Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Inorganic carbon containing
Reexamination Certificate
2000-05-19
2002-07-23
Wood, Elizabeth D. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Inorganic carbon containing
C502S200000, C423S365000
Reexamination Certificate
active
06423662
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to certain metal-containing catalysts and to methods for preparing metal-containing catalysts for alkylene oxide polymerization.
Alkylene oxides such as ethylene oxide, propylene oxide and 1,2-butylene oxide are polymerized to form a wide variety of polyether products. For example, polyether polyols are prepared in large quantities for polyurethane applications. Other polyethers are used as lubricants, brake fluids, compressor fluids, and many other applications.
These polyethers are commonly prepared by polymerizing one or more alkylene oxides in the presence of an initiator compound and a catalyst. Recently, the so-called double metal cyanide (DMC) catalysts have been used commercially as polymerization catalysts for alkylene oxides. These catalysts are described, for example, in U.S. Pat. Nos. 3,278,457, 3,278,458, 3,278,459, 3,404,109, 3,427,256, 3,427,334, 3,427,335, 5,470,813 among many others. Although these catalysts are described very broadly in the patent literature, only a limited number of forms of the catalyst have been shown to be active alkylene oxide polymerization catalysts.
The active catalysts are typically prepared by mixing an excess of a water soluble salt of a metal M with a water soluble compound containing an anion of the type M
1
[(CN)
r
(X)
t
], in aqueous solution. An excess of the M salt is essential to produce an active catalyst. In addition, the active forms of the catalyst all require the presence of an organic complexing agent. In conventional processes, this is provided by either adding the complexing agent to one or both of the starting solutions or by separately adding the complexing agent immediately after mixing the starting solutions. A catalyst complex containing the insoluble M
b
[M
1
(CN)
r
(X)
t
]
c
associated with the complexing agent and bound water, precipitates and is washed, usually multiple times, with mixtures of the complexing agent and water.
The preparation method just described has several disadvantages. First, the variety of compositions that can be made is usually limited to those having a single type of M ion.
Second, because the salt of the metal M is water-soluble, at least a portion of the excess salt remains in the aqueous phase when the catalyst complex first precipitates. This salt is lost when the precipitated catalyst is isolated. Thus, some of the salt is wasted, and, unless the product is subsequently analyzed, it is often not known how much of the excess salt is incorporated into the catalyst. This can be important, as it is believed that the activity of the catalyst complex depends on the presence of an excess of the salt.
In addition, the preparation method described above uses much more of the complexing agent compound than actually becomes bound into the catalyst complex. This results in excess raw material costs and increases the overall cost of making the catalyst complex.
Thus, it would be desirable to provide a method by which controlled amounts of excess metal salt can be incorporated into a metal-containing cyanide catalyst. It would further be desirable to provide a less expensive method of making these metal-containing catalyst complexes, and to reduce the quantities of raw materials and the number of steps required to prepare these catalyst complexes.
SUMMARY OF THE INVENTION
In one aspect, this invention is a method for preparing a metal-containing catalyst, comprising the steps of:
a) forming a first solution of a metal salt in water;
b) forming a second aqueous solution of a metal cyanide compound or a mixture thereof with a supplementary compound having a transition metal-containing anion which forms an insoluble salt with the metal in said metal salt;
c) mixing said first and second solutions in proportions such that no more than a stoichiometric quantity of the metal salt is present in the mixture, based on the number of equivalents of the metal cyanide compound and any supplementary compound present, under conditions such that the metal salt, the metal cyanide salt and the supplementary compound, if present, react to form an insoluble precipitate;
wherein step c) is performed in the presence of an organic complexing agent compound, step c) is followed by washing the insoluble precipitate with an organic complexing agent compound, or both, then
d) removing excess water and any excess organic complexing agent from the insoluble precipitate to form an isolated precipitate; and
e) mixing the isolated precipitate with an impregnating solution containing an additional quantity of a metal salt dissolved in water or a mixture of water and a soluble organic complexing agent, under conditions such that the impregnating solution is substantially absorbed by the isolated precipitate, wherein the concentration of the metal salt in the impregnating solution is such that about 0.1 to about 1.5 moles of metal salt are provided in said impregnating solution per mole of metal cyanide compound and transition metal-containing anion in the isolated precipitate.
The method of the first aspect of the invention provides a convenient way to make metal-containing catalyst complexes having a controlled content of excess metal salt. The method further avoids or minimizes losses of the metal salt during washing steps.
In another aspect, this invention is a method for preparing a metal-containing catalyst, comprising the steps of:
a) forming a first solution of a metal salt in water;
b) forming a second aqueous solution of a metal cyanide compound or a mixture thereof with a supplementary compound having a transition metal-containing anion which forms an insoluble salt with the metal in said metal salt;
c) in the substantial absence of an organic complexing agent, mixing said first and second solutions in proportions such that no more than a stoichiometric quantity of the metal salt is present in the reaction mixture, based on the number of equivalents of the metal cyanide compound and any supplementary compound present, under conditions such that the metal salt, metal cyanide salt and supplementary compound, if present, react to form an insoluble precipitate;
d) removing excess water from the insoluble precipitate to form an isolated precipitate
e) mixing the isolated precipitate with an impregnating solution containing an additional quantity of a metal salt dissolved in a mixture of water and a soluble organic complexing agent, under conditions such that the impregnating solution is substantially absorbed by the isolated precipitate, wherein the concentration of the metal salt in the impregnating solution is such that about 0.1 to about 1.5 moles of metal salt are provided in said impregnating solution per mole of metal cyanide compound and transition metal-containing anion in the isolated precipitate.
This second aspect of the invention provides a method by which a highly active metal-containing cyanide catalyst can be prepared, using a reduced amount of organic complexing agent and with an easily controlled excess of the metal salt. The activity of this catalyst is particularly surprising because conventional preparation methods for metal-containing catalysts require the addition of copious amounts of complexing agent during the initial precipitation of the catalyst complex.
In addition, this method provides a convenient way to make specialized catalyst complexes, because different metal salts can be used to make the initial precipitate and in the impregnating solution.
In a third aspect, this invention is a method for preparing a metal-containing cyanide catalyst, comprising the steps of:
a) forming a first solution of a metal salt in water;
b) forming a second aqueous solution of a metal cyanide compound or a mixture thereof with a supplementary compound having a transition metal-containing anion which forms an insoluble salt with the metal in said metal salt;
c) mixing said first and second solutions in proportions such that no more than a stoichiometric quantity of the metal salt is present in the reaction mixture, based on the combined num
Dianis William P.
Molzahn David C.
Dow Global Technologies Inc.
Wood Elizabeth D.
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