Char Structure Research Articles

Nanostructured poplar wood via delignification and ammonium dihydrogen phosphate-SiO2 modification towards remarkable flame retardant performance: Synergistic effect and enhanced mechanism

Developing efficient methods to prepare high-performance flame retardant and smoke suppression wood is crucial for the application. Herein, nanostructured poplar wood (DWI-4) with remarkable flame retardant and smoke suppression performance was fabricated by impregnating ammonium dihydrogen phosphate (ADP) and nano-silica (SiO2) into delignified wood (DW-4). With the delignification treatment, lignin was partially removed, and numerous pores and cracks were developed on the cell wall of wood, allowing more ADP-SiO2 particles to be impregnated into wood. As a result, ADP-SiO2 particle was not only anchored in the lumens (pores) of wood, but also was penetrated and embedded into the cell wall, achieving the synergistic modification of the lumen and cell wall of wood. As anticipated, the produced DWI-4 featured outstanding flame retardant and smoke suppression performance. The peak heat release rate (pHRR) of DWI-4 was as low as 38.2 kW m−2, which was only 8 % of that of natural wood (NW). And the total heat release (THR) and total smoke production (TSP) demonstrated reductions of 73.9 % and 64.4 % comparing to NW. Moreover, the compressive strength of DWI-4 increased by 31.4 % comparing to NW. The structure of residual char of DWI-4 was more stable and the gas intensity produced by the combustion of DWI-4 decreased remarkably. Therefore, the synergy of delignification and ADP-SiO2 impregnation significantly enhanced the flame retardant and smoke suppression performance of wood and the enhanced mechanism was revealed. The nanostructured poplar wood with excellent flame retardant and smoke suppression performance was prepared, providing an effective method for the functional improvement of wood and expanding the fields of application.

Catalytic steam reforming of waste tire pyrolysis volatiles using a tire char catalyst for high yield hydrogen-rich syngas

The production of hydrogen and syngas (H2/CO) from waste tires by pyrolysis catalytic steam reforming was investigated in a two-stage fixed bed reactor. In this study, tire char served as a sacrificial catalyst, facilitating the combination of catalytic steam reforming and char steam gasification reactions. The tire char acted as both a catalyst and a gasification reactant, enhancing the gas product yield. The process parameters investigated were, a reforming temperature range of 700–1000 °C, steam space velocity between 2 and 12 g h−1 g−1char and reaction times of 0.5–2 h. The influence of the parameters on the yield and composition of the product gases and the characteristics of the used catalyst were analyzed in detail. The results indicated that higher temperature and steam space velocity increased H2 and CO yields in the presence of a tire char catalyst. Elemental analysis of the used tire char, surface morphology and pore structure provided insights into the extent of tire char consumption in the reaction. Prolonged reaction time allowed for more thorough reactions between the pyrolysis volatiles and tire char, promoting the production of H2. At a reaction time of 2 h, the H2 yield reached 223 mmol g−1, representing 74 wt% of the maximum hydrogen yield.

Evaluation of char properties from co-pyrolysis of biomass/plastics: effect of different types of plastics

Co-pyrolysis of biomass/plastics is a viable method to obtain high-quality carbon materials. The synergistic effect in the char production process of co-pyrolysis of biomass/plastics affects the properties of the obtained char. However, the synergistic effect research on the char production process of co-pyrolysis of biomass/plastics is facing challenges owing to highly varying composition of different plastics. In this study, the synergistic effect during co-pyrolysis of bamboo (BM) and plastics (polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), polycarbonate (PC), and polybutylene terephthalate (PBT)) was investigated. TG results showed that PP, PS, PET, and PBT promoted the release of biomass volatiles and increased co-pyrolysis char yield. Notably, the O-aromatic structure in PC underwent cleavage and deoxygenation reactions, inhibiting the production of co-pyrolysis char during co-pyrolysis process. Char yield from co-pyrolysis process decreased from 24.80% for bamboo pyrolysis to 15.74% for co-pyrolysis of bamboo/PC. The results of physicochemical tests on char samples indicated that the addition of polyhydrocarbon plastics (PP and PS) increased H/C ratio, O/C ratio, heating value and oxidative reactivity of the char compared to bamboo char due to the vapor deposition of hydrocarbons derived from thermal decomposition of plastics on the biomass char. While, co-pyrolysis of biomass and polyester plastics (PET, PC, PBT) improved the pore structure of char and increased oxygen content.

