Coke Matrix Research Articles

Anchoring ultrafine Au nanoclusters on sulfonate groups functionalized carbon matrix for efficient catalytic reduction of nitrophenol

Despite immense research efforts in the field of Au supported on carbon matrix, the rational design and fabrication of ultrafine Au/carbon matrix nanocatalysts with effective reactivity and high stability are still challenging. The main obstacles are faced with adjusting the size of Au nanoclusters and strengthening the bond of Au and carbon. In this work, sulfonate groups (−SO3H) introduced onto activated coke (AC) matrix was prepared for steadily anchoring ultrafine Au nanoclusters (∼2 nm). The obtained Au/SO3H-AC exhibited superior reactivity for 4-nitrophenol reduction within 3 min using NaBH4 as reducing agent. The superior performance and stability are attributed to the − SO3H groups with hydrophilic property, benefiting for substrates readily dispersion and for Au species (including oxidized Au+ and Au3+) bind and stabilization, possibly by tightly interacting with the O atoms bound to S atom of − SO3H. In addition, several lines of evidence demonstrate the oxidized Au species can serve as electron relay system, ensuring the sustained reaction. Given that the Au nanoclusters in this study have superior reactivity and stability, this work proposes a novel strategy for preparing other supported metal nanocomposites.

Difference in Radial Direction of Lumpy Coke Sampling from Raceway of Large Blast Furnaces: Microstructure, Alkali Enrichment, and Solution Loss Reaction

In this article, the morphology, chemical structure, alkali enrichment, and solution loss reactivity in the radial direction of the lumpy feed coke and its corresponding raceway coke from two large blast furnaces are comparatively using multiple characterization methods. The results indicate that the erosion of coke and pore development not only occurs on the surface but also in the center, which can be described as gradient reaction model. The enrichment level of K is higher than Na. K content decreases gradually from the edge to the center of the raceway coke, and the formation of nepheline causes cracks in coke observed by morphology. The crystallite order of the raceway coke is higher than that of the feed coke, with the enrichment of alkali metals, the raceway coke shows variability in the radial direction, and the orderliness gradually decreases from the surface to the interior. With the enrichment of alkali metals, the microcrystalline ordering of the raceway coke decreases from the surface to the interior, and the increase in the concentration of carbon dioxide after the entry into the raceway leads to the preferential reaction of the carbon dioxide with the coke matrix which contains K and many reactive sites.

Numerically estimated hot strength of coke produced by briquetting and carbonization of lignite

This research aimed to investigate the hot strength of coke prepared by briquetting and carbonization of lignite (Coke D) and mechanisms causing the strength, which have not been well understood. The Coke D samples underwent heating in a nitrogen atmosphere and up to 1000 °C. Three different gasification conditions were employed: inert condition (Inert), 6 min CO2 gasification time (React6), and 9 min CO2 gasification time (React9). The samples were imaged by three-dimensional X-ray computed tomography (CT), and their pore structure was evaluated. Coke D-Inert and Coke D-React6 exhibited decreasing porosity due to the expansion of coke matrix at elevated temperatures. Conversely, the porosity of Coke D-React9 increased owing to the significant disappearance of coke matrix by gasification, despite some expansion of coke matrix. Furthermore, material constants (i.e., Young's modulus) were predicted using the finite element method with coke models derived from the CT images. In the numerical simulation, fracture strains obtained from experiments in our previous work were applied as boundary conditions. The estimated Young’s modulus was 30.6 (maximum value 48.1; minimum value 14.9) on the outer side and 24.4 (max. 41.5; min. 12.4) on the inner side in Coke D-Inert, 16.6 (max. 21.1; min. 13.7) on the outer side and 17.1 (max. 20.4; min. 13.7) on the inner side in Coke D-React6, and 29.4 (max. 30.9; min. 26.5) on the outer side and 22.5 (max. 26.0; min. 19.6) on the inner side in Coke D-React9. Comparing Young's modulus of Coke D-React6 and Coke D-React9, Coke D-React9 showed a higher Young's modulus. These results suggested the significant impact of fracture strain on the predicted value of Young's modulus. The fracture strain was likely influenced by the effects of creep and matrix disappearance due to the reaction with CO2. Nano-indentation measurements of Coke D-Inert (average value 23.4; max. 29.4; min. 15.3) and Coke D-React9 (average 25.4; max. 28.3; min. 22.4) microstructures suggested no change in the material constants at room temperature but the potential for alterations at elevated temperatures.

