乙烯在丝光沸石和改性丝光沸石孔道内的吸附行为

采用频率响应(FR)法研究乙烯在丝光沸石和经CuO和Cs+离子改性的丝光沸石上的吸附机理. 分别测得和解析了252和273 K、压力在26.6-3990 Pa范围内的FR谱图, 发现乙烯在丝光沸石上吸附的速控步骤是传质过程, 同时存在两个不同的吸附过程. 这两个过程分别归属于乙烯在质子酸吸附中心上的吸附(低频吸附)和Na+吸附位上的吸附(高频吸附), 252 K时两个吸附位的吸附值分别是0.692和0.828 mmol·g-1. CuO分子进入分子筛孔道后, 位于质子酸吸附位之间不但使得低频吸附位值增加而且还覆盖了Na+吸附位, 体系中以化学吸附过程为主; Cs+离子的引入使得高频吸附位值增加但中和了质子酸吸附位, 体系中以物理吸附过程为主. CuO的最佳用量是5%. 将FR法与吸附等温线及Langmuir模型相结合能够深入研究乙烯在分子筛上的平行吸附过程.

Ethene Adsorption on Mordenite and Modified Mordenite

The frequency response (FR) technique were applied to study adsorption mechanism of ethene on parent mordenite and the mordenite modified by CuO and Cs+. The FR spectra of ethene on parent mordenite and modified mordenite were recorded and analyzed at temperature of 252 and 273 K and in the pressure range of 26.6-3990 Pa. The results showed that adsorption of ethene was the rate controlling step and there were two parallel adsorption processes in ethene/parent mordenite system. Those two processes were attributed to adsorption process of ethene on proton acid sites (low frequency adsorption) and on sodium cation sites (high frequency adsorption), and the numbers of sites available for adsorption of ethene were 0.692 and 0.828 mmol·g-1, respectively. The number of adsorption sites in low frequency adsorption was increased by the introduction of CuO, which was located among the proton acid sites and covered the sodium cation sites in high frequency adsorption. Chemical adsorption was the main sorption process in mordenite channels modified by CuO. The number of adsorption sites in high frequency adsorption was increased by the introduction of Cs+, which counteracted proton acid sites in low frequency adsorption. Physical adsorption was the main sorption process in mordenite channels modified by Cs+. The effective mass fraction of CuO for modification was 5%. The ethene adsorption processes on zeolites can be studied in detail by combining the FR spectra, isotherms, and Langmuir model.