甲烷在碳基材料和MOFs上极低压力下的吸附平衡

Adsorption equilibrium of methane on carbon based materials and MOFs at very low pressure

为研制新型吸附式天然气(ANG)吸附剂,比较了极低压力下甲烷在典型碳基吸附剂和MOFs上的吸附平衡。碳基吸附剂选择SAC-02活性炭、GS(2D)单层石墨烯和GS(3D)层状石墨烯;MOFs为由溶剂热法制备的MOF-5(S)、HKUST-1、ZIF-8以及由机械球磨得到的MOF-5(M)。试样首先由77K下氮气的吸附等温线确定孔大小及分布(PSD)、比表面积和微孔容积,然后在温度283~303K、压力0~0.1MPa测试甲烷的吸附平衡数据,并由Henry定律常数计算甲烷在试样上的极限吸附热。结果表明,碳基吸附剂的比表面积和微孔容积为影响其甲烷吸附量的关键因素;相对于MOF-5(S),MOF-5(M)的比表面积和微孔容积增大且PSD集中于微孔。设计ANG用MOFs应考虑ANG储存的压力范围。

In order to develop new kinds of adsorbents for adsorbed natural gas（ANG）, an analysis of adsorption equilibrium of methane on a series of carbon-based adsorbents and MOFs adsorbents at very low pressure was carried out. The carbon-based adsorbents included the activated carbon SAC-02, monolayer graphene sheets GS（2 D）, layered graphene sheets GS（3 D）, and the MOFs included the MOF-5（S）, HKUST-1 and ZIF-8 synthesized by solvent-thermal method, and the MOF-5（M） prepared by mechanical ball milling. The pore size distributions, specific surface areas and micropore volumes of the prepared samples were obtained by nitrogen adsorption isotherms at 77 K, and the adsorption equilibrium data of methane on the samples were measured at283-303 K and 0-0.1 MPa. Henry＇s law constants were determined and employed to calculate the limit isosteric heats of methane adsorption on the samples. The results indicates that the adsorption capacity of methane on a carbon-based adsorbent is mainly related to its specific surface area and micropore volume, and, compared to MOF-5（S）, MOF-5（M） has larger specific surface area and pore volume and its pore size distribution is more concentrated in the micropores. It suggests that the storage pressure of ANG system should be taken into account while developing an ANG storage medium from MOFs.