CH4 Sorption Capacity Research Articles

Porous liquids based on ZIF-67@ZIF-8 through the strategy of interface layer reconstruction for CO2 selective sorption

Porous liquids (PLs) are a new type of porous materials that combine both the porosity of solids and the fluidity of liquids, which have attracted widespread attention. In this paper, we firstly report a novel type III porous liquid through the interfacial layer reconstruction strategy, which are composed of ZIF-67@ZIF-8 as porous cavity and ionic liquid [P6,6,6,14][NTf2] as sterically hindered solvents, respectively. At 25 °C, it showed superior fluidity and the viscosity of PLs is 0.1911 Pa·s (25 °C). Moreover, ZIF-67@ZIF-8 PLs have the potential for CO2/N2 and CO2/CH4 selective separation. Under 10 bar, the CO2 adsorption capacity of ZIF-67(S)@ZIF-8-PLs is 1.37 mmol/g that is higher than that of ZIF-67(S)-PLs. Under the same conditions, the CO2 adsorption capacity of PLs is 22.68 times higher than that of N2. Under 2.5 bar, ZIF-67@ZIF-8 PLs showed very low CH4 sorption capacity of 0.005 mmol/g, which is less than that of CO2 (0.279 mmol/g). Notably, this study opens a new horizon to prepare PLs with superior gas selective separation based on interfacial layer reconstruction strategy considering the multiple structures of metal–organic frameworks as porous cavities

High-Pressure Adsorption of CO2 and CH4 on Biochar-A Cost-Effective Sorbent for In Situ Applications.

The search for an effective, cost-efficient, and selective sorbent for CO2 capture technologies has been a focus of research in recent years. Many technologies allow efficient separation of CO2 from industrial gases; however, most of them (particularly amine absorption) are very energy-intensive processes not only from the point of view of operation but also solvent production. The aim of this study was to determine CO2 and CH4 sorption capacity of pyrolyzed spruce wood under a wide range of pressures for application as an effective adsorbent for gas separation technology such as Pressure Swing Adsorption (PSA) or Temperature Swing Adsorption (TSA). The idea behind this study was to reduce the carbon footprint related to the transport and manufacturing of sorbent for the separation unit by replacing it with a material that is the direct product of pyrolysis. The results show that pyrolyzed spruce wood has a considerable sorption capacity and selectivity towards CO2 and CH4. Excess sorption capacity reached 1.4 mmol·g-1 for methane and 2.4 mmol·g-1 for carbon dioxide. The calculated absolute sorption capacity was 1.75 mmol·g-1 at 12.6 MPa for methane and 2.7 mmol·g-1 at 4.7 MPa for carbon dioxide. The isotherms follow I type isotherm which is typical for microporous adsorbents.

Effects of pore fluids on methane sorption in the Lower Bakken Shales, Williston Basin, USA

Compositional variation and distribution of pore fluids (water, oil, and asphaltenes) as a function of thermal maturity can greatly affect methane sorption in organic-rich shales. Five Lower Bakken organic-rich shale samples with varied thermal maturity from marginal maturity to oil-to-gas cracking were used in this study to assess this effect. Pore fluids were extracted from samples at four sequential stages: as–received, oven–dried, pentane–extracted, and dichloromethane–extracted; Four aliquots for each sample were used to quantify the effect of water, mobile oil, and asphaltenes on gas sorption. CH4 sorption isotherms were measured at 35 °C, 50 °C, and 65 °C.The results show that presence of pore fluid reduces the CH4 sorption capacity of shale, and the extent of this reduction depends largely on the types of pore fluids. The reduction of CH4 sorption capacity basically follows a linear correlation with moisture content. The effect of mobile oil is 4–5 times greater than that of water. Asphaltenes have no effect on methane sorption capacity for the marginally mature–mature samples but cause a drastic decrease of sorption capacity at the early oil–to–gas cracking. The surfaces of OM–hosted pores are probably coated by asphaltenes, while mobile oil is distributed in the center of the pores, and water mainly occupies the clay-mineral-hosted pores. The sorption sites will increase significantly once oil cracking to gas starts, which is probably associated with pyrobitumen formation. The affinity of CH4 for sorption on pyrobitumen is stronger than that on residual kerogen.

