Azeotropic Behavior Research Articles

Isobaric vapor–liquid equilibrium for binary system of 2-ethylthiophene + n-octane at 101.33 kPa

Isobaric vapor–liquid equilibrium (VLE) data of 2-ethylthiophene and n-octane binary system were measured at 101.33kPa with a modified Rose-Williams still. Gas chromatography was used to analyze compositions of the samples from the vapor–liquid equilibrium system. The VLE measurement passed the thermodynamic consistency test proposed by Herington and no azeotropic behavior was found. The experimental data were correlated by Wilson, the non-random two-liquid (NRTL) and universal quasi-chemical activity coefficient (UNIQUAC) models, respectively. The corresponding parameters for the three models were obtained. Results showed that the Wilson model gave better predictions than NRTL and UNIQUAC models.

General reflection on critical negative azeotropy and upgrade of the Bancroft's rule with application to the acetone + chloroform binary system

The possible shapes of continuous critical loci for binary systems exhibiting a negative azeotrope which persists up to the critical region are reviewed and extensively discussed. Such a review made it possible to prove that the existence of an intersection point – in a (P, T) projection – between the critical line and one of the vaporization curves was a sufficient condition for a binary system to exhibit a critical azeotrope. The Bancroft's rule which until now stated that the existence of an intersection point between the two vaporization curves in a (P, T) plane was a sufficient condition to observe an azeotropic behavior was thus upgraded to take into account the crossing of the critical line and one of the vaporization curves. Such a point was logically called a Bancroft point of the second kind.In a second part, mixture critical points of the acetone+chloroform binary system were measured in order to determine if such a system exhibited a Bancroft point of the second kind and consequently if the negative azeotrope persisted up to the critical region. Along the critical line, the acetone mole fraction was varied between 0.06 and 0.92.

Effect of ionic strength on the reactivity ratios of acrylamide/acrylic acid (sodium acrylate) copolymerization

ABSTRACTThe ionic strength (IS) of polyelectrolyte solutions plays an important role in influencing reaction kinetics. The largely unstudied effect of IS on monomer reactivity ratios and copolymerization rates of acrylamide (AAm) and acrylic acid (AAc), in the form of sodium acrylate (NaAc), is investigated. Salt addition affects the nature of overall charges of the polyelectrolyte solution and diminishes the electrostatic repulsions between reacting chains. Therefore, changing the IS of the solution by incorporating salts affect not only the point estimates of the monomer reactivity ratios but also the overall behavior of the copolymerization (with a transition to azeotropic behavior). Experimental results on copolymerization rates confirm the observed trends in reactivity ratio behavior. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40949.

Isothermal VLE measurements for the binary mixture of 2,3,3,3-tetrafluoroprop-1-ene (HFO-1234yf) + 1,1-difluoroethane (HFC-152a)

Isothermal vapor–liquid equilibrium (VLE) data for the binary mixture of 2,3,3,3-tetrafluoroprop-1-ene (HFO-1234yf)+1,1-difluoroethane (HFC-152a) were measured at temperatures from 283.15K to 323.15K using a recirculation apparatus. The experimental data were correlated by using PR EoS with vdW mixing rule, the comparison between the correlation results and experimental data showed a good agreement. HFO-1234yf (1)+HFC-152a (2) system shows not only azeotropic behavior but also near azeotropic behavior with a very small temperature glide of less than 0.4K within the complete range of composition and of temperature.

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.

