172
6 Waste Plastics Management and Conversion into Liquid …
Chemical activation could occur before or after the carbonization process through
the impregnation of the raw material or charcoal with activating chemical agents. The
activation reactions take place at a lower temperature compared to that of physical
activation. The chemical agents are strongly dehydrating and oxidizing chemicals
that can be alkali (such as KOH, K 2 CO 3 , NaOH, and Na 2 CO 3 ), alkali earth metal
salts as Lewis acid (such as AlCl 3 and ZnCl 2 ) or mineral acids (such as H 3 PO 4
and H 2 SO 4 ). The activating agents promote the decomposition of the materials and
reduce the deposition of tars and volatile matter contents, which improve the yield
of activated carbon products. After the carbonization process, the activated carbon
is washed with acid or alkali (depending on the type of the activating agent used in
the activation process) in order to remove the chemical components occupied in the
pores of the activated carbon structure and to improve the adsorption capacity [25].
Direct chemical activation of plastics such as PVC and PET has been widely
reported in the literature. For example, KOH activation PVC and PET in a nitrogen
stream at 850 °C for 90 min resulted in activated carbon with extremely high surface
areas of 2666 and 2831 m
2 /g. The activated charcoals when used as adsorbents
showed maximum removal capacity, being higher than 2 mmol of pollutant per
gram of adsorbent, much higher than the widely used commercial activated carbon
adsorbent, Calgon Filtrasorb 400 (F400) with the maximum removal capacity of
around 1 mmol of pollutant per gram of adsorbent [24, 31]. The use of K 2 CO 3
as an activating chemical agent has shown to create activated carbons with high
surface areas. For example, activated carbon with a maximum surface area of about
2800 m
2 /g was obtained by K 2 CO 3 chemical activation of polyurethane foam [32].
As already mentioned, heat treatment of PVC results in the generation of HCl that
is corrosive to the conversion system, but studies showed that the residual carbon of
this treatment can be used for the production of activated carbon with a high specific
surface area [33]. As an example, the carbon residues from the heat treatment of PVC
were oxidized at 300 °C for 3 h with airflow and then carbonized for 2 h with nitrogen
flow, followed by impregnation with KOH and activated at 750 °C in presence of
nitrogen for 1 h. These treatments resulted in activated carbons with a maximum
surface area of 1700 m
2 /g [34].
6.5 Industrial Application Examples of Waste Plastics
Conversion Technologies
Plastics to fuels have attracted an increasing interest in the energy industry owing to
the rising awareness of the detrimental effects of single-use plastics on the environment, and numerous economic and environmental benefits of converting the waste
plastics into fuels. Some industrial application examples of liquid fuel production
from waste plastics are reviewed as follows.
The plastics-to-fuel technologies provide the potential to create alternative fuels
from waste plastics. Table 6.4 shows a list of industrial application examples of
6 Waste Plastics Management and Conversion into Liquid …
Chemical activation could occur before or after the carbonization process through
the impregnation of the raw material or charcoal with activating chemical agents. The
activation reactions take place at a lower temperature compared to that of physical
activation. The chemical agents are strongly dehydrating and oxidizing chemicals
that can be alkali (such as KOH, K 2 CO 3 , NaOH, and Na 2 CO 3 ), alkali earth metal
salts as Lewis acid (such as AlCl 3 and ZnCl 2 ) or mineral acids (such as H 3 PO 4
and H 2 SO 4 ). The activating agents promote the decomposition of the materials and
reduce the deposition of tars and volatile matter contents, which improve the yield
of activated carbon products. After the carbonization process, the activated carbon
is washed with acid or alkali (depending on the type of the activating agent used in
the activation process) in order to remove the chemical components occupied in the
pores of the activated carbon structure and to improve the adsorption capacity [25].
Direct chemical activation of plastics such as PVC and PET has been widely
reported in the literature. For example, KOH activation PVC and PET in a nitrogen
stream at 850 °C for 90 min resulted in activated carbon with extremely high surface
areas of 2666 and 2831 m
2 /g. The activated charcoals when used as adsorbents
showed maximum removal capacity, being higher than 2 mmol of pollutant per
gram of adsorbent, much higher than the widely used commercial activated carbon
adsorbent, Calgon Filtrasorb 400 (F400) with the maximum removal capacity of
around 1 mmol of pollutant per gram of adsorbent [24, 31]. The use of K 2 CO 3
as an activating chemical agent has shown to create activated carbons with high
surface areas. For example, activated carbon with a maximum surface area of about
2800 m
2 /g was obtained by K 2 CO 3 chemical activation of polyurethane foam [32].
As already mentioned, heat treatment of PVC results in the generation of HCl that
is corrosive to the conversion system, but studies showed that the residual carbon of
this treatment can be used for the production of activated carbon with a high specific
surface area [33]. As an example, the carbon residues from the heat treatment of PVC
were oxidized at 300 °C for 3 h with airflow and then carbonized for 2 h with nitrogen
flow, followed by impregnation with KOH and activated at 750 °C in presence of
nitrogen for 1 h. These treatments resulted in activated carbons with a maximum
surface area of 1700 m
2 /g [34].
6.5 Industrial Application Examples of Waste Plastics
Conversion Technologies
Plastics to fuels have attracted an increasing interest in the energy industry owing to
the rising awareness of the detrimental effects of single-use plastics on the environment, and numerous economic and environmental benefits of converting the waste
plastics into fuels. Some industrial application examples of liquid fuel production
from waste plastics are reviewed as follows.
The plastics-to-fuel technologies provide the potential to create alternative fuels
from waste plastics. Table 6.4 shows a list of industrial application examples of