fluidized
bed of coke in the form of small granules at about 900 to 1050F.
The resid charge undergoes conversion on the surface of the coke
particles during a residence time on the order of two minutes,
depositing additional coke on the surfaces of particles in the
fluidized bed. Coke particles are transferred to a bed fluidized by
air to burn some of the coke at temperatures upwards of 1100F.,
thus heating the residual coke whlch is then returned to the
coking vessel for conversion of additional charge.
These coking processes are known to induce extensive
cracking of components which would be valuable for catalytic
crackLng charge, resultLng in gaGollne of lower octaine number
(Erol~ thermal cracklrlg) I:han woul~ be obtaLnecl by catalytLc
; crackLng of the same componellts. The gas olls produced are oleflnic,
i containing slgnLeLcanl: amounts of cZ:Lole~:Lns which are prone to
degradat:Lon to colce ln furnace tubes and on cracking catalysts.
It :Is often desirable to treat the gas oils by expensive hydro-
genation techniques before charging to catalytlc cracking. Coking
~6~
1 does reduce metals and Conradson Carbon but still leaves an inferior
gas oil for charge to catalytic cracking.
Catalytic charge stock may also be prepared from resids
by "deasphalting" in which an asphalt precipitant such as liquid
propane is mixed with the oil. Metals and Conradson Car~on are
drastically reduced but at low yield of deasphalted oil.
Solvent extractions and various other techniques have been
proposed for preparation of FCC charge stock from resids. Solvent
extraction, in common with propane deasphalting, functions by
selection on chemical type, rejecting from the charge stcck the
~ aromatic compounds which can crack to yield high octane components
;~ of cracked naphtha. Low temperature, liquid phase sorption on
catalytically inert silica gel is proposed by Shuman and Brace,
; OIL AND GAS JOURNAL, April 16, 1~53, Page 113.
Of the types of catalytic cracking systems, the one of
greatest present interest in Fluid Catalytic Cracking (FCC). The
installed plants of this type are characterist-Lcally large, and
usually designed to process from about 5,000 to 135,000 bbls/day
of fresh feed. Briefly, the catalyst section of the plant consists
of a cracking section where a heavy charge stock is cracked in
contact with fluidized cracking catalyst, and a regenerator section
where fluidized catalyst coked in the cracking operation is
regenerated by burning with air. ~11 of the plants utilize a relatively
large Lnventory of cracking catalyst whlch ls contin1l0usly ci.rcu:Latlng
between the cracklng and regenerator ~ectLons. Tlle s:lze of thia
clrcll:LatLng lnventory ln exlstlng plants is withln the range of 50
to 600 tons, the newer plants belng ~es:Lgned for short tlme rlser
cracklng w:Lth smaller catalyst inventory than that ln old~r plants.
Because the catalytlc activLty of the clrculatlng inventory
of catalyst tends to decrease with age, fresh makeup catalyst usually
5 _
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~;
,,
~..f~
1 amounting to about one to two percent of the circulating inventory,
which corresponds to about 0.1 to 0.25 lbs. per bbl. of fresh feed, is
added per day to maintain optimal catalyst activity, with daily
withdrawal plus losses of about like amount o aged circulating
inventory, commonly referred to as "equilibrium" catalyst. The
considerations which are involved in setting catalyst makeup policy
are adequately reviewed in "Dynamic Optimi~ation of Catalyst Make-Up
Rate for Catalytic Cracking Systems" W. Lee, Ind. Eng. Chem. Process
Des. Development, Vol. 9, No. 1, pp. 154-158 (Jan. 1970). That
article pro~ides equations of state and an algorithm for optimizing
the makeup rate.
In general, the oils fed to this process are principally the
petroleum distillates commonly known as gas oils, which boil in the
temperature range of about 650F. to 1000F~, supplemented at times by
coker gas oil, vacuum tower overhead, etc. These oils generally have
an API gravity in the range of about 15 to ~5 and are substantially
free of metal contaminants.
The charge stoc~, which term herein is used to refer to the
total fresh feed made up of one or more oils, is cracked in the
reactor section in a reaction zone maintained at a temperature of
about 800F. to 1200F., a pressure of about 1 to 5 atmospheres, and
with a usual residence time for the oil of from about one to ten
seconds with a modern short contact time riser design. The catalyst
residence tLme 1~ from about one to flfteen seconds. 'rhe crackecl
product~3 are separated Erom the coked catalyst and passed to a maln
dLstillatlon tower where separatlon of gases and recovery oE gasoline,
fuel oll, and recycle stock Ls efEected.
