Ethane Mole Fraction Research Articles

Thermal conductivity measurements of liquid ethane and ethane + propane binary mixtures

Based on the transient hot-wire apparatus, the thermal conductivity of ethane was measured in the temperature range of 146–247 K and pressure < 14 MPa in the liquid phase. The thermal conductivity of ethane + propane binary mixture was measured in the temperature range of 156–288 K and pressure < 25 MPa in the liquid phase. The mole fractions of ethane in binary systems are 0.198, 0.525, and 0.736. The deviation between experimental results and REFPROP calculation falls within 3 % of ethane and mixture. Subsequently, the previous established thermal conductivity model, derived from dimensional analysis, was employed to predict the thermal conductivity of n-alkanes mixture. The mixture critical parameters were obtained first by the mixing rules, and the thermal conductivity of the mixture were calculated. Comparisons were made between the experimental data of ethane and the previously constructed n-alkane model, resulting in an average absolute relative deviation (AARD) of 4.42 %. Similarly, the experimental data of the ethane + propane mixture was compared with the mixture prediction model proposed in this study, yielding an AARD of 1.92 %. The relative deviation between experimental data and model calculations demonstrates good consistency.

Numerical simulation of flow boiling heat transfer characteristics of R134a/Ethane binary mixture in horizontal micro-tube

The cryogenic organic Rankine cycle (ORC) is appropriate for recovering the cold energy of liquefied natural gas (LNG) for power generation. However, pure working fluids in ORC are challenging to match the evaporation curve of LNG appropriately, which causes a large amount of exergy loss. Thus, adopting mixture working fluid is a good option due to their temperature-varying evaporation and condensation process. This study investigates the heat transfer characteristic of R134a/ethane (widely adopted in cryogenic ORC as pure working fluid) binary mixture in the horizontal micro-tube through numerical simulation. The law of boiling heat transfer characteristics with vapor quality, heat flux, mass flow, ethane mole fraction, and other factors are obtained. The simulation illustrated that the boiling heat transfer coefficient increases with the heat flux and mass flow. Furthermore, compared with R134a, ethane has higher thermal conductivity, lower vapor density, and latent heat of vaporization. Hence, the heat transfer coefficient of the R134a/ethane mixture increases with the ethane’s mole fraction. The fluid disturbance mainly influences the pressure drop and the turbulence intensity significantly when the fluid is transformed into a gas–liquid flow. This study could provide insights into boiling heat transfer improvement of binary mixtures for ORC power generation applications.

Modelling and optimization of ethane recovery process from natural gas via ZIF-8/water-glycol slurry with low energy consumption

Effective recovery of ethane from natural gas plays an increasingly important role as ethane is a good raw material for ethylene production. The conventional cryogenic separation process (CryoPro) is energy intensive. Absorption-adsorption coupling separation process (SorbPro) using ZIF-8 slurry may be a more energy-efficient technique as its operating conditions are milder (i.e., 273.15 K, ∼1 MPa). This paper aims to conduct the process modelling and optimization of SorbPro for CH4/C2H6 separation. The equilibrium stage method is used to model the mass transfer units (absorption-adsorption column, desorber, etc) and the key process operating parameters are optimized simultaneously by genetic algorithm. The results show that the ethane mole fraction can be enriched from 22 mol% in the feed gas to 90.04 mol%, the ethane recovery ratio reaches 90.34%, and the energy consumption per Nm3 ethane is 0.6792 kW h/Nm3, which is 25.6% lower than that of the CryoPro (0.9128 kW h/Nm3). It indicates that the SorbPro may be a more promising approach for recovering ethane from natural gas.

Toward an optimized design of the LNG production process: Measurement and modeling of the solubility limits of p-xylene in methane and methane + ethane mixtures at low temperature

Accurate knowledge of the solubility limits of impurities in LNG allows an optimized design of the purification units installed upstream of the liquefaction train and the prevention of solid formation in the main cryogenic heat exchanger that would reduce the performance of the heat exchanger, increase maintenance operations and cause potential safety problems. The solubility of p-xylene in methane and in methane + ethane (5 and 10% mole fraction of ethane) has been measured at p = 5 MPa from T = 183 down to T = 123 K. The experimental results have been obtained by a static-analytic method with analysis of the fluid phase samples by gas chromatography. Solubility of p-xylene in methane and methane + ethane mixtures has been measured for the first time in this temperature range. The obtained data have been modelled by the Soave-Redlich-Kwong (SRK) cubic Equations of State (EoS), tuning pure component parameters, alpha functions, and binary interaction parameters, considering thermodynamic constraints. A robust multi-phase flash algorithm was established for vapor-liquid-liquid-solid (VLLSE) equilibrium by applying phase stability analysis. The revamped thermodynamic methods and data allow accurate prediction of the multiple phase boundaries that can be present when cooling a typical natural gas mixture.

