Mineral oils: processes and products – Chemical conversion of hydrocarbons – Cracking
Reexamination Certificate
2000-07-20
2001-08-28
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Cracking
C208S120150, C208S113000, C502S304000, C502S341000, C502S344000, C502S345000, C502S346000, C502S347000, C502S348000, C423S239100, C423S247000
Reexamination Certificate
active
06280607
ABSTRACT:
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
x
, CO, and NO
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
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
x
evolution from the regenerator. Some of the spinel-based (SO
x
reduction) additives act to lessen the amount of NO
x
emission, but with limited success. Thus, there remains a need for more effective NO
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
x
control performance.
In one aspect, the invention provides compositions for reducing NO
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
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
x
gas emissions in FCC processes. The NO
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
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
x
reduction process. Preferably, the oxide support has a surface area of at least 50 m
2
/g, more preferably about 70-200 m
2
/g.
The alkali and/or alkaline earth metal may be any alkali metal, alkaline earth metal or combinations thereof. The NO
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
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
x
reduction component may be varied considerably relative to the amount of acidic oxide support. Preferably, the NO
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
x
reduction component may contain minor amounts of other materials which preferably do not adversely affect the NO
x
reduction function in a significant way. More preferably, however, the NO
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
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
x
reduction component.
Where the NO
x
reduction composition is used as an additive particulate (as opposed to being integrated into the FCC catalyst particles themselves), the amount of NO
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
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 &mgr;m. T
Barbato-Grauso Mary Jane A.
Peters Alan W.
Rakiewicz Edward F.
Rudesill John A.
Weatherbee Gordon Dean
Artale Beverly J.
Griffin Walter D.
W R Grace & Co.-Conn.
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