CA1122912A - Method for removing pollutants from catalyst regenerator flue gas - Google Patents

Method for removing pollutants from catalyst regenerator flue gas

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Publication number
CA1122912A
CA1122912A CA297,023A CA297023A CA1122912A CA 1122912 A CA1122912 A CA 1122912A CA 297023 A CA297023 A CA 297023A CA 1122912 A CA1122912 A CA 1122912A
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Prior art keywords
catalyst
sulfur
cracking
flue gas
metal
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CA297,023A
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French (fr)
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William A. Blanton, Jr.
Robert L. Flanders
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Chevron USA Inc
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Chevron Research and Technology Co
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Priority claimed from US05/786,723 external-priority patent/US4115250A/en
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D53/00Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34Chemical or biological purification of waste gases
    • B01D53/74General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86Catalytic processes
    • B01D53/8603Removing sulfur compounds
    • B01D53/8609Sulfur oxides
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D53/00Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34Chemical or biological purification of waste gases
    • B01D53/74General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86Catalytic processes
    • B01D53/864Removing carbon monoxide or hydrocarbons
    • CCHEMISTRY; METALLURGY
    • C10PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10GCRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G11/00Catalytic cracking, in the absence of hydrogen, of hydrocarbon oils
    • C10G11/02Catalytic cracking, in the absence of hydrogen, of hydrocarbon oils characterised by the catalyst used

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Environmental & Geological Engineering (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • General Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Biomedical Technology (AREA)
  • Analytical Chemistry (AREA)
  • Health & Medical Sciences (AREA)
  • Organic Chemistry (AREA)
  • Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
  • Catalysts (AREA)
  • Treating Waste Gases (AREA)
  • Exhaust Gas Treatment By Means Of Catalyst (AREA)

Abstract

ABSTRACT OF THE DISCLOSURE
Carbon monoxide and sulfur oxides are removed from flue gas pro-duced in a catalyst regenerator in an FCC system and sulfur from the flue gas is shifted to form hydrogen sulfide, which is recovered in the gases re-moved from the cracking reactor in the system by introducing sufficient mol-ecular oxygen into the catalyst regenerator to provide an atmosphere therein having a molecular oxygen concentration of at least 0.1 volume percent, re-acting carbon monoxide in the regenerator flue gas with oxygen in contact with a particulate carbon monoxide combustion promoter physically admixed with the cracking catalyst, reacting sulfur oxides in the regenerator flue gas with silica-free alumina included as a discrete phase in the FCC cat-alyst to form a sulfur-containing solid in the catalyst, and forming hydro-gen sulfide in the cracking reactor by contacting the sulfur-containing solid with the hydrocarbon feed.

Description

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1 BACKGROUND OF THE_INVENTION
2 This inrention relates to a method for reduci~g the
3 amount of carbon ~onoside and sulfur oxides in the flu2 gas
4 produced in a catalyst reg~nerator in a fluid catalytic cracking system.
6 ~odern hydrocarbmn catalytic crac~ing systems use a 7 mo~ing bed or fluidized bed of a particulate catalyst~ The 8 cracking catalyst is subjected to a continuous cyclic ccacking 9 reaction a~d catalyst regeneration procedure. In a fluidized catalytic cracking (FCC) system, a stream of hydrocarbon feed is 11 contacted ~ith fluidized catalyst particles in a hydrocarbo~
12 cracki~g zone, or reactor, usually at a temperature of bout 800-13 1100F. The reactions of hy~rocarbons in the hydrocarbon stream 14 at this te~perature result in deposition of carbonaceous coke on the catalyst particles. The resulting fluid products are 16 thereafter separated from the coked catalyst and are withdr~n 17 from the cracking zone. The coked catalyst is then stripped of 18 volatiles and is passed to a catalyst regeneration zone. In the 19 catalyst regenerator, the coked catalyst is contacted ~ith a gas contai~ing a controlled amount of molecular oxygen to burn off a 21 desired portion of the coke from the catalyst and simultaneously 22 to heat the catalyst to a high temperature desired when the 23 catalyst is again contacted with the hydrocarbom stream in the 24 cracking zone. After regeneration, the catalyst is ret~r~ed to the cracking zone, ~here it is used to ~aporize the hydrocarbons 26 and to catalyze hydrocarbon cracking. The flue gas formed by 27 combustion of coke in the catalyst regenerator is separately 2~ removed from the regenerat~r. This flue gas, ~hich may be 29 treated to removP particulates and carbon monoxide from it, is normally passed into ~he atmosphere. Concern ~ith control of 31 pollutants in flue gas has resulted in a s~arch for impro~ed llZ~2~lZ

1 methods for controlling such pollutants, particularly sulfur 2 oxides and carbou monoside.
3 The a~ount of conversion obtained in an FCC cracki~g 4 operation is the Yolume percent of fresh hydroc~rbon feed changed to gasoline and lighter products during the conversion s~ep. The 6 end boiling point of gasoline for the purposs of determinin~
1 conversion is conYentionally defined as 430F. Conversion is 8 often used as a measure of the severity of a com~ercial FCC
9 operation. At a gi~en set of operating conditions, a m~re ~ctive catalyst gives a greater conversion than does a less aotive 11 catalyst. The ability to provide highe~ conversion in a gi~en 12 FCC unit is desirable in that it allo~s the FCC unit to b-13 operate~ in a more flexible manner. Feed throughput in the unit 14 can be increased, or alternatively a higher degree of conversion can be maintained vith a constant feed throughput rate.
16 The hydrocarbon feeds processed in commercial FCC units 17 normally contain sulfur, usually termed "feed sulfur". It has 18 been found that about 2-10% or more of the feed sulfur in a 19 hydrocarbon feedstream processed in an PCC syst~m is inYari~ly transferred frou the feed to the catalyst particles as ~ part of 21 the coke formed on the catalyst particles during cracki~g. The 22 sulfur deposited on the catalyst, herein termed "coke sulfur", is 23 eventually cycled from the conversion zone along with the coked 24 catalyst iDto the catalyst regenerator. Thus, about 2-10~ or ~ore of the sulfur in the hydrocarbon feed is continuously passed 26 from tha cracking zone into the catalyst regeneration zons in the 21 coked catalyst. In an ~CC catalyst regenerator, sul~ur contained 28 in the coke is burned along ~ith the coke carbon, forming gaseous 29 s~lfur dioxida and sulfur trioxid~, ~hich are c~n~entio~ally removed fro~ the regenerator ~n the flue gas.

