WO2001090217A1

WO2001090217A1 - Method for preparing metal cyanide catalysts and for using same

Info

Publication number: WO2001090217A1
Application number: PCT/US2000/018623
Authority: WO
Inventors: Katherine S. Clement; Louis L. Walker; David C. Molzahn
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 2000-05-19
Filing date: 2000-07-07
Publication date: 2001-11-29
Anticipated expiration: 2002-11-19
Also published as: AR024683A1; AU2000260776A1

Abstract

Metal cyanide catalyst dispersions in initiator compounds are prepared by precipitating the catalyst in an aqueous phase, mixing the resulting slurry with the initiator and stripping off the water and other volatiles. Using this method, an active alkylene oxide polymerization catalyst is prepared, and the preparation method is greatly simplified. Further, it is not necessary to use a separate organic complexing agent in the preparation.

Description

METHOD FOR PREPARING METAL CYANIDE CATALYSTS AND FOR USING

SAME

This invention relates to methods for making metal cyanide catalysts complexes and to methods for polymerizing alkylene oxides in the presence of a metal cyanide catalyst.

Polyethers are prepared in large commercial quantities through the polymerization of alkylene oxides such as propylene oxide and ethylene oxide. This polymerization reaction is usually conducted in the presence of an initiator compound and a catalyst. The initiator compound usually determines the functionality (number of hydroxyl groups per molecule of the polymer) and in some instances imparts some desired functionality. The catalyst is used to provide an economical rate of polymerization.

Metal cyanide complexes are becoming increasingly important alkylene oxide polymerization catalysts. These complexes are often referred to as "double metal cyanide" or "DMC" catalysts, and are the subject of a number of patents, including, for example, U.S. Patent Nos. 3,278,457, 3,278,458, 3,278,459, 3,404,109, 3,427,256, 3,427,334, 3,427,335 and 5,470,813, among many others. In some instances, these complexes provide the benefit of fast polymerization rates and narrow polydispersities. Additionally, these catalysts are associated with the production of polyethers having very low levels of monofunctional unsaturated compounds.

Development efforts have focussed mainly on one specific metal cyanide catalyst complex, zinc hexacyanocobaltate, complexed with a specific complexing agent, t-butanol. The catalyst is typically prepared in a multistep process. First, separate solutions of zinc chloride and potassium hexacyanocobaltate are prepared. These solutions are then mixed together, followed immediately by adding a mixture of water and the complexing agent, t-butanol. A catalyst complex precipitates and is recovered and washed multiple times with mixtures of water and t-butanol. This washing process removes unwanted occluded ions, particularly potassium and chlorine, and contributes the complexing agent to the structure of the catalyst complex. Often, a polyether polyol is included in one or more of these washings. Finally, the catalyst complex is dried and ground. It is then mixed with an initiator compound and an alkylene oxide to prepare the desired polyether.

The process just described is complex, requiring several washing steps. It also requires that excesses of water and t-butanol be used. The t-butanol complexing agent itself causes the complex to be difficult to handle. Often, a polyether polyol must be added to facilitate easy handling of the catalyst complex.

Thus, it would be desirable to provide a less expensive, more convenient method for preparing a metal cyanide catalyst complex and a simple method for using such catalyst complexes.

In one aspect, this invention is a method for preparing an active metal cyanide catalyst, comprising

(I) mixing an aqueous solution or dispersion of a metal cyanide compound with an aqueous solution or dispersion of a metal salt in the presence of an organic complexing agent, under conditions such that a precipitate is formed in a supematant liquid, wherein a) the metal cyanide compound is represented by the general formula B_u[M¹(CN)_r(X)J_v in which B represents a hydrogen or a metal ion that forms a water-soluble salt with the M¹(CN)_r(X)_t group, u and v are integers that reflect an electrostatically neutral compound, M¹ is a transition metal ion; each X independently represents a group other than cyanide that coordinates with the M¹ ion, r is from 4 to 6 and t is from 0-2; and b) the metal salt is represented by the general formula M_xA_y wherein M is a metal ion that forms an insoluble precipitate with the metal cyanide grouping M¹(CN)_r(X)_t, A represents an anion, and x and y are integers that reflect an electrostatically neutral salt;

