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Table of Content
05 November 2022, Volume 73 Issue 11
    Reviews and monographs
    Research progress of synthesis and properties of coal-based zero-dimensional nanocarbon materials and their applications in energy conversion and storage
    Wangjun HOU, Lingpeng YAN, Zheyong CAO, Jingxia ZHENG, Yongzhen YANG
    2022, 73(11):  4791-4813.  doi:10.11949/0438-1157.20220868
    Abstract ( 554 )   HTML ( 39)   PDF (5610KB) ( 240 )  
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    Coal is the most widely distributed and abundant carbon-containing resource in nature. Its molecular structure has natural similarity with nano-carbon materials, and it is a high-quality nano-carbon material precursor. Over the years, various nanocarbon materials prepared from coal have been widely used in the fields of energy, information, environment, and biomedicine, etc. Among them, coal-based zero-dimensional nanocarbon materials, such as nanodiamonds, fullerenes, carbon nano-onions, and carbon dots, show excellent fluorescence, electrochemical, and catalytic performances due to their small nanometer size, large specific surface area, and unique spherical structure, showing great application potential in the fields of energy conversion and storage. This paper reviews the preparation methods and properties of various zero-dimensional nanocarbon materials based on coal and its derivatives as precursors. This review summarizes the application research progresses of zero-dimensional nanocarbon materials in lighting display, electrochemical energy storage, photo/electrocatalysis, etc. Moreover, this review proposes the current problems, challenges, and improvement strategies of coal-based zero-dimensional nanocarbon materials, and further prospects their future development. This work provides the theoretical and practical support for promoting the high value-added conversion and utilization of coal as well as the large-scale preparation of coal-based zero-dimensional nanocarbon materials.

    Development and prospect of pivotal materials and technologies in sodium-ion batteries
    Liubin SONG, Yixuan WANG, Yinjie KUANG, Yubo XIA, Zhongliang XIAO
    2022, 73(11):  4814-4825.  doi:10.11949/0438-1157.20220728
    Abstract ( 507 )   HTML ( 40)   PDF (2646KB) ( 231 )  
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    Due to the advantages of large reserves, low cost and high safety by sodium-ion battery, it is an effective substitute for lithium-ion battery. To a certain extent, sodium-ion battery can alleviate the limited development of energy storage battery by the shortage of lithium resources. This review not only has combed and analyzed the research status, challenges and future development trend as well as has selected the latest frontier overview of sodium-ion batteries, including cathode, anode and advanced characterization technology and so on, but also has discussed the current research hotspots of sodium-ion batteries, as to find the latest research hotspots and development trends and promote the efficient development of sodium-ion batteries. It is hoped that this paper can provide some enlightenment for the exploration and development of sodium-ion batteries.

    Viscosity estimation of fluid mixtures based on Eyring's absolute rate theory
    Chenyang ZHU, Xiangyang LIU, Maogang HE, Guangjin CHEN
    2022, 73(11):  4826-4837.  doi:10.11949/0438-1157.20221029
    Abstract ( 134 )   HTML ( 12)   PDF (1137KB) ( 80 )  
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    Viscosity, as one of the transport properties, is essential information of fluids in industrial and scientific areas. In order to develop a practical viscosity model based on Eyring's absolute rate theory, which is simultaneously applicable to both pure and mixture fluids at high pressures, a mixing rule is presented to extend our previously proposed viscosity model to the mixture calculations. Then, in order to verify the reliability of the present model, 27 pure fluids including alkanes, aromatics, esters, and alcohols are selected and their viscosities are correlated to obtain the model parameters. After that, the viscosity model coupled with the proposed mixing rule is applied to 27 binary mixtures and 3 ternary mixtures. For each binary mixture, an extra binary interaction parameter is introduced, which can be obtained by fitting to its viscosity data. While for ternary mixtures, no additional parameter is required. The results show that the present model gives rather high accuracy for all fluids. The average absolute relative deviations for the viscosities of pure fluids, binary mixtures, and ternary mixtures are 1.54%, 2.35%, and 3.86%, respectively, and the maximum deviations are 8.62%, 12.9%, and 19.7%, respectively. Such performance indicates the present model can be an effective tool for viscosity estimations in both industry and research. Finally, the proposed model is compared with the free volume model, which has higher computational accuracy than the latter for both high viscosity and interassociative fluids.

    Experiment and model for isochoric heat capacity of CO2-hydrocarbon liquid phase mixtures
    Yahui GAO, Shuqian XIA
    2022, 73(11):  4838-4849.  doi:10.11949/0438-1157.20221032
    Abstract ( 107 )   HTML ( 17)   PDF (1942KB) ( 66 )  
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    Carbon dioxide (CO2) enhanced oil recovery (EOR) technology has been extensively studied in recent years. A full understanding of the heat capacity properties of CO2-hydrocarbon mixtures is critical for the successful implementation of this project, while there is limited research on this. An adiabatic calorimeter was set up based on the adiabatic calorimetry method, and the isochoric heat capacity (Cv ) data of CO2-hydrocarbon (n-hexane, n-octane, undecane, cyclohexane, ethylbenzene) binary liquid phase mixtures were measured at temperatures range from 317.15 K to 353.15 K and pressures up to 29.49 MPa, and a total of 335 data points were obtained. In addition, a predictive model (PR equation of state combined with thermodynamic relationships) and an empirical model were applied for calculating the Cv data, and the calculation average absolutely relative deviations (AARD) were 0.81%—3.66%, and less than 2.56%, respectively. The empirical model has a simpler form, while the prediction ability of PR model is powerful. These experimental Cv data and the developed two models are crucial for the implementation of CO2-EOR project.

    Studies on three-dimensional phase diagram of the quinary system NaBr-KBr-MgBr2-CaBr2-H2O at 298.15 K
    Changwei PENG, Shihua SANG, Ruizhi CUI, Hongbao REN
    2022, 73(11):  4850-4858.  doi:10.11949/0438-1157.20220811
    Abstract ( 90 )   HTML ( 10)   PDF (1048KB) ( 35 )  
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    In order to rationally develop the bromine-rich underground brine resources in the Sichuan Basin, the complete phase equilibria and phase diagram of the quinary system NaBr-KBr-MgBr2-CaBr2-H2O at 298.15 K were studied. According to the solubility data measured in the experiment, a complete three-dimensional phase diagram, as well as the dry basis projected phase diagrams of the saturation surface with NaBr·2H2O, MgBr2·6H2O and CaBr2·6H2O were plotted respectively, and the corresponding water content diagrams were drawn respectively. The results show that the phase diagram of the quinary system at 298.15 K contains ten univariate curves, three invariant points and six crystallization regions (KBr crystallization region, NaBr crystallization region, NaBr·2H2O crystallization region, MgBr2·6H2O crystallization region, CaBr2·6H2O crystallization region, KBr·MgBr2·6H2O crystallization region). The KBr crystallization region is the largest and the CaBr2·6H2O crystallization region is the smallest, which indicates that the solubility of CaBr2·6H2O is the largest and the KBr solubility is the smallest in this system.

    Theoretical study on the mechanism of hydrolysis/alcoholysis/ammonolysis of butanediol terephthalate dimer
    Xiaosong LUO, Jinbao HUANG, Mei ZHOU, Xin MU, Weiwei XU, Lei WU
    2022, 73(11):  4859-4871.  doi:10.11949/0438-1157.20221121
    Abstract ( 96 )   HTML ( 9)   PDF (2398KB) ( 69 )  
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    Using the density functional theory M06-2X/6-311G(d) method, the quantum chemical theory of the hydrolysis/alcoholysis/ammonolysis reaction mechanism of butylene terephthalate dimer was studied. The possible reaction paths of the hydrolysis/alcoholysis/ammonolysis process were proposed, and the geometric structure optimization and frequency calculation of various intermediates, transition states and products involved in the reaction were carried out to obtain the thermodynamic and kinetic parameter values. The calculation results show that the reaction activation energy of the cracking process of butanediol terephthalate dimer can be reduced under the condition of hydrolysis/alcoholysis/ammonolysis, which makes the reaction easier, the reaction energy barriers of the main elemental reaction steps in hydrolysis/alcoholysis/ammonolysis are about 170.0, 155.0 and 165.0 kJ/mol, respectively. The hydrolysis products of butanediol terephthalate dimer are mainly terephthalic acid and 1,4-butanediol, and the alcoholysis products of butanediol terephthalate dimer are dimethyl terephthalate and 1,4-butanediol, ammonolysis products mainly include aromatic nitrile and 1,4-butanediol, among which 1,4-butanediol will be further degraded to form tetrahydrofuran. In the process of butanediol terephthalate dimer hydrolysis/alcoholysis/ammonolysis, the decomposition reaction in methanol medium is better than that in ammonia atmosphere, and the reaction in ammonia atmosphere is better than that in water molecular environment, and the increase of reaction temperature can increase its spontaneity.

