Surface Properties Of Coal Research Articles

Synergetic studies on the thermochemical activation and polyaniline integration on the adsorption properties of natural coal for chlorpyrifos pesticide: steric and energetic studies

Three types of synthetic coal-derived adsorbents were characterized as potential enhanced structurers during the removal of chlorpyrifos pesticide. The raw coal (CA) was activated into porous graphitic carbon (AC), and both CA and AC were blended with polyaniline polymers (PANI/CA and PANI/AC) forming two advanced composites. The adsorption performances of the modified structures in comparison with CA were evaluated based on both the steric and energetic parameters of the applied advanced isotherm model (the monolayer model of one energy). The uptake performances reflected higher capacities for the PANI hybridized form (235.8 mg/g (PANI/CA) and 309.75 mg/g (PANI/AC) as compared to AC (156.9 mg/g) and raw coal (135.8 mg/g). This signifies the impact of activation step and PANI blending on the surface and textural properties of coal. The steric investigation determined the saturation of the coal surface with extra active sites after the activation step (Nm(AC) = 62.05 mg/g) and the PANI integration (Nm(PANI/CA) = 113.5 mg/g and Nm(PANI/AC) = 169.7 mg/g) as compared to raw coal (Nm(CA) = 39.6 mg/g). This illustrated the reported uptake efficiencies of the modified samples, which can be attributed to the enhancement in the surface area and the incorporation of additional chemical groups. The results also reflect that each site can be loaded with 3–4 molecules of chlorpyrifos, which are arranged vertically and adsorbed by multi-molecular mechanisms. The energetic studies (< 40 kJ/mol) suggested the physical uptake of pesticide molecules by dipole bonding and hydrogen bonding processes. The thermodynamic functions donate the exothermic properties of 47reactions that occur spontaneously.

Synergetic studies on the nitrogen functionalization and polyaniline hybridization on the uptake performances of acephate pesticides by raw coal: Steric and energetic studies

Three forms of modified coal-based adsorbents were developed and characterized as potential enhanced structurers during the removal of acephate pesticide. The raw coal (CA) was oxidized by nitric acid, forming nitrogen functionalized coal (N.CA), and both CA and N.CA were hybridized with polyaniline polymers (PANI/CA and PANI/N.CA). The adsorption performances of the modified structures in comparison with CA were evaluated based on both the steric and energetic parameters of the applied advanced isotherm model (the monolayer model of one energy). The uptake performances reflected higher capacities for the PANI hybridized form (261.9 mg/g (PANI/CA) and 316.6 mg/g (PANI/N.CA) as compared to N.CA (232.3 mg/g) and raw coal (201.2 mg/g). This signifies the impact of nitrogen functionalization and PANI hybridization on the surface properties of coal. The steric investigation determined the saturation of the coal surface with extra active sites after the nitric acid treatment (Nm (N.CA) = 103.5 mg/g) and the PANI hybridization (Nm (PANI/CA) = 119.07 mg/g and Nm (PANI/N.CA) = 146.4 mg/g) as compared to raw coal (Nm (CA) = 81.9 mg/g). This illustrated the reported uptake efficiencies of the modified samples, which can be attributed to the enhancement in the surface area (5.4 m2/g (CA), 18.3 m2/g (N.CA), 27.7 m2/g (PANI/CA), and 36.2 m2/g (PANI/N.CA)) and the incorporation of additional chemical groups (NO, C-N, and N-H). The results also reflect that each site can be loaded with three molecules of acephate, which are arranged vertically and adsorbed by multi-molecular mechanisms. The energetic studies (<40 kJ/mol) suggested the physical uptake of pesticide molecules by dipole bonding and hydrogen bonding processes. The thermodynamic functions reflect the exothermic properties of reactions that occur spontaneously.

