基于模型化合物的煤表面活性基团低温氧化研究

发布时间：2018-03-15 02:21

  本文选题：煤自燃　切入点：模型化合物　出处：《中国矿业大学》2014年博士论文　论文类型：学位论文

【摘要】：煤自燃是煤炭工业中普遍存在的一种严重灾害，研究煤自燃的特性和机理对防治灾害降低损失具有重要的意义。煤的低温氧化是煤自燃发展过程中的一个重要阶段，是影响煤炭自燃发生和发展的关键阶段。而煤是一种由相似但不相同分子结构构成的复杂有机矿物燃料，其结构异常复杂，并含有多种易氧化的活性基团。直接研究其中某种活性基团氧化过程中的结构变化往往达不到预期的效果。因此，可采用模型化合物，将复杂大分子体系分解为简单小分子结构，从而研究复杂煤分子中表面活性基团的低温氧化特性。 根据煤化学和煤的大分子模型理论，煤氧复合过程中，煤分子中的含氧官能团、侧链和桥键等活性基团易被氧化，即煤氧化自热效应的导因，而煤中芳香环的化学性质相对稳定，较难参与氧化反应，且苯环数目对活性基团的特性影响不大。因此，本文选择用芳环与某些煤中代表性的活性基团组成煤自燃模型化合物：苯乙醚、苯乙醛、苯丙醇、苯甲酸、二苯基甲烷、二苯基硫醚进行模拟实验研究。 对6种模型化合物进行“气-液”和“气-固”反应条件下的程序升温氧化实验。通过对不同温度下的各类氧化产物进行气相色谱、红外光谱以及色谱-质谱联用分析。发现模型化合物的低温氧化与煤的低温氧化类似，其氧化过程中存在临界温度，即温度超过一定值时，模型化合物的氧化活性会迅速增强；模型化合物的低温氧化是一个多步的复杂反应，包含对氧气的化学吸附和中间产物生成这一过程。通过对模型化合物氧化产物的定性分析发现其主要成分包含CO、CO2、苯、苯酚及其它各类氧化的中间产物或副产物，也与煤自燃产物相一致。在此基础上，对各模型化合物氧化反应历程进行了分析。 通过模型化合物的耗氧特性，分析了模型化合物氧化过程中的活化能及指前因子等氧化动力学参数；结果表明，6种模型化合物中苯乙醛（—CHO）和二苯基甲烷（—CH2—）的活化能较小，，氧化活性较强。但因醛基—CHO在煤中的含量较低，故煤中的亚甲基桥键—CH2—对煤的自燃特性具有重要影响。通过TG/DTA技术研究了模型化合物在低温氧化过程中的放热特性，发现煤自燃模型化合物在低温氧化最初阶段有微幅的增重，随着温度的进一步升高进而迅速失重，并最终维持稳定。相比之下，模型化合物的DTA曲线在整个低温氧化过程中存在不止一个吸/放热峰，表明模型化合物的中活性结构的在不同温度阶段有复杂的热变化。 通过对煤中活性官能团氧化特性的分析，选取植酸、2,6-二叔丁基对甲酚、没食子酸正丙酯等五种抗氧化剂进行模型化合物的低温氧化抑制实验，并应用于煤样自燃抑制实验。结果表明，2,6-二叔丁基对甲酚和植酸在160℃之后对煤的氧化有良好的抑制效果。同时，通过各抗氧化剂对煤自燃阻化实验结果分析其氧化抑制机理。
[Abstract]:Coal spontaneous combustion is a common serious disaster in coal industry. It is very important to study the characteristics and mechanism of coal spontaneous combustion to prevent disaster and reduce loss. The low temperature oxidation of coal is an important stage in the development of coal spontaneous combustion. Coal is a kind of complex organic mineral fuel, which is composed of similar but different molecular structure, and its structure is extremely complex. And it contains many kinds of easily oxidized active groups. The structural changes in the oxidation process of some active groups are often not as good as expected. Therefore, model compounds can be used. The complex macromolecular system was decomposed into simple small molecular structures, and the oxidation characteristics of surface active groups in complex coal molecules were studied at low temperature. According to the theory of macromolecular model of coal chemistry and coal, the oxygen-containing functional groups, side chains and bridge bonds in coal molecules are easily oxidized in the process of coal-oxygen compounding, that is, the conduction of coal oxidation autoheating effect. However, the chemical properties of aromatic rings in coal are relatively stable, and it is difficult to take part in oxidation reactions, and the number of benzene rings has little effect on the properties of active groups. In this paper, aromatic rings and some representative active groups in coal are selected to form coal spontaneous combustion model compounds: phenylether, phenylacetaldehyde, phenylpropanol, benzoic acid, diphenyl methane and diphenyl sulfide. The temperature programmed oxidation experiments of six model compounds were carried out under the conditions of "gas-liquid" and "gas-solid" reactions. The oxidation products at different temperatures were analyzed by gas chromatography. Infrared spectrum and chromatography-mass spectrometry analysis showed that the oxidation of the model compound at low temperature is similar to that of coal at low temperature. The oxidation activity of the model compound increases rapidly when the temperature exceeds a certain value. The oxidation of model compounds at low temperature is a multistep complex reaction involving the chemical adsorption of oxygen and the formation of intermediate products. Phenol and other kinds of oxidation intermediates or by-products are also consistent with coal spontaneous combustion products. On this basis, the oxidation reaction mechanism of each model compound is analyzed. The oxidation kinetic parameters such as activation energy and preexponential factor during oxidation of the model compounds were analyzed through the oxygen consumption characteristics of the model compounds. The results showed that the activation energies of phenylacetaldehyde and diphenyl methane (Ch _ 2) in the six model compounds were small. The oxidation activity is strong. However, because of the low content of aldehyde Cho in coal, the methylene bridge bond (Ch 2-) in coal has an important effect on the spontaneous combustion characteristics of coal. The exothermic properties of the model compounds in the process of low temperature oxidation have been studied by TG/DTA technique. It was found that the model compound of coal spontaneous combustion increased slightly in the initial stage of oxidation at low temperature, and then lost weight rapidly with the further increase of temperature, and finally maintained stability. There is more than one heat absorption / exothermic peak in the DTA curve of the model compound during the whole process of low temperature oxidation, which indicates that the active structure of the model compound has complex thermal changes at different temperatures. By analyzing the oxidation characteristics of active functional groups in coal, five kinds of antioxidants, such as phytate 2, 6 and 2 tert-#china_person0#, were selected to carry out the low temperature oxidation inhibition experiments of the model compounds, such as cresol, n-propyl gallate, and so on. The results showed that the oxidation of cresol and phytic acid to coal was inhibited after 160 鈩

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