CO2 CH4 Gas Mixture Research Articles

Determination of hydrate phase equilibrium (H-L-V) data for the binary CO2–CH4 gas mixture in the presence of 1,3 dioxolane

Present work details the determination of three phase hydrate equilibrium data (H-L-V) using temperature search method for the binary CO2/CH4 gas mixture (50:50 molar ratio) in presence of 1,3 dioxolane (DIOX). DIOX concentration used for phase equilibrium determination were 1,3 and 5.56 mol% respectively. In the presence of DIOX, it was observed that phase equilibrium curve was shifted right with respect to the curve using same gas mixture with no additive (pure water). This indicates that the presence of DIOX moderates the hydrate formation equilibrium conditions. Also, as DIOX concentration increases from 1 mol% to 5.56 mol%, a decrement in phase equilibrium pressure at same temperatures was observed, confirming the potential of DIOX as an effective thermodynamic promoter. Enthalpy of hydrate dissociation was calculated for CO2/CH4 gas mixture in presence of DIOX using Clausius- Clapeyron plot and it was found to be 90.81±6.55 KJ/mol which confirms the sII structure of CO2-CH4-DIOX mixed hydrate. Besides providing the phase equilibrium data of formed hydrates with CO2/CH4 gas mixture using different concentration of DIOX, the present study will aid in determining suitable experimental conditions for examining kinetics and performing separation studies of CO2/CH4 gas mixture through hydrate formation.

Inducing hierarchical pores in nano-MOFs for efficient gas separation.

The synthesis of metal-organic frameworks (MOFs) and their processing into structures with tailored hierarchical porosity is essential for using MOFs in the adsorption-driven gas separation process. We report the synthesis of modified Cu-MOF nanocrystals for CO2 separation from CH4 and N2, prepared from DABCO (1,4-diazabicyclo[2.2.2] octane) and 9,10 anthracene dicarboxylic acid linkers with copper metal salt. The synthesis parameters were optimized to introduce mesoporosity in the microporous Cu-MOF crystals. The volumetric CO2 adsorption capacity of the new hierarchical Cu-MOF was 2.58 mmol g-1 at 293 K and 100 kPa with a low isosteric heat of adsorption of 28 kJ mol-1. The hierarchical Cu-MOF nanocrystals were structured into mechanically stable pellets with a diametral compression strength exceeding 1.2 MPa using polyvinyl alcohol (PVA) as a binder. The CO2 breakthrough curves were measured from a binary CO2-CH4 (45/55 vol%) gas mixture at 293 K and 400 kPa pressure on Cu-MOF pellets to demonstrate the role of hierarchical porosity in mass transfer kinetics during adsorption. The structured hierarchical Cu-MOF pellets showed stable cyclic CO2 adsorption capacity during 5 adsorption-desorption cycles with a CO2 uptake capacity of 3.1 mmol g-1 at 400 kPa and showed a high mass transfer coefficient of 1.8 m s-1 as compared to the benchmark zeolite NaX commercialized binderless granules, suggesting that the introduction of hierarchical porosity in Cu-MOF pellets can effectively reduce the time for CO2 separation cycles.

Study on CO2 based thermal plasma torch and its effective utilization for material processing in atmospheric pressure

