MXPA01002738A - Bimetallic cyanide catalysts for producing polyether polyols - Google Patents

Abstract

The invention relates to novel bimetallic cyanide catalysts for producing polyether polyols by polyaddition of alkylene oxides to starter compounds with active hydrogen atoms. The catalyst contains a) bimetallic cyanide compounds, b) organic complex ligands which are different from c), and c) carboxylic acid esters of polyvalent alcohols. The degree of activity of the inventive catalysts in the production of polyether polyols is increased considerably.

Description

Bimetallic Cyanide Catalysts for the Preparation of Polyether Polyols Description of the Invention The present invention relates to novel bimetallic cyanide (DMC) catalysts for the preparation of polyether polyols by polyaddition of alkylene oxides to initiating compounds showing active hydrogen atoms.

Bimetallic cyanide (DMC) catalysts for the polyaddition of alkylene oxides to initiator compounds showing active hydrogen atoms are known (see, for example, US 3404109, US 3829505, US 3941849 and US 5158922). The use of these DMC catalysts for the preparation of polyether polyols produces in particular a reduction of the part of the monofunctional polyethers with terminal double bonds, the so-called monooles, in comparison with the conventional preparation of polyether polyols by alkaline catalysts, such as alkali hydroxides. The polyether polyols thus obtained can be processed into valuable polyurethanes (for example, elastomers, foams, coatings). DMC catalysts are usually obtained by reacting an aqueous solution of a metal salt with an aqueous solution of a metal cyanide salt in the presence of an organic complexing ligand, for example an ether. In a typical catalyst preparation, Ref: 127442 Aqueous solutions of zinc chloride (in excess) and potassium hexacyanocobaltate are mixed and then dimethoxyethane (glyme) is added to the suspension formed. After filtering and washing the catalyst with an aqueous glyme solution, an active catalyst of general formula is obtained Zn3 [Co (CN) 6], - x ZnCl2- and H20-z glima (see for example document EP700949).

DMC catalysts are known from JP 4145123, US 5470813, EP 700949, EP 743093, EP 761708 and WO 97/40086 which, by the use of tert-butanol as complex organic ligand (alone or in combination with a polyether (EP 700949, EP 761708, WO 97/40086)), further reduce the part of the monofunctional polyethers with terminal double bonds in the preparation of polyether polyols. Furthermore, by using these DMC catalysts the induction time of the polyaddition reaction of the alkylene oxides with the corresponding initiator compounds is reduced and the activity of the catalyst is increased.

The aim of the present invention was to provide even better DMC catalysts for the polyaddition of oxides of alkylene to the corresponding initiator compounds, which show an increased catalyst activity with respect to the types of catalyst known hitherto. These result, by shortening the alkoxylation time, to a better profitability of the polyether polyol preparation process. Ideally, the increased activity catalyst can be used in such small concentrations (25 ppm or lower) that an expensive separation of catalyst and product is no longer necessary, and the product can be used directly for the preparation of polyurethane.

Surprisingly, it has now been found that DMC catalysts containing a carboxylic acid ester of polyhydric alcohols as the complexing ligand possess a strongly increased activity in the preparation of polyether polyols.

The object of the present invention is, therefore, a bimetallic cyanide (DMC) catalyst that contains: a) one or more, preferably one, bimetallic cyanide compounds, b) one or more, preferably one, complex organic ligands other than c), and c) one or more, preferably one, carboxylic acid esters of polyhydric alcohols.

In the preparation of bimetal cyanide compounds a), the catalyst according to the present invention can optionally comprise d) water, preferably 1 to 10% by weight, and / or e) one or more water-soluble metal salts, preferably from 5 to 25% by weight, of formula (I) M (X) ". In the formula (I), M is selected from the metals Zn (II), Fe (II), Ni (II), Mn (II), Co (II), Sn (II), Pb (II), Fe ( III), Mo (IV), Mo (VI), Al (III), V (V), V (IV), Sr (II), W (IV), W (VI), Cu (II) and Cr ( III). Especially preferred are Zn (II), Fe (II), Co (II) and Ni (II). The X's are the same or different, preferably the same, and anions, preferably selected from the group of halides, hydroxides, sulfates, carbonates, cyanates, thiocyanates, isocyanates, isothiocyanates, carboxylates, oxalates or nitrates. The value of n is 1, 2 or 3.

