CA1124224A

CA1124224A - Process for removing pollutants from catalyst regenerator flue gas

Info

Publication number: CA1124224A
Application number: CA295,966A
Authority: CA
Inventors: Robert L. Flanders; William A. Blanton, Jr.
Original assignee: Chevron Research and Technology Co
Current assignee: Chevron USA Inc
Priority date: 1977-04-11
Filing date: 1978-01-31
Publication date: 1982-05-25
Also published as: FR2387282B1; JPS53128568A; IT7822198A0; JPS6312114B2; IT1096173B; FR2387282A1; DE2815069A1; NL7803830A; GB1591594A; BE865823A; DE2815069C2

Abstract

ABSTRACT OF THE DISCLOSURE
PROCESS FOR REMOVING POLLUTANTS
FROM CATALYST REGENERATOR FLUE GAS

Carbon monoxide and sulfur oxides are removed from flue gas produced in a catalyst regenerator in as FCC system and sulfur from the flue gas is shifted to form hydrogen sulfide, which is recovered in the gases removed from the cracking reactor in the system by reacting carbon monoxide in the regenerator flue gas with oxygen in contact with a particulate carbon monoxide combustion promoter, reacting sulfur oxides in the regenerator flue gas with particulate alumina physically mixed with the FCC catalyst to form a sulfur-containing solid, and forming hydrogen sulfide in the cracking reactor by contacting the sulfur-containing solid with the hydrocarbon feed.

Description

llZ4~24 BACKGROUND OF THE INV~N ION

2 This invention relates to a method for reducing the

3 amount of carbo~ monoxide and sulfur oxides in the flue gas

4 produced in a catalyst regenerator in a fluid catalytic cracking system.
6 ~odern hydrocarbon catalytic cracking systems use a 7 moving bed or fluidize~ bed of a particulate catalysmhe 8 cracking catalyst is subjected to a continuous cyclic ~racking 9 reaction and catalyst rege~eration procedu_e. In a fluidized catalytic cracking t~CC~ system, a stream of hydrocarbon fe~d is 11 contacted with fluid~zed catalyst particles in a hyd.ocarbon 12 cracki~g zone, or reactor, usually at a temperatu-e of about 800-~ 11COaFo The reactions o~ hydrocarbons in the hy2rocarbon stream 14 at this temperature rasult in deposition of carbonaceous coke on the catalyst particles. The resulting fluid p~oducts are 16 thereafter s~parated from the coked catalyst and ara withdra~n 17 from the crac~ing zone. The co~ed cat~lyst is then stripped of 18 volatiles and is passed to a catalyst rQgeneration zone. In the 19 catalyst regsnerator, the coked catalyst is contactsd with a gas containing a controlled amount of molecular ox~gen to burn off a 21 desired p~rtion of the coke from the catalyst amd simultaneously 22 to heat the catalyst to a high temperatu-s dQsired when tha 23 catalyst is again contacted with the hydrocarbon stream in the 24 cracking zone. ~fter regeneration, the catalyst is returned to the crac~ing zone, where it is used to vaporize the hydrocarbons 26 and to catalyze hydrocarbon crac~ing. The fluê gas formed by 27 combustion of co~e in the oatalyst regenerator is separ~tely 28 remo~ed from the regenerator. This flue gas, whlch may be 29 treated to remove particulates and carbcn mor,oxide from it, is normally passed into the atmosphere. Ccncern with control of 31 pol1~tants in flue gas has resulted in a sea~ch for ~mproved ~.~ Z~224 1 methods for cont.olling such pollutants, particularly sulfur 2 oxides and carbon monoxide.
3 The amount of conversion obtained in an FCC cracking 4 operation is the volume perc~nt of fresh hydrocarbon feed changcd to gasoline and lighter products during the conversion step. The 6 end boilirg point of gasoline for the purpos~ of de~ermining 7 conversion is convqntionally defined as 430F. Conversion is 8 often used as a measure of the severity of a commercial FCC
9 operation. At a given set of operatîng conditlons, a ~re active catalyst gives a greater conversion than does a less active 11 catalyst. The a~ility to provide higher conversion ir ~ given 12 ~CC unit is d~sirable in that it allows ~hs FCC urit to be 13 operated in a more flexible manner. Feed throughput in the unit 14 can be increased, or alternat vely a higher degree of conversion ca~ ~e maintainsd with a constant feed throughput rate.
16 The hydrocarbon feeds prccessed ln commercial ~CC units 17 normally contain sulfur, usually termed "feed sulfur". It has 18 been found that about 2-105 or more of the faed sulfur in a 19 hydrocarbon feedstream processed in an FCC system is lnvariably tra~sferred from the feed to the catalyst particles as a part of 21 the coke formed on.the catalyst particles during cracklng. The 22 sulfur deposit6d on tha ca~alyst, herein te med "coke sulfur"~ is 23 eventually cycled from the conversion zone along wlth the coked 24 catalyst into the catalyst regenerator. Thus, about 2-10% or more of the sulfur in tbe hydrocarbon f~ed is continuously passed 26 ~ro~ the cracking zone into the catalyst regeneration zone in the 27 coked catalyst. In an FCC catalyst regenerator, sulfur contained 28 in the co~e is burned along with the coke car~on and hydrogen, 29 forming gaseous sulfur dioxide and sulfur trioxide, ~hi_h ar_ conventionally re~oved from ths regenerator in the flue gas.

1 ~ost of the feed sulfur does not become coke sulfur in 2 the cracking reactor. Instead, it is ccnverted either to 3 normally gaseous sulfur compounds such as hydrogen sulfide and 4 car~on oxysul~ide~ or to normally liquid organic sulfur S compaunds. These organic sulfur compounds are carried along with 6 the vapor products and recovered from the cracking re2ctor.
7 ~out 90% or more of the feed sulfur is thus continuously removed 8 from the cracking reactor in the stream of processed, cracked 9 hydrocarbo~s, ~ith abou~ 40-60% of t~is sulfur being in the form of hydrogen sulfide. Provisions are conventionally made to 11 recover hydrogen sulfide from the ef.luent from the cracking 12 reactor. Typically, a very-lo~-molecular-weight off-gas vapor 13 straam is separa~ed from the C3+ l~guid hydrocarbons in a gas 14 recovery unit, and the off-gas is treated, as by scrubbing il ~i h an amine solution, to remove the hydrogen sulfide. Removal 16 of sul~ur compounds such as hydrogen sulfide from the fluid 17 effluent from an FCC cracking reactor is relatively simpl~ and 18 inexpensive compared to removal of sulfur oxldes ~rom an FCC
19 reganerator flue gas by conventional methods. ~oreover, l all the sulfur ~hich must ~e recovered ~rom an FCC opera~ion could be 21 recovered in a slngle recovery operation pe~form6d on 'he reactor 22 off-gas, the use of t~o separate sulfur recovery operations in an 23 FCC unlt could be obviated.
24 It has been suggested to diminish the amount of sulfur oxides i~ PCC regenerator flue gas by desulfurizing a hydrocarbon 26 feed in a separate desulfurization unlt prior to cracking or to 27 desulfurize the regenerator flue gas its~lî, by 2 conventio~al 28 flae gas desulfurization proccdure, after removal from th~ FCC
29 regenerator. Cl2arly, ~oth of the foregoing alternativcs require elaborate, extraneous processi~g operations and entail large 31 capi~al and utilities expenses.

