GB2094657A

GB2094657A - Cracking catalyst sulfur oxide gettering agent compositions

Info

Publication number: GB2094657A
Application number: GB8206982A
Authority: GB
Original assignee: WR Grace and Co
Current assignee: WR Grace and Co
Priority date: 1981-03-13
Filing date: 1982-03-10
Publication date: 1982-09-22
Also published as: NL8200987A; GB8414412D0; DE3208931C2; GB2094657B; BE892458A; JPS57162645A; IT1152770B; CA1182805A; GB2140791B; AU8122182A; MX157849A; IT8220091A0; LU84006A1; DE3208931A1; GB2140791A; FR2501531A1; FR2501531B1; AU554468B2

Abstract

Catalytic cracking catalysts which contain alumina/lanthanum oxide sulfur oxide gettering agents are used to reduce sulfur oxide emissions from fluid catalytic cracking (FCC) units. Also disclosed are sulfur oxide absorbing/ gettering agents which comprise lanthanum oxide distributed upon an alumina surface.

Description

SPECIFICATION Cracking catalyst sulfur oxide gettering agent compositions The present invention relates to catalysts which are used to catalytically crack hydrocarbons and to sulfur oxide absorbing/gettering agent compositions which may be used to control sulfur oxide emissions.

More specifically, the invention contemplates the preparation and use of catalytic cracking catalysts which are capable of reducing the amount of sulfur oxides (SOx) emitted to the atmosphere during regeneration of the catalyst, and to highly efficient SOx control agents which may be used to control SOx emissions from a variety of processes.

Cracking catalysts which are used to crack hydrocarbon feedstocks become relatively inactive due to the deposition of carbonaceous deposits on the catalyst. These carbonaceous deposits are commonly called coke. When the feedstocks contain organic sulfur compounds, the coke on the catalyst contains sulfur. After the cracking step, the catalyst passes to a stripping zone where steam is used to remove strippable hydrocabons from the catalyst. The catalyst then goes to the regenerator, where the catalyst is regenerated by burning the coke in an oxygen-containing gas. This converts the carbon and hydrogen in the coke to carbon monoxide, carbon dioxide and water. The sulfur in the coke is converted to oxides of sulfur, 502 and S03, i.e, SOx.

Generally, the greater the amount of sulfur in the feedstock, the greater the amount of sulfur in the coke.

Likewise, the greater the amount of sulfur in the coke, the greater the amount of sulfur oxides in the flue gas exiting from the regenerator. In general, the amount of SO2 and SOB, i.e. SOx, in the flue gas amounts to about 250 to 2,500 parts per million by volume.

The prior art has suggested various methods for removing or preventing the liberation of SOx to the atmosphere during oxidative combustion of sulfur containing fuels/residues. Typically, fluid catalytic cracking (FCC) combustion units have been equipped with conventional scrubbers in which the SOx components are removed from flue gas by absorption/reaction with gettering agents (sometimes referred to as ''Sox acceptors") such as calcium oxide. In some instances, hydrocarbon feedstocks are pretreated (hydrotreated) to remove sulfur. It has also been claimed that sulfur oxide emissions from FCC units may be controlled by use of a cracking catalyst in combination with a sulfur absorber or gettering agent. It has also been claimed that these sulfur gettering agents are more effective when used in the presence of oxidation catalysts.

Oxidation catalysts are currently being used in FCC units to oxidize CO to CO2 in the catalyst bed during the coke-burning step in the regenerator. The oxidation of CO to CO2 in the catalyst bed yields many benefits.

One benefit is the reduction of CO emissions. Another is the avoidance of "after-burning", i.e., the oxidation of CO to CO2 outside the catalyst bed, which results in a loss of heat energy and causes damage to the cyclones and flue gas exit lines. The major benefit in using oxidation catalysts to oxidize CO to CO2 in the catalyst regenerator bed derives from the heat released when the CO is oxidized to CO2. This heat raises the catalyst bed temperature and thereby increases the coke-burning rate. This gives a lower residual carbon level on regenerated catalyst (CRC). This, in turn, makes the regenerated catalyst more active for the cracking step. This increases the amount of useful products produced in the FCC unit.

In view of the fact that CO oxidation catalysts are currently being used in many FCC units for economic reasons, SOx gettering agents for use in FCC units must be compatible and effective in the presence of oxidation catalysts. Furthermore, SOx gettering agents for use in FCC units must be effective under the actual conditions seen in FCC units, such as temperatures of 800-1000 F (427 - 538"C) and catalyst residence times of 3 to 15 seconds in the reducing atmosphere of the reactor, temperatures of 800-1000 F (427-538 C) in the steam atmosphere of the stripper, temperatures of 1100-1400 F (593-760 C) and catalyst residence times of 5 to 15 minutes in the oxidizing atmosphere of the regenerator.Additionally, SOx gettering agents for use in FCC units must be effective in the presence of the materials present in FCC units, such as cracking catalysts of various compositions, oil feedstocks of various compositions and their cracked products, and, as stated earlier, oxidation catalysts to oxidize CO to CO2.

The following U.S. patents disclose the use of cracking catalysts which contain various sulfur and carbon monoxide emission control agents.

