三元链状分子系统液液平衡的Monte Carlo模拟和分子热力学模型

在格子模型基础上,采用构型偏倚蒸发法（CBVM）对三元链状分子系统的液液平衡进行了Monte Carlo模拟,分别考查了分子链长和链节间相互作用参数对相区的影响。模拟发现,在保持交换能参数一定的情况下,互溶区随高分子之一的链长的增加而减小。在各组分链长不变的情况下,分相区随交换能的减小而增加。修正的Freed模型（RFT）可较满意地再现模拟结果,而Ftory—Huggins模型总是过低地估计互溶区。RFT模型可满意地关联和预测苯-庚烷-二甘醇系统的二元和三元液-液平衡数据。     

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.     

Phase behaviors of binary polymer solutions: The extended lattice fluid model

The generalized lattice–fluid (GLF) model is extended to predict phase behaviors of polymer/solvent systems. The GLF model gives some difficulties in describing liquid–liquid equilibria (LLE) of binary polymer solution systems due to general assumptions on its derivation. An extended lattice–fluid (ELF) model is proposed by introducing a new universal constant (C₀) and a model parameter (κ₁₁). The proposed model is then compared with experimental data for polymer/solvent systems and polymer1/polymer2 systems, which exhibit lower critical solution temperature (LCST) behaviors. Theoretical predictions and experimental results are in good agreement. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1143–1150, 1998     

用NRTL方程关联和预测离子液体-醇-水体系的液液相平衡

引 言 离子液体是指在室温或室温附近温度下呈液态的由离子构成的有机熔融盐,其特点是:几乎没有蒸气压,热稳定性好,大多数离子液体可以在高达300℃的温度范围内不分解,还对大量常见的有机物或无机物有良好的溶解性能,用离子液体替代传统的有机溶剂作为反应和分离的介质,也能有效地消除VOCs污染.因此,离子液体的研制和应用受到了广泛的关注[1-3].     

A molecular thermodynamic model for binary lattice polymer solutions

A molecular thermodynamic model for binary lattice polymer solutions with concise and accurate expressions for the Helmholtz energy of mixing and other thermodynamic properties is established. Computer simulation results are combined with the statistical mechanics to obtain the expressions. Yan et al.'s model for Ising lattice and the sticky-point model of Cumming, Zhou and Stell are incorporated in the derivation. Besides the nearest neighbor cavity correlation function obtained from the Ising lattice, the long range correlations beyond the close contact pairs are represented by a parameter λ, the linear chain-length dependence of which is obtained by fitting the simulated critical parameters of two systems with chain lengths of 4 and 200. The predicted critical temperatures and critical compositions, spinodals and coexistence curves as well as internal energies of mixing for systems with various chain lengths are in satisfactory agreement in comparison with the computer simulation results and experimental data indicating the superiority of the model over other theories. The model can serve as a basis to develop more efficient models for practical applications.     

On the predictive capabilities of CPA for applications in the chemical industry: Multicomponent mixtures containing methyl-methacrylate,dimethyl-ether or acetic acid

The predictive performance of the CPA (Cubic-Plus-Association) equation of state for applications relevant to the chemical industry is illustrated in this work. Three such applications inspired by industrial requests/interest are illustrated here, all of which involve aqueous multicomponent mixtures exhibiting vapor–liquid (VLE) and/or liquid–liquid (LLE) equilibrium. The first two cases include mixtures of methyl-methacrylate with acetone or methanol and dimethyl-ether with ethanol, respectively. In these two cases, the classical form of CPA is used. The third case involves aqueous mixtures with acetic acid, esters, ethers and alcohols, and in this case for water–acetic acid the CPA-Huron Vidal (CPA-HV) version of the model is used. For the latter binary mixture, new CPA-HV binary parameter sets are estimated using, among others, data for activity coefficients at infinite dilutions. The modeling approach is similar in all three cases, i.e. the binary parameters are solely fitted to binary data and thus all multicomponent calculations are considered predictions.It is shown that CPA correlations for binary systems are excellent in all cases using temperature independent parameters except for the acetic acid–water system for which different parameter sets at different temperatures can be recommended. Even with the use of CPA-HV mixing rules, modeling of the acetic acid–water system with few interaction parameters remains a challenging task. Excellent simultaneous VLE and LLE correlation is obtained for complex systems such as aqueous mixtures with ethers and esters. The multicomponent results are, with a few exceptions, very satisfactory, especially for the vapor–liquid equilibrium cases. For the demanding aqueous acetic acid–water containing systems, one parameter set is recommended at the end for modeling ternary or multicomponent mixtures containing acetic acid and water.     