Reuse of greenhouse gases is one of the promising approaches towards controlling global warming to some extent. As a part of that, an attempt has been made to utilize CO2 gas as one of the primary gases to form a thermal plasma jet for material processing. For that purpose, a unique direct current (DC) non-transferred arc thermal plasma torch was designed and its current-voltage characteristics and electro-thermal efficiency with different discharge currents and gas compositions were studied. The torch is made of rod type cathode and a nozzle type anode, which can produce a stable thermal plasma jet under different gas compositions. CH4 was used as a secondary mixing gas in an Ar-CO2 gas composition to produce a carbon-rich thermal plasma with high electro-thermal efficiency. The maximum electro-thermal efficiency of 73 % were reached while the torch operated at 100 A current with 6 slpm of CH4 flow along with 15 and 20 slpm of Ar and CO2 gas flow, respectively. Torch efficiency decreased to 12 % with increase in discharge current from 100 A to 200 A. Optical emission spectrum of the plasma jet was recorded at the exit of the torch nozzle to understand the emission characteristics of the plasma and estimate temperature and electron density. Temperature of the plasma increased from 13,400 to 17,800 K with respect to the discharge current. Thermodynamical studies were carried out for the given experimental conditions to understand the thermal decomposition of CO2-CH4 gas mixture and select the suitable condition for the material processing. Under the selective conditions, plasma torch was utilized for the spheroidization of tungsten metal powder and carburization of the AISI 316 L stainless-steel coupons in atmospheric pressure without using any shielding gases. Results showed that around 85 % of the metal powders were spheroidized perfectly at 15 kW input power. Plasma carburization results showed that the microhardness of the steel surface reached 605 HV with a short processing time of 3 min which was 4 times higher than the untreated steel surface. This work provides useful insight for the utilization of CO2 as primary plasma forming gas to generate thermal plasma for material processing.

Quantitative Raman Spectroscopic Determination of the Composition, Pressure, and Density of CO2-CH4 Gas Mixtures

The Raman spectra for pure CO2 and CH4 gases and their ten gas mixtures were collected at pressures and temperatures ranging from 2 MPa to 40 MPa and room temperature (∼24°C) to 300°C, respectively. A systematic analysis was carried out to establish a methodology for the quantitative determination of the composition, pressure, and density of CO2-CH4 mixtures. The shift in the peak position of the υ1 band for CH4 was sufficiently large to enable the accurate determination of the pressure of pure CH4 and CH4-dominated fluids (>50 mol% CH4). An equation representing the observed relationship of the peak position of the υ1 band of CH4, density, and composition was developed to calculate the density of CO2-CH4 mixtures. The Raman quantification factor F (CH4)/F (CO2) was demonstrated to be near a constant value of 5.048 ± 0.4 and was used to determine the CH4 to CO2 molar ratio in an unknown CO2-CH4‐bearing fluid with high internal pressure (>10 MPa) based on the Raman peak area ratio. The effect of temperature on the variation in Raman spectral parameters was also investigated at temperatures up to 300°C. The results showed that the effect of temperature must be considered when Raman spectral parameters are used to calculate the pressure, density, and composition of CO2-CH4 gas mixtures. Raman spectroscopic analysis results obtained for six samples prepared in fused silica capillary capsules were validated by comparison with the results obtained from microthermometry measurements.

Experimental Study of Desorption and Seepage Characteristics of Single Gas and CO2–CH4 Gas Mixture in Coal

Experimental Study of Desorption and Seepage Characteristics of Single Gas and CO2–CH4 Gas Mixture in Coal

High-efficiency separation of CO2 from CO2-CH4 gas mixtures via gas hydrates under static conditions

Hydrate technology with high gas storage capacity and excellent safety features has attracted much attention for capturing CO2 from biogas to produce purified CH4. When considering operational efficiency, it is desirable to overcome technical barriers such as slow hydrate generation and low separation efficiency. Therefore, based on the properties of surfactant-enhanced hydrate generation kinetics, this work first systematically evaluated the performance of 500 ppm SDS on the separation efficiency of 40 mol% CO2 and 60 mol% CH4 simulated biogas. The experimental results show a significant increase in gas capture at higher driving forces, with the rise being dominated by the CH4 component, indicating that larger driving forces reduce hydrate selectivity to CO2-CH4 and weaken gas separation efficiency, with a maximum CO2 recovery of 84.24 ± 1.19% at 275.15 K and 8 MPa. Interestingly, hydrate growth mainly occurred in the liquid phase, leading to the separation factor being positively correlated with the induction time with sufficient CO2 dissolution. In comparison, the gas capture per unit volume of solution could be improved by more than a factor of 2 at higher gas–liquid ratios. The best separation factor of 7.84 ± 0.73 was achieved, and separation factors in general gradually decreased with increasing gas–liquid ratio; however, there was high-pressure failure behavior. Furthermore, the impact of the defoamer on separation efficiency was deeply investigated for SDS decomposition foaming, with results showing that the defoamer would alleviate hydrate decomposition foaming behaviour while having no significant effect on hydrate generation kinetics and separation efficiency.

