Low Equilibrium Pressures Research Articles

Hydrate phase equilibrium measurement of 50 mol.% carbon dioxide / 33 mol.% dimethyl ether / 17 mol.% propane in the presence of tetrahydrofuran, cyclopentane, tetra‑n‑butylammonium bromide, and tetra‑n‑butylammonium chloride

Hydrate-based cold storage and refrigeration offer notable efficiency and safety advantages. By leveraging the high cold storage density of CO2 hydrate and the low phase equilibrium pressure and GWP of DME and C3H8 hydrates, a gas mixture hydrate (50 mol.% CO2, 33 mol.% DME, 17 mol.% C3H8) was used as a refrigerant for phase equilibrium assessment. Results showed phase equilibrium temperatures of 274.5 to 278.9 K at pressures from 0.4 to 0.86 MPa, aligning with conventional air conditioning pressures. Additives like THF, CP, TBAB, and TBAC improved conditions. Liquid promoters (THF, CP) increased temperatures by 4.5 to 7.9 K, while solid promoters (TBAB, TBAC) raised them by 5.3 to 11.1 K. Liquid promoters shifted the phase equilibrium curve for CO2-DME-C3H8 hydrate almost parallel to the right, while solid promoters steepened the curve slope. A predictive model was developed, showing good molar phase change enthalpy.

Thermodynamic and Kinetic Regulation for Mg‐Based Hydrogen Storage Materials: Challenges, Strategies, and Perspectives

AbstractMg‐based hydrogen storage materials have drawn considerable attention as the solution for hydrogen storage and transportation due to their high hydrogen storage density, low cost, and high safety characteristics. However, their practical applications are hindered by the high dehydrogenation temperatures, low equilibrium pressure, and sluggish hydrogenation and dehydrogenation (de/hydrogenation) rates. These functionalities are typically determined by the thermodynamic and kinetic properties of de/hydrogenation reactions. This review comprehensively discusses how the compositeization, catalysts, alloying, and nanofabrication strategies can improve the thermodynamic and kinetic performances of Mg‐based hydrogen storage materials. Since the introduction of various additives leads the samples being a multiple‐phases and elements system, prediction methods of hydrogen storage properties are simultaneously introduced. In the last part of this review, the advantages and disadvantages of each approach are discussed and a summary of the emergence of new materials and potential strategies for realizing lower‐cost preparation, lower operation temperature, and long‐cycle properties is provided.

Hydrogen storage properties of Zr-based multicomponent alloys with C14-Laves phase structure derived from the Zr–Cr–Mn–Fe–Ni system

This study focused on assessing the crystal structure and hydrogen storage properties of two multicomponent alloys having the Zr33(CrMnFeNi)67 and Zr33Cr22Mn15Fe25Ni5 compositions. Both alloys were designed by thermodynamic calculations derived from the TiZrCrMnFeNi system after removing the titanium element from the original composition and keeping the high fraction of zirconium to explore new Zr-based compositions with a strong tendency to crystallize as a C14 Laves phase. The arc-melted Zr-based alloys exhibited a significant presence of C14 Laves phases and small amounts of NiZr intermetallic phase. Hydrogen storage properties investigated through pressure-composition-temperature (PCT) absorption and desorption isotherms revealed that the Zr33Cr22Mn15Fe25Ni5 alloy could absorb 1.8% (H/M = 1.2) of hydrogen with fast kinetics at room temperature after a simple heat activation, while the Zr33(CrMnFeNi)67 alloy could reversibly absorb 1.6% (H/M = 1) with equally fast kinetics. Zr-rich alloys exhibited a low hydrogen equilibrium pressure in the PCT isotherms. After full hydrogenation at room temperature, the initial metallic C14 Laves phases were converted to the respective Laves phase hydrides in both cases. Under cycling, the fractions of the secondary NiZr and the C14 phase change as the samples become more activated. The microstructural analysis, before and after the cycling, showed a very homogeneous microstructure and good distribution of the elements in both alloys.

