Search

Sustainable use of croplands is facing a challenge to maintain organic carbon (C) in soil. Pyrolyzed coal or coal char (CC) is a porous C material produced from the pyrolysis of coal containing high organic C, large surface area, and low bulk density like biochar (BC). This study evaluates corn (Zea mays L.) grain yield and selected soil properties in soil amended with CC and BC at two rates (22 and 44 Mg ha−1) with farmyard manure (FM) (66 Mg ha−1) and without FM addition. This field experiment was performed in sandy loam soil at the University of Wyoming's Sustainable Agricultural Research and Extension Center (SAREC), Lingle, WY, USA. Two years of field study results indicated CC and BC applied at 22 Mg ha−1 with FM resulted in significantly greater average corn grain yields (13.04–13.57 Mg ha−1) compared to the no char's treatment (11.42 Mg ha−1). Soil organic matter (SOM) content was significantly greater in the higher application rates of CC and BC than in treatments without chars. Overall, soil nitrate nitrogen (NO3-N), phosphorous (P), and potassium (K) were found significantly greater in CC and BC co-applied with FM treatments. Soil water-holding capacity (WHC) significantly improved in sandy loam soil (up to 27.6% more than the no-char treatment) at a greater concentration of char materials. This study suggests that char materials applied at a moderate rate (22 Mg ha−1) with FM can improve soil properties and crop yield. [ABSTRACT FROM AUTHOR]

Copper slag is not only a waste but it has many valuable and recoverable metals present in it such as iron. Therefore, this study focuses on the utilization of waste materials i.e., copper slag and tire char for iron recovery. Four calcium salts, i.e., CaCO3, Ca(OH)2, CaCl2, and CaSO4, with different dosages, reduction temperature, reduction time, and atmospheric conditions were investigated in order to find best reaction mechanism for iron recovery. Among these salts, the optimum conditions were determined: using CaCO3 under 0.384 of CaO/SiO2 molar ratio in a 60-min reduction period at 1473.15K temperature, that gives 91.14% iron recovery. Both FESEM-EDS data and chemical titration showed more than 70% of the highest iron grade in the recovered product. The analysis results indicate that main impurity in the whole procedure was carbon from coal char that reduces the iron grade. This research not only provides a novel way to recover iron from copper slag, but also provides a future direction to handle copper slag and tire char waste materials. [ABSTRACT FROM AUTHOR]

A macro-thermobalance (macro-TGA) was applied to investigate the steam co-gasification characteristics of the chars produced from Huainan coal (HN), two types of biomasses, sawdust (SD) and wheat straw (WS), and coal-biomass blends at 900–1200 °C under rapid heating conditions. The gasification reaction kinetics were determined by the homogeneous reaction model (VM), shrinking core model (SCM) and random pore model (RPM), and the optimal model was selected by deviation calculation. The results show that the char gasification reactivity increased with the increase of temperature. The promotion effect of biomass semi-coke on coal char mainly occurred in the stage when the carbon conversion rate was greater than 0.5, which is mainly attributed to the migration of active AAEMs to the surface of coal char to catalyze the gasification reaction in the later stage. However, with the increase in temperature, this promoting effect is weakened due to the increasing influence of mass transfer effects over chemical rate control, and increased volatilization of the inorganic species. The RPM model is suitable for describing the coal char gasification process, while the SCM was the model that best fitted the biomass semi-coke and coal/biomass blends, which elucidates the kinetic mechanisms governing the gasification process.

Copyright of Low-Carbon Chemistry & Chemical Engineering is the property of Low-Carbon Chemistry & Chemical Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The heat of hydration is fundamental in understanding the hydration mechanism of cementitious materials, and temperature can significantly affect the heat of hydration. A recent study has shown that coal-derived char can be used as a green additive for improving the engineering properties of conventional cement grout. However, the impact of temperature on heat of hydration of char-cement grout is currently unknown. In this study, the heat of hydration (with degree of hydration) of cement and char-cement grouts at 5, 23, and 35 °C are investigated. This study reveals that incorporating char into the cement grout enhances its degree of hydration at temperatures ranging from 5 to 35 °C, highlighting the potential advantages of using coal char in grouting applications, especially at low temperature.

Soil degradation due to loss of soil organic carbon is a serious concern in semiarid agroecosystems. Biochar and other organic char products have long been known to increase soil organic carbon. In this study, three-year field observations were carried out on use of coal char (CC) and biochar (BC) as soil amendments in unirrigated semiarid rangeland soil. Coal was pyrolyzed at three different temperatures of 650, 750, and 800 °C to form CC650, CC750, and CC800, respectively, and BC was obtained from a local commercial producer. Manure, CC, and BC were incorporated in soil at 10% (v/v). Analyses of plant growth (aboveground biomass) and soil properties were performed and compared with the control treatment without char. In all three years, CC applied with manure (CC650M) produced significantly greater grass biomass, by 95, 42, 101%, and BC applied with manure (BCM) increased grass biomass by 89, 39, 52% in 2018, 2019, and 2020, than the controls in the respective years. Soil tests a year after application of char indicated significantly increased soil organic matter (OM) with CC and BC treatments (1.60–2.93%) compared with the control (1.37%). However, further detailed studies are required to investigate CC and BC interactions with soil in unirrigated semiarid rangelands. [ABSTRACT FROM AUTHOR]

Sustainable use of croplands is facing a challenge to maintain organic carbon (C) in soil. Pyrolyzed coal or coal char (CC) is a porous C material produced from the pyrolysis of coal containing high organic C, large surface area, and low bulk density like biochar (BC). This study evaluates corn (Zea mays L.) grain yield and selected soil properties in soil amended with CC and BC at two rates (22 and 44 Mg ha−1) with farmyard manure (FM) (66 Mg ha−1) and without FM addition. This field experiment was performed in sandy loam soil at the University of Wyoming’s Sustainable Agricultural Research and Extension Center (SAREC), Lingle, WY, USA. Two years of field study results indicated CC and BC applied at 22 Mg ha−1 with FM resulted in significantly greater average corn grain yields (13.04–13.57 Mg ha−1) compared to the no char’s treatment (11.42 Mg ha−1). Soil organic matter (SOM) content was significantly greater in the higher application rates of CC and BC than in treatments without chars. Overall, soil nitrate nitrogen (NO3-N), phosphorous (P), and potassium (K) were found significantly greater in CC and BC co-applied with FM treatments. Soil water-holding capacity (WHC) significantly improved in sandy loam soil (up to 27.6% more than the no-char treatment) at a greater concentration of char materials. This study suggests that char materials applied at a moderate rate (22 Mg ha−1) with FM can improve soil properties and crop yield.

