Reforming And Partial Oxidation Of Methane Based On DC Corona Discharge Technique

Statistics show that a large amount of methane is released from the landfill system each year. Facing the increasingly severe energy and environmental problems, it is becoming a hotspot worldwide to utilize methane as clean energy. Traditional combustion method for power generation is limited by the yield of CH4 as well as the location of landfill sites, which influences the transportation distance. However, the problems can be overcome via producing more valuable liquid chemical products. As non-thermal plasma technique could realize the activation of molecules under relatively moderate conditions, it is expected to become a favorite alternative for the conversion of methane. DC corona plasma was chosen in this paper to study the direct conversion of methane under ambient temperature and atmospheric pressure.Experiments were conducted to examine the reforming reaction of CH4 with the discharge structure of needle to plane and CO2 as the source of oxygenous radicals. Acetylene (C2H2) was generated during the discharge process. When discharge current was fixed at 0.4 mA, the molar ratio of CH4 and CO2 at 2 and the total gas flow rate at 45 mL/min, the selectivity and the yield of C2H2 was obtained as 36% and 12.8%, while the largest specific energy requirement was 0.97 mmol/kJ, respectively. With the introduction of proper amount of H2, the conversion of CO2 was promoted. Furthermore, conversion of CH4 and production of C2H2 were both facilitated when steam was involved in the reforming reaction, which could lead to the generation of OH when attacked by high energy electron.A gas-liquid multiphase discharge system was constructed by employing liquid solution as the ground electrode, therefore, OH could be introduced into the system to activate CH4. Analysis results showed that liquid organic products were produced with air as the gaseous oxygenous radical source, such as formic acid and methanol, particularly formic acid. With discharge current setting at 0.2 mA, discharge gap at 1 cm, CH4/air ratio at 1:1 and phosphate buffer solution (PBS, pH= 7) as the liquid electrode, the yield of formic acid per energy consumption was achieved as 6.58 mmol/(kWh). When H2O2 solution was applied as the liquid electrode, the selectivity of formic acid was increased. Conversely, in the presence of CO2 or Na2SO3, the production of formic acid was decreased significantly, for the scavenging effect on OH.Based on the generation process under plasma condition, methylene blue (MB) was used as an oxidation indicator to figure out the generation and function mechanism of OH in the gas-liquid multiphase system. Results reflect that DC corona discharge can indeed produce OH in the system full of droplets, and the electron dissociation of H2O plays a major role.Thus, DC corona discharge plasma can directly convert CH4 to C2H2 or formic acid under ambient temperature and atmospheric pressure, which is expected to become a new technology for the utilization of CH4 in exhaust gas.