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 biodeg radable and the components used to manufacture tires cannot readily be reco vered. In this investigation, the thermochemical recycling of rubber from o ld tires by pyrolysis and hydropyrolysis has been studied using a swept fix ed 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 (te mperature, heating rate, gas flow, reaction time, hydrogen pressure) on yie lds of oils, gases and solid residue has been determined. The oils, have be en characterized using a combination of spectroscopic and chromatographic a nalytical techniques (TLC-FID, CC-MS, simulated distillation, and FTIR). Wh ile the main variable affecting tire conversion is temperature, oil composi tion is influenced mainly by hydrogen pressure, with the oils becoming ligh ter as the pressure is raised. No relationship between functional group com position of the oils determined by TLC-FID and FTIR and process variables w as found. CC-MS showed that the oils are mainly comprised of single ring al kyl-aromatic species together with a large amount of limonene. Based on thi s finding, a possible reaction pathway for rubber conversion through polyis oprene depolymerization and further cyclization is discussed.