Absolute Adsorption Capacity Research Articles

Influence of Supercritical Conditions on Isothermal Adsorption Capacity Calculation of Methane and Model Optimization.

The study of isothermal adsorption models for coal and methane under supercritical conditions helps us to understand the gas content distribution in coal seams and improve gas management in coal mines. Coal samples from the Hebi mine and Longshan coal mine were selected for this research. Using the weight method, isothermal adsorption curves of supercritical methane at temperatures of 308, 313, and 318 K were measured. The adsorption phase density of supercritical methane was obtained by using the intercept method and model fitting, and the absolute adsorption capacity of methane was calculated. Simultaneously, the pore volume and specific surface area of the coal samples were tested, and the isothermal adsorption model for supercritical methane was studied and optimized. The results indicate that using mercury intrusion, low-temperature N2, and low-temperature CO2 adsorption methods for testing coal sample pore structures allows for multiscale characterization of the coal pore structure. Based on the Gibbs excess adsorption theory, the phase density of methane obtained from the intercept method and model fitting effectively represent the isothermal adsorption curve of supercritical methane. By combination of the specific surface area and pore volume distribution of the coal with the absolute adsorption capacity of methane, the number of methane adsorption layers on the coal surface was calculated to be between 1.11 and 1.3 layers. This suggests that the isothermal adsorption model for supercritical methane on coal is not solely micropore filling or single molecular layer adsorption but primarily single molecular layer adsorption with concurrent micropore filling adsorption. Based on this adsorption mechanism, an L-DA isothermal adsorption model for supercritical methane on coal was established. The L-DA isothermal model shows good fitting results and effectively explains the adsorption characteristics of supercritical methane on coal.

Prediction Model of Lean Coal Adsorption of Power Plant Flue Gas.

To minimize errors in calculating coal flue gas adsorption capacity due to gas compressibility and to preclude prediction inaccuracies in abandoned mine flue gas storage capacity for power plants, it is imperative to account for the influence of compression factor calculation accuracy while selecting the optimal theoretical adsorption model. In this paper, the flue gas adsorption experiment of a power plant with coal samples gradually pressurized to close to 5 MPa at two different temperatures is carried out, and the temperature and pressure data obtained from the experiment are substituted into five different compression factor calculation methods to calculate different absolute adsorption amounts. The calculated adsorption capacities were fitted into six theoretical adsorption models to establish a predictive model suitable for estimating the coal adsorption capacity in power plant flue gas. Results reveal significant disparities in the absolute adsorption capacity determined by different compression factors, with an error range of 0.001278-7.8262 (cm3/kg). The Redlich-Kwong equation of state emerged as the most suitable for the flue gas of the selected experimental coal sample and the chosen composition ratio among the five compression factors. Among the six theoretical adsorption models, the Brunauer-Emmett-Teller model with three parameters demonstrated the highest suitability for predicting the adsorption capacity of coal samples in power plant smoke, achieving a fitting accuracy as high as 0.9922 at 49.7 °C.

Understanding roles of moisture in CO2 adsorption and desorption hysteresis on deep gas-bearing shales under high temperature and pressure

To understand injectivity and storage stability of CO2 into gas-bearing shale reservoirs, CO2 adsorption and desorption on the dry and moist shales with diverse properties were conducted at 353.15 K and pressures up to 14 MPa. Multiple characterizations were combined to examine pore characteristics of the shales before and after CO2 adsorption/desorption. The resultant CO2 adsorption and desorption hysteresis on the shales was revealed ultimately. Results indicated that both the excess and absolute adsorption isotherms of CO2 witness slow increase stage, rapid increase stage, and decrease stage. The adsorption capability of the shales positively depends on the TOC content and pore abundance. Moreover, the clay minerals and oxygenic functional groups also benefit CO2 adsorption. The moisture significantly reduces the experimentally-determined maximum absolute adsorption capacity of the shales by 5.78–46.39 % due to pore space occupation. During the adsorption/desorption, the CO2 molecules could interact with the shales, thereby initiating extraction of partial organic matter, transformation of CO2 from supercritical state to gas state, and dissolution of inorganic minerals. Those effects consume CO2 and dominantly change the micropore structure of the dry shales and the mesopore structure of the moist shales, thus leading to CO2 adsorption and desorption hysteresis. Notably, the moisture dramatically raises the hysteresis degree on the shales by 8.42–59.45 % because of its solubility to CO2 and promotion to mineral dissolution. Overall, shale reservoir moisture could weaken injectivity but strengthen storage stability of CO2. Hence, the critical moisture content and occurrence pattern of organic matter and clay minerals are required for target shale reservoir selection.