Isobaric Vapor–Liquid Equilibrium for the Binary Systems (Diethylamine + Ethanol), (Ethanol + N,N-Diethylethanolamine), and (Diethylamine + N,N-Diethylethanolamine) at p = (80.0 and 40.0) kPa

In this work, isobaric vapor–liquid equilibrium (VLE) data for the three binary systems composed of diethylamine (1) + ethanol (2), ethanol (1) + N,N-diethylethanolamine (2), and diethylamine (1) + N,N-diethylethanolamine (2) at p = (80.0 and 40.0) kPa have been measured using a modified Rose–Williams still. All of the experimental data passed thermodynamic consistency tests, including the area test of Herington and the point test of Van Ness and co-workers. No azeotropic behavior was observed at the two reduced pressures. The Wilson, NRTL, and UNIQUAC activity coefficient models were used to correlate the experimental data. The obtained results indicated that the UNIQUAC model was more suitable than the Wilson and NRTL models for correlating the measured isobaric VLE data.

Isobaric (vapour + liquid) equilibria for three binary systems (toluene + anisole, n-butylbenzene + anisole, and guaiacol + anisole) at 101.33 kPa

Bio-oil, derived from biomass flash pyrolysis, has been recognized as an important renewable resource for resolving the current energy crisis. However, the pyrolysis oil consists of complicated composition and has some undesired properties, including acidity, relatively high viscosity, limited thermal stability, low heating value, which hinder the direct application of bio-oil. So, separation and purification of the pyrolysis oil are important and the phase equilibrium data of the bio-fuel related mixtures is essential for the design and simulation of the processes. In this context, isobaric vapor–liquid equilibrium (VLE) data for the three binary mixtures in the pyrolysis oil, toluene+anisole, n-butylbenzene+anisole, and guaiacol+anisole, have been measured at 101.33kPa by a modified Rose–Williams still. All of the experimental VLE data were checked by the Herington analysis method and were verified the thermodynamic consistency. No azeotropic behavior was observed in the three binary systems. The measured data were well correlated by the non-random two-liquid (NRTL), universal quasi-chemical activity coefficient (UNIQUAC), and Wilson model, respectively. The corresponding parameters for the three models were obtained. The average absolute deviations of the temperature and the vapor compositions correlated by the three models for all the systems are below 0.55K and 0.019, respectively.

Isobaric Vapor–Liquid Equilibrium for the Binary System (Ethane-1,2-diol + Butan-1,2-diol) at (20, 30, and 40) kPa

The isobaric vapor–liquid equilibrium (VLE) data were measured for the binary system (ethane-1,2-diol + butan-1,2-diol) at (20, 30, and 40) kPa using a modified dynamic recirculating still. The thermodynamic consistency of the experimental data was confirmed using the Herington and van Ness semiempirical method. The Wilson and universal quasichemical (UNIQUAC) models were used to correlate the activity coefficients with the liquid-phase composition. The average absolute deviation of the bubble-point temperature and vapor molar fraction for all of the systems obtained from the Wilson and UNIQUAC models are less than 0.18 K and 0.0011, respectively. Furthermore, the binary system (ethane-1,2-diol + butan-1,2-diol) exhibited azeotropic behavior. In addition, the data were calculated using the UNIFAC (Do) model (modified UNIFAC model) in which ethane-1,2-diol was treated as two groups (−CH2OH), and butan-1,2-diol was split to four groups (−CH2OH, −CHOH, −CH2, and −CH3). The new group-interaction parameter for CH2–CH2OH was obtained and used to estimate the VLE data for the binary system (butan-2-ol + butan-1-ol) at 101.3 kPa. The results are consistent with those of the literature data.

Isobaric vapor–liquid equilibria of the binary mixtures propylene glycol methyl ether + propylene glycol methyl ether acetate, methyl acetate + propylene glycol methyl ether and methanol + propylene glycol methyl ether acetate at 101.3 kPa

Isobaric vapor–liquid equilibrium (VLE) data for three binary systems (PM+PMA, MeAc+PM and MeOH+PMA) at 101.3kPa were measured in a double circulating still of modified Othmer type. The thermodynamic consistency of the experimental data was checked by Herington method. The experimental data were correlated with NRTL and Wilson models. The binary interaction parameters of both models have been obtained by simplex method. The root mean square deviations (RMSD) for the vapor phase fraction and the boiling temperature are less than 0.01 and 0.5K, respectively. The results indicate that the calculated values by NRTL and Wilson models are in good agreement with the experimental data and no azeotropic behavior has been found in the three binary systems. The research findings would provide basic data for the design and analysis of distillation process.

