超临界正己烷—甲醇溶液体系的Monte Carlo模拟：浓度对溶液构型？…

用Ｍｏｎｔｅ Ｃａｒｌｏ分子模拟方法对正己烷－甲醇溶液体系处于临界状态时微观结构随浓度变化的情况进行了研究。模拟采用随机边界条件，得到了不同浓度条件下体系各基团的径向分布函数。结果表明，在溶液临界状态，正己烷分子有较强的聚集行为，随着溶液中甲醇浓度的变大，正己烷分子的聚集程度逐渐下降；甲醇分子周围正己烷分子的分布有一个最佳的浓度范围，在甲醇浓度为２２．５％时，配位数达到最大；超临界正己烷－甲醇溶液     

超临界相CO加氢合成甲醇,异丁醇的研究

以正十一～十三烷的混合物为超临界介质,在反应温度３６０～４１０℃、合成气压力７５ＭＰａ、进气空速１７００ｈ－１、介质压力１７８ＭＰａ、总压９３ＭＰａ的实验条件下,研究了固定床反应器中Ｚｎ－Ｃｒ、Ｃｕ－Ｚｎ－Ｃｒ催化剂在超临界相和气相条件下合成甲醇、异丁醇的性能。结果表明,超临界相反应的ＣＯ转化率高于气相反应。在超临界条件下反应,醇类选择性随着温度升高下降较慢,而气相反应醇类选择性随着温度升高下降较快。气相反应产物以甲醇、异丁醇为主,含少量乙醇和正丙醇,超临界相反应的产物分布与气相反应的明显不同,甲醇含量减少,乙醇、正丙醇和异丁醇都有不同程度增加。超临界流体的存在对合成醇链增长有影响,在不同催化剂上的产物分布有较大差异     

超临界正己烷甲醇溶液体系的 Monte Carlo 模拟──浓度对溶液构型影响的考察

用ＭｏｎｔｅＣａｒｌｏ分子模拟方法对正己烷－甲醇溶液体系处于临界状态时微观结构随浓度变化的情况进行了研究。模拟采用随机边界条件，得到了不同浓度条件下体系各基团的径向分布函数。结果表明，在溶液临界状态，正己烷分子有较强的聚集行为，随着溶液中甲醇浓度的变大，正己烷分子的聚集程度逐渐下降；甲醇分子周围正己烷分子的分布有一个最佳的浓度范围，在甲醇浓度为２２．５％时，配位数达到最大；超临界正己烷－甲醇溶液中甲醇分子的作用在不同浓度条件下具有不同的特点，当甲醇浓度较低时，甲醇分子之间有氢键的作用，随着甲醇浓度的提高，甲醇分子之间氢键的作用变得越来越弱，而且分子的取向变得越来越无序。     

低碳醇合成中异丁醇形成机理及提高其收率的途径

在压力１０ＭＰａ，温度３６０～４２０℃，尾气空速３０００～７０００ｈ￣（－１）的反应条件下，采用分别富集甲醇、乙醇、正丙醇和异丙醇的方法，研究Ｚｎ－Ｃｒ－Ｋ氧化物催化剂上异丁醇的形成机理，并探讨利用甲醇循环提高其收率的可能性。结果表明，低碳醇的形成是以碳链增长形式进行的，ＣＯＨ→ＣＣＯｏＨ慢的α－加成反应是链增长的起始步骤，也是低碳醇合成反应的控制步骤，β－加成是生成低碳醇的特征反应，ＣＯＨ→ＣＣＯＨ→ＣＣＣＯＨ→ＣＣ（ＣＨ＿３）ＣＯＨ是异丁醇的形成机理。甲醇富集对提高异丁醇收率有明显的促进作用，采用甲醇循环技术提高异丁醇收率是可行的。     

甲醇-正己烷和甲醇-环己烷溶液构型的分子模拟

用Ｍｏｎｔｅ Ｃａｒｌｏ分子模拟方法研究了不同温度条件下甲醇－正已烷、甲醇－环已烷溶液体系微观结构的变化情况。模拟表明，无论是甲醇－正已烷体系，还是甲醇－环已体系，在其溶液的近临界区，甲醇周围溶剂介质的密度最小，而甲醇分子之间的积聚最为明显。通过对氢健分析的结果表明，在溶液临界区，氢键作用与非氢键作用的距离不可区分。     

