Utilization Of Low-rank Coal Research Articles

The improvement in the quality of 6–0 mm low-grade high-sulfur lignite via a compound dry separation bed

ABSTRACT The drastic decline in high-quality coal leads to the extensive development and utilization of low-rank coal in China. This study employs a compound dry separation bed to desulfurize and reduce the ash content of lignite. It focuses on the influence of multistage separation trough angles (θ), vibration frequency (f) and vibration amplitude (A) on the spatial distribution of the sulfur content and systematically analyses the particles migration behavior. The results indicate considerable differences in the sulfur content spatial distribution when θ = 45°, f = 26 hz, and A = 3.2 mm, and the degree of sulfur desorption reaches its maximum value (S sulfur = 1.18–1.21) meanwhile. Separation and quality enhancement tests conducted under optimal parameters achieved a clean coal yield of 70.29%, a sulfur content of 0.74%, an ash content of 7.29% and a probable error (E p ) of 0.08 g/cm3, demonstrating high-precision dry desulfurization and quality enhancement of lignite.

Lignite degraded by Trichoderma citrinoviride: Products, processes and mechanisms

The biodegradation of lignite facilitates the efficient utilization of low-rank coal, and its degradation products, processes, and mechanisms are important areas of research. In this study, the biodegradation process of the lignite was analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and gas chromatography-mass spectrometry (GC-MS). Firstly, the structural changes of lignite caused by Trichoderma citrinoviride were analyzed. Secondly, the main product detected by GC-MS from the degradation of lignite by Trichoderma citrinoviride was identified as erucylamide, with a conversion rate of 12.23%. The main product that was volatilized at 280 °C during the degradation of lignite by Trichoderma citrinoviride was first identified by GC-MS. Finally, the oxidase, LiP, MnP, Lac, and PPO secreted by Trichoderma citrinoviride were the main factors contributing to the degradation of lignite, and the degradation processes and mechanisms were inferred based on enzyme activities. This study provides fundamental experiments and data support for research on lignite in the field of the biochemical industry.

Utilization of Low-Rank Coal and Zn-Bearing Dusts for Preparation of K, Na-Embedded Porous Carbon Material and Metallized Pellets by Synergistic Activation and Reduction Process.

A technology was developed for managing Zn-bearing dust, facilitating the recycling of hazardous solid waste and the production of porous carbon materials. In the one-step process, Zn-bearing dusts were employed not only as raw materials to prepare reduced Zn-bearing dust pellets but also as activators to prepare K, Na-embedded activated carbon. In the process, the Fe, C, Zn, K, and Na in the dusts were rationally utilized. Under optimal conditions, the reduced pellets and porous carbon materials were simultaneously produced and characterized using XRD, SEM/EDS, FTIR, and adsorption of nitrogen techniques. The results indicated that the reduced pellets, with low levels of harmful elements and high iron grade and strength, could be directly used as burden for enhancing blast furnace operation without additional agglomeration. Meanwhile, the K and Na-embedded porous carbon material demonstrated superior SO2 and NO adsorption capacities compared to the commercial activated carbon, making it suitable for purifying SO2 and NO-bearing flue gas. The hazardous solid wastes were effectively used to treat flue gases through this technology. The mechanism in the synergistic reduction and activation process was elucidated. The coupling effect between the reduction reactions of Fe2O3, Fe3O4, FeO, MgFe2O4, CaFe2O4, ZnFe2O4, KFeO2, and NaFeO2 in the dusts and activation reaction of C in the coal promoted the synchronous reduction and activation process.

Preparation of lignite-based porous carbon for high performance supercapacitor and the correlation between pore structures and electrochemical performance

Porous carbon exhibits considerable potential in energy storage field due to its remarkable electrical conductivity and adjustable pore structure. Nevertheless, the electrochemical performance of the material will be significantly impacted by its unreasonable pore structure. In this study, lignite was used as raw material to prepare lignite-based porous carbon by one-step activation method and the pore structure was optimized to improve its electrochemical performance and expand the utilization of low-rank coal. The results reveal that the porous carbon prepared at 600 °C has a higher specific surface area (940 m2 g−1) and a suitable pore structure (71 % mesopore), which enable adequate charge storage and fast transport of electrolyte ions, resulting in excellent electrochemical performance. In the three-electrode system, the lignite-based porous carbon exhibits a notable specific capacity of 331 F g−1 at the current density of 0.5 A g−1 and retains 96.4 % initial capacitance after undergoing 10,000 cycles. When assembled into a symmetrical supercapacitor, the device provides an energy density of 6.5 Wh kg−1 at a power density of 250 W kg−1. Even after 10,000 cycles, the capacitance retention rate is kept at 91 %, and the coulombic efficiency remains close to 100 %. These findings demonstrate that cost-effective porous carbon can be prepared by a simple route using lignite, hence exhibiting promise as electrode materials for high-performance supercapacitors.

