Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
1998-06-09
2004-02-03
Wood, Elizabeth D. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S232000, C502S240000, C502S258000, C502S261000, C502S262000, C502S305000
Reexamination Certificate
active
06686309
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a catalyst for selective hydrogenation of diolefinic and styrenic compounds in unsaturated gasolines without hydrogenating the aromatic and mono-olefinic compounds. It can also eliminate marcaptans when they are present in thirst gasolines.
BACKGROUND OF THE INVENTION
Steam cracking gasolines ale known to contain gum precursors such as diolefins, also styrenic compounds (such as styrene itself), mixed with mono-olefinic and aromatic compounds. Upgrading mono-olefinic compounds involves selective hydrogenation of diolefins and styrenic compounds.
Cracking of hydrocarbons to produce olefins produces a liquid fraction with a portion of the compounds having a boiling point corresponding to traditional gasoline cuts: This mixture contains high quantities of aromatic and mono-olefinic compounds, which endow it with good fuel properties and enable it to be upgraded, either in the “gasoline pool” or as a source of aromatic compounds. However, such cracking gasolines contain large quantities of highly reactive compounds such as diolefins, which are guns precursors, and styrenic compounds (in particular styrene). Such gasolines are thus unstable which means that a hydrogenation process must be carried out before they are used. Further, depending on the conversion process, such gasolines can contain non negligible quantities of mercaptans, which must be eliminated in order to obtain “sweetened” gasolines, negative to the Doctor test.
Two main types of catalyst are generally used for hydrogenating diolefins and styrenic compounds: catalysts using noble group VIII metals such as palladium, and those using non noble group VIII metals such as nickel. (In the present description, the periodic table considered is that from the Chemical Abstracts Service (CAS)). However, the second type of catalyst generally has a lower activity and undersired oligomerising properties, which necessitates frequent regeneration and the use of a distillation column after hydrogenation to eliminate the heavy compounds. An example of the use of that type of catalyst is described in U.S. Pat. No. 3,691,066. Catalysts based on noble metals are generally more active than catalysts based on non noble metals.
Regarding mercaptan elimination, catalysts using non noble group VIII metals such as nickel can transform mercaptans into sulphides. However, as indicated above, that type of catalyst generally has oligomerising properties, which necessitates frequent regeneration and the use of a distillation column after hydrogenation to eliminate the heavy compounds Further, such catalysts can only treat feeds containing large quantities of marcaptans such as that found in catalytic cracking gasolines.
In addition, while catalysts based on noble group VIII metals are generally more active than catalysts based on non noble metals for hydrogenating diolefinic and styrenic compounds, they do not always transform mercaptans. Their use thus means that the hydrogenated gasoline must be sweetened, for example using a process as described in our French patent applications FR-A-2 753 717 and FR-A-2 753 718.
It should also be noted that the use of group VIII metal—group VIB metal systems has already been described in the literature, for example by M. Yamada, J. Yasuinaru, M. Houaila, D. Hercules in: “Distribution of Molybdenum Oxidation States in Reduced Mo/Al
2
O
3
Catalysts. Correlation with Benzene Hydrogenation Activity”. J. Phys. Chem., 95, 7037-7042 (1991) or by A. Jimenez-Gonzalez, D. Schmeissr in “electron Spectroscopic Studies of Mo and Pt Modified &ggr;-Al
2
O
3
Model Catalyst”. J. Catal., 130, 332-346 (1991). These documents, however, relate to total hydrogenation reactions.
A first aim of the present invention is to provide a novel catalyst which can carry out selective hydrogenation of diolefins and styrenic compounds in an unsaturated gasoline cut with improved performance. In this case, the catalyst of the invention has the advantage of achieving diolefins and styrenic compound conversions which are higher than that achieved with a palladium catalyst alone. The catalytic performances of this catalyst are also more stable over time than those of the monometallic system.
A further aim of the present invention is to provide a novel catalyst the use of which on an unsaturated gasoline cut containing diolefins, styrenic compounds and mercaptans enables hydrogenation of the diolefins and styrenic compounds and transformation the mercaptans in a single operation.
SUMMARY OF THE INVENTION
The catalyst of the invention is defined as comprising a particulate support constituted by grains of at least one refractory oxide, on which palladium is deposited, distributed at the periphery of the grains of the support, and at least one metal selected from molybdenum and tungsten, in the form of at least one oxide.
More particulary, the grains of the support are, for example in the form of beads or cylinders (for example cylindrical extrudes); the palladium can then be distributed in a peripheral layer of said grains with a penetration to a depth which does not exceed 80%, for example, of the radius of the beads of cylinders.
In the catalyst of the invention, the palladium content is generally in the range 0.2% to 5% by weight and the molybdenum and/or tungsten content is in the range 0.5% to 5% by weight.
The support is generally selected from refractory oxides such as alumina, silica, silica-aluiminas, magnesia or mixtures thereof. Alumina is the preferred support, mole particularly an alumina with a specific surface area in the range 5 to 200 m
2
/g, preferably 10 to 110 m
2
/g, more advantageously 20 to 80 m
2
/g. The pore volume of the refractory oxide support is, for example, 0.4 to 1 cm
3
/g.
Regarding the preparation of the catalysts of the invention, the group VIII clement and the group VIB element can be introduced using techniques which are known to the skilled person. As an example, if the group VIII metal is palladium, it can be introduced by impregnating with an aqueous or organic solution of a palladium precursor. This precursor can, for example, be an inorganic compound, for example palladium chloride or palladium nitrate, or an organometallic compound, such as palladium bis &pgr;-allyl or palladium bis-acetylacetonate. The tungsten, as an example of a group VIB element, can be introduced by impregnating the support with fin aqueous or organic solution of a tungsten precursor, for example ammonium metatungstate, ammonium paratungstate, tungsten chloride or carbonylated tungsten compounds. The molybdenum can be introduced by impregnating the support using an aqueous or organic molybdenum precursor, for example ammonium heptamolybdate.
The elements can be introduced using common or separated solutions, The two elements ale preferably introduced separately and advantageously, the compound comprising the group VIB element is introduced prior to introducing the compound comprising the group VIII element.
After introducing the different elements, the catalyst is generally dried at a temperature of 90° C. to 150° C., for example at about 120° C., then calcined at temperatures of generally 150° C. to 700° C.
When the catalytic elements are introduced in a plurality of impregnation steps, the catalyst may undergo different treatments between two impregnation steps, for example drying at a temperature of 90° C. to 150° C., for example at about 120° C., and calcining in air at a temperature of 400° C. to 500° C., for example at about 450° C.
In order that the group VIB metal or metals is in the form of oxides in the catalyst, before use it generally undergoes a treatment in a reducing atmosphere, for example in a stream of hydrogen, at a temperature in the range from ambient temperature to 500° C., more particularly in the range from ambient temperature to 250° C.
The gasoline cut to be treated may have a high diolefin content, corresponding, for example, to a MAV (maleic unhydride value) determined using the UOP 326-82 method, in the range 20 to 100, and styrene contents of up to 5%
Cameron Charles
Didillon Blaise
Gautreau Christophe
Uzio Denis
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
Wood Elizabeth D.
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