Frontiers of Chemical Science and Engineering

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Development of a hydrodynamic model and the corresponding virtual software for dual-loop circulating fluidized beds
Shanwei Hu, Xinhua Liu
Front. Chem. Sci. Eng.    https://doi.org/10.1007/s11705-020-1953-6
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Dual-loop circulating fluidized bed (CFB) reactors have been widely applied in industry because of their good heat and mass transfer characteristics and continuous handling ability. However, the design of such reactors is notoriously difficult owing to the poor understanding of the underlying mechanisms, meaning it has been heavily based on empiricism and stepwise experiments. Modeling the gas-solid CFB system requires a quantitative description of the multiscale heterogeneity in the sub-reactors and the strong coupling between them. This article proposed a general method for modeling multi-loop CFB systems by utilizing the energy minimization multiscale (EMMS) principle. A full-loop modeling scheme was implemented by using the EMMS model and/or its extension models to compute the hydrodynamic parameters of the sub-reactors, to achieve the mass conservation and pressure balance in each circulation loop. Based on the modularization strategy, corresponding interactive simulation software was further developed to facilitate the flexible creation and fast modeling of a customized multi-loop CFB reactor. This research can be expected to provide quantitative references for the design and scale-up of gas-solid CFB reactors and lay a solid foundation for the realization of virtual process engineering.

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Characterization of particle deposition during crossflow filtration as influenced by permeate flux and crossflow velocity using a microfluidic filtration system
Hongzhan Di, Gregory J. O. Martin, Dave E. Dunstan
Front. Chem. Sci. Eng.    https://doi.org/10.1007/s11705-020-1962-5
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Particle deposition during crossflow filtration is significantly influenced by the operating conditions, in particular the permeate flux and crossflow velocity. However, there is a lack of detailed knowledge about how deposit layer structures and distributions depend on operating parameters. This study uses a microfluidic visualisation filtration system to examine the influence of operating conditions on the deposition process during crossflow ultrafiltration from a microscopic perspective. Increasing the permeate flux caused an increasing amount of deposition and a thicker deposit layer. Higher crossflow velocities reduced the extent of deposition. The degree of deposition varied over a range of operating conditions due to the altered hydrodynamic forces exerted on the particles, which can be examined by the deposition probability according to an existing model. Building on this, an empirical correlation between the deposition probability and volume of deposition as function of filtration time was developed, which gave good agreement with experimental results. The effect of solution conditions was also involved in this correlation as a interaction energies. This could be useful for predicting the dynamic deposition process during crossflow filtration over a range of operating and solution conditions.

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FeNi doped porous carbon as an efficient catalyst for oxygen evolution reaction
Jun-Wei Zhang, Hang Zhang, Tie-Zhen Ren, Zhong-Yong Yuan, Teresa J. Bandosz
Front. Chem. Sci. Eng.    https://doi.org/10.1007/s11705-020-1965-2
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Polymer-derived porous carbon was used as a support of iron and nickel species with an objective to obtain an efficient oxygen reduction reaction (OER) catalyst. The surface features were extensively characterized using X-ray diffraction, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. On FeNi-modified carbon the overpotential for OER was very low (280 mV) and comparable to that on noble metal catalyst IrO2. The electrochemical properties have been investigated to reveal the difference between the binary alloy- and single metal-doped carbons. This work demonstrates a significant step for the development of low-cost, environmentally-friendly and highly-efficient OER catalysts.

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Effects of functional groups for CO2 capture using metal organic frameworks
Chenkai Gu, Yang Liu, Weizhou Wang, Jing Liu, Jianbo Hu
Front. Chem. Sci. Eng.    https://doi.org/10.1007/s11705-020-1961-6
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Metal organic frameworks (MOFs) are promising adsorbents for CO2 capture. Functional groups on organic linkers of MOFs play important roles in improving the CO2 capture ability by enhancing the CO2 sorption affinity. In this work, the functionalization effects on CO2 adsorption were systematically investigated by rationally incorporating various functional groups including –SO3H, –COOH, –NH2, –OH, –CN, –CH3 and –F into a MOF-177 template using computational methods. Asymmetries of electron density on the functionalized linkers were intensified, introducing significant enhancements of the CO2 adsorption ability of the modified MOF-177. In addition, three kinds of molecular interactions between CO2 and functional groups were analyzed and summarized in this work. Especially, our results reveal that –SO3H is the best-performing functional group for CO2 capture in MOFs, better than the widely used –NH2 or –F groups. The current study provides a novel route for future MOF modification toward CO2 capture.

