WO1986006090A1

WO1986006090A1 - Alkaline earth metal, aluminum-containing spinel compositions and methods of using same

Info

Publication number: WO1986006090A1
Application number: PCT/US1986/000788
Authority: WO
Inventors: Jun S. Yoo; John A. Karch; Richard F. Poss; Emmett H. Burk, Jr.; Cecelia A. Radlowski
Original assignee: Katalistiks, Inc.
Priority date: 1985-04-18
Filing date: 1986-03-18
Publication date: 1986-10-23
Also published as: BR8606629A; JPS62502968A; EP0219538A1; AU5773786A

Abstract

A process for reducing the sulfur oxide content of a sulfur oxide-containing gas which includes contacting said gas with a material at conditions to associate at least a portion of said sulfur oxide contained in said gas with said material, comprising utilizing as the material a spinel composition comprising an alkaline earth metal component, an aluminum component and at least one of certain additional metal component in an amount effective to promote the oxidation of SO2 to SO3 at SO2 oxidation conditions and/or to promote the reduction of SO3 at SO3 reduction conditions. Improved spinel compositions are also disclosed.

Description

ALKALINE EARTH METAL, ALUMINUM-CONTAINING SPINEL COMPOSITIONS AND METHODS OF USING SAME

RELATED APPLICATION

This is a continuation-in-part of co-pending application Serial No. 649,238 filed September 10, 1984, which in turn is a continuation-in-part of co-pending application Serial No. 615,414, filed May 30, 1984, which in turn is a continuation of co-pending application Serial No. 445,305, filed November 29, 1982.

BACKGROUND OF THE INVENTION

This invention relates to improved alkaline earth metal, aluminum, additional-metal-containing spinel compositions, particularly for use in the combusting of solid, sulfur-containing material in a manner to effect a reduction in the emission of sulfur oxides to the atmosphere. In one specific embodiment, the invention involves the catalytic cracking of sulfur-containing hydrocarbon feedstocks in a manner to effect a reduction in the amount of sulfur oxides emitted from the regeneration zone of a hydrocarbon catalytic cracking unit.

Typically, catalytic cracking of hydrocarbons takes place in a reaction zone at hydrocarbon cracking conditions to produce at least one hydrocarbon product and to cause carbonaceous material (coke) to be deposited on the catalyst. Additionally, some sulfur, originally present in the feed hydrocarbons, may also be deposited, e.g., as a component of the coke, on the catalyst. It has been reported that approximately 50% of the feed sulfur is converted to H₂S in the FCC reactor, 40% remains in the liquid products and about 4 to 10% is deposited on the catalyst. These amounts vary with the type of feed, rate of hydrocarbon recycle, steam stripping rate, the type of catalyst, reactor temperature, etc.

Sulfur-containing coke deposits tend to deactivate cracking catalyst. Cracking catalyst is advantageously continuously regenerated, by combustion with oxygen-containing gas in a regeneration zone, to low coke levels, typically below about 0.4% by weight, to perform satisfactorily when it is recycled to the reactor. In the regeneration zone, at least a portion of sulfur, along with carbon and hydrogen, which is deposited on the catalyst, is oxidized and leaves in the form of sulfur oxides (S0₂ and S0₃, hereinafter referred to as "SOx") along with substantial amounts of CO, C0₂ and H₂0.

Considerable recent research effort^* has been directed to the reduction of sulfur oxide emissions from the regeneration zones of hydrocarbon catalytic cracking units. One technique involved circulating one or more metal oxides capable of associating with oxides of sulfur with the cracking catalyst inventory in the regeneration zone. When the particles containing associated oxides of sulfur are circulated to the reducing atmosphere of the cracking zone, the associated sulfur compounds are released as gaseous sulfur-bearing material such as hydrogen sulfide which is discharged with the products from the cracking zone and are in a form which can be readily handled in a typical facility, e.g., petroleum refinery. The metal reactant is regenerated to an active form, and is capable of further associating with the sulfur oxides when cycled to the regeneration zone.

Incorporation of Group II metal oxides on particles of cracking catalyst in such a process has been proposed (U.S. Patent No. 3,835,031 to Bertolacini) . In a related process described in U.S. Patent No. 4,071,436 to Blanton, et al. , discrete fluidizable alumina-containing particles are circulated through the cracking and regenerator zones along with physically separate particles of the active zeolitic cracking catalyst. The alumina particles pick up oxides of sulfur in the regenerator, forming at least one solid compound, including both sulfur and aluminum atoms. The sulfur atoms are released as volatiles, including hydrogen sulfide, in the cracking unit. U.S. Patent No. 4,071,436 further discloses that 0.1 to.10 weight percent MgO and/or 0.1 to 5 weight percent Cr₂0₃ are preferably present in the alumina-containing particles. Chromium is used to promote coke burnoff.

A metallic component, either incorporated into catalyst particles or present on any of a variety of "inert" supports, is exposed alternately to the oxidizing atmosphere of the regeneration zone of an FCCU and the reducing atmosphere of the cracking zone to reduce sulfur oxide emissions from regenerator gases in accordance with the teachings of U.S. Patents Nos. 4,153,534 and 4,153,535 to Vasalos and Vasalos, et al., respectively. In Vasalos, et al., a metallic oxidation promoter such as platinum is also present when carbon monoxide emissions are to be reduced. These patents disclose nineteen different metallic components, including materials as diverse as alkaline earths, sodium, heavy metals and rare earth, as being suitable reactants for reducing emissions of oxides of sulfur. The metallic reactants that are especially preferred are sodium, magnesium, manganese and copper. When used as the carrier for the metallic reactant, the supports that are used preferably have a surface area at least 50 square meters per gram. Examples of allegedly "inert" supports are silica, alumina and silica-alumina. The Vasalos and Vasalos, et al . , patents further disclose that when certain metallic reactants (exemplified by oxides of iron, manganese or cerium) are employed to capture oxides of sulfur, such metallic components can be in the form of divided fluidizable powder.

