Low-rank Coal Research Articles

Co-pyrolysis of low-rank coal and rice stalk: A comprehensive study on product distributions, product properties, and synergistic effects

Co-pyrolysis of low-rank coal and rice stalk is an important way to achieve hierarchical and efficient utilization of energy. This work explored how blend ratios (0–100 wt%) and temperatures (773–1073 K) affect pyrolysis product distribution and characteristics. The results showed that a higher rice straw ratio (80 wt%) significantly reduced the yield of char (22.38–26.9 wt%) compared with 20 wt% of rice straw at different temperatures. The yield and physicochemical properties of target products were closely related to process parameters, which can provide a promising opportunity to acquire desired products by reaction conditions optimization. Co-pyrolysis was able to inhibit the production of large aromatic ring structures in char. High temperature promoted the generation of cross-linked structures, which was influenced by the blend ratio. The synergistic effects of BET surface area and pore volume were most pronounced when the J content was 40 wt% at 873 K, and their increments were 59.6 m2/g and 0.027 cm3/g, respectively. For the char derived from lower rice straw proportions (0, 20, and 40 wt%), the main combustion range and the maximum combustion rate temperature showed a progressive shift towards higher values with temperature increasing. The research is valuable of guiding high-value utilization of agricultural residues and energy transitions.

Experimental investigation on pore characteristics of vitrain and durain in low rank coal based on fractal theory

The macro petrographic compositions and its pore characteristics of coal reservoir play critical role in the accumulation and development of coalbed methane (CBM). In this paper, the pore characteristics of vitrain and durain were analyzed through the experiment and fractal theory. The results indicated that the micropores and microfractures develop in vitrain, and that transitional pores develop in durain. The pore volume and specific surface area (SSA) of vitrain are larger than those of durain, with the micropore SSA of vitrain being 35% higher than that of durain. The threshold pressure and tortuosity of vitrain are greater than that of durain, but the mean pore size of vitrain is smaller than that of durain. The fractal dimension D1 of vitrain is greater than that of durain, while the fractal dimension D2 is opposite, indicating that the pore surface of vitrain is coarser, and the pore structure of durain is more complex. The fractal dimension Dk of vitrain is larger than that of durain, the mean fractal dimension Ds of vitrain is smaller than that of durain, which shows that the diffusivity of vitrain is weak but the seepage capacity is strong due to the developed fractures. The difference in material composition and pore characteristics between vitrain and durain provides a new understanding for the development of CBM in low rank coal.

Physical Characteristics of Coal Reservoirs and CBM Favorable Area Prediction in the Huaibei Coalfield, Northern China.

To quantitatively characterize middle-high-ranked coal reservoirs, the physical characteristics of seven coal samples from the Huaibei Coalfield in northern China were investigated in detail based on experiments including proximate analysis, coal petrology, low-temperature nitrogen adsorption (LTNA), mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), and methane isothermal adsorption. The results show that coal maceral in the Huaibei Coalfield is dominated by vitrinite, with a large change in the maximum vitrinite reflectance ranging from 0.7 to 2.5%. The various coal metamorphisms can be attributed to the combined influence of magmatic activities of the Tanlu and Taihang Mountains during the Yanshanian. The coal quality can be characterized by medium-high ash yield, low to very low sulfur content, low phosphorus, and medium-high calorific value. From low-ranked coals to medium-ranked coals, the volume of adsorption and seepage pores decreases but the fracture volume increases due to the stronger dehydration and coal matrix shrinkages. From medium-ranked coals to high-ranked coals, adsorption pores have a significant advantage, suggesting a stronger CH4 adsorption capacity. There is a positive correlation among the fixed carbon content, coal rank, and Langmuir volume, which can be attributed to the transformation of coal chemical composition and structure by coal metamorphism. The deep Xiaoxi in the Suixiao coal mining area, deep Nanping, deep Taoyuan-Qinan, deep Pengqiao, northern Zhuxianzhuang in the Suxian coal mining area, deep Renlou-Zhaoji, and Xutuan deep in the Linhuan mining area are predicted to be favorable areas for CBM exploration in the Huaibei Coalfield.

