NO.sub.x reduction compositions for use in FCC processes

Abstract

Compositions comprising a component containing (i) an acidic oxide support, (ii) an alkali metal and/or alkaline earth metal or mixtures thereof, (iii) a transition metal oxide having oxygen storage capability, and (iv) a transition metal selected from Groups Ib and/or IIb of the Periodic Table provide NO.sub.x control performance in FCC processes. The acidic oxide support preferably contains silica alumina. Ceria is the preferred oxygen storage oxide. Cu and Ag are preferred Group I/IIb transition metals. The compositions are especially useful in the cracking of hydrocarbon feedstocks having above average nitrogen content.

Description

BACKGROUND OF THE INVENTION

Public policy and cost/benefit pressures have created an increasing desire to reduce the amount of polluting gases released by industrial processes. As a result, there has been a drive to find ways of decreasing pollution by modifying industrial processes.

In the petroleum refining industry, fluid catalytic cracking (FCC) of hydrocarbons is a commonly used petroleum refining method. In an FCC process, catalyst particles (inventory) are repeatedly circulated between a catalytic cracking zone and a catalyst regeneration zone. In regeneration, coke deposits (from the cracking reaction) on the catalyst particles are removed at elevated temperatures by oxidation. The removal of coke deposits restores the activity of the catalyst particles to the point where they can be reused in the cracking reaction.

While FCC processes are efficient from the point of catalyst use, the regeneration step typically results in the evolution of undesirable gases such as SO.sub.x, CO, and NO.sub.x. Various attempts have been made to limit the amounts of these gases created during the FCC regeneration step or otherwise to deal with the gases after their formation. Most typically, additives have been used either as an integral part of the FCC catalyst particles themselves or as separate admixture particles in the FCC catalyst inventory in attempts to deal with these problematic gases. For example, magnesium aluminate spinel additives are often used to prevent or minimize emission of SO.sub.x from the regenerator. Various noble metal catalysts have been used to minimize the emission of CO from the regenerator.

Unfortunately, the additives used to control CO emissions typically cause a dramatic increase (e.g., 300%) in NO.sub.x evolution from the regenerator. Some of the spinel-based (SO.sub.x reduction) additives act to lessen the amount of NO.sub.x emission, but with limited success. Thus, there remains a need for more effective NO.sub.x control additives suitable for use in FCC processes.

SUMMARY OF THE INVENTION

The invention provides compositions suitable for use in FCC processes which are capable of providing superior NO.sub.x control performance.

In one aspect, the invention provides compositions for reducing NO.sub.x emissions in FCC processes, the compositions comprising a component containing (i) an acidic oxide support, (ii) an alkali metal and/or alkaline earth metal or mixtures thereof, (iii) a transition metal oxide having oxygen storage capability, and (iv) a transition metal selected from Groups Ib and/or IIb of the Periodic Table. The acidic oxide support preferably contains silica alumina Ceria is the preferred oxygen storage oxide. Cu and Ag are preferred Group I/IIb transition metals.

In another aspect, the invention encompasses FCC processes using the NO.sub.x reduction compositions of the invention either as an integral part of the FCC catalyst particles themselves or as separate admixture particles in the FCC catalyst inventory.

These and other aspects of the invention are described in further detail below.

DETAILED DESCRIPTION OF THE INVENTION

The invention encompasses the discovery that certain classes of compositions are very effective for the reduction of NO.sub.x gas emissions in FCC processes. The NO.sub.x reduction compositions of the invention are characterized in that they comprise a component containing (i) an acidic oxide support, (ii) an alkali metal and/or alkaline earth metal or mixtures thereof, (iii) a transition metal oxide having oxygen storage capability, and (iv) a transition metal selected from Groups Ib and/or IIb of the Periodic Table.

The acidic oxide support should be of sufficient acidity for the composition to act as an effective NO.sub.x reduction additive. The support preferably contains acidic silanol or bridged hydroxyl groups. These acid groups are preferably characterized by NMR shifts in the region of -90 to -100 ppm compared to a TMS (trimethyl silane) standard. The support may be crystalline or amorphous. Preferably, the acidic oxide support contains at least some alumina. More preferably, the oxide support contains at least 50 wt.% alumina. The oxide support is preferably an oxide selected from the group consisting of alumina, silica alumina, and lanthana alumina. Amorphous silica aluminas are most preferred. Where an amorphous silica alumina support is used, the support preferably has an alumina to silica molar ratio of about 3-50:1.

