Abstract
Pyrolysis of polyethylene terephthalate (PET) produces polycyclic hydrocarbons and biphenyl derivatives that are harmful to human health and the environment. Therefore, a palladium metal catalyst (5 wt.% Pd loaded on activated carbon) was used to prevent the formation of harmful materials. When a Pd catalyst/PET ratio of 0.01 was applied in pyrolysis of PET, it did not show a meaningful difference in the generation of polycyclic hydrocarbons and biphenyl derivatives. However, when a Pd catalyst/PET ratio of 0.05 was used during pyrolysis, it prevented their formation and generation at experimental temperature ranges (400–700 °C). For example, the concentration of 2-naphthalenecarboxylic acid produced, which is a typical polycyclic hydrocarbon material, was reduced by 44%. In addition, the concentration of biphenyl-4-carboxylic acid, which is contained in biphenyl derivatives, was reduced by 79% compared to non-catalytic pyrolysis at 800 °C. This was because the ring-opening reaction and free radical mechanism caused by the Pd catalyst and thermal cracking were dominant during the pyrolysis of PET. Apart from these materials, amine compounds were generated as products of the pyrolysis of PET. Amine concentration showed a similar trend with polycyclic hydrocarbons and benzene derivatives. Based on these results, the total concentration of polycyclic hydrocarbons and biphenyl derivatives was compared; the results confirmed that the concentrations of all substances were reduced. This research suggests that a metal-supported catalyst will help create a more environmentally friendly and reliable method of industrial plastic waste disposal.
Highlights
Polyethylene terephthalate (PET) is an essential material because it is a major component of plastic applied in various areas, such as food packing, electric wire, and medical tools
The formation of harmful materials obtained during pyrolysis, such as polycyclic hydrocarbon and benzene derivatives, required inhibition; the Pd catalyst was applied in this reaction
The Pd catalyst/polyethylene terephthalate (PET) ratio was set at 0.01 and 0.05 to identify the effect on the formation of harmful materials according to the quantity of Pd
Summary
Polyethylene terephthalate (PET) is an essential material because it is a major component of plastic applied in various areas, such as food packing, electric wire, and medical tools. Thermal treatment is gaining attention because it does not require complex skills or labor-intensive processes [15]; it can use all parts of the plastic unlike traditional methods [29]. Despite these benefits, a critical disadvantage in applying the pyrolysis of plastic waste is that harmful materials such as polycyclic compounds and biphenyls that cause serious environmental pollution and human health problems are emitted during plastic pyrolysis [30,31,32]. We used an activated carbon-supported Pd catalyst (Pd/C) in the pyrolysis of PET waste to diminish polycyclic hydrocarbons and biphenyl derivatives generated from the thermal decomposition reaction. The effect of catalyst/PET ratio on the PET pyrolysis was investigated, considering that the amount of catalyst used in a catalytic process is a crucial factor to determine the viability of the process [45]
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