Bioelectrochemical element conversion reactions towards generation of energy and value-added chemicals

In the past decades, the bioelectrochemical system (BES) has developed into a versatile platform to sustain the conversion of various substances for the generation of energy and energy-efficient production of chemicals. Taking advantage of microbial extracellular electron transfer, the BES is able to perform a variety of value-added element conversion reactions, including production of electric energy from organic carbon, synthesis of chemicals from carbon dioxide, oxidation of sulfide into element sulfur, reduction of nitrate/nitrite into nitrous oxide and reduction of metal ions into solid metals and/or metal oxides. While the potential for using BES as an energy and resource factory has been fully recognized, governing the element conversion pathways into the desired energy and products in BES is still a great challenge. This review provides comprehensive insights into the microbial extracellular electron transfer principles as well as behaviors of key chemical elements in BESs. Individual element conversion processes and their integrations on the BES platform are analyzed. The physicochemical, chemical and microbial mechanisms involved in these processes are explored, and the coupling patterns of electron transfer and element conversion reactions are elucidated. Furthermore, the challenges to design, construct and operate a BES with improved electron transfer efficiency and product specificity are discussed, and research needs are proposed. Additionally, BES technologies from the perspectives of waste remediation, energy production, resource recovery and chemical synthesis are envisaged.     

Numerical study on a slit fin-and-tube heat exchanger with longitudinal vortex generators

A 3-D numerical simulation is performed on laminar heat transfer and flow characteristics of a slit fin-and-tube heat exchanger with longitudinal vortex generators. Heat transfer enhancement of the novel slit fin mechanism is investigated by examining the effect of the strips and the longitudinal vortices. The structure of the slit fin is optimized and analyzed with field synergy principle. The result coincides with the guideline ‘front coarse and rear dense’. The heat transfer and fluid flow characteristics of the slit fin-and-tube heat exchanger with longitudinal vortex generators are compared with that of the heat exchanger with X-shape arrangement slit fin and heat exchanger with rectangular winglet longitudinal vortex generators. It is found that the Colburn j-factor and friction factor f of the novel heat exchanger with the novel slit fin is in between them under the same Reynolds number, and the factor j/(f^1/3) of the novel heat exchanger increased by 15.8% and 4.2%, respectively.     

Experimental study on explosion characteristics of hydrogen–propane mixtures

The explosion characteristics of a hydrogen–propane mixture under different initial temperatures and at different hydrogen addition, equivalence, and dilution ratios were studied using a 20-L apparatus. First, the effects of hydrogen addition and equivalence ratio were studied. The results showed that the maximum explosion pressure and the maximum rate of pressure rise first increased, then decreased from lean to an equivalence ratio of 1.6, and reached the maximum value at the equivalence ratio of 1.2. The maximum explosion pressure and the maximum rate of pressure rise increased with the increasing hydrogen proportion of the mixtures, and the time to the maximum explosion pressure decreased. Furthermore, the mixed fuel with the equivalence and hydrogen addition ratios of 1.0 and 0.4, respectively, was explored under nitrogen or carbon dioxide dilution. Carbon dioxide exhibited a stronger dilution effect than nitrogen. For the mixed fuel with the equivalence and hydrogen addition ratios of 1.0 and 0.4, respectively, the maximum explosion pressure saliently decreased with the increasing initial temperature in the range of 25 °C-120 °C. The variation trend of experimental results was consistent with theoretical predictions.     

Study on catalytic properties of potassium carbonate during the process of sawdust pyrolysis

In order to investigate the effect of potassium carbonate on biomass pyrolysis properties, sawdust was used as raw material and different amounts of K₂CO₃ were added by impregnation method to carry out thermogravimetric and pyrolysis experiments. The effects of pyrolysis temperature and the amount of K₂CO₃ addition on the pyrolysis of sawdust were studied using a self-made fixed-bed pyrolysis furnace. Calculation of pyrolysis kinetics shows that the existence of K₂CO₃ catalyst changes the pyrolysis path of sawdust, so that the activation energy of pyrolysis sawdust decreases at low temperature and increases at high temperature. The pyrolysis experiments shows that the addition of K₂CO₃ and the increase of pyrolysis temperature both reduce the yield of the pyrolysis oil of sawdust and increase the yield of the pyrolysis syngas. However, K₂CO₃ catalyst promotes the yield of char, the increase of pyrolysis temperature decreases the yield of char. Analysis of the pyrolysis products finds that the addition of K₂CO₃ and the increase of pyrolysis temperature both improve quality of the pyrolysis oil, form more microporous surface of char, and increase the hydrogen content in the pyrolysis syngas. It is considered that the optimal process for producing pyrolysis syngas is 900 °C of pyrolysis temperature and 10% of K₂CO₃ addition.     