(II) diluting the precipitate in an initiator compound without first isolating a dried precipitate, and

(III) removing the water from the resulting dispersion. This method provides a convenient way to make metal cyanide catalysts as fine dispersions in an initiator compound. In this process, multiple process steps, particularly catalyst washings, are eliminated. In preferred embodiments, it is possible to eliminate washing, drying and catalyst grinding steps. In addition, the organic complexing agent can be the same material as the initiator compound. Surprisingly, a very active catalyst is prepared.

In a second aspect, this invention is a process wherein a dispersion made in accordance with the first aspect is mixed with an alkylene oxide and the resulting mixture subjected to conditions sufficient to polymerize the alkylene oxide to form a poly(alkylene oxide) based on said initiator compound.

In the first step of the invention, an aqueous solution or dispersion of a metal compound is mixed with an aqueous solution or dispersion of a metal salt. The metal compound is represented by the general formula B_u[M¹(CN)_r(X),]_v, in which M\ X, r, t, u and v are as described before.

M¹ is preferably Fe* Fe⁺², Co Co⁺², Cr⁺², Cr* Mn⁺², Mn* lr* Ni⁺², Rh* Ru⁺² ₍ V"⁴ and V*. Among the foregoing, those in the plus-three oxidation state are more preferred. Co* and Fe* are even more preferred and Co* is most preferred.

Preferred groups X include anions such as halide (especially chloride), hydroxide, sulfate, carbonate, oxalate, thiocyanate, isocyanate, isothiocyanate, C carboxylate and nitrite (NO₂ ^~), and uncharged species such as CO, H₂O and NO. Particularly preferred groups X are NO, NO₂ ^"and CO. r is preferably 5 or 6, most preferably 6; t is preferably 0 or 1 , most preferably 0. w is usually 2 or 3, and is most typically 3. In most cases, r + 1 will equal six.

Mixtures of two or more metal cyanide compounds can be used. In addition, the metal cyanide solution may also contain compounds that have the structure B_u[M²(X)_e]_v, wherein M² is a transition metal and u, v and X is as before. M² may be the same as or different from M¹. The X groups in any M²(X)_β do not have to be all the same.

B is preferably hydrogen, sodium or potassium and is most preferably hydrogen. Compounds in which B is hydrogen are conveniently formed by passing an aqueous solution of the corresponding alkali metal salt through a cation-exchange resin that is in the hydrogen form.

The metal salt is represented by the general formula M_xA_y. M is preferably a metal ion selected from the group consisting of Zn⁺², Fe⁺², Co⁺², Ni⁺², Mo"⁴, Mo*, Al*, V⁴⁴, V*, Sr⁺², W⁴, W Mn* Sn* Sn⁴⁴, Pb* Cu La* and Cr*. M is more preferably Zn Fe⁺², Co⁺², Ni* La* and Cr*. M is most preferably Zπ⁺².

Suitable anions A include halides such as chloride and bromide, nitrate, sulfate, carbonate, cyanide, oxalate, thiocyanate, isocyanate, perchlorate, isothiocyanate, an alkanesulfonate such as methanesulfonate, an arylenesulfonate such as p- toluenesulfonate, trifluoromethanesulfonate (triflate) and a C_{1 4} carboxylate. Chloride ion is especially preferred.

Mixtures of two or more metal salts can be used. In such cases, the metals in the metal salt compounds do not have to be the same.

The solutions are mixed in proportions such that at least a stoichiometric amount of the metal salt is provided, based on the amount of metal cyanide compound. Preferably about 1.2 to about 2 equivalents of metal ion (M) are delivered per equivalent of M¹(CN)_r(X)_t ion (or combined equivalents of M¹(CN)_r(X)_t and M²(X)_e ions, when M²(X)₆ ions are present). It is preferred that the mixing be done with agitation. Agitation is preferably continued for a period after the mixing is completed. The metal cyanide catalyst precipitates and forms a fine dispersion in the aqueous supernatant. The catalyst is represented by the formula M_b[M¹(CN)_r(X)_t]_o[M²(X)₆]_d, where d is zero or a positive number, b, c and d together reflect an electrostatically neutral complex, and M, M\ M², X, r and t are as defined before.

