N-butane System Research Articles

Phase Equilibria and Critical Point Predictions of Mixtures of Molecular Fluids Using Grand Canonical Transition Matrix Monte Carlo

Mixtures of molecular fluids are encountered often in chemical industry, and the vapor–liquid coexistence curves are required for efficient design of separation processes. Hence, a computational scheme employing the Wang–Landau and grand canonical transition matrix Monte Carlo molecular simulation techniques is used for the first time to compute the fluid phase diagrams of molecular mixtures. Binary mixtures of n-alkanes, viz., methane–ethane, ethane–propane, propane–n-butane systems, are studied here as examples of molecular mixtures. The total molecule number probability distribution, obtained from the GC-TMMC simulations, allows us to directly calculate coexistence properties such as pressure, density, and composition. On comparison with experimental data, reported in the literature, it was observed that the predicted VLE properties, with the exception of pressure, are in close agreement with the corresponding experimental values. The deviation of calculated pressure from experiments could be attribute...

Global phase behaviour in methane plus n-alkanes binary mixtures

The methane plus linear alkanes series is one of the simpler and most common type of mixtures presented in the industry and its accurate representation is paramount because of the diversity of its applications. From a theoretical perspective, its structural simplicity due to the low degree of synergy and the absence of short-range dispersive forces suggests that a good model should represent these systems with acceptable accuracy. Based on these ideas and the relatively regular behaviour of n-alkanes, these systems have become particularly suitable for trial calculation in convoluted models, in order to verify their capabilities in both quantitative and qualitative predictions. In this contribution, the soft-SAFT equation of state is used for the construction of the serial prediction domain global phase diagram (spd-GPD) of the methane plus linear alkanes series. The main goal is to address the capability of the equation of state to predict the global behaviour of the binary mixtures until methane plus n-decane, with special emphasis in accurately reproducing the mechanism and topology of mixtures. All systems shown here are predicted with quantitative accuracy, including a complete description of their taxonomy. The information obtained from the equation of state allows the validation of some predictions of the spd-GPD in the absence of experimental data. Following this analysis, the double retrograde behaviour lies between the methane plus propane and methane plus n-butane systems, while the tricritical transition of the series is found between the methane plus n-pentane and methane plus n-hexane mixtures. Also, the presence of the molar density inversion phenomenon is predicted to begin between the methane plus n-hexane and methane plus n-heptane systems, while no signals of mass density inversions are found on these mixtures.

Transferable Force Field for Alcohols and Polyalcohols

A new force field has been developed for alcohol and polyalcohol molecules. Based on the anisotropic united-atom force field AUA4 developed for hydrocarbons, it only introduces one new anisotropic united atom corresponding to the hydroxyl group OH. In the case of polyalcohols and complex molecules, the calculation of the intramolecular electrostatic energy is revisited. These interactions are calculated between charges belonging to the different local dipoles of the molecule, one dipole being defined as a group of consecutive charges globally neutral. This new method allows avoiding the use of empirical scaling parameters commonly introduced to calculate 1-4 electrostatic interactions. The transferability of the proposed potential is demonstrated through the simulation of a wide variety of alcohol families: primary alcohols (methanol, ethanol, propan-1-ol, hexan-1-ol, octan-1-ol), secondary alcohols (propan-2-ol), tertiary alcohols (2-methylpropan-2-ol), phenol, and diols (1,2-ethanediol, 1,3-propanediol, 1,5-pentanediol). Monte Carlo simulations carried out in the Gibbs ensemble lead to a good agreement between calculated and experimental data for the thermodynamic properties along the liquid/vapor saturation curve, for the critical point coordinates and for the liquid structure at room temperature. Additional simulations were performed on the methanol + n-butane system showing the capability of the proposed potential to reproduce the azeotropic behavior of such mixtures with a good agreement.

