CA1110567A - Catalytic cracking with reduced emission of noxious gases - Google Patents

Abstract

CATALYTIC CRACKING WITH REDUCED EMISSION
OF NOXIOUS GASES
ABSTRACT
A cyclic, fluidized catalytic cracking process providing reduced emissions of noxious effluents in regeneration zone flue gases is operated with homogeneous or non-homogeneous, regenerable, fluidized, solid particles which are circulated throughout the catalytic cracking process cycle and which comprise (l) a molecular sieve-type cracking catalyst, comprising a cracking catalyst matrix containing crystalline aluminosilicate distributed throughout said matrix and (2) a metallic reactant which reacts with sulfur oxides to form a metal and sulfur-containing compound in the solid particles. The method involves the introduction of a compound of the metal or metals in the metallic reactant into the cracking process cycle and incorporating the metallic reactant into the solid particles in situ.

Description

, lll ll B~CKGROIJ~D OF THE INVENTI()N
~ ieLd of the Invention This invention is ,lirected to a cyclic, fluldi~e~l atalytic cracking process which is suitable for use ~ith sulf~lr-containing hydrocarbon feedstocks and which is characterized by ~ a marked diminution in the emission of sulfur oxides in the regenerator stack ga,es.
Dis~ussion of the Prior Art Cracking catalyst which has become relatively inactive due to deposition of carbonaceous depcsits, commonly ~ called "coke," during the cracking of hydrocarbons in the reaction zone is continuously withdra~n from the reaction zone. Such spent catalyst from the reaction zone is passed to a stripping zone where strippable carbonaceous deposits, namely hydrocarbons, are stripped from the catalyst which in turn is passed to a regeneration zone where the , activity of the catalyst is restored by removing the non-strippab]e I carbonac~ous deposits by burning the coke in oxygen-containing gas to form carl~on monoxide and carbon dioxide. ~ot regenerated catalyst is ¦
then continuously returned to the reactor to repeat the cycle. ¦
In catalytic cracking, a problem arises from the incomplete com-bustion of carbon monoxide to carbon dioxide in the regeneration zone, leaving a significant amount of carbon monoxide in the regeneration zone flue gases. Aside from the undesirability of discharge o carbon monoxidè
to the atmosphere, carbon monoxide and residual oxygen in the regeneratio~
zone f:Lue gases tend to react and thereby cause burning in ducts and flues in the plant and damage to such structures by excessive temperatures.
Further, when h-igh-sulfur feedstocks, that is, petroleum hydrocarbon fractions containing organic sulfur compounds, are charge~ to a fluid-type catalytic cracking unit, the coke cleposited on the catalyst contains sulfur. During regeneration of the coked, deactivated catalyst, the

- 2 -, .
`

coke is burned from the catalyst sur~aces; and, in this combu~tion process, the sulfur present is converted to sul~ur dioxide, to~e-ther wlth a minor proportion o:~ sul:Eur trioxide, and t~us included in the regeneration zone :Elue gas effluent stream. When crackin~ a high-sulfur Eeedstock, emissions oE
sulfur oxides are ~ften in the range o:~ about 1200 parts per million.
Pollution control standards have been developed for emission of carbon monoxide and for particulate matter and are expected to be considered soon for other emissions, such as the sulfur oxides, particularly sulfur dioxide. Consequently, much attention is beiny devoted to reducing the level o:f emissions of various combustion products and particulates from regeneration zone e:Efluent streams associated with petroleum cracking units. It is necessary that the method selected for reducing such emissions be effective without lowering the activity and selecti~Tity of the cracking catalyst. It is like-wise necessary that the method selected. not substitute one form of undesirable emission with another problem, for example, an increase in particulate emission or operating costs. In view of these considerations, a highly desirable approach to a reduc-tion in the emission of sulfur oxides from petroleum cracking units lies in the use of a cracking catalyst which is modified to minimize emissions of sulfur oxides, while maintaining cata-lyst activity, stability, and resistance to attrition, under conventional cracking conditions in either existing or new cracking units.
Although metals are generally avoided in cracking cata-lysts and it is consldered problematical to crack metal-contain-ing stocks in the presence of a cracking catalyst, South African Patent No. 7924/72 and its later issued counterpart, U~.
patent No. 3,909,392 (1975~, to be discussed in greater detail _3_ ~; ., herelnbelow, disclose the use in conjunction with cracking catalysts of combustlon catal~sts or promoter~ within the re~enerat~on zone, which include a metallic bar, mesh networ]c, or screen - 3a -~i I
i~.

in the combustion zone; and fluidizable metal compounds, particularly powdered oxides of transition group metals -- for example, ferric oxide, manganese dtoxide, and rare earth oxides -- which are added to the catalyst charge or confined wl~hin the regenerator vessel. Belgian patent No. 82~,266 (1975) discloses a method very similar to that of U.S. patent No. 3,909,392 which involves a catalytic cracking catalyst in physical assoclation with a carbon monoxide-oxidation promoting catalyst of a metal having an atomic number of at least 20 and mentions metals from Groups I~, IIB, and III to VIiI of the Periodic Chart -- in particular platinum, palladium, rhodium, molybdenum, tungsten, copper, chromium, nickel, manganese, cobalt, vanadium, iron, cerium, ytterbium, and uranium -- as useful oxldation promoters. Further, U.S. patent No.

3,808,121 discloses the regeneration of a cracking catalyst in the presence of a carbon monoxide oxidation catalyst which is retained in the regeneration zone, Published Dutch patent application No. 7,412,423 discloses that a cracking catalyst containing less than 100 parts per million, calculated as metal, based on total catalyst, of at least one metal component selected from the group consisting of metals from Periods 5 and 6 of Group VIII of the Periodic Chart, rhenium~ and compounds thereof, showed ¦
particularly spectacular reductions in the carbon monoxide content in flue gases from catalytic cracking catalysts. This patent also discloses a molecular sieve-type cracking catalyst which is prepared in the sodium form, ion-exchanged with ammonium ions, and then impregnated with rare earth metals.

With regard to sulfur oxide emissions, although various methods for ¦
processing flue gas have been devised, for example, washing or scrubbing,¦
chemical absorption, neutrali~ation, and chemical reaction or conversicn,¦

all such methods Eor removal of sulfur oxides require extensive and expensive auxiliary equipment, thus increasing both operating and ~ U567 . ;

capital costs An approach set fort~ in U.S. patent No. 3,699,037 contemplates the addltion of at least a stoichlometric amount of a calcium or magnesium compound to the cracking cycle in relation to the !¦ amo~lnt of sulfur deposltLon on catalyst. Thls added material i5 in-I tended to react w:lth sulfur oxides and then, being in a finely sub-d:L~Lded corlditlon, exit Erom the cracking cycle as particula~e matter ln the regeneration ~one flue gas stream. Contlnued additlon of such material obviously increases operating costs. Slmilarly, U.S. patent Nos. 3,030,300 (1962) and 3,030,314 (1962) disclose a catalytic cracklng o process whlch involves adding con~inuously to a moving bed cracking process cycle one or more compounds of boron, alkali metals and alka]ine earth metals to thereby provide catalyst particles whlch have increased resistance against impact breakage and surface abraslon and whlch comprlse a siliceous catalyst particle having a microporous, catalyticall~
actlve core whlch ls provlded wlth an adherent, protective coating of a glaze comprised oE silica and one or more compounds of boron, alkali metals and alkallne earth metals.
U.S. patent No. 3,835,031 (1974) discloses a cyclic, fluidized catalytic cracking process which provides reduced emissions of sulfur oxides in the regenerator stack gases. The method is operated with a catalyst whlch comprises a molecular sleve in a silica-alumina matrix and which is impregnated with one or more &roup IIA metal oxides.
U.S. patent Nos. 3,388,077 (1968); 3,409,390 (1968); and 3,849,343 (1974) disclose a method for effecting the conversion of a noxious waste gas stream containing carbon monoxide and sulfur oxides, which comprises contacting the stream with a catalytic composite of a porous refractory carrler material, a catalytically actlve metalllc component, for example, a platinum group metal, and an alkaline earth component selected from the group consisting of calcium, barium, and strontium.

Thus far, no one has disclosed the method of this invention.
SU~MARY OF THE INVENTION
This invention is a cyclic, fluidized catalytic cracking process providing reduced emissions of sulfur oxides in regeneration zone flue gases. In several embodiments, this invention also provides substantially complete combustion of carbon monoxide in the regeneration zone and absorption of the heat evolved during such combustion by solid particles which are circulated to the reaction zone and stripping zone before returning to the regeneration zone. Such solid particles comprise molecular sieve-type cracking catalyst and a metallic reactant and can also contain amorphous cracking catalyst and solids which are substantially inert to the cracking of hydrocarbons.
The metallic reactant can be incorporated into the molecular sieve type cracking catalyst, amorphous cracking catalyst, substantially inert solid. Such incorporation can be achieved either before or after the particular substrate is introduced into the cracking process cycle.
Conditions are employed in the cracking process cycle such that a stable metal- and sulfur-containing compound forms in the solid particles in the regeneration zone and a sulfur-containing gas is withdrawn from the stripping zone.
Thus the present invention provides, in a process for the cyclic, fluidized, catalytic cracking of hydrocarbon feedstock containing about 0.2 to about 6 weight percent sulfur as organic sulfur compounds wherein:
(i) said feedstock is subjected to cracking in a reaction zone in contact with fluidized solid particles comprising molecular sieve-type cracking catalyst; (ii) solid particles including catalytic particles which are deactivated by sulfur-containing carbonaceous deposits, are separated from reaction zone effluent and pass to a stripping zone wherein volatile deposits are removed from said solid particles by contact with a stripping gas; (iii) stripped, solid particles are separated from stripping zone effluent and pass to a catalyst regeneration zone and nonstripped, sulfur-containing, carbonaceous deposits are removed from the stripped, solid particles by burning with an oxygen-containing gas thereby forming sulfur oxides; and (iv) resulting solid particles are separated from regeneration zone effluent gas and recycled to the reaction zone; a method for reducing emlssions of sulfur oxides in the regeneration zone effluent gas which comprises:
(a) providing in said fluid catalytic cracking-regeneration process cycle fluidizable, solid particles, other than said molecular sieve-type cracking catalyst, containing metallic reactant consisting essentially of at least one metallic element selected from the group consisting of magnesium, calcium, strontium and barium in free or combined form, and wherein said metallic reactant is present in sufficient amount to effect :
the absorption of at least about ;0 weight percent of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone;
(b) cracking said feedstock at a temperature from about 850 to about ~ .
1,200F. and in contact with said cracking catalyst and said metallic ~ :
reactant; ~ :
(c) stripping volatile deposits from said solid particles at a temperature from about 850 to about 1,200F. with a stripping gas which contains st~am, wherein the ratio by weight of steam to said molecular sieve-type cracking catalyst is from about 0.0005 to about 0.025, said stripping being conducted at a temperature and with steam such that passage of said solid particles through said cracking and stripping zoDes provides said metallic reactant in an amount of active form suitable for accomplish-ing said absorption of at least about 50 weight percent of the sulfur oxides produced by said burning in said regeneration zone;
(d) passing to the regeneration zone stripped, solid particles having metallic reactant in an active form for absorbing at least about 50 weight percent of the sulfur oxides in said regeneration zone;

- 6(a) -`
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0S~7 (e) burning in said regeneration zone said sulfur-containing carbonaceous deposits from the stripped, solid particles at a temperature from about 1,050 to about 1,450F., said burning being conducted at a temperature and with oxygen-containing gas having molecular oxygen such that at least about 50 weight percent of the sulfur oxides produced by said burning in said regeneration zone can be absorbed by said metallic reactant;
(f) absorbing with the solid particles at least about 50 weight percent of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone;
(g~ passing from the regeneration zone to the reaction zone said particles containing at least about 50 weight percent of the sulfur oxides produced in said regeneration zone;
(h) withdrawing an effluent gas from the regeneration zone containing molecular oxygen and having a low concentration of sulfur oxides of less than about 600 ppmv;
(i) substantially converting said absorbed sulfur oxides to a sulfur-containing gas in said reaction and/or stripping zone.
DETAILED DESCRIPTION O~ T~E INVENTION
In the development of catalysts for the reduction of emissions of ~0 sulfur oxides in the flue gases from th~ regeneration zone of a fluid cracking operation, it is important that such catalysts exhibit not only the capability to initially perform the specified function but also that they have the capability to perform satisfactorily for prolonged periods of time. Thus, in the development of such catalysts, attention must be directed to the activity and stability characteristics of the catalysts.
Activity in this regard is a measure of a catalyst's ability to reduce the emissions of sulfur oxides in the regeneration zone flue gases at a - 6(b) -specified severity level, where severity level means the conditions used -- that is, the temperature, pressure, contact time, etc. The sta~ility of a catalyst is a measure oE the abllity of the catalyst to malntain the activity characteristics over a specified period of time.
Stability referR to the rate oE change with time of the activity paramete-;s, with fl smaller rate implying a more stable catalyst. The stability should be such that the activity characteristics can be ¦ retained during prolonged periods of operation.

