pρT Measurements Research Articles

PρT measurements of 3-aminopropan-1-ol and N-(2-hydroxyethyl)morpholine from (293.15 to 473.15) K and up to 40 MPa and modeling with modified Tait and PC-SAFT equations

New density data has been reported for 3-aminopropan-1-ol (AP) and N-(2-hydroxyethyl)morpholine (NHEM) at temperatures ranging from (293.15–473.15) K at 19 pressures ranging from (0.1–40) MPa. The experimental measurements were carried out using an Anton Paar high-pressure vibrating tube densimeter with a combined expanded uncertainty of 1 kg m−3 at a 95 % confidence level. Contributions considered in the uncertainty analysis included the impurities in the materials used and apparatus specification. In addition, the density and speed of sound at ambient pressure (81.5 kPa) and temperatures (293.15–343.15) K were measured. The experimental density data were correlated with the modified Tait equation. Values of thermal expansion coefficient (αP ) and isothermal compressibility (κT) were calculated. The work is completed with the modeling of the experimental data using the perturbed-chain statistical associating fluid theory equation of state (PC-SAFT EOS). The parameters of the PC-SAFT equation of state, for the pure compounds, were determined by fitting the equation to the liquid PρT experimental data. Thermodynamic properties such as thermal expansion coefficient (αP), isothermal compressibility (κT), isobaric heat capacity (CP), and speed of sound (u) were calculated with the obtain parameters. Good agreement between experimental data and derived properties represented the modeling accuracy with the obtained parameters.

Experimental study of PVT and phase-transition properties of binary water+n-hexane mixture near the upper critical endpoint

The PρT and phase transition (LLV and LV) properties (PS,TS,ρS) of binary water+n-hexane mixture with fixed concentration of 0.5 mol fraction of n-hexane (equimolar mixture) were measured. Measurements were focused in the immediate vicinity of the upper critical endpoint (UCEP) and supercritical regions in order to closely study the features of the mixture critical behavior near the UCEP. Measurements were made along 15 liquid and vapor isochores between (63.16 and 554.41) kg·m−3 and over a temperature range from (373.15 to 673.15) K at pressures up to 53.3 MPa. Phase transition phenomena on isochoric heating of the binary mixture was detailed study. For each isochore most measurements were made in the immediate vicinity of the LLV and LV phase transition temperatures (in the single-, two-, and three-phase regions) where the break of the P-T isochore's slopes are observing. Temperatures and pressures (PS,TS) at the LLV and LV phase transition points for each fixed density (isochore, ρ) were measured using the isochoric P-T break-point technique in the immediate vicinity of the UCEP of the mixture. The UCEP property data TUCEP = 469.15 K, PUCEP = 5.229 MPa, and ρUCEP = 263.95 kg·m−3 for the binary H2O + n-hexane mixture (x = 0.5 mol fraction of n-hexane) were extracted from the detailed PρT and three-phase equilibrium data (PLLV, TLLV, ρLLV) measurements near the UCEP. The combined expanded uncertainty of the density, ρ, pressure, P, temperature, T, and concentration, x, measurements at the 95% confidence level with a coverage factor of k = 2 is estimated to be 0.2% (density in the liquid phase), 0.3% (density in the gas phase), 0.5% (density in the critical and supercritical regions); 0.05% (pressure); 15 mK (temperature); and 0.01 mol% (concentration). The excess molar volumes (VmE) of the binary mixture were calculated using the measured molar volumes Vm of the mixture and the reference molar volumes of the pure components (water and n-hexane) for various experimental temperatures and pressures in the supercritical region. Also, the measured PρT data at low densities (vapor phase) and high temperatures were used to calculated the second, third, and cross-term virial coefficients of the mixture.

