Table of Content
05 March 2019, Volume 70 Issue 3
Reviews and monographs
Applications and perspectives of NH3 separation and recovery with ionic liquids
Shaojuan ZENG, Dawei SHANG, Min YU, Hao CHEN, Haifeng DONG, Xiangping ZHANG
2019, 70(3):  791-800.  doi:10.11949/j.issn.0438-1157.20181067
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As one of the typical alkaline and poisonous pollutants, ammonia (NH3) is widely considered as a primary factor for the formation of fog and haze, which has caused a wide range of environmental problems and serious harm to human health. The traditional technologies for NH3 separation, like water scrubbing and acid scrubbing, have been applied in industries. However, some inherent drawbacks, such as severe corrosion, heavy pollution, high energy consumption, and hard to recover NH3 resources come with yet. Ionic liquids (ILs) provide a novel way for efficient and energy-saving separation of NH3 owing to their extremely low vapour pressure, good chemical/thermal stability and tuneable acidity and alkalinity. In this review, the recent advances on conventional ILs, functionalized ILs and IL-based solvents and materials for NH3 absorption/adsorption have been overviewed. The NH3 absorption capacities in different ILs were summarized and the effect of cations, anions and functional groups on NH3 absorption and the mechanisms have been discussed, and the research and development trend of this direction are discussed.

Electrochemical reactions and reactors for biomass valorisation
Feng LUO, Li LIN, Zhenchen LI, Wenyu LI, Xianlin CHEN, Sha SHA, Tao LUO
2019, 70(3):  801-816.  doi:10.11949/j.issn.0438-1157.20180965
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Electrochemical conversion of biomass to fuel and high value-added chemicals is an important direction for the chemical industry, and this could also facilitate the sustainable development of society. With the increasing energy supply from renewable sources, and currently the limited installation of large-scale energy storage and conversion systems, electrochemical conversion of biomass together with the efficient utilization of renewable energy is drawing attention from both academia and industry. This perspective describes recent development in this field, and focuses on key reactions and related electrochemical reactor design. The electrochemical conversion of platform molecules derived from biomass has made some progress, but the electrochemical conversion from biomass to platform molecules faces greater challenges. Selectivity improvement in these electrocatalytic conversion relies on suitable electrode material and electrocatalysts. Reaction-separation coupled electrochemical reactors can increase product yield, especially for direct electrocatalytic conversion of biomass.

Thermodynamics
Solubility and ternary phase diagram of azithromycin dihydrate in water-organic solvent
Xiaoxue CAO, Shaochang JI, Wenjie KUANG, Anping LIAO, Ping LAN, Jinyan ZHANG
2019, 70(3):  817-829.  doi:10.11949/j.issn.0438-1157.20180910
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The solubility of azithromycinin water+isopropanol and propanone+water solvent mixtures were measured at temperatures from 293.15 K to 323.15 K by an analytical method. The water activity of transformation at 293.15, 298.15, 303.15 and 308.15 K were measured, and the phase diagram of alcohol- azithromycin -water at that temperature was obtained through solubility property. The solubility data were correlated by the modified Apelblat equation, λh equation and van’t Hoff equation. The results showed that the solubility of azithromycin dihydrate obviously increased with the increase of temperature and the volume fraction of isopropanol and propanone, and the water activity of transformation increased and the coexist area decreased with the increase of temperature. The modified Apelblat equation was the best choice in the correlation of the solubility data.

