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Table of Content
05 February 2020, Volume 71 Issue 2
    Reviews and monographs
    Progress in pore size regulation of metal-organic frameworks
    Ye YUAN, Ming WANG, Yunqi ZHOU, Zhi WANG, Jixiao WANG
    2020, 71(2):  429-450.  doi:10.11949/0438-1157.20190801
    Abstract ( 950 )   HTML ( 78)   PDF (2053KB) ( 987 )  
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    Metal-organic frameworks (MOFs) have attractecl wide attention due to their flexible pore structure, large porosity and specific surface area. Designing and constructing MOFs with suitable pore size distribution to achieve the desired function is related to the application of MOFs in the fields of separation, catalysis, proton conduction, etc. In this paper, the main methods of regulating MOFs pore size are reviewed, including in-situ synthesis, post-synthesis modification, intercalation regulation and auxiliary synthesis. The characteristics and shortcomings of the four regulation methods are summarized, and the future direction of MOFs pore size regulation is also prospected.

    Mechanism of generation and inertial separation of satellite droplets in microchannels
    Taotao FU, Chunying ZHU, Youguang MA
    2020, 71(2):  451-458.  doi:10.11949/0438-1157.20190749
    Abstract ( 517 )   HTML ( 14)   PDF (1516KB) ( 215 )  
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    Due to the nonlinear dynamic characteristics, the liquid-liquid interface rupture process is often accompanied by the generation of satellite droplets, which poses a challenge to the uniformity and precision of droplets-based microfluidic technology. The complex dynamic characteristics of interfacial instability of microfluidics are explained, and the factors influencing the interfacial instability are analyzed. In addition, the phenomenon and mechanism of satellite droplet formation associated with the interfacial instability are revealed. Based on the new concept of the inertial microfluidics, the mechanism of the separation of satellite droplet by using the inertial microfluidics is highlighted. The integration principle of generation-inertial microfluidics separation for the satellite droplet is proposed, as well as the parallelization criterion for the corresponding numbering-up. The implementation of this topic is beneficial for the realization of the target of precision in producing monodisperse droplets with microfluidics technology, laying a solid foundation for the interfacial dynamics and manipulation of microfluidics and complex fluids.

    Advanced process control of pharmaceutical crystallization
    Shaolei ZHAO, Yaoguo WANG, Teng ZHANG, Lina ZHOU, Junbo GONG, Weiwei TANG
    2020, 71(2):  459-474.  doi:10.11949/0438-1157.20190728
    Abstract ( 537 )   HTML ( 23)   PDF (2949KB) ( 295 )  
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    As an important means of solid-liquid separation, the crystallization from solution is a key technology for achieving high value of pharmaceutical products. The precise control of pharmaceutical crystallization process can tailor the solid properties such as polymorph, crystal habit, particle size and particle size distribution, which has a significant effect on the overall efficiency of the solid production process and the quality of the final product. On the basis of the domestic and international research progresses on the topic of pharmaceutical crystallization and process control, this review systemically summarizes the theoretical models, monitoring methods and control strategies of advanced process control of pharmaceutical crystallization. It will mainly focus on the analysis and discussion of the application of process control technologies in product engineering and the trend of development towards complex systems.

    Research progress of antifouling aromatic polyamide reverse osmosis membrane
    Liuyi REN, Song ZHAO, Zhi WANG, Fangzheng YAN, Yingying LIU, Xianglei HAN, Jixiao WANG
    2020, 71(2):  475-486.  doi:10.11949/0438-1157.20190815
    Abstract ( 575 )   HTML ( 24)   PDF (1600KB) ( 383 )  
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    Polyamide reverse osmosis membrane has the aduantages of high seleetive permeability and good chemical stability, and is widely used in the field of water treatment. However, the problems caused by membrane fouling, such as decreased flux and reduced membrane life, have severely restricted its development and application. The development of antifouling reverse osmosis membrane is an important solution to alleviate membrane fouling. In this review, the mechanisms of antifouling reverse osmosis membrane are divided into fouling resistance, fouling release and antibacterial. The progress in inhibiting the membrane fouling by using single antifouling mechanism and integrating multi-mechanisms is introduced briefly. Finally, the prospects of antifouling reverse osmosis membranes are proposed.

    Research progress in effect of gel on crystallization process
    Wencheng ZHANG,Junbo GONG,Weibing DONG,Songgu WU
    2020, 71(2):  487-499.  doi:10.11949/0438-1157.20190754
    Abstract ( 573 )   HTML ( 30)   PDF (1200KB) ( 428 )  
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    Compared with the traditional solution phase crystallization, when the gel is used as a crystallization medium, it can suppress convection and reduce the diffusion of the solute molecules. So a high supersaturation without causing explosive nucleation can be obtained and allowing the solute molecules continuous growth on the crystal surface. Gel is also possible to provide as a template or active nucleation sites by designing a specific gel agent. It makes the crystallization in gel is an effective control means and causes extensive attention. This paper reviews how polymer gel, supramolecular gels and inorganic gels can effectively control the nucleation and growth rate, regulate polymorphism, crystal habit and particle size. The role of microgels in solution phase crystallization and the future development trend of gel phase crystallization are briefly introduced.

    Thermodynamics
    Thermodynamic analysis and kinetics of cyclization of TOME
    Hongxiao LIU, Weizhen SUN, Ling ZHAO
    2020, 71(2):  500-506.  doi:10.11949/0438-1157.20191485
    Abstract ( 404 )   HTML ( 50)   PDF (658KB) ( 276 )  
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    Thermodynamic analysis of the cyclization reaction of tetramethyl-keto-methyl cenoate (TOME) was performed using the group contribution method. The results indicate that under standard pressure, the reaction is endothermic and it is spontaneous when the temperature is greater than 403 K. The Gibbs free energy decrease with the increase of temperature, indicating that the reaction occurs more easily at higher temperatures. The cyclization kinetics of TOME at atmospheric pressure and temperature range of 463—493 K was studied by batch experiments. The kinetic fitting results show that the reaction is a first-order reaction, and the increase of temperature can significantly accelerate the reaction rate. The activation energy of the reaction is estimated to be 143.72 kJ?mol -1 in the studied temperature range.

    Liquid-liquid equilibria for quaternary systems polyoxymethylene dimethyl ethers + water + cyclohexane + sodium chloride
    Chaoxing KOU, Yang LIU, Aiwu ZENG
    2020, 71(2):  507-515.  doi:10.11949/0438-1157.20190758
    Abstract ( 301 )   HTML ( 9)   PDF (1105KB) ( 136 )  
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    Polyoxymethylene dimethyl ethers (DMMn) are low molecular acetal polymer, which were considered as new environmentally friendly diesel additive. The liquid-liquid equilibria (LLE) data of the systems (DMM1—4 + water + cyclohexane + NaCl) at T = 293.15, 308.15 K and pressure p = 101.325 kPa were measured. According to the verification with the Eisen-Joffe equation, the experimental data has good consistency with R2 being approximately unity. Under the salting effect of NaCl, the separation effect of oil-water is improved obviously and the distribution coefficients of DMM1—4 are greater than 1. When the content of NaCl is 10%(mass), the water in the organic phase is negligible. All the experimental LLE data obtained were correlated with the NRTL and the CHEN-NRTL activity coefficient models. The results show that the CHEN-NRTL model is superior to NRTL model for these systems at studied temperature. The experimental data and model parameters obtained from the fitting will provide an effective reference for the process simulation of DMMn product extraction and distillation.

    Fluid dynamics and transport phenomena
    Static pressure distribution in coupled cyclone with built-ingranular bed filter
    Sihong GAO, Yuxue LIU, Yiping FAN, Chunxi LU
    2020, 71(2):  516-525.  doi:10.11949/0438-1157.20191220
    Abstract ( 397 )   HTML ( 13)   PDF (4768KB) ( 150 )  
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    A coupled scheme of cyclone with built-in granular bed filter (C-CGBF), combining the centrifugation and filtration in one device, is designed for dry gas purification in a wide range of application temperature. The static pressure distribution in the C-CGBF is measured under the fixed bed operation regime. The results reveal that there is an apparent relation between the swirling intensity and the inlet gas velocity, according to the static pressure distribution in the annular space of the C-CGBF. The influence of the negative pressure core and the swirl field in the C-CGBF is no longer distinct below the measuring point N8 (H=2175 mm). The static pressure distribution of the device shows a clear asymmetric distribution in the circumferential direction, which also reflects the uneven distribution of the gas phase flow in the device in the circumferential direction.