Comparative study of the carbon structure of chars formed from coal with plastic waste and coal tar pitch additives

Comparative study of the carbon structure of chars formed from coal with plastic waste and coal tar pitch additives

Assessing Carbon Stocks and Ecosystem Functioning in Char (Buchanania lanzan) Forests of Central India

The present study assessment of plant community structure, carbon stock and CO2 sequestration of char (Buchanania lanzan) dominant forest sites in Central India during 2020-22. The forest vegetation was analysed using 20 quadrats (each 10 x 10 m in size for tree layers, 5 x 5 m in size for sapling layers and 1 x 1 m size for seedling layers) within the representative one-hectare plot on each site. The biomass, carbon stock, and carbon dioxide sequestration from three district (Mahasamund, Gariaband, and Kabirdham) char dominated forest sites of dry deciduous forests in Central India were estimated using the non-destructive allometric equation approach. The results revealed that the density of tree, sapling and seedling were ranged from 430-605 stems ha-1, 120-600 stems ha-1 and 28000-34500 stems ha-1, respectively. The basal area of tree and sapling layers were varied from 18.15-29.68 m2 ha-1 and 0.33-1.04 m2 ha-1, respectively. The diversity indices of tree layer viz; Shannon index, Simpson index, Evenness, species richness and beta diversity were ranged from 2.40-2.72, 0.17-0.22, 1.08-1.18, 2.26-3.11 and 5.0-6.0, respectively on different forest site in Central India. The total biomass, carbon stock and CO2 sequestration potential of tree layers were varied from 105.72-216.96 Mg ha-1, 50.22-103.06 Mg ha-1 and 184.29-378.22 Mg ha-1, respectively on char dominant various forest sites in Central India. The correlation coefficients were statistically significant performed between basal area and biomass, carbon stock and CO2 sequestration potential with R2 values of 0.988 at p<0.01 levels. After doing this study, it can be concluded that estimating the biomass and carbon stock in Central India will be useful for managing forests sustainably.

Effect of twin-roll temperature and interface adhesion on ablative performance and char structure of ethylene propylene diene monomer-based ablative insulator

Effect of twin-roll temperature and interface adhesion on ablative performance and char structure of ethylene propylene diene monomer-based ablative insulator

Rapid pyrolysis of cellulose: Revealing the role of volatile matter and char structure evolution

The complexity of the cellulose structure hinders its energy conversion and utilization. Pyrolysis is not only an independent thermochemical conversion technology but also a necessary stage in the gasification process. The real-time capture of volatile components in cellulose pyrolysis is difficult, and the evolution of char structures is lacking, which is extremely challenging. In this work, elemental analysis, industrial analysis, thermogravimetric analysis, infrared spectroscopy (FTIR), Raman spectroscopy (Raman), and X-ray diffraction spectroscopy (XRD) were used to characterize the raw materials and products. Combined with rapid pyrolysis experiments, the pathways of cellulose pyrolysis volatiles and char structure evolution were explored. Dehydrated sugars are the initial products formed below 350 ℃, which quickly dehydrate to form furan compounds at 400 ℃ and then break CC bonds at 600 ℃ to generate fatty aldehydes, ketones, and carboxylic acids. Biochar generated at low temperatures (<300°C) has strong lipid solubility. An increase in pyrolysis temperature leads to a continuous decrease in the content of H and O in biochar, which destroys its functional groups and physical structure, and ultimately tends to form graphite-type char with aromatic structures. Based on the correlation between the volatile matter release characteristics and the evolution of the semichar structure, a cellulose pyrolysis pathway was established, providing theoretical support for the high-value utilization of cellulose.

