Pressure-volume-temperature Properties Research Articles

Computer simulations of poly(ethylene oxide): force field, pvt diagram and cyclization behaviour

Parametrization of a force field capable of quantitatively describing the gas, liquid and crystal phases of alcohols, ethers and polyethers is described. Two applications are reported, the first employing atomistic simulations to study PVT (pressure, volume, temperature) and cohesive properties of oligomeric poly(ethylene oxide) (PEO) and related small-molecule liquids, and the second to study the extent of ring formation in polymerization of poly(ethylene glycols) (PEGs) and hexamethylene diisocyanate (HDI). The atomistic simulations, focusing extensively on liquids and amorphous poly(ethylene oxides), demonstrate the ability to predict densities with an accuracy of 1%–2% over extended ranges of at least 200K in temperature and 180MPa in pressure. Densities of related small-molecule liquids, dimethyl and diethyl ether and ethanol at or close to saturation pressure are also well reproduced to temperatures close to the critical temperature. Densities calculated for methoxy-terminated oligomers are used to predict the density of melt and amorphous high-molar-mass PEO with an accuracy of better than 1%. Similarly, solubility parameters have been calculated as a function of chain length for poly(ethylene glycol) oligomers and used effectively to obtain estimates of the solubility parameter of high-molar-mass material. Additionally, crystal structures can also be well predicted. For the polymerization studies the Monte Carlo network simulation method was modified to mimic diffusion of reactants during the polymerization. Application to the PEG/HDI ‘linear’ polymerization system, using chain configurations generated with the atomistic force field, reveals a major improvement in the ability of the method to predict the extent of ring formation without adjustable parameters for polymerization conditions ranging from the bulk to highly dilute reaction conditions. ©1997 SCI

Computer simulations of poly(ethylene oxide): force field, pvt diagram and cyclization behaviour

Parametrization of a force field capable of quantitatively describing the gas, liquid and crystal phases of alcohols, ethers and polyethers is described. Two applications are reported, the first employing atomistic simulations to study PVT (pressure, volume, temperature) and cohesive properties of oligomeric poly(ethylene oxide) (PEO) and related small-molecule liquids, and the second to study the extent of ring formation in polymerization of poly(ethylene glycols) (PEGs) and hexamethylene diisocyanate (HDI). The atomistic simulations, focusing extensively on liquids and amorphous poly(ethylene oxides), demonstrate the ability to predict densities with an accuracy of 1%–2% over extended ranges of at least 200K in temperature and 180MPa in pressure. Densities of related small-molecule liquids, dimethyl and diethyl ether and ethanol at or close to saturation pressure are also well reproduced to temperatures close to the critical temperature. Densities calculated for methoxy-terminated oligomers are used to predict the density of melt and amorphous high-molar-mass PEO with an accuracy of better than 1%. Similarly, solubility parameters have been calculated as a function of chain length for poly(ethylene glycol) oligomers and used effectively to obtain estimates of the solubility parameter of high-molar-mass material. Additionally, crystal structures can also be well predicted. For the polymerization studies the Monte Carlo network simulation method was modified to mimic diffusion of reactants during the polymerization. Application to the PEG/HDI ‘linear’ polymerization system, using chain configurations generated with the atomistic force field, reveals a major improvement in the ability of the method to predict the extent of ring formation without adjustable parameters for polymerization conditions ranging from the bulk to highly dilute reaction conditions. ©1997 SCI

Precise measurement of the PVT of polypropylene and polycarbonate up to 330�C and 200 MPa

An apparatus for measuring the pressure—volume—temperature (PVT) properties of polymers using a metal bellows has been developed at temperatures from 313 to 623 K and pressures up to 200 MPa. A calibration of the device was performed by measuring PVT of mercury and water. The experimental uncertainty of specific volumes was estimated to be within ±0.2%, while that of temperatures was within ±0.1 K below 300°C and ±0.3 K above 300°C. The estimated uncertainty of pressures was ±0.1 MPa below 100 MPa and ±0.25 MPa above 100 MPa. The PVT properties of polypropylene and polycarbonate were measured by the apparatus in the temperature ranges from 40 to 300°C and from 40 to 330°C, respectively, and pressures from 10 to 200 MPa. The effects of a sample cup and sample forms were investigated. The use of the sample cup showed a little effect on the measurments of PVT properties for both samples. The shape (pellet and pillar) of the samples caused a small difference in the specific volumes only under high temperatures and low pressures. The PVT properties in a melt state were correlated by the Simha-Somcynsky equation of state, showing a good agreement with measurements. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 141–150, 1997