Performance Comparison of Waste Cooking Oil on Coal Slime Flotation with Sunflower Oil and Gas Oil

This study explores the potential use of waste cooking sunflower oil (WSO) as an eco-friendly collector for coal slime flotation. WSO and coal slime are both wastes and are hazardous to human health and the environment, if not disposed of properly. In this study, co-disposal of the two wastes was investigated; a gas oil (petroleum derived oil) and crude sunflower oil (CSO) were used for collector efficiency comparisons. This study also presents a green, low-cost and environmentally friendly alternative. Kinetic flotation tests were carried out to study the flotation selectivity, flammability and combustible recovery. Contact angle measurements were performed with 3 different oils (CSO, WSO and gas oil) by sessile drop technique to determine the hydrophobicity and surface properties of coal. Fourier-transform infrared (FTIR) spectroscopy was utilized to analyze the chemical composition of both waste oil and coal samples. &#x0D; Keywords: Sunflower oil, waste cooking oil, gas oil, coal slime, flotation

Interactions between surface properties of pristine coals and the intrinsic microbial communities involved in methane formation

As climate change continues, there is growing interest in the biological, in situ conversion of coal to methane, which is a cleaner and more efficient source of energy. The purpose of this study was to reveal the relationship between the surface properties of coals and the intrinsic microbial communities involved in methane formation. The material examined included nine coals varying in maturity and methane-bearing capacity. Compilation of data on wettability (θw) (measured by a sessile drop method) and microbial community composition (next-generation sequencing (NGS)) revealed that the occurrence of Bacteroidetes, Firmicutes and methanogenic Euryarchaeota was significantly, positively (P < 0.05) correlated with θw of coal. The dependence was the opposite for Actinobacteria. These results suggest that the groups of microorganisms responsible for the decomposition of organic matter in bituminous coals (hydrophobic) and lignites (hydrophilic) differ, which may impact methane formation in the seams. This is because Bacteroidetes and Firmicutes stimulate this process, while the influence of Actinobacteria is the opposite. Our work demonstrates for the first time the links between the surface properties of coals, geotectonic conditions, microbial ecophysiology and the methane-bearing capacity of the coals.

Progress of Dispersants for Coal Water Slurry

Dispersants, serving as an essential raw material in the formulation of coal water slurry, offer an economical and convenient solution for enhancing slurry concentration, thus stimulating significant interest in the development of novel and efficient dispersants. This paper intends to illuminate the evolution of dispersants by examining both the traditional and the newly conceived types and elaborating on their respective mechanisms of influence on slurry performance. Dispersants can be classified into anionic, cationic, amphoteric, and non-ionic types based on their dissociation properties. They can be produced by modifying either natural or synthetic products. The molecular structure of a dispersant allows for further categorization into one-dimensional, two-dimensional, or three-dimensional structure dispersants. This document succinctly outlines dispersants derived from natural products, three-dimensional structure dispersants, common anionic dispersants such as lignin and naphthalene, and amphoteric and non-ionic dispersants. Subsequently, the adsorption mechanism of dispersants, governed by either electrostatic attraction or functional group effects, is elucidated. The three mechanisms through which dispersants alter the surface properties of coal, namely the wetting dispersion effect, electrostatic repulsion effect, and steric hindrance effect, are also explained. The paper concludes with an exploration of the challenges and emerging trends in the domain of dispersants.

Synergistically effective flotation enrichment of vitrinite by Na removal for high-Na high-inertinite low-rank Zhundong coal

The highly effectively removing Na and enriching vitrinite for high-Na high-inertinite low-rank Zhundong coal is of great significance for its efficient and clean utilization. The effect of Na removal by low concentration HCl and AcOH on vitrinite enrichment before and during the flotation process of Zhundong coal are investigated. The vitrinite content in raw coal is only 48.67%, it can be increased to 61.85% and the yield of clean coal is only 26.44% by flotation for raw coal. However, if Na is nearly fully removed by HCl and AcOH before flotation, the vitrinite content can reach as high as 70.22% and the yield of clean coal can be significantly increased to 39.77% for AcOH-treated coal. The comprehensive efficiency is significantly improved to 57.38% from 33.60% for raw coal. When directly adding low concentration AcOH and HCl during flotation process of raw coal, the flotation effects are nearly the same to those of the above Na-removed coals in advance. The results clearly indicate that the effective removal of organic Na on surface and in macropores of coal plays a decisive role in synergistically enriching vitrinite by flotation. Further studies on vitrinite-rich coal (VC) and inertinite-rich coal (IC) and their Na-removed samples show the improvement of flotation effect can be attributed to the effective adjustment of the surface properties of Zhundong coal accompanying the Na removal, which not only improves the hydrophobicity of coal, but also promotes the hydrogen bonding interactions between collector and coal, especially vitrinite.

