Detailed studies were carried out on the initial stages of carbonization of sub-bituminous coal using reactive force field (ReaxFF) molecular dynamics simulations. Evolution of different gaseous species during carbonization were analyzed at different temperatures and densities. Elementary reactions were identified leading to the formation of small gaseous species. Cleavage of homolytic O–H bond was found to be the first step of sub-bituminous coal carbonization. CH₄ formed mainly due to reaction of ·CH₃ with hydrogen radical/hydrogen abstraction. Among others, C₉H_mO_n radicals were the most abundant species at any simulations condition considered here, where m = 9, 8 or 7 and n = 1, 2 or 3. Bond dissociation energy (BDE) of the identified reactions decreased by ∼3.0 kcal/mol for endothermic reactions and increased by ∼3.0 kcal/mol for exothermic due to change in enthalpy at higher temperature. It was observed that the formation of 5-membered carbon only rings and sp-hybridized carbon species played crucial role in the subsequent growth. The results agree with available experimental observations and computational studies. This work provides new insights on the carbonization mechanism of sub-bituminous coal.

使用反作用力场（ReaxFF）分子动力学模拟对亚烟煤碳化的初期进行了详细研究。在不同的温度和密度下分析了碳化过程中不同气态物种的演变。鉴定出基本反应，导致形成小的气态物质。发现均裂OH键的裂解是亚烟煤碳化的第一步。CH _4的形成主要是由于·CH ₃与氢自由基/氢提取反应的缘故。其中，C ₉ H _m O _n在这里考虑的任何模拟条件下，自由基都是最丰富的物种，其中m = 9、8或7且n = 1、2或3。对于吸热反应，已识别反应的键解离能（BDE）降低了约3.0 kcal / mol。由于在高温下焓变而使放热增加约3.0 kcal / mol。观察到仅五元碳环和sp-杂化碳物种的形成在随后的生长中起关键作用。结果与可用的实验观察和计算研究相吻合。这项工作为亚烟煤的碳化机理提供了新的见解。