Methane Permeability Research Articles

Experimental Study of Different Gases on Permeability of Tectonic Coal

Abstract In order to investigate the change law of different gas permeability of tectonic coal under circumstances of different gas pressure and different stress condition, take the tectonic coal with low permeability and outburst hazard as research object and study on the different gas permeability change law of tectonic coal in complete stress-strain process by using the triaxial servo-controlled seepage equipment for thermo-fluid-solid coupling of coal containing gas. The experimental results show that the complete stress-strain curve of coal containing methane is similar to that of coal containing carbon dioxide, which can be divided into five stages with unique characteristics respectively, and there are the minimum value of permeability corresponding to the neighboring juncture between stage II and phase III in complete stress-strain process. In addition, there are existing Klinkenberg effects not only for absorbing gas, such as methane and carbon dioxide but also for non-absorbing gas such as helium gas in the gas-bearing coal seam. Moreover, the Klinkenberg effect on the methane permeability of coal exists in all the stress condition of coal in complete stress-strain process and that on carbon dioxide permeability of coal only appears in the coal compaction named by phase I. Therefore, occurrence of Klinkenberg effect have something to do with structure of coal mass, but also are related to gas type and stress condition of coal mass.

Simulation of methane permeability in carbon slit pores

Using a one-site spherical CH 4 molecular model, we predict permeabilities in carbon slit pores of width 0.65–0.75 nm, based on adsorption isotherms obtained from grand canonical Monte Carlo (GCMC) simulation and diffusivities from equilibrium molecular dynamics (EMD). In the range of temperature of 298–318 K and pressure of 0.01–80 bar, the permeability within the slit pore is more strongly influenced by adsorption isotherms than by diffusion. It is found that the permeabilities predicted by the slit pore model far exceed those experimentally measured in practical membrane systems, consistent with our recent observations based on simulations of carbon dioxide permeability in slit pores. These results suggest that the pore entrance resistance (or pore mouth barrier), not considered in simulations of transport in semi-infinite slit pores, may be a dominating factor in nano-porous membrane transport.

Montney Fracturing-Fluid Considerations

Summary The Montney gas reservoir has become a critically important component of current western Canadian gas supply and offers exciting future potential. However, this reservoir often presents variable and unique stimulation challenges. Unlike reservoirs that display little water sensitivity, such as the U.S. Barnett Shale and possibly the Muskwa in the Northeastern British Columbia Horn River Basin, recovery of water-based fluids in the Montney can be a key consideration in achieving economic production rates. The use of water-based fracturing fluids in low-permeability reservoirs can result in loss of effective frac half-length caused by phase trapping associated with the retention of the introduced water-based fluid to the formation. This problem is increased by the water-wet nature of most tight-gas reservoirs (where no initial liquid-hydrocarbon saturation is or ever has been present) because of the strong spreading coefficient of water in such a situation. The retention of increased water saturation (Sw) in the pore system after the injection of water-based completion fluids can restrict the flow of produced gaseous hydrocarbons, such as methane. Capillary pressures of 10 MPa-20 MPa, or much higher, can be present in low-permeability formations at low-water saturation levels. Inability to generate sufficient capillary-drawdown force using the natural reservoir-drawdown pressure can result in extended fluid-recovery times or permanent loss of effective fracture half-length. Furthermore, use of water in subnormally saturated reservoirs, where much of the connate water has been removed by long-term evaporation effects associated with gas migration, might also reduce permeability and associated gas flow through a permanent increase in Sw of the reservoir. Secondary costs, such as rig time for swabbing, can add to the negative economic impact. The Montney is found to be a dry-gas reservoir in some areas, transitioning to an oil reservoir in other areas. Because of this, it would not be surprising to encounter retrograde condensate production through transition areas. In such a case, if sufficient drawdown pressure is applied to reduce reservoir pressure below the dewpoint, liquid hydrocarbons might condense from the produced gas phase, resulting in two-phase flow and potential trapping of the hydrocarbon liquid phase. Also, some areas of the upper Montney exhibit reservoir pressures in the 30 MPa range, whereas other areas exhibit lower pressures in the 17 MPa-21MPa range. The same drawdown on a lower-pressured reservoir could therefore result in condensate condensing from the gas phase, where it would not have in the higher-pressured reservoir. If a third aqueous fracturing fluid is introduced, three-phase flow might occur. The resulting reduced relative permeability to gas might drastically reduce production rates. Also, emulsion-formation potential exists, which could present an additional reduction in fluid flow and recovery. Choice of fracturing fluid must be carefully determined for each area of the Montney, balancing economics with production. It is important to always keep in mind that key reservoir properties can vary dramatically in the Montney, as a function of both geographic location and depth. This paper presents laboratory test results of regained methane permeability vs. drawdown pressure and contact time with Montney core under representative reservoir conditions. Water, foamed water and hydrocarbon-based fracturing fluid systems are evaluated. The testing was funded by and arranged for by operators in preparation for actual fracturing treatments in two different fields. Core plugs, time and funding were limited; therefore, only tests deemed necessary for decision-making were run. Limited repeat testing was therefore possible.