Effect of shale properties on CH4 and CO2 sorption capacity in Czech Silurian shales

The study involved an experimental assessment of the CO2 and CH4 sorption capacity of seven dark Silurian shale samples from three formations in the Barrandian Basin (Czech Republic). The shale samples had dominant inorganic matter consisting mainly of clay minerals, quartz, calcite and plagioclase, and very low organic matter. Most of the organic particles were the remains of zooclasts, especially graptolites and bitumens. The graptolite reflectance (Rr) reflecting the degree of thermal maturation of the shales ranges between 0.56% in the Kopanina Formation and 1.09% in the Litohlavy Formation, with the exception of the probably thermally altered part of the Motol Formation, which has reflectance higher than 1.70%. The total organic carbon (TOC) content was found to be in the range of 0.34–2.37 wt%. The porosity values were from 4.6% to 18.8%. In all shale samples, the high pressure excess sorption isotherms of CO2 and CH4 were measured at a temperature of 45 °C for both gases at pressures up to 8 MPa for CO2 and up to 15 MPa for CH4 on dry samples, using a manometric sorption apparatus. The Gibbs equation was used for evaluation of the maximum excess sorption (nmax,CO2 and nmax,CH4). The nmax,CO2 values ranged from 0.118 mmol/g to 0.244 mmol/g, while the nmax,CH4 values were more than twice lower (0.050 mmol/g - 0.088 mmol/g). The xCO2/CH4 ratio ranged from 1.47 to 2.98, with a median value of 2.54, calculated without the sample from the Kopanina Formation (4.36). The influence of the shale parameters on the CO2 and CH4 sorption capacity was determined. No relation has been proven between the value of Rr and the TOC-normalized CO2 and CH4 sorption capacities. The CO2 sorption capacity showed a negative correlation with TOC and with clay minerals but a positive correlation with quartz, while the behaviour of CH4 was opposite in these cases. A strong positive correlation was found between the volume of micropores and the CO2 excess sorption capacity, and negative dependence was found for CH4. The CO2 sorption capacities always depend on the micropores content, and the CH4 capacities depend on the shale components.

CO2 and CH4 sorption on carbon nanomaterials and coals – Comparative characteristics

The aim of this research was to compare the structure, sorption properties and the kinetics of sorption to CO2 and CH4 in nanomaterials with a very orderly structure and in structurally heterogeneous coal. The authors tested synthetic materials such as multiwall carbon nanotubes (MWCNT) and reduced graphene oxide (rGO) as well as natural materials such as coals of various ranks. The value of the surface area of Langmuir and Brunauer, Emmett and Teller, in MWCNTs and rGO was much higher than in the coal. The course of CH4 and CO2 sorption of the materials was investigated and the parameters of sorption isotherms in the pressure of 0–2.0 MPa were determined. The nanomaterials reached the sorption equilibria much faster than the coal. The highest total CH4 sorption capacity was found in low-rank coal. The highest CO2 total sorption capacity was found in MWCNTs and low-rank coal. The highest relative mean drop in CH4 and CO2 sorption capacity resulting from the increasing measurement temperature was found in the MWCNTs and the low-rank coal. The authors analysed the courses of CH4 and CO2 sorption kinetics in the materials of highly different structures. The kinetics of CH4 and CO2 accumulation in MWCNT and rGO nanomaterials progressed almost instantaneously, and their rate was many times higher than in the case of kinetics on hard coals.

Effects of Moisture Contents on Shale Gas Recovery and CO2 Sequestration.