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1 Most of the feed sulfur does not become coke sulfur in 2 the cracking reactor. Instead, it is converted either to 3 ~ormally gaseous sulfur compounds such as hydrogen sulfide and 4 carbon oxysulfide, or to normally liquid organic sulfur compounds. Thes~a sulfur compounds are carried along ~ith the 6 vapor products recovered from the crac~ing reactor. About 90~ or 7 more of the feed sulfur is thus conti~uously re~oved from the a cracking reactor in tha stream of processed, cracked 9 hydrocarbons, ~ith about 40-60~ of this sulfur be~ng in the form of hydrogen sulfide. eroviSions are conventionally made to 11 recover hydrogen sulfide from the effluent from the cra_king 12 reactor. Typically, a very-low-molecular-weight off-gas vapor 13 stream is separated from the C3~ liquid hydrocarbons in a gas 14 recovery unit, and the off-gas is treated, as by scrubbing it with an amine solution, to remo~e the hydrogen sulfide. ReDoval 16 of sulfur compounds such as hydrogen sulfide from the fluid 17 effluent fro~ an FCC cracking reactor is relatively simple ~nd 18 inexpensive compared to remeval of sulfur oxides from an FCC
19 regenerator flue gas by conventional methods. ~oreover, if all the sulfur ~hich must be recovered from an FCC operation could be 21 recovered in a single recovery operatioa perfor~ed on the raactor 22 off-gas, the use of tvo separate sulfur recovery operations i~ an 23 FCC unit could be obviated.
24 It has been suggested to diminish the amount of sulfur o~ides in FCC regenerator flue gas by desulfurizing a hydrocarbo~
26 feed in a separate desulfurization uuit prior to cracking or to 27 desulfurize the regenerator flue gas itself, by a con~entio~al 28 flue gas desulfurization procedure, after removal from the FCC
29 regeneratoc. Clearly, hoth of the foregoing alterna~ivas raguire elaborate, extraneous processing operations and entail large 31 capital and ~tilities e~penses.

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1 If sulfur normally removed from the FCC unit in the 2 resenerator flue gas as sulfur oxides is instead removed from the 3 cracking reactor as hydrogen sulfide along ~ith the processed 4 cracked hydrocarbons, the sulfur thus shiftsd to the reactor effluent is then simply a a small additio~ to the large amount of 6 hydrogen sulfide and organic sulfur already in~ariably present in 7 the reactor effluent. The small added expense, if a~y, of 8 removing e~en as much as 5-15% more hydrogen sulfide from an FCC
9 reactor off-gas by available means is substantially less than the expense of separate f~ed desulfurization or flue gas desulfuri-11 zation to reduce the lsvel of sulfur cxides in the regenerator 12 flue gas. ~ydrogen sulfide recovery systems used in pr3sent 13 commercial FCC units normally ha~e the capacity to remova 14 additional hydrogen sulfide from the reactor o~f-gas. ~resent off-gas hydrogen sulfide recovery facilities could normally 16 handle any additional hydrogen sulfide ~hich would be added to 17 the off-gas if the sulfur normally in the regenerator flue gas 18 were substantially all converted to hydrogen sulfide in the FCC
19 reactor off-gas. It is accordingly desirable to direct substan-tially all feed sulfur into the fluid cracked products removal 21 pathway from the cracking reactor and reduce the amount of sulfur 22 oxides in the regenerator flue gas.
23 It has been suggested, e.g., in ~.S. Patent 3,699,037, 24 to reduce the amount of sulfur oxides in FCC regenerator flue gas by adding particles o~ Group IIA ~etal oxides and/or carbonates, 26 such as dolomite, MgO or CaCO3, to the circulating catalyst in an 27 FCC unit. The Group IIA metals react ~ith sulfur osides in the 28 fluP sas to form solid sulfur-containing compounds. Th2 Gr~up 29 IIA metal o~ides lack physical strength, and reg~rdless of tha size of the particles introduced, they are rapidly redu~ed to 31 fi~es by attrition and rapidly pass out of the FCC unit ~ith the llZZ9:12 1 catalyst fines. Thus, addition of dolomite and the like Group 2 IIA materials must be continuous, and large amounts of material 3 must bs employed, in order to reduce the level of flue gas sulfur 4 oxides for any significant period of time~
It has also been sugg~sted, e.g., in ~.S. Patent 6 3,835,031, to reduce the amount ~f sulfur oxides in an FCC
7 regenerator flue gas by impregnating a Group IIA metal axide onto 8 a conventional silica-alumina cracking catalyst. The attrition 9 problem encountered ~hsn using unsupported Group IIA metals is thereby reduced. Hovever, it has been found that Group IIA metal 11 o~ides, such as magnesia, when used as a component o~ cracking 12 catalysts, have an undssirable effect on the activity and salec-13 tlvity of the cracking catalysts. The addition of a Gr~up IIA
14 metal to a crac~ing catalyst results in two particularly noticeable adverse consequences relative to the results obtained 16 in cracking ~ithout the presence of the Group II~ metals: (1) 17 the yield of the li~uid hydrocarbon fraction is substantially 18 reduced, typically by greater than 1 volume percent of the feed 19 volume; and ~2) the octane rating of the gasoline or naphtha fraction (7S-430F boiling range) is substantially reduced.
21 Both of the above-noted adverse consequencss are seriously detri-22 mental to the economic viability o~ an FCC cracking operation and 23 e~en complet~ removal of sulfur oxides from regenerator flue gas 24 would not compensate for the losses in yield and octane ~hi~h result from adding Group IIA metals to an FCC catal~st.
26 Alumina has been a component of many FCC and other 27 cracking catalysts, but primarily in intimate chemical 28 combination vith silica. Alumina itself has lov acidity and is 29 generally considered to be undesirable for use as a cra~king catalyst. The art has taught that alumina is n~t selective, 31 i.e., the cracked hydrocarbon products recoYered from an FCC or ~Z29~2 1 other cracking unit using an alumina catalyst ~ould not be 2 desired valuable products, but ~ould in lude, for example, rela-3 tively large amounts of C2 and lighter hydrocarbon gase~.
4 ~he conventional type of FCC catalyst regener~tion currently used in most systems is an incomplete combustion Rode.
6 In such systems, referred to herein as "standard regeneratlon"
7 syste~s, a substantial amount of coke carbon is left on 8 regenerated catalyst passed from the FCC regeneration zone to the 9 cracking zone. Typically, regenerated catalyst contains a substantial amount of coke carbon, i~sO~ more than 0.2 ~eight 11 perc~nt car~on, usually about 0.25 to 0.45 weight percent carbon.
12 The flue gas remo~ed from n PCC regenerator operating in a 13 standard regeneration ~ode is characterized by a relatively high 14 carbon ~onoxide~carbon dioxide concentration ratio. Th~
atmosphere in much or all of the regeneration zone is, ~ver-all, 16 a reducing atmosphere because of the presence of substantial 17 amounts of unburned coke carbon and carbon monoxide.
18 In general, reducing the level of carbon on r3gsnerated 19 catalyst belo~ about 0.2 ~eight percent has beeG difficult.
~ntil recently, there has been little incentive to atte~pt to 21 re~ove substantially all coke carbon from the catalyst, since 22 even a fairly high carbon content has had little adversa effect 23 on the activity and selectivity of amorphous silica-alu~ina 24 catalysts. Most of ths FCC cracking catalysts no~ used, however, contain zeolitas, or molecular sieves. Zeolite-contai~ing 26 ca~alysts have usually been found to have relatively hi~her 27 activity and selecti~ity ~hen their coke carbo~ content after 28 regeneration is relatively low. An incentive has thus ~risan for 29 attempting to reduce the coke content of reganerated FC~ catalyst to a very lo~ level, e.g., belo~ 0.2 weight percent.