Temporary pause in the growth of atmospheric ethane and propane in 2015–2018

Abstract. Atmospheric non-methane hydrocarbons (NMHCs) play an important role in the formation of secondary organic aerosols and ozone. After a multidecadal global decline in atmospheric mole fractions of ethane and propane – the most abundant atmospheric NMHCs – previous work has shown a reversal of this trend with increasing atmospheric abundances from 2009 to 2015 in the Northern Hemisphere. These concentration increases were attributed to the unprecedented growth in oil and natural gas (O&amp;amp;NG) production in North America. Here, we supplement this trend analysis building on the long-term (2008–2010; 2012–2020) high-resolution (∼3 h) record of ambient air C2–C7 NMHCs from in situ measurements at the Greenland Environmental Observatory at Summit station (GEOSummit, 72.58 ∘ N, 38.48 ∘ W; 3210 m above sea level). We confirm previous findings that the ethane mole fraction significantly increased by +69.0 [+47.4, +73.2; 95 % confidence interval] ppt yr−1 from January 2010 to December 2014. Subsequent measurements, however, reveal a significant decrease by −58.4 [−64.1, −48.9] ppt yr−1 from January 2015 to December 2018. A similar reversal is found for propane. The upturn observed after 2019 suggests, however, that the pause in the growth of atmospheric ethane and propane might only have been temporary. Discrete samples collected at other northern hemispheric baseline sites under the umbrella of the NOAA cooperative global air sampling network show a similar decrease in 2015–2018 and suggest a hemispheric pattern. Here, we further discuss the potential contribution of biomass burning and O&amp;amp;NG emissions (the main sources of ethane and propane) and conclude that O&amp;amp;NG activities likely played a role in these recent changes. This study highlights the crucial need for better constrained emission inventories.

Experimental and kinetic study on the pyrolysis and oxidation of isopentane in a jet-stirred reactor

An experimental and kinetic study on the pyrolysis and oxidation of isopentane (2-methylbutane) were conducted in this work. The experiments were performed in a jet-stirred reactor (JSR) at the equivalence ratios of 0.5, 1.0, 2.0 and ∞, across the temperature range from 700 to 1100 K, and at atmospheric pressure. Mole fractions of oxygen, hydrogen, CO, CO2, C1C6 hydrocarbons and methanol were measured using a gas chromatograph (GC), at the initial fuel mole fraction of 0.5% and residence time at 2 s. Three literature kinetic models, named as the Bugler model, the NUIGMech1.1 model, and the LLNL model, were employed to predict the speciation profiles measured in this work, and the ignition delay times in the literature. Based on the model performances and kinetic analysis, some modifications were made to the LLNL model, by supplementing the beta-scission reaction aC5H11 = C4H8–1 +CH3, and updating the rate constants for the reactions iC5H12 + OH = cC5H11 + H2O, iC5H12 + OH = bC5H11 + H2O, C3H4-a = C3H4-p, C3H4-a + H = C3H4-p + H, and C2H6 + CH3 = C2H5 +CH4. After the modifications, the model predictions on mole fractions of 1-butene, ethane, allene and propyne in JSR pyrolysis and oxidation were improved, and the overestimations on the ignition delay times at low temperatures are significantly reduced. Reaction pathway and sensitivity analyses were carried out using the modified model. The results indicated that fuel consumption in pyrolysis is sensitive to the unimolecular decomposition reaction iC5H12 = iC3H7 + C2H5 across the temperature range of 900–1100 K. In addition, fuel low-temperature oxidation reactivity is sensitive to the mutual conversion between HO2 and H2O2, while the competition between OH and HO2 formation has a more pronounced effect at increased temperatures.