~L~242Z4 1 If sulfur normally removed from the FCC unit in ths 2 regenerator flue gas as sulfur o~ides is instsad removed from the 3 cracking reactor as hydrogen sulfide along ~ith the procassed 4 cracked hydrocarbons, the sulfur thus shifted to the reactor

5 effluent is then simply a a small addition to the large amount of

6 hydrogen sulfide and organic sulfur already invariably present in

7 the reactor effluent. Ihe small adaed expense, if any, of

8 removing even as much as 5-15~ more hydroger. sulfide from an FCC

9 reactor off-gas by available means is substan.ially less than the expense of separate feed desulfurization or flue gas desulfuri-11 zation to reduce the level of sulfur oxides in the regenerator 12 flue gas. ~ydrogen sulfide recovary systems used lr. present 13 commercial FCC units normally have the capacity to remove 14 additional hydrogen sulfide from the reactor off-gas. Pr~sent off-gas hydrogen sulfide reco~ery facilities could no~mally 16 handle any additional hydrogen sulfide which would be added to 17 the off-gas if the sulfur normally in the regsnerator flue gas 18 were substantially all con~er~ed to hydrogen sulfide in the FCC
19 reactor off-gas. It is accordi~gly desirable to direct substan-tially all feed sulfur into the fluid cr~cksd products rQmoval 21 pathway from the cracking reactor and reduce the amou~t of sulfur 22 oxidcs in the regsnera~or flu~ gas.
23 It has been suggested, e.g., in U.S. Patant 3,699,037, 24 to reduce t~e amount cf sulfur oxides in FCC regenerator flue gas by adding particles of Grou~ ~IA metal oxides and/or carbonates, 26 such as dolomite, ~gO or CaCo3, to the ci_cula+ing catalyst in an 27 FCC unit. The Group IIA metals react ~ith sulfur oxides in the 28 flue gas to form solid sulfur-containing compounds. The Group 29 IIA metal oxides lack physical strengthl and regardless of the size of the particles introduced, they are rapidly r^duc~d to 31 fi~es by attrition and rapidly pass out of the ~CC uri' with tne ~1242'Z4 1 catalyst fines. Thus, addition of dolomite ~nd the like Group 2 IIA materials is a continuous, once through process, and large 3 amounts of material must be employed, in order to rsduce the 4 level of flue gas sulfur o~ldes for any significant period of tima.
6 It has also bee~ suggest~d, e.g., in ~.s. Pat-ent 7 3,835,031, to reduce the amount of sulfur oxides in an FCC
8 regenerator flue gas b~y impregnating a Group IIA metal ~xida onto 9 a conventional silica-alumina cracking catalysThe attrition problem encountered whsn using unsupported Group II~ metals ls 11 thereby reduced. However, it has beer. found that Group IIA metal 12 o~idas, such as mag~esia, when used as a component of cracking 13 catalysts, have an undesirable effect on the activity and selec-14 tiYity of the cracking catalysts. The addi~ion of a Group IIA
mçtal to a cracking catalyst results in two particularly 16 noticeable adverse consequences relative to the results obtained 17 in cracking without the presence of tha Group IIA metals: (1) 18 the yield or the liquid hydrocarbon fractio~ is su~stantially 19 reduced, typically by greater than 1 volume percent of the feed -20 volume; and (2) the octane rating of the gasoline or naphtha 21 fraction (75-430F boiling ra~ge) is substantially reduced.
22 Both of the above-noted adverse consequences are seriously detri-23 me~tal to the economic viability of an FCC cracking operation and 24 eve~ complete removal of sulfur oxides from regener~tor flue gas would not compensate for the losses in yield and octane ~hich 26 result from adding Group IIA metals to an FCC catalyst.
27 Alumina has ~een a component of mar.y FCC and o~her 28 cracking catalysts; bu~ primarily in intimate chemical 29 combination with silica. Alumina itself has low acidity and i5 generally considered to be undesirable for use as a cracking 31 catalyst. The art has taught that alumina is not selecti~e, .. .

42Z~

1 i.e., the cracked hydrocarbon products recovered from an FCC or 2 other cracking unit using an alumina catalyst would not be 3 de~ired valua~le products, but would include, for example, rela-4 tively large amounts of C2 and lighter hydrocarbon gases.
~he conventional type of FCC catalyst reganer~tion 6 curren,ly used in most systems is an incomplate combustlon mode.
7 In such systems, referred to herein as "standard regQneration"
8 systems, a substantial amount of coke carbon is left on 9 regenerated catalyst passed from the FCC regsneration z~ne to the cracking zone. Typically~ regenerated catalyst contains a 11 substantial amount of coka carbon, i.e., more than 0.2 ~eight 12 percent carbon, usually about Q.25 to 0.45 weight perce~t carbon.
13 The flue gas remored from an FCC regenerato. operating 1~ a 14 standard regeneratio~ mode is characterized by a relatively high carbor. monoxide/carbon dioxide concentration rztio. Th~
16 atmosph~re in much or all of the regeneration zone is, ~ver-all, 17 a r~ducing atmosphere because of the presence of substantial 18 amounts of unburned cok~ carbon and carbon ~or.oxide.
19 In general, reduci~g the level of carbon on regsnerated cata~yst below about 0.2 weight percent has been di-ficult.
21 Until recently, there has been little incentive 'o attempt to 22 remove substantially all coke carbon from the catalyst, slncs 23 eYen a fairly high carbon content has had little advsrse effect 24 on the activity and selectivity of amorphous silica-alu~ina catalysts. Most of the FCC cracking catalysts now used, ho~evar, contain zeolites, or molscular sieves. Zeolite-containing 27 catalysts have usually be6~ found to have rsla'ively highar 28 activity and selectivity when their coke carbon content after 29 rege~eration is relatively low. An incentive has thus ~risen for attempti~g to reduce the coke content of regen2ratsd FCC cztalyst 31 to a v6ry lo~ level, e.g., b610w 0.2 ~eight percent.
..