Effect of Carboxyl Group Position on Assembly Behavior and Structure of Hydrocarbon Oil-Carboxylic Acid Compound Collector on Low-Rank Coal Surface: Sum-Frequency Vibration Spectroscopy and Coarse-Grained Molecular Dynamics Simulation Study.

In this work, the assembly behavior and structure of a compound collector with different carboxyl group positions at the low-rank coal (LRC)-water interface were investigated through coarse-grained molecular dynamics simulation (CGMD) combined with sum-frequency vibration spectroscopy (SFG). The choice of compound collector was dodecane +decanoic acid (D-DA) and dodecane +2-butyl octanoic acid (D-BA). CGMD results showed that the carboxyl group at the carbon chain's middle can better control the assembly process between carboxylic acid and D molecules. SFG research found that the carboxyl group at the carbon chain's termination had a greater impact on the displacement of the methyl/methylene symmetric stretching vibration peak, while the carboxyl group at the carbon chain's middle had a greater impact on the displacement of the methyl/methylene asymmetric stretching vibration peak. The spatial angle calculation results revealed that the methyl group's orientation angle in the D-BA molecule was smaller and the carboxyl group's orientation angle in the BA molecule was bigger, indicating that D-BA spread more flatly on the LRC surface than D-DA. This meant that the assembled structure had a larger effective adsorption area on the LRC surface. The flotation studies also verified that the assembly behavior and structure of D-BA with the carboxyl group at the carbon chain's middle at the LRC-water interface were more conducive to the improvement of flotation efficiency. The study of interface assembly behavior and structure by CGMD combined with SFG is crucial for the creation of effective compound collectors.

Study on the evolution characteristics of molecular surface active sites of low-rank coal in low-temperature oxidation stage

Compared with other coal types of coal, low - metamorphic coal contains numerous active sites, making it susceptible to spontaneous combustion and posing significant risks during production, transportation, and storage. To further reveal the evolution characteristics and laws of low-rank coal's active sites during the process of low-temperature oxidation of coal (LTOC), X-ray photoelectron spectroscopy (XPS), 13C nuclear magnetic resonance (13C NMR), and Fourier transform infrared (FTIR) experiments were used to determine the basic structural parameters such as the valence state of non-carbon features, types of carbon elements in coal macromolecules, and structure and quantity of functional groups. Combined with molecular modelling software (GaussView 6.0) and macromolecular calculation software (Grimme-XTB), macromolecular models of coal at different temperature points were constructed, and the surface energy field distribution was calculated. The number and energy change information of chemical and physical adsorption sites of low-rank coal during heating were obtained. The results show that during the LTOC, the chemical adsorption sites such as aliphatic hydrocarbons (-CH3/-CH2) have higher reactivity and can be converted into oxygen-containing functional groups (-CHO, –OH, –COOH); the number of physical adsorption sites increased first and then decreased, and reached the maximum at 50 °C. Coal exhibited a higher affinity for O2 at this temperature. The peroxide (-C-O-O-H) undergoes thermal decomposition, leading to H2O and weight loss of coal. The –CO and –COO structures undergo decarboxylation to generate CO, CO2, and other gases. This study comprehensively revealed the evolution of active sites through two key coal oxygen processes, physical and chemical adsorption, based on the gradual temperature elevation of low-rank coal. This holds immense significance for improving and enriching the understanding of the mechanism of coal spontaneous combustion(CSC), preparing more targeted CSC inhibition, and formulating efficient fire prevention and extinguishing measures.

Pyrolysis behavior of low-rank coal in an H2-containing atmosphere and combustion properties of the prepared chars

