The absorbance is a measure that allows for assessing the discoloration
of the glycerin sample. In Fig. 7 it is noticed that 5% activated
coal shows the closest approach to the features of USP glycerin.
Although the coal-to-sample ratio of 5% caused the best discoloration
of the processed refined in this work, the obtained glycerin was more
absorbent in the visible than the USP grade glycerin. So, the discoloration
must be optimized to get glycerin with equal characteristics to
USP grade.