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Attorney Or Agent: Cross; Charles A.Artale; Beverly J.
Other References: Venuto and Habib, Fluid Catalytic Cracking with Zeolite Catalysts, Marcel Dekker, New York 1979, ISBN 0-8247-6870-1, pp. 32-37..
Richard F. Wormsbecher Alan W. Peters, and James M. Maselli, "Vanadium Poisoning of Cracking Catalysts: Mechanism of Poisoning and Design of Vanadium Tolerant Catalyst System", Journal of Catalyst, vol. 100, pp. 130-137 (1986)..
Occelii, M.L., "Metal Resistant Fluid Cracking Catalysts", ACS Symposium Series, Ch 21, pp. 343-362 (1990)..
"Shape Selective Catalysis in Industrial Applications", Chen et al. Marcel Dekker Inc., New York 1969, ISBN 0-8247-7856-1, pp. 7-38..
J. Catalysis 67, pp. 218-222 (1981) by Frilette et al..
Stud. Surf. Catal. 37, pp. 13-27 (1987)..
Journal of Catalysis, vol. 4, pp. 527-529 (1965); vol. 6, pp. 278-287 (1966); and vol. 61, pp. 390-396 (1980)..
Scherzer, "Octane Enhancing Zeolitic FCC Catalysts", Marcel Dekker, New York, 1990, ISBN 0-8247-8399-9, pp. 165-182..
Intercat, Refining Developments, "Additives Improve FCC Process", Hydrocarbon Processing, Nov. 1991, pp. 59-66, by A.S. Krisha, C.R. Hsieh, A.R. English, T.A. Pecararo and C.W. Kuehler, Cheveron Research and Technology Company, Richmond, CA..
"Fluid Catalytic Cracking Handbook", Sadeghbeigi, Gulf Publishing, Houston, Texas, ISBN 0-88415-290-1, Ch. 3, pp. 79 and 88-91..
Abstract: The sulfur content of liquid cracking products, especially the cracked gasoline, of the catalytic cracking process is reduced by the use of a sulfur reduction catalyst composition comprising a porous molecular sieve which contains a metal in an oxidation state above zero within the interior of the pore structure of the sieve as well as a cerium component which enhances the stability and sulfur reduction activity of the catalyst. The molecular sieve is normally a faujasite such as USY. The primary sulfur reduction component is normally a metal of Period 3 of the Periodic Table, preferably vanadium. The sulfur reduction catalyst may be used in the form of a separate particle additive or as a component of an integrated cracking/sulfur reduction catalyst.
1. A method of reducing the sulfur content of a liquid catalytically cracked petroleum fraction, which comprises catalytically cracking a petroleum feed fraction containing organosulfurcompounds at elevated temperature in the presence of an equilibrium cracking catalyst and a product sulfur reduction catalyst which comprises a porous molecular sieve having (i) a first metal component which is within the interior pore structure of themolecular sieve and which comprises vanadium in an oxidation state greater than zero and (ii) a second metal component comprising cerium which is within the interior pore structure of the molecular sieve, to produce liquid cracking products of reducedsulfur content.
2. A method according to claim 1 in which the product sulfur reduction catalyst comprises a large pore size or intermediate pore size zeolite as the molecular sieve component.
3. A method according to claim 2 in which the large pore size zeolite comprises a faujasite zeolite.
4. A method according to claim 2 in which the large pore size zeolite comprises zeolite USY.
5. A method according to claim 1 in which the second metal component is present in an amount from 0.5 to 10 weight percent of the catalytic composition.
6. A method according to claim 1 in which the product sulfur reduction catalyst comprises a USY zeolite having a UCS of from 2.420 to 2.455 nm; and a bulk silica:alumina ratio of at least 5.0 as the molecular sieve component.