Gasification Behaviors of Ferrocoke With and Without Water Vapor

High‐reactivity coke can improve the reaction efficiency in a blast furnace, hence reducing CO2 emission. Herein, traditional coke sample (QM), normal ferrocoke sample (TJ), and modified ferrocoke sample (LQ) are examined. The effect of water vapor on the gasification behaviors and structural evolution of the samples are investigated. Furthermore, the 3D structures of the coke matrix and iron particles are reconstructed by serial sectioning method. The results show that under a pure CO2 atmosphere, the TJ and LQ samples start the gasification reaction earlier than the QM sample. The TJ sample shows the highest reactivity. Under CO2 + H2O atmosphere, the conversion rate of TJ and LQ samples is slowed. The reoxidation of the metallic iron within the ferrocoke is found for the first time during gasification and causes this phenomenon. Under experimental conditions, when water vapor appears in the atmosphere, the product layer of ferrocoke becomes more porous, and the iron particles have higher possibilities to be oxidized by CO2.

Effect of CO2 Gasification on High‐Temperature Characteristics of Iron Coke: In Situ Compressive Strength

High‐temperature compressive strength of the ironmaking burden is crucial for evaluating its comprehensive performance. Iron coke is one of the novels and widely studied low‐carbon ironmaking charges. This study investigates the in situ high‐temperature compressive strength of iron coke after CO2 gasification. The mass loss, morphology, and micromorphology of the iron coke in the CO2 gasification roasting process are studied to clarify the high‐temperature compressive strength evolution mechanism. The results show that the reactivity of iron coke is inversely correlated to carbonization temperature. The high‐temperature compressive strength is mainly influenced by the coke matrix in the inner of the iron coke. Upon increasing the CO2 gasification roasting temperature, the density of the coke matrix in the iron coke decreases gradually, while the internal voids in the iron coke increase, resulting in decreased high‐temperature compressive strength. The initial compressive strength of iron coke with 40% iron ore content reaches >3800 N, while it decreases to <2000 N when roasted at 1150 °C for 30 min under a CO2 atmosphere. The high‐temperature compressive strength of iron coke with 40% iron ore content decreases around 40% when the CO2 gasification roasting period increases from 30 to 90 min at 1100 °C.

Behavior of coke in the blast furnace for smelting Bayan Obo Mine

A deep understanding of behavior about coke in the blast furnace for smelting Bayan Obo Mine is significantly important to guide its efficient smelting. The feed coke and tuyere coke were taken from 4# blast furnace in Baotou Steel as the research object. The differences in ash content, microscopic crystal structure, functional group, microscopic pore structure and alkali metal content were compared and analyzed. Then the behavior of coke in the blast furnace for smelting Bayan Obo Mine was obtained. The results show that the coke in the blast furnace undergoes a gasification reaction during the descending process, the chemical bonds are broken, the reactivity is improved, and the strength after the reaction is reduced. There are honeycomb-like pores on the surface of the tuyere coke, and the distribution of pore is uneven. In particular, the coke matrix eroded by slag and iron has rough pore walls, and the pores appear to merge. Alkali metals are enriched in the tuyere coke, the content of alkaline oxides is increased, the temperature of the violent reaction is decreased, and the activation energy of the reaction is decreased. The half-width of the (002) diffraction peak corresponding to the tuyere coke graphite carbon is sharply reduced, the flat peak disappears, and the peak shape is sharp. The grain size increases, the crystal structure tends to be ordered, and the degree of graphitization increases.

