离子液体的分子动力学模拟及应用
文献类型：学位论文
| 作者 | 周国辉 |
| 学位类别 | 博士 |
| 答辩日期 | 2009-06-02 |
| 授予单位 | 中国科学院过程工程研究所 |
| 授予地点 | 过程工程研究所 |
| 导师 | 张锁江 |
| 关键词 | 离子液体 氨基酸 脱硫 分子动力学模拟 分子力学力场 |
| 其他题名 | Molecular Dynamics Simulation Studies on Ionic Liquids and Its Application |
| 学位专业 | 物理化学（含：化学物理） |
| 中文摘要 | 离子液体是近年来国际绿色化学化工的前沿与热点。本论文采用分子模拟方法研究离子液体的结构-性质关系，为其大规模工业应用提供科学基础，具有重要的理论和实际意义。论文的主要创新性工作及研究成果如下： (1) 氨基酸鏻类离子液体的分子力学力场与离子间氢键。在AMBER力场的基础上，通过添加与磷原子相关的参数并对其他参数进行优化调整，建立了14种氨基酸鏻类离子液体（[P(C4)4][AA]）的全原子力场。采用量子化学优化计算离子构型、红外振动频率、原子电荷和二面角扭转曲线。进行了两个温度下NPT系综的动力学模拟，利用密度、恒压热容等数据验证了力场的准确性。通过分析径向分布函数（RDF）来研究其微观结构，发现阴阳离子是通过氨基酸上的O2原子与四丁基磷上的HP原子之间形成氢键的方式结合在一起。阴离子中的氨基、羟基、酰胺基和羧基官能团上的H原子与羧酸根O2原子及羰基O原子形成氢键，从而影响了体系的动力学性质。 (2) 氨基酸咪唑类离子液体中的烷基链团簇现象。基于1-烷基-3-甲基咪唑[Cxmim]+ (x = 2, 4, 6, 10)阳离子和甘氨酸（[Gly]-）阴离子的力场，对氨基酸咪唑类离子液体进行了分子动力学研究。模拟计算[C2mim][Gly]的密度和膨胀率，用以验证了力场的适用性，并预测了其他3种离子液体的密度数据。考察了阴阳离子之间的作用，通过分析基团间径向分布函数发现了咪唑环周围阴离子及咪唑环的分布规律。阳离子上H原子与[Gly]-上O2原子之间的作用强度顺序为H5 > H4 > H1；按照阳离子种类为[C10mim]+ > [C6mim]+ > [C4mim]+ > [C2mim]+。通过对[Cxmim][Gly] (x = 2, 4, 6, 10)中的团簇现象进行考察，发现侧链上碳数≥4的都可能存在团簇，碳数越多，团簇程度越高。分析空间分布函数（SDF）发现，[Gly]-阴离子集中分布在沿咪唑C-H键指向的方向上。但是因为[Gly]-有着与[BF4]-、[PF6]-等不同的非对称结构，我们发现了一种常规离子液体中不存在的特殊现象，与一个阴离子相作用的部分阳离子咪唑环彼此靠近，且所在的平面相互平行。 (3) 双氨基咪唑类离子液体高粘特性的分子动力学解释。基于1-烷氨基-3-甲基咪唑[aCxmim]+ (x = 3, 5, 7)阳离子和[Gly]-阴离子的力场，研究了双氨基咪唑类离子液体。模拟计算了[aC3mim][Gly]的密度和膨胀率，通过与实验值对比验证了力场的适用性，并预测了[aC5mim][Gly]和[aC7mim][Gly]的密度数据。分析了阴阳离子间的相互作用，通过对径向分布函数的分析发现了咪唑环周围阴离子和咪唑环的分布规律。阳离子上H原子与[Gly]-上O2原子之间的作用强度顺序为H5 > H4 > H1；按照阳离子种类为[aC7mim]+ > [aC5mim]+ > [aC3mim]+。末端氨基的氢可以与阴离子上的氧形成强烈的氢键，从而限制了侧链转动的灵活性，因此该类离子液体具有极高的粘度。 (4) 离子液体萃取脱硫初探 —— 含硫化合物与咪唑类离子液体间相互作用及影响因素。研究发现，离子液体在燃料油脱硫中有着突出的表现。本文通过动力学模拟研究了咪唑类离子液体与含硫化合物之间的作用，这对萃取剂选择及设计都有一定的指导意义。选取二苯并噻吩（DBT）和5,5-二氧-二苯并噻吩（DBTO2）作为模型化合物，建立了相应的力场用以模拟。发现DBTO2中的O2原子与离子液体咪唑环上的H原子之间存在强烈的氢键作用，因此DBT被氧化为DBTO2之后更加容易通过萃取脱除。对不同阳离子烷基侧链碳原子数而言，H4*-O2 氢键的作用强度顺序为：[C10mim]+ > [C4mim]+ > [C8mim]+ > [C6mim]+。对于不同阴离子，如，[C10mim][PF6]和[C10mim][BF4]，前者O2和H4*间的作用强度明显强于后者。模拟结果对油品性质和剂油比及温度等条件有一定的指导意义。 |
| 英文摘要 | Recently room temperature ionic liquids (RTILs, ILs) have become the frontier and hot spot of the international green chemisty and chemical engineering. In this work, molecular simulations are performed to establish the relationships between structures and properties. It provides the scientific foundation for large scale industrial applications, and that is of great value for theory and practice. The major innovative research results are listed as follows. (1) Molecular force field and hydrogen bond for tetrabutylphosphonium amino acid ionic liquids. An all-atom force field was set up for a new class of the ionic liquids (ILs), tetrabutylphosphonium amino acid ([P(C4)4][AA]), on the basis of the AMBER force field with determining parameters related to the phosphorus atom and modifying on several parameters. Ab initio quantum chemical calculations were employed to obtain molecular geometries, infrared frequencies, atom charges and torsion energy profiles. Molecular dynamics simulation was carried out in the isothermal-isobaric ensemble for fourteen tetrabutylphosphonium amino acid ILs at two temperatures to validate the force field against the experimental densities and heat capacities at constant pressure. Moreover, radial distribution functions (RDF) were investigated to depict the microscopic structures of these ILs. Hydrogen in azyl, hydroxyl, acylamino and carboxyl groups of anions can form hydrogen bonds with O2 or O in different anions. The existed hydrogen bonds explains to some extent the low electrical conductivities and high viscosities of the studied [P(C4)4][AA] ILs. (2) Aggregation of imidazolium amino acid ionic liquids. A series of amino acid ILs were studied by molecular dynamics, based on the force field of [Cxmim]+ (x = 2, 4, 6, 