C_8芳烃异构体+异丙醇或叔丁醇体系的恒压汽液平衡

这是为了较好地解决高效分离混合二甲苯所进行的一项基础性研究。准确测定了 0 .0 999MPa压力下邻、间、对二甲苯或乙苯 +异丙醇或叔丁醇八个体系的恒压汽液平衡数据 ,计算了该压力下八个体系中二组分的活度系数 ,作出了各体系的汽液平衡曲线及活度系数曲线 ,并讨论所呈现的规律。     

Wax phase equilibria: developing a thermodynamic model using a systematic approach

Reservoir hydrocarbon fluids contain heavy paraffins that may form solid phases of wax at low temperatures. Problems associated with wax formation and deposition are a major concern in production and transportation of hydrocarbon fluids. The industry has directed considerable efforts towards generating reliable experimental data and developing thermodynamic models for estimating the wax phase boundary.The cloud point temperature, i.e. the wax appearance temperature (WAT) is commonly measured in laboratories and traditionally used in developing and/or validating wax models. However, the WAT is not necessarily an equilibrium point, and its value can depend on experimental procedures. Furthermore, when determining the wax phase boundary at pipeline conditions, the common practice is to measure the wax phase boundary at atmospheric pressure, then apply the results to real pipeline pressure conditions. However, neglecting the effect of pressure and associated fluid thermophysical/compositional changes can lead to unreliable results.In this paper, a new thermodynamic model for wax is proposed and validated against wax disappearance temperature (WDT) data for a number of binary and multi-component systems. The required thermodynamic properties of pure n-paraffins are first estimated, and then a new approach for describing wax solids, based on the UNIQUAC equation, is described. Finally, the impact of pressure on wax phase equilibria is addressed.The newly developed model demonstrates good reliability for describing solids behaviour in hydrocarbon systems. Furthermore, the model is capable of predicting the amount of wax precipitated and its composition. The predictions compare well with independent experimental data, demonstrating the reliability of the thermodynamic approach.     

Weak molecular associations investigated by 1H-NMR spectroscopy on a neat organosiloxane-solvent mixture

The rational design of new sensitive materials for chemical sensors relies on the knowledge of molecular interactions between the chemical species in question with compounds that may potentially be present in the gas phase. In this context, the intermolecular interactions between a family of functionalized polysiloxanes and a series of organic compounds have been investigated. This work addresses the problem of determining the association constant or energy by studying neat liquid mixtures without solvents. An original approach has been proposed to obtain such information from the excess function of the difference in chemical shifts between both interacting species. Data obtained as a function of the composition of the mixtures have been fitted according to two models: either by considering the formation of a 1:1 complex governed by an equilibrium constant or by the existence of a local composition following the Wilson model. Both methods have been tested on model compounds and the results have been compared with solubility enthalpies calculated using Hansen coefficients.     

The surface tension of a solid at the solid-vacuum interface, an evaluation from adsorption and wall potential calculations

A method for the evaluation of quantities that are experimentally inaccessible such as the surface tension at the solid-vacuum interface and the superficial tension of the fluid in contact with the solid is presented. The approach is based on consideration of an equilibrium of a fluid in solid capillary wherein a balance between surface and capillary forces has been replaced by conceptual alternative interfacial and centrifugal forces. This approach involves the simultaneous numerical solution one the special forms of the Gibbs equation for solid-fluid interface and a generalized Kelvin equation derived earlier. The latter equation takes into account interactions between the solid thick cylindrical wall and confined fluid, this body-body interaction potential has been primarily calculated using the Lennard-Jones (6-12) expression for the atom-atom pair potentials and expressed by hypergeometrical functions having good convergences. All numerical calculations shown here have been performed for the model graphite-argon system at 90 K. Finally, an analysis of the accuracy of the proposed method is considered.     

