【作者】 李海波；

【导师】 杜谦；

【作者基本信息】 哈尔滨工业大学 ， 动力工程（专业学位）， 2020， 硕士

【摘要】 煤热解产生的碳黑颗粒物影响燃烧过程及其他污染物的生成,研究煤热解过程中衍生碳黑的生成机理对煤炭资源的清洁高效利用至关重要。研究表明,Na等碱金属元素会在煤热解过程中随挥发分一同释放,气态Na能够催化碳黑及其前驱体的氧化反应,并抑制多环芳烃的缩合,减少碳黑的生成及排放。但其中的反应机理尚不明确。本文通过煤和模型化合物的热解实验,分析Na对煤热解产生碳黑的理化性质的影响,并采用量子化学计算探究其作用机理。本文对伊敏褐煤酸洗煤(YMH)和担载Na Cl的酸洗褐煤(YMA)在1100℃～1400℃温度范围内进行热解实验,采集并分析热解产生的气溶胶颗粒。采用ICP-OES测得收集样品中各元素的含量;通过二氯甲烷萃取法计算碳黑产率;采用XPS和FTIR获得热解样品的化学结构信息。结果表明:热解气中含氧化合物可以抑制碳黑的生成,在1250℃时抑制作用最显著。气态Na可以促进含氧化合物与碳黑及其前驱体反应,降低芳香化合物的缩合程度,最终降低碳黑的产率。但在1100℃时Na对小分子芳香族及脂肪族团聚的催化作用占主导,导致碳黑的产率提高。选用芘作为模型化合物进行热解实验,研究方法与煤粉相同。结果表明:模型化合物在1100℃下不生成碳黑,物理吸附态Na主要在热解气中影响碳黑形成。在芘生成碳黑的过程中,碱金属Na有助于芳香环/六元环上短脂肪族侧链的取代与气化,并降低了多环芳烃间的缩合度,进而降低了碳黑的产率。选用结合能与芘相似的萘分子及其自由基作为多环芳烃缩合反应的模型,对碳黑的生成过程进行量化模拟。通过分析掺杂Na离子前后萘分子及其自由基的化学结构和表面静电势确定化学反应活性位点,利用分子间弱相互作用初步解释了Na离子抑制缩合的机理。采用M06-2X/6-31G(d)[1]组合计算Na离子催化前后的缩合反应路径,在M06-2X/6-31G(d,p)水平上计算路径的反应能垒,从能量的角度证明Na离子能够通过催化芳烃化合物之间的缩合反应抑制碳黑的生成。最后本文选用苯/苯基和芘自由基作为多环芳烃氧化裂解反应的模型,根据对反应物键长和键级的分析,设计反应路径,并在与计算多环芳烃缩合时相同的计算水平下对路径中的驻点及过渡态的结构进行优化和能量计算。从微观的角度解释碱金属Na在碳黑氧化裂解过程中的催化作用机制。更多还原

【Abstract】 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.更多还原