The behavior of free radicals during the carbonization of anthracite briquette

Abstract

The variation in behavior of free radicals during the pyrolysis and co-pyrolysis of anthracite and coal-based binder (AS) was determined by Electron paramagnetic resonance (EPR). Besides, Thermogravimetry (TG) and Carbon-13 nuclear magnetic resonance (13C NMR) were also applied to investigate the nature of pyrolysis and structural characterization of the coal samples. The results indicated that the induced effect of free radical existed in the co-pyrolysis of anthracite and AS, such that the free radical concentration (Ng) of AS carbonized briquette (ASB) at 300–500 °C is far higher than the additive value of Ng when anthracite and AS are separately carbonized. When the temperature exceeds 500 °C, the timely release of AS free radicals could combine with the aromatic free radicals of anthracite, leading to a slight decrease in the Ng value of ASB. Due to the limited combination, the rapid polycondensation of aromatic free radicals in anthracite was inhibited and more number of short side-chains and cross-links were generated in ASB. These effects delay the major polycondensation process of ASB to a higher temperature compared with other samples. As a result, the Ng value of ASB drops significantly above 700 °C and the line shape of it transforms closer to the Lorentz line shape. The lapping of free radical variation in anthracite and binder would broaden the temperature range for bonding-polymerization, which makes the free radicals of the blend components to rearrange and to form strong carbon–carbon bonds. Thus, the mechanical strength (M40) of carbonized briquette would be improved.