Multimetal cyanide compounds, their preparation and their use

Details Multimetal cyanide compounds, their preparation and their use Multimetal cyanide compounds, their preparation and their use

1999-06-02

2003-09-02

Wood, Elizabeth D. (Department: 1755)

Catalyst, solid sorbent, or support therefor: product or process

Catalyst or precursor therefor

Inorganic carbon containing

C502S200000, C423S364000, C423S367000, C423S371000, C423S384000, C423S414000

Reexamination Certificate

active

06613714

ABSTRACT:

The present invention relates to multimetal cyanide compounds, their preparation and their use as catalysts for the preparation of polyether alcohols.
Polyether alcohols are used in large quantities for producing polyurethanes. They are usually prepared by catalytic addition of lower alkylene oxides, in particular ethylene oxide and propylene oxide, onto H-functional initiator substances. Catalysts used are usually basic metal hydroxides or salts, with potassium hydroxide having the greatest industrial importance.
In the synthesis of polyether alcohols having long chains, as are used, in particular, for producing flexible polyurethane foams, secondary reactions occur as chain growth progresses and these lead to faults in the chain structure. These by-products are referred to as unsaturated constituents and have an adverse effect on the properties of the resulting polyurethanes. There has therefore been no lack of attempts in the past to prepare polyether alcohols having a low content of unsaturated constituents. For this purpose, in particular, the alkoxylation catalysts used are altered in a targeted way. Thus, EP-A-268 922 proposes using cesium hydroxide as a catalyst for the preparation of polyether alcohols. Although this does enable the content of unsaturated constituents to be reduced, cesium hydroxide is expensive and disposing of it can be problematic.
Furthermore, the use of multimetal cyanide complexes, usually zinc hexanocyanometalates, for preparing polyether alcohols having low contents of unsaturated constituents is known. There are a large number of documents which describe the preparation of such compounds. Thus, DD-A-203 735 and DD-A-203 734 describe the preparation of polyetherols using zinc hexacyanocobaltate.
The preparation of the zinc hexacyanometalates is also known. These catalysts are usually prepared by reacting solutions of metal salts, usually zinc chloride, with solutions of alkali metal or alkaline earth metal cyanometalates such as potassium hexacyanocobaltate. A water-miscible, heteroatom-containing component is generally added as a ligand to the resulting suspension immediately after the precipitation process. This component can also be present initially in one or both starting solutions. This water-miscible, heteroatom-containing component can be, for example, an ether, polyether, alcohol, ketone or a mixture thereof. Such processes are described, for example, in U.S. Pat. Nos. 3,278,457, 3,278,458, 3,278,459, 3,427,256, 3,427,334, 3,404,109, 3,829,505, 3,941,849, EP 283,148, EP 385,619, EP 654,302, EP 659,798, EP 665,254, EP 743,093, EP 755,716, U.S. Pat. Nos. 4,843,054, 4,877,906, 5,158,922, 5,426,081, 5,470,813, 5,482,908, 5,498,583, 5,523,386, 5,525,565, 5,545,601, JP 7,308,583, JP 6,248,068, JP 4,351,632 and U.S. Pat. No. 5,545,601.
DD-A-148 957 describes the preparation of zinc hexacyanoiridate and its use as catalyst in the preparation of polyether alcohols. Here, hexacyanoiridic acid is used as one starting material. This acid is isolated as a solid and is used in this form.
EP 862 947 describes the preparation of other double metal cyanide complexes, in particular the use of hexacyanocobaltic acid or its aqueous solutions as starting material. The double metal cyanides produced as described in EP 862 947 have a high reactivity in the ring-opening polymerization of alkylene oxides.