Kinetic and Morphology Study of Equimolar CO2–CH4 Hydrate Formation in the Presence of Cyclooctane and l-Tryptophan

This study investigates the kinetics and morphology of an equimolar CO2–CH4 gas mixture by inducing sI and sH hydrates in gas–water and gas–liquid hydrocarbon (LHC)–water systems using pure water a...

Effect of Cyclooctane and l-Tryptophan on Hydrate Formation from an Equimolar CO2–CH4 Gas Mixture Employing a Horizontal-Tray Packed Bed Reactor

A fundamental study on hydrate formation from an equimolar CO2–CH4 gas mixture has been carried out with two focal points: accelerating the kinetics of hydrate formation and enhancing the gas separ...

Effect of Bed Porosity on CO2 and CH4 Adsorption inside Packed Bed Column for CO2-CH4 Gas Mixture

Effect of Bed Porosity on CO2 and CH4 Adsorption inside Packed Bed Column for CO2-CH4 Gas Mixture

Effect of CH4 on the CO2 breakthrough pressure and permeability of partially saturated low-permeability sandstone in the Ordos Basin, China

The behavior of CO2 that coexists with CH4 and the effect of CH4 on the CO2 stream need to be deeply analyzed and studied, especially in the presence of water. Our previous studies investigated the breakthrough pressure and permeability of pure CO2 in five partially saturated low-permeability sandstone core samples from the Ordos Basin, and we concluded that rocks with a small pore size and low permeability show considerable sealing capacity even under unsaturated conditions. In this paper, we selected three of these samples for CO2-CH4 gas-mixture breakthrough experiments under various degrees of water saturation. The breakthrough experiments were performed by increasing the gas pressure step by step until breakthrough occurred. Then, the effluent gas mixture was collected for chromatographic partitioning analysis. The results indicate that CH4 significantly affects the breakthrough pressure and permeability of CO2. The presence of CH4 in the gas mixture increases the interfacial tension and, thus, the breakthrough pressure. Therefore, the injected gas mixture that contains the highest (lowest) mole fraction of CH4 results in the largest (smallest) breakthrough pressure. The permeability of the gas mixture is greater than that for pure CO2 because of CH4, and the effective permeability decreases with increased breakthrough pressure. Chromatographic partitioning of the effluent mixture gases indicates that CH4 breaks through ahead of CO2 as a result of its weaker solubility in water. Correlations are established between (1) the breakthrough pressure and water saturation, (2) the effective permeability and water saturation, (3) the breakthrough pressure and effective permeability, and (4) the mole fraction of CO2/CH4 in the effluent mixture gases and water saturation. These results deepen our understanding of the multi-phase flow behavior in the porous media under unsaturated conditions, which have implications for formulating emergency response plans for gas leakage into unsaturated zones. Finally, knowing the flow characteristic of gas mixture can guide CO2 storage, CO2-EOR and CO2-ECBM projects. Future studies should pay attention to the effects of saline water with different salt types and concentrations on the multi-phase flow behavior with applications to geological CO2 storage and energy storage using CH4.

Removal of high concentration CO2 from natural gas using high pressure membrane contactors

The feasibility of removing high concentration CO2 from natural gas using membrane contactors at elevated pressures was preliminarily investigated in this study. CO2-CH4 gas mixture and activated methyldiethanolamine (aMDEA) solution were used as simulated natural gas and absorbent, respectively. The stability of poly(vinylidene fluoride) (PVDF) hollow fiber membranes in aMDEA solution at room temperature was first investigated through Fourier transform infrared spectroscopy (FTIR) and contact angle (CA) analyses. The effect of operation pressure, membrane area and feed gas flow rate on CO2 removal performance as well as CH4 loss was studied. The results indicated that the CO2 removal efficiency was significantly improved with increasing operation pressure. For 70% CO2 in feed, the removal efficiency of CO2 increased from 33.3% at 1bar to 91.3% at 60bar under the experimental conditions. Meanwhile, the overall mass transfer coefficient (KOG) gradually decreased due to the decrease of CO2 diffusion coefficient. The CO2 outlet concentration, CO2 flux and CH4 loss were also affected by membrane area and feed gas flow rate. This study provides a reference for the understanding of removal of high concentration CO2 from natural gas using membrane contactors at elevated pressures.