It has been found that catalyst performance tends to be superior when an excess of metal salt is used. Thus, if only a stoichiometric amount of metal salt is used during the precipitation step, the catalyst can be treated with additional metal salt in a subsequent step. The additional metal salt can be of the form M³ A , where M³ is the same or different than M, and A, x and y are as defined before.

The metal cyanide catalyst is precipitated in the presence of an organic complexing agent. The term "complexing agent" is used herein to refer to a heteroatom-containing organic compound that becomes associated with the metal cyanide catalyst. The nature of the complexing is not fully understood and may be due to a combination of factors. The complexing may be due to the formation of a coordinate bond between a heteroatom of the complexing agent and one or more of the metal ions (M, M¹, M², M³) of the metal cyanide catalyst. Another explanation of the complexing is that it is due to the complexing agent occupying vacancies within the crystalline structure of the metal cyanide, or that it otherwise is occluded within or bound into the crystalline lattice. However, it is not intended to limit this invention to any particular complexing mechanism.

A great number of complexing agents are potentially useful, although catalyst activity may vary according to the selection of a particular complexing agent. Examples of such complexing agents include alcohols, aldehydes, ketones, ethers, amides, nitriles, and sulfides.

Suitable alcohols include monoalcohols and polyalcohols. Suitable monoalcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, octanol, octadecanoi, 3-butyn-1 -ol, 3-butene-1 -ol, propargyl alcohol, 2-methyl-2-propanol, 2-methyl-3-butyn-2-ol, 2-methyl-3-butene-2-ol, 3-butyn- 1 -ol, 3-butene-1-ol, and 1-t-butoxy-2-propanol. Suitable monoalcohols also include halogenated alcohols such as 2-chloroethanol, 2-bromoethanol, 2-chloro-l-propanol, 3-chloro-1-propanol, 3-bromo-1-propanol, 1 ,3-dichloro-2-propanoi, 1 -chloro-2-methyl- 2-propanol as well as nitroalcohols, keto-alcohols, ester-alcohols, cyanoalcohols, and other inertly substituted alcohols.

Suitable polyalcohols include ethylene glycol, propylene glycol, glycerine, 1 ,1 ,1-trimethylol propane, 1 ,1 ,1-trimethyloi ethane, 1 ,2,3-trihydroxybutane, penta- erythritol, xylitol, arabitol, mannitol, 2,5-dimethyl-3-hexyn-2,5-diol, 2,4,7,9-tetramethyl- 5-decyne-4,7-diol, sucrose, sorbitol, alkyl glucosides such as methyl glucoside and ethyl glucoside. Low molecular weight polyether polyols, particular those having an equivalent weight of about 350 or less, more preferably about 125-250, are also useful complexing agents.

Suitable aldehydes include formaldehyde, acetaldehyde, butyraldehyde, valeric aldehyde, glyoxal, benzaldehyde, and toluic aldehyde. Suitable ketones include acetone, methyl ethyl ketone, 3-pentanone, and 2-hexanone. Suitable ethers include cyclic ethers such as dioxane, trioxymethylene and paraformaldehyde as well as acyclic ethers such as diethyl ether, 1 -ethoxy pentane, bis(betachloro ethyl) ether, methyl propyl ether, diethoxy methane, dialkyl ethers of alkylene or polyalkylene glycols (such as ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and octaethylene glycol dimethyl ether).

Amides such as formamide, acetamide, propionamide, butyramide and valeramide are useful complexing agents. Esters such as amyl formate, ethyl formate, hexyl formate, propyl formate, ethyl acetate, methyl acetate, and triethylene glycol diacetate can be used as well. Suitable nitriles include acetonitrile, and proprionitrile. Suitable sulfides include dimethyl sulfide, diethyl sulfide, dibutyl sulfide, and diamyl sulfide.