Perturbed-chain equation of state for the solid phase

A perturbed chain equation of state for the solid phase has been derived. Although the equation is general with respect to intermolecular potential, we incorporate the Lennard-Jones potential in this work in order to compare results from the model with available Monte Carlo simulation data. Two forms of the radial distribution function for the hard-sphere solid chain reference state are used in the model. First, a theoretically rigorous approach is taken by using a correlation of actual solid-phase Monte Carlo hard-sphere chain data for the radial distribution function. This results in good agreement with the Monte Carlo data only at high density. Second, a simple extended-density approximation was used for the radial distribution function. This second approach was found to work well across the entire density range including the vicinity of the solid-fluid equilibrium.     

A thermodynamically consistent kinetic framework for binary nucleation

The traditional theory for binary homogeneous nucleation follows the classical derivation of the nucleation rate in the supposition of a hypothetical constrained-equilibrium distribution in the calculation of the cluster evaporation rate. This model enables calculation of the nucleation rate, but requires evaluation of the cluster distribution and cluster properties for an unstable equilibrium with supersaturated vapor. An alternate derivation of the classical homomolecular nucleation rate eliminated the need for this nonphysical approximation by calculating the evaporative flux at full thermodynamic equilibrium. The present paper develops that approach for binary nucleation; the framework is readily extended to ternary nucleation. In this analysis, the evaporative flux is evaluated by applying mass balance at full thermodynamic equilibrium of the system under study. This approach eliminates both the need for evaluating cluster properties in an unstable constrained-equilibrium state and ambiguity in the normalization constant required in the nucleation-rate expression. Moreover, it naturally spans the entire composition range between the two pure monomers. The cluster fluxes derived using this new model are similar in form to those of classical derivations, so previously developed methods for evaluation of the net nucleation rate can be applied directly to the new formulation.     

Extended Veytsman statistics for the solid–fluid transition in the framework of lattice fluid

Lattice fluid can describe a vapor–liquid transition but not a solid–fluid transition. In this work, we propose a simple and analytic term which yields a solid–fluid transition when coupled with a lattice based equation of state (EOS). The proposed term is derived based on the two assumptions that (1) solid can be considered as highly associated phase affected by strong attractive force and (2) this force is distinct from the conventional attractive forces yielding a vapor–liquid transition. To formulate these assumptions, we extend Veytsman statistics by modifying its density dependency. The derived term was combined with a quasi-chemical nonrandom lattice fluid theory (QLF) developed by the authors. The combined model was found to require only two parameters besides 3 QLF parameters for physical properties calculation of three phases. When tested against equilibrium properties of 8 components, the combined model was found to closely reproduce melting pressure, sublimation pressure, and vapor pressure, but underestimate solid density as well as heat of melting at the triple point temperature. It was found that the present approach can yield a solid–liquid transition at all temperatures.     

Thermodynamic Study of Solid–Liquid Equilibrium in NaCl–NaBr–H<Subscript>2</Subscript>O System at 288.15 K

The solubility data, composition of the solid solution and refractive indices of the NaCl–NaBr–H₂O system at 288.15 K were studied with the isothermal equilibrium dissolution method. The solubility diagram and refractive index diagram of this system were plotted at 288.15 K. The solubility diagram consists of two crystallization zones for solid solution Na(Cl,Br) · 2H₂O and Na(Cl,Br), one invariant points cosaturated with two solid solution and two univariant solubility isothermal curves. On the basis of Pitzer and Harvie-Weare (HW) chemical models, the composition equations and solubility equilibrium constant equations of the solid solutions at 288.15 K were acquired using the solubility data, the composition of solid solutions, and binary Pitzer parameters. The solubilities calculated using the new method combining the equations are in good agreement with the experimental data.     

Ternary phase equilibria for the sodium chloride–sodium sulfate–water system at 200 and 250 bar up to 400°C

Phase equilibria in the NaCl–Na₂SO₄–H₂O system were investigated at 200 and 250 bar for total salt concentrations ranging from 5 to 20 wt.% total salt over temperatures ranging from 320 to 400°C. In addition to providing data for this ternary system, the experiments also added information on the phase behavior of the two binary systems: NaCl–H₂O and Na₂SO₄–H₂O. For salt mixture compositions which were rich in sodium sulfate, a solid phase was observed to nucleate from the homogeneous liquid phase. Salt mixture compositions which had a high fraction of sodium chloride exhibited a vapor separation from a homogeneous liquid phase. By fitting curves to the solid–liquid and vapor–liquid separation temperatures, the temperature and composition of a constrained invariant point where liquid, solid salt and vapor are in equilibrium were estimated. These estimates were performed at discrete compositions of 5, 10, 15 and 20 wt.% total salt at pressures of 200 and 250 bar. The temperature and composition of the invariant point increased with increasing pressure following a simple thermodynamic model for boiling point elevation in a nearly ideal solution.     

