Catalytic cracking of metal contaminated mineral oil fractions

Metal contaminated heavy oils such as residual fractions from petroleum distillation are economically converted to gasoline and other light products in catalytic cracking by practice of a novel catalyst makeup policy of adding controlled proportions of both an active cracking catalyst and a substantially inert, large pore solid to replace the amount of catalyst withdrawn from the inventory of a continuous cracking unit wherein catalyst inventory is continuously circulated between a reactor for cracking charge hydrocarbons and a regenerator for burning off the carbonaceous deposit laid down on catalyst in the cracking reaction.

BACKGROUND OF THE INVENTION 
The invention is concerned with increasing the portion of heavy petroleum 
crudes which can be utilized as catalytic 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 residue or "resids." The undersirable CC (for 
Conradson Carbon) and metal bearing compounds present in the crude tend to 
be concentrated in the resids because most of them are of 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 
petroleum fractions boiling above the gasoline range, upwards of about 
400.degree. F. Catalytic cracking has been greatly improved by intensive 
research and development efforts and plant capacity has expanded rapidly 
to a present-day status in which the catalytic cracker is the dominant 
unit, the "workhorse" of a petroleum refinery. 
As installed capacity of catalytic cracking has increased, there has been 
increasing pressure to charge to those units greater proportions of the 
crude entering the refinery. Two very effective restraints oppose that 
pressure, namely Conradson Carbon and metals content of the feed. As these 
values rise, capacity and efficiency of the catalytic cracker have been 
adversely affected. 
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 for 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, a 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. 
Metal 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 molecules in 
which they occur are cracked and tend to build up to levels which become 
very troublesome. The adverse effects of increased coke are as reviewed 
above. The lighter ends of the cracked product, butane and lighter, are 
processed through fractionation equipment to separate components of value 
greater than fuel to furnaces, primarily propane, butane and the olefins 
of like carbon number. Hydrogen, being incondensible in the "gas plant," 
occupies space as a gas in the compression and fractionation 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 which two varieties are presently practiced commercially. In 
delayed coking, the feed is heated in a furnace and passed to large drums 
maintained at 780.degree. to 840.degree. F. 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.degree. 
to 1050.degree. F. 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 1100.degree. F., thus heating the 
residual coke which 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 cracking charge, resulting in 
gasoline of lower octane number (from thermal cracking) than would be 
obtained by catalytic cracking of the same components. The gas oils 
produced are olefinic, containing significant amounts of diolefins which 
are prone to degradation to coke in furnace tubes and on cracking 
catalysts. It is often desirable to treat the gas oils by expensive 
hydrogenation techniques before charging to catalytic cracking. Coking 
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 Carbon 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 stock 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, Apr. 16, 1953, Page 113. 
Of the types of catalytic cracking systems, the one of the greatest present 
interest is Fluid Catalytic Cracking (FCC). The installed plants of this 
type are characteristically 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 
chargestock 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. All of the plants utilize a 
relatively large inventory of cracking catalyst which is continuously 
circulating between the cracking and regenerator sections. The size of 
this circulating inventory in existing plants is within the range of 50 to 
600 tons, the newer plants being designed for short time riser cracking 
with smaller catalyst inventory than that in older plants. Because the 
catalytic activity of the circulating inventory of catalyst tends to 
decrease with age, fresh makeup catalyst usually 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 
of aged circulating inventory, commonly referred to as "equilibrium" 
catalyst. The considerations which are involved in setting catalyst 
make-up policy are adequately reviewed in "Dynamic Optimization 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 provides equations of state and an algorithm for optimizing 
the make-up rate. The same is hereby incorporated by this reference. 
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 650.degree. F. to 1000.degree. F., 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 45 and are substantially free of 
metal contaminants. 
The chargestock, 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 800.degree. F. to 
1200.degree. F., 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 time is from about 
one to fifteen seconds. The cracked products are separated from the coked 
catalyst and passed to a main distillation tower where separation of gases 
and recovery of gasoline, fuel oil, and recycle stock is effected. 