8. In a fluid catalytic cracking process in which a heavy hydrocarbon feed comprising organosulfur compounds is catalytically cracked to lighter products by contact in a cyclic catalyst recirculation cracking process with a circulatingfluidizable catalytic cracking catalyst inventory consisting of particles having a size ranging from about 20 to about 100 microns, comprising: (i) catalytically cracking the feed in a catalytic cracking zone operating at catalytic cracking conditions bycontacting feed with a source of an equilibrium cracking catalyst to produce a cracking zone effluent comprising cracked products and spent catalyst containing coke and strippable hydrocarbons; (ii) discharging and separating the effluent mixture into acracked product rich vapor phase and a solids rich phase comprising spent catalyst; (iii) removing the vapor phase as a product and fractionating the vapor to form liquid cracking products including gasoline; (iv) stripping the solids rich spentcatalyst phase to remove occluded hydrocarbons from the catalyst; (v) transporting stripped catalyst from the stripper to a catalyst regenerator; (vi) regenerating stripped catalyst by contact with oxygen containing gas to produce regenerated catalyst; and (vii) recycling the regenerated catalyst to the cracking zone to contact further quantities of heavy hydrocarbon feed, the improvement which comprises reducing the sulfur content of the gasoline portion of the liquid cracking products, bycatalytically cracking the feed fraction at elevated temperature in the presence of a product sulfur reduction catalyst which comprises a porous molecular sieve having (i) vanadium which is within the interior, pore structure of the molecular sieve andwhich is in an oxidation state greater than zero and (ii) a second metal component which is within the interior pore structure of the molecular sieve and which comprises cerium.
10. A method according to claim 8 in which the product sulfur reduction catalyst comprises a large pore size or intermediate pore size zeolite as the molecular sieve component and cerium as the second metal component.
11. A method according to claim 10 in which the large pore size zeolite of the product sulfur reduction catalyst comprises zeolite USY.
In application Ser. No. 09/144,607, filed 31 Aug. 1998, we have described catalytic materials for use in the catalytic cracking process which are capable of reducing the sulfur content of the liquid products of the cracking process. Thesesulfur reduction catalysts comprise, in addition to a porous molecular sieve component, a metal in an oxidation state above zero within the interior of the pore structure of the sieve. The molecular sieve is in most cases a zeolite and it may be azeolite having characteristics consistent with the large pore zeolites such as zeolite beta or zeolite USY or with the intermediate pore size zeolites such as ZSM-5. Non-zeolitic molecular sieves such as MeAPO-5, MeAPSO-5, as well as the mesoporouscrystalline materials such as MCM-41 may be used as the sieve component of the catalyst. Metals such as vanadium, zinc, iron, cobalt, and gallium were found to be effective for the reduction of sulfur in the gasoline, with vanadium being the preferredmetal. When used as a separate particle additive catalyst, these materials are used in combination with the active catalytic cracking catalyst (normally a faujasite such as zeolite Y, especially as zeolite USY) to process hydrocarbon feedstocks in thefluid catalytic cracking (FCC) unit to produce low-sulfur. Since the sieve component of the sulfur reduction catalyst may itself be an active cracking catalyst, for instance, zeolite USY, it is also possible to use the sulfur reduction catalyst in theform of an integrated cracking/sulfur reduction catalyst system, for example, comprising USY as the active cracking component and the sieve component of the sulfur reduction system together with added matrix material such as silica, clay and the metal,e.g. vanadium, which provides the sulfur reduction functionality.
Another consideration in the manufacture of FCC catalysts has been catalyst stability, especially hydrothermal stability since cracking catalysts are exposed during use to repeated cycles of reduction (in the cracking step) followed by strippingwith steam and then by oxidative regeneration which produces large amounts of steam from the combustion of the coke, a carbon-rich hydrocarbon, which is deposited on the catalyst particles during the cracking portion of the cycle. Early in thedevelopment of zeolitic cracking catalysts it was found that a low sodium content was required not only for optimum cracking activity but also for stability and that the rare earths such as cerium and lanthanum conferred greater hydrothermal stability. See, for example, Fluid Catalytic Cracking with Zeolite Catalysts, Venuto et al., Marcel Dekker, New York, 1979, ISBN 0-8247-6870-1.
We have now developed catalytic materials for use in the catalytic cracking process which are capable of improving the reduction in the sulfur content of the liquid products of the cracking process including, in particular, the gasoline andmiddle distillate cracking fractions. The present sulfur reduction catalyst are similar to the ones described in application Ser. No. 09/144,607 in that a metal component in an oxidation state above zero is present in the pore structure of a molecularsieve component of the catalyst composition, with preference again being given to vanadium. In the present case, however, the composition also comprises cerium. We have found that the presence of the cerium component not only enhances the stability ofthe catalyst, as compared to the catalysts which contain only vanadium or another metal component (other than rare earth) but that it also increases the sulfur reduction activity. This is surprising since cerium in itself has no sulfur reductionactivity.