Enhancement of hydrogen storage performance in shell and tube metal hydride tank for fuel cell electric forklift

Novel metal hydride (MH) hydrogen storage tanks for fuel cell electric forklifts have been presented in this paper. The tanks comprise a shell side equipped with 6 baffles and a tube side filled with 120 kg AB5 alloy and 10 copper fins. The alloy manufactured by vacuum induction melting has good hydrogen storage performance, with high storage capacity of 1.6 wt% and low equilibrium pressure of 4 MPa at ambient temperature. Two types of copper fins, including disk fins and corrugated fins, and three kinds of baffles, including segmental baffles, diagonal baffles and hole baffles, were applied to enhance the heat transfer in metal hydride tanks. We used the finite element method to simulate the hydrogen refueling process in MH tanks. It was found that the optimized tank with corrugated fins only took 630 s to reach 1.5 wt% saturation level. The intensification on the tube side of tanks is an effective method to improve hydrogen storage performance. Moreover, the shell side flow field and hydrogen refueling time in MH tanks with different baffles were compared, and the simulated refueling time is in good agreement with the experimental data. The metal hydride tank with diagonal baffles shows the shortest hydrogen refueling time because of the highest velocity of cooling water. Finally, correlations regarding the effect of cooling water flow rate on the refueling time in metal hydride tanks were proposed for future industrial design.

Interzeolite transformation from H+-type FAU zeolite into pure CHA zeolite via OSDA/seeds-free and steam-assisted conversion process

Pure CHA zeolite was transformed from FAU zeolite via organic structure-directing agent (OSDA)/seeds-free steam-assisted conversion (SAC). CHA zeolite was transformed using H+-type FAU zeolite with a low Si/Al ratio (Si/Al = 2.8) and a small amount of potassium hydroxide (KOH) and H2O. The Si/Al ratio of the CHA zeolite of the final product was the same as that of FAU-type zeolite as raw material because OH− ions derived from KOH reacted with H+ ions in FAU zeolite. Then, Si constituting FAU zeolite was little dissolved in a small amount of the basic solvent during the interzeolite transformation process. In general, in the interzeolite transformation process, the Si/Al ratio of the final product is lower than that of zeolite as raw material due to the dissolution of Si in the framework in the basic solvent. However, the interzeolite transformation process in this study can reduce the dissolving Si ratio using H+-type FAU zeolite. In addition, the PHI framework with low CO2 adsorption capacity arose with CHA zeolite transformed from Na+-type FAU zeolite via OSDA-free interzeolite SAC in a previous study. However, in this study, the PHI framework did not arise in OSDA-free steam-assisted interzeolite transformation process due to the use of H+-type FAU zeolite. Furthermore, the second particle morphology of CHA zeolite transformed from H+-type FAU zeolite was spherical, which has not been seen in CHA zeolite particles synthesized in previous reports. Finally, the CO2 adsorption capacity and performance of FAU and CHA zeolites were measured. CHA zeolite showed higher CO2 adsorption capacity than H+-type FAU zeolite as the starting material and high CO2 loadings at low CO2 equilibrium pressure. This study investigated that the synthesis condition, chemical properties, and CO2 adsorption performance of CHA zeolite transformed from H+-type FAU zeolite via the OSDA/seeds-free steam-assisted interzeolite transformation process.

Low Subcritical CO2 Adsorption-Desorption Behavior of Intact Bituminous Coal Cores Extracted from a Shallow Coal Seam.

This study focuses on improving fundamental understanding of low, subcritical CO2 adsorption-desorption behavior of bituminous coals with the aim to evaluate the utility of shallow-depth coal seams for safe and effective CO2 storage. Comprehensive data and a detailed description of coal-CO2 interactions, e.g., adsorption, desorption, and hysteresis behavior of intact bituminous coals at CO2 pressures <0.5 MPa, are limited. Manometric sorption experiments were performed on coal cores (50 mm dia. and 30- or 60-mm length) obtained from a 30 m deep coal seam located at the Upper Silesian Basin in Poland. Experimental results revealed that the adsorption capacities were correlated to void volume and equilibrium time under low-pressure injection (0.5 MPa). The positive deviation, observed in the hysteresis of adsorption-desorption isotherm patterns, and the increased sample mass at the end of the tests suggested CO2 pore diffusion and condensation. This behavior is vital for assessing low-pressure CO2 injection and storage capabilities of shallow coal seams where confining pressure is much lower than that of the deeper seams. Overall, CO2 adsorption depicts a type II adsorption isotherm and a type H3 hysteresis pattern of the IUPAC classification. Experimental results fitted better to the Brunauer-Emmett-Teller model than the Langmuir isotherm model. CO2 adsorption behavior of intact cores was also evaluated by characteristic curves. It was found that Curve I favored physical forces, i.e., the presence of van der Waals/London dispersion forces to describe the coal-CO2 interactions. However, analysis of Curve II indicated that the changing pressure-volume behavior of CO2 in the adsorbed phase, under low equilibrium pressures, cannot be ignored.

