Note: Descriptions are shown in the official language in which they were submitted.
1145730
001 -1-
002 BACKGROUND OF THE INVENTION
003 The present invention relates to a method for
004 reducing pollutant gas levels in flue gases generated in
005 catalyst regenerators in hydrocarbon catalytic cracking
006 systems.
007 Modern hydrocarbon catalytic cracking systems use a
008 moving bed or fluidized bed of a particulate catalyst.
009 Catalytic cracking is carried out in the absence of externally
010 supplied molecular hydrogen, and is thereby distinguished from
011 hydrocracking, in which hydrogen is added. In catalytic crack-
012 ing, catalyst is subjected to a continuous cyclic cracking
013 reaction and catalyst regeneration procedure. In a fluidized
014 catalytic cracking ~FCC) system, a stream of hydrocarbon feed
015 is contacted with fluidized catalyst particles in a hydrocarbon
016 cracking zone, or reactor, usually at a temperature of about
017 427-600C. The reactions of hydrocarbons in the hydrocarbon
018 stream at this temperature result in deposition of carbonaceous
019 coke on the catalyst particles. The resulting fluid products
020 are thereafter separated from the coked catalyst and are with-
021 drawn from the cracking zone. The coked catalyst is stripped
022 of volatiles, usually with steam, and is cycled to a catalyst
023 regeneration zone. In the catalyst regenerator, the coked
024 catalyst is contacted with a gas, such as air, which contains a
025 predetermined concentration of molecular oxygen to burn off a
026 desired portion of the coke from the catalyst and simul-
027 taneously to heat the catalyst to a high temperature desired
028 when the catalyst is again contacted with the hydrocarbon
029 stream in the cracking zone. After regeneration, the catalyst
030 is cycled to the cracking zone, where it is used to vaporize
031 the hydrocarbons and to catalyze hydrocarbon cracking. The
032 flue gas formed by combustion of coke in the catalyst
033 regenerator is removed from the regenerator. It may be treated
034 to remove particulates and carbon monoxide from it, after which
035 it is normally passed into the atmosphere. Concern with the
036 emission of pollutants in flue gas, such as sulfur oxides, has
037 resulted in a search for improved methods for controlling such
038 pollutants.
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001 -2-
002 The amount of conversion obtained in an FCC cracking
003 operation is the volume percent of fresh hydrocarbon feed
004 changed to gasoline and lighter products during the conversion
005 step. The end boiling point of gasoline for the purpose of
006 determining conversion is conventionally defined as 221C.
007 Conversion is often used as a measure of the severity of a
008 commercial FCC operation. At a given set of operating
009 conditions, a more active catalyst gives a greater conversion
010 than does a less active catalyst. The ability to provide
011 higher conversion in a given FCC unit is desirable in that it
012 allows the FCC unit to be operated in a more flexible manner.
013 Feed throughput in the unit can be increased, or alternatively
014 a higher degree of conversion can be maintained with a constant
015 feed throughput rate. The type of conversion, i.e., selec-
016 tivity, is also important in that poor selectivity results in
017 less naphtha, the desired cracked product~ and higher gas and
018 coke makes.
019 The hydrocarbon feeds processed in commercial FCC
020 units normally contain sulfur, usually termed "feed sulfur".
021 It has been found that about 2-10% or more of the feed sulfur
022 in a hydrocarbon feedstream processed in an FCC system is
023 invariably transferred from the feed to the catalyst particles
024 as a part of the coke formed on the catalyst particles during
025 cracking. The sulfur deposited on the catalyst, herein termed
026 "coke sulfur", is passed from the cracking zone on the coked
027 catalyst into the catalyst regenerator. About 2-10% or more of
028 the feed sulfur is continuously passed from the cracking zone
029 into the catalyst regeneration zone in the coked catalyst. In
030 an FCC catalyst regenerator, sulfur contained in the coke is
031 burned along with the coke carbon and hydrogen, forming gaseous
032 sulfur dioxide and sulfur trioxide, which are conventionally
033 removed from the regenerator in the flue gas.
