Methane-ethane Mixtures Research Articles

The Solubility of Binary Mixed Gases by the Fluctuation Theory

This paper is devoted to the solubility of mixed gases in a liquid, the goal being to predict their solubilities from binary data. Only sparingly soluble and weakly interacting gases are considered. On the basis of the Kirkwood-Buff theory of solution, two transcendental equations are derived that allow one to predict the solubility of binary mixed gases from the solubilities of pure individual gases. The suggested method was tested for the solubilities of methane-ethane, methane-n-butane, and methane-carbon dioxide gas mixtures in water at high pressures. Good agreement between experiment and predictions was found.

Raman Spectroscopic Studies of Methane—Ethane Mixtures as a Function of Pressure

Raman spectra of methane and methane–ethane mixtures (100, 85, and 49 mole % CH4) have been obtained as a function of pressure in the pressure range 0.1 to 15.3 MPaA (MPa absolute). For these mixtures methane v1 (symmetric C–H stretching) band positions are given as a function of pressure; for pure methane they are in agreement with previous results. The new data on the methane v1 band position of ethane-containing mixtures clearly depend on the kind of molecules surrounding the vibrating methane molecule. The v1 band position decreases with increasing pressure; the stronger the dependency, the higher the content of ethane. The ethane v1 band position in the two mixtures showed the same kind of dependency. A qualitative explanation for this behavior is attempted, relating it to changes in van der Waals-type interactions on pressure.

Developing a Microhumidity Generator for Methane-Ethane Gas Mixtures

Methods are examined for drying natural gases and checking the degree of dryness by means of an experimental equipment. The working conditions are defined for a generator giving trace concentrations in a methane-ethane gas mixture.

Diffusion modes of an equimolar methane-ethane mixture from dynamic light scattering

The hydrodynamic diffusion modes of an equimolar methane–ethane mixture have been investigated by dynamic light scattering. Measurements were performed over a wide temperature range between the plait critical point at 263.55 K and 310 K along the critical isochore. Two relaxation modes have been observed which are commonly associated with pure mass diffusion and pure thermal diffusion, but in near-critical binary fluid mixtures—according to recent theory—may alternatively be interpreted as two effective diffusivities resulting from a coupling between mass and thermal diffusion. Diffusivity values for the slow mode were obtained with typical standard deviations of 1% over the whole temperature range, whereas the low amplitude of the fast mode only allowed values of this component with a large measurement uncertainty. The results are discussed in connection with literature data available for the thermophysical properties of this binary fluid mixture and regarding the various possibilities of theoretical interpretation.

Combustion Kinetics of Light Hydrocarbons in the Presence of Nitrogen Oxide

An experimental analysis of the interactions between different hydrocarbons and NO is reported. All the experiments have been carried out in a perfectly stirred reactor, operated isothermally in the temperature range 1050-1250 K, with stoichiometric ratios ranging between 1.0 and 1.3. It has been found that, close to the higher temperature values investigated, the NO conversion as a function of the stoichiometric ratio shows a maximum around 1.15-1.20, both in the case of pure methane and methane-ethane mixtures in the feed. Moreover, the addition of NO significantly enhances the system reactivity at the lower temperatures investigated. The ethane content in the feed plays a different role depending upon the temperature value considered. At the lowest temperatures investigated the larger the amount of ethane, the higher the NO abatement, while at the higher temperatures the methane-ethane mixtures always show a larger NO conversion than that of pure methane. However, when increasing the ethane content in the feed, the NO conversion decreases. Finally, various detailed kinetic models (with particular reference to that developed by Miller and Bowman [Prog. Energy Combust. Sci. 1989, 15, 287]) have been discussed and used to interpret the experimental results.

Molecular simulation of adsorption of short linear alkanes and their mixtures in silicalite

AbstractConfigurational‐bias Monte Carlo simulations in the grand‐canonical ensemble are employed to compute adsorption isotherms of methane, ethane, propane, butane and binary mixtures of methane–ethane, methane–propane, ethane–propane, and methane–butane in the zeolite silicalite. Comparison of the simulation results with the limited expetiniental data available shows good agreement. For ethane at room temperature, a small inflection point in the isotherm was observed due to a surprising ordering of the ethane molecules in the zeolite. For the simulation of a methane–ethane mixture, at low pressure ethane is preferentially adsorbed, while at high pressures methane replaces ethane due to entropic effects.

Oxidation of methane–ethane mixtures into alcohols under enhanced pressures

Experimental investigation of the direct partial oxidation of methane–ethane mixtures into alcohols in the pressure range from 2 to 15 atm and at 100 atm was carried out and compared with the results of kinetic simulation of this process.

