Ethane Gas Mixture Research Articles

Experimental and Modeling Study on Phase Equilibria of the Methane + Ethane Gas Mixture

Experimental and Modeling Study on Phase Equilibria of the Methane + Ethane Gas Mixture

Use of Gas Hydrate with Propanone as the Promoter for Separation of Gas Mixtures Methane + Ethane

In this article, the gas hydrate technique with propanone as the promoter was employed to separate methane + ethane gas mixtures. Experiments were performed in two different aqueous propanone conce...

Gas Hydrate Sloughing as Observed and Quantified from Multiphase Flow Conditions

Sloughing of gas hydrates from deposits formed on the pipe wall is a phenomenon that can cause hydrate accumulation and blockage of the flow in oil/gas pipelines. While hydrate sloughing has been recognized as an important mechanism leading to hydrate blockage, its observation and measurements have not been reported. Experiments performed in a visual rocking cell to emulate multiphase flow conditions with a methane–ethane gas mixture, fresh water, and non-emulsifying oil or condensate as hydrocarbon liquid demonstrated that hydrate sloughing occurs at a wide range of subcooling and temperature gradient conditions. However, sloughing was not detected in a narrow operational window defined by both subcooling lower than 4 °C and temperature gradient in the cell lower than 1 °C. The potential existence of an operational window for conditions without sloughing might be valuable for the development of hydrate management strategies for blockage-free production.

Liquid Water–Hydrate–Vapor Equilibrium for Methane + Ethane Gas Mixtures: Application of Gas Hydrates for Separation

In this communication, liquid water–hydrate–vapor (Lw–H–V) phase diagrams for methane + ethane gas mixtures are predicted using van der Waals–Platteeuw solid solution theory. Experimental measurements were conducted and the results exhibited that methane was effectively separated from ethane by hydrate formation. To perform the experiments, methane + ethane gas mixtures were contacted to excess water at appropriate conditions. Once the hydrate phase was produced, the compositions in the gas and hydrate phases were measured meticulously and reported. Presented in this work, methane was enriched in the residual vapor phase, while ethane was enriched in the hydrate phase. The performed experiments justify the use of gas hydrate as a feasible method for separation. The model predictions of the pressure–composition diagram are also in good agreement with experimental results.

Investigating the partial structure of the hydrate film formed at the gas/water interface by Raman spectra

The morphology and structure of hydrate films of pure methane and methane+ethane mixtures were studied by suspending a single gas bubble in liquid water. The methane+ethane gas mixtures, containing 20mol% or 81–89mol% methane, were used to form hydrate films with different crystal structures. Polyhedral structures appeared on the background of uniform polycrystalline hydrate films formed by gas mixtures with a high methane mole fraction of 0.81–0.82. Some of the polyhedral structures are holes, and others are separated structure II polyhedral hydrate crystals. However, for pure methane, a gas mixture with a lower CH4 mole fraction of 0.2, or a gas mixture with a higher CH4 mole fraction of 0.89, the morphology is uniform through the whole hydrate film. The crystal structures in the hydrate film were determined using in situ Raman spectra. The results show that both pure methane and the gas mixture with a lower CH4 mole fraction of 0.2 form a hydrate film with structure I. The single polyhedral crystal appeared in the background of the uniform polycrystalline hydrate film formed by gas mixtures with a high methane mole fraction of 0.81–0.82 as a structure II CH4-C2H6 double hydrate crystal. The hole is mainly gas with an initial small amount of structure I hydrate, and that hole will be filled with structure II hydrate after a certain time. The experimental methods and the new findings presented in this work should be significant for the further research of hydrate growth kinetics.

Gas–liquid membrane contactor for ethylene/ethane separation by aqueous silver nitrate solution

Separation of light olefin from paraffin having the same carbon number is one of the most energy intensive separations in petrochemical processes, which uses very long distillation columns with very high number of trays. This is attributed to the very small differences in the relative volatilities. The purpose of this work is to study the absorption performance of a home-made PVDF hollow fiber membrane fabricated using thermally induced phase separation method. Separation of ethylene from an ethylene–ethane gas mixture, using a hollow fiber membrane based absorption–desorption system with aqueous silver nitrate as absorption solvent, and to enhance separation process with a purchased polypropylene hollow fiber membrane module used for stripping purposes. Experiments on the absorption of ethylene from ethylene–ethane mixture, into silver nitrate solutions were performed. The effects of initial ethylene concentration in feed gas, silver nitrate concentration in the inlet solvent, liquid and gas flow rates were investigated. Results reveal that ethylene/ethane separation factor increases with silver nitrate concentration and liquid flow rates. A two dimensional mathematical model was developed for this purpose. Model predictions were validated with experimental data. Model predictions were in good agreement with experimental results.

