CA1264693A - Reducing the temperature in a regeneration zone of a fluid catalytic cracking process - Google Patents

Abstract

"REDUCING THE TEMPERATURE IN A REGENERATION
ZONE OF A FLUID CATALYTIC CRACKING PROCESS"

ABSTRACT

A method for operating a fluid catalytic cracking unit comprising a regeneration zone and a reaction zone with a relatively reduced temperature in the regeneration zone while processing a high-coke-making hydrocarbon feedstock having a 50 volume percent distillation temperature greater than about 500°F (260°C) which method comprises contacting at conversion conditions the feedstock in a reaction zone with a fluidizable mixture of regenerated cracking catalyst and low-coke-make non-catalytic solid particles, comprising a refractory inorganic oxide, in a ratio of low-coke-make solid particles to cracking catalyst from about 1:100 to about 10:1, the low-coke-make solid particles having a surface area of less than about 5 m2/g and a coke making capability of less than about 0.2 weight percent coke in the ASTM
standard method For testing cracking catalyst by microactivity (MAT); separat-ing the resulting hydrocarbon products from the mixture of deactivated cracking catalyst and low-coke-make solid particles; recovering the hydro-carbon products; passing the mixture of cracking catalyst and low-coke-make solid particles to the regeneration zone for regeneration by removal of coke;
and passing the resulting regenerated mixture of cracking catalyst and low-coke make solid particles from the regeneration zone to the reaction zone to contact the feedstock as described above whereby the regeneration zone temperature is maintained at a reduced temperature as compared to an equivalent operation without the use of the low-coke-make solid particles while simultaneously not reducing the coke burning capacity of the regeneration zone or affecting the operation of the reaction zone.

Description

~3 "REDUCING THE TEMPERATURE IN A REGENERATION
ZONE OF A FLUID CATALYTIC CRACKING PROCESS"
FIELD OF THE INVENTION
The field of art to which this invention pertains is the reduction of the temperature in the regeneration zone of a fluid catalytic cracking process when it i5 operated with a high-coke-make feed stock. More specifically, the invention relates to reducing the maximum temperature reached in the reg~neration zone of a fluid catalytic cracking process without reducing the amount of coke burned therein by simultaneously circulating, in admixture with cracking catalyst, fluidi~able low-coke-make solid particles, which have a surface area of less than about 5 m2/g and which low-coke-make particles generate less than about ~.2 weight percent coke in the ASTM standard method for testing fluid cracking 1~ catalyst by microactivity test (MAT), in an amount sufficient to result in a ratio of low-coke-make particles to cracking ca~alys~ from about 1:100 to about 10:1, thereby lowering the regenerator temperature from about 10F ts about 25~F (6 to 139C) while simultaneously not adversely affecting the operation of the reaction zone.
BACK~ROUND OF THE INYENTION

In U.S. Patent Nos. 2,889,269 ~Nicholson) and 2,894,902 (Nicholson), methods are taught wherein finely divided catalyst and inert9 fluidizable heat transfer solid particles are circulated through a fluidized reactor-regenerator system for the purpose of removing heat from the regenerator. These methods areused primarily in conjunction with the fluid hydroforming of naptha and are not concerned with high-coke-make feed stocks and the problems of lowering regenerator temperature without interfering with reactor-side operations and coke-burning capacity on the regenerator-side. The '269 patent and the ~902 patent do not di.sclose or teach the proble~s addres~ed ~y the present invention, nor the us~ of fluidiza~le low-coke-make solid particles having a surface area of less than about 5 m /9 and a coke making capability of less than about 0.2 we~ight percent coke in the ASTM standard method for testing cracking catalyst by microactivity (MAT) - : . ... .. .

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in a fluid catalytic cracking process whereby the regeneration zone temperature is maintained at a reduced temperature while simultaneously not a~fecting the coke-burning capaci~y of the regenerator or the operation o~ the reaction zone.
In U.S. Patent No. 4~289,605 (Bartholic), a fluid catalytic cracking process is disclosed whereby a metal-containing hydrocarbon charge stock is contacted with an admixture of active cracking catalyst and inert porous solid particles. Preferred inert porous solid particles are characterized by having a~ least 50% of the pore volume comprising pores of at least 100 Angstroms in diameter and having a surface area of about 10 to 15 square meters per gram.
1~ A preferred type of inert porous solid particles is calcined kaolin clay. The primary purpose of the large pore inert soli~ is to selectively accept the largemolecules characteristic of the metal and Conradson Carbon content of the charge.
The '605 patent does not address the problem of controlling the temperature of the regeneration zone with a high-coke-make charge without adversely affecting the reactor-side operation no~ does it suagest that ~he key is in the use of low-coke-make solid particles which have a surface area of less than about 5 m2/q and qenerate less than about 0.2 weight percent coke in the ASTM standard ~ethod for resting cracking catalysts by microactivity test (MAT) which are added in amounts in addition to the established amount of catalyst needed to achieve the reactor-side objectives~0 and not in place of catalyst.
In British Patent Applications Nos. 2,116,062A and 2,116,202A (Occelli et al), a catalytic cracking composition comprising a solid cracking catalyst and a diluent containing a selected alumina or a selected alumina in combination with one or more heat-stable inorganic compounds wherein the aluminaceous diluent hasa s~rface area of 30-1000 m2/g and a pore volume of 0.05-2.5 cc/gram is disclosed.
The primary purpose of the high surface area diluent is to perm;t the catalyst system to function well even when the catalyst carries a substantially high level of metal on its surface. These appl~cations are not concerned with control of temperature~n the regenerator and do not disclose the circulation of low-coke-make solid particles, which have a surface area of less thanabout 5 m2/g and generate less than bbout 0.2 weight percent coke in the ASTM standard method for testing cracking catalysts by microactivity test (MAT), for the purpose of reducing the regeneration zone tempera~ure while simultaneously not adversely affecting the operation of the reaction zone.

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A common prior ~rt method o~ hea~ removal provides cos)lant ~illed coils within the regenerator, which coils are in con~act with ~1~e catalyst from which coke is ~eing removed. ~or example, Medlin ct al. U.S. Pa~ent No. 2,819,9Sl, McKinneylJ.S. Patent No~ 39990,992 and Vickers U,S. Pa~ent No. 49219,442 disclose fluid catalytic cracking processes using dual zone regenerators with cooling cQils mounted in the second zone. These cooling coils must always ~ filled with coolan~ and ~hus be removing h~at from the regenera~or, evcn durinE~ start-up ~hen such removal is particularly undesired, because the typical metallurgy of the coils is such tha~ the coils would be damaged by exposure ~o the high re~enerator tempera~ure(up to 1350F
10 (732C)) withou~ coolant ~rving to keep ~hem rela~ively e:ool. Fur~hermore, the cooling coils necessarily reduce ~he ~emperature o~ he regenerated ca~aly~ which is circulated to the reac~ion zone. Therefore, in order to maintain ~ constant reaction zone temperature, additional catalys~ mus~ be circulated ~hich in turn produces more o~ke ~hereby~urthcrreducingthe yicld o~Yaluable ~quid ptoducts.