An experimental study on permeability, diffusivity, and selectivity of CO 2 and CH 4 through [bmim][PF 6] ionic liquid supported on an alumina membrane: Investigation of temperature fluctuations effects

In order to define a new temperature correction factor in this study, accurate experimental values were presented for permeability and diffusivity of carbon dioxide and methane in imidazolium-based room temperature ionic liquid: [bmim][PF 6] (1-butyl-3-methylimidazolium hexafluorophosphate) immobilized on an inorganic membrane support. Results were presented as a function of temperature and pressure for temperatures within 300–320 K and pressures below 50 kPa. According to the literature, experimental values of permeability and diffusivity for CH 4 in [bmim][PF 6] vs. temperature are reported for the first time in this study. Results obtained for CO 2 permeability revealed good agreement with data reported by other researchers.

Gas transport in fluorothiophenyl modified PVC membranes

This work reports the modification of poly(vinyl chloride) by partially replacing the chlorine atoms of the chains with moieties derived from fluorinated nucleophilic compounds: 4-fluorothiophenol, 3,4-difluorothiophenol and pentafluorothiophenol. Membranes were cast from tetrahydrofuran solutions of the modified poly(vinyl chloride)s and the permeability and diffusion coefficients of hydrogen, nitrogen, oxygen, carbon dioxide and methane through the membranes were measured using permeation techniques. The influence of both the degree of modification and the number of fluorine atoms containing in functionalizing groups on the performance of the membranes was thoroughly investigated. A permselectivity study is also presented in order to evaluate the potential applicability of the membranes for gases separation.

Using poly( N,N-dimethylaminoethyl methacrylate)/polyacrylonitrile composite membranes for gas dehydration and humidification

The transport of water vapor through a composite membrane consisting of hydrophilic poly( N, N-dimethylaminoethyl methacrylate) (PDMAEMA) as the active layer and polyacrylonitrile (PAN) as the substrate was investigated, and the performance of the membrane for gas dehydration and humidification applications was evaluated. For gas dehydration, methane/water vapor mixtures were used as feed and vacuum was applied on the downstream side. The feed composition and operating temperature were found to have a significant effect on the membrane performance. The PAN substrate had little effect on the permeation of methane, but the resistance of the substrate to water vapor permeation was significant because of the substantially higher permeability of water vapor in the membrane. For gas humidification, liquid water was brought to be in contact with the active layer of the membrane and nitrogen gas flowed on the other side. With an increase in the gas flow rate, the mass transfer rate of water through the membrane to reach the gas stream increased, and the humidity level of the gas stream decreased. The humidification can be enhanced significantly by operating at a higher temperature. A phenomenological mass transfer equation was derived for membrane humidifiers to correlate the overall mass transfer coefficient and membrane area, and this equation could be used in process design and scale up.

How do polymerized room-temperature ionic liquid membranes plasticize during high pressure CO 2 permeation?

