2.3. Cases description
2.3.1. Lignin extraction processes with a preliminary acid hydrolysis
In the lignin extraction processes with a preliminary acid
hydrolysis the lignocellulosic material (sugarcane bagasse and rice
husk) enters to mix tank (1) where it is contacted with a sulfuric
acid solution 2% (v/v) in a solid ratio of 1:10, there the mixture is
heated (2) to a temperature of 90 C to subsequently enter a stirred
tank reactor (3) at an operational conditions of 110 C and 1 bar.
The mixture is cooled in a heat exchanger (4) at a temperature of
90 C to be filtered (5) and then to recover the liquid fraction rich
in xylose that is cooled at 25 C (6) to be mixed with a calcium
hydroxide (Ca(OH)2) (7) to neutralize the sulfuric acid in a detoxification
tank. (8) In this tank there are produced solid compounds
such as calcium sulfate (Gypsum) that are filtered (9) to separate
the xylose liquor, while the solid fraction is a mixture of cellulose,
hemicellulose and lignin which is the feed stream to the lignin
extraction processes. The lignin stream enters a mixing tank (10)
where it is contacted with a delignifying agent as sodium hydroxide,
organic solvents or mixtures of sodium hydroxide with other
compounds such as bisulfites or sulfides. Each lignin extraction
process is performed separately for a total of fourth processes:
Soda, organosolv, kraft and sulfite. Then, the mixture is brought
to a heat exchanger (11) in order to adapt to the operating conditions
of each process to complete in stirred tank reactor (12) where
the delignification is carried out. Finally treatments were performed
for the isolation of lignin mixture that is passed to a heat
exchanger (13) in order to lower temperature until about 25 C
and sent to final filtration step. (14) Finally the pulp is washed in
a tank. (15) In the Fig. 1 it is observed the process flow diagram
related with the lignin extraction process with a preliminary acid
hydrolysis.