3,542,670 3,699,037 3,835,031 4,071,436 4,115,249 4,115,250 4,115,251 4,137,151 4,151,119 4,152,298 4,153,534 4,153,535 4,166,787 4,182,693 4,187,199 4,200,520 4,206,039 4,206,085 4,221,677 4,238,317 As shown in the above noted references, organic sulfur present during regeneration of the cracking catalyst is ultimately oxidized to sulfurtrioxide (SO3) which reacts with a gettering agent to form a stable sulfate which is retained in the catalyst inventory of the FCC unit. Regenerated catalyst containing the sulfate compound is recycled to the cracking zone where the catalyst is mixed with oil and steam dispersant to effect the cracking reaction and conversion of the oil to useful products (gasoline, light olefins, etc.).

When the sulfate-containing catalyst is exposed to the reducing and hydrolyzing conditions present during the cracking step and the subsequent hydrolyzing conditions present in the steam stripper, the sulfate is reduced and hydrolyzed to form hydrogen sulfide (H2S) and restore or regenerate the gettering agent. The hydrogen sulfide is recovered as a component of the cracked product stream. The gettering agent is re-cycled to the regenerator to repeat the process. Through use of catalysts containing appropriate gettering agents, it is disclosed that the amount of sulfur oxides emitted from the regenerator may be significantly reduced.

However, it has been found that attempts to produce SOx-control cracking catalysts which can consistently achieve significant sulfur oxide emission reduction over long periods of time have in general been unsuccessful.

Accordingly, it is an object of the present invention to provide a cracking catalyst composition which effectively and economically reduces the emission of sulfur oxides from FCC units.

It is another object to provide a sulfur oxide gettering agent which is capable of removing sulfur oxides over a long period of time when subjected to multiple gettering/regeneration cycles.

It is a further object to provide a SOx control additive which may be added to the catalyst inventory of an FCC unit in amounts necessary to reduce sulfur oxide regenerator stack gas emissions to an acceptable level.

It is still a further object to provide highly effective sulfur oxide gettering agents which may be advantageously combined with conventional cracking catalyst compositions or used to control SOx emissions from a variety of processes.

These and still further objects will become apparent to one skilled in the art from the following detailed description, specific examples and drawing wherein the Figure is a graphical representation of data which illustrates SOx Index vs. La2O3 content of SOx gettering agents of the present invention.

Broadly, our invention contemplates catalytic cracking catalyst compositions which include an aluminalanthanum oxide SOx gettering agent. Furthermore, our invention contemplates an improved SOx gettering agent which comprises an alumina (Al203) substrate coated with lanthanum oxide (La2O3) in amounts which provides approximately a theoretical mono-layer of La203 molecules on the surface of the alumina substrate.

These gettering agents may be effectively combined with or included in particulate catalyst compositions used for the catalytic cracking of hydrocarbons, or alternatively the gettering agents may be used in any combustion process which generates SOx components that are to be selectively removed from the combustion products.

More specifically, we have found that a particularly effective SOx absorber/gettering agent suitable for use with catalytic cracking catalyst may be obtained by combining the soluble lanthanum salt solution with a porous alumina substrate in amounts which will distribute upon the surface of the alumina substrate a layer of lanthanum oxide approximately one molecule in thickness.

In practice, we find that the desired result is achieved with about 5 to 50 percent by weight La2O3 combined with an alumina substrate which has a surface area of from about 45 to 450 m2/g; preferably, about 12 to 30 percent by weight La2O3 combined with an alumina substrate which has a surface area of about 110 to 270 m2/g; and more preferably about 20 percent by weight La2O3 combined with an alumina substrate which has a surface area of about 180 m2/g.

Suitable alumina substrates are available from many commercial sources, and comprise the alumina hydrates, such as alpha alumina monohydrate, alpha alumina trihydrate, beta alumina monohydrate and beta alumina trihydrate. Also considered most suitable are the calcined versions of the above alumina hydrates. These include gamma alumina, chi alumina, eta alumina, kappa alumina, delta alumina, theta alumina, alpha alumina and mixtures thereof.

The lanthanum oxide component which is distended upon the alumina surface may be obtained as a commercially available lanthanum salt such as lanthanum nitrate or chloride or sulfate, or alternative, a mixed rare earth salt which contains other rare earth elements such as Nd, Ce, Pr and Sm may be utilized.

The rare earth component of a typical commercially available mixed rare earth salt solution which includes lanthanum has the following approximate composition, expressed as oxides: 60% La2O3, 20% Nd2O3, 14% CeO2, 5% Pr6O11 and 1% Sm2O3. It should be understood that in the event a mixed rare earth salt source is utilized the quantity of mixed rare earth salts used should be sufficient to provide the desired level of La2O3 on the alumina substrate.

The amount of lanthanum oxide utilized in the preparation of the novel SOx gettering agent is preferably that quantity which will provide a mono-layer of lanthanum oxide molecules over the surface of the alumina substrate. In the event the quantity of lanthanum oxide, as specified above, is substantially exceeded, i.e., multi-layer or bulk lanthanum oxide is formed, and the effectiveness of the SOx gettering agent is adversely affected. On the other hand, if insufficient lanthanum oxide is used, the effectiveness of the gettering agent is less than it could be.