Non-isothermal kinetics of coal/char conversion obtained by model-fitting and model-free methods are always very different, and the effect of heating rate β on the kinetics is unclear. In this study, the oxyfuel combustion kinetics of two coal chars (NCP anthracite, DT bituminous) at βs of 2.5–40 K/min are investigated through thermogravimetric analysis. The direct model-fitting methods (DMFMs), the isothermal model-fitting method (IMFM) and the model-free methods (MFRMs) were used to obtain the non-isothermal kinetics. The results show that all the above models can fit experimental data well, due to the coefficients of determination values of these models are all above 0.99. However, the activation energies, Es, at different βs obtained by the DMFMs differ greatly from the isothermal kinetic parameters, the maximum differences in Es are 43–57 and 22–35 kJ/mol for the NCP and DT chars, respectively; while the Es obtained by the IMFM are almost same for each char, and more consistent with the isothermal experimental results, indicating β has little influence on the E. Moreover, the MFRMs are difficult to distinguish the influence of coal rank, due to the obtained mean (E¯) values of both chars conversion are practically equal, and much lower than the isothermal experimental results. Therefore, the IMFM is more suitable than DMFMs and MFRMs, for determining the non-isothermal kinetics of char oxyfuel conversion.

Catalytic CO 2 methanation is a potential solution for conversion of CO 2 into valuable products, and the catalyst plays a crucial role on the CO 2 conversion and CH 4 selectivity. However, some details involved in the CO 2 methanation over the carbon supported Ni catalysts are not yet fully understood. In this work, commercial coal char (CC) supported Ni catalysts were designed and prepared by two different methods (impregnation-thermal treatment method and thermal treatment-impregnation method) for CO 2 methanation. Effects of the preparation conditions (including the thermal treatment temperature and time, the mass ratio of CC:Ni and the preparation method), as well as the reaction temperature of CO 2 methanation, were investigated on the catalyst morphology, reducibility, structure and catalytic performance. Fibrous Ni-CC catalyst is achieved and shows high CO 2 conversion (72.9%–100%) and CH 4 selectivity (>99.0%) during the 600-min methanation process. Adverse changes of the catalyst surface and textural properties, reducibility, particle size and morphology are the potential factors leading to the catalyst deactivation, and possible solutions resistant to the deactivation were analyzed and discussed. The CO 2 methanation mechanism with the CO route was proposed based on the oxidation-reduction cycle of Ni in this work. [Display omitted] • Ni-coal char catalysts are prepared by two methods and used for CO 2 methanation. • Fibrous Ni-based catalyst shows CO 2 conversion >72.9% and CH 4 selectivity >99.0%. • CO 2 methanation mechanism with the CO route is proposed based on redox cycle of Ni. • Potential factors leading to catalyst deactivation and the solutions are discussed. [ABSTRACT FROM AUTHOR]

Soil degradation due to loss of soil organic carbon is a serious concern in semiarid agroecosystems. Biochar and other organic char products have long been known to increase soil organic carbon. In this study, three-year field observations were carried out on use of coal char (CC) and biochar (BC) as soil amendments in unirrigated semiarid rangeland soil. Coal was pyrolyzed at three different temperatures of 650, 750, and 800 °C to form CC650, CC750, and CC800, respectively, and BC was obtained from a local commercial producer. Manure, CC, and BC were incorporated in soil at 10% (v/v). Analyses of plant growth (aboveground biomass) and soil properties were performed and compared with the control treatment without char. In all three years, CC applied with manure (CC650M) produced significantly greater grass biomass, by 95, 42, 101%, and BC applied with manure (BCM) increased grass biomass by 89, 39, 52% in 2018, 2019, and 2020, than the controls in the respective years. Soil tests a year after application of char indicated significantly increased soil organic matter (OM) with CC and BC treatments (1.60–2.93%) compared with the control (1.37%). However, further detailed studies are required to investigate CC and BC interactions with soil in unirrigated semiarid rangelands.

Molten carbonate direct carbon fuel cells (MC-DCFCs) allow the efficient and clean use of coal. In this study, a novel anode structure is designed, and the performances of six coal-based fuels are investigated in MC-DCFC. The mechanisms of performance differences are investigated, as well as the effect of operating temperature on performance. The results reveal the fuel cell performance in the following order: meagre coal (109.8) ≈ bituminous coal (108.7) > bituminous coal char (98.1) > lignite coal (83.7) > lignite coal char (71.3) > meagre coal char (53.2) in mW cm−2. Coal performs better because of its high carbon content, high volatile content, rich oxygen-containing functional groups, larger specific surface area, stronger thermal reactivity, and other factors. The electrochemical reactivity of coal fuel increased with higher reaction temperatures and varied throughout the temperature ranges. This study implies that using coal fuel to commercialize MC-DCFC could be a realistic alternative. [Display omitted] • Performance of six coal fuels are investigated in an MC-DCFC with a new anode. • Maximum peak power density of 109.8 mW cm−2 is obtained with a meagre coal. • Mechanism of their performance differences is analyzed. • Their performance stability are discussed. • Effect of operating temperature on the performance is explored. [ABSTRACT FROM AUTHOR]

Copyright of Clean Coal Technology is the property of Clean Coal Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A macro-thermobalance (macro-TGA) was applied to investigate the steam co-gasification characteristics of the chars produced from Huainan coal (HN), two types of biomasses, sawdust (SD) and wheat straw (WS), and coal-biomass blends at 900–1200 °C under rapid heating conditions. The gasification reaction kinetics were determined by the homogeneous reaction model (VM), shrinking core model (SCM) and random pore model (RPM), and the optimal model was selected by deviation calculation. The results show that the char gasification reactivity increased with the increase of temperature. The promotion effect of biomass semi-coke on coal char mainly occurred in the stage when the carbon conversion rate was greater than 0.5, which is mainly attributed to the migration of active AAEMs to the surface of coal char to catalyze the gasification reaction in the later stage. However, with the increase in temperature, this promoting effect is weakened due to the increasing influence of mass transfer effects over chemical rate control, and increased volatilization of the inorganic species. The RPM model is suitable for describing the coal char gasification process, while the SCM was the model that best fitted the biomass semi-coke and coal/biomass blends, which elucidates the kinetic mechanisms governing the gasification process. [Display omitted] • Macro-TGA was applied to analyze the steam gasification kinetics of blended chars. • The most synergistic interaction occurred as the carbon conversion rate X > 0.5. • The AAEMs in biomass ash act as a catalyst to enhance the coal char reactivity. • Kinetic parameters in the chemical rate control regime were obtained by three models. • SCM model was identified as best for steam-gasification of coal-biomass blends. [ABSTRACT FROM AUTHOR]

In slag tapping furnaces, char particles undergo a series of complex structural evolution before and after being captured by the liquid slag layer. The evolution results affect the carbon conversion rate and are affected by temperature fluctuations, especially in the ash melting temperature zone. Experimental study on structure evolution of bituminous char prepared at around ash melting temperature was carried out on a fixed bed. The morphology, specific surface area and mineral chemical composition were measured at different temperatures. Experimental results show that the number density and the size of ash droplets exuded on the char surface increased significantly with the increasing temperature. The ash specific surface area from gasification was slightly greater than that from combustion. The residual content of chloride in the char become 1% and the contents of Fe, K, Mg and Na decrease significantly during the pyrolysis process across the ash melting temperature zone. The diffraction intensity of oldhamite increase which indicates the reaction of carbon substrate with minerals during the evolution; the diffraction intensity of quartz dramatically decreases for the reason of anorthite generation. The ignition and burnout temperatures of char were found to increase and the combustion stability decreased with the increasing pyrolysis temperature. [ABSTRACT FROM AUTHOR]