BRIEF SUMMARY OF THE I~YENTI~N
One e~bodiment of the present in~ention relates to a method for cperating a fluid catalytic cracking uni1: comprising a regeneration zone and a reaction zone while processing a high-coke-make hydrocarbon feedstock having a 50 ~olume percent distillation temperature greater than abuut500F
~0 (260~0) wh~ch method co1nprises contacting, at endo~herm;c, coke-making con~ersion conditions, the feedstock in the reaction zone with a fluid~z~d heated mixture of regenerated cracking cat8lyst and low-coke-make non-catalytîc sol~ particles, comprising a refractory ~norganic oxide in a rat~o of low~coke-make solid particles to cracking catalyst fro~n about 1:100 to about 10:1, . . . ~
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, ~L~2~ 3 the low-coke-make solid particles having a surface area of less than ahout 5 m /9 and a coke making capability of less than about 0.2 weight percent coke in the ASTM standard method for testing cracking catalyst by microactivity test ~MAT); separating the resulting hydrocarbon prod~cts from the mixture of deactivated cracking catalyst and lo~-coke-make solid particles~ recoverina the resulting hydrocarbon products; passing the mixture of cracking catalyst and low-coke-make solid particles to ~he regeneration zone for reheating and regeneration by exothermic combustion of coke; and passing the resulting reheated and regenerated mixture o~ cracking catalyst and low coke-make solid particles ~rom the regeneration zone to the reaction zone to contact the feed~
stock as described above whereby the regeneration zone tempera~ure is maintainedat a reduced temperature as compared to an equivalent operation without the use of the low-coke-make solid particles whi:le simultaneously not reducing the cokeburning capaci.ty of the regeneration zone or adversely a~ectZng the operation of the react;on zone.
Another embodiment of the present inventi:on relates to a process fo~r catalytic cracking of a high-coke-make hydrocarbon feedstock having a 5Q Yol~me percent distillation temperature greater ~han about 500VF (260~C~ by contacting the feedstock at exothermic cracking conditions with a circulating~ heated particle form, solid cracking catalyst whereby components o~ the feedstock are converted to lower boiling hydrocarbons in a reaction zone wi.th concurrent cooling of the catalyst and deposition thereon of a deactiYating carbonaceous contaminant, regenerating the catalytic cracking activity of the contamlnated catalyst by burning carbonaceous deposits ~herefrom in a regeneration zone under exothermic condit;ons that result in the catalyst and the regeneration zone reachingan unacceptable or undesired maximum temperature condition, and c~rculating catalyst so regenerated from the regeneration zone to the reaction zone, wherein the improvement comprises reducing the maximum temperature reached in the ,~

~3 regenerati~n zone without reducing the amount of coke burned therein by simultaneously circulating, in admixture with the cracking ca~alyst, ~luidizablelow-coke-make solid particles, which comprise a refractory inorganic oxide and h~e a surface area of less than about 5 m2/g and which generate less than about 0.2 weight per~ent coke in the ASTM standard method for test~ng fluid cracking catalysts by microactivity ~est (MAT), said solid particles being present in an amount sufficient to result in a ratio of low-coke-nake solid particles to cracking catalyst from about l:~D0 to about 10:1, thereby lowering the regeneration temperature ~rom about 10F to about 2~0F (6 to 139C) while simultaneously not adversely affecting the operation of ~he reaction zone.

Other embodimen~s of d-e pnsent invention encompass f-lr~her d!e~ails such as f~dstQck descriptions, catalyst and low-coke-make solid characteristics, and ~perating conditions, all of ~rhich are hereinafter disclosed in ~e following discus~ion of each o~ these facets o~ the invention.

BRIEF DESCRlPllON OF THE DRA~ING

lS The drawing illustrates a preferred embodiment of thse present imen~ion and is an elevational view of apparatus witable ~or use in ~ccordance with the prescnt invention. Other types of apparatus may a~so be suitabk for use with theprcsent imcntion.

DETAILED DFSCRIPTION OF THE INVENTION

The fluid cataiyst GraCking process (hereir~f~r FCC) has l~en extensively relied upon for the conversion of starting materials, wch a3 e~acuum gas oils, and o~ relatively hea~y oils, in~o lighter and more ~aluable producSs. Ft:C
Involves the contact in a reaction zone oiE dle startin~ m~terial, ~ether It be vacuum gas oil or another oil, w~h a finely divided, w p~rSiculated, sDlid, catalytic material ~hich behaves as a fluid Yvl~n mi~ced wiSh ~ ~as or Yapor. This material 2S possesses the! abilit~ to catalyze the cracking reaction, and in so acting it 15 surface-deposited ~ieh ooke, a by-produc~ of the cracking reaction. Cuke i~ comprise~ ofhydro~en~ carbon and~ other m~terial ~uch as sulfur, ~nd it inserferes wi~ the catslytic activity of FCC cataly~ts. Facil1ties for the removal of coke ~rom FCC:

ca~al~rst, so called re~eneration facili~ies or reKenera~ors~ are ordinarily proYided within an ~CC unit. Regenerators contact the coke~on~aminated ca~alyst with an oxygen containing ~as at conditions such that the c~ke is oxidized and a considerable amount of heat is released. A portion of this heat escapes ~he regenerator with the S flue gas, comprised ~f excess regeneration gas and ~he gaseous products of coke oxidation, and the balance of ~he heat leaves the regenerator with the regenerated, or relatively coke îree, catalys~. Regenerators operating at supera~mospheric pressures are often fitted with energy-recovery turbines which expand the flue gas as it escapes from the regenerator and recover a portion of ~e energy liberated in 1~ the expansion.
The fluidized catalyst is continuously circulated from the reaction 20ne to the re~eneration zone and then aBain to the reaction zone. l he fluid catalyst, as well as pro~iding catalytic action, acts as a vehicle for the ~ransfer of heat from zone to zone. Catalyst exiting the reaction zone is spoken of as being "~pent", that is, partially deactiva~ed by the deposition of coke upon ~e catalyst. Catalyst from which coke has been substantially removed is spoken of as "regenerated catalyst".
The rate of conversion of the feedstock within the reaction zone ls controlled by regulation of ~he temperature, ac~ivity of ca~alyst and quantity of catalyst (i.e., catalyst to oil ratio) ~herein. The most common method of regulating the temperature is by reE~ulating the rate oiE circulativn OI catalyst from ~he regeneration zone to ~e reaction zone which simultaneou~ly increases ~he catalyst/oil ra~io. That is to say, if it is desired to increase the conversion rate, an increase in the rate of flow of circula~ing fluid catalyslt from the regenerator to the reactor is effected. Inasrnuch as ~he temperature within the regenera~ion zone under normal operations is considerably higher than the temperature within the reaction zone, this increase In influx of catalyst from the hotter regeneration zone to the cooler reaction 201-e effects an increase In reaction zone temperature.
Rec~ntly, politico-economic restraints which have been pu~ upon ~he traditional Jines of supply of cmde oil have made necessary the use, as startingmaterials in FCC units, of heaYier-than-normal oils. FC:C units n-ust now cope with feedstocks such ss residual oils and in ~ilR future may require the use of mix~ures of hea~y petroleum oils with coal or shale derived oils.
The chemical nature and molecul~r stn2cture of the feed to ~e FCC unit will affect the level of coke on spent catalyst. Generally speaking, the hlgher the molecular weight, the higher the Conradson car~on, the higl~r ~e heptane insolubles9 and the hi~her ~e carbon ~o hydrogen ratio, ~he higher will be the coke leYel on the spent ca~alyst. A150, high levels of combined ni~ogen, such as found in shale deriv~d oils, will also increase the coke le-/el on spent ca~alys~. The processing of heavier and heavier feedstocks~ and particularly the processing ofdeasphalted oils, or direct processing of a~mospheric bottoms ~rom a crude unitlc~mmonly referred to as reduced crude, does cause an increase in all of some nf these factors and does there~ore cause an ir crease in coke level on spen~ ca~alys~.
This increase in coke nn spent c~talyst results in a larger amount o~ coke burned in ~e reBenera~or per pound c>f catalyst c:irculatedO Heat is removed ~rom 1~ the regenerator in conven~ional ~CC uni~s in ~he flue gas and principally in the hot regenerated catalyst s~r~am. An increase in ~he level of coke on spent ca~alyst will increase the temperature in the regenera~or. However, there are limitatinns to ~he ~empera~ures that can be tolerated by PCC catalyst withou~ ~re being a substantial detrimen~al effect on catalyst activity. Generally, wi~ cornmonly IS available modern FCC catalyst, temperatures of regenerated catalys~ are u~ually m3intained below 1400~F (760C), since 10ss of actiYity would be Yery seYere a!:o~/e about 1400 - 1450F (760 to 788CJ, In order ~ burn a greater amount of coke in the re~eneration zone and yet maintain a maximum temperature below about 1400F (760C3, the prior art hasextensi~ely tau~ht ~e use of cooling coils installed in cr in communicaticn with ~he regeneration ;cone. Cooling coils which are associated wlth FCC re~ eneration zones must necessarily be constan$1y charge~ ~vith a cooJing nnedium and are considered ~o be a ~ulnerable link in the overall FCC process.
Objectives of ~e present invention are ~ reduce the temperature of ~e