034 Most of the feed sulfur does not become coke sulfur
035 in the cracking reactor. Instead, it is converted either to
036 normally gaseous sulfur compounds such as hydrogen sulfide and
037 carbon oxysulfide, or to normally liquid organic sulfur
. 11457~)0
001 ~ _3_
002 compounds. All these sulfur compounds are carried along with
003 the vapor cracked hydrocarbon products recovered from the
004 cracking reactor. About 90% or more of the feed sulfur is
005 continuously removed from the cracking reactor in the stream of
006 processed, cracked hydrocarbons, with about 40-60~ of this
007 sulfur being in the form of hydrogen sulfide. Provisions are
008 conventionally made to recover hydrogen sulfide from the
009 effluent from the cracking reactor. Typically, a
010 very-low-molecular-weight off-gas vapor stream is separated
011 from the C3+ liquid hydrocarbons in a gas recovery unit, and
012 the off-gas is treated, as by scrubbing it with an amine
013 solution, to remove the hydrogen sulfide. Removal of sulfur
014 compounds such as hydrogen sulfide from the fluid effluent from
OlS an FCC cracking reactor, e.g., by amine scrubbing, is rela-
016 tively simple and inexpensive, relative to removal of sulfur
017 oxides from an FCC regenerator flue gas by conventional
018 methods. Moreover, if all the sulfur which must be removed
019 from streams in an FCC operation could be recovered in a single
020 operation performed on the reactor off-gas, the use of plural
021 sulfur recovery operations in an FCC unit could be obviated,
022 reducing expense.
023 It has been suggested to diminish the amount of
024 sulfur oxides in FCC regenerator flue gas by desulfurizing a
025 hydrocarbon feed in a separate desulfurization unit prior to
026 cracking or to desulfurize the regenerator flue gas itself, by
027 a conventional flue gas desulfurization procedure, after its
028 removal from the FCC regenerator. Clearly, either of the
029 foregoing alternatives requires an elaborate, extraneous
030 processing operation and entails large capital and utilities
031 expenses.
032 If sulfur normally removed from the FCC unit as sul-
033 fur oxides in the regenerator flue gas is instead removed from
034 the cracking reactor as hydrogen sulfide along with the
035 processed cracked hydrocarbons, the sulfur thus shifted from
036 the regenerator flue gas to the reactor effluent constitutes
037 simply a small increment to the large amount of hydrogen
~14S7~)0
001 ~4~
002 sulfide and organic sulfur invariably present in the reactor
003 effluent. The small added expense, if any, of removing even as
004 much as 5-15% more hydrogen sulfide from an FCC reactor off-gas
005 by available means is substantially less than the expense of
006 reducing the flue gas sulfur oxides level by separate feed
007 desulfurization. Present commercial facilities for removing
008 hydrogen sulfide from reactor off-gas can, in most if not all
009 cases, handle any additional hydrogen sulfide which would be
010 added to the off-gas if the sulfur normally discharged in the
011 regenerator flue gas were substantially all shifted to form
012 hydrogen sulfide in the FCC reactor off-gas. It is accordingly
013 desirable to direct substantially all feed sulfur into the
014 fluid cracked products removal pathway from the cracking
015 reactor and thereby reduce the amount of sulfur oxides in the
016 regenerator flue gas.
017 It has been suggested, e.g., in U.S. Patent
018 3,699,037, to reduce the amount of sulfur oxides in FCC
019 regenerator flue gas by adding particles of Group IIA metal
020 oxides and/or carbonates, such as dolomite, MgO or CaCO3, to
021 the circulating catalyst in an FCC unit. The Group IIA metals
022 react with sulfur oxides in the flue gas to form solid sulfur-
023 containing compounds. The Group IIA metal oxides lack physical
024 strength. Regardless of the size of the particles introduced,
025 they are rapidly reduced to fines by attrition and rapidly pass
026 out of the FCC unit with the catalyst fines. Thus, addition of
027 dolomite and the like Group IIA materials is essentially a
028 once-through process, and relatively large amounts of material
029 must be continuously added in order to reduce the level of flue
030 gas sulfur oxides.
031 It has also been suggested, e.g., in U.S. Patent
032 3,835,031, to reduce the amount of sulfur oxides in an FCC
033 regenerator flue gas by impregnating a Group IIA metal oxide
034 onto a conventional silica-alumina cracking catalyst. The
035 attrition problem encountered when using unsupported Group IIA
036 metals is thereby reduced. However, it has been found that
~14S7~0
001 - ~5~
002 Group IIA metal oxides, such as ma~nesia, when used as a compo-
003 nent of cracking catalysts, have a rather pronounced
004 undesirable effect on the activity and selectivity of the
005 cracking catalysts. The addition of a Group IIA metal to a
006 cracking catalyst results in two particularly noticeable
007 adverse consequences relative to the results obtained in
008 cracking without the presence of the Group IIA metals: (1) the
009 yield of the liquid hydrocarbon fraction is substantially
010 reduced, typically by greater than 1 volume percent of the feed
011 volume; and (2) the octane rating of the gasoline or naphtha
012 fraction (24-221C boiling range) is substantially reduced.
