Kongjao et al (2010) [26] reported the purification of crude glycerol
(30 wt% glycerol content) from a waste used-oil methyl ester plant
using 1.19 M H2SO4 followed by neutralization and solvent extraction
to get purifies glycerol of around 93 wt% purity. In a similar work,
Ooi et al (2001) [29] demonstrated that crude glycerol was upgraded
from purity of 34 wt% to 52 wt% by using sulphuric acid. However,
the main issue in these processes is the use of sulphuric acid that has
corrosive nature of sulphuric acid and the non-biodegradability of
the produced sulfate salts