The catalysts according to the present invention containing bimetal cyanide compounds a) are the reaction products of water soluble metal salts and water soluble metal cyanide salts.

For the preparation of bimetallic cyanide compounds a) suitable water-soluble metal salts preferably have the general formula (I): M (X) ", wherein M is selects between the metals Zn (II), Fe (II), Ni (II), Mn (II), Co (II), Sn (II), Pb (II), Fe (III), Mo (IV), Mo (VI), Al (III), V (V), V (IV), Sr (II), W (IV), W (VI), Cu (II) and Cr (III). Especially preferred are Zn (II), Fe (II), Co (II) and Ni (II). The X's are the same or different, preferably equal to an anion, preferably selected from the group of halides, hydroxides, sulfates, carbonates, cyanates, thiocyanates, isocyanates, isothiocyanates, carboxylates, oxalates or nitrates. The value of n is 1, 2 or 3.

Suitable water-soluble metal salts are, for example, zinc chloride, zinc bromide, zinc acetate, zinc acetylacetonate, zinc benzoate, zinc nitrate, iron (II) sulfate, iron (II) bromide, iron (II) chloride, cobalt (II) chloride, cobalt thiocyanate (II), nickel (II) chloride and nickel (II) nitrate. Mixtures of different metal salts soluble in water can also be used.

For the preparation of bimetallic cyanide compounds a), suitable water-soluble metal cyanide salts preferably have the general formula (II): (Y), M '(CN) b (A) t, where M' is selected from the metals Fe (II), Fe (III), Co (II), Co (III), Cr (II), Cr (III), Mn (II), Mn (III), Ir (III), Ni (II) ), Rh (III), Ru (II), V (IV) and V (V). M 'is particularly preferably selected from the metals Co (II), Co (III), Fe (II), Fe (III), Cr (III), Ir (III) and Ni (II). The water-soluble metal cyanide salt may contain one or more of these metals. The Y are the same or different, preferably the same and alkali metal ions or alkaline earth metal ions. The A's are the same or different, preferably the same and anions selected from the group of halides, hydroxides, sulfates, carbonates, cyanates, thiocyanates, isocyanates, isothiocyanates, carboxylates, oxalates or nitrates. Both a and b and c are integers in which the values of a, b and c are selected so as to provide electrical neutrality to the metal cyanide salt; a is preferably 1, 2, 3 or 4, b is preferably 4, 5 or 6; c preferably has a value of 0. Examples of suitable water-soluble metal cyanide salts are, for example, potassium hexacyanocobaltate (III), potassium hexacyanoferrate (II), potassium hexacyanoferrate (III), calcium hexacyanocobaltate (III) and Lithium hexacyanocobaltate (III).

Preferred bimetal cyanide compounds a) included in the catalysts according to the present invention are compounds of general formula (III) MX [M \, (CN),] " where M is defined as in formula (I) and M 'as in formula (II), and x, x 'y and z are integers, and are selected so as to provide electrical neutrality to the bimetallic cyanide compound.

Preferably they are x = 3, x '= l, y = 6 and z = 2, M = Zn (II), Fe (II), Co (II) or Ni (II) and M' = Co (III), Fe (III), Cr (III) or Ir (III).

Examples of suitable bimetal cyanide compounds a) are hexacyanocobaltate (III) of zinc, hexacyanidate (III) of zinc, hexacyanoferrate (III) of zinc and hexacyanocobaltate (III) of cobalt (II). Further examples of suitable bimetallic cyanide compounds can be found, for example, in US 5158922 (column 8, lines 29-66). Zinc hexacyanocobaltate (III) is especially preferred.

The complex organic ligands b) comprised in the DMC catalysts according to the present invention are known in principle, and are described in detail in the state of the art (see, for example, US 5158922, especially column 6, lines 9-65). , US 3404109, US 3829505, US 3941849, EP 700949, EP 761708, JP 4145123, US 5470813, EP 743093 and WO 97/40086). The preferred complexing organic ligands are organic compounds soluble in water with heteroatoms, such as oxygen, nitrogen, phosphorus or sulfur, which can form complexes with the bimetallic cyanide compound a). Suitable organic complexing ligands are, for example, alcohols, aldehydes, ketones, ethers, esters, amides, ureas, nitriles, sulphides and mixtures thereof. The preferred complexing organic ligands are water-soluble aliphatic alcohols, such as ethanol, isopropanol, n-butanol, isobutanol, sec-butanol and tert-butanol. Especially preferred is tert-butanol.