According to the present invention, the sulfur removal catalyst composition comprises a porous molecular sieve which contains (i) a metal in an oxidation state above zero within the interior of the pore structure of the sieve and (ii) a ceriumcomponent. The molecular sieve is in most cases a zeolite and it may be a zeolite having characteristics consistent with the large pore zeolites such as zeolite beta or zeolite USY or with the intermediate pore size zeolites such as ZSM-5. Non-zeoliticmolecular sieves such as MeAPO-5, MeAPSO-5, as well as the mesoporous crystalline materials such as MCM41 may be used as the sieve component of the catalyst. Metals such as vanadium, zinc, iron, cobalt, and gallium are effective. If the selected sievematerial has sufficient cracking activity, it may be used as the active catalytic cracking catalyst component (normally a faujasite such as zeolite Y) or, alternatively, it may be used in addition to the active cracking component, whether or not it hasany cracking activity of itself. The present compositions are useful to process hydrocarbon feedstocks in fluid catalytic cracking (FCC) units to produce low-sulfur gasoline and other liquid products, for example, light cycle oil that can be used as alow sulfur diesel blend component or as heating oil.
According to the present invention, the sulfur removal catalyst comprises a porous molecular sieve which contains a metal in an oxidation state above zero within the interior of the pore structure of the sieve. The molecular sieve is in mostcases a zeolite and it may be a zeolite having characteristics consistent with the large pore zeolites such as zeolkite Y, preferably zeolite USY, or zeolite beta or with the intermediate pore size zeolites such as ZSM-5, with the former class beingpreferred.
Exemplary non-zeolitic sieve materials which may provide suitable support components for the metal component of the present sulfur reduction catalysts include silicates (such as the metallosilicates and titanosilicates) of varying silica-aluminaratios, metalloaluminates (such as germaniumaluminates), metallophosphates, aluminophosphates such as the silico- and metalloaluminophosphates referred to as metal integrated aluminophosphates (MeAPO and ELAPO), metal integrated silicoaluminophosphates(MeAPSO and ELAPSO), silicoaluminophosphates (SAPO), gallogermanates and combinations of these. A discussion on the structural relationships of SAPO's, AIPO's, MeAPO's, and MeAPSO's may be found in a number of resources including Stud. Surf. Catal. 37 13-27 (1987). The AIPO's contain aluminum and phosphorus, whilst in the SAPO's some of the phosphorus and/or some of both phosphorus and aluminum is replaced by silicon. In the MeAPO's various metals are present, such as Li, B, Be, Mg, Ti, Mn, Fe,Co, An, Ga, Ge, and As, in addition to aluminum and phosphorus, whilst the MeAPSO's additionally contain silicon. The negative charge of the Me.sub.a Al.sub.b P.sub.c Si.sub.d O.sub.e lattice is compensated by cations, where Me is magnesium, manganese,cobalt, iron and/or zinc. Me.sub.x APSOs are described in U.S. Pat. No. 4,793,984. SAPO-type sieve materials are described in U.S. Pat. No. 4,440,871; MeAPO type catalysts are described in U.S. Pat. Nos. 4,544,143 and 4,567,029; ELAPO catalystsare described in U.S. Pat. No. 4,500,651, and ELAPSO catalysts are described in European Patent Application 159,624. Specific molecular sieves are described, for example, in the following patents: MgAPSO or MAPSO-U.S. Pat. No. 4,758,419. MnAPSO-U.S. Pat. No. 4,686,092; CoAPSO-U.S. Pat. No. 4,744,970; FeAPSO-U.S. Pat. No. 4,683,217 and ZnAPSO U.S. Pat. No. 4,935,216. Specific silicoaluminophosphates which may be used include SAPO-11, SAPO-17, SAPO-34, SAPO-37; other specificsieve materials include MeAPO-5, MeAPSO-5.
