Binary Vapor Research Articles

Thermal Stability and Vapor–Liquid Equilibrium for Imidazolium Ionic Liquids as Alternative Reaction Media

Ionic liquids (ILs) are emerging as a new family of environmentally benign solvents alternative to the conventional solvents for most catalytic reactions due to their nonvolatility. In such applications, thermal stability and solubility are vital for the selection of a suitable IL solvent for a particular reaction. In this work, the thermal stability of three commonly used imidazolium ILs (bmim[BF4], bmim[PF6], bmim[Tf2N]) was studied with both nonisothermal and isothermal thermogravimetric analysis (TGA). The decomposition kinetics indicated the relative anion stability for imidazolium based ILs was Tf2N > PF6 > BF4. In addition, the solubility data of three organic compounds (methanol, ethyl acetate, and benzene) in ILs were specified by the binary vapor–liquid equilibrium (VLE) at elevated temperatures. The results indicated bmim[Tf2N] was the best solvent for the organics investigated. For the same IL, the solute with a higher polarity tends to possess a lower activity coefficient. The activity coeffi...

Flame Spread over Binary Mixed Liquid Fuels—Super-Flash/Super-Flash Mixed Condition

In this study, we investigate the flame spread characteristics of binary mixed liquid fuels that are both in super-flash condition. We propose a method for estimating flashpoint and flame spread rate for binary mixed liquid fuels from binary vapor concentration distribution and compare these estimated values with experimental results. In addition, we measure the flame height and center of the flame leading edge for binary mixed liquid fuels. The results show that, when the flashpoint of each single fuel is known, the flashpoint of the binary mixed liquid fuel can be calculated. Moreover, the fuel that most influence combustion changes near the intersection of vapor concentration distribution in accordance with Raoult’s law. Photographs of the flame indicate discontinuity. We can calculate flame spread rate by using the ratio of each diffusion coefficient to judge equivalently. Finally, it is found that the flame height and center of flame leading edge are proportional to total vapor concentration of the binary mixed liquid fuels.

On the critical thickness and wavelength of a condensing thin liquid film in a binary vapor mixture system

We study the linear stability of a condensing thin liquid film of a binary vapor mixture by solving directly the bulk equations of the gas phase. The boundary layer of a finite thickness is introduced above the liquid film, within which the variables are disturbed. The dynamics of the liquid film is described by the long-wave equation. The neutral stability condition predicts the existence of a critical thickness below which a flat film is stable due to the mass gain effect. However, if we consider the thickening of the liquid film by condensation, the relative neutral stability can be defined such that the growth rate of a disturbance is equal to that of the basic film thickness. The critical thickness and wavenumber obtained from the relative neutral stability condition significantly change from the original ones. Employing the asymptotic analysis for large wavenumbers, the critical thickness and wavelength are numerically calculated for the water–ethanol system. Their dependence on the boundary layer thickness, temperature and ambient vapor concentration is investigated. The critical wavelength obtained from our theory has the same trend in the temperature and concentration as the initial drop distance observed in the experiment.

Monte Carlo simulations of phase behavior and microscopic structure for supercritical CO2 and thiophene mixtures

The phase equilibria of thiophene in supercritical carbon dioxide are calculated by Monte Carlo simulations in Gibbs ensemble using a united atom force field. To validate the simulations, binary vapor–liquid coexistence curves were computed for two different temperatures using Monte Carlo simulations. An excellent agreement between simulations and experimental data is obtained. The effects of pressure on structural properties were studied for thiophene–CO2 binary mixtures. The radial distribution functions and local composition of thiophene in CO2 were investigated over a range of pressures. A weak dependence of thiophene structural properties with pressure was observed in supercritical phase. Local solution structure of thiophene in supercritical CO2 was studied by computing angular–radial distribution functions and spatial distribution functions with three-dimensional probability distributions. The characteristic angular–radial distributions show a mutually parallel arrangement between thiophene plane and CO2 molecules within the first solvation shell. Spatial distribution functions (SDFs) results show that CO2 molecules have two higher probability distributions around thiophene molecules located above and below the thiophene ring.

