a filtration method is disclosed for recovering purified polyether polyol comprising the steps of providing an aqueous solution of a polyether polyol containing an alkali metal catalyst residual formed from a transesterification process utilizing an alkali metal catalyst , contacting the aqueous solution with a stoichiometric excess of magnesium sulfate , magnesium sulfite or a combination thereof to form a second aqueous solution , wherein said stoichiometric excess is based on the amount of said alkali metal catalyst residual . water is removed from the second aqueous solution at a temperature above a set limit of said polyether polyol to produce a dehydrated slurry containing a polyether polyol phase substantially free of residual alkali metal and a precipitated solid phase comprising sulfate and / or sulfite salts of the alkali metal catalyst , magnesium hydroxide , and excess magnesium sulfate and / or sulfite , wherein the particle size distribution of said precipitated solid phase is controlled to minimize the amount of particles therein that are smaller than 3 microns . the dehydrated slurry is then passed through a filtration system to separate the polyether polyol phase from the precipitated solid phase .