~LlZ4;~:Z4 1 Several methods have been suggested for burning sub-2 stantially all carbon monoxide to carbon dioxide during 3 regeneration, to avoi~ air pollution, recover heat and prevent 4 afterburning. Among the procedures suggested for use ln obtaining complete carbon monoxide combustion 'n an FCC regens-6 rator have been: (1) increasing the amount of o~ygen introduced 7 into the regenerator relative to standard regeneration; and 8 eitber (2~ increasing thé average opsrating temperature in the 9 regenerator or (3) including vari OQS carbon monoxide oxidation promaters in the cracking catalyst to promots carbon monoxide 11 burning. Various solutions have also been suggested for the 12 problem of afterburning of carbon monoxide, such as addition of 13 extraneous comDustibles or use of ~ater or hsat-accepting solids 14 to absorb the heat of combustion of carbon monoxide.
1~ ~hen using carbon monoxide combustlon promoters hereto-16 fore commercially available, such as Group VIII noble m2tals in 17 PCC catalysts, to provide complste carbon mono~ide combustion, it 18 has been fou~d quits dif~icult to maintain the amount of coke on 1g regenerated catalyst at a~ acceptably low level. Promoter materials when added to t~e catalyst have been been found to 21 provide adequats C0 combustion in many cases, but have not been 22 ~ell accep~ed commercially because o~ the resul~ing high level of 23 coke on regenerated catalyst, which has lo~ered conversion.
24 Complete combustion systems using an unusually high temper~ture in the catalyst reganerator to accompllsh comp1~te 26 carbon monoside combustion are also not altogether satisfac~ory.
27 Some of the heat generated by carbon monoxide ccmbus+.ion is lost 28 i~ the flue gas, because CO combustion takes place essentially in 29 a dilute catalyst phase in an after-burning mode, and high temperatures can permanen~ly adversely affect the activi~y nd 31 selectivity of the FCC catalyst.

~Z4;~:24 1 Several types of addition of Group VIII noble metals 2 and other carbon monoxide combustion pro~oters to PCC systems 3 haYe been suggested in the art. In ~.S. ~atent 2,647,860 i~ is 4 prop~sed to add 0.1-1 welght percent chromic o~i~e to ~n FCC
catalyst to promote ccmbustion of carbon monoxide to carbon 6 dioxide and to prevent afterburning. ~.S. Patent 3,364,136 7 proposes to employ particles containing a small pore (3-5 A.3 8 molecular sieve ~it~ which is associated a transitior metal from 9 Groups IB, IIB, VIB, VII3 and YIII of the Deriodic Table, or compounds ther~of, such as a sulfide or oxide. Represen~ative 11 matals disclosed include chromium, nicke1, iron, molybdenum, 12 cobalt, platinum, palladium, copper and zi~c. The metal-lo~ded, 13 small-pore zeolite may be used in an PCC system in physical 14 mixture with cracking catalysts containing larger-pore zeolites active for crac~ing, or the small-pore zeolite may be ~ncluded in 16 the same matrix witA zeolites active for crac~lr.g. The small-17 pore, metal-loaded zeolites are supplied for the purpose of 18 incr~asing the C02/C0 ratio in the flue gas produced in the FCC
19 regenerator. In ~.S~ ~atent 3,788,977, it is proposed to add uranium or platinum impregnated o~ an ~norganic oxide such as 21 alumi~a to an ~CC system, either in physical mixture ~it~ FCC
22 catalyst or incorporated into the same amorphous matrix as a 23 zeolite used for cracking. Uranium or platinum is added for the 24 purpose of producing gasoline fractions having high aromatics conter.ts, and no effect on carbon monoxide combus.ion ~h~n using 26 the additive is discussed in the patent. In ~.S. Patent 27 3,808,121 it is propos~d to supply larg~-siz2 particles of a 28 carbon monoxide ccmbustion promoter in an ~CC regenerator. The 29 snaller-size catalyst particles are cycled between the FCC
crac~ing reactor and the catalyst regenerator, while, because of 31 their sizQ, the larger promoter particles r~main in 'he , g _ l~ Z~Z4 1 regenerator. Carbon monoxide oxidation proinoters such as cobalt, 2 coppe., nickel, manganese, copper chromite, etc., impregnated on 3 an inorga~ic oxide such as alumina are disclosed fo. use.
4 Relgian patent publication 820,181 suggests using catalyst particles con~aining Flatinu~, palladium, iridium, rhodium, 6 osmium, ruthenium or rhenium or mixtures or compounds ~hereof to 7 promote carbon monoxide oxidation in an FCC catalyst regenerator.
8 ~n amount between a trace and 100 ppm of the active metal is 9 added ~o FCC catalyst oar'icles by incorpora.ion during ca+alyst manufacture or by addition of a compound of the metal t~ the 11 hydIocarbon fsed to an FCC unit using the catalyst. Th~
12 publication notes that addition of the promoter metal increases 13 coke a~d hydrogen format~on during cracking. The catalyst 14 containing the promoter m~tal can be used as such or can be added 1~ in physical mi~ture with unpromoted FCC cracklng catalyst.
16 Applicants' smployer and/or affiliates thereof 17 purchased quantites of particulate additiqes from catalys~
18 ma~ufacturers. The additives were sold by the manufacturers for 19 the purpose o~ introducing the additives into circulation in admixture vith FCC catalyst in FCC uni+s to promote combusticn of 21 carbcn monoxide during catalyst regeneration ir the ur.its.
22 Arplicants' employer and/or affillatos thereof used the additives 23 in their commercial FCC operations. One such additive ~as 24 understood to contain a mixture of platinum-alumina oarticles and silica-alumina particles~
26 SUWWARY OF TH _INV~NTION
27 In an embodi~ent of the invention e~ployed in a 28 cataly~ic hydrocarbon cracking process wherein a cracking 29 catalyst is cycled betveen the cracking zone and a catalyst regeneration zone, a sulfur-containir.g hydrocarbon stream is 31 cracked in contact w th the catalyst i~ the cracking zone, and a ~L~Z4;~2~
carbon monoxide-containing and sulfur-containing flue gas is formed in the regeneration zone by burning sulfur-containing coke off the catalyst with an oxygen-containing gas, the invention relates to a method for reducing the amount of carbon monoxide and sulfur oxides in the flue gas, which eomprises: reacting carbon monoxide and oxygen to form carbon dioxide in the regeneration zone in contact with a carbon monoxide oxidation promoter comprising a metal or compound of a metal selected from platinum, palladium, iridium,rhodium,osmium, ruthenium, eopper and ehromium; forming a sulfur and aluminum-containing solid in the regeneration zone by reaeting sulfur trioxide with alumina, the alumina being included in a seeond partieulate solid physically admixed with the eatalyst, and the seeond partieulate solid being substantially free from the noble metal or metal eompound; and removing sulfur from the reaetant and forming hydrogen sulfide in the eraeking zone by eontaeting the sulfur and aluminum-eontaining solid with the hydroearbon stream.
In one more limited embodiment of the method of the invention, the carbon monoxide combustion promoting metal is incorporated into the cracking catalyst itself, and an alumina-containing particulate is physieally mixed with the promoted eatalyst and the mixture is eireulated in a eraeking system.
In another more limited embodiment of the method of the invention, the earbon monoxide eombustion promoting metal is ineorporated in a first partieulate solid while the alumina for removing sulfur oxides is ineorporated in a second particulate solid, with both the first and seeond particulate solids being physically mixed with the craekinq eatalyst, and the resulting three-component mixture is eireulated in a eraeking system. It is preferred that the earbon monoxide oxidation promoter ineludes from 0.01 to 20 weight pereent of the metal, ealeulated B