Compounds having an S=O group, such as dimethyl sulfoxide and sulfolane, are also useful complexing agents.

Preferred complexing agents are those that contain hydroxyl groups and also function as an initiator compound when the catalyst is used to polymerize an alkylene oxide.

The complexing agent is either added to one or both solutions of starting materials before they are mixed, or else is added to them immediately after they are mixed together. Once the starting solutions and complexing agent are mixed, they are agitated for several minutes until the catalyst complex precipitates and a slurry is formed.

If the starting metal cyanide compound is an alkali metal salt, it is preferable to remove at least most of the alkali metal ions from the catalyst slurry. As the alkali metal ions will usually be dissolved in the supernatant fluid, a convenient method of removing them is through a solid/liquid separation technique, such as filtration or, more preferably, centrifugation followed by decanting. If more complete removal of the alkali metal ions is desired, the precipitate may be washed one or more times with water, more complexing agent, or a mixture of water and complexing agent, but this is not required. There is no need to dry the precipitate at any point in this procedure, it being an advantage of this process that the process steps attendant to drying, especially grinding the dried catalyst, can be eliminated.

If the metal cyanide compound is in the hydrogen form (i.e. B is hydrogen), there is no need to separate the precipitated catalyst complex from the supernatant fluid.

If desired, the precipitated catalyst complex may be washed with or diluted with additional quantities of the complexing agent, if the complexing agent is different from the initiator compound, but this is usually not preferred. If the complexing agent is an initiator compound, there is no need to perform any such washings.

The precipitated catalyst (and optionally the supernatant fluid) is then dispersed into the initiator compound without isolating a dried catalyst. The initiator compound is a material having at least one heteroatom-containing group that will react with an alkylene oxide to form a covalent bond between a carbon atom of the alkylene oxide and the heteroatom, and opening the ring of the alkylene oxide to form a terminal hydroxyl group. Suitable initiator compounds are alcohols, thiols (R-SH compounds) and aliphatic carboxylic acids. The initiator compound may contain as few as one or as many as eight or more such heteroatom-containing groups, depending on the desired nominal functionality of the product polyether. In addition, the initiator compound may contain one or more other functional groups that may be desirable in the product polyether, such as alkenyl or alkynyl unsaturation.

Suitable initiator compounds include monoalcohols such methanol, ethanol, n- propanol, isopropanol, n-butanol, isobutanol, t-butanol, 1 -t-butoxy-2-propanol, octanol, octadecanol, 3-butyn-1-ol, 3-butene-1 -ol, propargyl alcohol, 2-methyl-2-propanol, 2- methyl-3-butyn-2-ol, 2-methyl-3-butene-2-oi, 3-butyn-1 -ol, and 3-butene-1-ol. The suitable monoalcohol initiator compounds include halogenated alcohols such as 2- chloroethanol, 2-bromoethanol, 2-chloro-1 -propanol, 3-chIoro-1 -propanol, 3-bromo-1- propanol, 1 ,3-dichloro-2-propanol, 1 -chloro-2-methyl-2-propanol as well as nitroalcohols, keto-alcohols, ester-alcohols, cyanoalcohols, and other inertly substituted alcohols. Suitable polyalcohol initiators include ethylene glycol, propylene glycol, glycerine, 1 ,1 ,1-trimethylol propane, 1 ,1 ,1-trimethylol ethane, 1 ,2,3- trihydroxybutane, pentaerythritoi, xylitol, arabitol, mannitol, 2,5-dimethyl-3-hexyn-2,5- diol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, sucrose, sorbitol, alkyl glucosides such a methyl glucoside and ethyl glucoside. Low molecular weight polyether polyols, particular those having an equivalent weight of about 350 or less, more preferably about 125-250, are also useful initiator compounds.

When the initiator compound is different from the complexing agent, it is preferred that the complexing agent is the more volatile of the two, so that any excess complexing agent can be stripped away from the final initiator/catalyst complex dispersion if desired. This is especially important if the complexing agent is an alcohol having an undesirable functionality.