These key features are more easily attainable by introducing the ~0 effective agent for producing reduced sulfur oxide emissions, in this invention the metallic reactant, into the cracking process cycle and incorporating it into the solid particles in situ, rather than compositin~
it with the molecular sieve-type cracking catalyst during manufacture of such cracking catalyst. Introducing the metallic reactant into the cracking process cycle as opposed to compositing it with the molecular sieve-type cracking catalyst during cracking catalyst preparation has ¦ been found to result in greater reduction in sulfur oxide emissions in ¦ regeneration zone flue gases. Adding the metallic reactant to the ¦ cracking process cycle also is advantageous in that a larger degree of I control is maintained over any potential deleterious effect of the ¦ metallic reactant on the cracking reaction as the rate and/or amount of such metallic reactant introduced into the cracking cycle can be l varied. Also, such metallic reactant previously composited with the 2s ¦ cracking process cycle can be lost as fines during attrition of the cracking catalyst. Adding the metallic reactant to the cracking process cycle and incorporating it into the solid particles in situ allows for maintenance of a deslred amount`of metallic reactant on the outside or l accessible portions of the cracking catalyst.
¦ T~is invention is an improvement in a cycllc, fluidized catalytic crack~ ~ ~rocess whereln a hydr-c~rbon ~eedst-ck co~t n~g organic sulfur compaunds is subiected to cracking in a reaction zone under fluidizlng conditlons with -homogeneous or non-homogeneous, regenerable, fluiclized, solid particles which comprise a metal-lic reac-tant and a molecular sieve-type cracking catalyst S comprisin~ a crackin~ catalyst matrix containing crystalline aluminosilicate distributed throughout said matrix, wherein said cracking catalyst is concomitantly deactivated by sulfur-containing carbonaceous deposits. The fluidized solid particles are separated from cracked hydrocarbon reaction zone effluent and passed to a stripping zone wherein the deactivated cracking catalyst is stripped of strippable carbonaceous deposits by contact with a stripping gas. The fluidized solid particles are then separated from the gaseous stripping zone effluent and passed to a regeneration zone wherein the stripped, deactivated cracking catalyst is regenerated to high activity by burning the non-strippable, sulfur-containing carbonaceous deposits from the stripped, deactivated cracking catalyst in contact with an oxygen-containing gas stream, thereby forming carbon monoxide, carbon dioxide and sulfur oxides, which react with the metallic reactant to form a metal- and sulfur-containing compound in the solid particles. The fluidized solid particles containing the regenerated crackin~ catalyst are separated from the regenera-tion zone effluent flue ~ases and recycled to the reaction zone.
The improvement comprises introducing a material contain-ing a metal in the metallic reactant into the cracking process cycle and incorporating the metallic reactant into the solid . particles within the cracking process cycle; by employing a strlpping gas which contains steam; by regenerating the stripped deactivated cracking catalyst at regeneration temperatures in the range where the metal- and sulfur-containing compound in the solid particles is stable; and by providing sufficient ~.
oxygen to the regeneration zone in the oxygen-containing s~ ~

r:eqene~at~on ~s ,~t~e~ th~t ~lue gases cantaining molecular oxygen are ~lthdrawn ~rom the xe~enerati,on zone.

~

~ 8a -, ~u~7 j A sultable hydrocarbon Eeedstock for use in the process may contain from about 0.2 to about 6 weight percent of sulfur in the form of organLc sulEur compounds. ~dvantageously, tlle feedstock contains from about 0.5 to about 5 weLght percent sulEur and more advantageously Erom about 1 to about ~i weight percent sulEur, whereln the sulfur is present in the form of organic sulfur compounds.
The cracking catalyst matrix of the rnolecular sieve-type cracking catalyst preferably is a combination of at least two materials selected l from the group consisting of silica, alumina, thoria, and boria, and lo more preferably is silica-alumina. This cracking catalyst matrix contains preferably from about 10 to about 65, more preferably from about 25 to about 60 weight percent of aLurnina; preferably from about 35 to about 90, more preferably from about 35 to about 70 weight percent of i silica; and preferably from about 0.5 to about 50, more preferably from s ¦ about 5 to about 50 weight percent of crystalline aluminosilicate. The l molecular sieve-type cracking catalyst makes up preferably from about 10 ! to about 99.9975, more preferably from about 30 to about 99.99, and most preferably from about 90 to about 99.9 ~eight percent of the solid I particles.
1 The metallic reactant consists of at least one free or combined ¦¦ metallic element which is selected from the group consisting of magnesium, calcium, strontium, and barium. Consequently, the metallic ¦ reactant may be selected from the group consisting of magnesium, calcium, strontium, barium, their compounds, and mixtures thereof. More preferably, the metallic reactant is selected from the group consisting of magnesium and calcium.
I The oxide or oxldes of the metallic element or elements of the ') metallic reactant are believed to be primarily responsible for the ~i absorption of sulfur oxides in the regeneration zone. Consequently~
i it is advantageous to introduce the metallic element or elements of ,~

' ! ~

the metallic reactant into the catalytic cracking process cycle in the Eorm of the oxide or oxides. It is sufEicient, however, for the practice of this process that one or more suitable metallic elements be seLected Eor use ax the meta]1ic reactant and introduced ln^o the process cycle. The metallic element or eLements oE the metlLllc reactant are actLvaied Eor the absorption of sulEur oxides in the re~enerat:Lon ~zone as a consequence of the process steps of this invention. The activation is believed to involve either a partial or subst mtially ,~complete conversion of the metal or metals of the metallic reactant to 1the corresponding oxide or oxides. This activation is substantially unaffected by the precise manner in which such metallic element or ~1 elements may be chemically combined when initially introduced into the ~'process cycle, The metallic reactant is present in sufficient average amount in the regeneration zone to absorb a major portion of the sulfur oxides , produced by the burning of sulfur-containing carbonaceous deposits i1 therein. At least about 50%, and advantageously more than about 80%
of the sulfur oxides produced by such burning are absorbed by the metalli , reactant in the regeneration zone, As a result, the concentration of .
,, sulfur oxides in the regeneration zone effluent gas stream from this '1 novel process can be maintained at less than about 600-lO00 parts per million by volume (ppmv), advantageously at less than about 600 ppmv, ~ and more advantageously at less than about 400 ppmv.

` The amount of metallic reactant employed, calculated as the metal ~ or metals, is preferably in the range of from about 25 parts per million ¦ to about 7 weight percent, more preferably in the range of from about O.Ol weight percent to about 5 weight percent9 and most preferably in the range of from about O.l weight percent to about 0.5 weight percent of the solid particles.
, " - 10 -~, i :. ' 3L~ ;i'67 ', Certain individual solids in the solid particles of the method of this invention can contain an amount of the metallic reactant which is greater than the sverage amount thereof in the solid pnr~icles, provided l that such cer~ain :Lndividual solids are admixed with other individual ¦ soLids in the solld particles containing a smaller amount oE the metallic reactclnt such that the solid particles contain the above-mentioned average levels of the metallic reactant.
The stripped, deactivated catalyst is regenerated at regeneration l temperatures in the range where a stable metal- and sulfur~containing lo compound is formed ln the solid particles from the metal in the metallic reactant and sulfur oxide. The regeneration temperatures are preferably in the range of from about 1,050F. to about 1,450F. and more pre-ferably in the range of from about 1,180F. to about 1,350F. The hydroca~bon feedstock is cracked at reaction temperatures in the range ~5 where the metal- and sulfur~containing compound in the solid particles reacts to form a sulfide of the metal in the metallic reactant. The cracking reaction temperature is preferably in the range of from about 850F. to about 1,200F., and more preferably in the range of from about 870F. to about 1,100F. The strippable deposits are stripped ¦ from the deactivated cracking catalyst with a steam-containing gas and at stripping temperatures in the range where the sulfide of the metal in the metallic reactant reacts with water to form hydrogen sulfide gas.
l The stripplng temperatures are preferably in the range of from cabout ~ 850F. to about 1,200F., and more preferably in the range of from about 870F. to about 1,000F. The weight ratio o~ steam-to-molecular sieve-type cracking catalyst being supplied to the stripplng zone is preferably in the range of from about 0.0005 to about 0.025, and more preferably in the range of from about 0.0015 to about 0.0125. The regeneration æone flue gases contain preferably at least 0.01 volume percent and more preferably at least 0.5 volume percent of oxygen in order for the desired reduction of emissions of noxious gas to be achieved.

