Jialiang Zhang

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

Abstract The catalytic effect of H2 in the one-step synthesis of ethylene glycol (EG) from methanol dehydrogenation 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 Hα spectral line. H atoms appear to be the catalytically active species in the reaction. In the DBD plasma, the stable ground state H2 molecule undergoes cumulative collision excitation 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 active 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.

Plasma-Triggered CH4/NH3 Coupling Reaction for Direct Synthesis of Liquid Nitrogen-Containing Organic Chemicals

Nitrogen-containing organic chemicals such as amines, amides, nitriles, and hydrazones are crucial in chemical and medical industries. This paper reports a direct synthesis of N,N-dimethyl cyanamide [(CH3)2NCN] and amino acetonitrile (NH2CH2CN) through a methane/ammonia (CH4/NH3) coupling reaction triggered by dielectric barrier discharge plasma, with by-products of hydrazine, amines, and hydrazones. The influence of CH4/NH3 molar ratio, feedstock residence time, and specific energy input on the CH4/NH3 plasma coupling reaction has been investigated and discussed. Under the optimized conditions, the productivities of (CH3)2NCN and NH2CH2CN reached 0.46 and 0.82 g·L–1·h–1, respectively, with 8.83% CH4 conversion. In addition, through combining the optical emission spectra diagnosis and the reaction results, a possible CH4/NH3 plasma coupling reaction mechanism has been proposed. This paper provides a potential fine application of CH4 and NH3 in green synthesis of liquid nitrogen-containing organic chemicals, such as nitriles, amines, amides, and hydrazones.