Functional Groups In Coal Research Articles

Modes of occurrence of beryllium in the Ge-rich coal deposit, Lincang, SW China: Theoretical insight into organic association and distribution

The coal-hosted germanium (Ge) deposit in Lincang, China, contains an abnormally high concentration of beryllium (Be), which is of significant organic affinity. However, the specific species of Be at the atomic scale remain unclear. In this study, thirteen model compounds representing O/S/N-containing functional groups in coal were calculated to probe the local environment of Be. The results indicate that hydroxyl and carboxyl groups are the primary acceptors of Be. Various Be-O complexes with a saturated four coordination of Be can achieve best stabilization. In contrast, the heteroatoms S and N are less likely to act as the acceptors for Be. In addition, the calculation results provide theoretical insights into the vertical distribution of Be. Unlike the upper coal seam, a fraction of Be in the middle and lower seams occurs in a mineral phase, which can be attributed to the limited capacity of organic matter to bond with all available Be. Furthermore, competition from other organically-associated metals, such as Ge and W, for bonding sites affects the local distribution of Be. This study reveals the molecular mechanism for Be enrichment in the organic matter of the Lincang Ge deposit, and suggests potential strategies for the removal of organically bonded Be in coal through the destruction of O-bridged complexes.

Micromechanism of the effect of coal functional groups on the catalytic/esterification reaction of acetic acid

Acidification modification has proven to be a successful approach for enhancing the permeability of low-permeability coal seams and increasing coalbed methane extraction. To explore the influence of acetic acid on the organic structure of coal, a combined approach of experimental research and quantum chemical calculation is employed to examine the reaction mechanism of coal organic structure in response to acetic acid. Fourier transform infrared spectroscopy reveals a reduction in the content of hydroxyl and C–O bonds in the treated samples, along with the appearance of an absorption peak of C=C bonds. This demonstrates that the main site of acetic acid acidification modification on coal molecules is the hydroxyl functional group. Therefore, glycerol can be used as a simplified model of coal molecules for further investigation. In addition, three typical functional groups (phenyl, hydroxyl, amino) are selected as the research objects. The electronic density topological properties, molecular surface electrostatic potential, Mayer bond orders and CM5 charge of coal molecules were calculated based on quantum chemical theory. This reveals the intrinsic strength of each chemical bond between single atoms in a molecule, thereby predicting potential reaction pathways between acetic acid and coal molecules. The micro-mechanism of acetic acid catalyzing/esterifying the organic structure of coal is studied using transition state methods. The computational results show that there are two main modes of reaction between acetic acid and coal molecules: (1) acetic acid catalyzes the dehydration reaction of coal molecules; (2) acetic acid reacts with coal molecules to form ester intermediates, followed by decomposition through various reactions. Among the 14 reaction pathways, acetic acid provides protons or groups to trigger the dehydration of coal molecules. Interestingly, it is found that the overall hydroxyl group participates in the reaction is easier than the individual hydrogen atom on the hydroxyl group, and the overall carboxyl group participates in the reaction is easier than the individual hydroxyl group. This indicates that the higher the overall atomic reactivity of acetic acid, the lower the reaction barrier. Compared with catalytic reactions, acetic acid tends to undergo esterification reactions with hydroxyl groups, with the phenyl ring functional group significantly affecting the reaction barrier. The introduction of various oxygen-containing functional groups like ketone, aldehyde, and ester in the reaction products will hinder the adsorption of non-polar methane, reduce the adsorption capacity of coal seams for gas, and play an essential role in promoting gas desorption. The research findings can provide theoretical guidance for the organic acidification modification of low-permeability coal seams to enhance gas permeability and coalbed methane extraction.

Experimental Study on Combined Microwave-Magnetic Separation-Flotation Coal Desulfurization.