~24224 as the elemental metal.
In another embodiment, the present invention relates to a composition of matter comprising a physical mixture of:
(1) particulate hydrocarbon cracking catalyst; (2) a first - lla -~L~Z~2Z~

1 particulate solid comprlsing an inorganic o~ide associa~ed ~ith 2 0.01 to 2 weight percent platinum or a platinum compouna, 3 calculated as the metal, the first particulate solid being in 4 admixture with the catalyst in an amount sufficient to p ovide 0.01 to 100 parts per million, by ~eight, of platinum, ~ith 6 respect to the catalyst; and (3) a second particulzte solid 7 comprising at least 60 ~eight percent alumina, the second 8 particulate solid being substantially free from platinum, and the 9 second particulate solid being in admixturs with the catzlys, in an amount sufficient to provide 0.1 to 25 wQight percent alumina, 11 ~ith respect to the cztalyst.
12 We have found that the use of a partlculate carbon 13 moroxide com~ustion promoter containing a metal or metal compound 14 very active for C0 combustion promotion in conjunction ~ith the use of particulate alumina for reaction with sulfur oxides in 16 regenerator flue gas provides a synersistic metho2 for re~oving 17 both car~on monoxide and sulfur oxides from the regenera~or flue 18 gas. 3y proceeding according to a preferrsd embodiment of the 19 method of the invention, it is possible to add exac~ly ~he desired amount of C0 combustion promoter to burn the exactly 21 desired amount of carbon monoxide in the flue gas, and likewise 22 to add exac'ly the d~sired amount of alumina reactant to provide 23 a titrated amount of sulfur oxides removal ~rom the reganerator 24 flue gas~ Advantages of adding the separate promoter particles and alumina reactant particl~s include the ability to change the 26 mode of opQration in relation to carbon monoxide combustion or to 27 sulfur oxides ~emoval without recourse to changing the ~hole 28 catalyst inventory of a catalytic crac~ing unit.
29 DETAILED_DFSCRIPTIC~ OF 'rH:E INV_NmION
The present invention is used in connection ~ ~h a 31 fluid catalyst cracklng process for crzc~ing hydrocarbon feeds.

l~.Z4Z2~

1 The same sulfur-containing hydrocarbon feed normally pr~c~ssed i~
2 ccmmercial FCC systems may be processed in z cracking systsm 3 employing the present invention. Suitabl~ fsedstocks i~clude, 4 for exa~ple, gas oils, light cycle oils, heavy cycle oils, atc., vhich usually contain about 0.1-10 ~eight percent sulfur~ Sulfur ~ay be present in the feed as a thiophene, disulfide, thioether, 7 etc. Suitable feedstocks normally boil in the _ange from about 8 400-1100~ or higher. A suitable feed may incIude recycled 9 hydrccarbons which have already been cracked.
~he cracking catalyst employed may be a conventional 11 particulate cracking catalyst including silica and aiunina. The 12 catalyst nay be a conventional amorphous cracking catalyst 13 containing a mlxture of silica and alumina, or more preferably 14 the catalyst may be conventional zeolite-containing cra_king 1~ catalyst including a crystalline aluminosilicate zeolite 16 associated with an amorphous matrix which is generally sillca-17 alumina. Th~ amorphous matrix generally const-tutes 85-95 weiqht 18 percent of tha cracking cata~yst, with the remaining 5-15 ~eig~t 19 percent bei~g a zeolite component dispersed on or embedled in +he matrix. The zeolite may be rare earth-exchanged or hydrogen 21 exchanged. Conventional zeolite-contalning cracking catalysts 22 often include an X-type zeolite or a Y-type zeolite.
23 Cracking conditions employed in the cracking ~r 24 conversion step in an FCC system are frequently provlde~ in part by pre-heating or heat-excha~gir.g hydrocarbon feeds to bring them 26 to a temperature of about 600-750F before introducing them into 27 the cracking zone; ho~ever, pre-heating of the feed is not 28 essential. Cracking conditions include a catalys+/hydrocarbon 29 weight ratio of about 3-10. A hydrocarbon weigh. space velocity i~ th cracking zo~e of about 2-50 per hour is preferably used.
31 The average amount of coke contained in the catalyst after ,.
- t3 -~L12~24 1 contact ~ith the nydrocarbons in the cracking zone, when t.he 2 catalyst is passed to the regenerator, is preferably bet~een 3 about 0.5 ~eigh~ percent and about ~5 weight percent, depsnding 4 in part on the carbon content of regensrated catalyst in ~he particular system, as ~ell as ths heat ~alanca of the pa~icular 6 system.
7 The catalyst regeneration zone used in an FCC system a empl~ying an smbodiment of the present invention may be of 9 conventional design. The gaseous atmosphere inside the regeneration zone is normally co~prised of a mixture of gases in 11 concentrations which vary according to tha locus withln the 12 rsgensrator. The concentrations ~ f gases also ~ary acco-di~g to 13 the coke concentration on catalyst particlss entering the 14 regenerator and according to the amount of molecular oxygen and steam passed into the regeneralor. Generally, the gaseous 16 atmosphere in a regenerator contains 5-25~ steam, varying amounts 17 of o~ygsn, carbon mono~ide, nitrogen, carbon dioxider sulfur 18 dioxide, a~d sulfur trioxide. I~ order ~o facilitate rsmoval of 1~ sulfur conten.s from the regenerator flus gas ~ithin the regenC-rator according to the invention, it is prsfer_ed that rslatively 21 coke-free particles containing active alumina must contact ths 22 gaseous regenerator at~osphere at a locus at ~hich the atmosphere 23 contains sulfur trioxide or molecular oxygen and sulfur dioxids.
24 In rege~erators of conventional design, the flue gas includes the desired components ar,d catalys' rormally contac~s the flue gas at 26 this point, af~er havlng been freed of a substzn.ial amount of 27 coke. ~hen regeneratcrs of this type are e~ploycd, contact 28 between relatively coke-free alumina-containlng ?artlcles and the 29 oxygen ar.d sulfur dioxide or sulfur trioxide is fac_litated.
According to one aspect of the i~ventlon, a carbon 31 ~onoYide combQstion promoter is em~loyed ln an FCC system. The ~.

