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Wasted coal liquefaction residual was used to synthesize activated carbon fibers (ACFs) for CO

When entrained-flow gasification technology is applied on a large scale, the release of hazardous trace elements (HTEs) from the use of coal in gasification poses a potential threat to environmental and human health. An adsorption method combining granular activated carbon (GAC) and zeolite as adsorbents to remove the HTEs is proposed. A pilot-scale experiment proved that this method can effectively remove HTEs, especially, the removal rate for mercury and beryllium achieved 99%. Additionally, adsorption studies using GACs were conducted through laboratory batch experiments employing several kinetic and isotherm models. The results show favorable levels of mercury, arsenic, and beryllium adsorption by GAC. GAC derived from low rank bituminous coal has the good comprehensive adsorption performance of HTEs. Langmuir presented the best fit of arsenic and beryllium adsorption, and Freundlich presented the best fit of mercury. The kinetics studies showed that experimental data follow Pseudo-second order. Zeolite’s capacity for ion exchange greatly affects its adsorption performance, which supplements the adsorption capacity of GAC for metal and metalloid ions. This study provides an approach that is fast, and easily integrates with existing processes for removing HTEs in entrained-flow coal gasification wastewater.

Zeolite membranes are widely used in separation, catalysis, sensors and other fields because of their good diffusion performance, shape selection and catalysis capabilities. However, the slow synthesis rate of zeolite membranes restricts their industrialization process, and the random orientation seriously affects their performance. Therefore, this paper investigates the methods for accelerating the synthesis rate of zeolites and the roles of different methods was explored. The synthesis conditions of oriented zeolite membranes are also summarized. Microwave method can efficiently synthesize oriented zeolite membranes, but it has the defects of harsh synthesis conditions and high equipment requirements. Using physical methods and chemical methods to introduce hydroxyl radicals, which is also an effective method to improve the synthesis rate of zeolites. However, there is a lack of research on how to realize the directional synthesis of zeolite membranes during this process. Synthesis conditions, template and support properties affect the directional synthesis of zeolite membranes. Therefore, while introducing free radicals, adjusting the composition of the synthetic solution or introducing inhibitors that affect the growth direction of zeolite in the synthetic system can realize the efficient directional synthesis of zeolite membrane, which is another potential method to promote the industrialization of directional zeolite membrane besides microwave method.

Pyrolysis can be considered as the initial stage or/and paralleling part of coal combustion, gasification, and direct liquefaction, and pyrolysis itself constitutes one of the fundamental technolog...

Zhundong coal can significantly reduce the preparation temperature of activated carbon (AC) due to the high contents of alkali and alkaline earth metals (AAEMs) present in it. Moreover, because of its lower operating temperature and the presence of carbon matrix, Zhundong coal can effectively inhibit the release of AAEM during the preparation of AC. For these reasons, the preparation of AC from Zhundong coal is a promising approach for the clean utilization of Zhundong coal. Accordingly, this study was aimed to investigate optimum conditions for the preparation of AC from Zhundong coal. For this purpose, at first, Raman spectroscopy was used to determine the conditions for an optimal carbonization process using a coal sample; then, the evolution of the pore structure of AC under different conditions was examined by small-angle X-ray scattering (SAXS) and the N2 adsorption analyser. Furthermore, environmental scanning electron microscopy (ESEM) was performed to analyze the surface morphology of AC. Finally, by dividing the activation process into gas–solid diffusion and activation reactions, a mechanism for the evolution of pore structure during the preparation of AC was proposed. The results showed that the char with an amorphous structure and less graphite-like carbon, which was obtained by heating Zhundong coal from room temperature to 600 °C at 5 °C min−1 under the protection of N2 and then maintaining it at this temperature for 60 min, is suitable for the subsequent activation process. At low temperatures, the diffusion of H2O was dominant in the activation process, and the weak gas–solid reaction resulted in poor development of the pore structure; on the other hand, the CO2 activation reaction mainly occurred on the surface of the char due to the poor diffusion of CO2, and then, the produced pores could improve the diffusion of CO2; this led to significant development of the pore structure. With an increase in temperature, the H2O diffusion reaction was enhanced, and the pore structure of AC was completely developed; however, the diffusion of CO2 reduced with an enhancement in the CO2 activation reaction, leading to the consumption of carbon matrix by CO2 gasification instead of pore formation by the CO2 activation reaction. Therefore, proper utilization of the unique characteristics of H2O and CO2 during pore formation is important to control the activation process.

