基于蒙特卡洛方法的煤吸附水机理

H_2O adsorption mechanism in coal basing on Monte Carlo method

为研究煤对水的吸附机理,建立煤大分子结构模型,采用巨正则系综蒙特卡洛方法,在分子尺度研究分析了压力1~100 k Pa不同温度下水在煤中的吸附行为,为涉及煤水相互作用的进一步研究奠定理论基础。结果表明:水的吸附量和等量吸附热与温度负相关,与压力正相关。在大于临界压力的某一压力下,两吸附位的势能概率分布间形成高原区,说明比例相当。超过该压力,相互作用更强的氢键占主要地位,吸附量开始急剧增大,发生毛细凝聚,形成水团簇。随着压力增大,吸附继续由较弱的H_2O-煤相互作用的吸附位向较强的H_2O-H_2O相互作用的吸附位移动,直至全部作用在由已吸附的H_2O形成的第2吸附位,等量吸附热趋于平稳。得到了水在煤中吸附过程概率密度的三维分布,从而更直观全方位地认识水的吸附行为及机理。

The macromolecular coal structural model is constructed and the H2O adsorption behavior in coal is simulated using Grand Canonical Monte Carlo method at 1-100 kPa and at 298.15,303.15,313.15 and 318.15 K to investigate the H2O adsorption mechanism on molecular scale which lays a theoretical foundation for further research involving the interaction between coal and water.The results show that the adsorbed amount and isosteric heat of H2O show a negative correlation with temperature and a positive correlation with pressure.When pressure is greater than a critical pressure,there is a plateau area of potential energy probability distribution between two adsorption sites indicating equal proportion.When exceeding the pressure,the adsorbed amount increases sharply then capillary condensation occurs with water cluster because of the control of stronger hydrogen-bond interaction.With the increase of pressure,the adsorption process transfers from weaker adsorption sites provided by H2O-coal interaction to stronger adsorption sites provided by H2O-H2O interaction,until total sites are secondary adsorption sites forming from adsorbed H2O then the isosteric heat tend to be steady.The 3D probability density distribution provides a more intuitionistic comprehensive understanding to H2O adsorption behavior and mechanism in coal.