Microwave synthesis of amino-functionalized MCM-41 from coal gasification fine slag for efficient bidirectional adsorption of anionic and cationic dyes.

Coal based solid waste has been recognized as a sustainable raw material for the preparation of high added value materials for wastewater treatment. In this paper, a preparation route was designed for the rapid, efficient, and low-cost preparation of MCM-41 zeolite using coal gasification fine slag as raw material. Functionalization modification of MCM-41 was carried out by grafting amino groups on its surface to improve its application performance. Moreover, the prepared functionalized material is used for bidirectional adsorption of anionic and cationic dyes. The experimental results indicate that MCM-41 zeolite with highly ordered pore structure was rapidly prepared using the advantages of fast heating and strong permeability of microwave synthesis method, with a specific surface area of up to 862.03 m2/g. Amine functionalized MCM-41 exhibits strong adsorption capacity for both cationic and anionic dyes, with maximum adsorption capacities for methylene blue and Congo red being 292.40 mg/g and 354.61 mg/g, respectively. The study of adsorption kinetics and adsorption mechanism indicate that the adsorption process is mainly controlled through chemical adsorption, including electrostatic attraction, hydrogen bonding, and π-π interactions. The results of this study will provide useful references for the use of coal based solid waste to prepare functional materials for the treatment of organic wastewater.

Correlation between Flow Temperature and Average Molar Ionic Potential of Ash during Gasification of Coal and Phosphorus-Rich Biomass.

The co-gasification of biomass and coal is helpful for achieving the clean and efficient utilization of phosphorus-rich biomass. A large number of alkali and alkaline earth metals (AAEMs) present in the ash system of coal (or biomass) cause varying degrees of ash, slagging, and corrosion problems in the entrained flow gasifier. Meanwhile, phosphorus is present in the slag in the form of PO43-, which has a strong affinity for AAEMs (especially for Ca2+) to produce minerals dominated by calcium phosphates or alkaline Ca-phosphate, effectively mitigating the aforementioned problems. To investigate the changing behavior of the slag flow temperature (FT) under different CaO/P2O5 ratios, 72 synthetic ashes with varying CaO/P2O5 ratios at different Si/Al contents and compositions were prepared, and their ash fusion temperatures were tested. The effects of different CaO/P2O5 ratios on the FT were analyzed using FactSage thermodynamic simulation. A model for predicting slag FT at different CaO/P2O5 ratios was constructed on the basis of the average molar ionic potential (Ia) method and used to predict data reported from 19 mixed ashes in the literature. The results showed that Ia and FT gradually increased with a decreasing CaO/P2O5 ratio, and the main mineral types shifted from anorthite → mullite → berlinite, which reasonably explained the decrease in ash fusion temperatures in the mixed ash. The established model showed good adaptability to the prediction of 19 actual coal ash FTs in the literature; the deviation of the prediction was in the range of 40 °C. The model proposed between FT and Ia based on the different CaO/P2O5 ratios can be used to predict the low-rank coal and phosphorus-rich biomass and their mixed ashes.

Aromatics production from relay catalytic pyrolysis of cow manure using Ru/C and ZSM-5 dual catalysts synthesized from coal gasification fine slag.

Resource utilization of solid waste can aid in gradual substitution of fossil fuels while achieving waste recycling. In this study, residual carbon and ash slag from the coal gasification fine slag were separated by froth flotation, and then was used to prepare Ru/C and ZSM-5 dual catalysts with carbon-rich and ash-rich components as raw materials, respectively. The performance of two catalysts for catalytic upgrading of volatiles from pyrolysis of cow manure (CM) to produce light aromatic hydrocarbons was systematically investigated. The direct pyrolysis products of CM mainly included alcohols, ketones, ethers, and other oxygen-containing compounds. When ZSM-5 was used as the catalyst, the yield of monocyclic aromatic hydrocarbons (MAHs) increased significantly due to the better catalytic cracking and aromatization abilities of ZSM-5 catalyst. However, the yield of phenols in the pyrolysis products improved when Ru/C was used as the catalyst due to the cleavage effect of Ru/C on the C-O bond. When Ru/C and ZSM-5 were used as dual catalysts in relay catalytic pyrolysis of volatiles, the increase in MAHs yield in the pyrolysis product was higher than the total increase obtained under Ru/C and ZSM-5 single catalysis. The possible pathways for the generation of MAHs from CM under Ru/C and ZSM-5 relay catalytic pyrolysis were revealed by the pyrolysis experiment performed on model compounds.