Vapor−Liquid Equilibria of the 1,1,1-Trifluoroethane + n-Butane System

Binary vapor-liquid equilibrium data were measured for the 1,1,1 -trifluoroethane (HFC-143a) + n-butane (HC-600) system at temperatures from (313.15 to 363.15) K. This experiment was carried out with a circulating-type apparatus with online gas chromatography. The experimental data were correlated well by Peng-Robinson-Stryjek-Vera equation of state with the Wong-Sandler mixing rules. The average absolute deviation of pressure and vapor composition between the measured data and the correlation was below 0.98 % and 0.0128, respectively.

Vapor−Liquid Equilibrium for the Difluoromethane (R32) + n-Butane (R600) System

Vapor−liquid equilibria (VLE) for the difluoromethane (R32) + n-butane (R600) system that shows liquid-phase immiscibility below 246 K were measured at (263.15, 278.15, and 293.15) K by means of a static analytical method. The (T−P−x−y) VLE data were correlated using various equations of state and various mixing rules to compare the ability of these models to correlate data for this strongly nonideal system. The correlation of the VLE data and published VLLE data shows that the system is azeotropic at temperatures higher than the upper critical end point, UCEP, (246 K), heterohomoazeotropic between (246 and 230) K, and heteroazeotropic below 230 K. A comparison with the available VLE data in the literature was performed.

VLLE measurements and correlation for the pentafluoroethane (R125) + n-butane (R600) system

Hydrocarbon and hydrofluorocarbon mixtures are possible substitutes for chlorinated refrigerants. This family of mixtures, as pointed out in our studies on VLLE for the difluoromethane (R32) + propane (R290) and (R32) + n-butane (R600) systems, shows the possibility of liquid–liquid phase splitting. In this work, the liquid immiscibility of the pentafluoroethane (R125) + (R600) system has been measured with the cloud-point method down to 200 K in a sealed glass cell of about 30 cm 3 and equipped with magnetic stirrers. The temperature is maintained at ±3 mK and measured to within ±0.1 K. Uncertainty in pressure is estimated to be within ±4 kPa. The bulk composition is gravimetrically measured with an uncertainty of ±0.005 in mole fraction. Having measured P– T– x data , the VLLE parameters are derived using the Redlich–Kwong–Soave (RKS) and Peng–Robinson (PR) equations of state (EoS), both with the Huron–Vidal mixing rule with the NRTL equation for the excess Gibbs free energy at infinite pressures.

High pressure phase equilibria and critical phenomena of water + iso-butane and water + n-butane systems to 695 K and 306 MPa

The equilibrium surface ( x, p, T, V m) for water+ iso-butane was measured and additional equilibrium data for water+ n-butane are reported. Mole fractions of water for water+ iso-butane from 0.5 to 0.98, pressures up to 306 MPa and temperatures up to 695 K were studied. Critical curves, represented as the envelope of the isopleths starting at the critical point of water (647 K), went through a temperature minimum and then increased at higher pressures and higher temperatures, giving evidence for (gas+gas) equilibria of the third type. The results are compared with the phase equilibrium of previously measured (water+ n-alkane) mixtures. The excess molar volumes, V E, and excess molar Gibbs energies, G E, for water+ n-butane on the phase equilibrium surfaces have been calculated for 600 and 620 K from 40 to 200 MPa. All the V E and G E values were found to be positive.

VLLE measurements and their correlation for the R32 + R600 system

Studies on VLE for the binary difluoromethane (R32)+propane (R290) system revealed the possibility of a liquid phase splitting at low temperatures. This was confirmed by successive measurements on the mutual solubility, and the upper critical solution temperature (UCST) was found at temperature T=230 K. A similar phase behaviour was expected for the R32+ n-butane (R600) system. Experiments on the immiscibility of liquid phase system have been carried out at temperatures down to 220 K using a dedicated apparatus enabling the visual observation of the liquid phase split. The UCST was found at T=246 K. The VLLE were correlated applying an equation of state. The present results are consistent with the VLE data measured at temperatures above the UCST within the estimated uncertainty of the experiment. The observed liquid phase split provides important new information on the fluid behaviour of HFCs+HCs systems and it is also important for engineering, due to its potential influence on the operation of refrigerating machines.

