不同煤阶煤分子表面吸附水分子的机理

摘要

采用量子化学方法中包含色散矫正的密度泛函理论(DFT-D3),对4种不同煤阶(无烟煤、烟煤、次烟煤、褐煤)的煤分子表面吸附水分子的微观机理进行研究.通过优化煤分子表面吸附水分子的平衡构型,对煤分子表面进行静电势分析,计算相互作用能,并通过约化密度梯度(RDG)判断水分子在不同煤阶煤分子表面的作用类型.研究表明,煤分子与水分子间最大相互作用能为-11.91 kcal/mol,煤吸附水的过程属于物理吸附,且相互作用能的大小由弱相互作用力的类型和作用力个数共同决定.褐煤具有较大静电势的分子表面积最多,褐煤更易与极性水分子形成相互作用.4种不同煤阶煤分子吸附水分子的最大相互作用能大小顺序为:褐煤＞次烟煤＞烟煤＞无烟煤.各煤阶最大相互作用能对应的平衡吸附构型下煤分子与水分子的作用类型依次为:范德华作用力,氢键作用,氢键与范德华作用力的共同作用,两个氢键的共同作用.%The adsorption mechanism of water molecule on the molecular surface of different rank coals was investigated by the density functional theory with dispersion correction (DFT-D3) in the quantum chemistry method.Anthracite,bituminous,subbituminous and lignite were selected as the typical coal ranks.The equilibrium configurations of water molecule adsorbed on the surface of coal molecules were optimized,the analysis of electrostatic potential on the surface of coal molecule was conducted,and the interaction energy between coal molecular surface and water was cal culated,also,the interaction types of water molecule on the molecular surface of different rank coals were confirmed by calculating the reduced density gradient function (RDG).Research indicates that the maximum interaction energy between coal molecules and water molecule can be-11.91 kcal/mol which confirms that the adsorption process of water molecule on coal molecule surface belongs to physical adsorption,and the interaction energy depends on the type and number of weak interaction forces.Lignite has the largest molecular surface area with large electrostatic potential,revealing that lignite is more likely to interact with polar water molecule.The maximum interaction energy of four different rank coals molecule adsorbed water molecule can be in the order of lignite ＞ subbituminous ＞ bituminous ＞ anthracite.The interaction between anthracite and water molecule belongs to van der Waals force;the interaction between bituminous and water molecule is hydrogen-bonding effect;the interaction between subbituminous and water molecule is a joint contribution of van der Waals force and hydrogen-bonding;and the interaction between lignite and water is the combined effect of two strong hydrogen bonds.