The H2 atmosphere exerts an important influence on both the pyrolysis behavior of low-rank coal and the efficient application of the resultant char. Thermogravimetry-mass spectrometry in conjunction with the Fourier transform infrared was applied to examine the pyrolytic properties of low-rank coal in an H2-containing atmosphere. The coal chars’ carbon chemical structure, surface morphology, pore structure, and combustion reactivity were subjected to characterization by Raman spectroscopy, scanning electron microscopy, CO2 adsorption, and thermal analysis, respectively. The results indicate that the H2-atmosphere enhanced the volatiles release during the pyrolysis stage of low-rank coal. H2-containing atmosphere accelerated the synthesis of H2O through the transformation of the hydroxyl group in coal during coal pyrolysis; the H2 and CH4 production was increased through the chemical interaction of active hydrogen group with aromatic or aliphatic C–H groups; CO2 and CO evolution reduced owing to the dissociation inhibition of carbonyl groups and functional groups containing oxygen. H2-containing atmosphere enhanced the order of carbon structure (as the proportion (20–60%) of H2 contained in the pyrolysis atmosphere increases, the IG/IAll (12.72, 13.14, and 14.03%, respectively) of char-H2 increased), which was not conducive to the pore structure (the specific surface area are 373.7, 364.6, and 357.9 m2·g−1, respectively) development of char-H2. Lower volatile content as well as ordered carbon structure reduced the combustion reactivity of chars-H2 (S are 2.27 and 2.04, respectively). Similarly, lesser development of pore structure also reduced the combustion reactivity of chars-H2 (S is 1.81). Char-H2 (pyrolysis atmosphere with H2 ratio of 20, 40%) meets the grindability index requirements of blast furnace coal injection and char-H2 (pyrolysis atmosphere with H2 ratio of 60%) meets the strength requirements of ferroalloy smelting.

Mineralogical, Petrographical and Geochemical Properties of the Late Oligocene Coal Seam (Seam-VI): Insights into Elemental Enrichments and Palaeodepositional Environment (İbrice field, Thrace Basin)

The Thrace Basin hosts several mineable coal seams (upwards numbered I to VII) within the coal-bearing Late Oligocene-age Danişmen Formation. For the first time, the properties of the Seam-VI in the İbrice (Malkara) area have been investigated in order to evaluate elemental enrichments and palaeoenvironmental conditions. The xylite-rich and mineral-rich lithotypes were identified from the studied coal samples representing the whole-coal thickness. The coal samples, on a dry basis, display variable ash yields (13.2–63.0%), total C (21.2–57.8%), and total S (0.9–4.1%) contents. The minerals identified using XRD-whole rock analysis include clay minerals, quartz, pyrite, calcite, dolomite, and feldspars. Siderite is only identified in a single sample. Aragonite is detected in two samples, which contain fossil shell remains. The SEM observations agree with XRD data, and apatite, barite, biotite, pentlandite, sphalerite, Ti-oxide, and zircon were also identified as accessory phases. Huminite is the predominant maceral group in the studied samples, while liptinite and inertinite group macerals display variable proportions. The mean %Rr values of ulminite macerals are around 0.40-0.41±0.01-0.02%, indicating relatively low-rank coal. This study implies that the precursor peat-mires of the Seam-VI were mainly developed under forested mire conditions, where woody peat-forming plants were abundant, and occasionally the contributions of herbaceous plants were important. The coexistence of syngenetic pyrite and carbonate minerals (e.g., siderite and carbonate mineral bands) could be related to the development of weakly acidic to neutral conditions within palaeomires. Furthermore, the predominance of clay minerals and the presence of detrital accessory minerals (e.g., apatite, pentlandite, and Ti-oxides) can also be indicators of clastic influx into palaeomires. Although aluminosilicate minerals (e.g., clay minerals) are abundant in dominant phases, SEM-EDX data shows that accessory minerals mainly control the elemental enrichments in the Seam-VI. The Mn enrichments in the samples seem to be controlled by Mn-bearing siderite micronodules. Considering the presence of sulphide mineralization and metallic ore deposits in the Strandja and Rhodope massifs, enrichments of Cr, Co, Ni, Ge, and Mo are related to As-bearing pyrite grains and accessory sphalerite and pentlandite grains within clay mineral aggregates in the samples. In addition, the Sr-bearing barite overgrowths around feldspar grains and syngenetic carbonate mineral bands could also cause Sr enrichments. Overall, clastic influx ratios into palaeomires and pH conditions during peat accumulation controlled the elemental enrichments in the Seam-VI.

