Properties of supercritical N2, O2, CO2, and NH3 mixtures from the virial equation of state

We report virial coefficients up to sixth order in density for N₂ , O₂ , NH₃ , and CO₂ , covering temperatures from 50 to 1,000 K. The reported values include coefficients and their first three temperature derivatives, for the pure species as well as all of those needed to evaluate full composition dependence of mixtures formed from any or all of these compounds. The values are obtained by calculation of appropriate cluster integrals using Mayer sampling Monte Carlo, with intermolecular interactions described by the Transferable Potential for Phase Equilibria (TraPPE) force field. All coefficients are fit as a function of temperature, yielding a thermodynamic model with analytic dependence on temperature, density, and composition. The coefficients and properties computed from them are compared to experimental data where available.     

A modified perturbed chain-statistical associating fluid theory equation of state for water which includes an association dependent hard sphere diameter

The concept of an association dependent hard sphere diameter is introduced as a means to obtain an accurate perturbed chain-statistical associating fluid theory (PC-SAFT) equation of state model for water. The new approach is demonstrated to be a step change in accuracy for the representation of pure water properties as compared with standard PC-SAFT applications. Extension of the approach to mixtures is discussed.     

Computational screening of metal‐organic frameworks for xenon/krypton separation

A variety of metal‐organic frameworks (MOFs) with varying linkers, topologies, pore sizes, and metal atoms were screened for xenon/krypton separation using grand canonical Monte Carlo (GCMC) simulations. The results indicate that small pores with strong adsorption sites are desired to preferentially adsorb xenon over krypton in multicomponent adsorption. However, if the pore size is too small, it can significantly limit overall gas uptake, which is undesirable. Based on our simulations, MOF‐505 was identified as a promising material due to its increased xenon selectivity over a wider pressure range compared with other MOFs investigated. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Liquid‐liquid phase split in ionic liquid + toluene mixtures induced by CO2

High pressure carbon dioxide was dissolved in ionic liquid + toluene mixtures to obtain the conditions of pressure and composition where a liquid‐liquid phase split occurs at constant temperature. Ionic liquids (ILs) with four different cations paired with the bis(trifluoromethylsulfonyl)imide ([Tf₂N]^?) anion were selected: 1‐hexyl‐3‐methylimidazolium ([hmim]⁺), 1‐hexyl‐3‐methylpyridinium ([hmpy]⁺), triethyloctylphosphonium ([P₂₂₂₈]⁺), and tetradecyltrihexylphosphonium ([P₆₆₆₁₄]⁺). The solubility of CO₂ was measured in the liquid mixtures at temperatures between 298 and 333 K and at pressures up to 8 MPa, or until the second liquid phase appeared, for initial liquid phase compositions of 0.30, 0.50, and 0.70 mole fraction of IL. Ternary isotherms were compared with the binary solubility of CO₂ in each IL and pure toluene. The lowest pressure for separating toluene in a second liquid phase was achieved by decreasing the temperature of the system, increasing the amount of toluene in the initial liquid mixture and using [hmim][Tf₂N]. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2968–2976, 2015     

K2CO3-Na2CO3-H2O三元体系288 K相平衡研究

采用等温溶解平衡法研究了三元体系K2 CO3 -Na2 CO3 -H2 O 2 88K时的相平衡及平衡液相的主要物化性质 (密度 ,电导率 ,pH)。研究发现 :该三元体系有复盐NaKCO3 ·6H2 O形成 ,根据溶解度数据绘制了相图 ,相图中有 2个共饱点E、F ,三条单变度曲线AE、BF、EF ;平衡固相分别为K2 CO3 ·3/ 2H2 O、Na2 CO3 ·10H2 O、NaKCO3 ·6H2 O。实验结果表明K2 CO3 对Na2 CO3 有强烈的盐析作用 ;并简要讨论了实验结果。     

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.     

