Calculation of pure compound saturated enthalpies and saturated volumes with the PRSV equation of state. Revised k1 parameters for alkanes

The Stryjek-Vera (1986a) modification of the Peng-Robinson (1976) equation of state has been used to predict heats of vaporization, enthalpies of saturated phases and saturated volumes for pure compounds ranging in molecular complexity from diatomic gases to compounds showing polarity and association. Heats of vaporization at the normal boiling temperature are reproduced within 2% for the majority of the compounds tested. Similar results were obtained for the enthalpy of the saturated phases. Revised k₁ parameters of the PRSV equation of state are reported for alkanes. An empirical correction has been developed for calculating saturated liquid volumes from the liquid volumes given by the PRSV equation of state. For the range of reduced temperatures from 0.5 to 0.99, deviations from experimental values are smaller than 4%. Saturated vapor volumes calculated from the PRSV equation of state were found to be satisfactory for most technical calculations.     

基于第一原理力场预测热力学参数的探讨

讨论用第一原理全原子力场计算热力学参数的可行性.新开发的TEAM力场,在用气、液相基本性质验证后,不加任何参数调整,直接用于计算具有代表性的几个分子液体在不同热力学状态下的密度、蒸发焓、混合焓、亨利常数、饱和蒸气压等热力学参数.初步结果表明：液体密度和蒸发焓的预测结果良好,在较大范围内可获得与实验数据相吻合的结果;而混合焓的准确预测需要纯液体内聚能的高精度模拟数据;亨利常数的计算对液体的密度极为敏感.后两种性质的计算均可用全原子力场但需要高质量的力场参数.为了采用全原子力场计算气液相平衡数据,提出了一种半经验的、基于积分Clausius-Clapeyron方程的循环自洽方法计算液体的饱和蒸气压.     

Theoretical Investigation of Some High‐Performance Novel Amine Azide Propellants

Monomethylhydrazine (MMH) is currently the most widely used hypergolic propellant, due to its high performance and low ignition delay. However, its toxicity is a major concern. The present work aims at developing high‐performance hypergolic fuels that are based on tertiary amine azide functionality. A number of potential amine azide candidates have been proposed, and some of their physical and chemical properties have been computed using state‐of‐the‐art molecular modeling techniques. Gas‐phase heats of formation have been calculated using the CBS‐QB3 method, and the first‐principle COSMO‐RS method has been used to compute heats of vaporization and vapor pressures. A density correlation, based on molecular‐volume calculation, has been established to predict the densities of the candidate molecules. Finally, the liquid‐phase heats of formation and densities have been used to predict the specific and density impulses of the proposed candidate molecules. The results show that many of the molecules proposed here have much higher density impulse than that of MMH, and may be considered for experimental studies.     

OPTIMIZATION OF THE COMPOSITIONS FOR CFC ALTERNATIVE MIXTURE REFRIGERANTS

In this work,eight commonly used and recently developed cubic EOSs have beenextensively tested for the calculation of thermodynamic properties,including vapor pressure,vaporand liquid densities and heat of vaporization for 26 pure CFCs and their alternatives.The modifiedDu-Guo EOS is recommended for the vapor-liquid equilibria calculations of mixtures for its goodaccuracy.A method for the development of the optimized mixture compositions of CFC alternativeshas been proposed by using minimization of deviations between the vapor pressures of CFC and thealternative mixtures of interest.As examples,two binary mixtures R22-R142b and R22-R152a,and aternary R22-R142b-R152a have been tested.The results show that the vapor pressure of R12 can bewell duplicated by a mixture refrigerant with the optimized composition.On the other hand,thedeviations between the heat of vaporization are somewhat apparent within 10 percent.Moreover,allthe mixtures discussed here are of the characteristics of being near azeotropic,and     

正常沸点下液体蒸发焓的基团贡献计算法

用分子热力学方法建立了纯物质汽液平衡的推广vanderWaals模型 ,并据此得到了一个计算正常沸点下液体蒸发焓的方程 .它只含有一个与分子大小有关的参数 .这个参数的值与正常沸点下液体的摩尔体积成正比 ,且具有基团加和性 .为此 ,用 484个有机物回归得到了 45个基团增量 .对这些有机物的蒸发焓计算结果表明 ,与实验值的平均绝对偏差 (AAD)为 1.39% ,优于文献发表的其他方法     

ON THE PREDICTION OF HEATS OF VAPORIZATION OF PURE COMPOUNDS

An expression to predict the values of the latent heat of vaporization of pure compounds at their normal boiling point has been developed. A knowledge of the critical temperature, critical pressure, normal boiling point and acentric factor of the compound coupled with the use of generalized correlations for second virial coefficient and liquid molar volume allows to obtain good estimates, particularly for alcohols and ketones. Results for 71 various substances are compared with experimental values and with the results of eight other equations available in the literature. The possibility of using the calculated heats of vaporization at the normal boiling point to estimate values at other temperatures is discussed.     