FeCl3 induced catalytic activation prepared porous carbon with carbon nanotube skeleton from coal for supercapacitor electrodes

Poor conductivity and pore utilization of porous carbon (PC) have limited its use for supercapacitor electrodes. A simple FeCl3 induced catalytic KOH activation method was used to adjust the pore structure and graphitic carbon skeleton of coal-based PC. Under atmosphere of activation, the Fe component can be transformed into Fe3C, and then the Fe3C may act as catalysts for the deposition of activated gases, such as CO and CH4, to form carbon nanotubes (CNTs). As a result, the CNTs as graphite skeleton in situ growth in the PC (PC-CNTs), which enhances the conductivity and stability of the materials. The PC-CNTs sample shows hierarchical porous structure with surface area (SBET) of 2178.11 m2 g−1. As supercapacitor electrode, it exhibits a specific capacitance of 224.41 F g−1 at a current density of 1 A g−1, and maintains 182.66 F g−1 at 10 A g−1. Furthermore, a PC-CNTs//PC-CNTs symmetrical supercapacitor retains 98 % of its initial capacitance after 20,000 cycles at 1 A g−1. This study employed in situ pyrolysis gas from coal as a carbon source to prepare CNTs for adjusting the pore structure and graphitization of PC, which provides new insights for the utilization of low-rank coal in supercapacitor applications.

Novel insight into calcium-catalyzed steam gasification behaviors of lignite

Lignite is a low-rank coal with abundant reserves, and direct combustion causes serious environmental pollution. Calcium-catalyzed steam gasification is a cleaner technology that can convert lignite into high-value fuels and chemicals. However, the detailed structural evolution of calcium species during lignite steam gasification remains inadequately understood. The present work addresses this issue by subjecting the calcium-catalyzed steam gasification process of lignite to a detailed analysis, focusing on both the pyrolysis and gasification stages. The transitions in the chemical structures of the lignite and calcium catalysts during the pyrolysis stage were investigated in situ by Fourier Transform Infrared Spectroscopy. The morphological and chemical characterization of chars was performed using SEM-EDS, Raman spectroscopy, XPS, and N2 adsorption/desorption. The catalytic performance and gas composition were investigated by TGA and a fixed-bed reactor during the gasification stage. The results verify that the calcium catalyst reduced the initial gasification temperature of lignite by 150 °C, resulting in a 13.91% increase in the H2 concentration of the synthesis gas and an improvement of the H2/CO ratio to 20.96. The active Ca-C site and intermediate Ca-O-C formed during the co-pyrolysis stage increase the defect density of char, and the transformation of organic calcium species catalyzes the gasification of lignite. The enhanced concentration of H2 in the syngas can be attributed to the catalytic effect of CaO on the water–gas shift reaction during the gasification process. These results are expected to guide efforts in supporting catalytic conversion processes and promoting the efficient utilization of low-rank coal.

Evaluating the low-rank coal degradation efficiency bioaugmented with activated sludge

Microbial bioaugmentation of coal is considered as a viable and ecologically sustainable approach for the utilization of low-rank coals (LRC). The search for novel techniques to derive high-value products from LRC is currently of great importance. In response to this demand, endeavors have been undertaken to develop microbially based coal solubilization and degradation techniques. The impact of supplementing activated sludge (AS) as a microbial augmentation to enhance LRC biodegradation was investigated in this study. The LRC and their biodegradation products were characterized using the following methods: excitation-emission Matrices detected fluorophores at specific wavelength positions (O, E, and K peaks), revealing the presence of organic complexes with humic properties. FTIR indicated the increased amount of carboxyl groups in the bioaugmented coals, likely due to aerobic oxidation of peripheral non-aromatic structural components of coal. The bacterial communities of LRC samples are primarily composed of Actinobacteria (up to 36.2%) and Proteobacteria (up to 25.8%), whereas the Firmicutes (63.04%) was the most abundant phylum for AS. The community-level physiological profile analysis showed that the microbial community AS had high metabolic activity of compared to those of coal. Overall, the results demonstrated successful stimulation of LRC transformation through supplementation of exogenous microflora in the form of AS.