The complex organic ligand is added during the preparation of the catalyst or immediately after precipitation of the bimetallic cyanide compound a). Usually the organic ligand of excess ation is used.

The DMC catalysts according to the present invention contain the bimetallic cyanide compounds a) in amounts of 20 to 90% by weight, preferably 25 to 80% by weight, based on the amount of catalyst prepared, and the organic ligands of complex ation b) in amounts of 0.5 to 30, preferably 1 to 25% by weight, based on the amount of catalyst prepared. The DMC catalysts according to the present invention usually contain from 1 to 50% by weight, preferably from 1 to 20% by weight, based on the amount of catalyst prepared, of the acid ester carboxylic of polyhydric alcohols.

The esters of carboxylic acids of polyhydric alcohols comprised in the catalysts according to the present invention are, for example, esters of C2-C30 carboxylic acids of aliphatic or alicyclic alcohols with two or more hydroxyl groups per molecule, such as ethylene glycol, 1,2-propanediol , 1,3-propanediol, diethylene glycol, triethylene glycol, 1,2,3-propanetriol (glycerin), 1,3-butane diol, 1,4-butane diol, butanetriol, 1,6-hexanediol, 1,1-trimethylolethane, 1,1,1-trimethylolpropane, pentaerythritol, carbohydrates (sugars) or sugar alcohols such as sorbitol or sorbitan.

Suitable sugars are monosaccharides such as glucose, galactose, mannose, fructose, arabinose, xylose or ribose; disaccharides such as sucrose or maltose and oligo- or polysaccharides such as starch.

As the carboxylic acid component, the C2-C02 carboxylic acids, such as aryl-, aralkyl- and alkylcarboxylic acids, are particularly preferred, alkylcarboxylic acids such as acetic acid, butyric acid, isovaleric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid or linolenic acid.

Esters of carboxylic acids of alcohols Preferred polyhydroxyl esters are 1, 2, 3-propanetriol (glycerin), 1,1-trimethylolpropane, pentaerythritol, maltose or sorbitan esters with 2-C18 alkylcarboxylic acids.

Especially preferred carboxylic acid esters of polyhydric alcohols are mono-, di-, tri- or tetra-esters of 1,2,3-propanediol (glycerin), pentaerythrite or sorbitan with C2-C18 alkylcarboxylic acids.

The processes for the preparation of carboxylic acid esters of polyhydric alcohols, or of the isolation of fats, are generally well known and are described in detail, for example in "Kirk-Othmer, Encyclopedia of Chemical Technology", vol. 9, 31 ed. , 1980, p. 795 and following; "Ropp, Lexikon Chemie", page 1571, 10th ed. , Sttugart / New York, 1997, "Ullmann's Encyclopedia of Industrial Chemistry", volume A10, 5th ed. , 1987, p. 173 to 218.

It is also possible to use mixtures at will of the esters of carboxylic acids of polyhydric alcohols indicated above. The polyhydric alcohols can be esterified with the same or different carboxylic acids.

The analysis of the catalyst composition is carried out conventionally by means of elemental analysis, thermogravimetry or extractive separation of the carboxylic acid ester part of polyhydric alcohols, with a gravimetric determination then.

The catalysts according to the present invention can be crystalline, partially crystalline or amorphous. The analysis of the crystalline character is conventionally carried out by X-ray powder diffractometry.

Especially preferred are the catalysts according to the present invention which contain: a) zinc hexacyanocobaltate (III), b) tert-butanol, and c) a carboxylic acid ester of polyhydric alcohol.

The preparation of the DMC catalysts according to the present invention is conventionally carried out in aqueous solution by the reaction of metal salts, especially of formula (I), with salts of metal cyanide, especially of formula (II), ß) complexing organic ligands b) which are different from the esters of carboxylic acids of polyhydric alcohols and 7) esters of carboxylic acids of polyhydric alcohols For this, it is preferred to first react the aqueous solutions of the metal salt (for example zinc chloride, used in stoichiometric excess (at least 50 mol% based on the metal cyanide salt)) and the cyanide salt metal (for example potassium hexacyanocobaltate), in the presence of the complex organic ligand b) (for example tert-butanol), forming a suspension containing the bimetal cyanide compound a) (for example zinc hexacyanocobaltate), water d) , metallic salt in excess e), and organic ligands of complexation b).