Two metal components are incorporated into the molecular sieve support material to make up the present catalytic compositions. One component is cerium which is thought to be present in the form of cations within the pore structure of the sieve. The other metal component can be regarded as the primary sulfur reduction component although the manner in which it effects sulfur reduction is not clear, as discussed in application Ser. No. 09/144,607, to which reference is made for a description ofsulfur reduction catalyst compositions containing vanadium and other metal components effective for this purpose. For convenience this component of the composition will be referred to in this application as the primary sulfur reduction component. Inorder to be effective, this metal (or metals) should be present inside the pore structure of the sieve component. Metal-containing zeolites and other molecular sieves can be prepared by (1) post-addition of metals to the sieve or to a catalystcontaining the sieve(s), (2) synthesis of the sieve(s) containing metal atoms in the framework structure, and by (3) synthesis of the sieve(s) with trapped, bulky metal ions in the zeolite pores. Following addition of the metal component, washing toremove unbound ionic species and drying and calcination should be performed. These techniques are all known in themselves. Post-addition of the metal ions is preferred for simplicity and economy, permitting available sieve materials to be converted touse for the present additives. A wide variety of post-addition methods of metals can be used to produce a catalyst of our invention, for example, aqueous exchange of metal ions, solid-state exchange using metal halide salt(s), impregnation with a metalsalt solution, and vapor deposition of metals. In each case, however, it is important to carry out the metal(s) addition so that the metal component enters the pore structure of the sieve component.
Because of the concern for excessive coke and hydrogen make during the cracking process, the metals for incorporation into the additives should not exhibit hydrogenation activity to a marked degree. For this reason, the noble metals such asplatinum and palladium which possess strong hydrogenation-dehydrogenation functionality are not desirable. Base metals and combinations of base metals with strong hydrogenation functionality such as nickel, molybdenum, nickel-tungsten, cobalt-molybdenumand nickel-molybdenum are not desirable for the same reason. The preferred base metals are the metals of Period 3, Groups 5, 8, 9, 12, (IUPAC classification, previously Groups 2B, 5B and 8B) of the Periodic Table. Vanadium, zinc, iron, cobalt, andgallium are effective with vanadium being the preferred metal component. It is surprising that vanadium can be used in this way in an FCC catalyst composition since vanadium is normally thought to have a very serious effect on zeolite cracking catalystsand much effort has been expended in developing vanadium suppressers. See, for example, Wormsbecher et al, Vanadium Poisoning of Cracking Catalysts: Mechanism of Poisoning and Design of Vanadium Tolerant Catalyst System, J. Catalysis 100, 130-137(1986). It is believed that the location of the vanadium inside the pore structure of the sieve immobilizes the vanadium and prevents it from becoming vanadic acid species which can combine deleteriously with the sieve component; in any event, thepresent zeolite-based sulfur reduction catalysts containing vanadium as the metal component have undergone repeated cycling between reductive and oxidative/steaming conditions representative of the FCC cycle while retaining the characteristic zeolitestructure, indicating a different environment for the metal.
Vanadium is particularly suitable for gasoline sulfur reduction when supported on zeolite USY. The yield structure of the V/USY sulfur reduction catalyst is particularly interesting. While other zeolites, after metals addition, demonstrategasoline sulfur reduction, they tend to convert gasoline to C.sub.3 and C.sub.4 gas. Even though much of the converted C.sub.3.dbd. and C.sub.4.dbd. can be alkylated and re-blended back to the gasoline pool, the high C.sub.4 -- wet gas yield may be aconcern since many refineries are limited by their wet gas compressor capacity. The metal-containing USY has similar yield structure to current FCC catalysts; this advantage would allow the V/USY zeolite content in a catalyst blend to be adjusted to atarget desulfurization level without limitation from FCC unit constraints. The vanadium on Y zeolite catalyst, with the zeolite represented by USY, is therefore a particularly favorable combination for gasoline sulfur reduction in FCC. The USY which hasbeen found to give particularly good results is a USY with low unit cell size in the range from 2.420 to 2.450 nm, preferably 2.435 to 2.450 nm (following treatment) and a correspondingly low alpha value. Combinations of base metals such asvanadium/zinc as the primary sulfur reduction component may also be favorable in terms of overall sulfur reduction.
The amount of the primary sulfur reduction metal component in the sulfur reduction catalyst is normally from 0.1 to 10 weight percent, typically 0.25 to 5 weight percent, (as metal, relative to weight of sieve component) but amounts outside thisrange, for example, up to 10 weight percent may still be found to give some sulfur removal effect. When the sieve is matrixed, the amount of the primary sulfur reduction metal component expressed relative to the total weight of the catalyst compositionwill, for practical purposes of formulation, typically extend from 0.05 to 5, more typically from 0.1 to 3 weight percent of the entire catalyst.