While the precise mechanism is not fully understood, it is believed that the active specie is a Laps, molecule fixed on the alumina surface in some sort of a surface complex of La2O3 and Awl203. This surface la203 on Al2 03 complex is very reactive in combining with sulfur oxides to form a thermally stable solid sulfate or sulfate-type compound. Furthermore, this thermally stable solid sulfate or sulfate-type compound can be easily reduced-hydrolyzed to produce volatile hydrogen sulfide and restore or regenerate the original surface La2O3 on A1203 complex. The hydrogen sulfide can be recovered as a component of the product stream.The restored or regenerated gettering agent can be recycled to repeat the absorption and regeneration steps.

To prepare our novel SOx gettering agent, the alumina substrate is uniformly and thoroughly admixed with a quantity of lanthanum salt solution which will provide the desired uniform dispersion of lanthanum oxide on the surface. Typically, the soluble lanthanum salt, preferably lanthanum nitrate, is dissolved in water to provide a desired volume of solution which has the desired concentration of the lanthanum salt. The alumina substrate is then impregnated, as uniformly as possible, with the lanthanum salt solution to give the desired amount of lanthanum on the alumina. The impregnated alumina is then calcined at a temperature sufficient to decompose the lanthanum salt and fix the result lanthanum oxide uniformly onto the alumina surface.While it is contemplated that calcination temperatures of up to about 1 5000F may be used, calcination temperatures on the order of 10000F have been found to be satisfactory.

In one preferred embodiment of the invention, the alumina substrate to be impregnated is in the form of microspheroidal particles, with about 90% of the particles having diameters in the 20 to 149 micron fluidizable size range. The gettering agent prepared using these microspheroidal particles may be advantageously physically mixed with FCC catalysts in amounts ranging from about 0.5 to 60 percent by weight of the overall composition.

In another preferred embodiment of the invention, the alumina substrate to be impregnated is in the form of particles which have an average particle size of less than 20 microns in diameter, and preferably less than 10 microns in diameter. The finished gettering agent prepared using these fine particles may be incorporated in a cracking catalyst composition during the formation of the catalyst particles.

Typically, the lanthanum impregnated alumina is added to an aqueous slurry of catalyst components prior to forming, i.e. spray drying in the case of FCC catalysts.

In another embodiment of the invention, the alumina substrate to be impregnated is in the form of particles one millimeter or greater in diameter. The finished gettering agent prepared using these particles can be used in either a fixed-bed or moving-bed configuration to reduce SOX emissions from a variety of processes.

Therefore, it is seen that the present gettering agent may be used as a separate additive which is added to the catalyst as a separate particulate component, or the gettering agent may be combined with the catalyst during its preparation to obtain catalyst particles which contain the gettering agent as an integral component. Additionally, the gettering agent may be used by itself to reduce SOx emissions from a variety of processes.

Cracking catalysts which may be advantagously combined with the SOx gettering agent of the present invention are commercially available compositions and typically comprise crystalline zeolites admixed with inorganic oxide binders and clay. Typically, these catalysts comprise from about 5 to 50 percent by weight crystalline aluminosilicate zeolite in combination with a silica, silica-alumina, or alumina hydrogel or sol binder and optionally from about 10 to 80 percent by weight clay. Zeolites typically used in the preparation of cracking catalysts are stabilized type Y zeolites the preparation of which is disclosed in U.S. 3,293,192, 3,375,065, 3,402,996, 3,449,070 and 3,595,611.Preparation of catalyst compositions which may be used in the practice of our invention are typically disclosed in U.S. patents 3,957,689,3,867,308,3,912,611 and Canadian 967,136.

In a preferred practice of the invention, the cracking catalyst gettering composition will be used in combination with a noble metal oxidation catalyst such as platinum and/or palladium.

In another preferred practice of the invention, the SOx gettering agent is combined with a cracking catalyst which comprises an alumina sol, i.e. aluminum chlorhydroxide solution, bound zeolite/clay composition as disclosed in Canadian Patent 967,136 admixed with a particulate platinum containing oxidation catalyst to obtain a composition which comprises 0.5 to 60 percent by weight gettering agent, 40 to 99 percent by weight cracking catalyst, and 1 to 5 parts per million platinum.

In still another preferred practice of the invention, the Sx gettering agent is combined with a zeolite cracking catalyst which possesses an essentially silica-free matrix. These catalysts are obtained by using the procedure set forth in Canadian 967,136 by mixing together the following materials: 5 to 50 weight percent zeolite, 10 to 80 weight percent alumina hydrate (dry basis), and 5 to 40 weight percent aluminum chlorohydroxide sol (awl203), and water.The mixture was spray-dried to obtain a finely divided catalyst composite and then calcined at a temperature of about 1 000"F (538 C). The Sox gettering agent may be included as a component in the spray dried slurry in lieu of some of the alumina hydrate or the SOx gettering agent may be physically blended with the catalyst in the amount of about 0.5 to 60 weight percent.