Main controlling factor and mechanism of gas-in-place content of the Lower Cambrian shale from different sedimentary facies in the western Hubei area, South China

The Lower Cambrian shale gas in the western Hubei area, South China has a great resource prospect, but the gas-in-place (GIP) content in different sedimentary facies varies widely, and the relevant mechanism has been not well understood. In the present study, two sets of the Lower Cambrian shale samples from the Wells YD4 and YD5 in the western Hubei area, representing the deep-water shelf facies and shallow-water platform facies, respectively, were investigated on the differences of pore types, pore structure and methane adsorption capacity between them, and the main controlling factor and mechanism of their methane adsorption capacities and GIP contents were discussed. The results show that the organic matter (OM) pores in the YD4 shale samples are dominant, while the inorganic mineral (IM) pores in the YD5 shale samples are primary, with underdeveloped OM pores. The pore specific surface area (SSA) and pore volume (PV) of the YD4 shale samples are mainly from micropores and mesopores, respectively, while those of the YD5 shale samples are mainly from micropores and macropores, respectively. The methane adsorption capacity of the YD4 shale samples is significantly higher than that of the YD5 shale samples, with a maximum absolute adsorption capacity of 3.13 cm3/g and 1.31 cm3/g in average, respectively. Compared with the shallow-water platform shale, the deep-water shelf shale has a higher TOC content, a better kerogen type and more developed OM pores, which is the main mechanism for its higher adsorption capacity. The GIP content models based on two samples with a similar TOC content selected respectively from the Wells YD4 and YD5 further indicate that the GIP content of the deep-water shelf shale is mainly 3−4 m3/t within a depth range of 1000–4000 m, with shale gas exploration and development potential, while the shallow-water platform shale has normally a GIP content of <1 m3/t, with little shale gas potential. Considering the geological and geochemical conditions of shale gas formation and preservation, the deep-water shelf facies is the most favorable target for the Lower Cambrian shale gas exploration and development in the western Hubei area, South China.

Molecular simulation of CH4 and CO2 adsorption behavior in coal physicochemical structure model and its control mechanism

In order to clarify the microscopic coupling mechanism among chemical composition and structure, nanopores and gas adsorption, this study used molecular simulation to investigate the adsorption behavior of CH4 and CO2 molecules in different coal physicochemical structure models under various environment conditions. The results show that with the dissolution of low molecular weight compounds (LMWCs), the absolute adsorption capacity for CO2 and CH4 in aromatic pores gradually increases, and slit pores show a more obvious promotional effect on gas adsorption. On the other hand, observing the radial distribution function(RDF) between the main functional groups in coal and CH4/CO2, oxygen-containing functional groups and aromatic structures display a significant impact on the distribution of gas molecules on coal surface, especially –COOH and -O- groups. While free LMWCs are easy to generate competitive adsorption with gas molecules. Further, on the basis of adsorption heat and energy changes in coal-gas system, it concludes that CH4 molecules on the coal surface always keep physical adsorption, but CO2 molecules are dominated by physical adsorption with weak chemical adsorption. Finally, the relationship among chemical composition and structure, nanopores and gas adsorption is established to reveal the microscopic coupling effect during gas adsorption.

