Research On The Mechanism Of The Influence Of Alkali Metal Na On The Sooting Of Polycyclic Aromatic Hydrocarbons During Coal Pyrolysis

The carbon black particles produced by coal pyrolysis affect the combustion process and the generation of other pollutants,which will pollute the environment and harm human health.Therefore,it is very important to study the formation mechanism of derived carbon black during coal pyrolysis for clean and efficient utilization of coal resources.The results show that the formation and emission of carbon black can be reduced by catalytic cracking of tar and condensation of aromatics.But the mechanism is still unclear.In this paper,the mechanism of gasification of alkali metals in the process of carbon black formation from coal pyrolysis is studied.The results show that Na and other alkali metal elements will be released together with volatile components during coal pyrolysis,which can catalyze tar cracking and inhibit the condensation of PAHs,and finally inhibit the formation of carbon black.Through the pyrolysis experiments of coal and model compounds,the effect of Na on the physical and chemical properties of carbon black produced by pyrolysis was analyzed,and its mechanism was explored by quantum chemical simulation calculation.In this paper,the pyrolysis experiments of acid washing(YMH)and acid washing lignite(YMA)with physical adsorbed Na(ANa)were carried out.ICP-OES was used to measure the content of elements in the samples,and the yield of carbon black was calculated by dichloromethane extraction method;XPS and FTIR were used to analyze the chemical structure of pyrolysis samples.The range of temperature in the experiment is 1100??1400?.The results showed that the aromatics and aliphatics in the volatile matter began to transform into carbon black at about 1175?,and the oxygen-containing compounds in the pyrolysis gas could inhibit the formation of carbon black,and the most significant effect was at about 1250?.Gaseous Na can promote the reaction of oxygencontaining compounds with carbon black and its precursors,reduce the condensation degree of aromatic compounds,and ultimately reduce the yield of carbon black.However,at 1100 ?,the catalytic effect of Na on the aggregation of small aromatic and aliphatic molecules is dominant,which leads to the increase of carbon black yield.The pyrolysis experiments of model compounds and coal powder adopt the same research method.pyrene was selected to carry out model compound pyrolysis experiment,and the yield and structure of carbon black produced by model compound pyrolysis before and after supporting alkali metal Na were analyzed.The results show that the model compound does not produce carbon black at 1100?,and the physical adsorbed Na mainly affects the formation of carbon black in the pyrolysis gas.In the process of model compound(pyrene)carbon blackening,alkali metal Na promoted the substitution and gasification of short aliphatic side chains on aromatic / six membered rings,inhibited the condensation reaction between polycyclic aromatic hydrocarbons,and then reduced the carbon black yield of model compound.Naphthalene molecules with binding energy similar to pyrene were selected as the model of condensation reaction of PAHs in the process of tar carbon blackening to simulate the condensation of PAHs to produce carbon black.The active sites of chemical reaction are determined by analyzing the chemical structure and surface electrostatic potential of naphthalene molecules and their free radicals before and after Na ion doping,and the weak interaction between molecules is preliminarily used The mechanism of Na ion inhibiting condensation was explained.Based on the above analysis,the condensation reaction path before and after Na ion catalysis was designed and calculated at the level of M06-2X/6-31G(d),and the reaction energy barrier of the path was calculated at the level of M06-2X/6-31G(d,p).From the perspective of energy,it was proved that Na ion can inhibit the formation of carbon black by catalyzing the condensation and oxidative cracking of polycyclic aromatic hydrocarbons.Finally,benzene/phenyl and pyrene radicals were selected as the model of oxidative cracking of PAHs.According to the analysis of the bond length and bond order of the reactants,the reaction path was designed,and the structure of the stagnation point and transition state in the path was optimized at the same calculation level as that in the calculation of PAH condensation.Finally,the reaction energy barrier was calculated.The catalytic mechanism of alkali metal Na in the oxidative cracking of carbon black was explained from the microscopic point of view.