Measurement and prediction of the bubble/dew point locus in the near-critical region and of the compressed fluid densities of the methanecarbon dioxide- n-butane ternary system

The bubble/dew point locus in the near-critical region, the critical points and the compressed fluid densities of two ternary mixtures of the methanecarbon dioxide- n-butane system were measured in a ROP computer-controlled, mercury-free, high-pressure PVT system. The Soave-Redlich-Kwong (SRK) and Patel-Teja (PT) equation of state (EOS) coupled with different mixing rules were used to predict the experimental VLE data. The average absolute deviations between the predicted and experimental bubble/dew point pressures were less than 2.5 for all the models tested. The PT EOS and the volume-translated SRK EOS proposed by Peneloux and Rauzy [Peneloux, A. and Rauzy, E., 1982. A consistent correction for Redlich-Kwong-Soave volumes. Fluid Phase Equilibria, 8: 7–23] were used to predict the compressed fluid densities, giving satisfactory results.

High-pressure vapor-liquid equilibria involving mixtures of nitrogen, carbon dioxide, and n-butane

A new high-pressure vapor-liquid equilibrium apparatus has been constructed with the capability of measuring the compositions and densities of the coexisting equilibrium phases at constant temperature and/or pressure. This apparatus was tested with the carbon dioxide + n-butane system with excellent agreement observed between our results and previously published data. Data are also reported for the nitrogen + n-butane system and the previously unmeasured nitrogen + carbon dioxide + n-butane system. These data were modeled with the Peng-Robinson equation of state. Excellent fits were obtained for the compositions in the carbon dioxide + n-butane system, but a poor fit was obtained for the nitrogen + n-butane data. The ability of the Peng-Robinson equation of state to accurately predict the phase behavior of the ternary mixture is dependent on the fits of the binary data, and therefore the ternary data are also not fit well. In all cases the liquid densities are poorly predicted with the Peng-Robinson equation of state.

Lattice vibrations of a monolayer of n-hexane adsorbed on graphite

The incoherent inelastic neutron spectrum of a monolayer of n-hexane adsorbed on graphite has been analyzed. The two-dimensional lattice structure that was used in the analysis of a monolayer of n-butane on graphite is adopted. The intramolecular valence force fields of the n-butane system require only a minor modification of the CCC/CCC bending interaction and HCCH torsion force constants, while the intermolecular pairwise potentials transfer with no modification. The frequency dispersions and hydrogen amplitudes calculated from normal mode analysis are used to construct the neutron scattering cross sections. These are then summed for all normal modes and folded with both the instrumental resolution function and the incident beam profile to form a composite time-of-flight spectrum. The agreement between the calculated and observed spectra is even better than that obtained in our earlier analysis of n-butane. The intermolecular potential constants for the hydrogen–substrate and hydrogen–hydrogen pairs are 0.04 and 0.003 mdyn/A, respectively.

Liquid-vapour critical region of the most volatile component of the ternary system. II. Data reduction

Wichterle, I. and Uchytil, P., 1984. Liquid-vapour critical region of the most volatile component of the ternary system. II. Data reduction. Fluid Phase Equilibria, 16: 117–126. A correlation of binary vapour-liquid equilibrium data at conditions around the critical point of the more volatile component was proposed. The fractional function with three adjustable parameters was used to express the dependence of K-value on pressure or composition. This function secures the boundary conditions ensuing from the existence of critical point. By introducing hypothetical states (vapour pressure above or critical pressure below the critical temperature), the proposed function is continuous regardless of temperature. The experimental data on vapour-liquid equilibria in the ethane - propane and ethane - - n-butane systems were reduced using the model presented. The necessary analytical description of ternary (including binary) critical locus was achieved via a simple function.