Low-rank coal, such as Shengli lignite (SL) and Datong bitumite (DT), has abundant reserves and is low in cost. Due to its high moisture content, abundant oxygen-containing groups, high ash content and low calorific value, low-rank coal is mainly used in a low-cost method of direct combustion. For better value-added utilization of SL and DT, a novel strategy has been developed for the preparation of oxygen-rich hierarchical porous carbons (HPCs) by hydrothermal carbonization (HTC), followed by steam activation. In this paper, firstly, the physical and chemical properties of SL and DT were improved by HTC pretreatment, bringing them closer to high rank coal. Then, the effects of HTC pretreatment and activation temperature on the properties of the HPCs were investigated in detail. The results show that the HPCs have mainly microporous structures (the microporosity of 200-SLHPC-900 is 79.58%) based on the N

Activated carbon (AC) is negatively charged in aqueous solution, which seriously restricts its application range. Quaternary ammonium salt as a common cationic surfactant was utilized to modify the surface charge distribution of materials. The evolution of the surface charge distribution of AC modified by benzalkonium chloride (BAC), diallyl dimethyl ammonium chloride (DDA) and 3-chloro-2-hydroxypropyl tri-methyl ammonium chloride (CTA) was investigated. Results showed that the surface charge of AC modified by CTA does not change significantly. BAC has a high molecular weight, low surface electrostatic potential and large steric hindrance due to its hydrophobic long-chain alkyl. The diffusion of BAC molecules from solution to AC changed its charge distribution. But these molecules were difficult to combine with AC surface, and most of them were adsorbed into the pores of AC to form aggregates, resulting in a significant reduction in the surface area. BAC modified AC could enhance the adsorption capacity of F

In this study, a typical Zhundong coal sample was examined, and a series of step-wise pyrolysis experiments, where the temperature was gradually elevated in small increments, were carried out by using an entrained-flow bed reactor. In addition, chars from pyrolysis were investigated by X-ray diffraction and Raman spectroscopy with the aim of revealing the microcrystalline parameters and degree of crystallinity, defects, and disorder. Then, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were employed to observe the changes in the chemical surface properties of Zhundong coal before and after pyrolysis. The XRD and Raman spectra indicate that the transition from small aromatic ring systems to large aromatic ring systems in coal with the increase in pyrolysis temperature results in the increase in the lateral size of the basic lattice unit of carbon. Furthermore, condensation and the combination of aromatic rings cause the stacking height of the basic lattice units to first decrease and then increase. When the pyrolysis temperature is lower than 1000 °C, the content of graphite decreases, and the inter-layer spacing of the lattice changes slightly with an increase in temperature. As the pyrolysis temperature continues to rise, the content of graphite increases, the inter-layer spacing of the lattice decreases sharply, reaching a minimum of 0.347 nm at 1500 °C, which represents the degree of increase in the graphitisation of coal char and the transformation of the microcrystalline structure of coal char to that of graphite. FT-IR and XPS analyses show that exchangeable sodium is primarily connected with oxygen functional groups in coal char, and the oxygen functional groups are easily decomposed during coal pyrolysis. Meanwhile, the content of C H/C C/C C groups increases with increasing pyrolysis temperature, while that of C O decreases. As a result, there are more hydrocarbon groups on the surface of the coal char, whereas less oxygen functional groups are exposed to the coal char surface.

The preparation of activated carbon (AC) is a promising approach for the efficient utilization of Zhundong high-alkali coal. The volatilization and release of alkali and alkaline earth metal (AAEM) species can be effectively inhibited by using a lower operating temperature and a carbon matrix. However, the long time of the pyrolysis and activation process may promote the release of the AAEM from the coal during the process. Therefore, it is necessary to explore the transformation of AAEM during the preparation of AC from Zhundong high-alkali coal, and the cleanness of this process is evaluated accurately. In this study, the evolution of AAEM, distribution, and chemical speciation is characterized before and after the preparation of AC from the coal, and then thermodynamic calculations were performed using FactSage to simulate the transformation of AAEM in the coupled process of pyrolysis and activation. The results showed that in the process of AC preparation, the AAEM species inside the carbon matrix moved towards the surface of the AC with the aid of released volatiles and the activation reaction. Some Na and K species were released due to their weak binding with the carbon matrix and this resulted in the loss of Na and K content, whereas Mg and Ca were closely combined with the carbon matrix and were enriched in the AC. Furthermore, the defects and amorphous structure of the AC prepared with H2O activation were more than that of the AC prepared with CO2 activation, which meant that more of the AAEM species were exposed to the high temperature environment. As a result, the loss of AAEM content in the AC with H2O activation was higher than that in the AC with CO2 activation. In this process, a small amount of highly volatile and corrosive AAEM was produced, and the release of volatile matter and the consumption of the carbon matrix were the main factors for the AAEM loss. Therefore, the preparation of AC from Zhundong high-alkali coal is a viable method for its clean use.