10) cations and [Gly]- anion. Simulations were carried out in the isothermal-isobaric ensemble for four [Cxmim][Gly] (x = 2, 4, 6, 10) ILs at 298.15K. The [C2mim][Gly] was simulated at other two temperatures to calculate volme expansivity and heat capacity. The densities and volume expansivity of [C2mim][Gly] were in good agreement with the experimental results. The RDFs were studied to describe the local structures of these liquids. The site-site RDFs of the H atoms in cations and O2 in the anion reveal that the interaction between them is in the order H5 > H4 > H1 and [C10mim]+ > [C6mim]+ > [C4mim]+ > [C2mim]+. The rule of aggregation in [Cxmim][Gly] (x = 2, 4, 6, 10) was investigated in detail. Aggregation of the alkyl chains was observed in the ILs with alkyl side chains longer than or equal to C4. It can be found from the spatial distribution functions that the anion distributed at the above and below the imidazolium ring along the axis of the C-H bond. One [Gly]- anion maybe catch more than two imidazolium rings that would be align approximately parallel to each other and this unnormal structure might be caused by the special structure of [Gly]-. (3) Molecular simulations of high viscosities for double amino-functionalized imidazolium ionic liquids. A series of dual amino-functionalized imidazolium-based ILs were studied by molecular dynamics, based on the force field of [aCxmim]+ (x = 3, 5, 7) cations and [Gly]- anion. Simulations were carried out in the isothermal-isobaric ensemble for four [aCxmim][Gly] (x = 3, 5, 7) ILs at 298.15K. The [aC3mim][Gly] was simulated at other two temperatures to calculate volume expansivity and heat capacity. The densities and volume expansivity of [aC3mim][Gly] were in good agreement with the experimental results. The RDFs were studied to describe the local structures of these liquids. The site-site RDFs of the H atoms in cations and O2 in the anion reveal that the interaction between them is in the order H5 > H4 > H1 and [aC7mim]+ > [aC5mim]+ > [C3mim]+. Hydrogen in azyl of side chain can form strong hydrogen bonds with O2 in anions, that will significantly reduce the rotation freedom of side chain, so the viscosity of this kind ILs is very high. (4) Investigation of desulfurization by ionic liquids —— Interaction between sulfur compounds and imidazolium ionic liquds and desulfurization influences. Ionic liquids have shows an excellent performance for removing the sulfur compounds in the transportation fuel. In this work, molecular dynamic simulation is used to screen suitable ionic liquid instead of the “try and error” method which is very low efficiency and low accuracy. An all-atom force field was set up for dibenzothiophene (DBT) and dibenzothiophene 5,5-dioxide (DBTO2). They were used as model compounds to study the interaction between ILs and them. We depicted the interaction between model compounds and a serial of 1-alkyl-3-methylimidazolium ionic liquids (ILs) [Cxmim]+ (x = 4, 6, 8, 10). The results discovered that the oxygen atoms of DBTO2 form much stronger hydrogen bonds with the hydrogen atoms in imidazolium ring than that of DBTO2, which means DBTO2 is extracted by ILs more easily than DBT. Comparing the different ILs in this work has some active effects on selection of extractant. Besides, comparison of different sulfur contents, temperatures and containing water or not will help to control the amount of extractant and the operating condition. |
| 语种 | 中文 |
| 公开日期 | 2013-09-16 |
| 页码 | 139 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1312]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 周国辉. 离子液体的分子动力学模拟及应用[D]. 过程工程研究所. 中国科学院过程工程研究所. 2009. |
入库方式： OAI收割
来源：过程工程研究所
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