At least enough of the dispersion of the metal cyanide catalyst complex is added to the initiator to provide a catalytically effective amount of the catalyst complex in the initiator mixture. Thus, the amount of catalyst complex added is generally at least about 50 ppm, based on the combined weight of the initiator plus catalyst complex, preferably at least about 200 ppm, more preferably at least about 1000 ppm. Preferably, the initiator/catalyst complex mixture as prepared according to the invention will contain from about 0.2 weight percent, more preferably from about 0.5 weight percent, most preferably from about 1 weight percent, to about 50 weight percent, preferably about 25 weight percent, more preferably about 10 weight percent, metal catalyst complex, based on the combined weight of metal catalyst complex (as M_b[M¹ (CN)_r(X)_t]_c[M²(X)J_d • nM³ _xA_y) and initiator. It is more preferred to form a dispersion that has a higher concentration of the metal catalyst than will be used in the subsequent alkylene oxide polymerization. Such a more concentrated dispersion can be divided and/or diluted with additional initiator when it is used to prepare a polyether.

After the metal catalyst solution and initiator are mixed, any remaining water is removed. Removal is conveniently performed by stripping the water and other volatiles through the application of heat and/or vacuum. If the complexing agent is a different material than the initiator compound, excess quantities of it can be removed as well.

The resulting product is usually a fine dispersion of the metal cyanide catalyst complex in the initiator. The metal cyanide catalyst complex is present in an active form, and no other treatment or preparation is required. The metal-containing cyanide catalyst can be represented by the general formula:

M_b[M¹(CN)_r(X),]_c[M²(X)_e]_d . nM³ _xA_y

wherein M, M¹, M², M³, X, A, b, c, d, r, t, x and y are ail as defined before, n is a number indicating the relative number of moles of M³ _xA_y. M³ may be the same or different than M. M³ will be different from M, for example, when a stoichiometric amount of a metal salt M A is used in precipitating the catalyst complex, and the precipitated catalyst is then treated with an additional quantity of an M³ _xA_ysalt. Among the catalysts of particular interest are:

Zinc hexacyanocobaltate • nZnCI₂;

Zn[Co(CN)_sNO]-nZnCI₂; Zn_s[Co(CN)₆]₀[Fe(CN)₅NO]_p ^» nZnCI₂ (o, p = positive numbers, s=1.5o + p);

Zn_s[Co(CN)₆]_o[Co(NO₂)₆]_p[Fe(CN)₅NO]_q • nZnCI₂ (o, p, q = positive numbers, s=1.5(o+p)+q);

Zinc hexacyanocobaltate • nLaCI₃;

Zn[Co(CN)₅NO]^« nLaCI₃; Zn[Co(CN)J_o[Fe(CN)₅NO]_p ^» nLaCI₃ (o, p = positive numbers, s=1.5o + p);

Zn_s[Co(CN)_e]_o[Co(NO₂)_β]_p[Fe(CN)₅NO]_q • nLaCI₃ (o, p, q = positive numbers, s=1.5(o+p)+q);

Zinc hexacyanocobaltate • nCrCI₃;

Zn[Co(CN)₅NO]^« nCrCI₃; Zn_s[Co(CN)₆]_o[Fe(CN)_sNO]_p ^» nCrCI₃ (o, p = positive numbers, s=1.5o + p);

Zn_s[Co(CN)_e]_o[Co(NO₂)J_p[Fe(CN)₅NO]_q • nCrCI₃ (o, p, q = positive numbers, s=1.5(o+p)+q);

Magnesium hexacyanocobaltate • nZnCI₂;

Mg[Co(CN)₅NO] • nZnCI₂; Mg_s[Co(CN)₆]_o[Fe(CN)₅NO]_p ^» nZnCI₂ (o, p = positive numbers,s=1.5o + p);

Mg_s[Co(CN)₆]_o[Co(NO₂)_β]_p[Fe(CN)₅NO]_q • nZnCI₂ (o, p, q = positive numbers, s=1.5(o+p)+q);

Magnesium hexacyanocobaltate • nLaCI₃;