013 Both of the above-noted adverse consequences are seriously
014 detrimental to the economic viability of an FCC cracking opera-
015 tion, so that even complete removal of sulfur oxides from
016 regenerator flue gas would not normally compensate for the
017 simultaneous losses in yield and octane which result from
018 adding Group IIA metals to an FCC catalyst.
019 Alumina has been a component of many FCC and
020 moving-bed cracking catalysts, but normally in intimate
021 chemical combination with at least 40 weight percent silica.
022 Alumina itself has low acidity and has generally been
023 considered to be undesirable for use as a cracking catalyst.
024 The art taught that alumina is not selective, i.e., the cracked
025 hydrocarbon products recovered from an FCC or other cracking
026 unit using an alumina catalyst would not be desired valuable
027 products, but would include, for example, relatively large
028 amounts of C2 and lighter hydrocarbon gases.
029 U.S. Patent 4,071,436 discloses the use of alumina
030 for reducing the amount of sulfur oxides in the flue gas formed
031 during cracking catalyst regeneration. The alumina can be used
032 in the form of a particulate solid mixed with cracking catalyst
033 particles. In some cases, alumina contained in the cracking
034 catalyst particles is also suitable; however, alumina contained
035 in conventional cracking catalysts is usually not very active,
036 since it is intimately mixed with a large fraction of silica.
037 U.S. Patents 4,115,250 and 4l115,251 disclose the
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001 -6-
002 synergistic use of oxidation-promoting metals for carbon
003 monoxide burning in combination with the use of alumina for
004 reducing the amount of sulfur oxides in cracking catalyst
005 regenerator flue gas. When alumina and highly active
006 oxidation-promoting metals are both included in the same
007 particle, alumina in the particle is ineffective for removing
008 sulfur oxides from the regenerator flue gas, especially in the
009 presence of even a small amount of carbon monoxide. On the
010 other hand, when the alumina and combustion-promoting metal are
011 used on separate particles circulated together in a cracking
012 system in physical admixture, the ability of the alumina to
013 reduce the level of sulfur oxides in the flue gas can be consid-
014 erably enhanced.
015 In reducing the level of sulfur ox ~es in catalyst
016 regenerator flue gas using alumina, as disclosed in U.S.
017 Patents No. 4,017,436, No. 4,115,250 and No. 4,115,251, in a
018 catalytic cracking system under commerci~al operating conditions
019 it has now been noted that silicon and silicon compounds, espe-
020 cially silica, in the particulate catalyst used in a catalytic
021 cracking system, can exert an unexpected detrimental effect on
022 the activity and stability of alumina contained in particles
023 other than the catalyst particles in the particulate inventory,
024 with respect to the capacity and rate of reaction of the alu-
025 mina in forming sulfur-containing solids in a catalyst regene-
026 rator. Silicon contained in æeolitic crystalline alumino-
027 silicates apparently does not migrate to any substantial
028 extent, and therefore does not cause alumina deactivation. Pre-
029 viously, it was known that contamination of alumina by silica
030 presented a problem when the silica was chemically combined
031 with alumina prior to introduction into the circulating
032 particulate solids inventory, or, more generally, when the
033 silica was already present in the same particles as the
034 alumina. It has now been found that under the conditions found
035 in commercial catalytic cracking and regeneration systems,
036 silica can migrate from particles of higher silica concen-
037 tration to particles of lower or zero silica concentration
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002 during circulation of a mixture of such particles in a cracking
003 system. Silica which is subject to such migration may be
004 termed "amorphous" or "non-crystalline" silica, to distinguish
005 it from silica in the form of zeolitic crystalline aluminosili-
006 cates, which is relatively stable and is subject to little or
007 no migration between particles under commercial FCC operating
008 conditions. It is believed that the silicon is carried between
009 particles in the hot gases, such as steam, which are present in
010 catalytic cracking systems. The present invention is directed,
011 in part, to overcoming the problem of deactivation of alumina
012 resulting from silica migration from high-silica-content parti-
013 cles to alumina-containing particles in the particulate solids
014 inventory in a catalytic cracking system.