Molecular Simulation Study Based on Adsorption of Gas (CO2,O2,CH4) on Coal

This study aimed to further explore the adsorption properties of different gases (CO2, O2, and CH4) on the coking coal surface by establishing a molecular model. Changes in the absolute adsorption capacity and the isosteric heat of adsorption of gases under different temperatures, pressures, and compositions were simulated using grand canonical Monte Carlo (GCMC) and molecular dynamics simulations. Interaction energy and energy distribution were used to analyze the adsorption behavior of gases, and the diffusion properties were investigated using the diffusion coefficient and diffusion activation energy. The absolute adsorption results fit well with the Langmuir–Freundlich model. The absolute adsorption capacity had a significant positive correlation with pressure and the corresponding mole fraction, and a significant negative correlation with temperature. The competitiveness, based on binary adsorption selectivity, was in the order of CO2 &gt; O2 &gt; CH4. The isosteric heat of adsorption of CH4 was slightly higher than that of O2, and that of CO2 was 1.49–1.64 times that of O2 and CH4. The isosteric heat of the adsorption of gases was also barely influenced by temperature and pressure. The interaction energy between CO2 and coal was greater than that of O2 or CH4, but the high pressure and high content were not conducive to the adsorption of O2 by CO2. The preferred adsorption site for CO2 was stronger than that for O2 and CH4, and its peak value negatively correlated with the molar fraction. The diffusion coefficient for single component gases initially increased and then decreased with increased pressure, showing a positive correlation with temperature. A close inverse correlation existed between diffusion activation energy and pressure. These results revealed the microscopic adsorption and diffusion regularities of CO2, O2, and CH4 in the coal model, indicating great significance in accurately predicting coal fires.

Direct characterization of gas adsorption and phase transition of a metal organic framework using in-situ Raman spectroscopy

Adsorbents are widely used in gas separation and storage processes. Performance improvements are largely achieved through the continual development of new materials with unique sorption properties. Adsorption characterization techniques, therefore, play a central role in material research and development. Here, in-situ Raman spectroscopy is presented as a multi-purpose laboratory tool for analyzing adsorption performance. In contrast to conventional laboratory techniques requiring macroscopic samples, adsorption analysis via Raman spectroscopy can be performed on samples of less than 1 mg. Furthermore, simultaneous Raman multi-phase measurements of the adsorbent structure as well as the free and bound adsorbate, are shown to provide molecular insights into the operation of functional adsorbents at conditions representative of industrial applications, which are often not attainable in conventional crystallography. Firstly, a Raman-based method is demonstrated for directly quantifying absolute adsorption capacity within individual particles. The technique is validated for Raman measurements of carbon dioxide on silica gel and compared to gravimetric and volumetric analyses. Secondly, Raman spectroscopy is applied to study a novel functional material, ZIF-7, and directly probe its pressure-regulated gate-opening mechanism, which was only observed through indirect means. These Raman measurements confirm that the sharp increase in capacity corresponds to a structural transition in the material and reveal that multiple adsorption sites contribute to the overall capacity. The Raman methods presented here can be applied to a wide range of adsorbent-adsorbate systems and present a basis for further studies into the kinetics of sorption processes.

Determination of adsorption parameters in shale gas resource/reserve calculation: Case study of Wufeng Formation–Longmaxi Formation in the Sichuan Basin