The heat exchanger network (HEN) of syngas-to-methanol process was designed and optimized based on pinch technology under the stable operation conditions to balance the energy consumption and economic gain. Inevitably, the fluctuations of production affect the stable operation of HEN in real industrial processes. The flexibility analysis of HEN was carried out in this study to minimize such disturbances by using the downstream paths method. The results show that 2/3 downstream paths cannot meet flexibility requirements, indicating that HEN doesn’t have enough flexibility to accommodate the disturbances in the actual production. The flexible HEN was then designed with the methods of dividing and subsequent merging, which led to 13.89% and 20.82% reduction in energy consumption and total cost, respectively. Thanks to enough area margin and additional alternative heat exchangers, the flexible HEN is found to be able to resist interferences and maintain the production stability and safety, only sacrificing the increase of total cost increase by 4.08%.

Ozone-biological activated carbon (O3-BAC) process has been proved to be an efficient and cost-effective technology in advanced treatment of drinking water. However, O3-BAC raises strict requirements in adsorption, hydrodynamic and regeneration performances, which one single activated carbon could hardly all-sided meet. Blending activated carbons seems to be an appropriate and economically feasible method to deal with the issue. Thus, the uniformity and stability of activated carbon blends during water treatment, especially in backwashing process are of great importance. In this paper, cyclic experiments of downward adsorption and upward backwash on 11 typical commercial granular coal-based activated carbons and their blends were carried out in column test. Hydrodynamic performances such as bed expansion rate and bed pressure drop were measured. The uniformity and stability of activated carbon blends were investigated by determining iodine number of samples collected from different heights of activated carbon bed. Then, both traditional regression methods and back-propagation neural network model were utilized to predict superficial velocity at 30% bed expansion rate and maximum bed pressure drop of activated carbon blends. The results indicate that water backwashing process has no effect on the composition proportion of activated carbon blends, and slightly changes the particle distribution of activated carbon bed regarding pore structure and adsorption capacity. A three-layer back-propagation neural network model for superficial velocity at 30% bed expansion rate yields mean relative errors of 2.17%, which is much lower than that given by traditional regression methods such as 5.53% (weighted average), 4.08% (linear) and 4.06% (polynomial). Moreover, the back-propagation neural network model for maximum bed pressure drop yields mean relative errors of 1.37%, which is much lower than that given by traditional regression methods such as 4.31% (weighted average), 4.28% (linear) and 4.22% (polynomial). The non-linear relationships can be accurately identified by the back-propagation neural network model.

Preparing carbonaceous mesophase pitch precursor by thermal treatment of isotropic pitch is a feasible and effective method for fabricating various high-performance carbon materials including high-modulus carbon fiber, needle coke, graphite, etc. However, the industrial production of qualified mesophase with desirable properties needs to be further improved in many regions. Especially, during pitch preparation, the transformation from isotropic phase to mesophase is difficult to be controlled since it significantly depends on reaction conditions, raw material and preparation parameters. While the optimization of the production conditions of mesophase with special properties requires time-consuming and costly exploratory experiments due to the lack of the fundamental understanding in the transformation behavior from isotropic phase to mesophase. This paper elaborates a fundamental work seeking a more suitable and accurate thermodynamic model and a parameter estimation method to describe phase transition behavior using benzene-soluble (BS) and benzene-insoluble (BI) fractions of coal tar-based pitch as indicators of isotropic phase and mesophase, respectively. The combined equation of simplified statistical associating fluid theory with anisotropic pseudopotential (SSAFT-APP) is used to describe phase transition, and the related parameters of each equation are estimated based on average molecular weight and carbon aromaticity of BS and BI fractions, respectively. The mesophase content of various samples prepared by annealing the mixtures of BS and BI fractions under different mixing ratios are used to calibrate the computed data. The results show that BS fraction has a restraining effect on the formation of mesophase when BI fraction is lower than 60 wt%, while this effect becomes weak with a higher content of BI fraction. A phase diagram is proposed by substituting the estimated parameters in SSAFT-APP equation with experimental data. Mesophase is able to be generated when the adding amount of BI fraction is increased to 12 wt%, and 100% mesophase could be obtained when the ratio of BI fraction is higher than 94 wt%. This work is expected to shed light on the phase transition behavior between isotropic phase and mesophase during pitch preparation from coal tar. In addition, based on the thermodynamic study optimizing preparation conditions and a novel method for obtaining the products with an optimal proportion between isotropic phase and mesophase is proposed.