    Fluid dynamics and transport phenomena
    Mixing/separation characteristics of great different particles in gas-solid fluidized bed
    Weixing JIN, Jun YAN, Chenglin E, Yiping FAN, Chunxi LU
    2022, 73(11):  4872-4883.  doi:10.11949/0438-1157.20220890
    Abstract ( 91 )   HTML ( 9)   PDF (3191KB) ( 54 )  
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    The mixing/separation characteristics of the two-component large-difference particle system composed of FCC catalyst (dp =90 μm) and molecular sieve (dp =1875 μm) in fluidized bed were investigated experimentally. The results show that in the dense phase bed,pressure drop in unit height at the dilute dense phase interface will rise sharply with the gradual increase of the initial proportion of large particles X0. At low gas velocity,the mass fraction of large particles in the dense phase bed is uniformly distributed in the radial direction. At high gas velocity,a “U” shape distribution with a high sidewall and low center appears. The whole bed mixing uniformity is better when X0<20.0%,and the uniformity will gradually decrease with the increase of apparent gas velocity ug and X0. In the dilute phase space,entrained large particles gradually increase with the increase of ug,and decrease with the increase of X0. When X0=68.5%,entrainment meets maximum. The mass fraction of large particles in the dilute phase space,in the radial direction, appears “M” shape distribution,and the “M” shape distribution will gradually change to inverted “U” type distribution with the increase of height. Based on the experimental results,the empirical correlations for calculating the total mixing height and separation efficiency are proposed.

    Flow and heat transfer characteristics of particles flowing along the plate with different mixing elements
    Xing TIAN, Jiayue ZHANG, Zhigang GUO, Jian YANG, Qiuwang WANG
    2022, 73(11):  4884-4892.  doi:10.11949/0438-1157.20221011
    Abstract ( 65 )   HTML ( 3)   PDF (4615KB) ( 36 )  
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    The shell-and-plate heat exchanger plays a significant role in the concentrating solar power systems. For improving the heat transfer performance of the shell-and-plate heat exchanger, the effects of plane, trapezoidal mixing element, elliptical mixing element, trapezoidal-elliptical mixing element and trigonal mixing element on particle flow and heat transfer were studied by discrete element method. The research shows that the blending rate of the plane is almost zero, and the blending rate of the trapezoidal blending unit is the highest. When particles flow around the trapezoidal mixing element, elliptical mixing element, trapezoidal-elliptical mixing element and trigonal mixing element, the temperature boundary layer is destroyed and redeveloped in the downstream region of the mixing elements. In the upstream region of the mixing elements, the mixing elements have an impediment to particle movement. The elliptical mixing element is the most impeded to its upstream particles. The feature velocity of particles is maximum in the downstream of the trapezoidal mixing element. When the particles move along the plane, there is no mixing phenomenon and the mixing efficiency of the plane is approximately zero. The average mixing efficiency of trapezoidal, elliptical, trapezoidal-elliptical and trigonal mixing elements are 3.8, 2.6, 3.2 and 2.5, respectively. The mixing efficiency of trapezoidal mixing element is the highest. In the downstream region of mixing elements, the heat transfer coefficients of trapezoidal, elliptical, trapezoidal-elliptical and trigonal mixing elements are significantly larger than that of the plane (average increased by 41.5%, 31.5%, 28.9% and 25.3%). Compared with other mixing elements, the flow and heat transfer characteristics of trapezoidal mixing element is the best.

    Study on growth process of semiclathrate hydrate on the surface of TBAB solution droplets suspended by ultrasonic
    Pengcheng JING, Litao CHEN, Chuanliang YAN, Chuanxiang JIANG, Yuxiang XIA, Changhong YU, Haotian WANG
    2022, 73(11):  4893-4902.  doi:10.11949/0438-1157.20220953
    Abstract ( 71 )   HTML ( 4)   PDF (3769KB) ( 37 )  
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    Tetrabutylammonium bromide (TBAB) aqueous solution droplets were suspended by ultrasonic levitation technique. The hydrate growth process at different TBAB mass fraction (15%, 20%, 25%) was observed and compared with the pendent droplets. Experiments show that the droplets suspended by ultrasonic are in a state of rapid rotation, the droplets are oblate spheroids, and the hydrate growth rate is faster, but when the droplets contain bubbles, the induction time of hydrate formation is prolonged. It is concluded that the growth mode of TBAB hydrate in ultrasonic suspension can be divided into two categories: from inside to outside and from outside to inside. From the outside to the inside, it can be divided into three types: single flat top, double flat top and wrapped. The heat transfer models of suspension droplets and pendent droplets are established. Through comparison, it is found that ultrasonic can improve the heat transfer efficiency of suspension droplets, accelerate the formation and growth of hydrate. This experiment provides a new method for observing hydrate formation.

    Experimental study of flow boiling pressure drop of R290 in a horizontal tube based on flow pattern
    Hanwen XUE, Feng NIE, Yanxing ZHAO, Xueqiang DONG, Hao GUO, Jun SHEN, Maoqiong GONG
    2022, 73(11):  4903-4916.  doi:10.11949/0438-1157.20220762
    Abstract ( 64 )   HTML ( 9)   PDF (3471KB) ( 50 )  
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    Propane (R290) is a natural refrigerant with excellent performance, and its two-phase flow pressure drop characteristics play an important role in heat exchanger design and refrigeration system optimization.Its boiling pressure drop characteristics are important for heat exchanger design and performance analysis in refrigeration facilities. Despite that there are studies about the pressure drop of R290, there are few studies on analyzing the pressure drop combined with the flow pattern. There is also a lack of work on the pressure drop of R290 under low mass flux (G<200 kg·m-2·s-1) and low saturation pressure (p<0.5 MPa) conditions. An experimental study on the pressure drop characteristics of R290 in a horizontal tube was conducted with mass fluxes ranging from 70 kg·m-2·s-1 to 190 kg·m-2·s-1, heat fluxes ranging from 10.6 kW·m-2 to 73.0 kW·m-2, saturation pressures ranging from 0.215 MPa to 0.415 MPa, covering the entire vapor quality range. The influence of experimental conditions and the flow pattern on the frictional pressure drop and the acceleration pressure drop have been analyzed. By comparing the existing frictional pressure drop correlations and using Rev/Rel and Froude number Fr to represent the two-phase interaction based on the Friedel model, a new flow pattern-based frictional pressure drop correlation for two phases was obtained. The new correlation can predict the pressure drop well with an ARD (average relative deviation) of -0.2%, an AARD (average absolute relative deviation) of 5.2%, and 97.9% of data points within ±30% error bands. Compared with the experimental data in the literature, the average ARD of the 10 groups of data prediction results is 10.0%, the average AARD is 19.3%, and λ30% is 80.3%, which shows that the new model has certain prediction accuracy and applicability.

    Numerical simulation of power-law fluid flow characteristics in impinging stream reactor
    Jianwei ZHANG, Baoshuai LI, Xin DONG, Ying FENG
    2022, 73(11):  4917-4927.  doi:10.11949/0438-1157.20220901
    Abstract ( 93 )   HTML ( 11)   PDF (3801KB) ( 64 )  
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    The flow characteristics of power-law fluid in impinging stream reactor are studied by numerical simulation method. The distribution laws of radial jet spread rate, radial velocity decay rate, shear stress and apparent viscosity of clean water and power-law fluid with different mass fraction under different nozzle spacing and inlet velocity are analyzed. The research shows that the radial velocity distribution law of radial jet in power-law fluid is similar to that of clear water radial jet. With the increase of nozzle spacing, the spread rate increases and the radial velocity decay rate decreases. The average shear stress increases first and then decreases. When L=3D, the average shear stress is the largest, which is more conducive to fluid mixing. With the increase of inlet velocity, the spread rate decreases, and the radial velocity decay rate and average shear stress increase. The average shear stress of power-law fluid is greater than that of clean water, and with the increase of the mass fraction of power-law fluid, the expansion rate of power-law fluid increases, about 1.3—3.3 times that of clean water, but the radial velocity decay rate of power-law fluid decreases from -1.268—-1.125 to -1.144—-1.082, gradually smaller than that of clean water. The shear stress in the radial jet region of power-law fluid is “M” shaped distribution, and the apparent viscosity is "W” shaped distribution. The rheological properties of the fluid have a significant impact on the flow law of the fluid in the impinging stream reactor.