Similarly, a vast number of sorbents have been proposed for desulfurization of non-FCCU flue gases in zones outside the unit in which SOx is generated. In some such non-FCCU applications, the sorbents are regenerated in environments appreciably richer in hydrogen than the cracking zone of an FCC unit. Cerium oxide is one of fifteen adsorbents disclosed for flue gas desulfurization in a publication of Lowell, et al. , "SELECTION ON METAL OXIDES FOR REMOVING SOx FROM FLUE GAS," Ind. Eng. Chemical Process Design Development, Vol. 10, Nov. 3, 1971. In U.S. Patent No. 4,001,375 to Longo, cerium on an alumina support is used to adsorb SO₂ from non-FCCU flue gas streams or automobile exhaust at temperatures of 572 to 1472°F, preferably 932 to 1100°F. The sorbent is then regenerated in a separate unit by contacting it with hydrogen mixed with steam at 932 to 1472°. During regeneration the desorbed species is initially S0₂ and H₂S along with excess reducing gases which can be used as feedstock for a Clause unit. The Longo patent is not concerned with reducing emissions from an FCC unit and the reducing emissions from an FCC unit and the reducing atmosphere employed in practice of this process differs significantly from the hydrocarbon-rich atmosphere in a catalytic cracker. Thus, a hydrocarbon cracking reaction zone is preferably operated in the substantial absence of added hydrogen while the presence of sweeping ^•amounts of hydrogen gas is essential to the regeneration step in practice of the process of Longo.

D. W. Deberry, et al. , "RATES OF REACTION OF S0₂ WITH METAL OXIDES," Canadian Journal of Chemical Engineering, 49^ 781 (1971) reports that cerium oxide was found to form sulfates more rapidly than most of the other oxides tested. The temperatures used, however, were below 900°F and thus below those preferred for use in catalyst regenerators in FCC units.

Many commercial zeolitic FCC catalyst contain up to 4% rare earth oxide, the rare earth being used to stabilize the zeolite and provide increased activity. See, for example, U.S. Patent No. 3,930,98-7 to Grand. The rare earths are most often used as mixtures of La₂0₃, Ce0₂, _?^r ₆°_ll' d₂O₃ and others. Some catalyst is produced by using a lanthanum-rich mixture obtained by removing substantial cerium from the mixture of rare earth. It has been found that the mere presence of rare earth in a zeolitic cracking catalyst will not necessarily reduce SOx emissions to an appreciable extent.

In accordance with the teachings of U.S. Patent No. 3,823,092 to Gladrow, certain zeolitic catalyst compositions capable of being regenerated at a rate appreciably faster than prior art rare earth exchanged zeolitic catalyst compositions with a dilute solution containing cerium cations (or a mixture of rare earths rich in cerium) . The final catalyst contain 0.5 to 4% cerium cations which are introduced to previously rare earth exchanged zeolitic catalyst particles prior to final filtering, rinsing and calcining*. Cerium is described as an "oxidation promoter". 'There is not recognition or appreciation in the patent of the effect of the cerium impregnation on SOx stack emissions. Such impregnation of rare earth exchanged zeolitic catalyst particles is not always effective in producing modified catalysts having significant ability to bind oxides of sulfur in a FCC regenerator and release them in a FCC cracking reaction zone.

Thus, considerable amount of study and research effort has been directed to reducing oxide of sulfur emissions from various gaseous streams, including those from the stacks of the regenerators of FCC units. However, the results leave much to be desired. Many metallic compounds have been proposed as materials to pick up oxides of sulfur in FCC units (and other desulfurization applications) and a variety of supports, including particles of cracking catalysts and "inerts", have been suggested as carriers for active metallic reactants. Many of the proposed metallic reactants lose effectiveness when subjected to repeated cycling. Thus, when Group II metal oxides are impregnated on FCC catalysts or various supports, the activity of the Group II metals is rapidly reduced under the influence of the cyclic conditions. Discrete alumina particles, when combined with silica-containing catalyst particles and subjected to steam at elevated temperatures, e.g., those present in FCC unit regenerators, are of limited effectiveness in reducing SOx emissions. Incorporation of sufficient chromium on an alumina support to improve SOx sorption results in undesirably increased coke and gas production.

U.S. Patents, 4,469,589 and 4,472,267, relate to improved materials for reducing SOx emissions comprising spinels preferably alkaline earth metal, aluminum-containing spinels, which materials may contain one or more other metal components capable of promoting the oxidation of sulfur dioxide to sulfur trioxide at combustion conditions. In specific examples, these patents disclose that magnesium, aluminum-containing spinel is impregnated with such other metal components (e.g., cerium and platinum) using conventional techniques. In addition, these patents disclose that in situations where the spinel normally contains aluminum ions, other trivalent metal ions, such as iron, chromium, vanadium, manganese, gallium, boron, cobalt and mixtures thereof, may replace all or a part of the aluminum ions. The specification of each of these patents is incorporated herein by reference.

Various methods have been described for the preparation of alkaline earth aluminate spinels, and particularly of magnesium aluminate spinels. According to the method disclosed in U.S. Patent No. 2,992,191, the spinel can be formed by reacting, in an aqueous medium, a water-soluble magnesium inorganic salt and a water-soluble aluminum salt in which the aluminum is present in the anion. This patent does not teach controlling pH during the time the two salts are combined.