Petroleum refiners usually pay close attention in the
fluld catalytic cracking process (hereinafter referred to as the
i -6-
i'';~'l
.
1 FCC process) to supplying feedstocks substantially free oE metal
contaminants. The reason for this is that the ~etals present in
the charge stock are deposited along with the coke on the cracking
catalyst. Unlike the coke, however, they are not removed by
regeneration and thus they accumulate on the circulating inventory.
The metals so deposited act as a catalyst poison and, depending on
the concentration of metals on the catalyst, more or less adversely
affect the efficiency of the process by decreasing the catalyst
activity and increasing the production of coke, hydrogen and dry
gas at the expense of gasoline and/or fuel oil. Excessive accumula-
tion of metals can cause serious problems in the usual ~CC operation.
For example, the amount of gas produced may exceed the capacity of
the downstream gas plant, or excessive coke loads may result in
regenerator temperatures above the metallurgical limits. In such
cases the refiner must resort to reducing the feed rate with
attendant economic penalty. Thus, a catalyst inventory that
contains excessive deposits of metal is normally regarded as
highly undesirable.
The principal metal contaminants in crude petroleum oils
are nickel and vanadium, although iron and small amounts of copper
also may be present. Additionally, trace amounts of zinc and sodium
are sometimes found. It is known that almost all of the nickel and
vanad:ium in crude oils is assoclated with very large nonvolatile
hyclrocrlrbon mol.ecules, suctl as metrl:L porphyrln~ ~md rlsphalteneo.
~5 Crude c;l:ls, oE course, vary Ltl metaL conten~, but usua:Lly thLs
cOnteQt Ls Elubstantial. An Arrlb Light whole crude, for example,
n~ay assay 3.2 ppm (l.e. parts by weL~,ht of metal per m^llLlon
parts of crude) of nickel and 13 ppm of vanadLum. A typlcal K~ait
whole crude, generally considered oE average metals content~ may
assay 6.3 ppm of nickel and 22.5 ppm of vanadium. Regardless of
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1 the crude source, however, it is known that distillates produced from
the crude are almost free of the metal contaminants which concentrate
in the residual oil fractions.
Petroleum engineers concerned with the FCC process have
several ways for referring to the metal content of a charge stock.
One of these is by reference to a "metals factor", designated F .
The factor may be expressed in equation form as follows:
F = ppm Fe + ppm V ~ 10 (ppm Ni f ppm Cu)
A charge stock having a metals factor greater t~an 2.5 is
10 considered indicative of one which will poison cracking catalyst
to a significant degree. This factor takes into account that the
adverse effect of nickel is substantially more than that of vanadium
-` and iron present in equal concentrations with the nickel.~ ;
; Another way of expressing the metals content of a char~e
stock is as "ppm Nickel Equivalent" which is defined as
ppm Nickel Equi~alent = ppm nickel + 0.25 ppm
.~
vanadium ;,
For the purpose of this specification, the value of ppm Nickel Equivalent
will be used in discussing metals content of metal-contaminated oils,
distillate stocks, and catalysts. As shown above, no mention is
made of copper because this metal usually is not present to any
significant extent. Eowever, it is to be understood herein that
i~ it is present in significant concentration, it is to be included
:Ln the comp~ltation of Nickel Equivalent and weighted as nickel.
~ 25 It lf~ current practlce Ln FCC technology to control the
! I metals content of the charge stock so that it does not exceed about
0.25 ppm Nickel Equivalent. Catalyst makeup is managed to control
the activity of the circulating inventory. With thls practice, for
example, in a plant utilizing 50,000 bbl/day of fresh feed, and an
equilibrium catalyst withdrawal of 9 tons per day, the withdrawn
:.
~ - 8 -
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: :.: . : , : : -
- :,
- . .. .
1 catalyst under steady state conditions will contain about 300 ppm
Nickel Equivalent of metals, taking into account that the fresh
catalyst contributes 70 ppm to this value. Thus, the circulating
inventory is maintained at about 300 ppm Nickel Equivalents of metal,
which is considered tolerable, the usual range being at about 200
to 600 ppm, with preferred operation being at about 200 to ~00 ppm.
It is to be understood, of course, that the metals content of the
charge stock may vary from day to day without serious disruption,
provided that the weighted average of the metals content does not
exceed about 0.25 ppm nickel equivalent of metal.
