2.3.2. Lignin extraction processes without a preliminary acid
hydrolysis
In the Fig. 2 is observed the lignin extraction process without a
preliminary acid hydrolysis. Lignocellulosic material enters to a
mix tank (1) where is contacted with a delignifying agent. There
fourth lignin extraction processes are carried out: Soda, organosolv,
kraft and sulfite. Successively the mixture is brought to a heat
exchanger (2) in order to adjust the mixture to required operating
conditions for each of the processes. Then the stream is entered
into a stirred tank reactor (3) where is performed the delignification
process and lignin is separated from the lignocellulosic matrix.
The resulting stream is cooled (4) at a temperature of 25 C and is
separated by filtration. (5) Finally the pulp is washed in a tank. (6)
Given the fact that the present work is based on the lignin recovery,
it is assumed here that all the hemicellulose remains together
with cellulose in the solid fraction. After extractions, small fractions
of sugars (1.1% wt of hexoses and 1.3% wt of xylose) are considered
in the lignin liquor stream when no hydrolysis steps are
involved as recommended by Dhepe and Sahu (2010) and
Mousavioun and Doherty (2010).