Petroleum refiners usually pay close attention in the fluid catalytic 
cracking process (hereinafter referred to as the FCC process) to supplying 
feedstocks substantially free of metal contaminants. The reason for this 
is that the metals present in the chargestock 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 accumulation of metals can cause 
serious problems in the usual FCC 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 vanadium in crude oils is 
associated with very large nonvolatile hydrocarbon molecules, such as 
metal porphyrins and asphaltenes. Crude oils, of course, vary in metal 
content, but usually this content is substantial. An Arab light whole 
crude. for example, may assay 3.2 ppm (i.e. parts by weight of metal per 
million parts of crude) of nickel and 13 ppm of vanadium. A typical Kuwait 
whole crude, generally considered of average metals content, may assay 6.3 
ppm of nickel and 22.5 ppm of vanadium. Regardless of 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 chargestock. One of these is by 
reference to a "metals factor", designated F.sub.m. The factor may be 
expressed in equation form as follows: 
EQU F.sub.m =ppm Fe+ppm V+10 (ppm Ni+ppm Cu) 
A chargestock having a metals factor greater than 2.5 is 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 chargestock is as "ppm 
Nickel Equivalent" which is defined as 
EQU ppm Nickel Equivalent=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. However, it is to be understood herein that if it is present in 
significant concentration, it is to be included in the computation of 
Nickel Equivalent and weighted as nickel. 
It is current practice in FCC technology to control the metals content of 
the chargestock so that it does not exceed about 0.25 ppm Nickel 
Equivalent. Catalyst make-up is managed to control the activity of the 
circulating inventory. With this 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 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 
400 ppm. It is to be understood, of course, that the metals content of the 
chargestock 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 chargestock, 
refer to the time-weighted average taken over a substantial period of time 
such as one month, for example. Because of the large inventory of catalyst 
relative to the total metals introduced into the system by the chargestock 
in one day, for example, the metals content of the catalyst changes little 
each day with fluctuations in the quality of the chargestock. 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 calculating inventory of 
catalyst, by its metals content, provides a time-average value of the 
metals content of the chargestock. It is in this context, then, that the 
phrase "metals content of the chargestock" is used herein. 
For the purpose of this invention, chargestocks to the FCC process that 
contain up to about 0.40 ppm Nickel Equivalent of metal contaminants will 
be regarded as substantially free of metal contaminants. Chargestocks that 
contain at least about 0.50 ppm Nickel Equivalents of metal will include 
those chargestocks referred to as metal-contaminated. 
The effects of nickel, 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 of the API 
Division of Refining under the title "Deposited Metals Poison FCC 
Catalyst" and published at pages 112-122 of the Oil and Gas Journal for 
May 15, 1972, the full contents of which are incorporated herein by 
reference. 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 make-up as percent of catalyst inventory. Although 
the authors note that different cracking catalysts may respond differently 
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 cracking 
catalysts without substantial conversion. These are frequently referred to 
as "Conradson Carbon" from the analytical technique of determining their 
concentration in petroleum fractions. The Cimbalo article above cited 
classifies coke on spent catalyst in four groups: catalytic coke resulting 
from cracking of charge components; cat-to-oil, related to reactor 
stripper efficiency; carbon residue (Conradson) as just discussed; and 
contaminant coke derived from dehydrogenation reactions promoted by the 
heavy metal poisons nickel, vanadium, etc. The residual 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 chargestocks 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 interest becomes apparent when 
we consider, for example, that typically only about 26 volume % of an Arab 
light whole crude is the 650.degree.-1000.degree. F. gas oil fraction, 
while the total 650.degree. F. 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 FCC chargestock. However, it is 
generally recognized that coker gas oil, because of its high unsaturated 
and high aromatics content, is a poor quality feed. 