l~.Z4224 1 carbon monoxide combustion promotsrs which are suitable for use 2 according to the inv~ntion are the metals platinum; palladium, 3 iridium, rhodium, os~ium, ruthenium, coppsr and chro~ium, or 4 compounds thereof, such as the oxides, sulfides, sulfates, etc.
S At least one of the foregoing metals or metal compounds is used, 6 and miYtures of two or more of the metals are also suitable. For 7 example, mixtures of platinum and palladlum or copper and 8 chromium are suitable. Tha effect of +he abo~e-mentioned carbon 9 monoxids com~ustion promoter metals may be enhanced by _ombining them with small amounts of other mstals or metalloids, particu-11 larly rhenium, tin, ger~anium or lead.
12 The carbon monoxide com~ustion promotar is employed ln 13 the PCC system in cne or both of two ~ays: (1) the promoter is 14 incorporated, preferably at a very small concantration, int~ the ECC catalyst or into a substantial port-on (a.g., more than 10~) 16 of t~e FCC catalyst, as by impregnation, ion exchznge, etc.; or, 17 more preferably, (2) the promoter is prasent in the system in 18 association with a relatively small a00unt of a particulate solid 19 other than the catalystt such as particles Oc alumina, silica, etc., suitable for circulation in an FCC system, o- the promoter 21 is present in an insubstantial portlon (e.g., lass than S~ and 22 preferably less than 1~) of the FCC catalyst particles, with ~he 23 promoter metal thus being present in physical mixture with all or 24 substantially all of the FCC catalyst. When used in th~
preferred physical mixture with the FCC catalyst, the promo'-r 26 matal is preferably prase~t in a particulate solid in a 27 relatively high concentration. Howe~er, the over-all 28 concentratio~ of the promoter with raspect to the total catalyst 29- is comparable to the amount used ~hen the promoter is added to the catalyst itself.

Z~ZZ4 1 Irrespective of whether the promoter employed is 2 incorporated in the FCC catalyst or is incorporated in a separate 3 particulate solid physically mixed with the catalyst, the total 4 amount of promoter ~etal added to the system is preferably sufficient to promote combustion of most or su~stantially all of 6 the carbon ~onoxide produced in an FCC regenerator.
7 Platinum is a partlcularly preferred promoter for use 8 in the present method. The total amount of platlnum added to an 9 FCC systam, if the platinum is present on the catalys~ itself, is preferably ~atween about 0.05 and 20 ppm (weight), vith respect 11 to the total amount of catalyst in the system. In the preferred 12 case in which the platinum is prese~ on only a small fraction of 13 particles in the sys~em~ i.e., when +he platinum s located on 14 the particulate solid physically admixed wi~h the FCC catalyst, it is preferred that the total amount of platinum added ~o an FCC
16 system ~e bet~een about 0.01 and 100 parts ~er million, by 17 weight, with an amount between about 0.1 and 10 parts per million 18 bei~g particularly preferred, Yith respec~ 'o the total amount of 19 catalyst in ths system. It will be apparent that the amount o.
platinum present in a given discrete particle added to an FCC
21 system will be greater when fewer particles containing the 22 promoter are added. ~he concentration of platinum can range u2 23 to 2 weight percent, or higher, if desired, in cases where a very 24 small number of particulate, platinum-containing materlal is added .o an PCC system. Preferably, however, +he amount of 26 plati~u~ added to a particulate solid is kept a+ less than 1 27 ~elght percent of the total welght of the particles. An amount 28 of platinum added to discrete solids of a~out 0.01 to 1 weight 29 percent of the total ~eigh+ or the discre.e solids is a prefsrred range for use.

~L~ Z42;~:4 1 The amount of Group VIII noble metals other than 2 platinum is generally between about 2 times to 10 times higher 3 total concentration in the system, ~ith respect to the total 4 amount of catalyst, than is us~d when a platinum promoter is employed. Thus, the amoun~ of the Group VIII metal such as 6 palladium, iridium, etc., car~ be calculated from the foregoing 7 description of the concentratlon of a platinum promoter, at least 8 twice as much and preferably S times as much of other Group VIII
9 ~o~le metals is used. The concentratio~ of 'he other Group VIII
noble metals on any discrete particle in the FCC system is 11 usually kept below about 2 ~eight percent, and prefe~ably belo~
12 about 1 ~eight percent.
13 Th~ amount of copper used in an FCC system as a 14 promoter is generally about 100 to about S000 times higher total concentration in the system, with respect to the to~al amount of 16 catalyst used, than the amount of platinum which would be used in 17 the same system. The concentration of copper promoter sn any 18 discrete particle is usually kept below about 20 weight parcent, 19 and preferably below about 10 weight percent.
Ths a~ount of chromium used in an FCC system ~s a 21 promoter is generally bet~een about S00 and about 25,000 times 22 hig~er total concentration in the system, with respect to th~
23 total amount of catalyst, than the amount of p1atinum which wou~d 24 be employed in the same system. The conce~tration of chromium added in, e.g., a chromium compound impregna~ed on any discrete 26 particle in the FCC system is usually kept belov about 20 welght 27 percent of the total particle weight, and pref~rably below abou.
28 10 weight per cent.
29 ~he-promoter metal, o~ metal compound, can be added to the ECC catalyst itself. It is, however, preforred to add th~
31 promotsr metal to the FCC system in a form which is associated l~ Z~24 1 with a discrete particulate solid, which is physically admixed 2 with the FCC catalyst in circulation in the system. The 3 particulate solid to be mixed with the catalyst can be any 4 material whi~h is suitable for circulat~on in ar FCC system in S particulate form in admixture with the catalyst. Particularly 6 suitable materials are the porous inorganic o~ides, such as 7 alumina and silica, or mixtures of two or more inorga~ic oxides, 8 such as sil-ca-alumina, natural and synthetic clays znd the like, 9 crystalline aluminosilicate zeolites, etc. Gamma alumina is particularly good. The promoter metal can be 2dded to a 11 particulate solid in any suitable manner, as by impregnation or 12 ion exchange, or can be added to 2 precursor of a particulate 13 solid, as by coprecipitation from an aqueous solutlon ~ith an 14 inorganic o~ide precursor sol. The particulate solid can be formed into particles of a size suitable for use in an FCC system 16 by conventional means, such as spray-drying, crushing of larger 17 particles to ths desired slze, etc.
1 a A particulats solid which contains at least one 19 promoter metal or metal compound of the type mentioned bove can be admixed with the bulk of FCC catalyst prior to charging the 21 catalyst to an FCC un~t. Likewise, the particulats solld 22 containing a promoter can be added to an PCC unit separately fro~
23 the catalyst in the desired amount.
24 ~hen the promoter metal is employed in the system, a~d particularly ~hen the promoter metal is present in a relatively 26 high co~centration in a particulate solid physically admixed ~lth 27 the cracklng catalyst, it is preferred to perform at least a 28 major portion of the combustio~ of all carbon mono~id- in th 29 catalyst regenerator in a dense catalyst phase ,egion witnin the regenerator. By a dense catalyst phase region, is mean~ that 'he 31 catalyst de~si~y in the region is at least 10 pounds per cubic 32 ~ foot.