Studies on NOx formation and reduction characteristics in high-ash, low-volatile coal combustion by mechanism experiments and industrial-scale trials

Mechanism experiments were performed to investigate NOx formation and reduction during the combustion of high-ash, low-volatile coal. Additionally, industrial-scale trials were conducted to study the effects of air-staging degree on the combustion and NOx emission characteristics of high-ash coal on a 350 MW supercritical down-fired boiler. The results showed that the total BET specific surface area, total pore volume and porosity values of high-ash coal (HAC) and ultra-high-ash coal (UHAC) were all larger than those of normal-ash coal (NAC), whereas NAC contained more N-5 and N-6 than HAC and UHAC. The carbon layer structure of HAC char was less ordered and the content of hydroxyl group was relatively high. The overall NO reduction ratio obtained using the HAC char was higher than the value for the UHAC char. However, in the high temperature range of 1300–1400 °C, NO reduction associated with UHAC char was accelerated because of catalysis by ash. On increasing the excess oxygen ratio λ from 1.0 to 1.2, the char-N conversion shown by the UHAC char slowly increased and remained the lowest among the three chars. When burning UHAC, as the ratio of secondary to tertiary air fluxes, Rst, was decreased from 1.56 to 0.57, heating of the fuel-rich coal/air flow slowed and pulverized coal combustion was inhibited. The situation associated with HAC was different. At the Rst of 1.11, the ignition distance of fuel-rich flow was the shortest at 1.50 m, and the overall temperature in the furnace was the highest. However the NOx emissions at the furnace exit were as high as 715 mg/m3 (6 % O2) in this condition. Decreasing Rst to 0.57 reduced this value to 634 mg/m3 (6 % O2) with carbon levels in the fly ash and slag of 5.17 % and 3.67 %, respectively. Air-staging combustion is evidently a reasonable approach to controlling NOx emissions when burning HAC. While for UHAC, it was necessary to appropriately reduce the air-staging degree to enhance combustion and maintain low NOx emissions.

Co-Pyrolysis of Mushroom Residue Blended with Pine Sawdust/Wheat Straw for Sustainable Utilization of Biomass Wastes: Thermal Characteristics, Kinetic/Thermodynamic Analysis, and Structure Evolution of Co-Pyrolytic Char

Co-pyrolysis technology is considered to be one of the most promising methods for the sustainable utilization of biomass wastes, as it can realize waste reduction and convert wastes into high-value-added products with little impact on the environment. The evaluation of thermal characteristics and product properties is necessary for understanding this technique. In this paper, thermal characteristics and kinetic and thermodynamic analysis during the co-pyrolysis of mushroom residue (MR) with pine sawdust (PS) or wheat straw (WS) were investigated in a TGA. The carbon structure and surface textures of co-pyrolytic char were explored using Raman spectroscopy and a scanning electron microscope. As the PS or WS mass ratio increased, the devolatilization index increased obviously, indicating that volatile release was promoted and concentrated. Weak interactions were observed between 250 and 400 °C during the co-pyrolysis process, which primarily affected the mass transfer, resulting in a change in the thermal decomposition temperatures and rates. The interactions had no prominent influence on the volatiles’ yields. The non-additive performance of average activation energies for the blends was observed due to the interactions, and the lowest average activation energy was obtained when the PS or WS mass ratio was 50%. The lower average pre-exponential factor of the blends indicated the reduced complicacy of the pyrolysis reaction. The relatively small deviation between the activation energy and enthalpy change (4.94–5.18 kJ·mol−1) signified the energy sensitivity of product formation. PS promoted the formation of small aromatic rings (&lt;6 fused rings) in co-pyrolytic chars, whereas WS favored the production of larger rings (≥6 fused rings). The surface textures of the co-pyrolytic chars became porous, and the greater fractal dimensions of the surface morphology for the co-pyrolytic chars indicated that the char surface became irregular and rough.

Magnetic biochar from spent coffee grounds as filler in bioplastic composites

This study focuses on the synthesis of magnetic biochar derived from spent coffee grounds and their use in biodegradable pectin composite films. X-ray diffraction and Raman spectroscopy confirmed an amorphous char structure with embedded crystalline magnetite in the magnetic biochar. For the composite films, the hysteresis loops show a magnetic behavior reminiscent of a soft magnet with a low coercive field of 90 Oe and 14 % remanence. Thermogravimetric analysis revealed improved thermal stability of the composite films compared to pure pectin films. The proposed approach offers enhanced thermal properties and magnetic functionality, with potential applications in sustainable packaging, electromagnetic shielding and environmental sensing.