015 SUMMARY OF ~H~ IN~ENTION
016 In an embodiment of the present invention, an
017 improvement is provided in a process for cracking a sulfur-
018 containing hydrocarbon stream in the absence of externally
019 supplied molecular hydrogen including the steps of (a) cycling
020 an inventory of particulate solids involving acidic cracking
021 catalyst particles between a cracking zone and a catalyst
022 regeneration zone; (b) cracking the sulfur-containing hydro-
023 carbon stream in the cracking zone in contact with the cracking
024 catalyst particles, the catalyst particles containing at least
025 20 weight persent of a silicon component, calculated as silica
026 and excluding silicon in the form of zeolitic crystalline
027 aluminosilicate, in a cracking zone at cracking conditions
028 including a temperature in the range from 425C to 700C, where-
029 by sulfur-containing coke is deposited on the catalyst parti-
030 cles, and removing the hydrocarbon stream from the cracking
031 zone; (c) passing coke-containing catalyst particles from the
032 cracking zone and an oxygen-containing gas into the catalyst
033 regeneration zone, burning the sulfur-containing coke therein
034 at a temperature in the range from 538C to 816C to form a
035 flue gas containing sulfur oxides, and removing the flue gas
036 from the catalyst regeneration zone; (d) forming a sulfur-con-
037 taining solid in the regeneration zone by reacting the sulfur
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001 -8-
002 oxides with alumina in at least one particulate solid in the
003 particulate solids inventory other than the catalyst particles,
004 the particulate solid containing less than 20 weight percent
005 silicon, calculated as silica; (e) returning the resulting coke-
006 depleted catalyst particles from the catalyst regeneration zone
007 to contact with the hydrocarbon stream in the cracking zone;
008 and (f) forming hydrogen sulfide in the cracking zone by
009 contacting the sulfur-containing solid with the hydrocarbon
010 stream; the method for reducing poisoning of alumina in the
011 particulate solid for reaction with sulfur oxides caused by
012 migration of silicon or a silicon compound from the catalyst
013 particles onto the particulate solid, comprising:
014 employing in the particulate solid from 100 parts per
015 million by weight to 1.0 weight percent, relative to the amount
016 of alumina in the particulate solid and calculated on an elemen-
017 tal basis, of a promoter comprising at least one element or com-
018 pound of an element selected from sodium, manganese and
019 phosphorus.
020 Sulfur oxides can be removed from the regenerator
021 flue gas by reaction with high-surface-area alumina present in
022 particles other than the catalyst, circulated in physical
023 mixture with siliceous catalyst particles in a cracking system.
024 Silicon and/or silicon compounds such as silica migrate from
025 the catalyst particles to the alumina particles, especially in
026 a steam-containing atmosphere such as a catalyst stripper or
027 regenerator. Poisoning of the active alumina component by con-
028 tamination with silica migrating from the catalyst particles is
029 reduced, according to the invention, by employing alumina-
030 containing particles including at least one element or compound
031 of an element selected from sodium, manganese and phosphorus.
032 It has been found that active alumina loses at least part of
033 its capacity to react with sulfur oxides when contaminated with
034 migrating silica. The loss of activity can be substantially
035 lessened by including at least one of the above-mentioned
036 elements, or a compound ~hereof, in the alumina-containing
037 particles.
1~457~0
001 -9-
002 DETAILED DESCRIPTION OF THE INVENTION
003 The present invention is used in connection with a
004 fluid catalyst cracking process for cracking hydrocarbon feeds.
005 The same hydrocarbon feeds normally processed in commercial ~CC
00~ systems may be processed in a cracking system employing the
007 present invention. Suitable feedstocks include, for example,
008 petroleum distillates or residuals, either virgin or partially
009 refined. Synthetic feeds such as coal oils and shale oils are
010 also suitable.
011 Suitable feedstocks normally boil in the range from
012 about 200-~00CC or higher~ A suitable feed may include recy-
013 cled hydrocarbons which have already been subjected to
014 cracking.
015 The cracking catalysts with which the present inven-
016 tion finds utility are those which include a substantial concen-
017 tration of silica and which are recognized by those skilled in
018 the art to be suitably acidic and active for catalyzing
019 cracking of hydrocarbons in the absence of externally supplied
020 molecular hydrogen. The invention is most useful in connection
021 with catalysts containing at least 20 weight percent silica,
022 especially at least 30 weight percent silica, excluding silica
023 in the form of zeolitic crystalline aluminosilicates. Silica
024 is generally included in commercially used cracking catalysts
025 in combination with one or more other inorganic oxides such as
02~ alumina, magnesia, et:c. Many commercial catalysts presently
027 include a zeolite component associated with a non-crystalline
028 silica-alumina or silica-containing clay matrix. Non-zeolite-
029 type catalysts including silica, such as amorphous silica-
030 aluminas, silica-magnesias, clays, etc., are also within the
031 scope of the invention, however. Particularly suitable
032 cracking components are the acidic, zeolitic crystalline
033 aluminosilicates such as X-type and Y-type faujasites,
034 preferably in the hydrogen form, the rare earth form, or other
035 equally stable form. Zeolitic crystalline aluminosilicates are
03~ preferred acidic cracking components in that silicon included
037 in zeolites is not particularly subject to migration between
038 particles during use in catalytic cracking, and thus do not
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.