Optimization of Flotation Conditions for Long-Flame Coal Mud by Response Surface Method

With the application of modern coal mining technology and the fact that there are fewer and fewer high-quality coal seams, the quality enhancement and utilization of low-rank coal are gaining more and more attention. To solve the problems of high consumption of chemicals and low recovery of refined coal in the flotation separation process of low-rank coal, the long-flame coal from the Inner Mongolia Autonomous Region of China was selected as the research object, and the factors affecting the flotation process were analyzed and optimized by adopting the response surface method and establishing a regression model with high precision and reliability. The test results showed that the primary and secondary relationships of the factors on the fine coal yield were as follows: slurry concentration > frother dosage > collector dosage; and the primary and secondary relationships of the factors on the flotation refinement index were as follows: slurry concentration > collector dosage > frother dosage. The optimal conditions for flotation were 2453.09 g/t of collector, 795.84 g/t of frother, and 50.04 g/L of slurry concentration. Under these conditions, the fine coal yield was 51.51%, and the relative error of 53.71% was 4.27%. The flotation refinement index was 21.34%, and the relative error with the predicted value of 21.58% was 1.12%. The relative error of the experimental results was within a reasonable range, which indicated that the regression model obtained by the response surface method was highly reliable. The research results are of great significance to strengthen the comprehensive utilization of long-flame coal in full particle size and improve the economic benefits of coal enterprises.

The coupling transformation process of biodegradation and pyrolysis for Dananhu low-rank coal

The study presented a novel approach for coupling biodegradation and pyrolysis to transform low-rank coal. In the first stage, four kinds of bacteria, Planomicrobium huatugouensis (P. huatugouensis), Sphingomonas polyaromaticivorans (S. polyaromaticivorans), Pseudomonas putida (P. putida), and Bacillus subtilis subsp. subtilis (B. subtilis subsp. subtilis), were used to transform the Dananhu low-rank coal. After the first stage, the coal that has not been biodegraded (residual coal) undergoes the second stage of pyrolytic transformation, which is carried out by a thermogravimetric analyzer combined with Fourier-transform infrared spectrometry (TG-FTIR). The results showed that the maximum coupling transformation rate of biodegradation and pyrolysis could reach 73.95%, which was 21.88% higher than the thermal transformation rate of Dananhu low-rank coal and 27.37% higher than the optimal microbial transformation rate. This indicated that coupling transformation could significantly improve the utilization rate of Dananhu low-rank coal. In the stage of biodegradation transformation, bacteria destroyed the carboxyl groups, ether bonds, and other oxygen-containing functional groups in Dananhu low-rank coal, converting the large molecules of coal into liquid molecules, meanwhile, the compact coal structure became loose, and the residual coal was also pyrolyzed easily than Dananhu low-rank coal. During the pyrolysis process, a large number of fatty chains, carboxyl groups, oxy groups, and hydroxy groups were decomposed to produce lots of gas-phase products. The pyrolysis products showed an increase in the release of CO and CH4, and an increase in the proportion of aliphatic hydrocarbons in the volatiles. The high efficiency of coupling transformation is due to the combination of the advantages of the two technologies, which is achieving the green and energy-efficient utilization of low-rank coal.

Catalytic upgrading of Naomaohu coal pyrolysis volatiles over NiAl and NiLiAl oxides