Enhanced flotation separation of low-rank coal by using polar/nonpolar binary compound collector

ABSTRACT The surface hydrophobicity of low-rank coal is meager, hindering the efficient adsorption of hydrocarbon oil on its surface. Consequently, the hydrophobicity modification of the coal surface is adversely affected, making flotation separation of the coal-gangue challenging. To achieve accurate separation of low-rank coal and gangue, this paper proposes the concept of a polar-nonpolar binary mixed collector to enhance the technology of flotation separation of low-rank coal. The study examined the effects of single polar/nonpolar collectors and compounded collectors on low-rank coal. The results showed that the flotation efficiency of oleic acid and lauric acid methyl ester as single collector was superior to all others. Moreover, the flotation efficiency of single nonpolar or polar collector was lower than that of nonpolar/polar compounded collector. Furthermore, the flotation yield of coal concentrate initially increased and then decreased with the increase of dodecane mass fraction. The ideal nonpolar and polar ratios ranged from 6: 4 to 8: 2. We analyzed the mechanism for boosting the floatability of low-rank coals using the combined collector through adhesion angle, contact angle, and X-ray photoelectron spectroscopy (XPS) tests. The adhesion angle displayed a much greater increase following treatment with the compounded collector than with the single collector. Within 10–20 seconds, the growth was swift. The adhesion angle significantly exceeded that of the single collector following treatment with the compounded collector. Furthermore, the inclusion of a suitable quantity of polar reagents proved effective in augmenting the coal samples’ hydrophobic C-C/C-H chemical structure whilst decreasing the content of hydrophilic oxygen-containing groups. The use of alkyl acid ester addition in the composite reagent significantly improves the separation efficiency of a single flotation reagent and is expected to break through the current technical bottleneck of poor effect and high cost of flotation reagents.

Kinetic analysis and mathematical modeling of low-rank coal drying by using swirl fluidized bed dryer on varied angles of guide vane and temperatures

ABSTRACT Low-rank coal is currently widely used as fuel to cover the increasing needs of boilers. This kind of coal must be upgraded due to its high moisture content to increase its quality. The drying using a fluidized swirl bed has not been studied to reduce the moisture content of Low-Rank Coal. In contrast, the drying kinetic model has never been found. This study used the angle of guide vanes (AGV) 10°, 20°, and 30° to produce swirl flow. Experiments with varying temperatures used temperatures of 40°C, 45°C, and 50°C. The purpose of this work was to determine the drying characteristics, the best-drying kinetics models, the effective moisture diffusion value, SMER, MER, and SEC on swirl fluidized bed drying. The study results show that the Khazaei and Rational drying kinetic model was the most suitable for the two experimental variations. For experiments with varying AGV, the R2 values obtained are 0.9989–0.9992 and 0.9980–0.9983, while for the variable temperature, the values are 0.9990–0.9992 and 0.9983–0.9992 for each model. The research also found that the smaller AGV angle and higher temperature result in a faster drying rate and consume less energy.

Study on coarse-grained coal water removal characteristics via steam flash drying for low-rank coal upgrading

Low-rank coal drying plays a crucial role in achieving clean and efficient coal utilization. This study introduces steam flash drying, a novel method specifically designed for upgrading low-rank coal. Unlike conventional drying techniques, steam flash drying utilizes steam as the heat medium, generating a certain amount of condensation. This paper presents a comprehensive analysis of the calculated condensate quantity and the experimental measurement of coal particles' water-holding capacity to determine the initial moisture content before drying. Furthermore, the study investigates the steam flash drying effect on different-sized coal particles at a temperature of 497 K. The findings demonstrate that particles above 3 mm have lower water-holding capacity. The initial moisture content is determined by the particles' water-holding capacity and the combined raw coal water content and condensate content. The research reveals a diminishing flash-drying effect with increasing particle size, characterized by a rapid decrease followed by a gradual decline, observed at a critical point of 6 mm. By strategically adjusting the particle size distribution and employing mixing techniques, the coal drying effect can be significantly enhanced by 22%, ultimately leading to a remarkable 17% increase in processing capacity per unit volume. As a result, this study provides a theoretical foundation and optimization strategies for the clean and efficient utilization of coal through steam flash drying.

Laboratory investigation and core flood demonstration of enhanced biogenic methane generation from lignite.

