VACUUM PYROLYSIS OF USED TIRES

Vacuum Pyrolysis of Used Tires

Vacuum Pyrolysis of Used Tires

Abstract

The vacuum pyrolysis of used tires enables the recovery of useful products, such as pyrolytic oil and pyrolytic carbon black (CBp). The light part of the pyrolytic oil contains dl-limonene which has a high price on the market. The naphtha fraction (initial boiling point (IBP) < 160 ?C) can be used as a high octane number component for gasoline. The middle distillate (IBP 204 ?C) demonstrated mechanical and lubricating properties similar to those of the commercial aromatic oil Dutrex R 729. The heavy oil was tested as a feedstock for the production of needle coke. The surface chemistry of the recovered CBp has been compared with that of commercial carbon black through ESCA analysis. It was found that the surface morphology of CBp produced by vacuum pyrolysis, as opposed to atmospheric pyrolysis, resembles that of commercial carbon black. The CBp contains a higher concentration of inorganic compounds (especially ZnO and S) than commercial carbon black. The composition of the inorganic part depends on the pyrolysis conditions. An acid-base demineralization treatment was shown to significantly reduce the ash concentration of the CBp, thereby improving its quality. The pyrolysis process feasibility looks promising. One old tire can generate upon vacuum pyrolysis, incomes of at least $2.25 US, excluding revenues from the tipping fees, with a potential of up to $4.83 US/tire upon further development of the market and product improvement.

Introduction

The continuing accumulation of used tires is one of the worst solid waste problems facing industrialized countries. It is estimated that North America discards approximately one used tire per person per year [1]. The incineration of tires is both costly and complex, while stockpiling used tires is the subject of growing concern. Moreover, the possibility of tire fires on these sites poses an ever-increasing threat to the environment. On the other hand, tires represent a source of energy and chemicals. By thermal decomposition, it is possible to recover useful products in an environmental friendly way. There have been numerous attempts to pyrolyze tires [2,3]. In this study the tire pyrolysis is performed under vacuum.

Vacuum Pyrolysis

Pyrolysis of rubber is an old concept. Rubber is treated at high temperatures in the absence of air to prevent oxidation. The long polymer chains of the rubber decompose at high temperatures to smaller hydrocarbon molecules. When the pyrolysis is performed under vacuum, the spectrum and quality of products obtained is distinct from the other (usually atmospheric pressure) pyrolysis process [4]. The advantage of a reduced pressure is that secondary decomposition reactions of the gaseous hydrocarbons are limited. Preliminary studies of the tire vacuum pyrolysis process were performed with a bench scale reactor and with cross-ply tires as feedstock. The influence of the pyrolysis temperature on the product composition at a total pressure of 0.3 kPa is shown in Fig. 1. The decomposition of the elastomer in the tire is complete at a pyrolysis temperature of 420 ?C. A further increase of the pyrolysis temperature does not change ...