Atomistic simulation of the thermodynamic and transport properties of ionic liquids

Atomistic simulations have emerged in recent years as an important compliment to experiment for understanding how the properties of ionic liquids are controlled by their underlying chemical structure. The ability to obtain reliable thermodynamic and transport properties from a simulation depends both on the quality of the force field and on the use of a proper simulation method. Properties such as densities and heat capacities may be obtained readily using standard techniques. With more effort and advanced simulation methods, solid-liquid and vapor-liquid phase equilibria may also be determined. Transport properties can also be computed, but the notoriously slow dynamics of many ionic liquid systems means that great care must be taken to ensure that the simulations are accurate.     

Dynamic method for computation of chemical and phase equilibria

A generalized approach for the calculation of complex chemical and phase equilibria is presented that is based on the simulation of the dynamic evolution of a mixture from non-equilibrium initial composition towards the final equilibrium composition. The proposed method is able to solve pure chemical or phase equilibria as well as simultaneous chemical/phase equilibria. The advantage of our approach compared to conventional equilibrium calculations is the fact that the approach is physically motivated and can handle chemical and phase equilibria as well as simultaneous chemical and phase equilibria.     

水合物法分离H2+CH4体系的模拟计算

This paper presents two novel conceptions in multi-stage hydrate separation technology for H2 CH4 system, i.e. the multi-stage equilibria adsorption and the reaction adsorption. It is assumed that there already exists clathrate structure before the hydration reaction, and the hydration reaction is taken as gaseous adsorption in the crystal structure of hydrate. During the simulation of multi-stage equilibria adsorption, gases and water interact on every equilibrium stage till establishing full equilibria, wherein the gases that just entered one stage are in equilibrium with the liquid phase of the previous stage, and the water that just entered one stage is in equilibrium with the gas phase of the previous stage as well. A kinetic model of hydrate growth for methane is introduced into the reaction adsorption so that this simulation is closer to the reality. As hydrogen doesn‘t react with water to form hydrate, the amount of hydrogen adsorption is calculated according to the proportion of methane and hydrogen adsorbed in the small cavities. Simultaneously, the plate column is employed as an example, where the gas-hydrate phase loads and hydrogen mole fraction are calculated by the multi-stage equilibria adsorption and reaction adsorption methods, and the results calculated by the two said methods are compared.     

Molecular thermodynamics approach on phase equilibria of dendritic polymer systems

We suggest a molecular thermodynamic framework to describe the phase behavior of dendritic polymer systems. The proposed model, which is based on the lattice cluster theory, contains correlations of molecular structure and specific interactions such as hydrogen bonding to the phase equilibria of branch-structured polymer systems. We examine liquid-liquid equilibria (LLE) of hyperbranched polymer solutions and vapor-liquid equilibria (VLE) of dendrimer solutions in the viewpoints of effects of a branched structure and specific interaction formations among endgroups of dendritic polymer and solvent molecules. We investigate VLE of dendrimer/solvent (Benzyl Ether Dendrimer/Toluene) systems by the combination of a new lattice-based model and atomistic simulation technique. The interaction energy parameters are obtained by the pairs method [Baschnagel et al., 1991] including Monte Carlo simulation with excluded volume constraint. In the pairs method [Baschnagel et al., 1991], we do not simulate the whole molecule as in molecular dynamics or molecular mechanics, but only monomer segments interacting with solvent molecules. The proposed model shows improvements in prediction for both phase equilibria (VLE and LLE) due to the branched structure and specific interaction due to endgroups at periphery of dendritic polymer molecule. Atomic simulation technique gives good result in prediction without fitting variables. Our results show that the specific interactions between the endgroup and the solvent molecule play an important role in phase behavior of the given systems.     

一个反应-三相恒沸精馏系统的模拟研究——(Ⅰ)醋酸-乙醇-水-醋酸乙酯四元体系的热力学模型和计算

本文提供醋酸—乙醇—水—醋酸乙酯四元体系的热力学模型和计算方法,为带反应器的恒沸精馏计算所需的相平衡和热量平衡计算提供方法和依据.该四元体系的液相具有强极性,在一定温度下分层;气相存在醋酸分子缔合.除醋酸外的其它三组分间存在三元或二元共沸物.计算模型考虑到这些特点.ASOG模型用于计算活度系数,并与UNIFAC模型作了比较.用经验方法处理醋酸分子在气相中的缔合.热力学性质的计算结果与实验数据(共150组)在合理的误差范围内吻台.本文的模型和方法用于带反应器的精馏塔计算时可拟合实际生产数据.     