In the calculation of shale gas resources/reserves, isothermal adsorption parameters are mainly determined by dry sample data at the laboratory temperature, and the regression effect of total organic carbon content (TOC) isothermal adsorption parameters is poor. Based on the physical significance of key parameters in Langmuir and Henry adsorption models, the problems in determining the isothermal adsorption parameters in the calculation of shale gas reserves/reserves are analyzed by taking the marine shale in the Upper Ordovician Wufeng Forming–Lower Silurian Longmaxi Formation in the Sichuan Basin as an example. Based on a large number of measured isothermal adsorption data, the effects of TOC, temperature and water saturation on the shale gas adsorption parameters are analyzed. The influence model of TOC, temperature and water saturation on isothermal adsorption parameters of shale gas is established, and a novel method for calculating the adsorption parameters of shale gas from under experimental conditions to original reservoir conditions is proposed. The results are obtained as follows. First, there are problems in the calculation of shale gas resources/reserves, such as poor and contradictory fitting relation between isothermal adsorption parameters and TOC, difficulty in the conversion of Van't Hoff equation, and difficulty in direct application of water saturation (Sw) in resource/reserves calculation. Second, the problem of poor direct fitting relation between Langmuir pressure (pL) and TOC is solved by integrating the Langmuir adsorption model with the Henry adsorption model and by establishing a new parameter – Henry constant a for methane adsorption capacity of shale. Third, when Sw<40%, the Langmuir volume (VL) is linearly negatively correlated with Sw; when Sw<20%, a is constant relatively; by establishing the relationship between the normalized absolute adsorption capacity and Sw (<50%) under the pressure exceeding 30 MPa, the effect of Sw on the isothermal adsorption capacity can be calculated. Fourth, the in-situ stress in the Wufeng Formation–Longmaxi Formation shale reservoir affects the adsorption capacity of shale. For shale reservoirs with the same TOC, the higher the in-situ stress, the smaller the VL and a values. Under high pressure (>30 MPa), the effect of Sw on the methane adsorption capacity of shale shows a similar trend, and the effect of water molecules on the adsorption capacity on shale pore surface is constant. It is concluded that the proposed novel method for determining the isothermal adsorption parameters of shale with different TOC, temperature and water saturation conditions provides a technical support for the accurate calculation of shale gas resources/reserves and contributes to the scientific development of shale gas industry.

Isothermal adsorption characteristics of various phases of CO2 and CH4 in different rank coals

ABSTRACT Using the remaining coal seams of closed coal mines for CO2 geological storage can effectively slow down the greenhouse effect and realize the redevelopment and utilization of closed coal mines. The burial depth of coal seams in closed coal mines in China covers an extensive range, and CO2 and CH4 could exist in various phases in the coal. The existing experimental objects for CO2 adsorption in coal are mainly associated with the supercritical and gaseous phases, and a research gap comparison between the CO2 adsorption characteristics in the liquid phase and those of other phases is very obvious. Herein, the isotherm adsorption experiments of CO2 and CH4 in different phases on different rank coal samples are methodically conducted in the pressure range of 0-12MPa. The experimental results indicate that the excess adsorption capacity of gaseous CO2 and CH4 (gas pressure <4MPa) rapidly raises with the growth of the adsorption pressure; however, a significant difference for the case of the medium- and high-pressure stage (>4MPa) is detectable. With the growth of the adsorption pressure, the excess adsorption capacity of the supercritical CH4 gradually reaches the maximum value and then remains stable, where the maximum experimental value is 1.009 mmol/g. While the excess adsorption capacity of CO2 near the critical pressure of liquid and supercritical state rapidly reduces and then tends to be stable. The maximum adsorption capacity is capable of touching 2.096 mmol/g, which is stable around 0.5 mmol/g. The analysis indicates that the change in the excess adsorption amount of CO2 near the critical pressure corresponds to the change in its density. The absolute adsorption capacity of CO2 and CH4 monotonically grows in the pressure range of 0-12MPa, and the absolute adsorption capacity of the same coal sample follows the following order: liquid CO2 > supercritical CO2 > CH4. The maximum adsorption capacity values for these substances in order are 2.493, 2.345, and 1.296 mmol/g. With the growth of the coal rank, the Gibbs free energy, specific surface area, and adsorption capacity of the understudied coal samples exhibit a U-shape relationship as a function of their coal ranks.

Thermochemical method for controlling pore structure to enhance hydrogen storage capacity of biochar

Developing new carbon-based hydrogen storage materials can significantly promote solid-state hydrogen storage technology. Biochar with high hydrogen storage capacity can be prepared by KOH melt activation, which has a high proportion of micropores (96.56%) compared with the porous carbon in the existing literature. Its specific surface area and pore volume are 2801.88 m2/g and 1.44 cm3/g, respectively. The size of the nanopores is affected by the activation ratio, but the temperature has little effect at the low activation ratio. SEM results show that the KOH activation process gradually shifts from the biochar's inside to the outside. A low KOH/char ratio (less than 2:1) can promote the formation of small aromatic rings. Due to its high specific surface area and microporosity, the absolute adsorption capacity of hydrogen in biochar is 2.53 wt% at −196 °C and 1 bar, rising to 5.32 wt% at 50 bar. The hydrogen adsorption process conforms to the Langmuir model. Microporous, mesoporous, and macroporous exhibit different hydrogen adsorption characteristics in various pressure ranges. However, ultramicroporous (<0.7 nm) always plays a decisive role in the hydrogen storage of biochar.