Evaluation of empirically derived PVT properties for Pakistani crude oils

This study evaluates the most frequently used pressure-volume-temperature ( PVT) empirical correlations for Pakistani crude oil samples. The evaluation is performed by using an unpublished data set of 22 bottomhole fluid samples collected from different locations in Pakistan. Based on statistical error analysis, suitable correlations for field applications are recommended for estimating bubblepoint pressure, oil formation volume factor (FVF), oil compressibility and oil viscosity.

Experimental study ofPVT properties of HFC-125 (CHF2CF3)

Pressure-volume-temperature (PVT) properties and vapor pressures of HFC125 (pentafuoroethane; CHF2CF3) have been experimentally obtained. Vapor pressures of HFC-125 have been measured in the range of temperatures from 223 to 338 K and pressures up to 3.54 M Pa with uncertainties of 5 mK and 2.5 kPa, respectively. The vapor pressure equation for this substance was correlated based on the present data. PVT properties of HFC-125 have been determined with a constant-volume apparatus in the range of temperatures from 280 to 473 K, pressures up to 17 M Pa, and densities up to 1145 kg · m−3 with uncertainties of 5 mK, 2.5 kPa, and 0.01%, respectively. All of the available experimentalPVT property data were compared with the equation of state correlated by Wilson et al.

A new technique for simultaneous measurement of PVT and phase equilibria properties of fluids at high temperatures and pressures

This paper describes the development and use of a technique to measure simultaneously pressure-volume-temperature (PVT) and phase equilibria compositions of fluid mixtures. This technique enables the analysis of reservoir fluids encountered in depletion recovery and EOR processes at pressures and temperatures commonly found in petroleum reservoirs. These fluids may include hydrocarbons, CO 2 and water. A mercury free Ruska PVT Model 2370 is assembled to a Hewlett Packard 5880 gas chromatograph (GC) and a specially designed sampling device capable of measuring compositions on-line at high pressures and temperatures. The significance of this experimental setup is: (1) a superior on-line sampling technique for compositional analysis, (2) capability of simultaneous measurement of all phase volumes, and (3) a closed sampling loop part of the PVT system. A negligible volume (0.1–0.5 μl) is withdrawn for compositional analysis and sent to the GC through specialized sampling valves. Because the volumes used for analysis represent less than 1 × 10 −5% of the sample volume, the mass withdrawn for analysis is negligible as well and does not affect the overall composition or the equilibrium of the system. This is referred to as a PVT-VLLE (vapor-liquid-liquid-equilibrium) apparatus. Although commissioning and validating experiments are worthy, they are generally not the most exciting papers to read and are probably considered minimal in nature. This paper, however, has some exciting potential. It describes a one-of-a-kind apparatus that could greatly contribute to our knowledge of process and mechanism in miscible- and steamflooding. This setup was validated by obtaining a good agreement (better than 0.1%) between the measured and reported compositions from standard mixtures. Phase compositions and densities of a binary mixture of n- hexane (n-C6) n- pentane (n-C 5) were also measured and compared with the predicted values from the Soave-Redlich-Kwong Equation-of-State (EOS). Deviations of the experimental vapor and liquid compositions from the EOS predictions were less than 1%. Phase equilibria compositions of hydrocarbon mixtures of similar molecular weight and structure are well predicted with an EOS. The deviations on the molar liquid and vapor volumes were less than 20%; however, it is well known that cubic EOS's do not predict volumetric properties as accurately as compositions. The phase compositions and three-phase pressures of a binary system of n-octane/water are measured and compared with data published by Heidman et al. (1985). The measured three-phase pressures and compositions agree well with the published data. This confirms that this experimental procedure can be well suited for multiphase analysis of hydrocarbon/water mixtures. The quantitative determination of water in all the equilibrium phases at high pressures and temperatures requires detailed and novel procedures, but these are not the focus of this paper at this point.

