Ethane In Aqueous Solutions Research Articles

Mole fraction measurement of methane and ethane in aqueous solutions of NaCl and MgCl2 during hydrate growth

In this paper, the mole fraction of methane and ethane in aqueous solutions of NaCl and MgCl2 during hydrate growth in a semi-batch stirred tank reactor is reported. Methane mole fraction measurements in aqueous solutions of NaCl were conducted at molalities of 0.529 and 1.092, temperatures of 275.15–290.15 K, and pressures of 40–68 bar. The same conditions were provided to measure the mole fraction in the aqueous solution of MgCl2 at molalities of 0.325 and 0.670 mol kg−1. We also report the mole fraction of ethane in aqueous solution of NaCl at molalities of 1.901 and 3.020 mol kg−1, temperatures of 273.15–278.15 K, and pressures of 11–24 bar; however, molalities of 0.325 and 0.791 mol kg−1, temperatures of 279.15–283.15 K, and pressures of 14–29 bar were investigated for the C2H6-MgCl2 system. Furthermore, the effects of pressure and salt concentrations on the mole fraction of these gases in aqueous phase in the presence of hydrate were investigated. It was observed the mole fraction of hydrate formers in the aqueous phase are close to solubility of this gases at experimental temperature and corresponding equilibrium pressure. In addition, it was found the mole fraction of methane and ethane in bulk liquid phase remain constant during the hydrate growth period, whereby the fugacity of the aqueous phase was constant throughout this period.

Equilibrium conditions for clathrate hydrates formed from carbon dioxide or ethane in the presence of aqueous solutions of 1,4-dioxane and 1,3-dioxolane

Equilibrium conditions for clathrate hydrates formed from carbon dioxide or ethane in aqueous solutions of 1,4-dioxane and 1,3-dioxolane were determined experimentally using an isochoric method. Addition of the 1,4-dioxane and 1,3-dioxolane to water shifted the equilibrium conditions of carbon dioxide hydrates to a higher temperature, indicating that they promote carbon dioxide hydrate formation. In contrast, 1,4-dioxane and 1,3-dioxolane inhibited ethane hydrate formation at pressures greater than 0.7MPa.

Solubilities of Carbon Dioxide, Methane, and Ethane in Sodium Chloride Solution Containing Gas Hydrate

Studies on two-phase equilibria between the water-rich phase (LW) and the gas hydrate phase (H) are important in understanding gas behavior in water at hydrate forming conditions for processes such as carbon dioxide sequestration and natural gas recovery. A new indirect method was developed in this study and applied for measurements of gas solubilities of carbon dioxide, methane, and ethane in aqueous solutions containing gas hydrates with and without sodium chloride. Effects of temperature, pressure, and salt concentrations on the solubility of these gases in the aqueous phase in equilibrium with the hydrate phase were investigated for P = (10 to 20) MPa. Solubilities for these gases were found to increase as temperature increases. Methane and ethane were found to show a salting-out effect, whereas carbon dioxide showed a salting-in effect in hydrate forming conditions. Solubilities of methane and ethane decreased with pressure, but those of carbon dioxide showed very weak pressure dependence.

Cobalt(II) phosphine complexes stable in aqueous solution: spectroscopic and kinetic evidence for low-spin Co(II)P 6 and Co(II)P 3S 3 with tripodal 1,1,1-tris(dimethylphosphinomethyl)ethane

Co(II) species produced by the controlled potential electrochemical reduction of Co(III)P 3S 3 and Co(III)P 6 complexes with 1,4,7-trithiacyclononane and tripodal 1,1,1-tris(dimethylphosphinomethyl)ethane in aqueous solution were characterized at ambient temperature by the EPR and spectrophotometric methods: the Co(II)P 6 and Co(II)P 3S 3 species are in the low-spin t 2g 6e g 1 state with large Jahn–Teller distortion. Kinetic studies of the redox reactions involving these Co(III)/(II) species revealed that the electron self-exchange reactions for the Co(III)/(II) couples are very fast ( k ex∼10 4 dm 3 mol −1 s −1), which is consistent with the results for other low-spin/low-spin Co(III)/(II) couples. It was concluded that the nephelauxetic effect of the P donor atom stabilizes the low-spin state in Co(II).