One-parameter modified nonrandom two-liquid (NRTL) activity coefficient model

The nonrandom two-liquid (NRTL) model is utilized widely in phase equilibria calculations and employs three adjustable parameters (two interaction parameters and the non-randomness factor) that are determined through regression of experimental data for a specific binary vapor–liquid equilibrium (VLE) system. The two interaction parameters (a12 and a21) account for the difference between the pure-component liquid interactions (g11 and g22) and mixed-component liquid interactions (g12 and g21). The main disadvantage of the NRTL model is the strong correlation between the two parameters of the model.In this work, we propose a new modification to the NRTL model which addresses the limitation of the original model. The newly modified model recasts the formulation of the NRTL model parameters in such a way that the new parameters reflect two different characteristics. It also allows one of the two new model parameters to be generalized in terms of pure-component properties, which reduces the NRTL model to a one-parameter model. The original and modified NRTL models yield comparable precision in representing experimental equilibrium properties. Some of the benefits of our modification include easy generalizability of the parameters, ability to classify VLE behaviors based on a single model parameter and fewer convergence problems in parameter regressions.

Sn compensation via SnSex binary vapor supply during Cu2ZnSnSe4 formation

An elemental stacked Mo/Sn/Cu/Zn/Se precursor was prepared by sputtering pure elemental targets of Sn, Cu, and Zn sequentially onto Mo-coated glass substrates, followed by thermal evaporation of Se. To compensate for typical Sn loss observed during the thermal annealing of precursors in a tube-type rapid thermal annealing reactor, a custom-designed quartz/Se/Sn cover was added to the sample tray. It was found that Sn was supplied in the form of a binary compound, SnSex, and thus, the delamination of Cu2ZnSnSe4 (CZTSe) from the Mo layer was well suppressed. It was also found that an increase in the Se layer thickness (1, 3, and 5μm) in the precursor structure could result in more severe delamination of CZTSe from the Mo layer and an increase in the Sn thickness (300–500nm) in the quartz/Se/Sn cover could lead to the incorporation of more Sn and Se into the CZTSe structure.

Mie Potentials for Phase Equilibria: Application to Alkenes

Transferable united-atom force fields based on Mie potentials are presented for alkenes. Monte Carlo simulations in the grand canonical ensemble, combined with histogram reweighting, are used to determine vapor–liquid coexistence curves, vapor pressures, heats of vaporization, boiling points, and critical properties for 1-alkenes from ethene to 1-octene. To assess the transferability of the optimized parameters, additional calculations are performed for the cis and trans isomers of 2-butene and 2-pentene and the dienes 1,3-butadiene and 1,5-hexadiene. Saturated liquid densities for the 1-alkenes, 2-pentenes, and 1,5-hexadiene are predicted to within 1 % of experimental data, while deviations of (2 to 5) % from experiment were observed for cis-2-butene and 1,3-butadiene, respectively. Vapor pressures for the alkenes are predicted to within (2 to 15) % of experiment, with errors increasing with chain length and at lower temperatures. Critical temperatures are predicted to within 1 % of experiment for all molecules except for 1,3-butadiene, where the critical temperature is under-predicted by 3.5 %. Transferability is further evaluated through calculations of binary mixture vapor–liquid equilibria. Predictions of the Mie potentials for ethane + propene and 1-butane + 1-hexene are indistinguishable from experimental data.

Vapor–Liquid Equilibrium Data for Binary Systems of n-Dodecane + {Propan-1-ol, Butan-1-ol, 2-Methylpropan-1-ol} at 40 kPa

Isobaric (T–x–y) binary vapor–liquid equilibrium (VLE) data were measured and modeled for the n-dodecane + {propan-1-ol, butan-1-ol, or 2-methylpropan-1-ol} systems at 40 kPa. A low pressure dynamic still, capable of measuring systems of high relative volatility, was used for the measurements. The vapor and liquid equilibrium compositions were determined using a gas chromatograph with a thermal conductivity detector. The experimental data were regressed using the combined method (γ–φ approach). The nonrandom two-liquid (NRTL) activity coefficient model was used to describe the liquid phase nonideality, and the vapor phase was assumed to be ideal. The NRTL model parameters were determined using nonlinear least-squares regression. The experimental data were found to be well correlated with the thermodynamic modeling. No azeotropic behavior has been observed. The three investigated systems show a large positive deviation from Raoult’s law.