Construction of Deoxynivalenol Enrichment and Detection System Based on Magnetosome Surface Display

Deoxynivalenol (DON) is a mycotoxin commonly found in cereals. It has strong toxicity with high stability, thus it is easy to remain in food and cause serious poisoning symptoms to consumers. To establish an efficient and simple DON detection system, a biological nano magnetic particle called bacterial magnetosomes (BMs) extracted from magnetotactic bacteria with ultrasonic crushing and magnetic adsorption was used in this study. A single-stranded DNA aptamer specifically binding to DON was coupled to the surface of MBs by two different crosslinking agents, glutaraldehyde and polyethyleneimine (PEI), respectively, to synthesize two kinds of BMs-aptamer complexes for enriching DON. Then, the adsorption rate of the complex to DON was determined by HPLC. In the results, the absolute DON adsorption capacity of 1 mg BMs-aptamer complex was 27.24 ng when glutaraldehyde was used as crosslinker and 27.64 ng when PEI was used as crosslinker. The optimization results of desorption conditions showed that under the optimal elution conditions (DNase I+methanol for 2 times), the elution rate of DON adsorbed by BMs-glutaraldehyde-aptamer reached 72.7%, while the elution rate of DON adsorbed by BMs-PEI-aptamer complex reached 64.1%. Overall, the current study enriched the applications of magnetosomes in mycotoxin detection, and also provides new idea for the efficient enrichment and recovery of DON.

Thermodynamic analysis of the difference in adsorption characteristics of CH4 and CO2 on continental shale

In order to explain the difference in adsorption characteristics of CH4 and CO2 on continental shale from the perspective of thermodynamics, the isothermal adsorption experiments of CH4 and CO2 adsorbed by shale in Yanchang Formation in Ordos Basin were carried out, and the excess adsorption capacity was corrected to absolute adsorption capacity. Then the Clausius-Clapeyron equation was used to analyze the isosteric heat of adsorption of CH4 and CO2 on shale. The results show that, for calculating the absolute adsorption capacity, Ozawa empirical formula or Van der Waals approximation method should be used to calculate the adsorption phase density. The absolute adsorption capacity should be selected as the basic data for calculating the isosteric heat of adsorption. The reason is that the excess isosteric heat of adsorption has a negative value in the low adsorption capacity stage, which is contradictory to the fact that the adsorption process is exothermic, and is significantly higher than the absolute isosteric heat of adsorption. There is a good linear positive correlation between the isosteric heat of adsorption and the adsorption amount of CH4 and CO2 adsorbed by continental shale, and the isosteric heat of adsorption of CH4 is greater than that of CO2. The absolute initial isosteric heat of adsorption of CH4 and CO2 adsorbed by shale is 52.04 kJ/mol and 27.71 kJ/mol, indicating that the adsorption force of CH4 on Yanchang Formation shale is stronger than that of CO2.

Molecular Simulation of Methane Adsorption Behavior on Coal: Effects of Maturity and Moisture Content

Abstract The adsorption behaviors of multiphase fluids in coal are vital for estimating their transfer and flow mechanisms. In this study, taking the classical coal structures as instances, the impacts of maturities and moisture contents of coal on the methane adsorption capacities and thermodynamic properties were analyzed and determined by molecular simulations. Specifically, the simulated pressures were varied from 0 to 16 MPa, and three temperatures (298 K, 323 K, and 348 K) were considered. In addition, the competitive adsorption capacities of water/methane molecules were evaluated and the critical value of moisture content affecting the isosteric adsorption heat of methane was determined. Furthermore, a quantitative relationship between the gas adsorption amount and adsorption equilibrium pressure under a three-phase “solid–gas–liquid” action was established. The simulated results showed that taking the intermediate-rank coals as examples, the absolute adsorption capacities of methane molecules on different moist coals reduced by 28.3%, 35.1%, 46.9%, and 62.3%, respectively (at uniform pressure–temperature status) in comparison to their dry status. In addition, when the moisture content was lower than 1.4 wt%, the average isosteric adsorption heat remained almost stable. However, when the moisture content exceeded 1.4 wt%, the average isosteric adsorption heat increased sharply with the increase in the water content. Finally, linear function formulas yielded a good fitting accuracy range for the low- and intermediate-rank coals; in comparison, for the high-rank coal, an exponential function formula obtained a better fitting accuracy than a linear one.

