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6.3.5 Combustion Process
Combustion of fossil fuels was replaced by biomass and wastes for energy and heat
generation. This process is a technically feasible method to reduce harmful greenhouse
gases (carbon dioxide) into the environment. However, replacing conventional fossil
fuels ended up generating a huge amount of ash-related problems (slagging, corrosion,
and fouling). Alkali metal usage can overcome these problems (Hansen et al. 2000).
Brominated fuel possesses a promising effect on volatilization of metals like potassium,
iron, copper, zinc, and lead (Vehlow et al. 2003). Halogen hydrides and small-chain
halogenic organic compounds were resulted from decomposition of organic halogenated compounds. Chlorinated plastics (waste electrical and electronic equipments,
polyvinyl chloride, textiles) and halogen hybrids (hydrogen chloride, hydrogen bromide) were the chief products produced through combustion method (Wu et al. 2014).
Brominated flame retardants containing wastes generate polybrominated
dibenzo-p-dioxins and polybrominated dibenzofurans through the course of combustion process (Wang and Zhang 2012). Under thermal conditions they are involved
in the recycling process. Polybrominated diphenyl ethers act as a substrate for production. Insufficient combustion process or disturbed process leads to fire accidents,
uncontrolled burning, and gasification.
6.3.6 Gasification Process
Pyrolysis under elevated temperature generates fuels (oil, gas) possessing higher
heating value. Liquid fuels produced from circuit boards through pyrolysis at
800 °C in static temperature conditions possessed brominated compounds; this
made them unusable without further downstream processing (William and Paul
2007). Partial oxidation of waste electrical and electronic equipment plastic at an
elevated temperature (1200 °C) decreased the brominated or chlorinated dioxins in
gas products. Nevertheless the halogen compounds in gaseous products were not in
permissible limits for use as fuels. Majority of organo-brominated compounds in
brominated flame retardants are broken down into hydrogen bromide and bromine
at higher temperature due to their fundamentals (Jin et al. 2011). Usage of calcium
oxide deliberately increases the inorganic bromine formation from the organic bromine compounds. Burning circuit boards at elevated temperature effectively breaks
down organo-brominated compounds.
Steam gasification emerges as a promising technique because of using carbonate
in the recycling of waste electrical and electronic equipment plastics. Halogenated
compounds present within waste electrical and electronic equipment plastics were
retrieved in the form of stable organic salts (Zhang et al. 2013). Lithium carbonate,
sodium carbonate, and potassium carbonate are used as a catalyst in steam gasification under mild conditions. During steam gasification the carbonate or biomass
cannot account for the halogen emission but accelerates the transformation of tar
and char into gas products from plastics (Lopez et al. 2015).
6 Chemical Recycling of Electronic-Waste for Clean Fuel Production
6.3.5 Combustion Process
Combustion of fossil fuels was replaced by biomass and wastes for energy and heat
generation. This process is a technically feasible method to reduce harmful greenhouse
gases (carbon dioxide) into the environment. However, replacing conventional fossil
fuels ended up generating a huge amount of ash-related problems (slagging, corrosion,
and fouling). Alkali metal usage can overcome these problems (Hansen et al. 2000).
Brominated fuel possesses a promising effect on volatilization of metals like potassium,
iron, copper, zinc, and lead (Vehlow et al. 2003). Halogen hydrides and small-chain
halogenic organic compounds were resulted from decomposition of organic halogenated compounds. Chlorinated plastics (waste electrical and electronic equipments,
polyvinyl chloride, textiles) and halogen hybrids (hydrogen chloride, hydrogen bromide) were the chief products produced through combustion method (Wu et al. 2014).
Brominated flame retardants containing wastes generate polybrominated
dibenzo-p-dioxins and polybrominated dibenzofurans through the course of combustion process (Wang and Zhang 2012). Under thermal conditions they are involved
in the recycling process. Polybrominated diphenyl ethers act as a substrate for production. Insufficient combustion process or disturbed process leads to fire accidents,
uncontrolled burning, and gasification.
6.3.6 Gasification Process
Pyrolysis under elevated temperature generates fuels (oil, gas) possessing higher
heating value. Liquid fuels produced from circuit boards through pyrolysis at
800 °C in static temperature conditions possessed brominated compounds; this
made them unusable without further downstream processing (William and Paul
2007). Partial oxidation of waste electrical and electronic equipment plastic at an
elevated temperature (1200 °C) decreased the brominated or chlorinated dioxins in
gas products. Nevertheless the halogen compounds in gaseous products were not in
permissible limits for use as fuels. Majority of organo-brominated compounds in
brominated flame retardants are broken down into hydrogen bromide and bromine
at higher temperature due to their fundamentals (Jin et al. 2011). Usage of calcium
oxide deliberately increases the inorganic bromine formation from the organic bromine compounds. Burning circuit boards at elevated temperature effectively breaks
down organo-brominated compounds.
Steam gasification emerges as a promising technique because of using carbonate
in the recycling of waste electrical and electronic equipment plastics. Halogenated
compounds present within waste electrical and electronic equipment plastics were
retrieved in the form of stable organic salts (Zhang et al. 2013). Lithium carbonate,
sodium carbonate, and potassium carbonate are used as a catalyst in steam gasification under mild conditions. During steam gasification the carbonate or biomass
cannot account for the halogen emission but accelerates the transformation of tar
and char into gas products from plastics (Lopez et al. 2015).
6 Chemical Recycling of Electronic-Waste for Clean Fuel Production