Liquid–liquid equilibrium correlations using lattice fluid equation of state with hydrogen bonding

The nonrandom lattice equation of state with hydrogen bonding (NLF-HB EOS) was examined for the correlation of liquid–liquid equilibria (LLE) for binary alcohol and hydrocarbon mixture in a wide pressure range. For hydrocarbon + alcohol mixtures the consideration of a hydrogen-bonding term in the lattice equation of state clearly improves the prediction for vapor–liquid equilibrium (VLE) as shown in previous works, but the prediction of LLE is still in question. In this paper, LLE data for alcohols (methanol and ethanol) + hydrocarbons (n-hexane to n-hexadecane) were correlated by NLF-HB EOS and results were compared with a cubic equation of state (Peng–Robinson EOS with the T–K Wilson based G^E model). Both equations of state showed similar degree of accuracies but with different number of adjustable parameters. The Peng–Robinson EOS based approach requires six temperature dependent coefficients for accurate calculation whereas NLF-HB EOS requires only two temperature dependent coefficients. The effects of varying hydrogen-bonding energies for NLF-HB EOS are discussed.     

正丁醇-水-醋酸丁酯三元物系液-液平衡数据的测定、关联和预测

测定了由正丁醇、水和醋酸丁酯形成的三元物系及部分互溶二元物系在20℃、30℃和40℃的LLE(液液平衡)数据,并与文献中已有的正丁醇-水的LLE实测数据核对,说明了测定方法的可靠性.用NRTL和UNIQUAC方程分别进行了三元和二元LLE数据的关联和预测.根据溶液热力学特性对二元LLE模型参数进行了鉴别.在三元LLE数据的关联中,对两种目标函数(摩尔分数和分配系数)进行了比较,并对前一种目标函数中的权重取值问题进行了考察.通过对部分互溶二元物系参数的评选,提高了利用二元参数对三元物系进行预测的准确度.     

DETERMINATION,CORRELATION AND PREDICTION OF LIQUID-LIQUID EQUILIBRIUM DATA OF n-BUTYL ALCOHOL-WATER-BUTYL ACETATE TERNARY SYSTEM

Liquid-liquid equilibrium(LLE)data have been determined for the n-butyl alcohol-water-butyl acetateternary system and the related binary systems at 293.15,303.15 and 313.15 K.The experimentally determinedLLE data for the n-butyl alcohol-water binary system have been found to be in satisfactory agreementwith the available literature data.The correlation and prediction of the LLE data have been done byusing NRTL and UNIQUAC models.The model parameters of binary systems have been identified witha thermodynamic criterion.In the correlation of ternary LLE data,two objective functions(mole fractionand distribution constant)have been used for purpose of comparison.The effect of weighting in the firstobjective function has been examined.In predicting the ternary LLE with different sets of parameter valuesobtained for each of the constitutent binary systems,improved prediction results have been obtained bycomparing the results of different combinations of the sets of parameter values and choosing those givingthe best result.     

UNIFAC模型法计算含己内酰胺体系的相平衡(英文)

An extended liquid-liquid equilibrium (LLE) UNIFAC model is proposed to describe phase equilibria of mixtures containing caprolactam. In this model, caprolactam is introduced as a new group. New group interaction parameters are calibrated from 156 sets of liquid-liquid equilibrium data. The present model gives satisfactory correlation and prediction in liquid-liquid equilibrium, including quaternary systems containing the mixed solvent of an alcohol and an alkane. The model can be applied to predict caprolactam solubility in water and benzene accurately. Freezing point and vapor-liquid equilibrium of binary systems containing caprolactam are also predicted with the extended LLE UNIFAC model. Satisfactory prediction results are obtained.     