Modeling of adsorption isotherm of a binary mixture with real adsorbed solution theory and nonrandom two‐liquid model

Gas‐phase adsorption equilibria of diluted mixtures of methyl‐ethyl‐ketone and isopropylanol on activated carbon were investigated. Experimental isotherms were determined by a constant volume method. Single‐component adsorption isotherms were fitted by the frequently used Toth model with good accuracy. Then adsorption isotherms were determined for different binary mixtures (with different initial ratio of the two components). Binary mixtures adsorption isotherms were calculated using the adsorbed solution theory. Ideal adsorbed solution theory (IAST) could not represent experimental data, but it was observed that increasing amount of MEK led to higher nonideality of the mixture. Then UNIversal QUAsi Chemical (UNIQUAC) and nonrandom two‐liquids (NRTL) models were considered to describe activity coefficients of the adsorbed phase. The fitted parameters of UNIQUAC model depend on the ratio of the two components, whereas the NRTL model is able to fit all experiments with the same parameters, whatever the initial ratio may be. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Predicting the Solubility of Solid Phenanthrene: A Combined Molecular Simulation and Group Contribution Approach

A simple correction to the infinite dilution activity coefficient computed via molecular simulation for a nonelectrolyte solid solute in solution is proposed. The methodology adopts the concept that the activity coefficient may be fundamentally interpreted as a product of a residual and combinatorial term. The residual contribution is assumed to be insensitive to concentration, and the combinatorial term is modeled using the athermal Flory–Huggins theory. The proposed method uses only properties for the solute computed at infinite dilution to estimate solution‐phase properties at finite concentrations. Properties of the pure solid solute are estimated using the group contribution method of Gani and coworkers, allowing for efficient blind solubility predictions to be made. The method is applied to predict the solubility of solid phenanthrene in 17 different solvents. For all cases, the combinatorial correction lowers the predicted solubility relative to the infinite dilution approximation, and in general, improves agreement with experiment. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2647–2661, 2013     

超临界二氧化碳-乙醇二元体系的高压相平衡

High-pressure phase behavior of supercritical (SC) CO2 ethanol system was investigated at 333.2 K,348.2K, 353.2K, 368.2K, 413.2K and 453.2K and pressure from 2.0MPa to 14.3MPa. The measurement was carried out in a cylindrical autoclave with a moveable piston and a window for adjustment and observation of phase equilibria at given T and p. The samples were taken from two coexisting phases and were analyzed to obtain their compositions. It is shown that the solubility of SC CO2 in ethanol increases drastically with pressures at the given temperature, but the content of ethanol in CO2-rich phase increase faintly.     

Adsorption thermodynamics of CO2 on nitrogen-doped biochar synthesized with moderate temperature ionic liquid

The purpose of this work was to investigate the thermodynamic characteristics of carbon dioxide (CO₂) adsorption on a promising nitrogen-doped biochar at constant temperature and isopiestic pressure. The biochar was prepared as a CO₂ adsorbent based on catalytic pyrolysis of pristine coconut shells using urea as the nitrogen source and moderate temperature ionic liquid as a catalyst. The results showed that CO₂ adsorption on the biochar was a spontaneous, dominantly physical, exothermic, and entropy decrement process that could be well described by the slip model and the dual-site Langmuir model. Those thermodynamic parameters, including interface potential, exhibited a series of interesting tendencies with the changes in adsorption temperature and pressure. Under the conditions of 273 K and 100 kPa, the adsorption capacity and the interface potential were 4.6 mmol/g and −16.7 J/g, respectively. And the site energy ranged from 2.57 to 5.13 kJ/mol in the test conditions, which became narrow with increasing temperature. The temperature exhibited positive effects on interface potential, enthalpy change, entropy change, enthalpy change, internal energy change but negative effects on adsorption capacity, Gibbs free energy change, and Helmholtz free energy change. Interestingly, the pressure exhibited the opposite effect trends. The peak pressure with maximum temperature effect at a given temperature and the peak temperature with maximum pressure effect at a given pressure were found to exist for some thermodynamic parameters. These exhibited a different but significantly beneficial perspective to understand the mass and energy transfer during CO₂ adsorption on the biochar at constant temperature and isopiestic pressure, which have rarely been reported before.     