In order to reduce the content of sulfur and ash in coal, improve the desulfurization and deashing rates, a combined experiment method of microwave magnetic separation-flotation was proposed for raw coal. The desulfurization and deashing rates of three experiment methods, namely, single magnetic separation, microwave magnetic separation, and microwave magnetic separation-flotation, were compared. Taking the microwave magnetic separation-flotation experiment method as the main line, the effects of the microwave irradiation time, microwave power, grinding time, magnetic field intensity, plate seam width, foaming agent dosage, collector dosage, and inhibitor dosage on desulfurization and deashing were discussed, and the mechanism of microwave irradiation on magnetic separation and flotation was revealed. The results show that under the conditions of a microwave irradiation time of 60 s, a microwave power of 80% of the rated power (800 W), a grinding time of 8 min, a plate seam width (the plate seam width of a magnetic separator sorting box) of 1 mm, a magnetic field intensity of 2.32 T, a foaming agent dosage of 90 g/t, a collector dosage of 2125 g/t, and an inhibitor dosage of 1500 g/t, the desulfurization and deashing effect is the best. The desulphurization rate is 76.51%, the sulfur removal rate of pyrite is 96.50%, and the deashing rate is 61.91%. Microwaves have the characteristic of selective heating, and the thermal conductivity of organic matter in coal is greater than that of mineral. Microwave irradiation can improve the reactivity of pyrite in coal, pyrolyze pyrite into high-magnetic pyrite, improve the magnetic properties, and improve the magnetic separation effect. Therefore, microwave irradiation plays a role in promoting magnetic separation. Through microwave irradiation, the positive and negative charges in coal molecules constantly vibrate and create friction under the action of an electric field force, and the thermal action generated by this vibration and friction process affects the structural changes in oxygen-containing functional groups in coal. With the increase in the irradiation time and power, the hydrophilic functional groups of -OH and -COOH decrease and the hydrophilicity decreases. Microwave heating evaporates the water in the pores of coal samples and weakens surface hydration. At the same time, microwave irradiation destroys the structure of coal and impurity minerals, produces cracks at the junction, increases the surface area of coal to a certain extent, enhances the hydrophobicity, and then improves the effect of flotation desulfurization and deashing. Therefore, after the microwave irradiation of raw coal, the magnetic separation effect is enhanced, and the flotation desulfurization effect is also enhanced.

Study on the effects of inorganic salts and ionic surfactants on the wettability of coal based on the experimental and molecular dynamics investigations

Through the evaluation and preparation of a novel inorganic salt composite solution consisting of sodium dodecyl benzene sulfonate (SDBS), the nonionic surfactants polyethylene glycol pisooctyl phenyl ether (Triton X-100), and inorganic salt Na2SO4, based on surface tension, contact angle, settling time, wetting rate, and changes in the surface microstructure and functional groups of coal, this study analyzed the wetting behavior of the solution on coal dust and its adsorption capacity on the surface of coal particles. The results demonstrate that the composite solution of inorganic salts can significantly enhance the wettability of coal samples, reducing the contact angle to 21.54° and lowering the surface tension to 26.10 mN/m. After treatment with the solution, the relative content of oxygen-containing functional groups in the microscopic structure of the coal sample increased to 59.6 % and pores more prominent than 25 nm increased to 34.63 %. Molecular dynamics (MD) simulations of the water-inorganic salt composite solution-coal system are conducted using Materials Studio software, revealing that after the addition of the composite solution, the self-diffusion coefficient (D) of water molecules is 6.3 × 10-9 m2/s, the starting point of the composite solution is 15 Å, and the system's interaction energy increase to 14000 kcal/mol. It further elucidated the modification of the surface molecular structure of coal dust by the inorganic salt composite solution, increasing hydrogen bonds, enhancing wetting, and demonstrating a solid adsorption capability of the inorganic salt composite solution on the surface of coal dust.