Characterization of Heavy Oils. 2. Definition of a Significant Characterizing Parameter To Ensure the Reliability of Predictive Methods for PVT Calculations

A new and significant characterizing parameter (q{sub 30}) which is easy to calculate is defined. This parameter can indicate in advance whether the PVT (pressure-volume-temperature) calculations performed on a crude oil using a predictive method will be in good agreement with experimental data. This parameter leads to a new classification of crude oils. When q{sub 30} is small, the crude oil is considered as classical and all of its PVT properties can be accurately predicted. When q{sub 30} is large, the crude oil is classified as critical-like; i.e., the prediction of some PVT properties may lead to significant deviations when compared to experimental values. In the latter case, a tuning process is proposed which in all cases improves the agreement between experimental and calculated data. Moreover, variance analysis theory is applied to estimate the experimental errors during a differential vaporization.

Some considerations on equation of state and phase relations: Polymer solutions and blends

AbstractWe review briefly the general assumptions underlying hole theories of the configurational thermodynamic functions for single and multiconstituent systems. From the original Simha‐Somcynsky theory several important modifications have recently evolved. First, there is a revision of the combinatorial entropy originating from the mixing of segments and holes in the spirit of Huggins's theory. With consistent additional modifications of the configurational free energy, quantitatively significant consequences for certain aspects of phase equilibria can arise. Finally, allowance for nonrandom mixing of constituents species and holes has been made. We illustrate the theory's potentials first in terms of pressure‐volume‐temperature (PVT) data for high and low molar mass species and their miscible mixtures. The influence of PVT properties on the miscibility behavior of solutions and blends is examined next. Of particular concern are the connections between predictability of lower from upper mixing spinodals, pressure effects, and the binary interaction χ‐function.

Measurements of pressure-volume-temperature properties of 1,1,2,2-tetrafluoroethane

The experimental vapor pressures and pressure-volume-temperature (PVT) properties of an important alternative refrigerant, 1,1,2,2-tetrafluoroethane (HFC-134), have been measured by means of the constant-volume method coupled with expansion procedures in an extensive range of temperatures, pressures, and densities. One hundred seventeen PVT property data were measured along 14 isochores in a range of temperatures from 318 to 443 K, pressures from 0.4 to 9.8 MPa, and densities from 18 to 1103 kg/m 3

PVT properties and equations of state of polystyrene: molecular weight dependence of the characteristic parameters in equation-of-state theories

The pressure-volume-temperature (PVT) properties of styrene oligomers and polymers were studied experimentally in the liquid state. The data were fitted to various equations of state and the characteristic parameters in the equations of state, P∗, V∗ and T∗, were obtained. A comparison was made of the performance of the various theories in fitting the data. The molecular weight dependence of the characteristic parameters was measured and the results indicated that the main variation arose from an increase in degrees of freedom per mer for lower molecular weights.

Correlating the PVT Properties of Nigerian Crudes

Existing correlations for predicting solution gas oil ratio, Rs, and oil formation volume factor, Bo, gave standard deviations as high as 50 and 12 percent, respectively, for Nigerian crudes. New correlations developed using 503 Pressure-Volume-Temperature (PVT) data points from 100 Nigerian crude oil reservoirs of the Niger Delta Basin are presented. The correlations for Rs and Bo predict values from different reservoirs within 6 and 2 percent standard deviations, respectively, and will apply to crudes of specific gravity range 0.811 to 0.966. These correlations are applicable to other crudes with characteristics similar to those of Nigerian crudes.

Equation of state of copolymer melts: The poly(vinyl acetate)–polyethylene pair

AbstractThe pressure—volume—temperature properties of a series of copolymers ranging in content from 18 to 40 wt % of vinyl acetate, and up to a maximum pressure of 1800 kg/cm2 are studied. The results for the melt state can be satisfactorily fitted by the scaled equation of state, developed previously and applied to single‐component systems and to mixtures. The dependence of the scaling parameters for the copolymers on composition deviates from that expected for a mixture, where volumes at elevated pressures can be predicted without further recourse to experiment. These differences are discussed in terms of the sequential structure of the copolymer chain and its series of interfaces between the two species.