    Analysis of composite modified surface inhibiting particle fouling accumulation characteristics
    Zuodong LIU, Yuchen WANG, Weiwei XING, Bo ZHAO, Zhiming XU
    2022, 73(11):  4928-4937.  doi:10.11949/0438-1157.20220806
    Abstract ( 77 )   HTML ( 9)   PDF (4031KB) ( 40 )  
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    Particle fouling of heat exchange equipment generally refers to the accumulation of solid particles suspended in the fluid on the heat exchange surface. In this research, an anti-fouling Ni-P-TiO2 composite modified surface was created and applied in a plate heat exchanger to prevent the accumulation of nano-MgO particle fouling on the heat exchange surface. The effects of cooling water flow rate (0.1—0.3 m/s), input temperature (30—40℃), and nano-MgO concentration (100—400 mg/L) on the anti-fouling property of Ni-P-TiO2 composite modified surface were investigated experimentally. The results showed that the asymptotic values of the nano-MgO particle fouling thermal resistance on the Ni-P-TiO2 composite modified heat exchanger surface were significantly reduced under all experimental conditions. Compared with the original plate heat exchanger, with the cooling water flow rate increasing (0.1—0.3 m/s), the fouling thermal resistance asymptotic values on Ni-P-TiO2 composite surface were decreased by 27.85%—34.41%, with the cooling water inlet temperature increasing (30—40℃), the values were decreased by 25.15%—39.14%, and the values were decreased by 26.15%—45.36% with the nano-MgO particle concentration increasing (100-400 mg/L) accordingly. The antifouling property of Ni-P-TiO2 composite modified surface was analyzed combined with the surface energy, and the surface energy of the created Ni-P-TiO2 composite modified surface was found to be near to the surface energy of the nano-MgO particle fouling deposition, which agreed to Zhao's "optimal surface energy" anti-fouling theory. Compared with the 316 stainless steel surface, the Ni-P-TiO2 composite modified surface not only inhibited particle fouling accumulation, but also reduced particle strength of fouling deposition, so that particle fouling deposition was easier to remove from the composite modified surface, which achieved the purpose of enduring and efficient fouling inhibition and mitigation on heat exchange surface.

    Experimental study on condensation heat transfer of R134a in mini channel with micro diamond fins
    Ran LIU, Jie LI, Yubing WANG, Hongbo ZHAN, Dalin ZHANG
    2022, 73(11):  4938-4947.  doi:10.11949/0438-1157.20221047
    Abstract ( 59 )   HTML ( 3)   PDF (4487KB) ( 47 )  
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    An experimental system of condensation heat transfer using air jet impinged cooling method was established to investigate the condensation heat transfer characteristics of R134a in mini channel with micro diamond fins. The experiments were performed at vapor quality between 0 and 1, saturation pressure between 0.50 MPa and 1.50 MPa, mass flux of refrigerant between 160 kg/(m2·s) and 380 kg/(m2·s), and heat flux between 10.1 kW/m2 and 59.8 kW/m2. The local condensation heat transfer coefficient of the channel under different working conditions was obtained, and the influences of vapor quality, saturation pressure, mass flux and heat flux on the condensation heat transfer were analyzed. The experimental results show that, in condensation process, the local condensation heat transfer coefficient decreases with the decrease of vapor quality, mass flux and heat flux, and increases with the decrease of saturation pressure. Based on the experimental data, a calculation formula of condensation heat transfer suitable for the tiny diamond-shaped discrete rib channels in this experiment is proposed.

    Experimental study on boiling dynamics modulation by porous foam deaeration board
    Yiran WANG, Chaoyang GUAN, Xiang GAO, Hongxia CHEN
    2022, 73(11):  4948-4956.  doi:10.11949/0438-1157.20220939
    Abstract ( 89 )   HTML ( 6)   PDF (3218KB) ( 34 )  
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    Deaeration boards (DBs) with different hydrophobicity were prepared and suspended over the monocrystalline silicon surfaces. The effects of DB on the boiling bubble dynamics were systematically investigated through high-speed video. The size evolution of boiling bubbles during the growth and departure stages was monitored. The results show that both the height and wettability of DB have important effects on the dynamic characteristics of boiling bubbles. When the height is less than the maximum growth height, the DB forces the bubble departure and reduces the maximum bubble departure diameter. When the contact angle of DB is 150°, the deaeration effect is the best, and the departure stage can be shortened to 3 ms, and the instantaneous deaeration rate can reach 5.46 mm3/ms, which is 3.96 times that on the surface with the wetting contact angle at 100°. The coupled control of the deaeration height, wettability and the microstructure of the heat exchange surface of the deaeration board can jointly realize the early intervention of the bubble growth stage and the forced promotion of the detachment stage, so as to truly realize the full enhancement of the boiling dynamics.

    Analysis of flow and heat transfer characteristics of lubricating oil in circular tube with coaxial crossed vortex generators
    Zhimin LIN, Chongzhao WANG, Guozhi QIANG, Shushan LIU, Liangbi WANG
    2022, 73(11):  4957-4973.  doi:10.11949/0438-1157.20221006
    Abstract ( 96 )   HTML ( 10)   PDF (4554KB) ( 69 )  
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    Using lubricating oil as the working fluid, the numerical method was used to simulate the flow and heat transfer in the tube of the coaxial cross isosceles trapezoidal vortex generator inserted in the circular tube. The influence of the different structural parameters of the vortex generators such as twisted ratio (Tr=3, 4, 5, 6), spacing ratio (Ss/W=0.8, 0.9, 1.1, 1.2) and base tape width ratio (Wb/W=0.30, 0.45, 0.60, 0.75) on the characteristics of flow and heat transfer were analyzed. The results show that under the same Re condition, all the averaged Nusselt number Num, secondary flow intensity parameter Se and heat transfer enhancement factor JF are increased with decreasing twisted ratio and spacing ratio, but they have no obvious law with the change of base tape width ratio. However, the friction factor f increases with decreasing twisted ratio and with increasing base tape width ratio, and the spacing ratio has only little effect on friction factor. Given the same geometrical parameters of coaxial crossed isosceles trapezoidal vortex generators, both JF and Se increase with increasing Reynolds number. In the range of Re=50—1000, compared with the smooth round tube, the Num of the coaxial crossed vortex generator with different structural parameters interpolated increased by 32.8%—208.6%, f increased by 3.38—8.92 times, and the maximum JF can reach 1.434. The average Nusselt number Num is related to the secondary flow intensity parameter Se as a power function. The intensity of secondary flow in a circular tube fitted with vortex generator inserts determines its convective heat transfer intensity.

    Catalysis, kinetics and reactors
    Reactor simulation and optimization for CO oxidative coupling to dimethyl oxalate reactions
    Ziyi CHI, Chengwei LIU, Yuling ZHANG, Xuegang LI, Wende XIAO
    2022, 73(11):  4974-4986.  doi:10.11949/0438-1157.20220761
    Abstract ( 111 )   HTML ( 8)   PDF (2997KB) ( 74 )  
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    The oxidative coupling of CO and methyl nitrite (MN) to produce dimethyl oxalate (DMO) is a key step in the process of synthesis gas to ethylene glycol, and the existing industrial equipment has the problem of low efficiency. A two-dimensional heterogeneous reactor model with a kinetic model including side reactions of dimethyl carbonate and methyl formate was established to simulate and optimize the tubular fixed-bed reactor, with focus on the influences of coolant-flow schemes and operation conditions. The results showed that ∂2T/∂z2 at hot spot reflected the potential of thermal runaway sensitively and reliably. The evenness of the temperature distribution indicated co-current coolant-flow was preferred to be employed to achieve a higher conversion, compared with the conventional isothermal and counter-current schemes. Moreover, it was found that MN accelerated reactions, while CO and NO inhibited the reactions by adsorption competition with MN, and the elevated total pressure moderated the reaction and hot spot temperature. Compared with the influence of CO, the hot spot temperature was more sensitive to the contents of MN and NO, which should be strictly controlled. The genetic algorithm was used to optimize the process conditions of the reactor, and found that the annual production capacity of EG by one reactor unit could reach 120000 t.

