Hydrogenative pyrolysis of waste tires

Abstract

Hydrogenative pyrolysis of waste tires, using 1,2,3,4-tetrahydronaphthalene (tetralin) as a model hydrogen donor, was carried out in a stirred batch reactor under a nitrogen atmosphere. The temperature, kept constant during each run, was varied in the range 260–430°C. Either tire granules (≈ 2 mm size) or tire particles (size less than 500 μm) were used. Liquid-phase and gas-phase samples were withdrawn at regular intervals during each reaction run. The gas samples and the gas present in the reactor at the end of each run were collected in a bag and analyzed. The analysis of samples was performed by gas-chromatography, usually with flame ionization detection (FID), although a mass spectrometry detector (MSD) was used for initial identification of the reaction products. More than 150 major chemical compounds in the gas and liquid phases, produced by the tire depolymerization, were detected and their concentrations were evaluated as a function of the reaction time. Liquid samples were also analyzed with a thermogravimetric (TG) balance to ascertain the presence of compounds having such high boiling points as to be undetectable by gas-chromatography. In order to check if the compounds detected represented all the tire pyrolysis products a mass balance was performed. The results of the investigation permit the identification of the most convenient operating conditions for obtaining complete depolymerization. Correspondingly, the recovery of chemicals achievable was determined.