Vapor–liquid equilibria for binary system of 2,3,3,3-tetrafluoroprop-1-ene (HFO-1234yf) + isobutane (HC-600a)

Isothermal vapor–liquid equilibrium data for the binary mixture of 2,3,3,3-tetrafluoroprop-1-ene (HFO-1234yf)+isobutane (HC-600a) were measured at temperatures from 283.15 to 323.15K using a recirculation apparatus. The experimental data were correlated using the Peng–Robinson equation of state with vdW mixing rule and Wong–Sandler mixing rule, respectively. The comparison between the correlation results and experimental data showed a good agreement, and Wong–Sandler mixing rule gave more accurate calculations for this binary system. Azeotropic behavior was found at high mole fraction of HFO-1234yf.

Isobaric vapor–liquid equilibrium for binary systems of n-undecane + p-, o-, m-xylene at 10 kPa

Isobaric vapor–liquid equilibrium (VLE) data were determined at the pressure of 10kPa for the three binary mixtures composed of n-undecane+p, o, m-xylene by using a recirculation type still. All the data passed the thermodynamics test and no azeotropic behavior was observed. The three binary VLE data were correlated with Wilson, NRTL, and UNIQUAC models and all shows good fitting results. As a whole, NRTL for n-undecane+p-xylene system, UNIQUAC for n-undecane+o-, m-xylene systems represent the VLE data better slightly.

Separation of methyl acetate + methanol azeotropic mixture using ionic liquid entrainers

Two ionic liquids (ILs), namely 1-butyl-1-methylpyrrolidinium dicyanamide [BMPYR][DCA] and 1-ethyl-3-methylimidazolium thiocyanate [EMIM][SCN], were studied as agents for the separation of the methyl acetate+methanol azeotropic mixture by extractive distillation. Isothermal vapor–liquid equilibria of the ternary systems with the ILs and all the constituting binary subsystems were measured by headspace gas chromatography (HSGC) to examine the effect of the IL additives on the separation factor. Two HSGC methods were combined to this end: one employing a commercial headspace autosampler and the other employing our own setup with external equilibrium cell and forced circulation of the vapor phase through the GC sampling loop. The HSGC methodology developed herein presents distinct advantages compared to conventional dynamic measurements using recirculation stills. The measurements were conducted at 327.31K, a temperature close to the normal boiling point of the methyl acetate+methanol azeotropic mixture, and at various compositions covering well the composition ranges of involved binaries and ternaries, particularly at compositions keeping constant IL contents. The ample experimental data allowed us to test the performance of several activity coefficient models and data treatment strategies. Using binary information only and the NRTL model gave fairly accurate predictions of the effect of ILs on separation factors. We found that both [BMPYR][DCA] and [EMIM][SCN] increase considerably the methyl acetate/methanol separation factor, breaking the azeotropic behavior at rather low levels of IL mole fractions (>0.043 and 0.087, respectively). As potential entrainers to separate methyl acetate from methanol by extractive distillation, [BMPYR][DCA] and [EMIM][SCN] outperform other ILs previously tested for this purpose in the literature.

Isobaric Vapor–Liquid Equilibrium and Isothermal Interfacial Tensions for the System Ethanol + 2,5-Dimethylfuran

This work reports isobaric vapor–liquid equilibrium (VLE) data experimentally determined at (50, 75, and 94) kPa and over the temperature range (334 to 364) K together with atmospheric interfacial tensions (IFT) measured at 298.15 K for the binary system composed by ethanol + 2,5-dimethylfuran. VLE determinations were carried out in a dynamic VLE cell, whereas a maximum differential bubble pressure tensiometer was used for performing IFT measurements. According to the experimental results, the binary system ethanol + 2,5-dimethylfuran exhibits positive deviation from ideal behavior and azeotropic behavior can be observed over the whole determined pressure range. The concentration of the azeotrope enriches in ethanol as pressure (and/or temperature) increases. The interfacial tension in turn, exhibits positive deviation from the linear behavior. The reported VLE data of the binary mixture are thermodynamically consistent according to Fredenlund’s test and were well correlated by traditional activity coeffi...

