Low-temperature Adsorption Research Articles

Multicomponent digital core construction and three-dimensional micro-pore structure characterization of shale

The components and pore structure of shale are complex due to the heterogeneous distribution of organic matter and the complex distributions of the minerals. The digital core, possessing the advantages of being economical and reusable, can be widely used to directly characterize the three dimensional (3D) micro-pore structure and to numerically simulate its physical properties. During construction of a digital shale core, it is a challenge to solve the multicomponent segmentation for the digital shale core, the contradiction between the sample size and image resolution, and the identification of the pore types in the 3D pore space. Therefore, an automatic workflow based on the gray gradient-maximum entropy-3D morphology was developed. The gray gradient-maximum entropy algorithm was used to segment each sub-image of focused ion beam scanning electron microscope images to generate segmented images. On this basis, the pore size distribution was optimized via 3D morphological erosion. Based on the concept of pore clusters, the organic and inorganic pores were identified using the 3D morphological method for the first time. The construction of a multicomponent digital shale core was realized. The 3D micro-pore structure of the organic and inorganic pores was characterized by pore connectivity, heterogeneity, and pore size distribution. The accuracy of the proposed method was verified using low-temperature N2 adsorption experiment data. The results of this study provide new insight into the multicomponent digital shale core construction and lay the foundation for the characterization of the petrophysical properties and micro-/nano-scale fluid flow simulations of shale.

Novel proposal and assessment of a solar-powered supercritical CO2 cycle integrated with adsorption desalination system for electricity, heating and desalination

This paper presents a thermodynamic performance evaluation of a novel solar based supercritical CO2 (S-CO2) cycle and low temperature adsorption desalination (AD) cycle for power, heating, and freshwater. This novel technology utilizes molten salt as a medium for thermal energy transfer in the solar tower collector and generates power and heating by utilizing the S-CO2 cycle, as well as the AD cycle with heat recovery using aluminium fumarate material to produce freshwater. A parametric investigation is established in order to numerically assess the influence of different parameters on the performance parameters of the novel proposed system. Results show that the thermal efficiency of the solar tower receiver improves from 89.12% to 90.53%, when DNI rises from 900 W/m2 to 1100 W/m2. The thermal and exergy efficiencies of the S-CO2 power cycle are found to be higher at 1100 W/m2 and it is ranged from 33.4% to 44.81% and 54.2%–72.52% respectively, with the rise in inlet pressure of the expander from 12000 kPa to 18000 kPa. In addition, the thermal efficiency of electrical and heating was obtained 25.33% and 10.13%, respectively, at operating conditions. The highest SDWP was achieved 12.5 m3/ton/day and 0.62 GOR at a fixed operating condition.

Ciprofloxacin Adsorption onto a Smectite–Chitosan-Derived Nanocomposite Obtained by Hydrothermal Synthesis

The employment of compounds obtained from natural sources to produce adsorbents and their application in the elimination of antibiotics from industrial effluents have gained significant attention because of their low production cost and sustainability. Herein, chitosan (biopolymer) and smectite (abundant clay mineral) were used for the low-cost and eco-friendly synthesis of a new type of adsorbent. A low-energy-consumption hydrothermal process was applied to the synthesis of the chitosan-derived carbon–smectite nanocomposite with cobalt (H_Co/C-S). The produced nanocomposite was characterized using elemental analysis, ICP-OES, XRPD, low-temperature N2 adsorption–desorption isotherms, FTIR analysis, and point of zero charge. H_Co/C-S (SBET = 0.73 m2 g−1, d001 = 1.40 nm, pHPZC = 5.3) was evaluated as a ciprofloxacin adsorbent in aqueous solution. Experimental data were fitted with different kinetic models and interpreted by selected adsorption isotherms. The pseudo-second-order model was found to be the most appropriate, while ciprofloxacin adsorption onto H_Co/C-S was best described by the Redlich–Peterson isotherm (R2 = 0.985). The maximum adsorption capacity of H_Co/C-S, according to the Langmuir isotherm (R2 = 0.977), was 72.3 mg g−1. Desorption and thermodynamic studies were performed. The obtained results indicated that the new hierarchically designed H_Co/C-S has promising potential to be further tested for application in real wastewater treatment.