Over the last several decades, coalbed methane (CBM) has emerged as an important energy source in developing nations like India as well as worldwide and is expected to play a significant role in the energy portfolio of the future. The current scenario of rapid exhaustion of fossil fuels is leading to the need to explore alternative and efficient fuel resources. The present study demonstrates enhanced methane production per gram of lignite (lowest-rank coal). Optimization of the bioconversion of lignite to methane revealed 55°C temperature and 1.5g/L NaCl concentration as ambient conditions for the process. A scale-up study in the optimized condition showed 2,800mM methane production per 25g of lignite in anaerobic conditions. Further, Fourier transform Infrared (FTIR) and Gas Chromatography Mass Spectrometry (GCMS) analysis showed bioconversion of lignite into simpler intermediate substrates required for methane production. The results highlighted that the bacterial action first converts lignite into volatile fatty acids, which subsequently get converted into methane. Further, the exploration of indigenous microbial consortia in Tharad well (THAA) mainly comprises the order Methanosarcinales and Methanomicrobiales. The pathogenicity of the microbial consortium THAA was declared safe for use in mice via the oral route by The Energy and Resources Institute (TERI), India. The study demonstrated the development of indigenous consortia (TERI THAA), which can potentially enhance methane production from the lowest coal grade under extreme conditions in Indian coal beds.

Graphitization: Microstructural and microtextural transformations of residual char from international coal combustion ash

Natural graphite is a critical raw material and its substitution in some applications will contribute to reduce its supply risk. Coal ash, which is still produced in high amounts, contains a carbonaceous solid residue (char) that may be a substitute of natural graphite. For this purpose, char may be graphitized and used in electrocatalysis reactions, however char properties depend on coal rank, composition and combustion conditions that affect the graphitization process. Research on industrial coal char graphitization is limited, resulting in restricted comprehension of the contributing factors. In order to provide novel insights, industrial residual chars (derived from Poland, Portugal, Romania and South Africa) subjected to high-temperature treatments (carbonization at 1000 °C followed by treatment at 2600 °C under environmental pressure) were examined regarding their microstructural and microtextural transformations. The samples were studied by focussing on its heterogeneity, namely its specific properties and interactions, including elemental composition, optical character, and structure. Furthermore, the evolution of structural order of selected char morphotypes in samples derived from coal of similar rank was assessed using Raman microspectroscopy.The results highlighted a set of aspects that could have influenced the transformations experienced by the different chars during high temperature treatments (graphitization). It was found that Hydrogen might play a role in the graphitization ability of isotropic chars derived from low rank coal. The prior preferential orientation of the Basic Structural Units (BSU) contributes to achieve a higher graphitization degree, but it can be enhanced or hindered by other factors, e.g., hydrogen content. Raman microspectroscopy showed that char morphotypes from the same group underwent different transformations during graphitization, indicating that morphotypes or sections with unfused optical character may be more prone to graphitization. However, the existence of disordered domains and specific microtextures, such as polyhedral pores identified under TEM, likely hindered further graphitization. Further research on this topic is needed.

In situ coal permeability and favorable development methods for coalbed methane (CBM) extraction in China: From real data

Permeability plays a significant role in the economic viability of coalbed methane (CBM) development. In China, in situ permeability obtained from injection fall-off tests range from 0.0001 to 41 mD at depths of 130–1728 m, with the majority (78%) falling between 0.01 and 1 mD. Coal reservoirs with high rank, common cleat mineralization, and depth-dependent high stress may result in extremely low permeability. Low-rank coal and cataclastic coal exhibit more favorable permeability conditions at shallow depths. Heterogeneity in coal rank, coal texture, and stress magnitude results in a discrete distribution of permeability both regionally and vertically. Most deep seams are highly compressed with extremely low permeability (<0.1 mD) as high stress levels. Multilateral horizontal wells work best with high permeability seams, while vertical wells with conventional hydraulic fracturing demonstrate limited adaptability to deep and low-permeability seams due to insufficient proppant-supported fractures. With increasing depth, both vertical and horizontal wells should employ larger fracturing scales to create effectively supported zones with higher fracture conductivity and reduced stress sensitivity to enhance CBM productivity. Horizontal wells with large-scale volume fracturing demonstrate superior performance compared to vertical wells in extracting CBM from deep, low-permeability, and high gas saturation reservoirs.

Investigation on Adsorption Pore and Fractal Analyses of Low-Rank Coals in the Northern Qaidam Basin.