Separation of methane–ethane gas mixtures via gas hydrate formation

In this study, a new technique to separate methane–ethane binary mixtures via gas hydrate formation has been developed. The experimental data of mixed methane–ethane gas hydrate formation have been studied at various compositions of mixture (0.1, 0.2, 0.3, 0.5, 0.68, 0.8 and 0.9mol fractions of methane). In order to determine the composition of gas during hydrate formation, an algorithm has been introduced based on Langmuir adsorption model. This algorithm can discuss with regard to the system behavior during mixed gas hydrate formation at various mole fractions of methane and ethane; for example it explains how the hydrate formation process becomes 2 stages at low mole fractions of methane. The results show that two gases were fully separated at low and high mole fractions of methane in the mixture.

Stratigraphic and structural control on the distribution of gas hydrates and active gas seeps on the Posolsky Bank, Lake Baikal

The distribution and origin of shallow gas seeps in the vicinity of the Posolsky Bank in Lake Baikal were studied based on the integration of detailed seismic, multibeam, and hydro-acoustic water-column investigations. In all, 65 acoustic flares have been detected on the Posolsky Fault scarp near the crest of the bank and in a similar, nearby setting at water depths of −43 to −332 m. The seismic data reveal BSRs (bottom-simulating reflectors) occurring up to water depths of −300 m. Calculations involving hydrate stability, heat flow, and topographic modulation based on BSR occurrence and multibeam bathymetry enabled prediction of a methane–ethane gas mixture and heat-flow values that would account for gas hydrate stability in the lake sediments under prevailing ambient conditions. These predictions are supported by ground truth data. The findings suggest that seeps concentrated along the crest of the Posolsky Bank are fed mainly by gas coming from below the base of the gas hydrate stability zone, which would migrate updip via permeable stratigraphic pathways beneath the bank. Gas would ultimately be released into the water column where these pathways are cut off by faults.

Raman Studies of Methane−Ethane Hydrate Metastability

The interconversion of methane-ethane hydrate from metastable to stable structures was studied using Raman spectroscopy. sI and sII hydrates were synthesized from methane-ethane gas mixtures of 65% or 93% methane in ethane and water, both with and without the kinetic hydrate inhibitor, poly(N-vinylcaprolactam). The observed faster structural conversion rate in the higher methane concentration atmosphere can be explained in terms of the differences in driving force (difference in chemical potential of water in sI and sII hydrates) and kinetics (mass transfer of gas and water rearrangement). The kinetic hydrate inhibitor increased the conversion rate at 65% methane in ethane (sI is thermodynamically stable) but retards the rate at 93% methane in ethane (sII is thermodynamically stable), implying there is a complex interaction between the polymer, water, and hydrate guests at crystal surfaces.

Highly Selective Sorption of Small Unsaturated Hydrocarbons by Nonporous Flexible Framework with Silver Ion

Ag2[Cr3O(OOCC2H5)6(H2O)3]2[alpha-SiW12O40] [1] is a nonporous flexible ionic crystal composed of 2D-layers of polyoxometalates ([alpha-SiW12O40](4-)) and macrocations ([Cr3O(OOCC2H5)6(H2O)3](+)) stacking along the b-axis. The silver ions are located in the vicinity of the oxygen atoms of the polyoxometalates. The sorption amounts of small unsaturated hydrocarbons such as ethylene, propylene, n-butene, acetylene, and methyl acetylene into 1 are comparable to or larger than 1.0 mol mol(-1) and large hystereses are observed, while those of paraffins and larger unsaturated hydrocarbons are smaller than the adsorption on the external surface (<0.2 mol mol(-1)). Fine crystals of 1 exhibit ethylene/ethane and propylene/propane sorption ratios over 100 at 298 K and 100 kPa, and the values are larger by 1 order of magnitude among those reported. The results of sorption kinetics, in situ IR spectroscopy, single crystal X-ray crystallography, and in situ powder XRD studies show that small unsaturated hydrocarbons penetrate into the solid bulk of 1 through the pi-complexation with Ag(+). The sorption property of 1 is successfully applied to the collection of ethylene from the gas mixture of ethane and ethylene.