To address the issues of ignition difficulty, incomplete burnout, and high NOx emissions during coal char combustion in industrial applications, a series of co-firing experiments involving bituminous coal and its medium-temperature pyrolysis char were conducted using a micro fluidized bed analysis system. The experiments explored co-firing behaviors and NOx emission characteristics for five different fuel blending ratios in an environment with 21 % oxygen concentration, across temperatures between 923 K and 1223 K. The study delved into the synergistic effects of coal and char co-firing, as well as the influence of combustion temperature and fuel blend ratio on the co-firing efficiency and NOx emissions. The results show a synergistic effect in the co-firing of bituminous coal and char, influenced by reaction temperature and coal-to-char blend ratio, which evolves as combustion progresses. In the 923–1073 K range, initial coal addition to the blend enhances reactivity. However, as the reaction advances or coal content exceeds 75 %, this synergy shifts to an inhibitory effect. At temperatures above 1023 K, increased proportions of coal in the blend are associated with improved burnout rates, especially when the coal content is at or above 50 %. Moreover, at a combustion temperature of 1123K, there is a marked decrease in nitrogen oxide emissions, with coal blend ratio of 25 % and 50 % showing particular efficacy in reducing these emissions. These results provide valuable insights for the efficient and clean utilization of coal char in industrial combustion processes. • The synergistic effect of co-firing depends on the temperature and the blend ratio, and changes with the reaction process. • Between 923 and 1073K, bituminous coal initially enhances fuel reactivity but later or above 75 % content, it hinders the reaction. • Temperatures over 1023 K combined with coal contents at or exceeding 50 % lead to increased burnout rates. • NOx emissions attain lowest value at 1123 K, with coal proportions of 25 % and 50 %. [ABSTRACT FROM AUTHOR]

The NO heterogeneous reduction by char is one of the most prominent options to control NOx emissions from coal-fired power plants. Experiments on the char-NO heterogeneous reaction were carried out in an electrically heated fixed-bed reactor to investigate the effect of temperature, type of char, pretreatment method, additives and reaction atmosphere on the NO reduction capacity of char. The results showed that temperature plays a crucial role in the NO reduction by different char. The kinetic analysis showed that char-NO heterogeneous reaction is controlled by chemical kinetic below Tt and by diffusion kinetic above Tt. The value of transition temperature Tt depends on the types of char and ranges from 600 °C to 800 °C. The synergistic effect of specific surface area, mineral abundance and reactivity combine to result in the reduction efficiencies of different char. Oxygen has a promoting effect on the char-NO heterogeneous reaction, and the oxygen content of the promoting peak moves to low oxygen content with increasing temperature. At 1050 °C, the denitrification efficiency at 0.25% O2 content is 12.7% higher than that under oxygen-free conditions. At high temperatures, the promotion of the char-NO heterogeneous reaction by CO and the inhibition of the reaction by CH4 were more obvious. [ABSTRACT FROM AUTHOR]

To study the effect of anion in sodium salts on catalytic gasification and provide some useful information for the recovery and reutilization of catalysts, the catalytic reactivity of Na2CO3, Na2SO4, NaNO3 and NaCl was compared. In addition, the melting process of catalyst, mineral composition, specific surface area and CO2 adsorption ability of chars loaded with catalyst was measured by in situ hot stage microscope, XRD, BET and TGA. Moreover, the mineral transformations of catalytic gasification ash were also investigated by FactSage. The results indicate that anions in sodium salts have a significant effect on gasification. Among them, Na2SO4 and Na2CO3 can greatly accelerate the catalytic gasification rate of coal char. The char loaded with Na2SO4 or Na2CO3 shows more specific surface area and more adsorption capacity of CO2 than other chars. Simultaneously, the pictures captured by hot stage microscope reveal that Na2SO4 and Na2CO3 melt, become liquid film and then spread over char surface and neighboring particles; this facilitates the contact between carbon and catalyst and accelerates the gasification reaction. Na2SO4 is suitable for catalytic gasification from the aspects of its catalytic activity and convenience of recovery and reutilization. [ABSTRACT FROM AUTHOR]

Partial gasification of coal char was conducted with addition of metal oxides for co-production of fuel gas and methane decomposition catalysts. Effect of the metal composition (Ni, Co and Fe based mono- or bi-metals) was investigated on the fuel gas production and the resultant catalyst surface and textural properties, morphology and performance in catalytic methane decomposition (CMD). Besides H 2 -rich fuel gas production (the combustion energy up to 11.03–23.42 MJ/kg char) from the gasification, the gasification residue can directly serve as the effective and efficient catalyst for CMD. The Fe and Fe–Co composite oxides were found to be better among the mono- and bi-metallic oxides for the fuel gas production during the gasification, respectively. The Ni-based mono-/bi-metallic catalysts could display high and stable methane conversion (up to 80%) during the 600-min CMD test at 850 °C. Promotional role of the second metal in CMD was discussed on the carbon diffusion, metal mobility and reducibility, formation and growth of the deposited carbons. The formed carbon morphology after CMD was analyzed based on the Kirkendall effect and Tammann temperature and further correlated to the potential catalyst deactivation. [Display omitted] • Partial gasification of coal char (<39%) is studied with addition of metal oxides. • Co-production of H 2 -rich (>60%) fuel gas and CH 4 pyrolysis catalysts are achieved. • Effects of Ni, Co and Fe mono-/bi-metals are studied at the content of about 10%. • Kirkendall effect and Tammann temperature are used to analyze the formed carbons. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the evolution of the chemical structure of coal char during pyrolysis. Two bituminous coals (coals A and B) and one lignite (coal C) were pyrolyzed in a fixed bed in N2 from 600 °C to 1100 °C. The chemical structure of coal char was characterized by Raman spectroscopy and X-ray diffraction (XRD). The carbon and oxygen functionalities of coal char were analyzed by X-ray photoelectron spectroscopy (XPS). The Raman spectroscopic parameters AD/AG (AD1/AG, AD2/AG, and AD3/AG) increased from 600 °C to 900 °C and then decreased after 900 °C, indicating that the degree of order of coal char first decreased and then increased with increasing pyrolysis temperatures (600–1100 °C). The content of graphite-like microcrystalline carbon decreased and then increased with an increase in temperature. Prominent diffraction peaks of microcrystalline carbon for coal chars A and B were observed, but only minerals were shown in diffraction patterns of coal char C since the ash content of coal chars A and B is much lower that that of coal char C. The lateral size of the crystallite plane (La) generally increased between 600 °C and 1100 °C. The relative content of C=O and COOH in coal chars A and B generally decreased as the temperature increased, suggesting an increase in the degree of order at higher temperatures. The oxygen functionalities of coal char were composed of organic oxygen and oxygen-containing bonds of minerals. [ABSTRACT FROM AUTHOR]