PρT measurements and modelling of (n-decane + m-xylene) mixtures from 293.15 K to 363.15 K at pressures up to 60 MPa

In this work, the experimental measurements for liquid densities of n-decane and m-xylene binary mixtures were performed over the entire composition range with a high-pressure vibrating-tube densimeter. The range of temperatures for the present measurements was from 293.15 K to 363.15 K and the pressures were up to 60 MPa. The combined expanded uncertainty of the density measurements is estimated to be 0.001ρ with 0.95 confidence. Experimental density values were correlated by the modified Tammann-Tait equation. The simplified Perturbed Associating Fluid Theory (sPC-SAFT) and Cubic Plus Associated (CPA) equations of state (EoS) were applied to predict the densities of n-decane and m-xylene and their mixtures. Reasonably results were observed between the experimental data and calculated results for the two equations, and the deviation is less than 0.48% and 0.89% with sPC-SAFT and CPA EoS, respectively. In addition, excess molar volumes were determined from the experimental density data as well as from sPC-SAFT and CPA models. The effects of pressure and temperature on the excess molar volume were also discussed.

Thermodynamic Properties of Amines under High Temperature and Pressure: Experimental Results Correlating with a New Modified Tait-like Equation and PC-SAFT

New experimental densities for diethylamine (DEA), dibutylamine (DBA), and tributylamine (TBA) at 11 isotherms in the range of 293.15–473.15 K and 18 isobars up to 37.5 MPa are reported. PρT measurements (176 experimental data points) have been performed using a high-pressure vibrating-tube densimeter. These data were correlated with a new modified Tait-like equation considering standard deviations of less than 2 × 10–4 g·cm–3, and then isothermal compressibility (κT) and thermal expansion coefficient (αP) were calculated. This study is supported by the results of modeling using the perturbed-chain statistical associating fluid theory (PC-SAFT). The parameters of PC-SAFT equation of state (EoS), for pure solvents, were rigorously determined by fitting the equation to the liquid PρT experimental data. In this study, the correlations, which are based on minimizing the total objective functions (density, pressure, and temperature) simultaneously, were developed to estimate the PC-SAFT parameters. The model r...

Density, speed of sound and derived thermodynamic properties of a synthetic natural gas

Densities (ρ) and speed of sound (SOS) of a synthetic natural gas (∼88 mol% methane) were determined simultaneously at temperatures between 323 and 415 K and pressure up to 58 MPa. Densities and speed of sound were measured using a high pressure and high temperature Vibrating Tube densitometer (VTD) and an in-house acoustic cell, respectively. Moreover, to extend the PρT measurements to a wider range of temperature, isochoric measurements were conducted in a temperature range of 210–270 K.The AGA8-DC92, GERG-2008, SBWR and PR-78 equations of state (EoS) were used to evaluate the experimental data. Finally, the SBWR EoS was tuned on the experimentally measured density to determine other thermodynamic properties such as isobaric heat capacity (Cp), isochoric heat capacity (Cv) and Joule-Thomson coefficients (μJT).

PρT and saturation properties of isopentane at T = (280–440) K and up to 200 MPa

We measured the PρT and saturation properties of isopentane within the temperature range of 280–440K at pressures up to 200MPa using a metal-bellows variable volumometer. The mass fraction purity of the isopentane sample was 0.998. The expanded uncertainties (k=2) in the temperature, pressure, and density measurements were estimated to be less than 3mK, 1.43kPa − 0.2% (P≦200MPa), and 0.11%, respectively. In the region above 100MPa at T=280K and 440K, the uncertainty in the density measurement increased from 0.11% to 0.14% and 0.22%, respectively. Eleven PρT measurements were carried out at temperatures and pressures reported in the literature for comparison. Additionally, the results of the present measurements were compared with those of the available equation of state.

PρT measurements and derived properties of liquid 1,2-alkanediols

The densities of compressed liquid 1,2-alkanediols (C2, C3 and C4) were measured with a vibration tube densimeter over the temperature range from 278.15K to 358.15K and pressures up to 60MPa, with an uncertainty of ±0.0012g·cm−3. Densities were correlated with pressure and temperature by the TRIDEN 10-parameter equation. Values of the isothermal compressibility, isobaric thermal expansivity and internal pressure were calculated from the experimental results. Reported data are compared with predictions obtained using the PC-SAFT equation of state. The influence of the carbon-chain lengths over the obtained thermophysical properties was studied.