Interfacial tension of binary mixtures exhibiting azeotropic behavior: Measurement and modeling with PCP-SAFT combined with Density Gradient Theory

This work focuses on modeling and experimental investigation of temperature dependent interfacial properties of binary DMF/n-alkane (C7, C10, C12) mixtures. The systems consisting of solvents with very different polarity show azeotropic behavior. New experimental vapor–liquid and liquid–liquid interfacial tension data are provided between 298.15 and 328.15K using the drop volume method. The Perturbed Chain Polar Statistical Associating Fluid Theory (PCP-SAFT) equation of state was combined with the Density Gradient Theory (DGT) to calculate phase equilibria and interfacial properties. Modeling results are in good agreement with the corresponding experimental data. Thereby, the binary parameter βij within the DGT framework does not equal one. Investigating density and concentration profiles in the interface revealed characteristic trends which are related to the azeotropic behavior of the mixtures.

Breaking Azeotropes by Azeotropic and Extractive Distillation in a Dividing-Wall Column

This study gives a brief overview about using dividing-wall column (DWC) technology in azeotropic and extractive distillation processes aimed to break azeotropes. The relevant case study considered here is the bioethanol dehydration process that requires significant energy to overcome the azeotropic behaviour of ethanol-water mixture. The results of the rigorous Aspen Plus simulations show that energy savings of 10 – 20 % are possible for the novel process intensification alternative based on DWC, while using less equipment units as compared to the conventional azeotropic and extractive distillation configurations.

Vapor Pressure and Octane Numbers of Ternary Gasoline–Ethanol–ETBE Blends

The objective of this study was to examine key gasoline properties, such as octane rating and volatility of ternary blends with ethanol and ethyl-tert-butyl-ether (ETBE). Ethanol and ETBE were added in various concentrations in specific refinery gasoline pool components, so a total of 30 gasoline-ethanol-ETBE samples were prepared and tested. Vapor pressure and octane numbers [research octane number (RON) and motor octane number (MON)] were determined for the mixtures containing 0.9-5.5% v/v ethanol and 2.0-9.8% v/v ETBE. Ethanol was always considered a valuable component for refinery gasoline pool due to its good antiknock characteristics. However, its azeotropic behavior in gasoline is considered as a drawback for the vapor pressure of the blend. On the other hand, the use of ETBE in gasoline increases the octane number and lowers the vapor pressure, thus allowing refinery blenders to use a higher vapor pressure base gasoline in the final fuel formulation. Experimental results indicated that ethanol concentration up to 5% v/v in the gasoline formulation increased the vapor pressure of the mixture. The addition of both ethanol and ETBE in the base gasoline resulted in ternary mixtures which smoothed the behavior of the vapor pressure while they acted as excellent octane improvers.

Vapor–liquid equilibrium measurements of dimethylsulfide, +ethanol, +dimethylether, +methylacetate with a static total pressure method

Isothermal vapor–liquid equilibrium (VLE) of three binary mixtures was measured with a static total pressure apparatus: dimethylsulfide+ethanol at 350.4K, +dimethylether at 336.7K, +methylacetate at 350.3K. The Barker method was used to convert the total pressure and total composition measurements into vapor–liquid equilibrium data. Legendre polynomial and Wilson model were used as the liquid activity coefficient model to obtain the compositions of the vapor and liquid phases. All systems exhibited positive deviation from Raoult's law. The dimethylsulfide+ethanol system showed azeotropic behavior (x1az=0.058, Taz=350.4K, Paz=341.9kPa).