Abstract This study examined an isothermal CO2 gasification of four chars prepared via two different methods, i.e., conventional and microwave-assisted pyrolysis, by the approach of thermogravimetric analysis. Physical, chemical, and structural behaviours of chars were examined using ultimate analysis, X-ray diffraction, and scanning electronic microscopy. Kinetic parameters were calculated by applying the shrinking unreacted core (SCM) and random pore (RPM) models. Moreover, char-CO2 gasification was further simulated by using Aspen Plus to investigate thermodynamic performances in terms of syngas composition and cold gas efficiency (CGE). The microwave-induced char has the largest C/H mass ratio and most ordered carbon structure, but the smallest gasification reactivity. Kinetic analysis indicates that the RPM is better for describing both gasification conversion and reaction rates of the studied chars, and the activation energies and pre-exponential factors varied in the range of 78.45–194.72 kJ/mol and 3.15–102,231.99 s−1, respectively. In addition, a compensation effect was noted during gasification. Finally, the microwave-derived char exhibits better thermodynamic performances than the conventional chars, with the highest CGE and CO molar concentration of 1.30% and 86.18%, respectively. Increasing the pyrolysis temperature, gasification temperature, and CO2-to-carbon molar ratio improved the CGE.

The endless and dramatic increase of global energy demand makes it imperative to develop sustainable, affordable, and efficient materials to act as electrocatalysts in the clean energy technologies. Electrocatalysts based on coal chars are promising materials as they can be considered as value-added by-products from coal combustion contributing to industrial ecology and circular economy. Therefore, herein we report the application of three sets of coal char (char concentrates before and after carbonization and demineralized and graphitized char concentrates) obtained from four different countries (Portugal, Romania, Poland, and South Africa) as oxygen reduction reaction (ORR) electrocatalysts. All electrocatalysts presented moderate ORR activity with some showing selectivity for the indirect two-electron process while others for a mixed regime between the two- and four-electron process. Still, the positive results obtained are better or in some cases comparable to commercial graphene. Moreover, all electrocatalysts presented good tolerance to methanol poisoning. More importantly, the results of this study demonstrate that pristine coal chars are promising materials to prepare efficient ORR electrocatalysts which will be of great importance in the near future. • Sustainable carbon-based material obtained from coal char recovered from fly ash. • Pristine coal char as graphene substitute for electrocatalysts production. • Promotion of circular economy using coal char as ORR electrocatalysts. [ABSTRACT FROM AUTHOR]

Nowadays, the increase of CO 2 concentration caused by the utilization of traditional fossil fuels has a negative impact on the environment and human health. Therefore, there is an urgent need to explore effective measures to control CO 2 emission. In this work, activated coal char for CO 2 capture was prepared with different carbonization temperatures by two-step method with KOH as the activator. The effects of carbonization temperature and adsorption temperature on the CO 2 adsorption performance of activated coal char were investigated. Elemental analysis, BET, XPS and SEM analysis of the activated coal char were performed. The results showed that the microporous structure has an important influence on the adsorption performance of activated coal char. With the increase of carbonization temperature, the microporous volume increases first following by a decrease and the amount of CO 2 adsorption also shares the same trend. For the adsorption temperature, as the adsorption temperature rises, the CO 2 adsorption capacity of activated coal char decreases. The maximum CO 2 adsorption capacity of 4.8 mmol/g was achieved at optimal conditions of carbonization temperature 600 °C, adsorption temperature 0 °C and pressure 1 bar. In addition, the activated coal char with a carbonization temperature of 600 °C also shows good selectivity for CO 2 over N 2 , which indicated its prospects in the practical CO 2 capture applications. • Effect of carbonization temperature on the texture characteristic of activated char and its CO 2 adsorption properties were investigated • Activated coal char shows a superior CO 2 adsorption performance. • Specific surface area and micropore volume of activated coal char play a leading role in CO 2 adsorption. [ABSTRACT FROM AUTHOR]

[Display omitted] • The spent carbon catalysts after the MDR are recycled for supercapacitor electrodes. • Porous carbon can be obtained from the spent catalysts with S BET of 616–865 m2 g−1. • The prepared electrodes show the specific capacitance of 151–190 F g−1 at 0.5 A g−1. • The assembled capacitor displays the capacitance retention of 90% after 5000 cycles. Methane dry reforming (MDR) is a potential solution to utilize the two greenhouse gases, CH 4 and CO 2 , but little work has been done to provide a strategy for recycling the spent catalysts especially for the carbon-based catalysts. Nowadays the use of low-cost and efficient electrode materials has received increasing attention for supercapacitors. In this work, the spent carbon-based catalysts recycled from MDR were used as the electrode materials of supercapacitors after KOH activation. The results show that the obtained porous carbon has a surface area up to 616–865 m2 g−1, and the specific capacitance value of 151–190 F g−1 can be achieved at a current density of 0.5 A g−1. The assembled electrochemical capacitor can power 10 LED-lights for more than 120 s by a single charge. This work provides a promising strategy for recycling the spent carbon-based catalyst with economic and environmental benefits. [ABSTRACT FROM AUTHOR]

Gasification reactivity and characteristics of three coal chars and two petcokes were investigated in detail. The temperature programmed reaction technique were used to test the gasification reactivity. The characteristics of the various chars were analyzed by XRD, SEM, N 2 adsorption technique and FT-IR. As expect, the coal chars and petcokes showed significantly different gasification reactivity. The reactivity of the two petcokes was much poorer than that of the three coal chars. The gasification reactivity of the coal char increased with the decreasing of coal rank. The gasification reactivity was closely related to the characteristics of samples. It was found that the lower degree of graphitization, less compact surface and more developed pore structure corresponded to higher gasification reactivity of chars. These characteristics of the carbon structure was more favorable to gas diffusion, and hence resulted in high gasification reactivity. In addition, coal char contained more oxygen-containing functional groups and active components such as Ca/Mg/Fe/K/Na compounds, which all had promoting effect on gasification reaction. • Gasification reactivity and characteristics of coals and petcokes was investigated. • Gasification reactivity of petcoke was significantly lower than coal. • Lower graphitization, higher surface area and porosity corresponded to higher reactivity. • Limited minerals and porosity led to low gasification reactivity of petcoke. [ABSTRACT FROM AUTHOR]