Phase Diagram for the Methane–Ethane System and Its Implications for Titan’s Lakes

Abstract On Titan, methane (CH4) and ethane (C2H6) are the dominant species found in the lakes and seas. In this study, we have combined laboratory work and modeling to refine the methane–ethane binary phase diagram at low temperatures and probe how the molecules interact at these conditions. We used visual inspection for the liquidus and Raman spectroscopy for the solidus. Through these methods, we determined a eutectic point of 71.15 ± 0.5 K at a composition of 0.644 ± 0.018 methane–0.356 ± 0.018 ethane mole fraction from the liquidus data. Using the solidus data, we found a eutectic isotherm temperature of 72.2 K with a standard deviation of 0.4 K. In addition to mapping the binary system, we looked at the solid–solid transitions of pure ethane and found that, when cooling, the transition of solid I–III occurred at 89.45 ± 0.2 K. The warming sequence showed transitions of solid III–II occurring at 89.85 ± 0.2 K and solid II–I at 89.65 ± 0.2 K. Ideal predictions were compared with molecular dynamics simulations to reveal that the methane–ethane system behaves almost ideally, and the largest deviations occur as the mixing ratio approaches the eutectic composition.

Experimental study of impurity freeze-out in ternary methane + ethane + benzene mixtures with applications to LNG production

The freeze-out of impurities in LNG production can pose significant operational risks and lead to costly blockage-induced plant shutdowns. Study of ternary and higher-order mixtures, which are more analogous to LNG, present the critical tests of thermodynamic models in terms of their utility and predictive accuracy. In this work, a visual CryoSolids apparatus was upgraded to allow analytical measurements of solvent composition in multi-component systems where a solid phase is present at equilibrium. The analytical system, which included a ROLSI sampling valve and capillary together with a gas chromatograph, was successfully commissioned and used to measure melting temperatures and solvent compositions of a ternary mixture containing methane, ethane, and benzene at temperatures down to 125 K and pressures up to 6 MPa. The effect on the solubility of benzene by adding ethane to the solvent was investigated by varying the ethane mole fraction from 0 to 0.96. The resulting temperature at which benzene melted into the liquid solvent decreased from 246 K at 4.7 MPa to 125 K at 5.7 MPa. The comparison of results with the ThermoFAST model showed that it could describe the new data with a deviation less than 1 K for ethane liquid phase mole fractions from 0 <xC2< 0.5, which increased to less than 4 K for 0.85 <xC2< 0.97. This result indicates that ThermoFAST satisfactorily represents SFE conditions in LNG mixtures of industrial relevance but needs improvement to cover wider ranges of composition.

Experimental Investigation of Surface Phenomena on Quasi Nonporous and Porous Materials Near Dew Points of Pure Fluids and Their Mixtures

Density and sorption measurements were carried out with ethane, carbon dioxide, and their binary mixture with an ethane mole fraction of 0.2003 using a modified gravimetric sorption analyzer. Three solid sinkers with a large surface-to-volume ratio and different (quasi nonporous) surface materials and zeolite 13X (as porous material) were investigated. In the vicinity of the dew point, the density measurements were distorted, thus implying an impact of surface phenomena. Three hypothetical regions were identified for distortion: (1) gas adsorption of a single layer or a few layers at pressures lower than 0.85 × ps, where ps is the dew-point pressure; (2) multilayer gas adsorption followed by the beginning of capillary condensation up to about 0.995 × ps; (3) domination of capillary condensation up to ps. With the goal to deliver a sound data basis for the development of an advanced description of fluid-mixture vapor–liquid–equilibrium through equations of state, we established an empirical method to correct the distorted density measurements. Sorption measurements with the well-investigated zeolite 13X were carried out to confirm the reliable performance of our instrument and to provide a background for the interpretation of the measurements with the solid sinkers. The results of these measurements support the hypothesis of the three regions of surface phenomena and reveal that a gold-plated solid surface reduces the extent of the observed effects.