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Industrial bio-based plant aggregates as hygric and insulating construction materials for energy efficient building
Yunhong Jiang, Mike Lawrence, Meng Zhang, Jiandong Cui
Front. Chem. Sci. Eng.    https://doi.org/10.1007/s11705-020-1960-7
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In this paper, the bulk density, microstructure, porosity and pore size distribution of the selected aggregates, including hemp shiv, flax shiv, rape shiv and wheat straw, are fully studied due to these properties are highly related to their excellent characteristics and more or less linked to the properties of the final product. The scanning electron microscope results showed all the selected aggregates have a highly porous and complex hierarchical structure, whereas the arrangement of pores and the thickness of cell wall are significantly different among these aggregates. All the selected aggregates had a low bulk density ranging from 30 to 130 kg∙m−3 and a high porosity between 75.81% and 88.74%. The thermal conductivity of the selected bio-aggregates ranged from 0.04 to 0.06 W∙m−1∙K−1. The thermal conductivity of the selected aggregates was not only depending on the bulk density of the sample but also depending on the raw material. Hemp shiv, rape shiv and flax shiv were excellent hygric regulators with moisture buffer value (MBV) ranging from 2.07 to 2.36 g∙m−2∙%RH−1, whereas, wheat straw had a lower MBV value ranging from 1.76 to 1.97 g∙m−2∙%RH−1. The results showed that particle size does not affect the MBV value. The MBV value increases linearly with bulk density.

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Efficient CO2 adsorption and mechanism on nitrogen-doped porous carbons
Yanxia Wang, Xiude Hu, Tuo Guo, Jian Hao, Chongdian Si, Qingjie Guo
Front. Chem. Sci. Eng.    https://doi.org/10.1007/s11705-020-1967-0
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In this work, nitrogen-doped porous carbons (NACs) were fabricated as an adsorbent by urea modification and KOH activation. The CO2 adsorption mechanism for the NACs was then explored. The NACs are found to present a large specific surface area (1920.72–3078.99 m2·g1) and high micropore percentage (61.60%–76.23%). Under a pressure of 1 bar, sample NAC-650-650 shows the highest CO2 adsorption capacity up to 5.96 and 3.92 mmol·g1 at 0 and 25 °C, respectively. In addition, the CO2/N2 selectivity of NAC-650-650 is 79.93, much higher than the value of 49.77 obtained for the nonnitrogen-doped carbon AC-650-650. The CO2 adsorption capacity of the NAC-650-650 sample maintains over 97% after ten cycles. Analysis of the results show that the CO2 capacity of the NACs has a linear correlation (R2 = 0.9633) with the cumulative pore volume for a pore size less than 1.02 nm. The presence of nitrogen and oxygen enhances the CO2/N2 selectivity, and pyrrole-N and hydroxy groups contribute more to the CO2 adsorption. In situ Fourier transform infrared spectra analysis indicates that CO2 is adsorbed onto the NACs as a gas. Furthermore, the physical adsorption mechanism is confirmed by adsorption kinetic models and the isosteric heat, and it is found to be controlled by CO2 diffusion. The CO2 adsorption kinetics for NACs at room temperature and in pure CO2 is in accordance with the pseudo-first-order model and Avramís fractional-order kinetic model.