    Microfluidic droplet coalescence study via microscopic image recognition
    Hao ZHANG, Kai WANG
    2020, 71(2):  526-534.  doi:10.11949/0438-1157.20190738
    Abstract ( 440 )   HTML ( 17)   PDF (3222KB) ( 559 )  
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    Microfluidic technology, as an important approach of manipulating micrometer-scale droplets, has received widespread attention. Microscope recording is the main research method of micro-fluidic process. In the past, key parameters were mainly obtained through manual observation and identification. The low efficiency and small amount of data limited the in-depth understanding of complex micro-fluidic processes. This paper proposes a method to studying microfluidic droplet coalescence based on MATLAB image processing program with background extraction, background subtraction, mask binarization, noise elimination, region filling, shape opening, boundary object removal, interference filtering and etc., which digitized the microscopic videos experimentally collected in a hexagonal microchannel. Furthermore, by identifying the droplet projection area, centroid, eccentricity and other information, the key parameters of microfluidic processes, including droplet speed and liquid film drainage time are also studied.

    Measurement of flow characteristics of settler in mixer-settler
    Sishi YE, Qiao TANG, Yundong WANG
    2020, 71(2):  535-543.  doi:10.11949/0438-1157.20190534
    Abstract ( 527 )   HTML ( 10)   PDF (3934KB) ( 217 )  
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    The mixer-settler is widely used in the rare earth solvent extraction process, and the phase separation process in the settler is very important. The velocity flow field in settler was measured by particle image velocimetry(PIV). Different operational parameters were estimated to study the flow characteristics in settler. These parameters were impeller speed in mixer, volume fraction of organic phase, and different baffle designs. The magnitude of velocity vector in settler had positive correlation with the impeller speed, which could be considered as energy input. The volume fraction of organic phase had little influence on the flow pattern. But it changed the flow direction of the aqueous phase, and strengthened the turbulence in settler. Adding baffle is a promising method to improve the performance of settling. The impact of number and position of baffles in settler on flow structure were surveyed and analyzed. Moreover, the entrainment in aqueous outlet was obtained by conductivity meter, giving clues for comparison and optimization of settler.

    Bubble formation of slurry system and size prediction in microchannel
    Jing LIU, Chunying ZHU, Hao ZHOU, Taotao FU, Youguang MA
    2020, 71(2):  544-551.  doi:10.11949/0438-1157.20190745
    Abstract ( 393 )   HTML ( 5)   PDF (1049KB) ( 169 )  
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    The bubble generation process in liquid-solid slurry system in T-junction microchannel was visually investigated by a high-speed camera. The glycerol-water solutions containing 0.35%(mass) of surfactant (SDS) and different concentrations of glass beads were used as the continuous phase, nitrogen as the dispersed phase. The effects of gas and liquid flow rates, particle concentration and superficial viscosity of slurry on the bubble generation frequency and bubble size under the Taylor flow were studied. The results show that under the Taylor flow regime, when the flow rate of the dispersed phase is constant, the frequency of bubble generation increases but its length decreases with the increase of the flow rate of the continuous phase. As the flow rate of the continuous phase is fixed, both the formation frequency and size of bubble increase with the increase of the flow rate of the dispersed phase. When particle concentration increases, the surface tension decreases of the slurry but its superficial viscosity increases, the bubble generation frequency rises while its size declines. A prediction model for bubble size in the T-type microchannel slurry system is proposed, and the model has good prediction accuracy.

    Dynamics of bubble formation in single step-type microchannel
    Ziwei LIU, Shiyi DAI, Cong DUAN, Zhiwei ZHANG, Zifan PANG, Chunying ZHU, Taotao FU, Youguang MA
    2020, 71(2):  552-565.  doi:10.11949/0438-1157.20190809
    Abstract ( 329 )   HTML ( 11)   PDF (3037KB) ( 177 )  
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    The bubble formation mechanism and size variation in stepped microchannels were studied by using a high-speed camera system. In the experiment, different concentrations of glycerin aqueous solution and nitrogen were used as the liquid phase and the gas phase, respectively. The mechanism of bubble formation process was explored by changing the gas-liquid flow, liquid viscosity and step width. It was observed that the bubble formation process in the step-type microfluidic chips was divided into expansion, pinch-off and energy storage stages. Increasing the gas phase, liquid phase flow rate, and decreasing the liquid phase viscosity could reduce the time consumed in each stage. The consumption time of the pinch-off stage gradually became longer as the viscosity of the liquid phase increases, making it the predominant stage in the bubble formation process. Finally, the prediction formula for the volume of bubbles was constructed based on the bubble formation mechanism in the step-type microfluidic chips.

    Mechanical meaning of criterion of wax oil gel point
    Wenwen LIU, Mengyun LYU, Xueyi LI, Jing HUANG, Lixun CHI, Feng YAN, Jinjun ZHANG
    2020, 71(2):  566-574.  doi:10.11949/0438-1157.20190560
    Abstract ( 343 )   HTML ( 3)   PDF (1217KB) ( 110 )  
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    Freezing point is an important indicator for evaluating the fluidity of oil products (including crude oil) in the petroleum industry, but its mechanical meaning has not been accurately quantified for a long time. In this paper, the stress and deformation of oil samples under the critical conditions in the gel point measurement experiment are quantitatively analyzed and numerically simulated. The study clarified the movement of this critical condition for the first time: It is a bow-shaped unyielding region rotating around a fixed center above the free surface. And the arc angle of the bow-shaped unyielding region is 137.5°. According to this result, the mechanical meaning of the gel point is, in fact, the temperature at which the yield stress of the crude oil reaches a certain critical value. This value is proportional to the oil density and the diameter of the test tube, so the critical yield stress is 14.14 Pa according to the GB 510—1983 and the critical yield stress is 19.99Pa according to the SY/T 0541-2009. The clarified mechanical meaning of the gel point will help to deepen the understanding of oil fluidity and its measurement and application.

    Study on performance of serrated spiral finned tube banks under wet flue gas condition
    Dan LIU, Yi CHENG, Mingyue HU, Qianyun SHENG, Hao ZHOU
    2020, 71(2):  575-583.  doi:10.11949/j.issn.0438-1157.20190568
    Abstract ( 368 )   HTML ( 3)   PDF (1143KB) ( 128 )  
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    The effect of fin arrangements and operating conditions has significance for the flue gas side performance characteristics of finned tube heat exchangers. The effects of fin pitches and water vapor content on the flow resistance and heat transfer characteristics of serrated spiral finned tube banks were investigated by using numerical simulation and experimental method. The results showed that the Nusselt number Nu increases with the increase of fin pitch when fin pitch ranges from 3.63 mm to 8.47 mm. Under different inlet flue gas temperatures, the Nu of 5.08 mm and 8.47 mm are higher than that for 3.63 mm by about 3%—6% and 9%—14%, respectively, while the Euler number Eu decreases with the increase of fin pitch, when fin pitch increases from 3.63 mm to 8.47 mm, Eu decreases by about 30% (for 5.08 mm) and 50% (for 8.47 mm). Appropriate increase of moisture content of flue gas is beneficial to improve heat transfer and resistance characteristics of toothed finned tube bundles.

