密度泛函理论在非极性纯流体表面性质研究中的应用

The density functional theory, simplified by the local density approximation and mean-field approximation, is applied to study the surface properties of pure non-polar fluids. A reasonable long rang correction is adopted to avoid the truncation of the potential. The perturbation theory is applied to establish the equation for the phase equilibrium, in which the hard-core chain fluid is as the reference fluid and the Yukawa potential is used as the perturbation term. Three parameters, elk, d and ms, are regressed from the vapor-liquid equilibria, and the surface properties, including density profile, surface tension and local surface tension profile are predicted with these parameters.     

AN EQUATION OF STATE FOR AQUEOUS ELECTROLYTE SYSTEMS——Prediction of The Solubility of Natural Gas in Formation Water

A new equation of state(PHSMSA EOS)based on perturbation theory is developed for calculating high-pressure phase equilibria of aqueous electrolyte systems containing supercritical gases,light hydrocarbons andpolar components.The binary interaction parameters are determined:for ion-ion pairs by regression of ionicactivity coefficient data;for molecule-molecule pairs by fitting the VLE data of binary nonelectrolyte mixtures;and for ion-molecule pairs by fitting the gas solubility data of ternary gas-water-salt systems.The new EOShas been tested on the prediction of solubilities of methane,nitrogen and natural gas mixtures in brine.Sat-isfactory agreement with the experimental data measured by authors and other investigators is observed.     

GC-MCSPT-A MODIFIED HARD-SPHERE THREE-PARAMETER EQUATION OF STATE WITH GROUP MODEL FOR VLE PREDICTION

1 INTRODUCTIONModels for calculating fluid phase equilibria can be classified into two categories,i.e.the excessGibbs energy model(or the activity coefficient model)and the equation-of-state model.Theformer has achieved a great success in correlating low-pressure phase equilibria of polarmixtures.However,its applicability in the field of high pressure has been limited due to thedifficulty to determine the standard state.     

酮麝香-二甲苯麝香双液相萃取结晶

To evaluate the effect of two liquid phase on the separation of musks mixture, the phase equilibria of musk ketone musk xylene dimethyl sulfoxide heptane system were studied for the first time. The whole and every part of the phase equilibrium for the quaternary system were shown by three-dimensional phase diagrams, the liquid-liquid equilibria, solid-liquid equilibria and solid-liquid-liquid equilibria of the quaternary system were also shown. As a result, the compositions of musks in the equilibrium liquid phases were different from those in the feed, that is, musk ketone was enriched in dimethyl sulfoxide phase while musk xylene was enriched in heptane phase. So these equilibrium liquid phases were useful in separating musk ketone and musk xylene. On the basis of these results, a new process “two liquid phase extractive crystallization” was proposed to separate the eutectics of musk ketone and musk xylene.     

NO_x Absorption in Full Scale Plant Columns with Structured Packings

A mathematical model of nitrogen oxide(NO_x)absorption is adopted and solved for adiabatic operation of a column with structured packings on the basis of the film theory.Removal rate,outlet concentration,oxidation degree of NO_x and outlet acid concentration,liquid acid temperature are simulated and tested.The gas phase reactions and equilibria,gas phase mass transfer,interracial equilibria,and liquid phase reactions are considered in the model.Absorption of nitrogen oxides is studied in packed with Mellapak 250Y columns in series in an industrial process of 20000 t oxalic acid per year.Favorable agreement is shown between the model predictions and the on-site observations.     

液丝破裂过程的VOF模拟

Study on pinching liquid filament in literature was reviewed. The breakup of liquid filaments under surface tension is governed by incompressible, two-dimensional (2-D), Navier-Stokes Equations. Surface tension was expressed via a CSF (continuous surface force) model that ensures robustness and accuracy. A new surface reconstruction scheme, alternative phase integration (API) scheme was proposed to solve the kinematic equation,and was compared with other three referential schemes. A general-purpose computer program has been developed for simulating transient, 2-D, incompressible fluid flows with free surface of complex topology. The transient behavior of breaking Newtonian liquid filaments under surface tension was simulated successfully using the developed program.The initial wave growth predicted using API-VOF (volume of fluid) scheme was in good agreement with Rayleigh‘‘s linear theory and one-dimensional (l-D) long-wave theory. Both long wave theory and two-dimensional (2-D) API-VOF model on fine meshes show that as time goes on, these waves pinch off large droplets separated by smaller satellite ones that decrease in size with decreasing wavelength. Self-similar structure during the breakup was found using 1-D and 2-D models, and three breakups were predicted for a typical case. The criterion of filament breaking predicted by the 2-D model is that the wavelength is longer than the circumference of a filament. The predicted sizes of main and satellite droplets were compared with published experimental measurements.     

