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As the most commonly used method for industrial activated carbon preparation, physical activation is usually accompanied by significant loss of raw materials, especially when the pore structure of activated carbon is well developed. This not only reduces yields, but also increases costs. To enhance both yield and pore structure of activated carbon, we proposed a facile and scalable method called "fast pyrolysis-physical activation". After fast pyrolysis, although the initial pore volume of the semi-coke decreases, the rapid release of volatiles promotes the increase of mesopore and macropore volumes and the development of micron-scale cracks, which is beneficial for CO 2 mass transfer and reduces diffusion resistance. Therefore, compared to slow pyrolysis, the activated carbon produced through this method has a higher pore volume (increased by 25.9 %–30.0 %) and a larger S BET (increased by 26.7 %–38.3 %), while the yield remains almost unchanged. Consequently, due to the increase in pore volume and high yield of the activated carbon, the CO 2 adsorption capacity (25 °C, 1 bar) of ACB-K700 increases from 2.02 mmol/g to 2.37 mmol/g compared to ACB-M700, and the total CO 2 adsorption capacity of activated carbon prepared from the same mass of raw coal (1 g) increases from 1.07 mmol to 1.16 mmol. Due to the pre-formed pores inside the semi-coke, the gas activator molecules are able to penetrate deep into the particles, which not only reduces the ineffective etching that occurs on the surface, but also promotes the development of pore structure. In conclusion, this study provides a new pore development model for physical activation, and also provides a new method to produce activated carbon rapidly and massively, while the pore structure is well developed. • A new pore-forming mechanism is proposed based on fast pyrolysis-physical activation. • The S BET significantly increases by 26.7–38.3 % at similar yields (49.12–53.01 %). • The rapid escape of volatiles increases the pore volume for semi-coke. • Pre-formed pores in the semi-coke reduces ineffective etching of activator. • The CO 2 absorption capacity at 25 °C and 1 bar can be up to 2.37 mmol/g. [ABSTRACT FROM AUTHOR]

Microwave heating has been widely used in multi-particle system due to its high heating rate and low energy consumption. However, the mechanism of hot spots evolution during microwave heating of millimeter multi-particle system is still not clear. In this study, the phenomenon of the formation and development of multiple hot spots has been observed in the microwave heating experiment and numerical simulation. Besides, the transform of the resonance mode in the container was observed and analyzed by numerical simulation, which means the heating properties of the particles are affected by the combination of dielectric characteristics and particle size. For millimeter particles, the resonance mode of microwave absorption converts from the bonding mode to the mixed-mode (bonding mode + central mode) with the increase of ε r '. Additionally, for millimeter carbonous particles, the resonance mode change occurs roughly at ε r ' = 14, and the effect of particle size on microwave absorption is mainly reflected in energy efficiency. Altogether, this work promotes the understanding of microwave heating of multi-particle systems and provides references for the efficient heating of different materials. [Display omitted] • The multiple hot spots was discovered during microwave heating of multi-particles. • The resonant mode of particles converts with the change of dielectric properties. • For millimeter carbonous particles, the resonance mode change occurs at ε r ' = 14. • Microwave absorption is affected by both particle size and dielectric properties. [ABSTRACT FROM AUTHOR]

Porous materials such as activated cokes have been widely utilized in the adsorption removal of atmospheric SO 2 emission. Pore configuration of coke is a key factor affecting its SO 2 rapid adsorption dynamics, which is critically important for fluidization adsorption craft. Herein, activated coke adsorbents with typically microporous structure and hierarchically porous structure were prepared by a catalytic physical activation method from Chinese large-reserve Zhundong coal, which were used as model adsorbents to investigate the effect of pore configuration on SO 2 fluidized adsorption dynamics. SO 2 fluidized-state adsorption experiments indicate that hierarchically porous coke has a more rapid initial adsorption dynamic than microporous type coke, and coke with 44.2% meso-/macropores volume shows the highest initial adsorption rate of 7.37 mg g−1·min−1. Additionally, the fitting of Weber-Morris model provides the dominate factors for SO 2 adsorption kinetics in each sub-process: SO 2 adsorption capacity of microporous-dominated adsorption stages account for 70%–80% of total, and when it comes close to adsorption saturation, the main dominant factor of kinetic becomes the ratio of meso-/macropores volume. This work is of significance for the application of SO 2 adsorption craft in fluidized bed and also provides insight into the role of hierarchically porous configuration in gas molecule rapid adsorption. Image 1 • Model adsorbents for investigating the effect of pore structure on adsorption dynamics are provided. • Hierarchically porous coke shows higher initial adsorption rate of SO 2 in fluidized bed. • Dominate factors of SO 2 adsorption dynamics in each sub-process are elucidated. [ABSTRACT FROM AUTHOR]