2~ rcgeneration zone and to trans~er heat from the regeneration zone to the reacl:ion ~e while simultaneously no~ affecting me opera~ion of the reaction zone. or 1 imi t; ng the coke-burning capacity of the regeneration zone.
We have discovered a method for reducing the temperature in a regenera-tion zone of a fluid catalytic cracking process wherein a combination of catalyst

3~ and low-coke-m~ke solid Darticles of fluidizable part~cle s{ze is con~acte~with the hydrocarbon feedstock and subsequently both the catalyst and the low~cokeo make solid particles are regenerated and recycled.
We h~ve discovered that it is highly desirable to circulate catalyst .Darticles which contri~ute to the crackin~ o~ the feed by virtue of their cataly~ic 3~ cracking activity but which produce coke on the~r surface as by-product of this process with another class of particles which exhib~t very l~ttle tendency to produce coke. The important performance cri~eria for selection of the la~er class of partic!e ~or use with the present invention is ~he abili~y to no~ contribute significantly to the formation of additional coke on the mixture of low coke make solid particles and catalyst particles above the level of coke which would have been deposited on the catalyst particles had they been present in ~he reaction environment alone. This latter class of particles will herein be referred to as low coke make solid particles.
The present invention provides a process for the continu~us cataly~ic conversion of a wide variety of hydrocarbon oils to lower molecular weight products, 1~ while maximizin~ production of highly valuable liquid pro~ucts, and making it possible, if desired, to avoid vacuum dis~illation and other expensive treatments such as hydrotreatin~. Preferred feedstocks for the present invention include residual hydrocarbon oil or any other hydrocarbon feedstock having a 50 volume percent distillation temperature greater than a~out S00F (260C). The term "residual lS hydrocarbon oil" includes not only those predominantly hydrocarbon compositions which are liquid at room temperature, but also ~hose predominantly hydrocarbon compositions which are asphal~s or ~ars a~ ambient temperature bu~ liquefy when heated to temperatures in the range of up ~o about 800F ~427~C) or more. Suitable feedstocks for use in the present invention are residual oils whether of petroleum ori~in Qr not. For example, the imention may be applied to the processing of such widely diverse materials as heavy bottoms from crude oil, heavy bitumen crude oil, those crude oils known as "heavy crude" which approxirnate the properties of reduced crude, shale oil, tar sand extract, products from coal liquefaction and solvated coal, atmospheric and vacuum reduced crude, extract and/or bottoms from2~ solvent de-asphaltin~, aromatic extract from lube oil refining, tar bottoms, heavy cycle oil, slop oil, other refinery waste streams and mixtures thereof. Such mixtures can for instance be prepared by rnixing available hydrocarbon fractions~
including oils, tar, pitches and the like. Likewise, the invention rnay be applied to hydrotreated feedstocks, but it is an advantage of the invention that it can successfully convert residual oils which have had no prior hydrotreatment.
However, a preferred application of the process is the treatment of reduced crude, i.e., that ~raction of crude oil boiling at and above 6S0F (343~Cl, alone or in admixture with virgin gas oils. While the use of material, that has been subjected to prior vacuurn distillation is not excluded, it is an advanltage of the invention that it can 3~ satisfactorily process feedstock ~hich has had no prior racuum distillation, thus - ' , -': "

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'' '' saving on capitaJ investment and operating costs as compared to conventional FCCprocesses ~hat require a vacuum distillation unit. However, suitable feeds~ocks also include gas oil and vacuum gas oil.
An essential element in the process o~ the present invention is the circulation of low_coke-rnake solid particles of fluidizable particle size during the conversion of the hydrocarbon feedstock. Suitable low-coke rnake solid particlespreferably comprise a refractory inorganic oxide such as corundum, mulli~e, fused alumina, Iused silica, alpha alumina, low-surface area calcined clays or the like.
Re~ardless o~ which ~yp~ of low-coke-make solid particles are selected, ~hese lû particles must exhibit very little tendency to enhance the amount of coke deposited on the solids (catalyst plus low-colce-make solid particles) which are present in the reaction environment. Fur~hermore, it is essential that the low-coke-make solid particles possess a surface area o~ less than about 5 m2/g and generate less than about 0.2 wei~ht percent coke on the spent lo~coke-make solid particles in th~
ASTM standard meth~d for testing fluid cracking catalysts by microactivity test (MAT). If the additional solid particles were to contribute significantly to theformation of additional coke, then the additional heat release in ~the F5::C
reyenerator would tend to nullify or inhibit the souaht after regenerator temperature reduction. Similarly, the low surface area characteristic of ~he low-coke~nake solid ~0 particles permits the rapid and complete stripping of hydrocarbonaceous reaction products from the lo~coke~make solid particles in the reaction zone before particles are transferred to the regeneration zone thereby preventing the cornbustible hydrocarbons from entering the regeneration zone andproducing a~ditional heat release. The low-col:e-make solid particles must have no 2S adverse effect upon the hydrocarbon conversion process, and be stable or resistan~
to physical breakdown due to the thermal and mechanical forces to which they aresub3ected in the process. The size of the low-coke-make solid particles may varyfrom about S to about 20û0 mlcrons and are preferably in the shape o~ spherical or spheroidal particles. In an embodiment of the presen~ invention where an admixture of catalyst and low~coke-make solid particles is introduced to the hydrocarbon feedstock, the ran~e of catalyst and low~coke~nake particle slze may, for exampie, be substantially the same, overlap, or be different. The apparent bulk density of ~e low~coke-make solid particles may vary from a~out 0.3 ~/ml to about 4 g/ml.
Low coke make solids which are essential in the process of the present invention are those malterials which haYe a coke deposit of 0.2 weight percent coke _g_ " ,, . ~ :
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or less on the spent low-coke~nake solid after ~he solid alone has been subjected to the ASTM standard method ~or testing cracking catalyst by microactivity test (MAT3. This microactivity test is rnore formally known as ~he Standard Me~hod for Testing Fluid Cracking Catalysts by Microactivity Test and is designa~ed as test D
3~07-8û. This microacti~ity tes~ is also men~ioned in U.S. Patent No. 4,4937902.The microactivity test is conducted in a laboratory test apparatus which is designed and operated in accordance with the Standard Method~ Briefly, ~he microac~ivity test comprises loading a sample of particles weighing 4 grams into the reactor and injecting a standard ~atch of gas oil in an amount of 1.33 grams over a 7S second period into the reactor which is maintained at 900F (482C). The resulting particles to oil weight ratio is about 3 and ~he weight hourly space velocity is about 16. Then the conversion of the feedstock and the coke remainin~ on the spent particles may bedetermined by standard techniques.
The following discussion is not meant ~o be exhaustive but is presented to illustrate the primary advantage to be derived by the utilization of low.. coke--make solid particles in the present imention. The circulation of the lo~coke-make solid particles causes a significant reduction in ~he operating temperature of the regenerator beyond that which could be achieved if the catalyst is drculated without the low-cok~make solid par~icles. This feature of reduced regenerator temperature is o~ paramount importance tD the hydrocarbon conversion industry since many of the currently popular FCC feedstocks contain significant quanti~ties o~
non-distillable components which form coke and which coke ultimately must be removed ~rom the circulating solid particles durin~ regeneration. The combustion of hi8h levels ~ carbon or coke durin~ re~eneration produces extraordinary quantities 2S of heat which must be dissipated in some manner, since modern FCC catalysts are extr~mely sensitive to exposure to relatively high temperatures which e~ust in high temperature regenerators and this temperature sensitivity eventually ~eads to the degradation of a catalyst's activity and selectivity. Therefore, the resulting lower regenera~or temperatures which are available in connection with the present invention help to maintain the cracking activity and selectivity of the catalys~ and also provide increased flexibility in the choice of operating conditions. The circulation of low~coke-make solid particles also reduces the quantity of make-up catalyst required ~o maintain a given level o~ acti~ity since the catalyst wilî
maintain its activity longer.
3S Another essential elemcnt of the process of the present invention is a --~ O--" '' .