~i~24~Z4L

1 Particularly when using a separate particulate promot~r 2 physically mixed with the cracking catalyst, it ls also preferred 3 to introduce sufficient oxygen into the regsneration zone in an 4 FCC system so that a minimum molecular oxygen content of 0.5 volume percent, and preferably at least 1.0 volllme percent, is 6 mai~tained in the atmosphere in the regeneraticn zone.
7 Particularly when using a separats particulate promoter 8 physically mixed with the crac~ing catalyst, it is also preferred 9 to burn a sufficient amount of ccke off the catalyst in the tO regeneration zone so that the average concentration of carbon in 11 regenerated catalyst cycled from the regeneratlon zons to the 12 crac~ing zone is belo~ 0.2 weight p~rcent.
13 Purther according to the ir.vention, sulfur oxldes are 14 removed from the flue gas in an FCC regeneration ~one by reacting sulfur trioxide with alumina in the regensration zone. The 16 aIumina used for the reaction has a surface area Oc at least 50 17 m2/g, e.g., gamma- or eta-alumina. Suitable alumina is not in 18 intimate com~ination ~ith more than 40 weight percent silica, and 19 preferably is substantially free from admixture wlth silica.
Alumina from any particular sou-ce is suitable for use ln the 21 present method if it cortains an average of abcut 0.1 to 100 22 weight percent of "reactive alumina", as detsrmined ~y t eating 23 particles containing the alumina by the followl~g steps:
24 (1) passing a stream of a gas mixtur~ contain~ng, ~y 2~ volume, 10~ ~ater, 1% hydrogen sulfide, 10~ hydrogen ~nd 79~
26 nitrogen over the solid particle continuously at a temperature of 27 1200P and atmospheric pressure until the weight of the soll d 28 particle is suDstantially constant;
2g (2) passing a strezm of a gas mix~ure contalning, ~v volume, lG% ~ater, 15~ carbon dioxide, 2% oxygen and 73% nitrog~n 31 over the solid particle resulting from step (1) at ~ t~?erature ~12~224 1 of 1200F and at~ospheric pressure until tha we1ghL of the solid 2 particle is substantially constant, the ~eight of the particle at 3 this time being designated "Na"; and 4 (3~ passing a stream of a gas mixture containing, by volume, 0.05% sulfur dioxide, and, in addition, the same gases in 6 the same proportions as used in step (2), over the solid particle 7 rasulting from step (2) at a temperature of 1200F and 8 at~ospheric pressure until the weight of the solid pariicle is 9 substantially constantr the weight of the solid particl~ at this time ~eing designated "Ws~'.
11 The weight fraction of reactive alumina in ths solid 12 particle, designatad "Xa", is determine2 by the formula 3 Xa = ~s_~a ~ Mole_ul~ t _AlUm__a _ 14 ~a 3 x Molecular ~t. Sulfur Trio~ide ~he alumina used is included in a particulate solid 16 suitable for circulaticn in an FCC system. Sui+able par'icles 17 normal1y ~ust have a~ alumina content of at least 60 weight 18 perce~t and, preferably, the alumina cont-nt of ~he particlqs is 19 90 ~eight percent or more.
In a preferred embodlment, particles of gamma-alumina 21 are used. Alumina can be formed into ?articles of suitable size 22 for circulation ~ith PCC catalyst in an FCC system by spray-23 drying, crushing larger particles, etc.
24 The alu~ina is added to an FCC system and circulated in physical mixture ~ith an FCC catalyst. The amount of alumina 26 added is preferably more than 0.1 welght percQnt and less than 25 27 weight percent of the total amount of catalyst clrculating i~ the 28 FCC system. The addition of an amount of alumina betwee~ 1.0 and 29 15 weight percent of the total catalys+ inveutory is particularly preferred. The size, shape and density of the alumina-cont~ining 31 particles used in the process is preferab1y regula.ed tc provide ~.242Z4 1 particles which circulate in substantially ~he same manner as the 2 catalyst particles.
3 The added alumina reactC with suifur trioxid~ or sulfur 4 dioxide and oxygen in the FCC catalyst regenerator to form at S least one solid compound includi~g sul~ur and aluminum, such as a 6 sulfate of aluminum. In this ~ay, sulfur oxides are removed fro~
7 the regenerator atmosphere and are not removed from .he 8 regenerator in the flue gas.
9 Particles co~taining the solid aluminum- and sulfur-containing material are passed to the cracki~g zore in ~he FCC
11 system along ~lth the catalyst. In the cracking zons, alumina is 12 regenerated and hydroger sul~ide is formed by contacting the t3 sulfur-containing solid with the stream of hydrocarbon being 14 treated in the cracker. In addition to forming hydrogen sulfide, the reaction bet~een the sulfur- and aluminum-containing solid 16 and the hydrocarbon feed may produce some other fluid sulfur 17 compcunds such as carbonoxysulfide, organic sulfides, etc. Th3 18 result-ng vapor sulfur compounds exit the crackir.g zone as a part 19 of the stream of cracked hydrocarbons, along ~ith the fluid sulfur compounds formed directly from sulfur in the hydrocarbcn 21 reed. Off-~as subsequently separated from the crack~d 22 hydrocarbon stream thus includes hydrogan sulfide formel direc+ly 23 from the feed sulfur and hydrogen sulfid~ formed by rea_tion of 24 the sulfur- and aluminum-containing solid with thê hydrocarbon strea~ in the cracking zone.
26 It is essential to operation cf the present invention 27 that the parti~les which contain alumina to be rezcted ~ith 28 sulfur trioxide in the regenerator must be substantially rr~e 29 from zuy of the promoter metals or metal compoun2s described above for USê in carbon monoxide cc3bustion promotion, tha~ is, 31 platinum, palladium, lridlu~, rhcdium, csmium, ruthenium, copper ~..

