煤自燃在世界各主要产煤国均普遍存在，严重危害煤矿安全生产。研究煤自燃机理有助于揭示其本质从而防止其发生。由于煤物理和化学结构的复杂性，当前对于煤自燃自由基链式反应过程中的基本反应途径和细节仍缺乏足够多的了解。而作为煤自燃自由基链式反应理论中的起始和关键环节，链式反应的触发渠道及机理尚需进一步深入研究。持久性自由基作为一类赋存于有机质中的特殊活性物质，由于含有未配对电子导致其对有机碳结构的自氧化分解具有积极的触发和促进作用，近年来逐渐引起学界关注。煤化作用使得原煤中亦含有丰富的持久性自由基，但目前对于其在煤自燃自由基链式反应过程中发挥的具体作用及机理还不清楚。为此，本文聚焦于煤中的持久性自由基，对其赋存特征、演变规律、活化触发煤氧化特性以及触发煤氧化后的自由基链式反应传播历程等展开了实验研究和量子化学计算，最终系统揭示了持久性自由基触发煤自燃潜力及其作用机理。研究结果对丰富煤自燃自由基链式反应理论及开发新型煤自燃阻化技术具有重要理论和现实意义。取得主要创新性成果如下：

通过原位电子顺磁共振和原位漫反射傅里叶变换红外光谱实验，明确了持久性自由基在不同变质程度煤中的赋存特征，以及其在煤自燃过程中的动态变化规律，阐释了煤氧化分子结构改变对持久性自由基的影响。结果表明，高变质程度煤中的持久性自由基浓度较高。煤中的持久性自由基对温度表现出较强的敏感性，热分解和热氧化作用下整体表现出相似的变化规律。即随着反应温度的升高，其信号强度、对外能量交换作用增强，碳中心自由基增多。区别在于热氧化过程中持久性自由基的信号强度、浓度、能量交换作用均得到了提高，种类则更加复杂。煤氧化自由基链式反应生成的大量瞬时性自由基将为持久性自由基的形成提供物质基础，而煤中芳香大分子网络结构产生的共轭效应和空间位阻则有利于自由基的稳定。

采用煤基模型化合物，通过X射线光电子能谱和原位电子顺磁共振技术，揭示了煤自燃过程中持久性自由基的生成机理，确定了生成持久性自由基的关键条件，明确了反应特征参数。结果表明，煤中过渡金属氧化物会催化一些典型煤结构氧化生成持久性自由基。其中，酚羟基结构（Ar-OH）最具潜力，其将反应生成多种持久性自由基。反应过程中将经历物理吸附、化学吸附、电子转移、热分解等环节。除物理吸附外其余反应环节的自由能变和焓变均大于0，加热方能发生。反应过程中，从110℃起缓慢展现出持久性自由基信号，210℃以后信号显著增强。此类反应绝氧条件下亦可发生，煤中过渡金属元素将被还原成低价态，Ar-OH结构则被催化氧化为-C=O并最终解离出指标性气体CO。反应后期生成的持久性自由基中，未配对电子均位于芳环。

利用自旋捕获技术研究了煤中持久性自由基的活化特性，并基于8类典型煤结构模型，采用量子化学计算揭示了持久性自由基活化产物对煤氧化自由基反应的触发特性及潜力。结果表明，持久性自由基在光照或受热时可活化并诱导产生超氧阴离子自由基（O₂^•−）和羟基自由基（•OH），二者因极强的氧化性可直接参与煤的氧化进程，使得持久性自由基具备触发煤氧化自由基反应的潜力。•OH氧化性最强，其产量与光照时间、加热温度及煤中持久性自由基含量成正比。•OH能在常温下自发氧化煤中的活性官能团同时放出大量反应热（能垒＜40 kJ/mol，焓变为-69.10 kJ/mol），随后其氧化产物还将自发与氧气发生0能垒的自由基二聚反应并再次释放反应热（焓变为-110.21 kJ/mol）。从动力学和热力学层面对比发现，这些由持久性自由基活化产生的•OH在触发煤氧化反应时，其潜力显著大于煤自燃过程中的其他重要氧化剂。