:~.ZZ9i2 1 SeYeral ~ethods have been suggested for burning sub-2 stantially all carbon mono~ide to carbon dioxide during 3 regeneration, to aYoid air pollution, recover heat and prevent 4 afterburning. Among the procedures suggestsd for use in obtaining complete carbon monoxide combustion in an ~CC regene-6 rator ha~e been: (1) increasing the amount of oxygen introd~cad 7 into the regenerator relative to standard regeneration; and 8 either (2) increasing the average operating temperature in the 9 regenerator or (3) including YariOUS carbon ~onoxide o~idation promoters in the cracking ~atalyst to promote carbon monoxide 11 burning. Various solutions hare also been suggested for the 12 problem of afterburning of car~on monoxide, such as addition of 13 extraneous combustibles or use of ~ater or heat-accepti~g solids 14 to absorb the heat of combustion of carbon monoxide.
Nhen using carbon monoxide combustion promoters hereto-16 fore commercially available, such as Group YIII noble metals in 17 FCC catalysts, to provide complete carbon monoxide combustion, it 18 has been found quite difficult to maintain the amount of co~e on 19 regenerated catalyst at an acceptably lo~ level. Promot~r materials Yhen added to the catalyst have ~een been found to 21 provide adequate CO combustion in many cases, but have not been 22 ~ell accspted commercially because of the resulting high level of 23 coke on reg6nerated catalyst, which has lowered conv~rsion.
24 Complete combustion systems using an unusually high temperature i~ the catalyst regenerator to accomplish complete 26 carbon monoxide combustio~ are also not altogether satisfactory.
27 Some of the heat generated by carbon monoxide combustion is lost 28 in the flue gas, because CO combustion takes place essentially in 29 a dilute catalyst phase in an after-~urning mode, znd high temperatures ca~ per~a~ently adYersely affect the actiYity and 31 selectiYity o~ the ~CC catalyst.
..

ll;~Z~12 1 Several types of addition of Group VIII noble ~etals 2 and other carbon monoxide combustion promoters to FCC systems 3 ha~e bee~ suggested in the art. In ~.S. Patent 2,647,860 it is 4 proposed to add 0.1-1 weight percent chromic o~ide to an PCC
catalyst to promote co~bustion bf carbon mono~ide to carbon 6 dioxide and to prevent afterburning. U.s. Patent 3,364,136 7 proposes to employ particles containing a small por3 (3-5 A.~
8 molecular sieve vith ~hich is associated a transition m~tal from 9 Groups IB, IIB, VIB, VIIB and VIII of the Periodic Tabl~, or compounds thereof, such as a sulfide or oxide. Representative 11 metals disclosed i~clude chromiu~, nickel, iron, molybdenum, 12 cobalt, plati~um, pallad~um, copper and zinc. The metal-loaded, 13 small-pore zeolite may be used in an FCC system in physical 14 mixture ~ith cracking catalysts containing larger-pore zeolites active for cracking, or the small-pore zeolite may be i~cluded in 16 th6 same matrix ~ith zeolites active for cracking. The small-17 pore, metal-loaded zeolites are supplied for the purpose of 18 increasi~g the C0z/CO ratio in the flue gas produced in the FCC
19 regenerator. In U.S. Patent 3,788,977, it is proposed to add uranium or platinu~ impregnated on an inorganic oxide such as 21 alumina to an FCC systsm, either in physical mixture with FCC
22 catalyst or incorporated into t~e same amorphous matrix as a 23 zeolite used for cracking. Uranium or platinum is added for the 24 purpose of producing gasoline fractions havi~g high aromatics contents, and no effect on carbo~ ~ono~ide combustion ~he~ using 26 the additive is discussed in the patent. In ~.S. Patent 27 3,808,121 it is proposed to supply large-size particles of a 28 carbon ~onoxide co~bustion promoter in an FCC regenerator. The 29 s~aller-size catalyst particles are cycled bet~een the PCC
cracking reactor and the catalyst regenerator, ~hile, b3cause of 31 their size, the larger promoter particles remain in the ~.

