Study On The Characterization Of Solid Products From The Decomposition Of Methane And The Technology Of Decomposition Of Waste Bio-oil By Low Temperature Plasma

In recent decades,low temperature plasma has drawn wide attention in the fundamental researches and industrial applications,with the merits of high chemical reactivity,flexible instrument,rapid start-up and shutdown,etc.In this dissertation,rotating gliding arc(RGA)plasma and inductively coupled radiao frequency plasma(ICP)were proposed.Based on a comprehensive investigation of the basic physical properties,the aforementioned plasma was used to synthesize H2 and carbon materials synergetically from the decomposition of CH4.Especially,the propertis of carbon was comprehensively characterized.Furthermore,waste bio-oil was firstly used as a sustaibable precursor in plasma reaction.It was anticipated that an innovative and green alternative to reuse waste bio-oil could be realized by our systematical analysis of the oil decomposition reaction as well as the distribution of products.Herein,the basic research content and conclusions were demonstrated below:(1)The basic physical properties of RGA plasma were comprehensively characterized.Several methods,such as optical emission spectroscopy(OES),imaging diagnostics and numerical simulation,were performed to investigate the arc dynamic behavior,V-I characteristics,spectroscopic information and so on.It was demonstrated that the formation of active species such as excited molecules,ions,atoms and radicals were determined by the types of carrier gases used in plasma reaction.By analyzing the optical spectrum,the electron excitation temperature(0.8?1.7 eV),electron density(4?6×1015cm-3),vibrational temperature(3874?5105 K)and rotational temperature(1160?1508 K)were calculated.The electrical parameters,such as discharge period,breakdown voltage,and waveforms,were affected by the types of carrier gases,applied voltage and gas flow rate.In addition,the discharge mode was switched depended on the variation of operating conditions.Based on results of COMSOL simulation,the dynamic structure and location of arc could be regarded as a superposition of electron convection,electron migration and electron diffustion.(2)RGA plasma was used to decompose CH4 and the influences of CH4 concentration,residence time,carrier gas types,applied voltage are conducted in terms of the product distribution,electrical and spectroscopic parameters.In addition,the properties of solid phase product are comprehensive characterized.According to the results,C2 Swan band,CH(B??Z X2?,A2??X2?)band and H2(d3?u?a3?g)Fulcher band were observed in the CH4/Ar spectrum,while the CH4/N2 spectrum was dominated by the emission transition of CN radicals.H2 and C2H2 were primary products in gas phase.Increasing the applied voltage and residence time promoted the conversion of CH4,and shifted the distribution of gas products to high selectivities of H2 and C2H2.However,the augment of CH4 concentration declined the specific energy density and inhibited the formation of H2.The morphology,structure,graphitized degree of the obtained plasma carbon in CH4/N2 and CH4/Ar discharge was comparatively investigated.By tuing the operating conditions such as residence time,applied voltage and gas flow rate,two-dimensional graphene sheets could be synthesized.Benefiting from its strong hydrophobicity,plasma carbon could be used to modify the commercial sponge,aiming at the applications of oil-water separation and selective adsorption of organic solvents.(3)Kinetic model of CH4/Ar discharge was builted,providing insight into the mechanism of RGA assisted decomposition of CH4.It was demonstrated that the electron induced dissociation reaction(E+CH4=>E+CH34+H)was the main routef or CH4 conversion.And the electron induced excitation reaction could effectively break down the barrier of conventional thermal equilibrium,and lowered down the energy required for corresponding reactions.H and CH3 radicals played significant roles in the conversion of CH4 as well as the formation of H2 and C2H2.(4)RGA plasma was firstly proposed for the decomposition of waste bio-oil.A high-speed camera and oscilloscope was used to characterize the arc motion and electrical parameters in oil discharge.The variation of oil feeding mode,oil flow rate,gas flow rate and applied voltage on the distribution of gas products are investigated,which indicated H2,CO,C2H4 and C2H6 were the main gas products.The augment of applied voltage favored the generation of H2 and converstion of oil.Based on the deoxygenation and chain breakage induced by plasma,waste bio-oil was also converted into liquid products,including short-chain alkane,ester and ketone.In addition,soild carbon was also collected,which exhibited a low graphitized degree and amorphous structure.(5)The basic propertis of ICP were characterized by electrical and spectroscopic diagnostics,which indicated that the variations of input power,gas pressure and gas flow rate would affect the discharge mode,coil voltage and current,electron temperature and density.Amongst,input power was intimately related with the energy transfer efficiency,thus,was regarded as a key parameter to control plasma density and reactivity.When the heating temperature were in a range of 700?900?,CH4 could be converted into vertical graphene through a 500 w ICP.And the augment of H2 concentration facilitated the increase of lateral size of the obtained graphene.When the heating temperature and H2/Ar ratio were 800? and 3/2,respectively,vertical graphene,with a rich edge structure and high aspect ratio,was firstly successfully synthesized with waste bio-oil as the precursor.