Room-temperature ionic liquids (RTILs) are a class of organic solvents that have been explored as novel media for CO 2 separations. Polymerized RTILs (poly(RTILs)) can be synthesized from RTIL monomers to form dense, solid gas selective membranes. It is of interest to understand the permeation properties under single gas and mixed gas conditions at elevated pressure of CO 2. The ionic nature of the polymers may result in tight arrangements between the oppositely charged ionic domains in the poly(RTIL) eventually preventing the membrane from excessive swelling and deterioration of its performance at increased pressure and/or temperature. In this work we characterize the permeation behaviour of three different poly(RTILs) at single and mixed gas pressures up to 40 bar and over a temperature range from T = 10–40 °C. We find that CO 2 is an equally strong plasticizer in single gas as well as mixed gas experiments: the permeability of CO 2 increases by more than 60% over a pressure range of 40 bar. Methane does not plasticize the poly(RTIL) by itself in single gas experiments, however the presence CO 2 accelerates its transport by more than 250%. The plasticization effect of CO 2 is fully reversible on the time scale of the diffusional processes. Even though the poly(RTILs) are glassy in nature, the plasticization behaviour is distinctly different from regular glassy polymers such as polyimides, polysulfones or polycarbonates due to the reversibility of swelling extent. Tailoring the length of the side chain of poly(RTIL) indicates that short side chains suppress plasticization and acceleration of the methane permeability up to a pressure of 10 bars CO 2: longer side chains however do not. This suggests the interpretation that a molecular energy balance of ionic attraction and swelling-induced relaxation exists: however, the swelling-induced relaxations overrule the ionic interaction.

Crystallinity effect on the gas transport in semicrystalline coextruded films based on linear low density polyethylene

AbstractThis article describes the diffusion and permeability of oxygen, carbon dioxide, methane, ethane, ethylene, propane, and propylene in 1‐octene based polyethylene of densities 0.94, 0.92, 0.904, and 0.87. The isotherms obtained in the time‐lag experimental device display a diffusion coefficient and permeability behavior similar to that of glassy polymers. We apply the dual model to semicrystalline polymers assuming that Henry's sites are related to the amorphous phase, which decreases when the crystallinity percentage increases. Whereas the interphase of the polymeric matrix and the crystalline phase prevails and acts as Langmuir sites. Their effect is to increase both, the tortuosity of diffusion trajectories and the chain immobilization. We now explain this effect using thermodynamic considerations. In fact, the tortuosity is related to the change in activation entropy, and the chain immobilization to the cohesive energy of the polymeric matrix. In those terms, the diffusion coefficient does not follow the same crystalline percentage dependence than the solubility. According to the previous findings, the solubility changes in proportion to amorphous percentages. Instead, diffusion coefficient has exponential dependence. Furthermore, we show that the permeability changes as a consequence of the modification of diffusion and solubility, according to the product of both quantities. Comparison with previous publication has been included. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 634–642, 2010

On the Effects of the External Surface on the Equilibrium Transport in Zeolite Crystals

With the aid of molecular simulation techniques (molecular dynamics, grand-canonical Monte Carlo, and reactive flux correlation function RFCF), the influence of the external surface on the equilibrium permeation of methane and ethane into and out of an AFI-type zeolite crystal has been studied. In particular, “extended dynamically corrected transition state theory”, which has been proven to describe the transport of tracers in periodic crystals correctly, has been applied to surface problems. The results suggest that the molecules follow paths that are close to the pore wall in the interior and also at the crystal surface. Moreover, the recrossing rate at the surface turns out to be non-negligible, yet, in contrast to the intracrystalline recrossing rate, remains almost constant over loading which gives indication to diffusive barrier crossing at the crystal surface. As a consequence of very different adsorption and desorption barriers, the corresponding permeabilities are shown to be not equal for one and the same condition (T and p). The critical crystal length, beyond which surface effects can be certainly neglected, is computed on basis of flux densities. Entrance/exit effects, in the present cases, are practically important solely for ethane at low pressures. The influence of the type of external surface on the surface flux is, hereby, rather small, because the transport at the surface is controlled by the slow supply from the gas phase. This has been evidenced by a simplified thermodynamic model that has been derived within this work and which is based on rapidly assessable simulation data. Finally, we propose a procedure for estimating the importance of different factors that have an impact on surface effects.