lllU567 In one embodlment of this invention, the material containing a j metal in the metallic reactant is an oil- or water-soluble or -dispersibl ¦ compound and the me~allic reactant is lncorporated into ~he molecular l sleve-type cracking catalyst. In such case, the metallic reactant i8 r) l lncorpo~tecl into either the crystalline aluminos:Llicate. or the matrix :Ln thc mo!eculnr s:Leve-type cracking cata:Lyst. In this embodiment o~
this inven~ion, the solid particles can comprise additionally at least one component selected from the group consisting of solids which are l substantially inert to the ~racking of hydrocarbon feedstock and an ¦ amorphous cracking catalyst; and ~he metallic reactant ls incorporated ¦ lnto such component. In this embodiment, the compound which is ¦ introduced into the catalytic cracking process cycle, whlch comprises ¦ the cracking reaction zone, the stripping zone, and the regeneration ¦ zone is preferably a metal salt. Examples include metal diketonates ¦ and metal carboxylates having from 1 to 20 carbon atoms. More preferably, such compound is magnesium acetylacetonate.
In another embodiment of this invention, the material containing a metal in the metallic reactant is the metallic reactant in powder form -~
l for example magnesium oxide. In still another embodiment, such material ¦ is a composite of the metallic reactant supported on either an amorphous cracking catalyst or a solid which is substantially inert to the cracking reaction.
l This invention relates to an improved fluid catalytic cracking 1 process, including an improved process for the regeneration of cracking catalyst employed in ~luid catalytic conversion and an improved process for reducing emissions of sulfur oxides in cracking catalyst regenera~ion zone effluent gas9 involving the conversion of sulfur-containing hydro-carbon feedstocks wherein the cracking catalyst is deactivated by the deposition of sulfur~containing coke on the cracking catalyst surface.
The solid particles of the method of this invention, comprising molecular s~eye~t~pe crackin~ catal~st, are cixculated in well-dispersed physical associat~on wlth one another throughout the cracking process cycle, which comprises -the cracking zone, the stripping zone, and the re~enerat.ton zone. The conditions employed efEoct reduction of sulfur oxides in the regeneration zone flue CJcl~eF~, The cracking catalyst and metallic reactant o~ the method of this invention serve separate and essential functions. The cracking catalyst serves to catalyze the cracking reaction, while the metallic r~actant is substantially inert toward the crackin~ reaction and has little, if any, adverse effect on the catalytic conversion operation under the conditions employed.
~ith regard to the reduction of sulfur oxides in the regenera-tion zone flue gas, the solid particles adsorb sulfur oxides in the regeneration zone. The molecular sieve-type cracking catalyst itself often serves as an adsorbent for sulfur oxides.
The metallic reactant reacts with the adsorbed sulfur oxides to form a metal- and sulfur-containing compound, in particular, metal sulfates, and specifically alkaline earth sulfates, in 2Q the solid particles. Provided that such metal- and sulfur-containing compound is stable under the operating conditions in the regeneration zone, it would be carried on the surfaces of the solid particles to the reaction zone and stripping zone where it would be reduced and separated as a sulfur-containing gas, in particular, as hydrogen sulfide.
It is understood that the activity i.n reducing the emission of sulfur oxides in the regeneration zone flue gases may vary from metal to metal in the classes of those which may serve as a metal in the metallic reactant. Similarly, many of the specific metals which may serve as a metal in the metal-lic reactant do not necessarily yield equivalent results when i6~

compared with other ~peci~ic metal~ which may be used in the ~ :
metallic reactant or when utilized under varyincJ conditions.
The solid particles a~ the method o~ this invention are inely divided and have, ~or example, an average particle size in the range o~

~ ,,, '':
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~ 13a -."~,.

i6~

from about 20 microns or less ~o about 150 microns, such that they are ln a Eonn suitable for fluidization. Suitable cracking catalyst matrices incl~de those containing ~3ilica and/or alumina. Other re~ractory metal ~ oxicles may be employed, ILmited only by their ability to be eEfectively reKenerated under the se:Lected conditions. Admixtures of clay-extended al~l~llnas mlly also ~e employed. Preferred catalysts lnclude combinations oE silica and alumina, admlxed with "molecular sieves", also known as zeolites or crystalline aluminosilicates. Suitable cracking catalysts contain a sufficient amount of crystalline aluminosi:Licates to materially increase the cracking activity of the catalyst, limited only by their ability to be effectively regenerated under the selected conditions.
The crystalline aluminosilicates usually have silica-to-alumina mole ratios of at least about 2:1, for instance about 2 to 12:1, preferably from about 4 to about 6:1. Cracking catalysts with silica bases having t5 a major proportion of silica, for example, from about 35 to about 90 weight percent silica and from about 10 to about 65 weight percent alumina are suitable. Such catalysts may be prepared by any suitable method, such as milling~ co-gelling, and the like, subject only to provision of the firished catalyst in a physical form capable of fluidizatlon.

Suitable "molecular sieves" include both naturally occurring and synthetic aluminosilicate materials such as faujasite, chabazite, X-type an(l Y-type aluminosilicate materials, and ultrastable, large-pore I crystalline aluminosilicate materials. When admixed with, for example, 2s ¦ silica-alumina to provide a petroleum cracking catalyst, the molecular ¦ sieve content of the fresh finished catalyst particles is suitably ¦ within the range of from about 0.5 to about 50 weight percent, desirably fr~m about 5 to about 50. An equilibrium "molecular sieve" cracking l cat:alyst may contain as little as about 1 weight percent crystalline 1 material. The crystalline aluminosilicates are usually available or l - 14 -made in sodium ~arm; the sod~um camponent i~ then usually reduced to as s~all an amount as possible, ~enerally less than about 0.30 welght percent, -through ion exchange with hydrogen ions, h~drogen-precursors such as ammonium ions, or polyvalent metal ions, includin~ calcium, strontium, bartum, and the rare earths, such as cerlum, lan-thanium, neod~minium, and naturally-occurring rare ear-ths and their mixtures. The usable crystal-line materials are able to maintain their pore structure under the high temperature conditions of catalyst manufacture, hydro-carbon processing, and catalyst regeneration. The crystalline ;~
aluminosillcates often have a uniform pore structure of exceed-ingly small size, the cross-section diameter of the pores being in the size range of from about 6 to about 20 angstroms, pre-ferably from about 10 to about 15 angstroms.
Catalytic cracking of heavy mineral oil fractions is one of the major refining operations employed in the conversion of crude Qilsto desirable fuel products such as high-octane gas-oline fuels used in spark-ignited, internal combustion engines.
Illustrative of "~luid" catalytic conversion processes is the fluid catalytic cracking process wherein high molecular hydro-carbon liquids or vapors are contacted with hot, finely-divided, solid catalyst particles, either in a fluidized bed reactor or in an elongated riser reactor, and the catalyst-hydrocarbon mixture is ~aintained at an elevated temperature in a ~luidized or dispersed state for a period of time sufficient to effect the desired degree of cracking to lower molecular weight hydro-carbon typically present in motor gasoline and ~ist1llate- fuels.
Suitable hydrocarbon feeds for the cracking process boil generally above the gasoline boiling range, for example, within the range of from about 400F. to about 1,200F., and are usually cracked at temperatures ranging from about 850F. to S6~

a~ut 1,20QQF~ Such ~eeds include various miner~l o.il fractions boilln~ above the gasGline range such as li~h-t gas - 15a -~; :

5~7 ¦¦ oils, heavy gas oils, wide-cut gas oils, vacuum gas oils, kerosenes, ~ decanted oils, residual fractions, reduced crude oils and cycle oils ¦I derived from any of these as well as suitable fractions derived from l shale oils, tar sands processing, syn~hetic oils, coal liquefaction and S ¦ the Like. Suc:l fractions may be employed singly or in any desired l combinu~iJn.

! The method of this invention can be employed in any conventional catalytic cracking scheme but is advantageously practiced in a fluid l catalytic cracking system where at least a substantial portion of the IO hydrocarbon conversion is effected in a dilute-phase transfer line or riser reactor system utilizing very active catalysts employed at relatively high space velocities. Preferably, cracking occurs essentiall~
exclusively in the riser reactor and a following dense catalyst bed is ~s ¦ not employed for cracking. In a typical case where riser cracking is employed for conversion of a gas oil, the throughput ratio, or volume ratio of total feed to fresh feed, may vary from about 1 to 3. The conversion level may vary from about 40 to about 100 weight percent, and advantageously is maintained above about 60 weight percent, for example, between about 60 and 90 weight percent. By conversion is meant the percentage reduction by weight of hydrocarbons boiling above about ¦ 430F. at atmospheric pressure by the formation of lighter materials or ¦ coke. The weight ratio of total cracking catalyst-to-oil in the riser ¦ reactor may vary wlthln the range of from about 2 to about 20 in order ¦ that the fluidized dispersion will have a density within the range of from about 1 to about 20 pounds per cubic foot. Desirably, the catalyst-to-oil ratio is maintained within the range of from about 3 to about 20, preferably 3 to about 7. The fluidiæing velocity ~n the rlser reactor l may range from about 10 to about 100 feet per second. The riser reactor ¦ generally has a ratio of leng~h-to-average diameter of about 25. For production of a typical naphtha product, the bottom section mixing temperature wlthin the riser reactor is advantageously maintained at about 1,000F. to about 1,100F. for vaporization of the oil feed, and 90 that the top section exit temperature will be about 950F. For cracking resids and F,ynthetic fuels, substantially higher temperatures would be necessary. I]nder these conditions, including provlsion for a rapid separation of spent catalyst from effluent oil vapor, a very short period of contact between the catalyst and oil will be established.
Contact time within the riser reactor will generally be within the ranga of from about l to about 15 seconds, and preferably within the range of from about 3 to about 10 seconds. Short contact times are preferred because most of the hydrocarbon cracking occurs during the initial increment of contact time, and undesirable secondary reactions are avoided. This is especially lmportant if hlgher product yield and selectivity, including lesser coke production, are to be realized.
Short contact time between catalyst particles and oil vapors may be achieved by various means. For example, catalysts may be injected at one or more points along the length of a lower, or bottom, section of l the riser. Similar]y, oil feed may be injected at all the points along the length of the lower section of the riser reactor, and a different injection point may be employed for fresh and recycle feed streams. The lower section of the riser reactor may, for thi3 purpose, include up to about 80 percent of the total riser length in order to provide extremely short effective contact times inducive to optimum conversion of petroleum feeds. Where a dense catalyst bed is employed, provision may ¦ also be made for injection of catalyst particles and/or oil feed directly into the dense-bed zone.
While the conversion conditions set forth above are directed to the i production of gasol:lne as fuel for spark-ignition internal combustion engines, the processing scheme may be suitably varied to permit maximum production of heavier hydrocarbon products such as jet fuel, diesel fuel, heating oil and chemicals, in particular, olefins and aromatics.

' i67 lll .' l In the cataly~Lc process, some non-volatile carbonaceous material, ¦ or "coke", is deposited on the catalyst partlcles. Coke comprises highly condensed aromatic hydrocarbons whlch generally contain a minor amount Or hyclrogen, say from abo~t 4 to about 10 weight percent. When s ~.he hyclrocarbcll ~eedstock contalns organic sulfur compounds, the coke also co~c~lns sul~ur. As coke builds up on the catalyst, the activity of the catalyst for cracking and the se:lectivity of the catalyst for producing gasoline blending stocks diminishes. The catalyst particles ¦ may recover a major proportion of their original capabilities by o ¦ removal of most of the coke therefrom in a suitable regeneration process.

The spent catalyst from the petroleum converslon reactor is stripped prior to entering the regenerator. The stripping vessel for use in a fluidized bed catalytic cracking unit may suitably be maintained essentially at conversion reactor temperature in the range of from about 850 to about 1,200F. and desirably will be maintained above about 870F. Preferred stripping gas is steam, although steam,containing nitrogen or other steam-conta~ning inert or flue gas, may also be employed. The stripping gas is introduced at a pressure of generally at least about 10, preferably about 35 pounds per square inch gauge, suitable to effect substantially complete removal of volatile compounds from the spent conversion catalyst.
The method of this invention can be employed with any conventional cracking catalyst regeneration scheme but is advantageously employed with a regeneration system involving at least one dense-bed and at least one dilute-phase zone. Stripped spent catalyst particles may enter the dense-bed section of the regenerator vessel through suitable lines evolving from the stripping vessel. Entry may be from the bottom or from the side, desirably near the top of the dense-bed fluidized zone.

Entry may also be from the top of the regenerator where catalyst has first been contacted with substantially spent regeneration gas ln a restrlcted dilute-phase zone.