Experimental study on the mechanism of coal spontaneous combustion inhibition by degradation of white-rot fungus

To investigate the mechanism of inhibition of spontaneous combustion of coal by degradation of white-rot fungus, the changes of macroscopic oxidizing characteristics and microstructure of the degraded coal were investigated by the programmed temperature-raising test and the in situ Fourier-transform infrared spectroscopy experiments. The difference in gas production between the degraded coal and the blank samples indicated that the degradation inhibited the oxidation process of coal, and the intensity of the inhibition effect was different at different oxidation stages. The strongest inhibition effect was found in the accelerated oxidation stage, i.e. 80–140 °C. To further analyze the micro-mechanism of the degradation of Phanerochaete chrysosporium affecting the spontaneous combustion of coal, the relative contents of active functional groups in coal samples were compared. The results showed that the degradation affected the relative contents of hydroxyl, aliphatic hydrocarbon, and oxygenated functional groups in coal. Among them, the most significant changes of –OH and –CO- were observed at 80–140 °C. Thus, it was analyzed that Phanerochaete chrysosporium could degrade the macromolecular structure of coal by generating biological enzymes to reduce the number of oxidizable functional groups such as –OH, –CH2, –CH3, –CO-, and so on, thus reducing the risk of spontaneous combustion of coal.

Effect of ionic liquid-surfactant compound solutions on the wettability and functional groups of coal

In order to investigate the feasibility of ionic liquid-surfactant compound solutions for coal dust suppression, three ionic liquids and sodium alpha-olefin sulfonate (AOS) were selected to be compounded respectively. The compound solutions were optimized by surface tension tests and coal dust settling experiments, and FTIR and SEM tests were carried out on coal samples treated with the optimum wetting agent. The results show that when the concentration is 0.3 wt%, and the ratio of [Bmim][Cl]/AOS is 4:6, the wetting rate of compound solution is the maximum. The content of hydrophilic functional groups OH…O and C-O in the coal samples increases significantly, and the degree of benzene ring substitutions is elevated; while hydrophobic functional groups –CH, aromatic ring C = C, and benzene ring 3 substitutions (3H) are destroyed by dissolution. The micromorphology of the coal surface changes with the appearance of many cracks and pores and an increase in surface roughness. [Bmim]+ can adsorb on the drain absorption points on the coal surface by electrostatic effect, turning them into water absorption sites and attracting the surrounding AOS molecules to arrange the composite adsorption layer more closely. These results can contribute to the development of novel wetting agents with specific structures and provide theoretical guidance for the reduction of coal dust concentrations.

Visualization and Analysis of Mapping Knowledge Domains for Coal Functional Groups

ABSTRACT In this paper, a systematic review of the research on functional groups in coal is presented. In recent years, the research on functional groups in coal has been extended from the macroscopic level to the microscopic layer, and a large number of studies have shown that functional groups have significant effects on various properties of coal, such as gas adsorption and spontaneous combustion. To understand the current status and future trends of research on functional groups in coal, this study analyzed 3956 papers on this topic published in the Web of Science (WOS) core database from 2000 to 2022. The spatial and temporal distribution characteristics of publications, authors, countries, institutions, and major journals were visualized using VOSviewer and CiteSpace. Keyword co-occurrence and burst analysis are used to reveal the research status and hotspots in this field. The results show that the development of research on functional groups in coal goes through three stages: the fluctuating development period, the steady development period, and the results explosion period; China, USA, Australia, Japan, and India are the most active countries in the field of coal functional groups research, and China has a greater advantage in the number of publications and influence. A core group of institutions, mainly research universities, has been formed in this field, and Fuel, Energy and Fuels and Fuel Processing Technology are the main source journals for published results on coal functional groups. At present, the framework of basic theories and research methods is complete, and the study of functional groups for gas adsorption, the analysis of the evolution of functional groups in the process of coal thermodynamic behavior, and the characteristics of functional group categories and distribution in coal are the main knowledge framework basis for the study of functional groups in coal. The research on coal functional groups has been extended to the molecular level, and in the future, quantum chemistry, molecular simulation, and fine characterization research of functional groups will become the frontier of research in the field of coal functional groups.