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1 regenerator. Carbon mono~ide oxidation promoters such ~s cobalt, 2 copper, nickel, manganese, copper chromite, etc., impregnated on 3 an inorganic oxide such as alumina are disclosed for use.
4 Belgian patent publication 820,181 suggests using catalyst S particles contaiGing platinum, palladium, iridium, rhodium, 6 osmiumO ruthenium or rheni~m or mixtures or compounds thereof to 7 promote carbon ~ono2ide oxidation in an FCC catalyst regenerator.
8 An amount bet~een a trace and 10q ppm of the active metal is 9 added to FCC catalyst particles by incorpcration during catalyst manufacture or by additio~ of a compound of the metal to the 11 hydrocarbon feed to an FCC unit using ths catalyst. Th2 12 publication notes that addition of the promoter metal increases 13 cok6 and hydrogen formation during cracking. The catalyst ~ containing the promoter metal can be used as such or can be add~d in physical mixture with unpromoted FCC cracking catalyst.
16 Applicants' employer and/or affiliates thereof pur-17 chased guantities of particulate additives from catalyst manu-18 facturers. The additives were sold by the manufacturers for the 19 purpose of introducing the additives into circulation in ad~iYture ~ith FCC catalyst in FCC units to promote combustion o~
21 carbon mono~ide during catalyst regeneration in the units.
22 Applicants' employer and/or affiliates thereof used the additives 23 in their commercial FCC operations. One such additive ~as 24 understood to contain a mixture of platinum-alumina particles and 2S silica-alumina particlss.
26 SUM~ARY_QF THE INV NTION
27 In an embodiment of the invention employed in a 28 catalytic hydrocarbon cracking process vherein a cracking 29 catalyst is cycled betiee~ the cracking zone and a catalyst regen~ration zone, a sulfur-containing hydrocarbon stream is 31 crac~ed in contact ~ith the catalyst in the cracking zone, and a ~ZZ9~2 1 carbon monoxide-containing and sulfur-containing flue g~s is 2 form~d in the regeneration zone by burning sulfur-containing coke 3 off the catalyst with an oxygen-containing gas, the inv~ntion 4 relates to a method for reducing the amount of carbon monoride
5- and sulfur oxides in the flue gas, ~hich comprises: reacting
6 carbon mono~ide and o~ygen to form carbon dio~ide in the
7 regeneration zone in contact ~ith a carbon mono~ide oxidation
8 promoter comprising a metal or compound of a metal selected from
9 platinum, palladium, iridium, rhodium, osmium, rutheniu~, copper and chromium associated ~ith a particulate solid, the particulate 11 solid being physically admixed ~ith the crac~ing catalyst;
12 introduci~g sufficient molecular oxygen into the regeneration 13 zone to proride an atmosphere therein having a molecular oxygen 14 concentrat.ion of at least 0.5 Yolume percent; removing sufficient coke from the catalyst in the regeneration zone to provids an 16 average carbon content of less than 0.2 weight percent in 17 catalyst passsd from the regeneration zone to the cracking zone;
18 including in said catalyst a substantially silica-free alumina 19 phase, said catalyst bsing substantially free from said metal or compound of said metal; forming a sulfur- and aluminum~containing 21 solid in the catalyst in the regeneration zons by reacti~g sulfur 22 trioxide ~ith alumina present in said alumina phase in said 23 catalyst, and remo~ing sulfur from the catalyst and îorming 24 hydrogen sulfide in the cracking ~one by contacting the sulfur and aluminum-containing solid with the hydrocarbon stre~m.
26 ~e have found that the use of a particulate carhon 27 monoYide co~bustion promoter containing a metal or metal compound 28 very active for CO combustion promotion, in con3unction ~ith the 29 use of a catalyst containing a discrete~ silica-free alu~ina 39 phase for reaction ~ith sulfur oYides in regenerator flue gas, 31 provides a synergistic method for removing both carbon ~ono~ide 32 ~ a~d sulfur oxides from the regenerator flue gas~

1 1 _ DET~ILED DESCR~ION_OF THE INVENTEQN
2 The present i~ention is used in connection ~ith a 3 fluid catalyst cracking process for cracking hydrocarbon feeds.
4 The same sulfur-containing hydrocarbon feed nor~ally pr~cessed in commercial FCC systems may be processad in a cracking sys~em 6 employing the present invention. Suitabl~ feedstocks include, 7 for eYample, gas oils, light cycle oils, heavy cycle oils, Ptc~, 8 which usually contain a~out 0.1-10 weight percent sulfur. Sulfur 9 may be present in the feed as a thiophene, disulfide, thioether, etc~ suitable feedstocks normally boil in the range from about 11 400-1100F or higber. A suitable feed may include recycled 12 hydrocarbons ~hich hav~ already been cracked.
13 Crac~ing conditions employed in the cracking or 14 conversion step in an FCC system are frequently pro~ided in part by pre-heating or heat-exchanging hydrocarbon feeds to bring the~
16 to a temperature of about 600-750F before introducing them into 17 the cracking zons; howe~er, pre-heating of the feed is not 18 essential. Cracki~g conditions include a catalyst/hydrocarbon 19 ~eight ratio of about 3-10. A hydrocarbon ~eight space velocity in the cracking zone of a~out 5-50 per hour is preferably used.
21 The average amount of coke contained in the catalyst after 22 contact ~ith the hydrocarbons in the cracking zone, ~hen the 23 catalys' is passed to the regenerator, is preferably bet~een 24 about 0.5 ~eight percent and about 25 ~eight percent, depending in part on the carbon content of regenerated catalyst i~ tha 26 particular system, as ~ell as the heat balance of ~he particular 27 system.
28 The catalyst regeneration zone used in an ~CC system 29 employing an em~odiment of the present invention may be of con~entional design. The gaseous atmosphere inside the 31 regeneration zone is normally comprised of a ~ixture of gases i~

