Abstract
Several million tons of end of life tires (ELTs) are piled annually as a result of human activities. Various methods have been proposed for the extraction and recycling of the resource potential of ELTs. The chemical composition of ELTs seems to enable their usage as a fuel after mechanical separation of a steel cord. Indeed, in the rubber of ELTs, up to 90 mass% accounts for carbon and hydrogen. Currently, it is by incineration that a significant proportion of ELTs is utilized. However, ELTs contain not only sulfur, which is used for vulcanization, but also nitrogen-containing additives. The behavior of these heteroatoms during oxidation is poorly investigated. It has been shown that the pyrolysis liquid fuel obtained from ELTs contains such sulfur compounds as mercaptans and nitrogen in the form of hydrocyanic acid and cyanogen. Deep oxidation of ELTs results in the oxidation of sulfur compounds to dioxide, but the oxidation products have been found to contain traces of cyanogen. Taking this into account, one should pay attention to the ways of transforming heteroatoms during the process of ELT oxidation and the products of ELT pyrolysis as potential sources of highly toxic gas emissions.
Highlights
Mankind manufactures several million tonnes of tires annually; likewise, several million tonnes of tires come to the end of their lives annually
From a waste point of view, is a special case of end of life tires (ELTs) direct combustion, because in it, the main part of energy potential of ELTs is converted into synthetic liquid fuel, which should still be subjected to oxidation for obtaining energy
The derivative thermogravimetry demonstrated the formation of toxic compounds from heteroatoms during the process of ELT heat treatment
Summary
Mankind manufactures several million tonnes of tires annually; likewise, several million tonnes of tires come to the end of their lives annually. End of life tire (ELT) utilization is currently a global problem and there is no reliable method of ELT processing. Numerous approaches are targeted to recycle and reuse the tire rubber in various applications, including landfill, retreading, recycling, and combustion. Conversion into liquid fuels has been investigated, including gasification, hydrothermal liquefaction, and pyrolysis [1]. Recovery of energy has drawn the greatest attention of waste tires researchers [2]. Most widely used is the direct burning of ELTs to produce thermal energy [3], as well as ELT conversion into liquid fuels by pyrolysis [4,5]. The gaseous products obtained in the process of pyrolysis can be used for the production of synthetic fuels [6]
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