Mg[Co(CN)_sNO]^» nLaCI₃; Mg_s[Co(CN)₆]_o[Fe(CN)₅NO]_p ^» nLaCI₃ (o, p = positive numbers, s=1.5o + p);

Mg_s[Co(CN)_β]₀[Co(NO₂)₆]_p[Fe(CN)₅NO]_q • nLaCI₃ (o, p, q = positive numbers, s=1.5(o+p)+q);

Magnesium hexacyanocobaltate • nCrCI₃;

Mg[Co(CN)_sNO] • nCrCI₃; Mg_s[Co(CN)_e]₀[Fe(CN)_sNO]_p ^» nCrCI₃ (o, p = positive numbers, s=1.5o + p);

Mg_s[Co(CN)_e]_o[Co(NO₂)₆]_p[Fe(CN)₅NO]_q • nCrCI₃ (o, p, q = positive numbers, s=1.5(o+p)+q); as well as the various complexes such as are described at column 3 of U. S. Patent

No. 3,404,109. The catalyst complex of the invention is used to polymerize alkylene oxides to make polyethers. In general, the process includes mixing a catalytically effective amount of the catalysfinitiator dispersion with an alkylene oxide under polymerization conditions and allowing the polymerization to proceed until the supply of alkylene oxide is essentially exhausted. The concentration of the catalyst is selected to polymerize the alkylene oxide at a desired rate or within a desired period of time. An amount of catalyst sufficient to provide from about 5 to about 10,000 parts by weight metal cyanide catalyst (calculated as M_b[Mⁱ(CN)_r(X),]_o[M²(X)_e]_d • nM³ _xA_y, exclusive of any associated water and initiator) per million parts combined weight of alkylene oxide, and initiator and comonomers, if present. More preferred catalyst levels are from about 20, especially from about 30, to about 5000, more preferably to about 1000 ppm, even more preferably to about 100 ppm, on the same basis.

Among the alkylene oxides that can be polymerized with the catalyst complex of the invention are ethylene oxide, propylene oxide, 1 ,2-butylene oxide, styrene oxide, butadiene monoxide and mixtures thereof. Various alkylene oxides can be polymerized sequentially to make block copolymers. More preferably, the alkylene oxide is propylene oxide or a mixture of propylene oxide and ethylene oxide and/or butylene oxide. Especially preferred are propylene oxide alone or a mixture of at least 75 weight % propylene oxide and up to about 25 weight % ethylene oxide.

In addition, monomers that will copolymerize with the alkylene oxide in the presence of the catalyst complex can be used to prepare modified polyether polyols. Such comonomers include oxetanes as described in U.S. Patent Nos. 3,278,457 and 3,404,109, and anhydrides as described in U.S. Patent Nos. 5,145,883 and 3,538,043, which yield polyethers and polyester or polyetherester polyols, respectively. Hydroxyalkanoates such as lactic acid, 3-hydroxybutyrate, 3-hydroxyvalerate (and their dimers), lactones and carbon dioxide are examples of other suitable monomers that can be polymerized with the catalyst of the invention.

The polymerization reaction typically proceeds well at temperatures from about 25 to about 150°C or more, preferably from about 80-130°C. A convenient polymerization technique involves charging the catalyst dispersion to a reactor and pressurizing the reactor with the alkylene oxide. Polymerization proceeds after a short induction period as indicated by a loss of pressure in the reactor. Once the polymerization has begun, additional alkylene oxide is conveniently fed to the reactor on demand until enough alkylene oxide has been added to produce a polymer of the desired equivalent weight.

Another convenient polymerization technique is a continuous method. In such continuous processes, the activated catalyst/initiator dispersion is continuously fed into a continuous reactor such as a continuously stirred tank reactor (CSTR) or a tubular reactor. A feed of alkylene oxide is introduced into the reactor and the product continuously removed.

The catalyst of this invention is especially useful in making propylene oxide homopolymers and random copolymers of propylene oxide and up to about 15 weight percent ethylene oxide (based on all monomers). The polymers of particular interest have a hydroxyl equivalent weight of from about 800, preferably from about 1000, to about 5000, preferably about 4000, more preferably to about 2500, and unsaturation of no more than 0.02 meq/g, preferably no more than about 0.01 meq/g.

