Dong Kui, Zhai Zhiwei, Guo Aijun
Department of Geosciences and Engineering, Taiyuan University of Technology, Taiyuan 030024, China.
Shanxi Key Laboratory of Coal and Coal-Measure Gas Geology, Taiyuan 030024, China.
ACS Omega. 2021 Nov 23;6(48):32395-32407. doi: 10.1021/acsomega.1c02573. eCollection 2021 Dec 7.
The mechanisms of CO/CH adsorption in coal are the theoretical foundation for CO sequestration in coal seams targeted for enhanced coalbed methane recovery. Herein, by changing the model (low rank coal: WMC, middle rank coal: XM and high rank coal: CZ) with plenty of side aliphatic chains and functional groups established in the literature, the influence and mechanism of pore parameters and functional groups(-CH, -OH, -CO, -C=O) on the adsorption of CO and CH in different rank coals are systematically studied. Using the Connolly surface algorithm to calculate the pore volume ( ) and the specific surface area ( ) of coal with different functional groups, it can be seen that the influence of the functional group change on the pore structure is related to the coal rank. Changing the various functional groups in the original coal structure to a unified functional group (-CH, -OH, -CO, or -C=O) will increase the accessible pore volume ( ) and the specific surface area ( ), except in low-rank and middle-rank coal, where the ordered arrangement of -C=O will decrease and . The adsorption capacities of different pore parameters and functional groups were calculated by Grand Canonical Monte Carlo simulation and density functional theory. On pure adsorption, the pore parameters exert greater influence than the functional groups. By comparing the adsorption energy of the original pore structure containing functional groups and that of modified pores without functional groups, the contributions of the pore structure and original functional groups on CO/CH adsorption are 71 and 29% and 83 and 17%, respectively. Small-diameter pores and -CO have a strong adsorption capacity. In terms of competitive adsorption, the -C=O functional groups and pore diameters ranging from 1.0 to 2.0 nm can significantly enhance the selectivity of CO over CH. The CH and CO adsorption does not occur via rigorous monolayer adsorption; multilayer adsorption can occur for CH and CO with pore diameters of 1.0-2.0 and 1.0-2.2 nm, respectively, thus causing micropore filling. These quantitative results establish a foundation for the development of adsorption theory for CO/CH in coal.
煤中CO/CH吸附机制是针对强化煤层气开采的煤层CO封存的理论基础。在此，通过改变文献中建立的具有大量侧链脂肪族链和官能团的模型（低阶煤：WMC、中阶煤：XM和高阶煤：CZ），系统研究了孔隙参数和官能团（-CH、-OH、-CO、-C=O）对不同阶煤中CO和CH吸附的影响及机制。利用康诺利表面算法计算具有不同官能团的煤的孔容（ ）和比表面积（ ），可以看出官能团变化对孔隙结构的影响与煤阶有关。将原始煤结构中的各种官能团改变为统一的官能团（-CH、-OH、-CO或-C=O）会增加可及孔容（ ）和比表面积（ ），但低阶和中阶煤中-C=O的有序排列会使 和 减小。通过巨正则蒙特卡罗模拟和密度泛函理论计算了不同孔隙参数和官能团的吸附容量。在纯吸附方面，孔隙参数的影响大于官能团。通过比较含官能团的原始孔隙结构和不含官能团的改性孔隙的吸附能，孔隙结构和原始官能团对CO/CH吸附的贡献分别为71%和29%以及83%和17%。小直径孔隙和-CO具有较强的吸附能力。在竞争吸附方面，-C=O官能团和直径为1.0至2.0 nm的孔隙可显著提高CO对CH的选择性。CH和CO的吸附并非通过严格的单层吸附发生；对于CH和CO，分别在直径为1.0 - 2.0和1.0 - 2.2 nm的孔隙中会发生多层吸附，从而导致微孔填充。这些定量结果为煤中CO/CH吸附理论的发展奠定了基础。