The work primarily focuses on combustion kinetics of devolatilized coal char fines (75–120 µm), including the estimation of kinetic parameters and char morphological transformation in oxy-fuel environment (O2-CO2 and O2-N2). Experimental work has been carried out to study the effect of higher CO2 concentration and elevated O2 concentrations on the ignition, burnout behavior of pulverized coal char both non-isothermally and isothermally. The coal chars obtained from pyrolyzing three different types of coal are used in experiments; a high ash (HA) coal, a medium ash (MA) coal, and a low ash (LA) coal. Three different kinetic models, namely VM, GM and RPM, have been employed to determine the kinetic parameters. The kinetic parameters are observed to be a strong function of oxygen concentration for all the three models. The estimated activation energy employing non-isothermal analysis for LA coal char using VM lies in the range of 203–212 kJ/mol. In comparison, the activation energy predicted by GM for HA coal char lies in the range 137–144 kJ/mol. Moreover, the activation energy estimated for MA coal char by RPM varies in the range of 134–142 kJ/mol. It is also explored during the non-isothermal analysis that an increase in char particle size from 75–120 µm to 250–300 µm shows a small increase in the values of apparent activation energy and pre-exponential factor. The activation energy values calculated employing the isothermal method are 106–126 kJ mol−1 (using RPM) for coal char MA and 96–135 kJ mol−1 (using GM) for coal char HA. Both the isothermal and non-isothermal kinetic analysis reveals that the combustion of coal char LA follows VM while coal char MA and HA follows RPM and GM in order. SEM images and BET surface area analysis for partially converted coal chars are further analyzed to justify the suitability of different reaction mechanism followed by various coal chars. [ABSTRACT FROM AUTHOR]

Mass transfer usually affects the rate of chemical reactions in coal. The effect of internal diffusion on char gasification with CO2 in the temperature range from 1123 K to 1273 K was investigated via thermogravimetric analysis and assessment of char morphology features. The results revealed that the effect of internal diffusion on the initial reaction rate was more significant with an increase of particle size, due to the concentration gradient of the gasification agent within the solid particles. In the early stage of gasification, the generation of new micropores and the opening of closed pores led to an increase in specific surface area. As the reaction proceeded, the openings were gradually expanded and the specific surface area continued to increase. However, with further reaction, disappearance of edge pores, melting and collapse of the pore structure led to a decrease in specific surface area. The intrinsic activation energy and reaction order based on the nth-order model were 157.67 kJ·mol−1 and 0.36, respectively. Thus, temperature zones corresponding to chemical reaction and diffusion control were identified. Moreover, the calculated effectiveness factor provided a quantitative estimation of internal diffusion in the initial stage. [ABSTRACT FROM AUTHOR]

Global energy consumption has been rising since the early 2000s, and most of the energy supply still comes from burning fossil fuels. Considering the detrimental environmental impacts of fossil fuels, such as CO 2 emissions, it is crucial to develop clean energy technologies, such as storage devices that can advance long-term reversible and sustainable energy resources. In this work, we demonstrate the direct use of coal char in anodes tailored for both lithium-ion and sodium-ion batteries. The findings show that acid treatment followed by high-temperature argon annealing results in coal char particles with the desired porous structure, surface properties, and turbostratic nanodomains that deliver high reversible capacity and maintain good electrochemical performance at high rates up to 10C. Long-term cycling stability for 500 cycles can be achieved in cells comprising NMC cathodes at 1C with 73.2% capacity retention. This study sheds light on potential energy storage use cases for coal char outside its traditional utilization. Image 1 • Coal char materials were modified to obtain desired porous structure, surface properties, and turbostratic nanodomains. • Modified coal char materials exhibited stable cycling performance in both Li-ion batteries and Na-ion batteries. • High reversible capacities were observed at high rates up to 10 C. • A practical Li-ion full cell maintained a capacity retention of 73.2% at 1C over 500 cycles. [ABSTRACT FROM AUTHOR]

Coal O2/CO2 combustion is a promising carbon capture and storage technology for coal-fired power plant. Char consumption rate prediction is essential for the boiler design, but challenging for O2/CO2 combustion since char reaction behavior within dual reactive gas media is complex. There is also a doubt of whether or not the O2 reaction and CO2 reaction occur independently, whereby the overall rate would be simply additive, or the two reactions compete for the same char actives, in which case the rate prediction could be more complicated. Here, the competitive behavior for O2 and CO2 reactions of char active sites was investigated via thermogravimetric approach, with a focus on the effect of temperature and inherent mineral composition. For char combustion within O2/CO2 environment with molar fractions of 30/70, the contribution of O2 to char consumption is the same as the O2 reaction alone. However, as being out-competed by O2, only 37% CO2 could occupy char active sites and react. Consequently, the overall char reaction rate within O2/CO2 is only 83% of the sum of that for individual gases at 900 °C. With increasing temperature, this ratio becomes even smaller, as the contribution of CO2 that being out-competed (to the sum of individual gases) is larger. With increasing O2 fraction, it occupied more active sites, thus further inhibiting CO2 reaction. The inherent alkali and alkaline earth metal provides the char with more active sites, thus muting the competition and inhibition for CO2 gasification. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the evolution of the chemical structure of coal char during pyrolysis. Two bituminous coals (coals A and B) and one lignite (coal C) were pyrolyzed in a fixed bed in N2 from 600 °C to 1100 °C. The chemical structure of coal char was characterized by Raman spectroscopy and X-ray diffraction (XRD). The carbon and oxygen functionalities of coal char were analyzed by X-ray photoelectron spectroscopy (XPS). The Raman spectroscopic parameters AD/AG (AD1/AG, AD2/AG, and AD3/AG) increased from 600 °C to 900 °C and then decreased after 900 °C, indicating that the degree of order of coal char first decreased and then increased with increasing pyrolysis temperatures (600–1100 °C). The content of graphite-like microcrystalline carbon decreased and then increased with an increase in temperature. Prominent diffraction peaks of microcrystalline carbon for coal chars A and B were observed, but only minerals were shown in diffraction patterns of coal char C since the ash content of coal chars A and B is much lower that that of coal char C. The lateral size of the crystallite plane (La) generally increased between 600 °C and 1100 °C. The relative content of C=O and COOH in coal chars A and B generally decreased as the temperature increased, suggesting an increase in the degree of order at higher temperatures. The oxygen functionalities of coal char were composed of organic oxygen and oxygen-containing bonds of minerals.

The coal ashrepresents an important industrial waste source. The most important waste produced by the energy industry is the ash resulted of coal burning into the large combustion plants. The physical and chemical properties of ash vary substantially between producers and depend on the quality andthe composition of coalthat are used in modern power plants, as well as on combustion conditions. The diverse chemical, mineralogical and morphological properties of ash offer an opportunity to process it and recover various fractions with particular attributes. The main constituents are Al2O3, Fe2O3, CaO, MgO andin smaller quantities Na2O and K2O. Also, the ash from burning lignite of the Oltenia mining field has an important coalchar content, which could be exploited. In this work will be presented some results ofspecific investigations, which allow the rational regarding recovery of coal char from ash.