Design and evaluation of a novel dispersant with “surface-to-surface” adsorption function for preparing low-rank coal water slurry

It is important to improve the performance of low-rank coal water slurry (CWS) for the development of coal gasification. In this study, to prepare high-quality Shenhua coal water slurry, a novel GON-APEG dispersant with “surface-to-surface” adsorption function was designed and synthesized by grafting the allyl polyoxyethylene ether (APEG) onto the edge of graphite oxide nanosheet (GON) through esterification and emulsion polymerization. The influences of GON-APEG on the properties of CWS, the adsorption isotherm of GON-APEG, and the surface properties of coal were studied, and compared with GON, sodium lignosulphonate (SL), and polycarboxylate (PC) dispersants. The GON-APEG was superior to other dispersants in viscosity-reducing and stabilizing ability. Under the optimum dosage of 0.3 wt%, the maximum coal content of CWS with GON-APEG was 64.5 wt%. All the CWSs with different dispersants belonged to typical yield pseudoplastic fluid. Meanwhile, the adsorption isotherms of four dispersants had a good correlation with the Langmuir model, and the saturated adsorption capacity of GON-APEG was greater than SL and PC dispersants. The GON-APEG decreased the contact angle of water on the coal surface and increased the absolute value of Zeta potential of coal to the greatest extent. The excellent performance of GON-APEG in CWS was due to its strong interaction with coal derived from “surface-to-surface” adsorption mode, which was beneficial to regulate the surface properties of coal. In sum, this study provides a new idea for improving the properties of Shenhua coal water slurry and developing the efficient dispersants in other fields.

Characterizing water vapor adsorption on coal by nuclear magnetic resonance: Influence of coal pore structure and surface properties

Steam injection is a novel and promising technology for enhancing coalbed methane (CBM) recovery. Accurate descriptions of the migration and adsorption of water vapor on coal is crucial for determining the occurrence state of the CBM and improving CBM production. This study quantitatively characterized the dynamic transport and adsorption processes of water vapor in coal pores and fractures using nuclear magnetic resonance (NMR). The results demonstrated that water vapor was preferentially adsorbed in the coal micropores, which was mainly related to capillary condensation, whereas liquid water filled a wide range of pores and fractures. Due to the differences in the microstructure and surface properties among different coals, the water vapor adsorption behaviors varied significantly. Among the coals used in this study, water vapor was most easily adsorbed on the bitumite with the biggest specific surface area, pore volume, pore area, the highest content of oxygen-containing functional groups, and the strongest wettability. Additionally, the coal pore structure had a greater impact on the water vapor adsorption capacity than the oxygen functional groups and the wettability. This research is of great significance for understanding the flow behaviors of water vapor in porous media and the interactions between coal and water.

Vapour Sorption on Coal: Influence of Polarity and Rank

The surface properties of coal, interactions with gaseous and vapour media, and knowledge of the pore structure are important in terms of preparation, use, and utilisation of coal. This publication combines new unpublished data with analyses included in earlier publications by the research team to expand and systematise information on the sorption of water vapour, methanol vapour, and the saturated and unsaturated hydrocarbons hexane, 1-hexene, heptane, 1-heptene, octane on coals of different ranks. The study showed that the affinity of coal for water and methanol is related to the content of oxygen in the coal rather than the rank of the coal. Water sorption is a multilayer phenomenon, while methanol sorption is a monolayer phenomenon. The water monolayer is greater than that of methanol for low-rank coal, but for the higher-rank coals it is the opposite. The sorption capacity of the applied hydrocarbons depends on the presence or absence of a double bond and the size of the molecule. It increases in the order: n-octane &lt; n-heptane/n-hexane &lt; 1-heptene &lt; 1-hexene. The effect of a double bond is dominant over the influence of the length and shape of the molecule.