Another process for producing magnesium aluminate spinel is set forth in U.S. Patent No. 3,791,992. This process includes adding a highly basic solution of an alkali metal aluminate to a solution of a soluble salt of magnesium with no control of pH during the addition, separating and washing the resulting precipitate; exchanging the washed precipitate with a solution of an ammonium compound to decrease the alkali metal content; followed by washing, drying, forming and calcination steps.

There remains a need for improved spinel catalyst components exhibiting good SOx removal properties. SUMMARY OF THE INVENTION

This invention relates to a novel process for the use of improved alkaline earth metal, aluminum and at least one additional metal-containing spinel compositions. Such spinels find particular use in diminishing the emissions of sulfur oxides from combustion zones, and more particularly in conjunction with catalytic compositions employed in hydrocarbon cracking processes.

This invention further relates to compositions of matter which include, in intimate admixture, combinations of solid particles capable of promoting hydrocarbon conversion, e.g., cracking, and discrete entities comprising the above-noted spinels.

Other objects and advantages of this invention will be apparent from the following detailed description.

DESCRIPTION OF THE INVENTION

In one broad embodiment, the present invention involves a spinel composition comprising an alkaline earth metal component, an aluminum component and at least one additional metal component including a metal selected from the group consisting of Group IB metals, Group IV metals, Group VA metals, the platinum group metals, the rare earth metals, Te, Nb, Ta, Sc, Zn, Y, Mo, W, Tl, Re, U, Th and mixtures thereof in an amount effective to promote the oxidation of So₂ to S0₃ at S0₂ oxidation conditions and/or to promote the reduction of S0₂ at S0₃ reduction conditions. In accordance with another aspect, the present invention involves a conversion process which is carried out, preferably in the substantial absence of added free hydrogen, in at least one chemical reaction zone in which sulfur-containing hydrocarbon feedstock is contacted with particulate material to form at least one product, preferably a hydrocarbon product, and sulfur-containing carbonaceous material deposited on the particulate material and at least one regeneration zone in which at least a portion of the sulfur-containing carbonaceous material deposited on the particulate material is contacted with gaseous oxygen to combust at least a portion of the sulfur-containing carbonaceous material and to produce combustion products including sulfur oxide at least a portion of which is sulfur trioxide. The present •improvement comprises using a particulate material comprising (A) a major amount of solid particles, capable of promoting the desired hydrocarbon chemical conversion at hydrocarbon conversion conditions and (B) a minor amount of discrete entities comprising an effective amount, preferably a major amount by weight, i.e., at least about 50% by weight, of at least one of the above-noted alkaline earth metal, aluminum, additional metal-containing spinel compositions in an amount sufficient to reduce the amount of sulfur oxide in the flue gas from the regeneration zone.

In one preferred embodiment, the discrete entities also include a minor, catalytically effective amount of at least one crystalline aluminosilicate effective to promote hydrocarbon conversion, e.g., cracking, at hydrocarbon conversion conditions. Also, it is preferred that the present spinel compositions further comprise at least one further additional metal component including a metal selected from the group consisting of iron, chromium, vanadium, manganese, gallium, boron, cobalt and mixtures thereof in an amount effective to further promote the oxidation of S0₂ to SO₃ at S0₂ oxidation conditions and/or to further promote the reduction of S0₃ at S0₃ reduction conditions. More preferably, this further additional metal component includes iron. The discrete entities are present in an amount sufficient to reduce the amount of sulfur oxides in the regeneration zone effluent when used in a reaction zone-regeneration zone system as described herein,

It is preferred that the additional metal included in the presently useful spinel compositions include a metal selected from the group consisting of Zr, Sn, Sb, Ag, Cu, Bi, Tl, Te and mixtures thereof, more preferably from the group consisting of Zr, Sn, Sb, Cu, Bi and mixtures thereof.

The preferred relative amounts of the solid particles and discrete entities are about 80 to about 99 parts and 1 to about 20 parts by weight, respectively. This catalyst system is especially effective for the catalytic cracking of a hydrocarbon feedstock to lighter, lower boiling products. The present catalyst system preferably also has improved carbon monoxide oxidation catalytic activity stability. The improvement of this invention can be used to advantage with the catalyst being disposed in any conventional reactor-regenerator system, e.g., in ebullating catalyst bed systems, in systems which involve continuously conveying or circulating catalyst between reaction zone and regeneration zone and the like. Circulating catalyst systems are preferred. Typical of the circulating catalyst bed systems are the conventional moving bed and fluidized bed reactor-regenerator systems. Both of these circulating bed systems are conventionally used in hydrocarbon conversion, e.g., hydrocarbon cracking, operations with the fluidized catalyst bed reactor-regenerator systems being preferred.

The catalyst system used in accordance with certain embodiments of the invention is preferably comprised, of a mixture of two types of particles.

Although the presently useful solid particles and discrete entities may be used as a physical admixture of separate particles, in one embodiment the discrete entities are combined as part of the solid particles. That is, the discrete entities, e.g., comprising calcined microspheres containing the above-noted spinel compositions, are combined with the solid particles, e.g., during the manufacture of the solid particles, to form combined particles which function as both the presently useful solid particles and discrete entities. The discrete entities in such combined particles preferably exist as a separate and distinct phase. One preferred method for providing the combined particles is to calcine the discrete entities prior to incorporating the discrete entities into the combined particles.

The form, i.e., particle size, of the present catalyst particles, e.g., both solid particles and discrete entities as well as the combined particles, is not critical to the present invention and may vary depending, for example, on the type of reaction-regeneration system employed. Such catalyst particles may be formed into any desired shape such as pills, cakes, extrudates, powders, granules, spheres and the like, using conventional methods. With regard to fluidized catalyst bed systems, it is preferred that the major amount by weight of the present catalyst particles have a diameter in the range of about 10 microns to about 250 microns, more preferably about 20 microns to about 250 microns.