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~: , , fluidizable FCC catalyst. In general, it is pre~erred ~o employ a catalys~ havin~ an effective level o~ cracking activity, providing high levels of conversion and pr~ductivity at low residence times. That catalys~ may be in~roduc~d into the process in its virgin form or9 in other than virgin form; e.g., equilibrium catalyst S which has been previously used. One may employ any hydrocarbon cracking catalyst having the abov~mention~d characteristics. A particularly preferred class of catalysts include those which have pore structures into which molecules of feed material may enter for adsorption and/or for contac~ with active catalytic siteswithin or adjacent the pores. Yarious types of catalysts are available within this classification, including f~r example the layered silicates, e.g., smecti~es. Although the most widely available catalysts within this classification are the well-known zeolit~containing catalysts, non-zeolite ca~alysts are also contemplated for thepresent invention as well. The preferred zeolite-containing catalysts may include any zeolite, whether natural, semi-synthetic or syntheticJ alone or in admixture with lS other materials which do not significantly impair the catalyst, provided ~he resultant catalyst has the activity and pore structure referred to above. For example, if the catalyst is a mixture, it may include the zeolite component associa~ed with or dispersed in a porous refractory inorganlc oxide carrier. In such a case, the catalyst may for example contain ahou~ 1% to about 60%, more preferably about 1% to about 40% and most preferably about S96 to about 25% by weight, based on the total weight of catalyst (water-free basis~ o~ ~he zeolite, with the balance of the catalyst being the porous refractory inorganic oxide alone or in combinationwith any of the known adjuvants for promoting ~r suppressing Yarious desired or undesired reactions. For a general explanation oi the genus of zeolitic cataiysts 2S useful in the invention, attention is drawn to the disclosures of the articles entitled "Refinery Ca~alysts Are a Fluid Business'l and "Making Cat Crackers Work on a Varied Diet," appearing respectively in the July 269 1978 and September 13, 197 issues of Chemical Week magazine.
For the rnost part, ~he zeolite components of the zeoli~e-containin~ catalysts will be those which are known to ~e usefulin F CC processes. In general7these are crystalline aluminosilicates, typically m ade up of tetra coordinated aluminum atoms associated tnr3ugh oxygen atoms with adjacent silicon a~oms in the crystal structure. However,the term "zeolite" as used in this disclosure contempla~es not only aluminosilicates, but also ~ubstances in which the aluminum has been partly or w~lolly replaced, such as ~or instance by , .

gallium, phosphorus, and other me~al atoms, and further includes substances in which all or part of the silicon has been replaced, such as for instance by germanium. Ti~anium and zirconium su~stitution may also be praetical.
Most zeolites are prepared or occur naturally in the sodium form, so that sodium cations are associated with the electro negative sites in ~he crystal s~ructure. The sodium cations tend ~o make zeoli~es inactive and much less stable when exposed to hydrocarbon conversion eonditions, particularly high ~emperatures.
Accordingly, the zeolite may be ion exchanged, and where the zeolite is a component of a c~talyst composi~ion, such ion exchan~ing may occur ~efore or after incorporation of the zeoli~e as a component of ~he composition. Suitable cations for replacemen~ of sodium in the zeolite crystal structure include ammonium (decomposable to hydrogen)9 hydro~en, rare earth metals, alkaline earth metals, etc.
Various suitable ion exchange procedures and cations which may be exchanged intothe zeolite crystal structure are well known to those skilled in ~he art.
lS Examples of $he naturally occurring crystalline aluminosilicate zeolites which may be used as c~r included in the catalyst for the presen~ invention are faujasite, mordenite, clinoptilote, chabazite, analyci~e, erloni~e, as well as levynite, dachiardite, paulingi~e, noseli~e, ferrioriee, heulandite, scolccite, stibite, harmotome, phillipsite, brewsterite, flarite7 datolite, ~melinite, caumni~e, leucite, ~0 lazurite, scaplite, mesolite, ptholite, nepheline, matrolite, offretite and sodalite.
Examples of the synthetic crystalline aluminosilicate zeolites which are useful as or in the catalyst for carrying out ~he present im~ention are Zeolite X, U.S.
Patent No. 2,882,244; Zeolite Y, U.S. Patent No. 3,130,Q07; and Zeolite A, U.S.
Patent No. 2,882,243; as well as Zeolite B~ U5. Patent No. 3,008,308; Zeolite D,Canada Patent No. 661,981; Zeoli~e E, Canada Patent No. 614,495; Zeolite F, U.S.Patent No. 2,996,3S8; Zeolite H, U.S. Patent No. 3,01n,789; Zeolite J, ~l.S. Patent No. 3,001,869; Zeolite L, Belgian Patent No. 575,117; Zeolite M, U.S. Patent No.2,995,423; Zeolite O, U.S. Pa~ent No. 3,140,252; Zeolite Q, U.S. Patent No.
2,991,151; Zeolite S, U.S. Patent No. 3~054,657; Zeolite T, U.S. Patent No.
2,950,9~2; Zeolite W, U.S. Patent No. 3,012,853; Zeolite Z, Canada Patent No.
614,495; and Zeolite Ome~a, Canada Patent No. 817,915. Also, ZK-4HF, alpha beta and ZSM-type zeolites are useful. Moreover, ~he zeolites described in U.S. Patent Nos. 3,140,249, 3,140,253, 3,944,4B2 and 4,137,1Sl are also useful.

The crystalline alum;nosilicate zeolites having a faujasite-typ2 crystal " '~ ' structure are particularly pre~erred ~or i~se in the present invention. This includes particularly natural faujasite and Zeolite X and Zeolite Y.
Commercial zeolite-containing catalysts are available with carriers containing a Yariety of me~al oxides and combinations thereof, inluding for example silica, alumina, magnesia9 and mixtures thereof and mixtures of such oxides with clays as e.g. described in U.S. patent No. 3,0349948. One may for example ~elect any of ~e zeolite-containing molecular sieve fluid cracking ca~alysts which are suitable for production of gasoline from vacuum gas oils. However, certain advantages may be attained by judicious selection of ca~alysts having marked resistance to metals. A metal resistant zeolite catalyst is, for instance, described in U.S. Patent No. 3,944,482l in which the ca~alyst contains 1-40 weight percent of a rare earth~xchanged zeolite, the balance being a refractory metal os~ide having specified pore volume and size distribution.
In general9 it is preferred to employ catalysts having an overall particle size in the range of about 5 ~o abou~ l60 and more preferably about 30 to about l20 microns.
The catalys~ composition rnay also include one or more combustion promoters which are useful in the subsequent step ~ regenerating the ca~alyst.
Cracking of residual oils results in substantial deposition of coke on the ca~alysS, which coke reduces the activity of the catalyst. Thus, in order to restore the activity of ~e catalyst ~he ~~oke is burned off in a regeneration step, in which the coke is converted to combustion gases including carbon monoxide and/or carbon dioxide. Various substances are Icnown which, when incorporated in cracking catalyst in small quantities, tend to promote conversion of the coke to carbon dio~ude. Such promoters, normally used in effective amoun~s ranging from ~ traceup to about lO or ~0% by weight of the catalyst, may be of any type which generally promotes combustion of carbon under regenerating conditions, or rnay be somewhatselective in respect to completing the combustion of CO.
In accordance with the present invention, a stream is formed comprising a suspension of hydr~carbon feedstockg catalyst and low~coke,rnake solid particles~
The resulting suspension is conducted in a generally upward fashion ~o permït the desired hydrocarbon conversion to be performed~ It is also foreseen that diluentstreams, such as steam or light hydrocarbon gases, n ay also be introduced into the bottom of the reactor riser in order to maximize ~he degree of vaporixation ~ the feed.