Isothermal PρT measurements on Qatar’s North Field type synthetic natural gas mixtures using a vibrating-tube densimeter

Pressure–density–temperature (PρT) measurements of five natural gas mixtures that represent Qatar’s North Field natural gas reservoirs were carried out at temperatures from (250 to 450)K and at pressures up to 65MPa by using a Anton Paar® (Graz, Austria) vibrating tube densimeter DMA 512P high-pressure cell. Total 20 isotherms from 250K by 10K intervals up to 450K were measured. Experimental density data were compared with two main industry standard equations of state (EOS) namely AGA8-DC92 EOS and GERG2008 EOS. Comparisons of the experimental data with respect to AGA8-DC92 EOS and GERG2008 EOS resulted in prediction deviation ranges of (0.05 to −0.5)% and (0.25 to −0.5)% respectively.

PρT measurements and derived properties of liquid 1-alkanols

The density of compressed liquid (C2 to C11) 1-alkanols was measured with a vibration tube densimeter over the temperature range from (278.15 to 358.15) K and pressures up to 60 MPa, with an uncertainty of ±0.0012 g · cm −3. Density values were correlated with pressure and temperature by the TRIDEN 10-parameter equation. Isothermal compressibility, isobaric thermal expansivity and internal pressure were calculated from the experimental results. The influence of the carbon-chain lengths over the thermophysical properties obtained was studied.

Densimeters for very accurate density measurements of fluids over large ranges of temperature, pressure, and density

This paper comprehensively describes those types of densimeters that allow very accurate density measurements of fluid substances over large ranges of temperature and for high pressures and that also cover the entire density range from low gas densities up to high densities of compressed liquids. Densimeters meeting these requirements are based on special applications of hydrostatic balances in combination with magnetic suspension couplings. These densimeters can be subdivided into two-sinker densimeters, and single-sinker densimeters which allow pρT measurements with total uncertainties in density of about 0.01% to 0.02% (level of confidence 95%) depending on their individual design. Besides a discussion of the design of such densimeters, it is also shown which substances in which ranges of the fluid state have been investigated with these instruments. Using nitrogen as an example, the experimental results obtained with these densimeters are discussed and compared with the pρT data obtained with other types of densimeters. A description of the features of other types of densimeters is outside the scope of this paper, but they are briefly summarized at the beginning of this paper.

PρT measurements of nonafluorobutyl methyl ether and nonafluorobutyl ethyl ether between 283.15 and 323.15 K at pressures up to 40 MPa

In this paper, experimental densities for nonafluorobutyl methyl ether and nonafluorobutyl ethyl ether from 283.15 to 323.15 K at pressures up to 40 MPa are reported. The density measurements were performed by means of a high pressure vibrating tube densimeter. Data reliability was checked by comparing experimental results obtained for tetrachloromethane—whose density is close to those of the fluids studied—with recommended literature data. Furthermore, the isobaric thermal expansion, isothermal compressibility, and internal pressure have been calculated from these density data.

PρT measurements of polyethylene glycol dimethylethers between 278.15 and 328.15 K at pressures to 12 MPa

In this paper we present a new experimental apparatus designed to measure pressure–density–temperature (pρT ) properties with a high-pressure vibrating tube densimeter. Data reliability has been verified by comparing our experimental results for methanol, n-heptane, toluene, and HFC-134a with literature data. In this work we also report new experimental densities from 278.15 to 328.15 K, and up to 12 MPa, of triethylene glycol dimethylether (TrEGDME) and tetraethylene glycol dimethylether (TEGDME). The isobaric thermal expansion coefficients, isothermal compressibility, and internal pressure have been calculated. The dependence of these properties on the length of polyethylene glycol dimethylether, CH3O–((CH2)2O) n –CH3, is analyzed.