The solid particles are capable of promoting the desired hydrocarbon conversion. The solid particles are further characterized as having a composition (i.e., chemical make-up) which is different from the discrete entities. * In one preferred embodiment, the solid particles (or the solid portion of the combined particles described above) are substantially free of magnesium-aluminum-σontaining spinel .

The composition of the solid particles useful in the present invention is not critical, provided that such particles are capable of promoting the desired hydrocarbon conversion. Particles having widely varying compositions are conventionally used as catalyst in such hydrocarbon conversion processes, the particular composition chosen being dependent, for example, on the type of hydrocarbon chemical conversion desired. Thus, the solid particles suitable for use in the present invention include at least one of the natural or synthetic materials which are capable of promoting the desired hydrocarbon chemical conversion. For example, when the desired hydrocarbon conversion involves one or more of hydrocarbon cracking, disproportionation, isomerization, polymerization, alkylation and dealkylation, such suitable materials include acid-treated natural clays such as montmorillonite, kaolin and bentonite clays; natural or synthetic amorphous materials, such as amorphous silica-magnesia and silica-zirconia composites; crystalline aluminosilicate often referred to as zeolites or molecular sieves and the like. In certain instances, e.g., hydrocarbon cracking and disproportionation, the solid particles preferably include such crystalline aluminosilicate to increase catalytic activity. Methods for preparing such solid particles and the combined solid particles-discrete entities particles are conventional and well known in the art. Certain of these procedures are thoroughly described in U.S. Patents 3,140,253 and RE.27,639.

Compositions of the solid particles which are particularly useful in the present invention are those in which the crystalline aluminosilicate is incorporated in an amount effective to promote the desired hydrocarbon conversion, e.g., a catalytically effective amount, into a porous matrix which comprises, for example, amorphous material which may or may not be itself capable of promoting such hydrocarbon conversion. Included among such matrix materials are clays and amorphous compositions of silica-alumina, magnesia, silica-magnesia, zirconia, mixtures of these and the like. The crystalline aluminosilicate is preferably incorporated into the matrix material in amounts within the range of about 1% to about 75%, more preferably about 2% to about 50% by weight of the total solid particles. The preparation of crystalline aluminosilicate-amorphous matrix catalytic materials is described in the above-mentioned patents. Catalytically active crystalline aluminosilicates which are formed during and/or as part of the methods of manufacturing the solid particles, discrete entities and/or combined particles are within the scope of the present invention. The solid particles are preferably substantially free of added rare earth metal, e.g., cerium, component dispersed on the amorphous matrix material of the catalyst, although such rare earth metal components may be associated with the crystalline aluminosilicate components of the solid particles.

The presently useful spinel compositions may be conveniently prepared using various co-precipitation techniques. One particularly preferred manufacturing technique comprises.

(a) combining (a) an acidic aqueous solution containing at least one alkaline earth metal component and (b) a basic aqueous solution containing at least one aluminum component in which the aluminum is present as an anion into an aqueous medium to form a combined mass including a liquid phase and an alkaline earth metal, aluminum-containing precipitate, provided that at least one of the acidic solution and the basic solution includes at least one additional metal component in an amount sufficient so that the alkaline earth metal, aluminum-containing spinel composition includes at least one additional metal component in an amount effective to promote the oxidation of SO₂ to S0₃ at S0₂ oxidation conditions, and further provided that the pH of the liquid phase during the combining is maintained in the range of about 7.0 to about 9.5, preferably in the range of about 7.0 to about 8.5; and

(b) calcining the precipitate to form an alkaline earth metal, aluminum-containing spinel composition.

In a preferred embodiment, the above-noted step (a) comprises substantially simultaneously adding the acidic aqueous solution and the basic aqueous solution to an aqueous liquid. In another preferred embodiment, the pH of the liquid phase is maintained in the range of about 7.0 to about 7.5 until no further acidic aqueous solution is to be combined.

The present spinel compositions may be used, for example, in the form of particles of any suitable shape and size. Such particles may be formed by conventional techniques, such as spray drying, pilling, tableting, extrusion, bead formation (e.g., conventional oil drop method) and the like. When spinel-containing particles are to be used in a fluid catalytic cracking unit, it is preferred that a major amount by weight of the spinel-containing particles have diameters in the range of about 10 microns to about 250 microns, more preferably about 20 microns to about 125 microns. This invention relates to alkaline earth metal and aluminum-containing spinel composition which also includes as an integral part of the spinel structure at least one of certain additional metal components in an amount effective to promote the oxidation of S0₂ to SO₃ at S0₂ oxidation and/or to promote the reduction of SO₃ at S0₃ reduction conditions. The amount of additional metal component needed to function in the above-noted manner depends, for example, on the particular additional metal being utilized. However, incorporating one or more of such additional metals into the spinel structure has been found (1) to be effective to promote the oxidation of S0₂ to S0₃ (thereby minimizing, even eliminating, the need for a separate oxidation catalyst or component to promote the oxidation of

50₂ to S0₃); and/or (2) to promote the reduction of S0₃ at SO₃ reduction conditions (thereby allowing for more complete S0₃ reduction and/or

50₃ reduction at less severe (lower temperature) conditions). Such additional metal components incorporated into the spinel structure result in improved, high performance and/or cost effective, SOx reducing agents relative to spinel compositions

T in which the additional metal component(s) is (are) included without becoming an integral part of the spinel structure.

The spinel structure is based on a cubic close-packed array of oxide ions. Typically, the crystallo-graphic unit cell of the spinel structure contains 32 oxygen atoms. With regard to magnesium aluminate spinel, there often are eight Mg atoms and sixteen Al atoms to place in a unit cell (8M A1₂0. ). Other alkaline earth metal ions, such as calcium, strontium, barium and mixtures thereof, may replace all or a part of the magnesium ions.