It is important, for the purpose of the present invention,
to understand that all references to the metals content of an oil,
or of a charge stock, refer to the time weighted average taken over a
substantial period of time such as one month, for example. ~ecause
of the large inventory of cata~yst relative to the total metals
introduced into the system by the charge stock in one day, for example,
the metals content of the catalyst changes little each day with
fluctuations in the quality of the charge stock. However, a persistent
increase in the metals content of the latter will in time result in
a well-defined, calculatable increase in the metals content of the
circulating inventory of catalyst, which determines the performance
of the FCC unit. In fact, it is evident that the circulating
inventDry of cataLyst, by its metal content, provides a tLme-
nverage value Oe the meta1s content Oe the charge stock. tt is ln
thls context, thenl that the phrase "metals content of the charge
stock" ls ~Isecl herein.
For the purpose oE thls In~ent:Lon, char~e stocks t:o the FCG
process that contain up to about 0.~0 ppm Nickel Equivalent of metal
contamlnants will be regarded as substantially free of metal contami-
nants. Charge stocks that contain at least about 0.50 ppm Nickel
~ _ 9 _
.: .
1 Equivalents of metal will include those charge stocks referred to as
metal-contaminated.
The effects oE nickel9 vanadium and other heavy metals on
- activity and selectivity of FCC catalysts are discussed in detail
by Cimbalo, Foster and Wachtel in a paper presented at the 37th
midyear meeting to the API Division of Refining under the title
"Deposited Metals Poison FCC Catalyst" and published at pages
113 - 122 of the Oil and Gas Jourllal for May 15, 1972. Those
authors show that metal contaminants of cracking catalyst decline
in poisoning activity through repeated cycles of oxidation and
reduction and propose a value of "effective metals" determined
by multiplication of actual metal concentration by a fraction related
to the rate of fresh catalyst makeup as percent of catalyst inventory. -~
Although the authors note that different cracking catalysts may
respond difEerently to metal poisoning and that differences in
operation of the regenerator may affect rate of metal deactivation,
they establish a single standard for determination of "effective
metal" values to be applied generally, presumably having regard to
specific catalyst and operating conditions.
The residual fraction of single stage atmospheric
distillation or two stage atmospheric/vacuum distillation also
contains the bulk of the crude components which deposit as resinous or
tar-like bodies on crackLng catalysts without substantial conversion.
These are Ereq~ently reEerred to as "Conradson Carbon" Eroln the
nnnLytical technique oE deterlnirling theLr concentratLon -Ln petroLe~lm
Eractlons. The CLmbalo article above cited classLELes colce on spent
catalyst in four groups: catalytic coke resulting Erom craclcing oE
charge components; cat-to-oil, related to reactor strlpper efElciency;
carbon residue (Conradson) as just discussed; and contaminant coke
--10~
.,
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l derived from dehydrogenation reactions promoted by the heavy metal
poisons nickel, vanadium, etc. The resldual stocks not only provide
metal poisoning of the catalyst but also show high Conradson Carbon
values which are reflected by coke of that class very nearly equal
to the Conradson Carbon Number. It will be seen that the increment
of Conradson Coke results from deposition on the catalyst of non-
volatile hydrocarbons in the charge without significant change in
nature of the deposited hydrocarbons.
With very limited exceptions, residual oils have not been
successfully included in the charge stocks to the FCC process. The
reasons for this are not fully understood, although from the foregoing
discussion it is apparent that their high metals content is certainly
a major contributing factor, as is the typically high Conradson Carbon.
~There has been interest in using them, however. The reason for this
- 15 interest becomes apparent when we consider, for example, that typically
only about 26 volume % of an Arab light whole crude is the 650-1000F.
gas oil fraction, while the total 650F. plus resid constitutes about 43
volume %. Thus, were it feasible to efficiently operate with residual
oil fractions, a very substantial increase in the amount of gasoline
plus fuel oil derivable from a barrel of crude could be obtained. In
some refineries, the vacuum resid remaining after the distillation
of the gas oil is coked and the coker gas oil is included in the
~CC charge stock. Ilowever, it is generally recognized that coker gas
oLI, because oE lts higtl unsaturated ancl high aromatics content, is
a poor quallty Eeed.
-Lt has been proposed Ln t~e pr:Lor art to hydrotrelt
residual o:Lls uncler such condltions that the metals content is brought
into the range commonly assocLated with gas olls. Such hydro~reated
residual oils, substantially free of metal contaminants, may then
be used as charge stock or a component thereof for the FCC process.