Advantages of Structure and Electrochemical Properties of Graphene Prepared from Tectonically Deformed Coal.

Asa low-cost carbon-rich resource, coal has been widely used to prepare excellent electrochemical energy-storage carbon materials such as graphene. However, the different structures of carbon source will affect the performance of carbon materials. To explore the feasibility of preparing high-performance graphene from the carbon source affected by tectonic stress in coal, in this paper, series products of coal-based graphene are prepared by tectonically deformed coal (TDC) and normal structural coal (NSC). The structural parameters are characterized by HRTEM, XRD, Raman, and low-temperature CO2 and N2 adsorption, and the electrochemical performance of coal-based graphene lithium battery is tested by galvanostatic charge-discharge and cyclic voltammetry. The results show that tectonic stress makes the proportion of the medium-long aromatic fringes, preferred orientation degree (POD), and multilayer stacking in TDC aromatic fringes slightly higher than those in NSC. At the same temperature, the relatively large microcrystalline size, the high order degree, and more pore structures make the local molecular oriented (LMO) domain vertical height (d) and graphitization degree (G) of the coal-based graphite microcrystalline structure prepared by TDC better than those of NSC, which indicates that the carbon source in TDC contains more graphitizable carbon structures. This makes the graphene prepared by TDC not only possess perfectly ordered crystal planes but also relatively abundant nanochannels. High lithium-storage capacity and low charge-transfer resistance make the electrochemical performance of graphene prepared by TDC as an anode electrode material for lithium-ion batteries superior to that by NSC.

Magnetic Carbon Nanocomposites: Preparation from Cellulose via Chemical Activation with FeCl3 and Characterization

We have studied the preparation of magnetic graphitic carbon composites, which combine the adsorption properties of activated carbon with magnetic properties and properties intrinsic to graphite. The preparation method is efficient; it comprises modifying flax shive cellulose with citric acid to enhance the chelating ability of the flax shive cellulose matrix, impregnating the modified cellulose with iron chloride, and pyrolysis in an inert atmosphere to control the composition, morphology, specific surface, and porosity of hybrid carbon materials. The scenario of cellulose matrix pyrolysis was suggested using thermogravimetry. X-ray structural analysis was used to characterize the graphitic composites. The citric acid modification of cellulose helps to prepare a high-graphite (74%) carbon composite where the graphitization level of the graphite structure approaches the graphitization level of commercially available graphite at 700°С. Low-temperature N2 adsorption–desorption and ζ-potential measurements helped to suggest the adsorption mechanism for environmentally hazardous dyes. The greatest equilibrium adsorption of Methylene Blue (MB) and Methyl Orange (MO) dyes was 127.4 and 23.7 mg/g, respectively. The prepared composites can be used as adsorbents and fillers in polymer composite materials.

Recovery of Metal Ions from Aqueous Solutions by γ-Alumina Creates Value-Added Catalyst Products

Mining and extracting metals from hard rock adversely impact the environment. These impacts could be mitigated by capturing dissolved metals from water (i.e., mine runoff, industrial wastewaters, or even tap water) and converting the metals to products with potential economic benefits (i.e., upcycled into high-value products). We sought to identify a sorbent that can remove dissolved metals from water and in the process of this low-temperature surface adsorption create a catalytic material of potential economic value. We discovered that γ-aluminum oxide (γ-Al2O3) can produce a reactive catalyst after removing metal ions (copper (Cu), palladium (Pd), nickel (Ni), and cobalt (Co)) from water, even for dissolved metals at environmentally relevant concentrations. The resulting metal-coated γ-Al2O3 behaved, comparable to high-temperature produced catalysts, as a mono- or bimetallic catalyst capable of oxidizing or reducing pollutants (methylene blue, 4-nitrophenol, nitrite, and nitrate). Mono- or bimetallic catalysts synthesized from tap water with metal ions present efficiently oxidized methylene blue (by Cu/γ-Al2O3) or reduced nitrate (by Pd–Cu/γ-Al2O3) into less harmful species (i.e., ammonium and dinitrogen gas). Results demonstrated the versatile use of γ-Al2O3 that removes metal ions from water (i.e., water purification) and produces a valuable γ-Al2O3-based byproduct with proven catalytic reactivity (i.e., catalyst production) and commercial markets.