The transformation of alkali and alkaline earth metals (AAEMs) in Zhundong coal during pyrolysis in an entrained flow bed reactor was elucidated, which provides theoretical guidance for selecting suitable processing technology for Zhundong coal. A typical coal was sampled, and a series of pyrolysis experiments with gradual and small increments in temperature was performed using an entrained flow bed reactor. Chars from pyrolysis at different temperatures were characterised using an improved sequential extraction method, inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray diffraction (XRD), and field emission scanning electron microscopy coupled with energy dispersive spectroscopy (FESEM-EDS) to determine the occurrence modes, chemical composition, and the distribution of AAEMs on the surface of coal char as a function of the change in pyrolysis temperature. In addition, thermodynamic “FactSage” software was used to simulate the evolution of AAEM species during the entire pyrolysis process. Thus, a transformation mechanism of AAEMs in Zhundong coal during pyrolysis is proposed. The results show that as the pyrolysis temperature increases, the contents of water-soluble and exchangeable sodium in coal char decrease, and their release results in a decrease in total sodium content. The insoluble potassium decomposes slightly at high temperatures, and the change in the total potassium content is not obvious. HCl-soluble magnesium and calcium species also decompose at high temperatures and then react with SiO2 and/or Al2O3 to form insoluble silicates or aluminosilicates. As a result, the surface of the coal char becomes enriched in insoluble magnesium and calcium. The variation trend of AAEMs obtained by the FactSage simulation is generally consistent with the experimental results. Upon the process of pyrolysis, the surface of the char sample becomes rough and is covered by cracks and holes. Consequently, some of the water-soluble AAEM species become gaseous and are released from the coal char upon an increase in the pyrolysis temperature. Then, some minerals reach the surface of the char through cracks and holes at high temperatures. The char matrix exhibits an inhibition effect on the release of these species, resulting in the enrichment of the char surface with AAEMs. Therefore, Zhundong coal is suitable for preparing high value-added carbon materials by pyrolysis.

In this study, a high-sulfur and high-ash yield coal sample obtained from the Yanshan coalfield in Yunnan, China was analyzed. A series of char samples was obtained by pyrolysis at various temperatures (300, 400, 500, 600, 700, 800, and 900 °C) and at a fast heating rate (1000 °C/min). A comprehensive investigation using inductively coupled plasma mass spectrometry (ICP-MS), a mercury analyzer, ion-selective electrode (ISE) measurements, X-ray diffraction (XRD) analysis, and Fourier transform infrared (FTIR) spectroscopy was performed to reveal the effects of the pyrolysis temperature on the transformation behavior of trace elements (TEs) and the change in the mineralogical characteristics and functional groups in the samples. The results show that the TE concentrations in the raw coal are higher than the average contents of Chinese coal. The concentrations of Be, Li, and U in the char samples are higher than those in raw coal, while the opposite was observed for As, Ga, Hg, and Rb. The F and Se concentrations are initially higher but decrease with pyrolysis temperature, which is likely caused by associated fracturing with fluoride and selenide minerals. Uranium shows the highest enrichment degree, and Hg shows the highest volatilization degree compared to the other studied TEs. As the temperature increases, the number of OH groups decreases, and the mineral composition changes; for example, pyrite decomposes, while oldhamite and hematite occur in the chars. It is suggested that the behavior and fate of TEs in coal during fast pyrolysis are synergistically influenced by self-characteristic modes of occurrence and mineralogical characteristics.