0$67 Catalyst re~enexati~on ls accomplished by burning the coke deposits from the catalyst surface with a molecular oxygen-containing gas, such as air. Many regeneration techniques are practiced commercially whereby a significant restoration of catalyst activit~ is achieved in response to the degree of coke removal. As coke is progressively removed from -the catalyst, removal of the remaining coke becomes most difficult and, in practice, an intermediate level of restored catalyst activity is accepted as an economic compromise.
The burning of coke deposits from the catalyst requires a large volume of oxygen or air. Although the disclosed inven-tion is not to be limited thereby, it is believed that oxida-tion of coke may be characterized in a simplified manner as the oxidation o~ carbon and represented by the following chemical equations:
(a~ C ~ 2 ~~ C2 (b~ 2C ~ 2 ~~ 2CO
(c~ 2co ~ o2 ~ 2C02 Reactions (a~ and (b) both occur under typical catalyst regen-eration conditions wherein the catalyst temperature may range from about 1050 to about 1450F. and are exemplary of gas-solid chemical interactions when regenerating catalyst at temperatures within this range. The effect of any increase in temperature is reflected in an increased rate of combustion of carbon and a more complete removal of carbon, or coke, from the catalyst particles. As the increased ra-te of combustion is accompanied by an increased evolution of heat, whenever sufficient free or molecular oxygen is present, the gas-phase reaction (c) may occur~ This latter reaction is initiated and propagated by free radicals and can be catalyzed.

~19--The bu~-ning o~ ~ulfur~containing coke depQsits from the cataly~s-t als~ results in the formation of sulfur oxides;
and, although the disclosed in~ention is not to be limited thereby, this burnin~ may be represen-ted by the followin~
chemical equations: `
(d) S (in coke)~ ~2 -~ SO2 (e) SO2~ 1/2 2 -~ SO3 ~eactions ~d) and (e) also occur under typical cracking catalyst regeneration conditions. While reaction (d) is fast, reaction (e) is relativel~ Islow. Reaction (e~ can be catalyzed by any catalyst which catalyzes reaction (c~ above. Molecular sieves adsorb sulfur oxides, and therefore reaction (e) can occur on the cracking catalyst in the solid particles of the method of thi.s invention. Other components of the solid particles can also adsorb sulfur oxides. The resulting sulfur trioxide can then react wlth a suitable metal, or more particularly an oxide of the metal in the metallic reactant, to form a stable metal sulfate in the solid particles. When the solid particles are separated frol~ the regeneration zone flue gases, the metal sulfate in the solid particles is circulated to the reaction zone. Thus, the sulfur is rendered unavailable for exit as gas eous sulfur oxides in the regeneration zone flue gas.
The sulfate remains on the solid particles as they pass to the cracking r~action zone and, in the reducing atmosphere thereint is converted to the sulfide of the metal in the metal-lic reactant and possibly to hydrogen sulfide. Upon stripping with a steam containing stripping ~as in the stripping zone, the sulfur is convexted to hydrogen sulfide and exits in the strip- -ping zone e~fluent stream. The metallic reactant is thereby regenerated and made available again for reaction with sulfur oxides in the next pass through the regeneration zone. Hydro~en 1~

6~

sulfide can then be recQvered with the cracking products from the strIppIn~ zone, separated and converted to elemental sulfur in conventional ~acilities.
Although the dlsclosed invention is not to be limited thereby, lt is ~elie~ed -that these reactions can be summarized:
Regenerator MO-t 52 ~ 1/2O2 or MO ~ SO3~ MSO~
Reactor 4 ~ H2 -~M5-~ ~H2O~ I2S ~ 3H20 Stripper MS ~ H20~ MO -~ H2S
These reactions are made possible through the use of both the molecular sie~e-type cracking catalyst and metallic reactant of the method o~ thls invention. The hi~h cracking activity normally present in the molecular sieve catalyst remains sub-stantially una~fected by the presence of the metallic reactant so that the anticipated conversion of feedstock and yield of cracked products are realized together with the diminution of ~ -emission of sulfur oxides.
The metallic reactant can be in a ~inely divided form, such as a powder, separate from the molecular sieve-type crack-in~ catalyst or any other support. In such case, the metallic reactant is a po~der which is separately introduced into the catalytic cracking process cycle and admixed with the molecular sieve-type crackin~ catalyst in situ in the catalytic cracking process cycle, but not before the molecular sieve-type cracking `
catalyst is introduced into the crackin~ process cycle. Gener-ally, such powdered metallic reactant is ad~antageous in that apowder is easy to char~e to and handle in a fluidized catalytic cracking process system. The particle size of the powder should be selected SQ as to avoid se~re~ation of the particles at the fluidizing ~elocities. Desirably, the particles in such powder are not SQ ~inute that pr~blems occur such as excessi~e emission with the gases from the bed as entrained particulate matter;

haweyer~ filter~, c~clones~ preci~tatoXs~ and the like are usuall.~ employed in conjunction With fluidized catal~tic crack-ing operations to reco~er ~ost o~ the entrained particulate matter and return it to the system to abate losses. The powder should be sufficiently strong that excessi~e attrition and de-cJradation of the sized powder may be avoided. Frequently, the avera~e particle size of the powdered metallic reactant is from about 0.5 or 1 to 100 microns, preferably less than about 50 microns, in diameter. Tt has been noted that microsized particles, that is, ha~ing an average particle siæe of less than about 1 micron, for lnstance, about 0.01 to 0.5 micron, may tend to form ag~regates of larger size which may beneficial-ly be employed in the process of this invention. Illustrative of powdered metallic reactants which may be employed in this invention are magnesium oxide and calcium oxide, dolomite and Trimex, manufactured by Trimex Corporation and described in U.S. Patent 3,630,696.
Alternatively, the metallic reactant can be incorporated onto a suitable support other than the molecular sieve-type cracking catalyst, outside the cracking process cycle, and the composite is then introduced into the cracking process cycle where it becomes a p~rt of the solid particles. Such support can be an amorphous cracking catalyst or a solid which is sub-stantially inert to the cracking reaction and can, for example, be ceramic in nature. In such case, the supported metallic reactant is then a~mixed with the molecular sieve-type cracking catalyst within the cracking process cycle, but no-t before the molecular sie~e-type cracking catalyst is introduced into the crackin~ process cycle. Desirably~ the support used is porous and ~requently has a surface area, including the area of the pores on the surface, of at least about 10, preferably at least 5~7 ~bout 50, ~ua~ ~ete~s per ~x~ llust~ative of the supports are s~l~c~, alu~n~, s~l~ca~alumina and the like. The metallic reactant ma~ ~e ~ncorp~rated into such substrate by ion ex-change, impregnation or other means -- by contacting the substrate or a c ~ onent thereofwlth a solution or solutions of a c~ound or ~compounds of the metal in the metallic reactant in an appropri-ate amount necessary to provide the desired concentration of the metallic reactant within the scope of the invention. The metal-lic reactant may be combined with such substrate either in any step during preparation of the substrate or after the substrate has been prepared. One ~ethod of incorporation is to ion-ex- -change the substrate. ~l~o useful is the ion-exchanging of siliceous solids or clays with a solution or solutions of a compound or compounds of the metallic element or elements of metallic reactant. guitable compounds for this purpose include the metal halides, preferably chlorides, nitrates, amine halides oxides, sulfates, phosphates and other water-soluble inorganic salts; and also the metal carboxylates of from 1 to 5 carbon atoms, and alcoholates.
Alternatively, the metallic reactant can be incorporated into the molecular sieve-type cracking catalyst, or portion thereof, in the solid particles in the method of this invention, in the catalytic cracking process cycle, but not before the molecular sieve-type cracking catalyst is introduced into the ~5 cracking process cycle. In such case, the metallic reactant is introduced into the cracking catalyst during the cracking pro-cess cycle. In such case, care should be taken in selection of the method of introduction so that the cracking activity and selectivity of the cracking catalyst are not adversely affected.
In any of the above cases, the precise manner in which ~r:
`~ ~J.

the metal or metals of the metallic reactant are incorporated into the moleculax sieve~type crackin~ catalyst, amorphous crackin~ catalyst, or substantially lnert substrate is not known with absolute certainty The metals may enter into a complex combination with the carrier material and other com-ponents Oe the solid par-ticles of this in~ention. Therefore, it is understood that the use of the terms "metallic reactant"
and "incorporated" into the substra-te connotes the metals of such component existing ~ithin the carrier material in a combined form and/or in the elemental state.
Impregnation may be practiced in any way which will not destory the structure of the substrate. The metallic reactant may be impregnated onto the molecular sieve-type cracking catalyst only within the cracking process cycle or into a sup-port inert to the hydrocarbon cracking or amorphous cracking catalyst either within or outside the cracking -23a~

~ rl 'I
ll process cycle. Impregnation dlffers from cation exchange. Impregnation ~ results in greater deposition and a primarily physical association on ¦ the surface of the substrate, whlle ion exchange results in a primarily chemical association and a greater diffusion and therefore less surface deposition. In impregnation, the metal is deposited and no significant ion excharlge occurs between the metal and the substrate. In i~pregnating a substrate, the metal or metals in the metallic reactant can be present in or as a water-soluble or organic solvent-soluble or -dispersible I¦ compound or compounds in an amount or amounts sufficient to contain the lo I quantity of metal or metals desired on the substrate, and the substrate is contacted therewith. The composite may be dried to remove the solvent, leaving the metallic reactant deposited on the substrate.
Preferably, water-soluble nitrate salts are employed in the impregnating solution since residue from the thermal decomposition of nitrate salts is relatively innocuous to the activity of the hydrocarbon cracking catalyst. The halogen and sulfate salts of the metal to be impregnated may also be employed; however, since the by-products resulting from thermal decomposition of such salts may be deleterious to the activity of the hydrocarbon cracking catalyst, these salts are most often employed when depositing the metallic reactant on substrates which are substantially inert to the cracking reaction and which do not significantly adversely affect the hydrocarbon cracking l reaction.