As indicated above, the gettering agent may be utilized in the form of a separate particulate additive which is physically blended with a particulate catalyst or the gettering agent may be incorporated in the catalyst particle by admixing the additive with the catalyst components prior to forming of the catalyst. In addition it is contemplated that the gettering agent may be utilized in any combustion/reaction process where it is desirable to collect or remove sulfur oxides from a product gas stream. Typically, the SOx gettering agent may be used in a fluidized coal combustion process to remove SOx formed during burning of the coal.The SO, gettering agent may then be removed from the combustion/reaction zone periodically or continuously to restore or regenerate the gettering agent by subjecting itto reduction-hydrolysis in the presence of hydrogen or carbon monoxide-hydrogen reducing gas mixtures (i.e. syn-gas) and H2O. Using this technique, the SOx component of the combustion products is selectively removed as a stable sulfate, and the sulfate is subsequently reduced-hydrolyzed to liberate H2S and restore or regenerate the gettering agent. The H2S may be recovered using conventional adsorbing techniques.

Having described the basic aspects of our invention, the following examples are given to illustrate specific embodiments thereof.

Example 1 A solution of lanthanum nitrate was prepared by dissolving 79.7 g of lanthanum nitrate, La(NO3)3.6H2O, in a sufficient amount of water to give 100 ml ofsolution. 10 ml this solution contains 3.0 g of lanthanum expressed as lanthanum oxide, La2O3.

Example 2 36.8 g (27 g dry basis) of a commercial alpha alumina monohydrate having an average particle size (APS) of 67 microns with 96 weight percent of the particles in the 20 to 149 micron size range were impregnated with 10 m I of solution described in Example 1. The impregnated alumina was heated to 10000F (538 C) and held at 1000 F for 30 minutes. The resultant La203/A1203 sample contained 10 weight percent La2O3.

Example 3 Alpha alumina monohydrate of the type described in Example 2 was calcined in air for one hour at 9000F (482"C). 27 g of this calcined alumina was impregnated with 10 ml of solution described in Example 1. The impregnated sample was heated to 10000F (583 C) and held at 10000F (538 C) for 30 minutes. The resultant La2O3 sample contained 10 weight percent lanthanum oxide La2O3.

Example 4 The procedure of Example 3 was repeated except that the alumina hydrate was calcined for one hour at 1 2500F (677 C) prior to impregnation with lanthanum nitrate solution.

Example 5 The procedure of Example 3 was repeated, except that the alumina hydrate was calcined for one hour at 1650"F (899 C) prior to impregnation with lanthanum nitrate solution.

Example 6 The procedure of Example 3 was repeated, except that the alumina hydrate was calcined for one hour at 18500F (1010 C) priorto impregnation with lanthanum nitrate solution.

Example 7 The procedure of Example 3 was repeated, except that the alumina hydrate was calcined at 19500F (1066 C) prior to impregnation with lanthanum nitrate solution.

Example 8 Alumina hydrate of the type described in Example 2 was calcined in airfor one hour at 1250#F (677#C). 5 ml of the solution described in Example 1 was mixed with 5 ml of water to yield 10 ml of solution having a lanthanum concentration of 1.50 g of lanthanum expressed as La2O3. 28.5 of the calcined alumina were impregnated with the 10 ml of solution. The impregnated sample was heated to 10000F (538 C) and held at 10000F (538 C) for 30 minutes. The resultant La203/A1203 sample contained 5 weight percent La2O3.

Example 9 Alumina hydrate of the type described in Example 2 was calcined in air for one hour at 1250 F (677"C). 24 g of this calcined alumina was impregnated with 10 ml of solution described in Example 1. The impregnated sample was heated to 1000 F (538 C) and held at 1000 F (538 C) for 30 minutes. After being allowed to cool to room temperature, the impregnated and calcined sample was given a second impregnation with 10 ml of solution described in Example 1. After this second impregnation, the sample was heated to 1 000"F (538 C) and held at 1000 F (538do) for 30 minutes.The resultant La203/AI203 sample contained 20 weight percent La2O3.

Example 10 A solution of lanthanum nitrate was prepared by dissolving 99.89 of La(NO3)3.6H2O in water to give 100 ml of solution. 8 ml of solution contains 3.0 g of lanthanum expressed as La2O3.

Example 11 Alumina hydrate was calcined in air for one hour at 12500F (677 C) as in Example 9.21 g of this calcined alumina were impregnated with 8 ml of solution described in Example 10. The impregnated sample was heated to 1 0000F (538 C) and held at 1000 F (538 C) for 30 minutes. After being allowed to cool to room temperature, the impregnation and calcined sample was given a second impregnation with 8 ml of solution described in Example 10. After this second impregnation, the sample was heated to 10000F (538 C) and held at 1000 F (538 C) for 30 minutes.After being allowed to cool to room temperature, this doubly impregnated and calcined sample was given a third impregnation with 8 ml of solution described in Example 10. After this third impregnation, the sample was heated to 1000 F (538"C) and held at 1 0000F for 30 minutes. The resultant La203/A1203 sample contained 30 weight percent La2O3.

Example 12 The procedure of Example 11 was repeated, except that 18.0 g of calcined alumina was used, and after the third impregnation and calcination, the sample was given a fourth impregnation and calcination at 10000F (538 C). The resultant La2O3/A12O3 sample contained 40 weight percent La2O3.