The Nearly Classical Behavior of a Pure Fluid on the Critical Isochore Very Near the Critical Point Under the Influence of Gravity

Comprehensive measurements of the isothermal compressibility along the critical isochore in the critical region of pure sulfur hexafluoride (SF6) and pure carbon dioxide (CO2) were carried out. All measurements were performed with a multicell apparatus, especially designed for pρT measurements in the critical region. The height of the measuring cells was either 30 or 11 mm. Independent of the cell height, we found for both fluids nearly “classical” values for the critical exponent γ in the limiting approach to the critical point. However, at a certain distance from the critical point {(T − T c) ≈ 90 mK or τ ≈ 2.82 × 10−4 for SF6 and (T − T c) ≈ 55 mK or τ ≈ 1.81 × 10−4 for CO2}, we observed a transition to values of the critical exponents which nearly meet the predictions of the renormalization-group theory. Since in the fitting range (T − T c ≥ 1 mK) the correlation length (ξ ≤ 0.5 μm) is very much smaller than the geometrical dimensions of the measuring cells, we conclude that the reason for the different behavior is an explicit gravity effect governing the inner critical region. The two different loci of the transition points for sulfur hexafluoride and carbon dioxide can be attributed to the different gravity impact on the fluid corresponding to the different critical densities of the two substances.

A new evaluation of pϱT measurements on the methanol vapor-steam mixture and its pure components with corrections for adsorption and impurity effects

The evaluation of low-density isochoric measurements on methanol vapor-steam mixtures performed in a large temperature range by our group some years ago proved to be unsatisfactory, because the nonideality behavior as well as the effects of experimental errors, of impurities, of physical and chemical adsorption at the walls of the measuring vessel and of thermal decomposition of the substances at higher temperatures could not separately be treated. Furhermore, the same effects would have already to be taken into account in the evaluation of the measurements on the corresponding pure components to derive reliable second cross virial coefficients B 12. A new analysis of the older measurements on steam considering these influences led to improved values for the second virial coefficient B of steam after all. The evaluation scheme, which is based on isothermal values recalculated using a second-order Taylor series, in terms of temperature, is used to extract more reliable values for B of methanol vapor (373–628 K). In contrast to the findings for steam the measurements on methanol vapor were not influenced by adsorption, but suffered from an unknown impurity. Finally, improved B 12 values of the methanol vapor-steam mixture (373–527 K) were deduced considering the adsorption of the steam as well as the impurity of methanol vapor.

Dimerization in acetic acid vapor and evaluation of pϱT measurements with an equation of state for a reactive fluid

Quasi-isochoric pϱT measurements on the vapor of acetic acid were performed in the low-density region by means of a quartz glass cell of constant volume. Nine isochores extending over the temperature range between 410 and 574 K were measured at densities from 20 up to 51 mol m −3. Including data from literature experimental results are available in the temperature range between 298 and 574 K. Isothermal values needed in the evaluation were calculated in most cases from isochoric or isobaric data by means of a first-order Taylor series, in terms of temperature. The evaluation accounts for the fact that a strong dimerization depending on temperature occurs in acetic acid vapor. An exact statistic-mechanically based equation proposed by Lawson and Dahler as well as by Bich is used. The model considers the equilibrium and the density balance between monomers and dimers as constraints as well as the intermolecular forces between the components of the vapor. The temperature dependence of the dimerization constant and that of the enthalpy of dimerization are deduced for the temperature range between 298 and 500 K.