ON THE PREDICTION OF HEATS OF VAPORIZATION OF PURE COMPOUNDS

An expression to predict the values of the latent heat of vaporization of pure compounds at their normal boiling point has been developed. A knowledge of the critical temperature, critical pressure, normal boiling point and acentric factor of the compound coupled with the use of generalized correlations for second virial coefficient and liquid molar volume allows to obtain good estimates, particularly for alcohols and ketones. Results for 71 various substances are compared with experimental values and with the results of eight other equations available in the literature. The possibility of using the calculated heats of vaporization at the normal boiling point to estimate values at other temperatures is discussed.     

Heats of vaporization of then-fatty acid esters

Heats of vaporization at both 25°C and normal boiling points are given for then-fatty acid methyl and ethyl esters and then-alkyl acetates. The validity of the reported heats of vaporization is supported by: (i) their agreement with those estimated by alternate methods, and (ii) the equations correlating heats of vaporization with homolog carbons have the proper slopes (approximately 4.96). Equations also are given for correlating heats of vaporization with boiling points, and boiling points and molar volumes with homolog chainlength.     

THE MODIFIED PGR EQUATION OF STATE: PURE-FLUID PREDICTIONS

The Park-Gasem-Robinson (PGR) equation of state (EOS) has been modified to improve its volumetric and equilibrium predictions. Specifically, the attractive term of the PGR equation was modified to enhance the flexibility of the model, and a new expression was developed for the temperature dependence of the attractive term in this segment-segment interaction model.

The predictive capability of the modified PGR EOS for vapor pressure and saturated liquid and vapor densities was evaluated for selected normal paraffins, normal alkenes, cyclo-paraffins, light aromatics, argon, carbon dioxide, and water. The generalized EOS constants and substance-specific characteristic parameters in the modified PGR EOS were obtained from pure component vapor pressures and saturated liquid and vapor molar volumes. The calculated phase properties were compared with those of the Peng-Robinson (PR), the simplified-perturbed-hard-chain theory (SPHCT), and the original PGR equations. Generally, the performance of the proposed EOS (%AAD of 1.3, 2.8, and 3.7 for vapor pressure, saturated liquid, and vapor densities, respectively) was better than the SPHCT and original PGR equations in predicting the pure fluid properties.     

DMF的力场构建及乙腈-甲醇-DMF三元体系的汽液相平衡模拟

采用量子化学和Gibbs系综Monte Carlo模拟相结合的方法,对TraPPE-UA力场中缺失的N,N-二甲基甲酰胺（DMF）力场参数进行了补充,为含DMF多元体系的汽液相平衡模拟奠定了基础。采用新构建的力场参数,在NVT-Gibbs系综中计算了DMF的汽液相平衡性质,结果表明该力场能准确计算出DMF的饱和液相密度、蒸气压、沸点、临界值和蒸发焓。在NPT-Gibbs系综中,采用TraPPE-UA力场分别计算了乙腈-甲醇、DMF-甲醇、DMF-乙腈二元混合物的汽液相平衡性质,并与实验值进行了比较。模拟结果与实验值较为吻合,验证了力场模型的可靠性。最后在NPT-Gibbs系综中采用TraPPE-UA力场对乙腈-甲醇-DMF三元体系的汽液相平衡数据进行了预测,为设计和优化乙腈和甲醇的萃取分离过程提供了基础数据。     

Unified equation of state based on the lattice fluid theory for phase equilibria of complex mixtures part I. Molecular thermodynamic framework

Consistent calculation of fugacities of fluid mixtures remains as one of the most important subjects in contemporary molecular thermodynamics. In practice, equations of state (EOSs) and g^E-models have been used. However, most EOSs are erroneous for condensed phases at high densities and g^E-models are inapplicable for pressuresensitive systems. Recently to remedy the shortcomings in both approaches, there has been a surge of new g^E-EOS mixing rules. By equating any set of EOS and g^E-models, the limitations in both approaches could be resolved significantly. However, the self-consistency in the underlying concept of those mixing rules remains controversial. During the last several years, the present authors proposed a new lattice-fluid EOS and its simplification relevant to phase equilibrium calculations. Without employing any g^E-EOS mixing rule and with only two parameters for a pure component and one adjustable interaction energy parameter for a binary mixture, results obtained to date demonstrated that the EOSs are quantitatively applicable to a great variety of phase equilibrium properties of mixtures, especially, for complex and/or macromolecular systems. In the present article we summarize the EOSs and extended the applications to liquid-liquid Equilibria. In part I, we discussed briefly the molecular thermodynamic aspects of general derivation of the EOS and a brief discussion of applying the EOSs to pure fluids while the illustrative application to various real mixture systems is discussed in part II.     