Catalytic upgrading of volatiles is an essential technology to improve the product distribution of pyrolysis for the clean and efficient utilization of low-rank coals. In this work, novel acid-base bifunctional catalysts composed of Ni/Li/Al oxides were designed and prepared using LDH precursors with tunable chemical composition and structural properties. The catalysts were systematically characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), physisorption, NH3-temperature programmed desorption (NH3-TPD), CO2-temperature programmed desorption (CO2-TPD), H2-temperature programmed reduction (H2-TPR), and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). A two-stage fixed bed reactor was employed to evaluate the performance of the catalysts. Characterization results suggest that the crystal size of NiO and the surface area of the catalyst decreased with increasing Li content and decreasing Ni content in the catalyst, while the pore volume and pore diameter were positively correlated with Li content. Moreover, the addition of Li reduced the amount of weak acid sites and raised the amount of total basic sites. Consequently, the bifunctional catalysts boosted the yield of light tar and the contents of aromatics and phenols in tar. Specifically, with the highest total acid sites (569 μmol/g) promoting the cracking of heavy pitch components, Ni2.5Li0.5Al1 decreased the content of pitch in tar to 23.8 wt%, representing a 42.7 % drop from the corresponding non-catalytic pyrolysis. Accordingly, it improved the light tar yield to 7.2 wt%, which was 18 % higher than non-catalytic pyrolysis. 450 °C is identified as a suitable temperature for the catalytic upgrading of volatiles from Naomaohu coal; higher catalysis temperatures at 500 °C and 550 °C led to lower tar yield and lower phenols content, along with higher gas yield and more carbon deposition.

Mild Alkaline-Enhanced depolymerization of Long-Flame coal for the synthesis of Coal-Derived fluorescent carbon dots with application as probes

The intricate composition and structural of low-rank coal have hindered its broad utilization in the field of material science. The study utilized an alkaline hydrothermal method to enhance the depolymerization of long-flame coal and achieve the purification of fluorescent carbon dots for the first time, which were then being employed for the trace detection of Cu2+ or Fe3+ ions. The carbon extraction efficiency reached 58 %, with the carbon dots averaging size of 1.36 ± 0.42 nm, the sp2 hybridized structure of the carbon dots indicated successfully purification under alkaline conditions. After reduction with sodium borohydride, defects in the core region of the carbon dots were repaired, and the C = O functional groups were transformed into O–H groups, leading to an increase in fluorescence intensity. At a concentration of 0.25 g/L of carbon dots, demonstrated high emission intensity at both long and low emission wavelengths, which can be used as LED luminescent material. Furthermore, the application of these carbon dots in detecting heavy metal ions (Cu2+, Fe3+) in aqueous solutions was explored, showing as low as detection limit of ∼ 0.04 μM. This study achieved higher depolymerization of coal and purification of fluorescent carbon dots for use in probe-based detection, providing fresh perspectives on the high-value utilization of low-rank coal.

Equilibrium study for mercury removal using sub-bituminous coal and its application on ex-gold mining soil contaminated with mercury

Optimizing the potential utilization of low-rank coal, such as sub-bituminous coal (SC), can improve and maintain soil quality and productivity through amelioration technology. This potential is especially in controlling heavy metals such as Hg. This study aimed to examine the geochemistry of SC and the adsorption mechanism of Hg with SC through an adsorption isotherm model approach developed for experimental equilibrium. The geochemical of SC has an atomic composition of C (43.60%), O (40.64%), N (11.96%), Si (1.57%), Al (1.06%), Ca (0.92%), Mg (0.14%) and K (0.11%) and oxide composition dominated by SiO2 (57.07%), as well as O-H and N-H functional groups, C-H C-H, C=C-H, C=O, and C=C-H and minerals (quartz, magnetite, mica and muscovite). Characteristics of SC have a proximate composition (16.99% moisture, 97.81% volatile matter, 69.63% ash, and 28.19% fixed carbon) and chemical properties of pH, EC, CEC, OC, and total N (5.23, 1.38 dS m-1, 35.33 cmol(+) kg-1, 9.81% C, and 0.16% N). The adsorption capacity and coefficient of Hg2+ by SC were 304.32 mg g-1 and 78.67 L kg-1 at pH 1.26 and Hg2+ concentration 100 mg L-1 with a removal efficiency of 76.08%. Hg2+ adsorption isotherms occurred in Langmuir (RL = 0.97 and R² = 1)>Freundlich (1/n = 1.05 and R² = 0.9999) models. The application of 40 t SC ha-1 on ex-gold mining soil contaminated with Hg significantly decreased the total Hg in the soil by 2.50 mg kg-1 and a removal efficiency of 36.37% with increased pH H2O (0.35), OC (0.041% C), and CEC 2.14 cmol(+) kg-1, compared to control.