The northern Qaidam Basin has abundant coal and coalbed methane (CBM) resources, and quantitative evaluation of adsorption pore characteristics has great significance for optimum selection of CBM-favorable areas. Based on vitrinite reflectance, coal maceral, proximate analysis, low-temperature N2 adsorption, and methane isothermal adsorption experiments, the heterogeneities of adsorption pores (pore diameter <100 nm) were quantitatively characterized, and relationships between fractal dimensions and physical parameters of low-ranked coal reservoirs were revealed. The results show that the micropore volume percentage ranges between 33.70 and 86.44% with an average of 64.94%. Based on N2 adsorption/desorption curves and pore diameter distribution characteristics, the adsorption pore structures of low-ranked coals were divided into 3 types. According to the FHH model, fractal dimension D1 (relative pressure between 0 and 0.5) and D2 (relative pressure between 0.5 and 1) were calculated. Fractal dimension D1, representing adsorption pore surface area, ranges from 2.001 to 2.345, with lower values. Fractal dimension D2 (adsorption pore structure) is from 2.641 to 2.917, with relatively high values, which has a decreasing tendency from west to east in the study area. There are positive relationships between fractal dimension D1 and Langmuir volume and specific surface area, whereas negative correlations are found between fractal dimension D2 and Langmuir pressure, ash yield, moisture content, volatile content, and average pore diameter. Combined with the related data for middle- and high-rank coals, the characteristics of pore surface and methane adsorption capacity can be analyzed based on the variation of vitrinite reflectance. Furthermore, the complexity of pore structure can also be predicted according to the averaged pore size and micropore content to some degree.

Coal quality enhancement by using bio extracts of carissa carandas fruits in combination with Hydro Fluoric acid

ABSTRACT This paper addresses the imperative need for environmentally sustainable beneficiation technologies tailored for low-rank coals, constituting about 50% of global coal deposits. The focus is on recent advancements in bio-beneficiation methods for sub-bituminous coals in thermal power stations, employing ”bio extract of Carissa carandas fruits” with lower concentrations of Hydrofluoric acid. The objective is to enhance coal quality by reducing ash content and adjusting mineral composition to mitigate clinker formation during combustion. The research investigates simultaneous coal treatment with bio extract and low-concentration Hydrofluoric acid. While traditional beneficiation techniques, such as physical, chemical, and physicochemical methods, have been extensively used, a research gap is identified in green methods utilizing biomaterial extracts to remove/reduce metal oxides from coal and the need to regulate the silica-to-alumina ratio in coal composition, for resolving the issue of clinker formation. The investigation demonstrates the bio extract’s efficacy in leaching alumina, iron oxide, and alkali/alkaline earth metal oxides from coal, significantly reducing ash content. Consequently, there is a remarkable increase in coal’s gross calorific value post bio-beneficiation, accompanied by a significant reduction in sulfur content in addition to the decrease in tendency of clinker formation of coal during combustion. This study is a significant contribution to the field of environmentally friendly coal beneficiation and to reduce the tendency of clinker formation during combustion.

Study on the slurry characteristics and surface microscopic interactions mechanism of diesel modified low-rank coal

In this study, the slurry formation properties and multi-phase dispersion mechanism of hydrocarbon modified low-rank coal (LRC) were explored by combining experiments and simulations, aiming to provide some theoretical guidance for the slurrying of surface-modified LRC. The experimental results revealed that compared with the LRC water slurry (LRCWS), the consistency of the diesel modified low-rank coal water slurry (M−LRCWS) is decreased, the pseudo plasticity is enhanced, and the constant viscosity concentration is increased by 1.89 %. The results of XPS analysis indicated that the surface C/O of M−LRC increases from 5.67 (LRC) to 6.83, and the content of oxygen-containing groups decreases by 3.10 %, indicating that the surface non-polarity is enhanced. In molecular dynamics simulation, compared with the two dispersed systems of COAL/ Sodium poly[(naphthaleneformaldehyde) sulfonate] (MF)/H2O (CMW) and COAL/ Dodecane (DD)/MF/H2O (CDMW), the Ebin of water molecules in both of systems is negative, indicating that water molecules are easy to combine with the coal surface. The absolute Ebin of the CDMW system is 2612.56 kcal/mol lower than that of CMW. The adsorption force of coal molecules to water molecules is weakened, which leads to a decrease in the content of water molecules adsorbed on coal. The results show that the surface hydrophobicity of LRC modified by DD is enhanced, so the proportion of free water in the system increases, which is beneficial to increase the concentration of coal water slurry. The simulation results confirm the experimental results.