The complex organic ligand b) may in this case be present in the aqueous solution of the metal salt and / or the metal cyanide salt, or added directly to the suspension obtained after the precipitation of the bimetallic cyanide compound a) . It has proved advantageous to mix the aqueous solutions and the complex organic ligand b) with strong agitation. The suspension formed is usually treated in the following with the carboxylic acid ester of polyhydric alcohols c). The carboxylic acid ester of polyhydric alcohols c) is preferably used here in a mixture with water and complex organic ligand b).

The isolation of the catalyst from the suspension by known techniques, such as centrifugation or filtration. In a preferred embodiment, the isolated catalyst is then washed with an aqueous solution of complex organic ligand b) (for example by resuspension and subsequent re-isolation by filtration or centrifugation). In this way, for example, the water-soluble by-products, such as potassium chloride, of the catalyst according to the present invention can be separated.

Preferably, the amount of organic complexing ligand b) in the aqueous wash solution is between 40 and 80% by weight, based on the entire solution. Furthermore, it is advantageous to add to the aqueous washing solution some of the carboxylic acid ester of polyhydric alcohols, preferably in the range of 0.5 to 5% by weight, based on the total solution.

It is also advantageous to wash the catalyst more than once. For this purpose, for example, the first washing process can be repeated. However, it is preferred to use non-aqueous solutions for the other washing processes, for example a mixture of complex organic ligands and carboxylic acid esters of polyhydric alcohols.

The washed catalyst is then dried, where appropriate after spraying, at temperatures in general from 20 to 100 ° C and at pressures in general of 0.1 mbar at normal pressure (1013 mbar).

Another additional object of the present invention is the use of DMC catalysts according to the present invention in a process for the preparation of polyether polyols by polyaddition of alkylene oxides to initiator compounds which show active hydrogen atoms.

Preference is given to alkylene oxides: ethylene oxide, propylene oxide, butylene oxide, and mixtures thereof. The formation of the polyetherpolyol chain by alkoxylation can be carried out, for example, only with a monomeric epoxide or also statistically or blockwise with 2 or 3 different monomeric epoxides. More details are given in "Ullmann's Encyclopédie der der Industriellen Chemie", English edition. 1992, vol. A21, p. 670 to 671.

As starter compounds which show active hydrogen atoms, compounds of molecular weights of 18 to 2000 and 1 to 8 hydroxyl groups are preferably used. Examples are: ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,4-butanediol, hexamethylene glycol, bisphenol A, trimethylolpropane, glycerin, pentaerythritol, sorbitol, cane sugar, degraded starch or Water .

Advantageously, those initiator compounds are used which show active hydrogen atoms which, for example, were prepared by conventional alkaline catalysis of the abovementioned low molecular weight initiators, and represent oligomeric alkoxylation products with molecular weights of 200 to 2000.

The polyaddition catalysed by the catalysts according to the present invention of alkylene oxides to initiator compounds which show active hydrogen atoms is generally carried out at temperatures of 20 to 200 ° C, preferably in the range of 40 to 180 ° C, in particular preferred at temperatures of 50 to 150 ° C. The reaction can be carried out at global pressures from 0 to 20 bar Polyaddition can be carried out in solid or in an inert organic solvent such as toluene and / or THF. Solvent is usually between 10 and 30% by weight, based on the amount of polyetherpolyol to be produced.

The catalyst concentration is selected so that a good control of the polyaddition reaction under the given reaction conditions is possible. The catalyst concentration is generally in the range from 0.0005% by weight to 1% by weight, preferably in the range of 0.001%. by weight at 0.1% by weight, particularly preferably in the range from 0.001 to 0.0025% by weight, based on the weight of the polyetherpolyol to be produced.

The molecular weight of the polyetherpolyol produced according to the process of the present invention is in the range of 500 to 100,000 g / mol, preferably in the range of 1,000 to 50,000 g / mol, particularly preferably in the range of 2,000 to 20,000 g. / mol.

The polyaddition can be carried out continuously or discontinuously, for example in a batchwise or semi-liquid process.

The catalysts according to the present invention can be used, due to their clearly increased activity, at very low concentrations (25 ppm and below, based on the amount of polyetherpolyol to be produced). In the use of the polyether polyols produced in the presence of catalysts according to the present invention for the preparation of polyurethanes (Kunstoffhandbuch, Vol 7, Polyurethane, 3rd ed., 1993, pp. 25 to 32 and 57 to 67), the separation of the catalyst from the polyether polyol can be suppressed without the quality of the polyurethane product obtained being adversely affected.

