Gas Adsorption Ability Research Articles

DFT-based adsorption studies of CNCl, HCN, and NH3 on metal-doped diamane

Density functional theory was used to comprehensively investigate the adsorption of cyanogen chloride (CNCl), hydrogen cyanide (HCN), and ammonia (NH3) by metal-doped diamanes. Because the weak gas adsorption ability of pure diamane renders it unsuitable for use as a gas sensor, the adsorption performance thereof was enhanced by doping with alkaline earth and transition metals. The adsorption capacities of monometallic-doped diamanes improved significantly for CNCl, HCN, and NH3. Notably, Be-doped diamane (BeD) delivered the highest adsorption performance for CNCl and HCN, whereas the addition of Au, Ag, and Cu, respectively, to diamane as dopants (AuD, AgD, and CuD) demonstrated enhanced adsorption effects for NH3. The adsorption capacities of the bimetallic co-doped diamanes for CNCl, HCN, and NH3 were significantly enhanced. In particular, diamane co-doped with Cu and Ag (Cu-AgD) exhibited superior adsorption for HCN and NH3, whereas Au and Cu co-doped diamane (Au-CuD) and Au and Ag co-doped diamane (Au-AgD) demonstrated improved adsorption effectiveness for NH3. The charge transfer, band gap, density of states, and charge density differences of these adsorption systems were investigated. Finally, recovery time analysis identified AuD, AgD, CuD, Au-CuD, Au-AgD, and Cu-AgD as potential candidates for reusable sensors.

Study on the Catalytic Activity Modification of Pr and Nd Doped Ce0.7Zr0.3O2 Catalysts for Simultaneous Removal of PM and NOX

Cerium-zirconium composite oxides (Ce0.7Zr0.3O2) have a remarkable effect on catalytic removal of carbon particles (PM) and nitrogen oxides (NOX) emitted from diesel engine, in order to further improve the thermal stability, oxygen storage capacity and low temperature catalytic REDOX performance of cerium zirconium composite oxides (Ce0.7Zr0.3O2), a small amount of Pr and Nd rare earth elements are doped to improve the catalytic activity of cerium zirconium composite oxides. In this paper, the composite oxide of Pr6O11–Nd2O3–CeO2–ZrO2 is prepared by unsteady co-precipitation method, and the physicochemical properties of the composite oxide catalyst are analyzed by BET, SEM, XRD and ICP. The gas adsorption capacity and catalytic activity of composite oxide catalysts are measured by temperature programmed reaction technology (TPR). The results show that the composite oxide of Pr0.05Nd0.05Ce0.6Zr0.3O2 prepared by using rare earth elements Pr and Nd inhibits the growth process of grain, refining the grain, and improving the sintering phenomenon at high temperature. The addition of Pr and Nd causes lattice defects, increases the number of oxygen vacancies, and improves the mobility of lattice oxygen, namely promotes oxide oxygen storage property, gas adsorption and catalytic oxidation reduction ability. After modification, Pr0.05Nd0.05Ce0.6Zr0.3O2 has good resistance to high temperature aging performance, prolongs the service life, reduces the PM lowest ignition temperature and minimum catalytic activity temperature of nitrogen oxide, and promotes the NOX reduction rate. For Pr0.05Nd0.05Ce0.6Zr0.3O2, the lowest ignition temperature of PM is about 150 °C, and the lowest catalytic activity temperature of NO is about 130 °C. The maximum CO2 production rate is 68.3%, and the maximum NO reduction rate is 45%.

Enhanced Field Emission and Low-Pressure Hydrogen Sensing Properties from Al-N-Co-Doped ZnO Nanorods.