Enhanced recovery of shale gas with CO2 injection has attracted extensive attention as it combines the advantages of improved efficiency of shale gas recovery and reduced greenhouse gas emissions via CO2 geological sequestration. On the other hand, the microscopic mechanism of enhanced shale gas recovery with CO2 injection and the influence of the subsurface water confined in the shale nanopores remain ambiguous. Here, we use grand canonical Monte Carlo (GCMC) simulations to investigate the effect of moisture on the shale gas recovery and CO2 sequestration by calculating the adsorption of CH4 and CO2 in dry and moist kerogen slit pores. Simulation results indicate that water accumulates in the form of clusters in the middle of the kerogen slit pore. Formation of water clusters in kerogen slit pores reduces pore filling by methane molecules, resulting in a decrease in the methane sorption capacity. For the sorption of CH4/CO2 binary mixtures in kerogen slit pores, the CH4 sorption capacity decreases as the moisture content increases, whereas the effect of moisture on CO2 sorption capacity is related to its mole fraction in the CH4/CO2 binary mixture. Furthermore, we propose a reference route for shale gas recovery and find that the pressure drawdown and CO2 injection exhibit different mechanisms for gas recovery. Pressure drawdown mainly extracts the CH4 molecules distributed in the middle of kerogen slit pores, while CO2 injection recovers CH4 molecules from the adsorption layer. When the water content increases, the recovery ratio of the pressure drawdown declines, while that of CO2 injection increases, especially in the first stage of CO2 injection. The CO2 sequestration efficiency is higher under higher water content. These findings provide the theoretical foundation for optimization of the shale gas recovery process, as well as effective CO2 sequestration in depleted gas reservoirs.

CO2 and CH4 sorption properties of granular coal briquettes under in situ states

The aim of this work was an experimental research into the sorption properties of coal briquettes under the various states of stress. The present state of knowledge when it comes to the impact of stress on the CO2 and CH4 sorption properties of coal is limited. Hence, in situ sorption capacity or sorption-induced deformation may vary considerably from these specified in the unloaded conditions. As part of this paper, a research device that enables the sorption measurements for coal samples submitted to loads of up to 40 MPa is presented. Sorption experiments with pure CO2 and pure CH4 were carried out by means of the volumetric method, under isobaric-isothermal conditions. Dry coal material in the form of granular coal briquettes was used. Presented results aimed to prove the existence of a relation between the stress state, sorption capacity and volumetric deformation of coal. Gas sorption and desorption processes on coal may be triggered by the action of mechanical factor. The mechanical load applied to the coal sorbent reduces its sorption capacity but has no direct effect on swelling. The sorption or desorption induced volumetric changes of coal occur regardless of the stress state and regardless of the mechanism of the sorption process itself. Deeper coal seams with reduced CO2 and CH4 sorption capacity may not be as useful for ECBM techniques as the shallower coal seams. Reduction of the sorption capacity with depth may also explain the growing threat of coal and methane outbursts in the USCB mines observed in recent years.

The effects of shale composition and pore structure on gas adsorption potential in highly mature marine shales, Lower Paleozoic, central Yangtze, China

The Ordovician Wufeng Formation and Silurian Longmaxi Formation are two of the most organic-rich and gas-prospective shale formations in the central Yangtze area, China. In this study, we investigate the controls exerted by shale composition and pore structure on methane sorption of these highly matured marine shales (Ro ranges from 2.0% to 4.0%). Samples were analyzed by SEM pore imaging of Ar-ion milled samples, high pressure methane adsorption, and low temperature nitrogen adsorption. In the high TOC Wufeng and lower Longmaxi formations, numerous organic matter pores are present. A positive correlation exists between TOC, BET surface area, and CH4 sorption capacity, indicating that porosity associated with organic matter is the key factor controlling methane sorption capacity of shale samples. In the organic-lean upper Longmaxi Formation, pores within clay particles and carbonate minerals are the major pore types. Organic-lean shale samples from the upper Longmaxi Formation have higher clay content, lower BET surface area, and lower adsorption capacity than organic-rich shales. Within several low TOC samples, a relatively strong correlation exists between illite content and methane sorption capacity, which is interpreted to result from clay mineral-hosted porosity.

