A fast heating-rate thermogravimetric study of the pyrolysis of scrap lyres

Pyrolysis of scrap tyres has been investigated by means of non-isothermal t hermogravimetric analysis, at heating rates ranging from 5 to 900 degrees C /min and particle sizes of 1 and 3 mm. The occurrence of primary and second ary pyrolysis stages has been recognized at low heating rates. Based on exp erimental findings and on the relevant literature on pyrolysis of rubber co mponents, a series-parallel reaction network and a kinetic model are propos ed. Accordingly, the first stage of weight loss is related to depolymerizat ion of the rubber components. The residue, upon cyclization and crosslinkin g, degrades in the secondary stage at larger temperatures. Kinetic paramete rs of primary and secondary pyrolysis and of the cyclization/crosslinking s tages are determined on the basis of experimental results obtained under ch emical kinetic controlled pyrolysis conditions. At large heating rates distinction between primary and secondary pyrolysis is no longer observed and a single peak of the pyrolysis rate is observed. This phenomenology can be partly related to decreasing extent of cyclizatio n/crosslinking that take place as the heating rate is raised. Moreover, rad ial non-uniformities of either temperature, overall volatile pressure or co ncentration can be established at larger heating rates. These can be furthe r responsible for the modification of the pyrolysis pattern. (C) 1999 Publi shed by Elsevier Science Ltd. All rights reserved.