The second metal component of the sulfur reduction catalyst composition comprises cerium which is present within the pore structure of the molecular sieve and is thought to be present in the form of cations exchanged onto the exchangeable sitespresent on the sieve component. The cerium component significantly not only improves the catalyst stability in the presence of vanadium (or other primary sulfur reduction metal component) but also enhances the sulfur reduction activity of the catalyst. For example, higher cracking activity can be achieved with a Ce/V/USY catalyst compared to a V/USY catalyst, while comparable gasoline sulfur reduction is obtained. In application Ser. No. 09/______, filed concurrently with this application (Mobil IPCase 10101-1, PL 98-75), we show that other rare earths are effective for improving catalyst stability when vanadium is present and that combinations of rare earth with cerium are capable of improving sulfur reduction.
The amount of cerium is typically from 0.1 to 10 wt. percent of the catalyst composition, in most cases from 0.25 to 5 wt. percent. Relative to the weight of the sieve, the amount of the rare earth will normally be from about 0.2 to 20 weightpercent and in most cases from 0.5 to 10 weight percent of the sieve, depending on the sieve:matrix ratio.
The rare earth component can suitably be incorporated into the molecular sieve component by exchange onto the sieve, either in the form of the unmatrixed crystal or of the matrixed catalyst. When the composition is being formulated with thepreferred USY zeolite sieve, a very effective manner of incorporation is to add the rare earth ions to the USY sieve (typically 2.445-2.465 nm unit cell size) followed by additional steam calcination to lower the unit cell size of the USY to a valuetypically in the range of 2.420 to 2.450, preferably 2.430 to 2.445 nm., after which the primary metal component may be added if not already present. The USY should have a low alkali metal (mainly sodium) content for stability as well as forsatisfactory cracking activity; this will normally be secured by the ammonium exchange made during the ultrastabilization process to a desirable low sodium level of not more than 1 weight percent, preferably not more than 0.5 weight percent, on thesieve.
The metal components are incorporated into the catalyst composition in a way which ensures that they enter the interior pore structure of the sieve. The metals may be incorporated directly into the crystal or into the matrixed catalyst. Whenusing the preferred USY zeolite as the sieve component, this can suitably be done as described above, by recalcining a USY cracking catalyst containing the cerium component to ensure low unit cell size and then incorporating the metal, e.g. vanadium, byion exchange or by impregnation under conditions which permit cation exchange to take place so that the metal ion is immobilized in the pore structure of the zeolite. Alternatively, the primary sulfur reduction component and the cerium component can beincorporated into the sieve component, e.g. USY zeolite or ZSM-5 crystal, after any necessary calcination to remove organics from the synthesis after which the metal-containing component can be formulated into the finished catalyst composition by theaddition of the cracking and matrix components and the formulation spray dried to form the final catalyst.
The alternative to the use of the separate particle additive is to use the sulfur reduction catalyst incorporated into the cracking catalyst to form an integrated FCC cracking/gasoline sulfur reduction catalyst. If the sulfur reduction metalcomponents are used in combination with a sieve other than the active cracking component, for example, on ZSM-5 or zeolite beta, when the main active cracking component is USY, the amount of the sulfur reduction components (sieve plus metals) willtypically be up to 25 weight percent of the entire catalyst or less, corresponding to the amounts in which it may be used as a separate particle additive, as described above.
Other catalytically active components may be present in the circulating inventory of catalytic material in addition to the cracking catalyst and the sulfur removal additive. Examples of such other materials include the octane enhancing catalystsbased on zeolite ZSM-5, CO combustion promoters based on a supported noble metal such as platinum, stack gas desulfurization additives such as DESOX.TM. (magnesium aluminum spinel), vanadium traps and bottom cracking additives, such as those describedin Krishna, Sadeghbeigi, op cit. and Scherzer, Octane Enhancing Zeolitic FCC Catalysts, Marcel Dekker, New York, 1990, ISBN 0-8247-8399-9. These other components may be used in their conventional amounts.
Very significant reductions in gasoline sulfur can be achieved by the use of the present catalysts, in some cases up to about 60% relative to the base case using a conventional cracking catalyst, at constant conversion, using the preferred formof the catalyst described above. Gasoline sulfur reduction of 25% is readily achievable with many of the additives according to the invention, as shown by the Examples below. The extent of sulfur reduction may depend on the original organic sulfurcontent of the cracking feed, with the greatest reductions achieved with the higher sulfur feeds. The metals content of the equilibrium catalyst in the unit may also affect the degree of desulfurization achieved, with a low metals content, especiallyvanadium content, on the equilibrium catalyst favoring greater desulfurization. Desulfurization will be very effective with E-catalyst vanadium contents below 1,000 ppm although the present catalyst remain effective even at much higher vanadiumcontents. Sulfur reduction may be effective not only to improve product quality but also to increase product yield in cases where the refinery cracked gasoline end point has been limited by the sulfur content of the heavy gasoline fraction; by providingan effective and economical way to reduce the sulfur content of the heavy gasoline fraction, the gasoline end point may be extended without the need to resort to expensive hydrotreating, with a consequent favorable effect on refinery economics. Removalof the various thiophene derivatives which are refractory to removal by hydrotreating under less severe conditions is also desirable if subsequent hydrotreatment is contemplated.