1 Processes to achieve such metals and sulEur reduction are disclosed
in U.S. Patent 3,891,541~ issued June 24, 1975 and U.S. Patent
3,876,523, issued April 8, 1975, for example. The combination of
hydrotreating to reduce metals and sulfur content followed by cracking
also is disclosed in a publication by Hildebrand et al. in the
Oil and Gas Journal, pp. 112-124, December 10, 1973. However, no
installation is known which has adopted the proposed scheme, probably
because the cost and severity associated with the operation involves a
heavy economic penalty.
The concurrent problems of heavy metal and Conradson Carbon
content oE heavy stocks have been approached by the ex~edient of
catalyst modification. Patent 3,944,482 proposes a cracking catalyst
of active aluminosilicate zeolite dispersed in a matrix of large pore
refractory inorganic oxide. The patentee suggests that the tendency
~; 15 of the metals to deposit in large pore structures renders the matrix a
sacrificial componellt which protects the active zeolite cracking
surfaces of the zeolite from metal contamination. The eEfectiveness
of large pore structures in adsorbing and/or converting metal bearing
; components oE crude is widely recognized. Many hydrotreating
catalysts are preferably prepared by deposit of a ~roup VI metal with
nickel or cobalt on a large pore alumina or the like. See also Patent
3,947,347 on demetallizing petroleum fractions in admixture with
; hydrogen over a large pore catalyst without added hydrogerlatlon meta]
catalysts and patenta 2,472,723 and ~,006,077.
Whether or not the charge stock contains heavy metaLs,
activLty oE the catalyst ad~led as makeup has a proEound eefect on
operatLon of an FCC Unit and Ls arl important eactor consLdered by the
reElner in order to accomplish his ob~ectives. tt is usual to
-12-
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.. ~.
< 1 consider crack:ing catalysts in terms of capability to produce gasoline.
This takes no account of the very significant proportion of catalytic
cracking capacity in refineri.es producing only minor gasoline yields.
In a market having a small. demand for gasoline as compared with the
5 demand for light distillate fuels (No. 2 heating oil, jet fuel, diesel
fl~el, kerosene) FCC Units are opera~ed to minimize gasoline and maximize
the distillates boiling above gasoline. Such units will genera].ly
employ a catalyst of rela-tively low activity. To meet the demand for
catalysts of various activity levels, catalyst manufacturers stand
10 prepared to deliver different grades of catalyst over a range of
activities. One way to accomplish this without conducting manufacturing
~ operations in accordance with a large number of schemes is to manu-
: facture one or a few different catalysts of differing activity. Inter-
mediate grades are conveniently achieved by blending substantially inert
15 particles of like ~luidization properties with an active fluid catalyst
to thereby provide a total catalyst of lower activity than the active
portions. By all these techniques including blending as in patent
2,455,915 and the inert, large pore matrix of patent 3,9447482, the
refiner has at hand a catalyst of fixed activ:ity which he adds to
; 20 his unit in order to maintain an equilibrium activity according to the equation:
AF = AE(5+K)
where ~ i8 activity of fresh catalyst
25~ Ls equ:llibrlulll activlty o:~ the total cal:alyst inventory
l.n the ~n~:Lt
S :l.~ the rate o:E makellp :Ln percentage of total inve.ntory
per clay
1~ is a constant representing rate of catalyst deactl.vation
30This is essentially equation (15) of the Lee article cited
above, which see for derivation and more detalled explanat.ion of terms.
- 13 -
~ .
1 It will be apparent that activity is a relative term, the absolute value
of which is dependent on the test procedure. In this specification,
"activity" refers to the value determined by a micro-activity test (MAT)
conducted by cracking a Mid-Continent Gas Oil of the following properties:
Gravity, API 27.9
CCR, Wt. % 0.23 ~ :
Sulfur, W~. % 0.6
Initial Boiling Point, F. 482
50% Point 749
90% Point 979
The cracking test is conducted by contacting 1.2 grams of -~
the gas oil with 6.0 grams of catalyst (c/o = 5) at 910F. and feed
time of 96 seconds for WES~ of 7.5. The liquid product is distilled
and "conversion" is reported as 100 minus weight per cent based on
15 feed of liquid product boiling above 421~F. Activity is then calculated
!
as
= conversion
00 - conversion
Methods are known to the art for preparing cracking catalysts
of very low activities such as severely steamed amorphous silica-alumina
, 20
of activity at 1 or less to very high activ:Lties above 20 such as highly
active alumino-silicate zeolites. See patent 3,493,519. Such catalysts
of very high activity have not come to the market because existing
equipment for catalytic cracking is not capable of utilizing the activity,
I hence no refiner wlll pay the higher price whlch must be charged in view
i 25
o~ the hlgh production cost.
