汽油典型烃分子氧化生胶机理的分子模拟

Molecular Simulation of the Mechanism of Oxidation Gum Formation of Typical Gasoline Hydrocarbon

为深入认识汽油在使用过程中氧化生胶的反应机理,选取汽油中相同碳数的典型烃分子作为模型化合物,采用基于密度泛函理论的量子化学从头计算方法,建立了不同结构的汽油分子通过氧化链式自由基反应生成相对分子质量较大、极性较高的沉积物分子的反应网络。通过对比不同反应路径的反应能垒大小,得出容易氧化生胶的汽油烃分子的结构特点以及贡献生成沉积物的关键控速步骤和关键中间体,从而为抑制该氧化生胶过程提出关键措施。结果表明,汽油分子结构中存在双键α位C—H、叔位C—H或苯基α位C—H时,容易引发链式自由基反应,但能否继续向沉积物的反应方向进行取决于相对分子质量增大后的产物中是否仍然存在双键α位C—H、叔位C—H、苯基α位C—H或者C=O这种使得相邻C—H键变弱的吸电子基团。另外,在氧化生胶反应过程中,氢过氧化物(ROOH)和过氧自由基(ROO·)是最关键的2个中间体,抑制氧化生胶反应的关键在于清除它们。

In order to elucidate deeply the mechanism of gasoline oxidation during its storage and usage,the typical hydrocarbon molecules with the same carbon number were selected as the model compounds.Using the ab initio quantum method based on density functional theory,we calculated the chain free radical oxidation reaction network which produced deposit with high relative molecular mass and high polarity.By comparing the reaction energy barrier of different reaction paths,the key step of the deposit formation was obtained.Thus,structure characteristics of gasoline molecules contributing to the formation of deposit have been drawn up.The results showed that it is easy to initiate free radical chain reaction for the gasoline molecules which have C—H inαposition of C=C,tert C—H or C—H inαposition of phenyl.However,it depends on the structure of the intermediate products whether they could continue to react.Whether there was still a C—H inαposition of C=C,tert C—H,C—H inαposition of phenyl or whether bonds like C=O were generated,the electron-withdrawing group in the reaction process was the critical factor.Furthermore,ROOH and ROO· were the most critical intermediates.The crucial step is to remove the two free radicals.