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To develop efficient ionic liquid (IL)-based separation processes like extractive distillation, the knowledge of IL-involved vapor–liquid equilibria (VLE) is necessary. Since experimental measureme...

A study is performed of the accuracy of free energy F of a vapor–liquid system, calculated with modified fluid models in the quasi-chemical approximation (QCA) of the lattice gas model. Two ways of modifying the fluid model are discussed: (1) allowing for the softness of the lattice, which alters its weighted average parameter according to the density of the fluid and (2) jointly considering the translational and vibrational molecular motions in a rigid lattice. The effect the model of introducing the weighted average parameter of a soft lattice has on the calculated characteristics is analyzed. Calculations of the free energy using the analytical QCA formula (which contains no such modifications) are compared to thermodynamic relationships obtained with a chemical potential that considers them. It is found that both modifications of the fluid model result in distinctions between the two ways of calculating the free energy that grow along the density of the system. These distinctions are apparent at high densities and on the concentration dependence of pressure. The analytical QCA expression quantitatively estimates F values when there are small contributions from model modifications.

The problem of comparing thermosyphons in terms of engineering solutions used for cooling the pile foundations of residential buildings in the regions of the Far North is considered. For comparison, specific self-cooling units (SCU) of two types were selected, including liquid SCU 1 with a pipe diameter of 120 mm and a vapor-liquid SCU 2 with a pipe diameter of 50 mm. Simple analytical calculations proved the thermal efficiency of SCU 2 to be 1.4 times less than that of SCU 1, which is primarily related to the pipe diameter. Numerical calculations using the TEMPA software package have demonstrated that, despite the slightly greater cooling effect of SCU 1, the temperature field for September of the third calculation year is leveled for both devices.

Isoprenol (3-methyl-3-buten-1-ol) is an important intermediate in the chemical industry and is used, for example, in the production of various scent and flavor chemicals. Isoprenol is produced from aqueous formaldehyde and isobutene and is separated by distillation from mixtures containing formaldehyde, water, and isobutene in the process. As formaldehyde forms oligomers with both water and isoprenol, these mixtures are complex reacting systems, which are not easy to separate. Hence, for understanding and modeling the process, information on the vapor–liquid equilibria and the chemical equilibria in the system (formaldehyde + water + isoprenol) is essential. However, only very limited data on this system are available in the literature. Therefore, in the present work, vapor–liquid equilibria were measured in the following systems: system (water + isoprenol) at 20 and 90 kPa, system (formaldehyde + isoprenol) at 373 and 393 K, and system (formaldehyde + water + isoprenol) at 373 K. Furthermore, the chemical equilibria of the oligomerization reactions of formaldehyde and isoprenol were studied with 13C-NMR spectroscopy at temperatures ranging from 283 to 353 K. The experimental data were used to extend a physico-chemical model of the system (formaldehyde + water) from the literature to include isoprenol.

Several industries have steadily gained interest in gas hydrate technologies for their potential use in natural gas transport and storage applications. Additives which optimize the efficiencies of ...

Pigging technology is widely used in the oil and gas industry. During the course of pigging, after a water pressure test, the instability of the pig caused by terrain fluctuation can affect the stable operation of the pipeline and even cause burst accidents. This paper describes the four stages of pig movement in an inclined pipeline, with vapor-liquid eruption occuring in the last stage. A hydraulic transient model of the pigging operation after a water pressure test is established based on mass conservation and motion equations, the dynamic equation of the pig, and the vapor-liquid eruption model. The model can simulate the status of fluid flow in the pipeline, track the movement of the pig, and predict the pressure pulses. The simulation results are consistent with the data of two burst accidents, which verifies the correctness of the established model and the reliability of the calculated results. It can therefore provide a reliable and effective theoretical basis for developing a pigging plan on site.

The explosion characteristics of vapor-liquid two-phase n-heptane inside and outside (the boundary is the junction of premixed fuel and air) the original premixed zone studied, and the effects of concentration and initial temperature on the explosion development have been analyzed using a numerical method. The explosion overpressure increases with distance in a certain range outside the premixed zone with the change of premixed vapor-liquid two-phase n-heptane concentrations. The peak overpressure of rich fuel is larger than that of lean and stoichiometric fuel. The fuel rich explosion outside the premixed zone results in a so-called "secondary explosion", and the explosion overpressure has two peaks with similar values. The initial temperature has a significant effect on the flame length (characterization by combustion rate) of two-phase n-heptane explosion. The flame length of a lean fuel explosion decreases with the increase of initial temperature. At an initial temperature of 253 K, the flame length is 4.15 times that of the premixed zone. With stoichiometric and rich fuel, the flame length increases with the initial temperature in the range of 273−333 K, and at 333 K the flame length is 5.26 and 5.99 times that of the premixed zone, respectively.