The effect of organic matter maturation and porosity evolution on methane storage potential in the Baltic Basin (Poland) shale-gas reservoir

Supercritical CH4 and subcritical CO2 and N2 gas adsorption measurements, combined with scanning electron microscopy (SEM) have been used to determine CH4 sorption capacity and pore characteristics for immature, mature and overmature shales from the Baltic Basin (Poland).Organic matter (OM) maturity exerts a dominant control on porosity evolution in micro- and mesoscale. In the Baltic Basin shales, the initial formation of micro- (<2nm) and mesopores (2–50nm) occurs in the oil window (beginning of catagenesis, vitrinite reflectance Ro~0.5-0.9%) due to primary cracking of kerogen that left OM highly porous. The expelled liquid hydrocarbons turned into solid bitumen that is responsible for pore blocking and significant decrease in micro- and mesopore volume in late mature shales (middle catagenesis Ro~0.9–1.2%). Micro- and mesopores were regenerated in advanced catagenesis (Ro~1.4–1.9%) due to secondary cracking of OM. The micropore volume in the Baltic Basin shales is mostly controlled by the OM content while the influence of clay content is minor and masked by OM.The CH4 adsorption in the Baltic Basin shales is predominantly controlled by OM micropore structure. The mesopore surface area and volume do not play an important role in CH4 sorption. The proposed adsorbed CH4 density equivalent (maximal absolute CH4 adsorption divided by micropore volume), revealed that the CH4 loading potential decreases in micropores with increasing maturity. The highest CH4 loading potential is linked to OM before metagenesis (Ro<2%) where the adsorbed CH4 density equivalent was found greater than the density of liquid CH4. This suggests that in addition to physical adsorption, absorption (dissolution) of CH4 in OM occurs. When OM content was reduced by the treatment with NaOCl solution, CH4 adsorption decreased significantly, suggesting that OM microstructure has much higher adsorption potential than that of clay microstructure.

Sorption charateristics of methane among various rank coals: impact of moisture

Enhanced coalbed methane (ECBM) in deep coal seams is being actively investigated around the world. Since the in situ coal seams are always saturated with water, methane sorption behavior on coal in the presence of water can help accurately assess the amount of recoverable methane. Thus, methane sorption isotherms have been measured on a high-rank anthracite, a low-volatile bituminous, a middle-volatile bituminous and a high-volatile bituminous coal with the manometric technology at 30 °C under six different moisture contents. The Dubinin–Astakhov (D–A) equation was used to fit the experimental sorption isotherm data. In all cases, the moisturized coals exhibited lower sorption capacity than the corresponding dry materials and moisture has a significant effect on CH4 sorption capacity. The maximum sorption capacity, V 0, displays a linear decline with the moisture content for the Changcun and Malan samples, but it is nonlinear for the other two coal samples. The net heat of CH4 sorption, βE, is also reduced by the presence of water, but varies only slightly between a relatively small span of about 8.8 and 10.0 kJ mol−1 for the dry samples studied, despite the difference in coal rank. In addition, the maximum sorption capacity of CH4 in dry coals presents the typical “U-shape” trend with coal rank. Moisture has a greater impact on the sorption capacity in low-rank coals than that in high-rank coals. The mechanisms responsible for the effect of moisture on CH4 sorption among various rank coals are also presented. The pore-blocking effect is the main influencing factor for high-rank anthracite, whereas, the competition sorption is dominant for low-rank coals.

Adsorption and transport of methane in landfill cover soil amended with waste-wood biochars

