BaX分子筛吸附C8芳烃作用机理

采用正则系综蒙特卡洛方法模拟等量4种C₈芳烃分子分别在SiFAU和BaX分子筛上的吸附行为，并结合量子化学计算和波函数分析，基于分子筛组成和结构、C₈芳烃分子结构和电子分布特征进行吸附机理研究。蒙特卡洛模拟结果表明：4种C₈芳烃分子的密度分布主要在分子筛超笼内，吸附能分布近似为正态分布，吸附状态多样化；SiFAU上吸附位随机且范围广，但对二甲苯无选择性；BaX上吸附位集中在超笼内的Ba附近，平均吸附热由高到低的顺序为对二甲苯、乙苯、邻二甲苯、间二甲苯，与BaX分子筛对C₈芳烃吸附选择性的实验结果顺序一致。波函数分析结果表明，4种C₈芳烃分子静电势分布相似，芳环区域静电势为负，静电势极小值点偏离于取代基方向。考虑乙苯侧链柔顺性，将C₈芳烃分子的负静电势面积与其在BaX分子筛上的平均吸附能进行关联，阐明电子分布特征对吸附性能的影响。

Adsorption Mechanism of C8 Aromatics Adsorbed by BaX Zeolite

The Monte Carlo method of canonical ensemble was used to simulate the adsorption performance of four C₈ aromatic molecules on SiFAU and BaX zeolites, and the adsorption mechanism was studied based on zeolite composition and structure, molecular structure of C₈ aromatics and electron distribution features in combination with quantum chemistry calculation and wave function analysis. The results of Monte Carlo simulation indicate the density distribution of four C₈ aromatic molecules mainly in the zeolite supercage, the adsorption energy distribution approximate to be normal distribution, and diversified adsorbed states. Moreover, the adsorption sites on SiFAU are random and widespread, but without selection to xylene; the adsorption sites on BaX are concentrated near Ba in the supercage, and the average adsorption heat is listed in descending order as follows: p-xylene>ethylbenzene>o-xylene>m-xylene, which is consistent with the experimental result for the adsorptive selectivity of BaX zeolite to C₈ aromatics. The results of wave function analysis suggest that four C₈ aromatic molecules have similar electrostatic potential distribution, the electrostatic potential is negative in aromatic ring area, and the minimum point of electrostatic potential is deviated from the direction of substituent group. Given the flexibility of ethylbenzene side chain, the negative electrostatic potential area of C₈ aromatic molecules is associated with its average adsorption energy on BaX zeolites, so as to demonstrate the effects of electron distribution characteristics on adsorption performance.