用变阱宽方阱链流体状态方程模拟离子液体相行为

An equation of state (EOS) for square-well chain fluids with variable range (SWCF-VR) developed based on statistical mechanics for chemical association was employed for the calculations of pressure-volume-temperature (pVT) and phase equilibrium of pure ionic liquids (ILs) and their mixtures. The new molecular parameters for 23 ILs were obtained by fitting their experimental density data over a wide temperature and pressure ranges. The molecular parameters of ILs composed of homologous organic cation and an identical anion such as [Cxmim][NTf2] are good linear with respect to their molecular weight, indicating that the molecular pa-rameters of homologous substances, subsequently pVT and vapor-liquid equilibria vapor-liquid equilibria (VLE) can be predicted using the generalized parameter when no experimental data were available. The new set of parameters were satisfactorily used for calculations of the property of solvent and ILs mixture and the solubility of gas in various ILs at low pressure only using one tem-perature-independent binary interaction parameter.     

规整填料塔吸收NOx过程的模拟和实验研究

A mathematical model of nitrogen oxide （NOx） absorption is adopted and solved for adiabatic operation of a column with structured packings on the basis of the film theory. Removal rate, outlet concentration, oxidation degree of NOx and outlet acid concentration, liquid acid temperature are simulated and tested. The gas phase reactions and equilibria, gas phase mass transfer, interracial equilibria, and liquid phase reactions are considered in the model. Absorption of nitrogen oxides is studied in packed with Mellapak 250Y columns in series in an industrial process of 20000 t oxalic acid per year. Favorable agreement is shown between the model predictions and the on-site observations.     

EQUATIONS OF STATE FOR HARD-SPHERE CHAIN FLUIDS AND SQUARE-WELL CHAIN FLUIDS

Based on the statistical theory for chemical association,equations of state for hard-spherechain fluids(HSCFs)and square-well chain fluids(SWCFs)can be derived through the n-particlecavity correlation function(CCF)of the corresponding reference system,where n is the chain lengthor the number of segments of a chain molecule.The reference system is a fluid composed of only cor-responding monomers.In this work,the n-particle CCF is approximated by a product of effectivetwo-particle CCFs which accounts for correlations in nearest-neighbour and next-to-nearest-neighboursegment pairs.The CCFs for SWCFs may be expressed by a product of the corresponding functionfor HSCFs and a perturbation term originated from the square-well attractive potential.All these ef-fective two-particle CCFs and perturbation terms are density dependent.The dependence is determinedmainly by using computer-simulation results.The obtained equations can excellently describecompressibility factors and second Virial coefficients for HSCFs     

超临界流体色谱手性分离布洛芬

The separation method using chiral stationary phase （CSP） for the preparation of enantioselective compound was widely used. In this work, supercritical fluid chromatography（SFC） was proposed to resolve the chiral mixtures. To determine the optimum operating conditions for the chiral separation of the racemic ibuprofen, the retention factors and resolutions with the change in pressure, temperature and the content of IPA （%, by volume） in supercritical CO2 were investigated. Experiments showed that the retention factor decreased with the increase of pressure and decrease in temperature. The retention factor was also influenced by the content of IPA in mobile phase, as the content of IPA in the supercritical fluid increased, the retention factor decreased. The resolution of the enantiomers became worse with the increase of IPA in the supercritical fluid. Through optimizing the experimental conditions, a SFC procedure with 13MPa, 311.15K and 4% IPA in CO2 was obtained. The peak shape of the enantiomers was symmetric with supercritical fluid chromatography when compared to the asymmetric peak shape obtained by the conventional liquid chromatography. This work demonstrated that the developed supercritical fluid chromatography procedure was suitable for the chiral separation of ibuprofen enantiomers.     

用密度泛函理论研究非极性混合流体表面性质

应用密度泛函理论研究了二元非极性混合流体的表面性质.分子作为球形链处理,不同分子内的两链节相互作用以硬核Yukawa势能表示.为了避免计算中势能作用数值积分截断导致的误差,采用了合理的长程校正方法.根据微扰理论建立了流体的状态方程以计算汽液相平衡.从纯流体汽液相平衡数据回归得分子的链节作用参数ε/k、d和m_s,这些参数预测纯流体表面张力时可获得较好结果.继而引入混合参数k_ij表示不同分子链节作用情况,计算了6种非极性混合流体的汽液相平衡、表面张力、表面密度剖面.结果表明,本方法应用于二元非极性流体混合物时汽液表面张力计算值与实验值符合良好,同时显示某些二元混合流体表面区可能出现组分的相对富集现象.     