ZnO nanostructures show great potential in hydrogen sensing at atmospheric conditions for good gas adsorption abilities. However, there is less research on low-pressure hydrogen sensing performance due to its low concentration and in-homogeneous distributions under low-pressure environments. Here, we report the low-pressure hydrogen sensing by the construction of Al-N-co-doped ZnO nanorods based on the adsorption-induced field emission enhancement effect in the pressure range of 10-7 to 10-3 Pa. The investigation indicates that the Al-N-co-doped ZnO sample is the most sensitive to low-pressure hydrogen sensing among all ZnO samples, with the highest sensing current increase of 140% for 5 min emission. In addition, the increased amplitude of sensing current for the Al-N-co-doped ZnO sample could reach 75% at the pressure 7 × 10-3 Pa for 1 min emission. This work not only expands the hydrogen sensing applications to the co-doped ZnO nanomaterials, but also provides a promising approach to develop field emission cathodes with strong low-pressure hydrogen sensing effect.

Highly sensitive Pt-functionalized In2O3/SnS2 nanoflowers to realize the rapid detection of H2S gas

Recently, SnS2 sensing material has received lots of attention in the application of gas detection owing to its merits of high physical affinity and appropriate bandgap width. Nevertheless, the gas sensors based on SnS2 sensing materials are subjected to the shortcomings of poor selectivity and long response/recovery induced by the low conductivity of SnS2 material. This article employs a secondary solvothermal method to prepare flower-like In2O3/SnS2 heterostructures modified by noble metal Pt nanoparticles to realize the rapid detection of H2S for the first time. The gas-sensing tests indicate that this heterostructure greatly improves the pure SnS2 material’s conductivity and enhances the adsorption capacity for H2S gas molecules. Compared with pure SnS2 and In2O3/SnS2 sensors, the Pt-In2O3/SnS2 sensor presents superior repeatability during multiple measurement cycles and excellent selectivity towards H2S at the optimum operating temperature of 220 ℃. The sensor also exhibits a fast response/recovery of 10 s/506 s together with a large gas response of 11.98 toward 200 ppm H2S. The strengthened sensing characteristics are primarily attributed to the abundant active sites in the Pt-In2O3/SnS2 composites, the excellent carrier transfer ability caused by the In2O3/SnS2 heterojunction, the strong gas adsorption ability induced by noble metal platinum, and the modulated Schottky barrier. Our work provides an effective route for the improvement of the gas sensitivity of SnS2-based H2S gas sensors.

Synthesis of magnesium hydroxide powder and dry powders for application in extinguishing petroleum fires

AbstractFire extinguishing agents are an important factor in the fight against fires. In this study, a new composite powder (CSPMS) was synthesized and used to extinguish fires caused by petroleum products. SiO2 nanoparticles, Mg(OH)2 nanoparticles, and nanocomposites of NH4H2PO4/chitosan (CSP) were combined to generate CSPMS powder. The structure and morphology of the material were characterized using methods such as XRD, SEM, FTIR, etc. The results showed that the synthesized Mg(OH)2 nanoparticle size ranged from 20 to 30 nm, and the NH4H2PO4 nanoparticle size ranged from 800 to 900 nm on the chitosan surface. The CSPMS material had particle sizes ranging from 2 to 3 µm, with a uniform distribution of SiO2 nanoparticles (50–100 nm) and Mg(OH)2 nanoparticles on the surface. The powdered materials were applied to extinguish gasoline and oil fires. CSPMS sample demonstrated the best fire extinguishing time and powder consumption (5.8 s and 12.2 g, respectively) and CO emission below the threshold of 400 ppm. Small‐scale fire extinguishing tests showed that CSPMS powder had better fire extinguishing capability, cooling time, and CO gas adsorption ability compared to commercial fire extinguishing powder.

DFT study on adsorption properties of TM(Ni, Co)Nx -doped graphene for high-temperature sensing of SF6 decomposed gases

Gas sensing is the key to online monitoring SF6 decomposition gases in gas-insulated switchgear (GIS) fault diagnosis. However, the gas sensors for high-temperature sensing of SF6 decomposed gases are still lacking. In this paper, the adsorption performance of TM(Co, Ni)Nx-doped graphene as gas-sensing materials for the SF6 decomposed gases of SO2, SOF2, and SO2F2 were studied by DFT calculations, especially for the case at high temperatures. The adsorption energy (Eads), adsorption distance (D), transferred charge (Qt), and molecular dynamics simulations were performed to study the gas adsorption ability of TMN2-doped graphene. The electronic structures were clarified by analysis of the density of states (DOS), the partial density of states (PDOS), electron density difference, and molecular orbitals. The molecular dynamics simulations at 873 K indicated the high thermodynamic stability of TM(Co, Ni)Nx-doped graphene, which promised their superior gas sensing performance to detect SF6 decomposed gases at high temperatures.

