Catalysts containing heteropolyanions usable in processes...

Details Catalysts containing heteropolyanions usable in processes... Catalysts containing heteropolyanions usable in processes...

2000-06-26

2003-06-24

Wood, Elizabeth D. (Department: 1755)

Chemistry of hydrocarbon compounds

Saturated compound synthesis

By condensation of a paraffin molecule with an olefin-acting...

C502S208000, C502S213000, C502S214000, C502S232000, C502S240000, C502S254000, C502S255000, C502S258000, C502S261000, C502S262000, C502S300000, C502S325000, C502S313000, C502S321000, C502S322000, C502S323000, C585S709000, C585S713000, C585S734000

Reexamination Certificate

active

06583330

ABSTRACT:

This invention relates to new catalysts that contain heteropolyanions of 12-tungstophosphoric acid or 12-tungstomolybdic acid and, for some of these, at least one metal of group VIII, deposited on substrates that develop a specific surface area and a high pore volume, such as zirconium oxide (ZrO
2
), silicas, silica-aluminas or aluminas.
These catalysts are used in particular in isomerization of paraffinic fractions that contain in large part n-paraffins that have, for example, 4 to 8 carbon atoms per molecule and in aliphatic alkylation of isoparaffins (for example isobutane and/or isopentane) by at least one olefin that comprises, for example, 2 to 6 carbon atoms per molecule (C
2
to C
6
).
This invention also relates to the preparation of these catalysts.
The elimination of lead and the very short-term reduction of the content of aromatic compounds of the gasolines, combined with the persistent requirement for preserving a high octane number (greater than or equal to 95), led to seeking catalysts and improved processes that make it possible to obtain gasolines with a high octane number, and, among them, the processes for isomerization of paraffinic fractions that contain in large part n-paraffins and aliphatic alkylation of the isoparaffins. These two processes are performed by an acid mechanism that uses carbocations as intermediate reaction products. They require the use of catalysts that develop a high acidity.
For isomerization of paraffinic fractions that contain in large part n-paraffins, these acid solids should result in a good activity at the lowest possible temperature, whereby the thermodynamic equilibrium promotes the low-temperature multibranched isomers.
The catalysts that are commonly used industrially are:
Pt/zeolite catalysts and more particularly Pt/mordenite catalysts,
catalysts with a base of Pt/halogenated alumina, and more particularly strongly chlorinated alumina,
catalysts with a base of sulfated zirconia.
For the aliphatic alkylation, these are the liquid acids HF and H
2
SO
4
that are used industrially, despite major problems of use and toxicity for the environment.
More recently, catalysts that contain heteropolyanions were studied for these two reactions. These heteropolyanions are generally in the form of salts of the 12-tungstophosphoric acid (U.S. Pat. No. 5,482,733) or of the 12-tungstosilicic acid (EP-A 0 623 386 and U.S. Pat. No. 5,391,532) that are exchanged by aluminum and deposited on various substrates such as Zr(OH)
4
or SiO
2
, or else in the form of 12-tungstophosphoric acid itself, supported on mesoporous solids such as MCM-41 (U.S. Pat. No. 5,366,945).
In the isomerization reaction of the paraffinic fractions that contain in large part n-paraffins, for example with 4 to 8 carbon atoms, the thermodynamic equilibrium between the various isomers varies considerably with the temperature. The branched hydrocarbons, which are those that have a high octane number, are more enhanced, the lower the temperature. The problem of the isomerization of these paraffinic fractions therefore consists in finding active catalysts at the lowest temperature.
As far as the reactions of aliphatic alkylation of isoparaffins by olefins are concerned, it was important to be able to use a solid catalyst that makes it possible to work under the simplest conditions possible and at operating temperatures that are higher than those imposed by the use of standard liquid acids, thus preventing the problems that are associated with cooling.
One of the objects of this invention is therefore to provide new catalysts that are improved in terms of the paraffin conversion reactions as well as in terms of the isomerization reactions of paraffinic fractions that contain in large part n-paraffins in the reactions of aliphatic alkylation of isoparaffins by the olefins.