THERMOPHYSICAL PROPERTIES OF ASSOCIATING FLUIDS IN NATURAL GAS INDUSTRY USING PC-SAFT EQUATION OF STATE

The perturbed-chain statistical associating fluid theory (PC-SAFT) is employed to calculate the thermophysical properties of some associating fluids that are widely used in the natural gas industry. Methanol, alkanolamines, and glycols are considered in this work. The alkanolamines include monoethanolamine (MEA), diethanolamine (DEA), and methyldiethanolamine (MDEA). Two new modified associating schemes are introduced to describe the alkanolamine associating behavior. The glycols considered in this work are monoethylene glycol (MEG), diethylene glycol (DEG), and triethylene glycol (TEG). The pure component parameters of these associating fluids are determined using vapor pressure and saturated liquid density data. The heats of vaporization and heat capacities of these compounds are then predicted. Sound velocities and Joule-Thomson coefficients are additionally predicted for methanol. The results indicate that PC-SAFT is accurate for correlating the vapor pressure and liquid density of methanol, the glycols, and alkanolamines. PC-SAFT is also accurate in predicting the Joule-Thomson coefficients and sound velocities of methanol. Although PC-SAFT is not accurate enough for predicting the thermal properties (heat capacities and heats of vaporization) of MEG and TEG, it reasonably describes the thermal properties of MEA, DEA, MDEA, and DEG.     

Modele mathematique d'une colonne de rectification discontinue—I. Etablissement du modele

A mathematical model of a batch distillation column referring to operation conditions for which usual simplifying assumptions are not admissible is desribed. This model is used to resolve systems with different heats of vaporization and takes into account vapor hold-up, anadiabatic column and plates efficiency. This method allows to determine simultaneously evolution of the concentration variation along the column and of vapor and liquid molar flows. Model equations, described for binary system rectification are easily used for a multicomponent system.     

On the representation of liquid properties of pure polar compounds by means of a modified redlich-kwong equation of state

The temperature-dependent parameters ω_a and ω_b of the Redlich-Kwong equation of state were evaluated from saturated liquid volumes and vapor pressures for three polar compounds, water, ammonia and sulfur dioxide, and then correlated in terms of T_r. To demonstrate the applicability of the resulting correlation, the values of ω_a and ω_b computed from these equations were used to evaluate the liquid properties of these compounds, such as vapor pressures and liquid volumes at saturation, and the heat of vaporization at the normal boiling point. In addition, the enthalpy departures of liquid water as well as the liquid volumes of compressed water were calculated. The results obtained from the proposed correlations are generally superior than those obtained from the equations of state recently proposed by Fuller, and Peng and Robinson.     

形状因子对应态原理预测流体的热力学性质

采用形状因子对应态原理,由纯流体的蒸汽压和饱和汽液相密度方程得到的保形参数,由此推算其它区域内的Ｐ－Ｖ－Ｔ性质、第二ｖｉｒｉａｌ系数、焓、熵、热容和混合物的汽液平衡等热力学性质,计算结果与文献值符合较一致     

Thermodynamic properties of the system toluene — 1, 1, 1-trichloroethane

Data on molar excess enthalpy on mixing at 298.15 K and 308.15 K, vapor-liquid equilibrium, latent heats of vaporization at 91.444 kPa and vapor pressures for the system toluene – 1, 1, 1-trichloroethane are presented. A simple adiabatic calorimeter designed for molar excess enthalpy measurements is described, tested and used.     

GIBBS ENSEMBLE MONTE CARLO SIMULATION OF VAPORLIQUID EQUILIBRIA FOR SIMPLE FLUIDS

The Gibbs ensemble Monte Carlo simulation method has been investigated and used to calculate the vaporliquid equilibria of a real binary mixture, argon-methane. In this simulation, the micro-structural and macroscopic properties, including the distribution function, internal energy, densities and compositions of coexisting vapor and liquid phases as well as the enthalpy of vaporization are obtained. Compared with experimental data and calculated results from equations of state, our simulated phase equilibrium properties are of good accuracy, which demonstrates that this simulation methods is a powerful tool in research on phase equilibria of fluids.     

Prediction of vapor-liquid equilibria by means of a modified clausius equation of state

The Clausius equation was modified for the calculation of vapor-liquid equilibria in binary and multicomponent systems. In the modification, the three parameters of the equation were considered temperature dependent. Molal volumes of saturated liquid and vapor together with the condition that the fugacities of the vapor and the liquid phase are equal at the condition of equilibrium were used for evaluating the parameters of pure components. Applications were made successfully to systems nitrogen-methane, nitrogen-oxygen, argon-oxygen, nitrogen-argon, argon-methane, carbon dioxide-hydrogen sulfide, carbon-dioxide-propane, hydrogen sulfide-n-butane and nitrogen-argon-oxygen.     

ESTIMATION OF HEAT OF VAPORIZATION OF PURE LIQUID AT ITS NORMAL BOILING TEMPERATURE

A new method is proposed to estimate the heat of vaporization of pure liquid at its normal boiling temperature. The properties required include the boiling temperature, critical temperature and critical pressure. For monohydric alcohol and monohydric organic acid, an adjusting-boiling-temperature strategy is proposed to reduce the calculation errors. The method is tested for 160 substances including many groups of compounds. The results show that the proposed method is better than the literature methods, especially for monohydric alcohol and monohydric acid.