Experimental study on thermal conversion characteristics of char in a pressurized O2/CO2/H2O atmosphere

Pressurized oxy-fuel combustion represents an advanced coal-fired power generation technology advantageous for CO2 capture and system efficiency enhancement. This study employed a pressurized tube furnace experimental system to investigate the thermal conversion characteristics of char in a pressurized O2/CO2/H2O atmosphere. The carbon conversion under varying pressures (0.1–1.3 MPa), atmospheres, and residence times were analyzed. The physical and chemical structural evolutions of char, which are directly related to its reactivity, were elucidated using nitrogen adsorption, XPS, Raman, and FTIR analysis. The findings indicate that both pressurization and increasing O2/CO2 enhanced char conversion. Transitioning from kinetic to diffusion control in the O2/CO2/H2O atmosphere necessitated high pressure. The influence of CO2 on the physical and chemical structure of char under pressurized conditions was found to be less significant compared to that of O2 and H2O. Furthermore, pressurization and elevated O2 ratios were observed to reduce the microporous structure's contribution to the specific surface area of the char. Pressurization also increased the degree of graphitization of the char. Elevated O2/CO2 concentrations facilitated the breakdown of C–C structures, the melting of large aromatic rings, and the reduction in the degree of graphitization, particularly under higher pressures. In the O2/CO2/H2O pressurized atmosphere, more oxygen-containing functional groups were formed within the char structure, with the C–OH structure forming initially, followed by the O–CO structure.

Structure characteristics and combustion kinetics of the co-pyrolytic char of rice straw and coal gangue

Co-combustion is a technology that enables the simultaneous and efficient utilization of biomass and coal gangue (CG). Nevertheless, the factors that affect the combustibility of co-pyrolytic char, which represents the rate-determining step of the entire co-combustion process, remain unclear. This study investigates the impact of the physicochemical properties of co-pyrolytic char, including pore structure, carbon structure, and alkali metals, on the combustion characteristics. The TGA analysis indicates that the ignition and burnout temperatures of the co-pyrolytic char increase as the CG mixing ratio increases, resulting in a prolonged combustion. This is due to the fact that the carbon structure of the co-pyrolytic char becomes increasingly aromatic, accompanied by a reduction in aliphatic hydrocarbons and oxygen-containing groups as the CG mixing ratio increases. Furthermore, the high ash content of the CG is another significant factor contributing to the observed reduction in combustibility. The reaction between mullite, quartz in CG, and alkali metals in biomass results in the formation of aluminosilicate, which reduces the catalytic ability of alkali metals. Furthermore, the char combustion kinetics are analyzed by the KAS method, and the results indicate that the introduction of CG increases the activation energy of the entire char combustion process. The activation energy of the 80RS20CG is within the range of 102.22–164.99 kJ/mol, while the RS char is within the range of 89.87–144.67 kJ/mol.

Decoupling study on the influence of the interaction between biomass hydrochar and coal during co-pyrolysis on the char structure evolution

Co-pyrolysis of biomass hydrochar (biomass processed by hydrothermal carbonization, HTC) and coal, is a viable method for the clean and high-efficiency co-utilization of conventional and renewable resources. Interaction between biomass hydrochar and coal during co-pyrolysis directly impacted the physiochemical structure evolution of char and its downstream application. However, interaction mechanism hasn't been systematically revealed till now. Therefore, this study conducted a decoupling investigation on co-pyrolysis of rice straw hydrochar (RSH) prepared at different HTC conditions and bituminous coal (BC) using a staged fixed-bed reactor. The results demonstrated that RSH volatiles increased the number of deposits and cracks formed on the surface of co-pyrolysis decoupled BC char. Additionally, volatiles from RSH prepared at higher HTC temperatures led to the decrease of surface deposits, surface functional groups (such as –OH, C–H, and C–O) and graphitization degree of BC char. However, volatiles prepared at different solid-liquid ratios had a negligible impact on physicochemical structure of BC char. At HTC temperature of 200 °C, volatiles from BC led to increased surface functional groups (such as –OH and CC) and graphitization degree of co-pyrolysis decoupled RSH char. Furthermore, volatiles from BC showed more noticeable effect on graphitization process of RSH char prepared at higher solid-liquid ratio.