Evaluation and optimization of tritium breeding,shielding and nuclear heating performances of the helium cooled solid breeder blanket for CFETR

Chinese Fusion Engineering Test Reactor (CFETR) is a new test tokamak device being designed in China aimed to bridge gaps between ITER and DEMO. As one of the candidate tritium breeding blankets, a conceptual design scheme of the helium cooled solid breeder blanket has been proposed and a series of preliminary analyses have been carried out to access the performances. However, both the required global tritium breeding ratio for CFETR not less than 1.2 and its poor working conditions under intense radiation need further thorough neutronics analyses and optimizations during the design phase. In this work, first, three-dimensional neutronics model of CFETR was built, and the neutron wall loading and global TBR were obtained. The nuclear and thermal calculation results were automatically coupled, which could make the neutronics calculation results more accurate and guaranteed they could always satisfy the corresponding thermal limits during the whole process. Then, the tritium breeding and shielding performances of both the outboard and inboard equatorial blanket modules were optimized for the comprehensive optimal schemes. The influences of Be/W armors on the shielding performance and TBR were also investigated. Finally, the nuclear heating rates and the neutron flux densities in different components were calculated based on the obtained comprehensive optimal scheme. In this paper, the neutronics analyses and optimizations verified that the optimized conceptual design could well meet the tritium self-sufficiency and neutron shielding requirements, and this could provide a valuable reference for the further thermal-hydraulic analysis and structural optimization of the CFETR helium cooled solid breeder blanket.     

The analytical solution for a model of direct contact evaporation in spray columns

Reference [1] presented a simple model on direct contact heat transfer between two immiscible liquids in a countercurrent spray column and got the numerical solution with the variable step Runge-Kutta method. This paper obtains the analytical solution of this model, from which the exact relationships between target quantities and influence quantities are given. In this solution the explicit formulae for the column height required for complete evaporation and the temperature of continuous phase at the end of evaporation are given, which will be very useful for the initial design of spray columns in engineering. The two formulae have the following forms     

A mononuclear copper(II) complex of a protonated unsymmetrical dinucleating Schiff base ligand

Reaction of the unsymmetrical and potentially dinucleating Schiff base ligand HL¹ with copper(II) salts has given mono- and dinuclear metal complexes. The structure of a mononuclear complex of diprotonated HL¹, [Cu(H₂L¹)(OH₂)](ClO₄)₃·H₂O·CH₃OH_, has been determined.     

La0.6Sr0.4Co0.2Fe0.8O3 as the anode and cathode for intermediate temperature solid oxide fuel cells

The perovskite material La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF-6428) has been considered as both the anode and cathode in solid oxide fuel cells (SOFCs) operating at intermediate temperatures (550–700°C). Solid electrolyte coulometry (SEC) has been used to measure the oxygen non-stoichiometry as a function of temperature and ambient oxygen partial pressure, thus enabling kinetic data relating to oxygen transport in cathodes to be correlated with the material oxygen vacancy concentration. The catalytic activity towards methane oxidation, and susceptibility to deactivation through carbon deposition have both been investigated by temperature programmed methods, and compared with data for the conventional Ni/YSZ anode material.     

A novel cobalt–free La0.5Ba0.5Fe0.95Mo0.05O3–δ electrode for symmetric solid oxide fuel cell

Cobalt − free perovskite oxide La_0.5Ba_0.5Fe_0.95Mo_0.05O_3−δ (LBFMo) was investigated as the electrode of symmetric solid oxide fuel cell (S − SOFC) based on 300−um − thick La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) electrolyte. The electrochemical performance of the S − SOFC with LBFMo|LSGM|LBFMo configuration was evaluated using ambient air as oxidant and H₂ as fuel. The maximum power density (P_max) of the S − SOFC achieves as high as 0.96 W cm⁻² at 800 °C; meanwhile, the total polarization resistance (R_pt) of the S − SOFC (including the contributions of both cathode and anode) is only ∼0.12 Ω cm². Impedance spectra analysis indicates the polarization associated with anode plays a more rate − limiting role in the whole electrochemical reaction process of the S − SOFC. In addition, using LBFMo as symmetric electrode, the S − SOFC also exhibits good cell stability. All results indicate that the LBFMo is a very potential candidate for S − SOFC electrode.