Reaction and phase equilibria of esterification of isoamyl alcohol and acetic acid at 760 mm Hg

The thermodynamic behavior of esterification reaction equilibrium and vapor–liquid equilibrium (VLE) of acetic acid and isoamyl alcohol mixture and its products, isoamyl acetate and water were investigated in this study. The experiments of chemical and phase equilibria were conducted in an Othmer type equilibrium cell. Since this esterification reaction proceeds very slowly, thus, a commercial Y type zeolite, NaY catalyst, was added to accelerate reaction rate such that the reaction equilibrium will be reached sooner and before phase equilibrium is considered. Using experimental data and phase and reaction equilibrium equations, the reaction equilibrium constants were calculated at different temperatures. The experimental results showed that the reaction equilibrium constant was very slightly dependent on temperature. The experimental data were then correlated by the Wilson, NRTL, and UNIQUAC models with the consideration of association effect of acetic acid in vapor phase. The concept of transformation composition by Barbosa and Doherty [D. Barbosa, M.F. Doherty, 1987, Proc. R. Soc. London Ser. A 413, 443–459.] was applied to construct three-dimensional figures showing experimental data and the calculated composition surfaces. It is observed from figures that the reactive azeotropy described by Barbosa and Doherty does not exist for this quaternary mixture. This study provides the required thermodynamic information for the development and design of this esterification process.     

Application of Liquid State Models for the Time Efficient Phase Equilibrium Calculation of Supercritical CO2 and H2O at High Temperatures and Pressures

There are numerous models available to compute phase equilibrium composition of supercritical CO₂ and H₂O at high temperatures and pressures. In this paper a different approach is proposed where liquid state models (LSM) are used following liquid–liquid equilibrium (LLE) flash calculation in order to obtain phase compositions (solubility of CO₂ in the H₂O rich phase and that of H₂O in the CO₂ rich phase). Four LSM (two two-parameter models UNIQUAC and LSG, and two three-parameter models NRTL and GEM-RS) are investigated. The original forms of these models are inappropriate to represent the literature values; the binary interaction parameters are related with both pressure and temperature. These modified versions are suitable to generate phase composition values within 2–7 % deviation. Further investigations show that the LLE calculation is more time efficient than vapor–liquid equilibrium computation, meaning our approach can save computational expense for the numerical simulation of CO₂ flows in a reservoir. Comparison of the time efficiency of these LSM models with respect to other equations of state is given.     

二组分气体在固体上吸附的研究(Ⅵ)──不同覆盖度下的二组分气体在灯黑上的吸附

通过测定不同覆盖度下的甲苯-正己烷、苯-正己烷、丙酮-正已烷和正戊烷-正己烷4个二组分气体在灯黑上的组成吸附等温线,发现它们有着共同的规律:随着覆盖度的增加,各体系的组成吸附等温线都向上靠近它们各自的气液平衡曲线。因此,基本上可以把二组分的气相与吸附相的平衡看成二组分的气液平衡,4个体系的组成吸附等温线基本上都可以通过理想溶液的相对挥发度方程式模拟得到。     

Markov chain model of mixed surfactant systems

A new model of mixed surfactant systems have been developed in the work presented. It includes two parameters only connected directly with the Gibbs free energy of the surfactant aggregation. They can be determined using both the aggregation equilibrium constant values or the phase composition data. It has been shown also the relation between these new parameters and the same of the regular solution approximation and the alternative models. The possibility to describe the available experimental information about the micelle composition as a function of the singly dispersed surfactant mixture composition better than by the other models has been shown also.     