A microporous MOF with a polar pore surface exhibiting excellent selective adsorption of CO2 from CO2-N2 and CO2-CH4 gas mixtures with high CO2 loading.

A microporous MOF {[Zn(SDB)(L)0.5]·S}n (IITKGP-5) with a polar pore surface has been constructed by the combination of a V-shaped -SO2 functionalized organic linker (H2SDB = 4,4'-sulfonyldibenzoic acid) with an N-rich spacer (L = 2,5-bis(3-pyridyl)-3,4-diaza-2,4-hexadiene), forming a network with sql(2,6L1) topology. IITKGP-5 is characterized by TGA, PXRD and single crystal X-ray diffraction. The framework exhibits lozenge-shaped channels of an approximate size of 4.2 × 5.6 Å2 along the crystallographic b axis with a potential solvent accessible volume of 26%. The activated IITKGP-5a revealed a CO2 uptake capacity of 56.4 and 49 cm3 g-1 at 273 K/1 atm and 295 K/1 atm, respectively. On the contrary, it takes up a much smaller amount of CH4 (17 cm3 g-1 at 273 K and 13.6 cm3 g-1 at 295 K) and N2 (5.5 cm3 g-1 at 273 K; 4 cm3 g-1 at 295 K) under 1 atm pressure exhibiting its potential for a highly selective adsorption of CO2 from flue gas as well as a landfill gas mixture. Based on the ideal adsorbed solution theory (IAST), a CO2/N2 selectivity of 435.5 and a CO2/CH4 selectivity of 151.6 have been realized at 273 K/100 kPa. The values at 295 K are 147.8 for CO2/N2 and 23.8 for CO2/CH4 gas mixtures under 100 kPa. In addition, this MOF nearly approaches the target values proposed for PSA and TSA processes for practical utility exhibiting its prospect for flue gas separation with a CO2 loading capacity of 2.04 mmol g-1.

An anionic metal–organic framework constructed from a triazole-functionalized diisophthalate featuring hierarchical cages for selective adsorptive C2H2/CH4 and CO2/CH4 separation

Exploring organic linkers is very important to target porous metal–organic frameworks with desired structures and properties. In this work, we devised a triazole-functionalized bent diisophthalate ligand, 5,5′-(triazole-2,5-diyl) diisophthalate (H4L), which was used to successfully construct an anionic copper-based MOF ([Cu6(L)3(H2O)4(HCOO)]·Me2NH2+·20DMF) under solvothermal reaction conditions. Single-crystal X-ray diffraction analyses reveal that the title MOF compound features three types of polyhedral cages with different shapes and sizes. More importantly, the title MOF compound after desolvation exhibits promising potential for industrially important C2H2/CH4 and CO2/CH4 separations. At 298 K and 1 atm, the C2H2 and CO2 uptakes reach 107.6 and 65.6 cm3 (STP) g−1, respectively. The adsorption selectivities are predicted to be 33.4–120.3 for an equimolar C2H2–CH4 gas mixture and 6.4–7.6 for an equimolar CO2–CH4 gas mixture at 298 K and pressures varying from 1 to 109 kPa. The highly selective adsorption of C2H2 and CO2 over CH4 might be attributed to the synergistic interplay between suitable pore sizes, functional active sites, such as open metal sites and Lewis basic nitrogen atoms in the pore surface, and the ionic nature of the framework.