001 -10-
002 contribute to poisoning of alumina activity for sulfur oxides
003 removal from flue gas. Preferably, the particulate solids
004 inventory used in a system in an embodiment of the invention
005 includes at least 75 weight percent of particles containing
006 from 5 to 30 weight percent of a zeolitic crystalline alumino-
007 silicate. On the other hand, acidic, non-crystalline catalyst
008 such as silica-aluminas can be used. For example, it may be
009 desirable, for economic reasons, to use a mixture of cracking
010 catalysts, one of which contains a zeolitic cracking component,
011 while the other contains only relatively inexpensive amorphous
012 silica-alumina, e.g., in systems where catalyst must be added
013 frequently as a result of high feed metals levels or the like.
014 A zeolite-containing cracking catalyst component may
015 be formed by treatment of kaolin clay, as by slurrying the
016 clay, sizing and spray drying, followed by treatment with
017 caustic at elevated temperature for a time sufficient to
018 generate a fraction of the desired zeolite in the treated clay,
019 with the clay acting as the matrix. The zeolite component in
020 the particles can then be converted to the ammonium and/or rare
021 earth form by ion-exchange, if desired. Of course, there is
022 usually still a substantial non-crystalline silica content in
023 catalysts manufactured in this manner. The zeolite can also be
024 manufactured separately and added to the desired matrix or
025 binder material. Conventional binders such as clays, acid-
026 treated clays, synthetic silica-alumina cogels, etc., can be
027 used as the binder, or as a component of the binder.
028 Cracking conditions employed in the cracking or
029 conversion step in an FCC system are frequently provided in
030 part by pre-heating or heat-exchanging hydrocarbon feeds to
031 bring them to a temperature of about 315-400C before
032 introducing them into the cracking zone; however, pre-heating
033 of the feed is not essential. Cracking conditions usually
034 include a catalyst/hydrocarbon weight ratio of about 3-10. A
035 hydrocarbon weight space velocity in the cracking zone of about
036 5-50 per hour is preferably used. The average amount of coke
037 contained in the catalyst after contact with the hydrocarbons
~14S7~o
001 -11-
002 in the cracking zone, when the catalyst is passed to the
003 regenerator, is preferably between about 0.5 weight percent and
004 about 2.5 weight percent, depending in part on the carbon
005 content of regenerated catalyst in the particular system, as
006 well as the heat balance of the particular system.
007 The catalyst regeneration zone used in an FCC system
008 employing an embodiment of the present invention may be of
009 conventional design. Preferably, the total pressure in the
010 regeneration zone is maintained at at least 20 psig. The
011 gaseous atmosphere within the regeneration zone normally
012 includes a mixture of gases in concentrations which vary
013 according to the locus within the regenerator. The
014 concentrations of gases also vary according to the coke
015 concentration on catalyst particles entering the regenerator
016 and according to the amount of molecular oxygen and steam
017 passed into the regenerator. Generally, the gaseous atmosphere
018 in a regenerator contains 5-25~ steam, varying amounts of
019 oxygen, carbon monoxide, carbon dioxide and nitrogen. The
020 present invention is applicable in cases in which an oxygen-
021 containing and nitrogen-containing gas, such as air, is
022 employed for combustion of coke in the catalyst regenerator.
023 As will be appreciated by those skilled in the art, air is
024 essentially invariably employed to provide the oxygen needed
025 for combustion in FCC regenerators.
026 Sulfur oxides are removed from the flue gas in a cata-
027 lyst regeneration zone by reacting sulfur oxides, e.g., sulfur
02~ trioxide, with alumina in the regeneration zone. The alumina
029 active for reaction with sulfur oxides usually has a surface
030 area of at least 50 m2/g, e.g., gamma- or eta-alumina.
031 Suitable alumina must not be in intimate combination with more
032 than 20 weight percent silica, based on the alumina and silica
033 concentrations in a given particle, and preferably the alumina-
034 containing particles used are substantially free from admixture
035 with silica. Alumina from any source is suitable for use in
036 the present method if it contains an average of about 0.1 to
037 lO0 weight percent of "reactive alumina", as determined by
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001 -12-
002 treating particles containing the alumina by the following
003 steps:
004 (1) passing a stream of a gas mixture containing, by
005 volume, 10% water, 1% hydrogen sulfide, 10% hydrogen and 79%
006 nitrogen over the solid particle continuously at a temperature
007 of 650C and atmospheric pressure until the weight of the solid
008 particle is substantially constant;
009 (2) passing a stream of a gas mixture containing, by
010 volume, 10~ water, 15% carbon dioxide, 2% oxygen and 73%
011 nitrogen over the solid particle resulting from step (1) at a
012 temperature of 650C and atmospheric pressure until the weight
01~ of the solid particle is substantially constant, the weight of
014 the particle at this time being designated "Wa''; and
015 (3) passing a stream of a gas mixture containing, by
016 volume, 0.0S% sulfur dioxide, and, in addition, the same gases
017 in the same proportions as used in step (2), over the solid
018 particle resulting from step (2) at a temperature of 650C and
019 atmospheric pressure until the weight of the solid particle is
020 substantially constant, the weight of the solid particle at
021 this time being designated "Wsl'.
