Characterization and potential applications of pyrolytic char from ablative pyrolysis of used tires

Pyrolysis has the potential of transforming used tires into useful recyclab le products. Pyrolytic char is one of the most important products of tire p yrolysis. The process economy depends strongly on its commercial value. A 2 -year study was undertaken to examine the chemistry and commercial applicat ions of pyrolytic char obtained from the commercialized process called Cont inuous Ablative Regenerator (CAR) system (Enervision Inc., Halifax, Canada) . The pyrolysis temperature was 550 degreesC, residence time 0.6 s, under N -2 flow and using similar to1 cm tire shreds. A small-scale unit, 0.25 ton day(-1), was used in the study. The process is unique in design and feature s several operating parameters, which favor optimum tire pyrolysis (e.g. no heat transfer medium, fast pyrolysis and rapid product quenching). The phy sical properties (porosity, particle and aggregate size, surface area), che mical properties (elemental analysis, ash content and composition) and aque ous adsorption properties (for metals, phenols and methylene blue) of the p yrolytic char were examined. As well, laboratory-scale production of activa ted carbon from tire pyrolysis char was examined as a means of upgrading. T he activated carbon was characterized in the same manner as the char. Resul ts revealed that the char must be post- carbonized (600 degreesC) to remove unwanted odor and trace oils. The resulting carbonized char has excellent adsorption capacity for phenol and metals (i.e. lead) from solution. It is believed that the high sulfur content in the char (2%) and the inherent com position of tire char is responsible for these properties. Activation using steam (900 degreesC, 3 h) produced an activated carbon with good surface a rea (302 m(2) g(-1)), excellent adsorption for phenol and methylene blue, b ut showed no improvement for metal removal. Norit SA3 and commercial charco al were used for comparison. Further studies will be conducted to examine t he char performance for Hg removal from air and water and its use in wastew ater treatment and as a stack gas scrubber medium. (C) 2001 Elsevier Scienc e B.V. All rights reserved.