~ Ancther method of physically depositing the metallic reactant on a substrate, particularly porous substrates such as crystalline alumino silicates, is adsorption of a fluid decomposable compound or compounds of the metal or metals in the metallic reactant on the substrate followed l by thermal or chemical decomposition of the compound or compounds. The ¦ substrate may be activated by heating to remove any adsorbed water and l then contacted with a fluid decomposable compound or compounds of the , 51~7 i metal or metals in the metallic reactant, therehy adsorbing the compound i or compo~mds onto the substrate. Typical of such compounds are the ¦
`metal alkyls, volatile metal halides and the like. The adsorbed compound or compounds may then be reduced therma].ly or chemically to its active state, ~hus leavl~g uniEormly dispersed on the substrate an active ~metallic reactant. Thermal reduction may be effected, for example, in the regeneration vessel during the regeneration process.
It is also advantageous to introduce a compound or compounds of the metal or metals in the metallic reactant into the cracking process cycle o and incorporate it in situ into the substrate. Such compound or com-pounds can be introduced in either oil- or water-soluble or -dispersible form and in the solid, liquid? or gaseous state at any stage of the cracking process cycle so that wide distribution in the solid particles lis achieved. For example, such compound or compounds can be admixed ,either with the feedstock or fluidizing gas in the reaction zone, with the regeneration gas, torch oil, or water in the regeneration zone, or ~with the stripping gas in the stripping zone, or can be introduced as a separate stream. Suitable compounds for in situ incorporation include metal salts. Examples include metal diketonates and metal carbo~ylates , having from 1 to 20 carbon atoms. A specific example is magnesium acetylacetonate.
Preferred embodiments of the method of this invention involve operation in conjunction with the regeneration scheme of U.S. patent , No. 3,909,392.
2s That patent is directed to an improved catalytic cracking process, including an improved process for the regeneration of catalysts , employed in fluid catalytic conversion of hydrocarbon feedstocks wherein `
the catalyst is deactivated by the deposition of coke on the catalytic surfaces. The process enables the coke level on regenerated catalyst to ~' be maintained at an extremely low level while simultaneously maintaining a fa~orable heat balance in the con~ersion unit ~nd providing a ~lue gas strea~ hav~ng an extremely low carbon monoxide content. Heat from the combustlon of carbon monoxide is absorbed by the re~enerated catalyst and~rovides part oE the process heat requlred in -the hydrocarbon conversion zone. In one embodimen-t o~ the process of that patent, the combustion oE carbon monoxide to carbon di.oxide is carried substantially to comple-tion within the regeneration vessel in a relatively dilute secondary catalyst regeneration zone advan-tageously at a temperature between about 1200 and 1500F., desirably between about 1250 and 1450F. The temperature of the secondary zone may be about 50 or 100F. higher than that of the first regeneration zone. Partially regenerated catalyst from a relatively dense primary catalyst re~eneration zone can be controllably flowed throu~h the secondary zone in an amount and at a rate sufficient to absorb substantially all of the heat released by the combustion occurring in the secondary zone.
Although most o~ the coke is burned from the catalyst in the primary zone, additional coke is burned from the partially regenerated catalyst while present in the secondary zone, and catalyst substantially ~ree o~ coke may be recovered for recycle to the hydrocarbon conversion level.
In a-~second emb~diment of the process of U.S. patent No. 3,909,392, substantially all of the combustion, including both the oxidation of coke or carbon on the catalyst and the ~xidation o~ carbon monoxide, occurs within a single, relatively dense phase regeneration zone in response to the proper control of principally the re~eneration temperature and gas velocity.
Similarly, when the process of the present invention is operated in embodiments involving the regeneration scheme of U.S. pat~nt No. 3,909,392, the major amount o~ heat liberated ,, ~rom the cQ~b.ustl~on ~ carb~n ~onoxide in the regeneration zone is absor~ed h~ the solid particles of this lnventlon which include the crack~n~ ca-tal~st and provides part of the ~26a-~. .

.1 1 ,1 1 ¦heat required in the cracking æone. Beneficially, in such embodiments, I _ ~¦the process oE the present invention enables considerable coke and ¦carbon monoYcicle to be combusted in the dense-phase zone, if one is ',present, wherein a substantially increased amount oE solid particles is ¦ present, a9 corE)ar~d to the dilute-phase zone, if one ls present, to dlsperse tlle heat evc):lved tilereErom. ~s the portion oF combustlon occurrLng :Ln the dense-ptlase zone is increased, the evolution oE heat ln ¦the d-LluLe-pllase zone :Ls substantial].y reduced, hence, the need to ¦provide rapid turnover of solid particles in the dilute-phase zone to lo 1 absorb the evolved heat is reduced or eliminated.

In such embodiments, the process includes the use of the solid particles of this invention which comprise molecular sieve-type cracking ¦catalyst and the metallic reactant of this method, in a system which 1 supports substantially complete combustion of carbon monoxide. The low catalyst coke levels achieved are less than about 0.2 weight percent, preferably less than about Q.05 weight percent. This process can result in flue gas having carbon monoxide levels of less than about 0.2 volume percent, for example about 500 to 1000 parts per million, and as low as l from about 0 to 500 parts per million. The process also includes ¦ provision for recovery of evolved heat by transfer directly to the solid particles within the regeneration vessel.
~ In such embodiments, the fluidizing gas in the dense zone of the ¦ regenerator may have a velocity, for example, in the range of from about 0.2 to 4 feet per second, desirably about 0.5 to 3 Eeet per second. The regeneration gas serving to fluidize the dense-bed contains free or molecular oxygen, and the oxygen is preferably charged to the regenerator , in an amount somewhat in excess of that required for complete combustion ' of coke (carbon and hydrogen) to carbon dioxide and steam. The amount i of oxygen in excess of that required for complete combustion of the coke , , may vary from about 0.1 to about 25 or more percent of the theoretical ,, !

.

, .. . .
~. ~

stQich~Qmetr~c oxy~en re~uirement ~or complete cambustion o~ the coke, but ~dv~nta~ously need not be greater than about 10 percent. ~or e~ample, when air is emplo~ed as the regenera-tion gas a 10 percent excess of air provides only about 2 volume percent oxy~en in the ef~luent spent gas stream. Advantageously the concentration o~ molecular or ~ree oxygen and carbon mon-oxide at any point wL~hln the regenerator is maintained outside of the explosive range at those conditions, preferably the concentration of carbon monoxide is below the explosive range at those conditions, to eliminate any risk of detonation.
The regeneration gas, in addition to free or molecular oxygen, may contain inert, or diluent, gas such as nitrogen, steam, etc., recycle gas from the regenerator effluent, and the like. Frequently the oxygen concentration of the regenera-tion gas at the inlet to the regenerator is from about 2 to 30 volume percent, preferably about 5 to 25 volume percent. Since air is conveniently employed as a source of oxygen, a major portion of the inert gas may be nitrogen. The inert gas may serve to dissipate excessive heat from the combustion of coke from the catalyst. A source of hot, inert gas is the effluent from the regenerator, and a portion of this gas may be recycled to the regenerator and, for instance, combined with sufficient incoming air or other oxygen-containing gas, including essen-tially pure oxygen, to provide the desired oxygen content, Thus, the recycle gas may be employed in direct heat exchange to increase the temperature of the regeneration gas to provide even further heat economies in the system.
Solid particles within the dilute-phase may partially be carried into the separation zone, usually comprising cylone separators in a plurality of stages, from which solid particles can be returned directly through dip-legs to the dense-bed zone, ~2~-~.j and s~ent re~eneration and co~bustion sases are collected in a plenu~ and flnally~ discharged ~or suitable recover~ of heat energy contalned thexeln. Recovery processes -28a~

, .
. ' lliO567 l¦ior heat from flue gas include 8team generation, spent catalyst stripping, ¦ indirect heat exchange with varlous refinery Streams SUCh as feed to the I par~lcular conversion process~ and employment in variou5 drying or evaporation arrangemen-ts.
The attached clrawing8~ Figures 1 and 2~ provide elevational views, p~rtly :L~ .sectlon, of embodLrnents of apparatus suitable for catalyst regeneration according to embodiments of the process of this inVention l :Lnvolving the regeneration scheme of ~.S. patent No. 3,909,392. Indeed~
1 guch embodiments may be employed beneficially in many existing petroleum hydrocarbon cracking process units~ particularly fluid catalytic cracking units having a variety of spatial arrangements of cracking, stripping and regeneration sections thereof.
I Figure 1 is illustrative of one such embodiment of this invention employing bottom entry of stripped, spent catalyst passing from the cracking reactor (not shown) to the regenerator. Solid particles con-taining spent catalyst impregnated with a metallic reactant from a stripping zone associated with the catalyst exit from the reactor, enter l from the bottom of regeneration vessel 1. The solid particles flow 1 upwardly through inlet lines 2 and 3 and discharge into the dense bed through discharge heads 4 and 5. The dense-phase bed is maintained within the lower section 6 of the regenerator vessel and extends upwardly to the phase interface 7. Solid particles within the dense-phase bed ~ are fluidized by the flow of com~ustion air through line 8, valve 9 and 25 1 line 10 to air ring 11. Substantially balanced air flow patterns through the regeneration zone may be achieved by the use of additional air rings, not shown, as required. Combustion of coke contained on the spent catalyst with air is initiated within the dense-phase bed. Higher ~ temperatures may be achieved by temporarily burning a stream of torch 30 ¦ oil, for example a decanted oil9 within the bed. Torch oil may be added ¦
: by passage through line 12, valve 13 and line 14 which terminates in a Il I

nozzle located above the alr ring 11. Fluidizing air velocities con-tinuously carry some oE the solid particles upwardly into the dilute-l phase zone which occupies the upper section 15 of the regenerator vesseL; that is, tlle section above the phase interface 7. Combustion ofcoke con~inue~ ln the dilute-phase æone and the largely spent combustion gas toge her with entrained solid particles is withdrawn illtO first-stage cyclone separators 20 and 21. Most of the solld particles are separated in the Eirst-stage cyclones and discharged downwardly through lo dip-legs 22 and Z3 into the dense-phase æone. Gases and remaining solid particles are passed through interstage cyclone lines 24 and 25 to second-stage cyclone separators 26 and 27 where substantially all of the remaining solid particles are separated and passed downwardly through dip-legs 28 and 29 into the dense-phase bed. Substantially spent combustion gas then passes through lines 20 and 31 into plenum 32 and finally is discharged from the regenerator vessel through line 33. This effluent may be suitably heat exchanged, not shown, with refinery stream or for production of process steam. Solid particles containing I regenerated catalyst from the dense bed is withdrawn through standpipes 34 and 35, fitted with collector heads 36 and 37, for return to the cracking reactor.
Although the supply of combustion alr normally provides an excess of oxygen over the amount required to effect complete combustion of lI the coke on the catalyst particles to steam and carbon dioxide, com-bustion of coke may not be completed in the dense-phase bed in one I embodiment of this invention which employs the regeneration scheme of U.S. patent No. 3,909,392. In thls situation, the combustion gases rising from the dense bed zone thus contain a substantial quantity of carbon monoxide as well as carbon dioxide and oxygen. The remaining coke on catalyst and the carbon monoxide are substantially completely burned in the dilute phase zone with evolution of much heat. When , , 1~ 5~

¦ carbon monoxide burns in the dilute phase a high temperature zone will lusually be present throughout much of the dilute phase zone and par-¦~ticularly at approximately the location indicated by X and can readily ¦Ibe viewed through a window, not shown, at that horizontal plane. Control of regeneration temperature within the dilute phase zone iæ effected in par~ through absorption of heat by the mass of solid particles elther carried upwardly by the rising combustion gas stream or educted upwardly from the dense~bed through eductor tube 40 and solid dis-o tributor head 41 where a rain, or fountain, of solid particles dis-perses into the dilute phase zone. Solid particles can be educted by means of air, steam or other inert gas entering through line 42, valve ¦¦ 43 and ~et tube 44 which extends a short distance into the lower end of eductor tube 40. Excessive temperature levels in the top section of the regenerator may be further controlled by distribution of steam, for example through lines 45 and 46, valve 47 and line 48 to steam pod 49.
Temperatures in the vicinity of the plenum may also be controlled with steam fed through line 50, valve 51 and line 52 to steam ring 53 which ! surrounds plenum 32. Additional cooling if desired may be provided by use of a water spray~ not shown, which may advantageously be directed ¦ within the region of interstage cyclone lines 24 and 25. Such lower temperatures favor the formation of stable metal- and sulfur-containing compounds in the regeneration zGne.
~ Figure 2 is illustrative of another embodiment of this invention l, employing the regeneration scheme of U.S. patent No. 3,909,392, with side entry of the solid particles containing stripped, spent catalyst and metallic reactant, from the cracking reactor to the regenerator.
, Solid particles containing spent catalyst impregnated with the metallic ~¦ reactant, enter regeneration vessel 101 flowing downwardly through inlet line 102 located on the side of the regeneration vessel to provide entry into the dense-phase bed maintained withln bottom section 106 a short ;67 !