The following examples explain the present invention, not having however some limiting character, Examples Catalyst preparation Example A Preparation of a DMC catalyst using glycerin tricaproate (catalyst A) To a solution of 4 g (12 mmol) of potassium hexacyanocobaltate in 70 ml of distilled water with vigorous stirring (24,000 rpm), a solution of 12.5 g (91.5 mmol) of zinc chloride in 20 ml is added. of distilled water. Immediately afterwards a mixture of 50 g of tert-butanol and 50 g of distilled water is added to the suspension formed and then stirred vigorously (24,000 rpm) for 10 minutes. Then, a mixture of 1 g of a glycerin caproate (company Aldrich), 1 g of tert-butanol and 100 g of distilled water is added and stirred for 3 minutes (1,000 rpm). The solid is isolated by filtration, then stirred (10,000 rpm) for 10 minutes with a mixture of 70 g of tert-butanol, 30 g of distilled water and 1 g of the above glycerin tricaproate and filtered again. Finally, stir once more (10,000 rpm) for 10 minutes with a mixture of 100 g of tert-butanol and 0.5 g of the glycerin tricaproate above. After filtration, the catalyst is dried at 50 ° C and normal pressure to constant weight.

Catalyst yield in dry powder form: 5.3 g.

Elemental analysis, thermogravimetric analysis and extraction: cobalt = 12.3%, zinc = 27.0%, tert-butanol = 7.2%, glycerin tricaproate = 3.7%.

Example B Preparation of a DMC catalyst using glycerin tricaprylate (catalyst B).

The procedure of example A was used, however using glycerin tricaprylate (Rilanit GTC (RI, Henkel company) instead of the glycerin tricaproate of example A.

Catalyst yield in dry powder form: 5.0 g.

Elemental analysis, thermogravimetric analysis and extraction: cobalt = 12.4%, zinc = 26.9%, tert-butanol = 8.6%, glycerin tricaprylate = 8.4%.

Example C Preparation of a DMC catalyst using pentaerythritol tetracaprylate (catalyst C).

The procedure of Example A was used, however, using pentaerythritol tetracaprylate (Rilanit PEC 4 | R |, Henkel company) instead of the glycerin tricaproate of Example A.

Catalyst yield in dry powder form: 4.0 g.

Elemental analysis, thermogravimetric analysis and extraction: cobalt = 13.8%, zinc = 28.6%, tert-butanol = 9.9%, pentaerythritol tetracaprylate = 8.6%.

Example D (comparative) Preparation of a DMC catalyst using tert-butanol without carboxylic acid esters of polyhydric alcohols (catalyst D, synthesis according to JP 4145123).

To a solution of 4 g (12 mmol) of potassium hexacyanocobaltate in 75 ml of distilled water with vigorous stirring (24,000 rpm), a solution of 10 g (73.3 mmol) of zinc chloride in 15 ml of water is added. distilled Immediately afterwards a mixture of 50 g of tert-butanol and 50 g of distilled water is added to the suspension formed and stirred vigorously (24,000 rpm) then for 10 minutes. The solid is isolated by filtration, then stirred (10,000 rpm) for 10 minutes with 125 g of a mixture of tert-butanol and distilled water (70/30, w / w) and filtered again. It is then stirred once more (10,000 rpm) for 10 minutes with 125 g of tert-butanol. After filtration, the catalyst is dried at 50 ° C and normal pressure to constant weight.

Catalyst yield in dry powder form: 3.08 g, Elemental analysis: cobalt = 13.6%, zinc = 27.4%, tert-butanol = 14.2%.

Preparation of polyether polyols General procedure 50 g of polypropylene glycol initiator (molecular weight = 1000 g / mol) and 3 to 5 mg of catalyst (15 to 25 ppm, based on the amount of polyether polyol to be produced) are placed in a 500 ml pressure reactor in an atmosphere protective (argon) and heated with agitation at 105 ° C. Next, propylene oxide (approximately 5 g) is added in one go, until the overall pressure increases to 2.5 bar. More propylene oxide is added only when a sharp drop in pressure is observed in the reactor. This sudden drop in pressure shows that the catalyst is activated. Subsequently, the remaining propylene oxide (145 g) is added continuously at a constant global pressure of 2.5 bar. After the complete addition of the propylene oxide and a further 2 hours of reaction time at a temperature of 105 ° C, the volatile fractions are distilled at 90 ° C (1 mbar) and then cooled to room temperature.