The presently useful alkaline earth metal and aluminum containing spinels include a first metal (alkaline earth metal) and aluminum as the second metal having a valence higher than the valence of the first metal. The atomic ratio of the first metal to the second metal in any given alkaline earth metal and aluminum containing spinel need not be consistent with the classical stoichiometric formula for such spinel. In one embodiment, the atomic ratio of the alkaline earth metal to aluminum plus the additional metal(s) in the spinels of the present invention is at least 0.17 and preferably at least about 0.25. It is preferred that the atomic ratio of alkaline earth metal to aluminum plus additional metal(s) in the spinel be in the range of about 0.17 to about 2.5, more preferably about 0.25 to about 2.0, and still more preferably about 0.35 to about 1.5.

The preferred spinel composition of the present invention includes magnesium and aluminum. The alkaline earth metal components useful in producing the presently useful spinel compositions preferably include those which are substantially soluble in the acidic aqueous medium used in the preferred manufacturing method described above. Examples of suitable alkaline earth metal component include nitrates, sulfates, formates, acetates, acetylacetonates, phosphates, halides, carbonates, sulfonates, oxalates, and the like. The alkaline earth metals include beryllium, magnesium, calcium, strontium, and barium. The preferred alkaline earth metal components for use in the present invention are those comprising magnesium.

Additional metals such as copper, zinc, silver and lead may replace a portion of the alkaline earth metal component of the present spinel compositions. Also, the remainder of the additional metals set forth herein may replace a portion of the aluminum component in the present spinel compositions. Such spinel compositions after one or more of these replacements, may provide substantial benefits, e.g., improved SOx reducing activity and stability, and attrition resistance.

As noted above, the aluminum components present in the basic solution useful in the preferred manufacturing method described above are those in which the aluminum is present as an anion. Preferably, the aluminum salt is present as an aluminate salt, more preferably as a alkali metal aluminate.

Any suitable acid or combination of acids may be employed in the acidic aqueous solutions used in the preferred manufacturing method described above. Examples of such acids include nitric acid, sulfuric acid, hydrochloric acid, acetic acid and mixtures thereof, with nitric acid, sulfuric acid and mixtures thereof being preferred. Any suitable basic material or combination of such materials may be employed in the basic aqueous solutions used in the preferred manufacturing method described above. Examples of such basic material include the alkali metal hydroxides, ammonium hydroxide and mixtures thereof, with alkali metal hydroxides, and in particular sodium hydroxide, being preferred ^'for use. The relative amounts of acids and basic materials employed are suitable to provide the desired alkaline earth metal, aluminum-containing precipitate and the pH control as noted above.

The additional metal component(s) may be included in the spinel composition by being included in the aqueous acidic and/or basic solutions noted^* previously in the preferred manufacturing method. It is preferred that the additional metal be present in such solution as a soluble form. Thus, the particular additional metal compound(s) selected should preferably be soluble (at the desired concentration) in the particular acidic or basic solution in question. It is well within the skill of the art to choose a suitable soluble additional metal component for use in the present process.

The precipitate, which is preferably dried, is calcined to yield the alkaline earth metal, aluminum, additional metal-containing spinel composition. Drying and calcination may take place simultaneously. However, it is preferred that the drying take place at a temperature below that which water of hydration is removed from the spinel precursor, i.e., precipitate. Thus, this drying may occur in flowing air at temperatures below about 500°F, preferably in the range of about 150°F to about 450°F, more preferably about 230°F to about 450°F. Alternatively, the precipitate can be spray dried.

The drying of the precipitate can be accomplished in various manners, for example, by spray drying, drum drying, flash drying, tunnel drying and the like. The drying temperature or temperatures is selected to remove at least a portion of the liquid phase. Drying times are not critical to the present invention and may be selected over a relatively wide range sufficient to provide the desired dried product. Drying times in. the range of about 0.2 hours to about 24 hours or more may be advantageously employed.

Spray drying equipment which is conventionally used to produce catalyst particles suitable for use in fluidized bed reactors may be utilized in the practice of the preferred manufacturing method described above. For example, this equipment may involve at least one restriction or high pressure nozzle having a diameter in the range from about 0.01 in. to about 0.2 in., preferably from about 0.013 in. to about 0.15 in. The pressure upstream of this high pressure nozzle may range from about 400 psig. to about 10,000 psig., preferably from about 400 psig. to about 7,000 psig. The material to be dried is sent through the nozzle system into a space or chamber. The pressure in the space or chamber downstream from the nozzle system is lower than that immediately upstream of the nozzle and is typically in the range from about 0 psig. to about 100 psig. , preferably from about 0 psig. to about 20 psig. Once through the nozzle, the material to be dried is contacted for a relatively short time, e.g., from about 0.1 seconds to about 20 seconds with a gas stream which is at a temperature of from about 200°F to about 1500°F, preferably from about 200°F to about 750°F. The gas stream which may be, for example, air or the flue gases from an inline burner (used to provide a gas stream having the proper temperature) or a substantially oxygen-free gas, may flow co-current, counter-current or a combination of the two relative to the direction of flow of the material to be • dried. The spray drying conditions, such as temperatures, pressures and the like, may be adjusted because, for example, of varying the composition of the material to be dried to obtain optimum results. However, this optimization may be achieved through routine experimentation.

An alternative to the high pressure nozzle described above is the "two-fluid" nozzle in which the material to be dried is dispersed by a stream of gas, typically air. The two fluid nozzle has the advantage of low operating pressure, e.g., from about 0 psig. to about 60 psig. for the material to be dried and from about 1Q psig. to about 100 psig. for the dispersing gas. The dispersing gas may also function as at least a portion of the drying gas stream. The various operating parameters noted above may be varied in order to achieve the correct or desired bound particle size.