Estimation of thermodiffusion coefficients in ternary associating mixtures

Following the non‐equilibrium thermodynamics formulation and taking into account the complexities in the structure of aqueous associating mixtures, expressions are proposed to estimate the thermodiffusion coefficients in ternary associating mixtures, such as water and alcohol mixtures. The model expressions are used to estimate the thermodiffusion coefficients in methanol–ethanol–water, dimethyl sulfoxide (DMSO)–ethanol–water and DMSO–t‐butanol–water mixtures at various concentrations. The perturbed‐chain statistical associating fluid theory (PC‐SAFT) equation of state is used to obtain the mixture properties, such as the derivatives of the chemical potentials needed to evaluate the thermodiffusion coefficient expressions. The results show that at certain concentrations of one component, variation of the concentration of the other two components can cause a sign change in the thermodiffusion coefficients. While the model cannot be evaluated due to the lack of any pertinent experimental data, the model predictions may be used to choose suitable mixture compositions in space experiments to be performed onboard the International Space Station (ISS) in near future. © 2011 Canadian Society for Chemical Engineering     

PC-SAFT理论对CO_2-甲醇体系相平衡的研究

主要结合统计缔合流体理论(PC-SAFT),采用已有的CO2与甲醇纯流体分子参数,同时利用CO2与甲醇纯流体分子参数回归二元交叉作用参数。以CO2、甲醇的纯流体分子参数及回归所得的二元交叉作用参数作为输入,来关联和预测CO2-甲醇二元体系相平衡性质。本文不仅对CO2-甲醇二元体系p-x和p-ρ相图的预测结果与实验数据进行了比较,而且分析了温度、压力和两相密度等因素对CO2-甲醇二元体系界面性质的影响。     

Grand canonical Monte Carlo simulation of adsorption of nitrogen and oxygen in realistic nanoporous carbon models

Adsorption of nitrogen and oxygen in nanoporous carbons (NPC) is simulated using grand canonical Monte Carlo simulations, where the Steele potential (developed for gas interactions with graphite) is used to represent gas–carbon interactions. NPC models used for the adsorption simulations are developed using an isothermal‐isobaric (constant NpT) ensemble Monte Carlo algorithm whereby an initial polymer chain is evolved through a series of atomic displacement and bond rearrangement steps into the final carbon structure. These constant NpT carbon models are representative of real NPCs in terms of local structure and chemical composition. Predictions of nitrogen and oxygen sorption from our model NPCs show good agreement with experimental data. The isosteric heats of adsorption of both adsorbates lie within the range of experimental values for NPCs. Furthermore, the adsorption isotherms of the two gases showsemi‐quantitative match with experimental adsorption isotherms. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Retardation of the phase segregation of liquid mixtures with a critical point of miscibility

The phase transition extraction (PTE) process consists of bringing a partially miscible mixture from the single‐phase to the two‐phase region of its phase diagram. Its most important characteristic is that the resulting phase separation is very fast, and hardly affected by coalescence‐retarding impurities. In this work we study two counter‐cases, where the PTE process appears to be severely retarded. First, we consider the ouzo effect, where the mixture forms very stable metastable micro‐emulsions, showing that this process can be generalized, leading to a reverse ouzo effect, where a modifier is added in large quantities. The second retardation technique consists of using very viscous solvents. We found that, in agreement with the predictions of the phase field model, the growth rate of the nuclei during the initial stage of phase separation does not depend on viscosity, while, on the other hand, when the size of the nuclei exceed their capillary length, gravitational effects become relevant and the settling time is proportional to the viscosity of the continuous phase. © 2018 American Institute of Chemical Engineers AIChE J, 64: 4047–4052, 2018     

Framework for correlating the effect of temperature on nonelectrolyte and ionic liquid activity coefficients

A power‐law expression is proposed for correlating the temperature dependence of infinite‐dilution activity coefficients ( ) for nonelectrolyte solute–solvent binary pairs and for pairs including an ionic liquid: , where θ_ij = 0 for Lewis–Randall ideal solutions, θ_ij = 1 for classic enthalpy‐based Scatchard–Hildebrand regular solution and van Laar models, and ?5 < θ_ij < 5 for most real binaries. The exponent θ_ij is a function of partial molar excess enthalpy ( ) and entropy ( ) such that . Real binaries are classified into seven types corresponding to distinct domains of and θ_ij. The new method provides a framework for correlating phase‐equilibrium driven temperature effects for a wide variety of chemical and environmental applications. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3675–3690, 2014     