llZZ912 1 concentrations ~hich vary according to the locus ~ithin the 2 rege~erator. The concentrations of gases also vary according to 3 the coke concentration on catalyst particles entering the 4 regenerator and according to the amount of molecular oxygen and S steam passed into the regenerator. Generally, the gaseous 6 atmosphere i~ a regenerator contains 5-25% steam, var~ing amounts 7 of oxygen, carbon monoxide, nitrogen, carbon dioxide, sulfur 8 dioxide and sulfur trioxide. In order to facilitate remo~al of 9 sulfur contents from the reg~nerator flue gas within the regene-rator according to the invention, it is preferred that r21atiYely 11 co~e-free particles containing active alumina must contact the 12 gaseous regenerator atmosphere at a locus at which the ~tmosphere 13 contains sulfur trioxide or molecular oxygen and sulfur dioxide.
14 In regenerators of conventional design, the flue gas includes the desired components and catalyst normally contacts the flue gas at 16 this point, after havi~g been freed of a substantial amount of 17 co~e. ~hen regenerators of this type are employed, contact 18 bet~een relatively coke-free alumina-containing particles and the 19 osygen and sulfur dioxide or sulfur trioxide is facilitated.
According to one aspect of the invention, a c~rbon 21 monoxide combustion promoter is employed in an ~CC syst~m. The 22 carbon mono2ide combustion promoters ~hich are suitable for use 23 according to the invention are the metals platinum, palladium, 24 iridium, rhodium, osmium, ruthenium, copper and chromium, or compounds thereof, such as the o~ides, sulfidss, sulfat~s, etc.
26 At least one of the foregoing metals or metal compounds i5 used, 27 and mistures of t~o or more of the metals are also suitable. For 28 example, mixtures of platinum and palladium or copper and 29 chromium are suitable. The effect of the above-mentioned carbon monoxide combustion promoter metals may be enhanced, in some 31 cases, by combining them ~ith small amounts of other metals or 32 ~ metalloids, particularly rheniu~, tin, germanium or lead.

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1 The carbon monoxide combustion promoter is employed in 2 the PCC system as follows: the promoter is present in the system 3 in association with a relatively small amount of a particulate 4 solid other than the catalyst, such as particles of alumina, S silica, etc., suitable for circulation in an FCC system, or the ; 6 promoter is present in an insubstantial portion (6. g., less than 7 S~ and preferably less than 1%) of the PCC catalyst particles, 8 with the promoter metal thus being present in physical mixture 9 ~ith all or substantially all of the FCC catalyst. ~hel used in physical mixture with the FCC catalyst, the promoter metal is 11 preferably present in a particulate solid i~ a relatively high 12 concentration. The total amount of promoter metal added to the 13 system is preferably sufficient to promots combustioG of most or 14 substantially all of the carbon monoxide produced in an FCC
regenerator.
16 Platinum is a particularly preferred pro~oter for usa 1~ in the present method. The platinum is present on only a small 18 fraction of particles in the system, i.e., the platinum is 19 located on the particulate solid physically admixed vith the FCC
catalyst~ It is preferred that the total amount of plati~um 21 added to an FCC system ~e ~et~een about 0.01 and 100 parts per 22 million, by ~eight, ~ith an amount between about 0.1 and 10 parts 23 per million being particularly preferred, ~ith respect to the 24 total a~ount of catalyst in the system. It ~ill bs app3rent that the amount of platinum present in a given discrete particle added 26 to an FCC system ~ill be greater ~hen fewer particles c~ntaining 27 the promoter are added. The concentration of platinum -an range 2a up to 2 ~eight percent, or higher, if desired, in cases ~here a 29 Yery small amou~t of particulate, platinum-containing m~terial is added to an PCC system. PreferablyJ ho~ever, the amount of 31 platinu~ added to a particulate solid is kept at l_ss than 1 32 ~ ~eight percent of the t~tal weight of the solid. An a~unt of ~lZ~912 1 platinum added to discrete solids of about 0.01 to 1 weight 2 percent of the total wsight of the discrete solids is a preferred range for use.
4 The amount of Group VIII noble metals other than platinum is generally bet~een about 2 times to 10 times higher 6 total concantration in the system, ~ith respect to the total 7 a~ount of catalyst, than is used for a platinum promoter. ~hus, 8 the amount of the Group ~III metal such as palladium, iridium, 9 etc., can be calculated from the foregoing description ~f the concentration of a platinum promoter, at least twice as much and 11 preferably 5 times as much of other Group VIII noble metals being 12 used. The co~centration of the other Group VIII noble metals on 13 any discrete particle in the FCC system is usually kept ~elo~
14 about 2 weight percent, and preferably ~elow about 1 weight percent.
16 The amount of copper used in an PCC system as a 17 promoter is generally about 100 to about 5000 times higher total 18 concentration in the system, with respect to the total amount of 19 catalyst used, than the amount of platinum which would be used in the same system. The concentration of copper promoter on any 21 discrete particle is usually ~ept below about 20 ~eight percent, 22 and preferably helo~ a~out 10 ~eight percent.
23 The amount of chromium used i~ an FCC system ~s a 24 promoter is generally bet~een about 500 and about 25,000 ti~es higher total co~centration in the system, ~ith respect to the 26 total amount of catalyst, than the amount of platinum which ~ould 27 be employed in the same system. The concentration of chromium in 28 a chromiu~ compound added by, e.g., impregnation, on any discrete 29 particle in the PCC system is usually kept below about 20 ~eight percent of the total particle ~eight, and prefera~ly belo~ about 31 10 ~eight percent.
..