    Experimental study and CFD simulation of heat transfer in polymerization reactor
    Xiugang WANG, Yufan WU, Luyang GUO, Qinghua LU, Xiaofeng YE, Yucai CAO
    2020, 71(2):  584-593.  doi:10.11949/0438-1157.20190812
    Abstract ( 593 )   HTML ( 14)   PDF (1061KB) ( 273 )  
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    The heat transfer performance of 5 L jacketed polymerizer was studied based on the combination of CFD simulation and heat transfer experiments. The liquid-solid coupled steady-state heat transfer model of the polymerizer was established to obtain the temperature distribution of the metal solid and the fluid in the reactor and the jacket. The CFD simulation results were validated by heat transfer experiments, and the maximum relative error of temperature at each test point was within 1%—5%. The convective heat transfer coefficients of the inner and outer walls of the reactor and the total heat transfer coefficients were obtained by simulation, and the empirical formulas of Nu on the reactor side and the jacket side were correlated. The results show that the variance of the fluid temperature distribution in the reactor is always below 0.002 in the three calculation domains. Among them, the temperature gradients in the solid domain and the heat transfer boundary layer are larger, and the thickness of the boundary layer is about 3.8 mm. In the experiment range, the inlet temperature and reaction exothermic have a significant influence on the reactor temperature, followed by the inlet flow rate, and the stirring speed has the weakest influence. The heat transfer coefficient on the jacket side is much smaller than the heat transfer coefficient on the side of the kettle. Increasing the heat transfer coefficient on the jacket side is the key to improving the heat transfer performance. The heat dissipation on the outer surface of the reactor is proportional to the temperature difference between the inside and outside, and the proportional coefficient is about 3.031 W·K -1.

    Experimental study on heat transfer performance of finned gravity heat pipe
    Yixin MA, Yu JIN, Hu ZHANG, Xian WANG, Guihua TANG
    2020, 71(2):  594-601.  doi:10.11949/0438-1157.20190933
    Abstract ( 434 )   HTML ( 11)   PDF (1447KB) ( 176 )  
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    The heat pipe is a kind of heat transfer element that utilizes phase change heat transfer of working medium, with the advantages of small heat transfer temperature difference, fast thermal response speed, large heat exchange capacity and so on. In order to study the heat transfer performance of finned gravity heat pipe, the heat transfer characteristics of finned heat pipe and flat heat pipe (combination of aluminum-acetone) are investigated experimentally. The dynamic temperature responses of finned heat pipe and flat heat pipe are obtained and compared. The steady state temperature distributions along the length direction of finned heat pipe and flat heat pipe are measured under different heating power. Then the effective thermal conductivity of flat heat pipe is calculated with the temperature difference across the uniform temperature section. Comparison is made to the test results of aluminum. The results show that the gravity heat pipe has faster thermal response and better temperature uniformity along the pipe. With the increment of heating power, the effective thermal conductivity of gravity heat pipe increases at first and then decreases which is almost 84—258 times of aluminum. Compared with flat gravity heat pipe, the finned heat pipe has higher temperature uniformity and heat dissipation ability. Thus the finned gravity heat pipe has wide application prospect in architecture heating, vehicle battery heat dissipation and waste heat utilization.

    Simulation study on influence of supplementary gas on dense-phase pneumatic conveying in horizontal pipe under high pressure
    Haijun ZHOU, Yuanquan XIONG
    2020, 71(2):  602-613.  doi:10.11949/0438-1157.20191275
    Abstract ( 382 )   HTML ( 7)   PDF (2093KB) ( 102 )  
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    In view of the defects and deficiencies of the existing mathematical model, a new three-dimensional (3D) unsteady mathematical model for dense-phase pneumatic conveying in horizontal pipe under high pressure was established based on the Euler-Euler model. This mathematical model introduced the modified kinetic theory of granular flows by Savage’s radial distribution function, the frictional stress model established on Berzi’s frictional pressure stress and the modified three-zone drag model to expound the conveying characteristics of all of three flow regimes: dilute regime, intermediate regime and dense regime. Meanwhile, this mathematical model was applied to explore the effects of supplementary gas on dense-phase pneumatic conveying in horizontal pipe under high pressure. The simulation results show that the pressure drop of horizontal pipe and its variation with the supplementary gas flow rates are predicted accurately, and the predicted solids volume fraction distribution at the cross section of horizontal pipe also basically agrees with the electrical capacitance tomography (ECT) diagram, which confirm the reliability and applicability of this mathematical model. The simulation results show that as the supplementary wind increases, the gas-solid two-phase velocity and turbulent kinetic energy and particle pseudo-temperature increase, and the solid phase volume concentration decreases.

    Power and flow characteristics of flexible-blade Rushton impeller
    Fengling YANG, Cuixun ZHANG, Tenglong SU
    2020, 71(2):  614-625.  doi:10.11949/0438-1157.20190960
    Abstract ( 420 )   HTML ( 7)   PDF (2673KB) ( 201 )  
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    Based on the traditional Rushton impeller, a flexible-blade Rushton impeller was developed. The emphasis was layed on characterization of the power and flow characteristics of this flexible-blade Rushton impeller. The power consumption as well as laminar and turbulent flow fields was numerically investigated by using the computational fluid dynamics (CFD) technique. Besides, they were experimentally validated by employing the dynamic torque sensor and particle image velocimetry (PIV), respectively. The results show that, when the viscosity of the fluid medium is close to that of glycerin, rubber can be used as the material for making flexible blade for the experimental scale stirred vessel. Power consumption of flexible-blade impeller is greater than the rigid impeller when Reynolds number is no more than 100. However, after that value, with the increase of Reynolds number, flexible-blade impeller consumes less power. The fluid-structure interaction (FSI) makes the flexible blades adaptable to the agitated fluid by deformation and accordingly, increases the radial flow capacity of the fluid. Specifically, when the viscosity fluid is low, flexible blade impeller can improve velocity of fluid near the blade and improve circulation capacity of fluid away from the impeller. When the agitated fluid has high viscosity, flexible-blade impeller can increase fluid velocity both near and far from the blade. As far as tailing vortex is concerned, flexible-blade impeller produces small magnitude vortex and is less energy consuming.

    Experimental study on mixing characteristics of flexible-blade Rushton impeller
    Fengling YANG, Cuixun ZHANG, Meiting LI
    2020, 71(2):  626-632.  doi:10.11949/0438-1157.20190961
    Abstract ( 419 )   HTML ( 5)   PDF (851KB) ( 234 )  
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    Rapid mixing is the key factor to efficient operation of many industrial devices involving fluid flow. During the past several decades, extensive contributions have been made to improve the mixing effect and efficiency either by modifying and developing new types of impellers, or by employing and developing new fluid mixing techniques. In this paper, the turbulent mixing characteristics of the flexible-blade Rushton impeller developed by ourselves were experimentally studied by the planar laser induced fluorescence (PLIF) technique. Roddinmin 6G was used as fluorescer. The agitated fluid was water. Result of the calibration experiment shows that the fluorescer luminosities are linear with their concentration, which can be used as a benchmark to measure the mixing time under the same experimental conditions. Diffusion processes of fluorescer show that flexible-blade Rushton impeller has better mixing performance than the standard Rushton impeller. It can improve the mixing uniformity and increase the mixing speed, especially at the initial stage of the mixing process. By comparison with standard Rushton impeller, it was found that mixing time of flexible-blade Rushton impeller is shorter, which is helpful to improve the fluid mixing efficiency. Results of this work lay a solid foundation for the industrial application of this impeller.

    Catalysis, kinetics and reactors
    Inhibition effect of impurities on hydrogenation of corn stover hydrolysate
    Lianxia HOU, Xin REN, Jinghong ZHOU, Xinggui ZHOU
    2020, 71(2):  633-641.  doi:10.11949/0438-1157.20190703
    Abstract ( 340 )   HTML ( 14)   PDF (2202KB) ( 126 )  
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    Ru/AC was used to catalyze the hydrogenation of corm stover with main components of glucose and xylose. The effect of various impurities in the hydrolysate on the catalytic performance was also investigated. The physiochemical properties of deactivated catalysts were extensively characterized by the techniques of N2 physisorption, CO chemisorption, thermogravimetric analysis, field emission scanning electron microscope and pyrolysis-gas chromatography/mass spectrometry. Results demonstrated that lignin and cellulose, among the impurities existed in the hydrolysate, significantly inhibited the hydrogenation while the other impurities such as inorganic salts, furan derivatives, organic acids and aromatic compounds showed obvious inhibitory effect only when high content impurities existed in solution. In addition, the deactivation of Ru/AC catalysts was mainly caused by the deposited impurities such as lignin and cellulase on the catalyst surface, which blocked channels in catalyst particles and covered the active sites, thus resulting in catalyst deactivation.