Berechnung und Modellierung komplexer Phasen- und Reaktionsgleichgewichte in wäßrigen Elektrolytlösungen

In many natural and industrial processes the thermodynamic properties of aqueous electrolyte solutions play an important role. Systems of interest are frequently characterized by a large number of components and possible reactions. Due to low solubility, some reaction products precipitate as solids. The thermodynamic modelling therefore implies the computation of simultaneous phase and chemical equilibria. The minimization of the Gibbs free energy and the K-value method are powerful algorithms for numerical computation and permit the simulation of complex electrolyte systems. The behaviour of the liquid solution has to be described by suitable activity coefficient models.     

Phase equilibria in polydisperse colloidal systems

Many materials containing colloids or polymers are polydisperse: they comprise particles with properties (such as diameter, charge, or polymer chain length) that depend continuously on one or several parameters. This effectively infinite number of distinguishable particle species makes the theoretical prediction of phase equilibria a highly non-trivial task. We give an overview of recent progress, focussing on the “moment free energy” method which reduces the problem to one involving only the densities of a finite number of quasi-species. Applications to isotropic–nematic phase equilibria of rod-like particles and to the phase behaviour of polydisperse hard spheres are described.     

含醇系统的汽液平衡的缔合模型

本文将无限线性缔合模型和ＲＫ方程式相结合建立了含醇系统的热力学模型，对含醇系统进行了相平衡计算。结果表明：对于纯物质，本模型在广阔的温度、压力范围内能描述ＰＶＴ关系；对于醇－醇系统和醇－烃系统，该模型仅需要一个物理作用参数就能获得与活度系数法大致相当的结果。     

PREDICTION OF PHASE EQUILIBRIA IN BINARY MIXTURES USING AN IMPROVED EQUATION OF STATE AND A THEORETICALLY CONSISTENT MIXING RULE

Prediction of thermodynamic properties and phase equilibria in fluid mixtures using a simple cubic equation of state is still a challenging problem. In this paper, we have predicted vapor/ liquid phase equilibria of several binary fluid mixtures using our previously developed improved Peng-Robinson equation of state and a theoretically consistent mixing rule. Our mixing rule combines the mixing rule of Wong-Sandier with a physically based combination rule. Mixtures are composed of nonpolar, nonassociating polar and associating polar fluids. Comparisons of theoretical predictions with experimental data show a very good performance of our approach in describing vapor/liquid phase equilibria of several mixtures, namely, carbon dioxide/ propane, ethane/hexane, butane/methanol, benzene/methanol, acetone/methanol, methanol/ ethanol, methanol/1-butanol, methanol/water and ethanol/water.     

Unified equation of state based on the lattice fluid theory for phase equilibria of complex mixtures part II. Application to complex mixtures

In part I of the present article [Yoo et al., 1995], new rigorous and simplified lattice-fluid equations of state (EOS) were derived and their characteristic features of the molecular thermodynamic foundation were discussed by applying to pure fluids. In this part II, both EOSs were extended to various phase equilibrium properties of mixtures. Comparison of the models with experimental mixture data ranges from density, to equilibria of vaporliquid, vapor-solid and liquid-liquid phases for nonpolar/nonpolar, nonpolar/polar, polar/polar mixtures. Both models were also applied to supercritical fluid phase equilibria and activities of solvents in polymer solutions. With two temperature dependent parameters for pure compounds and one temperature-independent binary interaction energy parameter for a binary mixtures, results obtained to date illustrated that both EOSs are quantitatively applicable to versatile phase equilibria of mixtures over a wide range of temperatures, pressures and compositions.     

Alumina Region of the Lithium Aluminosilicate System: A New Window for Temperature Ultrastable Materials Design

Revisiting classic phase diagrams and chemical phase relations in the solid state of a very well‐studied oxide system, such as the lithium aluminosilicate (LAS) system, can open a new window for the design of new advanced materials with improved properties. Crystal chemistry and phase equilibria are used to demonstrate the ability to design materials with particular desired properties in the alumina‐rich corner of the LAS phase diagram. The experimental results demonstrate the alumina and β‐eucryptite solid‐state compatibility.     