A complementary VOCs recovery system based on cryogenic condensation and low-temperature adsorption

The control of volatile organic compounds (VOCs) emission has a significant influence on the environment and human health. Liquid nitrogen (LN2) condensation is a highly efficient method for VOCs recovery with a wide range of applications, but it is poor in the treatment of light hydrocarbons, especially methane and ethane, and has some shortcomings such as high emission concentration and large carbon emissions. In this paper, a novel cryogenic condensation system combined with low-temperature adsorption was proposed. The low-temperature exhaust gas treated by cryogenic condensation equipment is introduced into an adsorption bed, resulting in lower temperature and higher adsorption capacity of the adsorption bed, which not only effectively improves the recovery rate of VOCs, but also solves the spontaneous combustion problem caused by the adsorptive heat effect of traditional room-temperature adsorption method. A thermodynamic calculation model was established, and related experimental verifications were carried out. The results show that the economic value of the recovered VOCs condensate is 1.24 times of the cost of consumed LN2 and the carbon emission reduction is 1683 t per year, achieving an acceptable breakthrough time of 16,971 s at an adsorption temperature of 198.15 K exceeding that at 238.15 K by a factor of 16 when the cryogenic condensation temperature is 138.15 K with a 600 m3/h of waste gas. The effects of cryogenic condensation temperature, adsorption temperature, inlet gas concentration, flow rate, and the proportion of components on the system performance are analyzed in detail.

Quasi-isothermal (Q-TG), cryoporometric (DSC) and adsorption characterization of activated carbons

In the presented paper, the structural and energetic heterogeneities of the activated carbons (ACs) surfaces were investigated. The ACs of well-developed microporosity were obtained from the spent coffee grounds as a result of pyrolysis (N2 or CO2) with the chemical activation of H3PO4 (I = 1, 1.5 or 2 w/w). The low-temperature N2 adsorption, the quasi-isothermal thermogravimetry as well as the low-temperature differential scanning calorimetry were employed. Moreover, the selected materials adsorption properties were studied in relation to methylene blue (MB). The micro/mesoporous structure of the carbons was proved. The different types of water clusters on the surface indicated the carbons surface heterogeneity. The activated carbons are characterized by the high sorption capacity (qe,exp = 200.3–237.67 mg g−1) as for MB. The adsorption process was described by means of the Radke–Prausnitz isotherm model.Graphical abstract

Effect of Modifying the Clinoptilolite-Containing Rocks of Transcarpathia on Their Porous Characteristics and Catalytic Properties in the Conversion of C6-Hydrocarbons

The efficiency of modifying the Ukrainian clinoptilolite-containing rocks to improve their adsorption and catalytic properties was evaluated based on the data of XRD, IR spectroscopy, low-temperature N2 adsorption, and testing in the micropulse catalytic transformation of C6-hydrocarbons. The effect of such modification on the distribution of reaction products was established.