Specific Recognition and Adsorption of Volatile Organic Compounds by Using MIL-125-Based Porous Fluorescence Probe Material.

The severity of the volatile organic compounds (VOCs) issue calls for effective detection and management of VOC materials. Metal-organic frameworks (MOFs) are organic-inorganic hybrid crystals with promising prospects in luminescent sensing for VOC detection and identification. However, MOFs have limitations, including weak response signals and poor sensitivity towards VOCs, limiting their application to specific types of VOC gases. To address the issue of limited recognition and single luminosity for specific VOCs, we have introduced fluorescent guest molecules into MOFs as reference emission centers to enhance sensitivity. This composite material combines the gas adsorption ability of MOFs to effectively adsorb VOCs. We utilized (MIL-125/NH2-MIL-125) as the parent material for adsorbing fluorescent molecules and selected suitable solid fluorescent probes (FGFL-B1) through fluorescence enhancement using thioflavin T and MIL-125. FGFL-B1 exhibited a heightened fluorescence response to various VOCs through charge transfer between fluorescent guest molecules and ligands. The fluorescence enhancement effect of FGFL-B1 on tetrahydrofuran (THF) was particularly pronounced, accompanied by a color change from yellow to yellowish green in the presence of CCl4. FGFL-B1 demonstrated excellent adsorption properties for THF and CCl4, with saturated adsorption capacities of 655.4 mg g-1 and 811.2 mg g-1, respectively. Furthermore, FGFL-B1 displayed strong luminescence stability and reusability, making it an excellent sensing candidate. This study addresses the limitations of MOFs in VOC detection, opening avenues for industrial and environmental applications.

Enhanced charge transfer and photocatalytic carbon dioxide reduction of copper sulphide@cerium dioxide p-n heterojunction hollow cubes

Hollow structure hybrids have gained considerable attention for their ability to reduce CO2 owing to their rich active sites, high gas adsorption ability, and excellent light utilization capacity. Herein, a template-engaged strategy was provided to fabricate copper sulphide@cerium dioxide (CuS@CeO2) p-n heterojunction hollow cube photocatalysts using Cu2O cubes as a sacrificial template. The sequential steps of loading of CeO2 nanolayer, sulfidation, and etching reaction facilitate the formation of CuS@CeO2 p-n heterojunction hollow cubes. Compared with the single CuS, CeO2, and their physical mixture, the CuS@CeO2 p-n heterojunction hollow cube photocatalyst expresses a higher performance toward photocatalytic CO2 reduction under solid–gas reaction conditions due to the faster separation of photogenerated charges. The further enhanced performance of CuS@CeO2 p-n heterojunction hollow cubes was achieved by decorating pt nanoparticles due to the fact that Pt nanoparticles had a high electron affinity and CO2 adsorption capacity, and the highest CO and CH4 yields of the optimized hybrid reached 195.8 μmol g-1 h−1 and 19.96 μmol g-1 h−1, respectively. This work might provide a strategy for designing and synthesizing efficient hollow heterostructured photocatalysts for solar energy conversion and utilization.

Research on Pore-Fracture Characteristics and Adsorption Performance of Main Coal Seams in Lvjiatuo Coal Mine

