为了探究低温等离子体活化转化煤层甲烷的机理, 采用自制的介质阻挡放电实验系统对体积组成为CH4 40%、O2 12%、N2 48%的模拟煤层甲烷进行等离子体活化转化。采用色谱分析方法对煤层甲烷介质阻挡放电稳定产物进行分析, 结果表明低温等离子体活化煤层甲烷的主要产物为CH3OH、CO和CO2。采用发射光谱原位诊断技术在200～700 nm波长范围内研究了放电气体的发射光谱, 检测到O·、CH·、C·、Hα、N2(A3+U)等激发态物种。基于发射光谱原位诊断和气相色谱分析结果, 对煤层甲烷活化转化的自由基反应过程进行了推断。同时, 明晰了反应气中N2对煤层甲烷活化和主要产物的生成具有促进作用, 即N2产生了存活时间更长的亚稳态离子, 该亚稳态离子将能量传递给反应气中的O2和CH4, 进而加速了煤层甲烷的活化和稳定产物的生成。

In order to study mechanism of activation and conversion of coalbed methane under cold plasma, the investigation was realized by dielectric barrier discharge of gas mixture of CH4, O2 and N2 (the volume fraction of CH4, O2 and N2 is 40%, 12% and 48%, respectively). In this study, a set of experimental system of plasma activation and conversion of coalbed methane was constructed. The experiment system was used to study affecting factors of activation and conversion of coalbed methane, such as discharge voltage and discharge frequency. Based on this, the stable products of coalbed methane conversion were analyzed by the gas chromatograph, As main stable products of conversion of coalbed methane under cold plasma, CH3OH, CO and CO2 were detected. In situ diagnosis technique of optical emission spectroscopy was used to study the emission spectra of the gas discharge in the spectra range of 200-700 nm, active species of O·, CH·, C·, Hα and N2(A3+U) were observed. Based on the detection of the active species, the analysis of stable products by gas chromatograph and the characterization of plasma, the course of free radical reaction of the activation and conversion of coalbed methane under cold plasma were inferred. Meanwhile, it is clarified that N2 in the mixture gas has promoting effect on activation of coalbed methane and production of main products. That is, N2 produces metastable ions with longer survival time. The metastable ions transfer the energy to O2 and CH4 in the mixture gas, which accelerates the activation of methane and formation of main stable products.