Enhanced selective electrosorption of Pb2+ from complex water on covalent organic framework-reduced graphene oxide nanocomposite

Selective capture of the toxic and ubiquitous heavy metal ions is crucially desired yet still significant challenge for water purification. Herein, a covalent organic framework-reduced graphene oxide nanocomposite (TpPa@rGO) was developed and employed as cathode for the first time to selectively remove Pb2+ from complex water via an electrosorption process. Specifically, the rGO provides the electrical conductivity and induces the electric double layer capacitance to attract cations approaching to the electrode surface, while the TpPa endows abundant highly selective redox-active sites to capture Pb2+. Thanks to the ingenious synergy of capacitive rGO and redox-active TpPa, more than 99.6% of Pb2+ can be effectively removed by the TpPa@rGO electrode in a mixed solution containing Pb(NO3)2 (50 mg L−1) and multicomponent nitrates (100 mg L−1 for each), as well as good cycling stability. Interestingly, the interfering ions can serve as additional electrolytes to accelerate the accumulation of Pb2+ around the TpPa@rGO electrode instead of competing for active sites, thereby increasing the absolute adsorption capacity of Pb2+ from 94.6 mg g−1 in single Pb(NO3)2 solution to 129.8 mg g−1 in the multicomponent solution. The enhanced selective electrosorption mechanism on Pb2+ removal by TpPa@rGO and their recyclability were also investigated. The capacitive matrix and additional electrolytes accelerate the ion transfer and enhance ion accessibility to the electrode, thereby anchoring the Pb2+ on the N/O groups of TpPa. This study may put forward a promising method for the selective capture of heavy metal ions in complex water.

Feasibility study on CO2-rich industrial waste gas storage and replacement in carbonate gas reservoir based on adsorption characteristics

The emission of CO2-rich industrial waste gas (CO2-rich IWG) poses a huge challenge to environmental protection. If the CO2-rich IWG could be used directly or after simple treatment for underground storage and replacement, then clean utilization of CO2-rich IWG will certainly be promoted. In this paper, the feasibility of CO2-rich IWG for underground storage and replacement in carbonate gas reservoirs was studied from the perspective of gas adsorption characteristics. Firstly, the reliability of the molecular model was verified by fitting Monte Carlo simulation data of four representative gases with isothermal adsorption experimental data. Then, molecular dynamics simulation was used to study the adsorption mechanism of various components on the calcite surface in CO2-rich IWG. Finally, the competitive adsorption mechanism between CO2-rich IWG and methane, and the multi-component competitive mechanism between dominant gases are studied. The results show that the adsorption capacity of each component on calcite surface is HF > CO2>SO2>H2S > NO2>CH4>CO. Hydrogen bond and electrostatic force are the main adsorption forces of HF. The electrostatic force between negatively charged atoms in the molecule and Ca2+ is the main adsorption force for CO2, SO2 and H2S. The weak van der Waals force is the main adsorption force for NO2, CH4 and CO. In the competitive systems, the absolute adsorption capacity of CO2-rich IWG is reduced by 25–50% compared with single component adsorption. However, in the competitive adsorption systems of HF/CH4, CO2/CH4, H2S/CH4 and SO2/CH4, the relative adsorption capacity of the four industrial waste gases to methane is increased by 9 times, 5.5 times, 4 times and 3.75 times as compared with the non-competitive ones. In the competitive adsorption systems of HF/CH4, CO2/CH4, H2S/CH4, and SO2/CH4 the negatively charged atoms are more likely to combine with Ca2+ to generate strong electrostatic attraction, while generating electrostatic repulsion to the negatively charged C atoms in CH4, leading to the weakening or even disappearance of CH4 adsorption. Therefore, CO2-rich IWG has a good application prospect in carbonate gas reservoirs, but the CO and NO2 should be removed before use.