水、甲醇和乙醇液体微结构性质的Car-Parrinello 分子动力学模拟

采用Car-Parrinello 分子动力学(CPMD)方法分别研究了水、甲醇和乙醇的液体微结构性质.研究结果显示:在水、甲醇和乙醇三个体系中O…O径向分布函数曲线的第一个峰位置分别为0.278、0.276 和0.275nm; O…H径向分布函数曲线的第一个峰位置分别为0.178、0.176和0.177 nm.表明基团(氢原子、甲基、乙基)的差异对O…O第一个峰的位置影响很小.但基团的差异对径向分布函数峰高的影响却很显著,由水到乙醇第一个峰的高度逐渐变高.空间分布函数表明氧原子和氢原子在溶剂分子周围有取向地分布,这与径向分布函数所表现出尖锐的第一个峰相一致.氢键分布分析显示,水、甲醇和乙醇的平均氢键数分别为3.62、1.99 和1.87,表明水形成了网状氢键结构,而甲醇、乙醇形成链状氢键结构.     

Zr-Mn-K催化剂超临界相合成甲醇与异丁醇的研究

用共沉淀法和超临界流体干燥法,分别制备了Ｚｒ－Ｍｎ－Ｋ沉淀型催化剂和超细催化剂．以正十一～十三烷的混合物为超临界介质,在反应温度３６０～４１０℃、合成气压力７．５ＭＰａ、ＧＨＳＶ１７００ｈ－１及介质压力２．０８ＭＰａ的实验条件下,分别考察了超细催化剂和沉淀催化剂的气相和超临界相催化合成气制甲醇、异丁醇的性能．气相和超临界相反应的研究均表明,超细催化剂催化合成异丁醇的活性高于沉淀催化剂;在超临界条件下反应,超细催化剂上产物的异丁醇含量较高（为２３％～３２％）,甲醇含量为２２％～３３％,其它醇均在１０％左右．气相与超临界相反应结果的对比显示,超临界流体促进产物的脱附与传递,提高了ＣＯ的转化率．但超临界流体对甲烷的萃取作用强于对醇的萃取,醇选择性低于气相反应．在超临界条件下合成甲醇、异丁醇仍遵循异丁醇形成的链增长机理,超临界流体改变了链增长各步骤的相对速度,致使超临界相反应的产物分布不同于气相反应的产物分布．     

甲醇在超临界环已烷中形成簇团的Monte Carlo初探

用Ｍｏｎｔｅ Ｃａｒｌｏ方法研究了甲醇－环己烷体系的微观结构随压力（密度）的变化情况，结果表明，在临界区域甲醇分子的聚集最为明显，形成的甲醇团簇尺寸最大，溶剂分子在甲醇周围的局部密度则在低于临界区或亚临界区较大。     

定标粒子理论预测乙醇－水体系汽液平衡盐效应

测定了７０℃下３个１－１型电解质（ＮａＣｌ、ＮａＢｒ、ＫＣｌ）在各种不同浓度的乙醇－水体系中的汽液平衡盐效应参数，并给出用定标粒子理论计算盐效应参数的方法。硬球作用项采用Ｍａｓｔｅｒｔｏｎ－Ｌｅｅ方程，软球作用项采用胡英的径向分布函数。分子间力在Ｌｅｎｎａｒｄ－Ｊｏｎｅｓ位能函数基础上计入偶极－偶极、偶极－诱导偶极、电荷－偶极、电荷－诱导偶极的贡献，其中离子－分子间的静电作用项仅限于规则排列的第一配位圈之内。将混合溶剂的局部介电常数视为液相浓度的函数，函数关系由实验拟合。在乙醇浓度变化的很大范围内，３个体系的预测与实验结果基本相符。     

正十六烷体系凝固过程的分子动力学模拟

采用分子动力学模拟的方法,根据体系热容和自扩散系数的突变,计算了正十六烷体系以及正十六烷和降凝剂α-辛基萘、α-十二烷基萘及α-十六烷基萘等α-烷基萘混合体系的凝点,凝点降低结果与实验值相一致.用径向分布函数及末端距离分布对凝固温度附近体系的微观结构变化进行了研究.结果表明,凝固过程中正十六烷分子倾向于转变成为全反式的构象,以利于分子间平行有序的排列,这和熵减小的原理相一致.结合正十六烷的构象变化,探讨了烷基萘降凝的机理.     