Messmethoden für Gasphasen‐Adsorptionsgleichgewichte

Measuring Techniques for Gas‐Phase Adsorption Equilibria As basic information for the design of technical adsorption processes at least the adsorption equilibria data of all pure components need to be known. These information are usually given as adsorption isotherms, i.e. the adsorption equilibrium is given as a function of the gas phase pressure or the concentration of the adsorbed component in a carrier gas at constant temperature. Adsorption equilibria data are mostly measured isothermal by changing the properties pressure or concentration. This article reviews the most commonly used techniques for the measuring of adsorption equilibria and the pros and cons for each method are discussed and compared. The second part focuses on gravimetric measurements of adsorption equilibria using magnetic suspension balances. This type of equipment allows the measuring of adsorption data over a large pressure‐ and temperature‐range and thus covers the relevant range for engineering technology purposes.     

用重整化群理论研究硬核Asakura-Oosawa流体的相平衡

An analytical equation of state (EOS) for hard core Asakura-Oosawa (AO) fluid is established by combining the AO potential, the first-order perturbation theory and the radial distribution function (RDF) for the hard sphere fluid.The phase equilibria are studied by using the renormalization-group (RG) theory. The obtained results agree well with the simulation data. Investigation shows that the attractive range parameter plays an important role in the phase equilibria for AO fluid.     

Gibbs系综蒙特卡罗方法模拟相平衡研究进展

Gibbs系综蒙特卡罗方法（简称GEMC）作为一种计算纯物质及混合物相平衡的模拟手段已经发展得较为成熟。本文描述了GEMC方法的基本原理和发展概况,介绍和评价了与GEMC方法紧密相关的力场,以第六届工业流体性质模拟挑战赛结果为例说明了GEMC模拟方法的有效性,并分类评述了国内外GEMC方法用于纯物质和混合物物系相平衡数据计算的发展情况。同时指出了GEMC方法的局限性,并展望了其未来的发展 趋势。     

应用广义简约梯度算法增强遗传算法求解化工冶金相平衡

研究可靠的相平衡计算对化工冶金过程有很重要意义,本文采用广义简约梯度法（GRG）来增强遗传算法（GA）用于相平衡计算过程,在遗传算法演化快结束时引入GRG算子,演化结束后使用GRG精修结果,克服了GA局部搜索能力不强的缺点,加快了搜索速度.KCl-FeCl₂体系相平衡计算结果显示这种混合算法（Hybrid Algorithms）能够提高GA效率的同时保留了全局收敛的优点,因此其在化工冶金相平衡计算中将有广泛的应用前景.     

混合物临界区域热力学性质研究进展

对近期混合物临界区域热力学性质的研究作了综述,介绍了混合物临界点和临界区域相平衡的实验测定及关联计算,对临界区域热力学性质的研究作了讨论。     

Predicting fluid phase equilibrium via histogram reweighting with Gibbs ensemble Monte Carlo simulations

One of the most challenging areas to which molecular simulation has contributed significantly over the last decades is without a doubt the accurate and efficient prediction of fluid phase equilibria. In this work we combine two of the most powerful methods that have greatly enhanced our ability to simulate accurately fluid phase equilibria: (a) the “Gibbs ensemble” method (A.Z. Panagiotopoulos, Molecular Physics 61 (1987) 813-826) and (b) the multiple histogram method (A.M. Ferrenberg, R.H. Swendsen, Physical Review Letters 61 (1988) 2635-2638). The result of such combination is a simple and very accurate method of predicting fluid phase equilibrium close to and away from the critical point.     

Phase equilibria of mixtures containing CO2 and organic acids using the UMR-PRU model

The UMR-PRU model, which has been successfully tested in the past to the predictions of different type of phase equilibrium and thermodynamic properties in binary and multicomponent systems, is applied in this work to phase equilibria in mixtures containing CO₂ and organic acids. New interaction parameters are determined by fitting only binary vapor–liquid equilibrium data and then they are used to predict the vapor–liquid, solid–gas and solid–liquid–gas equilibria in CO₂/organic acid systems. Furthermore, the UMR-PRU model with the newly derived interaction parameters is applied to the prediction of the phase equilibrium in ternary mixtures consisting of CO₂, organic acids and water. Satisfactory results are obtained in all cases.     

On the information and methods for computing phase equilibria and thermodynamic properties

The Helmholtz free energy or an equation of state relating temperature, pressure, volume and composition plays a key role in the calculation of phase equilibria and thermodynamic properties. Such information is usually available for vapor, partially available for liquids, and rarely available for solids. Depending on the information available, different methods are used for properties calculation. In this study, various methods were systematically presented and their relations with available information were comprehensively discussed.