构造煤微观结构部分组成因素对CO_(2)和CH_(4)竞争吸附能力的影响分析

Analysis of effects of microstructure of tectonically-deformed coal on the CO_(2)and CH_(4) competitive adsorption capacity

为明确构造煤微观结构部分组成因素对CO_(2)和CH_(4)竞争吸附能力的影响机制,基于巨正则蒙特卡洛、分子动力学方法和密度泛函理论,探讨了芳香单元延展度(L_(a))、芳香单元堆砌层数(N)、狭缝孔径(d)、表面缺陷(V)及含氧官能团(M)对CO_(2)和CH_(4)吸附能力的影响。结果表明:CO_(2)和CH_(4)吸附量及平均等量吸附热随L_(a)和d的增加而增大,随N的增加而减小;构造煤中V和M的存在会降低CO_(2)和CH_(4)的吸附量和平均等量吸附热;CO_(2)和CH_(4)在次生缺陷表面煤上的吸附强于其在单缺陷表面煤上的吸附;羧基最不利于CO_(2)在煤表面的吸附,羟基最不利于CH_(4)在煤表面的吸附;CO_(2)/CH_(4)的选择性系数始终大于1,狭缝孔径越小,CO_(2)竞争吸附优势越显著;煤表面吸附CO_(2)和CH_(4)后,费米能级处CO_(2)的电子态密度峰值大于CH_(4)的电子态密度峰值,说明CO_(2)在与CH_(4)竞争吸附过程中处于优势地位。研究从微观角度揭示了CO_(2)和CH_(4)在不同构造煤结构中的竞争吸附机理,其结论可为煤层气高效开采提供一定的理论依据。

In order to clarify the mechanism of the competitive adsorption of CO_(2)and CH_(4)influenced by microstructure of tectonically-deformed coal,based on Grand Canonical Monte Carlo,Molecular Dynamics method,and Density Functional Theory,the effects of the extension of basic structural unit(L_(a)),the number of basic structural unit(N),slit aperture(d),surface defects(V),and oxygen-containing functional groups(M)on the adsorption behavior of CO_(2)and CH_(4)were investigated.The results show that the adsorption amount of CO_(2)and CH_(4)and the average isosteric heat of adsorption increase with the increase of L_(a) and d but decrease with the increase of N.The presence of V and M in tectonically-deformed coal reduces the adsorption amount and average isosteric heat of adsorption.The adsorptions of CO_(2)and CH_(4)on the surfaces of secondary defects are stronger than that on the surfaces of single defects.The carboxyl is the most unfavorable for CO_(2)adsorption on coal surface,and the hydroxyl is the most unfavorable for CH_(4)adsorption on coal surface.The selectivity coefficients of CO_(2)/CH_(4)are always greater than 1,the smaller the slit pore size,the more significant advantage of CO_(2)competitive adsorption is.Furthermore,the peak value of the electron density of states of CO_(2)is larger than that of CH_(4)at Fermi level after CO_(2)and CH_(4)are adsorbed on the coal surface,indicating that CO_(2)plays a dominant role in the competitive adsorption process with CH_(4).Overall,the competitive adsorption mechanism of CO_(2)and CH_(4)in different tectonically-deformed coal structures is revealed from the microscopic point of view,and the results can provide a theoretical basis for the efficient exploitation of coalbed methane.