Characterisation and double parallel random pore model fitting kinetic analysis of faulty coal oxygen-enriched co-combustion

This study used various analytical techniques to explore the structural characteristics of anthracite, lean coal, and bituminous coal. Thermogravimetric analysis assessed the combustion performance of individual coals and their blends. Results revealed distinct structural differences among the three coals. Although lean coal's functional groups distribution resembled bituminous coal, its carbon ordering aligned with anthracite. Increasing the proportion of bituminous coal minimally improved combustion in air. Under O2 + N2, rising oxygen levels lowered ignition and burnout temperatures, enhancing the comprehensive combustion index. At high heating rates, 30 %O2 + 70 %CO2 outperformed 30 %O2 + 70 %N2. The fitting performance of the double parallel random pore model (DRPM) was superior to that of the random pore model (RPM). Kinetic analysis suggested a DRPM for lean coal and bituminous coal co-combustion, unfolding in two stages. Activation energy increased with O2 concentration in O2 + N2 but remained lower than in O2 + CO2.

Effect of acid-thermal coupling on the chemical structure and wettability of coal: An experimental study

Coal is the primary fossil fuel in China's energy sector. As the amount of mining continues to increase, the high concentration of dust generated poses a severe threat to equipment and frontline workers. The coupling influence of HCl and temperature on the structure and wettability of coal were conducted by experiments. The phenomenon indicates that the contact angle between coal treated with HCl of different temperatures and water is reduced, the settling distance in an aqueous solution is longer, and the effect is significant with the increase of temperature, demonstrating the acid-thermal coupling solution improves the wettability of coal. Secondly, detailed analysis of coal functional groups and surface element, shows that the percentage of hydrophilic groups increased, such as OH⋯O, free –OH, and hydrophobic groups were destroyed, such as the asymmetric deformation vibration of adjacent H. The L, ‘C', and DOC show an increasing trend, while I first increase and then decrease by analyzing the trends of IR indices of coal. The conclusions prove that the degree of coal deterioration changed after treatment with acid-thermal coupling conditions. The influence mechanism of acid-thermal coupling solution on coal was explored to provide ideas for improving the wettability of coal from the source.

Transformation simulation of N-containing functional groups in coal pyrolysis and combustion processes by using ReaxFF

In order to explore the formation mechanism of NOx precursors and NOx during coal pyrolysis and combustion, four typical N-containing functional groups in coal, including pyridine-N (N-6), pyrrole-N (N-5), protonation-N (N-Q) and oxidized pyridine-N (N-X), were taken for study. Firstly, the thermal reaction processes of N-containing functional groups under different conditions were simulated via ReaxFF, then the transformation processes of N-containing functional groups to NOx precursors were obtained via Ovito, finally the reaction networks of NOx precursors and NOx were built via ReacNetGenerator. According to the study results, we speculated that the transformation process of N-containing functional groups to NOx precursors involved 4 steps, including the ring opening of N-6 and N-5, the shift of N atom to the edge, the shortening of carbon chain and the formation of NOx precursors. Besides, we found that the increasing of temperature greatly promoted the transformation processes of NO to HNO and HO2N.

Synergistic Effect of Small Molecular Organic Matter and Functional Groups in Coal on Methane Adsorption.

Functional groups and small-molecule organic matter are two key parts of coal. To explore the microscopic mechanism underlying the synergistic effect of both parts on methane adsorption, the oxygen-containing (-OH, -COOH, and -C=O) and nitrogen-containing (-NH2) functional groups and two common small molecular organic matter methylbenzene and tetrahydrofuran-2-alcohol in coal are selected. The quantum chemical meta-GGA functional method is used to optimize all structures. The electrostatic potential analyses, weak interaction analyses, and theory of atoms in molecules have been used to delve further into the nature of this synergistic effect. Our results show that functional groups inhibit methane adsorption by coal molecules, and the inhibition effect is enhanced in the presence of methylbenzene. Interestingly, the synergistic effects between functional groups and small molecular organic matter are changed from inhibition to promotion after introducing tetrahydrofuran-2-alcohol, wherein -COOH has the best synergistic effect. This work not only offers a theoretical foundation for exploring the synergistic effect of small molecular organic matter and functional groups on methane adsorption by coal molecules but also lays a foundation for further research on gas prevention and extraction.