The natural presence of methane oxidizing bacteria (MOB) in landfill soils can stimulate the bio-chemical oxidation of CH4 to CO2 and H2O under suitable environmental conditions. This mechanism can be enhanced by amending the landfill cover soil with organic materials such as biochars that are recalcitrant to biological degradation and are capable of adsorbing CH4 while facilitating the growth and activity of MOB within their porous structure. Several series of batch and small-scale column tests were conducted to quantify the CH4 sorption and transport properties of landfill cover soil amended with four types of waste hardwood biochars under different levels of amendment percentages (2, 5 and 10% by weight), exposed CH4 concentrations (0–1 kPa), moisture content (dry, 25% and 75% water holding capacity), and temperature (25, 35 and 45 °C). The linear forms of the pseudo second-order kinetic model and the Langmuir isotherm model were used to determine the kinetics and the maximum CH4 adsorption capacity of cover materials. The maximum CH4 sorption capacity of dry biochar-amended soils ranged from 1.03 × 10−2 to 7.97 × 10−2 mol kg−1 and exhibited a ten-fold increase compared to that of soil with 1.9 × 10−3 mol kg−1. The isosteric heat of adsorption for soil was negative and ranged from −30 to −118 kJ/mol, while that of the biochar-amended soils was positive and ranged from 24 to 440 kJ/mol. The CH4 dispersion coefficients for biochar-amended soils obtained through predictive transport modeling indicated that amending the soil with biochar enhanced the methane transport rates by two orders of magnitude, thereby increasing their potential for enhanced exchange of gases within the cover system. Overall, the use of hardwood biochars as a cover soil amendment to reduce methane emissions from landfills appears to be a promising alternative to conventional soil covers.

Dispersive diffusion of gases in coals. Part II: An assessment of previously proposed physical mechanisms of diffusion in coal

Carbon dioxide (CO2) and methane (CH4) vary in their diffusion behaviour in coal, with CO2 being sorbed more extensively and diffusing faster than CH4. Several different mechanisms have been proposed to explain this behaviour. To test these mechanisms, we describe here experiments investigating the rates of gas sorption in an Australian, high-volatile, bituminous coal as a function of particle size, temperature and gas type on sorption kinetics. One explanation for greater CO2 uptake proposes that CO2 can penetrate finer pore throats than CH4. If this were true, we would expect that the CH4 sorption capacity in crushed coal would approach that of CO2. However, this was not found: crushing slightly increased both CO2 and CH4 sorption capacity, as well as the helium density. Another theory proposed that methane in coal has a greater activation energy associated with its diffusion; however, we found that the temperature dependence of both CO2 and CH4 sorption rates were similar. Experiments measuring the diffusion of other gases (ethane, argon, nitrogen and krypton) showed a relationship between the critical temperature and molecular diameter of the gas and its diffusion rate in coal. We suggest that absorption occurs once gas condenses on the coal surface, with the absorption rate depending on the size and shape of the molecule. The experiments discussed in this paper confirm the dispersive nature of gas diffusion in coal, and provide evidence to explain much of the variation in diffusion rates.

Influence of Coal Particle Size on Coal Adsorption and Desorption Characteristics

Abstract Accurate testing coal isotherm can play a significant role in the areas of coal seam gas drainage, outburst control, CO2 geo-sequestration, coalbed methane (CBM) and enhanced coalbed methane recovery (ECBM) etc. The effect of particle size on the CO2 and CH4 sorption capacity of bituminous coal from Illawarra, Australia was investigated at 35°C and at pressure up to 4 MPa. A unique indirect gravimetric apparatus was used to measure the gas adsorption and desorption isotherms of coal of different particle sizes ranging from around 150 urn to 16 mm. Langmuir model was used to analysis the experimental results of all gases. Coal particle size was found to have an apparent effect on the coal ash content and helium density results. Coal with larger particle size had higher ash content and higher helium density. The sorption isotherm was found to be highly sensitive with helium density of coal which was determined in the procedure of testing the void volume of sample cell. Hence, coal particle size had a significant influence on the coal sorption characteristics including sorption capacity and desorption hysteresis for CO2 and CH4, especially calculated with dry basis of coal. In this study, the 150-212 um (150 um) coal samples achieved higher sorption capacity and followed by 2.36-3.35 mm (2.4 mm), 8-9.5 mm (8 mm) and 16-19 mm (16 mm) particle size samples. However, the differences between different coal particles were getting smaller when the sorption isotherms are calculated with dry ash free basis. Test with 150 um coal samples were also found to have relatively smaller desorption hysteresis compared with the other larger particle size samples. The different results including adsorption/desorption isotherm, Langmuir parameters and coal hysteresis were all analysed with the CO2 and CH4 gases.