Gas prevention and control have always been the focus of coal mine safety. The pore structure characteristics and gas adsorption characteristics of coal seams are the key factors affecting gas adsorption and diffusion in coal seams. Lvjiatuo Mine has the characteristics of a high gas content when it enters deep mining. In order to clarify the influence of the pore-fracture structure characteristics of main coal seams in the research area on coal seam gas adsorption and diffusion, and to study the differences in gas adsorption and diffusion ability in different coal seams, low-temperature nitrogen adsorption (LT-N2GA), high-pressure mercury intrusion (MIP) and computerized tomography (μ-CT) were used as characterization methods, and methane isothermal adsorption experiments were carried out to systematically study the pore structure characteristics of five groups of coal samples, and the pore-fracture structure characteristics and gas adsorption characteristics of each main coal seam were obtained. The results show that: (1) in the LT-N2GA experiment, the adsorption–desorption curves of all coal samples are of type III, and mainly develop cone-shaped pores or wedge-shaped semi-closed pores, with an average pore size of 1.84~4.84 nm, a total pore volume of 0.0010~0.0023 mL/g, a total specific surface area of 0.16~0.24 m2/g, and a fractal dimension D1 of 1.39~1.87 and D2 of 2.44~2.60. The micropores of L12 are more developed, and the mesopores and macropores of L9 are more developed. (2) In the MIP experiment, the porosity of coal samples is 3.79~6.94%. The porosity of L9 is the highest, the macropore ratio is the highest, and the gas diffusion ability is also the strongest. (3) In the μ-CT experiment, the porosity of L8-2 and L12 is 12.12% and 10.41%, the connectivity is 51.22% and 61.59%, and the Df is 2.39 and 2.30, respectively. The fracture of L12 is more developed, the connectivity is better, and the heterogeneity of the pore of L8-2 is higher. (4) In the isothermal adsorption experiment of methane, the gas adsorption capacity basically increases with the increase in the buried depth of the coal seam, and the gas adsorption capacity of the No.12 coal seam is the highest. Based on the pore-fracture structure characteristics and gas adsorption characteristics of the main coal seams in the research area, the gas outburst risk of each coal seam is ranked as follows: No.12 coal seam > No.8 coal seam > No.7 coal seam > No.9 coal seam. The experimental results provide important help for researching the structural characteristics of coal seam pore fractures and preventing gas outbursts during deep coal seam mining.

Multi-scale pore fractal characteristics of differently ranked coal and its impact on gas adsorption

Well-developed pores and cracks in coal reservoirs are the main venues for gas storage and migration. To investigate the multi-scale pore fractal characteristics, six coal samples of different rankings were studied using high-pressure mercury injection (HPMI), low-pressure nitrogen adsorption (LPGA-N2), and scanning electron microscopy (SEM) test methods. Based on the Frankel, Halsey and Hill (FHH) fractal theory, the Menger sponge model, Pores and Cracks Analysis System (PCAS), pore volume complexity (Dv), coal surface irregularity (Ds) and pore distribution heterogeneity (Dp) were studied and evaluated, respectively. The effect of three fractal dimensions on the gas adsorption ability was also analyzed with high-pressure isothermal gas adsorption experiments. Results show that pore structures within these coal samples have obvious fractal characteristics. A noticeable segmentation effect appears in the Dv1 and Dv2 fitting process, with the boundary size ranging from 36.00 to 182.95 nm, which helps differentiate diffusion pores and seepage fractures. The D values show an asymmetric U-shaped trend as the coal metamorphism increases, demonstrating that coalification greatly affects the pore fractal dimensions. The three fractal dimensions can characterize the difference in coal microstructure and reflect their influence on gas adsorption ability. Langmuir volume (VL) has an evident and positive correlation with Ds values, whereas Langmuir pressure (PL) is mainly affected by the combined action of Dv and Dp. This study will provide valuable knowledge for the appraisal of coal seam gas reservoirs of differently ranked coals.

CO gas adsorption and detection ability of boron nitride nanosheet doping with group 8B transition metal: A theoretical investigation

CO gas adsorption and detection ability of boron nitride nanosheet doping with group 8B transition metal: A theoretical investigation

Three-Dimensional Printing of Recycled Polypropylene and Activated Carbon Coatings for Harmful Gas Adsorption and Antibacterial Properties.