Supersonic hot jet ablative testing and analysis of boron nitride nanotube hybrid composites

Boron nitride nanotubes (BNNTs) are high-strength, high-modulus nanotubes with high thermal and oxidative stabilities. Two hybrid composites were prepared with satin weave carbon fiber (CF) and resole-type phenolic resin: one with surface layers of BNNTs and one with alternating interlayers of BNNTs. The samples were subjected to hot jet tests that simulate realistic high-pressure-temperature conditions to understand the behavior of BNNTs under high-pressure erosion. Adding BNNTs to CF/phenolic laminates enhanced the ablation resistance by reinforcing the char material and mitigated localized thermal damage. Hybrid laminates exhibited up to 14 % lower weight loss, 55 % increase in flexural modulus, higher thermal diffusivity, and improved char yield and microstructure compared to CF/phenolic samples. The surface layer hybrid had many surviving nanotubes reinforcing the char and crystalline oxide structures that could mitigate further oxygen diffusion. Various characterization methods were used to deduce possible mechanisms and their products, indicating that BNNTs could serve as growth templates for direct crystalline boron oxide formation. Overall, hybrid BNNT/CF/phenolic laminates displayed better ablation resistance and favorable microstructure evolution under high-pressure conditions.

“One for two” strategy to construct an organic-inorganic polymer colloid for flame-retardant modification of flax fabric and rigid polyurethane foam

Polymeric materials such as fabric and foam have high flammability which limits their application in the field of fire protection. To this end, an organic-inorganic polymer colloid constructed from carboxymethyl chitosan and ammonium polyphosphate was used to improve the flame retardancy of flax fabric (FF) and rigid polyurethane foam (RPUF) based on a “one for two” strategy. The modification processes of FF and RPUF relied on pad-dry-cure method and UV-curing technology, respectively, and the modified FF and RPUF were severally designated as CMC/APP-FF and RFR-RPUF. Flame retardancy studies showed that CMC/APP-FF and RFR-RPUF exhibited limiting oxygen index values as high as 39.4 % and 42.6 %, respectively, and both achieved self-extinguishing behavior when external ignition source was removed. Thermogravimetric analysis and cone calorimetry test confirmed that CMC/APP-FF and RFR-RPUF had good charring ability and demonstrated reduced peak heat release rate values of 90.1 % and 10.8 %, respectively, distinct from before they were modified. In addition, condensed phase analysis showed that after burning, CMC/APP-FF became an integration char structure, whereas RFR-RPUF turned into a sandwiched char structure. In summary, the “one for two” strategy reported in this work provides a new insight into the economical fabrication of flame-retardant polymeric materials.

Investigation on the steam gasification mechanism of different chars using isotopic tracing method

Gasification can provide syn-gas for consequent chemical production from carbon resources. The control of CO2 emission produced from gasification calls for the lower temperature and the more biomass char for the feed compared with traditional gasification, and the mechanism for steam gasification of different chars is more important. The gasification behaviors of four biomass chars and four coal chars are studied. The mechanism is probed using H216O/H218O period step tracing method coupled with various solid-state analyses on char structures. The increment of intermediates with increasing conversion demonstrate other slow step exists during gasification, and the solid state spectra of chars after and before gasification demonstrates that the condensation of poly-aromatic clusters in chars occurs accompanied with gasification. The addition reactions of radicals generated from gasifying agents and unsaturated carbon bonds C = C in chars is the slower step during gasification and enhancing the addition of radicals to unsaturated C = C bonds may be helpful for the higher gasification rate.

Analysis of Structural Heterogeneity in Low-Rank Coal and Its Pyrolyzed Char Using Multi-Point Scanning Micro-Raman Spectroscopy.

Understanding the changes in carbon structure during the mid-low-temperature pyrolysis of low-rank coal is important for efficient utilization. Raman spectroscopy is commonly used to analyze the structural order of carbonaceous materials, but traditional methods may overlook the heterogeneity of coal/char. This research explores the heterogeneity of char structure derived from low-rank coal at 700 °C through multi-point micro-Raman analysis. The analysis of parameters such as area (A), intensity (I), full width at half maximum (FWHM/W), and peak position (P) reveals that the carbon structure becomes less ordered as coal transforms into char due to the deposition of small molecules on the surface. The study emphasizes the benefits of multi-point detection for gaining in-depth insights into the structural evolution of carbonaceous materials. The increased standard deviation of Raman parameters indicates diverse structural characteristics resulting from pyrolysis at this temperature, which traditional methods may not capture effectively. The mapping method used in this research visually illustrates the distribution of carbon structures in the region.