Enhanced flotation selectivity of fine coal from kaolinite by anionic polyacrylamide pre-conditioning

The flotation process of fine non-coking coal from kaolinite was enhanced by anionic polyacrylamide. The influence of anionic polyacrylamide on the surface properties of kaolinite and coal was analyzed by Fourier transform infrared spectrometer and contact angle tests. The Derjagin–Landau–Verwey–Overbeek theory was used to analyzed the effect of anionic polyacrylamide on the interaction between various particles. Flocculation behavior of kaolinite and coal particles were visualized through focused beam reflectance measurement and particle video microscope. Field emission scanning electron microscopy was employed to observe the effect of anionic polyacrylamide on the amount of kaolinite coating on clean coal surface. These results demonstrated that anionic polyacrylamide could interact with kaolinite and coal particles by hydrogen bonding. Anionic polyacrylamide could selectively flocculate kaolinite particles rather than coal particles because the repulsion energy between coal particles treated by anionic polyacrylamide was much larger than that between kaolinite particles treated by anionic polyacrylamide. The flotation separation index increased from 182 to 270 when the dosage of anionic polyacrylamide increased from 0 to 66 g/t. In addition, many kaolinite particles were coated on coal surface when anionic polyacrylamide was not added, while there were few kaolinite particles were coated on coal surface when anionic polyacrylamide was added. These results demonstrated that anionic polyacrylamide could not only reduce the kaolinite pollution for froth by selectively flocculation but also decrease the amount of kaolinite particles coating on clean coal surface. Ultimately, the flotation selectivity of fine non-coking coal from kaolinite was enhanced by anionic polyacrylamide pre-conditioning.

Effect of Nanomagnetite on Properties of Medium- and High-Rank Coals

Coal seams are natural gas reservoirs that provide potential for future CO2 capture and storage. Many problems must be resolved for CO2 storage in coal seams. To target problems of gas percolation, adsorption, and “stagnation” in gas reservoirs, the specific surface area, pore volume, permeability, and adsorption–desorption curves of three coal types with nanometer magnetite powder (NMP) mass fractions of 0%, 2%, 4%, and 6% were measured in dry state. The coal’s adsorption potential, specific surface area, and pore volume increased with an increase of NMP mass fraction. The specific surface area of coal mixed with NMP differed significantly from data that were calculated from the coal and NMP specific surface area, and the permeability was higher than for core without NMP, which indicates that the surface properties of coal can be changed by NMP addition. Although the permeability of coal core mixed with NMP exceeded that of the original coal core, an increase of NMP mass fraction resulted in an initial increase and then a decrease of coal core permeability from Pingdingshan and Anyang in China. NMP coverage of the coal surface increases the permeability for a coverage below 27%, and the permeability decreases when coverage exceeded 27%. Gas “stagnation” was affected by the ratio of equilibrium pressure to the saturated vapor pressure (p/p0) and by the coverage ratio. This research is significant for coal-bed methane exploration and underground gas storage construction.

Improved surface morphology by reforming of oxygen functional groups of Indian coal upon irradiating with microwave radiations

ABSTRACT The high-rank coal reserves are limited and getting depleted at an escalating rate to meet the demands of growing population. This concern has compelled the scientific community to use the young high ash coals. The coal water slurry fuel is one promising way to use low-quality coal as an economical liquid fuel. Due to poor physico-chemical and surface properties of such coals, these systems appear to be unsustainable. This research presents a sustainable solution to use the existing low-quality coals efficiently without any modification in the already installed systems. The Indian coal possessing high moisture and oxygen functional groups was successfully irradiated with microwaves, resulting in the improvement of morphological, physical, chemical and rheological characteristics. These changes are due to the elimination of the Hydroxyl (-OH−) and Carboxyl (-COOH−) groups, which are observed to contribute the most to the hydrophilicity of the coal particles. The morphological investigations reveal the breaking up of the bigger particles into fines upon microwave irradiation. The treated coals exhibit physico-chemical and surface properties similar to high-rank coals but still possess high ash that does not pose any issue with the normal operation of the system.

