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中国物理学会期刊

沸石分子筛对CH4/H2的吸附与分离性能

CSTR: 32037.14.aps.70.20210101

Molecular simulation for adsorption and separation of CH4/H2 in zeolites

CSTR: 32037.14.aps.70.20210101
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  • 基于分子模拟的高通量计算方法, 通过对199个沸石结构特征和吸附分离性能之间的关联性研究, 发现具有超微孔结构的沸石材料对CH4分子有良好的吸附分离性能, 等摩尔CH4/H2混合组份的CH4吸附选择性和单组份的CH4吸附量之间存在明显的线性关系. 通过使用巨正则蒙特卡罗模拟方法, 获得了3个孔道形沸石对CH4和H2的吸附等温线和等量吸附热等物理量. 结果表明在相同外界环境下, 孔道形沸石的孔结构(表面积和孔体积)对CH4吸附量的影响高于能量效应(吸附热). 结合甲烷蒸汽重整制氢的工业背景, 进一步研究了CH4/H2混合体系在不同组份下的分离选择性能, 结果表明, 超微孔沸石材料对CH4的吸附选择性与体相压力和进料比无关. 通过气体分子的质心分布密度发现, CH4在孔道形沸石中优先占据更小孔窗的空间, 而H2的分布范围更大但是未存在明显的优先吸附位点.

     

    Based on the high-throughput calculation method of molecular simulation, except the structures with zero surface area and less than zero adsorption capacity, four geometric descriptors (largest cavity diameter, specific surface area, pore volume and porosity), an energy descriptor (heat of adsorption), adsorption capacity, and adsorption selectivity coefficient of 199 zeolites are obtained. By studying the correlation between structural characteristics and adsorption separation performance, the result shows that when the largest cavity diameter is 6 Å, the surface area is 1400–2100 m2·g–1, and the pore volume is in a range of 0.2–0.3 cm3·g–1, the zeolite has the greatest influence on the adsorption capacity and adsorption selectivity for methane molecules. At the same time, it is found that the largest cavity diameter and porosity of zeolite molecular sieves have a positive correlation, and there is also an obvious linear relationship between the CH4 adsorption selectivity coefficient of the equimolar CH4/H2 mixed component and the single-component CH4 adsorption capacity. By using the grand canonical Monte Carlo simulation method, physical quantities such as adsorption isotherms and isosteric heats of adsorption for CH4 and H2 of three channel-shaped zeolites are obtained. The result shows that the pore structure (surface area and pore volume) of the channel-shaped zeolite has a greater influence on the CH4 adsorption capacity than the energy effect (heat of adsorption), under the same external environment. Combining with the industrial background of steam methane reforming hydrogen production, the separation and selectivity performance of the CH4/H2 mixed system under different components are further studied. The result reveals that there is no correlation between adsorption selectivity of ultra-microporous zeolite material for CH4 and bulk pressure or feed ratio. According to the centroid distribution density of gas molecules, it is found that CH4 preferentially occupies the space of smaller pore windows in the channel-shaped zeolite, while the distribution range of H2 is larger but there is no unambiguous preferential adsorption site.

     

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