Synergistic interactions between lignite and biomass during co-pyrolysis from volatile release, kinetics, and char structure

One of the most efficient techniques to achieve efficient utilization of both is coal and biomass co-pyrolysis. Despite a great deal of recent research on the co-pyrolysis process, it is still unknown how biomass affects the co-pyrolysis's synergistic effect and how volatiles interact. This study uses a thermogravimetric analyzer to examine the weight loss law of co-pyrolysis of wheat straw, rice straw, and bamboo powder with various amounts of Zhundong coal. According to the findings, there is a strong positive interaction, a mild positive interaction, and a negative interaction when three different types of biomass (wheat straw, rice straw, bamboo straw) are co-pyrolysis with Zhundong coal. The interaction between wheat straw and Zhundong coal is the strongest when the mass ratio of wheat straw to Zhundong coal is 6: 4. Using a thermogravimetric-infrared spectrometer, the changes in volatile functional groups during co-pyrolysis are investigated. It is discovered that adding wheat straw decreased the amount of CO2 produced by Zhundong coal pyrolysis. Regarding the mechanism of co-pyrolysis, the alkali and alkaline earth metals (AAEMs) on the surface of biochar catalyze the pyrolysis of Zhundong coal, while the “hydrogen donor” and “free radical donor” generated by biomass pyrolysis inhibited the cross-linking and polymerization of macromolecular volatiles produced by Zhundong coal pyrolysis. The activation energy of the mass ratio of wheat straw to Zhundong coal = 6: 4 sample is calculated by three model-free methods. The co-pyrolysis process's average activation energy is determined to be between 175.95 and 194.18 kJ/mol. Through scanning electron microscopy, it is found that the morphology of co-pyrolysis carbon is significantly different from that of single pyrolysis carbon. The porous structure of biochar promotes the secondary cracking of heavy volatiles produced by coal pyrolysis, while the cracking of volatiles further promotes the development of the pore structure of biochar.

Experimental Study on the Thermal Reduction of CO2 by Activated Solid Carbon-Based Fuels

Experimental Study on the Thermal Reduction of CO2 by Activated Solid Carbon-Based Fuels

Structure and morphology of chars and activated carbons obtained from thermal treatment of coal and biomass origin materials, including their wastes: Results from the ICCP Microscopy of Carbon Materials Working Group

This paper describes the evaluation of petrographic textures in char and activated carbon derived from coal, coal by-products and biomass, formed during carbonization and activation processes. This work represents the results of interlaboratory exercises from 2016 to 2022 of the Microscopy of Carbon Materials Working Group in Commission III of the International Committee for Coal and Organic Petrology. The interlaboratory exercises were run on photomicrograph samples. For textural characterization of carbon materials, the existing American Society for Testing and Materials (ASTM) classification system for metallurgical coke was applied. Morphological differences were evaluated in 29 carbon material types, including 22 char samples, and 7 activated carbon (AC) samples obtained experimentally using conventional direct/indirect and microwave heating technologies. This approach gives an extended view on the identification of microporous carbons, and how a certain heat treatment develops a certain optical texture and structure in a raw material. The requested evaluation of carbon materials was related to their porosity, origin, extent, and characteristics, which are particular to each carbon material type. Because carbon matrices can form a wide range of optical textures during heat treatment it is important to demonstrate which carbon occurrences will have a crucial role in industrial applications dominated by adsorption phenomena.The interlaboratory exercises included 17 participants from 14 laboratories. Four sets of digital black and white and colour photomicrographs were distributed, which in total comprised 184 fields of different types of carbon material. The results were evaluated based on four levels: (i) optical texture (isotropic/anisotropic), (ii) optical type and size (punctiform, mosaic, fiber, ribbon, domain), iii) morphology (porous, non-porous/massive), and (iv) particle origin (precursor type).The statistical method applied to evaluate the results was based on “raw agreement indices”. Comparative analyses of the average values of the level of overall agreement showed homogeneity in the results, the mean value was 89%, with a minimum value of 87% and a maximum value of 91% for those who participated in at least three out of four exercises.