    Kinetic predictions from adiabatic accelerating rate calorimetric data by using the model-free methods
    Suijun YANG, Jiong DING, Qiyue XU, Shuliang YE, Zichao GUO, Wanghua CHEN
    2022, 73(11):  4987-4997.  doi:10.11949/0438-1157.20221122
    Abstract ( 60 )   HTML ( 3)   PDF (1518KB) ( 41 )  
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    The adiabatic accelerating rate calorimetry (ARC) mainly adopts model-fitting method based on single experimental data for kinetic prediction, which is difficult to be applied to unknown mechanism and complex reactions. In this study, the reactions of n-order and Kamal autocatalytic model under adiabatic conditions are generated by numerical simulations, and the kinetic parameters are estimated by Vyazovkin and Friedman conversional methods. Then, under different onset temperatures and isothermal conditions, the adiabatic and isothermal reactions are predicted by using the kinetic parameters solved by the model-free methods, and compared with the simulated data. The results show that ARC can use the model-free methods to carry out adiabatic and isothermal kinetic prediction, and it has good prediction accuracy. The maximum relative error of Vyazovkin method is 39.9% and that of Friedman method is over 100%, and the Vyazovkin method is more suitable for prediction than Friedman method. It is recommended to carry out experimental measurements within the predicted temperature range of ±40℃. Kinetic predictions using the model-free methods have good accuracy and efficiency, which is of great significance for the kinetic analysis of new chemicals and complex reactions. This will effectively support the risk assessment of thermal runaway and the accident simulation.

    Performance enhancement of selective photo-oxidation for NO removal on ZnTi-LDH by Ni2+ substitution
    Zhihua DU, Juan YANG, Jun DAI, Chongchong LENG, Ge ZHANG
    2022, 73(11):  4998-5010.  doi:10.11949/0438-1157.20220912
    Abstract ( 84 )   HTML ( 8)   PDF (6515KB) ( 55 )  
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    Ni-substituted Zn-Ti layered double hydroxide (NiZnTi-LDH) with different Ni2+ substitution ratios were firstly synthesized by using NiCl2·6H2O as nickel source via hydrothermal method. The effects of Ni2+ substitution on the crystal phase, morphology, pore structure, surface oxygen vacancy and light absorption properties of ZnTi-LDH were investigated by X-ray diffraction, transmission electron microscopy, low temperature nitrogen adsorption, X-ray photoelectron spectroscopy and UV-visible diffuse reflectance. Using NiZnTi-LDH as catalyst, the photo-oxidation and elimination performance of NO under simulated sunlight and visible light irradiation were investigated respectively. The results showed that partial Ni2+ substitution for Zn2+ formed a new intermediate energy level in the band structure of ZnTi-LDH that consequently produced visible light response, meanwhile Ni2+ substitution generated oxygen vacancies (OV) on ZnTi-LDH surface. Under visible light irradiation, ZnTi-LDH had no NO oxidation activity, and the optimal 27% NiZnTi-LDH catalyst showed a NO removal rate of 52.1% with a De-NO x selectivity up to 97.4%. Under simulated solar light irradiation, 27% NiZnTi-LDH exhibited a NO photo-oxidation removal rate of 64.8% that was 2.76 times of ZnTi-LDH and De-NO x selectivity was 96.9%, meanwhile the produced NO3- accounted for 95.6% of total nitrate. Ni2+ substitution and the resulting OV not only promoted the separation of photogenerated carriers, but also facilitated the generation of superoxide radical (·O2-). As a result, the photo-oxidative activity of NO removal was enhanced and the production of toxic NO2 was effectively inhibited, consequently achieving deep photo-oxidation of NO to NO3-.

    Separation engineering
    Multiscale screening of ionic liquids as extractive solvents for oil-hydroxybenzene separation
    Qian LIU, Xianglan ZHANG, Zhiping LI, Zhuoqi LI, Hong YU
    2022, 73(11):  5011-5024.  doi:10.11949/0438-1157.20221062
    Abstract ( 86 )   HTML ( 8)   PDF (3255KB) ( 34 )  
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    Ionic liquids have been widely used as extractive solvents for the separation of oil-hydroxybenzene mixtures. However, due to the adjustability of cation and anion, the properties of different ionic liquids vary greatly. It is essential to quickly screen ionic liquids with application prospects. For the m-cresol-cumene separation system, the influences of different cation and anion structures on the separation performance of ionic liquids was investigated by COSMO-RS model, and the separation mechanism was analyzed by intermolecular interaction energy. On this basis, a multiscale ionic liquid screening method including the calculation of infinite dilution thermodynamic properties, the estimation of physical properties, the calculation of phase equilibria, and the evaluation of process performance was proposed. The multiscale method gradually screens ionic liquids from molecular scale to single-stage equilibrium scale, and then to multi-stage equilibrium scale. The results show that 1-ethyl-pyridinium thiocyanate ([C2py][SCN]) and 1-ethyl-pyridinium dicyanamide ([C2py][DCA]) are two ionic liquids with more application prospects for the separation of oleophenol obtained by final screening.

    Desolidification structure and optimization of specially-shaped hydrocyclone three-phase separation device for industrial waste oil
    Haifeng GONG, Xin LUO, Ye PENG, Bao YU, Yang YANG, Haohua ZHANG
    2022, 73(11):  5025-5038.  doi:10.11949/0438-1157.20220963
    Abstract ( 105 )   HTML ( 19)   PDF (6056KB) ( 76 )  
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    Dehydration and desolidification of industrial waste oil is an important part of waste oil resource process. In order to efficiently remove water and solid particle impurities in waste oil emulsion, a specially-shaped hydrocyclone three-phase separation device that can realize efficient separation of oil-water-solid phase was proposed. The device structure and its parameters play a key factor in the oil-water-solid three-phase separation efficiency. Therefore, a numerical model of the specially-shaped hydrocyclone three-phase separation device was established by coupling the multiphase flow governing equations, the population balance equation and the solid particle tracking equation under the condition of sparse particles, ignoring the influence of particle on the conservation of mass and momentum. The influence of the desolidification section structure of the separation device on the desolidification and dehydration efficiency was investigated, and the desolidification section structural parameters of the separation device were further optimized. Numerical and experimental results showed that the desolidification section structure variation of the device significantly affected the desolidification performance of the specially-shaped hydrocyclone three-phase separation device, but the effect on the dehydration rate is not obvious. When the diameters of the optimal bottom flow pipe, solid removal pipe and side flow pipe are 6, 15 and 6 mm respectively, the solid particle recovery rate and oil removal rate of the side flow outlet of the device reach the highest at the same time, which can reach more than 87%. It provides theoretical and technical support for the design and development of high-performance industrial waste oil recycling devices.

    Process system engineering
    Application of Bayesian optimization method in the production of 1,3-propanediol by Vibrio natriegens
    Xinye HUANG, Ye ZHANG, Shuyuan ZHANG, Zhen CHEN, Tong QIU
    2022, 73(11):  5039-5046.  doi:10.11949/0438-1157.20221102
    Abstract ( 123 )   HTML ( 13)   PDF (1207KB) ( 45 )  
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    1,3-Propanediol is an important chemical raw material. The preparation of 1,3-propanediol by biological fermentation has the advantages of simple operation, mild reaction conditions and few by-products. The use of Vibrio natriegens as a new industrial chassis to produce 1,3-propanediol has important application prospects, but the construction of high-yielding strains has the characteristics of long single experiment period, high cost, and strong nonlinearity. In order to fast optimize the combination of key gene intensity of 1,3-propanediol synthesis pathway, we use a Bayesian optimization method with Gaussian process regression algorithm as surrogate model and expected improvement as acquisition function. In each iteration, the Gaussian process regression algorithm is used to fit the current data and predict the probability distribution of unknown points. The expected improvement function maps the probability distribution to the solution space, selects the point corresponding to the maximum value in the solution space as the experimental point in the next iteration, and enters the next iteration after experiment. The Bayesian optimization method was used to optimize the key gene intensity combination in the process of constructing a high-yielding 1,3-propanediol-producing Vibrio natriegens. After three iterations, the optimal gene strength combination was searched. The 1,3-propanediol yield reached (13.01±0.63) g/L, which was 8.32% higher than the highest value in the first group of test points.

    Multi-objective optimization of work and heat exchange networks based on a decomposition algorithm
    Qucheng LIN, Zuwei LIAO
    2022, 73(11):  5047-5055.  doi:10.11949/0438-1157.20221173
    Abstract ( 85 )   HTML ( 13)   PDF (2066KB) ( 38 )  
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    Work and heat exchange network (WHEN) problems refer to the problem of synthesizing the networks considering the work integration and heat integration in the process design, which aims to increase the energy efficiency of the overall system and reduce the costs. In the previous works, the mathematical programming methods are generally used to model and optimize WHENs. However, due to the nonlinear constraints of the pressure transformation process and heat exchanger area calculation, as well as the binary variables of heat transfer matching, the overall model is often a highly nonconvex mixed integer nonlinear programming model, which is difficult to solve. This work proposed an efficient WHEN design method. In the model, turbo expanders and heat exchangers are used to exchange shaft work and heat, respectively. A decomposition algorithm is used in the solving procedure, which uses the genetic algorithm to optimize the key variables in the main problem and uses deterministic algorithms to solve the two sub-network design problems. Multi-objective optimization that minimizes economic and environmental impact is considered in the WHEN model. In the case study, we show the difference between the networks obtained with different optimization goals and the Pareto curve considering the multi-objective optimization, which verifies the efficiency of the proposed method.

