影响烷基芳烃蒸发损失的结构因素探索

STUDY ON STRUCTURAL PARAMETERS AFFECTING EVAPORATION LOSS OF ALKYL AROMATICS

针对蒸发损失这一质量指标对润滑油基础油(简称基础油)使用性能的重要性以及现有测试方法存在的不足,考虑到基础油蒸发损失与低压沸点之间存在密切关系,收集整理了106种烷基芳烃基础油的结构和其在1 333.22 Pa压力下的沸点数据,采用分子模拟方法计算得到了这些不同结构烷基芳烃分子的前线轨道能量和电荷分布等反映分子微观结构特征的参数,并计算了各分子不同类型的拓扑指数。采用遗传函数算法(GFA)对这些烷基芳烃在1 333.22 Pa压力下的沸点与其结构参数之间的关系进行了回归分析,建立了物理意义明确的烷基芳烃沸点与其结构参数之间的定量关系方程。方程相关系数的平方为0.978,交叉检验相关系数的平方为0.962,具有较高的可靠性和预测能力。该方程表明烷基芳烃的前线轨道能隙(LUMO-HOMO)、分子极化率和回转半径是影响其在1 333.22 Pa压力下的沸点高低的主要结构因素。烷基芳烃前线轨道能隙越窄,极化率越高,分子回转半径越大,则其在1 333.22 Pa压力下的沸点越高,导致其蒸发难度越大,蒸发损失越低。依据这3个结构参数,利用构建的定量关系方程,能够对烷基苯、烷基萘等芳烃在1 333.22 Pa压力下的沸点高低进行较为准确地预测,对于设计与优化蒸发损失较低的烷基芳烃基础油结构组成具有一定的指导意义。

Considering the close relationship between the evaporation loss and boiling point of base oil at lower pressure and the shortcomings of existing analysis methods,the structures of 106 kinds of alkylaromatics and their boiling points at 1 333.22 Pa were collected.Based on the data,the Eigenvalues of microstructures such as energies of frontier obitals and charge distributions and topological indexes were calculated by molecular simulation method.GFA method was selected to elucidate the relationship between the structures of alkyl aromatics and their boiling points at 1 333.22 Pa pressure,resulting in a quantitative equation with the square of correlation coefficient of 0.978 and the square of cross-validated coefficient of 0.962,which means that the equation has a strong predictability for boiling points of alkylaromatics at 1 333.22 Pa pressure,so as for its evaporation loss.The equation has clear physical meanings,which showed that LUMO-HOMO gap,molecular polarizability,and radius of gyration of alkyl aromatics were the three main structural parameters for prediction of boiling point at 1 333.22 Pa pressure.The narrower the LUMO-HOMO gap,the higher the molecular polarizability and the larger the radius of gyration,then the higher the boiling point at 1 333.22 Pa pressure,the greater the evaporation difficulty and the lower the evaporation loss.The established equation with these three structural parameters could be used to predict the boiling points of alkyl aromatics at 1 333.22 Pa pressure accurately.