Abstract:

The interaction between the gas and the membrane structure greatly affects the separation during the membrane separation of mixed gases. A carbon membrane model with carbon microcrystal structure based on PEK-C-based carbon membrane characterization was constructed by using molecular simulation to investigate the effects of carbon microcrystal pore size and specific surface area of the membrane on CO₂/CH₄ adsorption and diffusion. The results show that the adsorption sites of gas inside the carbon membrane are related to its microstructure. Gas molecules will be preferentially adsorbed in the pores formed by the random stacking of carbon microcrystals, while the gas adsorption location shifts to the interior of carbon microcrystals when the pore size of carbon microcrystals increases and the specific surface area increases. The molecular shape is the main factor influencing the diffusion when the pore volume of the carbon membrane is more minor, where the linear CO₂ is more easily diffused inside the carbon membrane than the ortho-tetrahedral CH₄. The carbon membrane has the best gas separation performance with an adsorption separation coefficient of 10.49 when the pore size of carbon microcrystals is 0.493 nm at 30℃ and 100 kPa. As the carbonization temperature increases, the specific surface area of the carbon film increases, which is not conducive to gas separation, indicating that the carbonization temperature should not be too high. The research results not only expand the mechanism of carbon membrane gas separation but also provide a basis for preparing high-performance carbon membranes.

Key words: molecular simulation, carbon membrane, adsorption, diffusion, microstructure, carbon microcrystal

摘要：

在混合气体的膜分离过程中，组分与膜结构的相互作用直接影响分离效果。采用分子模拟方法，建立基于PEK-C基炭膜结构表征的碳微晶基炭膜模型，探究膜的碳微晶孔径和比表面积对CO₂/CH₄吸附和扩散的影响。结果表明，气体在炭膜内的吸附位点与其微结构有关，碳微晶孔径与比表面积增加时，吸附位点由碳微晶外部孔隙向碳微晶内部转移；炭膜孔隙体积较小时，分子形状为影响扩散的主要因素，其中直线型的CO₂比正四面体型的CH₄更易于扩散；30℃、100 kPa下，碳微晶孔径为0.493 nm时炭膜具有最优的气体分离性能，其吸附分离系数为10.49；炭化温度升高，炭膜比表面积增大，不利于气体分离，表明炭化温度不宜过高。研究结果拓展了炭膜气体分离机理，可为高性能炭膜的制备提供依据。

关键词: 分子模拟, 炭膜, 吸附, 扩散, 微结构, 碳微晶