~.24;224 1 and chromium~ It has been found that ths presence of these 2 metals or compounds thereof i~ alumina-containing particlas to be 3 used for reaction with sulfur oxides is actually detrimen~al to 4 the capacity ol the a1umina to fo-m solld sulfur-containing materials in an ~CC regenerator. Thus, when .hese metals are 6 presen~ on particles of alumina to be reacted ~ith sulfur 7 trio~ide, the desired reaction of ths sulfur trloxide to form a 8 solid is impaired, a~d larger amounts of sulfur oxides exit the 9 FCC regenerator in the regenerator fluo gas, contrary to the object of the invention. Thus, the metal promo~ers disclosed, 11 although essential to operation of the invention, must be used in 12 a particulate solid in physical mixture ~ith th~ alum na which is 13 reacted with sulfur o~des. The promotor metals may, thus, De on 14 (1~ the FCC catalyst, or, preferably (2) on separate particles physically mixsd vith the FCC catalyst and with the sulfur oxides 16 controlling alumina particles.
17 Further acccrding to the invsntion, 2 composition o 18 matter is provided for use according to the method of the 19 in~ention described above. In a broad aspect, the composition includes a physical mi~ture of: (1) particulate cracking 21 catalyst; (2) a first particulate solid containlng a promoter 22 metal; and (3) a second particulate solid free from the promotsr 23 metal and containing at least 60 weight percent alumi~a.
24 Praierably, the composition includes a physical mixture of three componants. Pi-st, particulate cracklng catalyst. Second, the 26 composition includes a first particulate solid comprisi~g an 27 inorganic oxide such as alumina or silica-alumina associated ~ith 28 0.01 to 2 ~eight percent plztinum or a platinum compound, wnerein 29 the amount of platinum is calcalated on tho basis o~ the elemer.tal metal. Ths flrst particulate solid is in admixture -31 with the cracking catalyst in an amount sufficient ~o p.o~lde a 1~.24;Z24 1 total of 0.01 to 100 Farts per million, by weight of platinum, 2 with respect to the weight amount of catalyst in the co~position.
3 Third, the composition includes a second pa-ticulate soli~
4 comprising at least 60 weight percent, and prererably 90 weight percent, alumina. The seco~d particulate solid is substantially 6 free from platinum. The second solid is included in admi~ture 7 with the cracking catalyst in an amount sufficiert to provide a 8 total of 0.1 to 25 ~eight p6rcent alumina in the composition ~ith 9 respect to ihe ~eight amount of catalyst in the composition.
The composition mi~ture according to the invention car.
11 be formed by mixing the three components and the mixtur_ can be 12 employed by char~ing ~t to a catalytic cracking system in the 13 same manner in which crac~i~g catalyst ls normally char~ed to the 14 system. Alter~atively, the composition can be formed in a ca~alytic cracking system by separately charging the com~onents, 16 or one of +he components to an FCC system and forming the mixture 17 of tha three components ~ithin ths FCC system.
18 The follo~ing illustrative embodiment describes a 19 preferred ambodiment of the operation of 'he present invention.
ILI.USTRATIVE E~BODIM NT
21 A conventional FCC system and eguilibrium, zeolit~-22 containing, crac~ing catalyst of a commercially available type 23 are employed for cracking about 19,000 barrels per day of a 24 hydrocarbon feed having a boiling range of about 580F to about 1100P. The hydrocarbon feed contains about 0.8 weigh' Dercent 26 feed sulfur. The cracking zone used contains a combination of 27 riser cracking and dense-bed cracking modes. Cracking conditions 28 employed include a reactor temperature of abou~ 920F, a hydro-29 carbon veight hourly cpace velocity of a~ou 5 per hour and a conversion rate (defined as percent of feed cor.verted to 430F
31 and lighter comporents) of about 85~. ~he averagc amoun~ of coke .~

~.24ZZ~

1 on spent catalyst is about 1.5 weight percsnt. ~he coke on spent 2 catalyst includss about 0.7 weight percent sulfur. The amount of 3 carbon o~ regenerated catalyst is about 0.5 ~sight percent. The 4 flue gas e~iting the catalyst regenerator includes about 650 parts per million (volume) sulfur oxides (calculated as sulfur 6 dioxide~, about 0.3 vclume percent oxygen, and has a C0/CO2 ratio 7 of about 0.6. Catalyst r~generation conditions used in the 8 regenaration zone include a temperature of about 1200F.
9 Catalyst is circulated continuously bet~een the cracking zone and regeneration zone at the rate of about 16 tons per minute, ~ith a 11 total catalyst inventory in the systsm of about 180 tons.
12 According to the inv6ntlon, a particulate solid 13 consisting essentially of gamma alumina is added to the catalyst 14 in circulation in the unit in an amount sufficient to provide 10 ~eigh~ percent alumina, with respect to the total ~eight of 16 catalyst in the system. The alumina employed is a commsrci~lly 17 aYailable ~ype which which has been sp~ay-dried to provils 18 particles of tAe same size and fluidizable properties as the 19 catalyst. The alumina employed has a surface area of about 180m2/g. Aftsr the circulation of alumina is equilibrated, the 21 amount of sulfur oxides, calculated as sulfur dioxide, in the 22 flue gas exiting _he catalyst regene.ator is agai~ measured and 23 is found to be l~ss than 200 parts par million (volume). Alumina 24 is t~ereafter continuously added to the unit to retain about 10 veight percent alumina in admixture with the FCC catalyst, to 26 replen~sh any alumina lost ~y normal a.trition.
27 Further according to the in~en~ion, 60 pounds of 28 particles containing 0.6 ~eight ?ercent pla+inum ~.~pregnated on 29 a~ alumina carrler are introduced into circulation in the FCC
unit along ~ith the catalyst. Introduction of the platinum-31 alumina particles is then corltinued at the rate of about 7 pou~ds ~.
- ~4 -42~