    Cold-start stack temperature prediction model for proton exchange membrane fuel cells
    Huiying ZHANG, Weihua CAI, Ming GAO, Yuhang WANG, Suoying HE
    2022, 73(11):  5056-5064.  doi:10.11949/0438-1157.20221149
    Abstract ( 66 )   HTML ( 5)   PDF (3871KB) ( 50 )  
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    In order to quickly and accurately predict the start-up duration of a proton exchange membrane fuel cell (PEMFC) during the cold-start process and the application effect of the start-up method, two real-time prediction models of the stack temperature change trend are proposed. The two prediction models take the stack temperature and the temperature increment as the prediction targets of the BP neural network, named model T and model K, respectively. Meanwhile, four different prediction accuracy evaluation criteria are used to evaluate the accuracy of the prediction results. The prediction model is verified based on the experimental data of three cold-start conditions in the literature. The results show that the average relative error of model K is lower than that of model T under the three cold-start conditions, which are 0.4553, 0.9537, and 1.0844, respectively. Model T lacks training samples in the early prediction stage, and the stack temperature variation trend of the prediction results is zero, so model K has a greater advantage in the early prediction stage. The stack temperature change trend prediction method can provide a reference for the user’s current PEMFC cold-start implementation effect.

    Optimal design of membrane separation process for capturing CO2 from flue gas of coal-fired power plant
    Guixian LI, Ke WANG, Jian WANG, Wenliang MENG, Jingwei LI, Yong YANG, Zongliang FAN, Dongliang WANG, Huairong ZHOU
    2022, 73(11):  5065-5077.  doi:10.11949/0438-1157.20221035
    Abstract ( 78 )   HTML ( 12)   PDF (2949KB) ( 64 )  
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    Global CO2 emissions continue to rise, leading to frequent climate problems. With the goal of "carbon peak and carbon neutralization", it has become an urgent issue to capture CO2 from the flue gas of coal-fired power plants in an efficient and cost-effective way. The development of traditional chemical absorption method is seriously restricted by its high energy consumption, high cost and volatile solvent. The membrane carbon capture is considered as the most promising capture method because of its advantages such as simple operation, low energy consumption and small environmental pollution. Membrane-based carbon capture is considered as the most promising capture method because of its low capture cost and environment-friendly features. In this paper, a gas separation membrane model is established and solved with PI hollow fiber membrane as the separation membrane. And with the target of carbon dioxide capture in flue gas of coal-fired power plants, the membrane separation processes with different configurations of carbon dioxide capture are solved by multi-island genetic algorithm, and the key parameters (membrane area, operating pressure) in the separation process are optimized. The results show that in the two stage-one step membrane separation process, when the operating pressure of the first stage membrane and the second stage membrane are 5.8 bar and 7.1 bar, respectively, and the area of the first stage membrane and the second stage membrane is 448000 m2 and 180000 m2, the unit capture cost is 27.36 USD/t CO2. Compared with two stage-two step membrane separation and several other traditional CO2 capture methods (MEA method and phase change absorption method), the capture cost and energy consumption of CO2 by two stage-one step membrane separation is the lowest. This study will provide a basis for achieving low energy consumption and low cost for CO2 capture.

    Energy and environmental engineering
    3D characterization of pore structure and seepage simulation of tar-rich coal (long flame coal)
    Xiaole HUANG, Fu YANG, Lei HAN, Xing NING, Ruiyu LI, Lingxiao DONG, Husheng CAO, Lei DENG, Defu CHE
    2022, 73(11):  5078-5087.  doi:10.11949/0438-1157.20220937
    Abstract ( 114 )   HTML ( 8)   PDF (5329KB) ( 54 )  
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    The three-dimensional characterization of tar-rich coal (long flame coal) was carried out by X-ray CT (computed tomography) imager. An equivalent pore network model (PNM) of the statistical pore size distribution (PSD) is established. The effects of pressure gradient and flow direction on the seepage process are studied. The results show that pores, minerals, and matrix account for 11.30%, 1.03% and 87.67% of the total volume, respectively. The connected porosity is 5.13%. The number of pore equivalent radius within 3—8 μm accounts for 89.23%. The corresponding average coordination number is 2.87, which indicates that the pore connectivity is poor. The number of throats with an equivalent radius less than 2 μm accounts for 73%. The equivalent length of the throat is mainly distributed between 10—30 μm. At the same pressure gradient, three directions of pore pressure, seepage velocity, and flow path distribution are different, showing anisotropy. With the increase of pressure gradient, the seepage velocity increases gradually. The seepage velocity shows an obvious nonlinear relationship with pressure. The harmonic average permeability in three directions is 0.1403 mD, which is close to the measured value (0.1345 mD) of another tar-rich coal in the Yushenfu mining area. The difference is within 5%.

    Synergistic effect during catalytic co-pyrolysis of bio-oil distillation residue and waste plastic
    Runtao WANG, Zejun LUO, Chu WANG, Xifeng ZHU
    2022, 73(11):  5088-5097.  doi:10.11949/0438-1157.20220920
    Abstract ( 92 )   HTML ( 12)   PDF (2203KB) ( 50 )  
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    The work aims to explore co-pyrolysis characteristics of bio-oil distillation residue (DR) and waste medical syringe (MS) by thermogravimetric analyzer and the two-stage fix-bed reactor. The effects of mixing ratio of DR and MS, non-catalytic, in-situ catalytic and ex-situ catalytic co-pyrolysis on product distribution and chemical components of liquid products were investigated. Based on chemical components of liquid products, the relative selectivity and synergistic effect of co-pyrolysis products of DR and MS were studied. The results showed that the liquid yield had an increasing trend with the increasing of mixing ratio, and in-situ catalytic and ex-situ catalytic co-pyrolysis had a higher relative content of aromatic hydrocarbons compared to non-catalytic co-pyrolysis, while the relative content of oxygenates was lower. For synergistic effect of DR and MS on aliphatic compounds and oxygenates, in-situ catalytic co-pyrolysis was contrary to ex-situ catalytic and non-catalytic co-pyrolysis. For monocyclic aromatic hydrocarbons, the synergistic parameters of DR and MS using different catalytic modes are as follows: non-catalytic > ex-situ catalytic > in-situ catalytic. For aliphatic hydrocarbons, when DR∶MS=1∶1, the synergistic parameter values of non-catalytic, in-situ catalytic and ex-situ catalytic co-pyrolysis are the largest, which are -20.7%, 25.2% and -41.2%, respectively. For alicyclic hydrocarbons, when DR∶MS=2∶1, the synergistic parameters values of non-catalytic, in-situ catalytic and ex-situ catalytic co-pyrolysis reach the maximum values, which are 184.2%, 132.5% and 50.0%, respectively. For PAHs, DR and MS showed negative synergy under different catalytic modes.

    Enhance nitrogen removal via endogenous denitrification in a sludge double recirculation-anaerobic/aerobic/anoxic process
    Xinjie GAO, Zaizhou XU, Yongzhen PENG, Yuwei HUANG, Jing DING, Zeming AN, Chuanxin WANG
    2022, 73(11):  5098-5105.  doi:10.11949/0438-1157.20221008
    Abstract ( 99 )   HTML ( 4)   PDF (2032KB) ( 51 )  
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    At present, how to economically and effectively realize the deep denitrification of low C/N domestic sewage is still a major challenge faced by sewage treatment plants. Theoretically, the endogenous denitrification in post anoxic zone can achieve advanced nitrogen removal. However,due to lacking external carbon source, it was often difficult to meet the discharge standard and saving-energy at the same time. In this study, a novel sludge double recirculation-anaerobic/aerobic/anoxic (AOA) process was set up. This process was conducive to the enrichment and cultivation of denitrifying glycogen accumulating organisms (DGAOs) and dominated by Candidatus Competibacte, which could develop and utilize of intracellular carbon sources. The TIN removal efficiency of 91.81% and the TIN concentration in effluent was 4.36mg·L-1 in the long-term treatment of low C/N ratio (3.2) real municipal wastewater. In addition, the specific endogenous denitrification rate was increased with a higher MLSS in the anoxic zone after setting secondary sludge recirculation. This was the mainly reason for achieving advanced nitrogen removal. With the improvement of the nitrogen removal efficiency, the sufficient intracellular carbon sources storage in anaerobic zone was increase, and the endogenous denitrification enhanced. The nitrogen removal performance showed a positive cycle. Finally, the additional carbon source generation, which was from the bottom of the secondary sedimentation tank and introduced to the system through the secondary sludge recirculation, further enhanced the nitrogen removal. This study clarified the mechanisms and key factors for advanced nitrogen removal in sludge double recirculation-AOA system, and provided feasibility for the increased nitrogen removal efficiency in low C/N municipal wastewater treatment.

