Study On Oxidative Dry Reforming Of Methane By Gliding Arc Plasma Catalysis

Dry reforming of methane is a strongly endothermic reaction and has drawback of high energy cost.Oxidative reforming(partial oxidative)is a mild exothermal reaction and has merit of low energy cost.Although oxidative dry reforming of methane(combination of oxidative reforming and dry reforming)could reduce energy cost by using the heat.released from oxidation of methane,traditional catalytic technique bears a drawback of local hot-spot which results in catalyst sintering and subsequently deactivation.Plasma catalysis technique could avoid this problem due to occurrence of oxygen oxidation in plasma zone and subsequently almost oxygen-free atmosphere in catalyst zone.Therefore,plasma catalysis technique provides a novel route for oxidative dry reforming of methane.In this work,to achieve efficient plasma catalytic oxidative dry reforming of methane,shade-like gliding arc plasma with rotated electrode and its separated combination with catalyst were first investigated,then votex gliding arc plasma with rotating gas flow and its integrated combination with catalyst were investigated.Plasma catalytic oxidative dry reforming of methane at CH4/CO2/O2 molar ratio of around 3/1/1 was mainly studied.A portion of methane was introduced to catalytic zone after plasma to avoid the coke issue of plasma electrodes in the presence of high-concentration CH4.Hence,CH4/CO2/O2 molar ratio in plasma zone was around 1.5/1/1.Main results are summarized as follows:(1)Separated combination of shade-like gliding arc plasma and catalyst for oxidative dry reforming of methane was investigated.For shade-like gliding arc plasma only,in this experimental condition,reactants conversions gradually decreased with increasing feed gas total flow rate and linearly increased with specific energy input(SEI),and hardly changed with discharge frequenciey.Subsequently,for separated combination of shade-like gliding arc plasma and Ni/CeO2/Al2O3 catalyst,additional methane could improve CO2 conversion and methane conversion rate.Increasing catalytic reactor temperature and reducing gas hourly space velocity(GHSV)could enhance the conversions of CH4 and CO2.At CH4/CO2/O2 molar ratio of 2.8/1/0.9,total flow rate of 1.9 SLM,plasma power of 106 W,GHSV of 9600 h-1 and catalyst mid-bed temperature of 700 ?,CH4 conversion of 96%,CO2 conversion of 95%,H2 selectivity of 100%,CO selectivity of 100%and syngas concentration of 98%were obtained.(2)Oxidative dry reforming of methane in vortex gliding arc plasma and its plasma diagnosis were investigated.Oxygen could be completely consumed in plasma zone.With increasing O2/CH4 molar ratio,SEI and discharge frequency,conversions of CH4 and CO2 exhibited increasing tendency.Vortex gliding arc plasma exhibited increasing tendency of CH4 and CO2 conversions as feed gas flow rate increased in this experimental condition.Analysis of electrical characterization and diagnosis of optical emission spectra for vortex gliding arc plasma in H2O/N2 and CH4-CO2-O2 atmosphere were also studied.Voltage waveform showed gliding period of arc,which gradually shrink as gas flow rate increased.In H2O/N2 atmosphere,with increasing SEI,rotational temperatures of OH radical and N2 gradually increased,vibrational temperature of N2 gradually decreased.In this experimental condition,vibrational temperature of N2,rotational temperatures of OH radical and N2 were in the range of 3418-3788 K,1642-1916 K and 3289-3794 K,respectively.In CH4-CO2-O2 atmosphere,rotational temperatures of OH radical and CO and electron density gradually decreased with the increase of SEI.Rotational temperatures of OH radical and CO and electron density were in the range of 3600-4000 K,2400-2600 K and 1.4 × 1014-4.7 × 1014 cm-3,respectively.(3)Integrated combination of votex gliding arc plasma and catalyst for oxidative dry reforming of methane was investigated.Ni-based catalyst could be in situ auto-reduced by the outgoing gas from plasma during reaction process and no pre-reduction process was needed.This plasma catalytic reforming exhibited merits of quick response and good stability.Plasma could satisfy the energy required of this combination system and no extra heat was needed when no additional methane was introduced to catalytic zone.At total flow rate of 4 SLM,CH4/CO2/O2 molar ratio of 1.5/1/0.9,SEI of 21 kJ/mol and GHSV of 18400 h-1,CH4 conversion of 92%,CO2 conversion of 20%,CO selectivity of 100%,H2 selectivity of 82%,syngas concentration of 72%,energy efficiency of 84%and syngas energy cost of 0.3 kWh/Nm3 could be attained.Extra energy was required for this combination system when additional methane was introduced to catalytic zone.At total flow rate of 3.9 SLM,CH4/CO2/O2 molar ratio of 2.5/1/1,SEI of 27 kJ/mol,GHSV of 4300 h-1 and heater temperature of 850 ?,CH4 conversion of 99%,CO2 conversion of 79%,CO selectivity of 100%,H2 selectivity of 93%,syngas concentration of 93%,energy efficiency of 78%and syngas energy cost of 1.0 kWh/Nm3 could be obtained.A novel route for high quality syngas production of combination of plasma catalytic reforming and water electrolyzer was proposed,which could efficiently convert CH4,CO2 and H2O.High quality syngas with syngas concentration of up to 95%and(H2-CO2)/(CO+CO2)molar ratio of 2.0 could be achieved.Assuming the energy efficiency of water electrolyzer is 80%,the overall energy efficiency and energy cost were 79%and 1.8 kWh/Nm3,respectively.