Microwave heating has attracted extensive attention due to its advantages of low energy consumption and rapid heating. Due to its kinetic and thermal effects, microwave-induced activated coke discharge has been widely used in material preparation and reaction enhancement. However, the mechanism of microwave discharge for millimeter activated coke has not been clarified. In this work, we have investigated the mechanism of microwave discharge between millimeter activated cokes by experiments and simulations. Experimental results presented that the increase in particle size caused the inter-particle discharge transferred from weak sparks to large-scale violent discharge. Simulation results indicated that the increase in particle size led to enhanced microwave field resonance between particles, thereby promoting the inter-particle electric field, electron temperature and active species density. Finally, the particle size of cokes affected the deposition of microwave energy in discharge regions between particles. The influence of particle size on microwave-induced activated coke discharge was reflected in two mechanisms, namely, the microwave resonance enhanced mechanism that promoted the microwave energy deposition between particles and the focused microwave energy mechanism that dominated the inter-particle microwave energy deposition distribution concentrated in the center regions of the particle gap. [Display omitted] • Microwave discharge becomes intenser with the rising particle size. • A slight rise in electric field leads to exponential increase in electron density. • Electron density increases from 1011 m−3 to 1019 m−3 with the rising particle size. • The enhanced mechanism for microwave discharge with rising particle size is revealed. [ABSTRACT FROM AUTHOR]

Abstract The pelletization of CaO for calcium looping process(CLP) are highly desirable for post-combustion capture of CO 2. The influence of particle size of the calcium precursor and binder on sorbent CO 2 capture performance were investigated. Different calcium precursors: limestone and nano CaCO 3 , and different binders: calcium aluminate cement, micro Al 2 O 3 and nano Al 2 O 3 were used for pellet preparation. After calcination, CaO mixed with calcium aluminate cements served to produce calcium aluminate (Ca 12 Al 14 O 33) pinning sites, acting as a thermally stable and mechanically hard support for CaO bulk. XRD and SEM showed that nano calcium precursor led to higher mayenite production and a homogeneous mixture of mayenite and CaO, having a perfect dispersion effect to avoid sintering. Durability studies showed that composite pellet with nano CaCO 3 /cement captured 0.20 gCO 2 /g calcined sorbent after 15 cycles, while the capacity of limestone/cement was only 0.14g/g. The influence of binder particle size was further investigated and nano CaCO 3 /nano Al 2 O 3 showed better CO 2 capture performance compared with calcium aluminate cement and micro Al 2 O 3. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • One-pot route was developed to synthesize CaCO 3 /graphite nanosheets composites. • H 3 BO 3 impregnation enhances the antioxidative ability of graphite nanosheets. • CaCO 3 /graphite nanosheets composites are highly efficient for heat energy storage. • The composites show better heat storage performance than pure CaCO 3. • Only 3 wt% of graphite nanosheets is required to stabilize the cyclic heat storage. Abstract Reversible carbonation/calcination of CaCO 3 is a promising technology for thermochemical energy storage in concentrated solar power plants. However, the major drawback of this technology is the rapid deactivation of CaO due to sintering. In this study, newly developed CaCO 3 /graphite nanosheets composites were synthesized as the heat storage medium through a one-pot route varying the graphite nanosheets load (3–12 wt%). The impregnation of the composites with H 3 BO 3 solutions enhance the initial weightlessness temperature of graphite nanosheets from 900 °C to 1050 °C in pure CO 2 atmosphere, thus upgrading the stability of graphite nanosheets during heat storage/release process. The performances of the synthesized composites were evaluated by thermogravimetric analysis, which simulates the heat storage cycle. The composites showed improved heat storage/output capacity and faster heat input/output rate compared to pure CaCO 3. Only 3 wt% of graphite nanosheets was needed to effectively stabilize the heat storage capacity of the material. The heat storage capacity of composites with 3 wt% graphite nanosheets is 1313 kJ/kg composite after 50 cycles, corresponding to 2.9 times as much as that of pure CaCO 3. This high stability is attributed to the unique synthetic strategy in which the CaCO 3 nanoparticles uniformly coated on graphite nanosheets surface, and their sintering and aggregation were prevented. This work brings the development of this technology to a level closer to its industrial application. [ABSTRACT FROM AUTHOR]

Commercialization of ZnO-based anodes remains hampered by their rapid capacity fading upon cyclical charge and discharge. Design and synthesis of suitable carbon scaffolds for coating ZnO active materials has been regarded as the most effective strategy to overcome this problem. We herein report a confined growth strategy for the synthesis of a novel ZnO/carbon mesoporous composite that consists of small ZnO nanoparticles whose growth is confined in rationally designed N-rich carbon spheres (referred to as ZnO-NMPCS). Such a mesoporous nanocomposite has several structural merits such as small ZnO nanoparticles, a homogeneous distribution, an interconnected spherical framework with a large surface area, and a N-rich carbon lattice; these merits not only provide a robust scaffold for stable lithiation/delithiation of ZnO active materials but also ensure sufficient Li + storage space/sites and fast ions/electrons transport. As a result, the developed nanocomposite exhibits excellent Li + storage properties in terms of high capacity, fast rate capability, and long cycling lifespan (425 mAh g −1 after 1800 cycles at 5 A g −1 ). This work offers an effective confined growth strategy to overcome the long-term roadblock to ZnO-based anodes; the carbon scaffold also provides a general platform for the confined growth of other metal oxide nanocrystals. [ABSTRACT FROM AUTHOR]