    Thermodynamic analysis and optimization of 10 t/d hydrogen liquefaction process
    Haocheng WANG, Jingyao YANG, Xueqiang DONG, Hao GUO, Yanxing ZHAO, Maoqiong GONG
    2022, 73(11):  5106-5117.  doi:10.11949/0438-1157.20221084
    Abstract ( 77 )   HTML ( 10)   PDF (4014KB) ( 77 )  
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    According to the requirements for the development of a 10 t/d hydrogen liquefaction unit, a continuous conversion dual-pressure Claude hydrogen liquefaction process with liquid nitrogen precooling was constructed. The hydrogen liquefaction process is based on a liquid-nitrogen-precooled dual pressure Claude cycle using continuous ortho-to-para hydrogen conversion method. The influence of key factors on process performance is analyzed, including expander isentropic efficiency, recuperator minimum approach and feed hydrogen pressure drop, etc. The thermodynamic parameter ranges of the liquefaction process and key equipment are provided, which could be a reference for the design of expanders and recuperators. Under the basic operation conditions (a severe operation condition for hydrogen expanders), the maximum liquid hydrogen output is 12.96 t/d with para-hydrogen concentration of 97%. The calculated overall specific power consumption is 10.50 kWh/kg LH2 (the compression power of feed hydrogen is not included), with process exergy efficiency of 35.06%. The simulation methods and simulation results could be a reference for the development of continuous ortho-to-para conversion type large scale hydrogen liquefaction systems.

    Study on the control effect of electrokinetic drainage of pore water on nitrogen release flux at the mud-water interface
    Junjun GU, Rui LI, Xingyi WU, Xianqiang TANG, Yanping HU
    2022, 73(11):  5118-5127.  doi:10.11949/0438-1157.20221012
    Abstract ( 53 )   HTML ( 1)   PDF (2956KB) ( 19 )  
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    Pore water is a crucial storage medium and a key source of sediment nitrogen. The separation and removal of nitrogen rich pore water is a potential scheme to control the release of endogenous nitrogen. A novel electrokinetic drainage of pore water device was used in a simulation study to understand its efficacy on internal nitrogen release. A total of three groups of experiments were set up: control, gravity drainage (0 V/cm voltage gradient) and intermittent energization (0.5 V/cm voltage gradient, 4 h On/4 h Off). In this research, we analyzed the characteristics of nitrogen concentration and release flux at the sediment-water interface, monitored the pore water and sediment nitrogen fraction, pH and other physicochemical parameters, and then assessed the effect of electrically induced and discharged pore water on the release flux of nitrogen at the sediment-water interface and the influencing factors. The results show that electrokinetic drainage of pore water can reduce the nitrogen release flux at the sediment-water interface effectively. The cumulative dissolved total nitrogen (DTN) release flux at the sediment-water interface was 282.28 mg N/m2 after 632 h of intermittent energization, which was 95.61% lower than that in the control group. Electric drainage of pore water makes the anode pore water acidic and the cathode pore water alkaline, and the change of pH promotes the activation of transformable nitrogen (TTN) in the sediment. The removal rate of sludge ion-exchanged nitrogen (IEF-N) increased from 11.11%—12.97% to 12.59%—22.31%. After electric drainage of pore water, the total nitrogen removal amount of sediment is 47015.72 mg/m3, and the cumulative energy consumption is 162.38 kWh/m3.

    Analysis of bacterial function in combined PN/A granular sludge and solid phase denitrification processes
    Li ZHANG, Jianhua WU, Shuhui CUI, Feng YAN, Hao SUN, Feiyue QIAN
    2022, 73(11):  5128-5137.  doi:10.11949/0438-1157.20221125
    Abstract ( 56 )   HTML ( 1)   PDF (5770KB) ( 30 )  
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    For the control of residual nitrate in the effluent of partial nitritation and anaerobic ammonium oxidation (PN/A) system, a novel system was developed for the advanced nitrogen removal by coupling solid-phase denitrification (SPD) and PN/A granular sludge. On the basis of increasing the autotrophic denitrification efficiency of granular sludge step by step, the SPD of three fillers, quartz sand, polybutylene succinate (PBS) and hydroxybutyrate valeric acid copolyester (PHBV), was systematically investigated. The results indicated that the denitrification performance of PHBV was the best, the optimal total nitrogen (TN) removal efficiency exceed 93% in the PN/A-PHBV system, which was significantly higher than sand (83.6%) and PBS (85.8%) in high hydraulic pressure condition. According to the results of pyrosequencing analysis and the FAPROTAX function predicted, the dissolution level of solid carbon source is an important factor affecting the diversity of biofilm flora. Among them, the hydrolytic bacteria Clostridium-sensu-stricto-7, which was dominant on the surface of PHBV, formed a stable cooperative relationship with denitrifying bacteria such as Comamonadaceae, in addition to effectively eluting autotrophic denitrification functional bacteria, the functional potential of the flora to participate in multi-element cycling was significantly improved. The results of this study have significance in guiding for systematic optimization of the PN/A-SPD combination process and promoting its engineering application.

    Material science and engineering, nanotechnology
    High-throughput computational screening strategy for high-performance COF materials: separation of hexane isomers
    Shiyang YE, Min CHENG, Xu JI, Yiyang DAI, Yagu DANG, Kexin BI, Zhiwei ZHAO, Li ZHOU
    2022, 73(11):  5138-5149.  doi:10.11949/0438-1157.20220988
    Abstract ( 128 )   HTML ( 18)   PDF (2966KB) ( 107 )  
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    Separation of double-branched isomers from hexane isomers can increase the octane number of gasoline and reduce engine knocking. Aiming at the disadvantages of high energy consumption of traditional distillation methods and the disadvantages of high cost, low working capacity and poor stability of new MOF adsorbents, the separation performance of 688 covalent organic frameworks (COFs) for hexane isomers was investigated by high-throughput computational screening method. Firstly, the geometric properties of all COFs were calculated, and 209 COFs that can accommodate all hexane isomers were selected through the range of 6.2—15 Å of pore limiting diameter (PLD). Then the adsorption and desorption processes of hexane isomers by the above COFs at 433 K were simulated by grand canonical Monte Carlo (GCMC) method. The COFs with regeneration capacity (R) >80% and the highest adsorbent performance score (APS) were sorted, and the COF-DL229 2-fold with the highest APS value was selected. Its APS value is 23.36 mol/kg and R is 99.38%. The correlation between six geometric properties and APS was analyzed. It was found that the APS value of COF can be improved by higher void fraction (VF), higher pore volume (PV) and lower density (ρ). Finally, based on PV, VF and ρ, the screening path of high APS value COF is designed by using decision tree algorithm, which has certain guiding significance for the design of COF for adsorption and separation of hexane isomers in the future.

    Upgrading dispersion and interfacial morphologies for thermally conductive polypropylene composites by in situ growth of carbon nanotubes at graphene oxide
    Huan XU, Lyu KE, Shenghui ZHANG, Zilin ZHANG, Guangdong HAN, Jinsheng CUI, Daoyuan TANG, Donghui HUANG, Jiefeng GAO, Xinjian HE
    2022, 73(11):  5150-5157.  doi:10.11949/0438-1157.20220835
    Abstract ( 65 )   HTML ( 4)   PDF (3729KB) ( 36 )  
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    Conventional 2D graphene oxide (GO) nanosheets have shown promise in the applications of thermally conductive polymer nanocomposites, which is unfortunately dwarfed by the local aggregation of GO due to the extensive interplanar interactions. Here, a microwave-assisted synthetic approach was proposed to enable in situ growth of carbon nanotubes (CNTs) at both the basal planes and the edges of GO templates, engendering a minute-level and straightforward route to create 3D hierarchical nanohybrids (GO-CNT). The nanohybrids and GO [1%, 2% and 3%(mass)] were incorporated into polypropylene (PP) using common extrusion compounding amenable to scale up. Unlike the prominent local aggregation of GO in PP composites, GO-CNT was properly exfoliated and dispersed regardless of the loadings. This contributed to multiple improvements in mechanical properties and thermal conductivity for GC/PP, as exemplified by the highest yield strength (38.0 MPa) and thermal conductivity [0.76 W/(m·K)] for GC3, displaying remarkable increase of 20% and 230% compared to those of pure PLA. This work affords elucidation of direct covalent functionalization of 2D nanosheets and property-by-morphology understanding in polymer composites, which may motivate further extension to other polymer composite systems.