Separation vessels are traditionally designed based on rules of thumb that guide the designer to a feasible solution. Despite its widespread use, this approach presents important limitations, which...

This work studied the separation effect of 1-hexyl-3-methylimidazolium-based ionic liquids (1-hexyl-3-methylimidazolium tetrafluoroborate [HMIM][BF4] and 1-hexyl-3-methylimidazolium trifluoromethan...

A unified description of three types of two-phase interfaces (vapor–liquid, solid–vapor, and solid–liquid) at a vapor–liquid meniscus inside a slit-like pore are considered on the basis of the lattice gas model. This approach allows equally accurate calculations of molecular distributions in heterogeneous distributed models of transitional regions at all interfaces. It is assumed that pore walls cannot be deformed, and they create an external field for a stratifying fluid. Adsorption films form at solid–mobile phase interfaces due to the potential of adsorbate–adsorbent interaction. The state of the coexisting vapor-in-a-pore and liquid-in-a-pore phases satisfy the equality of the chemical potential that excludes the appearance of metastable states. Conditions for distinguishing regions of the system that lie beyond solid–liquid–vapor three-phase contact are discussed. A procedure is discussed for introducing a contact angle into a liquid–vapor–solid pore wall system through molecular distributions of the adsorbate in a slit-like pore. Dependences of the width of the considered interfaces and the contact angle as a function of the pore width and pore wall potential are found.

The computation methods of the thermodynamic properties are used for theoretical studies of multicomponent refrigerant blends (MRBs) for low-temperature throttling refrigeration units, providing cryostatting modes for cooled objects in the temperature range of –90 – –160 °С. The article presents the comparative analysis of the state equations for calculating thermodynamic properties of multicomponent refrigerant mixtures. Quantitative and qualitative differences in the results of calculations in the lowtemperature region are determined.

A compilation of available experimental data for acetone-water mixtures with the reciprocal salt system Na+, K+ || Cl−, SO4 2− is presented. Significant inconsistencies among experimental data are pointed out. New freezing point measurements are reported for the binary acetone-water system at 12 different compositions. UNIQUAC parameters are determined on the basis of the available data from literature. Modeling results are presented. Vapor-liquid, liquid-liquid, and solid-liquid equilibria together with thermal properties are reproduced well by the model using only 14 parameters. The major drawback of the model is that the calculated liquid-liquid equilibrium regions of systems with KCl and NaCl are larger than the experimentally determined regions. The model is valid in the temperature range from −16 to 100 °C.

The continuum quasichemical approximation is used to improve the accuracy of describing molecular distributions in a vapor–liquid system. It considers displacements of the molecular center of mass from the center of a cell within the lattice gas model. It also allows for (as in its discrete variant) direct correlations of interacting molecules. The probability density of a molecule being inside the cell is used as a continuous function of its coordinate. An algorithm for solving a system of integral equations is developed with respect to the pair distribution function. The effect the continuum description of the particle distribution has on the concentration dependences of the main thermodynamic functions is investigated. The approach is shown to explain the concentration dependence of the parameter of effective lateral interaction.

Methanol and methylal form a minimum boiling point azeotrope and cannot be separated by conventional distillation. In this paper, the azeotrope was separated by extractive distillation with cyclohe...

The experimental vapor–liquid equilibrium (VLE) data for a ternary system of β-caryophyllene + dipentene + α-pinene and two binary systems composed of β-caryophyllene (1) + dipentene (2) and dipent...

The vapor–liquid–solid (VLS) mechanism is probably the most versatile method to fabricate semiconductor nanowires and several investigations assume a compositionally homogeneous catalyst particle. In this investigation we address the compositional homogeneity of the catalyst particle during growth of nanowires. Using diffusion calculations, we show that the particle is indeed homogeneous during VLS growth, but can have a strong concentration gradient during vapor–solid–solid growth, that is, growth with a solid particle. We also show that the response to a concentration change is extremely fast, meaning that if the concentration at the surface of the particle changes, the entire particle reaches this new concentration effectively instantaneously.

