Influence of process variables on oils from tire pyrolysis and hydropyrolysis in a swept fixed bed reactor

Scrap tires are a growing environmental problem because they are not biodegradable and the components used to manufacture tires cannot readily be recovered. In this investigation, the thermochemical recycling of rubber from old tires by pyrolysis and hydropyrolysis has been studied using a swept fixed bed reactor. This is the first time that such a reactor has been used to carry out tire hydrogenation. The effect of the main process variables (temperature, heating rate, gas flow, reaction time, hydrogen pressure) on yields of oils, gases and solid residue has been determined. The oils, have been characterized using a combination of spectroscopic and chromatographic analytical techniques (TLC-FID, CC-MS, simulated distillation, and FTIR). While the main variable affecting tire conversion is temperature, oil composition is influenced mainly by hydrogen pressure, with the oils becoming lighter as the pressure is raised. No relationship between functional group composition of the oils determined by TLC-FID and FTIR and process variables was found. CC-MS showed that the oils are mainly comprised of single ring alkyl-aromatic species together with a large amount of limonene. Based on this finding, a possible reaction pathway for rubber conversion through polyisoprene depolymerization and further cyclization is discussed.