    Regulation of gelation rate on the morphology of helical fibers during microfluidic spinning
    Zhihao WANG, Xin SONG, Yaran YIN, Xianming ZHANG
    2022, 73(11):  5158-5166.  doi:10.11949/0438-1157.20220900
    Abstract ( 109 )   HTML ( 8)   PDF (2874KB) ( 40 )  
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    The preparation of alginate fibers by microfluidic spinning has been recognized in many fields, but the fast gelation reaction limits the flexible regulation of the helical fiber morphology. Regarding this, a series of alginate fibers were prepared in a coaxial capillary microfluidic device. The outer phase was the calcium chloride solution, and the inner phase adopted the mixed aqueous solution of sodium alginate with sodium citrate to reduce the gelation rate. The effects of gelation rate and flow rates of inner and outer phases on the fiber distribution and helical morphology were systematically investigated. The result indicates that the reduction of gelation rate favors the formation of helical fibers and affects the distribution of fibers such as straight, helical, wavy, and blocked. Furthermore, two types of helical fibers, namely thick and thin helical fibers, are recognized. Their morphological characteristics show significant differences in relation to the gelation rate and two-phase flow rates. By comparison, the diameter and pitch of thick helix, and the amplitude of thin helix are more vulnerable to the gelation rate and two-phase flow rates. The gelation rate and shear force are the dominant factors regulating the pitch of thick and thin fibers, respectively. On this basis, the two helical fibers can be well distinguished by the relation of pitch and the inner/outer rate ratio.

    Microwave synthesis of AgInS2 quantum dots in organic solvent and application for white light-emitting diodes
    Ting CHEN, Zehao HU, Zhe QIN, Yuanhong CHEN, Yanqiao XU, Jian LIN, Zhixiang XIE
    2022, 73(11):  5167-5176.  doi:10.11949/0438-1157.20220758
    Abstract ( 66 )   HTML ( 5)   PDF (3341KB) ( 37 )  
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    AgInS2 quantum dots (AIS QDs) have shown broad application prospects in the field of optoelectronics and biomedicine due to the advantages of environmental friendliness, tunable emission wavelength, long fluorescence lifetime and large Stokes shift. In this study, AIS quantum dots were prepared in octadecene solvent by microwave-assisted heating method. The effects of reaction time on the phase, morphology and fluorescence properties of AIS QDs were systematically investigated by X-ray diffraction, transmission electron microscope, and photoluminescence spectroscopy, respectively. The surface bonding of the AIS QDs was characterized by Fourier infrared spectroscopy and X-ray photoelectron spectroscopy. The results showed that AIS QDs could be synthesized within 5—25 min when the microwave power was 800 W. With the increase of reaction time, the particle size of AIS QDs increased gradually from 3 nm to 4 nm, and the PL peak position could be tuned in the range of 592.0—619.6 nm. The fluorescence intensity increased simultaneously and reached the maximum value at 15 min with photoluminescence quantum yield (PLQY) of 16.16%, In addition, the fluorescence properties of QDs were further improved by ZnS surface modification to passivate the defects, resulting in the enhanced PLQY of 31.21%. Furthermore, white light-emitting diode (WLED) devices were fabricated by using AIS@ZnS QDs and commercial phosphors as light conversion layer. The luminous efficiency (LE) of the fabricated WLED device was as high as 74.90 lm/W under the driving current of 20 mA, and the corresponding color rendering index (CRI) and correlated color temperature (CCT) were 83.31 and 3823 K respectively, indicating that the prepared QDs have great applications in solid-state lighting.

    Process safety
    Diffusion features of jet leakage with liquid hydrogen in large space
    Jinfeng LI, Kai FANG, Haohao XU, Xinkun LI, Junlong XIE, Jianye CHEN
    2022, 73(11):  5177-5185.  doi:10.11949/0438-1157.20220948
    Abstract ( 85 )   HTML ( 6)   PDF (2802KB) ( 46 )  
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    A three-dimensional unsteady CFD numerical calculation model of liquid hydrogen jet leakage in large space was established, and the law of leakage and diffusion was studied. The numerical results reveal that four stages of hydrogen cloud occur, namely free discharge stage, sedimentation stage caused by phase change, ascent stage and stabilization stage. Besides, the hydrogen cloud would move longer distance against the ground because the effect of inertial force was more significant and the effect of buoyancy force was difficult to manifest, which also increased the hazard of spill.

    Special column for Thermalchemical conversion of biomass and organic solid wastes
    Research and progress of volatile-char interaction during biomass and coal (co-)pyrolysis/gasification process
    Meng MA, Yonghui BAI, Juntao WEI, Lunjing YAN, Peng LYU, Jiaofei WANG, Xudong SONG, Weiguang SU, Guangsuo YU
    2022, 73(11):  5186-5200.  doi:10.11949/0438-1157.20220827
    Abstract ( 140 )   HTML ( 10)   PDF (3980KB) ( 97 )  
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    The synergistic thermochemical conversion of biomass and coal is a technical means to realize the efficient coupling utilization of non-fossil energy and fossil energy, which has great practical significance to realize the goal of “Dual Carbon”. Due to the high volatile composition and oxygen-enriched characteristics of carbonaceous fuels such as biomass, the volatile-semi-coke interaction inevitably occurs in the thermochemical conversion process and affects the properties of raw materials and equipment process parameters. This article reviews the research progress of volatile-char interaction between biomass and coal during the (co-)pyrolysis/gasification process, and three specific contents of the volatile-char interaction on catalytic cracking of volatiles, the effect on char chemical structure and properties, and research approach of decoupling of synergetic thermochemical transformation are summarized. In view of the current research methods and thought used in the mechanism analysis of volatile-char interaction, some new insights were proposed and the future research directions of the interaction were prospected, so as to provide theoretical guidance for further understanding the physicochemical nature of the interaction.

    Evolution of surface functional groups in the pyrolysis of lignin with the introduction of polyethylene and transition metals
    Kun QIN, Zhanghong WANG, Huiyan ZHANG
    2022, 73(11):  5201-5210.  doi:10.11949/0438-1157.20220849
    Abstract ( 75 )   HTML ( 3)   PDF (6683KB) ( 57 )  
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    Lignin (LG) has high oxygen content and complex chemical structure, making it difficult to utilize as a resource. The introduction of blending agent and catalyst can greatly strengthen the decomposition of LG and effectively improve its utilization efficiency, but the specific mechanism of this process needs to be further analyzed. In present work, the effects of the addition of low density polyethylene (PE) and transition metals regarding to Ni, Fe and Mn on the evolution of surface functional groups of LG derived from black liquor were investigated by using in situ Fourier infrared spectroscopy (in situ FTIR). LG began to decompose gradually from the C—C bond at about 200℃ (at 2044 cm-1), while the oxygen-containing surface functional groups including —OH, C—O, C—O—C and C̿    O at 1040—1645 cm-1 and 3450—3600 cm-1 began to decrease after 500℃. The addition of PE can start to promote the removal of oxygen-containing surface functional groups of LG at about 400℃, and can achieve the removal of most oxygen-containing surface functional groups at about 500℃. Furthermore, the introduction of Ni can enhance the interaction between LG and PE, resulting in the removal of most oxygen-containing surface functional groups in the rapid decomposition stage of PE at about 460℃. In addition, the process parameters including the type of transition metal, the concentration of transition metal, the mixing ratio of LG and PE and the heating rate all show certain degree effects on the interaction between LG and PE. This study provides important technical guidance for the resource utilization of LG from the perspective of the quality of pyrolysis process and the change of surface functional groups.