Isothermal vapor–liquid equilibrium data for the ethylene + 1,1,2,3,3,3-hexafluoro-1-propene binary system between 258 and 308 K at pressures up to 4.56 MPa

Isothermal vapor–liquid equilibrium data are reported for ethylene+1,1,2,3,3,3-hexafluoro-1-propene mixtures at six temperatures in the 258.35–307.38K range, and pressures up to 4.56MPa. The experimental data were measured using an apparatus based on the “static-analytic” method equipped with a movable ROLSI™ capillary sampler for repeatable and reliable equilibrium phase sampling and handling. The isothermal P–x–y data are well correlated with a model comprised of the Peng–Robinson equation of state containing the Mathias–Copeman alpha function, Wong–Sandler mixing rule, and NRTL local composition model. The combined model is termed “PR-MC-WS-NRTL”. The studied system does not exhibit azeotropic behavior nor liquid–liquid immiscibility over the range of investigated temperatures. Mixture critical points are calculated from the experimental vapor–liquid equilibrium data via the extended scaling laws and the PR-MC-WS-NRTL model, and are found to be in good agreement with the experimental isothermal phase envelopes.

Measurement and Modeling of Vapor–Liquid Equilibria for Systems Containing Alcohols, Water, and Imidazolium-Based Phosphate Ionic Liquids

Vapor–liquid equilibiria (VLE) were measured for systems containing 1-methyl-3-ethylimidazolium diethylphosphate ([EMIM][DEP]) ionic liquid (IL) in the temperature range from 310 K to 390 K. The systems include 1-propanol + [EMIM][DEP], 2-propanol + [EMIM][DEP], water +1-propanol + [EMIM][DEP], and water + 2-propanol + [EMIM][DEP]. [EMIM][DEP] was divided into one 1,3-dimethylimidazolium dimethylphosphate ([MMIM][DMP]) and three methylene (CH2) electrically neutral groups. And then the experimental VLE data for binary systems containing [EMIM][DEP] were regressed using the modified UNIFAC model with the maximum average relative deviation (ARD) of 2.7 %. The newly obtained interaction parameters between groups allowed the reliable prediction of other binary and ternary systems containing [MMIM][DMP] and [EMIM][DEP] without parametrization. It was found that both of the ILs can give rise to the salting-out effect, and lead to a breaking of the azeotropic behavior of alcohols + water mixtures. [MMIM][DMP] shows a higher separation ability for the azeotropic mixture studied than [EMIM][DEP].

Measurement and correlation of the (vapor + liquid) equilibria of pure 4-ethylmorpholine, 1,2-dimethylisopropylamine and N,N-dimethylethanolamine, and their binary aqueous solutions

The vapor pressures of (4-ethylmorpholine+water), (1,2-dimethylisopropylamine+water), (N,N-dimetylethanolamine+water) binary mixtures, and of pure 4-ethylmorpholine, 1,2-dimethylisopropylamine and N,N-dimethylethanolamine components were measured by means of two static devices at temperatures between {273 (or 283) and 333 (or 363)}K. The data were correlated with the Antoine equation. From these data excess Gibbs functions (GE) were calculated for several constant temperatures and fitted to a fourth-order Redlich–Kister equation using the Barker’s method. The (4-ethylmorpholine+water), and (1,2-dimethylisopropylamine+water) binary systems show positive azeotropic behavior. The aqueous solutions of 4-ethylmorpholine and 1,2-dimethylisopropylamine exhibit positive deviations in GE for all investigated temperatures over the whole composition, where the aqueous solution of N,N-dimetyhlethanolamine show a S shape for GE for (273.15<T<313.15)K. Additionally, the Wilson, NRTL or UNIQUAC models have been used and quite good results were obtained in the prediction of the total pressure.