In .summary, the refiner who presently wishefl to charge residual
tocks is compelled to ad~ust hls operatlon~ to the opt:Lon3 avallable to
hlm. The catalyst makeup rate to his ca~alytic cracker is determined
by the activi.ty considerations spelled out in the Lee article. To avoid
adverse effects of metals deposited on the catalyst, the refiner
,`,
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hydrotreacs the resid, sends it to a coker or deasphalter or lives with
the problem of metal on cracking caealyst of whatever fr~sh activity
he selects.
SU~ RY OF T~IE, INVE~TION
A techniqlJe for operation of catalytic cracking equipment
is now provided whieh decouples ~intenanee of equilibrium activity
from management of the metals problem. This is accomplished by a
catal~;st makeup policy for concurrent addition to the unit of two
inventory eomponents, namely an active cracking catalyst and a large
pore inert solid for selective acceptance of the large molecules
characteristic of metal and Conradson Carbon content of the charge.
Instead of following the eonventional teehniques of calculating the
amount of fresh catalyst required for maintenance of equilibrium
activity or as modified by Lee to consider deaetivation rate of catalyst,
the system of this invention is based on determination o~ a makeup
rate whicll wlll maintain a desired metals level on total inventory
inelu~ing fresh catalyst, partially deactivated eatalyst, eompletely
deactivated catalyst (essentially inert porous solids of small pore
si~e) and catalytically inert material of large pore size character-
istie of praetiee of the inven~ion. When charging residual stocks,
the ma~eup rate so determined will be unconventionally high, say
upwards of 10~ of inventory per day. The aetivity of eatalyst required
to maintain equi]ibrium aetivity is then ealeulated by the equation
ahove. 'I'he mLt i9 then supplit-.d wi~h a q~lantlty of aetive e~talyst
alld a quantLty Oe large pore Lnert solid such ~.hat blend of the two
exhibits the desiretl ~etlvlty and quantity of the two satisfles the
malcellp ra~e for metals leveL mnlntenanee.
Thus, in aeeorclanee wlth the present invention there :Ls
provided in a proeess for catalytie eraeking of a meta]-eontaining
hydroearbon ~harge by contacting the eharge at eracking temperature with
a particle form solid craeking eatalyst whereby components of the charge
.
- ~5
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., .
:-. , - ' ' : '
are converted to lower boiling hydrocarbons with concurrent deposition
on the catalyst of metals from the charge and of an inactivating
carbonaceous contamlnant, regenerating catalytic cracking activity of
the contaminated catalyst by burning carbonaceous deposit therefrom while
retaining metals deposited on the catalyst, and contacting catalyst so
regencrated with additional such charge, whereby the catalyst
accumulates metal to detriment of the cracking reaction and declines
.~ in re~enerated activity over repeated cycles of charge contact and
regeneration; the average activity and metals content of the catalyst
inventory being maintained at substantially constant equilibrium values
: by replacing a portion of the catalyst inventory with fresh ca~alyst
of activity above and metals content belo~ said equilibrium values;
the improvement whereby said equilibrium values of
activity and metals content are decoupled for separate
-~ control which comprises replacing a portion of said
catalyst as aforesaid by fresh active cracking catalyst
and a large pore inert solid at a rate to maintain said
equilibrium metal value, the total quantity of said
resh catalyst and said inert solid per unit of time being
substantially equivalent to total metal input with said
charge per unit of time divided by said equilibrium metal
value, said total quantity having a cracking activity
~F determined by the equation,
AF = ~E(S~K)
S
where ~E ls saLd activity equilibrium value
S ls sa.id total qu;ltltity per urllt oE tlme., ancl
:Ls a constant represel~ting rate of decay of catalytic
activity;.
the fraction of said fresh catalyst in said total quantity
bei~g substantially equivalent to ~ divided by the activity
of said fresh catalyst.
