Experimental Study On Reverse Reaction Control Of CO₂ Conversion By Atmospheric Pressure Plasmatron

Global warming caused by greenhouse effect has caused serious damage to the environment.As CO₂ is one of the most important greenhouse gases,its conversion and utilization have attracted the attention of researchers.Gliding arc plasma decomposes CO₂ through the most efficient vibration excitation,so it has a good application prospect in the field of CO₂ conversion.However,traditional gliding arc faces the problems of low CO₂ conversion and energy efficiency.The improved atmospheric pressure plasmatron has the advantages of uniform gas treatment and large reaction area,which is very suitable for efficient CO₂ conversion.However,the reverse reaction of CO₂decomposition in plasmatron causes CO₂ regeneration,which seriously affects the effect of CO₂conversion.Based on this,this paper developed two ways to inhibit the reverse reaction of CO₂ decomposition:water cooling inhibition and biochar synergy,and systematically studied the inhibition of the reverse reaction of atmospheric pressure plasmatron for CO₂ conversion.The main research contents and conclusions of this paper are as follows:（1）Optimization and physical characterization of plasmatron.A double inlet reactor was developed.Its electrical parameters,arc movement,active particle distribution and spectroscopy were analyzed by high-speed camera,oscilloscope and emission spectrometer.Fluent simulation showed that the double inlet reactor had a longer gas residence time and improves the product conversion effect.The plasmatron has a three-dimensional jet region,and the volume of the plasma region are significantly larger than that of the traditional gliding arc.The addition of quartz cover and biochar makes the discharge more stable,which provides support for the experiments of water cooling and biochar.The electron temperature,electron density,vibration temperature and rotation temperature of CO₂ jet plasma are 1.10～1.55 e V,2.63～6.48×10¹⁵ cm^-3,6000～9000 K and 2000～2400 K.Suitable electron temperature and higher vibration temperature are conducive to efficient CO₂ vibration excitation and decomposition.The rotation temperature shows that plasmatron is warm plasma,which has the advantages of high chemical selectivity,low energy consumption and high energy density.The O atom density in the process of plasma CO₂ decomposition is calculated for the first time,which is 3.17～6.76×10¹⁶ cm^-3.which establishes the basis for understanding the reaction mechanism and verifying the chemical reaction model.（2）The research on the reverse reaction of CO₂ decomposition and water cooling inhibition was carried out.The influence and distribution of the reverse reaction are studied.Water cooling inhibition reactors are developed.The effects of voltage,gas flow and cooling position are studied,and the reaction mechanism is discussed.The results show that the increase of temperature intensifies the reverse reaction,which reduces the CO₂ conversion rate to 4.0%and the energy efficiency to 9.4%when it is stable.Compared with the optimal value,it decreased by 69%and 65%.Inhibiting the reverse reaction is very important for possible industrial application.CO₂ plasmatron shows two sections:the main discharge area and afterglow area.According to its distribution characteristics,it is more reasonable to use the upper and lower sections of water cooling.Adding water cooling can greatly improve the CO₂ conversion effect and improve the reaction stability.The maximum CO₂ conversion rate can reach 18.9%and maintain high energy efficiency of 33.9%,while the conversion of traditional gliding arc plasma is generally less than 10%.Low flow rate（2～6 L/min）is suitable for all cooling reactor,and high flow rate（≥7 L/min）is suitable for cooling of the upper section.Mechanism analysis shows that water cooling improves CO₂ conversion by inhibiting the reverse reaction and VT relaxation process.（3）The research on biochar synergistic inverse reaction inhibition was carried out.The characteristics of biochar and the influence of the position relationship between biochar and plasma on the reaction effect are studied.The dominant factors of biochar characteristics and the mechanism of plasma CO₂ and C reaction are discussed.The results show that plasmatron coupled biochar can significantly improve the conversion of CO₂,such as from 12.9%to 27.1%.The walnut shell biochar prepared at 600℃has the best results.The CO₂ conversion and energy efficiency are 27.5%and 33.9%respectively.Carbon content is one of the most decisive factors affecting the reaction of carbon dioxide and biochar.Optimizing the contact between biochar and plasma can greatly improve the CO₂ conversion effect,with the highest CO₂ conversion rate of47.3%and energy efficiency of 77.0%,which is much higher than other low-temperature plasma conversion effects.CO₂ conversion is divided into two stages.The first stage is CO₂ decomposition.In the second stage,biochar participates in CO₂conversion by reacting with O₂,CO₂（v）and remaining CO₂.The interaction of plasma chemistry and thermochemistry promotes CO₂ conversion.