Example 13 A solution of mixed rare-earth nitrates was prepared by mixing 153.1 g of a commercial mixed rare-earth nitrate solution with water to give 100 ml. 8 ml of the solution contained 3.0 g of mixed rare-earths expressed as the oxides. The rare earth component of this solution, expressed by weight as oxides, has the following composition: 60% La2O3, 20% Nd2O3, 14% CeO2, 5% Pr6O and 1% Sm203.

Example 14 The procedure of Example 9 was repeated, except that the impregnations were carried out with 8 ml of the solution described in Example 13. The resultant sample contained 20 weight percent mixed rare-earth oxides. Sixty percent of these rare-earth oxides were lanthanum oxide, so the resultant sample contained 12 weight percent La2O3.

Example 15 The procedure of Example 11 was repeated, except that the impregnations were carried out with 8 ml of solution described in Example 13. The resultant sample contained 30 weight percent mixed rare-earth oxides of which 60% were lanthanum oxide. The resultant sample contained 18 weight percent Lea203.

Example 16 A solution of mixed rare-earth nitrates was prepared by mixing 152.8 g of a commercial mixed rare-earth nitratesolutionwithwaterto give 100 ml. 10 ml of solution contains3.75g of mixed rare-earth expressed as the oxides. The rare earth component of this solution, expressed as oxides, has the following composition: 60% La2O3, 20% Nd2O3, 14% CeO2, 5% Pr6O and 1% Sm203.

Example 17 The procedure of Example 9 was repeated, except that the impregnations were carried out with 10 ml of solution described in Example 16. The resultant sample contained 25 weight percent mixed rare-earth oxides. Sixty percent of these rare-earth oxides were lanthanum oxide, so the resultant sample contained 15 weight percent La2O3.

Example 18 Fine-size alpha alumina monohydrate was calcined in air for 1 hour at 1250 (677 C). This calcined alumina had an average particle size of 15 to 20 microns. 2000 g (dry basis) of this calcined alumina was mixed with a solution which contained 592 g of La(NO3)3.6H2O dissolved in 1400 ml of water in a mechanical mixer. The solution was added at a rate 100 ml per minute to this alumina. The impregnated alumina was removed from the mixer, heated to 1000 F (538 C) and held at 10000F (538 C) for 30 minutes. The sample contained 10 weight percent La2O3 and had an average particle size of less than 10 microns.

Example 19 Alpha alumina monohydrate was calcined in air for 1 hour at 12500F (6770C) to obtain a product having an average size of 15 to 20 microns in diameter. 2000 g (dry basis) of this calcined alumina was mixed with a solution of 670 g of La (NO3)3.6H2O dissolved in 1400 ml of water in a mixer. The solution was added at a rate of 100 ml per minute. The impregnated alumina was removed from the mixer, heated to 10000F (538 C) and held at 1 0000F (538 C) for 30 minutes. This impregnated and calcined alumina was returned to the mixer and given a second impregnation with 670g of La(NO3)3.6H2O in 1200 ml of water which was added at a rate of 100 ml per minute. The impregnated material was heated to 1000 F (538 C) and held at 1000 F (538 C) for 30 minutes. The finished material contained 20 weight percent La2O3 and had an average particle size of less than 10 microns.

Example 20 The finished SOx agent of Example 18 was incorporated within the particle of an alumina-bound cracking catalyst. The catalyst was prepared by mixing together the following materials: The SOx gettering agent of Example 18, a rare earth ion-exchanged Y-type crystalline-aluminosilicate, clay, aluminum chlorhydroxide sol (approximate formula: Al2Cl(OH)5) and water. The mixture was spray-dried and then calcined for 2 hours at 1 0000F (538 C). The proportion of starting materials were such that the finished catalyst contained 20 percent of the SOx gettering agent of Example 18, 12 percent of rare earth ion-exchanged Y-type crystalline aluminosilicate, 54 percent clay and 14 percent alumina.The finished catalyst had an average particle size (APS) of 116 microns with 65 weight percent of the particles in the 20 to 149 micron size range.

Example 2 1 The procedure of Example 20 was repeated except that the SOx gettering agent of Example 19 was used.

In this Example, the finished catalyst had an average particle size (APS) of 77 microns with 87 weight percent of the particles in the 20 to 149 micron size range.

Example 22 An alumina sol-bound cracking catalyst was prepared by mixing together the following materials: A rare earth ion-exchanged Y-type crystalline aluminosilicate (CREY), clay, aluminum chlorhydroxide sol (approximate formula: Al2Cl(OH)5) and water. The mixture was spray-dried and then calcined for 2 hours at 1 0000F (538 C). The proportion of starting materials were such that the finished catalyst contained 12 percent of a rare earth ion-exchanged Y-type crystalline aluminosilicate, 78 percent clay and 10 percent alumina.

The finished catalyst had an average particle size (APS) of 71 microns with 97 weight percent of the particles in the 20 to 149 micron size range.

29.89 g (dry basis) of this alumna-bound cracking catalyst was thoroughly mixed with 0.1110 g (dry basis) of an oxidation catalyst which comprises 810 ppm platinum on a gamma alumina support having a particle size in the fluidizable range.