Solubility of light hydrocarbons and their mixtures in pure water under high pressure

New solubility data of methane, ethane, n-butane and their mixtures in pure water are obtained at 344.25 K, from 2.5 to 100 MPa. The results agree well with those of the literature in the case of pure hydrocarbons in water, but differ significantly for hydrocarbon mixtures. In contrast to the conclusion reached by Amirijafari and Campbell [B. Amirijafari, J. Campbell, Solubility of gaseous hydrocarbon mixtures in water, Soc. Pet. Eng. J. (1972) 21–27.], the experimental solubility data of methane–ethane mixtures shows an ideal solution behavior, while the solubility data of methane– n-butane mixtures shows a weaker non-ideality than that observed by McKetta and Katz [J.J. McKetta, D.L. Katz, Methane– n-butane–water system in two-and three-phase regions, Ind. Eng. Chem. 40 (1948) 853–863]. The pure hydrocarbon solubility data are satisfactorily correlated using the Soreide and Whitson modification [I. Soreide, C.H. Whitson, Peng–Robinson predictions for hydrocarbons, CO2, N2, and H2S with pure water and NaCl brine, Fluid Phase Equilib. 77 (1992) 217–240] of the Peng–Robinson equation of state.

Properties of coexisting fluid phases of a binary system methanolethane by computer simulation

Methaneethane and methanolethane binary mixtures were simulated by the Gibbs ensemble Monte Carlo method. Thermodynamic properties and structural characteristics of coexisting fluid phases were calculated. Reasonable agreement with experiment was obtained, in particular, for the liquid-liquid-vapour coexisting pressure in the methanolethane system at 298.15 K. A lyophobic effect, which affects the phase behaviour and the hydrogen-bonding characteristics of the liquid phase, was observed. In order to improve agreement with experiment, the values of the Lennard-Jones interactions parameters for CH 3OH and C 2H 6 molecules were adjusted.

A Generalized Intermediate Approach to Combustion Chemistry: Application to Methane Ignition and Flame Propagation

A chemical reaction mechanism for methane combustion was developed by a method different in principle from previous efforts that start from detailed chemistry and use steady-state and other approximations. It describes, accurately and with the same parameter set, such different phenomena as flames and high and intermediate temperature ignition. The approach used for chemistry simplification resolves the main features of hydrocarbon oxidation into steps, each with simple kinetic sense, describing thermal decomposition of fuel, true and degenerate chain branching, propagation, termination, and the formation of final products. Rate coefficient expressions for elementary reactions were taken from the literature, while those of generalized reactions were optimized using an automated regression procedure against ignition and flame speed data. The predicted composition and pressure dependences for ignition and combustion of methane and methane-ethane mixtures are in good agreement with experiment.

Virial coefficients of methane-ethane mixtures in the temperature range from 0 to 60�C determined with an automated expansion apparatus

An automated expansion apparatus has been set up which can be used for PVT measurements on gases from Il to 60 C at pressures from 2 to 7 NIPa. It consists of two chambers connected by an expansion valve. The ratio of the two volumes is 1:54. The measurements along one isotherm. which take 20 h, can be per formed routinely and without operator attendance. The uncertainty of the com pressibility factor is estimated to be 10−3. The compressibility factors of binary mixtures of the main components of most natural gases, methane and ethane, were determined on high-grade gas, the mole fractions of ethane being 0.05, 0.15. and 0.25. Seven isotherms were measured of each of the mixtures. Data from the literature for the virial coefficients of the pure substances were used to establish a virial equation of state which approximates the measured com pressibility factors with a standard deviation of 0.4 x 10 '. This is substantially smaller than the uncertainty. The interaction virial coefficients were calculated from this equation of state. The results obtained are in good agreement with other available data.

Determination of the compressibility factorZ(p, T) of three methane-ethane mixtures using the dielectric constant method

The compressibility behavior of three mixtures of the CH4 C2 H6, system has been investigated experimentally by means of the dielectric constant method. Precise ( ± 1 ppm) measurements of the dielectric constant (e) as a function of the pressure (P) along one isotherm (T) are combined with the first three dielectric virial coefficients (A,B, andC) in order to obtain accurate values of the molar density (p). The compressibility factorZ=P/( p RT) was obtained from the measured values ofp,P, andT. The coefficientA, is determined from the measurements of e as a function ofP, while the higher-order coefficients (B, andC,) are obtained by an expansion technique. We report the measured values ofZ at 295.15 K up to 12 MPa for three mixtures of CH4-C2-H6 containing, respectively. 9.54, 35.3, and 75.4% (molar) of ethane. Their exact composition was determined by weighing during the mixing process. The first three dielectric virial coefficients and the mixed second dielectric virial coefficient for the CH4,-C2, H6 system agree with the calculated or the literature values within the limits of uncertainties. For the mixture containing 90.46% CH4+C2H6, deviations in compressibility are of the order of 0.4% from GERG.

Adsorption of gas mixtures on solid surfaces, theory and computer simulation

A treatment of the thermodynamics of mixed gas adsorption is presented in which the gas-solid interface is three dimensional. Such a treatment yields an additional term as compared to two dimensional approaches. This additional term has significant consequences for the derivation of adsorbed solution theories, particularly at higher temperatures. Results are presented for a Grand Canonical Monte Carlo study of a model methane-ethane mixture in a carbonaceous slit pore. Comparison of single component and mixture results provides an unambiguous means of testing theories of adsorbed solutions and bears out the thermodynamic treatment presented in the previous section of the paper.

