MER型沸石吸附分离CO2/CH4的分子模拟

Molecular simulation of adsorption separation of CO2/CH4 by MER-type zeolites

MER型沸石在吸附分离CO2/CH4方面展现出良好的工业应用前景,受到广泛关注,但还缺乏理论基础数据。本文采用巨正则蒙特卡洛(GCMC)模拟方法,以全硅MER型沸石作为对照,模拟分析了CO2/CH4在Na^+、K^+、Cs^+和Ca^2+交换的MER型沸石中的吸附分离行为。结果表明:不同阳离子交换的MER型沸石对CO2和CH4的吸附符合Langmuir-Freundlich吸附等温线模型,平衡吸附量的大小顺序为:Ca-MER>Na-MER>K-MER>CsMER,与沸石的自由体积和比表面积大小顺序一致,且近似成线性关系,选用高价阳离子MER型沸石可以提高吸附量;CO2和CH4主要分布在沸石的pau笼中,在d8R笼和ste笼中也有少量分布;骨架外阳离子与CO2的强吸附作用和独特的八元环窗口孔径是MER型沸石对CO2/CH4混合组分表现出超高吸附选择性的原因,吸附选择性高达1000以上。综合吸附量、吸附热和吸附选择性分析指出,Na-MER和K-MER型沸石是优良的CO2吸附剂。本研究为MER型沸石吸附分离CO2/CH4提供了理论依据和实验指导。

Adsorption separation of CO2/CH4 by MER-type zeolites has attracted widespread attentions because of its good industrial application prospect,but it is still lack of theoretical data.Cationexchanged(Na+,K+,Cs+and Ca2+)MER-type zeolites were first modeled,and then the adsorption behavior of CO2 and CH4 on the zeolites were simulated by Grand Canonical Monte Carlo(GCMC)simulation method,with the silicon MER-type zeolite as the reference.The results showed that the adsorption of CO2 and CH4 was consistent with the Langmuir-Freundlich adsorption isotherm model.The order of equilibrium adsorption capacities of CO2 and CH4 on the zeolites is:Ca-MER>Na-MER>K-MER>Cs-MER,which is consistent with the orders of the free volume and specific surface area of the zeolites.The equilibrium adsorption capacity changed approximately linearly with the free volume and specific surface area of the zeolite.The MER-type zeolites with multivalent cation had a higher adsorption capacity for CO2 and CH4.The probability density distribution results confirmed that CO2 and CH4 were mainly distributed in pau cage,and a small amount in d8R cage and ste cage in the MER-type zeolites.The adsorption selectivity of the cation-exchanged MER-type zeolites to CO2/CH4 mixture was up to more than 1000,which was attributed to the strong binding energy between the extra-framework cation and carbon dioxide as well as the unique octet ring window aperture.Na-MER and K-MER zeolites are excellent CO2 adsorbents due to their high adsorption capacity,favorable adsorption heat and high adsorption selectivity.This study provides theoretical basis and experimental guidance for the adsorption separation of CO2/CH4 by cation-exchanged MER-type zeolites.