2.2. Preparation of activated carbon
Dried grape stalks were impregnated with different weight ratios
of ZnCl2/grape stalk. The impregnation was performed by shaking at
150 rev/min by using an orbital flask shaker (Gallenkamp) for contact
times of 24, 36 and 48 h. The impregnated materials were filtered and
dried at 105 °C for 24 h and then activated. The activation experiments
were carried out in a cylindrical stainless steel reactor with 15 cm height
and 6 cm in diameter. In a typical run, 40 g of the dry sample impregnated
with ZnCl2 was placed into the reactor and CO2 was passed through
at a flow rate of 0.1 dm3/min; the system was heated at a rate of
20 °C min−1 in a muffle furnace. In the experiments devoted to the
study of temperature, the sample was heated to 500, 600 and 700 °C
and maintained in each case at that temperature for 120min. The influence
of carbonization time was explored using 30, 60, 90 and 120 min
times at the best temperature selected in the previous series of experiments.
After the activation, the sample was allowed to cool down
under CO2 flow prior to remove it from the furnace. The activated samples were washed with
3MHCl solution to remove the zinc compounds.
Then, they were washed several times with hot and finally cold distilled
water until the pH of the wash water was neutral. The wet samples were
dried at 105 °C for 24 h. After these procedures applied, the production
yield of activated carbon was calculated by dividing the mass of the resultant
activated carbon by the initial mass of grape stalk used for
activation.