, !
' The apparatus for ~onduc~ing ghe pr~:ess of the prese~t imention provi~s ~or rapidly vaporizin~ a~ much feed as possible and ef~iciently admixing th~
hydrocarbon f~dstock, catalyst and low- coke--make solid par~icles thereby permitting the resul~ant mixture ~o flow as a dilute suspension in a progressiv~ ~low mode. At the end o~ a predetermined residence time, ~he ca~lys~ ard low-coke~
make solid particles are separated from the hydrocarbons and it is preferred that all or at least a substantial portion of ~e hydrocarbons be abruptly separated from the catalyst and lo~coke-rnake solid particles. This separa~ion may be conduc~ed in any convenient manner and may include the use of cyclones and tJ-e like~ 1~ is preferred lû that ~he suspension as hereina~ove described be transpor~ in what is referred to as a reactor riscr which is situa~ed in a nearly ver~ical position as opposed to the horizontal and have a leng~h to diameter ratio of at least about 10, more preferably about 20 to ~5 or more. 1~ ~ular, the reactor riser can be of uniform diameter throughout or may be provided with a eontinuous or step-wise incrcase in diameter 1~ along the reac~or path ~o maintain or ~ary the veloc}~y ~ong the ~EIow pa~h. In gencral, the reactor c~nfiguration is such as to pro~ide a relatively hi~h velocity of flow and dilute suspension of ~alyst and low-coke~rnake solid par~ides. Por example, ~he average velocityin the reactor riser will usually be at least abou~ 25 (7.62 m/s) and more typically a~ least abou~ 35 feet per second ~10.7 m/s). This velocity m~y range up to about 55 ~16.8 m/s) or about 75 (22.9 m/s) feet per s~eond or higher. The velocity capabilities of the riser will ~n general be sufficient to prevent substan~
`tial bùild-up of a c~talyst bed ~n the bottom or other portions of the riser~ whereby the eatalyst loading in the riser can be maintained below about 4 or 5 pounds (64.1 or 80.1 kg/m3) and below about 2 pounds pEr cubicfoot (32 kg/m3), respectively, 2S at the upstream (e.g. bottom) and downstream (e.g. top) ends of the r~ser.The progre~sive ~ow mcde im olves, for example, ~lowing of ~atalyst, feed, low~coke~nake solids and produc~ a~ a stream in a pos~tlve5y controlled and rnaintained direction established by the eJongated nature o~ ~e reaction zoneO This Is not to suggest however that there must be strictly li~ar ~low. As ls well known, turbulent ~low and nslippag~ of catalyst and low coke make solids may occur ~
some extent especlally ~n certain ranges of vapor velocity and sorne c~Salyst lo;~dings, ~Ithough It has been rep~rted advisable tu employ sufficlently low ~talyst loadings to restrict dippage ~nd back-mixin~. Most preferably the reac~or Is onewhich abruptly ~eparatcs a substantial portion o~ all of the vaporized cracked products from the cstaJyst and low~coke~nake solids at one or more points aJong the~

riser, and preferably separates ~bs~antially all of ~e vapt)rized cr~cked pr~ducts from the catalyst and low-cok~make solids at the downstream end of the riser.
Preferred conditions iEor opera~ion s)~ ~e pr~c~s o~ ~he present invention are described below. In our process it is preferred to restric~ preheating 3 of the feed so that the feed is capable of absorbin~ a lar~ er amount o~ heat from the catalyst and low_coke~nake solids while the catalyst and low-cok~rnake solids raise the feed ~o conversion tennperature, a~ ~e same time minirnizing u~ilization of external fuels to heat the feedst~k. Thus, where ~he natur~ of the feedstock permi~s, it may be fed at ambient ~emperature while heavier feedstocks may be fed at pre-heat temperatures of up ~o about 600F (316C), ~ypically abou~ 200F (93.3C) to about 500F (260C)~ but higher preheat temperatures are not necessarily excluded.
The catalyst and low-coke-make solid particles fed to the reactor riser may varywidely in temperature, for example from about 1100 to about 1700F (593 to 927C)~
more preferably about 1200 to abou~ 1600F (649 to 871.1C).
The conversion of the hydrocarbon feedstock to loweq molecular weight products may be conduc~ed at a temperature ~ a~ut 8S0 to about 1400F (454 to 760C) measured àt ~e reactor Yessel outlet. Depending upon she Semperat-lre selected and the properties of the feed, all of the feed may ~r may r~t ~aporize in the reactor riser.
~Ithough ~he pressure in the reactor vessel may range ârom abou~ 10 to about 7n psia, (68.9 to 482.6 kPaj, a preferre~ pressure range ~s from abou~ 15 to about 55 psia `(103.4 to 379.2 kPa). The residence time of feed and product vapors in the reactor riser may be in the range of about 0.5 to about 6 seconds. The residence time is dependent u~on the feedstock, type and quanti~y of catalys~ and loke-coke-~ake solid particles, the 2S temperature ~nd pre~ure. One skilledin ~he hydrocar ~ proces~n~ art wi~ readily bc able to select a suitable residence Sime in order to ~ioy the benefits aiEforded by the present invenSion. IS is preferred Shat the catalyst to oil ratios be maintained from about 1 to about 30 mass of catalyst per ~ss of feedsto~k and ~ha~ the ~ow-t:oke.make solid particles ~ present in an amount sufficient to ~esult in a ~ass ratio of 3~ lo~cokffnake soUd partides ~ cracklllg catalyst from ~Itout 1~1~ t3 about la~l.
In general, the com~ination OI catalyst to oil ratio, lo~cake~nake ~slids to oil ratio, tempera~ures~ pressures and residence ~imes should be ~h as ~o ef~a substan~ial c~nverdon of the residual hydr~carbon fecdstock~ It is an advanta8e o~
the process that Yery high l~vels of conversion can be attais~d h a single pass; ~or example, the conv~rdon may ~ in excess o~ 60% and rnay r~n~e to a~out 90~6 or ' .

higher. Preferably, the afor~men~ioned condi~ions are main~ained a~ levels sufficient to maintain conversion levels in the ran~e of about 60 to about 90% and more preferably about 65 to abou~ 85%. The foregoing con~ersion levels are calculated by subtracting from lQ0% the percen~age obtained by dividing the liquid volume of fresh feed into 100 ~imes the volume of liquid produc~ boiling at and above 430F (221.1C). These sulbstantia1 1eve1s of conversion may and usua11y d~ resu1t in relatively large yields of coke, such as for example about 3.5 to about 20% by w~i~ht based on the fresh feed.
The present process preferably includes s~ripping of spent ca~alys~ and low-coke-make solid particles after disengagement from the produ~ ,rapors.
Persons skilled in ~he art are acquainted with appropriate stripping agen~s and conditions for stripping spent catalyst.
Substantial conversion of hydrocarbon oil to ligher products in accordance with the invention ~ends ~o produce sufficiently large coke yields and lS coke laydown on ~he catalyst and low-coke-make solids to require ~me care in regeneration thereof. In order to maintain adequate activity in the c~alyst, it is desirable to reger.erate under condi~ions of tirne, temperature and a~mosphere sufficient to reduce the percent by weigh~ of carbon rernaining on the ca~lyst ~o about 0.25% or less. The amounts of coke which must therefore be burned of~ in ~he regeneration zone when processin~, residual oils are substantial. Some coke ~illInevitably be deposited on the low~coke~nake solid particles and ~e burning Qf this coke from the lo~ke-make solid particles in the regeneration zone ~vill herein be referred to as regeneration even though ~15 burning is not an actual regeneration of catalytic activity. Th~ term coke when u5ed ~0 describe ~he present Imention, 2S ~hould be understood to Include any non~vaporized hydrocar~ns present Qn the catalyst and lo~coke-malce solids after stripping. Regeneration of the catalyst and lo~coke-make sol~ds by ~urnin~ away of coke teposltcd on ~e catalyst and low~
coke-make solids during the conversion of She feed may ~e performed at any suitable temperature in the range from about about 1100F to about 1600~F (~593~3 to 871.1C~
To ensure complete ccmbustion of coke w~hin the re~enera~or, a s~re~m of hot catalyst from the regenerator may be recycled to the regenerator inlet.
Heat released by combu~tion of coke in the re~enerator Is absort3ed by the catalyst and the low-coke-make solid particles, ~nd can ~e readily re~ined thereby until the regenerated mixture of ~oLids are l~ræught in~ contact ~with fr~sh 33 feed. When processing residual hydrocarbon oll to the leYels of conversion Invol~ed .. ...