The polyether polyols obtained were characterized by determining the OH number, the content of double bonds and the viscosity.

The course of the reaction was observed by the time-reaction graphs (consumption of propylene oxide (g) versus reaction time (min)). The induction time was determined from the cutoff point of the tangent at the steepest point of the time-reaction graph with the baseline prolongation of the curve. The propoxylation times determining the activity of the catalyst correspond to the period of time between the activation of the catalyst (end of the induction period) and the end of the addition of propylene oxide. The total reaction time is the sum of the induction and propoxylation times.

Example 1 Preparation of polyetherpolyol with catalyst A (15 ppm) Induction time: 210 min Propoxylation time: 275 min Total reaction time: 485 min Polyetherpolyol: OH number (mg KOH / g) 29.8 Content in double bonds (mMol / kg): 6 Viscosity at 25 ° C (mPas): 965 Without the separation of the catalyst the metal content in the polyol is: Zn = 4 ppm, Co = 2 ppm.

Example 2 Preparation of polyetherpolyol with catalyst B (25 ppm) Induction time: 180 min Propoxylation time: 115 min Total reaction time: 295 min Polyetherpolyol: OH index (mg KOH / g) 29.6 Content in double bonds (mMol / kg): 9 Viscosity at 25 ° C (mPas): 914 Example 3 Preparation of polyetherpolyol with catalyst C (25 ppm) Induction time: 130 min Propoxylation time: 145 min Total reaction time 275 min Polyetherpolyol: OH index (mg KOH / g) 29.4 Content of double bonds (mMol / kg): 9 Viscosity at 25 ° C (mPas): 917 Comparative Example 4 Catalyst D (15 ppm) shows no activity under the reaction conditions indicated above.

Examples 1 to 3 show that the novel DMC catalysts according to the present invention can be used in such low concentrations, due to their clearly increased activity, in the preparation of polyether polyols, that the removal of the catalyst from the polyol can be suppressed.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (2)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. A bimetallic cyanide (DMC) catalyst characterized in that it contains: a) one or more bimetallic cyanide compounds, b) one or more complex organic ligands other than c), and c) one or more carboxylic acid esters of polyhydric alcohols.
2. 2 . The catalyst WC s-g? I the claim l-5n 1, character-grit perch acptLene additionally water d) and / or a metal salt soluble in water e). The catalyst EfC according to the - eivirdicacicries 1 and 2, characterized perqué the bimetallic cyanide compound is zinc hexacyanocobaltate (III). The DMC catalyst according to any one of the reivi-X-li --- acr? Is 1 to 3, characterized by the complexity of the aganic complex is tert-butanol. The DMC catalyst according to any of the - Lvir? Dijrar.ift-ßs 1 to 4, ---- a-3ct --- ci2a - b par-that letter! Cr-rit-Lere zader from 1 to 50% by weight, preferably from 1 to 20% by weight, of a carboxylic acid ester of polyhydric alcohols. A DMC catalyst according to any of the -D-ávirriicaa-cries 1 to 5, < When the carboxylic acid ester of polyhydric alcohols is activated, the carboxylic ester of polyhydric alcohols is a mono-, di- or triester of glycerin, or a mono-, di-, tri- or tetraester of pentaerythritol or sorbitan, with an alkylcarboxylic acid with 2 to 18 carbon atoms. A process for the preparation of a DMC catalyst according to any of claims 1 to 6, characterized by the steps aatp-ta -3: reaction in aqueous solution of a.) metal salts with metal cyanide salts ß) organic ligands of complexation, which are different from esters of carboxylic acids of polyhydric alcohols, and 7) esters of carboxylic acids of polyhydric alcohols, ü) isolation, washing and drying the catalyst obtained in step i). A process for the preparation of polyether polyols by polyaddition of alkylene oxides to compounds showing active hydrogen bonds, characterized pcrqi-e is in the presence of one or more DMC catalysts, according to any of claims 1 to 6. A polyetherpolyol obtainable by the process according to claim 8. The use of one or more DMC catalysts according to any one of claims 1 to 6, for the preparation of polyether polyols, by polyaddition of alkylene oxides to initiator compounds that show active hydrogen atoms.