1 per day. ~he amount of platinum added to the sys+em is thereby 2 mai~tai~ed at an equilibrium level of about 5 parts per million, 3 by ~eight, with respect to ths total amou~t o~ catalyst in the 4 system. Most of the oarbon monoxide is burned in a dense catalyst phase region in the regenerator. A sufficlent amount of 6 oxygen is added to the regenerator to provide at least 0.5 volume t percent o~ygen in the regenerator atmosphere. After addition of 8 both the alumina sulfur-oxides-reactant particles a~d the 9 platinum-alumina carbon-monoxide-combustion promoter par icles, the CO/C02 ratio and sulfur oxides level in the flue gas exiting 11 the regeneration zone are measured. The CO/C02 ratio ls found to 12 be substantially reduced to below 0.005, while the sulfur oxides 13 level, calculated as S~2, is found to have further decr~ased tO
14 below 50 parts per ~illion (volume).
~s can be sesn from the foregoing illustrative 16 embodimsnt, the method cf the present invention provides a simple 17 and economical method for controlling both the amount of carbon 18 monoxide and the amount of sulfur oxides present in flue gas 19 removed from an FCC catalyst regenerator. A large numb-r of variations, modifications and equivalents of the embodiment 21 illustrated will be appar~nt to those skilled in the art and are 22 intended to be included withi~ the scope of th~ appended cl~ims.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a catalytic hydrocarbon cracking process wherein a cracking catalyst is cycled between a cracking zone and a catalyst regeneration zone, a sulfur-containing hydrocarbon stream is cracked in contact with said catalyst in said cracking zone, and a sulfur-containing flue gas is formed in said regeneration zone by burning sulfur-containing coke off said catalyst With an oxygen-containing gas, the method for reducing the amount of carbon monoxide and sulfur oxides in said flue gas which comprises:
(a) reacting carbon monoxide and oxygen to form carbon dioxide in said regeneration zone in contact with a carbon monoxide oxidation promoter comprising a metal or compound of a metal selected from platinum, palladium, iridium, rhodium, osmium, ruthenium, copper and chromium;
(b) forming a sulfur- and aluminum-containing solid in said regeneration zone by reacting sulfur trioxide with alumina, said alumina being included in a particulate solid physically admixed with said catalyst, said particulate solid being substantially free from said metal or metal compound; and (c) removing sulfur from said particulate solid and forming hydrogen sulfide in said cracking zone by contacting said sulfur-and aluminum-containing solid with said hydrocarbon stream.

2. In a catalytic hydrocarbon cracking process wherein a cracking catalyst is cycled between a cracking zone and a catalyst regeneration zone, a sulfur-containing hydrocarbon stream is cracked in contact with said catalyst in said cracking zone, and a sulfur-containing flue gas is formed in said regeneration zone by burning sulfur-containing coke off said catalyst with an oxygen-containing gas, the method for reducing the amount of carbon monoxide and sulfur oxides in said flue gas which comprises:
a) including in said catalyst a carbon monoxide oxidation promo-ter comprising at least one metal, or compound of a metal, selected from platinum, palladium, iridium, rhodium,osmium, ruthenium, copper and chromium, and reacting carbon monoxide and oxygen to form carbon dioxide in said regeneration zone in con-tact with said promoter;
b) forming a sulfur- and aluminum-containing solid in said re-generation zone by reacting sulfur trioxide with alumina, said alumina being included in a particulate solid physically admixed with said catalyst, said particulate solid being substantially free from said metal or metal compound; and c) removing sulfur from said sulfur- and aluminum-containing solid and forming hydrogen sulfide in said cracking zone by con-tacting said sulfur- and aluminum-containing solid with said hydrocarbon stream.

3. A method according to Claim 2 wherein a sufficient amount of said particulate solid is admixed with said catalyst to provide between 0.1 and 25 weight percent alumina, with respect to said catalyst.

4. A method according to Claim 2 wherein said metal is platinum.

5. A method according to Claim 3 wherein said catalyst includes between 0.01 to 100 parts per million, by weight, of platinum, calculated as the elemental metal.

6. In a catalytic hydrocarbon cracking process wherein a cracking catalyst is cycled between a cracking zone and a catalyst regeneration zone, a sulfur-containing hydrocarbon stream is cracked in contact with said catalyst in said cracking zone, and a sulfur-containing flue gas is formed in said regeneration zone by burning sulfur-containing coke off said catalyst with an oxygen-containing gas, the method for reducing the amount of carbon monoxide and sulfur oxides in said flue gas which comprises:
(a) reacting carbon monoxide and oxygen to form carbon dioxide in said regeneration zone in contact with a carbon monoxide oxidation promoter comprising a metal or compound of a metal selected from platinum, palladium, iridium, rhodium, osmium, ruthenium, copper and chromium, said promoter being associated with a first particulate solid, said first particulate solid being physically admixed with said catalyst;
(b) forming a sulfur- and aluminum-containing solid in said regeneration zone by reacting sulfur trioxide with alumina, said alumina being included in a second particulate solid being substantially free from said promoter metal or metal compound;
and (c) removing sulfur from said second particulate solid and forming hydrogen sulfide in said cracking zone by contacting said sulfur- and aluminum-containing solid with said hydrocarbon stream.

7. A method according to Claim 6 wherein a sufficient amount of said second particulate solid is admixed with said catalyst to provide between 0.1 and 25 weight percent alumina, with respect to said catalyst.

8. A method according to Claim 6 wherein said metal is platinum and a sufficient amount of said first particulate solid is admixed with said catalyst to provide between 0.01 and 100 parts per million of platinum, by weight, calculated as the elemental metal, with respect to said catalyst.

9. A method according to Claim 6 wherein said carbon monoxide oxidation promoter includes 0.01 to 20 weight percent of said metal, calculated as the elemental metal.

10. A composition of matter comprising a physical mixture of:
(1) particulate cracking catalyst;
(2) a first particulate solid comprising an inorganic oxide associated with 0.01 to 2 weight percent platinum or a platinum compound, calculated as the metal, said first particulate solid being in admixture with said catalyst in an amount sufficient to provide 0.01 to 100 parts per million, by weight, of platinum, with respect to said catalyst; and (3) a second particulate solid comprising at least 60 weight percent alumina, said second particulate solid being substantially free from platinum, and said second particulate solid being in admixture with said catalyst in an amount sufficient to provide 0.1 to 25 weight percent alumina, with respect to said catalyst.