Transformation of nitrogen, sulfur and chlorine during waste tire pyrolysis

Abstract

The transformation of N/S/Cl during pyrolysis of waste tire were investigated by Thermogravimetry-Mass Spectrum (TG-MS) and flow tube furnace reactor. The pyrolysis of waste tire included four stages, i.e., dehydration below 200 ℃, decomposition of tire additives at 200∼300 ℃, degradation of natural rubber at 300∼420 ℃, and cracking of synthetic rubber at 420∼500 ℃. The activation energy Eα were calculated according to the Coats-Redfern integral method, ca. 154.72∼158.23 and 200.46∼231.58 kJ/mol for degradation of natural rubber and synthetic rubber, respectively. Most of nitrogen (60.32∼67.78 wt.%), sulfur (56.73∼62.38 wt.%), and chlorine (58.60∼64.92 wt.%) were remained in the pyrolytic char. For the pyrolytic oil composition, expect for alkanes, alkenes, aromatic hydrocarbons, and oxygenates, the S-containing disulfide and sulfurous acid ester, N-containing quinoline and pyrimidine diamine, and Cl-containing silane, dichlorododecylmethyl- were detected. The nitrogen, sulfur, and chlorine in pyrolytic gas had diverse types. The N-containing pollutants mainly derived from inorganic ammonium and heterocyclic-N. NH3 had a wide releasing temperature range, while NO, HCN, and HNCO were mainly generated at 300∼600 °C. The C–S and -SH radicals mainly contributed to S-containing pollutants, i.e., H2S, COS, CS2, SO2, CH3SH, and C6H5SH. The Cl-containing pollutants exhibited dominant release within the temperature range of 300∼600 °C. Overall, higher heating rate promoted gas emissions, especially for NO, HCN, CH3SH, and HCl. This article provides basic knowledge on hazardous N/S/Cl transformation in solid char, liquid oil, and gas during pyrolysis of waste tire that will provide valuable information for future control technologies of pollutants emission.