The acidic oxide support further preferably has sufficient surface area to promote the NO.sub.x reduction process. Preferably, the oxide support has a surface area of at least 50 m.sup.2 /g, more preferably about 70-200 M.sup.2 /g.

The alkali and/or alkaline earth metal may be any alkali metal, alkaline earth metal or combinations thereof. The NO.sub.x reduction component preferably contains an alkali metal selected from sodium, potassium and mixtures thereof. The amount of alkali/alkaline earth metal present in the NO.sub.x reduction component of the invention is preferably about 1-10 parts by weight (measured as alkali/alkaline earth metal oxide) per 100 parts by weight of the oxide support material. While the alkali/alkaline earth metal content is expressed as the amount of corresponding oxide, preferably the alkali/alkaline metal is present in cationic form rather than as discrete oxide.

The transition metal oxide having oxygen storage capability may be any transition metal oxide having oxygen storage capability similar to that of ceria Preferably, at least a portion of the oxygen storage oxide is ceria. More preferably, the oxygen storage oxide consists essentially of ceria Other non-stoichiometric metal oxides having known oxygen storage capability may also be used. The oxygen storage oxide is preferably present as a microdispersed phase as opposed to large bulk oxide particles or ions located at exchange sites in the oxide support. The amount of the oxygen storage oxide present in the NO.sub.x reduction component may be varied considerably relative to the amount of acidic oxide support. Preferably, the NO.sub.x reduction component contains at least about 1 part by weight of oxygen storage oxide per 100 parts by weight of the oxide support material, more preferably at least about 2-50 parts by weight per 100 parts of the oxide support material.

The Group Ib and/or IIb transition metal may be any metal or combination of metals selected from those groups of the Periodic Table. Preferably, the transition metal is selected from the group consisting of Cu, Ag and mixtures thereof. The amount of transition metal present is preferably at least about 100 parts by weight (measured as metal oxide) per million parts of the oxide support material, more preferably about 0.1-5 parts by weight per 100 parts of the oxide support material.

The NO.sub.x reduction component may contain minor amounts of other materials which preferably do not adversely affect the NO.sub.x reduction function in a significant way. More preferably, however, the NO.sub.x reduction component consists essentially of items (i)-(iv) mentioned above. Where the composition of the invention is used as an additive particle for an FCC process, the NO.sub.x reduction component may be combined with fillers (e.g. clay, silica, alumina or silica alumina particles) and/or binders (e.g. silica sol, alumina sol, silica alumina sol, etc.) to form particles suitable for use in an FCC process. Preferably, any added binders or fillers used do not significantly adversely affect the performance of the NO.sub.x reduction component.

Where the NO.sub.x reduction composition is used as an additive particulate (as opposed to being integrated into the FCC catalyst particles themselves), the amount of NO.sub.x reduction component in the additive particles is preferably at least 50 wt %, more preferably at least 75 wt. %. Most preferably, the additive particles consist entirely of the NO.sub.x reduction component The additive particles are preferably of a size suitable for circulation with the catalyst inventory in an FCC process. The additive particles preferably have an average particle size of about 20-200 .mu.m. The additive particles preferably have a Davison attrition index (DI) value of about 0-45, more preferably about 0-15.

If desired, the NO.sub.x reduction composition of the invention may be integrated into the FCC catalyst particles themselves. In such case, any conventional FCC catalyst particle components may be used in combination with the NO.sub.x reduction composition of the invention. If integrated into the FCC catalyst particles, the NO.sub.x reduction composition of the invention is preferably represents at least about 0.02 wt. % of the FCC catalyst particle, more preferably about 0.1-10 wt. %.

While the invention is not limited to any particular method of manufacture, the NO.sub.x reduction component of the invention is preferably made by the following procedure:

(a) impregnate the acidic oxide porous support particles with an alkali/alkaline earth metal oxide source and an oxygen storage oxide source to achieve the desired alkali/alkaline earth metal and oxygen storage oxide content, (b) calcine the impregnated support of step (a), (c) impregnate the calcined support from step (b) with a source of Group Ib and/or IIb metal,and (d) calcine the impregnated support from step (c).

