Palladium catalyst and process for producing ether

Details Palladium catalyst and process for producing ether Palladium catalyst and process for producing ether

2002-05-01

2003-12-02

Keys, Rosalynd (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C568S599000, C568S664000, C568S670000

Reexamination Certificate

active

06657089

ABSTRACT:

TECHNICAL FIELD
This invention relates to palladium catalysts useful in the production of hydroxyethers which are useful as oil stain removers, water-soluble organic solvents, polar oils, emulsifiers, lubricants, humectants or the like, or as intermediates for producing surf actants, and also to a process for producing hydroxyethers by use of the palladium catalysts.
BACKGROUND ART
Known as hydrogenolytic processes for acetal compounds are (1) a process which uses a mixture of an alkylaluminum halide compound or an aluminum halide and lithium aluminum hydride [E. L. ELIEL et al., J. Am. Chem. Soc., 84,2371 (1962)] and (2) a process which uses a hydrogenation catalyst comprising a metal such as palladium, platinum or rhodium supported thereon in a hydrogen atmosphere (JP-A-54-135714).
However, the process (1) involves a problem in safety because the reagents to be used therein have considerable inflammability and are required in stoichiometric amounts. Thus the process is also accompanied by a problem in that a large amounts of wastes are produced. The process (2), on the other hand, is free of such problems and is advantageous. However, in the case where the acetal compound is an acetal of a polyhydric alcohol such as a cyclic acetal, the process involves a problem in that the resulting product inevitably has a mixed composition of monoethers, diethers and the like through transacetalization (or acetal exchange) or the like.
An object of the present invention is to provide a catalyst capable of obtaining a monoether with high selectivity in the synthesis of an ether and also a process for synthesizing a monoether with high selectivity through hydrogenolysis of a cyclic acetal by using the catalyst.
DISCLOSURE OF THE INVENTION
The present inventors have found that the above-described problems can be solved by using a catalyst comprising palladium supported on a mesoporous aluminosilicate which is a porous carrier having a substantially uniform pore size greater than that of zeolite. The inventors have also found that a catalyst especially excellent in activity in the production of an ether can be provided by supporting palladium on a mesoporous aluminosilicate treated beforehand with ammonia or a salt thereof.
Specifically, the present invention provides a process for producing an ether, which comprises reacting a cyclic acetal and hydrogen in the presence of a palladium catalyst supported on a mesoporous aluminosilicate
The present invention also provides a palladium catalyst comprising palladium supported on a mesoporous aluminosilicate which has been treated with ammonia or a salt thereof.
BEST MODES FOR CARRYING OUT THE INVENTION
The term “mesoporous aluminosilicate” as used herein, which is a carrier in the palladium catalyst according to the present invention, means an aluminosilicate having a uniform pore size of from 2 to 50 nm. This uniform pore size can be determined by a powder X-ray diffraction pattern, and is preferably from 2 to 10 nm, particularly from 2 to 6 nm. A monoether can be obtained with high selectivity in the present invention because transacetalization is controlled inside of such mesoporous pores. Therefore, the best results can be obtained by using a catalyst having a pore size and a palladium dispersion state which are suitable for substrates.
The palladium catalyst according to the present invention can be produced by synthesizing a mesoporous aluminosilicate having a pore size greater than that of zeolite and then having palladium supported on the mesoporous aluminosilicate.
The mesoporous aluminosilicate can be synthesized, for example, by the process disclosed in Bull. Chem. Soc. Jpn., 63, 988 (1990). From the standpoint of synthesis, however, the percentage of Al based on Si is preferably 10 wt. % or lower, and the pore size of the mesoporous aluminosilicate is preferably 2 to 10 nm, especially at 2 to 6 nm.
In the present invention, it is preferred to have palladium supported on a mesoporous aluminosilicate after treating the mesoporous aluminosilicate with ammonia or a salt thereof.
As a method for treating a mesoporous aluminosilicate with ammonia or its salt in advance, it is preferred to subject a synthesized mesoporous aluminosilicate to neutralization or ion exchange with ammonia or its salt. In this method, ammonia may be used in the formof either gas or an aqueous solution. Examples of the salt of ammonia can include ammonium salts of inorganic acids such as ammonium chloride, ammonium sulfate and ammonium carbonate; and ammonium salts of lower organic acids (carbon number: 1 to 3) such as ammonium acetate, ammonium formate and ammonium lactate, with ammonium chloride being particularly preferred. The ammonia salt for use in this treatment can be used in the form of an aqueous solution. It is necessary to use ammonia or its salt in an amount sufficiently greater than that of contaminated sodium ions. Specifically, a mesoporous aluminosilicate may be dispersed at 0 to 100° C., preferably at room temperature to 80° C. in an aqueous solution of ammonia or its salt in a sufficiently excess amount such as 1 to 100 molar times, preferably 1 to 50 molar times as much as the molar amount of aluminum in the mesoporous aluminosilicate to bring the mesoporous aluminosilicate into contact with the solution of ammonia or its salt, followed by rinse. Before palladium is supported, the thus-treated mesoporous aluminosilicate may be calcined at 200 to 700° C., preferably at 300 to 600° C., or may be used without calcination for supporting palladium. By treating the mesoporous aluminosilicate with ammonia or its salt as described above before palladium is supported thereon, the amount of sodium ions contaminated in the mesoporous aluminosilicate can be significantly decreased, leading to an improvement in the palladium supporting efficiency through ion exchange and also to a significant improvement in the catalytic reaction activity of the supported palladium. When employed especially in synthesizing an ether from a polyhydric alcohol and a carbonyl compound, the reaction activity and selectivity to the monoether formation are improved significantly.
Processes for supporting palladium on the mesoporous aluminosilicate include, for example, impregnation process, ion exchange process, and CVD process. In general, impregnation process is used widely. As a process for having palladium supported on the mesoporous aluminosilicate, however, ion exchange process is preferred.
The process in which palladium is supported by ion exchange is suitable for the catalyst preparation process according to the present invention, because this process makes it possible to have palladium supported rather readily in a highly dispersed state.
Examples of palladium salts usable in this supporting process include PdCl
2
, Pd(OAc)
2
, Pd(NH
4
)Cl
2
, and [Pd(NH
3
)
4
]Cl
2
, with PdCl
2
and Pd(OAc)
2
being particularly preferred. An ion exchange process using PdCl
2
, Pd(OAc)
2
or the like includes, for example, a process in which PdCl
2
is dissolved in aqueous ammonia or Pd(OAc)
2
is dissolved in a liquid mixture of acetone and water, and a mesoporous aluminosilicate or a salt thereof is dispersed in the resultant solution to bring the mesoporous aluminosilicate or its salt into contact with the solution. A process using a solution of PdCl
2
in aqueous ammonia is preferred. No particular limitation is imposed on the amount of PdCl
2
or the treatment temperature, but the amount of PdCl
2
is preferably from 0.01 to 500 wt. %, more preferably from 0.1 to 200 wt. % based on the amount of mesoporous silicate, and the treatment temperature is preferably from 0 to 100° C., more preferably from room temperature to 80° C.
The amount of palladium supported on the mesoporous aluminosilicate is preferably from 0.1 to 10 wt. % of the whole amount of the catalyst. The amount greater than this range has a higher possibility of giving an adverse effect such as sintering when palladium is supported.
Subsequent to supporting of palladium on the mesoporous aluminosili

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