Hybrid swarm optimization for vapor–liquid equilibrium modeling

A hybrid algorithm based on particle swarm optimization and ant colony optimization was used to describe the vapor–liquid equilibrium of complex mixtures. The proposed PSO+ACO algorithm is tested on several benchmark functions from the usual literature. Firstly, nine binary vapor–liquid phase systems containing supercritical fluids and ionic liquids were evaluated for optimizing the equation of state method. Next, twenty binary vapor–liquid phase systems were described using two activity coefficient models optimized by the hybrid algorithm. The results of vapor–liquid equilibrium modeling were compared with the Levenberg–Marquardt algorithm, and show that the application of PSO+ACO algorithm on thermodynamic models such as equation of state methods and activity coefficient models, is crucial, and that the hybrid PSO+ACO algorithm is a good tool to optimize the interaction parameters to describe the vapor–liquid equilibrium of several systems.

Considering the dispersive interactions in the COSMO-SAC model for more accurate predictions of fluid phase behavior

A term to consider the contribution of the dispersive interactions to the non-ideality of mixtures is introduced into the COSMO-SAC model on the basis of molecular simulation data from classical model force fields. This dispersion term is a one-constant Margules equation, where the constant is determined from the molecular dispersion parameter of the components. Furthermore, an atomic contribution method is proposed to calculate the dispersion parameter for a given molecule. For binary systems containing molecules consisting of C, H, N, O, F and Cl atoms, a total of 13 global parameters is introduced with the COSMO-SAC-dsp model. These parameters are obtained from regression to a large training set of binary vapor–liquid equilibrium (VLE) data from experiment. The overall deviations for VLE calculations on this training set are reduced by 25% in terms of the vapor pressure and 12% in terms of the vapor phase mole fraction. This dispersion term can provide a significant improvement for infinite dilution activity coefficient predictions, where the accuracy was increased by around 33%.

Graphene oxide hydration and solvation: an in situ neutron reflectivity study.

Graphene oxide membranes were recently suggested for applications in separation of ethanol from water using a vapor permeation method. Using isotope contrast, neutron reflectivity was applied to evaluate the amounts of solvents intercalated into a membrane from pure and binary vapors and to evaluate the selectivity of the membrane permeation. Particularly, the effect of D2O, ethanol and D2O-ethanol vapours on graphene oxide (GO) thin films (∼25 nm) was studied. The interlayer spacing of GO and the amount of intercalated solvents were evaluated simultaneously as a function of vapour exposure duration. The significant difference in neutron scattering length density between D2O and ethanol allows distinguishing insertion of each component of the binary mixture into the GO structure. The amount of intercalated solvent at saturation corresponds to 1.4 molecules per formula unit for pure D2O (∼1.4 monolayers) and 0.45 molecules per formula unit (one monolayer) for pure ethanol. This amount is in addition to H2O absorbed at ambient humidity. Exposure of the GO film to ethanol-D2O vapours results in intercalation of GO with both solvents even for high ethanol concentration. A mixed D2O-ethanol layer inserted into the GO structure is water enriched compared to the composition of vapours due to slower ethanol diffusion into GO interlayers.

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J0550101 ニ成分混合凝縮液膜の臨界厚さおよび臨界波数について([J055-01]マイクロ・ナノスケール熱流体現象(1))

A modified Patel–Teja cubic equation of state. Part II: Parameters for polar substances and its mixtures