Pebax–polydopamine microsphere mixed‐matrix membranes for efficient CO2 separation

ABSTRACTNovel facilitated‐transport mixed‐matrix membrane (MMM) were prepared through the incorporation of polydopamine (PDA) microspheres into a poly(amide‐b‐ethylene oxide) (Pebax MH 1657) matrix to separate CO2–CH4 gas mixtures. The Pebax–PDA microsphere MMMs were characterized by Fourier transform infrared spectroscopy, scanning electron microcopy, X‐ray diffraction, differential scanning calorimetry, and thermogravimetric analysis. The PDA microspheres acted as an adhesive filler and generated strong interfacial interactions with the polymer matrix; this generated a polymer chain rigidification region near the polymer–filler interface. Polymer chain rigidification usually results in a larger resistance to the transport of gas with a larger molecular diameter and a higher CO2–CH4 selectivity. In addition, the surface of PDA microspheres contained larger numbers of amine, imine, and catechol groups; these were beneficial to the improvement of the CO2 separation performance. Compared with the pristine Pebax membrane, the MMM with a 5 wt % PDA microsphere loading displayed a higher gas permeability and selectivity; their CO2 permeability and CO2–CH4 selectivity were increased by 61 and 60%, respectively, and surpassed the 2008 Robeson upper bound line. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44564.

Detailed study on self- and multicomponent diffusion of CO2-CH4 gas mixture in coal by molecular simulation

Gas diffusion plays a key role in CO2-enhanced recovery of coal bed methane (ECBM), where more than one types of gases coexist and multicomponent gas diffusion occurs. Such process is now usually described by non-coupled two-component gas diffusion equations which exclude the interactions between gases. Self-diffusion and mutual diffusion of CO2–CH4 mixture are investigated through molecular simulation for the first time. The self-diffusion coefficients of CO2andCH4 decrease with gas concentration but increase with temperature. The mutual diffusion coefficients of binary gas mixture of CO2–CH4incoal are computed through Maxwell–Stefan diffusion theory. A 2D diffusivity matrix |D| (with diagonal element Di and non-diagonal element Dij) is obtained to depict the mutual diffusion of the gas mixture. It is found that CO2 (CH4) diffusion is coupled with CH4 (CO2). The diffusion coupling strength of CO2andCH4 decreases with increasing gas concentration. Temperature positively affects Dij but minimally influences Di, resulting in large ratios of Dij/Di at high temperatures. It means that CO2–CH4 diffusion correlation interactions, which are not present in non-coupled pure gas diffusion equations, are necessary to analyze gas mixture diffusion in coal. In this case, non-coupled pure gas diffusion equations are inadequate for description of CO2–CH4 mixture diffusion. The coupling between the gases can be ignored only at very high temperatures (T>400K), which means a large depth of coal bed in ECBM engineering.

Formation conditions of leucogranite dykes and aplite-pegmatite dykes in the eastern Mt. Capanne plutonic complex (Elba, Italy): fluid inclusion studies in quartz, tourmaline, andalusite and plagioclase

Leucogranite and aplite-pegmatite dykes are associated with the Mt. Capanne pluton (Elba) and partly occur in the thermally metamorphosed host rock (serpentinites). Crystallization conditions of these dykes in the late magmatic-hydrothermal stage are estimated from fluid inclusion studies and mineralogical characterisation, obtained from detailed microthermometry, Raman spectroscopy, and electron microprobe analyses. Fluid inclusion assemblages are analysed in andalusite, quartz, and plagioclase from the leucogranite dykes, and in tourmaline and quartz from the aplite-pegmatite dykes. The fluid inclusion assemblages record multiple pulses of low salinity H2O-rich magmatic and reduced metamorphic fluid stages. Magmatic fluids are characterized by the presence of minor amounts of CO2 and H3BO3, whereas the metamorphic fluids contain CH4 and H2. The highly reduced conditions are also inferred from the presence of native arsenic in some fluid inclusions. Several fluid inclusion assemblages reveal fluid compositions that must have resulted from mixing of both fluid sources. In leucogranite dykes, magmatic andalusite contains a low-density magmatic CO2-rich gas mixture with minor amounts of CH4 and H2. Accidentally trapped crystals (mica) and step-daughters (quartz and diaspore) are detected in some inclusions in andalusite. The first generation of inclusions in quartz that crystallized after andalusite contains a highly reduced H2O-H2 mixture and micas. The second type of inclusions in quartz from the leucogranite is similar to the primary inclusion assemblage in tourmaline from the aplite-pegmatite, and contains up to 4.2 mass% H3BO3, present as a sassolite daughter crystal or dissolved ions, in addition to a CO2-CH4 gas mixture, with traces of H2, N2, H2S, and C2H6. H2O is the main component of all these fluids (x = 0.91 to 0.96) with maximally 7 mass% NaCl. Some accidentally trapped arsenolite and native arsenic are also detected. These fluids were trapped in the leucogranite at about 670–720 °C and 270–310 MPa, which is determined by combining isochore reconstruction, limits of the stability field of magmatic andalusite, and the water-saturated granite solidus. Trapping conditions of the aplite-pegmatites are at similar temperatures and slightly lower pressures, at 230–270 MPa. The third type of fluid inclusion assemblages in quartz in the leucogranite represents a continuously trapping event down to 200 °C and 50 MPa, whereas the aplite pegmatite records a distinct trapping event of inclusions in quartz at about 250–300 °C and 50–100 MPa.