Selective adsorption mechanism of CO2/CH4/N2 multi-component gas mixtures by N/S atoms and functional groups in coal

The modification of coal samples will effectively enhance their selective adsorption properties for different gases. To investigate this phenomenon, the adsorption mechanism of CO2/CH4/N2 binary gas mixture by single benzene ring layer doped system and microporous system formed by N/S atoms with different functional groups in coal was investigated at microscopic level, and electrostatic potential, diffusion characteristics, fluid type, radial distribution function (g(r)) and coordination number (CN) were analyzed. The results showed that the interaction of N/S atoms with oxygen-containing functional groups in coal enhanced the electrophilic capacity of the system and enhanced the adsorption capacity of CO2 in the gas mixture, and the Freundlich adsorption capacity of CO2 in the N-doped system was higher than that in the S-doped system. The interaction between N atoms and oxygen-containing functional groups in coal will effectively enhance the adsorption selectivity of CO2 in the gas mixture, with the best capture effect between 80% and 70% of CO2 concentration. The high-energy adsorption sites in N/S-modified coal samples are more inclined to be occupied by CO2, and the fatty functional groups are more likely to trap CH4 and N2. These findings indicate that N-doped modification of coal samples with high oxygen content can lead to solid adsorbents with high adsorption capacity and strong selectivity, which provides theoretical guidance for the development of new and efficient adsorbents.

Periodic action mechanism of soaking on the evolution of lignite pore structure and microactive groups

As the mining of the overlying coal seam advances, the risk of spontaneous combustion (SC) of water-immersed and air-dried coal in the overlying goaf increases. The structure of functional groups in coal is the fundamental factor for the occurrence of oxidation and heat production, and the surface pores are the main sites of oxidation reactions. In order to explore the mechanism of action of water immersion on the macrostructure and micro-group of lignite, the water-immersed coals (WIC) of 30 days (I30), 60 days (I60), 90 days (I90), 120 days (I120) and 150 days (I150) were prepared. The surface pore characteristics of coal and the evolution of active functional group structure were studied by nitrogen adsorption and infrared spectroscopy. The adsorption capacity of pores and surface structure of coal were quantitatively characterized by pore adsorption kinetic equations and fractal methods. The results showed that the fine-necked bottle-shaped pore structure of water-immersed lignite decreased, and the wedge-shaped pores and parallel plate slits increased. After water-soaking, the specific surface area of lignite increased first and then decreased, the pore volume and pore diameter increased gradually, D1 decreased gradually, D2 increased gradually, and the pore adsorption potential increased gradually, which characterized the gradual pore structure complexity and enhanced adsorption capacity. Water-soaking triggered the conversion of active carbon-hydrogen bonds at the α-position of lignite molecules into active carbon–oxygen single bonds with alcohol-oxygen bonds. I90 and I120 have the highest content of active functional groups, indicating that the oxidation activity of lignite immersed in water for 90–120 days is the highest. This study provides a new method for the quantitative characterization of coal adsorption and has reference value for the study of SC mechanism of water-immersed, air-dried coal in the overlying goaf of close distance coal seam.

Pyrolysis behavior of tar-rich coal with various coal-forming environments: A TGA and in-situ transmission FTIR study

