褐煤表面吸水机理及润湿性调控的分子模拟研究

发布时间：2018-06-15 17:35

本文选题：褐煤 + 润湿性　；参考：《太原理工大学》2017年硕士论文

【摘要】：褐煤储量丰富,应用前景十分广阔。但丰富的孔隙结构和大量的含氧基团造成褐煤具有高含水的特性,限制了其高效利用。如何降低褐煤表面亲水性,抑制水分复吸,成为褐煤提质利用的技术关键。目前主要的脱水干燥技术有蒸发干燥和非蒸发干燥技术,这些方法具有能耗大、环境污染严重等缺陷。采用药剂对褐煤表面强极性含氧官能团进行吸附覆盖,阻断其与水分子的相互作用,可有效降低褐煤表面亲水性。本文首先选取经典的褐煤模型,采用量子化学密度泛函理论研究了褐煤表面不同含氧官能团对水分子的吸附行为和吸附能力。采用非极性的正辛烷、正十二烷和正十六烷,运用分子动力学(MD)模拟方法考察其在褐煤表面的吸附形貌及吸附能力。由于非极性烷烃在褐煤表面吸附作用不强,故选取具有两亲结构的表面活性剂十二烷基磺酸钠(SDS)、十二烷基苯磺酸钠(SDBS)和十二烷基三甲基溴化铵(DTAB),采用MD方法研究其在褐煤表面的吸附行为及对褐煤润湿性影响。分子模拟计算得到的主要结论如下:(1)水分子在羧基位点形成两个氢键,而在其他含氧官能团位点形成一个氢键。含氧官能团中氧原子得电子,导致O-H、C=O和C-O键长发生变化,由于吸附态的不同使得水分子的键角变化出现差异性。不同位点吸附强弱顺序为:羧基酚羟基醇羟基羰基醚键。(2)对单分子烷烃进行量子化学计算,发现随着链长的增加,?LUMO-HOMO越低,单分子与褐煤作用时能量越大。随着烷烃链长的增加,烷烃-水体系中烷烃的扩散系数逐渐增大。通过对烷烃-褐煤体系MD计算,结果表明烷烃链长越短,扩散系数及其与褐煤表面的相互作用能越大。(3)吸附DTAB的褐煤的表面积最大,DTAB与褐煤表面的相互作用最强,径向分布函数表明其极性基与褐煤表面的含氧基团吸附距离最小。而阴离子型表面活性剂在褐煤表面的吸附作用较弱。(4)对褐煤-表面活性剂-水体系吸附形貌及相对浓度分布进行分析,发现水分子散落的分布在吸附DTAB的褐煤表面;SDBS离子中的苯环的空间排布靠近褐煤体相;三种表面活性剂的极性基团基本上吸附在褐煤表面,而烷基链伸向水相中,烷基链的伸展长度的次序为:SDSSDBSDTAB。通过计算吸附表面活性剂的褐煤与水分子的吸附能以及水分子的扩散系数,结果表明:DTAB降低褐煤表面亲水性效果最好,SDBS次之。
[Abstract]:Lignite is rich in reserves and has a broad application prospect. However, the rich pore structure and a large number of oxygen groups lead to the high water content of lignite, which limits its efficient utilization. How to reduce the surface hydrophilicity of lignite and restrain moisture reabsorption become the key technology of lignite extraction and utilization. At present, the main dehydration and drying techniques are evaporative drying and non-evaporative drying, which have the disadvantages of high energy consumption and serious environmental pollution. The surface hydrophilicity of lignite can be effectively reduced by using medicament to cover the surface of lignite with strong polar oxygen-containing functional groups and blocking the interaction between lignite and water molecules. In this paper, the classical lignite model is used to study the adsorption behavior and adsorption ability of different oxygen-containing functional groups on the surface of lignite by using the quantum chemical density functional theory (DFT). Non-polar n-octane, n-dodecane and n-hexadecane were used to study the adsorption morphology and adsorption capacity on lignite surface by molecular dynamics (MD) simulation. Because the adsorption of nonpolar alkanes on lignite surface is not strong, Therefore, the surface active agents (sodium dodecyl sulfonate, sodium dodecylbenzenesulfonate) and dodecyl trimethylammonium bromide (DTABN) with amphiphilic structure were selected to study their adsorption behavior on the surface of lignite and their effects on the wettability of lignite by MD method. The main results of molecular simulation are as follows: (1) Water molecules form two hydrogen bonds at carboxyl sites and one hydrogen bond at other oxygen-containing functional groups. The oxygen atoms in the oxygen-containing functional groups get electrons which lead to the change of the bond lengths of O-HN Con O and C-O, and the differences of the bond angles of water molecules due to the different adsorption states. The order of adsorption strength at different sites is: carboxyphenol hydroxyl alcohol hydroxyl carbonyl ether bond. The quantum chemical calculation of monomolecular alkanes is carried out. It is found that the lower the chain length, the greater the energy between monolayer and lignite. With the increase of alkane chain length, the diffusion coefficient of alkane in alkane-water system increases gradually. The MD calculation of alkane lignite system shows that the shorter the alkane chain length, the greater the diffusion coefficient and the interaction energy between DTAB and lignite surface. 3) the surface area of DTAB adsorbed on lignite is the largest and the interaction between DTAB and lignite surface is the strongest. The radial distribution function shows that the adsorption distance between the polar group and the oxygen group on the surface of lignite is the smallest. The adsorption morphology and relative concentration distribution of lignite surfactants on lignite surface were analyzed. It was found that the spatial arrangement of benzene rings in the surface of DTAB adsorbed lignite is close to the bulk phase of lignite, and the polar groups of the three surfactants are basically adsorbed on the surface of lignite, while the alkyl chain extends to the water phase. The order of stretching length of alkyl chain is: SDSSDBSDTAB. By calculating the adsorption energy of lignite and water molecule and the diffusion coefficient of water molecule, the results show that the hydrophilicity of lignite surface reduced by 1: DTAB is better than that of SDBs.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TD849.2

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