3.2.3. Effect of the impregnation time
The effect of impregnation time on the activated carbon properties
was studied in the range of 12–48 h at a carbonization temperature of
700 °C and a carbonization time of 120 min. The results are shown in
Table 2. It has been determined that the impregnation time has also a
significant effect on the surface area of the activated carbon. The surface
area of the activated carbon significantly increased with the increasing
impregnation time up to 36 h, thereafter it did not change much. But,
it was observed that the yield of activated carbon decreased abruptly
when the yields of activated carbon obtained from the samples activated
with longer impregnation time decreased due to the rapid evolution of
volatile materials to form stable compounds, as explained by Haimour
and Emeish (2006) [32]. During the chemical activation step, it was
observed that the samples activated only with ZnCl2 for longer than
48 hours were partially activated by effect of the air-oxygen and their
colors turned black. These changes show that the decomposition of the
precursor also began before starting heating and thus, the yields decrease
more due to the removal of volatile components formed at this
stage. Therefore, impregnation time of 36 h was accepted as the optimum
time.