CO2 solubility and diffusivity in 1-ethyl-3-methylimidazolium cation-based ionic liquids; isochoric pressure drop approach

In this study, an experimental approach based on the isochoric pressure drop principle was implemented to measure (at low equilibrium pressure, 1.3–3.6 bar) the solubility and binary diffusivity of CO2 (constant and variable) in four imidazolium-based room-temperature ionic liquids (RTILs), namely, 1-ethyl-3-methylimidazolium acetate ([emim][Ac]), 1-ethyl-3-methylimidazolium dicyanamide ([emim][DCA]), 1-ethyl-3-methylimidazolium methyl sulfate ([emim][MeSO4]) and 1-ethyl-3-methylimidazolium ethyl sulfate ([emim][EtSO4]). The molar fraction of the dissolved CO2 and Henry's law constant were measured from experimental data. Constant binary diffusion coefficients were measured from the transient thin-film and semi-infinite volume models. In the original approach, the variable diffusivity coefficient model was used to measure the concentration-based variable diffusion coefficient. Anion interaction of the RTILs was found to have a strong influence on the CO2 solubility, and Henry's law constant and the studied anions were ranked as [Ac]− >> [EtSO4]− > [DCA]− > [MeSO4]−. Increasing temperature is not likely for CO2 solubility while it favors CO2 diffusivity. Thin-film model diffusivity measurements were found to be more suitable for [emim][MeSO4] and [emim][EtSO4], while semi-infinite volume model was suitable for [emim][Ac] and [emim][DCA]. Variable diffusion coefficients were found not to be a monotonous function of time, which increased in early stages and decreased after a certain time. Gibbs free energy, enthalpy, and entropy values indicate the strength of the favorable interaction between CO2 and RTILs, mildly exothermic in nature and falling in the range of physisorption.

Water Vapor Adsorption Capacity Loss of Molecular Sieves 4A, 5A, and 13X Resulting from Methanol and Heptane Exposure.

Zeolite-based molecular sieves are applied in industrial dehydration units for their high water uptake capacities and extremely low equilibrium pressure of water vapor. During their operational life, they tend to lose their water vapor adsorption capacity slowly. To optimize the usage of molecular sieves in dryer units, it is vital to understand the mechanism(s) leading to deactivation. In this work, the capacity loss was studied by exposing LTA- and FAU-type zeolites to methanol and heptane vapors under relatively harsh conditions using repetitive adsorption/regeneration cycles. A simple microflow unit was designed and used for the deactivation experiments. The water vapor adsorption capacity of the resulting samples was measured using a gravimetric analyzer. In addition, they were characterized by classic XRD, 13C NMR, and TGA techniques. The crystallinity of fresh and spent zeolite XRD patterns was not drastically affected even after exposure to the contaminants. It was found that methanol easily gave rise to a severe loss of water vapor adsorption capacity, much more so than heptane. Water vapor uptake in the methanol exposed samples is ∼50% lower than that for the fresh zeolites. This is attributed to nonvolatile, residual hydrocarbons.

Hydrogen absorption/desorption reactions of the (TiVNb)85Cr15 multicomponent alloy

Ti-V-Nb-Cr alloys have been reported as potential candidates for hydrogen storage applications. Investigating the processes of absorption and desorption is paramount to understand the hydrogen storage properties of these novel alloys and to develop more efficient hydrogen storage materials. In this work, we investigated the hydrogen absorption/desorption reactions of the (TiVNb)85Cr15 BCC multicomponent alloy by laboratory and synchrotron X-ray diffraction, Pair Distribution Function (PDF) analyses, Transmission Electron Microscopy (TEM) and thermo-desorption analyses (TDS). Hydrogen absorption behavior was studied by pressure-composition-isotherm (PCI) at room temperature, which demonstrated levels of absorption around 2 H/M (H/M = hydrogen-to-metal ratio) with low equilibrium pressure. The results showed a multi-step hydrogenation process: alloy ↔ BCC solid solution ↔ BCC intermediate hydride ↔ FCC dihydride. PDF analyses showed that the partially hydrogenated alloy at different levels of H/M and the fully hydrogenated alloy can be reasonably described by models with phases presenting random atomic distribution in the metal crystallographic sites. Moreover, the partially hydrogenated sample prior to the complete formation of the intermediate hydride showed evidence of two co-existing BCC phases.