Automated procedure for coke microstructural characterization in imagej software aiming industrial application

Coke strength is closely related to its microstructure, which can be defined as the spatial distribution of the coke matrix and its porosity. Even though the importance of coke microstructure is recognized and many studies were conducted on the subject, up to date there is no standard methodology established to evaluate such material, which makes it difficult to compare and correlate coke microstructure and quality parameters. Among the techniques available to obtain microstructural parameters that may be related to coke strength, the association of optical microscopy and image analysis shows greater potential. However, representatively characterizing coke microstructure has proven to be a complex activity due to coke high heterogeneity, a result of the different behavior of coal components during carbonization and the thermal gradient differences in the cokemaking process. For this reason, it is essential to establish experimental conditions such as the number of samples analyzed, coke particle size and analyzed area for each sample, to circumvent the heterogeneity problem. In this work, it was shown that the analysis of 56.8 mm2 of each of five polished blocks for coke sample, made with coke particles of 22.4–19.0 mm, was the best condition to align representativeness and operational practicality. Besides, a macro was developed to automate the image analysis routine using the ImageJ software, where each step of the procedure was optimized especially for metallurgical coke. Combining the best experimental parameters determined with the fast automated image processing generated a reliable and representative way to characterize the coke porous microstructure.

Effect of Changes in Mechanical Properties of Coke Matrix Caused by CO<sub>2</sub> or H<sub>2</sub>O Gasification Reaction on the Strength of Lump Coke

In this study, we evaluated the effect of the CO2 or H2O gasification reaction on the mechanical property of the coke matrix by measuring the elastic modulus of the coke matrix before and after the gasification reaction. We also investigated the effect of the distribution of the elastic modulus in the coke matrix on the strength of the lump coke by conducting the fracture analysis for the coke model with porosity of 0–0.4 in which the distribution of the elastic modulus obtained by the experiment was reflected. The nanoindentation measurements of the elastic modulus of the coke matrix before and after the gasification reaction implied that the distribution of the elastic modulus in the coke matrix differs depending on the gasification agent. In the case of the CO2 gasification reaction, both the coke matrices with high and low elastic moduli were consumed by the gasification. On the other hand, in the case of the H2O gasification reaction, only the coke with an elastic modulus of over 30 GPa before the reaction was consumed by the gasification reaction. Also, the numerical results showed that the distribution of the elastic modulus in the coke matrix affects the strength of the coke model with low porosity whereas the one did not affect that with high porosity.

Degradation behaviors of coke under complex solution loss conditions

Solution loss reaction of coke provides reducing agent for ironmaking, which is an important chemical reaction in blast furnace. The coke itself is also degraded by the loss of carbon. In this paper, the degradation behavior of coke under complex conditions including alkali metal enrichment, simulated blast furnace temperature and atmosphere was studied. The pore size and pore wall thickness distribution of coke were measured by a microscope to characterize the structure of coke. The gasification reaction rate of coke matrix was measured by a thermogravimetric analyzer to characterize the matrix reactivity of coke. The results show that a coke has high CRI and low CSR, but it has high matrix reactivity and thick pore wall, which may lead higher strength after solution loss under alkali metal enrichment and simulated blast furnace atmosphere and heating conditions.

The use of waste ion exchange resins as components of the coal charge for the production of metallurgical coke

In this research an innovative method to utilise waste ion exchange resins (WIER) is investigated. The aim of the study is to evaluate the impact of WIER addition to coke quality. For this purpose, industrial tests were performed with different share of WIER and the resultant cokes were studied by means of standard coke analytical techniques, as well as microscopic examinations. By combining optical and SEM petrographical examination it is revealed that the pyrolyzed IER occurs predominantly as separate spheres within the coke matrix, by having extremely durable sulfur bridge bonds. This observation can explain the improvement of the mechanical strength of the produced coke expressed by “cold” indices of MICUM test. Moreover, the coke parameters related to susceptibility to gasification with CO2, like CRI and CSR parameters, seem to be also affected since the chars created from WIER in the coke matrix are more reactive than the coke matter originated from coal. This first step towards a potential recycling of WIER shows that by the addition of WIER up to 3% the coke quality parameters, such as sulfur content or abrasion (M10), are adversely affected. The coking plants may still accept this small (1–3%) impact of polymer waste in the coal feedstock, without significant impacts in their production yields.