In this work, the parameters of the equation of state formed by the Patel–Teja pressure–volume–temperature relationship and the alpha function of Heyen have been estimated for 184 polar substances. To obtain the parameters of the proposed model, pseudo-experimental data have been generated using the DIPPR correlations for vapor pressure and liquid density. The proposed model in conjunction with the Wong–Sandler mixing rules and the NRTL activity model have been used to describe the vapor liquid equilibria of some complex mixtures. Three kinds of binary systems have been analyzed and they are those of the type: polar substance/aromatic, polar substance/n-alkane and polar substance/n-alkanol. Based on the homologous series concept, generalized expressions for the binary interaction parameters in the Wong–Sandler-NRTL mixing rules were developed in order to correlate vapor–liquid equilibrium at low pressures for the selected mixtures. For n-alkanes and aromatic compounds, the acentric factor has been used to generalize the binary interaction parameters for mixtures with a polar substance and these kinds of compounds. In the case of systems composed by a polar substance and an alcohol, the reduced dipole moment of the alcohols is used to develop the generalized expressions. Ninety-two binary mixtures were analyzed and a relative average absolute deviation of 1.21% was estimated for the bubble pressure. Finally, the model was validated by predicting binary vapor–liquid equilibrium at high pressures and for ternary mixtures. In both cases, the results are satisfactory. The average absolute deviations in bubble pressure are 2.34% for high pressure predictions and 1.15% for ternary mixtures.

Vapor–Liquid Equilibrium Data for the Morpholine-4-carbaldehyde + n-Hexane or n-Heptane Binary Systems Using a Static-Synthetic Apparatus

Precise isothermal binary vapor–liquid equilibrium (VLE) measurements were performed for the morpholine-4-carbaldehyde + n-hexane or n-heptane systems at (343.15, 363.15, and 393.15) K using a static-synthetic apparatus. The P–x data measured were processed using both the model-dependent and model-independent approaches. Infinite dilution activity coefficients were estimated by the extrapolation of VLE data by three different methods. Excess enthalpy and entropy data were predicted from VLE data using the Gibbs–Helmholtz relation.

Flammability Limits of Binary Mixtures of 1,2-Ethanediol + Steam and 1,2-Propanediol + Steam

Flammability limits of binary vapor mixtures of 1,2-ethanediol + steam and 1,2-propanediol + steam were measured by the ASHRAE method. The test temperatures were 473 K for 1,2-ethanediol + steam and 463 K for 1,2-propanediol + steam. The observed values were analyzed by the extended Le Chatelier’s formula. It was found that the experimental results were excellently reproduced by the formula. In addition, the experimental results were compared with the estimated values based on the adiabatic flame temperature method. The observed values of lower flammability limits were in good agreement with the estimated values, and those of upper flammability limits were within acceptable deviations.

A novel dynamic recirculating apparatus for vapour–liquid equilibrium measurements at moderate pressures and temperatures

A novel dynamic recirculating apparatus has been constructed for the measurement of isobaric and isothermal vapour–liquid equilibrium (VLE) measurements for pressures up to 750kPa and temperatures up to 600K. The apparatus has been constructed from 316 stainless steel (SS) and features Pyrex sight glasses in strategic positions to allow for the observation of flow patterns and circulation rates. The capabilities of the apparatus have been demonstrated through the measurement of pure component vapour pressures and binary vapour–liquid equilibrium data. Vapour pressure measurements were undertaken for cyclohexane, n-heptane, n-octane, ethanol and 1-propanol. Isobaric VLE data have been measured for the (cyclohexane+ethanol) system at pressures of 40.00, 69.81, 97.72 and 150.0 kPa and isothermal VLE data have been obtained for the (2-propanone+2-butanol) system at a temperature of 373.15K. The experimental azeotropic temperatures and compositions for the cyclohexane+ethanol isobaric data sets have been determined and correlated to linear functions. The experimental VLE data were correlated to the Wilson, NRTL and UNIQUAC models using the γ−ϕ approach with the truncated two-term virial equation of state (with the Hayden and O’Connell method for second virial coefficients). Thermodynamic consistency testing for the VLE data sets was performed with the Herington area test for the isobaric data and the point test of Van Ness and Fredenslund for the isothermal data.