Example 23 26.89 g (dry basis) of the cracking catalyst described in Example 22 was thoroughly mixed with 0.1110 g (dry basis) of the oxidation catalyst, also described in Example 22.3.00 g (dry basis) of a commercial alpha alumina monohydrate was added to this mixture and thoroughly mixed.

Example 24 26.89 g (dry basis) of the cracking catalyst described in Example 22 was thoroughly mixed with 0.1110 g (dry basis) of the oxidation catalyst, also described in Example 22.3.00 g (dry basis) of the La203/A1203 composition prepared in Example 2 was added to this mixture and thoroughly mixed.

Examples 25-36 The procedure of Example 24 was repeated except that the third component to be mixed was the composition prepared in Example 3. Like-wise, the procedure was repeated, except that the third components were, in turn, the compositions prepared in Examples, 4,5,6,7,8,9, 11, 12, 14, 15, 17.

Example 37 29.89 g (dry basis) of the finished caatalyst of Example 20 was thoroughly mixed with 0.1110 g (dry basis) of the oxidation catalyst described in Example 22.

Example 38 29.89 g (dry basis) of the finished catalyst of Example 21 was thoroughly mixed with 0.1110 g (dry basis) of the oxidation catalyst described in Example 22.

Example 39 A laboratory scale catalytic cracking unit was used to test the catalyst compositions for their ability to reduct SOx (S02 + 503) emissions from the regenerator.

Prior to testing in the lab unit, the catalysts or catalyst mixtures were steam deactivated with 100 percent steam at 15 psig (103 kPa) at 13500F (732"C) for 8 hours. This steam deactivation simulates the deactivation which occurs in a commercial cat-cracking unit. The ability of a catalyst or catalyst mixture to reduce SOx emissions in the lab test unit after this steam deactivation will be a measure of its ability to reduce SOx emissions in commercial units.In contast, the ability of a fresh or undeactivated catalyst or catalyst mixture to reduce SOx emissions in a lab test is inconclusive as far as projecting the ability of the catalyst or catalyst mixture to reduce SOx emissions in commercial units, because the catalyst or catalyst mixture would be deactivated in the commercial unit soon after being charged to the commercial unit and may become ineffective in reducing SOx emissions.

In the lab unit, a low sulfur gas oil was cracked over the catalyst or catalyst mixture at a temperature of 980"F.(527"C). Regeneration of the catalyst or catalyst mixture, i.e., the coke-burning step, was carried out with air at 1 250#F.(6770C). The air used for coke-burning step contained 2000 ppm SO2. This is equivalent to the amount of SO2 which would be formed in the regenerator if a high sulfur gas oil had been used for the cracking step.

The regenerated catalyst or catalyst mixture was then subjected to the cracking and steam-stripping steps to release, as H2S, the SOx captured in the regenerator.

The regneration and the cracking and steam-stripping steps were repeated. During this second cycle, a portion of the catalyst or catalyst mixture was removed after the regeneration step, and another portion of the catalyst or catalyst mixture was removed after the cracking and steam-stripping steps.

An Sox Index which gives a measure of the SOx captured in the regenerator and released in the reactor and stripper was defined as

A sample calculation for the catalyst mixture described in Example 31 and listed in Table I is given below.

SOx Index = [ (0.167)-(0.097)j1000 = 70 It should be noted that the SOx Index is a measure of the amount of SOx captured in the regenerator and released in the reactor and stripper. A catalyst or catalyst mixture which captures SOx in the regenerator, but does not release it in the reactor and stripper would have an SOx Index of zero. Such a catalyst or catalyst mixture would soon become saturated, likely after one or two cycles, and lose its effectiveness for reduction of SOx emissions.

For long-term effectiveness, a catalyst or catalyst mixture must not only capture SOx in the regenerator but be able to release it in the rector and stripper, and thereby restore its ability to repeat the process.

The greater the Davison SOx Index, the greater the long-term effectiveness of the catalyst or catalyst mixture in reducing SOx emissions from the regenerator. As stated above, a Davison SOx Index of zero means that the catalyst is not effective, long-term, for the reduction of SOx emissions from the regenerator.

At the other extreme, a Davison SOx Index of 100 means essentially 100 percent effectiveness, long-term, in the reduction of SOx emissions from the regenerator.

The catalyst mixtures described in Examples 22, 23, 26,31, 32, 33,34 and 35 were tested for their ability to reduce SOx emissions according to the procedure described above. The SOx Indices are given in Table I. A graphical representation of the data in Table I (except for the catalyst mixture described in Example 22) is set forth in the Figure wherein SOx index is plotted against percent La203 content of the SOx gettering agent in the mixture. The curve plotted in the Figure indicates the maximum SOx index is obtained when the SOx gettering agent contains about 20 percent La2O3. More broadly, the data in Table I shows that the maximum in the SOx index is obtained at La2O3 concentrations on Awl203 greater than 12 percent and less than 30 percent (Examples 32 and 34).

TABLE I Catalyst Mixture Described in Example SOx Index 22 10 23 18 26 42 34 58 35 70 31 69 32 56 33 44 Example 40 The catalyst mixtures described in Examples 37 and 38 were tested for their ability to reduce SOx emissions according to the procedure described in Example 39. The SOx Indices obtained are given in Table II.