022 The weight fraction of reactive alumina in the solid
023 particle, designated "Xa", is determined by the formula
Xa Ws-Wa x Molecular Wt. Alumina
8~5 Wa 3 x Molecular Wt. Sulfur Trioxide
028 The alumina used in embodiments of the present inven-
029 tion is included in particulate solids, other than catalyst
030 particles, which are physically suitable for circulation in the
031 cracking system. Suitable particles normally have an alumina
032 content of at least 80 weight percent and, preferably, the
033 alumina content of such particles is 90 weight percent or more.
034 In a particularly preferred embodiment, the alumina-containing
035 particles consist of gamma-alumina. Alumina can be formed into
036 particles of suitable size for circulation with FCC catalyst in
037 an FCC system by spray-drying, crushing larger particles, etc.
038 In carrying out the invention, alumina-containing
039 particles are introduced into a cracking system and circulated
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001 -13-
002 in physical mixture with silica-containing cracking catalyst.
003 The amount of separate, alumina-containing particles employed
004 in the particulate solids inventory is preferably 25 weight
005 percent, or less, of the total particulate solids inventory
006 circulating in the cracking system. The addition of an amount
007 of alumina between 1.0 and 25 weight percent of the total
008 particulate solids inventory is particularly preferred. The
009 size, shape and density of separate, alumina-containing parti-
010 cles circulated in admixture with catalyst particles is pref-
011 erably such that the alumina-containing particles circulate in
012 substantially the same manner as conventional catalyst
013 particles in the particular cracking system, e.g., beads are
014 used in a moving-bed, bead~catalyst unit, whereas 50-100 micron
015 diameter particles are quite suitable in an FCC unit. Alumina
016 reacts with sulfur trioxide or sulfur dioxide and oxygen in the
017 cracking catalyst regenerator to form at least one sulfur-con-
018 taining solid, such as a sulfate of aluminum. In this way, sul-
019 fur oxides are removed from the regenerator atmosphere and are
020 not discharged from the regenerator in the flue gas.
021 Particles containing the solid aluminum- and sulfur-
022 containing material are passed to the cracking zone along with
023 the other particulate solids, such as regenerated catalyst. In
024 the cracking zone, alumina is regenerated and hydrogen sulfide
025 is formed by reaction of sulfur in the sulfur-containing solid
026 by contacting the sulfur-containing solid with the stream of
027 hydrocarbon being treated in the cracker. In addition to
028 forming hydrogen sulfide, the reaction between the sulfur- and
029 aluminum-containing solid and the hydrocarbon feed may produce
030 some other sulfur~compounds such as carbon oxysulfide, organic
031 sulfides, etc., which are vapor-phase at cracking conditions.
032 The resulting hydrogen sulfide and other vapor-phase sulfur
033 compounds exit the cracking zone as a part of the stream of
034 cracked hydrocarbons, along with a much larger amount of
035 vapor-phase sulfur compounds formed directly from sulfur in the
036 hydrocarbon feed during the cracking reactions. Off-gas subse-
037 quently separated from the cracked hydrocarbon stream thus
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.
001 -14-
002 includes hydrogen sulfide formed directly from the feed sulfur
003 and hydrogen sulfide formed by reaction of the sulfur- and
004 aluminum-containing solid with the hydrocarbon stream in the
005 cracking zone.
006 I have found that, by including at least one of
007 sodium, manganese or phosphorus in the alumina-containing
008 particles employed to react with sulfur oxides, deactivation of
00g the alumina for reaction with SOx, caused by silica migration,
010 can be substantially reduced. Although sodium, manganese and
011 phosphorus, or compounds thereof, are the most useful materials
012 for addition to alumina to prevent deactivation by migrating
013 silica, several other materials can have a positive effect in
014 many cases. These include lithium, potassium, nickel,
015 lanthanum, tin and iron. On the other hand, these last-
016 mentioned Inaterials do not appear to be as effective as sodium,
017 manganese or phosphorus, judging from data presently available.
