Abstract:

Adsorbed natural gas is considered as the most promising method for CH₄ storage in the future. The key is to find suitable adsorbents to achieve good absorption/desorption performance. Methods of grand canonical Monte Carlo and equilibrium molecular dynamic simulation were adopted in this article to research the adsorption and diffusion of CH₄ in nanoporous carbons. Some factors influenced the adsorption and diffusion of CH₄ in nanoporous carbons including the size of graphite slice unit, different density of nanoporous carbons and the surface functionalization of nanoporous carbons were investigated, respectively. Results showed that the types and proportions of graphite slices used to generate the nanoporous carbons had little impact on CH₄ adsorption. The density of nanoporous carbons had an effect on CH₄ adsorption. The optimal density of pristine nanoporous carbons was about 0.50 g·cm^-3 and the optimal density of modified nanoporous carbons was at around 0.72 g·cm^-3. When modified with different functional groups, the CH₄ adsorption capacity in the modified nanoporous carbons was in the sequence of CH₃-NPC > OH-NPC > CO-NPC > COOH-NPC > NPC. For the diffusion of CH₄ nanoporous carbons, nanoporous carbons with low density and COOH group had high self-diffusion coefficient.

Key words: CH₄, nanoporous carbons, adsorption, diffusion, molecular simulation

摘要：

吸附天然气被认为是未来最具有发展前景的CH₄储存方式之一，其中的关键是寻找合适的吸附剂，使其具有良好的CH₄吸脱附性能。以纳米多孔碳材料作为多孔活性炭的结构，采用巨正则蒙特卡洛（GCMC）和平衡分子动力学（EMD）的方法研究CH₄在纳米多孔碳材料中的吸附和扩散行为，通过考察不同因素的影响，期望获得高的CH₄吸附量和自扩散系数。其中，研究的主要因素有：构成多孔碳材料的石墨片微元的大小、多孔碳材料的不同密度、多孔碳材料的表面基团改性。结果表明：多孔碳材料对CH₄的吸附受石墨片微元种类和混合比例的影响不大；在所研究的多孔碳材料密度范围内，存在最优密度，能够获得最大的CH₄吸附量，此最优密度在0.50 g·cm^-3左右，但是多孔碳材料的表面经羟基修饰后，最佳材料密度发生了偏移，此时最优密度在0.72 g·cm^-3左右；此外，经表面改性后的多孔碳材料吸附量大小顺序为：CH₃ > OH > CO > COOH；对于CH₄在多孔碳材料中的扩散，总体规律是低的密度，并且经过COOH修饰，其CH₄自扩散系数最大。

关键词: CH₄, 多孔活性炭, 吸附, 扩散, 分子模拟