This study examined an isothermal CO2 gasification of four chars prepared via two different methods, i.e., conventional and microwave-assisted pyrolysis, by the approach of thermogravimetric analysis. Physical, chemical, and structural behaviours of chars were examined using ultimate analysis, X-ray diffraction, and scanning electronic microscopy. Kinetic parameters were calculated by applying the shrinking unreacted core (SCM) and random pore (RPM) models. Moreover, char-CO2 gasification was further simulated by using Aspen Plus to investigate thermodynamic performances in terms of syngas composition and cold gas efficiency (CGE). The microwave-induced char has the largest C/H mass ratio and most ordered carbon structure, but the smallest gasification reactivity. Kinetic analysis indicates that the RPM is better for describing both gasification conversion and reaction rates of the studied chars, and the activation energies and pre-exponential factors varied in the range of 78.45–194.72 kJ/mol and 3.15–102,231.99 s−1, respectively. In addition, a compensation effect was noted during gasification. Finally, the microwave-derived char exhibits better thermodynamic performances than the conventional chars, with the highest CGE and CO molar concentration of 1.30% and 86.18%, respectively. Increasing the pyrolysis temperature, gasification temperature, and CO2-to-carbon molar ratio improved the CGE. [ABSTRACT FROM AUTHOR]

Coal and coal char thermal degradation in a CO2 atmosphere is particularly important to understand and model as a rate‐determining step in the gasification process. The work presented here aims to provide a global kinetic model that accurately represents the thermal degradation of Sanxing (SX) coal and coal char under a CO2 atmosphere and to determine the kinetic parameters of the thermal degradation. In the work presented, a novel approach has been used that involves a triple‐Gaussian DAEM that simultaneously considers the primary pyrolysis, secondary pyrolysis, and the process of newly generated char gasified by CO2. The result of the model shows accurate reproduction of the thermal degradation behavior of SX coal and chars and provides significant information about the relative occurrence of the three steps. For SX coal and Char500, the residual error of the triple‐Gaussian DAEM is approximately 0.35 to 0.22 times that of the double Gaussian DAEM. For Char850, the ratio is lower, approximately 0.12 times that of the double Gaussian DAEM. This indicates that the triple‐Gaussian DAEM is more suitable for describing the thermal degradation of chars acquired at high temperatures (500–850°C) under a CO2 atmosphere. [ABSTRACT FROM AUTHOR]

A facile one-pot process for synergistic conversion of coal char and methane is conducted by employing K 2 CO 3 as the catalyst. Besides syngas production, valuable carbon products are obtained and used to serve for supercapacitor electrodes. Effect of the operating parameters (including the catalyst dosage, gas feed flow rate, reaction temperature and time) is evaluated on electrochemical performance of the as-prepared carbon. The appropriate surface and structural properties enable the prepared carbon electrode to have a remarkable capacitive performance, along with a specific capacitance up to 125 F/g at a scan rate of 5 mV/s and 133 F/g at a current density of 1 A/g. According to the potential capacitive contribution of the carbon species, the high capacitive performance is mainly attributed to formation and growth of abundant carbon fibers in the one-pot process. [ABSTRACT FROM AUTHOR]

The present work develops a novel mathematical model for coal char activation with CO 2 , steam, and a CO 2 /steam mixture. The main assumption is that CO 2 and steam react with distinct active sites, considered by attributing a unique char structure effect to each gasifying agent; the CO 2 -char reaction increases the pore length, whereas the steam-char reaction increases the pore radius. Additionally, pore overlapping effect was taken into account and the radial pore growth was computed by means of a population balance equation. Model predictions of both the pore size distribution and specific surface area changes were compared with experimental data, resulting in an outstanding fit. This supports the model main assumption, which reconciles discrepancies between various authors regarding the overall reaction rate during activation of coal chars with CO 2 /steam mixtures. Finally, the maximum specific surface area occurs under chemically-controlled conditions, where all particle zones reach their maximum surface areas simultaneously, while for activation with diffusional limitations each particle zone attains its maximum specific surface area at a different time. Image 10006 [ABSTRACT FROM AUTHOR]

This paper aims at studying sulfur conversions in a pilot-scale circulating fluidized bed (CFB) gasification system of two-stage air supply. The effects of different air supply approaches, secondary air supply heights and gasification agent compositions on gasifier temperature, sulfur conversions and the release of hydrogen sulfide (H2S) and carbonyl sulfide (COS) were investigated. Two-stage air supply approaches optimized CFB gasifier temperature profile and enhanced sulfur conversions to gas. Sulfur conversions to gas decreased with the increase of secondary air supply nozzle location height. The increased steam-to-carbon ratio promoted sulfur release, leading to more H2S and less COS release. [ABSTRACT FROM AUTHOR]

• A simultaneous SO 2 /NO removal technology has been proposed. • Pellets made of carbide slag and coal char was prepared by extrusion-spheronization. • The pellets possess efficient simultaneous SO 2 and NO removal property. • Carbide slag provides a significant catalytic effect on NO reduction. • Addition of supporter highly enhances mechanical strength of the pellets. In this work, a simultaneous SO 2 /NO removal method using pellets made of carbide slag and coal char by extrusion-spheronization process was proposed. The effects of char type, reaction temperature, O 2 concentration, initial NO/SO 2 concentration and the addition of supporters on the simultaneous SO 2 /NO removal performance of the pellets made of carbide slag and coal char were investigated in a bubbling fluidized-bed reactor. CaO derived from carbide slag not only acts as an excellent desulfurizer but also catalyzes the reduction of NO by coal char. The results show that the pellets made of carbide slag and coal char possess better simultaneous SO 2 /NO removal performance than the pellets made of carbide slag and bio-char. The optimal reaction temperature range for SO 2 /NO removal by the pellets made of carbide slag and coal char is 850−875 °C. The addition of the supporters such as Al 2 O 3 and high alumina cement enhances the mechanical strength of the pellets. The pellets made of carbide slag and coal char seems promising for efficient simultaneous SO 2 /NO removal in the circulating fluidized bed decoupling combustion. [ABSTRACT FROM AUTHOR]

Cement soil stabilization is a commonly used method to improve in-situ soil properties catering to different geotechnical applications. However, cement manufacturing is typically associated with high CO 2 emissions and energy consumption. Coal char is a sustainable and environmentally friendly material derived from the coal pyrolysis process. Traditionally used for combustion and gasification, recent research has revealed its potential to improve the engineering performance of cement-based construction and building materials. This study explores the innovative use of coal char in cement soil stabilization. Examining various cement contents (5%, 10%, and 20%) and char contents (10%, 20%, and 30%), the properties of char-cement stabilized soils, including mineralogy, density, water content, thermal conductivity, unconfined compressive strength (UCS), and mechanical properties under triaxial compression, are comprehensively investigated and compared with cement stabilized soil. It is found that char promotes both cement hydration and reaction between soil minerals and cement. The thermal conductivity and UCS of char-cement stabilized soil are 0–9% lower and 8–16% higher, respectively than that of cement stabilized soil. Under triaxial compression, the addition of char in stabilized soil leads to 23.7% increase in shear strength, 17.7% increase in cohesion, and 16.7% increase in the angle of internal friction. In conclusion, the introduction of coal char into traditional cement soil stabilization demonstrates a novel approach to achieving sustainability and enhancing engineering performance in relevant geotechnical applications. • Geotechnical properties of coal char-cement stabilized soil are investigated. • Coal char addition helps improve thermal and strength performance of stabilized soil. • Cohesion and friction angle of stabilized soil increase with adding coal char. [ABSTRACT FROM AUTHOR]