Hydrogen and Ethylene Production through Water-Splitting and Ethane Dehydrogenation Using BaFe0.9Zr0.1O3- δ Mixed-Conductors

Hydrogen production from water-splitting has attracted significant interest because of its use in refining, chemicals’ production and as an alternative fuel. A promising technology for hydrogen production through water-splitting at moderate temperatures is the use of mixed ionic-electronic conducting (MIEC) membranes [1-2]. Using an inert gas on the oxygen-lean side, oxygen permeation rates are slow unless vacuum is used (or higher pressure on the feed side). Fuel addition in the oxygen-lean stream raises the oxygen chemical potential difference and hence the oxygen permeation and hydrogen production rate increase significantly [1-5]. One such fuel is ethane whose partial dehydrogenation leads to a valuable chemical, namely ethylene. Coupling water-splitting and ethane dehydrogenation using a MIEC membrane can reduce the complexity and capital cost of producing both (process intensification). This study investigated the co-production of hydrogen and ethylene using BaFe0.9Zr0.1O3- δ membranes. Experimental measurements performed in a button-cell reactor showed significant oxygen permeation, ethane conversion and selectivity to ethylene. The performance of a 1.1 mm thick membrane operating at inlet XH2O=50% at the steam side (balance is nitrogen) was investigated as a function of temperature and inlet ethane mole fraction at the oxygen-lean side (balance is helium). At T=900 °C and XC2H6=10%, the oxygen permeation flux (JO2) was ≈ 2.0 μmole/cm2/sec, while the ethane conversion and selectivity to ethylene were 95% and 83%, respectively. At these conditions, the combination of gas-phase and surface reactions lead to the production of other products, such as hydrogen, methane, acetylene, carbon monoxide and carbon dioxide. When using ethane, the oxygen permeation through BaFe0.9Zr0.1O3- δ increases due to electrochemical reactions of these products with oxygen ions on the membrane surface, while the electron transfer process takes place through a redox mechanism that involves iron and its different oxidation states [5]. Lowering the temperature to T=850 °C decreased the oxygen permeation flux to ≈ 1.0 μmole/cm2/sec and conversion of ethane to 79% while ethylene selectivity increased to 93%. Under long-term operation, BaFe0.9Zr0.1O3- δ shows good stability. To further increase the performance of the material, we investigated the limitations imposed by surface reactions and charged species diffusion in an effort to identify the rate-limiting step in the overall oxygen permeation process.

Hydrogen and Ethylene Production through Water-Splitting and Ethane Dehydrogenation Using BaFe0.9Zr0.1O3- δ Mixed-Conductors

In this work, we investigated the application of ion transport membranes (ITM) in the co-production of hydrogen (H2) and ethylene (C2H4) through water (H2O) splitting and ethane (C2H6) oxidative dehydrogenation, respectively, using BaFe0.9Zr0.1O3-δ (BFZ) mixed ionic-electronic conducting (MIEC) materials. Experimental measurements showed that a 1.1mm thick BFZ membrane exhibited an oxygen flux (JO2) of ≈ 2.0 µmole/cm2/sec when operating at T=900°C with inlet steam mole fraction at the feed side equal to XH2O=50% and inlet ethane mole fraction at the fuel side equal to XC2H6=10%. Under the same conditions, ethane conversion and selectivity to ethylene were 95% and 83%, respectively. Lowering the temperature to T=850°C decreased JO2 to ≈ 1.0 µmole/cm2/sec and conversion of ethane to 79%, but the selectivity to ethylene increased to 93%. The proposed technology shows significant performance advantages compared to traditional ethane cracking and hence is a promising method for chemical conversion processes.

An analytical solubility model for nitrogen–methane–ethane ternary mixtures

Saturn's moon Titan has surface liquids of liquid hydrocarbons and a thick, cold, nitrogen atmosphere, and is a target for future exploration. Critical to the design and operation of vehicles for this environment is knowledge of the amount of dissolved nitrogen gas within the cryogenic liquid methane and ethane seas. This paper rigorously reviews experimental data on the vapor-liquid equilibrium of nitrogen/methane/ethane mixtures, noting the possibility for split liquid phases, and presents simple analytical models for conveniently predicting solubility of nitrogen in pure liquid ethane, pure liquid methane, and a mixture of liquid ethane and methane. Model coefficients are fit to three temperature ranges near the critical point, intermediate range, and near the freezing point to permit accurate predictions across the full range of thermodynamic conditions. The models are validated against the consolidated database of 2356 experimental data points, with mean absolute error between data and model less than 8% for both binary nitrogen/methane and nitrogen/ethane systems, and less than 17% for the ternary nitrogen/methane/ethane system. The model can be used to predict the mole fractions of ethane, methane, and nitrogen as a function of location within the Titan seas.