Gas seepage equation of deep mined coal seams and its application

In order to obtain a gas seepage law of deep mined coal seams, according to the properties of coalbed methane seepage in in-situ stress and geothermal temperature fields, the gas seepage equation of deep mined coal seams with the Klinkenberg effect was obtained by confirming the coalbed methane permeability in in-situ stress and geothermal temperature fields. Aimed at the condition in which the coal seams have or do not have an outcrop and outlet on the ground, the application of the gas seepage equation of deep mined coal seams in in-situ stress and geothermal temperature fields on the gas pressure calculation of deep mined coal seams was investigated. The comparison between calculated and measured results indicates that the calculation method of gas pressure, based on the gas seepage equation of deep mined coal seams in in-situ stress and geothermal temperature fields can accurately be identical with the measured values and theoretically perfect the calculation method of gas pressure of deep mined coal seams.

Permeability and separability of methane and carbon dioxide across meso-porous Mg–Al hydrotalcite and activated carbon media

Hydrotalcite and activated carbon (AC) are known to exhibit certain level of affinity for CO 2. If the materials are constructed for use as an adsorptive film or adsorbent in gas separation application, more of CO 2 can be permeated and separated from the other component gas mixture. In this study, permeability of carbon dioxide across the materials was found to increase almost linearly with increase in the respective gas flow rate but the permeability was nearly independent of pressure, attesting to their meso-porosity. The permeability remained constant at ≈6×10 −3 mol m/m 2 s Pa, apparently due to the dominance of Knudsen diffusion mechanism. The separability of gas increased with increase in the inlet flow rate and pressure. Hydrotalcite film deposited on porous alumina substrate demonstrated the highest separability factor of 91, followed by bast AC (separability factor=13) and core AC (separability factor=11). Methane was found to permeate preferentially through the three porous media due to hindered diffusion of CO 2 as a result of the affinitive force attributed to high charged density in the interlayer spacing of Mg–Al hydrotalcite structures that sequestered CO 2.

Utilization of stabilized and solidified sewage sludge as a daily landfill cover material

To evaluate the effectiveness of stabilized and solidified sewage sludge for use as a daily landfill cover material, unconfined compressive strength, CBR (California Bearing Ratio), hydraulic conductivity, rainfall drainage ability, and erosion resistance were examined. In addition, material segregation of the solidified sewage sludge was investigated. The experiment results showed that the solidified sewage sludge material had enough equipment transportability. The measured hydraulic conductivity was similar to the hydraulic conductivity of typical clayey soil. The solidified sewage sludge samples were not significantly segregated during the 28-day-submerged periods. Moreover, the stabilized sewage sludge materials were environmentally safe according to the results of heavy metal leaching andE. coli. detection experiments. The permeability of ammonia, methane, and carbon dioxide gas through the sewage material was determined. Our results indicate that the stabilized and solidified sewage sludge materials may provide an alternative daily landfill cover material that is cost-effective and environmentally friendly.

Gas permeability, diffusivity and solubility of nitrogen, helium, methane, carbon dioxide and formaldehyde in dense polymeric membranes using a new on-line permeation apparatus

A novel permeation apparatus was developed for the selective on-line measurements of gas fluxes. The development of the apparatus was motivated by the need to measure transient fluxes, directly, rapidly, precisely and selectively. To achieve these goals, a residual gas analyzer was used as a selective pressure transducer. Lag-time experiments allowed the simultaneous determination of permeation characteristics, such as permeability and diffusion coefficients. These coefficients are constant within the studied feed pressure interval (0.1–0.01 atm at 28 °C). Pure nitrogen, helium, carbon dioxide, methane and formaldehyde permeation was performed through polydimethylsiloxane, polyisoprene, polyoctenamer, and polyurethane membranes. Classical transport properties were very similar to literature values. The highest permeability, diffusivity and solubility values are found for the polydimethylsiloxane membranes. Carbon dioxide presents the lowest diffusivity and the largest solubility in all membranes, and formaldehyde permeation behaviour is similar to that of carbon dioxide. Physical properties of penetrants (critical volume and normal boiling temperature) and of membranes (glassy transition temperature) are good indicators of the permeation behaviour. This study documents a novel permeation approach to allow precise on-line transient fluxes to be quickly and directly measured.