The effects of sulfides and sulfur/phosphorus‐containing compounds on coke formation during thermal cracking of light naphtha

AbstractIn this study, coke deposits during thermal cracking of light naphtha in the presence of sulfur‐ and sulfur/phosphorous‐containing compounds with different addition methods were investigated from the points of morphology and structure. Sulfur/phosphorous‐containing compounds were applied by continuous addition, pretreatment, and pretreatment followed by continuous addition. As for continuous addition, the amount of coke was decreased with increasing the mass concentration of sulfides in short‐term cracking periods. Catalytic coke was inhibited because of passivating the metal by sulfides at the initial stage of coking process. When phosphides were combined with the mixture of sulfides, the coke formation was further decreased as the synergistic effects of adsorption of sulfur and phosphorous onto the metal led to the decreased activity of metal surface. In the case of pretreatment with sulfur/phosphorous, the reduction in coke formation at the initial stage of cracking process was due to the adsorption of S/P‐containing radicals on the oxide film. In further cracking operation, an enrichment of Fe and Ni in the oxide layer from the pretreatment process leads to the appearance of coke filaments in coke layers. The combined addition method, the surface pretreatment with dimethyl disulfide (DMDS)/triphenyl phosphite (TPPI) followed by continuous addition of sulfides/TPPI in the feed, shows the best coking inhibition performance. The inhibition rate is up to 88.8% and 78.5% respectively when the cracking time is 1 and 3 h. The combined application strengthened the coverage of catalytic activity sites by sulfur/phosphorous‐containing radicals. The scanning electron microscope (SEM) results showed that the structural characteristics of coke deposit at the applied conditions were mainly amorphous coke. Variant coke filaments were also observed at the conditions of pretreatment and pretreatment followed by continuous addition. The analyses of Raman spectra indicated that the application methods decreased the graphitization degree of coke deposited and increased the structure defects of the coke matrix. During naphtha cracking, sulfur/phosphorous‐containing compounds reduced dehydrogenation and condensation by which hydrocarbons were degraded to coke.

Effect of high petroleum coke additions on metallurgical coke quality and optical texture

Abstract The objective of the present study was to evaluate the effect of high additions of petroleum coke on the rheological properties of coking coal and the quality of cokes produced on pilot scale at the Usiminas R&D Center. For this purpose, blends using petroleum coke additions of 5%, 10%, 20%, 30% and 40% were produced. The results showed that the blends were able to satisfactorily absorb up to 30% of petroleum coke, keeping the quality (DI, CRI and CSR) similar to the industrial mixture. The observed main textural components were: mosaic, fragmentary, fusite and anisotropic inert. In general, before CRI, cokes showed good cohesion, with the petroleum coke having been absorbed by the coke matrix. After the reaction with CO2, there was verified a preferential consumption of the textures fusite, fragmentary and anisotropic inert due to the Boudouard reaction, besides the deterioration of the interfaces between the petroleum coke and coke matrix. In addition, the results showed that the increase of mosaics contributes to the increase of cokes DI15-150 and CSR. Finally, for the coal blend employed, it is suggested the utilization of a maximum of 30% additions of petroleum coke.

Molecular basis for coke strength: Stacking-fault structure of wrinkled carbon layers

A macromolecular model with formula C60468H2193O527N468S49 was constructed for Pingyao coke by using microstructural characteristics and theoretical calculations. The coke model geometry was obtained by simulated annealing algorithm in molecular dynamics simulations with reactive force field (ReaxFF). ReaxFF parameters were modified iteratively until the model geometry agreed with X-ray photoelectron spectroscopy and X-ray diffraction data. The model indicates that the carbon matrix in coke is composed of wrinkled carbon layers, which agrees with reported high-resolution transmission electron microscope results. Neighboring carbon layers are not synclastic and have some stacking faults (such as arch-shaped moieties and screw dislocation), which result in increased layer spacing or non-parallel layers. To investigate the molecular basis for coke strength, ReaxFF simulations of the coke compression process were performed at 300 K and 3500 K, respectively. Results showed that the stacking-fault structure of wrinkled carbon layers was the main microscopic cause of coke strength. Wrinkled carbon layers can disperse the external force, and stacking-fault moieties restrained the interface slippage of carbon layers. Coke structural changes that were caused by the external force presented different characteristics at different temperatures. High temperatures aid the coke matrix reconstruction and prompt the formation of large and planar carbon layers.

