甲烷在石墨烯与活性炭上的吸附平衡

Adsorption Equilibrium of Methane on Graphene Sheets and Activated Carbon

为研制ANG新型碳基吸附剂，分别选用比表面积为2074m2·g-1的椰壳活性炭SAC-02和345m2·g-1的石墨烯，在温度区间263～313K、压力范围0～6MPa，依据容积法的原理测试了甲烷在其上的吸附平衡数据，并由吸附等温线和等量吸附热的比较，分析了甲烷在两吸附剂上吸附平衡．结果表明：甲烷在活性炭上的过剩吸附等温线为典型的I型，而石墨烯上在压力2MPa以下为I型，2—6MPa之间吸附量与压力接近线性关系．在273K和6MPa时，甲烷在石墨烯上吸附量为4．6mmol·g-1，活性炭的吸附量为11．2mmol·g-1；甲烷在石墨烯和活性炭上的等量吸附热分别为14．32kJ·mol-1～20．66kJ·mol-1和13．99kJ·mol-1-17．57kJ·tool-1，石墨烯表面对甲烷分子作用能强．

For developing a new kind of carbon-based adsorbent for storage of natural gas by adsorption, adsorption equilibrium of methane on graphene sheets （GS） was studied based on a sample of GS with SBET = 345 m2 · g-1 at the temperatures of 263 -313 K and the pressures of 0 N 6 MPa. In the meantime, isotherms of excess amount of methane on granular coconut shell SAC - 02 activated carbon （ SBET = 2074 m2· g-l ） at the same experimental condition as that of the GS were employed for comparison study. The absolute adsorption a- mounts of methane on the GS were calculated in terms of Gibbs＇ definition by applying the approximation of the state of adsorbed phase of supercritical gas proposed by Ozawa, and then were used to determine the isosteric heat of adsorption of methane by adsorption isosteres. It shows that, under the experimental conditions, the i- sotherm of excess adsorption amount of methane on the activated carbon can be described as type I; however, the isotherm of methane on the GS almost increases linearly and correlatively as pressure increases. The results also reveal that the specific adsorption amount of methane on the GS and activated carbon is respectively 4. 6 mmol · g- 1 and 11.2 mmol · g - 1. The isosteric heat of methane adsorption on the GS falls within 14. 32 · 20. 66 kJ·mo1-1, which is comparable to 13. 99 17. 57 kJ· mol-t of methane adsorption on the activated carbon. It suggests that interaction between methane molecules and the graphene layer is stronger than that between meth- ane and carbon surface, and the methane storage capacity of GS is closely related to its physical properties.