2.3.2.1. Acid pretreatment. The lignocellulosic raw material was
submitted to a hydrolysis step in order to solubilize the hemicellulosic
fraction. In this step the hemicellulose fraction is hydrolyzed
with sulfuric acid (2% by volume) at a temperature of 110 C for
5 h. This resulting stream is separated by filtration. Then the solid
fraction, rich in lignin and cellulose with remaining hemicellulose
is submitted to a lignin extraction process (Soda, kraft, organosolv,
lignosulfonate).
2.3.2.2. Soda process extraction. In the soda pulping stage lignocellulosic
material is contacted with sodium hydroxide 2% (w/v) in
a solid:liquid ratio 1:10 at a temperature of 90 C for 1.5 h. This
resulting stream is separated by filtration and the solid stream is
mainly cellulose and hemicellulose pulp, while the liquid fraction
is rich in lignin (black liquor) without considering any hemicellulosic
sugars in the composition.
2.3.2.3. Kraft process extraction. Kraft process it is used a solution of
sodium hydroxide and sodium sulfide with concentration 11.25%
and 3.75% (w/v) respectively in a solid:liquid ratio 1:5 at a
temperature of 170 C for 3.5 h. The solid and liquid fraction are
separated by filtration and lignin is diluted in the medium.
2.3.2.4. Organosolv process extraction. In the organosolv process are
used solvents as delignifying agent and the most common solvent
used in this kind of processes is ethanol (CH3CH2OH) with a
concentration of 50% (v/v) in a solid ratio 1:6 solid:liquid at a temperature
of 170 C for 1 h. The resulting stream is separated by
filtration.
2.3.2.5. Lignosulfonate process extraction. For the lignosulfonate
extraction the lignocellulosic material it is treated with a mixture
of sodium hydroxide 11% (w/v) and bisulfite acid (HSO3
) 2%
(w/v) in a solid:liquid ratio of 1:10 at a temperature of 120 C for
0.67 h. Lignin is dissolved in a liquid fraction and this resulting
stream is separated by filtration.
2.3.2.6. Xylose liquor production. Xylose liquor is the acid hydrolysis
main product. When lignocellulosic material is subjected to this
kind of hydrolysis the remainder liquid fraction is rich in C-5