Study On Hydrogen Production Characteristics Of Liquid-State Microwave Discharge Plasma Methane Water Reforming

With the continuous development of science and technology,more and more attention is paid to environmental quality.Hydrogen is an ideal secondary energy source,which has the advantages of large combustion heat value,combustion product is water,and will not produce secondary pollution.Natural gas reserves are abundant,and it is a relatively economical and reasonable choice of raw materials in the fossil fuel hydrogen production process.Traditional methane hydrogen production technology has high hydrogen production,but has the limitations of high fuel cost,expensive equipment,and high-temperature catalyst deactivation.Therefore,the catalyst-free,fast-response,.and plasma-reforming technology with high active materials came into being.In this study,direct coupled microwave plasma technology was used to achieve liquid-phase methane wet reforming for hydrogen production.On this basis,the effects of microwave power,methane flow,electrode structure and electrode position on hydrogen production were explored,and possible reaction paths were analyzed.The following conclusions were reached:(1)When the electrode structure of the intermediate air inlet is used,as the flow of methane increasing,the output flow increases,but the methane conversion rate and hydrogen production concentration continue to decrease,while the energy efficiency and selectivity of hydrogen production increase first and then decrease.With the increasing of applied power,the parameters such as gas flow.rate,methane conversion rate,energy efficiency of hydrogen production,hydrogen concentration,and selectivity tend to increase first and then decrease.The comprehensive hydrogen production energy efficiency is obtained when the applied power is 900W and the methane flow rate is 0.896L/min.The methane conversion rate was 94.29%,and the energy efficiency of hydrogen production reached 0.854mmol/kJ,and the hydrogen selectivity and carbon selectivity were 48.82%and 38.18%,respectively.The reason for the decrease of the following parameters may be the effect of electrode.burning.(2)When the electrode structure with intermediate air inlet is used,the curvature of the electrode tip is large.At the same time,because the tungsten copper alloy electrode itself has poor heat resistance,the electrode burning phenomenon often occurs,so the plasma system is unstable.Therefore,the peripheral air inlet is used.The electrode material is tungsten,which reduces the curvature of the electrode tip and has high heat resistance,and improves the stability of the plasma generation system.With the increasing of methane flow,the output gas flow continues to increase,but the methane conversion rate and hydrogen production concentration continue to decrease,and the hydrogen production energy efficiency and selectivity show a trend of first increase and then decrease.The comprehensive hydrogen production energy efficiency is obtained when the applied power is 900W and the methane flow rate is 0.896L/min,The methane conversion rate was 90.02%,and the energy efficiency of hydrogen production reached 0.800mmol/kJ,and the hydrogen selectivity and carbon selectivity were 46.88%and 38.98%,respectively.(3)When the peripheral air inlet structure is adopted,the influence of different electrode positions on methane wet reforming to produce hydrogen is explored with the top of the cavity as the zero point,experimental results show that the best hydrogen production energy efficiency is achieved at 0mm.When the applied power is 900W and the flow rate is 0.896L/min,the methane conversion rate was 89.38%,and the energy efficiency of hydrogen production reached 0.915mmol/kJ.At this time,the hydrogen selectivity and carbon selectivity were 53.16%and 38.98%,respectively.Compared with the intermediate air inlet electrode structure,although the peripheral air inlet electrode has a lower methane conversion rate,its hydrogen production energy efficiency has improved.The possible reason is that it’s beneficial to water to participates in the reaction and the hydrogen production flow increases.Therefore,the energy efficiency of hydrogen production is improved,and the hydrogen selectivity and carbon selectivity of the gas phase product are improved,but the hydrogen concentration in the product is slightly reduced.(4)The main intermediate active particles in the liquid microwave plasma methane wet reforming reaction include OH,C,C2,CH,H,O,etc.The main products are hydrogen,carbon monoxide,carbon dioxide,and a small amount of acetylene,ethylene,and ethane.Hydrogen mainly comes from the dimerization reaction of H.In addition,the decomposition of formaldehyde and water gas shift reaction are also one of the sources of hydrogen.CO can be generated by the decomposition of formaldehyde and the oxidation of carbon,and the generated CO reacts with OH to be converted into CO2.And hydrocarbons can be converted into each other through polymerization and oxidative dehydrogenation.