Oxygen bond cleavage and its migration mechanisms during pyrolysis of naomaohu sub-bituminous coal

Investigating the oxygen bond cleavage and its migration mechanisms during the pyrolysis process of sub-bituminous coals is essential for their classification utilization. The present study employed a fixed-bed pyrolysis technique (temperature range: 350–600 °C) to explore the cleavage of oxygen-containing bonds and subsequent behavior of oxygen migration and transformation during the pyrolysis process of Naomaohu sub-bituminous coal (NSBC). X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy results reveal that the organic oxygen in NSBC predominantly exists as the form of C–O bonds, accounting for 22.81 wt% of the total composition, mainly encompassing hydroxyl, carbonyl, ester, and ether groups. The organic oxygen in the light tar is mainly in the form of phenols, reaching 1.71 wt%, of which methyl substituted phenols is predominant at a final pyrolysis temperature of 600 °C. This can be attributed to the presence of more aryl ether bonds and hydroxyl groups in NSBC, which are prone to cleavage at higher temperatures, resulting in the formation of phenoxyl radicals. Additionally, the higher temperature facilitates the weakening of hydrogen bonds between phenolic hydroxyl groups, thereby enhancing the yield of phenolic compounds. The ester compounds present a decreasing trend with increasing temperature, primarily associated with the cleavage temperature of ester linkers being 350 °C, suggesting that an increase in temperature favors the cleavage of ester bonds. In addition, the cleavage of C–O bonds begins to accelerate significantly during the pyrolysis temperature range of 450–500 °C, subsequently accounting for the pronounced proliferation of phenols within this specific thermal interval. The oxygen content in semi-coke decreased with the increase of temperature, from 85.27 wt% at 350 °C to 37.17 wt% at 600 °C, while the oxygen content in the pyrolysis gas increases from 11.63 wt% at 350 °C to 47.53 wt% at 600 °C, indicating that a significant migration of organic oxygen to the pyrolysis gas during the pyrolysis of NSBC. This study can deepen the understanding of the transformation mechanism of oxygen-containing structure in NSBC pyrolysis process, and provide a theoretical basis for high-grade utilization of low-rank coals.

Synergistic consideration of co-treatment of sewage sludge, low-rank coal, and straw for sustainable resource utilization and enhanced energy efficiency: a review.

This article provides a comprehensive exploration of the imperative necessity for coupling the utilization of low-rank coal, sewage sludge, and straw. It studies the challenges and limitations of individual utilization methods, addressing the unique hurdles associated with feedstocks. It focused on achieving integrated and sustainable resource management, emphasizing efficient resource utilization, waste minimization, and environmental impact reduction. The investigation extends to the intricate details of reaction processes in co-processing, with a specific emphasis on the drying of raw materials to enhance combustion characteristics. The molding and preparation of feedstock are dissected, encompassing raw material selection, mixing, and the crucial addition of additives and binders. The proportions and homogenization of these feedstocks are intricately examined for uniformity and effectiveness. Furthermore, it presents theoretical approaches for investigating the co-combustion of these diverse feedstocks, contributing a solid foundation for future studies in this dynamic field. The findings presented in it offer valuable insights for researchers, practitioners, and policymakers seeking sustainable solutions in the co-disposal technology of these feedstocks. Therefore, it provides a holistic understanding of the challenges and opportunities in coupling the utilization of these selected feedstocks. By addressing individual limitations and emphasizing integrated resource management, the article establishes the groundwork for sustainable and efficient co-processing practices. The exploration of reaction processes gives a comprehensive framework for future research and application in the field of co-combustion technology. The insights gleaned from this study contribute significantly to advancing knowledge in the sustainable utilization of diverse feedstocks, guiding efforts towards environmentally responsible and resource-efficient practices.