- 15a
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~L26~
DESCRIPTION OF SPECIFIC EMBODIMENTS
The p~ocess of this invention contemplates an embodiment in
which an FCC Unit is operated at unconventionally high levels of metal
.i, :
~ , :
;
'''~' :
'
,:
::
- 15b
''',"','1:
,~
,. , - . , . ~ :
, . - , ~:
r~
1 on the circulating inventory of catalyst and inert material, herein-
after called "catalyst inventory" for simplicity despiLe the Eact that
it contains a high proportion of material not usually considered to be
catalyst. Alternatively, the metals content of the catalyst inventory
may be held at leve]s more usual in the art. ~tUS the invention makes
available to the refiner a broad scope of operation from metals levels
in the neighborhood of 2 wt % on catalyst (20,000 ppm) or above down to
any lower level desired. It will be recogniæed that level~ of nickel,
copper, vanadium and the like approximating 2% are high enough that
withdrawn catalyst is an ore rich enough to justify hydrometalurgical
processing to recover metal values and restore the mixture of porous
inert particies and inactivated catalyst to a state suitable for reuse
:~
as the inert component of FCC makeup in accordance with the invention.
Suitable hydrometallurgy may be treatment with sulfur dioxide and
~;, 15 water leach followed by liquid liquid ion exchange of the leach
- solution. ~t will be noted that the metal enrlched catalyst is unusually
~ well suited to hydrometallurgy since the metal values are on surfaces
- rather than combined with silica and the like in the body of the
"ore" as is the case with marly natural ores.
Whether the metals level on catalyst is held at a
value permitting use of withdrawn catalyst as ore or held to a lower
number such that withdrawn catalyst is discarded, operation of the
catalytic cracklng unlt is improved by addition of makeup constituted
by acti~e caka:Lyst and a Large pore inert soLld ln proportions
ca:Lculated ln accordance wlth prLnclples of the lnvent:Lon when cracklng
metal conta~llnated heavy stocks such as atmospherlc or vacuum resldue,
shale o:lls, tar sand liqulds, coal llqulds such as solvent reflned coal
and the like.
For practice of the -lnvention, the operator of a catalytic
3 cracker will maintaln a stock of two diEEerent solld materlals having
- 16 -
,~ .~ - .
1 physical characteristics (si~e, density, porosity, etc.~ suited to
operation of the type of unit. One stock is constituted by cracking
catalyst of any desired type, preferably a catalyst of high activity.
The catalyst is the more expensive component to be added as makeup
and it now becomes feasible in practice of the present inven~ion for
the refiner to justify the higher cost of more active catalyst. Thus
cracking ca~alysts of fresh MAT activity above 10 will be found useful
and catalysts of fresh ~T activity as high as 20 or above will show
economic advantage despite the high cost of such catalysts. The
invention can utilize the older amorphous silica-alumina ca-talysts,
but preference is noted for the more active catalysts constituted by
rare earth and/or hydrogen forms of crystalline ~eolites such as those
having the crystalline structure faujasite in a matrix of silica-alumina
or the like. Such catalysts are described in patents 3,140,2~ and
3,140,253. Many techniques and compositions for high activity have
been described. Although it is preferred to employ catalysts of
high activity, the particular means adopted to achieve that high
activity is not of particular significance and reference to knowledge
ln the art will suffice for the preser~t purposes.
The large pore inert material to be added wLth active
catalyst constitutes the real distinction from knowledge of catalyst
components normally taken into account by those responsible for
operation of catalytic cracking units. As noted above, dilution
o~ crackLn~ catalyst wLth lnert sollds :ls a convenLent mealls by whlch
a catalyst supplLer can malce ~everal act:lvity Levels avaLlable w-ltt
relatLvely Eewer methods oE catalyst ~lanufacture. Such blends are
sold on the basls oE overa:L:I actlvlty, se:l.ectlvlty and phys:lcal
propertles such as hardness, tendency to erode equipment and ~he llke.
DLlutiorl, if any, is a matter of llttle concern to the purchaser
except as it res-llts in reduced cost of the catalyst blend.
- 17 -
1 The large pore material is essentially inert in the sense that
it induces minimal cracking of heavy hydrocarbons by the standard micro-
activity test. Conversion by that test will be less than 20, preferably
about 10, representing essentially thermal cracking.
The microspheres of calcined kaolin clay yreferably used in
the process of the invention are known in the art and are employed as a
chemical reactant with a sodium hydroxide in the manufacture of fluid
zeolitic cracking catalysts as described in U.S. 3,647,718 to Haden et
al. In practice of the instant invention, in contrast, the microspheres
of calcined kaolin clay are no~ used as a chemical reactant. Thus
the chemical composition of the microspheres of calcined clay used in
practice of this invention corresponds to that of a dehydrated kaolin
; clay. Typically the calcined microspheres analqze about 51% to 53% (wt.)