Analysis of detailed kinetic schemes for combustion processes: Application to a methane-ethane mixture

Analysis of detailed kinetic schemes for combustion processes: Application to a methane-ethane mixture

Analysis of detailed kinetic schemes for combustion processes: Application to a methane-ethane mixture

The combustion kinetics of equimolar ethane-methane mixtures have been investigated in a perfectly jet stirred reactor in the temperature range 923–1,080 K and for normalized fuel/O 2 stoichiometric ratios of 0.24–1.5. The concentrations of the main molecular species have been measured by probe sampling and GC analysis. The experimental data have been compared with the model predictions of four detailed kinetic mechanisms previously reported in the literature. A simple procedure to extract the most important reactions from a detailed kinetic scheme has also been developed. With this procedure a reduced model has been identified which is able to reproduce the behavior of the original detailed model in the entire range of operating conditions investigated in the experimental part of this work. A good reduction in the number of reactions has been obtained, while the number of involved chemical species has been only slightly reduced.

An isomorphic generalization of the law of corresponding states for binary mixtures

An isomorphic equation of state for binary mixtures has been obtained on the basis of an asymmetric scaled equation for one-component liquids. To extend this equation to the whole range of concentrations a new isomorphic generalization of corresponding states was introduced. The resulting equation has been applied to methane-ethane mixtures and describes experimental P,V,T,X data in a wide region above the critical line. Good agreement with experimental data is observed.

Prediction of thermodynamic properties of fluid mixtures by molecular dynamics simulations: methane-ethane

NPT and NVT molecular dynamics simulation results are reported for the fluid methane-ethane mixture. Methane is modelled as Lennard-Jones fluid and ethane as a two-centre Lennard-Jones fluid with parameters obtained some time ago by fitting WCA-type perturbation theory results to two experimental vapour pressures and one bubble density for each substance. It has also already been shown that these effective pair potentials yield good predictions of the pressures and internal energies of the pure substances in the whole fluid region. In order to obtain an effective potential between the unlike molecules, previously derived fluctuation formulas for the dependence of the mixture excess properties on the unlike molecule interaction parameters are used. A test of these fluctuation formulas shows their statistical uncertainties to be small. Hence, the unlike interaction parameters can be determined from one mixture simulation and a fit to one experimental excess volume and one excess enthalpy. Then second virial coefficients, liquid excess properties, P, V, T data and enthalpy differences are calculated in the temperature range 100–400 K and pressures up to 30 MPa. Comparison is made directly with experimental data and partly also with the DDMIX equation of state showing mostly good to excellent agreement except in the critical region; for some state points in the gas the pressures are slightly too low. Technically, runs for several gas state points are NVT simulations whereas the other runs are NPT simulations part of which were checked again by NVT-simulations. The paper also compares pressures obtained by the Haar-Shenker-Kohler equation for the gas phase with NVT simulation results. All simulations were performed on a CYBER 205.

Selective adsorption of simple mixtures in slit pores: a model of methane-ethane mixtures in carbon

The authors report a study of Lennard-Jones mixtures in model carbon pores having parallel walls. The fluid potential parameters were chosen to model methane and ethane, and the 10-4-3 model was used for the solid-fluid potential. A density-functional theory with the nonlocal density approximation was used for the calculations. The authors focused on the selectivity of ethane relative to methane for a wide range of system parameters. Different types of selectivity isotherm were found, which can be explained microscopically in terms of intermolecular and surface forces. Macroscopically, each type of isotherm corresponds to a certain range of temperature in relation to the capillary critical temperatures. At very low temperatures where layering transitions occur, the selectivity isotherm is steplike. The density profiles show a strong surface segregation of ethane from methane. 48 refs., 23 figs.

Viscosity surface for mixtures of methane and ethane

The viscosity surface for methane-ethane mixtures has been correlated as a function of composition, density and temperature. The correlation is based on measurements, made at the National Institute of Standards and Technology, using a torsionally oscillating quartz crystal viscometer, which have been reported previously. The viscosity data cover the composition range including both pure fluids and three of their binary mixtures and include temperatures from 100 to 320K with pressures to 30 MPa. The correlation comprises contributions from the dilute gas state, based entirely on Chapman-Enskog mixture theory and an empirical excess function. The excess function exploits corresponding states arguments and, with suitable reductions of the viscosity, density and temperature, the data are seen to conform closely to a single function of the reduced quantities. The very steep rise of viscosity at high densities is described by a simple rational polynomial and this is added to another polynomial in reduced density and temperature to completely represent the reduced excess viscosity. For the 624 experimental points which were considered, the average absolute deviation from the correlation is less than 1.5%.

Isochoric specific heat in the methane-ethane system around the liquid-gas critical line

Experimental and theoretical studies have been made on the behavior of the isochoric specific heat for binary methane-ethane mixtures in the critical region.