High-efficiency co-liquefaction of low-rank coal and PAEs-rich PVC waste in supercritical water: Products upgrading and dechlorination

With the extensive use of phthalates (PAEs)-rich polyvinyl chloride (PVC) plastic products, the recycling of PAEs-rich PVC waste has become a great challenge. Meanwhile, the efficient utilization of low-rank coal is important in China due to the abundant reserves. In this study, a high-efficiency co-liquefaction treatment of PAEs-rich PVC waste and low-rank coal (Inner Mongolia lignite) was developed by using supercritical water (SCW) process based on the interaction between the two kinds of waste. The effects of temperature, time, solid-to-liquid ratio (MCoal+PVC:MH2O), and mass ratio of coal-to-PVC (MCoal:MPVC) on the co-liquefaction conversion, composition of liquefied oil and dechlorination of PVC waste were investigated. The co-liquefaction of low-rank coal and PAEs-rich PVC waste had a significant positive synergistic effect with a maximum synergistic efficiency of 7.53% in the temperature range of 350–450 °C. The conversion ratio of low-rank coal and PAEs-rich PVC waste by SCW co-liquefaction increased from 59.71% to 74.92% with the increase of reaction temperature from 350 to 450 °C. PAEs-rich PVC waste could be almost completely dechlorinated (>98%) by the SCW co-liquefaction process, and more than 90% of the DEHP could be decomposed. The addition of PAEs-rich PVC waste resulted in a significant decrease of the percentage of heteroatom-containing compounds in the oil products by the co-liquefaction. At 450 °C, the co-liquefaction oil contained 69.16% of hydrocarbons and 6.14% of phenolic compounds. Different from supercritical water gasification, the purpose of SCW co-liquefaction in this study is to improve the coal liquefaction conversion ratio and oil quality by introducing the PAEs-rich PVC waste. The synergistic SCW treatment of PAEs-rich PVC waste and low-rank coal has good application prospects in products upgrading of low-rank coal and safe recycling of PAEs-rich PVC waste plastics.

Catalytic ethanolysis of Hanglaiwan long flame coal to organic small-molecular compounds under mild conditions over SAPO-34-supported nickel nanoparticle catalyst

SAPO-34-supported nickel nanoparticle catalyst Ni/SAPO-34 was prepared by a modified deposition-precipitation method and nickel nanoparticles were uniformly dispersed onto the SAPO-34 crystal surface. Hanglaiwan long flame coal (HLFC) was subjected to the catalytic ethanolysis (CE) over Ni10%/SAPO-34 at 300 °C under 1 MPa of initial nitrogen pressure for 4 h to obtain more soluble organic small-molecule compounds (SOSMCs). Ni10%/SAPO-34 can effectively activate ethanol to release H+, +CH2CH3, and H-, and then precisely cleave >CH-O- and >Car-O- bridged bonds in HLFC. As a result, the total yield of soluble portion (SP) increases from 43.2 to 60.5 wt%. Arenes and oxygen-containing organic compounds are the main SOSMCs detected in SPCE from the CE and SPNCE from the ethanolysis, and the yields of arenes, hydroarenes, and phenols in SPCE are higher than those in SPNCE. In addition, compared to SPNCE, the condensation degree of aromatic rings in SPCE is higher. This investigation provides a promising alternative to the clean and value-added utilization of low-rank coals.

Study on classification separation of low-rank coal macerals using hydrocyclone and enhanced gravity separator

ABSTRACT Efficient enrichment of macerals improves the liquefaction efficiency of low-rank coal. The paper studied the characteristics of Shendong low-rank coal, including proximate and ultimate analyses, size and density compositions, and petrographic analysis, as well as the migration regularity of narrow particle size of low-rank coal macerals in the enhanced gravity field. On this basis, a novel classification separation process for low-rank coal macerals using Krebs hydrocyclone and enhanced gravity separator was proposed. The classification size was determined to be 0.074 mm and Krebs hydrocyclone achieved a satisfactory classification effect with a classification efficiency of 84.72%. Based on the enhanced gravity separation results of macerals from hydrocyclone underflow and overflow, the optimal sorting solutions for underflow and overflow were obtained through response surface analysis, respectively. Through the novel classification separation process, the vitrinite content of clean coal has been increased from 46.60% to 61.33% with an outstanding recovery of 77.40%. The novel classification separation process using hydrocyclone and enhanced gravity separator develops an excellent enrichment effect for low-rank coal macerals, which also provides a prospective approach for the cleaner utilization of low-rank coal.