In recent years, the utilization of three-dimensional (3D) printing has been expanding due to advances in technology and economic efficiency. One of the 3D printing technologies is fused deposition modeling, which can be used to create different kinds of products or prototypes from various polymer filaments. In this study, the activated carbon (AC) coating was introduced to the 3D outputs printed using recycled polymer materials to impart multi-functions such as adsorption of harmful gas and antimicrobial activities. A filament of uniform diameter (1.75 μm) and a filter template in the form of a 3D fabric shape were prepared through the extrusion and 3D printing processes, respectively, of the recycled polymer. In the next process, the 3D filter was developed by coating the nanoporous AC, produced from the pyrolysis fuel oil and waste PET, on the 3D filter template through direct coating. The 3D filters coated with the nanoporous activated carbon showed the enhanced adsorption capacity of 1038.74 mg of SO2 gas and the antibacterial properties of 49% removal of E. coli bacteria. As a model system, a functional gas mask that has harmful gas adsorption abilities and antibacterial properties has been produced by a 3D printing process.

CO2 adsorption enhancement and charge transfer characteristics for composite graphene doped with atoms at defect sites

The massive emission of carbon dioxide in the world causes global warming and a series of increasingly serious ecological problems. It is urgent to find efficient adsorbent for large-scale CO2 capture. Graphene as a solid adsorbent has exhibited great potential and development prospects in gas adsorption. Doping atoms at defect sites in composite graphene is considered as one of the promising approaches to enhance the gas adsorption ability. Nevertheless, composite graphene doping with different atoms has not been explored to a large extent so far. In this work, vacancy graphenes with single C-vacancy (VI-G) and with double C-vacancies (VII-G) are doped with nitrogen atoms and metal atoms M (M = Co, Mo, Mn, Fe) to form composite configurations. The Perdew-Burke-Ernzerho (PBE) functional is used under the generalized gradient approximation (GGA) basis set. A comprehensive study of the adsorption effect and charge transfer characteristics of CO2 molecule on different composite graphene configurations is carried out through DFT calculation. By analyzing the adsorption energy, adsorption distance, energy band structure, and atomic Mulliken population, it is found that the composite graphene doped with metal atoms such as Co-3N-VI, Mo-3N-VI, Mn-3N-VI, Fe-3N-VI, and Mo-4N-VII significantly enhanced the CO2 adsorption. Further analysis of charge density and density of states (DOS) demonstrates that CO2 adsorption on M-3N-VI and M-4N-VII reached the same conclusion. Thus, it is concluded that appropriate metal atoms can enhance the adsorption characteristics.

Improved surface flashover voltage of epoxy following polythiourea-assisted coating with high gas adsorption ability

Surface flashover as a well-known discharge phenomenon on the gas–solid interface can lead to the failure of power equipment. Although intensive studies have been devoted to improving the flashover voltage in gases, the perspective on exploiting gas characteristics has so far been ignored. We here directly utilize a polythiourea-assisted coating on epoxy to achieve beneficial gas adsorption and enhance the flashover voltage. The results show that the flashover voltage of the polythiourea-assisted epoxy is significantly improved in both N2 and SF6 compared with the blank epoxy. Combining the experimental and computational results, it is proved that the striking improvement in the flashover performance is attributed to the increased gas adsorption quantity resulting from the unique thiourea units in polythiourea. Although both esters in epoxy and thioureas in polythiourea act as active function sites for guest gases, polar thioureas not only lead to pronounced charge displacements but also own the larger density, which further enhances the adsorption energy and promotes the gas adsorption. The resulting increased gas adsorption quantity prevents the collision ionization effectively, thus improving the flashover voltage. Our research innovatively proposes a functional polythiourea-assisted coating that can enhance the flashover voltage by improving the gas adsorption ability.

Adsorption Mechanism and Optical Behaviors of Typical Volatile Organic Compounds on Pristine and Cu/Ni‐Modified C3N Monolayer: A First‐Principles Study