星形胶束自由能和聚集数的理论分析

ＡＢ型嵌段聚合物在选择性溶剂中将发生微相分离,形成一种球形胶束[1].所谓选择性溶剂是指此溶剂仅能溶解共聚物中某一链段,而对另一链段则为不良溶剂.对这一体系的实验研究是从80年代兴起的,主要采用现代测试技术来表征形成胶束的回转半径[2],动力学半径[3]、聚集数[4]和临界胶束浓度[5].从分子图景上看来,这种球形胶束包括两部分,内核(Ｃｏｒｅ)为密堆砌的链段Ａ;壳层(Ｃｏｒｏｎａ)为溶涨的链段.Ｈｅｌｆａｎｄ等[6]最早利用数值计算法来研究嵌段聚合物在本体中的微相分离的问题;Ｌｅｉｂｌｅｒ等[7]将此方法引入嵌段聚合物/均聚物体系.…     

Partial molar volume and solvation structure of naphthalene in supercritical carbon dioxide: a Monte Carlo simulation study

Monte Carlo simulations were used to investigate the solvation of naphthalene in supercritical carbon dioxide at a temperature of 308.38 K just above the solvent's critical temperature and at pressures of 74.6, 79.7, 87.8, and 310.2 bar covering a range from just below to far above the solvent's critical pressure and at a slightly elevated temperature of 318.15 K and a pressure of 93.0 bar. The Monte Carlo simulations were carried out in the isobaric-isothermal ensemble and employed the transferable potentials for phase equilibria (TraPPE) force field. Systems containing 2000 carbon dioxide molecules and from 0 to 4 solute molecules were used for all five state points, and additional simulations with 16 000 solvent molecules were carried out at the lower temperature and p = 79.7 bar. In agreement with experiment, the simulations yield large, negative partial molar volumes of naphthalene near the critical pressure at 79.7 bar, with values of -4340 +/- 750 and -3400 +/- 620 cm(3) mol(-1) for the 2000 and 16 000 molecule systems, respectively. Structural analysis through radial distribution functions and the corresponding number integrals yields good agreement with neutron diffraction data and shows evidence for a long-range density enhancement around solutes but lacking any specific solute-solvent clustering. Solvatochromic shifts estimated from the local solvent structure correlate well with the experimental data over the entire pressure range.     

梯度折射率聚合物细棒的制备和数学模拟

在聚甲基丙烯酸甲酯 (Poly(methylmethacrylate) ,PMMA)管中 ,加入单体甲基丙烯酸甲酯 (Methylmethacrylate ,MMA)和另一种高折射率的掺杂剂溴苯 (Bromobenzene ,BB) ,用界面凝胶均聚合方法制备了梯度折射率聚合物光纤预制棒 .这种光纤预制棒的梯度折射率是通过具有不同折射率的分子扩散而形成的 .通过对界面凝胶聚合过程的描述 ,该工作讨论了预制棒中聚合物的浓度分布及边界条件的假设 .并根据自由体积理论对其折射率分布进行理论模拟 .将得到的折射率抛物线分布与实验结果进行对比 ,结果表明聚合浓度的分布为ω =a(r/R) 2 +b时 ,理论预计的光纤预制棒的折射率分布与实验结果有着较好的符合 .同时 ,对聚合体系中BB对聚合物浓度分布的影响进行了讨论     

Aggregation of CO2 and Organic Liquid Molecules at Near Critical and Supercritical Condition of CO2

In order to study the aggregation of CO₂ and organic liquid molecules in the binary systems of CO₂+ organic liquid at near critical and supercritical condition of CO₂, the radial distribution function of CO₂-organic liquid molecules and organic liquid–organic liquid molecules in the liquid phase of the CO₂+ organic liquid systems is calculated by molecular dynamic simulation in this work and compared with the results of our previous works. The results of the research show that the aggregates of CO₂–CO₂ molecules, CO₂-organic liquid molecules and organic liquid–organic liquid molecules are coexisted in the liquid phase of CO₂+ organic liquid system, respectively.     

Phase diagram and high-pressure boundary of hydrate formation in the ethane-water system

Dissociation temperatures of gas hydrate formed in the ethane-water system were studied at pressures up to 1500 MPa. In situ neutron diffraction analysis and X-ray diffraction analysis in a diamond anvil cell showed that the gas hydrate formed in the ethane-water system at 340, 700, and 1840 MPa and room temperature belongs to the cubic structure I (CS-I). Raman spectra of C-C vibrations of ethane molecules in the hydrate phase, as well as the spectra of solid and liquid ethane under high-pressure conditions were studied at pressures up to 6900 MPa. Within 170-3600 MPa Raman shift of the C-C vibration mode of ethane in the hydrate phase did not show any discontinuities, which could be evidence of possible phase transformations. The upper pressure boundary of high-pressure hydrate existence was discovered at the pressure of 3600 MPa. This boundary corresponds to decomposition of the hydrate to solid ethane and ice VII. The type of phase diagram of ethane-water system was proposed in the pressure range of hydrate formation (0-3600 MPa).     

