Process for preparing double metal cyanide catalysts

A process for preparing a double metal cyanide catalyst (DMC) comprising reacting an aqueous solution of a cyanide-free metal salt, an aqueous solution of an alkaline metal cyanide salt, an organic complex ligand and optionally a complex-forming component, wherein the metal cyanide salt comprises potassium hexacyanocobaltate (III), potassium hexacyanoferrate (II), potassium hexacyanoferrate (III), calcium hexacyanocobaltate (III), lithium hexacyanocobaltate (III) or a mixture thereof,

• wherein the organic complex ligand comprises dimethoxyethane, tert-butanol, 2-methyl-3-buten-2-ol, 2-methyl-3-butyn-2-ol, ethylene glycol mono-tert-butyl ether, 3-methyl-3-oxetanemethanol, or a mixture thereof, and
• wherein the alkaline metal cyanide salt has an alkalinity, determined at 25° C. on a 24% by weight aqueous solution by titration with 0.1 mol/liter of hydrochloric acid, of between 0.700% and 3.000% by weight sodium hydroxide, based on the total weight of the alkaline metal cyanide salt used, and
• wherein the alkaline metal cyanide salt contains a metal hydroxide, a metal carbonate, a metal oxide, or a mixture of any two or more thereof and is obtained by addition of the metal hydroxide, the metal carbonate, the metal oxide, or the mixture of any two or more thereof, during the preparation of the alkaline metal cyanide salt.