A V/USY catalyst, Catalyst A, was prepared using a commercial H-form USY (crystal) with a bulk silica-to-alumina ratio of 5.4 and 2.435 nm unit cell size. A fluid catalyst was prepared by spray drying aqueous slurry containing 40 wt % of the USYcrystals, 25 wt % silica, 5 wt % alumina, and 30 wt % kaolin clay. The spray-dried catalyst was calcined at 540.degree. C. (1000.degree. F.) for 3 hours. The resulting H-form USY catalyst was impregnated with a vanadium oxalate solution to target 0.4wt % V by incipient wetness impregnation. The impregnated V/USY catalyst was further air calcined at 540.degree. C. (1000.degree. F.) for 3 hours. The final catalyst contains 0.39% V.
A Ce+V/USY catalyst, Catalyst B, was prepared from the same, spray-dried H-form USY catalyst intermediate as Catalyst A. The H-form USY catalyst was impregnated with a solution of Ce(NO.sub.3).sub.3 to target 1.5 wt % Ce loading using anincipient wetness impregnation method. Resulting Ce/USY catalyst was air calcined at 540.degree. C. (1000.degree. F.) for 3 hours followed by steaming at 540.degree. C. (1000.degree. F.) for 3 hours. Then the catalyst was impregnated with avanadium oxalate solution to target 0.4 wt % V by incipient wetness impregnation. The impregnated Ce+V/USY catalyst was further air calcined at 540.degree. C. (1000.degree. F.) for 3 hours. The final catalyst contains 1.4% Ce and 0.43% V.
All samples in Catalyst Series 2 were prepared from a single source of spray dried material, consisting of 50% USY, 21% silica sol and 29% clay. The starting USY had a bulk silica-to-alumina ratio of 5.4 and 2.435 nm unit cell size. The spraydried catalyst was slurried with a solution of (NH.sub.4).sub.2 SO.sub.4 and NH.sub.4 OH at pH of 6 to remove Na.sup.+, followed by washing with water and air calcination at 650.degree. C. (1200.degree. F.) for 2 hours.
A V/USY catalyst, Catalyst C, was prepared using the above H-form USY catalyst. The H-form USY catalyst was impregnated with a vanadium oxalate solution to target 0.5 wt % V by incipient wetness impregnation. The impregnated V/USY catalyst wasfurther air calcined at 650.degree. C. (1200.degree. F.) for 2 hours. The final catalyst contains 0.53% V.
A Ce+V/USY catalyst, Catalyst D, was prepared from the above H-form USY catalyst. The H-form USY catalyst was exchanged with a solution of CeCl.sub.3 to target 0.75 wt % Ce loading. Resulting Ce/USY catalyst was air calcined and impregnatedwith a vanadium oxalate solution to target 0.5 wt % V by incipient wetness impregnation. The impregnated Ce+V/USY catalyst was further air calcined. The final catalyst contains 0.72% Ce and 0.52% V.
A Ce+V/USY catalyst, Catalyst E, was prepared from the above H-form USY catalyst by an exchange with a solution of CeCl.sub.3 to target 3 wt % Ce loading. Resulting Ce/USY catalyst was air calcined and impregnated with a vanadium oxalatesolution to target 0.5 wt % V by incipient wetness impregnation. The impregnated Ce+V/USY catalyst was further air calcined. The final catalyst contains 1.5% Ce and 0.53% V.
A Ce+V/USY catalyst, Catalyst F, was prepared from the above H-form USY catalyst by an incipient wetness impregnation with a solution of CeCl.sub.3 to target 1.5 wt % Ce loading. Resulting Ce/USY catalyst was air calcined and impregnated with avanadium oxalate solution to target 0.5 wt % V by incipient wetness impregnation. The impregnated Ce+V/USY catalyst was further air calcined. The final catalyst contains 1.5% Ce and 0.53% V.
