高碱煤燃烧初期羧酸钠的迁移转化机理

Migration and Transformation Mechanism of Sodium Carboxylate in the Initial Stage of High Alkali Coal Combustion

基于密度泛函理论和过渡态原理,在M06-2X/6-311G(d)水平上研究了燃烧初期高碱煤羧酸钠的迁移转化机理,探讨了高碱煤基质中各种可能的单分子、双分子脱羧、脱碳、交联、自由基攻击的反应路径.计算结果表明,单分子脱羧释放二氧化碳为最有利的初级反应路径;羧酸钠和相关模型化合物(CM—COOH和CM—OH)在热解过程中发生的双分子脱羧反应需翻越的能垒较脱碳反应和交联反应的能垒低,即双分子脱羧最易进行;高碱煤基质中存在H自由基和甲基自由基并能够进入羧酸钠基,导致Na原子和NaCO_(2)自由基的释放.

Based on density functional theory(DFT)and transition state theory,the migration and transformation mechanism of sodium carboxylate in high alkali coal matrix at the initial stage of combustion were studied at the level of M06-2X/6-311G(d),and the possible reaction paths of single molecule,double molecule decarboxylation,decarburization,cross-linking and radical attack in high alkali coal matrix were discussed.The results show that the release of carbon dioxide from single molecule decarboxylation is the most favorable primary reaction path.The energy barrier of bimolecular decarboxylation of sodium carboxylate and related model compounds(CM—COOH and CM—OH)during pyrolysis is lower than that of decarboxylation and crosslinking,which means that bimolecular decarboxylation is the easiest reaction.H radical and methyl radical exist in high alkali coal matrix and can enter sodium carboxylate group,resulting in the release of Na atom and NaCO_(2) radical.