Effects of condensed-phase transitions in congruently vaporizing systems

When a binary system A _xB_(1 − x) vaporizes congruently, the composition of the equilibrium vapor is such that the atom fractions of the elements entering the vapor are the same as those in the condensed phase. With temperature, the congruently vaporizing composition may vary continuously or may change discontinuously when a condensed-phase transition occurs. Such variations in the congruently vaporizing composition can be detected by monitoring the composition of the vapor phase. Condensed-phase transitions can cause anomalous vaporization behavior such as inverse dependence of vapor pressure on temperature or even increase in vapor pressure at constant temperature, as well as drastic changes in the composition of the vapor with temperature. However, such occurrences might be missed or dismissed as spurious if consideration be given only to data which follow Clausius–Clapeyron straight lines. This paper illustrates these points with results reported in the literature for three binary systems Ga/S, Ga/Se, and Mn/Te. Certain effects associated with phase transitions in these systems are discussed in detail. Other systems in which anomalous effects might occur are discussed in brief. The potential of high-temperature mass spectrometry for the study of such effects is highlighted.     

A robust numerical model for characterizing the syngas composition in a downdraft gasification process

This study proposes a numerical model developed to characterize the chemical composition, heating value and temperature of the syngas produced by a downdraft gasifier fueled with residual biomasses. The process of gasification is essentially described through a global reaction that includes all the gaseous species and the yields of char and tar.The syngas chemical composition has been obtained solving a set of equations that are mass and energy balances, methanation and the water-gas shift reactions, which govern the gasification process. The proposed model was calibrated and validated through the comparison with two sets of experimental data. The comparison between the results of simulation and the experimental data has shown a very good agreement that allows pointing out the capability of the model to characterize the syngas composition and the temperature of the producer gas.Moreover, the performed sensitivity analysis shows the influence of moisture content and equivalent ratio on the chemical composition, equilibrium temperature and heating value of the producer gas.     

有效模拟原油中高分子有机烃类沉降量方法

用大的交互作用系数描述沥青与原油中轻烃不相容性的程度,根据沥青组分特征化方法,导出了气-液-沥青三相相平衡物料平衡方程组。用沥青沉降三相闪蒸数值算法进行有效的量化模拟计算。结合实例分析,给出了沥青参考逸度的计算、饱和压力和沉降量的拟合方法。     

Fluid phase stability and equilibrium calculations in binary mixtures: Part I: Theoretical development for non-azeotropic mixtures

A framework is proposed for the solution of fluid phase equilibrium (P–T flash) for binary mixtures described by equations of state of general form. The framework is based on decomposing the phase equilibrium problem into sub-problems with more convenient and tractable mathematical and numerical properties. Systematic procedures are used to identify the mapping of the problem in the density and composition space, referred to as the density–composition pattern, at specified temperature and pressure. A series of stability tests is then carried out to explore the existence or non-existence of phases. Once the existence of a phase has been determined, the limits of stability and physical bounds on the problem are used to define the search area for that phase in the density–composition pattern. Finally, all available information from this detailed analysis is used for the solution of phase equilibrium between the phases identified in order to find the stable state at the specified conditions. The features of the proposed approach are exposed in detail through an algorithm for the fluid phase equilibria of the augmented van der Waals equation of state applied to non-azeotropic mixtures.     

Reliable phase stability analysis for asymmetric models

A deterministic technique for reliable phase stability analysis is described for the case in which asymmetric modeling (different models for vapor and liquid phases) is used. In comparison to the symmetric modeling case, the use of multiple thermodynamic models in the asymmetric case adds an additional layer of complexity to the phase stability problem. To deal with this additional complexity we formulate the phase stability problem in terms of a new type of tangent plane distance function, which uses a binary variable to account for the presence of different liquid and vapor phase models. To then solve the problem deterministically, we use an approach based on interval analysis, which provides a mathematical and computational guarantee that the phase stability problem is correctly solved, and that thus the global minimum in the total Gibbs energy is found in the phase equilibrium problem. The new methodology is tested using several examples, involving as many as eight components, with NRTL as the liquid phase model and a cubic equation of state as the vapor phase model. In two cases, published phase equilibrium computations were found to be incorrect (not stable).