Abstract:

Pyrolysis, as one of the most important fields in Engineering Thermochemistry, is an important route to realize the efficient utilization of coal. It is vital to the efficiency and economy of the pyrolysis to improve the yield of tar or chemicals. Coal pyrolysis follows the free radical reaction mechanism, so the key to high tar yield is to stabilize the free radicals produced from coal pyrolysis. Based on the pyrolysis mechanism of coal and its low H/C atom ratio, a strategy to improve tar yield was constructed by coupling the catalytic activation of H-rich small molecules with traditional coal pyrolysis. The H-rich active free radicals generated by catalytic activation of small molecule gases such as methane and ethane, were used to stabilize the free radicals cracked from coal pyrolysis, which can inhibit further polymerization or cracking of these free radicals to form char and gas, and achieve the obvious increase in tar yield. The studies show that tar yield is remarkably improved when coal pyrolysis is integrated with methane activation by catalytic reforming or plasma, and tar quality is enhanced. The strategy is universal. The coupling effect is influenced by methane activation methods, catalyst, coal properties and so on. Isotopic tracer techniques confirm that small H-rich molecule free radicals participate in the formation of tar. In addition, these small H-rich molecule gases can be extended to pure methane, ethane, pyrolysis gas, and so on. Based on this strategy and the fact that organic solid wastes such as biomass, waste plastics and waste tires have a higher H/C atom ratio than coal and H-rich active species will be produced during the pyrolysis process, co-pyrolysis of coal with biomass, waste plastics and waste tires is further developed. It is found that the heating rate and their mixing model can strengthen the synergistic effect, further improving the tar yield in coal pyrolysis and the resource utilization of the waste. This integrated technology provides an important idea and method to solve low tar yield in traditional coal pyrolysis, and a new route to develop the advanced coal pyrolysis technology. More attention should be paid to the development of integrated reactors and high-performance catalysts for the activation of small molecules in the future.

Key words: coal pyrolysis, free radical, tar, small molecule activation, methane

摘要：

热解作为“工程热化学”的重要研究方向，是实现煤炭分质分级利用的重要途径。提高热解焦油或化学品产率是提升煤转化效率和经济性的关键。煤热解遵循自由基反应机理，因此稳定煤裂解产生的自由基是提高焦油产率的关键。基于煤的热解反应机理及煤中H/C原子比低的特征，本文提出了通过富氢小分子气体的催化活化耦合煤热解提高焦油产率的策略，利用甲烷、乙烷等小分子气体催化活化产生的富氢活性自由基来稳定煤热解产生的自由基，达到抑制煤裂解自由基间的聚合或裂解形成半焦及气体反应的发生，实现热解焦油产率的显著提高。研究表明，甲烷经催化重整或等离子体活化后与煤热解过程耦合，可显著提高焦油产率和一定程度提升焦油品质，该过程具有普适性。甲烷活化方式、催化剂性能、煤种性质等是影响耦合效果的关键因素。同位素示踪证实了富氢小分子自由基参与煤热解焦油的形成。这种富氢小分子气体可拓展至纯甲烷、乙烷、热解煤气等。在此基础上，基于生物质、废塑料、废轮胎等有机固废具有比煤更高H/C原子比及热解过程产生富氢活性物种的特性，发展了煤与生物质、废旧塑料、废轮胎等固体有机物的共热解，发现提高升温速率、改变共热解混合模式等可强化协同作用，实现煤热解焦油产率提高及生物质、废轮胎等资源化高效利用。这种基于小分子气体催化活化耦合传统煤热解技术，为解决现有热解过程存在的焦油产率低等问题提供了重要的思路和方法，为发展先进的煤炭分质分级转化技术提供了新途径。耦合反应器的开发及用于小分子气体活化的高性能催化剂制备是未来研究的重点。

关键词: 煤热解, 自由基, 焦油, 小分子活化, 甲烷