Large-scale simulation of gasification reaction with mass transfer for metallurgical coke: Model development

Large-scale simulation of gasification for a highly resolved coke model with hundreds of millions of voxels was carried out. Three-dimensional phenomena could be evaluated by the numerical simulation, while our previous study was limited to one-dimensional distribution due to the high computational load. The coke model was developed from micro X-ray CT images of a cylindrical coke sample with a radius of 20 mm, and the screen resolution was 20.6 µm/pixel. In the resolved pores, the mass transfer with CO2 gasification was analyzed, whereas voxels of the coke matrix adjacent to the pore vanished due to the reaction. Coke was found to degrade non-uniformly as the reaction progressed, and the areas with highly concentrated carbon matrix voxels remained unchanged. These characteristic areas were derived from the X-ray CT images. Focusing on the concentration distribution of CO2, it was found that the rate-controlling step changed from pore diffusion to chemical reaction with structural change at 1573 K.

Effect of potassium carbonate on the kinetic behaviors of coke gasification in a hydrogen-rich blast furnace

To simulate the composition of hydrogen-rich blast furnace (BF) gas, coke gasification reactions with and without potassium carbonate were carried out by thermogravimetry. The experimental temperature was 1173–1573 K. The effects of potassium carbonate on the kinetic behaviors of coke gasification under hydrogen-rich BF gas were compared and analyzed, and the mechanisms of influence were discussed. The results showed that potassium carbonate had a strong catalytic effect on the coke gasification reaction. The presence of potassium carbonate could reduce the internal diffusion and interfacial reaction activation energy in coke gasification, could increase the rate of internal diffusion and interfacial reactions, and had a greater effect on internal diffusion than on interfacial reactions. After potassium ions were adsorbed onto the surface of the coke, the CC bond length on the surface of the coke increased, the number of electrons of C atoms on the surface of the coke increased, and the energy of the coke matrix increased. These effects decreased the stability of the coke matrix structure, promoting the coke gasification reaction.

Petrographic Analysis of Cokes Reacted under Simulated Blast Furnace Conditions

Two cokes prepared from coals of different ranks were subjected to gasification and annealing under the simulated blast furnace (BF) conditions. The changes in coke petrography were studied using techniques and algorithms developed by Pearson Coal Petrography, Inc.; the coke microstrength was measured using ultramicro indentation. Gasification under the simulated BF conditions consumed both reactive maceral-derived components (RMDCs) and inert maceral-derived components (IMDCs) at the lump periphery; however, the degradation did not penetrate to the core of the coke lump during gasification. The annealing at 2000 °C after gasification further promoted the degradation of IMDCs and RMDCs located at the lump surface; the degradation penetrated toward the center of the coke lump during annealing. The consumption of the coke matrix in the lump core mainly concentrated on the IMDC microtexture, but the RMDC microtexture generally remained. Under the simulated BF gasification conditions, both bireflectance and m...

The impact of a Neogene basalt intrusion on the optical properties and internal structure of the dispersed organic matter in Carboniferous strata (SW-part USCB)

The S-7 borehole log from the Sumina area (USCB Poland) revealed the presence of three basaltic veins originating from a basalt dyke. Coal interlayers in the rocks surrounding the basaltic veins have been coked to form natural coke. Photometric measurements revealed that the optical properties of the studied natural coke samples are characteristic of semi-graphite (Rmax > 9%). The natural coke matrix of all of the analyzed samples has a biaxial negative optical character. Vitrinite in the examined natural coke samples is characterized by a lower optical anisotropy than that of the natural matrix and it has a biaxial positive optical character. Vitrinite in almost all samples taken at locations more distant from the intrusion has a biaxial positive optical character. A reversal of the changes of the true maximum vitrinite reflectance and bireflectance with changing distance from the second basaltic vein has been observed. The temperature regime that acted upon the dispersed organic matter located in the immediate vicinity of the intrusion, estimated on the basis of the selected experimental data, is suggested to be higher than 750°C.