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.

Reversal of global atmospheric ethane and propane trends largely due to US oil and natural gas production

Atmospheric non-methane hydrocarbon concentrations began declining in the 1970s. Surface and column measurements show that Northern Hemisphere ethane concentrations are now rising, probably due to North American oil and natural gas emissions. Non-methane hydrocarbons such as ethane are important precursors to tropospheric ozone and aerosols. Using data from a global surface network and atmospheric column observations we show that the steady decline in the ethane mole fraction that began in the 1970s1,2,3 halted between 2005 and 2010 in most of the Northern Hemisphere and has since reversed. We calculate a yearly increase in ethane emissions in the Northern Hemisphere of 0.42 (±0.19) Tg yr−1 between mid-2009 and mid-2014. The largest increases in ethane and the shorter-lived propane are seen over the central and eastern USA, with a spatial distribution that suggests North American oil and natural gas development as the primary source of increasing emissions. By including other co-emitted oil and natural gas non-methane hydrocarbons, we estimate a Northern Hemisphere total non-methane hydrocarbon yearly emission increase of 1.2 (±0.8) Tg yr−1. Atmospheric chemical transport modelling suggests that these emissions could augment summertime mean surface ozone by several nanomoles per mole near oil and natural gas production regions. Methane/ethane oil and natural gas emission ratios could suggest a significant increase in associated methane emissions; however, this increase is inconsistent with observed leak rates in production regions and changes in methane’s global isotopic ratio.

Contribution of oil and natural gas production to renewed increase in atmospheric methane (2007–2014): top–down estimate from ethane and methane column observations

Abstract. Harmonized time series of column-averaged mole fractions of atmospheric methane and ethane over the period 1999–2014 are derived from solar Fourier transform infrared (FTIR) measurements at the Zugspitze summit (47° N, 11° E; 2964 m a.s.l.) and at Lauder (45° S, 170° E; 370 m a.s.l.). Long-term trend analysis reveals a consistent renewed methane increase since 2007 of 6.2 [5.6, 6.9] ppb yr−1 (parts-per-billion per year) at the Zugspitze and 6.0 [5.3, 6.7] ppb yr−1 at Lauder (95 % confidence intervals). Several recent studies provide pieces of evidence that the renewed methane increase is most likely driven by two main factors: (i) increased methane emissions from tropical wetlands, followed by (ii) increased thermogenic methane emissions due to growing oil and natural gas production. Here, we quantify the magnitude of the second class of sources, using long-term measurements of atmospheric ethane as a tracer for thermogenic methane emissions. In 2007, after years of weak decline, the Zugspitze ethane time series shows the sudden onset of a significant positive trend (2.3 [1.8, 2.8] × 10−2 ppb yr−1 for 2007–2014), while a negative trend persists at Lauder after 2007 (−0.4 [−0.6, −0.1] × 10−2 ppb yr−1). Zugspitze methane and ethane time series are significantly correlated for the period 2007–2014 and can be assigned to thermogenic methane emissions with an ethane-to-methane ratio (EMR) of 12–19 %. We present optimized emission scenarios for 2007–2014 derived from an atmospheric two-box model. From our trend observations we infer a total ethane emission increase over the period 2007–2014 from oil and natural gas sources of 1–11 Tg yr−1 along with an overall methane emission increase of 24–45 Tg yr−1. Based on these results, the oil and natural gas emission contribution (C) to the renewed methane increase is deduced using three different emission scenarios with dedicated EMR ranges. Reference scenario 1 assumes an oil and gas emission combination with EMR = 7.0–16.2 %, which results in a minimum contribution C &gt; 39 % (given as lower bound of 95 % confidence interval). Beside this most plausible scenario 1, we consider two less realistic limiting cases of pure oil-related emissions (scenario 2 with EMR = 16.2–31.4 %) and pure natural gas sources (scenario 3 with EMR = 4.4–7.0 %), which result in C &gt; 18 % and C &gt; 73 %, respectively. Our results suggest that long-term observations of column-averaged ethane provide a valuable constraint on the source attribution of methane emission changes and provide basic knowledge for developing effective climate change mitigation strategies.

