Plasma bubble characteristics and hydrogen production performance of methanol decomposition by liquid phase discharge

The decomposition of hydrocarbons or alcohols by non-thermal plasma discharge has potential for rapid hydrogen production. Hydrogen production using liquid raw materials is more secure and economical for transportation. In this study, liquid plasma discharge was used to induce methanol decomposition and analyzed factors affecting the decomposition reaction as well as the evolution of the plasma bubble. A liquid plasma discharge reactor was designed for visualization. Liquid-phase discharge and methanol decomposition processes were imaged in detail using a high-speed camera. At the plasma-liquid interface of a bubble substrate, energy is concentrated and methanol is decomposed into gaseous products. The bubbles detach from the tip of the plasma bubble substrate and the decomposition reaction is continuous and stable. Two typical plasma discharge modes were obtained by adjusting the electrode spacing: gliding arc discharge (GAD) and glow discharge (GD). The voltage and current curves of GD approximate the sinusoidal waveform of the alternation current power supply, and the range of discharge power is 130.4-460.2 W. However, GAD has feature of the bipolar pulses with a high transient peak current (420.6-690.9 mA) that causes discharge power of GAD excitation is 30.7-110.3 W. Primary analyzes indicate that the energy consumption of GAD is less than that of the GD due to the difference in discharge characteristics. An optimized energy consumption of 1.63 kWh/Nm3H2 was achieved for hydrogen production. The maximum hydrogen proportion of the gaseous product is 63.21%, which corresponds to a carbon monoxide proportion of 26.38% as the main byproduct. The effects of the discharge power, electrode distance, and electrode diameter on methanol decomposition were analyzed.