Mechanism of the noncatalytic oxidation of soot using in situ transmission electron microscopy.

Soot generation is a major challenge in industries. The elimination of soot is particularly crucial to reduce pollutant emissions and boost carbon conversion. The mechanisms for soot oxidation are complex, with quantified models obtained under in situ conditions still missing. We prepare soot samples via noncatalytic partial oxidation of methane. Various oxidation models are established based on the results of in situ transmission electron microscopy experiments. A quantified maturity parameter is proposed and used to categorize the soot particles according to the nanostructure at various maturity levels, which in turn lead to different oxidation mechanisms. To tackle the challenges in the kinetic analysis of soot aggregates, a simplification model is proposed and soot oxidation rates are quantified. In addition, a special core-shell separation model is revealed through in situ analysis and kinetic studies. In this study, we obtain important quantified models for soot oxidation under in situ conditions.

Simulation Study on the Interaction between Chemically Reacting Double Coal Char Particles.

Due to the complex atmosphere of the entrained flow gasifier, it is difficult to obtain reactivity properties of coal char particles under high-temperature conditions by experiment. The computational fluid dynamics simulation method is a key way to simulate the reactivity of coal char particles. In this article, the gasification characteristics of double coal char particles under H2O/O2/CO2 atmosphere are studied. The results show that the particle distance (L) has an influence on the reaction with particles. With the gradual increase of L, the temperature first rises and then falls among the double particles due to the migration of the reaction area, and the characteristics of double coal char particles gradually approach that of single coal char particles. The particle size also has an influence on the gasification characteristics of coal char particles. As the particle size varies from 0.1 to 1 mm, the reaction area of particles becomes smaller at high temperature and finally attaches to the surface of the particles. The reaction rate and carbon consumption rate increase with increasing particle size. As the size of double particles is changed, the reaction rate trend of double coal char particles at the same particle distance is basically the same, but the change degree of reaction rate is different. With the increase of the distance between coal char particles, the change of the carbon consumption rate is larger for the small particle size.

Carbon coated In2O3 hollow tubes embedded with ultra-low content ZnO quantum dots as catalysts for CO2 hydrogenation to methanol.

CO2 hydrogenation coupled with renewable energy to produce methanol is of great interest. Carbon coated In2O3 hollow tube catalysts embedded with ultra-low content ZnO quantum dots (QDs) were synthesized for CO2 hydrogenation to methanol. ZnO-In2O3-II catalyst had the highest CO2 and H2 adsorption capacity, which demonstrated the highest methanol formation rate. When CO2 conversion was 8.9%, methanol selectivity still exceeded 86% at 3.0 MPa and 320 °C, and STY of methanol reached 0.98 gMeOHh-1gcat-1 at 350 °C. The ZnO/In2O3 QDs heterojunctions were formed at the interface between ZnO and In2O3(222). The ZnO/In2O3 heterojunctions, as a key structure to promote the CO2 hydrogenation to methanol, not only enhanced the interaction between ZnO and In2O3 as well as CO2 adsorption capacity, but also accelerated the electron transfer from In3+ to Zn2+. ZnO QDs boosted the dissociation and activation of H2. The carbon layer coated on In2O3 surface played a role of hydrogen spillover medium, and the dissociated H atoms were transferred to the CO2 adsorption sites on the In2O3 surface through the carbon layer, promoting the reaction of H atoms with CO2 more effectively. In addition, the conductivity of carbon enhanced the electron transfer from In3+ to Zn2+. The combination of the ZnO/In2O3 QDs heterojunctions and carbon layer greatly improved the methanol generation activity.