distance below phase interface 107. Fluidization of the solid particles ~I i8 effected by combustion air pa~sing through line 108, valve 109 and il line 110 to air ring 111. Additional air rings, not shown, may be employed as desired for further balancing of air flow patterns through the regeneration zones. As descrlbed in Figure 1, combustlon of coke on the spent catalyst particles i8 initiated within the dense-phase zone where higher temperatures as desired may be achieved by temporary burning of a torch oil stream within the zone. Such ~orch oil may be lo added through line 112, valve 113 and line 114 terminating in a nozzle.
Fluidizing air velocity may be controlled to continuously carry solid particles upwardly for purposes of heat absorption into the dilute-phase zone which occupies the upper section 115 of the regenerator vessel; that is, the section above the phase interface 107. Combustion of coke as well as of carbon monoxide may continue in the dilute-phase zone and the largely spent combustion gas together with the en~rained ¦ portion of solid particles is withdrawn into irst-stage cyclone ¦ separators 120 and 121. Most of these solid particles are separated in the first-stage cyclones and discharged downwardly through dip-legs 122 l and 123 into the dense-phase ~one. Gases and remaining solid particles subsequently pass through interstage cyclone lines 124 and 125 to second-stage cyclone separators 126 and 127 where substantially all of the remaining solld particles ara separated and passed downwardly ¦I through dip-legs 128 and 129 into the dense-phase bed. Substantially spent combustion gas then passes through lines 130 and 131 into plenum ~¦ 132 and finally is discharged from the regenerator vessel through line 133. Solid particles containing regenerated catalyst from tha dense bed is withdrawn through standpipes 134 and 135, fitted with collector heads Il 136 and 137, for return to the catalytic cracking reactor.
30 ¦¦ As described for the embodiment of Figure 1, carbon monoxide burns !¦ in the dilute-phase providing a high temperature zone throughout much 1!

S~7 ,, 1.1 ~l oE the dilute-phase zone and particularly at approximately the location ¦ indicated by X. Control of ~egeneration temperature within the dilute-¦phase zone is effected largely through absorption of heat by the mass ~¦oE solid particles carried upwarclly by the rising combustion gas ~strenm. Temperatures in the vicinity of the plenum, cyclone and connectin~, lines m~y, as required, be reduced with steam fed through line 1150, valve lSl and line 152 to steam ring 153 which surrounds plenum jl32. Water spray means, not shown, may similarly be employed.
In another, particularly preferred embodlment of this invention, 10 ~
' the apparatus shown in Figure 2 is employed with a significant change ¦¦ in operating parameters as compared to the above described embodiment.
¦~ In this embodiment, gas velocity and solid particles input are adjusted so that essentially complete combustion of coke and carbon monoxide is completed within the dense phase and the heat is dispersed throughout the bed.
When the system is operated according to either of the first two above-described embodiments, recovery of the heat released by the ¦ essentially complete combustion of coke and carbon monoxide is by j absorption in solid particles in both phases, and return of the solid ¦ particles to the dense-phase serves also to secure main~enance of the ¦ suitably high temperature within the dense-phase zone. The returned ¦ solid particles may carry with them additional heat to serve to raise l the temperature of the dense-phase zon2 to a temperature which favors 1 the removal of additional increments of coke deposits thereon such that the combustion of the final increments of coke becomes substantially complete. When the system is operated so that essentially all com-bustion is completed within the dense catalyst phase, the heat is dispersed throughout the phase as it is absorbed by the fluidized solid l par cle~ and tinal increments of coke 3re combu~ted. Accordi=gly, in l _ 33 -.

I

5~i~

~1 all embodiments, so]id particles containing the regenerated catalyst passing from the regenerator back to the cracking reactor suitably contains from about 0.01 to about 0.10 weight percent, desirably 0.01 to 0.05 weight percent and preferably about 0.01 to about 0.03 weight 1 percent of carbon or coke on catalyst, and can be withdrawn from the regenerator at an advantageous temperatUre for Use in the cracking renctor.
An outstanding advantage of thiS invention lies in providing a regenerated catalyst generally possessing enhanced activity and selec-tiv$ty characteristics more closely approaching those of fresh Con-¦ version catalyst~ particularly for use in conversions effected at veryshort contact times in riser reactors. The cracking activi.ty of sieve-l containing catalysts and their selectivity for converting hydrocarbon feeds to desLred products are both dramatically affected in a favorabledirection by the increased elimination of residual carbon or coke on the catalyst during regeneration. The low coke level on the reg~nerated catalyst iS especially preferred With fluid cracking catalysts containing catalytically active, crystalline aluminosilicates. Accordingly, higher ! yields of desirable conversion products may be achieved.
In those cracking processes using a lower dense phase zone and an upper dllute phase 7one in the regeneration zone~ the oxidation of the carbon monoxide to carbon dioxide may be accomplished to a major extent, often at least about 60 percent~ and frequently about 65 to 95 percent ¦ or more, to completion in the dense phase of the regenerator. The oxidation of carbon monoxide to carbon dioxide in the dense phase ~¦ provides heat to aid in sustaining the combustion of the coke deposits ~j from the fluid catalyst. Furthermore~ with a substantial portion of the I~ carbon monoxide being oxidized in the dense phase, a lesser amount of ! carbon monoxide iS present for combustion in the upper phase of ~he fluid l catalyst in the regenerator~ and thus 'lafterburningi' and high temperature~

}5~i7 ¦due to uncontrolled excessive carbon monoxide combustion in the upper ¦portion in the reg~nerator which may deleteriously affect materlals ¦ employed to construct the reactor, waste gas flue, the collectors for ¦ any particulate materials in the waste gas, for example, cyclones, and s ¦wh:Lch may lmpe:Lr catalyst actlvity, may be substantlally reduced or ¦ avoi~ed.
¦ Solid part-lcles containlng the regenerated catalyst particles ¦having unusually low residual coke contents are recovered from the ¦ dense-phase and passed at the substantially dense-bed temperature through a standpipe to the cracking reactor for contacting with fresh hydrocarbon feed or mixture thereof with recycle hydrocarbon fractions.
Since the oxidation of the carbon monoxide evolved from the combustion of the coke deposits on the catalyst may occur to a major extent in the dense-phase and in the preferred embodiments essentially completely occurs in the dense phase, the regenerated catalyst can be returned to the cracking reactor at a much higher temperature as well as a higher activity than theretofore conventional operations.
A maior benefit from the process of this invention relates to the 1 unusually low carbon monoxide content in the effluent gas stream from the regenerator which may be obtained. Whereas flue gas from conventional regeneration of cracking catalysts usually contains from about 6 to lO
percent carbon monoxide, a similar amount of carbon dioxide and very little oxygen, the carbon monoxide content of the flue gas from this ~ novel regeneration process may be maintained at less than about 0.2 volume percent, for example, about 500 to 1000 parts per million by volume (ppmv). Advantageously, the content is even lower, for example~ ¦
¦~ within the range from 0 to about 500 ppmv. This low concentration of Il carbon monoxide in the flue~gas stream permits the direct release of j~ effluent gases to the atmosphere while meeting ambient air quality I standards. If required, anV remaining carbon monoxide may suitably be .

~Q~7 burned in the exhaust from the re~ene~ator flue gas stack~
This ad~antage o~ the Ln~entiOn additionally permits the elimination of capital expendltures otherwise required for lnstallation o~ car~on monoxide boilers and associated turbine-type devices or other means for p~rtial xecovery of energy produced by the subsequent oxidation of the carbon monoxide while still meetlng the existing standards Eor ambient air quality for carbon monoxlde emissions.
The method of this invention provides additional benefits.
Such benefits relate to the problem of after-burning and heat balance. A major problem often encountered and sought to be avoided in the practice, particularly of fluid catalyst regenera-tion, is the phenomenon known as "afterburning", described, for example, in Hengstebeck, Petroleum Processing, McGraw-Hill Book Co., 1959, at pages 160 and 175 and discussed in Oil and Gas Journal, Volume 53 (No. 3~, 1955, at pages 93-94. This term is descriptive of the further combustion of carbon monoxide to carbon dioxide, as represented by reaction (c) above, which is highly exothermic. After~urning has been vigorously avoided in catalyst regeneration processes because it could lead to very high temperatures which may damage equipment and cause per-manent deactivation of cracking catalyst particles. Many fluid catalyst regenerator operations have experienced afterburning, and a very substantial body of art has developed around numerous means for controlling regeneration techniques so as to avoid afterburning. More recently, it has been sought to raise reg~n-erator temperatures for various reasons; elaborate arrangements have also been developed for control of regenerator tempera-tures at the point of incipient afterburning by suitable means for control of the oxygen supply to the regenerator vessel as set forth, for example, in U.S. Patents Nos. 3,161,583 and 3,206,393, as well ~ in U~.. Patent N~ 3,513,Q87, In typical contemporary pract~ce, accord~n~l~, with aYoidance -36a-~, .

56'7 ~ of afterburning, the flue gas from catalyst regenerators usually con-j tains very little oxygen and a substantial quantity of carbon monoxide I and carbon dioxid~ in nearly equimolar amounts.
5 j Further com`bustion of carbon monoxide to carbon dioxide is an atl:racl:ive sotlrce oF heat energy because reaction (c) ls highly exo-thermic ~l~terburning can proceed at temperatures above about 1100~.
alld lLberates approximately ~350 BTU per pound of carbon monoxide l oxidized. This typlcally represents about one-fourth of the total heat i evolution realizable by combustion of coke. The combustion of carbon monoxide can be performed controllably in a separate zone or carbon ¦ monoxide boiler~ after separation of effluent gas from catalyst, as ¦ described in, for example, U.S. Patent No. 2,753,925, with the released ¦ heat energy being employed in various refinery operations such as the 5 ¦ generation of high pressure steam. Other uses of such heat energy have been described in U.S. Patents Nos. 3,012,962 and 3,137,133 (turbine drive) and U.S. Patent No. 3,363,993 (preheating of petroleum feedstock). Such heat recovery processes require separate and elaborate equipment but do serve to minimize the discharge of carbon monoxide 20 into the atmosphere as a component of effluent gases, and hence, serve to avoid a potentially serious pollution hazard.
Moreover, silica-alumina catalysts, employed conventionally for many years in various processes for the cracking of petroleum hydro-carbons, are not particularly sensitive to the level of residual coke on catalyst provided that the coke level be no greater than about 0.5 weight percent. However, silira-alumina catalysts have largely been supplanted by catalysts additionally incorporating a crystalline alumino-¦ silicate component and known as zeolites or "molecular sieves". The j molecular sieve-containing catalysts are much more sensitive to the 30 ¦ residual coke level, being greatly affected both with regard to catalyst activity and to catalyst selectivity for conversion of feed to the i ¦desired product or products. Due to the difficulties encountared in conventional catalyst regeneration techniques for removal of the last LncremenLs of residual carbon, the practical coke level usually corresponds to a residual coke content on regenerated catalyst within the range fr~m abollt 0.2 to about 0.3 weight percent.
Siuce enhanced activity and selectivity are achievable with sieve-type cracking catalysts at low coke levels, an attractive incentive is provided for discovering a means for reducing residual coke levels still further. Coke levels below about 0.05 weight percent are greatly o ~ desired but usually cannot be achieved by commercially practicable means.

