Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Inorganic carbon containing
Reexamination Certificate
2002-08-20
2004-02-10
Wood, Elizabeth (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Inorganic carbon containing
C502S200000
Reexamination Certificate
active
06689710
ABSTRACT:
The invention also provides DMC catalysts which can be prepared by the process of the present invention.
Furthermore, the invention provides for the use of the DMC catalysts prepared by the process of the present invention for the ring-opening polymerization of alkylene oxides and also provides a process for preparing polyether alcohols by ring-opening polymerization of alkylene oxides using the DMC catalysts of the present invention.
The DMC catalysts prepared by the process of the present invention are weakly agglomerated if at all and have a high catalytic activity. For the purposes of the present invention, agglomeration is the assembly of primary particles to form secondary particles. The size and habit of the primary particles can be determined, for example, by means of scanning electron micrographs. Scanning electron micrographs also provide initial information on the agglomeration of the primary particles.
For the purposes of the present invention, solids are regarded as agglomerated if more than 50% of the secondary particles present in the solid consist of more than 20-30 primary particles. For the present purposes, solids are weakly agglomerated if more than 50% of the secondary particles consist of less than 10 primary particles.
One possible way of obtaining information on the state of agglomeration of solids is to combine scanning electron micrographs with particle size measurement by means of laser light scattering. The sizes of the primary crystallites can be determined very well from scanning electron micrographs. On the other hand, the size of the secondary particles can be readily determined by laser light scattering. Solids are then considered as not agglomerated or only weakly agglomerated when the mean secondary particle size determined by laser light scattering (X50 value) differs from the sizes of the primary particles by a factor of less than 10.
For the purposes of the present invention, a primary crystallite or primary particle is the individual crystallite which can be seen, for example, on scanning electron micrographs. These primary particles can then be assembled to form agglomerates, namely the secondary particles.
The process of the present invention in which the multimetal cyanide compounds having the desired crystal structure are not precipitated directly but instead are produced by a precipitation cyanometalate solution to the metal salt solution under high-shear stirring.
This high-shear stirring possibly has the effect, inter alia, of breaking agglomerates which form during the precipitation.
The agglomeration of the DMC catalysts should be suppressed as far as possible, since the reduction in the number of active centers in the DMC catalysts caused by the formation of agglomerates is assumed to be a possible cause of the secondary reactions which occur.
Precipitation under high-shear stirring is technically extremely complicated and problematical, particularly with a view to a reproducible, good quality of the catalyst, in the case of large batches as are necessary in the industrial preparation of the DMC catalysts. Precipitation under high-shear stirring is particularly problematical when crystalline solids having a high degree of crystallinity are to be obtained instead of amorphous materials.
It is an object of the present invention to provide multimetal cyanide catalysts which are not agglomerated or only weakly agglomerated, without complicated technical solutions being necessary. In particular, multimetal cyanide catalysts of the zinc hexacyanocobaltate type having a very good crystal structure should be provided.
We have found that this object is achieved by carrying out the preparation of multimetal cyanide catalysts in two stages, where the first step comprises a reaction stage in which the DMC catalyst after precipitation is initially present as an intermediate which differs from the desired crystal structure, and this intermediate is then converted into the desired crystal structure in a second step. This step in which the DMC catalyst is converted into the desired crystal structure will hereinafter be referred to as recrystallization.
The present invention accordingly provides a process for preparing DMC catalysts by reacting a metal salt with a cyanometalate compound, in which the reaction is carried out in two stages, where the first step initially comprises a reaction stage in which the DMC catalyst is present as an intermediate differing from the desired crystal structure, and this intermediate is then converted into the desired crystal structure in a second step.
Preparation of Multimetal Cyanide Compounds
Multimetal cyanide catalysts, also known as DMC catalysts, are effective catalysts for preparing polyetherols by ring-opening polymerization of alkylene oxides. Multimetal cyanide catalysts can be used in concentrations down to less than 100 ppm in alkylene oxide polymerization. WO 97/23,544 describes catalyst concentrations less than or equal to 15 ppm. However, multimetal cyanide catalyst concentrations of less than 100 ppm very frequently result in problems in the polymerization of the alkylene oxides. Thus, gradual deactivation of the catalyst can occur during the polymerization. In a batch process, significant quality fluctuations of the polyetherols prepared in this way can occur. It is thus possible for different molecular weight distributions, viscosities and contents of unsaturated constituents to be obtained from batch to batch.
A fall-off of the catalyst activity in the polymerization can lead to a complete cessation of the reaction and thus to dangerous situations in the production plants.
A great problem which occurs when using multimetal cyanide catalysts in catalyst concentrations of less than 100 ppm is the formation of a very high molecular weight tail in the polyethers. As described in U.S. Pat. No. 5,919,988, this high molecular weight tail can lead, in critical polyurethane foam formulations, to collapse of the foams.
To avoid or reduce the high molecular weight tail in the polyethers, a number of approaches have been explored. U.S. Pat. No. 5,777,177 describes a specific way of carrying out the polyether synthesis, which is said to be suitable, inter alia, for reducing the proportion of high molecular weight polyether.
In the preparation of multimetal cyanide catalysts, too, there has been no lack of attempts to improve the process for preparing multimetal cyanide catalysts so as to suppress the formation of high molecular weight polyethers when the catalysts are used for the synthesis of polyethers. Thus, U.S. Pat. No. 5,470,813 describes the preparation of improved multimetal cyanide catalysts which are essentially amorphous and are prepared by combining the starting materials for the precipitation under high-shear stirring. An improved embodiment of the process of U.S. Pat. No. 5,470,813 is disclosed in U.S. Pat. No. 5,712,216. Here, an improved multimetal cyanide catalyst is produced by reaction of aqueous cyanometalate and metal salt solutions in the presence of tert-butanol by adding the step and a subsequent recrystallization step enables them to be obtained in weakly agglomerated or unagglomerated form.
The DMC catalysts prepared by the process of the present invention preferably have a crystalline structure and preferably crystallize in a monoclinic crystal system.
The DMC catalysts prepared by the process of the present invention mostly have the formula (I)
M
1
a
[M
2
(CN)
b
(A)
c
]
d
.fM
1
g
X
n
.h(H2O).eL(I),
where
M
1
is a metal ion selected from the group consisting of Zn2+, Fe2+, Co3+, Ni2+, Mn2+, Co2+, Sn2+, Pb2+, Mo4+, Mo6+, Al3+, V4+, V5+, Sr2+, W4+, W6+, Cr2+, Cr3+, Cd2+, Hg2+, Pd2+, pt2+, V2+, Mg2+, Ca2+, Ba2+, Cu2+,
M
2
is a metal ion selected from the group consisting of Fe2+, Fe3+, Co2+, Co3+, Mn2+, Mn3+, V4+, V5+, Cr2+, Cr3+, Rh3+, Ru2+, Ir3+,
and M
1
and M
2
are i
Baum Eva
Franke Dirk
Grosch Georg Heinrich
Harre Kathrin
Munzinger Manfred
BASF - Aktiengesellschaft
Borrego Fernando A.
Wood Elizabeth
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