Catalyst based on a halogenated alumina, its preparation and...

Chemistry of hydrocarbon compounds – Saturated compound synthesis – By isomerization

Reexamination Certificate

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C585S747000

Reexamination Certificate

active

06297418

ABSTRACT:

The present invention concerns a catalyst based on a halogenated alumina, preferably chlorinated, its preparation and use in a process for the isomerisation of normal C
4
-C
6
paraffins.
Isomerisation of normal paraffins containing 4 to 6 carbon atoms per molecule has now assumed considerable importance in the petroleum industry, mainly because of the removal of lead alkyls from petrol.
Isomerisation of n-butane produces isobutane for the aliphatic alkylation of olefins and for the synthesis of MTBE (methyl tertiobutyl ether) by dehydrogenating isobutane, to produce an alkylate with a high octane number and MTBE respectively, which compounds can be incorporated into petrol fractions.
Isomerisation of normal C
5
-C
6
paraffins can transform paraffins with low octane numbers to isoparaffins weith high octane numbers.
Three types of catalyst are traditionally used to carry out the isomerisation of normal paraffins containing 4 to 6 carbon atoms per molecule, preferably 5 to 6 carbon atoms per molecule:
Friedel-Crafts type catalysts, such as aluminum chloride, which are used at low temperatures (about 80° C. to 130° C.);
catalysts comprising at least one metal from group VIII on a support based on a halogenated, preferably chlorinated, alumina, used at medium temperatures (about 150° C.);
zeolitic catalysts comprising at least one metal from group VIII deposited on a zeolite, used at high temperatures (250° C. and more); those catalysts lead to smaller gains in the octane number of the products obtained than with the two catalyst types described above but have the advantage of being easier to use and more resistant to poisons. Nevertheless, they cannot be used to isomerise n-butane since they also produce a lower acidity than the two types of catalyst described above.
A number of patents concern monometallic catalysts based on platinum deposited on a halogenated alumina and their use in isomerisation processes of normal paraffins. An example is United States patent U.S. Pat. No. 3,963,643 which involves treatment with a Friedel-Crafts type compound followed by treatment with a chlorinated compound containing at least two chlorine atoms.
More recently, U.S. Pat. No. 5,166,121 has claimed a catalyst comprising gamma alumina formed into spherules and containing between 0.1% and 3.5% of halogen on the support. An extremely small amount of halogen, preferably chlorine, is deposited on the support.
The invention concerns a catalyst containing at least one halogen, at least one metal from group VIII and a formed support comprising gamma alumina and optionally eta alumina, the catalyst being characterized in that the smallest average dimension of said support is in the range 0.8 mm to 2 mm, preferably in the range 1 mm to 1.8 mm, and in that the chlorine content is in the range 4.5% to 15% by weight, preferably in the range 5% to 12% by weight.
The support for the catalyst of the invention is alumina based, i.e., it essentially comprises alumina. The alumina support is gamma alumina to which eta alumina man optionally be added. When eta alumina is added to the gamma alumina, the alumina in the support generally comprises between 50% and 100% (limits excluded), preferably between 80% and 100% (limits excluded) (% by weight) of eta alumina, the complement being gamma alumina.
The smallest average dimension of the support of the catalyst of the invention is in the range 0.8 mm to 2 mm, preferably in the range 1 mm to 1.8 mm. Preferably, the support is essentially formed of spherules with an average diameter in the range 0.8 mm to 2 mm, preferably in the range 1 mm to 1.8 mm, or the support is essentially formed of extrudates whose smallest dimension is in the range 0.8 mm to 2 mm, preferably in the range 1 mm to 1.8 mm, i.e., the extrudates are formed using any extrusion technique which is known to the skilled person, for example a die with a diameter in the range 0.8 mm to 2 mm, preferably in the range 1 mm to 1.8 mm.
The gamma alumina present in the support of the catalyst of the invention has a specific surface area which is generally in the range 150 m
2
/g to 300 m
2
/g, preferably in the range 180 m
2
/g to 250 m
2
/g, and a total pore volume which is generally in the range 0.4 cm
3
/g to 0.8 cm
3
/g, preferably in the range 0.45 cm
3
/g to 0.7 cm
3
/g.
The eta alumina which may optionally be present in the support of the catalyst of the invention has a specific surface area which is generally in the range 400 m
2
/g to 600 m
2
/g, preferably in the range 420 m
2
/g to 550 m
2
/g, and a total pore volume which is generally in the range 0.3 cm
3
/g to 0.5 cm
3
/g, preferably in the range 0.35 cm
3
/g to 0.45 cm
3
/g.
The metal from group VIII is selected from the group formed by iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum, preferably selected from the group formed by platinum, palladium and nickel. In the preferred case where the metal is platinum or palladium, the content is in the range 0.05% to 1% by weight, preferably in the range 0.1% to 0.6% by weight. In the preferred case where the metal is nickel, the content is in the range 0.1% to 10% by weight, preferably in the range 0.2% to 5%.
The catalyst of the invention comprises at least one halogen, in an amount in the range 4.5% to 15% by weight, preferably in the range 5% to 12% by weight. The halogen is selected from the group formed by fluorine, chlorine, bromine and iodine. Preferably, the halogen is chlorine.
The catalyst of the invention is generally prepared by forming a support then depositing at least one metal from group VIII on the formed support, and finally halogenation, preferably chlorination, after an optional preferred step of activation in hydrogen. Each step in the process for preparing the support of the invention is described below.
When eta alumina is present in the support of the catalyst of the invention, the two types of alumina are preferably mixed and used together, using any technique which is known to the skilled person, for example by extrusion through a die, pelletization or bowl granulation. It is also possible to form the two types of alumina separately then mix the two formed types of alumina. In all cases, the smallest dimension of the geometric shape adopted by the support after forming is in the range 0.8 mm to 2 mm, preferably in the range 1 mm to 1.8 mm, so that, during the support chlorination step, a sufficient chlorine content is obtained for a reduced chlorination period.
At least one hydrogenating metal from group VIII, preferably selected from the group formed by platinum, palladium and nickel, is then deposited on the support using any technique which is known to the skilled person, for example anion exchange in the form of hexachloroplatinic acid in the case of platinum or in the form of the chloride in the case of palladium.
Once the metal(s) has/have been deposited, the catalyst may undergo activation in air at high temperature, for example at a temperature in the range 300° C. to 700° C., then treatment in hydrogen to obtain an active metallic phase. This hydrogen treatment procedure can, for example, comprise a slow rise of temperature in a hydrogen stream up to the maximum reduction temperature, generally between about 300° C. and 700° C., preferably between about 340° C. and 680° C., followed by holding that temperature, generally for 1 to 6 hours, preferably for 1.5 to 4.5 hours.
The halogen, preferably chlorine, is deposited from any known compound to effect halogenation, preferably chlorination, under suitable conditions (as regards the treatment of effluents, halogenation period, cost . . . ). Thus the use of hydrogen chloride is excluded from the scope of the invention (see examples). Halogenation, preferably chlorination, of the alumina is effected remote from or directly in the reaction unit in which the catalyst is used, preferably in an isomerisation unit, using any halogenating agent, preferably a chlorinating agent, which is known to the skilled person. Preferably, when the halogen is chlorine, carbon tetrachloride or chloroform

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