¦ Considerations such as larger regeneration vessels, greater catalyst I inventory, greater heat losses, and the like, all serve to discourage attainment of such ideal equilibrium catalyst activity lavels.
Many fluid cracking units are operated on the "heat balance"
¦ principal, depending upon combustion of coke for the evolution of heat required in the process. Such units, however, have not been able to , fully utilize the benefits of the cracking catalysts, par~icularly zeolite catalysts, which can especially be achieved in a riser reactor ~¦ where contact times between catalysts and oil vapors may be extremely Il short. The type of operation which affords high conversion coupled with the high selectivity, favors a low ratio of catalyst-to-oil in the j riser reactor which leads to less coke being available to generate heat ¦ by combustlon in the regenerator. Accordingly~ an external heat source jl ~uch as a feed preheat furnace, may frequently be added to increase the j temperature of the catalyst or, alternatively, the unit may be operated j at a lower temperature of fresh feed. Such undesirable features may be ¦ avoided or minimlzed by the process of this inventlon which permits ¦ effici~nt recovery of additional heat by the solid particles for transfer¦

30 ¦ to the riser reactor. The heat of combustion of coke in conventional operations is about 12,000 BTU per pound. The process of this invention l l 5~'~

¦may increase available heat by combustlon c,f the coke to about 17,000 or ~¦more BTU's per pound. This higher heat of combustion tencls to raise the '¦regenerator temperature, lower the level oE coke on the regenerated catnlyst, and lower the circulation rate of solid particles whlle pro-s viding improved ylelds at a given conversion level.

.
.' ' :zs~

~ 39 ~

~i E,YA~LE 1 Ten grams of a solution of 6.9 grams of a lubricating oll additive which contained 9.2 weight percent of magnesium, distributed as magnesium hydroxide, magnesium carbonate, and magnesium polypropyl benzene sulfonate, dissolved in 33.:l grams of catalytic light cycle oil, was crackecl in a bench scale cracking Itnit having a fluidized bed of 220 grams of an equillbrium, commercially available cracking catalyst which contained 2.5 weight percent of molecular sieve and about 0.6 weight ~0 percent of sodium and had been withdrawn from a commercial fluid catalytic crac~ing unit and then calcined. The cycle oil was cracked at 700F.
for 4 minutes. After purging the catalyst bed with nitrogen for 10 minutes at 1250F., the catalyst bed was cooled to 700F., and the cracking-purging-regeneration cycle was repeated until the magnesium, zinc, and phosphorus contents of the catalyst reached the level of 110), 703, and 59 parts per million, respectively. The zinc and phosphorus werc inherently present.

The procedure of Exan~ple 1 was repeated, except that the cracking-purging-regeneration cycle was repeated wlth a lOg solution containing 6.5g of the oil and 3.5g of a lube oil additive containing 1.6 wt. %
Zn, 1.3 wt. % P, and 4.Ç wt. % Mg until the magnesium, zinc, and phosphorus contents of the catalyst reached 2400, 1200, and 1097 parts per million, respectively.

The procedure of Example 2 was repeated, except that an equilibrium, commercially available cracking catalyst which contained 303 weight percent of molecular sieve in a silica-alumina matrix and had also been withdrawn from a commercial fluid catalytic cracking unit and calcined 1 was employed and the cracking-purging regeneration cycle was repeated until the magnesium, zinc~ and phosphorus contents of the catalyst reached 4600, 304, and 1,136 parts per milllon, respectively.

5~7 ! EXAMPLES 4-8 A bench scale laboratory regeneration unit was used to test the potency of a number of impregnated catalysts or providing reduced , emissions of sulfur dioxide in regeneration zone flue gases. A synthetic Elue gas composed of 1,500 parts per million of sulfur dioxide in a ¦ mixture o~ 4 volume percent of each of oxygen and water vapor in nitrogen was passed through a fixed fluidized bed of the molecular sieve-type cracking catalyst impregnated with a metal, which was maintained in a lo glass regenerator surrounded by a furnace to provide the desired regeneration temperature of 19 250F. The temperature of the catalyst was measured by thermocouples. A cyclone was used to separate entrained catalyst from the gas exiting from the regenerator and to return the catalyst to the catalyst bed. The time during which the regenerator was ¦ operated at a given set of conditions ranged from about 40 to about 90 minutes in order to allow sufficient time to establish the oxidation state of the metal on the catalyst in an actual fluid catalytic cracking unit operation.

! The sulfur dioxide content of the gas exiting from the regenerator ! was analyzed continuously with an ultra-violet analyzer. The amount of ~
sulfur d~oxide removed from the regeneration zone flue gas was determined . as the difference between the sulfur dioxide contents of the fresh ,i synthetic gas mixture and of the gas exiting from the regenerator. The volume percents of sulfur dioxide removed from the regeneration zone flue gas are shown as a function of elapsed time after beginning the ¦ experiment in Table 1. The volume percent removed decreased with time as the catalyst surface became saturated.
Example 4 was a comparative test using a flow rate of the synthetic flue gas mixture of 1084 milliliters per minute and the unimpregnated ~! equilibrium catalyst used in Examples 1 and 2, while Examples 5 and 6 ,~
,~ involved the impregnated catalyst produced in Examples 1 and 2, ~, .

.

s . o~ o~ ~ o .
~o o a~

~o P ,~ l l l l o ~ ~ ~ ~

X
I ,~
,~
oo

4~ ~ ~ cr~ oO
~ a~ oo . ~o .
t~ C~ o ~cJ oo r~ ~ I`
. . ~ U~ l l l l !~ oo ~ ~ o 20 l ! ~ ~ ~, ~ ~ .

25 ,, :j ~
. ~ o o o .
~ ~ I o o o , .
ll ~respectively, and flow rates for the synthetic flue gas mixture of 9~9 ¦and 1,014 milllliters per minute, respectively. Example 7 was a com-¦parative test using the unimpregnated catalyst used in Example 3 and a ¦ flow rate of the synthetic flue gas mixture of 891 milliliters per mlnute. Example 8 involved the impregnated catalyst produced in Exampl~
3 flnd a FIow rate of the synthetic flue gas mixture of 992 milliliters per minute. The flow rates were measured at 60F.

In Example 9, the procedure of Examples 4-8 was repeated, except that a synthetic flue gas mixture composed of 4 volume percent of each of carbon monoxide, oxygen, and water vapor in nitrogen was passed at a rate of about 1,000 milliliters per minute (measured at 6Q~F.) through a fluidized bed of a mixture of powdered magnesium oxide having a ls particle size of 5 microns and finer and an unimpregnated, calcined, equilibrium, commercially available, molecular sieve-type cracking catalyst contalning 5.3 weight percent of hydrogen and rare earth ion-exchanged, Y-type crystalline aluminosilicate and silica-alumina, which contained 30 weight percent of alumina, in place of the impregnated catalysts. The mixture contained 0,3 weight percent of magnesium oxide, and about 70 volume percent of carbon monoxide was converted to carbon dioxide. In Example 10, the unimpregnated catalyst used in Example 9 was used in the absence of magnesium oxide, under otherwise identical conditions, and 5B volume percent of carbon monoxide was converted to carbon dioxide In Example 11, a gas oil feed having a sulfur content of 1.67 weight percent was cracked in a commercial fluid catalytic cracking unit having a riser reactor. Conventional regeneration was employed A commercial, equilibrium molecular sieve-type cracking catalyst containing 2.5 weight perce=t of ~lecular sieve ~nd about 0 ~ weight percent of so~i~m wae 'i i used. In Example 12, a second gas oil feed having a sulfur content of 1.68 weight percent was cracked in the same commercial unit uslng the same regeneration scheme and the same cracking catalyst, but additionally the catalyst was impregnated w:Lth magnesium and zinc. The magnesium and zlnc were depo;ited on the catalyst by introducing into the reaction zorle small con:entrations of magnesium sulEonate and zinc dialkyldithio-phosphate in tle form of lubricating oil additive in the feedstock.
I After several lours of addition in this manner, levels of magnesium of lo 0.3 weight per:ent and of zinc of 0.1 weight percent were built up onthe cracking cltalyst. The operating conditions and composltion of the regeneration zone flue gases are shown in Table 2.
1, .

I` ~ .

1 i ~ ;87 o C U~ U~ ~ o o . c,~ O C~ D ~ O O O ~O O ~D
C~ ,~ ,, ~ oo 15 1 t~
O ~` o O o C~
l I~ O O ~I t~ S) I~ O ~ O O

I '`'I ~1 ~ ~ r~ o I
I
l ~ . N
. ~ ~3 U g t~ ~ O ~ c~ h i~i U ~ q U U o ~ ~ g ~ U
o ~ u u ~
o ~ u ~ o ~3 ~ h ~ lq o 5~
I S g oo ~ g o ~ o 1, o ~ oJ ~ ~) u ~ ~ c.) ~:: ,n o a~ rl ~1 ~ ~1 a ~i ~J 5:1 hS ~ ~0 ~ ~ rl ~ u O o ~1 ~1 25 i ~ ~ ~d o s u P' u u ~ )3 ~4 o oo lo'` o c~ 5J R o C~ C~ U~
I X h ~ o h ~

Claims (28)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a process for the cyclic, fluidized, catalytic cracking of hydrocarbon feedstock containing about 0.2 to about 6 weight percent sulfur as organic sulfur compounds wherein: (i) said feedstock is subjected to cracking in a reaction zone in contact with fluidized solid particles comprising molecular sieve-type cracking catalyst; (ii) solid particles including catalytic particles which are deactivated by sulfur-containing carbonaceous deposits, are separated from reaction zone effluent and pass to a stripping zone wherein volatile deposits are removed from said solid particles by contact with a stripping gas; (iii) stripped, solid particles are separated from stripping zone effluent and pass to a catalyst regeneration zone and nonstripped, sulfur-containing, carbonaceous deposits are removed from the stripped, solid particles by burning with an oxygen-containing gas thereby forming sulfur oxides; (iv) resulting solid particles are separated from regeneration zone effluent gas and recycled to the reaction zone; a method for reducing emissions of sulfur oxides in the regeneration zone effluent gas which comprises:
(a) providing in said fluid catalytic cracking-regeneration process cycle fluidizable, solid particles, other than said molecular sieve-type cracking catalyst, containing metallic reactant consisting essentially of at least one metallic element selected from the group consisting of magnesium, calcium, strontium and barium in free or combined form, and wherein said metallic reactant is present in sufficient amount to effect the absorption of at least about 50 weight percent of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone;
(b) cracking said feedstock at a temperature from about 850° to about 1,200°F. and in contact with said cracking catalyst and said metallic reactant;

(c) stripping volatile deposits from said solid particles at a temperature from about 850° to about 1,200°F. with a stripping gas which contains steam, wherein the ratio by weight of steam to said molecular sieve-type cracking catalyst is from about 0.0005 to about 0.025, said stripping being conducted at a temperature and with steam such that passage of said solid particles through said cracking and stripping zones provides said metallic reactant in an amount and active form suitable for accomplish-ing said absorption of at least about 50 weight percent of the sulfur oxides produced by said burning in said regeneration zone;
(d) passing to the regeneration zone stripped, solid particles having metallic reactant in an active form for absorbing at least about 50 weight percent of the sulfur oxides in said regeneration zone;
(e) burning in said regeneration zone said sulfur-containing carbonaceous deposits from the stripped, solid particles at a temperature from about 1,050° to about 1,450°F., said burning being conducted at a temperature and with oxygen-containing gas having molecular oxygen such that at least about 50 weight percent of the sulfur oxides produced by said burning in said regeneration zone can be absorbed by said metallic reactant;
(f) absorbing with the solid particles at least about 50 weight percent of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone;
(g) passing from the regeneration zone to the reaction zone said particles containing at least about 50 weight percent of the sulfur oxides produced in said regeneration zone;
(h) withdrawing an effluent gas from the regeneration zone containing molecular oxygen and having a low concentration of sulfur oxides of less than about 600 ppmv;
(i) substantially converting said absorbed sulfur oxides to a sulfur-containing gas in said reaction and/or stripping zone.

