混合超微孔材料中CO2/N2吸附与分离的理论研究

碳捕获与封存技术是一种具有前景的CO₂减排策略。本工作采用巨正则蒙特卡洛模拟研究了温度为298 K、压强在0~5 kPa范围内三种混合超微孔材料SIFSIX-X-Cu(以SiF₆ ^2-排列, Cu为金属中心, X=2, 3, O)中CO₂/N₂吸附与分离的行为。结果显示, 相比于SIFSIX-2-Cu, SIFSIX-3-Cu和SIFSIX-O-Cu中CO₂在0.5 kPa就达到吸附饱和, 且在1 kPa下的吸附量分别达到了2.70与2.39 mmol·g ^-1。CO₂/N₂混合气体中CO₂的吸附量几乎没有下降。SIFSIX-3-Cu和SIFSIX-O-Cu具有接近于CO₂分子动力学直径的孔径, 对CO₂亲和力较大, 吸附热分别达到了59和66 kJ·mol ^-1。密度泛函理论分析发现, 在两种结构中每个孔隙只吸附一个CO₂分子, 且几乎处于孔道的中心。本工作为低压下吸附与分离CO₂的混合超微孔材料的开发提供了理论指导。

Theoretical Investigation on Adsorption and Separation of CO2/N2 in Hybrid Ultramicroporous Materials

Carbon capture and storage(CCS) is a promising strategy for reduction of CO2 emissions. Herein, CO2/N2 adsorption and separation in three SIFSIX-X-Cu(arrayed via SiF62– with Cu metal center, X = 2, 3, O) hybrid ultramicroporous materials at 298 K within 0-5 k Pa were investigated by using grand canonical Monte Carlo(GCMC) simulation. Results showed that, in contrast to SIFSIX-2-Cu, CO2 adsorption in SIFSIX-3-Cu and SIFSIX-O-Cu reached saturation at 0.5 k Pa and their CO2 adsorption capacity were 2.70 and 2.39 mmol·g–1 at 1 k Pa, respectively. The CO2 adsorption capacity in CO2/N2 mixture barely decreased. SIFSIX-3-Cu and SIFSIX-O-Cu owned close pore sizes to CO2 dynamics diameter, thereby exhibiting high CO2 affinity with adsorption heat of 59 and 66 k J·mol–1, respectively. Density functional theory(DFT) analyses showed only one CO2 molecule could be adsorbed in each hole and located at the center of SIFSIX-3-Cu and SIFSIX-O-Cu. Our results provide a theoretical guidance for developing ultramicroporous materials in adsorption and separation of CO2 at low pressure.