AbstractIn this paper, the geometric and electronic structure of four gas molecules, including CH4, CH2O, CH3Cl and C6H6, on pristine and Cu/Ni‐modified C3N monolayer are investigated by using First principles. The calculations show that the Cu/Ni‐doping can effectively strengthen the gas adsorption ability of C3N. Upon gas‐C3N configuration, the adsorption energies are CH2O (0.11 eV) > C6H6 (0.09 eV) > CH3Cl (0.08 eV) > CH4 (0.05 eV). For Cu‐C3N configuration, the adsorption energies are C6H6 (3.26 eV) > CH3Cl (3.24 eV) > CH4 (3.22 eV) > CH2O (3.13 eV). For Ni‐C3N configuration, the adsorption energies are CH2O (1.48 eV) > C6H6 (0.66 eV) > CH3Cl (0.39 eV) > CH4 (0.11 eV). It is worth mentioning that the magnetic moment is reduced to 0 µB when CH2O are adsorbed on Cu/Ni‐C3N, and the maximum charge transfer is 0.71 e, 0.62 e, respectively. Moreover, its optical properties of adsorption of Volatile organic compounds (VOCs) gas molecules are studied. It can be found that the two main absorption peaks locate at 3.0 × 105 cm−1 nm and 2.8 × 105 cm−1 nm at the range of ultraviolet and visible light. The calculated results provide the theoretical reference for Cu‐C3N‐based VOCs sensors.

Study on coal molecular structure characteristics on methane adsorption performance under pyrolysis treatment

To reveal the effect of the molecular structure of coal on the gas adsorption ability of coal seams, this paper selects the high-quality bituminous coal in the Shenmu mining area of Shaanxi Province, China, as the research object. We changed the molecular structure of coal through pyrolysis experiments and studied the effect of changing coal molecular structure on methane adsorption capacity based on Langmuir adsorption equations, Infrared spectroscopy, X-ray diffraction, scanning electron microscopy and liquid nitrogen adsorption. The findings of the experiments reveal that d 002 reduces as pyrolysis temperature rises, but L a , N ave , and L c increase overall. The molecular structure of coal is restructured and layered, and the degree of polycondensation increases. Simultaneously, heating decomposes the active functional groups inside the coal sample, A C-O / A ar , A CH 2 / A CH 3 and A al / A ar decrease with the increasing pyrolysis temperature, and the aromatization degree of coal also deepens. The adsorption Langmuir constant a is well connected with d 002 , L a , N ave , L c , A C-O / A ar , A CH 2 / A CH 3 and A al / A ar . After high-temperature pyrolysis, A variety of chemical bonds in the coal sample are broken, resulting in the release of a substantial amount of light hydrocarbon, and then a large number of holes and cracks appear in the coal body, and the micropores are reduced, thus reducing the overall adsorption capacity of the coal. The findings of this study provide theoretical guidance for the development of new technologies to recover coal seam gas during mining.

Surface modification of tungsten oxide by oxygen vacancies for hydrogen adsorption

A model for describing the adsorption process of hydrogen on surface of tungsten oxide was proposed based on the first-principle calculations. Multiple factors such as type of active surface, adsorption site and distribution of oxygen vacancies were considered to evaluate the hydrogen adsorption capability of tungsten oxide. The adsorption Gibbs free energies, electronic structures and bonding characteristics under various conditions were examined to reveal the influence of oxygen vacancies on the surface. It is found that the capability of hydrogen adsorption of tungsten oxide can be significantly enhanced by adjusting the oxygen vacancy on the outermost layer of certain active surfaces. The modeling predicts that the surface structure stability and gas adsorption ability of tungsten oxide can be simultaneously improved through the formation of WH bonds. The proposed strategy for moderating surface provides a new approach to obtain excellent gas-sensitive metal oxide materials.

Pore Structure Characteristics and Adsorption and Desorption Capacity of Coal Rock after Exposure to Clean Fracturing Fluid.