018 The sodium, manganese or phosphorus component can be
019 combined with the alumina in any convenient manner. For
020 example, a water-soluble compound can be introduced into parti-
021 cles containing alumina by aqueous impregnation. The desired
022 material can be mixed with alumina prior to shaping, as by dry-
023 mixing, comulling, or the like. The amount of sodium,
024 manganese or phosphorus added, on an elemental basis, is
025 usually at least 100 parts per million, by weight, of the
026 alumina. The maximum amount added is 1.0 weight percent. Pref-
027 erably, not more than 0.5 weight percent of the promoter is
028 included with the alumina, on an elemental basis. The concen-
029 trations of promoter are based on the alumina content of the
030 alumina-containing particulate solid. Those skilled in the art
031 will recognize that the alumina may be combined as a mixture,
032 particle pack, or the like, with other materials, such as other
033 porous inorganic oxides, such as chromia, magnesia, titania,
034 etc.
035 Surprisingly, I have found that concentrations of
036 sodium, manganese or phosphorus in alumina of 0.1 weight per-
037 cent are more effective in preventing silica-deactivation
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.
001 -15-
002 of the alumina than are higher concentrations such as 0.5
003 weight percent or more.
004 EXAMPLE I
005 Samples of particulate alumina impregnated with water-
006 soluble salts of various promoters were prepared. The alumina
007 employed was Reynolds RH-30, a commercially available material.
008 Two samples of alumina containing each promoter were prepared,
009 one containing 0.1 weight percent promoter and the other con-
010 taining 0.5 weight percent. All samples were prepared by
011 aqueous impregnation with a water-soluble salt. Each sample
012 was calcined at 593C in dry air for 4 hours.
013 EXAMPLE II
014 An 0.5-gram portion of each sample prepared as
015 described in Example I was physically mixed with 4.5 grams of
016 an equilibrium zeolite-containing FCC catalyst of commercially
017 available type, containing about 37 weight percent silica, ex-
018 cluding silica in the form of zeolitic crystalline alumino-
019 silicate. Each of the catalyst-alumina particle mixtures was
020 then steamed for 96 hours at 650C to induce silica migration
021 from the catalyst particles to the alumina particles. The
022 rates of reaction of the steamed samples of alumina were then
023 determined by thermogravimetric analysis by the following
024 procedure: (1) a portion of each steamed catalyst-alumina
025 mixture was heated to 650C in a flowing atmosphere containing,
026 by volume, 2% 2' 15% CO2 and 10% H2O in N2 until the weight of
027 the sample was constant; (2) the atmosphere composition was
028 changed to 10% H2 and 10% H2O in N2 and maintained until the
029 weight of the sample was constant; (3) the atmosphere was
030 returned to the composition used in step (1) and maintained
031 until the sample weight was constant; and (4) 0.2% SO2 was
032 added to the atmosphere and the weight gained during 6 minutes
033 of exposure to SO2 was measured. The rate of reaction for the
034 samples is defined as the average weight gain per minute for
035 the first 6 minutes divided by the total weight of the sample
036 after step (3). The results for each promoted alumina, for a
037 control sample of unpromoted alumina, and for a sample of
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001 -16-
002 catalyst without alumina particles are shown in Table I.
003 Referring to Table I, it can be seen that sodium, manganese
004 and phosphorus promoters provide a substantially higher
005 activity for reaction with Sx after a sample has been sub-
006 jected to silica migration than do the other promoters tested,
007 particularly in the samples containing 0.1 weight percent of
008 the promoters.
009 TABLE I
010 Promoter Rate (ppm/minute)
011 0.1 wt.% 0.5 wt.%
012 Phosphorus 77 66
013 Manganese 71 63
014 Sodium 74 68
015 Nickel 69 61
016 Lanthanum 64 64
017 Tin 60 62
018 Iron 64 67
019 Copper 66 61
020 Vanadium 62 43
021 Titanium 63 51
022 Magnesium 60 56
023 Cerium 59 54
024 Lead 52 59
025 Boron 53 46
026 Molybdenum 46 50
027 Arsenic 57 52
028 None 54 54
029 Catalyst alone 51 51
030 EXAMPLE III
031 For purposes of comparison with the alumina particles
032 used in the improvement of the invention, particles of silica
033 gel were impregnated with sodium or manganese. The silica gel
034 used was Davison Grade 70 gel screened to 100-325 mesh. Four
035 samples of silica gel were impregnated with an aqueous solution
036 of either sodium nitrate or manganese nitrate in amounts
11457~0
001 -17-
002 sufficient to provide a sample containing 0.1 weight percent
003 sodium, 0.S weight percent sodium, 0.1 weight percent manganese
004 and 0.5 weight percent manganese.
