Zhang Zhiqiang, Yun Tao, Zhang Haiwen, Yan Kefeng
College of Mining Engineering, Taiyuan University of Technology, No. 79 West Yingze Street, 030024 Taiyuan, P. R. China.
Key Laboratory of Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, No. 2 Nengyuan Road, 510640 Guangzhou, P. R. China.
ACS Omega. 2018 Nov 1;3(11):14585-14591. doi: 10.1021/acsomega.8b01967. eCollection 2018 Nov 30.
A density function approach has been used to screen an appropriate surface modifier for oxidized coal to enhance its hydrophobicity in a flotation process. Two oxidized coal surface models, coal-COOH and coal-COONa, based on the substitution of 10-fused benzene rings with COOH and COONa functional groups, have been constructed to mimic the surface hydrophilic sites at acidic and alkaline pHs, respectively. A nonpolar molecule and five polar candidate molecules with different functional groups have been examined on each oxidized coal model surface. Our present study indicates that octane is ineffective toward increasing the surface hydrophobicity for both coal-COOH and coal-COONa models due to its preferential adsorption on hydrophobic aromatic sheet, although it can spontaneously bind to the coal model surfaces at 298 K. Unlike octane, 4-pentylpyridine will present the preferred hydrophobic conformation on both models. However, its adsorption process is favorable energetically only on the coal-COOH model. The optimized geometries of all four oxygen-containing molecules (1-methoxyheptane, 1-octanol, octanal, and octanoic acid) show that directional hydrogen bonds will be formed between their oxygenated groups and the COOH group of coal-COOH model. This results in the protrusion of the hydrocarbon chain toward the water phase, which is beneficial for increasing coal surface hydrophobicity. However, the calculated Gibbs free energies suggest that octanoic acid is the best candidate. The adsorption of all four oxygen-containing molecules on the coal-COONa model is a spontaneous process. However, only sodium octanoate can be regarded as the effective surface modifier according to its optimized adsorption conformation at alkaline pH.
采用密度泛函方法筛选出合适的氧化煤表面改性剂，以增强其在浮选过程中的疏水性。构建了两种氧化煤表面模型，即煤 - COOH和煤 - COONa，分别通过用COOH和COONa官能团取代10个稠合苯环来模拟酸性和碱性pH值下的表面亲水位点。在每个氧化煤模型表面上研究了一种非极性分子和五种具有不同官能团的极性候选分子。我们目前的研究表明，辛烷对提高煤 - COOH和煤 - COONa模型的表面疏水性无效，因为它优先吸附在疏水芳香片上，尽管它在298 K时能自发地与煤模型表面结合。与辛烷不同，4 - 戊基吡啶在两种模型上都会呈现出优选的疏水构象。然而，其吸附过程仅在煤 - COOH模型上在能量上是有利的。所有四种含氧分子（1 - 甲氧基庚烷、1 - 辛醇、辛醛和辛酸）的优化几何结构表明，它们的含氧基团与煤 - COOH模型的COOH基团之间将形成定向氢键。这导致烃链向水相突出，有利于提高煤表面的疏水性。然而，计算得到的吉布斯自由能表明辛酸是最佳候选物。所有四种含氧分子在煤 - COONa模型上的吸附都是自发过程。然而，根据其在碱性pH下的优化吸附构象，只有辛酸钠可被视为有效的表面改性剂。