In the hydraulic fracturing process, fracturing fluid contacts coal rock and physical and chemical reactions occur, which inevitably damage the pore structure of the coal rock and affect the adsorption and desorption capacity of the coal rock. In this paper, a low-temperature N2 adsorption method and scanning electron microscopy (SEM) were used to characterize coal samples. Using gas adsorption/desorption tests, high-, medium-, and low-rank coal samples before and after the clean fracturing fluid treatment were systematically studied. According to the relationship between coal pore structure parameters and gas adsorption/desorption characteristics, a correlation between the microscopic pore structure and the macroscopic gas adsorption/desorption characteristics of coal was obtained. The results show that the number of closed pores in high-, medium-, and low-rank coal samples increased after the clean fracturing fluid treatment. The micropore volume increased by 0.0009, 0.00143, and 0.0035 mL/g, respectively, and the specific surface area increased by 4.87, 9.06, and 57.60%. The fractal dimension also increased compared with that of raw coal. SEM analysis indicated that the influence degree of clean fracturing fluid treatment on the pore structure of different-rank coal samples was Gengcun low-rank coal > Pingba middle-rank coal > Jiulishan high-rank coal. The experimental results of methane adsorption and desorption showed that the adsorption capacity of the coal samples after clean fracturing fluid treatment was enhanced, which is related to increases in the micropore proportion, micropore volume, and specific surface area of the coal. The desorption capacity of the coal samples was also enhanced. The desorption rate of medium- and high-rank coal samples increased after the clean fracturing fluid treatment but that of low-rank coal samples decreased. The main reason is the increase in the number of micropores in low-rank coal, which enhances the gas adsorption ability and makes gas desorption difficult. Therefore, clean fracturing fluid is suitable for medium- and high-grade metamorphic coalbed methane mines. These research results provide a theoretical basis for the application of clean fracturing fluid in different coalbed methane wells.

Experimental investigation on the mechanism of low permeability natural gas extraction accompanied by carbon dioxide sequestration

The injection of CO2 into natural gas reservoir is regarded can increase natural gas recovery accompanied with CO2 sequestration. In this work, we first demonstrated that the gas adsorption ability in the sampled plunger low permeability sandstone core was only about 1/10 of that in the core powders, the former was more representative for use. The existence of bound water substantially weakened the gas adsorption in the core. The CO2 diffusion coefficients in low permeability cores were in the order of 10−8-10−9 m2/s, which increased with decreasing pressure but dramatically decreased with the existence of bound water. Last, long core experiments for natural gas recovery through CO2 flooding showed that the CO2 injection substantially increased the natural gas recovery ratio R. And we for the first time demonstrated that due to the higher CO2 density than that of natural gas through experiments, the CO2 injection at the relative low position showed higher R than that at the high injection position. And with the highest CO2 sequestration amount (M) reached 64.36 kg/m3. The injection of CO2 into low permeability natural gas reservoir to realize both natural gas recovery and CO2 sequestration are tested feasible and effective.

Effect of Mechanical Vibration with Different Frequencies on Pore Structure and Fractal Characteristics in Lean Coal

The mechanical vibrations caused by underground operations can easily lead to coal and gas outbursts in coal mines. Using the MVGAD-I experimental platform that we designed, the raw coal (0 Hz) was treated with vibration frequencies of 25, 50, 75, and 100 Hz, and the coal samples with different frequency vibrations were obtained. The total pore volume (TPV), specific surface area (SSA), pore size distribution, and the pore fractal dimension (PFD) of five coal samples were analyzed by mercury intrusion porosimetry and low-pressure nitrogen adsorption data. We found that the TPV, SSA, and PFD of the coal samples fluctuate with the increase of vibration frequency. The changes of the TPV and SSA of coal samples treated with 25 and 75 Hz vibrations were significantly greater than those subjected to vibrations of 50 and 100 Hz. Compared with the raw coal (0 Hz), the TPV and SSA of macropores, mesopores, and micropores increased the most in 75 Hz vibration coal sample. Therefore, the 75 Hz vibration excitation can improve the permeability of a body of coal mass and is conducive to the diffusion and seepage of coalbed methane and its production.. The influence of 25 Hz vibration on the TPV and SSA of macropores and mesopores is not obvious, but the TPV and SSA of minipores and micropores decrease significantly, which is not conducive to gas diffusion and adsorption. In addition, 25 and 75 Hz vibrations obviously damaged the fractal characteristics of both mesopores and micropores, resulting in the change of gas adsorption and diffusion ability. The rational use of a 75 Hz vibration is beneficial to both the production of gas and the prevention of outbursts, while a 25 Hz vibration should be avoided. The results are expected to reveal the microscopic mechanism of a vibration-induced outburst and provide theoretical guidance for employing the appropriate frequency of vibration to improve the rate of gas drainage and reduce the risk of outbursts.