It has been proposed in the prior art to hydrotreat residual oils under 
such conditions that the metals content is brought into the range commonly 
associated with gas oils. Such hydrotreated residual oils, substantially 
free of metal contaminants, may then be used as chargestock or a component 
thereof for the FCC process. Processes to achieve such metals and sulfur 
reduction are disclosed in U.S. Pat. No. 3,891,541, issued June 24, 1975 
and U.S. Pat. No. 3,876,523, issued Apr. 8, 1975, for example, the entire 
contents of which are incorporated herein by reference. 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, Dec. 10, 1973, the entire contents of this article 
being incorporated herein by reference. 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 of 
heavy stocks have been approached by the expedient of catalyst 
modification. U.S. Pat. No. 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 of the 
metals to deposit in large pore structures renders the matrix a 
sacrificial component which protects the active zeolite cracking surfaces 
of the zeolite from metal contamination. The effectiveness of large pore 
structures in adsorbing and/or converting metal bearing components of 
crude is widely recognized. Many hydrotreating catalysts are preferably 
prepared by deposit of a Group VI metal with nickel or cobalt on a large 
pore alumina or the like. See also U.S. Pat. No. 3,947,347 on 
demetallizing petroleum fractions in admixture with hydrogen over a large 
pore catalyst without added hydrogenation metal catalysts and U.S. Pat. 
No. 2,472,723 and 4,006,077. 
Whether or not the charge stock contains heavy metals, activity of the 
catalyst added as make up has a profound effect on operation of an FCC 
Unit and is an important factor considered by the refiner in order to 
accomplish his objectives. It is usual to consider cracking catalysts in 
terms of capability to produce gasoline. This takes no account of the very 
significant proportion of catalytic cracking capacity in refineries 
producing only minor gasoline yields. In a market having a small demand 
for gasoline as compared with the demand for light distillate fuels (No. 2 
heating oil, jet fuel, diesel fuel, kerosene) FCC Units are operated to 
minimize gasoline and maximize the distillates boiling above gasoline. 
Such units will generally employ a catalyst of relatively low activity. To 
meet the demand for catalysts of various activity levels, catalyst 
manufacturers stand 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 manufacture one or a few different catalysts of differing activity. 
Intermediate grades are conveniently achieved by blending substantially 
inert particles of like fluidization 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 U.S. 
Pat. No. 2,455,915 and the inert, large pore matrix of U.S. Pat. No. 
3,944,482, the refiner has at hand a catalyst of fixed activity which he 
adds to his unit in order to maintain an equilibrium activity according to 
the equation: 
##EQU1## 
where A.sub.F is activity of fresh catalyst 
A.sub.E is equilibrium activity of the total catalyst inventory in the unit 
S is the rate of make-up in percentage of total inventory per day 
K is a constant representing rate of catalyst deactivation 
This is essentially equation (15) of the Lee article cited above, which see 
for derivation and more detailed explanation of terms. 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 microactivity test (MAT) conducted by cracking a 
Mid-Continent Gas Oil of the following properties: 
______________________________________ 
Gravity, .degree.API 
27.9 
CCR, Wt. % 0.23 
Sulfur, Wt. % 0.6 
Initial Boiling Point, .degree.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 910.degree. F. and a feed time of 96 
seconds for WHSV of 7.5. The liquid product is distilled and "conversion" 
is reported as 100 minus weight percent based on feed of liquid product 
boiling above 421.degree. F. Activity is then calculated as 
##EQU2## 
Methods are known to the art for preparing cracking catalysts of very low 
activities such as severely steamed amorphous silica-alumina of activity 
at 1 or less to very high activities above 20 such as highly active 
aluminosilicate zeolites. See U.S. Pat. No. 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, hence no 
refiner will pay the higher price which must be charged in view of the 
high production cost. 
In summary, the refiner who presently wishes to charge residual stocks is 
compelled to adjust his operations to the options available to him. The 
catalyst make-up rate to his catalytic cracker is determined by the 
activity considerations spelled out in the Lee article. To avoid adverse 
effects of metals deposited on the catalyst, the refiner hydrotreats the 
resid, sends it to a coker or deasphalter or lives with the problem of 
metal on cracking catalyst of whatever fresh activity he selects. 