Ethyl propionate is usually produced from esterification of propionic acid and ethanol in the industry. However, the purification of ethyl propionate remains a challenge because the unreacted ethan...

It is a considerable challenge for the phase behavior of chemical separation industry to correlate and predict the vapor–liquid equilibria (VLE) data of the binary and ternary systems containing as...

Vapor–liquid equilibrium (VLE) data (T, p, x, y) are vital for the development of mixture thermodynamic models. Herein, we demonstrate the use of nuclear magnetic resonance (NMR) spectroscopy as an...

Isobaric vapor–liquid equilibria (VLE) at 50.0, 101.3, and 200.0 kPa, have been measured for the binary system methyl nonafluorobutyl ether (x1) HFE-7100 + (1 – x1) 2-propanol. Thermodynamic consis...

A new experimental methodology has been developed to measure bulk mass densities and interfacial tensions of mixtures at vapor−liquid−liquid equilibria (VLLE). This technique considers the use of a...

The thermodynamic properties of novel natural deep eutectic solvents (NDESs) based on amino acids are of great importance in extraction of pharmaceutical compounds. In this work, the vapor–liquid e...

This paper presents modified views on the vapor–liquid–solid mechanism of nanowire growth, relying on new experimental data on the wettability of a crystal surface by metal catalyst droplets presaturated with the crystallizing substance.

In this study, the experimental vapor?liquid equilibria data of the ternary Pb?Sn?Sb alloy system are determined using a new experimental method. The experimental VLE data passed the thermodynamic consistency test (Van Ness test), suggesting that the experimental results are reliable. The activities of the components of Pb?Sn?Sb ternary alloy and those of the corresponding three constituent binaries were calculated using the Wilson equation. The predicted values are in good agreement with the data determined from the experiments, and the average relative deviation and average standard deviation were smaller than ? 4.00% and ? 0.03 for all constituent binaries, respectively, which indicates that the Wilson equation is reliable for calculating the activity of the components of the Pb?Sn?Sb ternary alloy. The VLE data of the Pb? Sn and Sb?Sn binary alloys and Pb?Sn?Sb ternary alloy were calculated based on the VLE theory and the Wilson equation. The calculated VLE data were in good agreement with the data determined from the experiments, indicating that this method is reliable for calculating the VLE of alloy systems. The proposed study offers a valid method for analyzing the composition of products that are dependent on the distillation temperature and system pressure during vacuum distillation, which is of great significance to the experimental design of this process.

High-pressure vapor–liquid equilibrium (VLE) data for the carbon dioxide + p-cymene system at 313.15, 333.15, and 353.15 K and pressures up to 12.0 MPa were measured by a flow-type visualization ap...

Carbonate esters and esters were commonly used as solvents, reaction carrier, and additives in organic synthesis, the pharmaceutical industry, and processing industries. Vapor–liquid equilibrium (V...

Expressions for calculating Gibbs vapor–liquid surface tension σ are generalized to allow for the interaction between comparable components of a mixture with an arbitrary radius of the interaction potential. Calculations are performed within a modified lattice gas model reflecting a discrete-continuous distribution of mixture components in space with allowance for direct correlations in a quasi-chemical approximation. The calculating of σ is associated with the rejection priority of mechanical characteristics over chemical potential, which is traditional in continuum mechanics. The chemical potential governs local equilibrium distributions of components in the transitional region of a boundary, resulting in the need to use microscopic Gibbs–Duhem equations in a deformed lattice structure of a substance to determine the average distance between molecules (as lattice structure parameters) and to consider effective one-particle motions of components in a dense phase that alter these parameters. Calculations of the surface tension of dense mixtures in models ignoring the existence of vacancies and structural deformation are discussed.

A procedure to calculate the surface tension is developed based on a modified lattice gas model (MLGM) for the vapor–liquid system in a strict correspondence to the thermodynamic Gibbs definition for any curvature of the boundary. It is shown that MLGM enables a calculation of molecular distributions in a layered model of the transition region of the interface with regard to the softness of a lattice structure. The state of coexisting phases must satisfy the Yang–Lee theory of condensation, and additional conditions for chemical, thermal, and mechanical equilibria are imposed on the properties of the transition region of an equilibrium droplet with any curvature in each layer. The new calculation procedure for the surface tension is compared with the existing calculation procedures for equilibrium and metastable droplets. A difference in size dependences of the surface tension σ(R) for equilibrium and metastable droplets with a radius R in vicinity of the line σ/σbulk = 1, where σbulk is the bulk surface tension, allows us to formulate the accuracy and reliability criterion for different modeling methods: if the mentioned line exceeds the calculation accuracy σ(R), then it indicates that the method does not correspond to the Gibbs definition.