Nonrandom two-liquid activity coefficient model with association theory

Considered one of the most versatile and widely used classical thermodynamic models to correlate phase equilibria behavior of nonideal systems, the nonrandom two-liquid (NRTL) theory does not explicitly account for specific chemical associations such as hydrogen bonding. This deficiency has been recognized as the cause for unsatisfactory representation of association systems like methanol–alkanes binaries. This work presents a practical approach to integrate Wertheim's perturbation theory for association contribution with the classical NRTL model. Specifically, the association contribution is calculated from pre-determined molecule-specific association strengths while the physical interaction contribution is captured with NRTL binary interaction parameters. The resulting association NRTL model correlates fluid phase equilibria of association systems with few adjustable parameters and offers improved predictive capability for higher order systems.     

A practical equation of state for non‐spherical and asymmetric systems for application at high pressures. Part 1: Development of the pure component model

A practical, mathematically and computationally simple, equation of state (EOS) has been developed to accurately describe pure component phase behaviour of spherical and chain‐like molecules. The EOS consists of a newly developed hard sphere model and a perturbation term based on the Barker and Henderson approach using the Chen and Kreglewski intermolecular potential model and a double constrained summation as a mathematical expression thereof. The perturbed hard chain theory (PHCT) approach is used to extend the EOS to non‐spherical molecules. The EOS compares well with other more complex models such as the simplified perturbed hard chain theory (SPHCT) and statistically associating fluid theory (SAFT) models and will be extended to describe mixtures in Part 2 of this series. © 2011 Canadian Society for Chemical Engineering     

Calculation of complex phase equilibria in the critical region of fluid mixture based on multi-fluid lattice equation of state

Quantitative correlation of critical loci and multiphase behaviors has received considerable attention because the increased industrial importance of processes operating within the high-pressure region such as supercritical fluid extraction. However, in the critical region, classical thermodynamic models such as equations of state (EOS) frequently fail to correlate phase equilibrium properties. Recently, the present authors proposed a new lattice-hole EOS based on the multi-fluid approximation of the nonrandom lattice theory. The model requires only two molecular parameters reflecting size and interaction energy for a pure fluid and one additional interaction parameters for a binary mixture. In this work, the reliable applicability of the EOS was demonstrated to various phase equilibria of complex mixtures in the critical region. Demonstration of the EOS was made to calculate multiphase behaviors such as solid-liquidvapor (SLV) equilibria and critical loci of binary complex mixtures at high pressure. For P-T, P-x, and T-ρ phase diagrams tested, the model agrees well with experimental data. This paper was presented at the 8th APCChE (Asia Pacific Conferation of Chemical Engineering) Congress held at Seoul between August 16 and 19, 1999.     

High-pressure phase equilibria of systems carbon dioxide + n-eicosane and propane + n-eicosane

In this work we investigated the phase equilibrium behavior of the binary asymmetric systems propane (C3) + n-eicosane (C20) and carbon dioxide (CO₂) + n-eicosane (C20). We used a variable-volume view cell for obtaining fluid–fluid equilibrium (FFE), solid–fluid equilibrium (SFE) and solid–fluid–fluid equilibrium (SFFE) experimental data. We modeled the phase equilibria of both systems using the Peng–Robinson Equation of State for describing the fluid phases and an expression for the fugacity of pure solid n-eicosane with parameters fit to reproduce the pure n-eicosane melting line. We performed the phase equilibrium calculations by implementing path-following methods for tracking entire solid–fluid (SF) and solid–fluid–fluid (SFF) equilibrium curves for binary asymmetric mixtures. This made it possible to obtain complete isoplethic lines or complete three-phase equilibrium lines in single runs. Although the model is relatively simple, it is able to grasp the complex observed behavior for the systems studied here.     

微扰理论状态方程的发展现状

本文对近年来应用微扰理论和积分方程理论发展的半经验分子热力学状态方及其在非电解质和电解质溶液热力学性质及相平衡计算中的应用作了简要综述。     

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。     

High-pressure phase equilibria of systems carbon dioxide + n-eicosane and propane + n-eicosane

In this work we investigated the phase equilibrium behavior of the binary asymmetric systems propane (C3) + n-eicosane (C20) and carbon dioxide (CO₂) + n-eicosane (C20). We used a variable-volume view cell for obtaining fluid–fluid equilibrium (FFE), solid–fluid equilibrium (SFE) and solid–fluid–fluid equilibrium (SFFE) experimental data. We modeled the phase equilibria of both systems using the Peng–Robinson Equation of State for describing the fluid phases and an expression for the fugacity of pure solid n-eicosane with parameters fit to reproduce the pure n-eicosane melting line. We performed the phase equilibrium calculations by implementing path-following methods for tracking entire solid–fluid (SF) and solid–fluid–fluid (SFF) equilibrium curves for binary asymmetric mixtures. This made it possible to obtain complete isoplethic lines or complete three-phase equilibrium lines in single runs. Although the model is relatively simple, it is able to grasp the complex observed behavior for the systems studied here.