The evolution of semivolatile compounds and toxic by-products in the pyrolysis of polyethylene has been studied from 600 to 900℃. It has been tested that α,ω-olefin, α-olefin and n-paraffins are formed from the primary decomposition. At high temperatures, above 700-800℃, poly-aromatic hydrocarbons (PAHs) are formed. The compounds (PAHs) are widespread harmful and their presence in the combustion processes is associated with the evolution of pyrolytic puffs or gas portions inside the combustion chamber with a poor mixture of the semivolatiles evolved with oxygen. These portions of volatiles evolved can maintain their identity, and consequently the products that are inside this portion correspond to the volatiles evolved in the primary decomposition of the waste and to the secondary volatiles formed by cracking of primary volatiles. The collection of the semivolatile compounds evolved was carried out by XAD-2 resin, comparing the data at different temperatures. The yields of around 150 semivolatile compounds were determined. The thermal behaviour of different compounds was analysed and the data were also compared with those of the literature.
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