The objective of this work was to study the behavior of the azeotropic points of the methanol + DMC system under elevated pressures. We obtained isothermal vapor–liquid equilibria (VLE) data for this system at 383.15, 403.15, and 413.15 K by a static method. The azeotropic points were determined from the experimental VLE data. The temperature and pressure dependencies of the determined azeotropic points are discussed and compared with ones measured at reduced pressure. The experimental VLE data were represented by two activity coefficient models (non-random two-liquid and Wilson models). We also tested the modified UNIFAC (Dortmund) model for prediction of the VLE and azeotropic points. The azeotropic points of this system could be obtained over the pressure range from reduced pressures to elevated ones.

Vapor-liquid equilibria (VLE) and distribution coefficients (K-values) of carbon dioxide (CO2) - ethanol - water ternary systems and CO2 - ethanol - water - flavonoid (flavone, 6-methoxyflavone or 7-hydroxyflavone) quaternary systems were measured with a flow type apparatus at (313 to 353) K and (10 to 20) MPa. CO2 - ethanol - flavonoid ternary systems were measured at a nominal range of temperatures and pressures. The K-values of all flavonoids increased with increasing pressure. It was also indicated that the K-values of relatively lipophilic components such as flavone and 6-methoxyflavone increased with increasing water composition in feed while those of relatively hydrophilic components such as 7-hydroxyflavone increased with increasing ethanol composition in feed. A simple dimensionless relationship in terms of the K-values of the solvents (KCO2, KEtOH, KH2O) and the entropy-based solubility parameters of the vapor and liquid phases was developed to correlate the K-values of the three solutes in the CO2 - ethanol - water systems over the full range of conditions studied.

Carbonate esters and esters are widely used in the pharmaceutical industry. It is important to enrich the vapor–liquid equilibrium (VLE) database of these components. In this article, the isobaric ...

A mixture of acetic acid, n-propyl acetate, and isopropyl acetate, which needs to be separated, is obtained when isopropyl acetate is produced from acetic acid and propene. The vapor–liquid equilibria (VLE) for the acetic acid + n-propyl acetate + isopropyl acetate ternary system and three subsystems were studied with ebulliometry at (20, 40, 60, 80, and 101.3) kPa. The vapor-phase nonideality was described by the Hayden–O’Connell (HOC) equation, and the liquid-phase nonideality was represented by the NRTL model and the UNIQUAC model, respectively. The model parameters for acetic acid–n-propyl acetate, acetic acid–isopropyl acetate, and n-propyl acetate–isopropyl acetate were acquired from the experimental data with the aid of Aspen Plus. The maximum overall average deviation of temperature between the experiment and model predictions is 0.46 K for the NRTL-HOC model and 0.47 K for the UNIQUAC-HOC model. The VLE data and the model parameters acquired may provide basic information for the separation of iso...

Thermodynamic models such as the Wilson model and molecular interaction volume model (MIVM) are known for their use in the calculation of activity coefficients of symmetric systems like Pb-Sn and Pb-Sb, but are deficient in handling asymmetric systems like Ag-Sn and Cu-Sn. Unfortunately, in metallurgical field, including vacuum metallurgy, the symmetric systems only account for a small part of liquid alloys, while the asymmetric systems take up a majority proportion. To overcome this application limitation of the Wilson model and MIVM in vacuum metallurgy, the modified molecular interaction volume model (M-MIVM) was applied. In contrast with Wilson model and MIVM, the M-MIVM exhibited remarkable superiority in data fitting of activity coefficient of binary asymmetric systems, which effectively increased the accuracy of predicting the activities of the multicomponent systems containing corresponding binary asymmetric systems. Therefore, M-MIVM made possible a more accurate vapor-liquid phase equilibrium diagram of asymmetric systems. In addition, since M-MIVM is a modification of the MIVM, it retains MIVM's capabilities to predict separation coefficient and calculate vapor-liquid equilibrium (VLE) of symmetric systems under quasi-vacuum condition. These identified advantages made M-MIVM, when compared with existing models, to have better accuracy and wider scope of application in vacuum metallurgy.