The product polymer may have various uses, depending on its molecular weight, equivalent weight, functionality and the presence of any functional groups. Polyether polyols so made are useful as raw materials for making polyurethanes. Polyethers can also be used as surfactants, hydraulic fluids, as raw materials for making surfactants and as starting materials for making aminated polyethers, among other uses. The following examples are provided to illustrate the invention, but are not intended to limit its scope. All parts and percentages are by weight unless otherwise indicated. Catalyst loadings are based on weight of Zn₃[Co(CN)J₂ • nZnCI₂, calculated from the starting materials and ignoring any associated water and initiator.

Example 1

Zinc chloride (3.4 parts by weight ) is dissolved in 10.2 parts water to form a solution. To this are added 50 parts of a 700 molecular weight, nominally trifunctional poly(propylene oxide). A second solution is prepared from 4 parts potassium hexacyanocobaltate and 10 parts water. The potassium hexacyano-cobaltate solution is added to the zinc chloride solution, with stirring, over a period of about one minute. A precipitate forms. Additional water (about 40 parts) is added, the resulting slurry is centrifuged and the supernatant fluid decanted. The wet solids are resuspended in about 100 parts water, stirred, centrifuged and decanted a total of four times to remove potassium ions. The resulting wet, washed precipitate is then blended with about 50 parts of the polypropylene oxide) described above to form a catalyst/initiator mixture.

The catalyst/initiator mixture is dried at 80°C under vacuum to remove residual water.

The resulting catalyst initiator mixture contains about 92 mg/g of Zn₃[Co(CN)_e]₂ • ZnCI₂.

A portion (0.6) parts of the catalyst/initiator mixture is mixed with 10.24 more parts of the same polypropylene oxide) to provide a mixture containing about 5277 ppm catalyst. This mixture is charged to a pressure reactor, which is then purged with nitrogen and heated to 110°C. Propylene oxide is added to the reactor at a rate of about 0.4 parts/minute. The pressure inside the reactor increases to about 20-25 psig, after which it remains constant until ail propylene oxide is fed. About 29 parts of propylene oxide are fed over 70 minutes. A cloudy, water-white polypropylene oxide) having a molecular weight of about 2100 is obtained. Another portion (0.128 parts) of the catalyst/initiator mixture is mixed with 16.8 parts of the same polypropylene oxide) to provide a mixture containing about 698 ppm catalyst. This is reacted with propylene oxide as before, with a slightly lower propylene oxide feed rate. The reactor becomes pressurized to about 40 psig before polymerization begins, followed by a slow reaction for about 5 minutes. Thereafter, the reaction rate is limited by the rate at which the propylene oxide is fed. About 21 parts of propylene oxide are fed over 60 minutes. The resulting polyol has a molecular weight of about 1700. It is a slightly cloudy, water-white liquid.

Example 2 Potassium hexacyanocobaltate (8 parts) is dissolved in about 210 parts deionized water and then mixed with about 50 parts t-butanol. The resulting solution is added to a mixer, and a solution of 25 parts zinc chloride in 40 parts water is added dropwise over about 15 minutes with continued stirring. A slurry forms, which is centrifuged for 30 minutes at 3200 rpm. The supernatant liquid is decanted. The wet solids are dispersed into 175 parts t-butanol and then mixed into 265 parts of a 450 molecular weight, nominally trifunctional polypropylene oxide) initiator compound. The resulting catalyst/initiator dispersion is then stripped by rotary evaporation to remove water and excess t-butanol, yielding 274.7 parts of a liquid containing 2186 ppm residual water. The concentration of catalyst in the dispersion is 3.26 wt-%. The dispersion has the appearance of a milky liquid with no solids being discernible with the naked eye. When examined microscopically, the catalyst particles are uniform and have the appearance of broken glass.