These catalysts were then steamed deactivated, to simulate catalyst deactivation in an FCC unit, in a fluidized bed steamer at 770.degree. C. (1420.degree. F.) for 20 hours using 50% steam and 50% gas. The gas stream was changed from air,N.sub.2, propylene, and to N.sub.2 for every ten minutes, then circled back air to simulate the coking/regeneration cycle of a FCC unit (cyclic steaming). Two samples of deactivated catalysts were generated: the steam deactivation cycle was ended withair-burn (ending-oxidation) for one batch of catalysts, and the other ended with propylene (ending-reduction). The coke content of the "ending-reduction" catalyst is less than 0.05% C. The physical properties of the calcined and steam deactivatedcatalysts are summarized in Table 2.
All samples in Catalyst Series 3 were prepared from a single source of spray dried material, consisting of 40% USY, 30% colloidal silica sol, and 30% clay. The starting H-form USY had a bulk silica-to-alumina ratio of 5.4 and 2.435 nm unit cellsize. The spray-dried catalyst was air calcined at 540.degree. C. (1000.degree. F.) for 3 hours.
A Ce/USY catalyst, Catalyst G, was prepared using the above H-form USY catalyst. The H-form USY catalyst was impregnated with a solution of Ce(NO.sub.3).sub.3 to target 1.5 wt % Ce loading using an incipient wetness impregnation method. Resulting Ce/USY catalyst was air calcined at 540.degree. C. (1000.degree. F.) followed by steaming at 540.degree. C. (1000.degree. F.) for 3 hours.
A Ce+V/USY catalyst, Catalyst H, was prepared from Catalyst G. The Ce/USY catalyst was impregnated with a vanadium oxalate solution to target 0.5 wt % V by incipient wetness impregnation. The impregnated Ce+V/USY catalyst was dried and aircalcined at 540.degree. C. (1000.degree. F.) for 3 hours. The final catalyst contains 1.4% Ce and 0.49% V.
A Ce+V/USY catalyst, Catalyst I, was prepared from Catalyst G by an exchange with a solution of VOSO4 at pH .about.3 to target 0.5 wt % V loading. Resulting Ce+V/USY catalyst was dried and air calcined at 540.degree. C. (1000.degree. F.) for 3hours. The final catalyst contains 0.9% Ce and 0.47% V. Physical properties of calcined catalysts are summarized in Table 3.
The V and Ce+V USY catalysts from Example 1 were steam deactivated in a fluidized bed steamer at 770.degree. C. (1420.degree. F.) for 20 hours using 50% steam and 50% gas. The gas stream was changed from air, N.sub.2, propylene, and to N.sub.2for every ten minutes, then circled back air to simulate coking/regeneration cycle of a FCC unit (cyclic steaming). The steam deactivation cycle was ended with air-burn (ending-oxidation). Twenty-five weight percent of steamed additive catalysts wereblended with an equilibrium catalyst from an FCC unit. The equilibrium catalyst has very low metals level (120 ppm V and 60 ppm Ni).
The blended catalysts were tested for gas oil cracking activity and selectivity using an ASTM microactivity test (ASTM procedure D-3907). The vacuum gas oil feed stock properties are shown in Table 4 below. A range of conversions was scanned byvarying the catalyst-to-oil ratios and reactions were run at 527.degree. C. (980.degree. F.). Gasoline range product from each material balance was analyzed with a sulfur GC (AED) to determine the gasoline S concentration. To reduce experimentalerrors in S concentration associated with fluctuations in distillation cut point of gasoline, we quantitated S species ranging from thiophene to C.sub.4 -thiophenes in syncrude (excluding benzothiophene and higher boiling S species) and the sum wasdefined as "cut-gasoline S."
Performances of the catalysts are summarized in Table 5, where the product selectivity was interpolated to a constant conversion, 7 wt % conversion of feed to 220.degree. C.-(430.degree. F.-) material.
Table 5 compares the FCC performances of V/USY and Ce+V/USY/Silica-Alumina-Clay catalysts each blended with an equilibrium FCC catalyst (ECat).