Non-Equilibrium Dynamic Monte Carlo Simulations on Methane and Ethylene Permeations through MFI-type Silicalite Membranes.

The results of non-equilibrium dynamic Monte Carlo (DyMC) simulations on the permeation of methane and ethylene in MFI-type silicalite membranes are reported. The required parameter for the rate of jumping is estimated from our previous MD studies, and the validity of two different lattice models is examined in terms of the reproducibility of the self-diffusion coefficients using these estimated parameters. Our simulation results indicate that different lattice models are required for methane and ethylene. The permeability through silicalite membrane is estimated by non-equilibrium DyMC and compared with the expected values that are predicted by a previously reported method, the combined method of molecular simulation techniques with a permeation model (CMP). The simulated permeability of methane shows agreement with CMP values, and that of ethylene is reasonable when compared with the CMP values.

Transport of gases and vapors in methacrylic copolymers of varying side chain length

The gas transport properties of copolymers of dodecyl methacrylate with ethyl methacrylate and hydroxypropyl methacrylate have been studied. The diffusion, solubility and permeability of oxygen, nitrogen, carbon dioxide, methane, ethane and ethylene have been measured in the temperature range 0–50 °C, and activation energies and heats of solution have been obtained. A comparison with the data available in the literature on acrylates and other methacrylates of varying aliphatic side chain length has been performed. The diffusion coefficient of gases increases with the side chain length in a way similar to that found for homologous acrylates. A representation of log( D) as a function of the inverse of the fractional free volume shows that all acrylates and methacrylates of lineal alkyl side chain fall on the same straight line.

Diffusion of small molecules through modified poly(vinyl chloride) membranes

AbstractThe transport properties of a set of four copolymers based on poly(vinyl chloride) (PVC) have been studied. The nucleophilic substitution of chlorine atoms with 4‐mercaptophenol sodium salt, 2‐thionaphthalene, 4‐(1‐adamantyl) thiophenol, and thiophenolate sodium salt as the nucleophiles has been performed, from low conversion levels (3%) to high levels (40%), and the permeability, solubility, and diffusivity of oxygen, nitrogen, carbon dioxide, and methane have been measured. The introduction of bulky groups to the PVC chain leads to chain separation and results in large increases in the free volume at conversions up to 10%. This brings about a 5‐fold increase in the diffusion coefficients that is almost independent of the bulkiness of the substituent. Solubility is little affected and instead tends to decrease as substitution progresses. The substitution of more than 10% of the chlorine atoms does not result in an improvement in the transport properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 964–971, 2002

Diffusion of binary mixtures across zeolite membranes: entropy effects on permeation selectivity

Diffusion of binary mixtures across zeolite membranes is strongly influenced by the sorption behaviour of the individual components. When the components in the mixture have significantly different molecular sizes, size entropy effects tend to favour the sorption of the smaller species at high molecular loadings. This is the case, for example, for adsorption of methane and n-butane in silicalite. For mixtures of linear and branched alkanes having the same number of carbon atoms, configurational entropy effects tend to favour the sorption of the linear alkane becuase these molecules “pack” more efficiently inside the ordered zeolite structure. In estimating the permeation of mixtures across zeolite membranes, both size and configurational entropy effects need to be properly accounted for. A model to estimate the permeation fluxes across zeolite membranes is developed by combining the Real Adsorbed Solution Theory to describe the mixture sorption, and the Maxwell-Stefan diffusion equations. The utility of the model is demonstrated by means of two case studies: (1) permeation of methane and n-butane, and (2) permeation of n-hexane and 2,2 dimethylbutane across a silicalite membrane.