Effect of Soaking Time on the Spontaneous Combustion Characteristics of Lignite

ABSTRACT When mining deep coal seams, the overlying mined-out area must be pumped and drained, and the remnant coal in the mining void area is vulnerable to spontaneous combustion via water immersion and air drying. To investigate the effect of soaking time on the spontaneous combustion characteristics of lignite, low-temperature N2 adsorption experiments and Fourier transform infrared spectroscopy (FTIR) experiments were used in this study to investigate the changes in pore structure and functional group content of coal samples by increasing the soaking time. Based on programmed warming experiments, macroscopic characteristic indicators of coal spontaneous combustion (CSC) oxidizability, such as the oxygen consumption rate and index gas, were derived. Results showed that the effect of soaking caused the total pore volume and specific surface area of lignite to increase to different degrees, which enhanced the adsorption capacity of coal to oxygen and improved the effective contact of oxygen with the active sites on the coal surface. However, there was no consistency in the effect of different soaking times on the content of reactive functional groups of the coal, with higher methyl and methine contents after 60 days of soaking (S60) and 120 days of soaking (S120) than in the raw coal (RC), and less in 90 days of soaking (S90). The propensity of coal to spontaneously combust is determined by both the pore structure and reactive functional groups, which shows the propensity of spontaneous combustion S60>S120>RC>S90. Results from this study are important in understanding the mechanism of CSC of water-soaked lignite in mined-out areas and can provide theoretical guidance to prevent CSC in mining areas.

Novel Cs–Mg–Al mixed oxide with improved mobility of oxygen species for passive NOx adsorption

The development of passive NOx adsorbers with cost-benefit and high NOx storage capacity remains an on-going challenge to after-treatment technologies at lower temperatures associated with cold-start NOx emissions. Herein, Cs1Mg3Al catalyst prepared by sol–gel method was cyclic tested in NOx storage under 5 vol% water. At 100 °C, the NOx storage capacity (1219 μmol g−1) was much higher than that of Pt/BaO/Al2O3 (610 μmol g−1). This provided new insights for non-noble metal catalysts in low-temperature passive NOx adsorption. The addition of Cs improved the mobility of oxygen species and thus improved the NOx storage capacity. The XRD, XPS, IR spectra and in situ DRIFTs with NH3 probe showed an interaction between CsOx and AlOx sites via oxygen species formed on Cs1Mg3Al catalyst. The improved mobility of oxygen species inferred from O2-TPD was consistent with high NOx storage capacity related to enhanced formation of nitrate and additional nitrite species by NOx oxidation. Moreover, the addition of Mg might improve the stability of Cs1Mg3Al by stabilizing surface active oxygen species in cyclic experiments.

In Situ FTIR Spectroscopy for Scanning Accessible Active Sites in Defect-Engineered UiO-66.

Three UiO-66 samples were prepared by solvothermal synthesis using the defect engineering approach with benzoic acid as a modulator. They were characterized by different techniques and their acidic properties were assessed by FTIR spectroscopy of adsorbed CO and CD3CN. All samples evacuated at room temperature contained bridging μ3-OH groups that interacted with both probe molecules. Evacuation at 250 °C leads to the dehydroxylation and disappearance of the μ3-OH groups. Modulator-free synthesis resulted in a material with open Zr sites. They were detected by low-temperature CO adsorption on a sample evacuated at 200 °C and by CD3CN even on a sample evacuated at RT. However, these sites were lacking in the two samples obtained with a modulator. IR and Raman spectra revealed that in these cases, the Zr4+ defect sites were saturated by benzoates, which prevented their interaction with probe molecules. Finally, the dehydroxylation of all samples produced another kind of bare Zr sites that did not interact with CO but formed complexes with acetonitrile, probably due to structural rearrangement. The results showed that FTIR spectroscopy is a powerful tool for investigating the presence and availability of acid sites in UiO-66, which is crucial for its application in adsorption and catalysis.