1 5 _ ll'~Zgl2 1 The promoter metal, or metal compound, ca~ be addad to 2 a discrete particulate solid, ~hich is physically admixed ~ith 3 the PCC catalyst in circulation in the system. The particulate 4 solid to be ~ixed vith tha catalyst can ~e any material ~hich is suitable for circulation in an FCC system in particulate form in 6 admixture ~ith the catalyst. Particularly suitable ~aterials are 7 the porous inorganic oxides, such as alumina and silica, or 8 mixtures of t~o or more inorganic oxid~s, such as silica-alu~ina, 9 nat1lral and synthetic clays and the like, crystalline alumino-silicate zeolites, etc. Gamma alumina is particularly good. The 11 promoter metal can ~e added to a particulate solid in any 12 suitable manner, as by impregnation or ion exchange, or can be 13 added to a precursor of a particulate solid, as by copre-14 cipitation from a~ aqueous solution ~ith an inorganic oxide precuraor sol. The particulate solid can be formed into 16 particles of a size suitable for use in an ~CC system by 17 conventional means, such as spray-drying, crushing of l~rger 18 particles to the desired size, etc.
19 A particulate solid which contains at least one promoter metal or metal compound of the type mentioned above can 21 be admixed with the bulk of FCC catalyst prior to charging the 22 catalyst to an FCC unit. Like~ise, the particulate solid 23 containing a promoter can be added to an FCC unit separ~tely from 2~ ths catalyst in the desired amount.
~hen the promoter metal is employed in the system, and 26 particularly ~hen the promoter metal is present in a relatiYely 2~ high concentration in a particulate solid physically ad~ixed vith 28 the cracki~g catalystO it is preferred to perfor~ at least a 29 ~ajor portion of the c~mbustion of all carbon monoxide in the catalyst regenerator in a dense catalyst phase reyion ~ithin t~e 31 regenerator. 8y a de~se catalyst phase regionf ia meant that the 11~2Z9lZ

1 catalyst densit~ in the region is at least 10 pounds per cubic 2 foot.
3 ~hen using a separate particulate promoter physically 4 mi~ed ~ith the cracking catalyst, sufficient o~ygen must be S introduced into the regeneration zone in an FCC system so that a 6 minimum molecular oxygen content of at least 0.5-~olume percent, 7 preferably at least 1~0 v~lume percent, is maintained in the 8 atmosphere in the regeneration zone. The minimum molecular 9 o~ygen concentration is ~ormall~ found in the flue gas leaving the regeneration zone.
11 ~hen using a separate particulate promoter physically 12 ~ixed with t~e cracking catalyst, a sufficient amount of coks 13 must be burned off the catalyst in the regeneratio~ zone so that 14 the average concentration of carbon in regeneratsd catalyst cycled from the regeneration zone to the cracking zone is belov 16 0.2 veight percent.
17 According to another aspect of the i~ention, sulfur 18 o~ides are remo~ed from the flu~ gas in an FCC regeneration zone 19 by reacting sulfur trioxids vith alumina in the regeneration zone. The alumina used for the reaction is included in a 21 discrete alumina phase in the catalyst employed in the PCC
22 system, or in a substantial fraction of the particles of catalyst 23 used in the system. Suitable alumina is not in intimate 24 combination ~ith more than 40 ~eight percent silica and is preferably substantially free from silica in intimate 26 combination. ~lu~ina in a discrete phase in a catalyst is 27 suitable for use in the present method if it contains an a~erage 28 of about 50 to 5000 parts per million l~elght~ of "reactive 29 alumina", as determined by treating a catalyst parti~le containing the alumina phase by the follo~ing steps.

Z~lZ

1(1) passing a stream of a gas mi~ture containing, by 2volume, 10% vater, 1% hydrogen sulfide, 10% hydrogen and 79~
3 nitrogen over the catalyst particle continuously at a temperature 4 of 1200F and atmospheric pressure until the ~eight of the solld particle is substantially constant;
6l2) p.assing a stream of a gas mixt~re containing, by 7volume, 10~ ~ater, 15~ carbon dioside, 2% oxygen and 73% nitrogen 8 over the solid particle resulting from step (l) at a te~peratqre 9 of 1200~ and atmospheric pressure until the ~eight of the solid particle is substantially constant, the ~eight of the particle at 11 this time being designated "~a": and 12~3) passing a stream of a gas mixture containing, by 13 ~eight, 0.05~ sulfur dioxide, and, in addition, the same gasQs in 14 the same proportions as used in step (2), over the solid particle 15resulting from step (2) at a temperature of 1200P and 16 atmospheric press~re until the weight of the solid particle is 17 substantially constant, the ~eight of the solid particlQ at this 1 a time being designated "~s".
19The weight fraction of reactive alu~ina in the solid particle, designated "Xal', is determined by the formula 21Xa - Ws-Wa x ~
22Wa 3 x ~Qlecular wt. Sulfur Trioxide 23Various known and commercially used FCC catalysts 24 include at least a small amount of a discrete alumina phase containing reactive alumina, particularly those catalysts vhich 26 include a preponderance of alumina in their overall co~position.
27 On the other hand, many alumina-containing catalysts contain 28 substantially no reactive alumina. ~ost, if not all, 29 conventional catalysts include both silica and alumina, and it is felt that the absence of reactive alumina, ~e have noted, in many 31 alumina-containing catalysts is the result of intimate 1 combination of silica and alumina in the catalysts. Thus, ths 2 alumina phase must be substantially silica-free in order to 3 include alumia suitabla for reaction ~ith sulfur trioxide in the 4 rsgenerator flue gas.
~ost cracking catalysts contain 50 weight percent or 6 ~ore silica, ~hich tends to co~bi~e intimately ~ith alumina in a 7 manner that renders the alumina relatively inactive for reaction 3 ~ith sulfur oxides.
9 Catalysts containing a relati~ely large amou~t of alumina present as a discrete phase (free alumina) can be prepared 11 by employing starti~g materials containing 50~-60% or Dore of 12 alumi~a or a~ alumina precursor, as ~ell as by for~ing catalyst 13 from materials such as clays known to contain at least some 14 discrete, free alumina. A discrete alumina phase, or reactive alumina, can be added to a previously made catalyst by 16 impregnation, ~ut we have found that alumina cannot ~e 17 successfully added to a silica-containing catalyst by 18 impregnation unless the catalyst has first been heated to a 19 temperature bet~een about 800~F and about 1500F, preferably 1000-1400F.
21 Aside from ~he requirement that the catalyst include a 22 discrete, substantially silica-free alumina phase, the method of 23 the present invention places no particular limitations on t~s 24 type of cracking catalyst which can be used~ ~referred catalysts are those containing 1-50 ~eight percent of a zeolitic 26 crystalline alu~inosilicate, such as Zeolite ~ or Zeolite Y, 27 associated Yith a porous refractory matrix, such as one or more 28 inorga~ic oxides. The sodium cations in the zeolite component of 29 the catalyst are preferably ion e~changed for rare earths or hydrogen catio~s to enhance the activity and stability of the 31 catalyst.

