Study On Plasma Enhanced CH₄-CH₃OH-H₂O Conversion By Nanosecond Pulsed Dielectric Barrier Discharge

As the world energy market is severely impacted by the epidemic,the primary energy continues to decline.China’s "emission peak","carbon neutrality" strategy advocates green,clean and low-carbon development direction.The proportion of natural gas and renewable energy in the primary energy consumption structure will continue to increase.The main component of natural gas is methane(CH4).China’s natural gas market scale and consumption continue to grow.The green sustainable development of natural gas industry can be realized by developing reasonable natural gas conversion technology.At the same time,China is the largest producer of methanol(CH3OH)in the world.CH3OH is not only an important chemical raw material but also a cheap and clean energy source.The development of CH4-CH3OH direct conversion technology to produce high value-added liquid products has good economic prospects.However,the conversion of CH4 and CH3OH has many problems(high pollution consumption,high water consumption,high power consumption and large carbon emission)in traditional industries.Because the low temperature plasma can carry out molecular activation under mild conditions.Therefore,the direct conversion of CH4-CH3OH by low-temperature plasma can reduce energy consumption and improve energy utilization efficiency,which is in line with the goal of green,clean and low carbonization.In this paper,the conversion of the CH4-CH3OH-H2O into liquid chemicals driven by nanosecond pulsed dielectric barrier discharge plasma has been carried out.Analysis on electrical characteristics and conversion of different reaction parameters have been carried out,and the preliminary reaction path has been discussed.The effect of argon(Ar)and hydrogen peroxide solution(H2O2(aq))on the discharge process and the conversion effect of the CH4-CH3OH-H2O experiment were further analyzed.Firstly,the electrical characteristics and conversion of different reaction parameters were analyzed.The reaction parameters include the proportion of H2O,rising and falling time,repetition frequency,voltage amplitude,and pulse width.The results indicate that adding a certain amount of H2O can improve the reactant conversion and the total liquid selectivity.When the rising&falling time are ≥200 ns,the discharge waveform has a current plateau period,and the average electron energy is low.With the increase of repetition frequency,the number of microdischarges increases and the density of high-energy electrons increases.As the voltage amplitude increases,the electron density increases rapidly and the total liquid selectivity decreases rapidly.When the pulse width is≥200 ns,the voltage and current plateaus appear in the discharge waveform at the same time,and the primary and secondary discharges are carried out independently.When H2O ratio was 50%,voltage amplitude was 13 kV,repetition rate was 4 kHz,rising&falling time were 200 ns,pulse width was 0,CH4 and CH3OH conversion was 17.5%,and 50.3%,respectively,and total liquid selectivity was 12.3%.At the same time,based on the analysis of the reaction path in the existing literature,it is considered that ’CH2OH is an important intermediate,and the main liquid products C2H5OH and C3H7OH can be formed by ’CH2OH with ’CH3 and ’C2H5 carbon-carbon coupling respectively.Then,the effect of Ar addition on the formation of liquid products was studied,and then the influence of variable ratio and flow rate of mixed gas Ar/CH4 on CH4CH3OH-H2O system experiment was investigated.The experimental results show that the penning ionization effect induced by metastable Ar atoms increases the number of seed electrons and promotes effective electron collision.The addition of Ar can effectively reduce the breakdown electric field and make the primary discharge more likely to occur.The addition of Ar is beneficial to the formation of liquid products.When Ar:CH4=1:3 and the total gas flow rate was 60 mL/min,the maximum liquid selectivity was 19.4%.Finally,the effect of H2O2(aq)on the experiment was investigated.The total liquid selectivity was 18%when H2O2(aq)addition was 10 mL.