Microscopic Pore Structures and Their Controlling Factors of the Lower Carboniferous Luzhai Shale in Guizhong Depression, China

Microscopic pore structures are of great significance in evaluating shale gas reservoirs and understanding the occurrence state of shale gas. Integrating geochemical analysis, X-ray diffraction (XRD), low-temperature N2 adsorption (LTNA), mercury injection pressure (MIP), small-angle X-ray scattering (SAXS), and field emission scanning electron microscope (FE-SEM), this work systematically characterized microscopic pore structures and then discussed their controlling factors, for the Lower Carboniferous Luzhai (C1lz) shale in Guizhong Depression. The results show that pores in the Luzhai shale are generally shaped by ink bottles, parallel plates, and slits, which are characterized by a larger pore throat ratio, lower efficiency of mercury withdrawal, and poor connectivity. Micropores (<2 nm) and mesopores (2 nm-50 nm) provide the primary specific surface area (SSA) of shale reservoirs, dominantly controlled by the contents of TOC and clay minerals, whereas pore volume is mainly contributed from mesopores, which is positively correlated to quartz content. The fractal dimension (2.94) of macropores is higher than that (2.65) of mesopores, corresponding more complicated and heterogeneous pore structure. With increasing pore size, the correlation between TOC and fractal dimension of macropores weakens. The unconnected pores in mesoscopic range are more complex than connected pores, primarily resulting from morphology and deformation of clay minerals.

Pore Structure and Fractal Characteristics of Marine–Continental Transitional Black Shales: A Case Study of the Permian Shanxi Formation in the Eastern Margin of the Ordos Basin

To study the microscopic pore characteristics of marine–continental transitional shale, we studied the Daning–Jixian block of the Shanxi Formation using low-pressure CO2 adsorption (LP-CO2A) and low-temperature N2 adsorption (LT-N2A) methods in conjunction with field emission scanning electron microscopy (FE-SEM), geochemistry, and mineral composition analysis in order to obtain pore structure characteristic parameters. The fractal dimension of the pores was calculated using the Frankel–Halsey–Hill (FHH) model, and the study also discusses the factors that influence the pore structure. The study found that the marine–continental transitional phase shale of the Shanxi Formation has clay mineral contents ranging from 36.24% to 65.21%. The total organic carbon (TOC) contents range from 0.64% to 9.70%. Additionally, the organic matter maturity is high. The FE-SEM and gas adsorption experiments revealed that the transitional shale of the Shanxi Formation possesses a diverse range of pore types with relatively large pore sizes. The dominant pore types are organic and intragranular pores, with pore morphologies predominantly appearing as slit and parallel plate structures. According to the experimental data on gas adsorption, the total SSA values range from 11.126 to 47.220 m2/g. The total PV values range from 0.014 to 0.056 cm3/g. Micropores make up a greater proportion of the total SSA, whereas mesoporous pores make up a greater proportion of the total PV. The distribution of shale pore fractal dimensions D1 and D2 (D1 is 2.470 to 2.557; D2 is 2.531 to 2.755), obtained through LT-N2A data, is relatively concentrated. D1 and D2 have a positive correlation with the TOC content, clay mineral content, and BET-SSA, and D1 and D2 have a negative correlation with the quartz content. D2 is positively correlated with the Langmuir volume, showing that D2 can be used to evaluate the methane adsorption capacity.

New Insight into Temperature Effects on Low-Rank Coal Flotation Using Diesel as a Collector.

Efficient flotation of low-rank coal is of great significance for the development of green and low-carbon cycles. Temperature is a crucial parameter of flotation, but the mechanism of its effect on flotation lacks understanding. In this paper, the mechanism was studied by kinetic flotation, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, low-temperature liquid-nitrogen adsorption (LP-N2A), X-ray photoelectron spectroscopy (XPS), and molecular dynamics simulation. The flotation combustible recovery gradually decreases as temperature rises. Compared with 60 °C, the combustible recovery at 5 °C increases by 18.13%. The desorption energy for oil droplets decreases as the temperature rises. As a result, the oil droplets are easier to desorb at high temperatures. The SEM and LP-N2A results demonstrate that the pores and fractures of the coal sample are well developed. Also, the oil-water interfacial tension and viscosity of oil droplets decrease as the temperature rises, while the diffusion ability increases. These increase the volume of oil droplets that penetrate into the pores, resulting in poor spreadability of oil droplets on the coal surface. The average volume of bubbles gradually increases as temperature rises, which renders the flotation foam unstable and worsens the flotation. Therefore, the flotation performance is better at low temperatures.