:~ _ 1 9 _ - 1~2Z912 1 Alumina in the catalyst particles reacts ~ith sulfur 2 trioxide or sulfur dioxide and oxygen in the FCC catalyst 3 rege~erator to form at least one solid compound ~ncludi~g sulfur 4 and aluminum, such as a sulfate of aluminum. In this way, sulfur S oxides are remo~ed from the regenerator atmosphere and are not 6 released from the regenerator in the flue gas.
7 Catalyst containing the solid aluminum- and sulfur-8 contai~ing material is passed to the cracking zone in the PCC
9 s~stem. In the crac~ing zone, alumina is regenerated i~ the catalyst and hydrogen sulfide is formed by contac ing the sulfur-11 containing catalyst ~ith the stream of hydrocarbon bsing treated 12 in the cracking zone. In addition to forming hydrogen sulfide, 13 the reaction bet~een the sulfur- and aluminum-containing solid 14 ar.d the hydrocarbon feed may produce some other fluid sulfur compounds such as carbonoxysulfide, organic sulfides, etc. Ths 16 resulting fluid sulfur compounds exit the cracking zone as a part 17 of the stream of cracked hydrocarbons, along with the fluid 18 sulfur compounds formed directly from sulfur in the hydrocarbon 1g feed. Off-gas subsequently separated from the cracked hydrocarbon stream thus includes hydrogen sulfide forme1 directly 21 from tha feed sulfur a~d hydrogen sulfide formed by rea^tion of 22 the sulfur- and aluminum-containing solid with the hydrocarbon 23 stream in the cracking zone.
24 It is essential to operation of the present invention that the catal~st wXich contains a discrete alumina phase ~ith 26 alumina to be reacted ~ith sulfur trioxide in the regen rator 27 must be substantially free from any of the promoter met~ls or 28 metal compounds d~scribed above for use in carbon monoxide 29 combustion promotion, that is, platinum, palladium, iri~ium, rhodium, osmium, ruthenium, copper and chromium. It has been 31 found that the presence of these metals or compounds thereof in ..

llZZ9~2 1 catalyst particles containing an alumina phase vith alumina to be 2 used for reaction ~ith sulfur oxides is actually detrimental to 3 the capacity o~ ths al~mina to form solid sulfur-contai~ing 4 materials in an FCC regenerator in the presence of even small amounts of carbon monoside. Thus, ~hen these metals are present 6 on catalyst particles containing alumina to be reacted ~ith 7 sulfur trioxide, the desired reaction of the sulfur trioxide to 8 form a solid is i~paired, and larger amounts of sulfur oxides 9 exit the PCC regenerator in the regenerator flue gas, contrary to the object of the invention. Thus, the metal promoters 11 disclosed, although essential to operation of the inYention, must 12 be used in a particulate solid in physical ~ixture Yith the 13 catalyst containing a discrete alu~ina phase which is reacted 14 with sulfur oxides. The promoter metals must, thus, be on separate particles physically mixed with the PCC catalyst.
16 The follo~ing illustrative embodiment describes a 17 preferred embodi~ent of the operation of the present invention.
18 IkL~STR~TIVE E~M80DIl~1ENT
19 A conv~ntio~al PCC system and equilibrium, zeolite-containing, cracking catalyst of a commercially available type 21 containing an average of 180 ppm (~t.) of reactive alumina i~ a 22 discrete alumina phase are employed for cracking about 19,000 23 barrels per day of a hydrocarbon feed having a boiling range of 24 about 580F to about 1100F. The hydrocarbon feed contains about 0.8 weight percent feed sulfur. The crac~ing zo~e used contains 26 a combination of riser cracking and dense-bed crac~ing modes.
27 Cracking conditions employed include a reactor temperature of 28 about 920F, a hydrocarbo~ ~eight hourly space velocity of about 29 5 per hour and a convers~on rate (defined as percent of feed converted to 430P and lighter co~ponents) of about 85~. The 31 average amount of coke on spent catalyst is about 1.5 ~eight ~2;~9~