通过量子化学计算进一步揭示了持久性自由基触发煤氧化后的链式反应传播特性，掌握了链式反应传播历程、关键反应环节及中间体、反应热力学及动力学特征参数，建立了链式反应传播模型。结果表明，持久性自由基诱导生成的•OH在触发煤氧化自由基反应的同时亦促进煤体完成热量的原始积累，随着煤温的升高一些后续的自由基链式反应环节将相继突破能垒。当广泛存在的O₂突破能垒开始直接氧化煤中的活性官能团时，煤氧化进入快速反应阶段。链式反应过程中，由于受到多种自由基的攻击，煤中持续发生着活性官能团的脱H过程，所含H原子越多其链式反应路径越复杂。反应中间体烷基过氧自由基（ROO•）和烷氧自由基（RO•）具备开启循环自氧化反应的特性，有利于加快煤氧化进程。此外，持久性自由基触发的抽氢氧化反应，以及ROO•和过氧化物（ROOH）的形成、分解反应是链式反应过程中最为重要的放热环节。而O₂对活性官能团的抽氢氧化，ROO•、ROOH以及含-C=O基团的分解具有较高的反应能垒，是链式反应中的重要决速步。煤中持久性自由基的有效猝灭或消减其产生的•OH和O₂^•−将有利于防止煤的早期氧化及自热。而当煤氧化进入快速反应阶段时，有效防止ROO•和ROOH的分解将是关注的重点。

Coal spontaneous combustion is common in major coal producing countries around the world, seriously endangering coal mine safety production. Studying the mechanism of coal spontaneous combustion can help reveal its essence and prevent its occurrence. Due to the complexity of the physical and chemical structure of coal, there is still a lack of in-depth understanding of the basic reaction pathways and details in the free radical reaction process of coal spontaneous combustion. As the starting and key link in the theory of free radical chain reactions, the triggering channels and mechanisms of the free radical chain reaction in coal spontaneous combustion still need further in-depth research. As a special type of active substance that exists in organic matter, persistent free radicals have a positive triggering and promoting effect on the self oxidation decomposition of organic carbon structures due to their unpaired electrons, which has gradually attracted attention from the academic community in recent years. Raw coal also contains abundant persistent free radicals, but the specific role and mechanism they play in the free radical reaction process of coal spontaneous combustion are still unclear. Therefore, this study focuses on persistent free radicals in coal, and conducts experimental research and quantum chemical calculations on their occurrence characteristics, evolution laws, activation and triggering coal oxidation characteristics, as well as the propagation process of free radical chain reactions after triggering coal oxidation. Ultimately, the potential and mechanism of persistent free radicals triggering coal spontaneous combustion are systematically revealed. The research results have important theoretical and practical significance for enriching the theory of coal spontaneous combustion free radical chain reaction and developing new technologies for coal spontaneous combustion inhibition. The main innovative achievements are as follows:

Through in-situ electron paramagnetic resonance and in-situ diffuse reflectance Fourier transform infrared spectroscopy experiments, the occurrence characteristics of persistent free radicals in coal with different degrees of metamorphism and their dynamic changes during coal spontaneous combustion were clarified, and the influence of molecular structure changes on persistent free radicals during coal oxidation was explained. The results indicate that the concentration of persistent free radicals in highly metamorphic coal is relatively high. Persistent free radicals exhibit strong sensitivity to temperature, and show similar patterns of change overall under thermal decomposition and oxidation. As the reaction temperature increases, the signal intensity and external energy exchange increase, and the number of carbon center free radicals increases. The difference is that the signal intensity, concentration, and energy exchange of persistent free radicals are all increased during the thermal oxidation process, and the types are more complex. The large number of transient free radicals generated by the coal oxidation free radical reaction will provide the material basis for the formation of persistent free radicals, while the conjugation effect and steric hindrance generated by the aromatic macromolecule network structure in coal are conducive to the stability of free radicals.