2. The process as set forth in claim 1 wherein said particles of molecular sieve-type cracking catalyst comprise from about 90 to about 99.9 weight percent of the fluidizable solid particles in said process cycle.

3. The process as set forth in claim 2 wherein the ratio of steam to said cracking catalyst is from about 0.0015 to about 0.0125.

4. The process as set forth in claim 3 wherein the feedstock has a sulfur content in the range from about 1 to about 4 weight percent.

5. The process as set forth in claim 4 wherein the amount of said metallic reactant, calculated as the metal, is from about 0.1 to about 0.5 weight percent of said solid particles.

6. The process as set forth in claim 1 wherein air and essentially pure oxygen are supplied to said regeneration zone as sources of oxygen for burning of said sulfur-containing carbonaceous deposits.

7. The process as set forth in claim 3 wherein the amount of said metallic reactant in the solid particles is sufficient to effect absorption of at least about 80 percent of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone, said burning being conducted at a temperature and with oxygen-containing gas having molecular oxygen such that there is absorption of at least about 80 weight percent of the sulfur oxides produced by said burning in said regeneration zone, said stripping being conducted at a temperature and with steam such that said metallic reactant is provided in an amount and active form suitable for accomplishing said absorption of at least about 80 weight percent of the sulfur oxides produced by said burning in said regeneration zone, and said stripped, solid particles passing to the regeneration zone having said metallic reactant in an active form for absorbing at least about 80 weight percent of said sulfur oxides produced in said regeneration zone.

8. In a process for the cyclic, fluidized, catalytic cracking of hydrocarbon feedstock containing about 0.2 to about 6 weight percent sulfur as organic sulfur compounds wherein: (i) said feedstock is subjected to cracking in a reaction zone in contact with fluidized solid particles comprising molecular sieve-type cracking catalyst; (ii) solid particles including catalytic particles which are deactivated by sulfur-containing carbonaceous deposits, are separated from reaction zone effluent and pass to a stripping zone wherein volatile deposits are removed from said solid particles by contact with a stripping gas; (iii) stripped, solid particles are separated from stripping zone effluent and pass to a catalyst regeneration zone and nonstripped, sulfur-containing, carbonaceous deposits are removed from the stripped, solid particles by burning with an oxygen-containing gas thereby forming sulfur oxides; and (iv) resulting solid particles are separated from regeneration zone effluent gas and recycled to the reaction zone; a method for reducing emissions of sulfur oxides in the regeneration zone effluent gas which comprises:
(a) providing in said fluid catalytic cracking-regeneration process cycle fluidizable, solid support particles, other than said molecular sieve-type cracking catalyst, having incorporated therein metallic reactant consisting essentially of at least one metallic element selected from the group consisting of magnesium, calcium, strontium and barium in free or combined form, and wherein said metallic reactant is present in sufficient amount to effect the absorption of at least about 50 weight percent of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone;

(b) cracking said feedstock at a temperature from about 850° to about 1,200°F. and in contact with said cracking catalyst and said metallic reactant;
(c) stripping volatile deposits from said solid particles at a temperature from about 850° to about 1,200°F. with a stripping gas which contains steam, wherein the ratio by weight of steam to said molecular sieve-type cracking catalyst is from about 0.0005 to about 0.025, said stripping being conducted at a temperature and with steam such that passage of said solid particles through said cracking and stripping zones provides said metallic reactant in an amount and active form suitable for accomplishing said absorption of at least about 50 weight percent of the sulfur oxides produced by said burning in said regeneration zone, (d) passing to the regeneration zone stripped, solid particles having metallic reactant in an active form for absorbing at least about 50 weight percent of the sulfur oxides in said regeneration zone;
(e) burning in said regeneration zone said sulfur-containing carbonaceous deposits from the stripped, solid particles at a temperature from about 1,050° to about 1,450°F., said burning being conducted at a temperature and with oxygen-containing gas having molecular oxygen such that at least about 50 weight percent of the sulfur oxides produced by said burning in said regeneration zone can be absorbed by said metallic reactant;
(f) absorbing with the solid particles at least about 50 weight percent of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone;
(g) passing from the regeneration zone to the reaction zone said particles containing at least about 50 weight percent of the sulfur oxides produced in said regeneration zone;
(h) withdrawing an effluent gas from the regeneration zone containing molecular oxygen and having a low concentration of sulfur oxides of less than about 600 ppmv;
(i) substantially converting said absorbed sulfur oxides to a sulfur-containing gas in said reaction and/or stripping zone.

9. The process as set forth in claim 8 wherein the feedstock has a sulfur content in the range from about 0.5 to about 5 weight percent.

10. The process as set forth in claim 9 wherein the amount of said metallic reactant in the solid particles is sufficient to effect absorption of at least about 80 percent of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone, said burning being conducted at a temperature and with oxygen-containing gas having molecular oxygen such that there is absorption of at least about 80 weight percent of the sulfur oxides produced by said burning in said regeneration zone, said stripping being conducted at a temperature and with steam such that said metallic reactant is provided in an amount and active form suitable for accomplishing said absorption of at least about 80 weight percent of the sulfur oxides produced by said burning in said regeneration zone, and said stripped, solid particles passing to the regeneration zone having said metallic reactant in an active form for absorbing at least about 80 weight percent of said sulfur oxides produced in said regeneration zone.

11. The process as set forth in claim 8 wherein said metallic reactant is selected from the group consisting of magnesium and calcium.

12. The process as set forth in claim 8 wherein the amount of said metallic reactant, calculated as the metal, is from about 0.1 to about 0.5 weight percent of said solid particles.

13. The process as set forth in claim 9 wherein said support particles are selected from the group consisting of amorphous cracking catalysts and solids which are substantially inert to the cracking reaction.

14. The process as set forth in claim 13 wherein said support is selected from the group consisting of silica, alumina, thoria, and boria.

15. The process as set forth in claim 13 wherein said support comprises alumina.

16. The process as set forth in claim 13 wherein said particles of molecular sieve-type cracking catalyst comprise from about 90 to about 99.9 weight percent of the fluidizable solid particles in said process cycle.

17. The process as set forth in claim 16 wherein the ratio of steam to said cracking catalyst is from about 0.0015 to about 0.0125.

18. The process as set forth in claim 17 wherein the regeneration zone effluent gas stream contains at least about 0.5 volume percent of molecular oxygen.

19. The process as set forth in claim 18 wherein the feedstock has a sulfur content in the range from about 1 to about 4 weight percent.

20. In a process for the cyclic, fluidized, catalytic cracking of hydrocarbon feedstock containing about 0.2 to about 6 weight percent sulfur as organic sulfur compounds wherein: (i) said feedstock is subjected to cracking in a reaction zone in contact with fluidized solid particles comprising molecular sieve-type cracking catalyst; (ii) solid particles including catalytic particles which are deactivated by sulfur-containing carbonaceous deposits, are separated from reaction zone effluent and pass to a stripping zone wherein volatile deposits are removed from said solid particles by contact with a stripping gas; (iii) stripped, solid particles are separated from stripping zone effluent and pass to a catalyst regen-eration zone and non-stripped, sulfur-containing, carbonaceous deposits are removed from the stripped, solid particles by burning with an oxygen-containing gas thereby forming sulfur oxides; and (iv) resulting solid particles are separated from regeneration zone effluent gas and recycled to the reaction zone; a method for reducing emissions of sulfur oxides in the regeneration zone effluent gas which process comprises:
(a) adding to said fluid catalytic cracking-regeneration process cycle metallic reactant in liquid form consisting essentially of at least one compound selected from the group consisting of the compounds of magnesium, calcium, strontium and barium, and wherein said metallic reactant is present in said solid particles in sufficient amount to effect the absorption of at least about 50 weight percent of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone;
(b) cracking said feedstock at a temperature from about 850° to about 1,200°F. and in contact with said cracking catalyst and said metallic reactant;
(c) stripping volatile deposits from said solid particles at a temperature from about 850° to about 1,200°F. with a stripping gas which contains steam, wherein the ratio by weight of steam to said molecular sieve-type cracking catalyst is from about 0.0005 to about 0.025, said stripping being conducted at a temperature and with steam such that passage of said solid particles through said cracking and stripping zones provides said metallic reactant in an amount and active form suitable for accomplishing said absorption of at least about 50 weight percent of the sulfur oxides produced by said burning in said regeneration zone;
(d) passing to the regeneration zone stripped, solid particles having said metallic reactant in an active form for absorbing at least about 50 weight percent of the sulfur oxides in said regeneration zone;
(e) burning in said regeneration zone said sulfur-containing carbonaceous deposits from the stripped, solid particles at a temperature from about 1,050° to about 1,450°F., said burning being conducted at a temperature and with oxygen-containing gas having molecular oxygen such that at least about 50 weight percent of the sulfur oxides produced by said burning in said regeneration zone can be absorbed by said metallic reactant;
(f) absorbing with the solid particles at least about 50 weight percent of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone;
(g) passing from the regeneration zone to the reaction zone said particles containing at least about 50 weight percent of the sulfur oxides produced in said regeneration zone;
(h) withdrawing an effluent gas from the regeneration zone containing molecular oxygen and having a low concentration of sulfur oxides of less than about 600 ppmv; and (i) substantially converting said absorbed sulfur oxides to a sulfur-containing gas in said reaction and/or stripping zone.

21. The process as set forth in claim 20 wherein said metallic reactant is added to said process cycle dissolved in said feedstock.

22. The process as set forth in claim 21 wherein the feedstock has a sulfur content in the range from about 0.5 to about 5 weight percent.

23. A process as set forth in claim 21 wherein said metallic reactant is selected from the group consisting of magnesium and calcium.

24. A process as set forth in claim 23 wherein from about 0.1 to about 0.5 weight percent of said metallic reactant, calculated as the metal, is incorporated into the solid particles.

25. A process as set forth in claim 21 wherein the dissolved metal component is a metal salt.

26. A process as set forth in claim 21 wherein the dissolved metal component is selected from the group consisting of metal diketonates and metal carboxylates having from 1 to 20 carbon atoms.

27. A process as set forth in claim 21 wherein the dissolved metal component is magnesium acetylacetonate.

28. The process as set forth in claim 23 wherein said metallic reactant is present in sufficient amount to effect the absorption of at least about 80 percent of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone, said burning being conducted at a temperature and with oxygen-containing gas having molecular oxygen such that there is absorption of at least about 80 weight percent of the sulfur oxides produced by said burning in said regeneration zone, said stripping being conducted at a temperature and with steam such that said metallic reactant is provided in an amount and active form suitable for accomplishing said absorption of at least about 80 weight percent of the sulfur oxides produced by said burning in said regeneration zone, and said stripped, solid particles passing to the regeneration zone having said metallic reactant in an active form for absorbing at least about 80 weight percent of said sulfur oxides produced in said regeneration zone.