The direct synthesis of C2 hydrocarbons （ethylene, acetylene and ethane） from methane is one of the most important task in C1 chemistry. Higher conversion of methane and selectivity to C2 hydrocarbons can be real-ized through plasma reaction. In order to explore the reaction process and mechanism, the possible reaction paths （1）—（4） were proposed on coupling reaction of methane through plasma and studied theoretically using semi-PM3 method [PM3 is parameterization method of modified neglect of diatomic overlap （MNDO）] including determining the transition state, calculating the activation energy and thermodynamic state functions and analyzing the bond or-der and intrinsic reaction coordinate. The reaction heat results indicate that the reactions （2） and （4） are exothermic, while reactions of （1） and （3） are endothermic. The activation energy results show that activation energy for reac-tions （1） and （2） was much lower than that of reaction paths （3） and （4）. Therefore, paths （1） and （2） is the favorable reaction path energetically. More interestingly by comparing the intrinsic reaction coordinated （IRC） of the reaction paths （1） and （2）, it is found that the variations of bond lengths in reaction path （1） has a crucial effect on the poten-tial energy, while in reaction path （2）, the adjustment of the system geometry also contributes to the whole potential energy of the system.
The conversion of CH4 with oxygen and steam in a dielectric barrier discharge (DBD) was studied in the paper to discuss the effects of different factors, such as the content of feed-in gas, the applied voltage and frequency. The results showed that a lower ratio of CH4 to O2 always resulted in a higher conversion of CH4. When it was 2, the conversion reached 32.43% without steam introduced into the system. The main effect of steam was increasing the selectivity to CO. The reaction was accelerated and the selectivities to CO and hydrocarbons were enhanced by increasing the applied voltage. It was also observed that a higher frequency led to a lower current and then restrained the reaction.
Gliding arc gas discharge plasma was used for the generation of hydrogen from steam reforming of dimethyl ether(DME).A systemic procedure was employed to determine the suitable experimental conditions.It was found that DME conversion first increased up to the maximum and then decreased slightly with the increase of added water and air.The increase of total feed gas flow rate resulted in the decrease of DME conversion and hydrogen yield,but hydrogen energy consumption dropped down to the lowest as total feed gas flow rate increased to76 ml·min 1.Larger electrode gap and higher discharge voltage were advantageous.Electrode shape had an important effect on the conversion of DME and production of H2.Among the five electrodes,electrode 2#with valid length of 55 mm and the radian of 34 degrees of the top electrode section was the best option,which enhanced obviously the conversion of DME.
Effects of cooling methods on stability and methane conversion rate using dielectric-barrier discharges(DBD)were systematically investigated in this article.The results showed thatthe methane conversion rate was as high as 44.43% in a pure methane system at a flow rate of100 mL·min^(-1)and an input power of 234.2 W with air cooling.A dark greenish and soft film-likecarbon was deposited on the outer surface of quartz tube when the outer electrode was water-cooled,which decreased the methane conversion.With air cooling of inner electrode the selectivityof C_2 hydrocarbons was higher than that with other cooling methods,while the C_3 hydrocarbonshad higher selectivity with flowing water cooling.Cooling the inner electrode could restrain thecarbon deposition,but would decrease the methane conversion rate.The stability of both reactionand plasma operation can be improved through cooling the reactor.From thermodynamic analysis,it was found that the effective collisions frequency among the reactant molecules and free electrons(e^-)increased with temperature,which in turn led to a higher methane conversion rate and achange in the distribution of products.
Effects of additive gases on dimethyl ether(DME) conversion through dielectric barrier discharge(DBD) were investigated. Most of the additive gases tested in this work increased the conversion of DME,but decreased the yield of liquid product. However,the addition of O2 markedly increased both the conversion of DME and the yield of liquid product. The results show that when O2 volume fraction was 39.95%,the conversion of DME was close to 100% and the yield of liquid product reached 34.43%. Different additive gases resulted in different mass fractions variation of components in liquid products.