Enhancement of the performance of gas hydrate kinetic inhibitors with polyethylene oxide

Inclusion of polyethylene oxide into a kinetic inhibitor solution was found to enhance the performance of the inhibitor. Polyethylene oxide is a commercially available high molecular weight polymer that is not a kinetic inhibitor by itself. The hydrate formation experiments in the presence of the various inhibitor solutions were conducted in a vessel in a semi-batch manner at constant pressure and using methane and methane–ethane gas mixtures. In some experiments a non-aqueous liquid phase ( n-heptane) was also present. The induction time, the gas uptake and the temperature were measured. It was found that the induction time is prolonged in the presence of the additive by an order of magnitude in some cases compared to the inhibitor only.

Preliminary study of a new type of gas microstrip chamber on a sapphire substrate

First results of a series of studies on gas microstrip chamber prototypes prepared on sapphire substrates are presented. The sapphire substrates were prepared by ion-assisted deposition technique in one of the chambers and by placing an approximately 1 μm boro-silica glass film on a second chamber. Responses to X-rays and beta electrons and high rate performance were studied with argon-isobutane and argon—DME gas mixtures. Counting rates of 6 × 10 5 counts/mm 2s) were achieved for X-rays from an X-ray generator with ∼ 50% change in gas gain. The timing response (relative to a fast plastic scintillator) of ultraviolet-light-ionized photoelectrons were studied with an argon—ethane gas mixture. Timing peaks having widths of less than 85 ns (σ) were obtained. Details of the experimental setup and results are presented.

Electrical characterization of ZnSe epitaxial layer reactive-ion-etched by a gas mixture of ethane and hydrogen

The sheet resistances of ZnSe epitaxial layers etched by reactive ion etching (RIE) with use of a gas mixture of ethane and hydrogen were measured. The results showed that a high resistivity region was introduced by RIE. Characterization was done by transforming the measured resistances to the electrically active thickness estimated from the resistivity of as-grown ZnSe layers. The estimated electrically active thicknesses were smaller than the thickness of ZnSe epitaxial layers remaining after RIE, for both p- and n-ZnSe. The influence of heat treatment and current injection on the high resistivity regions differed between p- and n-ZnSe.

Role of Carbon and Hydrogen in Reactive Ion Etching of InP by Gas Mixture of Ethane and Hydrogen

InP crystals were etched by reactive ion etching (RIE) with ethane and hydrogen (C2H6/H2). Etched crystals and gas species were characterized by photoluminescence and mass spectroscopic measurements. Evaporation of phosphorus is induced by hydrogen, mainly originating from H2 gas. Incorporation of C increases with the gas species of hydrocarbon having multiple bonds. Near-bandgap emission with intensities greater than before RIE, which shows the hydrogen passivation, and defect-complex-related emission bands at 1.06-1.07 eV enhanced by RIE were observed. The role of gas species and the identification of defects are discussed on the basis of the experimental results.

Reactive ion etching of ZnSe by gas mixture of ethane and hydrogen

ZnSe epitaxial layers grown by gas source molecular beam epitaxy were etched by reactive ion etching (RIE) with a gas mixture of ethane and hydrogen (C2H6/H2). Smooth etching surfaces were obtained under the following RIE conditions: an ethane concentration (flow fraction) of 3%, total flow (C2H6+H2) of 55 sccm, total pressure of 15 Pa and radio frequency power density of 0.6 W/cm2. This ethane concentration is smaller than that in III–V semiconductors, 5%–7%. The etching rate of ZnSe was 21 nm/min and smaller than that of III–V semiconductors.

Photoluminescence characterization of InP surface reactive ion etched by a gas mixture of ethane and hydrogen

InP crystals were etched by reactive ion etching (RIE) with gas mixture of ethane and hydrogen (C2H6/H2), and etching damages were characterized by photoluminescence (PL) measurements of near-edge and defect-related emissions. Near-edge PL emission intensities after RIE were equal to or larger than those before RIE, except for the samples etched for 50 min. The damage introduced by RIE was restricted to the very-near-surface region which can be removed by HF treatment. The peak energy of defect-related 1.1-eV deep emission bands shifted toward the lower-energy side for the crystals with etching damages at the surface. The peak shift is attributable to the increase of defect complexes such as P-vacancy–P-interstitial or P-vacancy–In-vacancy.