Experimental And Numerical Simulation Of Selective Oxidation Of Methane Catalyzed By Plasma-assisted With Pt/BN

Natural gas is a clean resource with abundant reserves in the world.Its main component is methane,which can be directly converted into methanol and other oxygenated compounds that are convenient for transportation through partial selective oxidation reaction,and has extremely high economic value.Therefore,the development of efficient conversion technology of methane into liquid phase oxygenated compounds has become a challenging research subject.Among them,the plasma generates high-energy electrons at low temperature,which stimulates the selective oxidation reaction of methane to produce methanol and other oxygenated compounds,avoiding the excessive oxidation of intermediate products at high temperature in the traditional thermal catalytic process.However,the high energy electrons in plasma also easily cause the deep oxidation of oxygenated compounds.Therefore,how to regulate the discharge properties of plasma and how to cooperate with catalysts to promote the low temperature selective oxidation of methane is the key.We used commercial BN,ultralight BN aerogel and ultralight Pt/BN aerogel as catalysts to regulate the process conditions such as water vapor co-feeding and input power,and screened the optimal plasma catalytic activity of methane selective oxidation reaction.Oscilloscope was used to monitor the influence of the above process conditions on plasma discharge parameters in real time.It was found that filling Pt/BN-na catalyst alone or adding only water vapor did not increase the yield of C1 oxygenated compounds,and filling only ultra-light BN-based catalyst did not change the discharge parameters.However,when Pt/BN-na catalyst was co-fed with water vapor,methane conversion and oxygen compound selectivity were both improved.13%CH₄ conversion and 61%selectivity of total oxygenated compounds were obtained.A variety of vibration-excited and electron-excited molecules,free radicals,atoms,ions and electrons are generated in the process of partial oxidation of methane catalyzed by plasma,which is extremely complex and difficult to be observed by experimental means.How to understand the effect of catalyst packing,temperature,gas ratio,water and steam co-feeding on the discharge properties and reaction path is the key to understand the selective oxidation of methane catalyzed by plasma.By establishing a kinetic model of partial oxidation reaction of methane catalyzed by zero-dimensional plasma to simulate experimental conditions,we studied and analyzed the gas phase reaction of methane catalyzed by plasma.Effects of methane-oxygen raw material gas molar fraction,added gas water vapor,reaction temperature,species density in plasma gas phase,initial electron energy loss distribution,and the formation and consumption path of methanol,the main product of oxygen compound.The simulation results show that:（1）The initial electron energy distribution is affected by the intake ratio and the reduced electric field.Under the experimental conditions in this paper,methane occupies more initial electron energy deposition ratio than oxygen,reaching 92%.（2）In the gas phase formation path of methanol,the reaction CH₃O·+H·+M→CH₃OH+M has the highest time average reaction rate;In the gas-phase consumption path of methanol,the reaction CH₃OH+O·→CH₂OH+OH·has the highest time average reaction rate.（3）Water promotes not only the selective oxidation of chemisorbed hydrocarbon species from methane plasma catalyzed dissociation,but also the desorption of chemisorbed oxygenated species on Pt/BN-na catalyst surfaces.（4）Finally,the overall reaction flow chart is summarized.The results show that methyl and methoxy are crucial to the formation of methanol and other oxygenated compounds.