Improvement on slurry ability and combustion dynamics of low quality coals with ultra-high ash content

It is a significant subject that low quality coals could be used for high concentration slurry preparation because of the large reserve and low price. Nevertheless, due to the microstructure and surface properties of low quality coals, it is difficult to prepare qualified coal water slurry (CWS) directly. In this study, an improved flotation technique was employed to upgrade two low quality coals, then Jinda raw coal (JD-RC) and its upgraded coal (JD-UC), together with Jisuo raw coal (JS-RC) and its upgraded coal (JS-UC) were applied to CWS preparation and combustion dynamics analysis. Results showed that after two samples of low quality coals were upgraded, the maximum slurry concentration could be increased by 6%. It was attributed to the variation of free water content, which was mainly influenced by composition and pore structure of coal particles. Because of the remarkable decrement on specific surface area and porosity after flotation, the ignition temperature and apparent activation energy of CWS prepared by JD-UC were increased comparing to JD-RC. However, the ignition temperature and apparent activation energy of CWS prepared by JS-UC were lower than JS-RC, which was resulted from the higher combustible content in JS-UC. The results of this study provided a method for the preparation of high concentration CWS using low quality coals with ultra-high ash content.

Application of ultrasonic pretreatment for coking coal flotation and its mechanism

ABSTRACT This paper focuses on enhancing the flotation of coking coal with ultrasonic pretreatment and the corresponding improving mechanism. The effects of ultrasound on the coal surface properties and the dispersion of oil collector in flotation slurry were fully studied. The SEM, FTIR and XRF analyses indicated that, after the ultrasonic pretreatment, the fine particles covered on coarse coal particles were removed and the elements forming gangue minerals were decreased, which improved the surface hydrophobicity of the coal sample. What’s more, the optical microscope measurements for collector dispersion showed that the size of diesel oil droplets was greatly reduced after the ultrasonic treatment, suggesting the enhanced dispersion of collector in flotation pulp. As a result of synergistic effects of ultrasonic treatment on the coal surface cleaning and promotion of collector dispersion in pulp, a maximum combustible matter recovery of 79.79% was attained with the flotation process 2 (i.e., the ultrasonic treatment was performed after the addition of collector to the pulp). Furthermore, the enhanced collector dispersion in pulp caused by the ultrasonic treatment may be conducive to reduce the collector consumption in actual flotation practice.

Influence of pickling on the surface composition and flotability of Daliuta long-flame coal

Surface modification for low-rank coal with poor hydrophobicity is critical to its efficient flotation. In the present study, induction time and flotation results were employed to evaluate the coal sample's flotability in the pickling process, while the changes in coal surface properties were comprehensively investigated by various surface analysis technologies. The results suggested that the induction time between coal particles and bubbles decreased from 115 ms to 13 ms with increases in the concentration of hydrochloric acid, and the combustible matter recovery correspondingly exhibited an evident increase from 31.98 to 59.22%. Additionally, after pickling, a significant increase in the liberation of gangue minerals from coal particles was observed by XRD and SEM measurements. Furthermore, the XPS results indicated that the hydrophilic oxygen-containing functional groups of coal sample decreased after the pickling process. Consequently, the enhanced flotation performance could be attributed to the changes in surface chemical functional groups and increased liberation of gangue minerals from coal particles in the pickling process.

Evolution of structural and surface chemistry during pyrolysis of Zhundong coal in an entrained-flow bed reactor

In this study, a typical Zhundong coal sample was examined, and a series of step-wise pyrolysis experiments, where the temperature was gradually elevated in small increments, were carried out by using an entrained-flow bed reactor. In addition, chars from pyrolysis were investigated by X-ray diffraction and Raman spectroscopy with the aim of revealing the microcrystalline parameters and degree of crystallinity, defects, and disorder. Then, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were employed to observe the changes in the chemical surface properties of Zhundong coal before and after pyrolysis. The XRD and Raman spectra indicate that the transition from small aromatic ring systems to large aromatic ring systems in coal with the increase in pyrolysis temperature results in the increase in the lateral size of the basic lattice unit of carbon. Furthermore, condensation and the combination of aromatic rings cause the stacking height of the basic lattice units to first decrease and then increase. When the pyrolysis temperature is lower than 1000 °C, the content of graphite decreases, and the inter-layer spacing of the lattice changes slightly with an increase in temperature. As the pyrolysis temperature continues to rise, the content of graphite increases, the inter-layer spacing of the lattice decreases sharply, reaching a minimum of 0.347 nm at 1500 °C, which represents the degree of increase in the graphitisation of coal char and the transformation of the microcrystalline structure of coal char to that of graphite. FT-IR and XPS analyses show that exchangeable sodium is primarily connected with oxygen functional groups in coal char, and the oxygen functional groups are easily decomposed during coal pyrolysis. Meanwhile, the content of CH/CC/CC groups increases with increasing pyrolysis temperature, while that of CO decreases. As a result, there are more hydrocarbon groups on the surface of the coal char, whereas less oxygen functional groups are exposed to the coal char surface.

