Mineral oils: processes and products – Chemical conversion of hydrocarbons – Cracking
Reexamination Certificate
2000-05-11
2001-10-23
Griffin, Steven P. (Department: 1754)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Cracking
C208S120010, C208S120100, C208S120350, C502S060000, C502S064000
Reexamination Certificate
active
06306286
ABSTRACT:
This invention relates to a zeolite that is referred to as IM-5 and that is modified by adding phosphorus, from which optionally some metal Ti, B, Fe, Ga or Al has been removed, a catalytic composition that contains it, its preparation and its use in particular in a catalytic cracking process of a hydrocarbon feedstock. More specifically, it relates to an aluminosilicate molecular sieve that is stabilized by at least one phosphorus compound.
The prior art is illustrated by the patent U.S. Pat. No. 5,110,776 that describes a treatment with REY zeolite phosphate.
The molecular sieves of zeolitic nature are crystalline materials that comprise a three-dimensional network of tetrahedrons T′O
4
with T′ equal to Si, Al, B, P, Ge, Ti, Ga, Fe, for example. This network defines an intracrystalline microporous network with dimensions that are comparable to those of small to medium-sized organic molecules. The microporous network can be a system of channels and/or cavities, shaped by the crystalline network, which can be identified by its particular and specific X-ray diffraction diagram.
The potential applications of a zeolite (for example, in the processes of catalysis, adsorption, cationic exchange and purification) depend mainly on the size, the shape and characteristics (monodimensional, multidimensional) of its microporous network and its chemical composition. For example, in the zeolites of aluminosilicate type, the presence of AlO
4
−
tetrahedrons that are isolated in an Sio
4
tetrahedron matrix requires the presence of compensation cations to counterbalance the negative charge of the network. Typically, these cations have great mobility and can be exchanged by others, for example H
+
or NH
4
+
, whereby the latter can be transformed into H
+
via calcination, which results in an acidic microporous solid. The zeolite is then in its acid form, still called hydrogen form. When all of the compensation cations are organic alkylammonium or ammonium cations, the calcination results right in the acid form of the zeolite. These microporous acidic solids can be used in the processes of acid catalysis, and their activity and selectivity depend both on the force of the acid, the density of the acid sites, the dimensional characteristics of the space that is delimited in the network where the acid sites are located.
The size of the channels can be described by the number of T′O
4
tetrahedrons that are present in the ring that delimits the openings of pores, element that monitors the diffusion of molecules. Thus, the channels are classified in categories: the small pores (openings of annular pores delimited by a scheme of 8 T′O
4
tetrahedrons (8 MR), medium-sized pores (10 MR) and large pores (12 MR), whereby MR means membered ring in English.
This structural characteristic can obtain advantageous properties of shape selectivity with these materials in heterogenous catalysis. The term shape selectivity is generally used to explain specific catalytic selectivities that are due to steric constraints that exist inside the zeolitic microporous system. These constraints can act on the reagents (diffusion of reagents in the zeolite), on the products of the reaction (formation and diffusion of products that are formed outside of the zeolite) on the reaction intermediate products or on the reaction transition states that are formed in the micropores of the zeolite during the reactions. The presence of suitable steric constraints makes it possible in some cases to avoid the formation of transition states and reaction intermediate products that result in the formation of undesirable products and improves the selectivities in some cases.
The object of the invention relates to the IM-5 zeolite, optionally partially lacking in metal T, containing phosphorus and its use when it is partly dealuminified in catalytic cracking, by itself or mixed with a conventional catalytic cracking catalyst. The catalyst of this invention is particularly well suited for cracking of petroleum fractions for the purpose of producing a large amount of compounds that have 3 and/or 4 carbon atoms per molecule and more particularly propylene and butenes. The catalyst of this invention is particularly well suited to cracking of heavy petroleum fractions.
This invention also relates to the process of cracking of heavy petroleum feedstocks, in the presence of the catalyst that is defined above, as well as the processes for preparation of said catalyst. The cracking of hydrocarbon feedstocks that make it possible to obtain high gasoline outputs for an automobile of very good quality was imposed in the petroleum industry from the end of the 1930's. The introduction of the processes that operate in a fluid bed (FCC or Fluid Catalytic Cracking) or in a moving bed (such as the TCC), in which the catalyst permanently circulates between the reaction zone and the regenerator where coke is removed from it by combustion in the presence of a gas that contains oxygen, introduced significant progress relative to the technique of the fixed bed.
From the beginning of the 1960's, the most used catalysts in the cracking units have been zeolites that usually have a faujasite structure (FAU). These zeolites, incorporated in an amorphous matrix, for example that consists of amorphous silica-alumina and can contain variable proportions of clays, are characterized by cracking activities, relative to hydrocarbons, 1,000 to 10,000 times greater than those of the silica-alumina catalysts that are high in silica and that were used up until the late 1950's.
Toward the end of the 1970's, the lack of available crude oil and the growing demand for gasoline with a high octane rating led refiners to treat heavier and heavier crudes. The treatment of the latter constitutes a difficult problem for the refiner due to their high content of catalytic poisons, in particular in metal compounds (in particular nickel and vanadium), unusual values of Conradson carbon and primarily asphaltene compounds.
This necessity of treating heavy feedstocks and other more recent problems, such as the progressive but general elimination in the gasoline of lead-based additives, the slow but appreciable evolution in some countries of the demand for middle distillates (kerosenes and gas oils) have, moreover, prompted refiners to seek improved catalysts that make it possible to reach in particular the following goals:
better thermal and hydrothermal stability and better tolerance in metals,
lower production of coke with identical conversion,
better octane rating of the gasoline,
improved selectivity of middle distillates.
In the majority of cases, an effort is made to minimize the production of light gases that comprise compounds that have 1 to 4 carbon atoms per molecule and, consequently, the catalysts are designed to limit the production of such light gases.
In some special cases, however, there appears a significant demand for light hydrocarbons of 2 to 4 carbon atoms per molecule or in some of them, such as the hydrocarbons of C3 and/or C4 and more particularly propylene and butenes.
Obtaining a large amount of butenes is in particular advantageous in the case where the refiner uses an alkylation unit, for example C3-C4 fractions that contain olefins, to form an additional amount of gasoline with a high octane rating. Thus, the overall yield of good-quality gasoline that is obtained from the starting hydrocarbon fractions is appreciably increased.
Obtaining propylene is particularly desired in some less developed countries where there is a significant demand for this product.
To a certain extent, the catalytic cracking process can satisfy such demands provided that in particular the catalyst is adapted for the purpose of this production. An effective manner of adapting the catalyst consists in adding to the catalytic masses an active agent that exhibits the following two qualities:
cracking the heavy molecules with a good selectivity of hydrocarbons with 3 and/or 4 carbon atoms, in particular propylene and butenes;
b
Benazzi Eric
Canos Avelino Corma
Lacombe Sylvie
Mabilon Gil
Martinez Triguero Joaquin
Griffin Steven P.
Ildebrando Christina
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
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