SUMMARY OF THE INVENTION 
A technique for operation of catalytic cracking equipment is now provided 
which decouples maintenance of equilibrium activity from management of the 
metals problem. This is accomplished by a catalyst make-up policy for 
concurrent addition to the unit of two inventory components, 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 conventional 
techniques of calculating the amount of fresh catalyst required for 
maintenance of equilibrium activity or as modified by Lee to consider 
deactivation rate of catalyst, the system of this invention is based on 
determination of a make-up rate which will maintain a desired metals level 
on total inventory including fresh catalyst, partially deactivated 
catalyst, completely deactivated catalyst (essentially inert porous solids 
of small pore size) and catalytically inert material of large pore size 
characteristic of practice of the invention. When charging residual 
stocks, the make-up rate so determined will be unconventionally high, say 
upwards of 10% of inventory per day. The activity of catalyst required to 
maintain equilibrium activity is then calculated by the equation above. 
The unit is then supplied with a quantity of active catalyst and a 
quantity of large pore inert solid such that blend of the two exhibits the 
desired activity and quantity of the two satisfies the make-up rate for 
metals level maintenance.

DESCRIPTION OF SPECIFIC EMBODIMENTS 
The process of this invention contemplates an embodiment in which an FCC 
Unit is operated at unconventionally high levels of metal on the 
circulating inventory of catalyst and inert material, hereinafter called 
"catalyst inventory" for simplicity despite the fact 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 
levels more usual in the art. Thus 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 recognized that levels 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 particles and inactivated 
catalyst to a state suitable for reuse as the inert component of FCC 
make-up in accordance with the invention. Suitable hydrometallurgy may be 
treatment with sulfur dioxide and water leach followed by liquid-liquid 
ion exchange of the leach solution. It will be noted that the metal 
enriched 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 many 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 cracking unit is 
improved by addition of make-up constituted by active catalyst and a large 
pore inert solid in proportions calculated in accordance with principles 
of the invention when cracking metal contaminated heavy stocks such as 
atmospheric or vacuum residue, shale oils, tar sand liquids, coal liquids 
such as solvent refined coal and the like. 
For practice of the invention, the operator of a catalytic cracker will 
maintain a stock of two different solid materials having physical 
characteristics (size, 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 make-up and it now becomes feasible in 
practice of the present invention for the refiner to justify the higher 
cost of more active catalyst. Thus cracking catalysts of fresh MAT 
activity above 10 will be found useful and catalysts of fresh MAT 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 catalysts, but preference is noted for the more active 
catalysts constituted by rare earth and/or hydrogen forms of crystalline 
zeolites such as those having the crystalline structure faujasite in a 
matrix of silica-alumina or the like. Such catalysts are described in U.S. 
Pat. Nos. 3,140,249 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 
in the art will suffice for the present purposes. 
The large pore inert material to be added with 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 of cracking catalyst with inert solids is 
a convenient means by which a catalyst supplier can make several activity 
levels available with relatively fewer methods of catalyst manufacture. 
Such blends are sold on the basis of overall activity, selectivity and 
physical properties such as hardness, tendency to erode equipment and the 
like. Dilution, if any, is a matter of little concern to the purchaser 
except as it results in reduced cost of the catalyst blend. 
The large pore material is essentially inert in the sense that it induces 
minimal cracking of heavy hydrocarbons by the standard microactivity test. 
Conversion by that test will be less than 20, preferably about 10, 
representing essentially thermal cracking. 
The microspheres of calcined kaolin clay preferably 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. Pat. No. 3,647,718 to Haden et al. In 
practice of the instant invention, in contrast, the microspheres of 
calcined kaolin clay are not 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 analyze about 51% to 53% (wt.) 
SiO.sub.2, 41 to 45% Al.sub.2 O.sub.3, and from 0 to 1% H.sub.2 O, the 
balance being minor amounts of indigenous impurities, notably iron, 
titanium and alkaline earth metals. Generally, iron content (expressed as 
Fe.sub.2 O.sub.3) is about 1/2% by weight and titanium (expressed as 
TiO.sub.2) 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, is used in order to 
produce microspheres having adequate mechanical strength. 
To facilitate spray drying, the powdered hydrated clay is preferably 
dispersed in water in the presence of a deflocculating agent exemplified 
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 harder products are 
usually obtained. When 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 deflocculating 
agent. The components can be mechanically worked together or individually 
to produce slurries of desired viscosity characteristics. 
Spray dryers with countercurrent, cocurrent or mixed countercurrent 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.degree. 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.degree. to 600.degree. F. At 
these temperatures, free moisture 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 for 
calcination. 