Compared to the ECat base case, the addition of V/USY and Ce+V/USY catalyst changes the overall product yield structure only slightly. Yield changes in C4- gas, gasoline, light cycle oil, and heavy fuel oil are all small. Moderate increases inhydrogen and coke yields were observed. While the product yield changes were small, the V/USY and Ce+V/USY catalysts changed the gasoline S concentration substantially. When 25 wt % of Catalyst A (10 wt % V/USY zeolite addition, reference catalyst) wasblended with an equilibrium FCC catalyst, 29% reduction in gasoline sulfur concentration was achieved. In comparison, Ce+V/USY catalyst (Catalyst B) gave 56% reduction in gasoline S. Addition of Ce to the V/USY catalyst reduced the gasoline S content byadditional 27%, i.e., 93% improvement over the V/USY reference catalyst. Both catalysts have comparable vanadium loadings (0.39% vs. 0.43% V). In light of the fact that Ce by itself does not have any gasoline sulfur reduction activity (see below inExample 7), these results are quite unexpected and dearly demonstrate the benefits of cerium addition.
The performances of V and Ce+V catalysts from Example 2 are summarized in this example. The Series 2 catalysts were steam deactivated as described above by cyclic steaming (ending-reduction), then blended with an equilibrium catalyst from an FCCunit in a 25:75 weight ratio. The equilibrium catalyst has very low metals level (120 ppm V and 60 ppm Ni). The results are summarized in Table 6.
Table 6 compares FCC performances of V/USY and Ce+V/USY/Silica-Sol additive catalysts after cyclic steam deactivation (ending-reduction).
The deactivated additive catalysts were each blended with an equilibrium FCC catalyst. Compared to the ECat base case, addition of the V/USY and Ce+V/USY catalysts made very little changes in the overall product yield structure. The yields ofhydrogen, C4- gas, gasoline, light cycle oil, heavy fuel oil and coke were changed by less than 0.2 wt % each. Additions of the V/USY and Ce+V/USY catalysts changed the gasoline S concentration to different extents. When 25 wt % of Catalyst C(V/USY--reference catalyst) was blended with the equilibrium FCC catalyst, 5.2% reduction in gasoline sulfur concentration was achieved. For comparison, Ce+V/USY catalysts (Catalysts E and F) gave 17.4% reduction in gasoline S, respectively. Additionof Ce to the V/USY catalyst reduced the gasoline S content by additional 12.3%, i.e., 237% improvement over the V/USY reference catalyst.
The performances of the V and Ce+V catalysts from Example 2 after cyclic steam deactivation are summarized in this example. The catalysts of Example 2 were deactivated by cyclic steaming as described above (ending-oxidation) and were thenblended with an equilibrium catalyst from an FCC unit in 25:75 weight ratio. The equilibrium catalyst has very low metals level (120 ppm V and 60 ppm Ni). The results are summarized in Table 7.
Table 7 compares the FCC performances of V/USY and Ce+V/USY/Silica-Sol additive catalysts after cyclic steam deactivation (ending-oxidation).
Compared to the ECat base case, addition of V/USY and Ce+V/USY catalyst made slight changes in the overall product yield structure. There were moderate increases in hydrogen and coke yields. Also a small changes in C4- gas yield gasoline, lightcycle oil and heavy fuel oil were observed. Addition of the V/USY and Ce+V/USY catalysts changed the gasoline S concentration substantially. When 25 wt % of Catalyst C (V/USY--reference catalyst) was blended with an equilibrium FCC catalyst, 51.1%reduction in gasoline sulfur concentration was achieved. In comparison, the Ce+V/USY catalysts (Catalysts D and E) gave 58.1% and 61.3% reduction in gasoline S, respectively. Addition of Ce to the V/USY catalyst reduced the gasoline S content byadditional 7.0-10.2%, i.e., up to 20% improvement over the V/USY reference catalyst.
The product yields data of the V/USY and Ce+V/USY catalysts indicate that the yield changes from the ECat is due to addition of vanadium to the USY catalyst The product yields of V/USY catalyst is comparable to those of Ce+V/USY catalysts exceptthe gasoline S level. These results suggest that Ce increases the gasoline sulfur reduction activity of the V/USY additive catalyst with little effect on product yields.
Performances of the Ce and Ce+V catalysts from Example 3 after cyclic steaming deactivation (ending-reduction) as described above, are summarized in this example. The deactivated catalysts were blended with an equilibrium catalyst from an FCCunit in 25:75 weight ratio. The equilibrium catalyst has very low metals level (120 ppm V and 60 ppm Ni). The results are summarized in Table 8.
Table 8 compares FCC performances of Ce/USY and Ce+V/USY/Silica-clay additive catalysts after cyclic steam deactivation (ending-reduction).

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