The catalysts according to this invention are defined in general by the fact that they comprise at least heteropolyanions that are derived from tungstophosphoric acid or 12-tungstomolybdic acid, but preferably 12-tungstophosphoric acid, deposited on substrates that develop a specific surface area and a high pore volume, such as zirconium oxide, silicas, silica-aluminas or aluminas, preferably zirconium oxide.
Some of these catalysts also comprise at least one metal of group VIII. The latter are dedicated in particular to the isomerization of the paraffinic fractions that contain in large part paraffins that have, for example, 4 to 8 carbon atoms. The others, that do not contain a metal of group VIII, are more particularly suited to the aliphatic alkylation of isoparaffins (for example isobutane and/or isopentane) with at least one olefin that comprises, for example, 2 to 6 carbon atoms per molecule (C
2
to C
6
).
The substrate of the catalysts of the invention generally develops a specific surface area of 50 to 500 m
2
/g, preferably 80 to 500 m
2
/g, and most often 80 to 450 m
2
/g, and a pore volume of 0.2 to 0.9 cm
3
/g, preferably 0.3 to 0.9 cm
3
/g and most often 0.3 to 0.8 cm
3
/g; it is advantageously put in the form of balls or extrudates. The heteropolyanion content is 10 to 55% by weight relative to the entire catalyst, preferably 25 to 50% by weight.
The catalysts according to the invention that are particularly dedicated to the isomerization of paraffinic fractions that contain in large part n-paraffins comprise, in addition to the heteropolyanion and the substrate, at least one metal of group VIII that is selected from among, for example, platinum, palladium, rhodium, nickel and ruthenium in a content of 0.05 to 10% by weight, preferably 0.1 to 5% by weight and more preferably 0.2 to 1% by weight.
For the preparation of the catalysts of the invention, the heteropolyanions that are to be introduced can be obtained from aqueous solutions of corresponding heteropolyacids or salts of these acids. They are deposited on the substrates by any impregnation technique that is known to one skilled in the art and in particular by dry impregnation in the pore volume. Before impregnation, the substrates are advantageously calcined, for example, at a temperature of 200° C. to 800° C., preferably 350° C. to 600° C.
In the case of the catalysts to use in isomerization paraffinic fractions that contain in large part n-paraffins, at least one metal of group VIII is deposited on the substrate by any method that is known to one skilled in the art, for example by impregnation.
The heteropolyanion and the metal of group VIII can be co-impregnated on the substrate from a mixed solution of a precursor of the heteropolyanion (heteropolyacid or one of its salts) and a precursor of the metal of group VIII. At the end of the co-impregnation, the catalyst is dried in a drying oven for 6 to 12 hours at a temperature of 100° C. to 150° C., then calcined under air for a period of 0.5 to 4 hours, preferably 1 to 3 hours, at a temperature of 150° C. to 400° C., preferably 180° C. to 350° C.
The heteropolyanion and the metal of group VIII can also be impregnated consecutively, whereby the heteropolyanion is then preferably impregnated first. In this case, drying and calcination stages that are described above are in general used after the impregnation of the heteropolyanion, then after the impregnation of the metal of group VIII.
Among the above-mentioned metals of group VIII, platinum and palladium are preferred; all of the salts of these metals that are soluble enough in water can be used as precursors.
As a metal of group VIII, platinum can also be introduced into the catalyst by a mechanical mixture with a Pt/Al
2
O
3
catalyst or Pt/SiO
2
catalyst that is reduced in advance.
In the case of catalysts to be used in aliphatic alkylation that do not contain a metal of group VIII, the deposition of heteropolyanions for example by impregnation, as described above, and immediately drying and calcination stages are then carried out.
In all of the cases, at the end of the calcination, in general a treatment under hydrogen is carried out for a period of 0.5 to 4 hours, preferably 1 to 3 hours, at a temperature of 120° C. to 600° C

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