The production process consists of a pyrolysis stage and an activation stage.
In the pyrolysis process, the woods are crushed and sent to a pyrolysis unit.
The woods are held in the unit for two hours at 600 °C and 6 bar while recycled carbon dioxide flows through the unit at a rate of 6 m3/min.
During that period, the woods are carbonized.
Carbonization is the removal of volatiles and other impurities by thermal decomposition, which results in carbon-rich char.
Pyrolization of the woods yields char
Chemical-Activated Charcoal
Chemical-activation produces the same end result - a much increased internal surface area - but uses a chemical solution to chew away the internal structure.
Typically wood-based activated charcoals are commercially made using heat (450–900 °C) and phosphoric acid.
This “activation” process results in the creation of an enormous surface area — on the order of 600 to 1,200 square meters per gram (m2/g), depending upon the raw material used and the process.
Once again the industrial model is a large steel rotisserie.
The wood may be first pyrolized,
then the char is saturated with phosphoric acid
With H3PO4 dilute solutions (60, 70, and 80 wt% H3PO4), the loading of substance on CS
increases with concentration.
followed by controlled reheating to enhance the chemical erosion of carbon atoms,
and then an elaborate washing cycle to remove the acid.
This process is sometimes preferred because it requires less heat and time.
woods as received was ground, dried and sieved, and only the fraction of particle sizes comprised between 1 and 2 mm was selected for the preparation of activated carbons.
Approximately, 50 g of conditioned woods was impregnated with 200 ml of phosphoric acid solutions with concentrations of 60, 70 and 80 wt.% mixture stirred at 85 °C, maintaining for 4 h to ensure the access of H3PO4 to the interior of the woods.
the excess phosphoric acid will promote gasification of char and increased the total weight loss of carbon.
After mixing, carbonization of acid-impregnated woods was carried out in a stainless steel reactor provided with gas inlet and outlet, which was placed in a vertical cylindrical furnace.
The temperature within the furnace was first calibrated and the length and position of the constant temperature hot zone determined.
Heating from room temperature to the maximum heat treatment temperature 500 °C (i.e., carbonization temperature) in inert atmosphere of nitrogen (flow rate = 200 mL/min.
The heating rate was 3 °C/min and holding time 2 h).
After heating, the system was cooled down to room temperature under the same flow of nitrogen and the product obtained was washed with distilled water until pH 6 was reached in the residual liquid and finally oven-dried at 120 °C.
Carbon name | H3PO4(wt.%) | Carbonization temperature (°C) | Weight after impregnation (g) | Weight after carbonization (g) | Weight after washing/drying (g) | Bulk density (g/cm3) | Yield (%) |
woods | 60 | 500 | 50.5 | 23.2 | 18.4 | 1.0 | 36.8 |
the bulk density decreases with increasing acid concentration.
This means that increasing acid concentration results in carbon richer in carbon and is more porous.
Also, as seen the weight after impregnation increases as the acid concentration increases.
This means that the weight of residue after phosphoric acid impregnation shows a great influence of the H3PO4 concentration on the amount of H3PO4 loaded on woods.
Preparation of activated carbon Specified mass of the dried nutshell particles were soaked in 100 ml H3PO4 solution (40 and 60% concentration) to get the required impregnation ratios of C.
woods: H3PO4 of 1:1, 1:2 and 1:4.
Impregnation ratio is defined as the ratio of the weight of precursor, that is, weight of dried crushed woods to the weight of H3PO4.
The liquid/solid mixture was stirred continuously at ambient temperature for 2 h and left to soak for 12 h to allow penetration of the H3PO4 into the
woods
After the stipulated soaking time, the slurry was oven dried at 110°C for 24 h, so as to achieve adsorption of the H3PO4 on to the woods.
They both arrived at optimum activation temperature and time of 416°C and 30 min, respectively, during activation of woods using phosphoric acid, which was also adopted in this work.
The activation of the dried impregnated with phosphoric acid woods particles was performed in a batch reactor in nitrogen atmosphere at a heating rate of 10°Cmin-1 , set to three different
temperatures 200, 300 and 400°C for activation times of 20, 40 and 60 min at each activation temperature.
Following activation, the samples were cooled in nitrogen atmosphere for 12 h.
The product was washed with cold deionized water until phosphate ions were no longer detected by the lead nitrate test.
The product was finally air dried at 105°C for 3 h, after which it was ground and characterized.