苯与丙烯在MCM-22型分子筛内吸附行为的Monte Carlo研究

采用巨正则统计系综Monte Carlo模拟方法研究了不同温度、不同吸附方式下纯硅MCM-22型分子筛ITQ-1上苯与丙烯分子的吸附行为. 分子筛内吸附质粒子云分布模拟结果显示, 苯和丙烯主要吸附在超笼和十元环孔道内, 其中丙烯分子几乎充满了孔道内部大部分区域, 在链接超笼之间的十元环窗口也充满了丙烯分子, 而苯分子在超笼内和十元环孔道内的吸附却较为分散、均匀. 丙烯与分子筛之间相互作用能高于苯与分子筛之间的相互作用能, 使苯分子吸附相对丙烯分子更为稳定. 温度变化对分子筛上丙烯吸附远大于对苯吸附的影响, 100 kPa时温度由298 K升高至443 K导致丙烯分子吸附量迅速减少, 而对苯分子却没有显著的影响. ITQ-1分子筛上存在苯和丙烯分子的竞争吸附, 使两者吸附相互作用能最可几分布朝着折中方向移动. 苯与丙烯在分子筛内吸附等温线的模拟结果表明, 在温度较高、压力较低时, 丙烯的吸附量小于苯的吸附量.

Studies on Adsorption Behavior of Benzene and Propylene in MCM-22 by Grand Canonical Monte Carlo Simulation

The adsorption behavior of benzene and propylene in MCM-22 zeolite was studied by grand canonical Monte Carlo(GCMC) simulations. From the mass clouds of GCMC simulations, it can be found that the benzene and the propylene molecules show different adsorption behavior in the zeolite cavities. Both benzene and propylene molecules were mainly adsorbed in the 10-MR channels and the 12-MR supercages. But obviously, propylene has higher localization than that of benzene. Besides the two localizations, propylene can be steadily located in the short 10-MR windows interconnecting the 12-MR supercages, while the benzene can not do. From the potential energy distribution, it can be seen that both benzene and propylene have two-pinked and the potential energy of propylene is higher than that of benzene, so benzene can be adsorbed more steadily than propylene. When the temperature rises from 298 K to 443 K, the numbers of propylene reduce significantly, while benzene changes little. When benzene and propylene were adsorbed in zeolite at the same time, they have competitive adsorption, therefore the potential energy distribution is changed obviously. The adsorption isotherms of benzene and propylene at different temperatures and 1×10-3—5.0 kPa were simulated, the loadings of propylene are significantly lower than those of benzene.