2.2.3. Lignin precipitation
The lignin precipitation using CO2-AlK(SO4)212H2O was carried
out according to the method described by Luong et al. (2012) as
shown in Fig. 1. The lignin-rich IL solution (Filtrate 1) was purged
with CO2 gas for 30 min at 60 C. Then, 100 mL of 0.2 M
AlK(SO4)212H2O was added into the solution with slow stirring
carried out at room temperature (30 C) for 30 min. The solution
was left to stand overnight to allow lignin precipitation, which
was then separated by filtration before drying in a vacuum oven
at 50 C overnight. The IL solution (Filtrate 2) can be recycled for
another isolation process. The precipitation experiment was also
carried out on the lignin-rich IL solution without prior CO2 gas
purging using acidified H2SO4 and HCl of pH 0.7 and 2.0 solutions
which had the concentration of 1.0 M. The precipitation process
was carried out in triplicate and the mean value with standard
deviation was presented. The lignin yield, YL (%wt.) is defined as:
YL ¼
A
B 100 ð1Þ
and the lignin recovery, RL (%wt.) is defined as:
RL ¼
YL
C 100 ð2Þ
where A is the weight of lignin extracted by precipitation method
(mg), B is the weight of the respective OPB used in the IL dissolution
process (mg), and C is the lignin content (acid insoluble lignin + acid