添加气对非平衡等离子体转化低碳烷烃的影响

在常压下, 研究了添加气的种类(N₂, He, Ar, H₂, NH₃, CO和CO₂)对介质阻挡放电低碳烷烃(甲烷、 乙烷和丙烷)转化制低碳烯烃的影响. 结果表明, 以甲烷或乙烷为原料时, N₂, He, Ar和CO的引入有利于提高原料的转化率和总烯烃的选择性; 而CO₂, H₂和NH₃的引入对甲烷、 乙烷的转化率无明显影响, 但H₂和NH₃的引入会使总烯烃的选择性显著降低. 以丙烷为原料时, 所研究的添加气均可提高丙烷的转化率, 而只有CO的引入可提高总烯烃选择性. 综上所述, 80%(摩尔分数) CO添加量最有利于低碳烷烃转化成低碳烯烃, 对应的甲烷、 乙烷和丙烷的转化率分别提高了14.4%, 17.6%和42.8%, 总烯烃的选择性分别提高了19.9%, 25.0%和11.9%. 以CH₄为例, 通过对放电电流波形和等离子体区物种的发射光谱(OES)研究发现, 引入CO能显著增加等离子体的电子密度, 并且体系中出现激发态O^*物种(777.5和844.7 nm), 这种O^*物种能够促进C-H键的断裂, 有利于烯烃的生成. 因此, 等离子体区电子密度的增加和激发态O^*物种的出现可能是CH₄-CO体系中CH₄有效转化的主要原因.

Effect of Additive Gases on Light Alkanes Converting Under Dielectric Barrier Discharge

At atmospheric pressure, the influences of different types of additive gases(N₂, He, Ar, H₂, NH₃, CO, CO₂) on the transformation of low carbon alkanes(CH₄, C₂H₆ and C₃H₈) to light alkenes via the dielectric barrier discharge non-equilibrium plasma(DBD plasma) method were investigated. Results show that the additive gases have different effects on the reaction. For CH₄ or C₂H₆, the conversion and selectivity of feedstock increase with the introduction of N₂, He, Ar, CO. While CO₂, NH₃ and H₂ have no obvious effect to conversion of feedstock but NH₃ and H₂ inhibit the selectivity obviously. As for C₃H₈ feedstock, the conversion can be enhanced by all the additive gases mentioned above, while the selectivity decreased in different degrees except CO. Among these additive gases, 80%(molar fraction) CO exhibits the best activity both for the feedstock conversion and selectivity of total alkenes. The conversion of CH₄, C₂H₆ and C₃H₈ increase by 14.4%, 17.6% and 42.8%, respectively, and the corresponding selectivity of total alkenes increase by 19.9%, 25.0% and 11.9%, respectively. Studies on in situ optical emission spectroscopy(OES) and current waveform of discharge show that the introduction of CO can not only increase the electron density of plasma, but also generate the excited oxygen atoms(777.5 and 844.7 nm), the latter can effectively facilitate the C-H cleavage of methane to the formation of ethylene. Therefore, the existence of excited oxygen atoms and the increased electron density of plasma may be the main reasons to cause the effective transformation of methane to light alkenes when CO as additive gas.