In order to minimize contact between the chamber walls and wet material, the chamber downstream from the nozzle system is large in size, e.g., from about 4 to about 30 feet in diameter and from about 7 to about 30 feet long, often with an additional conical shaped portion for convenient withdrawal of the dried material. The spray drying apparatus may also include separation means, e.g., cyclone separators, in the outlet gas line to recover at least a portion of the dried material entrained in this stream.

Suitable calcination temperatures for the precipitate are in the range of about 1000°F to about 1800°F. However, it has been found that improved spinel formation occurs when the calcination temperatures is maintained within the range of about 1050°F to about 1600°F, more preferably about 1100°F to about 1400°F and still more preferably about 1150°F to about 1350°F. Calcination of the precipitate may take place in a period of time in the range of about 0.5 hours to about 24 hours or more, preferably in a period of time in the range of about 1 hour to about 10 hours. The calcination of the precipitate may occur at any suitable conditions, e.g., inert, reducing or oxidizing conditions, which oxidizing conditions be preferred. Spinel compositions resulting from the preferred manufacturing method described above have improved properties relative to spinels produced without the pH control. For example, such spinel compositions have improved capabilities, e.g., stability, of reducing sulfur oxide atmospheric emissions from hydrocarbon catalytic cracking operations.

In this invention, particulate material comprising the alkaline earth metal and aluminum-containing spinel composition also contains at least one of certain additional metal components. These additional metal components are defined as being capable of promoting the oxidation of sulfur dioxide to sulfur trioxide at combustion conditions, e.g., the conditions present in a hydrocarbon catalytic cracking unit regenerator and/or promoting the reduction of S0₃ at S0₃ reducing conditions, e.g., the conditions present in a hydrocarbon catalytic cracking unit reactor. Increased carbon monoxide oxidation may also be - obtained by including the additional metal components. Such additional metal components are an integral part of the alkaline earth metal, aluminum-containing spinel composition, i.e., such additional metal components are included in the structure of the spinel composition, e.g., replacing a portion of the alkaline earth metal ions and/or the aluminum ions that would be present in a spinel composition which contains only alkaline earth metal and aluminum as metal ions. Generally, the amount of the additional metal component or components present in the spinel composition is small compared to the quantity of the spinel composition as a whole. Preferably, the present spinel composition comprises a minor amount by weight of at least one additional metal, component, more preferably up to about 20%, e.g., about 10% to about 20% by weight (calculated as elemental metal). In a preferred embodiment, the atomic ratio of aluminum to additional metal component in the spinel composition is in the range of about 100:1 to about 1:100, more preferably about 20.1 to about 1:20. Of course, the amount of additional metal used will depend, for example, on the degree of sulfur dioxide oxidation desired, the degree of S0₃ reduction desired and the effectiveness of the additional metal component to promote such oxidation and reduction.

The alk'aline earth metal component of the present spinels preferably comprises magnesium. Also, in one embodiment the spinel-containing material, e.g., discrete entities further comprise up to about 50% by weight, for example, up to about 25% by weight, of free magnesia, calculated as MgO.

The spinel compositions of this invention exhibit superior properties as sulfur oxide reduction materials, e.g., in fluid catalyst cracking operations, when compared with spinel compositions which do not include at least one of the present additional metal components. For example, the products of this invention have suitable mechanical strength and bulk density, low attrition rate, suitable surface area and pore volume, and good fluidization characteristics.

The present spinel compositions exhibit surface areas ranging from about 25 to about

600 m2/g. , more preferably from about 40 m2/g. to about 400 m 2/g. and still more preferably from about 50 m 2/g. to about 300 m2/g.

The embodiments described below are exemplary, without limitation, of the process of this invention.

Example I

An aqueous solution of magnesium nitrate was prepared by dissolving 179.5 g. (1.21 moles) of crystalline magnesium nitrate in deionized water, followed by the addition thereto of sufficient concentrated nitric acid to provide 34.0 g. (0.54 mole) HN0₃.

An aqueous solution of sodium aluminate was prepared by dissolving 164 g. (1.0 mole) sodium aluminate (Na₂Al₂0.) and 22.4 g. (0.56 mole) sodium hydroxide in 800 g. deionized water.

The solutions of magnesium nitrate and sodium aluminate were added simultaneously, with stirring, to a heel of 2000 g. deionized water at respective rates set to maintain the pH of the mixture between 7.0 and 7.5. Upon completion of the addition of the magnesium nitrate solution, additional sodium aluminate solution was added until the pH of the mixture reached 8.5. The precipitate phase was allowed to stand for 24 hours, filtered, slurried with water and refiltered twice, and finally dried for 3 hours at 260°F in a stream of flowing air. The dried filter cake was ground in a hammermill. until the fine material passed through a 60-mesh screen. The ground material was then calcined in a stream of flowing air for 3 hours at 1350°F, to produce a magnesium, aluminum-containing spinel composition.

Examples II -V The preparative procedure of Example I was repeated, employing the respective additional metals (and further additional metals) shown in Table I and in amounts calculated to provide the weight % of the respective metals set forth in Table I .

Example VI Spinels and modified spinels prepared as in Examples I - V were fluidized in a gas stream, comprising (by volume) 5% 0₂, 10 % S0₂ and 85% N₂, after heating at 1100°F in a stream of nitrogen gas. After a 30-minute treatment with the S0₂~containing gas, remaining S0₂ was flushed out with nitrogen. After cooling, analyses for sulfur were conducted on the solids and on the gas stream to determine the efficiency of SOx pickup by formation of metal sulfates. The percent SOx pickup shown in Table I is equal to that percent of the total sulfur passed over the material which is picked up by the material.