Using coal based model compounds, the formation mechanism of persistent free radicals during coal spontaneous combustion was revealed through X-ray photoelectron spectroscopy and in-situ electron paramagnetic resonance technology. At the same time, the key conditions for generating persistent free radicals were determined, and the reaction characteristic parameters were clarified. The results indicate that transition metal oxides in coal catalyze the oxidation of some typical coal structures to form persistent free radicals.Among them, the phenolic hydroxyl structure (Ar-OH) in coal has the most potential, which will react to generate a variety of persistent radicals. During the reaction process, it will undergo physical adsorption, chemical adsorption, electron transfer, thermal decomposition, and other stages. Except for physical adsorption, the free energy change and enthalpy change of all other reaction steps are greater than 0, indicating that heating is necessary for the reaction to occur. During the reaction process, the signal of persistent free radicals slowly appears from 110 ℃, and the signal intensity significantly increases after 210 ℃. This type of reaction can also occur under anaerobic conditions. Transition metal elements in coal will eventually be reduced to low valence states, while the Ar-OH structure will be catalytically oxidized to -C=O and eventually dissociated into the indicator gas CO. For persistent free radicals generated in the later stages of the reaction, their unpaired electrons are all located in the aromatic ring.

The activation characteristics of persistent free radicals in coal were studied using spin trapping technology, and based on eight typical coal structure models. The triggering mechanism and potential of persistent free radicals on coal oxidation was revealed using quantum chemical calculations. The results indicate that persistent free radicals in coal can induce the production of a large amount of superoxide anion radical (O₂^•−) and hydroxyl radical (•OH) under light or heating conditions, which can directly participate in the coal oxidation process due to their strong oxidizing properties, making persistent free radicals have the potential to trigger coal oxidation free radical reactions. •OH has the strongest oxidizing ability, and its production is proportional to the duration of light exposure, heating temperature, and the concentration of persistent free radicals in coal. •OH can spontaneously oxidize the active functional groups in coal at room temperature and release a large amount of reaction heat (energy barrier<40 kJ/mol, enthalpy change equal to -69.10 kJ/mol). Subsequently, its oxidation products (carbon centered free radicals) will spontaneously undergo free radical dimerization with oxygen and release reaction heat again (enthalpy changes equal to -110.21 kJ/mol). From the perspective of kinetics and thermodynamics, it is found that the potential of these induced •OH to trigger coal oxidation free radical reactions is significantly greater than that of other important oxidants during coal spontaneous combustion, such as O₂. From the perspective of kinetics and thermodynamics, it is found that the •OH generated by persistent free radicals activation has significantly greater potential than other oxidants in coal spontaneous combustion processes when triggering coal oxidation reactions.

The subsequent chain reaction propagation characteristics of coal oxidation triggered by persistent free radicals were further revealed through quantum chemical calculations. At the same time, the chain reaction propagation process, key reaction links and intermediates, reaction thermodynamic characteristic parameters were mastered, and a chain reaction propagation model was established. The results indicate that the •OH induced by persistent free radicals not only triggers the coal oxidation free radical reaction, but also promotes the original accumulation of heat in the coal. As the coal temperature increases, some free radical chain reaction links will successively break through the energy barrier. When the widely present O₂ breaks through the energy barrier and directly oxidizes the active functional groups in coal, coal oxidation enters the rapid reaction stage. In the chain reaction process, due to the attack of various free radicals, the active functional groups in coal continue to undergo the process of dehydrogenation, and the more H atoms it contains, the more complex the chain reaction path becomes. As reaction intermediates, alkyl peroxide radical (ROO•) and alkoxy radical (RO•) have the characteristic of initiating cyclic auto oxidation reactions, which is beneficial for accelerating the coal oxidation reaction process. In addition, the hydrogen extraction reaction of persistent free radicals, as well as the formation and decomposition reactions of ROO• and peroxides (ROOH), are the most important exothermic links in the chain reaction process. The hydrogen extraction reaction of O₂, ROO•, ROOH, and the decomposition of -C=O groups have high reaction energy barriers and can be regarded as the rate determining step of chain reactions. The effective quenching of persistent free radicals in coal, or the reduction of their generated •OH and O₂^•−, will be beneficial in preventing early oxidation and self heating of coal. And when coal oxidation enters the rapid reaction stage, effectively preventing the decomposition of ROO• and ROOH will be the focus of attention.

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