Although multimetal cyanide catalysts have high polymerization activities, there has been no lack of attempts to achieve a further increase in the catalytic activity of the multimetal cyanide compounds. The multimetal cyanide compounds described are usually amorphous. The preparation of such multimetal cyanide compounds is disclosed, inter alia, in EP 654,302. It has also been able to be shown that the activity of these catalysts can be increased further by incorporation of polymers. Thus, EP 700,949 describes double metal cyanide complexes which have an increased reactivity and contain from 5 to 80% by weight, based on the catalyst, of polyethers having a molar mass of greater than 500 dalton. WO 97/40 086 describes double metal cyanide catalysts which have an increased reactivity and contain from 5 to 80% by weight of polyethers having molar masses of less than 500 dalton. WO 98/16310 discloses double metal cyanides which contain from 2 to 80% by weight of functionalized polymers. However, no use of polyetherols is described. The catalysts described in the abovementioned documents are amorphous. Advantages of the use of crystalline multimetal cyanide compounds are not disclosed there.
In contrast to the amorphous multimetal cyanide compounds, fewer possible ways of increasing the catalyst activity have been described in the case of the crystalline multimetal cyanide compounds. According to EP 755,716, active crystalline multimetal cyanide compounds are obtained when these catalysts comprise not only the multimetal cyanide component but also residues of metal salt. The amount of metal salt per mole of multimetal cyanide compound has to be less than 0.2 mol.
The further development of active crystalline multimetal cyanide compounds is desirable since crystalline materials are accessible to a far greater number of methods of examination. Thus, X-ray diffraction analysis can elucidate the structure of the materials, scanning electrode microscopy can give information on the morphology of the crystals and transmission electron microscopy even enables the outer surfaces of the crystals to be assigned to various crystallographic planes. All this leads to an improved understanding of the catalyst and its mode of action and provides further starting points for improving the activity.
It is an object of the present invention to develop catalysts in which no large amounts of polymeric compounds extraneous to the system remain. A further object is to prepare the multimetal cyanide compounds in a morphology which allows them to optimally display their intrinsic activity.
We have found that this object is achieved by altering the morphology of crystalline multimetal cyanide compounds by preparing them in the presence of surface-active substances.
The present invention accordingly provides a process for preparing multimetal cyanide compounds comprising the following process steps:
a) Addition of an aqueous solution of a water-soluble metal salt of the formula M
1
m
(X)
n
, where M
1
is at least one metal ion selected from the group consisting of Zn
2+
, Fe
2+
, Co
3+
, Ni
2+
, Mn
2+
, Co
2+
, Sn
2+
, Pb
2+
, Fe
3+
, Mo
4+
, Mo
6+
, Al
3+
, V
5+
, Sr
2+
, W
4+
, W
6+
, Cu
2+
, Cr
2+
, Cr
3+
, Cd
2+
, Hg
2+
, Pd
2+
, Pt
2+
, V
2+
, Mg
2+
, Ca
2+
, Ba
2+
and mixtures thereof,
X is at least one anion selected from the group consisting of halide, hydroxide, sulfate, carbonate, cyanide, thiocyanate, isocyanate, carboxylate, in particular formate, acetate, propionate or oxalate, and nitrate and m and n are integers which satisfy the valences of M
1
and X,
to an aqueous solution of a cyanometalate compound of the formula H
a
M
2
(CN)
b
(A)
c
, where M
2
is at least one metal ion selected from the group consisting of Fe
2+
, Fe
3+
, Co
3+
, Cr
3+
, Mn
2+
, Mn
3+
, Rh
3+
, Ru
2+
, Ru
3+
, V
4+
, V
5+
, Co
2+
, Ir
3+
and Cr
2+
and also mixtures thereof and M
2
can be identical to or different from M
1
,
H is hydrogen or a metal ion, usually an alkali metal ion, an alkaline earth metal ion or an ammonium ion,
A is at least one anion selected from the group consisting of halide, hydroxide, sulfate, carbonate, cyanate, thiocyanate, isocyanate, carboxylate and nitrate, in particular cyanide, where A can be identical to or different from X, and a, b and c are integers which are selected so that the cyanide compound is electrically neutral,
where one or both solutions may, if desired, comprise at least one water-miscible, heteroatom-containing ligand selected from the group consisti

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