Surface hydrophobicity of sub-bituminous and meta-bituminous coal and their flotation kinetics

This paper discusses the relationships between the surface properties of the sub-bituminous and meta-bituminous coal and their flotation properties. Additionally, it was investigated whether the flotation kinetic constants, obtained using various flotation kinetic models, can be used for prediction of the flotation response. Both coal samples had the very similar amount and type of impurities as confirmed by XRD. FTIR, contact angle, zeta potential and SEM measurements were used to study the coal surface properties. It was found that the meta-bituminous coal was significantly more hydrophobic than the sub-bituminous coal and the coal surface roughness was significantly more pronounced in the case of the sub-bituminous coal than that in the case of the meta-bituminous coal. For these reasons, the recovery of the meta-bituminous coal by flotation was dramatically higher than that of the sub-bituminous coal even in the presence of collector. Six flotation kinetic models successfully predicted the flotation data. Nevertheless, the modified first-order model was the only model that can be used to explain the flotation responses under a wide range of the experimental conditions. The reason is that for most flotation kinetic models, used in this study, particularly in the case of the sub-bituminous coal, the flotation rate constants decreased with increasing in collector dosage while the opposite is true in the case of the flotation recoveries.

Recovering clean low-rank coal using shale oil as a flotation collector

ABSTRACTShale oil (SO) was adopted as flotation collector to recover clean low-rank coal. Gas chromatography-mass spectrometry, flotation, X-ray photoelectron spectroscopy and contact angle measurements were performed to identify the chemical constituents and flotation performance of SO, and the surface properties of low-rank coal. The results indicated that the long-chain hydrocarbon and high viscosity of SO may lead to the higher combustible matter recovery and lower ash content of clean coal. The adsorption of SO significantly enhanced the carbon-bearing content and decreased the C−O content, which was favorable to enhance the hydrophobicity, and thus improve the flotability of low-rank coal.

Effects of high-temperature oxygen-deficient oxidation on the surface properties of sub-bituminous coal

ABSTRACTThe air oxidation of coal releases heat which increases coal temperature, as a result, the spontaneous combustion of coal happens. Generally, coal spontaneous combustion needs to be prevented artificially, however, most of the coal particles still suffer a high-temperature heating process under the oxygen-deficient condition. This paper aims to investigate the effect of high temperature (500°C, 600°C, and 700°C) oxygen-deficient (3% oxygen and 97% nitrogen) oxidation on the surface properties of sub-bituminous coal. SEM and XPS were applied to show the changes of surface properties of sub-bituminous coal. SEM results showed the number of pores and cracks on coal surface increased with the increasing heating temperature, and XPS results showed the content of hydrophobic functional groups on coal surface reduced whereas the content of hydrophilic oxygen-containing functional groups increased after the oxygen-deficient oxidation.

Preparing coal slurry from coking wastewater to achieve resource utilization: Slurrying mechanism of coking wastewater–coal slurry

Coking wastewater is used to prepare coal slurry, which can be used as combustion and gasification fuel. This promising technology simultaneously achieves resource utilization and wastewater management. Slurrying properties are essential to the industrial application of coal slurry. These properties are considerably influenced by coal surface properties and the adsorption of an additive by coal. In this study, the effects of the internal components (e.g., phenol, ammonia nitrogen, and metal ions) of coking wastewater on the adsorption of an additive by coal and on coal surface properties were measured. Results showed that the competitive adsorption between phenol and the additive reduced the amount of additive adsorbed on coal. However, phenol acted as an additive to improve the wettability of coal particles. Cations (Ca2+, NH4+, and Na+) adversely affected the slurrying because they weakened the negative charges of coal. Furthermore, a large amount of water was adsorbed due to the ionic bonding effects, thereby reducing the free water in the coal slurry system. The maximum slurrying concentration of CWCS was 0.8 percentage points higher than that of CWS, suggesting that coking wastewater enhanced the slurrying capability of the coal slurry by integrating the various effects induced by the different internal components.