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L. Carlsen and K. Abit
In AC production, temperature and activation time play a vital role in influencing
the characteristics and properties of the AC produced.
There are processes of physical and chemical activation and simultaneous
carbonization and steam/thermal activation. Physical activation includes the stage
of carbonization and activation, in which steam and carbon dioxide (CO 2 ) are the
most widely used reagents, significantly affecting the porosity of AC. Thus Gergova
et al. (1992) studied the porous structure of activated carbons from agricultural
by-products, and Alcaniz-Monge et al. (2012) prepared activated carbon fibres by
steam or carbon dioxide activation. The AC generation using chemical activation
involves a step in which chemicals, such as potassium hydroxide, phosphoric
acid, zinc chloride or other chemicals, can simply be used at room temperature
(Menéndez-Díaza and Martín-Gullónb 2006). However, depending on the chemicals
used, impurities such as zinc (Zn) and phosphorus (P) can be detected in the
final AC product, which at the same time may lead to an increase in AC cost by
adding the chemical used and purifying the reaction product from impurities. Such
chemical additives for AC activation are potentially harmful to human health and
the environment and also significantly increases the cost of the final AC product
compared to physical activation, for example, water vapor (cf. Abit et al. 2019)
Therefore, physical activation a priori appears as the more appropriate method
of activation to prevent environmental pollution and reduce the cost of the final
product, while obtaining relatively high surface area of AC.
For commercial purposes, coal activation is usually carried out in a mixture of
steam and CO 2 at temperatures above 800 ◦ C. Recently, studies have be reported
aiming to optimize the final activation temperature in order to reduce the cost
and duration of AC production (cf. Abit et al. 2019). Several studies have been
reported that the activation temperature has a large effect on the surface area and the
yield of AC (Chowdhury et al. 2011; Wang et al. 2017; Baçaoui et al. 2001). The
activation temperature varies from 200 to 1100 ◦ C. However, temperature range
from 400 to 500 ◦ C is often used for chemical activation and higher temperatures
(800–1000 ◦ C) for physical activation (cf. Abit et al. 2019). It should also be noted
that during chemical activation, the processing time of preparing AC is significantly
increased due to the long period for creating complete impregnation of raw materials
with chemical reagents. According to previously obtained research results, with
increasing activation time, the surface area according to the method of Brunauer,
Emmett and Teller (BET) (Thommes et al. 2015) gradually increases, while the
yield of AC decreases (Baçaoui et al. 2001). This may be due to the volatilization
of organic substances from agricultural raw materials.
The yield is an additional indicator that is studied during AC production.
The greater the yield of the carbonization-activation reaction, obviously the more
productive and cost-effective the technology for AC production will be.
The so-called BET surface area (Thommes et al. 2015) is another important
feature, showing the influence of production conditions on the characteristics of the
resulting AC. Basically, the surface area of BET increases with increasing activation
temperature. This may be due to the advancement of new pores due to the release of
volatile matter and the expansion of pores.
L. Carlsen and K. Abit
In AC production, temperature and activation time play a vital role in influencing
the characteristics and properties of the AC produced.
There are processes of physical and chemical activation and simultaneous
carbonization and steam/thermal activation. Physical activation includes the stage
of carbonization and activation, in which steam and carbon dioxide (CO 2 ) are the
most widely used reagents, significantly affecting the porosity of AC. Thus Gergova
et al. (1992) studied the porous structure of activated carbons from agricultural
by-products, and Alcaniz-Monge et al. (2012) prepared activated carbon fibres by
steam or carbon dioxide activation. The AC generation using chemical activation
involves a step in which chemicals, such as potassium hydroxide, phosphoric
acid, zinc chloride or other chemicals, can simply be used at room temperature
(Menéndez-Díaza and Martín-Gullónb 2006). However, depending on the chemicals
used, impurities such as zinc (Zn) and phosphorus (P) can be detected in the
final AC product, which at the same time may lead to an increase in AC cost by
adding the chemical used and purifying the reaction product from impurities. Such
chemical additives for AC activation are potentially harmful to human health and
the environment and also significantly increases the cost of the final AC product
compared to physical activation, for example, water vapor (cf. Abit et al. 2019)
Therefore, physical activation a priori appears as the more appropriate method
of activation to prevent environmental pollution and reduce the cost of the final
product, while obtaining relatively high surface area of AC.
For commercial purposes, coal activation is usually carried out in a mixture of
steam and CO 2 at temperatures above 800 ◦ C. Recently, studies have be reported
aiming to optimize the final activation temperature in order to reduce the cost
and duration of AC production (cf. Abit et al. 2019). Several studies have been
reported that the activation temperature has a large effect on the surface area and the
yield of AC (Chowdhury et al. 2011; Wang et al. 2017; Baçaoui et al. 2001). The
activation temperature varies from 200 to 1100 ◦ C. However, temperature range
from 400 to 500 ◦ C is often used for chemical activation and higher temperatures
(800–1000 ◦ C) for physical activation (cf. Abit et al. 2019). It should also be noted
that during chemical activation, the processing time of preparing AC is significantly
increased due to the long period for creating complete impregnation of raw materials
with chemical reagents. According to previously obtained research results, with
increasing activation time, the surface area according to the method of Brunauer,
Emmett and Teller (BET) (Thommes et al. 2015) gradually increases, while the
yield of AC decreases (Baçaoui et al. 2001). This may be due to the volatilization
of organic substances from agricultural raw materials.
The yield is an additional indicator that is studied during AC production.
The greater the yield of the carbonization-activation reaction, obviously the more
productive and cost-effective the technology for AC production will be.
The so-called BET surface area (Thommes et al. 2015) is another important
feature, showing the influence of production conditions on the characteristics of the
resulting AC. Basically, the surface area of BET increases with increasing activation
temperature. This may be due to the advancement of new pores due to the release of
volatile matter and the expansion of pores.