A portion of the dispersion (0.086 parts) is charged to a dried Wheaton vial fitted with a stir bar. The vial is sealed with a septum cap and purged with nitrogen. About 0.5 g of propylene oxide are added by syringe, and the septum cap replaced with a solid cap under nitrogen. The vial is then heated to 90°C for 4 hours. A slightly purplish polyol having a molecular weight of 2950 is obtained.

Claims

CLAIMS:

1. A method for preparing an active metal cyanide catalyst, comprising

(I) mixing an aqueous solution or dispersion of a metal cyanide compound with an aqueous solution or dispersion of a metal salt in the presence of an organic complexing agent, under conditions such that a precipitate is formed in a supematant liquid, wherein a) the metal cyanide compound is represented by the general formula B_u[M¹(CN)_r(X)_t]_v in which B represents a hydrogen or a metal ion that forms a water-soluble salt with the M¹(CN)_r(X)_t group, u and v are integers that reflect an electrostatically neutral compound, M¹ is a transition metal ion; each X independently represents a group other than cyanide that coordinates with the M¹ ion, r is from 4 to 6 and t is from 0-2; b) the metal salt is represented by the general formula M_xA_y wherein M is a metal ion that forms an insoluble precipitate with the metal cyanide grouping

M¹(CN)_r(X)_t, A represents an anion, and x and y are integers that reflect an electrostatically neutral salt;

(II) diluting the precipitate in an initiator compound without first isolating a dried precipitate, and (III) removing the water from the resulting dispersion.

2. The method of claim 1 wherein said metal cyanide compound includes B₃Co(CN)₆, where B is hydrogen or an alkali metal.

3. The method of claim 1 wherein the metal salt is a zinc salt.

4. The method of claim 3 wherein the initiator is a polyalcohol.

5. The method of claim 4 wherein the initiator compound is a low molecular weight polyether polyol having an equivalent weight of about 125-250.

6. The method of claim 2 wherein said solution or dispersion of a metal cyanide compound further contains a compound of the formula B_u[M²(X)₆]_v, where u and v are numbers that reflect an electrostatically neutral complex, and B is hydrogen or a metal ion that forms a water soluble salt with M²(X)₆.

7. A method for polymerizing an alkylene oxide, comprising

(I) mixing an aqueous solution or dispersion of a metal cyanide compound with an aqueous solution or dispersion of a metal salt in the presence of an organic complexing agent, under conditions such that a precipitate is formed in a supematant liquid, wherein a) the metal cyanide compound is represented by the general formula B_u[M¹(CN)_r(X)J_v in which B represents a hydrogen or a metal ion that forms a water-soluble salt with the M¹(CN)_r(X)_t group, u and v are integers that reflect an electrostatically neutral compound, M is a transition metal ion; each X independently represents a group other than cyanide that coordinates with the

M¹ ion, r is from 4 to 6 and t is from 0-2; b) the metal salt is represented by the general formula M A wherein M is a metal ion that forms an insoluble precipitate with the metal cyanide grouping M¹(CN)_r(X)_t, A represents an anion, and x and y are integers that reflect an electrostatically neutral salt;

(III) removing the water from the resulting dispersion; and

(IV) mixing the resulting dispersion with an alkylene oxide and subjecting the resulting mixture subjected to conditions sufficient to polymerize the alkylene oxide to form a poly(alkylene oxide) based on said initiator compound.

8. The method of claim 7 wherein said metal cyanide compound includes B₃Co(CN)_e, where B is hydrogen or an alkali metal.

9. The method of claim 8 wherein the metal salt is a zinc salt.

10. The method of claim 9 wherein the initiator is a polyalcohol.

11. The method of claim 10 wherein the initiator compound is a low molecular weight polyether polyol having an equivalent weight of about 125-250.

12. The method of claim 7 wherein said solution or dispersion of a metal cyanide compound further contains a compound of the formula B_u[M²(X)_e]_v, where u and v are numbers that reflect an electrostatically neutral complex, and B is hydrogen or a metal ion that forms a water soluble salt with M²(X)₆.

13. The method of claim 7 wherein the alkylene oxide is propylene oxide, ethylene oxide, 1 ,2-butylene oxide or a mixture of two or more thereof.