Pressure-temperature Behavior Research Articles

Isochoric pressure-temperature behavior of lactalbumin+water reactive mixtures under subcritical conditions

This study examines the pressure-temperature (P-T) behavior of reactive mixtures composed of lactalbumin and water under subcritical and isochoric conditions. The impact of density on the P-T behavior was investigated for an initial lactalbumin composition of 5%, covering a density range of 0.7597 g/mL to 0.85620 g/mL. Additionally, the effect of varying lactalbumin concentrations, ranging from 3% to 15% (w/w), at a constant initial density of 0.831 g/mL, was also studied. Isochoric lines and density values of the reactive mixtures were compared to those of pure water under identical pressure and temperature conditions in all experiments. Furthermore, the total soluble solids (TSS) content was analyzed after each experiment, along with the thermal stability of amino acids subjected to prolonged reaction periods and high temperatures.

Modelling a CO2 meter for a petroleum multiphase mixture at subsea conditions

Measuring high levels of carbon dioxide (CO2) in Brazilian pre-salt production flows remains a considerable technological challenge. The complexity of the three-phase flow and the variable CO2 solubility within each phase poses difficulties in accurately measuring CO2 in this scenario. Moreover, existing CO2 measurement techniques designed for single-phase fluids prove insufficient under mixed-phase conditions. This study proposes a methodology for a simple CO2 meter capable of determining the CO2 content in an oil and gas production stream. The proposed meter operates by analyzing the pressure change during a heating assay of an imprisoned sample. A computational model was developed in the ASPEN HYSYS® process simulator with the Peng-Robinson Equation of State to calculate the mixture properties emulating the isochoric process in the meter under different CO2 levels and initial conditions. The modelling results indicate that the pressure-temperature (P-T) behavior exhibits linearity with a slope that increases with higher CO2 content, which is characteristic of many pre-salt production fields. The model successfully reproduced published experimental data for an isochoric process.

Characterization of CO2 self-release during Heletz Residual Trapping Experiment I (RTE I) using a coupled wellbore-reservoir simulator

In order to quantify CO2 residual trapping in situ, two dedicated single-well push-pull experiments have been carried out at the Heletz, Israel pilot CO2 injection site. Field data from some parts of these experiments suggests the important effect of the hydrodynamic behavior in the injection-withdrawal well. In the present work a model capturing the CO2 transport and trapping behavior during Heletz Residual Trapping Experiment I is developed, with a special focus on coupled wellbore-reservoir flow. The simulation is carried out with the numerical simulator T2Well/ECO2N (Pan et al. 2011) which considers the wellbore-reservoir coupling. Of particular interest is to accurately model the period when the well is open to the atmosphere and self-producing CO2 and water in a geyser-like manner. It is also of interest to identify what conditions are causing the oscillating pressure-temperature behavior and the associated periodic gas-liquid releases, as well as to determine the amount of gas lost from the reservoir during this period. The results suggest that the behavior is due to cyclical CO2 exsolution from the aqueous phase along with a reduction of mobility of both CO2 and brine in the near wellbore-reservoir area, the latter being due to a zone of dispersed CO2 bubbles near the wellbore. This behavior could be successfully captured with a new set of relative permeability functions developed earlier for CO2 exsolution in laboratory experiments (Zuo et al., 2013).

Prediction of the density–pressure–temperature behavior in the isotropic–nematic phase transition of MBBA liquid crystal

In this work, it is proposed a perturbation theory in conjunction with the Convex Peg HERSW model and an adjustable intermolecular potential. The perturbation theory developed can quantitatively predict the density–pressure–temperature experimental behavior at the isotropic–nematic phase transition of MBBA at 1 atm.

Charge disproportionation and site-selective local magnetic moments in the post-perovskite-type Fe2O3 under ultra-high pressures

The archetypal 3d Mott insulator hematite, Fe2O3, is one of the basic oxide components playing an important role in mineralogy of Earth’s lower mantle. Its high pressure–temperature behavior, such as the electronic properties, equation of state, and phase stability is of fundamental importance for understanding the properties and evolution of the Earth’s interior. Here, we study the electronic structure, magnetic state, and lattice stability of Fe2O3 at ultra-high pressures using the density functional plus dynamical mean-field theory (DFT + DMFT) approach. In the vicinity of a Mott transition, Fe2O3 is found to exhibit a series of complex electronic, magnetic, and structural transformations. In particular, it makes a phase transition to a metal with a post-perovskite crystal structure and site-selective local moments upon compression above 75 GPa. We show that the site-selective phase transition is accompanied by a charge disproportionation of Fe ions, with Fe3±δ and δ ~ 0.05–0.09, implying a complex interplay between electronic correlations and the lattice. Our results suggest that site-selective local moments in Fe2O3 persist up to ultra-high pressures of ~200–250 GPa, i.e., sufficiently above the core–mantle boundary. The latter can have important consequences for understanding of the velocity and density anomalies in the Earth’s lower mantle.

