低碳烃活化与煤热解耦合过程中焦油形成规律和机制

Coal pyrolysis is an important multi-conversion technology for clean and efficient use of coal. Tar from coal pyrolysis is not only the main source of polycyclic aromatic hydrocarbons, but also a high-quality liquid fuel through hydrogenation processing to make up the shortage of crude oil. In our earlier study on the integrated process of coal pyrolysis with methane activation, we found that the free radicals from methane activation stabilize the radicals from coal pyrolysis to form tar through chemical combination. The result of integrated process experiment shows higher tar yield than hydrogenation pyrolysis of coal because of the heavier molecular weight of methyl radical than hydrogen radical. Assuming that even heavier ethyl radicals were involved in coal pyrolysis, much higher tar yield could be obtained. Based on this, this project proposed to investigate the basic rules and formation mechanism of tar in an integrated process of coal pyrolysis with low carbon hydrocarbon activation. Particularly, the effect of coal properties and process parameters on the rules of the integrated process of activation (steam reforming or partial oxidation) of ethane or propane, or the mixture of low carbon hydrocarbon with coal pyrolysis; the relation between the molecular size of low carbon hydrocarbon, yield and quality of tar in the integrated process. Moreover, vacuum ultraviolet single-photon ionization coupled with molecular-beam mass spectrometry technique and labeled isotope tracer method will be employed to identify the radicals and products from activation of low carbon hydrocarbon, and to further explore the transformation of low carbon hydrocarbon in the integrated process and the reaction mechanism. This research will be helpful for us to understand the reaction and stabilization of the free radicals in coal pyrolysis, and to develop the novel coal pyrolysis technology with high yield and high quality of tar.

煤热解是重要的煤炭分质清洁高效转化技术。煤热解产生的焦油既是多环芳烃的重要来源，也可加工成油品以弥补原油的不足。申请人在前期研究甲烷活化与煤热解耦合过程中，发现甲烷活化形成自由基参与了煤热解自由基的稳定，因甲基自由基的分子量高于氢自由基，使耦合过程焦油产率高于煤加氢热解焦油产率。若分子量更高的乙基自由基参与煤热解，有望得到更高的焦油产率。基于此，本项目提出开展低碳烃活化与煤热解耦合过程中焦油形成规律和机理的研究，重点研究煤的组成、结构以及工艺参数对乙烷、丙烷以及混合低碳烃活化（水蒸气重整和部分氧化）与煤热解耦合过程的影响规律，探讨低碳烃分子大小与耦合过程焦油产率和性质间的关系，同时利用真空紫外单光子电离分子束质谱和同位素示踪方法研究低碳烃在耦合过程中变迁规律、耦合过程的反应机理等。研究工作对深入认识煤热解过程自由基反应与调控，发展具有高品质和高产率煤焦油的热解工艺具有理论和现实意义。

煤热解过程中焦油的形成与煤中有机大分子受热裂解和裂解自由基的稳定有关，在热解过程中利用外部施加的小分子自由基使裂解自由基稳定，是提高焦油产率的有效途径。前期研究发现将甲烷活化与煤热解耦合可显著提高煤热解过程的焦油产率，且明显高于被认为是提高煤热解焦油产率最有效方法的加氢热解的焦油产率，究其原因应该与煤热解产生的自由基进行结合的外加自由基大小有关。为此，本项目提出开展低碳烃活化与煤热解耦合过程中焦油形成规律和机理的研究。重点研究乙烷、丙烷以及混合低碳烃活化（水蒸气重整和部分氧化）与煤热解耦合过程产物形成规律，同时利用真空紫外单光子电离分子束质谱技术和同位素示踪方法研究低碳烃耦合过程中变迁规律、耦合过程的反应机理以及与煤热解焦油产率和性质的关系等。通过低碳烃水蒸气（及二氧化碳）重整与煤热解耦合过程研究，得到了低碳烃活化与煤热解耦合过程焦油生成的基本规律以及工艺条件（反应温度、低碳烃流量、甲烷/乙烷混合比例等）对耦合过程产物分布及组成（特别是焦油产率及组成）的影响规律，制备了性能优良的低碳烃水蒸气重整催化剂Ce-Ni/Al2O3以及具有较好抗结炭性能低碳烃二氧化碳重整催化剂Ni/La2O3。进一步证明了低碳烃活化在煤热解过程焦油形成中的作用，明确了低碳烃分子大小与耦合过程焦油产率和性质间的关系；利用飞行时间质谱原位研究催化重整反应过程，认识不同催化剂上CH4与CO2的活化机理；采用同位素示踪法，认识了高的焦油产率与低碳烃活化产生自由基参与煤热解自由基的稳定有关，由于烷基自由基分子量明显大于氢自由基，当烷基自由基与煤热解自由基结合，对焦油量的贡献更大，使耦合过程的焦油产率高于加氢热解焦油产率。上述研究成果为获得高焦油产率的新型煤热解工艺开发以及过程优化提供重要基础。在项目执行期间，已在国内外本领域主流刊物发表论文6篇，参加12次国际和2次国内会议，交流论文14篇，其中特邀报告国际会议4次，国内会议1次；申请发明专利1项；培养博士研究生5名，硕士研究生7名。