    Study on catalytic reforming of tar at low temperature to produce hydrogen-rich gas by tire pyrolysis char
    Diancai YANG, Yuhan PAN, Qunxing HUANG, Xuguang JIANG, Fei WANG, Jianhua YAN
    2020, 71(2):  642-650.  doi:10.11949/0438-1157.20190831
    Abstract ( 422 )   HTML ( 8)   PDF (2284KB) ( 162 )  
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    Three pyrolysis carbon catalysts were prepared by pyrolysis, activation, impregnation and calcination using all-steel waste tires as raw materials, namely Raw char, raw pyrolytic activated carbon (AC) and Zn modified activated carbon (Zn/AC). The catalysts were characterized by N2 adsorption/desorption, SEM, EDS, XRD and other characterization methods. It was found that CO2/H2O activation significantly increase the BET specific surface area of the catalyst up to 380 m2·g-1, effectively improving the surface structure of the catalyst. Meanwhile, a large number of ZnO was loaded onto the surface by impregnation method. The catalytic performance of three catalysts was studied in the process of cellulose pyrolysis tar reforming to produce hydrogen. Results indicated that Raw char (600℃) has the best catalytic effect compared with the blank group (500℃). The volume fraction of H2 in gas production increased by 12.4% to 19.3%, followed by 17.8% of the Zn/AC (500℃) group, which achieved high yield of H2 by catalyzing cellulose tar at low temperatures.

    Sequence distribution oriented modeling of ethylene and 1-octene copolymerization process catalyzed by CGC
    Zhou TIAN, Dong JIAO, Jinqiang WANG, Boping LIU
    2020, 71(2):  651-659.  doi:10.11949/0438-1157.20190930
    Abstract ( 406 )   HTML ( 7)   PDF (1381KB) ( 144 )  
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    Constrained geometry catalyst (CGC) is particularly suitable for the preparation of high performance polyolefin elastomer (POE) using ethylene and α-olefin solution polymerization process. Based on the reaction mechanism of ethylene copolymerization with 1-octene catalyzed by CGC, a kinetic model was established and its kinetic parameters were determined. The kinetic model was validated by the consumption rate of ethylene and catalyst activity. Based on the kinetic model and sequence structure oriented copolymerization mechanism, a sequence distribution model of ethylene and 1-octene copolymerization was established. The model can accurately predict the sequence distribution, the content of short branch chains and their changing trend with reaction conditions. The results show that with the increase of 1-octene concentration, the average sequence length of ethylene decreases gradually and linearly, while the average sequence length of 1-octene increases linearly. The model can provide a theoretical reference for regulating the structure of the POE chain from the perspective of polymerization process.

    Preparation of hierarchical nitrogen-rich porous carbon from coal tar for catalytic desulfurization
    Minghui SUN, Jingyuan CHEN, Nan XIAO, Aobo CHEN, Xuzhen WANG, Jieshan QIU
    2020, 71(2):  660-668.  doi:10.11949/0438-1157.20190998
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    Nitrogen-doped porous carbon (NPCs) were prepared by one-step co-carbonization used the anthracene oil fraction form coal taras the carbon source and dopamine as the nitrogen source, based on the induced self-activation of the nano-calcium carbonate template in the carbonization process. The results from element analyses, cryogenic nitrogen adsorption-desorption test, scanning and transmission electron microscopy characterization show that NPCs have a high level of doping nitrogen and the developed micro-mesoporous hierarchical structure. Combined with the evaluation for catalytic oxidation of hydrogen sulfide to elemental sulfur at room temperature, it is found that the doped-nitrogen amount (6.4%-21.3%,mass fraction), the specific surface area, the channel texture and the corresponding desulfurization performance of NPCs can be controlled by changing the dosage of template agent, the feeding ratio of carbon/nitrogen source and the carbonization temperature. And the saturated sulfur capacity of NPCs can be up to 5.8 g H2S/(g cat.) when synthesized under the optimal process conditions.

    Separation engineering
    Simulation of oxygen production via VPSA optimized based on MPC control strategy
    Rui XING, Nan JIANG, Bing LIU, Yaxiong AN, Yayan WANG, Donghui ZHANG
    2020, 71(2):  669-679.  doi:10.11949/0438-1157.20190857
    Abstract ( 402 )   HTML ( 15)   PDF (1354KB) ( 228 )  
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    A rigorous mathematical model was established in the gPROMS software for vacuum PSA oxygen production. Based on the LiLSX adsorbent, a two-stage, eight-step vacuum PSA process was designed to produce O 2 with a purity of 92%. Changes in feed flow rate as well as the decrease of the adsorption property were set as disturbances to make the simulation work more close to reality. Meanwhile, time duration was set to change consistently according to the feedback of O 2 purity in product. The system identification model was then adopted and was used to predict the dynamic behavior of the VPSA process and to develop an MPC controller. Detailed performance under open-loop and closed-loop was listed and compared. The results demonstrated that the model shows an enhanced performance with the presence of random disturbances under closed-loop control. This suggested that the MPC control strategy can be implied to improve the oxygen-production process.

    Effects of solvent on formation of sulfamerazine solvates
    Xia ZHANG, Ling ZHOU, Qiuxiang YIN
    2020, 71(2):  680-687.  doi:10.11949/0438-1157.20190642
    Abstract ( 409 )   HTML ( 5)   PDF (1289KB) ( 149 )  
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    The solvent compounds of sulfamethylpyrimidine were screened in 17 kinds of solvents, such as alcohols, esters and amides, and the sulfamerazine solvates were investigated by powder X-ray diffraction, thermal gravimetric analysis, scanning electron microscopy and Fourier transform infrared spectroscopy. The results showed that sulfamerazine can form four solvates with N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethylsulfoxide respectively. TGA results showed that they all belong to the type of 1∶1 stoichiometric solvates. SEM results indicated that the morphology of the crystals changed significantly after the formation of the solvates, the morphology of the crystal changed from block shape to sheet and rod crystal. FTIR characterization analysis confirmed that the solvent and the solute molecules formed intermolecular hydrogen bonds in the solvates. The physicochemical properties of the used solvents for the screening were analyzed, and the results showed that the corresponding solvates were easy to form in the solvents with strong hydrogen bond acceptor ability. The packing efficiency of molecules in crystals further confirmed that sulfamerazine form hydrogen bond solvates. The changes of molecular packing, structure synthons and hydrogen bond network before and after the formation of solvates were determined according to the single crystal structures of compounds. Sulfamerazine form Ⅱ and its solvates formed a one-dimensional leader hydrogen bond network. For three solvates, in addition to the hydrogen bond network formed between the molecules of sulfamerazine, another hydrogen atom in the amino group of sulfamerazine was bonded to the oxygen atom of the solvent molecule to form an intermolecular N—H…O hydrogen bond.The results showed that the hydrogen bond played a decisive role in the supramolecular self-assembly process between the solute and the solvent, then affected the formation of solvates.

    Process system engineering
    Surrogate model of aromatic isomerization process based on adaptive sampling algorithm
    Yuheng XIE, Zhi LI, Minglei YANG, Wenli DU
    2020, 71(2):  688-697.  doi:10.11949/0438-1157.20190359
    Abstract ( 459 )   HTML ( 8)   PDF (1439KB) ( 236 )  
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    Isomerization is an important part in the production of aromatics. Improving the modeling and optimization efficiency of isomerization is of great significance to industrial production. However, the optimization process using the mechanism model directly takes a long time and the optimization efficiency is low. The surrogate model can effectively approximate the mechanism model and greatly reduce the computation time. The surrogate model sampling method has a great influence on the accuracy of the model. A new adaptive sampling algorithm based on sparsity and nearest neighbor expectation is proposed in this paper, which can balance global search and local search. By solving the optimization problem, we can find new sampling points that reflect the key information of the object function, and then add the new point to the sample set, so that the accuracy of the surrogate model is continuously improved. The results of multiple test functions show that compared with other adaptive sampling algorithms, the algorithm can effectively improve the accuracy and modeling efficiency of the surrogate model. The algorithm is also validated in the aromatic isomerization surrogate model. Compared with other algorithms, our algorithm model error is reduced by more than 5%, and the modeling time is reduced by more than 30%.