Second cross virial coefficient of the binary vapor mixture n-hexane/methanol from quasi-isochoric pϱT measurements

Quasi-isochoric pϱT measurements on n-hexane/methanol mixtures were carried out in the low-density region by means of a constant-volume quartz glass cell. Eight isochores were measured in the temperature range from 347 up to 600 K at densities between 35 and 57 mol m −3. Values of the second cross virial coefficient B 12 of n-hexane/methanol were derived and used to develop a correlation for the representation of its temperature dependence. The abilities of the scheme by Tsonopoulos, based on the theorem of corresponding states, and of the group contribution method by Brandani et al. were tested to predict B 12 for the n-hexane/methanol system. A relationship for the interaction parameter k 12 of the Tsonopoulos scheme was developed for binary mixtures of non-polar components with methanol. Furthermore, the parameter for the interaction between CH 2 and CH 3OH groups within the Brandani method was determined to be used for binary systems of methanol with n-alkanes.

Thermophysical properties of liquid m-xylene at high pressures

Experimental pρT measurements of m-xylene obtained with an expansion technique are reported from 230 to 298 K and up to 110 MPa, or freezing pressure when lower. The experimental results have been correlated in terms of a recently proposed equation of state which has been used to calculate the isothermal compressibility, κT, and the thermal expansion coefficient, αp, as functions of pressure and temperature. Experimental density results for liquid toluene, which was used to calibrate our experimental device, are also reported for the isotherms of 223 and 303 K. The ability of simple power functions recently proposed to correlate high-pressure results has been tested. The extrapolation capabilities of these functions have been confirmed using experimental results from the literature for the two compounds studied.

Application of simple expressions for the high-pressure volumetric behaviour of liquid mesitylene

Experimental pρT measurements of mesitylene (1,3,5-trimethylbenzene) obtained with an expansion technique have been used to calculate the molar density ρ and the mechanical coefficients κT(isothermal compressibility) and αp(thermal expansion coefficient) as functions of pressure (up to 110 MPa or freezing pressure, when lower) and temperature (between 238 and 298 K). The whole data set has been used to confirm the ability of simple power functions to represent the experimental measurements as well as to test the possibility of using the functions for extrapolation. These expressions simultaneously relate the pressure dependence of the mechanical coefficients with the divergence pressure along the so-called pseudospinodal curve.

Thermodynamic behaviour of liquid p-xylene near freezing

Experimental pρT measurements and derived thermodynamic properties of p-xylene (1,4-dimethylbenzene) have been obtained with an expansion technique for temperatures between 288 and 303 K and pressures up to 43 MPa, or freezing pressure when lower. The solid-liquid coexistence curve of this compound was also measured up to 40 MPa. The experimental results have been correlated in terms of a recently derived equation of state, which is introduced here and has been used to calculate the isothermal compressibility, κT, and the thermal expansion coefficient, αp, as functions of pressure and temperature. The equation of state depends only on six parameters, all of which are physically meaningful. Comparisons of several properties show good agreement with literature values.

The thermal behaviour of pure fluid substances in the critical region — experiences from recent pϱT measurements on SF6 with a multi-cell apparatus

Abstract Wagner, W., Kurzeja, N. and Pieperbeck, B., 1992. The thermal behaviour of pure fluid substances in the critical region - experiences from recent pϱT measurements on SF 6 with a multi-cell apparatus. Fluid Phase Equilibria . To determine the critical exponents β, γ, and δ for pure fluid substances a multi-cell apparatus has been developed and designed for highly accurate measurements of pϱT data in the immediate critical region. As a first application of this new apparatus, comprehensive pϱT measurements on sulfurhexafluoride have been carried out. In the temperature range from 318.23 K to 321.15 K (T c = 318.729 K) at densities from 590 kg·m −3 to 900 kg·m −3 (ϱ c = 742 kg·m −3 ), 3500 pϱT data including the densities of the saturated vapour and liquid have been measured. Due to a preliminary evaluation of these data (the measurements are being taken), the critical parameters T c , ϱ c , and p c as well as the critical exponents of SF 6 have been determined. The results for β, γ, and δ are in contradiction with the values according to the theoretically derived universality hypothesis of the renormalization group theory.