Thermodynamics and kinetics of methane hydrate formation and dissociation in presence of calcium carbonate

Huge amount of gas hydrate deposits are identified in deep marine sediments, which may be considered as a future source of energy. Since carbonate is one of the major components of marine sediments, in the present study attention has been given to characterize methane hydrate formation and dissociation in presence of calcium carbonate. Experiments were performed with 0%, 2%, 4%, 6% and 10% by weight of calcium carbonate in distilled water. Extensive investigations have been done on pressure-temperature equilibrium behavior of hydrate formation and dissociation at varying concentrations of calcium carbonate. Hydrate formation rate was found to vary with concentration of calcium carbonate as the solubility of calcium carbonate in water is controlled by the presence of simultaneous chemical equilibria involving a high number of species like Ca2+, CO32−, HCO3−, CO2, etc. Induction time for hydrate formation has also been measured at different concentrations of carbonate. Nucleation point for the hydrate formation was observed to be slightly higher at higher concentration of calcium carbonate due to increased heat absorption. Dissociation enthalpy of hydrates was calculated by using Clausius-Clapeyron at different measured conditions. Moles consumption of methane gas during hydrate formation at different concentrations of carbonate was measured using real gas equation and found to be minimum at 10 wt%.

Experimental Assessment of Saturation Behavior of Boiling Nanofluids: Pressure and Temperature

The need to dissipate heat fluxes more than those commonly handled by boiling flows is forcing designers to consider boiling nanofluids flows as cooling option. In modeling boiling flows in cooling applications, the dependency of temperature and pressure is of great importance. In the present study, pressure–temperature variations at saturation conditions are empirically measured for different types of water-based nanofluids with variable volume fractions. Titanium oxide, silver, gold and nickle nanoparticles are studied. Results show that, except for titanium oxide and gold nanofluids, nanoparticles do not influence saturation conditions of the pure water significantly. Two individual correlations are proposed in this study to simulate the saturation pressure–temperature behavior of gold and titanium oxide water-based nanofluids in different volume fractions.

Isobaric Thermal Expansion of Compressed 1,4-Dichlorobutane and 1-Bromo-4-chlorobutane: Transitiometric Results and a Novel Application of the General Density Scaling-Based Equation of State

A transitiometric method for determining isobaric thermal expansivity of liquid 1,4-dichlorobutane and 1-bromo-4-chlorobutane as a function of temperature and pressure through calorimetric measurements against pressure is described. Isobaric thermal expansivities of haloalkanes were determined over the temperature range from 273.15 to 423.15 K at pressures up to 200 MPa. Experimental results were used to model the general density scaling-based equation of state and to analyze the pressure–temperature behavior of the thermal expansion coefficient. We confirmed that investigated liquids present a characteristic pressure range in which (∂αP/∂T)P = 0.

Analysis of the Influence of the Molecular Volume to Predict Experimental Pressure-Temperature Behavior in the Isotropic-Nematic Phase Transition of PAP, 5CB, MBBA and EBBA

In this work, we have analyzed the experimental pressure-temperature behavior at the isotropic-nematic phase transition of the liquid crystals PAP, 5CB, MBBA, and EBBA at 1 atm by using the HERSW Convex Peg model in conjunction with the IPCM model. We have calculated the molecular volume values for the hard and attractive cores from theoretical quantum calculations at the PM3, PM6, B3LYP/6-311++G(d,p)//PM6, and M06/6-311++G(d,p)//PM6 levels of theory. The results suggest that the best theoretical prediction of the experimental pressure-temperature behavior is obtained when the molecular volume is evaluated at the DFT level.

Simulating protein unfolding under pressure with a coarse-grained model

We describe and test a coarse-grained molecular model for the simulation of the effects of pressure on the folding/unfolding transition of proteins. The model is a structure-based one, which takes into account the desolvation barrier for the formation of the native contacts. The pressure is taken into account in a qualitative, mean field approach, acting on the parameters describing the native stabilizing interactions. The model has been tested by simulating the thermodynamic and structural behavior of protein GB1 with a parallel tempering Monte Carlo algorithm. At low effective pressures, the model reproduces the standard two-state thermal transition between the native and denatured states. However, at large pressures a new state appears. Its structural characteristics have been analyzed, showing that it corresponds to a swollen version of the native structure. This swollen state is at equilibrium with the native state at low temperatures, but gradually transforms into the thermally denatured state as temperature is increased. Therefore, our model predicts a downhill transition between the swollen and the denatured states. The analysis of the model permits us to obtain a phase diagram for the pressure-temperature behavior of the simulated system, which is compatible with the known elliptical shape of this diagram for real proteins.