- SiO2, 41 to 45% A1203, and from 0 to 1% H20, the balance being minor
amounts of indigenous impurities, notably iron, titanium and alkaline
-~ earth metaLs. Generally, iron content (expressed as ~e203) is about
1/2% by weight and titanium (expressed as TiO2) is approximately 2%.
The microspheres are preferably produced by spray drying an
aqueous suspension of kaolin clay. The term "kaolin clay" as used
herein embraces clays, the predominating mineral constituent of which
is kaolinite, halloysite, nacrite, dickite, anauxite and mixtures
thereof. Preferably a fine particle size plastic hydrated clay, i.e.,
a clay containing a substantial amount of submicron size particles,
L~s used ln order to prod~lce mlcrospheres hav:Lng adequate nlechanLcal
strength.
~ rO facLlLtate ~pray drylng, the powdered hydrated clay
pre~erabLy d:Lspersed Ln ~ater Ln ~he presence oE a deE:Locculating
agen~ e~emp:Lifled by sodium silicate or a sodium condensed phosphate
salt such as tetrasodium pyrophosphate. By employing a deflocculating
agent, spray drying may be carried out at higher solids levels and
- 18 -
1 harder products are usually obtained. ~ten a deflocculating agent is
employed, slurries containing about 55 to 60% soLids may be prepared
and these high solids slurries are preferred to the 40 to 50% slurries
which do not contain a deflocculating agent.
Several procedures can be followed in mixing the ingredients
to form the slurry. One procedure, by way of example, is to dry blend
the finely divided solids, add the water and then incorporate the
def]occulating agent. The components can be mechanically worked together
or individually to produce slurries of desired viscosity characteristics.
Spray dryers with countercurrent, cocurrent or mixed counter-
current and cocurrent flow of slurry and hot air can be employed to
produce the microspheres. The air may be heated electrically or by
other indirect means. Combustion gases obtained by burning hydrocarbon
fuel in air can be used.
Using a cocurrent dryer, air inlet temperatures to 1200~F. may
be used when the clay feed is charged at a rate sufficient to produce
an air outlet temperature within the range of 250 to 600~F. At these
temperatures, free moistu~e is removed from the slurry without removing
water of hydration (water of crystallization~ from the raw clay
ingredient. Dehydration of some or all of the raw clay during spray
drying is contemplated. The spray dryer discharge may be fractionated
; to recover microspheres of desired particle size. Typically particles
having a diameter in the range of 20 to 150 microns are preferably
recovered Eor calcinatLon.
Whlle It :Ls preEerabLe ln some cases ~o ca:Lcine the
microspheres at temperatures 1~l the range oE about 1600 to 2100F.
:ln order to produce particles of maximtlm hardlless, lt ls possible to
dehydrate the mlcro~spheres by calcinat~on at lower temperatures; Eor
example7 te[nperatures in the range of 1000 to 1600~F., thereby
converting the clay into the material known as "metakaolin". After
.~
.
- 19 -
:'
.
,. , ,: - ,
1 calcination the microspheres should be cooled and fractionated, if
necessary, to recover the portion which is in desired si~e range.
Pore volume of the microspheres will vary slightly with the
calcination temperature and duration of calcination. Pore size
distribution analysis of a representative sample was obtained by a
conventional nitrogen desorption technique. Most of the pores were
found to have diameters in the range of 150 to 600 Angstrom units,
o
primarily 300 to 600 A . In general, the inert materials used in
accordance with the invention will have a majority of pores (determined
as pores constituting more than half the total pore volume) of at
least 100 Angstrom units diameter.
The surface area of the calcined microspheres is usually
within the range of 10 to lS m /g~. as measured by the well-known
B.E.T. method using nitrogen absorption. It is noted that the surface
areas of commercial fluid zeolite catalysts is coniderably higher,
generally exceeding values of 100 m /g. as measured by the B.E.T.
method.
Qther solids of low catalytic activity and of lilce pore
diameter and particle size may be employed. In general, solids of
low cost are recommended since it is contemplated that the high makeup
rate charac~eristic of the inventi.on is offset by low net cost of the
catalyst plus inert material to be added.