Experimental Study on OH*, CH*, and CO2* Chemiluminescence Diagnosis of CH4/O2 Diffusion Flame with CO2-Diluted Fuel.

OH* and CH* chemiluminescence in hydrocarbon flames are often applied to characterize flame structure, equivalence ratio, strain rate, heat release rate, etc. In this study, chemiluminescence images of OH*, CH*, and CO2* in the CH4/O2 diffusion flame were obtained using a CCD camera imaging system. The effect of CO2 dilution on the flame structure, strain rate, and other flame characteristics of CH4/O2 diffusion flame was discussed. The results show that CO2 dilution greatly affects flame morphology and chemiluminescence intensity. There are quantitative functions between the chemiluminescence peak intensity of OH* and CH* and the CO2 dilution level. The CO2* average intensity in the flame zone is better suited to characterize the dilution level than the CO2* peak intensity. Moreover, the strain rate of CO2-diluted laminar flame is defined. It is found that there is a linear relationship between the thickness of the OH* reaction zone and the square root of the strain rate.

Numerical Analysis of Fracture Failure Behavior of Refractory Lining in Coal-Water Slurry Gasifier.

Fatigue crack fracture is one of the main reasons for the failure of a refractory lining in a coal-water slurry gasifier. To explore the fracture failure behavior of a refractory lining during the operation of a gasifier, the stress intensity factor (SIF) and J-integral at crack front were calculated by the finite element method, and a crack growth model for the refractory was established. At the same time, the effects of different crack length, depth, and angle on the stress and SIF, as well as J-integral distribution around the crack-tip, were presented. The simulation results demonstrated that very large stresses occurring at the crack tip and the distribution regulation of K I and J-integral along the crack front for surface cracks were similar. The maximum values occurred near the two ends of the crack (θ = 0°, 180°), and the minimum values appeared near the deepest crack front (θ = 90°). K I and J-integral values at the same position increase with increasing crack length and depth and decrease with the angle of crack when the a/c was kept constant. Furthermore, J-integral results indicated that excessive crack depths were likely to cause destabilizing crack growth. These results have provided a reliable theoretical basis for fracture analysis and life prediction of the refractory lining in a gasifier.

Effect of Structural Optimization of Scrubbing Cooling Rings on Vertical Falling Film Flow Characteristics.

In order to study the influence of the structural optimization of the scrubbing cooling ring in the scrubbing cooling chamber on the flow characteristics of the vertical falling film, the flow characteristics of the turbulent falling film in the rising section of the development region at different internal platform heights of the scrubbing cooling ring and a high Reynolds number were studied by FLUENT software. First, the correctness of the model was verified by the maximum error of simulation and experimental results of no more than 9.836%. Then, the distribution of liquid film thickness (δ), velocity (V), and turbulence intensity (I z) at 0° of the tube in the axial direction x = 0-500 mm were calculated and obtained when the platform height (H) was 0-30 mm and the liquid film Reynolds number (Re l) = 1.1541 × 104-3.4623 × 104. The results showed that δ in the entrance region increased sharply due to the "jet" effect with solid wall constraints formed by the structure of the water inlet pipe and the scrubbing cooling ring. On the contrary, the liquid film in the fully developed region showed a stable fluctuation trend due to the weakening of the "jet" effect. When H = 30 mm, the change of δ was relatively stable and the change of I z was small, indicating that this platform height is conducive to the stable and uniform distribution of the liquid film. In addition, when Re l < 1.1541 × 104, the liquid film was unstable due to the low flow rate and insufficient cohesion of the liquid film, but V increased slightly. In addition, with the increase of Re l, δ did not change significantly along the axial direction, that is, the Plateau-Rayleigh hindered the growth of δ. Finally, the empirical formula for δ applicable to Re l = 1.1541 × 104-3.4623 × 104 at the axial fixed position was fitted for the first time.

Low-cost Y-type zeolite/carbon porous composite from coal gasification fine slag and its application in the phenol removal from wastewater: fabrication, characterization, equilibrium, and kinetic studies.