Example VII The sulfur-containing spinels from Example VI were heated to 1100°F in flowing nitrogen gas and then for 30 minutes in a stream of hydrogen. The spinel was flushed with nitrogen, and, after cooling was analyzed for sulfur removal by reduction of metal sulfates. The percent sulfate reduction shown in Table I is equal to the percent of sulfur originally associated with the material which is removed by the above-noted treatment.

Table I

SOx Sulfate

Example Additional Metal(s) Pickup, % Reduction, 1

I 51 63

II Cu, 2.5 weight 1 80 60

III Sn, 4.4 weight 1 58 84

IV Fe, 1.2 weight 1 70 83 Cu, 1.1 weight 1

_*

V Ce, 2.1 weight % 73 80 Fe, 5.1 weight %

As shown in Table I, a small amount of copper and tin (Examples II and III) greatly improved the effectiveness of the spinel base, both for pickup of SOx and for subsequent release of sulfur, as, for example, in the reactor section and catalyst regeneration section, respectively, of a fluid bed hydrocarbon catalytic cracking unit. The combinations of copper and iron, and cerium and iron (Examples IV and V, respectively) also greatly improved the effectiveness of the spinel base in the above testing. Other transition metals also exhibited improvement over the spinel alone, whether employed alone or in combinations. A spinel base prepared in accordance with Example I and impregnated with 4.5 weight % iron using conventional impregnation techniques gave 58% SOx pickup under similar test conditions.

While this invention has been described with respect to various specific examples and embodiments, it is to be understood that the invention is not limited thereto and that it can be variously practiced within the scope of the following claims:

Claims

IN THE CLAIMS

1. In a process for reducing the sulfur oxide content of a sulfur oxide-containing gas which includes contacting said gas with a material at conditions to associate at least a portion of said sulfur oxide contained in said gas with said material, the improvement comprising utilizing as said material a spinel composition comprising an alkaline earth metal component, an aluminum component and at least one additional metal component in an amount effective to promote the oxidation of SO, to S0₃ at S0₂ oxidation conditions and/or to promote the reduction of S0₃ at S0₃ conditions, which component comprises a metal selected from the group consisting of Group IB metals, Group IV metals, Group VA metals, the platinum group metals, the rare earth metals, Te, Nb, Ta, Sc Zn, Y, Mo, W Tl, Re, U, Th and mixtures thereof.

2. The process of claim 1 wherein the spinel composition has a surface area in the range of about 25 m 2/gm. to about 600 m2/gm.

3. The process of claim 1 wherein the atomic ratio of alkaline earth metal to aluminum plus said additional metal in said spinel composition is at least 0.17.

4. The process of claim 1 wherein said additional metal component is of a metal selected from the group consisting of Zr, Sn, Sb, Ag, Cu, Bi, Tl, Te and mixtures thereof.

5. The process of claim 1 wherein said spinel composition includes up to about 20% by weight, calculated as elemental metal, of at least one of said additional metal components.

6. The process of claim 1 wherein said spinel composition further comprises at least one further additional component in an amount effective to promote the oxidation of SO- to SO- at SO, oxidation conditions and/or to promote the reduction of S0₃ at SO- reduction conditions, which further additional component comprises a metal selected from the group consisting of iron, chromium, vanadium, manganese, gallium, boron, cobalt and mixtures thereof.

7. The process of claim 4 wherein said spinel composition further comprises at least one further additional component in an amount effective to promote the oxidation of SO- to S0₃ at SO- oxidation conditions and/or to promote the reduction of S0₃ at S0₃ reduction conditions, which further additional component comprises a metal selected from the group consisting of iron, chromium, vanadium, manganese, gallium, boron, cobalt and mixtures thereof.

8. The process of claim 5 wherein said spinel compositions further comprises at lease one further additional component in an amount effective to promote the oxidation of S0₂ to S0₃ at SO₂ oxidation conditions and/or to promote the reduction of S0₃ at S0₃ reduction conditions, which further additional component comprises a metal selected from the group consisting of iron, chromium, vanadium, manganese, gallium, boron, cobalt and mixtures thereof.

9. The process of claim 1 wherein said sulfur-oxide-containing material contacting occurs in the catalyst regeneration zone of a hydrocarbon catalytic cracking unit.

10. The process of claim 8 wherein said additional metal component comprises a metal selected from the group consisting of Zr, Sn, Sb, Cu, Bi and mixtures thereof.

11. The process of claim 1 wherein said alkaline earth metal component is magnesium component.

12. The process of claim 8 wherein said further additional metal component comprises iron.

13. The process of claim 1 wherein the atomic ratio of alkaline earth metal to aluminum plus said additional metal in said spinel composition is in the range of about 0.17 to about 2.5.

14. The process of claim 1 wherein said material further comprises up to about 50% by weight of free magnesia.

•15. The process of claim 4 wherein said material further comprises up to about 50% by weight of free magnesia.

16. The process of claim 8 wherein said material further comprises up to about 50% by weight of free magnesia.

17. In a hydrocarbon conversion process for converting a sulfur-containing hydrocarbon feedstock which comprises: (1) contacting said feedstock with solid particles capable of promoting the conversion of said feedstock at hydrocarbon conversion conditions in at least one reaction zone to produce at least one product and to cause deactivating sulfur-containing carbonaceous material to be formed on said solid particles thereby forming deposit-containing particles; (2) contacting said deposit-containing particles with oxygen at conditions to combust at least a portion of said carbonaceous deposit in at least one regeneration zone to thereby regenerate at least a portion of the hydrocarbon conversion catalytic activity of said solid particles and to form combustion products containing sulfur oxide; and (3) repeating step (1) and (2) periodically, the improvement which comprises: using, in intimate admixture with said solid particles, a minor amount of discrete entities having a composition different from said solid particles and comprising a spinel composition comprising an alkaline earth metal component, an aluminum component and at least one additional metal component in an amount effective to promote the oxidation of S0₂ to SO₃ at S0₂ oxidation conditions and/or to promote the reduction of S0₃ at S0₃ reduction conditions, which component comprises a metal selected from the group consisting of Group IB metals. Group IV metals, Group VA metals, the platinum group metals, the rare earth metals, Te, Nb, Ta, Sc, Zn, Y, Mo, W, Tl, Re, ϋ, Th and mixtures thereof.