TABLE II Catalyst Mixture Described in Example SOX Index 37 46 38 58 Example 41 The catalyst mixture in Examples 24, 25, 26, 27, 28 and 29 were tested for their ability to reduce SOx emissions according to the procedure described in Example 39. The Davison SOx indices obtained are given in Table lil.

The data in Table III show the effect of calcination of the alumina hydrate prior to impregnation with a solution of La(NO3)3.6H2O. In Example 24, the alumina hydrate was not calcined prior to impregnation. In Examples 25,26,27,28 and 29 the alumina hydrate was calcined at temperatures ranging from 900 F to 1950 F. (482" to 1066"C.) TABLE Ill Effect of Calcination of Alumina Prior to Impregnation Catalyst Mixture Described in Example SOx Index 24 32 25 35 26 42 27 35 28 29 29 36 Example 42 The cracking catalyst used in this example is a commercially available cracking catalyst containing 17 weight percent of a rare earth ion-exchanged Y-type crystalline aluminosilicate (REY), 63 weight percent clay and 20 weight percent silica-alumina sol binder.

29.89 g (dry basis) of this cracking catalyst was thoroughly mixed with 0.1110 g (dry basis) of an oxidation catalyst which comprises 810 ppm platinum impregnated on a gamma alumina support having a particle size in the fluidizable range.

Example 43 26.89 g (dry basis) of the cracking catalyst described in Example 42 was thoroughly mixed with 0.1110 g (dry basis) of the oxidation catalyst, also described in Example 42. 3.00 g (dry basis) of a commercial alpha alumina monohydrate was added to this mixture and thoroughly mixed.

Example 44 26.89 g (dry basis) of the cracking catalyst described in Example 42 was thoroughly mixed with 0.1110 g (dry basis) of the oxidation catalyst, also described in Example 42.3.00 g (dry basis) of the La203/AI203 composition prepared in Example 9 was added to this mixture and thoroughly mixed.

Example 45 The catalyst mixtures described in Examples 42, 43 and 44 were tested for their ability to reduce SOx emissions according to the procedure described in Example 39. The Sox Indices obtained are given in Table IV.

The results show that the silica-alumina sol cracking catalyst gave an SOx Index of zero (Example 42). Use of alumina as an SOx gettering agent gave an SOx Index of 5 (Example 43). Use of a La203/AI203 SO, gettering agent of this invention gave an SOx Index of 50 (Example 44), which represents a considerable improvement over the use of alumina.

TABLE IV Catalyst Mixture Described in Example SOx Index 42 0 43 5 44 50 Example 46 27.00 g (dry basis) of the cracking catalyst described in Example 22 was thoroughly mixed with 3.00 g (dry basis) of the La203/AI203 composition prepared in Example 9. This catalyst mixture was tested for its ability to reduce SOx emission according to the procedure described in Example 39. The SOx index obtained had a value of 48. This compares with an SOx index of 69 obtained for the catalyst mixture described in Example 31 which contains an oxidation catalyst. This shows that the SOx gettering agent of this invention works without the presence of an oxidation catalyst. It also shows that the presence of an oxidation catalyst increases the ability of the gettering agent to reduce SOx emissions.

Claims

1. A catalyst composition comprising: (a) a hydrocarbon cracking catalyst, and (b) a sulfur oxide gettering agent which comprises an alumina substrate coated with lanthanum oxide.

2. The composition of claim 1 wherein the said alumina substrate contains from about 5 to 50 percent by weight lanthanum oxide.

3. The composition of claim 1 or 2 wherein said alumina has a surface area of from about 45 to 450 m2/g.

4. The composition of claim 1 wherein said alumina has a surface area of about 110 to 270 m2/g and contains about 12 to 30 percent by weight lanthanum oxide.

5. The composition of any of claims 1 to 4 wherein said alumina is coated with essentially a monolayer of lanthanum oxide.

6. The composition of any of claims 1 to 5 wherein said alumina substrate is an alumina hydrate.

7. The composition of any of claims 1 to 6 wherein said alumina substrate has been calcined.

8. The composition of any of claims 1 to 6 wherein the alumina substrate has been calcined after coating with the lanthanum oxide.

9. The composition of any of claims 1 to 8 wherein the lanthanum oxide is included in a mixture of rare-earth metal oxides.

10. The composition of any of claims 1 to 9 wherein the said cracking catalyst comprises a crystalline zeolite admixed with an inorganic oxide matrix.

11. The composition of claim 10 wherein the said zeolite is selected from hydrogen and/or rare earth exchanged type X or type Y zeolite, ZSM zeolites and mixtures thereof.

12. The composition of any of claims 1 to 9 wherein the said cracking catalyst comprises a crystalline zeolite admixed with a matrix which contains clay and/or alumina hydrate and dried alumina sol.

13. The composition of any of claims 1 to 12 wherein the said catalyst composition includes from about 0.1 to 100 parts per million of a noble metal as an oxidation catalyst.

14. The composition of claim 13 wherein the said oxidation catalyst is added to said catalyst composition as noble metal impregnated on a particulate inorganic oxide.

