煤族组分骨架结构的分子模型构建及分子动力学模拟

Model construction and molecular dynamics simulation of coal group component skeleton structure

为从分子水平上进一步深入认知煤大分子网络结构形成的内在机制,对煤全组分分离所得重质组(HC)、疏中质组(LMC)、密中质组(DMC)和轻质组(LC)分别进行分级分次快速溶剂萃取,以获得各族组分骨架部分和小分子部分;采用FTIR,XPS,^(13)C NMP及元素分析获得骨架部分的结构特征参数,构建出重质组骨架(HC-S)、疏中质组骨架(LMC-S)和密中质组骨架(DMC-S)的分子结构模型;再对各分子结构模型进行分子力学和分子动力学模拟,获得其最低势能构型及模拟密度,并进一步探究各族组分骨架大分子形成多分子稳定聚集体的分子机制和能量机制。结果表明:HC-S的分子式为C_(246)H_(186)N_(4)O_(15),LMC-S为C_(216)H_(183)N_(5)O_(5)S,DMC-S为C_(195)H_(179)N_(3)O_(4)S。LMC-S模拟密度最大,HC-S次之,DMC-S最小,模拟密度与实验室检测密度基本一致。当12个DMC-S聚集时,由于不同分子中结构单元之间的N…H相互作用而形成DMC-S-12稳定构型,其尺寸约5 nm;当25个LMC-S聚集时,体系中产生较多的π-π相互作用而形成DMC-S-25较稳定构型,其尺寸约7 nm;HC-S则不会形成20个骨架分子以内的稳定聚集体。该机理能够很好吻合实验结果。LMC-S回转半径最大,DMC-S次之,HC-S最小,表明骨架分子LMC-S的柔韧性最小,其形成聚集体时将更疏松;HC-S的柔韧性最大,形成聚集体时将更致密;DMC-S则居中。该结果与实验现象吻合度良好。并给出了各族组分骨架单分子及其聚集体的模拟计算与实验结果总结对照表。

In order to further understand the internal mechanism of the structure formation of coal macromolecular network from molecular aspect,the group components including heavy component(HC),loose medium component(LMC),dense medium component(DMC),and light component(LC)were respectively extracted from the all-group component of coal and the skeleton structure of group components and small organic molecules were collected.The molecular models of group component skeletons(HC-S,LMC-S,and DMC-S)were constructed based on the parameters deduced from the results of XPS,13 C NMR,FTIR,and ultimate analysis.The configurations with the lowest potential energy and densities of simulated models were acquired using molecular mechanics and molecular dynamics simulations.Then,the molecular and energy mechanisms of the formation of multi-molecular stable aggregate were further explored.The results indicate that the molecular formulas of HC-S,LMC-S and DMC-S were C_(246)H(186)N(4)O(15),C(216)H(183)N(5)O(5)S and C(195)H(179)N(3)O(4)S respectively.The LMC-S model has the highest density,followed by HC-S and DMC-S.The density of the simulated models has a good agreement with the experiments values.In the case of the unit cell containing 12 DMC-S macromolecules,a stable aggregate with the size about 5 nm can be formed due to the interactions between nitrogen and hydrogen in the structural unit of different molecules.However,the stable aggregate(LMC-S-25)with the size about 7 nm was formed via the π-π conjugation effects.The stable aggregates of HC-S were not formed when the molecules number less than 20.The mechanisms are consistent with the experimental results.Besides,the LMC-S has the largest gyration radius,followed by DMC-S and HC-S,indicating the smallest flexibility of LMC-S and the incompact formed aggregates.On the other hand,HC-S has the highest flexibility and will become compact as for the formed aggregates.These analysis results coincide with the experimental phenomenon well.Finally,the comparison table between the simulation calculation and experimental results of skeleton monomers and their aggregates were given.