The Induction Time of Hydrate Formation From a Carbon Dioxide-Methane Gas Mixture

Kinetics of hydrate formation from CO2‒CH4 gas mixture has been investigated. Eight experiments in various pressures, gas compositions, and load factors (volume of injected water/volume of reactor) were performed in a 460 CC vessel. For each gas mixture, the induction time of hydrate formation has been measured and the pressure-temperature-time diagram has been plotted. The results of the experiments show that by increasing the composition of carbon dioxide in the gas, the induction time of hydrate formation decreased and by increasing the load factor, the hydrate formation rate increased.

MRI measurements of CO2–CH4 hydrate formation and dissociation in porous media

The sequestration of CO2 in natural gas hydrate reservoirs is an attractive idea for both yielding CH4 and reducing CO2 emissions. To investigate the kinetics of CO2–CH4 gas mixture hydrate formation and dissociation, two types of CO2–CH4 gas mixtures were applied to form hydrates in porous media with different porosities. The process of hydrate formation and dissociation was monitored in situ by magnetic resonance imaging (MRI) in this study. Hydrate saturation was calculated quantitatively using the mean intensity (MI) of each image. The results showed that the hydrates first formed in the centre of the porous media and then grew along the axis of the vessel. The hydrate saturation and the initial water saturation were linearly correlated when the initial water saturation changed from 5% to 40%. By comparing the formation process of two different CO2–CH4 gas mixtures, the formation rate of the 79.8% CO2/20.2% CH4 gas mixture hydrate was faster. The MRI data gave excellent information on the spatial distribution of water in the porous media during hydrate growth and dissociation.

Combination of surfactants and organic compounds for boosting CO2 separation from natural gas by clathrate hydrate formation

This study investigates the effects of several combinations of surfactants and organic compounds on the separation of CO2 from a CO2–CH4 gas mixture by clathrate hydrate formation. Seven additives, three surfactants (SDS, SDBS, DATCl) and four organic compounds (THF, 1,3-dioxolane, 2-methyl-tetrahydrofuran and cyclopentane) were tested for various operating conditions and at different concentrations. The influence of these additives on the quantity of gas removed, the selectivity of the separation toward CO2, and the kinetics of hydrate formation were analyzed through experiments in a batch reactor. It was found that a suitable combination of a surfactant and a organic compound can, in some cases, strongly enhance the hydrate crystallization. The best results were obtained with a combination of the additives SDS and THF.

In situ injection of THF to trigger gas hydrate crystallization: Application to the evaluation of a kinetic hydrate promoter

This paper investigates an original method to efficiently trigger gas hydrate crystallization. This method consists of an in situ injection of a small amount of THF into an aqueous phase in contact with a gas-hydrate-former phase at pressure and temperature conditions inside the hydrate metastable zone. In the presence of a CO2–CH4 gas mixture, our results show that the THF injection induces immediate crystallization of a first hydrate containing THF. This triggers the formation of the CO2–CH4 binary hydrate as proven by the pressure and temperature reached at equilibrium. This experimental method, which “cancels out” the stochasticity of the hydrate crystallization, was used to evaluate the effect of the anionic surfactant SDS at different concentrations, on the formation kinetics of the CO2–CH4 hydrate. The results are discussed and compared with those published in a recent article (Ricaurte et al., 2013), where THF was not injected but present in the aqueous phase from the beginning and at much higher concentrations.