Synergistic effects of mechanochemical activation and selective O-alkylation on the chemical structure and gaseous products evolution during coal flash pyrolysis

Mechanochemical activation offers significant advantages in enhancing the pore structure and active sites of materials, while selective O-alkylation boosts both the homogeneous and heterogeneous reactivity of coal. In this work, mechanochemical activation and selective O-alkylation are synergistically applied to modify pulverized coal. The evolution of the chemical structure was thoroughly characterized using ultimate analysis, Fouriertransform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR). Pyrolysis gas chromatography-mass spectrometry (PY-GC-MS) was utilized to investigate the release of crucial gaseous products during the pyrolysis. Additionally, this study focuses on the synergistic effects of mechanochemistry and selective O-alkylation on the chemical structure and pyrolysis characteristics. The results reveal that alkylation boosts the formation of C-O bonds and aliphatic carbon while reducing the presence of aromatic carbon. Moreover, by disrupting intermolecular forces, alkylation induces the fragmentation of expansive aromatic layers into smaller aromatic fragments, thereby generating additional structural defects. Furthermore, the electron transfer process facilitates the conversion of aromatic carbon into aliphatic forms through ring-opening reactions. On the other hand, incorporating alkyl functional groups and initiating ring-opening reactions of aromatic carbons lead to a rise in aliphatic hydrocarbons during the pyrolysis of alkylated coal. However, intensified mechanochemical action hinders the production of aliphatic hydrocarbons. Additionally, during alkylation, the creation of esters and ethers with elevated thermal stability delays the release of oxygen-containing gas products. The findings propose a new pretreatment method for coal utilization, promoting the development of new lowNOx combustion technology.