    Migration of sulfur and nitrogen during co-hydrothermal carbonization process of sewage sludge and high-sulfur coal
    Xiaoyang YANG, Baofeng WANG, Xutao SONG, Fengling YANG, Fangqin CHENG
    2022, 73(11):  5211-5219.  doi:10.11949/0438-1157.20220848
    Abstract ( 117 )   HTML ( 7)   PDF (3744KB) ( 92 )  
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    Co-hydrothermal carbonization experiments of sewage sludge and high-sulfur coal were carried out using a high temperature and high pressure reactor. The results showed that protein nitrogen (N-A) of sewage sludge was converted into heterocyclic nitrogen after hydrothermal treatment, and pyrrole (N-5) and pyridine oxynitride (N-X) of high sulfur coal were converted into pyridine (N-6) and quaternary nitrogen (N-Q). The sulfur of sewage sludge and high sulfur coal were converted into thiophene and sulfate. The increase in the proportion of nitrogen-containing aromatic heterocycles (e.g., N-6, N-5, and N-Q) in the hydrochar was attributed to the increase of the proportion of high-sulfur coal blends and temperature. Furthermore, the thiophene content of hydrochar increased to 22.61% and 24.98% gradually with increasing of high-sulfur coal blending ratio and temperature; and the sulfate content increased at higher temperature, however it decreased when increasing proportion of high-sulfur coal blend ratio. This study could provide the theoretical basis for the clean utilization of sewage sludge and high-sulfur coal efficiently.

    Effect of hydrothermal carbonization temperature on transformation path of organic nitrogen in sludge
    Shan CHENG, Rui LUO, Hong TIAN, Zhenqi WANG, Jingchun HUANG, Yu QIAO
    2022, 73(11):  5220-5229.  doi:10.11949/0438-1157.20220832
    Abstract ( 98 )   HTML ( 2)   PDF (2167KB) ( 47 )  
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    The migration and transformation path and characteristics of organic nitrogen during hydrothermal carbonization at different temperature were studied by using sludge and soybean protein. The nitrogen balance of the whole process showed that with the hydrothermal carbonization temperature increase from 150℃ to 240℃, the ratio of residual nitrogen in hydrochar to total nitrogen in sludge decreased from 68.9% to 29.8%. Proportion of nitrogen transferred to tar and aqueous solution increased from 4.2% to 35.0% and 18.8% to 30.4%, respectively, while the nitrogen in gas only counted for less than 0.02%. The main transformation path of proteins in sludge was to produce amines in tar, then water-soluble organic nitrogen, NH3 and NH4+ successively through decompose and hydrolysis. The reaction degree increased with the increase of temperature. More stable heterocyclic nitrogen compounds such as pyrrole and pyridine were formed through Maillard, Mannich and other reactions at high temperature. The residual nitrogen-containing substances in hydrochar include undecomposed protein, heterocyclic nitrogen, quaternary nitrogen and a small amount of nitrile. Nitrogen species in tar were amine and heterocyclic nitrogen compounds, while nitrile is not presented. The aqueous solution is dominated by organic nitrogen, followed by a large amount of NH4+. The nitrogen-containing gas released is mainly HCN.

    Coupling process simulation and random forest model for analyzing and predicting biomass-to-hydrogen conversion
    Li LIU, Peng JIANG, Wei WANG, Tonghuan ZHANG, Liwen MU, Xiaohua LU, Jiahua ZHU
    2022, 73(11):  5230-5239.  doi:10.11949/0438-1157.20220816
    Abstract ( 116 )   HTML ( 16)   PDF (4672KB) ( 61 )  
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    Biomass can replace fossil fuels, reduce greenhouse gas emissions, and is a promising renewable energy source. Co-production of multiple-products has been demonstrated efficient and economically viable process. The techno-economic feasibility of biomass conversion into hydrogen (H2) and activated carbon (AC) route has also been analyzed. However, the selection of raw materials and process parameters become the main barrier for scale-up production. The different types of biomass species and the process conditions affect the yield and quality of the products. In this paper, a process model was developed to simulate the biomass conversion process. H2 was produced from biomass through pyrolysis and chemical looping gasification processes. AC was fabricated from biomass through carbonization and activation processes. Then, machine learning was used to build a high-quality prediction model and accordingly explore the importance factors in producing demanded products. The results indicated that process parameters had greater influence than the raw materials on H2 concentration and yield. For example, hydrogen concentration was more relevant (61%) to the reforming temperature, hydrogen concentration in syngas and steam usage, hydrogen yield was more relevant (63%) to the dosage of activation agent and steam usage. Partial dependence plot (PDP) analysis provided the optimal range of processing parameters for maximized production of target products.

    Catalytic/inhibitory effects of inorganic elements on biomass char-CO2 gasification reactivity and model construction
    Qianshi SONG, Xiaowei WANG, Wei ZHANG, Xiaohan WANG, Haowen LI, Yu QIAO
    2022, 73(11):  5240-5250.  doi:10.11949/0438-1157.20220906
    Abstract ( 85 )   HTML ( 5)   PDF (1861KB) ( 42 )  
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    Based on the simple collision theory, a kinetic model of char gasification reaction with the influence of inorganic elements was established. In the modeling process, the effects of the content of seven inorganic elements, the catalytic/inhibitory factor, and the fully catalytic ratio of single inorganic element on the char-CO2 reactivity were considered. In the experimental part, four biomass samples were selected and placed in a micro-fluidized bed reactor to test the char-CO2 reactivity, and compared with the model calculated values. The results show that the model can accurately predict the char-CO2 reactivity, and also shows adaptability to different samples. The model can achieve quantitative prediction of char-CO2 reactivity by inputting sample characteristic parameters and reaction conditions. The establishment of this model shows that the general law of biomass thermal conversion process exists, which can provide a theoretical reference for further clarifying the gasification reaction law.

    Study on the steam gasification mechanism of waste PP plastics based on ReaxFF-MD and DFT methods
    Weiwei XUAN, Yanwu DONG, Hailun WANG
    2022, 73(11):  5251-5262.  doi:10.11949/0438-1157.20221000
    Abstract ( 97 )   HTML ( 6)   PDF (7755KB) ( 66 )  
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    Gasification technology is an important method for treating the increasing amount of waste plastics and producing H2-rich syngas. ReaxFF-MD and DFT methods were used to study the reaction mechanism of water vapor gasification of polypropylene (PP) plastics and the generation path of each product gas, and the effects of temperature and water content on the product distribution of syngas were further explored. The results show that the main reaction process in the early stage of steam gasification of PP plastics is the breaking of monomer bond with small dissociation energy at the places where the propylene (CH3—CH̿    CH2) monomer are formed. Subsequently, the monomer continue to dissociate into smaller C1—C2 hydrocarbon molecules, ·H, CH3· and other free radical fragments. In the steam reforming reaction stage, there are many ways to generate H2, but the collision of free ·H radicals generated from the C-containing structure in the early stage with H2O molecular is the main way, accounting for 70% of the total H2. At the same time, the accompanying generated ·OH radical is the main way of generating CO through the process of combining with small molecules and removing H. Increasing the temperature and water content can promote the steam reforming reaction of hydrocarbons, so as to improve the yield of H2 and CO, but the improvement effect is gradually weakened. The above results can be a guide to master the plastic gasification process and select proper experimental parameters.

    Biochars derived from Ca-rich mushroom residue for phosphorus-containing wastewater treatment
    Kun QIN, Jiale LI, Zhanghong WANG, Huiyan ZHANG
    2022, 73(11):  5263-5274.  doi:10.11949/0438-1157.20220916
    Abstract ( 108 )   HTML ( 9)   PDF (2017KB) ( 55 )  
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    In order to seek a reasonable way for the utilization of edible fungi residue and develop a green and high-efficient adsorbent for the treatment of phosphorus-containing wastewater, mushroom residue (MR) was employed as a raw material to prepare biochars under 800, 900 and 1000℃, and the adsorption capability of the biochars was investigated. It is found that the biochars are abundant in minerals, such as K, Na, Ca and Mg. Particularly, the content of Ca in the biochars are 4328.43—4919.38 mmol/kg and the Ca existed in biochars are mainly in the form of CaCO3. The increase of pyrolysis temperature results in the decomposition of part of CaCO3 into CaO. Moreover, the biochars possess relatively higher pHpzc of 11.86—12.04, developed pore structure with a specific surface area of 167.56—223.80 m2/g and abundant surface functional groups, such as C̿    O, C̿    C, C—O, Ca—O, as well. The adsorption of phosphate onto the biochars is in the order of MR-800C< MR-900C< MR-1000C and the adsorption processes can be well fitted by Langmuir model and pseudo-second-order model, indicating that the adsorption of phosphate using the bicohars are dominated by a chemical and homogeneous monolayer adsorption process. The theoretical maximum adsorption capacity of MR-800C, MR-900C and MR-1000C calculated from the Langmuir model are 104.17, 121.95 and 128.21 mg/g. Electrostatic interaction, complexation, and precipitation caused by CaO in the forms of CaHPO4 and Ca5(PO4)3(OH) are responsible for the adsorption of phosphate using the biochars. The results of this study indicate that edible fungus residue can be developed as an inexpensive and efficient adsorption material for phosphorus removal.