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Biodegradation and detoxification of the triphenylmethane dye coomassie brilliant blue by the extracellular enzymes from mycelia of Lactarius deliciosus
Jin Zhao, Qing-Xi Wu, Xiao-Du Cheng, Ting Su, Xiao-Hui Wang, Wen-Na Zhang, Yong-Ming Lu, Yan Chen
Front. Chem. Sci. Eng.    https://doi.org/10.1007/s11705-020-1952-7
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Fungi play an important role in dying wastewater treatment. In this work, the mycelia of Lactarius deliciosus exhibited an excellent capacity in decolorizing coomassie brilliant blue (CBB). The results demonstrated that the mycelia could treat CBB with high concentrations over a broad range of pH and temperature. The decolorization rate of 99.19% and the removal rate of 16.31 mg·L‒1·h were realized. The mycelia could be recycled from decolorizing process for 19 times, indicating a good re-usability. It verified that the lignin peroxidase (121.65 U·L‒1) and manganese peroxidase (36.77 U·L‒1) were involved in the degradation and decolorization process of CBB. Toxicity assessments indicated the seed germination rate was up to 82.22% while inhibition to Escherichia coli decreased dramatically and no significant effect on Caenorhabditis elegans growth was found. The removal of CBB was a synergistic process accomplished by adsorption and biodegradation. The mycelia could be used for eco-friendly CBB treatment.

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Adsorption performance and physicochemical mechanism of MnO2-polyethylenimine-tannic acid composites for the removal of Cu(II) and Cr(VI) from aqueous solution
Xiaoyan Deng, Luxing Wang, Qihui Xiu, Ying Wang, Hong Han, Dongmei Dai, Yongji Xu, Hongtao Gao, Xien Liu
Front. Chem. Sci. Eng.    https://doi.org/10.1007/s11705-020-1958-1
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In this work, an adsorbent, which we call MnPT, was prepared by combining MnO2, polyethylenimine and tannic acid, and exhibited efficient performance for Cu(II) and Cr(VI) removal from aqueous solution. The oxygen/nitrogen-containing functional groups on the surface of MnPT might increase the enrichment of metal ions by complexation. The maximum adsorption capacities of MnPT for Cu(II) and Cr(VI) were 121.5 and 790.2 mg·g-1, respectively. The surface complexation formation model was used to elucidate the physicochemical interplay in the process of Cu(II) and Cr(VI) co-adsorption on MnPT. Electrostatic force, solvation action, adsorbate–adsorbate lateral interaction, and complexation were involved in the spontaneous adsorption process. Physical electrostatic action was dominant in the initial stage, whereas chemical action was the driving force leading to adsorption equilibrium. It should be noted that after adsorption on the surface of MnPT, Cr(VI) reacted with some reducing functional groups (hydroxylamine-NH2) and was converted into Cr(III). The adsorption capacity declined by 12% after recycling five times. Understanding the adsorption mechanism might provide a technical basis for the procedural design of heavy metal adsorbents. This MnPT nanocomposite has been proven to be a low-cost, efficient, and promising adsorbent for removing heavy metal ions from wastewater.

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Integrated energy storage system based on triboelectric nanogenerator in electronic devices
Xiao Feng, Yang Zhang, Le Kang, Licheng Wang, Chongxiong Duan, Kai Yin, Jinbo Pang, Kai Wang
Front. Chem. Sci. Eng.    https://doi.org/10.1007/s11705-020-1956-3
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The emergence of electronic devices has brought earth-shaking changes to people’s life. However, an external power source may become indispensable to the electronic devices due to the limited capacity of batteries. As one of the possible solutions for the external power sources, the triboelectric nanogenerator (TENG) provides a novel idea to the increasing number of personal electronic devices. TENG is a new type of energy collector, which has become a hot spot in the field of nanotechnology. It is widely used at the acquisition and conversion of mechanical energy to electric energy through the principle of electrostatic induction. On this basis, the TENG could be integrated with the energy storage system into a self-powered system, which can supply power to the electronic devices and make them work continuously. In this review, TENG’s basic structure as well as its working process and working mode are firstly discussed. The integration method of TENGs with energy storage systems and the related research status are then introduced in detail. At the end of this paper, we put forward some problems and discuss the prospect in the future.

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