    Effect of combustion-supporting air on NOx emission of ethylene cracking furnace
    Guihua HU, Zhencheng YE, Wenli DU
    2020, 71(2):  698-707.  doi:10.11949/0438-1157.20190771
    Abstract ( 338 )   HTML ( 5)   PDF (1664KB) ( 138 )  
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    Coupled simulation and optimization of complex physical and chemical processes in ethylene cracking furnace can meet the demand for design and operation of high efficiency, low pollution and low cost in ethylene plant. Therefore, it has great significance for improving the competitiveness of the ethylene industry. Aiming at the disadvantage of simple combustion mechanism that it is difficult to accurately predict the distribution of NOx concentration produced by furnace combustion, are reduced GRI-Mesh 3.0 mechanism combined with eddy dissipation concept (EDC) model for cracking furnace was proposed. The combustion process of Sandia Flame D was simulated and the reliability of the coupled model was verified. Based on the established combustion model, the effect of combustion-supporting air on reducing NO emission of cracking furnace was studied. The results show that the best effect of reducing NO is when the air preheating temperature is 300—600 K and the excess air coefficient is 1.1 when the thermal efficiency of the cracking furnace is satisfied.

    Development of simulation strategy based on molecular weight distribution in polyester production process
    Cheng CHANG, Liangfang FENG, Xueping GU, Xi CHEN, Cailiang ZHANG
    2020, 71(2):  708-714.  doi:10.11949/0438-1157.20190499
    Abstract ( 476 )   HTML ( 10)   PDF (938KB) ( 406 )  
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    A polyester industrial production process simulation method targeting molecular weight distribution was proposed. The general process simulation software Aspen Plus could not calculate the molecular weight distribution index and molecular weight distribution curve under the step-growth reaction mechanism.To overcome this disadvantage, an external interface program was developed to calculate MWD and PDI with major data from the *.bkp/*.apw file running in the background. This strategy was validated by the pre-condensation process simulation of PBT industrial plant. The pre-condensation process model framework with rigorous process mechanism including phase equilibrium and reaction kinetics was established. The sensitivity analysis of the kinetic parameters to molecular weight and concentration of end carboxyl group was applied for the kinetic parameters tuning. Furthermore, the model was validated by process data and analysis data. The calculation errors of weight average molecular weight and PDI were 4.2% and 5.6%. The simulation strategy can be applied for molecular weight distribution in polyester industrial process.

    Surface and interface engineering
    Effect of floc surface morphology on membrane pollution prediction
    Cheng FANG, Sheng YANG, Yun WU, Hongwei ZHANG, Jie WANG, Lutian WANG, Songze HAO
    2020, 71(2):  715-723.  doi:10.11949/0438-1157.20190828
    Abstract ( 345 )   HTML ( 4)   PDF (1266KB) ( 242 )  
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    Existing prediction analysis of membrane fouling during coagulation-membrane filtration generally uses XDLVO theory to calculate the action energy of smooth interfaces, but the surface morphology of coagulated flocs will have a greater impact on the prediction results. In this study, a sinusoidal sphere model was used to simulate the surface of rough humic acid (HA) flocs. The interfacial interaction between coagulated flocs with different roughness and polyvinylidene fluoride (PVDF) membranes was quantitatively simulated by surface element integration (SEI) combined with XDLVO theory and compound Simpson rule. The interaction energies of smooth interfaces simulated by XDLVO theory are compared. The experimental results show that the model is suitable for the simulation of floc interfacial interaction energy in coagulation-membrane filtration system, and in the simulation process, the difference in interfacial interaction energy between 1—2 orders of magnitude due to the different roughness, and the fitting degree of rough flocs is better than that of completely smooth flocs and membrane fouling trend. High, that is, the introduction of floc surface morphology has a higher confidence in characterizing the trend of membrane fouling by the interaction between floc and membrane interface.

    Biochemical engineering and technology
    Investigation on migration process of oxygen and carbon monoxide in human hemoglobin
    Xue PENG, Chenlin LU, Diannan LU
    2020, 71(2):  724-735.  doi:10.11949/0438-1157.20190862
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    To reveal the relationship between CO and O2 competitive binding to the heme site of human hemoglobin (HbA) and its relationship with HbA structural transition, we used all-atom molecular dynamics simulations (MD) combined with Markov state models (MSMs) to study the migration of O2 and CO molecules from the aqueous solution into the heme site of α and β chains of HbA. Molecular dynamics simulations revealed the steady binding sites and instantaneous binding sites to O2 and CO of α and β chains of HbA, migration pathways and structural changes of HbA. It is shown that all discrete Xe binding sites and O2 migration pathways observed in experiments can be reproduced by molecular dynamics simulations. Molecular dynamics simulations revealed structural changes in the homeostatic binding sites and transient binding sites, migration channels, and alpha chains of O2 and CO binding αand β chains. Above results demonstrate the importance of instantaneous migration pathways formed due to the flexibility of HbA for gas migration. In addition, MSMs and transition path theory(TPT) were used to investigate the conformational transitions among different microstates in α chain, which provides the mechanism between gases migration behavior and HbA conformational transitions.

    Energy and environmental engineering
    Effect of coal layer thickness on secondary reaction during its infrared rapid pyrolysis
    Jinfeng MA, Xi ZENG, Fang WANG, Guojun KANG, Rongcheng WU, Guangwen XU
    2020, 71(2):  736-745.  doi:10.11949/0438-1157.20191264
    Abstract ( 273 )   HTML ( 6)   PDF (1351KB) ( 125 )  
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    Aiming at the problems of small sample addition amount (mg level) and difficult tar collection in the rapid pyrolysis of coal, this study uses the tablet method to prepare coal seams with a thin thickness (mm level) and uses an infrared heating device to investigate the large addition amount (g level), fast pyrolysis characteristics of thin coal seams. Compared to the stacking method of coals sample, in the experiment of thin coal layer, the effect of coal layer thickness on the secondary reaction was significantly inhibited, and the tar yield increased sharply, reaching 9.96% at 1000°C and 1.5 times of the Gray-King analysis. Furthermore, a synchronous increase in pyrolysis gas and tar was realized. The simulated distillation analysis shows that asphaltene was the main compound in the tar sample produced from the coal pyrolysis in the stacked state, while for the tar from the pyrolysis of tableting coal layer, it contained a large amount of light oil, phenol oil, naphthalene oil, washing oil and anthracene oil. From the GC-MS and FTIR analysis, it can be seen that with the decrease of thickness and number of the tableting layer, the kind of tar compounds and their corresponding contents increased, and the absorption of aromatic hydrocarbons and oxygen-containing functional groups was strengthened. All of these further verified the influence of coal layer on tar yield and quality in coal fast pyrolysis, and also revealed the primary reaction characteristics of high-temperature coal pyrolysis under the full suppression of secondary reaction.

    Preparation of O3 by O2 DBD microplasma
    Baowei WANG, Huijuan SU, Shumei YAO
    2020, 71(2):  746-754.  doi:10.11949/0438-1157.20191068
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    Dielectric barrier discharge (DBD) is considered to be the most efficient method for industrial production of ozone (O3). O3 was prepared by using DBD microplasma discharge with O2 as the raw material gas. The effects of the discharge interval, discharge length, discharge power and residence time on the production of O3 were studied. In addition, the modulated pulse was added to the sinusoidal AC power supply, and studied the effect of pulse duty cycle and modulation frequency. The results showed that the concentration of O3 decreased with the increase of discharge length, while the energy efficiency increased first and then decreased. At the discharge length of 0.75 mm, both were in a higher range. Excessive or too small discharge length was not conducive to the formation of O3. The suitable discharge length was 80-90 mm. With the increase of discharge power, the concentration of O3 rose first and then decreased, and the energy efficiency decreased almost linearly.The residence time of O2 was positively correlated with the concentration of O3, and negatively correlated with energy efficiency. The optimal discharge power was (6.7 ± 0.2) W, and the appropriate residence time was 1.0—1.4 s. It was found that the superposition of pulse modulation power supply on the basis of common sinusoidal alternating current is beneficial to the generation of O3, and the energy efficiency decreased with the increase of the duty cycle, increased with the enhancement of the modulation frequency. The appropriate duty cycle and modulation frequency was 60%, 800 Hz, respectively.