Tar-rich coal, abundant in northwestern China, undergoes variations in the coal-forming environment, resulting in diverse occurrences of tar-rich coal and its molecular structures across regions and layers. The pyrolysis process of these coals also differs accordingly. This study investigated four coal samples with different tar yields and indicative of various coal facies using thermogravimetric analysis and in-situ transmission FTIR, and revealed that coal facies significantly affect tar yield by controlling the molecular structure. In particular, coal samples formed in a stronger reducing environment contain higher levels of aliphatic and oxygen-containing functional groups. Consequently, during pyrolysis, a substantial proportion of Cal-Cal, Cal-H, Cal-O, and Cal-N bonds were broken, contributing to approximately 30–60 % of the total cracked bonds, and X18 exceeded Z52 by a significant 21.55 %, leading to higher tar yields. In-situ transmission FTIR observations indicated that coal samples formed in a stronger reducing environment exhibit higher contents of –CH2–, –CH–, C–O, and CO structures, which decompose more rapidly after 400 °C, and X18 with the highest decomposition of 18.51 % in C–O, while Z52 had the minimum. Moreover, coal samples formed in a stronger reducing environment exhibit a more significant reduction in –CH– structures compared to –CH2– and free-ends –CH3 structures beyond 400 °C, while coal samples formed in a weaker reducing environment display higher reductions in free-ends –CH3 and –CH2– structures than –CH– structures. The formation of gaseous products during coal pyrolysis is closely linked to the decomposition and evolution of residual coal functional groups, with increased accumulation observed under more enhancing and reducing conditions. These findings offer valuable insights into optimizing tar-rich coal resource utilization and the development of effective pyrolysis techniques.

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.

Effect of Ca–Fe composite catalysts on pyrolysis performance of demineralised anthracite and its char structure transformation

AbstractWhile catalytic pyrolysis with catalyst addition has been widely studied with a primary focus on optimising gas, tar and char yields, studies exploring the evolution of char structure during coal pyrolysis remain scarce. This knowledge gap potentially affects subsequent char gasification processes during coal conversion within gasifiers. This study presents demineralised anthracite (TM) prepared by HCl–HF acid washing. The pyrolysis performance of TM while adding Ca, Fe and Ca–Fe composite catalysts was investigated through thermogravimetric analysis. The char structure, morphology and functional groups in the obtained char samples were clarified through X‐ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy, respectively. The results indicated that de‐ashing by acid washing promoted the formation of C–O functional groups in coal due to the decomposition of C=O or a combination of oxygen with unsaturated carbon, or both. The TM sample exhibited improved thermal decomposition upon adding either Ca or Fe catalysts, which became more pronounced after adding the Ca–Fe composite catalyst under the same conditions. While the addition of Ca–Fe composite catalysts inhibited the crystalline carbon formation and char graphitisation degree compared to their individual additions, it led to enhanced decomposition of phenol C–O, thereby facilitating the thermal decomposition of TM.

Study on the Inhibition of Coal Spontaneous Combustion by Superabsorbent Antioxidant Inhibitors

ABSTRACT Aiming at the problems of short inhibition life and low efficiency of physical inhibitors for the prevention and control of coal spontaneous combustion, this paper utilizes super water-absorbent (SAR) resin with tea polyphenol (TP) and vitamin C (VC) to prepare an inhibitor that can continuously and efficiently inhibit coal spontaneous combustion. Through the procedure of heating, thermogravimetric experiments are performed to characterize the inhibition performance of super-water-absorbent antioxidant-type inhibitor, and the change of active functional groups in the original coal and inhibited coal samples. The experimental results show that the super-water-absorbent antioxidant retardant can inhibit the coal spontaneous combustion in the low-temperature oxidation stage by absorbing heat through water evaporation and lowering the temperature to isolate the oxygen, and in the super-temperature stage by reducing the number of active functional groups in the coal. Compared with that of the original coal, and the water retention of the highly absorbent resin played the role of cooling and oxygen barrier for the coal; the apparent activation energy of the resisted coal samples in the spontaneous combustion in the three stages of oxygen uptake and weight gain, pyrolysis, and combustion increased by 41.02 kJ/mol, 92.58 kJ/mol, and 133.7 kJ/mol. In the process of temperature increase, the content of -OH, -CH2, -COOH, C=C, and C-H functional groups in the resisted coal samples was lower than that of the original coal, and -OH and -CH2 in the resisted coal samples showed a tendency to decrease, which reduced the reactive functional groups. Therefore, the superabsorbent antioxidant inhibitors can inhibit coal spontaneous combustion reactions by reducing the activity of coal molecules and delaying the process of coal spontaneous combustion reactions through releasing water, absorbing heat, and covering oxygen. The results of this study can be used as a reference for the field of inhibition of coal spontaneous combustion by chemical inhibitors.