Helium recovery and blanketing effect with the hydriding reaction of ZrCo

The hydriding reaction with hydride materials such as ZrCo, which has low hydrogen equilibrium pressure at room temperature, can be used in the helium-3 purification process to remove tritium impurity from a mixture of helium-3 and tritium. However, the helium interferes with the hydriding reaction, so it is necessary to confirm whether the helium affects the reduction of the tritium partial pressure to the equilibrium pressure of ZrCo tritide. Various hydrogen and helium mixtures were applied to the hydriding reaction under two reaction temperatures and two final H/M ratios to determine whether helium affects the reduction of the hydrogen partial pressure. Regardless of the helium fractions in the feed gases, residual hydrogen pressures were similar to the equilibrium pressure of ZrCo hydride under the different temperature and final H/M ratio conditions. Applying ZrCo hydriding reaction with a circulation loop, the helium-3 purification process can efficiently remove the tritium impurity without creating the blanketing effect.

Influence of electrostatic field on the interaction of AB5-type alloy LaNi4.4Al0.3Fe0.3 with hydrogen

The effect of the electrostatic field on hydrogen absorption is experimentally studied for the case of AB5-type intermetallic compound LaNi4.4Al0.3Fe0.3 with low equilibrium pressure. Experimental facility contained control and measurement system for PCT-isotherms and a non-conductive polymer vessel immersed in a bath of a thermostat with transformer oil. The test sample with 100 g of the activated alloy powder was used. Electrostatic field was created between a copper tube, which simultaneously served as a hydrogen inlet, connected to a high voltage source and a grounded nickel plate rolled in the form of a cylinder around the outer wall of the vessel. The electrodes were arranged coaxially, the maximum voltage on the internal electrode was 15 kV. The high voltage source also allowed changing the polarity on the internal electrode.It was found that the electrostatic field had no effect on the already established equilibrium in the hydrogen-alloy system at a voltage at the electrode up to 15 kV, regardless of the polarity. However, the process of hydrogen absorption is noticeably slowed down when a voltage of up to 15 kV with negative polarity is applied to the internal electrode, and the effect increases with increasing voltage. At a voltage of 15 kV and the positive polarity of the internal electrode, there was no noticeable effect on the hydrogen absorption process.

Hydrogen storage properties of Zr2Co crystalline and amorphous alloys

To further explore the application feasibility of Zr2Co alloy in tritium-related fields, hydrogenation/dehydrogenation properties of this material of crystalline or amorphous structure, prepared by arc melting or melt spinning, were studied by pressure-composition temperature measurement, X-ray diffraction, differential scanning calorimeter, thermal desorption spectroscopy. It was found that the two kinds of Zr2Co alloys can absorb hydrogen in a close full concentration of ~9 mmol/g, and may have similar equilibrium hydrogen pressure in the order of 10−6 Pa at room temperature. In their hydrogenated samples various hydrides were observed to form, including ZrH2, Zr2CoH5, ZrCoH3 and an amorphous one with gradually decreasing general thermostability. The amorphous alloy exhibited easier hydrogen induced disproportionation caused by highly stable ZrH2 and much slower hydrogen absorption kinetics. This disproportionation behavior of the crystalline alloy was found to be entirely suppressed by changing heating process. The results firmly indicate that crystalline Zr2Co alloy could be more favorable for tritium treatment due to very low equilibrium pressure and the feasibility of eliminating the disproportionation.

Experimental investigations of AB5-type alloys for hydrogen separation from biological gas streams

AB5-type intermetallic compounds are suitable materials for hydrogen separation due to their ability selectively absorb hydrogen from different gas streams, including biologically produced ones. Recent studies show that metal hydride-based purification systems can effectively extract hydrogen from biogas with high CO2 concentration. Alloys LaNi5-xMx (M = Fe, Al, Mn, Sn) are prepared and activated during several cycles of H2 sorption/desorption and their PCT properties are measured in Sievert's type apparatus. Two compositions LaNi4.4Fe0.3Al0.3 and LaNi4.6Mn0.2Al0.2 are chosen for further investigations because they meet the requirements for biohydrogen separation system. After PCT measurements of 50-g samples, metal hydride powders are investigated by means of Quantochrome Nova 1200 and scanning electron microscopy to determine porosity, average particle size, specific surface area and permeability of metal hydride bed. Powder bed permeabilities are defined as 9.08 × 10−13 m2 for LaNi4.4Fe0.3Al0.3 and 6.86 × 10−13 m2 for LaNi4.6Mn0.2Al0.2 by Kozeny-Carman equation. AB5 type LaNi4.4Fe0.3Al0.3 and LaNi4.6Mn0.2Al0.2 alloys show good characteristics: low equilibrium pressures 0.025–0.03 MPa and acceptable reversible hydrogen capacity 1.1 %wt. for stationary hydrogen separation system.