    Co-combustion of oil sludge char and brown coal: characteristics and kinetics
    Hongyan WEN, Yuming ZHANG, Dexin JI, Guangyi ZHANG
    2020, 71(2):  755-765.  doi:10.11949/0438-1157.20190680
    Abstract ( 526 )   HTML ( 3)   PDF (2313KB) ( 186 )  
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    The combustion characteristics of sludge coke, lignite and their mixtures at different heating rates were studied by thermogravimetric analysis. Their combustion kinetic parameters were calculated by Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO) and Friedman (FR) methods. The results indicated that the combustion of the oil sludge char was mainly a fixed carbon combustion process, while that of the brown coal was characterized by a process of continuous combustion with a large amount of volatile and little fixed carbon. Compared with the combustion of the oil sludge char, the brown coal had a better combustion performance and its average activation energy was much lower. There was a significant positively synergistic interaction in the co-combustion process of the oil sludge char and the brown coal. When the proportion of brown coal in the blends reached up to 75%, the positively synergistic interaction effect was the strongest. The FR method better reflected the trend of the process, but its generated results were less accurate compared to that from KAS and FWO models. By comparing the theoretical and experimental values of the co-combustion kinetic parameters of the sludge char and the brown coal, it was found that application of thermogravimetric analysis to predict the combustion properties of the mixed fuel exhibited a high reliability, which can thus play an importantly guiding role in the application of the co-combustion technology of the oil sludge char and the brown coal.

    Domestication and identification of cold-resistant bacteria in SBBR reactor
    Han WU, Ying CHEN, Min LIU, Shuying WANG, Wei ZHANG
    2020, 71(2):  766-776.  doi:10.11949/0438-1157.20190731
    Abstract ( 406 )   HTML ( 6)   PDF (1179KB) ( 131 )  
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    Taking simulated domestic sewage as the treatment object, three different fillers are biofilm carriers, and three SBBRs of A, B and C are operated, and the biofilm of low temperature sewage is domesticated and treated by gradual cooling (25, 20, 15, 10, 6 and 5℃). During the 251 operating cycles, the COD effluent concentration of the three reactors was less than 50 mg/L. The ammonium removal efficiency of the B reactor was better than A and C. At 5℃, the ammonium concentration of effluent of A, B and C were 14.1, 3.79 and 14.1 mg/L, respectively. The results of high-throughput sequencing showed that the dominant microbial species in SBBR were mainly those can degrade organic matter at 5℃. Psychrophilic nitrifying bacteria (Candidatus Nitrotoga) were found only in B reactor. The abundance of other common nitrifying bacteria in the B reactor is higher than which in the A and C reactors. The nitrogen-fixing bacteria (Elstera), which adverse to remove ammonium,has the minimal distribution in the B reactor. These results can explain the difference of the pollutant removal of the three reactors from point of view of microorganism, which shows that B reactor has significant advantages in treating low temperature wastewater.

    Effect of cyclic adsorption performance of calcium-based sorbent on enhanced biomass gasification for hydrogen production
    Yang LI, Yang ZHANG, Xuanlong CHEN, Xun GONG
    2020, 71(2):  777-787.  doi:10.11949/0438-1157.20190782
    Abstract ( 372 )   HTML ( 3)   PDF (1620KB) ( 212 )  
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    The CO2 adsorption performance of the calcium-based adsorbent cycle plays an important role in continuous and efficient hydrogen production from enhanced biomass gasification. Six kinds of synthetic adsorbent powders (CaMg75, CaAl75, CaLa75, CaY75, CaNd75 and CaSi75) and six kinds of synthetic adsorbent particles (CaMg75p, CaAl75p, CaLa75p, CaY75p, CaNd75p and CaSi75p) were prepared by adding different inert carriers into CaO particles and extrusion-spheronization process , wherein the mass fraction of CaO were 75%. Meanwhile, calcium oxide powder (CaO) obtained by calcination of calcium carbonate and its corresponding calcium oxide particles (CaOp) were prepared. The above seven kinds of powders were tested by X-ray diffraction (XRD). Seven kinds of adsorbent powders and seven kinds of particles were tested by specific surface area and pore size tester. Thermogravimetric analysis (TG) was used to test the carbonation-calcination cycle of the above seven adsorbent powders and their corresponding adsorbent particles. Based on the thermogravimetric test results, the enhanced biomass gasification experiment for hydrogen production under the condition of adsorbent recycling was carried out with smoke bars as the original biomass. The results show that there are MgO, Ca3Al2O6, La2O3, Y2O3, Nd2O3 and Ca2SiO4 inert carriers in the powders of the six synthetic adsorbents. The inert carriers can not react with CO2, but also disperse CaO grains. The thermal stability is good. The sintering of the adsorbents can be delayed and the adsorptive performance of the adsorbents can be improved. They have good thermal stability and they can delay the sintering of adsorbent to improve the adsorptive performance of adsorbent. The extrusion-spheronization process destroys the original pore structure of the adsorbent, and the specific surface area of spherical particles of synthetic CaO adsorbent is lower than that of the same kind of powder, which leads to the decrease of adsorptive performance of adsorbent particles. With the increase of thermogravimetric cycles, the adsorption capacity of CO2 and conversion rate of CaO of adsorbents CaAl75p, CaY75p and CaSi75p in 25 cycles decreased gradually. However, the adsorption capacity of CO2 is always above 0.15 g CO2/g biomass, and the conversion rate of CaO is always above 30% respectively. Both data are much higher than that of CaOp, indicating that three adsorbents, CaSi75p, CaAl75p and CaY75p, have better cycling performance. In the enhanced biomass gasification hydrogen production cycle experiment, the volume fraction of H2 increases significantly after adding the above three adsorbent particles in five cycles, and the concentration of H2 increases from 46.2% to more than 60%. Addition of CaAl75p, CaY75p and CaSi75p could significantly increase concentration and yield of H2 in biomass gasification synthesis gas. The composition and yield of the gas change little during the five cycles, indicating that three kinds of adsorbents have good cyclic adsorption capacity and stability.

    Utilization of Fe-Zn-based waste desulfurizer to produce Fe-C materials for removing COD from waste water
    Xiaoling ZHANG, Fengqin YU, Lin HUANGFU, Chao WANG, Changming LI, Shiqiu GAO, Jian YU
    2020, 71(2):  788-798.  doi:10.11949/0438-1157.20190832
    Abstract ( 340 )   HTML ( 10)   PDF (2083KB) ( 124 )  
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    The Fe-Zn-based waste desulfurizer, coal and Na 2CO 3 were used as raw materials to carry out high-temperature carbon thermal reduction reaction, and iron-carbon materials were prepared to realize the separation of Zn and S. It is expected to realize the comprehensive utilization of waste desulfurizer. The effect of different preparation parameters ( e. g., ratios, temperature, time) were investigated to improve the removal efficiency of Zn/S and obtain high-quality Fe-C materials. The best results can be achieved with separation efficiency of Zn and S above 95% with the ratio of 1/1/1.5 for coal/waste desulfurizer/Na 2CO 3 at 900℃ for 2 h. Moreover, the specific surface area of the prepared Fe-C material can reach as high as 193.6 m 2/g with the mesoporous volume of 0.028 cm 3/g. In addition, the micro-electrolysis-Fenton test showed the removal efficiency of COD for the as-prepared Fe-C material are 41.78% and 73.56% without/with H 2O 2 (H 2O 2=COD=1500 mg/L), respectively, which is much better than commercial Fe-C material with the removal efficiency of 8.43% and 48.43% on the same condition. These results demonstrate the heat treatment process of waste desulfurizer with Buliangou-coal and Na 2CO 3 may be an effective way for its resource utilization to separate Zn and S as well as produce Fe-C material.