The sources of alkali/alkaline earth metal oxide and oxygen storage oxide are preferably slurries, sols and/or solutions of the metal oxides themselves or salts of the respective metals which decompose to oxides on calcination or combinations of oxides and salts. If desired, the individual constituents may be separately added to the support particles with a calcination step in between each addition. If desired, the impregnated particles are spray dried before the calcination of step (d). The calcination steps are preferably performed at about 450-750.degree. C.

The NO.sub.x reduction component may be used as a separate additive particle or as an integral part of an FCC catalyst particle. If used as an additive, the NO.sub.x reduction component may itself be formed into particles suitable for use in an FCC process. Alternatively, the NO.sub.x reduction component may be combined with binders, fillers, etc. by any conventional technique. See for example, the process described in U.S. Pat. No. 5,194,413, the disclosure of which is incorporated herein by reference.

Where the NO.sub.x reduction component of the invention is integrated into an FCC catalyst particle, preferably the component is first formed and then combined with the other constituents which make up the FCC catalyst particle. Incorporation of the NO.sub.x reduction component directly into FCC catalyst particles may be accomplished by an known technique. Example of suitable techniques for this purpose are disclosed in U.S. Pat. Nos. 3,957,689; 4,499,197; 4,542,188 and 4,458,623, the disclosures of which are incorporated herein by reference.

The compositions of the invention may be used in any conventional FCC process. Typical FCC processes are conducted reaction temperatures of 450 to 650.degree. C. with catalyst regeneration temperatures of 600 to 850.degree. C. The compositions of the invention may be used in FCC processing of any typical hydrocarbon feedstock Preferably, the compositions of the invention are used in FCC processes involving the cracking of hydrocarbon feedstocks which contain above average amounts of nitrogen, especially residual feedstocks or feedstocks having a nitrogen content of at least 0.1 wt. %. The amount of the NO.sub.x reduction component of the invention used may vary depending on the specific FCC process. Preferably, the amount of NO.sub.x reduction component used (in the circulating inventory) is about 0.1-15 wt. % based on the weight of the FCC catalyst in the circulating catalyst inventory. The presence of the compositions of the invention during the FCC process catalyst regeneration step dramatically reduces the level of NO.sub.x emitted during regeneration.

EXAMPLE 1

An amorphous silica alumina particulate support containing 6 wt. % silica was impregnated with a sodium carbonate solution, dried and calcined to achieve a 3.6 wt. % Na content measured as Na.sub.2 O based on the weight of the silica alumina. The Na-containing silica alumina particles were then impregnated with a solution of cerium nitrate and then dried to achieve a ceria content of about 1 wt. % based on the weight of the silica alumina particles. The Ce-containing composition was then impregnated with a silver nitrate solution to achieve a silver content of about 5 wt. % (oxide basis) based on the weight of the silica alumina particles. The impregnated particles were then dried and calcined at about 704.degree. C. to form a particulate composition in accordance with the invention.

EXAMPLE 2

An amorphous silica alumina particulate support containing 6 wt. % silica was impregnated with a sodium carbonate solution, dried and calcined to achieve a 6 wt. % Na content measured as Na.sub.2 O based on the weight of the silica alumina. The Na-containing silica alumina particles were then impregnated with a solution of cerium nitrate and then dried to achieve a ceria content of about 22 wt. % based on the weight of the silica alumina particles. The Ce-containing composition was then impregnated with a copper nitrate solution to achieve a copper content of about 2 wt. % (oxide basis) based on the weight of the silica alumina particles. The impregnated particles were then dried and calcined at about 704.degree. C. to form a particulate composition in accordance with the invention.

EXAMPLE 3

The 152 g of the composition of example 1 was admixed with 2908 grams of a commercial FCC catalyst (Grace Davison Orion.RTM. 842 equilibrium catalyst (ECAT)) and 10 g of a combustion promoter (Grace Davison CP-5). The admixture was then used to crack a hydrocarbon feedstock containing 0.3 wt. % nitrogen in a DCR pilot plant FCC unit The cracking was performed at a 75% conversion rate and 1000 g/hr catalyst feed rate. As a control example, the same catalyst admixture was run without the composition of example 1. The NO.sub.x emission measured from the FCC unit regenerator was 65% less when the composition of example 1 was used compared to the control example.