The high-pressure vapor–liquid equilibrium for the binary systems of carbon dioxide (CO2) and a series of 1-alkyl-1-methyl pyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquids ([CnC1pyr][N...

The NRTL equation provides a good representation of vapor-liquid equilibrium of mixed-refrigerants, but it needs three parameters for each pair of components, including a non-randomness parameter alpha. In order to reduce the number of adjustable parameters from three to two, this work aims to establish an adequate expression for alpha in terms of readily available molecular parameters. The regressed alpha coefficients vary from -1 to 10, while 74% of them are between 0 and 1. Alpha has a great effect on the AARDp, although there is a region with a small AARDp difference. The relationship between alpha and molecular weight, dipole moment is established. As expected, positive correlation between alpha and molecular weight, while negative correlation between alpha and dipole is found. Better AARDp (0.59%) is achieved by a proposed equation, comparing to alpha = (0.2, 0.3, 0.4 and 0.47), although it is slightly worse than the regressed alpha.

Vapor-liquid phase equilibria of the H2S H2O mixture were correlated by use of a cubic EOS-GEX over temperature and pressure range of 0.1–30 MPa and 278–627K. Average absolute deviations (AAD%) between the modeling results and the experimental data taken from literature for both the H2S-rich and the aqueous phases were found less than 5%. The new sets of EOS-GEX model parameters for H2S H2O mixture were evaluated from the experimental data over the above-mentioned temperature and pressure range. The proposed model was compared with the three previous published models and we discussed the advantages and the disadvantages for each of them. This study demonstrated that the advantages of the cubic EOS-GEX model in calculating phase equilibria of H2S H2O mixture over currently available models, especially at high pressures. The hydrate equilibrium, the salt effect, and the chemical reactions in the aqueous phase were not considered during phase equilibrium calculation in this study.

Nanowires growth via vapor-liquid-solid mechanism leads to high-quality SiC nanowires. C content is key issue affecting the morphology and composition of SiC nanowires. Here, we report the synthesis and growth mechanism of 3C-SiC nanowires containing reduced amount of C, which are grown on single-crystal Si via pyrolysis of polycarbosilane (PCS) by adjusting pyrolysis temperature and precursor. SiC nanowires have a diameter of 50 nm, while their thickness is 43.75 µm. High-temperature stability of precursors with multiple side-chain groups has an impact on the reaction rate, in result the solid precursor state and pyrolysis temperature at 1350 °C are beneficial to the formation of pure carbon-poor SiC nanowires.

The vapor–liquid–solid growth of III-V nanowires proceeds via the mononuclear regime, where only one island nucleates in each nanowire monolayer. The expansion of the monolayer is governed by the surface energetics depending on the monolayer size. Here, we study theoretically the role of surface energy in determining the monolayer morphology at a given coverage. The optimal monolayer configuration is obtained by minimizing the surface energy at different coverages for a set of energetic constants relevant for GaAs nanowires. In contrast to what has been assumed so far in the growth modeling of III-V nanowires, we find that the monolayer expansion may not be a continuous process. Rather, some portions of the already formed monolayer may dissolve on one of its sides, with simultaneous growth proceeding on the other side. These results are important for fundamental understanding of vapor–liquid–solid growth at the atomic level and have potential impacts on the statistics within the nanowire ensembles, crystal phase, and doping properties of III-V nanowires.

This work analyzes the effect of the vapor-liquid equilibria (VLE) on the productivity and the reactor performance during the Fischer-Tropsch Synthesis (FTS). A reactor model is developed considering the VLE and the local variation of the chain growth probability with temperature and the H2/CO ratio. The model describes the VLE with four different levels of complexity to assess the error introduced by making certain model simplifications. The results show that a simplified VLE model that only accounts for the VLE of CO and H2 offers an attractive alternative since it presents a good accuracy while saving computational time and efforts. Additionally, this work shows that the VLE significantly influences the liquid holdup and the pressure drop. Likewise, the catalyst efficiency is strongly affected by the liquid concentration, and therefore by the VLE. Thus, a full VLE description of reactants and products is needed for the accurate modeling of the FTS reactor.