    Molecular modeling of oxidation mechanism and organic nitrogen conversion in coal particle combustion: a case study on HSW coal of Ningdong
    Huifang YANG, Hailian GUAN, Ping LI, Ying XIA, Feng WANG, Wenjing XU, Hongcun BAI, Qingjie GUO
    2020, 71(2):  799-810.  doi:10.11949/0438-1157.20190657
    Abstract ( 482 )   HTML ( 9)   PDF (3071KB) ( 168 )  
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    Coal combustion is one of the important ways for effective utilization of coal. Identifying the mechanism of coal combustion from the atomic and molecular level, systematically grasping the influence of reaction conditions, revealing the path of migration and transformation of nitrogenous pollutants is of great significance for the efficient and clean utilization of coal. Based on the molecular structure model of Ningdong Hongshiwan coal constructed in the previous period, the combustion reaction simulation of coal macromolecular structure aggregation model was carried out by reactive molecular dynamics simulation method. The effects of chemical equivalent and reaction temperature were investigated to explore the coal structural evolution, combustion reactants and products in the combustion process. The organic nitrogen conversion pathway was also revealed. It was found that the fracture change of the coal structure was obvious with the continuous reaction. The results of coal combustion at different stoichiometric ratio and temperature indicated that the larger the stoichiometric ratio and also the higher the combustion temperature, the faster the O2 molecule consumption rate and the more CO2 were produced. From the analysis of nitrogen-containing molecules in the coal combustion process, it was found that HCN was an important nitrogen-containing intermediate, and NO and NO2 were the main nitrogen-containing products. Besides, the transformation pathway of organic nitrogen was obtained in coal combustion process, and the evolution of HCN, NO and NO2 were established.

    Pyrolysis characteristics and kinetics analysis of Qinghua coal, Ningxia based on chemical bonding characteristics of macerals
    Ning MAO, Qiang WANG, Yan YANG, Dunxin XU, Wei FENG, Jinpeng ZHANG, Hongcun BAI, Qingjie GUO
    2020, 71(2):  811-820.  doi:10.11949/0438-1157.20191156
    Abstract ( 402 )   HTML ( 6)   PDF (1347KB) ( 176 )  
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    X-Ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were used to characterize the functional group types, surface structure element valence distribution and chemical bond occurrence characteristics of Ningxia Ningdong Qinghua coal. Then the mass loss behavior of vitrinite and inertinite of Qinghua coal at different pyrolysis temperatures and the changes of key gas components were investigated by means of the thermogravimetry coupled with mass spectrometry (TG-MS). Furthermore, the differences of pyrolysis behavior between vitrinite and inertinite were discussed from the point of view of chemical bonding breaking and pyrolysis kinetics based on Coats-Redfern model. The results show that the pyrolysis weightlessness peaks of Qinghua coal macerals at different temperatures are in good agreement with the information of corresponding chemical bond breaking. The TG curves of different macerals of Qinghua coal are similar, but the mass loss rate of vitrinite is always higher than that of inertinite at the same pyrolysis temperature. In the fast pyrolysis stage, vitrinite exhibits greater mass loss rate and also maximum mass loss rate than inertinite. The main reason is that the relative content of aliphatic functional groups in vitrinite is higher, and more Cal—Cal bonds would break down during the fast pyrolysis stage. The order of activation energy and frequency factor of three main pyrolysis stages of Qinghua coal macerals at different pyrolysis temperatures is: fast pyrolysis stage > fast polycondensation stage > slow pyrolysis stage. In the fast pyrolysis stage, the average activation energies of vitrinite and inertinite are both about 75 kJ/mol, but the frequency factor of vitrinite is higher.

    Material science and engineering, nanotechnology
    Numerical simulation of lithium-ion battery with LiFePO4 as cathode material: effect of particle size
    Yu XU, Yiqin CHEN, Jinghong ZHOU, Zhijun SUI, Xinggui ZHOU
    2020, 71(2):  821-830.  doi:10.11949/0438-1157.20191199
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    When LiFePO4 (LFP) is used as a cathode material, the lithium-ion battery has high safety and long cycle life. It is currently the most widely used cathode material, but its battery rate performance is poor. One of the effective means to improve the rate performance of lithium-ion battery is to use LFP material of nanometer size. However, the mechanism of the LFP particle of nano size affecting the eletrochemical process during the charge and discharge of lithium-ion battery still remain unclear. In this work, a quasi-two-dimensional model of lithium-ion battery was established to simulate the discharge process. The influence of LFP particle size on the rate performance of lithium-ion battery was quantitatively studied. The diffusion rate and electrochemical reaction rate at solid-liquid interface were quantitatively analyzed. The results indicate that the resistance in solid phase is the key factor limiting the performance of lithium-ion battery. In the case of small particle LFP as electrode material, the diffusion path of lithium metal within the particles was shortened and the interface between electrode material and electrolyte increased, thus the electrochemical reaction rate was faster, presenting better rate performance. While in the case of large particle LFP as electrode material, the low solid phase diffusion rate of LFP material resulted in low electrochemical reaction rate and thus deteriorate rate performance of the lithium-ion battery. Size reduction of LFP could effectively shorten the migration path of the metal lithium in the electrode material and reduce solid phase diffusion resistance, therefore enhance the rate performance of the lithium-ion battery.

    Interaction between proteins and roughness-regulated TiO2 nanotube arrays
    Na WU, Yihui DONG, Xiaoyan JI, Chang an HUANGFU, Xiaohua LU
    2020, 71(2):  831-842.  doi:10.11949/0438-1157.20190954
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    A series of TiO2 nanotube arrays (TNAs) with different diameters and roughness were prepared by electrochemical anodization method by changing the fluoride ion concentration [0.4%,0.3%,0.2%(mass)] and applied voltage(15,25,35,45 V). The scanning electron microscopy (FESEM) and atomic force microscopy (AFM) results showed that the wall thickness of the prepared TNAs increased and the roughness decreased with the decrease of fluoride ion concentration in the electrolyte. The effects of surface roughness and diameter on the surface mechanical properties of TNAs and the interaction of Cytochrome C (Cyt C) were studied by AFM characterization. The results show that the adhesion is proportional to the contact area. With the increase of the diameter of the TNAs, the wall thickness decreases, the effective contact area between TNAs and Cyt C increases first and then decreases,and the forces of Cyt C with TNAs also increase first and then decrease. The roughness decreases when the diameter was fixed, the effective area of TNAs increases, and the interaction force also increases. It can be seen that the surface roughness and effective contact area of TNAs can be effectively controlled by changing the fluoride ion concentration of the electrolyte, which is further beneficial to promoting interaction with protein molecules.

    Preparation of PDMS/ZSM-5 membranes and pervaporation separation of n-butyl acetate and ethyl acetate from aqueous media
    Yanqing LIU, Tingting HU, Luoyi LU, Wei WANG, Yun ZOU, Zhangfa TONG
    2020, 71(2):  843-853.  doi:10.11949/0438-1157.20190559
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    To explore a new type of pervaporation membrane material suitable for the separation of n-butyl acetate and ethyl acetate from aqueous media, the zeolite ZSM-5 was used to modify the polydimethylsiloxane (PDMS) material with polyvinylidene fluoride (PVDF) as the support layer. The PDMS/ZSM-5/PVDF hybrid membrane was prepared by coating for pervaporation of n-butyl acetate and ethyl acetate from aqueous solution. SEM, contact angle measuring instrument, FTIR, TGA and XRD were used to characterize the physical and chemical properties of the membrane material, and the swelling behavior and pervaporation performance of the membrane material were investigated. The results indicated that ZSM-5 dispersed uniformly in the membrane material and no chemical change occurred between ZSM-5 and PDMS polymer chain. The hydrophobic and thermal stability properties of the filled film were obviously improved by incorporation of ZSM-5. With the increase of ZSM-5 content, the swelling degree and diffusion rate of the membrane in n-butyl acetate and ethyl acetate solvents increased. The permeation flux increased while the separation factor increased firstly and then decreased with the rise of the feed concentration and temperature. With the increase of ZSM-5 content in the PDMS/ZSM-5/PVDF hybrid membrane, the total flux increased, while the separation factor increased first and then decreased. The separation factor reached a maximum when ZSM-5 filling content was 10%(mass). For n-butyl acetate/water systems, the permeate flux and maximum separation factor are 319 g·m -2·h -1 and 131. For ethyl acetate/water systems, the permeate flux and maximum separation factor are 1385 g·m -2·h -1 and 121.