EXAMPLE 4

The 10 g of the composition of example 2 was admixed with 2000 grams of a commercial FCC catalyst (Grace Davison Orion.RTM. 922G ECAT) and 5 g of a combustion promoter (Grace Davison CP-5). The admixture was then used to crack a Countrymark hydrocarbon feedstock (0.13 wt. % N) in an FCC pilot plant (DCR) unit. The cracking was performed at a 75% conversion rate and 1000 g/hr catalyst feed rate. As a control example, the same catalyst admixture was run without the composition of example 2. The NO.sub.x emission measured from the FCC unit regenerator was 46% less when the composition of example 2 was used compared to the control example.

Claims

1. A NO.sub.x removal composition suitable for reducing NO.sub.x emissions during catalyst regeneration in a fluid catalytic cracking process, said composition comprising particles having a particle size of about 20-200 .mu.m and consisting essentially of (i) an acidic oxide support containing at least 50 wt. % alumina, (ii) about 1-10 parts by weight, measured as alkali metal oxide, of at least one alkali metal, (iii) at least 1 part by weight of CeO.sub.2 and (iv) about 0.01-5.0 parts by weight, measured as metal oxide, of a transition metal selected from Group Ib of the Periodic Table, all of said parts by weight being per 100 parts by weight of said acidic oxide support material.

2. The composition of claim 1 wherein said acidic oxide support is selected from the group consisting of alumina, silica alumina and lanthana alumina.

3. The composition of claim 2 said acidic oxide support is silica alumina.

4. The composition of claim 3 wherein said silica alumina is amorphous silica alumina.

5. The composition of claim 3 wherein said silica alumina has an alumina:silica mole ratio of about 3-50:1.

6. The composition of claim 1 wherein said alkali metal is selected form the group consisting of sodium, potassium, and mixtures thereof.

7. The composition of claim 1 wherein said Group Ib transition metal is selected from the group consisting of copper, silver and mixtures thereof.

8. The composition of claim 1 wherein said alkali metal is sodium.

9. A fluid cracking catalyst comprising (a) a cracking component suitable for catalyzing the cracking of hydrocarbons, and (b) a NO.sub.x reduction component consisting essentially of (i) an acidic oxide support containing at least 50 wt % alumina, (ii) about 1-10 parts by weight, measured as alkali metal oxide, of at least one alkali metal; (iii) at least 1 part by weight of a CeO.sub.2, and (iv) 0.01-5.0 parts by weight total, measured as metal oxide, of a transition metal selected from Group Ib of the Periodic Table, all of said parts by weight being per 100 parts by weight of said acidic oxide support material, said NO.sub.x reduction components comprising particles having a particle size of 20-200 .mu.m and being present in the cracking catalyst in a sufficient NO.sub.x reducing amount.

10. The cracking catalyst of claim 9 wherein said cracking catalyst comprises an admixture of component (a) and component (b).

11. The cracking catalyst of claim 9 wherein said catalyst comprises integral particles which contain both components (a) and (b).

12. The cracking catalyst of claim 9 wherein the NO.sub.x reduction component (b) comprises about 0.1 to 15 wt % of the cracking catalyst.

13. A method of reducing NO.sub.x emission during fluid cracking of a hydrocarbon feedstock into lower molecular weight components, said method comprising contacting a hydrocarbon feedstock with a cracking catalyst at elevated temperature whereby lower molecular weight hydrocarbon components are formed, said cracking catalyst comprising (a) a cracking component suitable for catalyzing the cracking of hydrocarbons, and (b) a NO.sub.x reduction component consisting essentially of (i) an acidic oxide support containing at least 50 wt. % alumina, (ii) about 1-10 parts by weight, measured as alkali metal oxide, of at least one alkali metal; (iii) at least 1 part by weight of a CeO.sub.2, and (iv) 0.01-5.0 parts by weight total, measured as metal oxide, of a transition metal selected from Group Ib of the Periodic Table, all of said parts by weight being per 100 parts by weight of said acidic oxide support material, said NO.sub.x reduction components comprising particles having a particle size of 20-200 .mu.m and being present in the cracking catalyst in a sufficient NO.sub.x reducing amount.

14. The method of claim 13 wherein said cracking catalyst is fluidized during contacting said hydrocarbon feedstock.

15. The method of claim 14 further comprising recovering used cracking catalyst from said contacting step and treating said used catalyst under conditions to regenerate said catalyst.

16. The method of claim 13 wherein said hydrocarbon feedstock contains at least 0.1 wt % nitrogen.