005 EXAMPLE IV
006 A 0.5 gram sample of the plain gel was mixed with 4.5
007 grams of the same equilibrium zeolite-containing FCC catalyst
008 used in the test of Example II. Four mixtures were made up
009 each containing 4.5 grams of the FCC catalyst and 0.5 grams of
010 the silica gel containing either 0.1 weight percent Na, 0.5
011 weight percent Na, 0.1 weight percent Mn or 0.5 weight percent
012 Mn. The five mixtures prepared as described were each steamed
013 for 96 hours at 650C. The rate of reaction, if any, for
014 reaction with sulfur oxides was then measured by the same
015 procedure described in Example II. The results for the unmixed
016 catalyst and each of the five mixtures are shown in Table II.
017 TABLE II
018
019 Rate (ppm/minute)
020 Promoter ~ 1 5 wt.%
022 Unmixed Catalyst 51 51
024 Catalyst with Plain
025 Silica Gel 29 29
027 Manganese Impregnated 40 37
029 Sodium Impregnated 31 27
030
031
032 Referring to Table II, it is apparent that all the
033 silica gel mixtures are substantially poorer for reacting with
034 sulfur oxides than is the FCC catalyst alone.
035 ILLUSTRATIVE EM~ODIMENT
036 A conventional, commercial FCC processing system
037 having a capacity of 22,000 barrels per day is employed. The
038 feed used is a mixture of hydrocarbons having a boiling range
039 of 3Q4-593C with a sulfur content of 0.85 weight percent. The
040 cracking reactor employs a combination of riser and dense-bed
` 11457~0
001 -18-
002 cracking. Cracking conditions employed include a reactor
003 average temperature of about 495C, a hydrocarbon weight hourly
004 space velocity of about 5 per hour and a conversion rate (feed
005 converted to 220C-) of about 85%. Catalyst is circulated at
006 the rate of about 8 metric tons per minute with a total inven-
007 tory of about 154 metric tons. The catalyst used contains Y-
008 type zeolitic crystalline aluminosilicate dispersed in a non-
009 crystalline silica-alumina matrix. A separate combustion pro-
010 moter is used to get complete combustion in the regenerator.
011 The silica concentration in the catalyst, excluding silica in
012 the form of zeolite, is about 40 weight percent. The spent
013 catalyst contains about 0.8 weight percent coke, and the coke
014 contains about 0.7 weight percent sulfur. Regeneration condi-
015 tions include a temperature of about 670C. After regene-
016 ration, the catalyst contains about 0.2 weight percent coke.
l? Prior to the introduction of alumina into the circulating inven-
018 tory to react with SOx, the flue gas removed from the catalyst
019 regenerator contains about 300 parts per million, by volume, of
020 SOx, calculated as SO2. For purposes of comparison, an un-
021 treated particulate gamma-alumina is first used to remove Sx
022 from the regenerator flue gas. Sufficient alumina is intro-
023 duced and circulated to provide 10 weight percent of the
024 particulate solids inventory. The amount of Sx initially
025 removed from the flue gas is relatively high, but over a period
026 of 5 days of operation it is observed that migration of silica
027 from the cracking catalyst particles reduces the activity of
028 the alumina, so that the amount of Sx in the flue gas
029 increases to about 220 ppm (volume). According to the inven-
030 tion, the unpromoted alumina is withdrawn from the FCC system,
031 and particles of alumina promoted with 0.1 weight percent phos-
032 phorus are introduced in an amount sufficient to provide 10
033 weight percent of the particulate solids inventory in the FCC
034 system. The promoted alumina has been prepared by spray-drying
035 the alumina and subsequent aqueous impregnation with ammonium
036 phosphate solution. After introduction of the phosphorus-
037 promoted alumina, the amount of Sx initially removed from
1 ~1457a~
001 -19-
002 the regenerator flue gas is again found to be relatively high.
003 After 5 days of operation, substantially less silica migration
004 deactivation of the phosphorus-promoted alumina is observed
005 than was found using the unpromoted alumina, resulting in a
006 flue gas Sx of only 140 ppm (volume).
007 The foregoing detailed description of the invention,
008 examples, and illustrative embodiment illustrate a preferred
009 mode of carrying out the invention. It will be clear to those
010 skilled in the art that other embodiments and obvious modifi-
011 cations, equivalents and variations of the invention can be
012 employed and adapted to a variety of catalytic cracking
013 systems. Such modifications, alterations and adaptations are
014 intended to be included within the scope of the appended
015 claims.
