Polymer recovery process in the filtration of polyether polyols

摘要

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.

主权项

1. A filtration method for recovering purified polyether polyol comprising the steps of:
(a) providing an aqueous solution of a polyether polyol containing an alkali metal catalyst residual formed from a transesterification process utilizing an alkali metal catalyst; (b) contacting the aqueous solution of a polyether polyol of step (a) 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; (c) removing water from said second aqueous solution of step (b) at a temperature in range from 125° C. to 145° C. to produce a dehydrated slurry containing a polyether polyol phase with a residual alkali metal content below 1 ppm 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, wherein the amount of particles in said precipitated solid phase that are smaller than 3 microns is below 15% by volume; (d) passing the dehydrated slurry of step (c) through a filtration system to separate the polyether polyol phase from the precipitated solid phase; and (e) recovering polyether polyol from the separated polyether polyol phase, wherein said polyether polyol is poly(tetramethylene ether) glycol or a copolymer thereof; wherein removing water from said second aqueous solution of step (b) is accomplished in a dryer recirculation system; and wherein controlling the particle size distribution of the precipitated solid phase of step (c) is accomplished by adjusting the pressure drop in the dryer recirculation system, and wherein the feed rate across the filtration system of step (d) is determined by the particle size distribution.