Carbon from microwave assisted pyrolysis of waste tires

• Carbon was characterized through chemical and morphological analyses.
• Crystalline zinc sulfides present in carbon are a probe of the pyrolysis temperature.
• Only 50% of the sulfur present in tires remains in the char.
• Surface area of char was inversely proportional to its hydrogen content.
• Char from waste tire may be used as fuel or to prepare activated carbon.

A correlation between experimental conditions of microwave assisted pyrolysis (MAP) of tires and some of the characteristics of char are reported. MAP is a complementary or even an alternative methodology to recycle waste polymeric materials. This appealing way was employed in managing waste tires since they contain a high amount of microwave absorbing materials such as metal wires, metal oxides, and carbon, which quickly adsorb microwave radiation (MW) and turn it into heat. Char obtained from MAP of tire was characterized through chemical (ultimate analysis and ion coupled plasma-mass spectroscopy), morphological (BET surface area, scanning electron microscopy), and X-ray diffraction (XRD) analyses. MAP variables such as MW power and tire mass, did not strongly affect the properties of samples. Char contained large amount of amorphous carbon and inorganic compounds formed from additives employed in tires formulation. Hydrocarbons were present only in not-fully pyrolyzed samples. XRD analyses of crystalline phases showed a marked MW effect: different crystalline ZnS forms, spharelite or wurtzite were present due to the different amount of waste tires employed. The presence of these compounds suggested that tires were heated to a temperature higher than the usually accounted.