Diatom frustule-graphene based nanomaterial for room temperature hydrogen storage

Development of a room temperature hydrogen storage material is vital for the realization of a hydrogen economy. Towards achieving this goal, we present the use of naturally occurring diatom frustule for the synthesis of a novel nanomaterial that can achieve a hydrogen storage capacity of ~4.83 wt% at 25 °C and ~20 bar H2 equilibrium pressure. We have effectively combined the large surface area of few layer graphene(G), the unique physical and chemical properties of diatom frustules(D) such as chemical inertness and good porosity and the ability of transition metals and their alloys (Pd3Co) to adsorb large amounts of hydrogen. The resulting nanomaterial (Pd3Co-D(100)-G) has a surface area of 163.25 m2/g and pore volume of 0.84 cm3/g. The observations in the present study suggest that increased surface area and porosity play a key role in achieving high hydrogen storage capacity at relatively low H2 equilibrium pressures and room temperature conditions.

Microstructure and Hydrogen Absorption Properties of a BCC Phase Accompanied Laves Alloy

A non-stoichiometry Zr0.7Ti0.4V1.5Cr0.4 alloy has been synthesized by arc melting following annealing treatment or melt-spinning to obtain the bulk and ribbon samples, respectively. XRD investigation reveals the multiphase structure consisting of C15-Laves, V-BCC and a small amount of α-Zr or Zr3V3O. The alloy shows easy activation and fast hydrogenation kinetics. The annealed alloy absorbs 2.51 wt% H at room temperature, higher than the melt-spun ribbons. Refined grains by melt-spinning accelerates the hydrogenation of bulk alloy. The absorption behavior in presence of 1 mol% air has been tested to evaluate the anti-poisoning ability. Pressure–composition–temperature characteristics and thermodynamics parameters indicate the low equilibrium pressure and high hydrides stability. Hydrides investigation reveals that the Laves phase dominant multiphase structure contributes to the enhanced hydrogen capacity and multi-stage hydrogen release in DSC curve.

Insights for Designing the Hydrocarbon Recovery from Ionic Liquids by Distillation in the Aliphatic/aromatic Separation by Liquid-liquid Extraction

Nowadays the aliphatic/aromatic separation by liquid-liquid extraction using ionic liquids (ILs) is an interesting topic in the search of a new class of separation processes for the oil industry. The wide majority of papers published until now has focused in maximizing the IL extractive properties as can be found in a recent review by Canales and Brennecke (2016); in addition, in the recent past, this search was also oriented to find a commitment election between IL extractive and physical properties, with especial focus on reducing the viscosity to limit its impact on mass transfer and pumping (Larriba et al., 2013a). However, the challenge in the development of this new liquid-liquid extraction technology based on ILs is the selective recovery of aromatics from the solvent. Although IL non-volatile character is suggested as a clear advantage for separation purposes, this is truly a limitation in the vapor-liquid separation as was reported in last papers dealing with the vapor-liquid equilibria involving aliphatics, aromatics, and ILs due to the pretty low equilibrium pressures (Navarro et al., 2015). In addition, the thermal stability of ILs is another drawback since scarce species could be used at industrial scale over 473 K (Navarro et al., 2013). Finally, extracted aromatics have not commercial purity and further purification is mandatory before the aromatic/IL separation (Larriba et al., 2013a). In this work, the simulation of three different recovery sections based on vapor-liquid separations was performed to give some remarks that can help to design distillation processes involving large amounts of ionic liquids. Seven ionic liquids among the most promising species proved so far were selected to completely cover the transferability between liquid-liquid and vapor-liquid equilibria (LLE and VLE, respectively). Aspen Plus commercial simulator was used implementing the Non-Random Two Liquids (NRTL) models from the experimental data regressions for the corresponding n-heptane + toluene + ionic liquid ternary systems. Aromatic recoveries and purities for three different process configurations were analysed in order to stablish the impact of the ionic liquid extractive and thermal properties on the design of a suitable recovery section from an industrial point of view.

