关键词: 煤热解, 自由基, 焦油, 小分子活化, 甲烷

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