Experimental investigation of changes in methane adsorption of bitumen-free Woodford Shale with thermal maturation induced by hydrous pyrolysis

This study quantifies the effects of organic-matter (OM) thermal maturity on methane (CH4) sorption, on the basis of five samples that were artificially matured through hydrous pyrolysis achieved by heating samples of immature Woodford Shale under five different time–temperature conditions. CH4-sorption isotherms at 35 °C, 50 °C, and 65 °C, and pressures up to 14 MPa on dry, solvent-extracted samples of the artificially matured Woodford Shale were measured. The results showed that CH4-sorption capacity, normalized to TOC, varied with thermal maturity, following1 the trend: maximum oil (367 °C) > oil cracking (400 °C) > maximum bitumen/early oil (333 °C) > early bitumen (300 °C) > immature stage (130 °C). The Langmuir constants for the samples at maximum-oil and oil-cracking stages are larger than the values for the bitumen-forming stages.The total pore volume, determined by N2 physisorption at 77 K, increases with increased maturation: mesopores, 2–50 nm in width, were created during the thermal conversion of organic-matter and a dramatic increase in porosity appeared when maximum-bitumen and maximum-oil generation stages were reached. A linear relationship between thermal maturity and Brunauer–Emmett–Teller (BET) surface area suggests that the observed increase in CH4-sorption capacity may be the result of mesopores produced during OM conversion. No obvious difference is observed in pore-size distribution and pore volume for samples with pores <2.0 nm with the increase of thermal maturity based on CO2 physisorption at 273 K.The isosteric heat of adsorption and the standard entropy for artificially matured samples ranged from 17.9 kJ mol−1 to 21.9 kJ mol−1 and from −85.4 J mol−1 K−1 to −101.8 J mol−1 K−1, respectively. These values are similar to the values of immature Woodford kerogen concentrate previously observed, but are larger than naturally matured organic-rich shales. High-temperature hydrous pyrolysis might have induced Lewis acid sites on both organic and mineral surfaces, resulting to some extent, in chemical interactions between the adsorption site and the methane C–H bonds.The formation of abundant mesopores (2–50 nm) within organic matter during organic-matter thermal maturation makes a great contribution to the increase in both BET surface area and pore volume, and a significant increase in 2–6 nm pores occurs at maximum-oil-generation and oil-cracking to gas, ultimately controlling the methane-adsorption capacity. Therefore, consideration of pore-size effects and thermal maturity is very important for gas in place (GIP) prediction in organic-rich shales.

High-pressure CH4 and CO2 sorption isotherms as a function of coal maturity and the influence of moisture

Methane (CH4) and carbon dioxide (CO2) sorption isotherms have been measured on an Australian subbituminous, a German high-volatile bituminous and a German anthracite coal in the dry and moisture-equilibrated state. The purpose was to study the variation of CH4 and CO2 sorption capacities of the dry coals as a function of rank and the influence of water on the sorption properties. Methane sorption isotherms were measured at 303, 308, 318 and 334K (30, 35, 45 and 61°C), and CO2 isotherms at 318, 334 and 349K (45, 61 and 76°C).The excess sorption capacity of coals is always higher for CO2 than for CH4. The CO2 and CH4 sorption capacity of dry coals as a function of rank follows a parabolic trend reported in earlier studies, with a minimum at ~1% vitrinite reflectance. This trend is more pronounced for CO2 than for CH4. For moisturised coals a linear increase in CO2 and CH4 sorption capacity with coal rank was observed. Moisture reduces the gas sorption capacity of coals significantly. Moisture content therefore is a first-order control for the gas sorption capacity of low rank coals up to bituminous rank, with much higher impact than temperature or maturity. The moisture-induced reduction in CO2 and CH4 sorption capacity decreases with increasing coal rank. It correlates linearly with the oxygen content, which in turn correlates qualitatively with the amount of hydrophilic and carboxylic functional groups as evidenced by FTIR analysis.The influence of sorbed water on the sorption capacity is highest at low pressures (low surface coverage θ<0.3). The dry/moist sorption capacity ratios converge towards 1 with increasing pressure (high surface coverage θ≈0.7).