Effects of reactor pressure and inlet temperature on n‐butane/dimethyl ether oxidation and the formation pathways of the aromatic species

Oxidation of n‐butane/dimethyl ether (DME)/O2/Ar system was studied by chemical kinetic modeling in a tubular reactor operated adiabatically and at constant pressure. Effects of the reactor pressure on the formation of various major, minor, and trace oxidation products were investigated for two different pressures (1 and 5 atm) and at six different inlet temperature values (700, 800, 900, 1100, 1300, and 1500 K). The analysis was carried out for two different concentrations of dimethyl ether in the inlet fuel mixture (20 and 50 mol %). Higher pressure (5 atm) resulted in higher mole fractions of methane, vinylacetylene, and cyclopentadiene; and lower mole fractions of formaldehyde, acetylene, acetaldehyde, ethane, propargyl, and propane. The mole fractions of CO and CO2 were not affected considerably by the pressure change. The main formation routes of benzene were developed at two different inlet temperature values (1100 and 1300 K), and the main precursors participating in these routes were found to be propargyl, propene, and diacetylene. A skeletal mechanism was developed for the oxidation of n‐butane/DME mixture from the detailed mechanism by reduction of the elementary reactions by 79%, and it was tested for accuracy by comparison with the data from the literature. © 2015 American Institute of Chemical Engineers Environ Prog, 35: 230–240, 2016

The fate of ethane in Titan’s hydrocarbon lakes and seas

Ethane is expected to be the dominant photochemical product on Titan’s surface and, in the absence of a process that sequesters it from exposed surface reservoirs, a major constituent of its lakes and seas. Absorption of Cassini’s 2.2cm radar by Ligeia Mare however suggests that this north polar sea is dominated by methane. In order to explain this apparent ethane deficiency, we explore the possibility that Ligeia Mare is the visible part of an alkanofer that interacted with an underlying clathrate layer and investigate the influence of this interaction on an assumed initial ethane–methane mixture in the liquid phase. We find that progressive liquid entrapment in clathrate allows the surface liquid reservoir to become methane-dominated for any initial ethane mole fraction below 0.75. If interactions between alkanofers and clathrates are common on Titan, this should lead to the emergence of many methane-dominated seas or lakes.

Detailed simulation of dual-reflux pressure swing adsorption process

A model for the detailed simulation of dual-reflux pressure swing adsorption process developed in the frame of the commercial software Aspen Adsim® is presented. For validation purposes, simulations were performed and model predictions were compared with published experimental results. At cyclic steady-state, model predictions were found to be in good agreement with reported experimental results in terms of (i) average ethane mole fraction in heavy product, (ii) average nitrogen mole fraction in light product, (iii) instantaneous heavy product composition profiles, and (iv) instantaneous column composition profiles. The predicted and experimental trends obtained by analyzing the effect of various operating parameters (light reflux flowrate, duration of feed/purge step, heavy product flowrate and mole fraction of heavy component in binary feed gas mixture) on process performance are also comparable. Overall, this simulation technique of dual-reflux pressure swing adsorption can serve as an effective tool for process design, cost reduction of laboratory and/or plant trails, and enhanced process understanding.

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.

Clathrate-hydrate formation from a hydrocarbon gas mixture: Compositional evolution of formed hydrate during an isobaric semi-batch hydrate-forming operation

The clathrate hydrate formation from a model natural gas, i.e., a mixture of methane, ethane, and propane in a 90:7:3molar ratio, under a constant pressure was experimentally investigated, focusing on the compositional evolution of hydrate crystals formed inside a gas-bubbling-type reactor during each semi-batch hydrate-forming operation. The experimental system used in this study was specially designed for obtaining several hydrate samples formed at different, arbitrarily selected stages during each hydrate-forming operation. Each hydrate sample was analyzed by a gas-chromatograph to determine the mole fractions of methane, ethane and propane encaged in the hydrate. These analyses revealed a monotonic increase in the methane fraction and decreases in the ethane and propane fractions during each operation until a quasi-steady state was established. Powder X-ray diffraction analyses showed that both structure-I and structure-II crystals were simultaneously formed during the quasi-steady period. The compositional evolution of the hydrates formed during the early stages before the quasi-steady state was reached deviated from corresponding predictions based on the thermodynamic-simulation scheme previously reported. A hypothetical explanation for the discrepancy between the experimental and simulation-based results was provided.