生物质焦油模化物的热裂解ReaxFF模拟研究

Simulation on thermal decomposition of biomass tar model compounds by ReaxFF

实现热裂解过程中焦油的有效脱除是生物质热利用技术中亟待解决的问题。通过密度泛函理论研究生物质焦油3种典型模型化合物(甲苯、苯酚和萘)的分子结构性质,并基于ReaxFF反应力场对焦油模型化合物的热裂解过程进行分子动力学模拟研究,从分子层面对焦油热裂解的复杂反应过程进行深入研究。探索反应温度对热裂解特性的影响,详细研究甲苯、苯酚和萘的热裂解机理及中间自由基、气体产物的演化过程。结果表明:C—H键的Mayer键级小于C—C键,易于断裂,芳香环侧链结构中氢的Mulliken电荷数大,具有更强的活性;3种焦油模型化合物的热稳定性依次为:萘>苯酚>甲苯,其中苯酚具有高活性的含氧官能团,二次裂解易生成气体产物,而甲苯和萘二次裂解易生成稠环芳烃;甲苯、苯酚和萘的一级反应动力学热解表观活化能分别为314.03、362.39、396.74 kJ/mol。

Effective tar removal in thermal decomposition is an urgent problem in biomass thermal utilization technology.The molecular structure properties of three typical model compounds(toluene,phenol and naphthalene)of biomass tar were studied by density functional theory,and the thermal decomposition process of tar model compounds was simulated by molecular dynamics based on ReaxFF(Reactive Force Field),which provided an in-depth study of the complex reaction process of tar thermal cracking at the molecular level.The influence of reaction temperature on pyrolysis characteristics was discussed.The pyrolysis mechanism of toluene,phenol and naphthalene,and the evolution process of intermediate radicals and gas products were studied in detail.The results show that the Mayer bond order of C—H bond is smaller than that of C—C bond,which is easier to break.The Mulliken charge of hydrogen in the side chain of aromatic ring is large,and it is more reactive.The thermal stability of the three tar model compounds is as follows:naphthalene>phenol>toluene.Phenol has highly active oxygen-containing functional groups,which make it easy to generate gas products during secondary cracking reaction,while toluene and naphthalene are easy to generate condensed aromatic hydrocarbons during secondary cracking reaction.The apparent activation energies by the first order kinetic pyrolysis of toluene,phenol and naphthalene are 314.03,362.39 and 396.74 kJ/mol,respectively.