Thermodynamic analysis of a waste heat utilization based efficient liquefaction and low-temperature adsorption carbon capture hybrid system

Cryogenic CO2 capture can obtain high-pressure and pure CO2, but existing methods are inefficient as they usually discharge the waste heat of refrigeration. Therefore, a new hybrid system is proposed to recycle the waste cooling, heat, and uncondensable CO2 of liquefaction CO2 capture into low-temperature adsorption CO2 capture. This enhances the overall energy efficiency and the CO2 recovery rate over existing cryogenic CO2 capture without external input. Moreover, it enables practical sub-zero temperature CO2 adsorption while lowering the desorption temperature to 70 °C. This system is analyzed by coupling the liquefaction CO2 capture and low-temperature adsorption CO2 capture thermodynamic models, whose heat and cooling needs are compared to that available by a vapor compression cycle. Results show that for 10% mol. CO2 flue gas, the proposed system is optimal at −53 °C and 5 MPa to yield a 2nd law efficiency of 9%, a CO2 recovery rate of 80%, and specific energy consumption of under 1.65 MJ/(kg of CO2). As the cooling demand is typically twice the heat needed for sorbent regeneration, a vapor compression cycle designed to meet the former can naturally meet the latter. Ultimately, the new hybrid system represents a new carbon capture technology with better potential to achieve carbon neutrality via waste heat utilization.

NO adsorption/desorption pathways over Pd/SSZ-13 low temperature NOx adsorbers investigated by operando FT-IR spectroscopy and microreactor study

In this study a Pd-doped SSZ-13 zeolite sample is synthesized, characterized and evaluated for potential use in the low-temperature NOx adsorption. TEM/HR-TEM and in-situ CO/NO adsorptions followed by FT-IR spectroscopy are used to gain information on the nature and accessibility of the Pd sites. It is found that over the calcined sample Pd is present as isolated Pd+ and Pd2+ cations formed by ion exchange with the Brønsted acid sites of the zeolite, and as Pd+ and Pd2+ species belonging to PdOx particles on the external surface of the zeolite. Isolated Pd2+ ions prevail on the calcined fresh sample. The NOx adsorption/desorption performances, investigated by microreactor studies and operando FT-IR under relevant operating conditions, indicate that significant amounts of NO are stored on the catalyst (i.e. ca. 80–95 μmol/gcat of NOx in the temperature range 50–150 °C) which suggests the participation in the NOx uptake of both isolated Pdn+ sites and PdOx particles. NO is adsorbed as nitrosyls (anhydrous and hydrated) over both Pd2+ and Pd+; at low temperatures the formation of nitrates is also observed. The NO uptake as nitrosyls occurs with evolution of NO2 according with a NO storage mechanism which implies (i) the initial adsorption of NO on Pd2+, followed by (ii) the reduction of Pd2+ to Pd+ by NO accompanied by NO2 release and eventually (iii) the adsorption of NO on Pd+. The suggested interconversion of Pd2+ into Pd+ during NO adsorption is herein discussed based on FT-IR evidences. The stored NOx species are decomposed upon heating; nitrates are responsible for low temperature NOx desorption (below 200 °C), whereas nitrosyls show much higher stability and lead to a high temperature NO desorption (above 200 °C). The presence of NO2 in the feed stream increases the NOx adsorption capacity and results in the formation of mainly surface/bulk nitrates and nitro-compounds at the expense of nitrosyls.

Low-Temperature NH3-SCR over Hierarchical MnO x Supported on Montmorillonite Prepared by Different Methods.