Facilitated acetylene transfer through membranes composed of sulfonate-containing aromatic polyamides and poly-N-vinylamides involving nanocluster silver

Abstract A series of approaches was considered to facilitate acetylene transfer in comparison with methane through membranes based on aromatic polyamides. One of the approaches is variation of composition of the rigid-chain polymer by progressive introduction of bulky sulfonic acid groups in chains. An effect of the polymer structure was found on the internal structure of the films made of sulfonate-containing polyamides. The variation of content of sulfonate-containing fragments results in the formation of channels of different types which provide selective transport of acetylene. There are several compositions of aromatic polyamides which form films with a higher selectivity of transport of acetylene in comparison with methane ( α =4–6). The films made of a mixture of the aromatic polyamide together with another polymer such as poly- N -vinylpyrrolidone or poly- N -vinylcaprolactam with a high local concentration of amide groups do not reveal a marked selective transfer of acetylene relative to methane. In order to facilitate acetylene transfer through the polyamide membranes, their modification by AgNO 3 aqueous solutions was performed. It is interesting to note that the modification effect on acetylene transfer through the films was observed only for films made of a mixture of two polymers: sulfonate-containing aromatic polyamide and poly- N -vinylcaprolactam (PVCL). Both content of sulfonic acid groups in the film-forming polyamide and that of the second PVCL in the mixture affect permeability and selectivity for acetylene in comparison with methane. Unlike methane, the acetylene transfer occurs even at room temperature, whereas the permeability of both acetylene and methane through unmodified films is just realised at higher temperature (140–160°C). The considerable increase of acetylene permeability is explained by formation of silver nanoclusters in the slightly swollen matrix. The presence of macromolecules of PVCL in the mixture is necessary as they are likely to be stabilizers forming metal clusters of a certain size. Metal silver clusters synthesized ‘in situ’ in the presence of the polymers facilitate the transfer of acetylene unlike methane due to an increase of acetylene solubility. We propose that acetylene molecules interact with positive surface charges of silver particles being in channels of such modified films. In addition, the role of water molecules in the acetylene transfer is likely to be essential.

Effect of physical aging on the gas transport properties of PVC and PVC modified with pyridine groups

The gas transport coefficients of polyvinyl chloride (PVC) and PVC modified with pyridine groups have been studied. It has been observed that there is a strong time dependence of the permeability and diffusivity of oxygen, nitrogen, carbon dioxide and methane in membranes prepared by solvent casting of PVC and pyridine modified PVC. For PVC there is a two-fold reduction of the diffusion coefficients during the first two days, and about one order of magnitude, a month after the membranes are prepared, and no stabilisation of the trend is seen after a month. Membranes prepared from modified PVC show a short-term diffusion rate reduction which is similar to that found in PVC, while at longer times the diffusion rate decrease levels off quickly, attaining constant values after about ten days. The time dependence of the transport coefficients is attributed to the samples’ physical aging and an attempt is made to fit the experimental data by considering a stretched exponential time dependence of the volume contraction on aging.

Effect of physical aging of poly(1-trimethylsilyl-1-propyne) films synthesized with TaCl5 and NbCl5 on gas permeability, fractional free volume, and positron annihilation lifetime spectroscopy parameters

The effect of physical aging on the gas permeability, fractional free volume (FFV), and positron annihilation lifetime spectroscopy (PALS) parameters of dense, isotropic poly(1-trimethylsilyl-1-propyne) (PTMSP) films synthesized with TaCl5 and NbCl5 was characterized. As-cast films were soaked in methanol until an equilibrium amount of methanol was absorbed by the polymer. When the films were removed from methanol, film thickness initially decreased rapidly and was almost constant after 70 h in air for both catalysts. This timescale was much longer than the timescale for complete methanol desorption (ca. 5 h). From the film-thickness data, the reduction in FFV with time was estimated. For samples prepared with either catalyst, the kinetics of FFV reduction were well-described by a simple model based on the notion either that free-volume elements diffuse to the surface of the polymer film and are subsequently eliminated from the sample or that lattice contraction controls polymer densification. Methane permeability decreased rapidly during the first 70 h, which was the same timescale for the thickness change. The decrease in methane permeability was smaller in films prepared with NbCl5 than with TaCl5. The logarithm of methane permeability decreased linearly as reciprocal FFV increased, in accordance with free-volume theory. The PALS results indicate that the concentration of larger free-volume elements (as indicated by the intensity I4) decreased with aging time and that the other PALS parameters were not strongly influenced by aging. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1222–1239, 2000