As an industrial solid waste, coal gasification fine slag (CGFS), which consists of many elements, such as silicon, aluminum, and carbon, could be used as an important resource. Therefore, this solid waste was used as a raw material to prepare high-value-added adsorption material for the treatment of industrial wastewater in this study. A hydrothermal synthesis method was applied to convert CGFS into a Y-type zeolite/carbon porous composite. The effects of time and temperature on the synthesis were studied. XRD, SEM, and other techniques were used to analyze the material and its physicochemical properties. Additionally, the adsorption performance of the material for phenol was studied. The results showed that the composite has better adsorption capacity for phenol than CGFS. The Freundlich model and pseudo-second-order kinetics well fitted the adsorption behavior of the composite, which demonstrated that the adsorption of phenol was dominated by chemical adsorption.

Hydrothermal carbonization of rape straw: Effect of reaction parameters on hydrochar and migration of AAEMs.

Hydrothermal carbonization (HTC) can improve biomass quality in both physical and chemical aspects for energy application. This study aims to investigate the characteristics and reactivities of rape straw (RS) hydrochars. Hydrochars were prepared at 160-240 °C with residence time of 15-120 min. Mass yield, energy yield, microstructure, functional group and migration of alkali and alkaline earth metals (AAEMs) were studied to evaluate the influence of different conditions on properties of hydrochar. The results showed that O/C and H/C ratio decreased, while the higher heating value (HHV) increased with increasing temperature and residence time. The effect of increasing temperature on hydrochar properties was more significant than residence time. The structure was changed, and hydrochar possessed a more stable form after the aromatization reaction. For the gasification reactivity of hydrochar, decomposition rate curves showed that the peak of pyrolysis and gasification moved to a higher temperature region with the increasing of HTC temperature because of the developed aromatic structures in hydrochar. The pyrolysis activation energy decreased from raw RS 71.68 to 41.03 kJ/mol in 240 °C, while gasification activation energy increased from 80.42 to 251.30 kJ/mol. Moreover, it was found that HTC can reduce the content of AAEMs efficiently and the best removal condition is 200 °C. Ca content dropped to a minimum value at 200 °C and then increased at higher temperature which may be caused by well-developed pore structure in hydrochars. This study provides basic data for comprehensive utilization of rape straw and migration mechanism of AAEMs in HTC process.

Study on Soot Emission Characteristics of Methane/Oxygen Inverse Diffusion Flame.

Inverse diffusion flame (IDF) is an effective and widely used reaction form in the process of noncatalytic partial oxidation (NC-POX) of gaseous hydrocarbons (such as natural gas and coke oven gas). However, soot is generated in the combustion chamber in the case of unreasonable feeding conditions, and thus causes serious damage to the wall and nozzle. In this study, the effects of the equivalence ratio ([O/C]e), the oxygen flow rate, and the Reynolds number on the soot and CH* emission characteristics of CH4/O2 inverse diffusion flame were comprehensively analyzed based on a hyperspectral imaging system. In addition, the relationship between CH* and soot is explored using Ansys Fluent simulation. The experimental results show that the soot radiation core generation area is located in the outer ring of the flame, and the radial distribution of the radiation intensity is bimodal. With the increase in [O/C]e, the initial position for soot radiation and the overall radiation intensity of soot decrease. In addition, the CH* radiation intensity decreases as [O/C]e increases, and CH* exists in the whole flame. The simulation results clearly show that the existence of CH* is conducive to soot production. The emission intensity and the core area of soot formation increase with the increase in the oxygen velocity. Additionally, the soot emission region increases and the flame tip changes from a round blunt to symmetrical tip with the increase in the Reynolds number.

Numerical Simulations of Solidification Characteristics of Molten Slag Droplets in Radiant Syngas Coolers for Entrained-Flow Coal Gasification.