in one embodiment of the present invention, a subs~an~ial amount of heat is ~enerated during coke burn~ff in the regenerator. Heat requiremen~s for the reactor include heatin~ and vaporizing the feed, supplying ~he endo~hermic heat of reaction for cracking, and makin~ up heat losses from the reactor. Heat from theregenerator is exported to the reactor via the circulation of ~he low-coke-make solid particles and catalyst. It is thus possible to control the regenerato~ temperature by varying the proportion of low-coke-rnake solids that are circulated be~ween the regenerator and the reactor with the catalyst. This provides the opportunity to have independent control of the regenerator temperature by adjusting the quan~ity o~ low-coke-make solids in the circulating mixture of low-cok~nake solids and catalyst.Reference will now be made to the attached drawin~ for discussion of Qne embodiment of the present inventionO A residual hydrocarbon feedstock entersinto reactor riser 2 via conduit 1 and is contacted with an admixture of regenerated catalyst and lo~Y-coke^make solid particles which is supplied via eonduit 13. The lS resulting combination of hydrocarbon, catalyst and low-coke-rnake solids travels in a generally upward fashion through reactor riser 2 wherein the majority of the hydrocarbon conversion occurs and enters reactor vessel 4 which has in~erior space 3. Interior space 3 serves as a disengagement area wherein the ca~alyst and the low-coke-make solids are ~eparated from the hydrocarbon vapors. The spent catalyst ~0 and low-coke--make solids are collected in ~he bottom of reactor vessel 4 and subsequently remove~ therefrom via conduit 7. Level sensing, recording and control device 20 maintains the flow rate in conduit 7 based on the differentials in pressures measured by pressure sensitive devices 18 and 19. Variations in particle inventory in reactor Yessel 4 will be reflected in a varying pressure dif~erential. Control device ~5 20 will then maintain a predetermined particle inventory by controlling control valve 21. The hydrocarbon vapors containing entrained fine par~icles o~ catalys~ and low-coke-make solids are passed into cyclone separator S and the hydrocarbon vapors containing a reduced concentration of solids are removed from reactor vessel Is ~ria conduit 6. The disengaged solids are returned to interior space 3 from the bot~om of cyclone #parator S. As is well known in the fluid cracking art, there may be a plurality o~ cyclone separators and the cyclones rnay be multistage, when the ~as phase from a first stage cyclone discharging ltO a second sta~ cyclone.
The spent catalyst and low~oke~rnake solid particles are contacted via conduit 7 with regene~ration air (or oxygen) supplied yla conduit B. ll~e admixture of 3~ air, spent catalyst and low-cok~nalce solid particles is introduced into regenerator ~17-~6~3 essel 10 which has interior space 9 Yia conduit 8. Condi~ions within regeneration vessel 10 are such that oxygen containing air and coke combine chemically ~o produce flue ~as while leaving the catalyst and the low-coke-make solid particles relatively free from coke. The resul~ing regenerated catalyst and low-coke-make solid particles are collected in an intermediate portion of reqenerator Yessel 1~ and are subsequently removed via conduit 13 and introduced into reactor riser 2 as described hereinabove. Control valve 14 is located in conduit 13 to control the flow of regenerated catalyst and lo~cok~make solid particles in response ~o a ~emperature measurement, and con~rol means 15 receives and transmits the appropria~e si~nalsvia means 16 and 17. Al~hough ~emperature sensing means 16 is shown ~o be at theupper end of reactor vessel 4 near cyclone separator 5, any other suitable temperature associated with reactor vessel 4 may be selected ~o directly controlvalve 14. Flue gas exits regeneration vessel 10 via gas-catalyst separation means 11 and conduit 12.
The following discussion is presented in order to enable those skilled in the art to more fully understand the speration of ~he process of ~he presen~
invention and to obtain the maximum benefits to be derived therefrom.
The following equation (1) may be used ~o estim~te the fluid catalytic cracker (FCC) regeneration zone or re~enerator temperature which will resul~ when ~0 low.coke_make solid particles with known specific heat and coke makin~ tendencies are circulated from the regeneration zone to the reaction zone:

(1) Final Regenerator Temperature = (A)(B~(C) ~ T Reactor The regenerator temperature predicted by the hereinabove equation assumes that all of the independent operating variables of the FCC unit are held2S constant, while the low-coke-make solid particles are ~ded in~o the circulating catalyst inventory. These independen~ operating variables include feed temperature, feed composi~ion, reac~or ~emperature, extent of carbon monoxide combustion in the regeneration zone, plant pressure and catalyst type. For the purpose of these calculations, the only change which is allowed in the operation of the FCC unit is the addi~ion of the low coke-rnake solid particles to the circulatin~
catalyst lnventory.
By holding all of the independent operating variables constant, the influence of the low-coke~ ake solid particles in lowering the regeneration zone ", ~, , -temperature c:an be more clearly seen. 0~ course9 in commercial pr~c~ice, once the re~enerati~n zon2 temperature is reduced to a desired l~vel, ~he hereinaboYe mentioned independent operating variables would normally be adjus~ed ~o take advantage o~ the reduced regeneration zone temperature.
The final re~enerator ~emperature is a furlction ~f ~he c~an~ity and specific heat of the lo~coke-make solid particles, the specific heat o~ ehe FCC
catalyst, the regenerator temperature before ~e addition of low coke~rnake solldparticles and the coke making tendency of the low coke make solid particles and the FCC catalyst.
In the hereinabove equation (1):

A = CPcatalys~
C~Catalys~ MS) ~ ( PLCMS (CLc~;~

B = (TRe~enerator lnitial ~ TReactor) ~ DCa~alyst (~ CLCMS) ~ DLCMS (CLCMS) .
DCatalyst ~vherein CLcMs is defined as the we}ght IEraction of the low colce make~ solid IS particles in the circula~ing FCC c:atalys~ inven~ory after ~he additlon of low coke make solid particles;
CpCata~y5t is defined as ~e s~cific l~at o~ ~he catalyst;
CpLCMS is defined as the specific heat of the low-coke~make 301id particles;
TRegenerator Initial ls de~ned as ~e FCC r~generator ternperature before tlte addition of the low coke-make ~ particles;
TReaCtor is defined as ~e FCC reac~or dense phase temperature;
DC~ ys~ is defined as dclta coke on thc catalyst twei~ht percen~ coke on spent FCC cat~iyst partides mim~s the weight percent coke on ~e regenerated 2S FCC ca~alyst particles); and DLCMs ~s def~ned as delta c3ke on the low-coke-n~ke solid part~cles (weight percent coke on low-coke-make sol~d particles withdrawn ~rom the reacltor minus weight percent coke on the low-cokeuTIake sol~d particles withdrawn from the regenerator.~
.

Examination of the "A" term presen~ed hereinabove indicates that low coke make solid particles with high specific hea~s should be more effec~ive since less material would be required to produce a given reduction in regenerator temperature. Note however, that even if the low-coke-rnake solid particles have a low specific heat, the process is 5till viable but more lo~coke-rnake solid particles will be required to achieve the same effect.
The "C" term presented hereinabove indica~es that low-coke-make solid particles which make little or no delta coke are more clesirable since additional coke produced by the low-coke-make solid par~icles causes additional heat release in the F~C regenerator which tends to nullify or inhibit the sou~ht after re~enerator temperature reduc~on.
Since the FCC reactor's heat demand is virtually constant and th~ FCC
unit operates in heat balance at constant operating conditions, any coke deposited on the low-coke~nake solid particles will displace coke that formerly would havelS been generated by the circulatlon of FCC catalyst. As a consequene of ~his, coke deposited on the low-coke-rnake solid particles will ~end to reduce the number of catalyst particles delivered to the riser per pound o~ feed as defined as the catalys~
to oil ratio. Thus the converslon observed in the FCC reactor will decrease. This is a strong incentive to select low~oke-rnake solid par~icles which make little or no 2û coke in order to have the least detrimental impact on the per~ormance of the FCC
reactor.
The following examples are presented in illustration of preferred embodiments of the present invention and are not intended to be an undue limitation on the generally broad scope of the invention as set out în the appended claims.

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'~ff~6~33 EXAMP E I

Tests were conducted in a commercial fluid catalytic crzcking plant to illust~ate ~he advantages of ~he present invention. The tests were based upon crackin~ a blend of Yacuum ~sas oil and atmospheric resid. Both the vacuum gas oil and the atmospheric resid were derived from a domestic crude oil and the blend contained 8.4 liquid volume percent atmospheric resid. An analysis of ~hese feedcomponents is presented in Table l.

