High-Efficiency Conversion Of Methane To Hydrogen And Acetylene In A Spark Discharge Plasma At Atmospheric Pressure

In recent years,more and more attentions have been paied to methane activation and conversion by low-temperature plasmas.A stable kHz spark discharge plasma was used for high-efficiency conversion of methane to hydrogen and acetylene at atmospheric pressure in this study.The problem derived from carbonaceous deposition which resulted in a rapid deterioration for discharge was overcomed and the energy efficiency was improved compared with other kinds of discharge.This study showed high-efficiency methane conversion to hydrogen and acetylene at a low energy cost by the stable kHz spark discharges.A valuable byproduct,carbon black,was also co-produced.Optical emission spectroscopy(OES)was adopted for the diagnosis of the spark discharge plasma for conversion of CH₄ at atmospheric pressure.In addition,a preliminary investigation on CO₂ reforming of CH₄ in this plasma reactor was made in this paper.The experimental results were mainly as follows:1)Discharge stability was confirmed by the concentration variation in the product streams with 220-min discharge time using pure methane as the feed gas.Many parameters such as electrode distance,specific energy input(SEI),feed methods,the diameter of tubular electrode and H₂ addition have been investigated.Utilizing this stable kHz spark discharge plasmas,hydrogen concentration in the product stream could be as high as 72.1 vol%at an energy cost of 6.7 eV per H₂ molecule produced and 81.5%of methane conversion.Acetylene concentration could reach 18.4 vol%at an energy cost of 21.2 eV per C₂H₂ molecule produced and 70.3%of methane conversion.This results showed that high-efficiency conversion of methane to hydrogen and acetylene could be realized at a low energy cost by the stable kHz spark discharges.The results of OES in kHz spark discharge showed that high selectivity of acetylene was very likely to be related to C₂ radicals.2)For CO₂ reforming of CH₄ in this plasma reactor,the effects of the CO₂/CH₄ molar ratio in the feed on the reactant conversions,product selectivities and energy costs have been studied.The results showed that methane conversion increased with increasing the CO₂/CH₄ ratio from 0 to 3.5.However,the CO₂ conversion reached a maximum at around 60%of CO₂ concentration in the feed.Energy costs for methane conversion in the reforming of CO₂-CH₄ was higher than pure methane conversion,but the total energy efficiency was improved. When the CO₂/CH₄ ratio in the feed was in the range of 1.5 to 2,the conversion ability for the total carbon atoms in the feed reached a maximum of 1.54μmol/J.