15. The compositions of claim 13 or 14 wherein the said oxidation catalyst is selected from plantinum, palladium and mixtures thereof.

16. The compositiion of any of claims 1 to 13 wherein the said lanthanum oxide is distributed on the surface of the said alumina in combination with an oxidation catalyst selected from platinum, palladium and mixtures thereof.

17. The composition of any of claims 1 to 16 wherein the particles of said gettering agent are physically admixed with particles of said catalyst.

18. The composition of any of claims 1 to 16 wherein said gettering agent is incorporated in the particles of said catalyst.

19. The composition of any of claims 1 to 18 wherein the said catalyst composition contains from about 0.5 to 60 weight percent of said sulfur oxide gettering agent.

20. The composition of claim 1 substantially as described in any one of Examples 20,21,24-38,44 or 46.

21. A sulfur oxide gettering agent composition which comprises alumina, and lanthanum oxide distributed essentially as a mono-layer on the surface of said alumina.

22. A sulfur oxide gettering agent composition which comprises from about 5 to 50 percent by weight lanthanum oxide uniformly distributed on the surface of an alumina having a surface are of at least 45 m2/g.

23. The gettering agent of claim 22 wherein said lanthanum oxide is distributed on the surface of said alumina as a mono-layer.

24. The gettering agent of any of claims 21 to 23 wherein said alumina has a surface area of about 110 to 270 m2/g and contains about 12 to 30 percent by weight lanthanum oxide.

25. The gettering agent of any of claims 21 to 24 wherein the lanthanum oxide is included in a mixture of rare-earth metal oxides.

26. The composition of any of claims 21 to 25 formed into microspheroidal particles and having about 90% of the particles in the 20 to 105 micron range in diameter.

27. The composition of any of claims 21 to 25 formed into particles and having about 90% of the particles in the 0.5 to 20 micron range in diameter.

28. The composition of any of claims 21 to 25 formed into particles greater than one-millimeter in diameter.

29. The composition of any of claims 21 to 28 wherein the said composition includes an oxidation catalyst.

30. The composition of claim 29 wherein the said composition includes a noble metal oxidation catalyst.

31. The composition of claim 30 wherein the said oxidation catalyst is included in amounts of from about 0.1 to 1000 parts per million by weight of the said composition.

32. The composition of claim 30 or 31 wherein the said oxidation catalyst is selected from platinum, palladium and mixtures thereof.

33. The composition of claim 32 wherein said oxidation catalyst is added to said composition as platinum and/or palladium impregnated on a particulate inorganic oxide.

34. The composition of claim 32 wherein the said lanthanum oxide is distributed on the surface of said alumina in combination with an oxidation catalyst selected from platinum, palladium and mixtures thereof.

35. The composition of claim 21 substantially as described in any one of Examples 2 to 12, 14, 15 and 17 to 19.

36. A method for controlling SOx emissions which comprises: (a) including in a reaction zone of gettering agent as claimed in any of claims 21 to 35 to combine with sulfur oxides in said zone; and (b) restoring or regenerating the sulfur containing gettering agent obtained in step (a).

37. The method of claim 36 wherein an oxidation catalyst is present in said zone.

38. The method of claim 36 or 37 wherein said gettering agent is restored or regenerated by reduction and/or hydrolysis in the presence of a reducing gas and/or steam.

39. The method of any of claims 36 to 38 wherein the restored or regenerated gettering agent is recycled to the reaction zone.

40. A method for cracking hydrocarbon feedstocks which contain organic sulfur compounds comprising: (a) reacting hydrocarbon feedstocks which contain organic sulfur compounds with the catalyst composition of any of claims 1 to 20 under catalytic cracking conditions to obtain a cracked product system and a catalyst composition combined with sulfur-containing coke; (b) passing the catalyst composition to a steam stripping zone to remove the strippable hydrocarbons from the catalyst composition; (c) passing the stripped catalyst composition to a regeneration zone wherein the sulfur-containing coke is oxidized to carbon monoxide, carbon dioxide, water, and sulfur oxides, and said sulfur oxides combine with the gettering agent component of said catalyst composition to form a thermally stable sulfate or sulfate-type compound; and (d) returning the regenerated catalyst composition obtained in step (c) to the reacting step (a) and steam-stripping step (b) wherein the sulfate-containing gettering agent is reduced and hydrolyzed to produce volatile hydrogen sulfide which is recovered as a component of the cracked product stream and to restore or regenerate the gettering agent which is recycled in the process.

41. The method of claim 40 wherein the gettering agent is included in the form of a particulate additive.

42. The method of claim 41 wherein an oxidation catalyst is included in amounts required to obtain a desired level of carbon monoxide and/or sulfur oxide oxidation.

43. The method of claim 42 wherein said oxidation catalyst is selected from platinum, palladium and mixtures thereof.

44. The method of claim 42 or 43 wherein the said oxidation catalyst is added in amounts ranging from about 0.1 to 1000 parts per million by weight of noble metal.

45. The method of any of claims 40 to 44 wherein the said hydrogen sulfide is recovered from said cracked gas stream.

46. The method of claim 40 substantially as described in Example 39.