Liquid-vapour critical region of the most volatile component of a ternary system. I. Vapour-liquid equilibria in the ethane - propane - n-butane system

Uchytil, P. and Wichterle, I., 1983. Liquid-vapour critical region of the most volatile component of a ternary system. I. Vapour-liquid equilibria in the ethane - propane - n-butane system. Fluid Phase Equilibria, 15: 209–217. Vapour pressure of propane was determined within 22–95°C temperature range. Vapour-liquid equilibria in the ternary ethane - - propane - n-butane system and in the binary ethane - propane and ethane - n-butane subsystems were measured isothermally at 31.19, 32.52, and 33.89°C in the narrow concentration range (mole fraction of ethane > 0.95). The critical pressures and temperatures of these systems were determined within the same concentration region.

Vapour-liquid equilibria in the ethane - propane - n-butane system at high pressures

Vapour-liquid equilibria in the ethane - propane - n-butane system at high pressures

Vapour-liquid equilibria in the ethane- n-butane system at high pressures

An equilibrium still with transparent static cell was constructed which enables the measurement of phase equilibria to be made at pressures up to the critical pressure. It was tested by vapour pressure measurement of pure n-butane within the temperature range 293–363 K. The vapour-liquid equilibria in the ethane- n-butane system were measured isothermally at 303.15, 323.15, 343.17, and 363.40 K. An interaction parameter in the mixing rule used in the Redlich-Kwong-Soave correlation method was evaluated.

Vapour—liquid equilibria in the propane— n-butane system at high pressures

The vapour—liquid equilibria in the propane— n-butane system were measured isothermally at 303.14, 323.10, 343.17, and 363.38 K. An interaction parameter in the mixing rule used in the Redlich—Kwong—Soave correlation method was evaluated.

Simulation of n-butane using a skeletal alkane model

A simulation of a fluid n-butane system has been carried out using a straight-chain skeletal model. The calculations reported here involve fluid densities from 288.80 to 721.99 kg/m3 at several distinct temperatures. In the course of this investigation the linear self-diffusion constant, the rate of torsional gauche/trans relaxation and rotational tumbling of the fluid have been studied. This model shows a high degree of cooperativity between the molecular vibration and rotation, and the bulk fluid motion.

Vapor-liquid equilibrium of methane-n-pentane system at low temperatures and high pressures

Measurements of the bubble-point compositions are reported and combined with dew-point data to give K-values for the methane--n-butane system at 40/sup 0/, 0/sup 0/, -20/sup 0/, -40/sup 0/, -60/sup 0/, -80/sup 0/, -100/sup 0/, -116.6/sup 0/, -120/sup 0/, -140/sup 0/, -160/sup 0/, -180/sup 0/, and -200/sup 0/F from the vapor pressure of n-butane up to critical point of the vapor pressure of methane. Experimental conditions were selected so that direct isobaric observations were also possible. Results showed significant deviations in the low-temperature range of the NGPSA critical loci as based on the experimental results of J. J. McKetta et al. from +40/sup 0/F to -140/sup 0/F. Data, however, are consistent in the high-temperature range as based on the data of B. H. Sage et al. from 70/sup 0/F to 250/sup 0/F. The 13 isotherms shown are constructed from data obtained from both experimental procedures.

Concentration Limits for n-Butane Low Temperature Flames

Abstract The spontaneous ignition composition limits of four flame systems—cool, blue, yellow plume and transition—have been mapped out for the n-butane system in a dynamic flow reactor at atmospheric pressure. The cool and blue flames occur within as well as outside the fuel-oxidizer concentration limits for n-butane hot flames.

Phase Equilibria in Hydrocarbon Systems Methane–n-Butane System in the Gaseous and Liquid Regions

Phase Equilibria in Hydrocarbon Systems Methane–n-Butane System in the Gaseous and Liquid Regions