介质阻挡放电甲醇脱氢偶联一步合成乙二醇反应中氢气的催化作用

利用原位发射光谱表征和在线色谱分析,研究了甲醇介质阻挡放电脱氢偶联一步合成乙二醇反应中氢气的催化作用,考察了放电频率、甲醇和氢气进料量以及反应压力的影响.结果表明,在介质阻挡放电产生的非平衡等离子体中,H2不但能显著提高甲醇转化率,而且能显著提高乙二醇的选择性.在300°C,0.1 MPa,反应器注入功率为11 W,放电频率为12.0 k Hz,甲醇气体进料量为11.1 m L/min,氢气进料量为80–180 m L/min的条件下,甲醇转化率接近30%,乙二醇选择性大于75%.乙二醇收率与激发态氢原子的Hα谱线强度之间存在同增同减关系.由此推测,氢原子是起催化作用的活性氢物种.活性氢物种的生成途径是:基态氢分子通过与电子碰撞变成激发态,激发态氢分子通过第一激发态氢自动解离为基态氢原子.放电反应条件通过影响氢分子解离来影响氢气的催化作用.氢气在非平衡等离子体中显示的催化作用有可能为开辟新的化学合成途径提供重要机遇.

The catalytic effect of H2 in the dehydrogenation coupling production of ethylene glycol from methanol using a dielectric barrier discharge

The catalytic effect of H2 in the one‐step synthesis of ethylene glycol (EG) from methanol dehydro‐genation coupling reaction using dielectric barrier discharge (DBD) was studied by in‐situ optical emission spectroscopy and online chromatographic analysis. The influence of discharge frequency, methanol and H2 flow rates as well as reaction pressure was investigated systematically. Results show that, in the non‐equilibrium plasma produced by DBD, H2 dramatically improved not only the conversion of methanol but also the selectivity for EG. Using the reaction conditions of 300 °C, 0.1 MPa, input power 11 W, discharge frequency 12.0 kHz, methanol gas flow rate 11.0 mL/min, and H2 flow rate 80–180 mL/min, the reaction of the CH3OH/H2 DBD plasma gave a methanol conversion close to 30%and a selectivity for EG of more than 75%. The change of the EG yield correlated with the intensity of the Hαspectral line. H atoms appear to be the catalytically active species in the reac‐tion. In the DBD plasma, the stable ground state H2 molecule undergoes cumulative collision excita‐tion with electrons before transitioning from higher energy excited states to the first excited state. The spontaneous dissociation of the first excited state H2 molecules generates the catalytically ac‐tive H atom. The discharge reaction condition affects the catalytic performance of H2 by influencing the dissociation of H2 molecules into H atoms. The catalytic effect of H2 exhibited in the non‐equilibrium plasma may be a new opportunity for the synthesis of chemicals.