Thermodynamic Characteristics of CH4 Adsorption on Shale at Different Temperatures

In order to clarify the effect of temperature on the isosteric heat of adsorption of CH4 onto shale, by using the isothermal adsorption data of shale in the temperature range of 300~473 K and the pressure range of 0.08~14 MPa, the isosteric heat of adsorption is calculated, respectively, in the temperature range of 300~308 K, 338~373 K, and 423~473 K. The results show that the influence of temperature on the isosteric heat of adsorption of CH4 onto shale is mainly reflected in three aspects: the variation range of the isosteric heat of adsorption, the absolute adsorption capacity at which the isosteric heat of adsorption reach the maximum, and the change rate of the isosteric heat of adsorption. Specifically, as the temperature range moves to a higher range, the variation range of the isosteric heat increases significantly, and the absolute adsorption capacity decreases. The curve shape of the change rate of the isosteric heat of adsorption in different temperature ranges remained the same (decreased first and then increased), but the change rate increased gradually as the temperature range moved to a higher temperature range.

Characterization of the Lower Cretaceous Shale in Lishu Fault Depression, Southeastern Songliao Basin: Implications for Shale Gas Resources Potential

Large thickness of shales over 180.0 m was developed in the source rocks of the Shahezi and Yingcheng formations in the Lishu Fault Depression. Moreover, the high amount of gas content and the total hydrocarbon value of gas logging in several boreholes illustrate that there is a great potential of shale gas resources in this region. Therefore, an integrated characterization of shales from the lower Cretaceous Shahezi and Yingcheng formations was provided to evaluate shale gas resources potential. The measurement results illustrated that the organic-rich shale samples with kerogen type Ⅱ during high to over thermal maturity had a higher content of brittle minerals (&gt;50%) and clay mineral dominated by illite. The shales had a total porosity of 3.11–4.70%, a permeability of 1.24 × 10−3–1.52 × 10−3 μm2, and possessed pore types including dissolution pores, inter-layer pores of clay minerals, micro-fractures, intra-granular pores, and organic pores, which were dominated by micropores and mesopores (0.5–1.7 nm, 2.2–34.3 nm) with a significant contribution from OM and clay minerals. According to the N2 adsorption isotherms, the pore volume was comprised primarily of mesopores with mean widths of 4.314–6.989 nm, while the surface area was comprised primarily of micropores with widths in ranges of 0.5–0.8 nm and 1.0–1.7 nm. Thus, the shales have a suitable porosity and permeability, indicating that fine storage capacity and favorable gas flow capacity occur in the Shahezi and Yingcheng formations, which exhibit a good reservoir quality and excellent exploration potential since the considerable thickness of shales could form a closed reservoir and served as cap rocks for in situ gas generation and accumulation. Especially, according to the measured CH4 excess adsorption amount and the calculated maximum absolute adsorption capacities of CH4 based on the Langmuir adsorption model, the estimated GIP values (1.388–3.307 m3/t) of the shales happened to be in a sampling depth under geological hydrostatic pressure and temperature conditions. This means that the shale storage capacity and high gas content from well site desorption completely met the standard of industrial exploitation when synthetically considering the GIP model. As a consequence, shales in the Shahezi and Yingcheng formations in the Lishu Fault Depression could be potential targets for shale gas exploration.

