Dissolved air flotation: A novel approach to recovery of organosolv lignin

A novel method of organosolv lignin recovery, consisting of simultaneous precipitation and dissolved air flotation (DAF), is proposed. DAF offers a low energy, low maintenance alternative to centrifugation and filtration. DAF of organosolv lignin is studied in order to determine the parameters resulting in the fastest settling and most complete precipitation. Temperature, mixing regime and air saturation pressure were found to be important parameters. Higher temperature resulted in faster settling, but lower final lignin yields at temperatures above 30 degrees C. At 40 degrees C lignin formed a fine precipitate that did not clarify. Rapid addition of black liquor to water resulted in faster clarification. This is due to a redistribution of microbubbles in the dilution water immediately prior to formation of precipitate. Higher air saturation resulted in faster clarification. The difference was more pronounced if black liquor addition rate was slow. (C) 2008 Elsevier B.V. All rights reserved