Calculation of phase envelopes of fluid mixtures through parametric marching

Two-dimensional cross-sections of the phase envelopes of fluid mixtures—in particular isotherms, isobars, and isopleths—are often computed point-by-point by incrementing a so-called marching variable and solving the equilibrium conditions at each step. The marching variable is usually pressure, temperature, or a mole fraction, depending on the application. These isolines, however, can have rather complicated shapes, so that a simple unidirectional “sweep” of the marching variable often gives merely a part of the desired isoline. It is then necessary to restart the sweep with different initial values, or to switch to another marching variable. This, however, makes it difficult to compute complete isolines automatically, without human interference. We propose here a new marching technique through which it is possible to follow isolines of arbitrary shape and thus to compute complete isolines, as long as they are contiguous.     

Twenty‐one new theoretically based cubic equations of state for athermal hard‐sphere chain pure fluids and mixtures

Eight new hard‐sphere equations of state (EOS's) were obtained from molecular simulation data for the pair correlation function g_HS(σ) vs. packing fraction η and combined with three theoretical schemes to obtain 21 new cubic EOS's for athermal hard‐sphere chains (AHSC's). The eight new hard‐sphere EOS models successfully reproduced isotropic fluid compressibility factor Z_HS and g_HS(σ) vs. η simulation data and predicted metastable liquid Z_HS vs. η and virial coefficients up through B₁₀. Moreover, calculated Z vs. η and reduced second‐virial coefficient vs. chain length m were compared with molecular simulation data for chains up to m = 201 for a set of representative (eight of twenty‐one) chain equations. Z vs. η for three AHSC binary mixtures was also successfully predicted. The results indicate that the new cubic EOS's give a satisfactory representation of simulation data for chain fluids and can be used to develop theoretically based cubic EOS's for “real” fluids including attractive effects. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1677–1690, 2015     

Modeling permporometry of mesoporous membranes using dynamic mean field theory

Mesoporous inorganic membranes have significant potential for important small‐molecule separations like carbon dioxide recovery from stack emissions. However, tailoring materials for a given separation remains an outstanding problem. Preferential adsorption, layering and capillary effects, and surface flow are key mechanisms that determine permeation rates and are ultimately linked to the mesopore characteristics. To further the understanding of these systems, a modeling approach based on dynamic mean field theory, which has previously been used to study the dynamics of adsorption in mesoporous materials, is proposed. This theory describes both relaxation dynamics and nonequilibrium steady states in membranes and is fully consistent with a mean field density functional theory of the thermodynamics. The capabilities and promise of the approach by modeling a permporometry experiment, in which a light gas permeates through a mesopore in the presence of a condensable vapor at a controlled relative pressure, are demonstrated. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2958–2967, 2015     

High‐pressure phase equilibria for a styrene/CO2/polystyrene ternary system

To reveal the possibility of supercritical (SC)‐CO₂‐assisted devolatilization of polystyrene, the equilibrium composition data for the CO₂ phase in a styrene/CO₂/polystyrene ternary system is determined by a semistatic experimental technique. The parameters in the lattice–fluid equation of state of Sanchez and Lacombe are determined for the investigated system. The distribution coefficients of styrene between the polymer and the supercritical fluid phases are investigated experimentally at 318 and 328 K over the pressure range of 12–20 MPa. The binary interaction parameter between styrene and CO₂ is obtained by regression of the vapor–liquid equilibrium data. The interaction parameter between CO₂ and polystyrene is calculated by using the sorption data from the literature, and the interaction parameter between styrene and polystyrene is optimized by using the measured data of this study. The investigation of the distribution coefficients indicates that styrene can be removed from polystyrene by SC‐CO₂ at near room temperature and moderately high pressures. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1938–1944, 2002