Thin liquid film drainage mechanism for bubble − particle attachment interactions in the low-rank coal flotation in the presence of salt and surfactants

Bubble-particle interaction is a fundamental process in froth flotation, where the attachment of bubbles and particles is the crucial process in effective flotation. However, modeling bubble-particle attachment interaction is challenging. This is because advanced methods like AFM (Atomic Force Microscope) characterizations are difficult to quantify hydrophobic interactions reproducibly for air bubbles and non-spherical particles. This study presents a methodology to obtain the hydrophobic force constants for bubble-particle attachment interaction in the presence of salt (KCl) and surfactants (DTAC and SDS). The hydrophobic interaction constants of bubble-particle interactions were acquired from first principles with the Stefan − Reynolds theory and Glembotsky experimental device. The Stefan − Reynolds theory was successfully applied in the determination of the real hydrophobic constants for bubbles and particles interaction in DI water (deionized water). However, in the coexistence of salt and surfactants, the real hydrophobic constants for bubbles and particles interaction cannot be obtained while the fictive hydrophobic constants were acquired with a linear extrapolation method. The results showed that the addition of inorganic salt and surfactants compressed the electronic double layer’s thickness and presented a higher hydrophobic force constant, enhancing the interaction between a bubble and a low-rank coal particle. In addition, the evaluations of hydrophobic constants reveal that the hydrogen bond energy and salt ions destruction energy should be considered to the comprehension of attachment interaction mechanism and the hydrophobic force source for bubble − particle attachment interactions.

Elucidation of the structural features of low-rank coals using two-dimensional gas chromatography/time-of-flight mass spectrometry (GC×GC/TOF-MS)

Thermal dissolution (TD) and ultrasonic-assisted extraction (UAE) were applied to the extraction of soluble components from Shengli lignite (SL) and Shenfu sub-bituminous coal (SS) using cyclohexane as the solvent. Comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GC × GC/TOF-MS) was used to analyze the complex molecular composition of soluble fractions. The powerful separation ability of GC × GC/TOF-MS enriches compounds with similar molecular characteristics. The extracts of SL exhibited a high relative abundance of oxygen-containing compounds, up to 81.10 % in SL100. The extracts of SS had a high relative abundance of hydrocarbons such as 70.30 % in SS100. Meanwhile, those hydrocarbons and oxygenates embraced a considerable variety of biomarkers of coal, which were the constituents of plants and microbes from ancient times, including aliphatic hydrocarbons, sesquiterpenoid compounds, long-chain fatty compounds, furans, and aromatic esters. TD at below 200 °C mainly induced the dissociation of intermolecular interactions, but both the dissociation of intermolecular interactions and the partial cleavage of weak covalent bonds at 300 °C.

Molecular structure model construction and pyrolysis mechanism study on low-rank coal by experiments and ReaxFF simulations

For an in-depth understanding of China's low-rank coal's organic structure and pyrolysis process, Meihuajing (MHJ) coal was typically studied. Firstly, the organic structures of MHJ coal were obtained, and its molecular model was constructed based on various physical characterizations. Then, the constructed molecular model was well verified, and the pyrolysis processes of this model under heat-up and isothermal conditions were explored using ReaxFF. The results indicated that the primary organic structure of MHJ coal was aromatic skeleton (76.03%). Naphthalene was more abundant in the aromatic skeleton than benzene and anthracene. Moreover, the chemical formula of the constructed molecular model was C388H259O89N5, which was well-validated regarding physical characterizations, thermogravimetric analysis, and ReaxFF simulations. As for pyrolysis simulation, increasing the heating rate primarily suppressed the secondary cracking reactions of tar while further raising the heating rate mainly slowed down the cracking reactions of coke. Besides, the pyrolysis process of MHJ coal was divided into three steps: the rapid cracking stage, the secondary reaction stage of tar, and the basic completion stage of pyrolysis.

Effect of Sodium and Potassium Ions on the Flotation of Low-Rank Coal in the Presence of Different Collectors: A Theoretical and Experimental Study

Effect of Sodium and Potassium Ions on the Flotation of Low-Rank Coal in the Presence of Different Collectors: A Theoretical and Experimental Study