Study on preparation of ultra-clean coal from bituminous coal using the ionic liquid extraction

ABSTRACT In order to realize clean and efficient utilization of low rank coal, ultra-clean coal preparation is an important method. A clean and efficient method of producing ultra-clean coal is urgently needed, given the high environmental impact and corrosiveness of the chemicals used in the traditional chemical preparation of ultra-clean coal. In this study, ultra-clean coal was prepared by leaching using acidic imidazole ionic liquids, and the effects of temperature, time and concentration on the reaction process were investigated. The ash composition of the sample and the ash removal mechanism under the ionic liquid were revealed, and the evolution law of the microstructure and functional group characteristics was clarified. The research showed that the concentration and temperature had a large influence on the ash content of the product during the leaching process, and the reaction time had a small influence. The minimum ash content of the ultra-clean coal could reach 0.89% (dry basis). In the ionic liquid system, iron, calcium and magnesium in the coal were effectively removed, the iron oxide content was significantly reduced and calcium salts except calcium sulfate were effectively removed, while periclase was almost completely removed. However, the removal of silicon and aluminum was poor. Most of the alumina and silica remained in the ultra-clean coal. Extracted coal had more cracks and rougher surface than raw coal, the BET surface area decreased from 2.8579 to 2.4032. Under the influence of ionic liquid, the Aar/Aal ratio, which evaluates the aromaticity of coal, increased from 0.3702 to 0.8569, indicating that the aromaticity of coal was significantly improved. The CH2/CH3 ratio describing the length and branching degree of aliphatic chains in coal decreased from 4.0849 to 3.1516 which showed that ionic liquids can effectively reduce the length of aliphatic side chains, weakening the coal’s oxidizing activity. The pyrolysis curve of coal shifted to the high temperature zone and the peak temperature increased, indicating the effect of ionic liquids on the chemical stability of coal.

MIL pretreatment on breaking hydrogen bond and swelling of coal: Experiment and simulation

Since direct combustion of low-rank coal is inefficient, expansion and dissolution are essential for better use of coal as an energy source. In this study, [C8mim]FeCl4 molecular configuration was synthesized by quantum chemical simulation method, and Magnetic ionic liquid (MIL) was used to modify coal to improve its swelling efficiency. The FT-IR and Raman properties of MIL were measured by simulation combined with practical methods. Dmol3 was used to study the hydrogen bond changes of coal molecules induced by MIL. When MIL interacts violently with organic matter in coal, the cross-linking network structure generated by non-covalent bonds is destroyed, resulting in the break of covalent bonds such as hydrogen bonds. Further experimental study shows that the pore structure and surface morphology of modified coal samples will be damaged, indicating that the MIL has the ability to dissolve hydrogen bonds and pretreat low-rank coal. It was found by TGA that MIL treatment can increase the tar yield of coal by up to 4.79% and reduce ash content by 3.51%. Through the integration of molecular modeling and experimental analysis, this study elucidates the fundamental principles underlying MIL pretreatment of coal, thereby providing a viable strategy for efficient quality improvement utilization of low-rank coal.

Study on low-rank coal surface wettability effect and recyclability of different anionic magnetic ionic liquids

Three types of magnetic ionic liquids (MIL) ([C12mim]FeCl4, [C12mim]2CoCl4, and [C12mim]2NiCl4) were chosen to study the enhancement of the quality and utilization of low-rank coal (LRC). The mechanism of coal wettability modification was explained from the macrocosm and microcosm points of view by contact angle, adhesion work, and adsorption studies, and the recovery of MIL was realized by salting out the separation-strong magnetic recovery (SMR). The contact angle and adhesion work results showed that [C12mim]FeCl4 had the greatest effect on coal wettability. The adsorption on the LRC surface was as follows: [C12mim]FeCl4 > [C12mim]2CoCl4 > [C12mim]2NiCl4. The adsorption thermodynamics indicated that MIL conformed to the Langmuir isotherm model, which is a spontaneous reaction of exothermic entropy minus physical adsorption. The adsorption kinetic process belong to the pseudo-second-order kinetic model and was influenced by the combined action of intraparticle and liquid film diffusion. From the contact angles and adsorption thermodynamics, it can be inferred that [C12mim]FeCl4 has the highest activity and can better adsorb onto the LRC surface, covering the oxygen-containing functional groups and reducing the wettability to achieve efficient quality improvement and utilization of LRC. Through the research of salting-out separation-SMR, the most suitable salting-out reagent was found to be NaCl, and the highest recovery was obtained when the concentration reached the solubility level. As the magnetic field strength increases, the recovery rate gradually increases. The recovery of [C12mim]FeCl4 was more than 90% when it reaches 1.5 T, and it could be recovered by magnetic separation.