    Connection between kinetics and particle formation process of vinyl chloride SET-DT suspension polymerizations
    Jianpeng HAN,Yongzhong BAO
    2020, 71(2):  854-863.  doi:10.11949/0438-1157.20190508
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    Single electron transfer-degenerative chain transfer (SET-DT) living radical suspension polymerizations of vinyl chloride (VC) were conducted using CHI 3 as an initiator, NaS 2O 4/NaHCO 3 as catalysts, polyvinyl alcohol (PVA) and/or methylcellulose (MC) as dispersant(s). Effects of dispersant type and concentration, agitation rate on VC polymerization rate and droplet/particle size distribution were investigated by using online gas chromatography and laser particle size analyzer. It was found that the polymerization rate of VC was greatest when MC was used as the dispersant, while the polymerization rate was lowest when PVA was used as the dispersant at a same agitation rate. The polymerization rate was increased with the increase of dispersant concentration when the dispersant type was fixed. In VC SET-DT suspension polymerization, the diffusion of free-radicals formed by decomposition of Na 2S 2O 4in the water phase into monomer droplets was related to the droplet size distribution and membrane structure of PVC particles. Thus, the polymerization kinetics was influenced by the particle formation process. Although all polymerizations conducted at different conditions exhibited the liquid-liquid dispersion, droplet coalescence and particle identification stages, the average sizes of droplets or particles corresponding to different stages were varied as dispersant and agitation rate varied. The use of MC as a dispersant results in fewer PVC resin films, which is conducive to the diffusion of free radicals generated in the water phase to the monomer phase and a large polymerization rate.

    Thermal endurance of binary eutectic phase change material D-dulcitol/inositol for medium temperature latent heat storage
    Sheng YANG, Xuefeng SHAO, Liwu FAN
    2020, 71(2):  864-870.  doi:10.11949/0438-1157.20190956
    Abstract ( 393 )   HTML ( 8)   PDF (2321KB) ( 189 )  
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    Thermal endurance of phase change materials is of significance in real-world latent heat storage. The binary eutectic mixtures of D-dulcitol/inositol for medium temperature latent heat storage was prepared by mixing their melts at given molar ratio and then cooled to be solidified in the present study. The mixture samples were heated using a vacuum tube furnace at four temperatures (463, 473, 483 and 493 K), and for each temperature point, the heating was lasted for 5, 10, 15 and 20 h. The latent heat of fusion of the mixtures were measured by a differential scanning calorimetry. The thermal degradation characteristics of the mixtures were analyzed using a constant temperature kinetic model based on the change of latent heat of fusion. In addition, the thermal endurance of the mixture was improved by adding the antioxidant 1010 (at 1.0%(mass)). The results showed that after heating at 463 K for 20 h, the enthalpy of the eutectic sugar alcohol decreased by 24.9%; after adding the antioxidant, its enthalpy decreased by only 8.25%. It was determined that the thermal degradation duration of the mixture was 154 h when its latent heat of fusion decreased a half at 463 K. By contrast, the duration increased about 4 times after adding the antioxidant. With temperature increasing to 473, 483 and 493 K, the thermal degradation durations of the mixture increased about 2.6, 1.6, and 1.1 times, and their thermal degradation rates decreased by 62.65%, 40.42%, 6.51%, respectively. The results showed that using the antioxidant 1010 can improve the thermal endurance of the mixture sugar alcohol.

    Effect of hard segment content on microcellular foaming process of thermoplastic polyether ester elastomer using supercritical CO 2 as blowing agent
    Rui JIANG, Dongdong HU, Tao LIU, Ling ZHAO
    2020, 71(2):  871-878.  doi:10.11949/0438-1157.20191196
    Abstract ( 651 )   HTML ( 10)   PDF (2601KB) ( 317 )  
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    Solid-state foaming process of TPEE composed of poly(tetra methylene glycol) (PTMG)“soft”blocks and poly(butylene terephthalate) (PBT)“hard”blocks using supercritical CO 2 (scCO 2) as the blowing agent was investigated. Plastic foams with average cell diameter of 2-17 μm and expansion ratio of 1-6 folds were prepared from TPEE. Three kinds of TPEE copolymers with different block ratio were used to investigate the influence of hard segment content on foaming behavior. The CO 2 dissolved into soft segments (PTMG) and hard segments (PBT) were carefully characterized by sorption process, meanwhile the gas diffusion coefficient was fitted from the Fick s diffusion law. The results show that the solubility and diffusivity of CO 2 in soft segments (PTMG) is significantly higher than that in hard segments (PBT). When the hard segment content rose from 29% to 65%, the melting point rose from 162.6℃ to 201.9℃ with a crystallinity rising from 20% to 40%. TPEE copolymers were foamed in a high-pressure chamber by using scCO 2. The effect of temperature and block ratio on the cell morphology was investigated. It was found that the content of hard segment had great influence on the solid-state foaming process. With higher hard segment content, the processing window was broadened and shifted to higher temperature.

    Preparation and adsorption performance of titanium based lithium ion sieve improved by LiNO 3
    Jiaming GUO, Mingyan LIU, Qiang WU, Yongli MA
    2020, 71(2):  879-888.  doi:10.11949/0438-1157.20191484
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    Titanium based lithium ion sieves have excellent lithium adsorption capacity and stability, and the improvement studies on its preparation and character are of great importance. A mixture of LiNO 3 and Li 2CO 3was used as the lithium source to synthesize laminar Li 2TiO 3 through the solid state reaction at 500℃, and lithium ion sieves were prepared after being put it in 0.2 mol·L -1 hydrochloric acid pickling solution for 24 h. Physicochemical properties of the ion sieves were characterized by X-ray diffraction (XRD), scanning electronmicroscopy (SEM), particle size distribution analysis and nitrogen adsorption-desorption measurements. Adsorption, regeneration properties of the ion sieves and adsorption mechanism were investigated. It is revealed that adsorption process conforms to the monomolecular and chemical adsorption. Furthermore, micro-scale particles with higher pore volume and higher specific area were obtained after modification. Adsorption capacity and pseudo-second-order kinetic constant of 25.01 mg·g -1 and 0.2762 g·(mg·h) -1, respectively, were obtained by pouring the lithium ion sieves in the solution of 70 mg·L -1 for 24 h. Hence, the increase in adsorption rate of 54.56% was observed. The removal rate of Li + (99.77%) can be reached using this ion sieves in the solution of concentration of 11.6 mg·L -1.

    Preparation of composite nanofiltration membrane with β-cyclodextrin as aqueous monomer and dye rejection properties
    Lixue LIU, Shaofeng ZHANG, Changwei ZHAO, Erhu BAOLE, Ling YU, Jun WANG
    2020, 71(2):  889-898.  doi:10.11949/0438-1157.20190919
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    Using β-cyclodextrin (β-CD) as the aqueous phase monomer and trimesyl chloride (TMC) as the oil phase monomer, a high-throughput β-CD/TMC composite nanofiltration membrane was prepared by the interfacial polymerization method. The pore model and electrostatic repulsion-steric hindrance model were used to explore the mechanism of dye separation. Infrared spectrometer, field emission electron microscope, contact angle measuring instrument and Zeta potential analyzer were used for analysis and characterization. The results showed that the peak of ester group which is generated by IP appeared in the FT-IR. Zeta potential analysis indicated that the surface of composite NF membrane was negatively charged. SEM images structure and contact angle values showed that when the concentration of β-CD was 4.0%, a lot of folds appeared on the membrane surface and the membrane was more hydrophilic. At the pressure of 0.2 MPa, the pure water flux can reach 207.81 L·m -2·h -1, the rejection of the Congo red, the Bengal rose, the reactive brilliant red X-3B and the methylene blue was 100%, 99.05%, 97.65% and 32.92%, respectively. The 6 h operation can effectively reject the dye reactive brilliant red X-3B with rejection higher than 97% flux goes down and then keeps the tendency of stable.