Different pressure–temperature behavior of the structured and unstructured regions of titin

Contrary to the classical view, according to which all proteins adopt a specific folded conformation necessary for their function, intrinsically unstructured proteins (IUPs) display random-coil-like conformation under physiological conditions. We compared the structured and unstructured domains from titin, a giant protein responsible for striated-muscle elasticity. A 171-residue-long fragment (polyE) of the disordered PEVK domain, and an Ig domain (I27) with ordered structure were investigated. FTIR (Fourier transform infrared) and fluorescence spectroscopy combined with a diamond anvil cell were used for investigation of the secondary structures under wide range of pressure and temperature. PolyE preserves its disordered characteristics across the entire range of investigated pressure (0–16kbar), temperature (0–100°C), pD (3–10.5) and different solvent conditions. The detailed temperature–pressure phase diagram of titin I27 was determined. At 30°C, increasing pressure unfolds titin I27 in one step at 10.5kbar. Increasing temperature at atmospheric pressure results in two transitions. At 50°C the secondary structure is loosened and the protein transforms into a molten-globule state. At 65°C the protein completely unfolds. Unfolding is followed by aggregation at ambient pressure. Moderate pressures (>2kbar), however, can prevent the protein from aggregation. Our experiments in wide range of physical parameters revealed four different structures for I27, while the unstructured character of the PEVK fragment is insensitive to these parameters.

Phase transition and metallization of FeO at high pressures and temperatures

[1] Wustite, Fe1-xO, is an important component in the mineralogy of Earth's lower mantle and may also be a component of the core. Therefore its high pressure-temperature behavior, including its electronic structure, is essential to understanding the nature and evolution of Earth's deep interior. We performed X-ray diffraction and radiometric measurements on wustite in a laser-heated diamond anvil cell, finding an insulator-metal transition at high pressures and temperatures. Our data show a negative slope for this apparently isostructural phase boundary, which is characterized by a volume decrease and emissivity increase. The metallic phase of FeO is stable at conditions of the lower mantle and core, which has implications for the highP-Tcharacter of Fe-O bonds, magnetic field propagation, and lower mantle conductivity.

Lattice phonons of solid phases (α,β,δ,ε) of carbon monoxide by optical studies

The phase diagram of solid carbon monoxide was investigated in the pressure range 0–10GPa and temperature range 30–300K by infrared and Raman spectroscopy. The tentative phase diagram known from the literature was expanded and specified in detail. The δ-phase region is divided into two subphases—δrot and δloc—similar to solid nitrogen. The pressure-temperature behavior of the elementary and combined excitations was also followed up. The vibron overtone region was carefully investigated by FTIR spectroscopy as a function of temperature at different pressures; the fundamental region was investigated by Raman spectroscopy. The features of the IR-active phonon sideband to the vibron overtone were investigated in detail in the entire pressure-temperature region. The lattice-phonon spectra were studied by Raman spectroscopy as a function of pressure (at lowest temperature) and by IR spectroscopy as a function of temperature at saturated vapor pressure.

Origin of diffuse scattering in relaxor ferroelectrics

High-pressure and variable temperature single crystal synchrotron X-ray measurements combined with first-principles based molecular dynamics simulations study diffuse scattering in the relaxor ferroelectric system PSN (PbSc$_{1/2}$Nb$_{1/2}$O$_3$). Constant temperature experiments show pressure induced transition to the relaxor phase at different temperatures characterized by butterfly and rod shaped diffuse scattering around the $\{$h00$\}$ and $\{$hh0$\}$ Bragg spots, respectively. The simulations reproduce the observed diffuse scattering features as well as their pressure-temperature behavior, and show that they arise from polarization correlations between chemically-ordered regions, which in previous simulations were shown to behave as polar nanoregions. Simulations also exhibit radial diffuse scattering (elongated towards and away from {\bf Q}=(000)), that persists even in the paraelectric phase, consistent with previous neutron experiments on (PbMg$_{1/3}$Nb$_{2/3}$O$_3$) (PMN)

Analysis of the experimental pressure–temperature behavior in the isotropic–nematic phase transition for p-azoxianisol by using different Convex Peg models

In this work, we analyzed the experimental pressure–temperature behavior in the isotropic–nematic phase transition for the liquid crystal p-azoxianisol at 1 atm by using different Convex Peg models (HERSW, HERSWS and HERSWE). Additionally, we proposed a new development for the HERSW and HERSWE models. The values of the molecular volumes of the hard and attractive cores used in these models were obtained from theoretical quantum calculations at B3LYP/6-311++G level including the solvatation model IPCM. HERSW and HERSWS models predicted adequately the I–V–N triple point. For such models, we analyzed, the case when a/b = 3.5 and λ = 3.5 (model HERSWS) and the particular cases when a/b = 3.5 and a/b λ = 1.75, a/b = 3.6 and a/b λ = 1.8 and finally, a/b = 3.7 and a/b λ = 1.85 for HERSW model. HERSWE could not predict the I–V–N triple point and it was not possible to analyze the experimental behavior. We found that the Convex Peg model HERSW with parameters a/b = 3.7 and a/b λ = 1.85 predicts quantitatively the experimental pressure–temperature behavior in the isotropic–nematic phase transition for the liquid crystal p-azoxianisol at 1 atm.

