Co-pyrolysis mechanism of low-rank coal and waste tire revealed via in-situ pyrolysis double ionization time-of-flight mass spectrometry

Co-pyrolysis of waste tire and low-rank coal provides an environmentally friendly and efficient solution to recycle the solid waste and obtain high value-added products. Herein, the co-pyrolysis mechanism of Naomaohu coal (NMH) and waste truck tire (WT) was explored through in-situ pyrolysis time-of-flight mass spectrometry (in-situ Py-TOF-MS). Results demonstrate that the release of NMH volatiles occurs at a higher temperature range (270 – 600 °C) than that of WT (150 – 550 °C), the key distinction lies in the sorts of their primary volatiles. NMH coal mainly produces alkenes, benzenes, phenols, and naphthalenes, with benzenes exhibiting the highest relative content (7.65 %). In contrast, WT primarily releases the alkenes, benzenes, and cycloolefins, and cycloolefins show the highest relative content (4.35 %). Moreover, WT pyrolysis generates abundant H-rich free radicals at low temperature, which can effectively suppress condensation reactions during co-pyrolysis, contributing to the generation of more high value-added compounds. During co-pyrolysis, the total phenols content declined to 3.11 %, especially for the diphenols. Nevertheless, the experimentally relative content of phenol (1.30 %) exceeded the theoretically calculated value (0.53 %), indicating that hydrogen free radicals facilitate the conversion of diphenols to phenol. Moreover, hydrogen radicals also inhibit the generation of char, resulting in a lower total radicals concentration in the co-pyrolysis char (5.17 ×10¹⁸spins/g) than its theoretical value (7.86 ×10¹⁸spins/g). The study explores the relationship between primary volatiles evolution behaviors and the radicals reactions during co-pyrolysis, which will provide a guidance to the regulation of co-pyrolysis products.