The modified coal char from low-rank coal by sulfonation, titanium impregnation and followed by alkyl silylation possesses high catalytic activity in styrene oxidation. The surface of coal char was undergone several steps as such: modification using concentrated sulfuric acid in the sulfonation process, impregnation of 500 mmol titanium(IV) isopropoxide and followed by alkyl silylation of n-octadecyltriclorosilane (OTS). The catalysts were characterized by X-ray diffraction (XRD), IR spectroscopy, nitrogen adsorption, and hydrophobicity. The catalytic activity of the catalysts has been examined in the liquid phase styrene oxidation by using aqueous hydrogen peroxide as oxidant. The catalytic study showed the alkyl silylation could enhance the catalytic activity of Ti-SO3H/CC-600(2.0). High catalytic activity and reusability of the o-Ti-SO3H/CC-600(2.0) were related to the modification of local environment of titanium active sites and the enhancement the hydrophobicity of catalyst particle by alkyl silylation.

• Fuel-N mainly released in the form of NO in O 2 /H 2 O combustion of demineralized char. • Increase of T r and O 2 concentration could inhibit NO emission in O 2 /H 2 O combustion. • C(O) amount reflected demineralized char reactivity and NO emission characteristics in combustion. • There was linear correlation between I (Gr+VL+Vr) /I D and demineralized char reactivity. Surface behavior and structural characteristics of char particles generally play a vital role in affecting char NO emission characteristics during combustion process. A typical bituminous Shenhua from northwest China was employed for demineralization in this research. The demineralized coal without catalytic interference of alkali metal salts was employed as the experimental sample. Moreover, by means of the utilization of isothermal combustion test, Temperature Programmed Desorption (TPD) and Raman spectrometer, the conversion ratio of nitrogen content in char to NO, as well as the evolution of char surface behavior and micro-structure in the process of O 2 /H 2 O combustion under different conditions were determined. With the increase of reaction temperature (T r) and O 2 concentration, more surface active sites (C f), oxygen containing functional groups (C(O)) and small aromatic ring structures generated on char particle surface inhibiting the emission of NO during O 2 /H 2 O combustion process. Under identical reaction conditions (Tr, O 2 and H 2 O concentration), the partially oxidized chars with moderate burnout degree (X c ≈ 0.3) had the largest amount of C f on particle surface. On the other hand, the amount of C f and small aromatic ring structures first increased and then decreased as the H 2 O concentration enhanced. When the C f amount and the value of I (Gr+VL+Vr) /I D reached the maximum at the H 2 O concentration of approximately 8.5 vol%, the conversion ratio of char-N to NO reached the minimum value. Meanwhile, the increase of H 2 O concentration initially accelerated the NO reduction rate and this positive effects gradually diminished when the H 2 O concentration exceeded the critical value (8.5 vol%). Thus, the optimal combustion condition for char combustion with the lowest NO conversion ratio in this study was: 1473 K, 30% O 2 and 8.5 vol% H 2 O. [ABSTRACT FROM AUTHOR]

• Group combustion characteristics of coal char and petroleum coke were studied. • Effect of particle concentration on delayed burnout time ratio was characterized. • Particles inside group combustion performed different combustion characteristics. • Oxygen diffusion and particle concentration were main causes for burning delay. The combustion characteristics of particle group are different from the combustion of a single particle, owing to the physicochemical effect and interaction among particles. The current work investigated the effect of the increasing particle concentration on the group combustion with the consideration of temperature and solid fuel type, including bituminous coal char and petroleum coke. A visual imaging technology was used to record and analyze the combustion process and group evolution of burning particles in the two-dimensional scale. Results showed that a delayed combustion phenomenon was found for both coal char and petroleum coke with the increasing particle concentration in a group. The burnout time increased in multiples from the combustion of a single particle, dispersed particles to a particle group. The total carbon conversion and combustion rate of the particle group significantly decreased with the increasing particle concentration in the group, especially for the bituminous char of a high reactivity. With increasing the combustion temperature, the burnout time was additionally prolonged from 20% to 80% between the internal and external particles in the particle group. The theoretical analysis with the consideration of Stefan flow, gas diffusion, and gas-solid reaction was used to propose the delayed combustion mechanism, and the results matched well with the experimental data. The increasing particle concentration in the group, which consumed the oxygen, generated the advance effect of Stefan flow, and hindered the oxygen diffusion, was the key factor to delay the group combustion. For the group combustion of petroleum coke with low reactivity, although the surface reaction was the controlling step, the reactant gas diffusion inside the group could not be ignored. For the group combustion of coal char particle with high reactivity, the diffusion of the reactant gas in the group was the dominant controlling step for the delayed combustion behavior. [ABSTRACT FROM AUTHOR]

The burning behaviors of Yimin lignite coal char were investigated in a horizontal tube furnace. The effects of temperature, oxygen concentration, particle size and water on the conversion of char nitrogen to NO during char combustion were mainly studied. The results show that the conversion rate of char nitrogen to NO decreases with temperature increasing. As the temperature increases, the growth rate of reaction rate of NO heterogeneous reduction is higher than that of NO heterogeneous formation. NO generated during combustion is significantly reduced on the surface of char. The conversion of char nitrogen to NO is the lowest at 3% oxygen concentration. Limited by the fixed bed conditions, it has not found that the particle size of char has a significant effect on the on the conversion rate of char nitrogen to NO. The addition of water will increase the total amount of NO emission and the conversion rate of char nitrogen to NO; and it will also accelerate the burnout of coal char. Experimental methods and results have guiding significance for related teaching experiments and industrial production. [ABSTRACT FROM AUTHOR]

Three rich-alkalis biomasses ashes, wheat straw ash (WSA), sea grape ash (SGA) and Ixeris Chinese ash (ICA) and calcium-based additives, were applied in char hydrogasification. Hydrogasification behavior of coal and biomass ash and saturated loading and loading methods of calcium-based additives were investigated. The loading calcium-based additives has affected on the methane release curves of SFC hydrogasification. The total amount of gaseous products and the CH 4 yield were obviously improved with the increase of the CaO loading. Hydrogasification of SF char with the 6% calcium-based loading presented the highest methane yield. SFC hydrogasification was divided into two stages according to the methane release rate curve of the calcium-based additives-loaded samples hydrogasification. The carbon and hydrogen reaction occurred in the second stage of coal hydrogasification. The calcium-based additives have effects on catalytic performance of three rich-alkalis biomass ashes for hydrogasification characteristics of Shenfu coal char. Loading methods of calcium-based additives and component of biomass ashes affected on the total CH 4 yield and the total amount of gaseous products of samples. Calcium-based additives emerged obviously synergistic reaction with WSA or SGA during char hydrogasification. Calcium-based additives reacted with Si of biomass ashes and produce more stable calcium silicate in the early stage of reaction. The promotion of biomass ashes on char hydrogasification mainly was attributed to the fixation of Si and Cl by CaO. [ABSTRACT FROM AUTHOR]