Modelling of polymerization kinetics and molar mass development in the nitroxide-mediated polymerization (NMP) of styrene in supercritical carbon dioxide using the PC-SAFT equation of state

A mathematical model for polymerization kinetics and molar mass development in the nitroxide-mediated polymerization (NMP) of vinyl monomers in supercritical carbon dioxide (scCO₂) has been developed. The method of moments is used for molar mass development. The perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state is used to estimate the number of stable phases present at equilibrium in the reaction mixture, critical number average chain length at which polymer particles are formed, and monomer concentration in each phase. Pure and binary PC-SAFT interaction parameters are estimated from liquid–liquid equilibrium (LLE) and liquid–vapour equilibrium (LVE) experimental data at 60 to 129°C. The effect of pressure on monomer conversion and molar mass development in the polymerization of styrene (Sty) using benzoyl peroxide (BPO) and 2,2,6,6-Tetramethylpiperidinyl-1-oxyl (TEMPO) at 120°C and 300–500 bar is studied. It was observed that increasing pressure increases polymerization rate without significantly affecting molar mass development.     

Representation of vapor–liquid and liquid–liquid equilibria for binary systems containing polymers: Applicability of an extended flory–huggins equation

For some binary systems, an extended Flory–Huggins equation is applicable to both vaporliquid equilibria (VLE) and liquid–liquid equilibria (LLE) using the same adjustable parameters. New LLE and VLE data are reported for polystyrene (PS) (MW = 100,000)/cyclohexane and for poly(ethylene glycol) (PEG) (MW = 8,000)/water. Experimental results for the PS/cyclohexane system agree well with the semiempirical model, whereas those for PEG/water do not, probably because, for PEG/water, the temperature range of the VLE data is about 55°C lower than that of the LLE data. Excellent fits were obtained for our previously published experimental results for PS/cyclohexane (upper critical solution temperature, UCST), PS/ethyl acetate (lower critical solution temperature, LCST), PS/tert-butyl acetate and PS/methyl acetate (both UCST and LCST), and PEG/water (closed-loop). The semiempirical model also fits well with new data obtained for the polymer blend PS/poly(vinyl methyl ether). © 1993 John Wiley & Sons, Inc.     

A molecular model for correlating vapor-liquid equilibrium of propane+hydrocarbon mixtures

Simple analytical expressions are proposed for the calculation of the equilibrium pressure and the mole fractions of both liquid and vapor phases of propane+hydrocarbon binary mixtures. The new proposed expressions are based on a simple analytical expression for the vapor pressure of pure non-polar fluids, which, for a given temperature, only requires as input the values of the Lennard-Jones molecular parameters and the acentric factor. A properly modified Lorentz-Berthelot mixing rule is used, the interaction parameters being given as simple functions of the temperature and concentration with eight constants for each binary mixture. A different model is proposed to calculate the vapor mole fraction in which four appropriate constants are needed for each mixture. Here, it is shown how the models can reproduce accurately and straightforwardly the vapor liquid equilibrium properties (pressure, liquid mole fraction, and vapor mole fraction) of binary mixtures containing propane.     

状态方程模拟醇胺系统的密度和汽液相平衡

通过考虑醇胺分子间的缔合作用,结合先前开发的非缔合变阱宽链流体状态方程(SWCF-VREOS)建立了一个缔合方阱链流体状态方程,并利用方程模拟了醇胺系统的密度和汽液相平衡。通过关联不同温度下醇胺的饱和蒸气压和液体体积得到了18种醇胺流体的分子参数,新方程计算的饱和蒸气压和液体密度总的平均误差分别为0.94%和0.88%。结合简单的混合规则,将此方程扩展到混合系统。研究发现,建立的方程可预测二元和三元醇胺混合物的密度。当引入一个与温度无关的可调参数时,方程能满意关联二元系统的汽液相平衡数据,并可进一步预测多元混合系统的汽液相平衡,预示着新方程可模拟醇胺系统的相行为。     

醇/烃系统的分子热力学(Ⅱ)1-2-4模型应用于汽液平衡

建立了1个醇/烃系统的分子热力学模型,用红外光谱法获得的醇的标准缔合常数应用于汽液平衡,能够很好地区分醇类缔合物质的化学作用和物理作用,所得化学参数和物理参数具有明确的物理意义.计算表明:本文提出的1-2-4缔合模型在应用1个二元可调参数的情况下能较好地描述含醇系统的汽液平衡性质.即使对于不同链长的正构醇采用统一的缔合常数,同样可获得较好的结果.     

