Preparation and characterization of low energy post-pyrolysis oxygenated tire char

Abstract

Char surfaces, obtained from pyrolysis of waste tires, were chemically modified in situ using a novel process of post-pyrolysis oxygenation. To enhance the adsorptive characteristics of pyrolytic char, low concentrations of oxygen were introduced into the pyrolysis reactor at various temperatures immediately after the pyrolysis process, without additional energy input. The chemically modified char was characterized using a range of analytical instruments. Proximate analysis showed a high amount of ash material in the chars after pyrolysis. X-ray photoelectron spectroscopy (XPS) and bulk metal content analysis showed that a high proportion of the char contained zinc. Pyrolysis of tires enriched the surface of the resultant chars with zinc through depolymerization and volatization of carbon and other organic compounds. Subsequent oxygenation of the chars resulted in the formation of zinc oxide (ZnO) and oxygenated carbon functional groups. Surface areas and pore sizes of the chars were relatively low. These characteristics were then correlated with aqueous copper removal through batch equilibrium studies. Surface atom abundance was found to be highly correlated with copper removal, but not surface areas. This characterization study further revealed that tire char surfaces tend to behave like graphite surfaces in their interaction with oxygen molecules during activation, while the presence of zinc on the char surface played an important role in copper removal.