Nitrogen Atom-Doped Layered Graphene for High-Performance CO2/N2 Adsorption and Separation

The development of high-performance CO2 capture and separation adsorbents is critical to alleviate the deteriorating environmental issues. Herein, N atom-doped layered graphene (N-MGN) was introduced to form triazine and pyridine as potential CO2 capture and separation adsorbents via regulation of interlayer spacings. Structural analyses showed that accessible surface area of the N-MGN is 2521.72 m2 g−1, the porosity increased from 9.43% to 84.86%. At ultra-low pressure, N-MGN_6.8 have exhibited a high CO2 adsorption capacity of 10.59 mmol/g at 298 K and 0.4 bar. At high pressure, the absolute adsorption capacities of CO2 in N-MGN_17.0 (40.16 mmol g−1) at 7.0 MPa and 298 K are much larger than that of N-doping slit pore. At 298 K and 1.0 bar, the highest selectivity of CO2 over N2 reached up to ~133 in N-MGN_6.8. The research shows that N doping can effectively improve the adsorption and separation capacity of CO2 and N2 in layered graphene, and the interlayer spacing has an important influence on the adsorption capacity of CO2/N2. The adsorption heat and relative concentration curves further confirmed that the layered graphene with an interlayer spacing of 6.8 Å has the best adsorption and separation ability of CO2 and N2 under low pressure. Under high pressure, the layered graphene with the interlayer spacing of 17.0 Å has the best adsorption and separation ability of CO2 and N2.

Feasibility study on using CO2-rich industrial waste gas replacement for shale gas exploration based on adsorption characteristics

Clean utilization of CO2-rich industrial waste gas (CO2-rich IWG) is of great significance to realize carbon neutralization. Due to the strong adsorption capacity of clay and organic matter in shale to CO2, it has a good potential for CO2-rich IWG storage and replacement. So, the feasibility of using CO2-rich IWG replacement for shale gas exploration from the perspective of adsorption was studied. A shale composite model was constructed based on the adsorption experiments, and the molecular simulation results were fitted with experiments for the model reliability. Then, the slit models of different minerals were constructed to study the adsorption mechanisms. Finally, the competitive adsorption mechanisms of different components with CH4 were revealed. The results show that the overall adsorption capacity on shale minerals are ranked as HF > CO2 > SO2 > H2S > NO2 > CH4 > CO；Hydrogen bond and electrostatic force are the main adsorption modes of HF, and electrostatic force between negatively charged atoms of gas molecule and mineral surface is the main adsorption modes of CO2, SO2 and H2S. That of NO2, CH4 and CO is the weak van der Waals force. In the competition with CH4, the absolute adsorption capacity of gas decreases, but the relative adsorption capacity increases. The relative adsorption capacities of HF, CO2, H2S and SO2 increase by 35, 26, 15 and 12 times, respectively. During competitive adsorption, negatively charged atoms in HF, CO2, H2S and SO2 are more likely to bind with free cations on the surface of illite and smectite, and generate electrostatic repulsion for C atoms in CH4, leading to the weakening or even disappearance of CH4 adsorption capacity.

Adsorption characteristics and controlling factors of marine deep shale gas in southern Sichuan Basin, China

Deep shale gas (3500–4500 m) is the important replacement field of shale gas production growth in the future China. The research on key parameters of deep shale-gas reservoir is critical to determine its basic geological characteristics and establish a suitable development mode. In order to clarify the adsorption characteristics and controlling factors of deep shale gas in Longmaxi Formation, the main tests such as high-pressure methane adsorption, low-temperature nitrogen and carbon dioxide adsorption coupled with the adsorption fitting model and comparative analysis were conducted. The results show that the adsorption isotherms of deep shale gas also have a downward trend in spite of the higher pressure, and there is no obvious difference in adsorption characteristics, which is mainly due to the similar characteristics of microscopic pore-structure between deep shale and shallower shale. It is found that different adsorption models can well fit the experimental adsorption curve of deep shale gas, but the absolute adsorption capacity converted from excess adsorption capacity shows the same fitting result, i.e., DA-LF model > DR model > Langmuir model. Furthermore, DR model based on micropore filling theory is more suitable for characterizing the adsorption law of deep shale gas combined with the correlation analysis between pore structure and adsorbed-gas capacity. In addition, TOC is the key material factor controlling the adsorption capacity, and specific surface area of micropore is the key spatial factor. Compared to shallower shale, the deep shale shows higher siliceous content, lower calcite content, lower TOC content and lower adsorbed-gas content (the proportion of adsorbed-gas is about 30%).