The high-temperature syngas and molten slag droplets discharged from entrained-flow coal gasifiers contain a large amount of heat energy, which can be efficiently recovered by radiant syngas coolers (RSCs). However, it is hard to know the solidification degree of molten slag droplets at the outlet of an RSC during industrial operations. In this work, the industrial-scale RSC and molten slag droplet models are established to predict the solidification degree of slag droplets at the outlet of the RSC. Then, the effects of slag diameter, syngas flow field, slag initial temperature, slag porosity, and slag pore structure are investigated by numerical simulations, and residence time as well as complete solidification time are calculated by coupling of a discrete-phase model and a solidification model. The results indicate that as the slag droplet diameter increases, the residence time of the slag droplet shortens, but the complete solidification time increases. When the slag droplet diameter is greater than or equal to 3.0 mm, the complete solidification time is larger than the residence time, and the slag droplet cannot solidify completely at the outlet of the RSC. The solidification degree in the windward zone is greater than that in the leeward zone. Although the slag initial temperature has little effect on the solidification, a lower slag initial temperature is still conducive to a greater solidification degree. Additionally, the pore structure facilitates solidification, and the promoting effect of penetrated pores is more remarkable than that of closed pores. A larger porosity is also beneficial to accelerate the solidification of molten slag droplets and increase the solidification degree.

Study on the pyrolysis characteristics and kinetic mechanism of cow manure under different leaching solvents pretreatment.

Cow manure (CM) is a kind of biowaste with potential for heat recovery and energy. The effects of different leaching solvents on the physicochemical structure of CM and the catalysis role of AAEMs on the thermal behavior were studied. TGA experiments showed that the maximum weight loss rate and the peak temperature of hemicellulose and cellulose increased after leaching, while the TG/DTG curve moved to a high temperature direction. The devolatilization index (Di) value of the raw and leaching samples increased with the increase of the heating rate, indicating that the higher heating rate promoted the release of volatile. The treatment with leaching not only removed AAEMs in CM effectively, but also led to a larger specific surface area and pore volume, and reduced the crystallinity of cellulose and crystal size in CM. Na salt and K salt were mainly in water soluble state, while Ca salt and Mg salt were mainly in acid soluble salt. Compared with the change of physical and chemical structure caused by leaching, the removal of AAEMs played a dominant role in the pyrolysis characteristics of the samples. The removal efficiency of AAEMs increased with the strength of acid. Based on Kissinger model, the Eα of Raw-CM, H2O-CM, CH3COOH-CM, HCl-CM, HNO3-CM and H2SO4-CM is 171.30 kJ/mol, 187.58 kJ/mol, 190.86 kJ/mol, 292.10 kJ/mol, 287.79 kJ/mol and 280.69 kJ/mol respectively. Both the raw and leaching samples followed the reaction order mechanism and tended to react according to a higher-order reaction model between n = 1.5 and n = 4. In contrast, CH3COOH is an ideal solvent for leaching pretreatment.

Analysis of Coal Gasification Reactivity, Kinetics, and Mechanism with Iron-Based Catalyst from Coal Liquefaction.

In this work, the effect of an iron-based catalyst from coal liquefaction on coal gasification was studied. Two catalyst loading methods and three catalyst loading contents were taken into consideration. Besides, the carbon structure, surface morphology, and element distribution of coal char and gasified semi-char were investigated, and the interactions between the catalyst and internal minerals of coal were studied. The results showed that the coal char prepared by wet impregnation had higher reactivity than that prepared by a dry mixing method. From the perspective of improving the coal reactivity, the optimal addition method should be wet impregnation with a 2% catalyst. The model-free and model-fitting methods were applied to study the catalytic gasification kinetics. The iron-based catalyst would be broken during wet impregnation, and the catalyst fragments could stick to the surface of coal char, resulting in higher reactivity. The graphitization of char increased with the addition of the iron-based catalyst. This can imply that the carbon structure cannot effectively represent the gasification reactivity in the presence of the iron-based catalyst. The Iron-based catalyst can accelerate the gasification rate alone and can also provide higher catalytic activity with the internal minerals of coal.

Co-Gasification of Cow Manure and Bituminous Coal: A Study on Reactivity, Synergistic Effect, and Char Structure Evolution.