TA~LE I - FE~ED STOCK ANALYSIS
-- htm~spneri:c Vacuum ~as. Dil -~ Pes~d~
Gravity,~API (kg/m3) 25.8 (899) l6.5 (955) Sulfur, weight percent 0 .93 l .49 Conradson Carbon, weight percent 0.29 8.5 l~ Nickel Plus Vanadium, PPM 0.2 34 Distillation I a P F (C) 5~0 ~2821 675 (3571.
5% ~35 (335~ 800 (426 690 (355) B90 ~476~
lS 40 752 (.400~ 980 ~526~.
835 (446). 1065 (~73) @ 57%
~32 (499 ) lO40 (559) E P F (C) lD76 (580) 36 Recovered 99 57 % ~ottoms 1 ~3 . . , ,' '' .. .... , , , ,; ~ : :.. ;:
- , .

' ~,~
: ., ~:

The tests wer2 conducted in an up~low riser with a zeolite ~lukl cracking catalyst. lhe oper~ng, conditions of bo~h ~ests inc~ude a reac~or pressure of 18psig ~1124 kPa gauge). The first test was conducted as a base case and is representative of a conventional FCC unit processing a feedstock comprising atmospheric resid. This S test was conducted at a catalyst ~s~ oil ra~io o~ 1~.7, a feed ~ernpera~ure of 4~1F (227C), and a reactor temperature of 972~ (~21C) with a resulting regenerator temPerature of 1363F (774C). The fresh feed conversion was 81.7 liquid volume percent while Froducin~
gasoline in an amount of 62.S liquid ~rolume percenlt and having a research octane number of 92.7. The coke yield was 5.6 weight perccnt of the feed.
~he second test was conducted as a comparative caæ and is illus~rative of one embodiment of the presen~ inven~ion. ~his ~est was conducted with the same ~eedstock comprising atmospheric resid as the ~irst tes~O This tes~ was conduc~ed a~
a catalyst to oil ra~io of 6.S, a feed temperature of 475F (246C) and reactor temperature of 970F (520C). In this test, the circulatinq catalyst stream to the reactor also lS contained low-coke-make inorganic oxide solid particles in an amount ~f 9 weight parts catalyst to one weight par~ low coke make so~ds or a catalyst to low-coke-rnake solids ratio of 9 :1 . The lo~coke-make inorganic o~ude solid particles used in this test were alpha alumina par~cles which po~es~ed a surface area oi le~ ~han about1 m2¦g and which particles generate 0 wei~ht percent carbon on the spent alpha alumina in the ASTM s~andard method ~or testing fluid cracking ca~alys~ by microactivity test ~MAT). The resultin~ ~olids Scatalyst plus low-coke~nake solid ` parti~es) to o~ ra~o was theref~re 7.~. The regenerator temperature was found to be only 1337~F (725C) as compared to 1368~F (742C) for the first test. The feed conversion was 80.S ~ ~ d volume percent while producin~ ~as~ne ~ an ~mounS of C2.7 liquid as Yolume percent and having a research octane num~er of 92.5. The coke yield ~as S.6 weight percent. It will be noted that the temperature of the feed in the second test as 47~F (246C) while the feed temperature in the first test was 441F (227C) or 34~F
(18.9C) less. It is well known for this type of FCÇ operation that an increase in the feed temperature causes an increase in the regenerator temperature. ~herefore9 with a 3Q lower feed temperature ~ the second test, a correspondingly lower regenerator temperature ~ould haYe been expected ~ch would haYe demonstrated an ~ven 8reater reduc~on in the re~enerator temperatwe. The res~ ~ of both tests are presented for ease D~ compar~onin Table 2.

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TABI E ? - TEST SUMMARY

Q~ratinR Conditions C:onfi~uration ConventionalCatalyst/LCM Sol ids Catalyst/LCM Solids, Mass Ratio100/0 90/10 FeedTemperature,F (C) 441 (227) 475 (246 ReactorPressure,PSlG (kPa nauge)18 (124) l~ (124) S Reactor Temperature, F (~C~972 (52l) 970 (520) Catalyst/Oil Ratio, KG/KG 6.7 6.7 Total So!idslOil Ratio, KG/KG 6.7 7.S
CatalystlLCM Sollds Ratio, KG/KG - 9 Regenerator Temperature, F (C)1368 (742)i337 (725) Product Distribution C~-, Wt. % 4.1 ~.0 C3, Liquid ~olume % 12.7 12.2 C4, L~iquid Volume % 15.6 14.8 Gaso~ne,Liquid Yolume ~ 62.5 62.7 Li8ht Cycle Oil,Liquid Yolume %ll.l 12.4 lS Clarified Slurry Oil~Liquid Volume % 7~2 70i Coke Yield, Wt. % 5.6 5.6 l`otal Yicld, Liquid Volume %109.1 109.~
Conversion, I.iquid Volume % 81.7 ~0.S
Gasoline Research Octane Number92.7 92.5 The above comparison demonstrates tlu~t the use of low coke make solid particles wlth the acking catalyst produced the sarne amount of coke ~s the c~talyst alon~ proiuced. The converslon and produc~ yields are comparable for both tests. From the operational standpoint, the extraordinary ad~rantage demonstrated 2S by the low-coke-rnake solids addition test ~as the abili~y to o~erate ~e catalvst regenerator at 1337F (725C) or 31F (17 2DC) less than the base or rontrol cace.
As mentioned hcreinabove, thc resultin~ lower regenerator temperature helps to maintain ~he cracking activity of the cataly~t5 proYides increaxd flexibili~y in the choice of operating conditions ~d eliminat~s, or at l~ast reduces, the requirement to provide cxternal coolin~ facilities for the cat~lyst r~enerator. The tempcra~ure of the regencrator may ~Iso be controlled indepcndently by varyin~ the proportion of low-coke-make ~olids irl l~e catalyst plus low-coke-make 301ids mixture.

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.:

.: ' This exarnple is presented to show the results of the testing of a variety of f luidizable solid particles in a test which is considered ~o b~ essentially equivalent to the hereinabove described ASTM standard method for testing crackin~
catalyst by microactiYi~y tes~ (MA~. The ~est utilized in ~his example used a feed which was a heart-cut gas oil from a Mid-Continent crude which gas oil had the properties presented in Table 3.

Table 3 - Mid-Continent Gas Oil Properties Gravi~y, API at 60F (kg/m3~31.8 (866 Sulfur, Wt. % 0.26 Nitrogen, Wt. % 0.03 Heavy Metals, ppm 3 Distillation IBP, F (C) 458 (236 2096 S81 (305) 660 (349~
70% 703 (373) 95% 775 (41 3) E.P., F (C) 810 (432) The hereinabove described gas oil feed which was used in this example was similar to, but no~ identical to, the ASTM standard feed referred to in the 2~ A TM standard procedure and was selec~ed in an attemp~ ~o duplicate ~he ASTM
standard feed.
The present test comprises loadin~ a sample of particles weighing 4 grams into the reactor and injecting the hereinabove described gas oil in an amoun~
of 1.3 grams over a 73 second period into the reactor which is maintained at 900F. (482PC~
2~ The resulting particles to oil weight ratio is about 3 and the weight hourly space elocity is abou~ 15.~.
Samples of alpha-alumina particles, gamma-alumina particles and calcined kaolin clay particles were separately tested in the hereinabove described test. Characteristics of these three materials and the resul~s of the separate tests are pre~nted in Table ~.

