沸石类咪唑骨架材料吸附分离天然气的分子模拟

采用巨正则蒙特卡洛方法研究C₂H₆, CO₂和CH₄三种气体在两种沸石类咪唑骨架材料 (ZIF)-ZIF-2和ZIF-71中的吸附与分离性能. 考察了C₂H₆, CO₂和CH₄三种气体在ZIF-2和ZIF-71中的单组分吸附等温线、吸附热; C₂H₆-CH₄, CO₂-CH₄ 与C₂H₆-CO₂等摩尔二元混合物的分离; 以及C₂H₆-CO₂-CH₄三元体系的分离性能. 研究结果表明: 低压下不同气体的吸附量大小与其吸附热关系紧密; 而高压下因有限的孔空间, 尺寸较小的气体分子吸附量增长趋向更快; 多组分吸附分离中, 低压下能量效应通常占据主导, ZIF优先吸附作用力较强的组分; 高压下堆积效应影响显著, ZIF会优先吸附尺寸较小的组分. ZIF-2和ZIF-71对这3种二元体系的分离性能良好. 对于三元混合物吸附分离, 在常温下3000-4000kPa范围内, ZIF-2具有良好的天然气净化性能, 可有效地分离出天然气中的C₂H₆和CO₂.关键词：巨正则蒙特卡洛模拟天然气分离沸石类咪唑骨架

Molecular simulations of adsorption and separation of natural gas on zeolitic imidazolate frameworks

Grand canonical Monte Carlo simulations were employed to investigate the adsorption and separation of C₂H₆, CO₂ and CH₄ on two zeolitic imidazolate frameworks (ZIF-2 and ZIF-71). The adsorption isotherm and isosteric heat of pure gas, the separation performance of C₂H₆-CH₄, CO₂-CH₄ and C₂H₆-CO₂ binary mixtures and C₂H₆-CO₂-CH₄ ternary mixtures on two ZIFs were simulated and discussed. For single component gas adsorption at a low pressure, the adsorption amount depended on isosteric heat; at a high pressure, due to the limited pore volume, ZIFs preferably adsorbed smaller size gas molecules. For gas mixture separation, energetic effect dominated at low pressure, therefore, ZIFs selectively adsorbed gas component with strong interactions; packing effect usually played an important role at high pressures, consequently, smaller size component would be more entropically favorable. Results demonstrated that both ZIF-2 and ZIF-71 were of good separation performance for these three binary mixtures. For the ternary mixture separation, it was found that ZIF-2 cowld effectively separate C₂H₆ and CO₂ from CH₄ at 3000-4000 kPa and room temperature.
Keywords：grand canonical Monte Carlonatural gas separationzeolitic imidazolate framework