1 percent. The coke on spent catalyst includes about 0.7 weight 2 percent sulfur. Th~ amount of carbon on regenerated catalyst is 3 about 0.5 veight percent. The flue gas exiting the catalyst ~ regenerator includes about 650 parts per million (volume~ sulfur S oxides ~calculated as sulfur dioxide)~ about 0.3 volume perc~nt 6 oxygen, a~d has a CO~C02 ratio of about 0.6. Catalyst 7 regeneration conditions used in the regeneration zone include a 8 temperature of about 1200F. Catalys~ is circulated continuously 9 bet~een the cracking zone and regeneration zone at the rate of about 16 tons per minute, ~ith a total catalyst inventory in the 11 system of about 180 tons.
12 According to the invention, 60 pounds of particles 13 containing 0.6 ~eight percent platinum impregnated on a~ alumina 14 carrier are introduced into circulation in the FCC unit along ~ith the catalyst. Introduction of the platinum-alumin3 16 particles is then continued at the rats of about 7 pounds per 17 day. The amount o~ platinum added to the system is thereby 18 maintained at an equilibrium level of about 5 parts per million, 19 by weight, ~ith respect to the total amount of catalyst in the system. Most of the carbon monoxide is burned in a dense 21 catalyst p~ase region in the regenerator. A sufficient amount of 22 02ygen is added to the regenerator to pro~ide at least 1.0 volume 23 percent oxygen in the regenerator atmosphere. A suffi~ient 24 amount of coke is burned off the cracking catalyst in the regenerator so that regenerated catalyst cycled to the crac~ing 26 reactor from the regenerator contains an average of not more than 27 0.2 ~eight percent carbon. After addition of the platinum-28 alumina carbon-~onoxide-combustion promoter particles, the C0/CO2 29 ratio and sulfur oxides level in the flue gas exiting the regeneration zone are ~easured. The C0 concentration is founa to 31 be substantially reduced to 500-1500 ppm (volume), ~hil~ the 1 sulfur oxides level, calculated as 52~ is found to have 2 decreased to below 200 parts per million (volume).
3 As can be seen from the f oregoing illustrativa 4 embodiment, the method of the present invsntion provides a simple and economical method for controlling both the amount of carbon 6 mono~ide and the amount of sulfur 02ides present in flue gas 7 removed from an FCC catalyst regenerator~ A large number of 8 variations, modifications and equivalents of the embodiment 9 illustrated ~ill be apparent to those skilled in the art and are intended to be included ~ithin the scope of the appended claims~

Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a catalytic hydrocarbon cracking process wherein a cracking catalyst is cycled between a cracking zone and a catalyst regeneration zone, a sulfur-containing hydrocarbon stream is cracked in contact with said catalyst in said cracking zone, and a sulfur-containing flue gas is formed in said regeneration zone by burning sulfur-containing coke off said catalyst with an oxygen-containing gas, the method for reducing the amount of carbon monoxide and sulfur oxides in said flue gas which comprises:
(a) reacting carbon monoxide and oxygen to form carbon dioxide in said regeneration zone in contact with a carbon monoxide oxidation promoter comprising a metal, or compound of a metal, selected from platinum, palladium, iridium, rhodium, osmium, ruthenium, copper and chromium, associated with a particulate solid, said particulate solid being physically admixed with said catalyst;
(b) introducing sufficient molecular oxygen into said regeneration zone to provide an atmosphere therein having a molecular oxygen concentration of at least 0.5 volume percent;
(c) removing sufficient coke from said catalyst in said regeneration zone to provide an average carbon content of less than 0.2 weight percent in catalyst passed from said regeneration zone to said cracking zone;
(d) including in said catalyst a substantially silica-free alumina phase, said catalyst being substantially free from said metal or compound of said metal;
(e) forming a sulfur- and aluminu-cotaining solid in said catalyst in said regeneration zone by reacting sulfur trioxide with alumina present in said alumina phase in said catalyst;

(f) removing sulfur from said catalyst and forming hydrogen sulfide in said cracking zone by contacting said sulfur- and aluminum-containing solid with said hydrocarbon stream.
2. A method according to Claim 1 wherein 2 sufficient amount of said particulate solid is admixed with said catalyst to provide between 0.1 and 100 parts per million, by weight, of said metal, calculated as the elemental metal, with respect to said catalyst.
3. A method according to Claim 2 wherein said carbon monoxide oxidation promoter includes 0.01 to 5 weight percent of said metal, calculated as the elemental metal.
4. A method according to Claim 1 wherein sufficient molecular oxygen is introduced into said regeneration zone to provide the atmosphere therein with a molecular oxygen concen-tration of at least 1.0 volume percent.
CA297,023A 1977-04-11 1978-02-16 Method for removing pollutants from catalyst regenerator flue gas Expired CA1122912A (en)

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GB1585506A (en) * 1976-04-29 1981-03-04 Atlantic Richfield Co Catalyst and process for conversion of hydrocarbons
US4166787A (en) * 1977-12-16 1979-09-04 Chevron Research Company Sulfur oxides control in catalytic cracking

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US3304254A (en) * 1965-01-21 1967-02-14 Mobil Oil Corp Catalytic hydrocracking with a physical mixture of a crystalline aluminosilicate and a porous support containing a hydrogenation component
US3312615A (en) * 1965-04-09 1967-04-04 Mobil Oil Corp Catalyst composition containing a crystalline alumino-silicate, a siliceous matrix and inerts for the conversion of hydrocarbons
US3699037A (en) * 1970-10-28 1972-10-17 Chevron Res Catalytic cracking
US3835031A (en) * 1973-05-23 1974-09-10 Standard Oil Co Catalytic cracking with reduced emission of sulfur oxides
US3949684A (en) * 1973-08-29 1976-04-13 Copeland Systems, Inc. Method for oxidation of sulfur-containing substances
DE2444511C3 (en) * 1974-09-18 1981-07-30 Volkswagenwerk Ag, 3180 Wolfsburg Thermal flow meter for gaseous media
CA1046484A (en) * 1976-04-12 1979-01-16 Elroy M. Gladrow Hydrocarbon conversion catalyst containing a co oxidation promoter
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