. . :: ~'.~ ... ,. -.. ~ . .
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, ~L~2~6~3 Table 4 - Test Results Coke on Spent ~ET Surface Pore ConversionSolicls Area, M_/G Volume, cc/~ Yol. % Wt. 96 alpha-alumina ~ 1 0 4.1 0 gamma-alumina 205 0.92 7.3 0.32 calcined kaolin clay 9 0.0154 6.6 O.OB
(3 hours At 1600F (871 .1 ~C ) ) S The gamma-alumina which was tested is representati~e of the alumina having a surface area of 30-1000 m21~ and a pore volume of 0.05 - 2.5 cc/g and which is taught as a diluen~ for catalytic cracking ca~alysS in Bri~ish Patent No.
2,116,062 (Occelli, e~ al.). The data from Table 4 show that ~amma-alunnina demons~ra~es a conversion o~ 7.3 volume percent, accumula~es 0.32 weight percen~coke on the spent gamma-alumina particles and has a surface area o~ 205 m21g. Inaccordance wi~h the present invention, the particles selected to perform the function o~ lo~coke-rnake solid particles n~ust necessarily produce less than about 0.2 weight percent coke on the spent particles in the ASTM standard method for testing cracking catalyst by microactivity test (MAT), have a surface area oiE less than about ~ rn2/~ and not substantially af~ect the operation of the reac~ion zone.
ThereIore, since the gamma-alumina accumula~ed a relatively substantial amount of coke and had a propensity to convert hydrocarbons thereby havinE~ the undesirable ability to affect the operation of an ~CC reaction zone9 gamma-alumina is not a satisfactory candidate for use as the lo~coke make solid particles in the presen~
2a imention.
The calcined kaolin clay which was tested as hereinabove described is believed to be representative of the calcined kaolin clay which is ~au~ht as a 5arge pore inert material to be added with active catalyst in U.S. Patent No. ~,289,605 ~Bartholic). The data from Table 4 show that calcined kaolin clay demonstrates a~S conversion of S.6 volume percent, accumul~tes 0.08 weight percent coke on the spent kaolin clay particles and has a surface area of 9 m21g. In accordance with the present invention, the particles selected to perform the function of low coke make solid particles must necessarily produce less than about 0.2 weight percent coke on the spent particles in the ASTM standard method for testing cracking catalyst by , ,. ~. ; ' :' : ~ .: .. : . -, ::, . . .
~ ' '' "'' ' :. ~ ''~' ' :

microac~ivity test (MAT), have a surface area of less ~han about S m21g and not substantially affect ~he operation of ~he reaction zone. Th~refore, since the calcined kaolin clay accumulated measurable coke9 had a propensi~y ~o convert hydrocarbons ~hereby als0 havin~ the undesirable ability ~o affect the ~peration of an FCC reaction zone and had a surface area of ~ m21g, the calcined kaolin clay, as tested, is not ~onsidered to be a sa~isfactory candidate for use as the low-coke~rnake s~lid particles in the present inven~ionO
In accordance with the present invention, preferred low~coke-make particles are fluidizable alpha alumina particles. The data ~rom Table 4 show that alpha-alumina demonstrates what is considered a minimal conversion of 4.1 ~rolume percent, accumulates no detectable coke on ~he spen~ alpha-alumina in ~he ASTM
standard method for testing fluid catalytic cracking catalys~ by microac~ivi~y test and has a surface area of less than 1 m2/g. In order to enjoy the maximum benefits from the process of the present invention it is preferable that the fluidizable lowO
lS coke-make solid par~icles have a surface ~rea of less than about S m2/g and generate less than about 0.2 weight percent coke on ~e spent lo~oke-make solid particles in the ASTM standard method for testing fluid cracldng catalyst by microactivity test ~MAT). Fluidizable low~coke-make solid particles which ~enerate substantially less than 0.2 weight percen~ coke on ~he spent low-coke~nake solid~0 particles in the ASTM standard method for testing f~uid cracking catalys~ by microactiv~y test (MAT~ are even more preferred. Most preferred low~oke~nake solid particles have a surface ar~a of less than about S m21g and generate less than a~out 0.05 weight percent coke on the spent low-coke~nake solid par~icles in theASTM standard method for testing fluid cracking ~talyst by microactivity test 2~ (MAT).
It ~s important ~o note ~:ha~ any coke ~hat is ~or~ednontthe fluid~zable solid particles added for purposes of temperature control is necessar~ly produced by nonselective oracking of the feed stream and thus has a sign;ficant adverse affect on the yield structure Of gh2 products from ~he r~actor. This adverse affect of the solid adjuvant is of course magnified as the level o~ coke formed increases and thus a low-coke-make characteristic is an essential feature both for proper operation of the reactor and for achiev~ng te~perature reduction in the regenerator, ~26-`' `' ~ ~ '` ' ~ ' ~, :' ' ` `"
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Claims (9)

CLAIMS:

1. A method for operating a fluid catalytic cracking unit compris-ing a regeneration zone and a reaction zone while processing a high-coke-make hydrocarbon feedstock having a 50 volume percent distillation temperature greater than about 500°F (260°C) which method comprises:
(a) contacting at endothermic, coke-making conversion conditions said feedstock in the reaction zone with a fluidizable heated mixture of regenerated cracking catalyst and low-coke-make non-catalytic solid particles, comprising a refractory inorganic oxide, in a ratio of low-coke-make solid particles to cracking catalyst from about 1:100 to about 10;1, said low-coke-make solid particles having a surface area of less than about 5 m2/g and a coke making capability of less than about 0.2 weight percent coke in the ASTM standard method for testing cracking catalyst by microactivity test (MAT);
(b) separating the resulting hydrocarbon products from the mixture of coke-containing cracking catalyst and low-coke-make solid particles;
(c) recovering the hydrocarbon products;
(d) passing said mixture of cracking catalyst and low-coke-make solid particles to said regeneration zone for reheating and regeneration by exothermic combustion of coke; and (e) passing the resulting reheated and regenerated mixture of cracking catalyst and low-coke-make solid particles from said regeneration zone to said reaction zone to contact said feedstock as described in step (a) whereby said regeneration zone temperature is maintained at a reduced temperature as compared to an equivalent operation without the use of said low-coke-make solid particles while simultaneously not reducing the coke burning capacity of the regeneration zone or affecting the operation of said reaction zone.

2. The method of Claim 1 wherein said low-coke-make solid particles comprise alpha-alumina.

3. The method of Claim 1 wherein said low-coke-make solid particles have a surface area of less than about 5 m2/g and a coke making capability of less than about 0.05 weight percent coke on the spent low-coke-make solid particles in the ASTM standard method for testing cracking catalyst by micro-activity test (MAT).

4. The method of Claim 1 wherein said low-coke-make solid particles have an overall particle size in the range from about 5 to about 2000 microns.

5. The method of Claim 1 wherein said mixture of regenerated catalyst and low-coke-make solid particles are fed to said reaction zone at a tempera-ture from about 1200°F to about 1600°F (649 to 871°C).

6. The method of Claim 1 wherein said conversion conditions include a pressure from about 15 psia to about 55 psia (103 to 379 kPa), a catalyst to oil weight ratio from about 1:1 to about 30:1, and a temperature from about 850° F to about 1400°F (454 to 760°C).

7. In a process for fluid catalytic cracking of a high-coke-make hydrocarbon feedstock having a 50 volume percent distillation temperature greater than about 500°F (260°C) by contacting the feedstock at endothermic cracking conditions with a circulating, heated particle form, solid cracking catalyst whereby components of the feedstock are converted to lower boiling hydrocarbons in a reaction zone with concurrent cooling of the catalyst and deposition thereon of a deactivating carbonaceous contaminant, regenerating the catalytic cracking activity of the contaminated catalyst by burning carbonaceous deposits therefrom in a regeneration zone under exothermic conditions that result in the catalyst and the regeneration zone reaching an unacceptable or undesired maximum temperature condition, and thereafter cir-culating catalyst so reheated and regenerated from the regeneration zone to the reaction zone, wherein the improvement comprises reducing the maximum temperature reached in the regeneration zone without reducing the amount of coke burned therein by simultaneously circulating, in admixture with the cracking catalyst, fluidizable low-coke-make solid particles, which comprise a refractory inorganic oxide and have a surface area of less than about 5 m2 /9 and which generate less than about 0.2 weight percent coke in the ASTM standard method for testing fluid cracking catalysts by microactivity (MAT), said solid particles being present in an amount sufficient to result in a ratio of low-coke-make solid particles to cracking catalyst from about 1:100 to about 10:1, thereby lowering the regeneration temperature from about 10°F to about 250°F (6 to 139°C) while simultaneously not affecting the operation of the reaction zone.

8. The improved process of Claim 7 wherein said low-coke-make solid particles comprise alpha-alumina.

9. The improved process of Claim 7 wherein said low-coke-make solid particles have a surface area of less than about 5 m2/g and a coke making capability of less than about 0.05 weight percent coke in the ASTM
standard method for testing cracking catalyst by microactivity test (MAT).