Abstract This work presents a new method of measuring the CO/CO 2 ratio at the surface of carbon particles during combustion. This thermogravimetric method deduces the ratio of CO to CO 2 by comparing the rate of consumption of carbon with the rate of oxidation of an external reference material with fast oxidation kinetics, in this case Cu. The method is useful when combustion is controlled by external mass transfer, commonly encountered in large-scale processes. The viability of this method has been demonstrated experimentally with graphite and a lignite char. It was found that in an atmosphere of ∼ 1% O 2 , the graphite produced CO 2 between 700 and 900 °C whilst the lignite char produced a mixture of CO and CO 2 between 700 and 800 °C with the proportion of CO increasing with temperature, and above 850 °C, only CO was produced. It was also found that for this particular lignite char, the ratio of CO/CO 2 increased with decreasing p O 2 in the environment. [ABSTRACT FROM AUTHOR]

• La-Fe based perovskite-type oxide was proposed to be used for catalytic gasification of coal char with CO 2. • The K+ at A-site contributed to the formation of oxygen vacancies and high valence iron ions in perovskite improved its catalytic performance. • The modified perovskite could maintain its crystal structure during cyclic reactions. Coal catalytic gasification is an effective way to realize clean coal utilization. The core of this technology is the preparation of highly efficient and stable catalysts. At present, perovskite-type oxides have attracted increasing attention as a promising catalyst because of its good thermal stability and redox activity. In this study, perovskite-type oxides were proposed to act as catalyst for coal char CO 2 gasification, and K was further used for LaFeO 3 catalyst modification to improve its catalytic activity. The catalytic performances of La 1-x K x FeO 3 (x=0-0.9) were tested by thermogravimetric analysis and fixed-bed tube reactor. The crystal structure was determined by X-ray diffraction (XRD), the percentage content and valence state of surface elements were examined by X-ray photoelectron spectroscopy (XPS), the surface morphology of perovskite samples was observed by scanning electron microscopy (SEM). Besides, the specific surface area and average particle diameter were analyzed by N 2 absorption/desorption technology (BET) and laser particle size analyzer, respectively. Results suggested that the perovskite-type catalyst can effectively lowered the initial reaction temperature and exhibited improved catalytic activity after a part of La3+ at A-site was replaced by K+. The time required to achieve 50% carbon conversion in the initial reaction was reduced by 87.3% when the molar ratio of K+ increased from 0 to 0.7. The La 0.3 K 0.7 FeO 3 perovskite also exhibited relatively stable catalytic activity during cyclic process, and its optimal temperature in coal char CO 2 gasification was approximately 850 °C. The XRD patterns indicated that the perovskite structure of catalyst can remain unchanged when K+ doping ratio was lower than 0.8. Therefore, 0.7 is a suitable doping ratio. The perovskite La 0.3 K 0.7 FeO 3 still exhibited perovskite crystal structure after 10 cycles of experiment. The XPS results indicated that additional oxygen vacancies and Fe4+ formed after K+ doping, which contributed to gas adsorption and electron transfer and improved oxidation performance. SEM and BET showed that the pore structure of catalyst was destroyed during cyclic gasification, resulted in the enlargement of particle size detected by laser particle size analyzer. Leading to the decrease in effective contact area and catalytic performance. Thus, K+-modified perovskite La 1-x K x FeO 3 is a kind of equipment-friendly, efficient and recyclable catalyst and can be used as a promising catalyst for coal char CO 2 gasification. [ABSTRACT FROM AUTHOR]

Highlights • Coal char mixed with iron powder reduces NO and produces CO at medium temperature. • Higher oxygen concentration could promote both NO reduction and CO production. • Reaction mechanism was proposed based experimental results. Abstract NO reduction by CO in a rotary reactor, separating NO adsorption and reduction processes in two different zones, was demonstrated by our group in previous studies. As an indispensable part of this system, it's necessary to further reduce the residue NOx at the outlet of reduction zone and supply fresh reducing gas CO for this reactor. The aim of this paper is to look for some cheap materials to meet both aims and investigate the corresponding reaction mechanism. Coal char was chosen for this purpose since it could serve as both reducing agent and catalyst of NO reduction, and could also be the source of CO production. For some cases, simple iron powder was also physically mixed which coal char, expecting to enhance the reaction rates of NO reduction. Some key factors were investigated for their influence of target reactions, such as temperature, oxygen concentration, CO concentration, and presence of H 2 O and SO 2. Experimental results showed that mixed iron powder could effectively serve as catalyst for NO reduction, lowering the required reaction temperature. Higher oxygen concentration could promote both NO reduction and CO production. Both coal char and produced CO act as the reducing agent of NO reduction. In order to explore the reaction mechanism, various tests were carried out for samples and reactions under different conditions, such as SEM, TG, XPS and in situ DRIFT. SEM images illustrated that coal char is sintered in the absence of oxygen at high temperatures, but Fe could inhibit this sintering process. TG tests showed that reaction rate of coal char is the fastest in the presence of oxygen, and iron powder would inhibit the weight loss rate. XPS results displayed that both elevated temperatures and the addition of iron species could increase surface oxygen content. In situ DRIFT spectra revealed that the introduction of NO formed various nitrates on the surface of the coal char. Based on the experimental results and characterizations, reaction mechanism over coal char with/without mixed iron powder was proposed. [ABSTRACT FROM AUTHOR]

Catalytic steam gasification of fine coal char particles was carried out using a self-made laboratory reactor to determine the intrinsic kinetics and external diffusion under varying pressures (0.1–0.5 MPa) and superficial gas flow velocities (GFVs) of 13.8–68.8 cm∙s–1. In order to estimate the in-situ gas release rate at a low GFV, the transported effect of effluent gas on the temporal gasification rate pattern was simulated by the Fluent computation and verified experimentally. The external mass transfer coefficients (kmam) and the effectiveness factors were determined at lower GFVs, based on the intrinsic gasification rate obtained at a high GFV of 55.0 cm∙s–1. The kmam was found to be almost invariable in a wider carbon conversion of 0.2–0.7. The variations of kmam at a median carbon conversion with GFV, temperature and pressure were found to follow a modified Chilton-Colburn correlation: S h = 0.311 Re 2.83 S c 1 3 (P P 0 ) − 2.07 (0.040 is atmospheric pressure. An intrinsic kinetics/external diffusion integrating model could well describe the gasification rate as a function of GFV, temperature and pressure over a whole gasification process. [ABSTRACT FROM AUTHOR]