While it is preferable in some cases to calcine the microspheres at 
temperatures in the range of about 1600.degree. to 2100.degree. F. in 
order to produce particles of maximum hardness, it is possible to 
dehydrate the microspheres by calcination at lower temperatures; for 
example, temperatures in the range of 1000.degree. to 1600.degree. F., 
thereby converting the clay into the material known as "metakaolin." After 
calcination the microspheres should be cooled and fractionated, if 
necessary, to recover the portion which is in desired size 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 obtained with a Desorpta analyzer using 
nitrogen desorption indicates that most of the pores have diameters in the 
range of 150 to 600 Angstrom units, 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 15 m.sup.2 /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 considerably higher, generally exceeding values 
of 100 m.sup.2 /g. as measured by the B.E.T. method. 
Other solids of low catalytic activity and of like pore diameter and 
particle size may be employed. In general, solids of low cost are 
recommended since it is contemplated that the high make-up rate 
characteristic of the invention is offset by low net cost of the catalyst 
plus inert material to be added. 
The invention is applied to a catalytic cracker for which a predetermined 
activity and metals level have been established. These may vary within 
rather wide ranges depending primarily on nature of the charge stock and 
the product slate dictated by market demand. Thus a cracker in a refinery 
serving a market which demands relatively large quantity of diesel fuel 
and distillate fuel oils will operate with a catalyst of relatively low 
activity as compared with one serving a market of high gasoline demand. 
Predetermined metals level on catalyst will normally be higher when 
practicing the present invention than would be the case with cracking 
catalysts of the prior art. The average metal content of the inventory 
circulated in the unit is determined by analysis and is the predetermined 
value which is to be held constant. 
From observation of unit behavior and monitoring of charge stock analysis, 
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 percent of 
circulating inventory per day which is readily converted to tons of 
make-up 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 Equivalents of metal, the rate of 
make-up is simply obtained by dividing total metal input with charge by 
the predetermined metals level on inventory in weight percent. 
Having established a make-up rate in terms of tons per day or percent of 
inventory per day, the activity level of active catalyst plus inerts to be 
added is determined by Lee's equation in the form: 
##EQU3## 
where A.sub.F =activity of make-up blend 
A.sub.E =equilibrium (predetermined) activity of inventory in the unit 
S=make rate determined as above 
K=a constant related to catalyst deactivation determined as explained by 
Lee 
In the preferred embodiments of the invention using make-up rates of 10% of 
inventory per day and higher, the make-up rate S is so high compared with 
the constant K that the latter becomes relatively unimportant to the 
calculation. Having determined the activity A.sub.F for the make-up blend 
of active catalyst and inerts, the proportion of the make-up components is 
derived from the known activity of active catalyst A.sub.c by dividing the 
desired blend activity by A.sub.c thus A.sub.F /A.sub.c =fraction of 
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 unit to maintain a constant 
inventory, i.e. an amount of so withdrawn catalyst equal to the amount of 
make-up 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, vanadium, copper, 
etc. 
Alternatively, the components of the make-up blend may be added separately 
to the unit for mixing as the inventory is 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 in units which provide short contact time of 
catalyst and charge stock in order that the two components of the make-up 
blend may act with maximum effectiveness. The desired result is 
advantageously achieved at contact times less than 20 seconds, preferably 
2 seconds or less. 
The fresh catalyst should have high activity, A.sub.MAT of at least 1.5, 
preferably 4 or greater. These high activities of the 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 is 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 make-up 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 contaminated resids. 
In accordance with usual practice in catalytic cracking, vapor pressure of 
hydrocarbons in the reactor is advantageously reduced by adding steam with 
the charge to the unit. According to one embodiment of the invention, the 
steam is provided by vaporization of water present as the internal phase 
of a water and oil emulsion with charge hydrocarbons. When that emulsion 
is heated by contact with hot regenerated catalyst at the bottom of the 
riser reactor, the emulsified water is vaporized with explosive violence 
to disperse the oil surrounding the water droplets in the emulsion and 
thus promote rapid effective contact of charge with catalyst for rapid 
vaporization of charge.