Mineral oils: processes and products – Chemical conversion of hydrocarbons – Cracking
Reexamination Certificate
1998-04-29
2003-01-21
Yildirim, Bekir L. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Cracking
C208S152000, C208S164000, C208SDIG001
Reexamination Certificate
active
06508930
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to the use of fluid catalytic converter (FCC) units. More specifically, it relates to methods for stabilizing the operation of multiple-catalyst-employing FCC units by use of predetermined amounts and ratios of certain catalysts used therein.
2. Description of the Prior Art
FCC units carry out processes that are employed throughout the petroleum refining, chemical and petrochemical industries. These processes are frequently destabilized by changes (deliberate, as well as unavoidable changes) such as (1) variation in the character of the feedstock being supplied to such units, (2) selection of different products to be made by such units, (3) selection of different grades of a product being made by such units, and (4) imposition of more stringent legal requirements (e.g., lower air pollution levels) upon such units.
Those skilled in this art will appreciate that any increase in a FCC operator's ability to anticipate the operation of, and/or more closely control, a process being carried out by a FCC unit will usually serve to minimize the use of, and hence the costs of, the very expensive catalyst consumed by that unit. The ability to anticipate the operation of such units also serves to reduce the complexities associated with the sometimes competing, and sometimes complimentary, effects caused by simultaneous use of several different catalysts species in such units. A FCC unit that is operating on a more stable basis also will generally tend to provide end products having more consistent quality attributes.
In order to better appreciate applicant's methods for stabilizing the operation of FCC units, it is helpful to envision their general mode of operation. Typically, a bulk catalyst inventory of tons, indeed, even hundreds of tons, of catalyst flow (often at high velocities) through the fluidized beds, reaction zones, and regeneration zones that make up such units. Next, it should be appreciated that the total catalyst inventory circulating through such a unit is usually comprised of a host catalyst (that carries out the primary catalytic function of the unit) and several distinct types of catalyst additives (that carry out secondary catalytic and/or sorbent functions). That is to say that various additives are used to carry out certain “secondary” functions that are, in some way or another, associated with the primary catalytic function. Preferably, the catalyst additives are distributed, to a high degree of homogeneity, in the host catalyst. Since the host catalyst carries out the primary catalytic function of a FCC unit (e.g., cracking a petroleum based feedstock), it usually comprises from about 80 to about 99 weight percent of the total catalyst inventory in such unit. Catalyst additives usually comprise the remaining 1.0 to 20.0 percent of their total catalyst inventory.
Each catalyst particle species (host catalyst or catalyst additive) introduced into a FCC unit will eventually disperse through the existing host catalyst/catalyst additive inventory and, at its own rate, be chemically deactivated, attrited, broken into smaller and smaller fragments that are eventually elutriated from the unit. The rate at which each catalyst particle species is chemically deactivated, attrited and elutriated is determined by the catalytic activity, hardness, durability, particle size and density characteristics of that particular catalyst particle species. Ideally, each different catalyst species will be introduced into the FCC unit in a manner and at a rate such that the overall host catalyst/catalyst additive system will settle down to some desired steady-state performance level as quickly as possible.
An FCC operator also would like to be able to respond, as quickly as possible to any changes (e.g., changes in quality or product distributions) that might arise so that the unit can be brought back to a steady-state mode of operation. Such responses usually need to be carried out while, to the fullest extent possible, maintaining one or more desired FCC unit performance levels and while maintaining, as much as possible, one or more “secondary” operating characteristics. For example, a FCC unit used to refine petroleum may be called upon to convert a given petroleum feedstock primarily into a gasoline product of a given octane rating at a given rate of production while, simultaneously, holding the unit's output of pollutants (e.g., SO
x
, NO
x
, CO, etc.) to certain legally prescribed levels—regardless of changes in the character of the petroleum feedstock (e.g., regardless of an increase in the sulfur content of the feedstock petroleum). Other common technical or economic operating goals or characteristics that a petroleum refinery operator might wish to achieve might include (but, by no means be limited to) (1) better control of the relative proportions of various end products being made by the unit (e.g., obtaining prescribed C
3
-C
4
product yields while limiting production of ethane, ethylene, methane and hydrogen), (2) low coke lay down rates (i.e., low rates of coke deposit on the FCC catalysts particles), and/or (3) achievement of economic goals (for example, obtaining the greater economic value, and hence profit, associated with gasoline products having higher research octane numbers).
The individual catalyst particles used in FCC units are usually comprised of a catalytically active component (e.g., a zeolite) and a generally “inert” matrix or binder material that serves primarily to hold particles of the catalytically active component (e.g., zeolite) in a catalyst/binder composite particle. This binder/catalyst format is generally used to make both host catalyst particles and catalyst additive particles. Depending on the nature of the catalytically active catalyst, the process being carried out, the severity of the temperature, pressure, particle velocity, etc. conditions in the FCC unit, economic considerations, and so forth, any given catalyst particle may have relatively small amounts (e.g., 1%) to relatively large amounts (e.g., 50%) of the catalytically active component embedded in a binder or matrix material such as alumina, silica, etc.
Hence, the “ratios” of any two or more catalysts used in a FCC process are often normalized to a common unit of comparison such as a common unit of weight (e.g., pounds). That is to say that the weight of a first type of active catalyst in a first particle species, is preferably compared to the weight of a different type of active catalyst in a second particle species. For example, if the first particle species and the second particle species weighed the same, but the first particle species were comprised of 10% by weight of active catalyst A and 90% by weight of binder material, and the second particle species were comprised of 50% by weight active catalyst B and 50% by weight binder material, then in order to get the same amount by weight of catalyst A and catalyst B for a “per unit weight” comparison, five times as much of the first catalyst species would be employed.
Next, it should be appreciated that in most cases, any given FCC function, operating characteristic or parameter is often regarded as being achieved through use of one particular catalyst species—even if this may not be literally true. That is to say that any given FCC function may be, and often is, influenced to some degree by other catalyst species that are placed in a FCC unit in order to carry out other, often entirely different, catalytic functions. By way of example only, a catalyst additive species that is used to reduce SO
x
emissions may also effect NO
x
emission, CO emissions, and perhaps even the primary catalytic function being carried out by the bulk catalyst. Indeed, such secondary effects are known to take place as a result of the use of (1) different catalyst additive species, (2) different bulk catalyst species and (3) a given bulk catalyst species used in conjunction with a given catalyst additive species.
Moreover, the complexities associate
Evans Martin
Paraskos John A.
Vierheilig Albert A.
Intercat, Inc.
Lillie Raymond J.
Olstein Elliot M.
Yildirim Bekir L.
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