Study On Conversion Of Methane To C₂ Hydrocarbons Through Dielectric-barrier Discharge

Methane is the principal component of natural gas, coal bed gas, associated gas from crude oil and refinery gas. The issue about how to convert methane to C2 hydrocarbons directly with high efficiency has recently been studied worldwide. Dielectric-barrier discharge (DBD) served as a promising approach has been widely used in methane conversion for its moderate and clean reactive conditions.It is all known that the reactor plays a key role in methane conversion. Therefore the effect of reactor size on methane conversion to C2 hydrocarbons via DBD was investigated. The frequency of 23.70 kHz of sine-voltage was used for the experiment. First the spatial temperature distribution of DBD plasma was measured with K-type thermocouples, and the highest temperature of 230℃appeared in the center of DBD plasma of which the edge was about 101.3℃. Seven DBD reactors on methane conversion were investigated. The results showed that the conversion of methane changed greatly among different reactors, and few differences of the selectivities of dominating products between these reactors were found.Effect of cooling methods on methane conversion was investigated specially. Methane conversion was about 44.43% with air cooling outer electrode. While cooling inner electrode using air or flowing water could increase selectivity of higher liquid hydrocarbons, and decreased the methane conversion, but it could restrain carbon deposition. Compared with flowing water cooling, the fixed volume of water in the inner electrode could obtain high conversion with relatively low input power. Lower conversions of methane cooling inner electrodes were attained with preheating.The methane conversion via gas recycles and packed bed DBD reactors were investigated. The results showed that the methane conversion could achieve maximum at the recycle ratio of 1.25. The methane conversion would be decreased when increased recycle ratio continually. While the highest C2 selectivity was reached at recycle ratio of 0.625. Adding inert packing into plasma area had a great influence on methane conversion, at the same time would be decreasing the energy consumed and increasing the energy efficiency.At last, comparison of the multi-tip rotary electrode reactors and DBD reactors conversion of methane had been studied. The main products were acetylene and few ethylene in multi-tip rotary electrode reactors and carbon more, while in DBD reactors main products of ethane and propane, almost no carbon deposition.