The pressure–volume–temperature properties of three well-characterized low-density polyethylenes

Pressure–volume–temperature relationships of three low-density polyethylenes are reported in the temperature range of 30°–225°C and in the pressure range of 0–2000 kg/cm2. The same materials had previously been studied by the IUPAC Working Party on Structure and Properties of Commercial Polymers with regard to basic characterization, melt rheology, processing, and end use properties. They were found to be remarkably equal in basic parameters and in some of the melt rheology, but differences among the three samples were found in other rheological properties and in the processing and end use properties of blown film. We find the PVT relationships of these three samples to be practically identical. A numerical equation of state based on the Tait equation is established. It reproduces the measured specific volume data of the melts to better than 0.002 cm3/g.

Retrograde Condensation in Porous Media

Abstract The effect of porous media on the phase behavior of hydrocarbon binaries was investigated both experimentally and theoretically. When liquid and vapor coexist in a porous medium, the interlace between them will be curved. Calculations of the effect of curvature on phase behavior show that equilibrium composition and Pressures would not be disturbed significantly except at very high surface curvatures. Such curvatures are unlikely in hydrocarbon reservoirs even where clay-size particles are present because the finest pores will particles are present because the finest pores will be occupied by connate water. Measured dewpoint or bubblepoint pressures were found to be independent of the presence of porous media. Liquid saturations calculated from previous conventional phase behavior studies were compared with saturations calculated from the dimensions of a limited number of capillary structures which could be observed through the sight glass of a Jerguson cell. Saturations calculated from conventional phase-equilibrium data fell between saturations phase-equilibrium data fell between saturations calculated with The assumption that all capillary structures had equal curvature and those calculated with the assumption that they bad equal volumes. Introduction Reservoir engineering frequently involves the use of pressure-volume-temperature (PVT) relationships for hydrocarbon mixtures. Examples arise in reservoirs, and gas-drive miscible displacements, condensation and revaporization in gas condensate reservoirs, and gas-drive miscible displacements. The PVT relationships used in such engineering calculations are usually based on measurements on equilibrium behavior of hydrocarbon mixtures contained in PVT cells. For some time there has been question as to whether phase - behavior calculations made on data measured in such cells would correctly represent the behavior of hydrocarbon mixtures held within the interstices of porous reservoir rocks. The results of several recently reported experimental studies indicate that the presence of a porous medium has a significant influence presence of a porous medium has a significant influence on the equilibrium behavior of hydrocarbon mixtures. Trebin and Zadora contend that the initial condensation pressures (dew points) of gas condensate mixtures in pressures (dew points) of gas condensate mixtures in porous media can be 10 to 15 percent higher than those porous media can be 10 to 15 percent higher than those observed in conventional PVT cells. Tindy and Raynal reported that saturation pressures of crude oil in porous media were several percent higher than those porous media were several percent higher than those measured in conventional test cells. On the other hand, earlier results reported by Weinaug and Cordell indicated that vapor-liquid equilibrium relationships of the system methane-n-butane and methane-n-pentane were not affected by the presence of dry sand. Oxford and Huntington studied the revaporization of n-hexane by nitrogen and found that withdrawal rate and the presence of brine in the porous medium had little effect on the revaporization process. In a study of the effects of wettability change, process. In a study of the effects of wettability change, Smith and Yarborough concluded that the detailed form of the capillary structures of retrograde liquid held in a porous medium had no effect on the revaporization process. porous medium had no effect on the revaporization process. Clark studied the adsorption and desorption of light paraffinic hydrocarbons in clay and partially water-saturated paraffinic hydrocarbons in clay and partially water-saturated sand and sand-clay packs to determine their effect on equilibrium behavior. Compressibility factors for propane at 100 degrees F in the presence of dry sand-clay propane at 100 degrees F in the presence of dry sand-clay packs were lowered by 13 percent. However, in sand-clay packs were lowered by 13 percent. However, in sand-clay mixtures containing water, the compressibilities differed by less than 1 percent from those obtained in the absence of the porous media. Clark also studied effect of a dry sand-clay media on the PVT properties of mixtures of methane and propane. Only small changes were observed, and these were considered to be inconclusive - partly because the fluid was not recirculated through the porous media to ensure homogeneity. In summary, porous media to ensure homogeneity. In summary, evidence for the effect of porous media on equilibrium behavior is somewhat contradictory.