Phase stability of TiH 2 under high pressure and temperatures

Phase stability of titanium hydride (TiH 2) was studied at high pressure-high temperature conditions using synchrotron radiation under non-hydrostatic conditions. Resistive heating method was used to heat the sample to a maximum temperature of 873 K in a diamond anvil cell (DAC) under pressure up to 12 GPa. Pressure–temperature behavior was studied by varying the temperature upto 823 K in steps of 50 K with pressure variations within 3 GPa. Structural phase transformation from tetragonal (I4/mmm) to cubic (Fm-3 m) was observed with increase in temperature. Tetragonal phase was found to be stabilized when the sample was subjected to pressure and temperature cycle.

On the Thermal Expansion of Water and the Phase Behavior of Macromolecules in Aqueous Solution

Water is crucial for the existence of life as we know it, and many have wondered what makes water so special. Here we point out the analogies between the pressure-temperature dependence of the isobaric thermal expansion of water (αp) and the pressure-temperature phase behavior of macromolecules in aqueous solutions. We suggest that αp could be the key to understand why water is to be the so-called ‘matrix of life’.

Post-Rh2O3(II)transition and the high pressure-temperature phase diagram of gallia: A first-principles and x-ray diffraction study

The high pressure-temperature behavior of gallium sesquioxide (gallia) has been investigated by combining first-principles density functional computations and high-pressure x-ray diffraction measurements up to $2\phantom{\rule{0.3em}{0ex}}\mathrm{Mbar}$. Calculations show that at $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the transformation from corundum-type $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ to ${\mathrm{Rh}}_{2}{\mathrm{O}}_{3}(II)$-type structure at $32\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ is followed by second one to the $Cmcm$ structure at $141\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. This post-${\mathrm{Rh}}_{2}{\mathrm{O}}_{3}(II)$ transition was successfully confirmed experimentally at $164\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ and $1300\ifmmode\pm\else\textpm\fi{}500\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Quasiharmonic free energy calculations show that both transformations display negative Clapeyron slope. Structural sequences, transition pressures, and Clapeyron slopes are found well comparable in gallia and alumina. Results are suggestive that the high-pressure stability of the $Cmcm$ structure is a general property even in group IIIB sesquioxides in the pressure range beyond $100\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, though the structure has cation sites with two distinct oxygen coordination numbers.

Spectroscopic identification, thermodynamic stability and molecular composition of hydrogen and 1,4-dioxane binary clathrate hydrate

We present the spectroscopic identification of the binary hydrogen and 1,4-dioxane clathrate hydrates in which H 2 molecules are encapsulated in small cages of the structure II hydrate framework. X-ray diffraction, solid-state NMR and Raman spectroscopy were used to confirm the mixed hydrate structure and more importantly the occupancy pattern of hydrogen in clathrate cages. The corresponding pressure–temperature behavior and direct gas release measurements were also determined to support the spectroscopic results. The direct volumetric measurements revealed that the favorable confinement of hydrogen molecules over 0.4 wt% could be obtained by the compositional tuning of the binary products.

Binary solid–liquid–gas equilibrium of the tripalmitin/CO 2 and ubiquinone/CO 2 systems

A conventional method was used to measure the melting points of the natural lipid tripalmitin and of the coenzyme ubiquinone (coQ10) under high pressure carbon dioxide. The pressure–temperature behavior of the binary three-phase solid–liquid–gas (SLG) equilibrium for these and other systems, namely naphthalene and biphenyl with carbon dioxide, ethylene and ethane, were investigated using the Peng–Robinson equation of state (PR-EoS) with the van der Waals one fluid (vdw-1) mixing rules and with the NRTL equation to calculate the solute activity in the liquid phase. When the interaction parameter in the vdw-1 mixing rules could be determined by the PR-EoS through the correlation of the solid–fluid phase equilibrium data, the two NRTL parameters were used as adjustable parameters. The results showed that fairly good correlations could be achieved for the experimental pressure–temperature data of all the asymmetric systems studied here, indicating that the NRTL parameters are crucial for describing the pressure–temperature behavior but have little effect on the phase compositions at the SLG equilibrium.