Hierarchical MnO x pillared or supported on montmorillonite were prepared by three methods, i.e., impregnation (IM), chemical precipitation (CP), and in situ deposition (SP). The catalysts were characterized by low-temperature N2 adsorption (BET), XRD, XPS, SEM, TEM, H2-TPR, NH3-TPD, NO-TPD, TPSR, in situ DRIFTS, and evaluation of catalytic performance for NH3-SCR. The best catalytic performance was obtained for catalysts prepared by SP in terms of activity and selectivity, obtaining >90% NO conversion with >95% selectivity to N2 in 100-300 °C and GHSV of 70,000 h-1. Compared to IM and CP, SP greatly simplified catalyst preparation, resulting in higher BET surface areas; a spongy pore structure; more highly dispersed, pillared MnO x species; and higher density of acid sites distributed on catalysts surface, which all contributed to its superior performance for NH3-SCR. The activity for low-temperature NH3-SCR of manganese catalysts could be widely tailored by preparation methods.

Resercoir space characteristics and pore structure of Jurassic Lianggaoshan Formation lacustrine shale reservoir in Sichuan Basin, China: Insights into controlling factors

The Jurassic Lianggaoshan Formation lacustrine shale oil is the most potential exploration target of unconventional hydrocarbon resource in Southwest China. In this study, nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), low-temperature N2 adsorption (LTNA), and high pressure mercury intrusion mercury injection capillary pressure are intergrated to reveal pore structure and its controlling factors of Lianggaoshan Formation lacustrine shale reservoir. Results indicate that three types of lithology combination are classified in the Jurassic Liangggaoshan lacustrine shale reservoir. Type A comprises pure shale. Type B is characterized by frequent shell limestone interbedding. Type C is characterized by frequent siltstone interbedding. The Type C shale is characterized by relatively high proportion of organic pores, high development and good connectivity of nanopores, and highest pore volume and Surface area. The nanopores of Lianggaoshan lacustrine shales are mainly dominated by mesopores and part of the macropores. Among them, the PV and SA are both mainly dominated by micropores. The enrichment of organic matter has little effect on the development of micropores, and does not affect the mesopore and macropore development. Quartz particles in Lianggaoshan lacustrine shale do not clearly facilitate the development of micropore and mesopore-macropore. Intraparticle pore in feldspar clast is an important component of mesopore and macropore. Clay minerals has no positive effect on the formation of micropore and mesopore-macropore.

Pore Structure and Adsorption Characteristics of Maceral Groups: Insights from Centrifugal Flotation Experiment of Coals.

Coal has various types of macerals, which have different pore structures and adsorption properties that change with coal's thermal metamorphism. In-depth study of the characteristics of different coal macerals, especially the pore structure and adsorption properties, can better predict the coal reservoir gas storage capacity and migration ability. In this study, the sub-samples enriched in a specific maceral group with different coal ranks and particle sizes were obtained by centrifugal flotation experiments. Then, experiments containing low-temperature N2 isotherm adsorption (LT-N2GA), low-temperature CO2 isotherm adsorption (LT-CO2GA), and methane isothermal adsorption were carried out on the sub-samples to quantitatively analyze the evolution characteristics of pore structure and adsorption properties of different maceral groups. The results showed the following: (1) The separation effect of the light maceral groups by centrifugal flotation experiments increased with the decrease of particle sizes, which were treated with the heavy liquid of low and medium densities, while that of the heavy maceral groups had the relatively best separation effect in the particle sizes of 0.1-0.125 mm, which were treated with the heavy liquid of high densities. (2) The vitrinite-enriched samples had more ultra-micropores (mainly within the diameter range of 0.4-0.65 nm), while the inertinite enriched samples had more mesopores and transition pores (mainly within the diameter range of 40-50 nm). (3) For the low-rank coal, inertinite had more potential methane adsorption capacity. However, for the medium- and high-rank coal, vitrinite had more potential methane adsorption capacity. (4) For the low-rank coal, the adsorption potential and adsorption space increased with the increase of the inertinite content, while the adsorption potential, adsorption space, and surface free energy for the medium- and high-rank coal increased with the increase of vitrinite content. It is expected that the results can deepen the understanding about the gas storage capacity and migration ability and be used in the prevention of gas outburst and the reduction of carbon emission.