Equilibrium Conditions of Methane and Ethane Hydrates in Aqueous Electrolyte Solutions

Abstract: In this work, we determined the equilibrium conditions for gas hydrates of methane and ethane in aqueous solutions containing various electrolytes, such as NaCl, NaBr, NaI, and Na2SO4. We have developed experimental apparatus in which a light beam through solutions was used to detect the formation and dissociation of gas hydrate. To model the experimental data of this work, a statistical thermodynamic model based on the classical adsorption model proposed by van der Waals and Platteeuw 1 is used. The water activity of the aqueous solutions containing electrolytes, which affects the gas hydrate stability, was evaluated by the model of Englezos and Bishnoi.2

Equilibrium Hydrate Formation Conditions for Hydrogen Sulfide, Carbon Dioxide, and Ethane in Aqueous Solutions of Ethylene Glycol and Sodium Chloride

Incipient equilibrium hydrate formation conditions for hydrogen sulfide, carbon dioxide, and ethane in aqueous solutions of ethylene glycol and sodium chloride were experimentally obtained in the temperature range 264−290 K and the pressure range 0.23−3.18 MPa. A variable-volume sapphire cell was used for the measurements.

Solubility of Methane and Ethane in Aqueous Solutions of Methyldiethanolamine

Data are presented for the solubility of methane and of ethane in a 3 kmol/m3 (34.7 mass %) solution of methyldiethanolamine. Temperatures in this study ranged from 25 to 130 °C and pressures to 13 MPa. The data were incorporated into a rigorous thermodynamic model that has been applied to other similar systems. The model is a combined Raoult's law−Henry's law approach. The solubilities in the alkanolamine solution are correlated in terms of the salting-in ratio, the ratio of the mole fraction solubility in the amine solution to that in pure water.

Solubility of Ethane in Aqueous Solutions of Triethanolamine

The solubility of ethane in three triethanolamine solutions (2, 3, and 5 mol dm-3) has been determined at five temperatures between 25 and 125 °C at pressures up to 20 MPa.

Solubilities of Ethane in Aqueous Solutions of Sodium Dodecyl Sulfate at Elevated Pressures

The solubilities of ethane in aqueous solutions of sodium dodecyl sulfate (SDS) were measured at 313.15 K and at pressures up to 3 MPa. The molalities of SDS (mSDS) in the aqueous solution were 0.0000, 0.0020, 0.0040, 0.0060, 0.0070, 0.0080, 0.0090, 0.0100, 0.0126, 0.0150, 0.0200, and 0.0300. The effect of SDS on the gas solubility in both concentration regions below and above the critical micelle concentration (cmc) was studied. The existence of the micelles of SDS in the solution is favorable to the dissolution of ethane due to the hydrocarbon-like interior of the micelles. The solubilities of ethane in each micelle at different pressures were evaluated based on some assumptions. It was found that the intramicellar solubility of ethane is less than that of the gas in n-dodecane. It was also found that the solubility of ethane in the micelles increases linearly with the partial pressure of ethane. The cmc of SDS was evaluated based on the solubility vs mSDS curves and the effect of dissolved ethane on the cmc was studied. It was observed that the cmc shifts toward a higher value with the increase in dissolved ethane.

Further evidence for a temperature-dependent hydrophobic interaction: the aggregation of ethane in aqueous solutions

A series of molecular dynamics simulations has been performed on a system comprising 256 water molecules and four ethane molecules at 279, 299, 313, 317, 322, 332 and 346 K. Radial distribution functions for the water-water and ethane-water pairs reveal a structuring of the first hydration shell of ethane, while the radial distribution functions for the ethane-ethane pair show a tendency for ethane particles to aggregate with increasing temperature in a small temperature range, with a maximum around 317 K. This behavior is consistent with an emtropy-driven hydrophobic attraction between the nonpolar solutes near room temperature.

