Single Column Stripping and Drying Process

Abstract

Organic materials are stripped and dried in a single column having two contact zones. A stripping gas is introduced into an upper contact zone and flows through the organic material in that zone. A drying gas is introduced into a lower contact zone. The drying gas contacts the organic material in both the upper and lower contact zones, and is removed from the top of the column together with the stripping gas. This process permits very efficiently removal of volatile organic compounds as well as efficient drying, while requiring on low levels of the stripping and drying gasses.

1 . A process for stripping and drying a starting organic material, comprising:
 a) introducing the starting organic material into an upper contact zone of a column that has an upper contact zone and a lower contact zone, and allowing the starting organic material to travel downwardly through the column, through the upper contact zone and then through the lower contact zone to a bottom section of the column;   b) introducing a stripping gas into the upper contact zone of the column and above the lower contact zone of the column such that the stripping gas moves upwardly through the upper contact zone, where it contacts the starting organic material and removes impurities therefrom, and then to a top section of the column;   c) introducing a drying gas into the lower contact zone of the column such that the drying gas moves upwardly through the lower contact zone where it contacts a portion of the organic material and removes moisture from therefrom, then moves upwardly through the upper contact zone where it contacts another portion of organic material, and then moves to a top section of the column;   d) removing the stripping gas and the drying gas from the top section of the column above the upper contact zone; and   e) removing the stripped and dried organic material from the bottom section of the column below the lower contact zone,   wherein the starting organic material is a liquid polyether having a molecular weight of from 500 to 10,000 or crude polymer polyol, the starting organic material contains from 50 to 5,000 ppm of volatile organic impurities and up to 50,000 ppm of water, and the stripped and dried organic material contains up to 10 ppm of volatile organic compounds and up to 200 ppm of water.   
     
     
         2 . The process of  claim 1  wherein the stripping gas is superheated steam. 
     
     
         3 . The process of  claim 1  wherein the drying gas contains no more than 50 ppm moisture. 
     
     
         4 . The process of  claim 3 , wherein from 0.002 to 0.03 parts by weight of stripping gas are passed through the column per part by weight of the organic material. 
     
     
         5 . The process of  claim 4 , wherein from 0.0001 to 0.1 parts by weight of drying gas are passed through the column per part by weight of the organic material. 
     
     
         6 . The process of  claim 5 , wherein the column is operated at a pressure of from 5 to 100 mbar. 
     
     
         7 . The process of  claim 6 , wherein the column is operated at a temperature of from 90 to 150° C. 
     
     
         8 - 10 . (canceled)