Energy and sizing analyses of parabolic trough solar collector integrated with steam and binary vapor cycles

In this study, solar field sizing and overall performance of different vapor cycles are examined. The systems considered are parabolic trough solar collectors integrated with either a binary vapor cycle or a steam Rankine cycle (SRC). The binary vapor cycle consists of an SRC as a topping cycle and an organic Rankine cycle as a bottoming cycle. Seven refrigerants are examined for the bottoming cycle: R600, R600a, R134a, R152a, R290, R407c, and ammonia. This study reveals that significant reduction in the solar field size is gained due to the performance improvement when the binary vapor cycle is considered as compared to a steam Rankine cycle with atmospheric condensing pressure; however, SRC with vacuum pressure has the best performance and smallest solar field size. It further reveals that the R134a binary vapor cycle has the best performance among the binary vapor cycles considered and, thus, requires the smallest solar field size while the R600a binary vapor cycle has the lowest performance. Finally, optimization shows that lowering the mass flow rate of the heat transfer fluid (HTF) per each solar collector row, within the range considered, results in a reduction of the required number of solar collector rows and, thus, in savings.

Simulation of an ammonia–water absorption chiller

An increased interest in absorption chillers has been observed [1] because these systems can utilize solar, geothermal and biomass energy sources, but also because they are quiet, vibration-free, require little maintenance and are ecological [2]. Instead of a compressor system, which uses electricity, an absorption cooling system, using renewable energy and kinds of waste heat energy, may be used for cooling. This paper presents the simulation of a single stage solar absorption chiller operating with an ammonia–water mixture under steady state conditions. This simulation is based on heat and mass balances for each component. The heat and mass transfers in the absorber, the condensation of binary vapor of ammonia–water in the condenser and a thermosyphon desorber placed under the purification column were modeled. The numerical model was compared and validated with experimental data obtained with a solar absorption chiller. The calculated results agree well with experimental data. Simulations based on experimental data were used to predict the temperature and concentration profiles in each heat exchanger. A parametric study was conducted to investigate the effect of evaporator and desorber temperature on the absorption chiller's performance. The COP decreases by 25% with a decrease of 10 °C in evaporator temperature and the COP increases by 4% with an increase of 10 °C in desorber temperature.

Experimental Measurements of Vapor–Liquid Equilibrium Data for the Binary Systems of Methanol + 2-Butyl Acetate, 2-Butyl Alcohol + 2-Butyl Acetate, and Methyl Acetate + 2-Butyl Acetate at 101.33 kPa

The isobaric vapor–liquid equilibrium measurements for the systems of 2-butyl acetate with three chemicals (methanol, 2-butyl alcohol, methyl acetate) were determined respectively in a modified Rose still at 101.33 kPa. Thermodynamic consistency of the three binary vapor–liquid equilibrium data had been confirmed by Herington methods. The three groups of experimental data were all correlated with NRTL and Wilson models, respectively. The binary interaction parameters of both models had been obtained by the simplex method. The NRTL and Wilson equations showed low deviation with respect to the experimental data.

The impact of volatile compounds released by paper on cellulose degradation in ambient hygrothermal conditions

The reactivity towards cellulose of various volatile compounds commonly released by paper was studied. Sheets of Whatman No. 1 (W1) and No. 40 (W40) were exposed to various concentrations of these compounds in vapour phase ranging from 20 to 80 ppm in closed vessels for 52 days in controlled ambient conditions, after which they were hygrothermally aged. The measured properties of the paper were copper number, degree of polymerization, zero-span breaking length, pH and yellowness index. The results showed that hydrogen peroxide was the most aggressive among the volatile compounds tested as it severely degraded W1 cellulose. The exposure of W1 to formic acid led to significant degradation, designating this volatile organic compound (VOC) as the most reactive toward cellulose among the carboxyl and carbonyl functionalized VOCs tested. On the other hand, acetic acid was found comparatively less reactive. Nitrogen oxides, which were produced up to 3 ppm from a side-reaction of the carboxylic acids with the magnesium nitrate used to control the relative humidity in the closed vessels, appeared to contribute significantly to the degradation despite their low concentration. Antagonistic effects were evidenced in binary vapour mixtures where the presence of aldehydes (formaldehyde and acetaldehyde) counteracted substantially the degradation induced by the most reactive compounds. It was also shown that acetaldehyde, hexanal and furfural in individual exposures had little to no reactivity. Upon exposure to formaldehyde, the rate of glycosidic bond cleavage of cellulose induced by the ageing of W1 was significantly reduced.