Pyrolysis of three different categories of automotive tyre wastes: Product yield analysis and characterization

Thermal pyrolysis of three automobile tyre waste (ATW's) - light vehicle tyre (LVT), medium vehicle tyre (MVT) and heavy vehicle tyre (HVT), was investigated in a thermogravimetric analyser and a batch reactor. Such investigations on the effect of the fractions of natural and synthetic rubbers on product yield and the type of tyres on the pyrolysis process and products have not reported in the literature. The product yields were influenced strongly by the reactor temperature with higher temperature favouring the formation of more gases and more char being formed at lower temperatures. The range of degradation temperature was found to be the smallest for LVT as it contained mostly natural rubber (NR), while it was the largest for HVT due to the presence of NR and synthetic butyl rubber(SBR), having widely different degradation temperatures. In the batch reactor, maximum liquid yields of 51%, 45% and 63.5% were obtained for LVT, MVT and HVT at the optimum temperatures of 650 degrees C, 750 degrees C and 750 degrees C respectively at a heating rate of 20 degrees C/min. The oil obtained from LVT shows high aromatic content while the oil from MVT and HVT has a high presence of napthelinic component. The reactor pressure profile showed that the LVT started producing the non-condensable gaseous fraction earliest due to faster degradation. More secondary reactions for MVT generated more gases, leading to the highest final reactor pressure and high concentration of non condensable gases. Gas chromatographic (GC) analysis indicated that H-2, CO, CO2, CH4, C-2, C3H8 and C-4 were the main gases obtained for all type of tyre wastes. Cracking of heavier hydrocarbons to the lighter ones and H-2 was more dominant in MVT, while this was least prominent in HVT, producing less H-2 and added oil. The activation energies for the pyrolysis reaction of LVT, MVT and HVT wastes were estimated to be 53.185, 62.489 and 64.574 kJ/mol respectively.