Spatial hydration structures and dynamics of phenol in sub- and supercritical water

The hydration structures and dynamics of phenol in aqueous solution at infinite dilution are investigated using molecular-dynamics simulation technique. The simulations are performed at several temperatures along the coexistence curve of water up to the critical point, and above the critical point with density fixed at 0.3 g/cm3. The hydration structures of phenol are characterized using the radial, cylindrical, and spatial distribution functions. In particular, full spatial maps of local atomic (solvent) density around a solute molecule are presented. It is demonstrated that in addition to normal H bonds with hydroxyl group of phenol, water forms pi-type complexes with the center of the benzene ring, in which H2O molecules act as H-bond donor. At ambient conditions phenol is solvated by 38 water molecules, which make up a large hydrophobic cavity, and forms on average 2.39 H bonds (1.55 of which are due to the hydroxyl group-water interactions and 0.84 are due to the pi complex) with its hydration shell. As temperature increases, the hydration structure of phenol undergoes significant changes. The disappearance of the pi-type H bonding is observed near the critical point. Self-diffusion coefficients of water and phenol are also calculated. Dramatic increase in the diffusivity of phenol in aqueous solution is observed near the critical point of simple point-charge-extended water and is related to the changes in water structure at these conditions.     

Dispersion Property of CO2 in Oil. Part 3: Aggregation of CO2 Molecule in Organic Liquid at Near Critical and Supercritical Condition of CO2

To study the dispersion property of CO₂ in organic liquids, the solubility of CO₂, the volume of CO₂ + organic liquids under different pressure at 318.15 K were measured and the radial distribution function of CO₂ molecule aggregate in the organic liquids was calculated by molecule dynamic simulation. The results show that the aggregate of CO₂ molecules in the organic liquids is formed obviously; the aggregation and disperse property of CO₂ molecule in the organic liquids is affected by the structure and polarity of the organic molecule at near critical and supercritical condition of CO₂ dominantly.     

Analysis of Decomposition for Structure I Methane Hydrate by Molecular Dynamics Simulation

Under multi-nodes of temperatures and pressures, microscopic decomposition mechanisms of structure I methane hydrate in contact with bulk water molecules have been studied through LAMMPS software by molecular dynamics simulation. Simulation system consists of 482 methane molecules in hydrate and 3027 randomly distributed bulk water molecules. Through analyses of simulation results, decomposition number of hydrate cages, density of methane molecules, radial distribution function for oxygen atoms, mean square displacement and coefficient of diffusion of methane molecules have been studied. A significant result shows that structure I methane hydrate decomposes from hydrate-bulk water interface to hydrate interior. As temperature rises and pressure drops, the stabilization of hydrate will weaken, decomposition extent will go deep, and mean square displacement and coefficient of diffusion of methane molecules will increase. The studies can provide important meanings for the microscopic decomposition mechanisms analyses of methane hydrate.     

Monte Carlo Simulation of the Local Ordering of Water Molecules. II. Spatial Correlations and Hydrogen Bonds

The Monte Carlo method is used to calculate spatial distribution functions of oxygen and hydrogen atoms within a large-size water model (33666 SPC/E water molecules) under atmospheric pressure at room temperature. The work focuses on structural interpretation of local densities of water at the distances of about 3–5 Å from its molecules. The distribution of the distances between water molecules connected by chains of two or more hydrogen bonds indicates that the molecules between the first and second peaks of the radial distribution function (RDF) are mainly second and, to a lesser extent, third neighbors along the chain of bonds.     

Structure and dynamics of the hydration shells of the Al3+ ion

First principles simulations of the hydration shells surrounding Al3+ ions are reported for temperatures near 300 degrees C. The predicted six water molecules in the octahedral first hydration shell were found to be trigonally coordinated via hydrogen bonds to 12 s shell water molecules in agreement with the putative structure used to analyze the x-ray data, but in disagreement with the results reported from conventional molecular dynamics using two-and three-body potentials. Bond lengths and angles of the water molecules in the first and second hydration shells and the average radii of these shells also agreed very well with the results of the x-ray analysis. Water transfers into and out of the second solvation shell were observed to occur on a picosecond time scale via a dissociative mechanism. Beyond the second shell the bonding pattern substantially returned to the tetrahedral structure of bulk water. Most of the simulations were done with 64 solvating water molecules (20 ps). Limited simulations with 128 water molecules (7 ps) were also carried out. Results agreed as to the general structure of the solvation region and were essentially the same for the first and second shell. However, there were differences in hydrogen bonding and Al-O radial distribution function in the region just beyond the second shell. At the end of the second shell a nearly zero minimum in the Al-O radial distribution was found for the 128 water system. This minimum is less pronounced minimum found for the 64 water system, which may indicate that sizes larger than 64 may be required to reliably predict behavior in this region.