18. The process of claim 17 wherein said spinel composition has a surface area in the range of about 25 m 2/gm. to about 600 m2/gm.

19. The process of claim 17 wherein the atomic ratio of alkaline earth metal to aluminum plus said additional metal in said spinel composition is at least 0.17.

20. The process of claim 17 wherein said additional metal component is of a metal selected from the group consisting of Zr, Sn, Sb, Ag, Cu, Bi, Tl, Te and mixtures thereof.

21. The process of claim 17 wherein said spinel composition further comprises at least one further additional component in an amount effective to promote the oxidation of S0₂ to S0₃ at SO₂ oxidation conditions and/or to promote the reduction of S0₃ at S0₃ reduction conditions, which further additional component comprises a metal selected from the group consisting of iron, chromium, vanadium, manganese, gallium, boron, cobalt and mixtures thereof.

22. The process of claim 21 wherein said additional metal component comprises a metal selected from the group consisting of Zr, Sn, Sb, Cu, Bi and mixtures thereof.

23. The process of claim 17 wherein said alkaline earth metal component is magnesium component.

24. The process of claim 21 wherein said alkaline earth metal component is magnesium component and said further additional metal component is iron component.

25. The process of claim 17 wherein said discrete entities further comprise up to about 50% by weight of free magnesia.

26. A composition of matter comprising, in intimate admixture, a major amount of solid particles capable of promoting hydrocarbon conversion at hydrocarbon conditions and a minor amount of discrete entities having a composition different .from said solid particles and comprising a spinel composition comprising an alkaline earth metal component, an aluminum component and at least one additional metal component in an amount effective to promote the oxidation of S0₂ to SO- at S0₂ oxidation conditions and/or to promote the reduction of S0₃ at S0₃ reduction conditions, which component comprises a metal selected from the group consisting of Group IB metals, Group IV metals, Group VA metals, the platinum group metals, the rare earth metals Te, Nb, Ta, Sc, Zn, Y, Mo, W, Tl, Re, U, Th and mixtures thereof.

27. The composition of claim 26 wherein said spinel composition has a surface area in the range of about 25 m 2/gm. to about 600 m2/gm.

28. The composition of claim 26 wherein the atomic ratio of alkaline earth metal to aluminum plus additional metal is at least 0.17.

29. The composition of claim 26 wherein said discrete entities contain at least about 70% by weight of said spinel.

30. The composition of claim 26 wherein said additional metal component is of a metal selected from the group consisting of Zr, Sn, Sb, Ag, Cu, Bi, Tl, Te and mixtures thereof.

31. The composition of claim 26 wherein said additional metal component comprises a metal selected from the group consisting of Zr, Sn, Sb, Cu, Bi and mixtures thereof.

32. The composition of claim 26 wherein said spinel composition further comprises at least one further additional component in an amount effective to promote the oxidation of S0₂ to S0₃ at SO- oxidation conditions and/or to promote the reduction of S0₃ at S0₃ reduction conditions, which further additional component comprises a metal selected from the group consisting of iron, chromium, vanadium, manganese, gallium, boron, cobalt and mixtures thereof.

33. The composition of claim 32 wherein said further additional metal is iron.

34. The composition of claim 26 wherein said additional metal component is present in an amount up to about 20% by weight at the spinel composition, based on elemental metal.

35. The composition of claim 26 wherein said discrete entities further comprise up to about 50% by weight of free magnesia.

36. A composition of matter comprising a spinel composition comprising an alkaline earth metal component, an aluminum component and at least one additional metal component in an amount effective to promote the oxidation of S0₂ to S0₃ at S0₂ oxidation conditions and/or to promote the reduction of S0₃ at S0₃ reduction conditions, which component comprises a metal selected from the group consisting of Group IB metals, Group IV metals, ^'Group VA metals, the platinum group metals, the rare earth metals Te, Nb, Ta, Sc, Zn, Y Mo, W, Tl, Re, U, Th and mixtures thereof.

37. The composition of claims 36 wherein said spinel has a surface area of about 25 m 2/gm.

2 to about 600 m /gm.

38. The composition of claim 36 which further comprises up to about 50% by weight of free magnesia.

39. The composition of claim 36 wherein said additional metal component is of a metal selected from the group consisting of Zr, Sn, Sb, Ag, Cu, Bi, Tl, Te and mixtures thereof.

40. The composition of claim 36 wherein said additional metal component comprises a metal selected from the group consisting of Zr, Sn, Sb, Cu, Bi and mixtures thereof.

41. The composition of claim 37 wherein said spinel composition further comprises at least one further additional component in an amount effective to promote the oxidation of SO₂ to S0₃ at S0₂ oxidation conditions and/or to promote the reduction of S0₃ at S0₃ reduction conditions, which further additional component comprises a metal selected from the group consisting of iron, chromium, vanadium, manganese, gallium, boron, cobalt and mixtures thereof.

42. The composition of claim 41 wherein said further additional metal is iron.

43. The composition of claim 36 wherein said^' additional metal component is present in an amount up to about 20% by weight at the spinel composition, based on elemental metal.

44. The composition of claim 36 wherein said alkaline earth metal component is magnesium component.