Method for separating lignin from black liquor includes the following
steps: a) precipitating lignin by acidifying black liquor and thereupon
dewatering, b) suspending the lignin filter cake obtained in step a) to
obtain a second lignin suspension and adjusting the pH level to
approximately that of the washing water of step d) below, c) dewatering
of the second lignin suspension, d) adding washing water and performing a
displacement washing at substantially constant conditions without any
dramatic gradients in the pH, and e) dewatering the lignin cake produced
in step d) into a high dryness and displacing the remaining washing
liquid in the filter cake, whereby a lignin product is obtained which
has an even higher dryness after the displacement washing of step d).
The lignin product or an intermediate lignin product obtained by the
method, and its use, preferably for the production of heat or chemicals
is also disclosed.
Öhman, Fredrik (Gavle, SE), Theliander, Hans (Gothenburg, SE), Tomani, Per (Huddinge, SE), Axegard, Peter (Solna, SE), 2013 Method for separating lignin from black liquor United States LignoBoost AB (Stockholm, SE) 8486224 http://www.freepatentsonline.com/8486224.html