As special waste biomass, cow manure (CM) is also the main pollutant in agricultural production. The combination of cow manure and coal is conducive to the sustainable development of energy and the solution to pollution problems. This work aims to investigate the co-gasification reactivity and synergy of cow manure and Meihuajing (MHJ) bituminous coal blends at 800-1100 °C using a thermogravimetric analyzer, and the correlation between char gasification reactivity and its structural characteristics is performed. The results indicate that the sensitivity of gasification reactivity to temperature is gradually weakened with the proportion of CM increasing. The synergistic effect on reactivity was observed in the co-gasification process of CM/MHJ. The addition of CM promoted the synergistic effect obviously at the low carbon conversion level, and the inhibitory effect with the CM addition on the order degree of char carbon structure was enhanced during the co-gasification process according to Raman spectroscopy analysis. The addition of CM promoted the porous structure evolutions, which make the pore size distribution and the specific surface developed remarkable. The changes in carbon and pore structures can be well related to the gasification reactivity. The findings in this study would be helpful in the understanding of the co-gasification synergy mechanism of cow manure and coal blends.

Investigating the Effect of Flux on Ash Fusibility of High-Calcium Coal.

The primary aim of this study is to understand the effect of metal oxide flux on the fusibility of high-calcium coal ash. Based on the decomposition rate, the evolution of mineral matters in high-calcium coal has been investigated. The ash fusion temperatures of samples are measured by adding different flux Al2O3, Na2O, K2O, MgO, and TiO2. The results show that Na2O is the most effective in lowering ash fusion temperatures and its flow temperature could be 110 °C lower than that of the original ash. FactSage is used to calculate the proportion of solid phase and the mineral compositions as a function of the ash compositions and temperature. With the increase of Na2O, mineral matters with a low melting point form in the mixture. Furthermore, the decomposition rate of mineral matters increases in the first stage. The phase diagrams and relative mineral variation illustrate that the mineral and the decomposition rate variations are the main reasons for the change of ash fusion temperatures.

Investigation into the co-pyrolysis behaviors of cow manure and coal blending by TG-MS.

In this study, the co-pyrolysis characteristics of cow manure (CM) and Meihuajing bituminous coal (MHJ) blends were investigated in detail. The mass loss behavior and gas evolution characteristics of the blends were analyzed online by thermogravimetry-mass spectrometry (TG-MS), and kinetic analysis was performed. The results demonstrate that the addition of CM to the MHJ increases the reactivity of blends, indicating that interaction between the CM and MHJ occurred during co-pyrolysis. For conventional gases, the release order of gases during CM and MHJ blend pyrolysis is H2O, CO2, CO, CH4, H2. For sulfur-containing gases, with increasing proportion of CM, the emissions of H2S, COS, and C4H4S increase and that of SO2 decrease, and the release temperature interval shifts to lower directions. The Coats & Redfern model was used, an increase of activation energy with CM addition was observed. The optimum blending ratio based on the lowest activation energy is CM:MHJ = 1:3 and the activation energy is 41.9 kJ/mol.

Superior adsorption capacity of functionalised straw adsorbent for dyes and heavy-metal ions.

Dyes and heavy-metal ions are common pollutants in printing and dyeing wastewater, and are thus attracting considerable attention. Herein, an eco-friendly straw-based adsorbent, WS-CA-AM, was prepared by grafting with acrylamide (AM) and citric acid (CA) groups to remove representative dyes and heavy metals from aqueous solution. The adsorption capacities of WS-CA-AM for methyl orange (MO) and methylene blue (MB) were 3053.48 and 120.84 mg/g, which were 54 and 3 times those of unmodified straw, respectively. Moreover, the adsorption capacities for MB, MO, Cr2O72- and Cu2+ in the mixed system increased by 210%, 133%, 196% and 151%, respectively, compared with those in the single system. The significant increase in adsorption capacity can be attributed to the collaborative effect through electrostatic attraction. The functional groups and adsorbed pollutants all served as adsorption sites for pollutants. These results indicate that WS-CA-AM is a potential applicant for the removal of dyes and heavy-metal ions from mixed aqueous solution.