Treatment of rotational isomers in free energy evaluations. Analysis of the evaluation of free energy differences by molecular dynamics simulations of systems with rotational isomeric states

Using 1,2-dimethoxy ethane in aqueous solution as an example, the applicability of the perturbation method and the thermodynamic integration technique to evaluate free energy differences is considered for systems with multiple rotational isomeric states. It is shown that the naive application of these methods to evaluate free energy differences for such systems, even in a simple case such as the free energy of hydration of 1,2-dimethoxy ethane, may lead to unreasonable results. This problem is due to the fact that, in a conventional simulation, it is unlikely that all isomeric states will be sampled with the appropriate equilibrium probabilities. A procedure is proposed to estimate the contributions of isomeric states in free energy difference calculations.

The effect of sodium chloride on the solubility of ethane in micellar solutions of sodium dodecyl sulfate

Experiments have been carried out to determine the solubility of ethane in aqueous solutions of sodium dodecyl sulfate containing sodium chloride. Addition of successive increments of NaCl to a micellar solution of sodium dodecyl sulfate (SDS) causes a small increase in gas solubility at low salt concentrations (<0.1 m). However, at higher salt concentrations NaCl suppresses the solubility of ethane. These salt effects are found to be independent of surfactant concentration. The variation in ethane solubility with salt concentration is interpreted as reflecting the combined effects of an increase in micellar SDS at the expense of the monomeric form which occurs at low salt concentrations and the salting out of ethane from the external aqueous phase. The intramicellar solubility of ethane is not affected by added salt, even in solutions having very high NaCl concentrations (>0.6 m) which are thought to contain SDS in the form of large aggregates which are thermodynamically unstable with respect to the hydrated solid state.

The solubility of gaseous hydrocarbons and the hydrophobic effect in aquaeous solutions of alkyl-ureas

The solubility of methane and ethane in aqueous solutions of some alkylderivatives of urea have been studied in order to evaluate the hydrophobic effect according to the Ben-Naim model [1]. The cosolutes used are monomethylurea (MMU), monoethylurea (MEU), symmetric dimethylurea (1,3-DMU) and symmetric diethylurea (1,3-DEU). The study is of potential interest for its biochemical and bio-physical implications [1, 2]. In fact, hydrocarbons can be considered as model molecules of some of the side chains of proteins and, at the same time, it is known the capability of alkylureas in denaturing globular proteins [3–5]. The standard free energies of solution for the gases are deduced from the Ostwald absorption coefficient γ s: ▪ From the temperature derivatives of the free energies, the standard enthalpies and entropies of solubilization are also obtained. It is already known that the last two quantities are negative for the apolar gases in water, and we found that the addition of the studied series of cosolutes do not introduce drastic variations in this behaviour. The signs of the enthalpy and entropy were ascribed [6] to an enhancement of water structure, promoted by the apolar gases. A quantitative scale of comparison for the intensities of the hydrophobic interactions was proposed by Ben-Naim and coworkers [1]. The mechano-statistical treatment leads, with certain assumptions, to the simple relation: ▪ where Δμ° Et and Δμ° Me are the free energies associated with the process of transfer, at constant P and T, of two molecules of methane from fixed positions at infinite distance to a defined distance R 1 in the presence of the solvent respect to the vacuum. The charges of δ G HI with the concentration of the cosolutes (alkylureas) and with the temperature, hence the signs and values of the corresponding δ H HI and δS HI, are analyzed and compared with the free energies of transfer Δμ° tr. Qualitative conclusions are tried on the mechanisms ruling the complex phenomenon of the solubilization of gaseous hydro-carbons in aqueous mixed solvents and on the self and cross interactions among the different species in solution.

The radiation-induced oxidation of ethane in aqueous solution

Aqueous solutions of ethane–oxygen mixtures have been irradiated with γ-rays, at room temperature; the major products were acetaldehyde, ethanol, and ethyl hydroperoxide, the last being formed at pH 5·5 and 10 but not at pH 1·2. Photolysis of hydrogen peroxide solutions containing dissolved ethane and oxygen resulted in the formation of ethanol and acetaldehyde only. The results have been interpreted in terms of reactions of ethyl peroxy radicals.