RETRACTED - High discharge capacities of Ti-based quasicrystal electrodes synthesized by mechanical alloying

ABSTRACTTi-based quasicrystals are well known to store a high capacity of hydrogen exceeding the density of liquid hydrogen. This fact is due to that TiZrNi contain a large number of tetrahedral sites formed with Ti and Zr atoms that are chemical affinity with hydrogen. TiZrNi quasicrystal absorbs hydrogen up to host metal ratio (H/M) value near to 2.0. The disadvantage is due to the low equilibrium pressure. To solve this problem, we substituted Ti with a small amount of vanadium (V), with the nominal composition Ti45−x VxZr38Ni17 (x = 5, 10, 15) and synthesized by mechanical alloying. The subsequent annealing in vacuum conditions converted the amorphous into an icosahedral quasicrystal (I-phase) with face-centered cubic (FCC) Ti2Ni-type crystal. As the results, we investigated the discharge capacity for both amorphous and quasicrystal electrodes using three electrodes system (working, reference and counter electrodes) at room temperature. The highest discharge capacities obtained were 81.45 mAh/g recorded for amorphous electrode and 318.4 mAh/g for quasicrystal whose compositions is Ti35V10Zr38Ni17 at discharge current density of 15 mA/g. X-ray diffraction measurement was performed to provide the structural information on materials before and after hydrogenation. Microstructures of the materials were studied using an electron scanning microscope and the chemical compositions were confirmed using an EDX-analysis.

Hysteresis phenomena on the crystal lattice of Ti0.8Zr0.2Mn1.5 in the hydrogenation and dehydrogenation process

The crystal structure changes in the hydrogenation and dehydrogenation process have been investigated by the in-situ synchrotron X-ray diffraction measurement to elucidate the mechanism of hysteresis phenomena in equilibrium hydrogen pressure. The hysteresis phenomena were observed on the crystal lattice. The lattice constants and volume of α-phase (hydrogen solid solution) and β-phase (hydride) in the dehydrogenation process with lower equilibrium pressure were smaller than those in the hydrogenation process with higher equilibrium pressure. This phenomenon is opposite to the general relationship between the lattice volume and the equilibrium pressure. The hysteresis phenomenon was also observed in the diffraction peak widths. The peak widths of β-phase in the dehydrogenation process were wider than those in the hydrogenation process. The hysteresis phenomena may be related to lattice defects and the hydrogen content in crystalline regions.

Investigation on LiBH4-CaH2 composite and its potential for thermal energy storage

The LiBH4/CaH2 composite are firstly studied as Concentrating Solar Power Thermal Storage Material. The LiBH4/CaH2 composite according to the stoichiometric ratio are synthesized by high-energy ball milling method. The kinetics, thermodynamics and cycling stability of LiBH4/CaH2 composite are investigated by XRD (X-ray diffraction), DSC (Differential scanning calorimeter) and TEM (Transmission electron microscope). The reaction enthalpy of LiBH4/CaH2 composite is almost 60 kJ/mol H2 and equilibrium pressure is 0.482 MPa at 450 °C. The thermal storage density of LiBH4/CaH2 composite is 3504.6 kJ/kg. XRD results show that the main phase after dehydrogenation is LiH and CaB6. The existence of TiCl3 and NbF5 can effectively enhance the cycling perfomance of LiBH4/CaH2 composite, with 6–7 wt% hydrogen capacity after 10 cycles. The high thermal storage density, high working temperature and low equilibrium pressure make LiBH4/CaH2 composite a potential thermal storage material.

Thermodynamic consistency of low pressure equilibrium data of water + congener mixtures using a versatile equation of state

A general thermodynamic consistency test is applied to analyze phase equilibrium data (TPxy data) for binary water + congener mixtures found in alcoholic distillation processes. The congeners, substances that are present at very low concentration in a must, considered in this study are: acetic acid, acetaldehyde, ethyl acetate, furfural, methanol, 1-propanol, methyl acetate and 2-butanol. The thermodynamic test combines the Peng–Robinson equation of state modified by Kwak and Mansoori for correlating phase-equilibrium data and the Gibbs–Duhem equation to check for consistency. The test is applied to analyze twenty five isothermal P-x-y data of water+congener mixtures obtained from the literature. Of the 25 sets of data, 18 are found to be thermodynamically inconsistent. In several cases, the results are in agreement with information from the literature in which these same systems are considered to be thermodynamically inconsistent using a test that uses activity coefficients for the liquid phase.