Microwave dielectric relaxation and molecular dynamics in binary mixtures of poly(propylene glycol) 2000 and poly(ethylene glycol)s of varying molecular weight in dilute solution

Molecular dynamics of binary mixtures of poly(propylene glycol) (PPG) and poly(ethylene glycol)s (PEGs) of varying molecular weight due to molecular interactions, chain coiling and elongation in dilute solution under various conditions, ie varying number of monomer units of PEG, method of mixing of polymers and solvent environment, has been explored using microwave dielectric relaxation times. The average relaxation time τ_o, relaxation time corresponding to segmental motion τ₁ and group rotations τ₂, of a series of binary mixtures of poly(propylene glycol) 2000 and poly(ethylene glycol) of varying molecular weight (ie PPG 2000 + PEG 200, PPG 2000 + PEG 300, PPG 2000 + PEG 400, and PPG 2000 + PEG 600 mixed by equal volume in the pure liquid states, and PPG 2000 + PEG 1500, PPG 2000 + PEG 4000 and PPG 2000 + PEG 6000 mixed equal weights in solvent) have been determined in dilute solution in benzene and carbon tetrachloride at 10.10 GHz and 35 °C. A comparison of the results of these binary systems of highly associating molecules shows that the molecular dynamics corresponding to rotation of a molecule as a whole and segmental motion in dilute solutions are governed by the solvent density when the solutes are mixed in their pure liquid state. Furthermore, the molecular motion is independent of solvent environment when the polymers are added separately in the solvent for the preparation of binary mixtures. It has also been observed that there is a systematic elongation of the dynamic network of the species formed during mixing of pure liquid polymers in lighter environment of solvent with increasing PEG monomer units, while the elongation behaviour of the same species in the heavier environment of carbon tetrachloride solvent is in contrast to the elongation behaviour of the polymeric species formed in pure PEG. The role of rotating methyl side‐groups in the PPG molecular chain has been discussed in term of the breaking and reforming of hydrogen bonds in complex polymeric species for the segmental motion. In all these mixtures, the relaxation time corresponding to group rotations is independent of the solvent environment and constituents of the binary mixtures. The effect of chain flexibility and coiling in these binary mixtures is discussed by comparing the relaxation times of the mixtures with their individual relaxation times in dilute solutions measured earlier in this laboratory. © 2001 Society of Chemical Industry     

Molecular thermodynamic analysis for phase transitions of linear and cross-linked poly(N-isopropylacrylamide) in water/2-propanol mixtures

Ternary liquid–liquid phase transitions of linear poly(N-isopropylacrylamide) (PNIPA) and the swelling behavior of cross-linked PNIPA gels in water/2-propanol mixtures were investigated using thermo-optical analysis (TOA) and a photon correlation spectroscopy (PCS) technique, respectively. Closed immiscibility gaps in ternary phase diagrams were obtained below 35 °C although all binary mixtures involved in this system were completely miscible. At a fixed concentration of PNIPA (1.0 wt%), a decrease in the lower critical solution temperature (LCST) occurred first, and with an increasing 2-propanol fraction of the solvent mixture, the upper critical solution temperature (UCST) subsequently developed. Corresponding to the linear PNIPA solution behavior, swollen PNIPA gels in pure water first shrank and then reswelled with increasing 2-propanol content in a typical reentrant transition. For theoretical treatment of the mixtures, a multi-component lattice theory of mixing and Flory–Rehner chain model for elasticity were employed for molecular thermodynamic analysis. A secondary lattice concept of specific interactions was used to model binary water/PNIPA solutions, and a temperature dependence of the intermolecular interactions for 2-propanol/PNIPA was used to describe island type ternary phase diagrams. The swelling transitions of cross-linked PNIPA gels were calculated using model parameters obtained from the ternary phase diagrams of linear PNIPA or from experimental conditions. The predicted results were in good agreement with experimental data without the need for further adjustable parameters.