Monte Carlo simulation of water adsorption on metal ions modified molecular sieves

doi:10.16085/j.issn.1000-6613.2017-2099

Abstract

Abstract: The adsorption dehydration by the metal ions modified molecular sieves attracted widespread attention, because of their low energy cost, high adsorption capacity and high degree purification, but it is still lack of fundamental data such as the equilibrium water adsorption capacity. The rational metal ion sites and configuration of the molecular sieves were obtained by utilizing the Sorption module in Materials studio software. At the same time, the X-ray diffraction spectra of NaX, NaY and NaA molecular sieves were calculated. The calculated results were consistent with the standard spectra in the International Molecular Sieve Association (IZA-SC) database. The Monte Carlo simulation method with "COMPASS" force field was used to simulate the process of water adsorption on the molecular sieves of NaX, NaY and NaA, and the molecular sieves modified with Ca²⁺, Fe³⁺, Mg²⁺, K⁺. The results showed that the adsorption isotherms of water on the molecular sieves belong to the typeⅠLangmuir adsorption isotherm. The equilibrium adsorption capacities of water on the molecular sieves without modification were 360.3mg/g, 393.8mg/g and 295.5mg/g for NaX, NaY and NaA, respectively. The adsorption performance of the X, Y and A molecular sieves modified with Mg²⁺ improved obviously. The equilibrium adsorption capacity of MgX reached 472.6mg/g, which was 112.3mg/g higher than that of the unmodified ones. This study can provide a theoretical basis and guidance for the research, development and application of the high efficient molecular sieve adsorbents for dehydration.

Key words: metal ions, molecular sieves, adsorption, COMPASS force field, Monte Carlo simulation

摘要： 金属离子改性分子筛吸附脱水具有节能环保、吸附容量高、净化精度高等特点，受到广泛关注，但还缺乏平衡吸附量等基础数据。本文利用Materials Studio软件中Sorption模块进行落位计算得到合理的金属离子落位和分子筛构型，同时利用Reflex模块计算分子筛的XRD谱图，计算结果与国际分子筛协会（IZA-SC）的XRD标准谱图一致。采用蒙特卡罗法（Monte Carlo）的"COMPASS"力场对NaX、NaY和NaA 3种分子筛以及Ca²⁺、Fe³⁺、Mg²⁺和K⁺改性分子筛吸附水进行分子模拟。结果表明，水的吸附属于第Ⅰ型Langmuir吸附等温线。NaX、NaY和NaA分子筛对水的平衡吸附量分别为360.3mg/g、393.8mg/g和295.5mg/g，Mg²⁺取代的X型、Y型和A型分子筛对水的吸附能力增加幅度最大。MgX的平衡吸附量达472.6mg/g，较未改性时增加了112.3mg/g。本研究可为高效分子筛脱水吸附剂的筛选及其应用提供一定的理论依据和指导。

关键词: 金属离子, 分子筛, 吸附, COMPASS力场, 蒙特卡罗模拟

CLC Number:

TQ013.1

XIAO Yonghou, ZHOU Mengxue, ZHAO Ying, WANG Chuanming, HE Gaohong. Monte Carlo simulation of water adsorption on metal ions modified molecular sieves[J]. Chemical Industry and Engineering Progress, 2018, 37(09): 3430-3436.

肖永厚, 周梦雪, 赵颖, 王传明, 贺高红. 金属离子改性分子筛吸附水的Monte Carlo模拟[J]. 化工进展, 2018, 37(09): 3430-3436.

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