Adsorption mechanism of CO2/CH4/N2 by the synergistic effect of N/S-doped and functional groups in coal at different temperatures and pressures

Doping-modified coal samples can effectively enhance the adsorption of CO2. In order to investigate the micro-mechanism of the adsorption of different gases by the synergistic effect of N/S atomic doping and functional groups in coal, the microporous constructed by N/S doping with different functional groups in coal at different temperatures and pressures were investigated based on a series of grand canonical Monte Carlo (GCMC) computational simulations. The adsorption amount, heat of adsorption, diffusion coefficient, interaction energy and relative density distribution of CO2/CH4/N2 by the model. It was found that coal samples with more N-doped carboxyl groups could adsorb CO2 better, and coal samples with more N-doped aliphatic functional groups should be selected for adsorption of CH4 and N2, and the N-COOH system had the most stable adsorption state of CO2, and the amount of N-modified coal samples adsorbed CO2 was higher than that of CH4 and N2 at the adsorption temperature of 293.15 K.The diffusion coefficients of the gas molecules showed an increasing trend with the adsorption temperature, and the relative density distributions of CO2/CH4/N2 in the N-doped micropore model were larger than those in the S-doped system. These noteworthy findings provide a valuable theoretical foundation for the advancement of novel adsorbent materials.

Inhibition of O-containing functional groups in coal on the release of alkali metals during co-pyrolysis of coal and biomass in a visual fixed bed combined with laser-induced breakdown spectroscopy

Co-pyrolysis of coal and biomass is a promising technology for clean and efficient utilization of these two carbon resources. In this study, a visual fixed bed (VFB) combined with laser-induced breakdown spectroscopy (LIBS) was applied to investigate the effect of O-containing functional groups (OCFG) in coal on the release of alkali metals (AMs) during the co-pyrolysis of coal and biomass. The results showed that low temperature pre-oxidation increased the content of OCFG in coal, especially C=O and O–C=O groups, and limited the release of AMs during the co-pyrolysis. The higher pre-oxidation degree, the stronger limitation on the release of AMs. The increase of OCFG declined the maximum release concentrations of AMs and the temporal release of AMs in the whole pyrolysis process rather than some period. The release ratio of AMs can be maximally reduced about 39% by the OCFG. The relationship between release of AMs and structure of chars during the pyrolysis was also investigated. It was obtained that the layering placement of biomass and coal showed the less volatilization of AMs than the mixing placement of them. This study provided the theoretical basis for mitigating equipment corrosion problems caused by AMs in industrial applications.

Adsorption of CO2/CH4/N2 by different functional groups in coal doped with N, S, and Na atoms: A DFT and GCMC study

Low-cost and high-performance carbon-based adsorbents can be obtained by doping modification to enhance the adsorption characteristics for carbon dioxide. In this work, the microscopic mechanism of synergistic adsorption of CO2/CH4/N2 by doping atoms and functional groups in coal was studied. Through density functional theory (DFT) and grand canonical Monte Carlo (GCMC) calculation methods, the interaction between doped N, S, Na atoms and functional groups of –OH, –COOH, –OCH3, –CH3 and –CH2CH3 in coal was simulated. According to the results, the acid group –COOH was more likely to interact with the alkali metal atom Na, which made doped system more stable. The Ph-oxygen-containing functional group-N system had the largest adsorption capacity for CO2, and the adsorbate accumulated in clumps near oxygen-containing functional groups and N atoms. The interaction energy between Ph-COOH-N and CO2 (−15.65 kcal/mol) was stronger than that of other systems, that is, the adsorption state was the most stable. Compared with other systems, the Ph-CH2CH3-Na system had the highest adsorption heat of CH4 and N2, 7.298 kcal/mol and 5.746 kcal/mol, respectively, which means Na doping would enhance the adsorption strength of the Ph-CH2CH3 system on CH4 and N2. These results show that N-modification of coal samples with high oxygen content can obtain significant carbon capture and stable adsorption state, which is conducive to large-scale industrialized CO2 capture.