'Lhe :Lnvention ls appl.ied to a catalyt.lc cracker for which a
precleterm:lned act.lvlty and metcl~.s level have been es~:abl:Lslled. These
may vary w:lthln rather wide ranges dependlng primarlly on nature o:E the
charge stoclc and the product slate dictated by market demancl. Thus a
craclcer :In a re~l.nery serv:l.ng a market whLch demc.mds re:lat:Lvely large
quantity of diesel fuel and dlstil.late Euel olls wil:L operate with a
catalyst of relati~ely low activlty as compared with one serving a
market of high gasoline demand. Predetermined metals level on
- 20 -
'~
~2~
1 catalyst will normally be higher when practicing the present invention
than would be the case with cracking catalysts of the prior art. The
greater proportion of metals in the large pcre inert solid easily
penetrated by the large metal bearing molecules, results in a level
of metal on the active cracking catalyst well below the average metal
content of the inventory circulated in the un-it. It is that latter
value of average metal content which is determined by analysis and is
the predetermined value which is to be held constant.
~rom observation of unit behavior and monitoring of charge
stock analyses, it is determined at what rate catalyst activity declines
and at what rate metals are deposited on the total inventory of catalyst
and inert materials. With this information, the refiner derives a
rate of metal deposition and thus maintains the metal level constant
at about the predetermined value. The rate of replacement will be
a value in per cent of circulating inventory per day which is readily
converted to tons of makeup per day having regard to the weight of
inventory in the circulating catalyst. In the preferred type of
operation charging a residual stock of at least 10 Nickel ~quivalents
of metal, the rate of makeup is simply obtained by dlviding total
metal input with charge by the predetermined metals level on inventory
in weight percent.
Having established a makeup rate in terms of tons per day
or percent of inventory per day, the activity level of active catalyst
pluA Inerts to be added 18 cletermlnecl by l,ee~s equatloll ln the form:
~F ~
g
where ~ = actlvLty o~ makeup bLend
= equlllbrium (prede~ermined) actlvlty of inventory in
the unlt
S ~ make rate determlned as above
- 21 -
. .
1 K = a constant related to catalyst deactlvation determined
as explained by Lee
In the preferred embodiments of the invention using makeup rates oE 10%
of inventory per day and higher, the makeup rate S is so high compared
with the constant K that the latter becomes relatively unimportant to
the calculation. Having determined the activity AF for the makeup blend
of active catalyst and inerts, the proportion of the makeup components
is derived from the known activity of active catalyst A by dividing
the desired blend activity by A thus ~F/A = fraction oE active catalyst
in blend. The two components may be premixed in the required proportions
and added to the unit intermittently or continuously at the rate S in
tons per day. Concurrently, there will be an amount of equilibrium
; catalyst withdrawn from the ~mit to maintain a constant inventory, i.e. an
amount of so withdrawn catalyst equal to the amount of makeup blend less
losses of catalyst due to attrition and the like. At high metal contents
in the neighborhood of 2%, the withdrawn catalyst becomes a valuable "ore"
for hydrowinning of nickel, vanadiurn, copper, etc.
Alternatively, the components of the makeup blend may be added
separately to the unit for mixing as the inventory i~ circulated. This
is particularly effective in FCC operations where any added material is
very quickly and very thoroughly mixed with the inventory being
circulated.
The invention is best utilized ln units which provide short
contact tLme oE catalyst ancl charge stock in order that the two components
Oe the makeup b:Lend may act with maxLmum eEEectLveness. The deslrecl
resuLt appears to be depos:Lt on the inert sollcl oE metAls and Conradson
Carbon (adclltLve coke) ancl c~ackLng on the actlve catalyst oE other
components of the charge stock. Th.Ls effect is advantageously achieved
at contac~ times less than 20 seconds, preEerably 2 seconds or less.
The fresh catalyst should have high activity, ~ T of at least
- 22 -
~ '
1 1.5, preferably 4 or greater. These high activities of thc active
catalyst component of the blend make possible high proportions of large
pore inert material, upwards of 50%, preferably more than 75%.
The combination of short contact time, high proportion of
large pore inert material, and high activity of the active catalyst
component of the blend provide further advantages in management of coke
make in the reactor and control of temperature in the regenerator of
an FCC unit. The active catalyst component acquires coke which i5
primarily due to catalytic cracking. Coke due to dehydrogenation by
contaminant metals is at a low-level for these short contact times.
Most of the Conradson Carbon coke (additive coke) is deposited on the
large pore inert component. Regenerator temperatures may be reduced
in this system of operation.
In general, the makeup rate according to the invention will
be in excess of 3% of inventory per day and in excess of 0.3 lb./
catalyst blend with inerts per barrel of feed, up to 20% of inventory
per day, with recommended levels of about 10% of inventory per day
for most operations in cracking of metal con-taminated resids.
,,
