Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From heterocyclic reactant containing as ring atoms oxygen,...
Reexamination Certificate
2002-09-24
2004-03-02
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From heterocyclic reactant containing as ring atoms oxygen,...
C568S579000, C568S606000, C568S613000, C568S617000, C568S618000, C528S403000, C528S409000, C528S410000, C528S412000, C502S102000, C502S104000, C502S175000
Reexamination Certificate
active
06699961
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a double metal cyanide complex catalyst and to a process for its preparation.
BACKGROUND OF THE INVENTION
Double metal cyanide DMC) compounds are well known catalysts for epoxide polymerization, i.e. for polymerizing alkylene oxides like propylene oxide and ethylene oxide to yield poly(alkylene oxide) polymers, also referred to as polyether polyols. The catalysts are highly active, and give polyether polyols that have low unsaturation compared with similar polyols made using strong basis catalysts like potassium hydroxide. Conventional DMC catalysts are prepared by reacting aqueous solutions of metal salts and metal cyanide salts to form a precipitate of the DMC compound. Beside for the preparation of polyether polyols the catalysts can be used to make a variety of polymer products, including polyester polyols and polyetherester polyols. The polyols can be used for preparing polyurethanes by reacting them with polyisocyanates under appropriate conditions. Polyurethane products that can be made include polyurethane coatings, elastomers, sealants, foams, and adhesives.
DMC catalysts are usually prepared in the presence of a low molecular weight organic complexing agent, typically an ether, such as dimethoxyethane (glyme), or an alcohol, such as tert-butyl alcohol. The complexing agent favourably impacts the activity of the catalyst for epoxide polymerization. Other known complexing agents include ketones, esters, amides and ureas.
In one conventional preparation, aqueous solutions of zinc chloride and potassium hexacyanocobaltate are combined. The resulting precipitate of zinc hexacyano cobaltate is combined with an organic complexing agent. An excess of metal salt is often used in such preparation. For instance, in EP-A-555053 a process for making easily filterable DMC catalysts is disclosed, wherein the order of reagent addition, the reaction temperature, and the stoichiometric ratio of the reactants are controlled. EP-A-555053 discloses that at least a 100% stoichiometric excess of the metal salt relative to the metal cyanide salt should be used. In the working examples dimethoxyethane is used as the organic complexing agent. Zinc hexacyanocobaltate catalysts prepared by this procedure generally have zinc chloride to zinc hexacyanocobaltate mole ratios of about 0.6 or more.
Similarly, in EP-A-654302 a process for preparing substantially amorphous DMC catalysts is disclosed. These catalysts are preferably made using a water-soluble aliphatic alcohol complexing agent, such as tert-butyl alcohol. Again, an excess amount of metal salt is used to make the catalyst. In this method it is essential that metal salt, metal cyanide salt and complexing agent are intimately mixed, e.g. by high shear stirring or homogenization; conventional mechanical stirring is insufficient. Zinc hexacyanocobaltate catalysts described therein have more than 0.2 moles of metal salt per mole of zinc hexacyanocobaltate present, typically more than 0.5 moles of metal salt per mole of zinc hexacyano-cobaltate.
EP-A-755716 discloses two different methods for preparing crystalline DMC complex catalysts. In one method, the catalyst is made by using an excess amount of the metal salt, but the excess is less than a 100% stoichiometric excess relative to the amount of metal cyanide salt. The resulting catalyst contains less than about 0.2 moles of the metal salt per mole of DMC compound in the catalyst. In a second method, a larger excess of the metal salt can be used, but the resulting catalyst is subsequently washed with a mixture of water and an organic complexing agent in a manner effective to produce a DMC catalyst that contains less than about 0.2 moles of the metal salt per mole of DMC compound in the catalyst.
In WO-A-97/40086 a method for preparing DMC complex catalysts is disclosed, wherein aqueous solutions of excess metal salt and metal cyanide salt are reacted in the presence of an organic complexing agent using efficient mixing to form a slurry, combining the slurry with a polyether having a molecular weight less than 500 isolating the catalyst, washing the catalyst with an aqueous solution containing additional organic complexing agent and finally recovering the solid DMC complex catalyst. The polyether used suitably is a polyether polyol, such as polyethylene glycol. The final solid DMC catalyst contains 5 to 80% by weight of polyether polyol
In EP-A-700949 a similar method as in WO-A-97/40086 is disclosed, the difference being that a polyether (polyol) having a molecular weight greater than 500 is used.
In the methods discussed the initial DMC complex is formed in an aqueous reaction medium. The metal salts used and the salt formed during the complex formation reaction are well soluble in water and hence will be present in the aqueous phase. Since these salts are generally detrimental to the activity of the DMC complex catalyst, they need to be removed before the DMC catalyst is actually used for catalysing any alkoxylation reaction. For instance, assuming that zinc chloride is used as the metal salt and potassium hexacyanocobaltate as the metal cyanide salt, the unreacted zinc chloride and the potassium chloride formed in the reaction between zinc chloride and potassium hexacyanocobaltate would pose a problem, as they are detrimental to the activity of the final DMC catalyst. Hence, these salts must be removed as quantitatively as possible, which is generally done by separating the DMC catalyst particles from the aqueous phase.
All methods discussed so far have in common that the separation of the DMC complex catalyst particles from the salts-containing aqueous phase is rather cumbersome. For instance, in the working examples of WO-A-97/40086 the separation of DMC complex catalyst from the aqueous phase involves centrifugation and decantation, techniques which are not very practicable when to be used on an industrial scale. The separation used in the examples of EP-A-555053 involved filtration using a horizontal basket centrifugal filter and a light weight nylon fabric filter medium. Separation of the formed DMC catalyst particles in the working examples of EP-A-654302 involves either centrifugation or filtration, while in the examples of EP-A-755716 filtration is used. It will be understood that filtration is also not optimal for use on an industrial scale, inter alia because of filter plugging problems that are likely to occur. Moreover, the separation techniques used in the prior art processes discussed above are likely to result in some water and hence some salts remaining in the product. This is undesired.
SUMMARY OF THE INVENTION
The present invention aims to provide a method for preparing a DMC complex catalyst, in which the separation from the aqueous phase of the DMC catalyst particles formed can be performed efficiently, smoothly and cleanly on an industrial scale without losing any catalytic activity. Accordingly, the method should result in a highly active DMC catalyst, or in other words, the method of the present invention should have no negative effect of the activity of the DMC catalyst.
These and other objects have been achieved by a method wherein a specific liquid is added after the formation of the DMC catalyst particles, which liquid effect a phase separation resulting in an aqueous (bottom) phase containing the salts and a catalyst-containing phase floating on the aqueous phase.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly, the present invention relates to a process for the preparation of a DMC catalyst, which process comprises the steps of
(a) combining an aqueous solution of a metal salt with an aqueous solution of a metal cyanide salt and reacting these solutions, wherein at least part of this reaction takes place in the presence of an organic complexing agent, thereby forming a dispersion of a solid DMC complex in an aqueous medium;
(b) combining the dispersion obtained in step (a) with a liquid, which is essentially insoluble in water and which is capable of extracting the solid DMC complex formed in step (a) f
De Groot Riemer Alberts
Eleveld Michiel Barend
Smit Johan Paul
Van Kempen Ronald
Acquah Samuel A.
Shell Oil Company
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