Existence state and structures of extracted coke and accompanied samples from tuyere zone of a large-scale blast furnace

An in-depth understanding about the existence state and structure of materials in the high-temperature zone of a blast furnace is critical to optimize both the ironmaking blast furnace and many other metallurgical processes based on carbothermic reduction. In the present study, coke as well as other accompanied samples (slag, metal and fines) were extracted from an industrial large-scale blast furnace (BF) tuyere zone and were comprehensively characterized to evaluate their existence state and structure. It was found that the weight percentage of slag and metal in the total extracted samples increases first and then keeps at a relative stable level, while the average coke particle size decreases firstly and then keeps at a relatively small size when the position is closer to the blast furnace center. This indicates that smelting and separation of slag and iron as well as the main coke degradation process occur mainly in the center part of BF, and the state in the region (deadman) is relatively stable with similar permeability. Tuyere cokes with various sizes are all extensively reacted with highly developed pores. Due to the improvement of coke pore size, blast furnace melts (bosh slag or molten coke/coal ash) can migrate into the coke matrix through those connected open pores. Coke carrying slag in its inner pores may enter the iron bath of the BF hearth, which might affect coke dissolution into hot metal and degrade the refractory of the hearth bottom. Alkalis content increase significantly when the distance to the tuyere entrance increases, indicating the alkali vapors are mainly recycled and enriched in the center part of blast furnace. The graphitization of coke in the high temperature zone start from the coke surface and the graphitization process may lead to the formation of coke fines.

Tribological Approach to Investigate the Interface Properties in Metallurgical Coke

Metallurgical coke is a brittle composite material comprising predominantly carbon derived from both reactive and inertinite coal macerals. During cokemaking, these macerals form the porous coke matrix. The interfaces between the distinct maceral derived components, known as textures in the final coke structure, are well-known to be a major source of weakness in some metallurgical cokes. In this paper, we present a novel approach which applies techniques used in tribology to investigate the strength of the interfaces as well as the wear properties of the different textural constituents in metallurgical coke, at room temperature. The wear mechanisms which occur in coke were investigated using three pilot oven cokes of different single coal origin. A range of high resolution analytical techniques, including coke petrography, optical microscopy, stereo microscopy, and scanning electron microscopy, were used to determine the wear modes. The technique has also proven to be an effective method to determine the relative strength of inerts and RMDC as well as the strength of the interface between these two textures, based on their susceptibility to different wear mechanisms. Further work is focused toward being able to predict the wear properties and relative strength of the inerts in a particular coke from their properties in the original coal(s).

Effect of pore structure and matrix reactivity on coke reactivity and post-reaction strength

Metallurgical coke accounts for a significant portion of the costs associated with blast furnace operations. The coke reactivity index (CRI) and coke strength after reaction (CSR), determined via the Nippon Steel Corporation test, are the most popular indexes for estimating the high-temperature properties of coke. Multiple factors affect the coke solution-loss reaction, and the CRI and CSR depend on the composition and structure of the coke. The pore structure is one of the most important factors affecting this reaction. The effect of the pore structure on the coke reactivity was determined by quantitatively evaluating the CRI and CSR of 10 types of coke. In each case, the corresponding structure was determined via image analysis. Furthermore, the initial reaction rate of the coke matrix was determined via thermogravimetric analysis of the fine grains. Mathematical models, quantitatively describing the CRI and CSR, were formulated via multiple linear regression, and the fit of the results to the experimental data was verified via the regression coefficient and a significance test. The models indicated that pores with sizes of 60–120 µm have a strong positive impact on CRI. In the case of invariant CRI, the high reactivity of the matrix has a positive impact on the post-reaction strength of the coke.