Measurements and simulation for ternary system KCl-PEG4000-H2O at 288, 298 and 308 K
Xudong YU, Qin HUANG, Lin WANG, Maolan LI, Hong ZHENG, Ying ZENG
2019, 70(3):  830-839.  doi:10.11949/j.issn.0438-1157.20181154
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The phase equilibrium relationship of the ternary system KCl-PEG4000-H2O at 288, 298 and 308 K was studied by isothermal dissolution equilibrium method. The corresponding phase diagram, density-composition diagram and refractive index-composition diagram were drawn. The results show that over the entire PEG 4000 composition rang studied only one liquid phase is obtained, without the biphase region formed at 288, 298 and 308 K. The phase diagram of system KCl-PEG4000-H2O consists of one homogeneous area with unsaturated liquid (L), an equilibrium area containing the solid phase of KCl and saturated liquid phase (S+L), one area with one liquid phase and two solid phases(2S+L). The area of (2S+L) decrease with the increasing of temperature, while the areas of (L) and (S+L) increase with the increasing of temperature. The solubility of KCl decreases with the addition of PEG 4000 at 288, 298 and 308 K. When wPEG4000 in the solution is less than 0.50, the temperature has little effect on the salting-out ratio of the system, while when wPEG4000 is higher than 0.50, the salting-out ratio of the system decreases with the increasing of temperature. The thermodynamics calculation of equilibrium data of system KCl-PEG4000-H2O at 288, 298 and 308 K was carried out by using the modified Pitzer equation, it can be seen from the comparison of experimental and calculation diagrams that the predictive solubilities agree well with the experimental values.

Fluid dynamics and transport phenomena
Numerical simulation and experimental validation of evaporation characteristics of scaled liquid hydrogen tank
Shunhao WANG, Wenli ZHU, Zhenggen HU, Rui ZHOU, Liu YU, Bin WANG, Xiaobin ZHANG
2019, 70(3):  840-849.  doi:10.11949/j.issn.0438-1157.20180926
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The ground-scale reduction tank is used to simulate the thermophysical process and operating characteristics of the arrow-loaded hydrogen tank, including the barrel section and the shell section which is used to support the barrel section. The barrel section and part of the shell section are insulated by foam, and the shell section structure is exposed in the environment, which becomes the main heat leakage source of the liquid hydrogen tank. Based on the computational fluid dynamics method, the evaporation characteristics of the liquid hydrogen scaled tank were numerically studied. The mathematical framework of two-phase hydrogen flow and phase change heat and mass transfer was constructed based on VOF two-phase flow model and Level-set interface tracking method. The mass transfer rate of the liquid interface is calculated based on the Lee model. The liquefaction/evaporation coefficient in the Lee model was obtained by comparison with the experimental results. By theoretical analysis of the icing characteristics of the low temperature surface with or without foam insulation, convective heat transfer or constant heat flux boundary conditions were applied to the exposed foam and aluminum shell surfaces respectively. When the tank pressure reached about 2 atm (0.2 MPa, absolute), the safety valve was opened and deflated to keep the internal pressure constant. This paper simulates the valve opening and closing based on the custom function method to achieve the purpose of controlling the tank pressure. Compared with the experimentally measured liquid level decline rate and unsteady gas phase temperature change, the constructed numerical model can well simulate the complex flow and phase change heat and mass transfer characteristics of the self-pressurization process in the liquid hydrogen tank, which contributed to the foundation for simulating the thermophysical process during the launch process of the real rocket-loaded liquid hydrogen tank.

Experimental visualization on thermal energy storage enhancement through metal foam filled annuli
Pan WEI, Jiabang YU, Zengxu GUO, Xiaohu YANG, Yaling HE
2019, 70(3):  850-856.  doi:10.11949/j.issn.0438-1157.20181024
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Intensified heat transfer research was carried out for the heat exchange basic unit-heat exchange tube in the tube-and-tube phase change regenerator. The metal foam was added on the side of the phase change material to enhance the heat storage. Phase interface was recorded by a high-definition camera during the charging process. T-type thermocouples were attached separately on the radial and axial sides of the PCM. Charging processes of smooth tube and metal foam tube were quantified under the flow rate of 0.15 m·s-1. The results demonstrated that the involvement of metal foam can significantly enhance the efficiency of thermal energy storage under the same charging condition (initial temperature, inlet temperature and flow rate). It took over 2.9 more times for the melting time of pure paraffin than that of metal foam under the same condition. The temperature response rate of metal foam tube was much higher and the temperature distribution was more uniform, in comparison with that of smooth tube.

Optimization of heat removal modes for heat exchanger in molten salt single storage tank
Suli SHI, Yuanwei LU, Qiang YU, Yuting WU
2019, 70(3):  857-864.  doi:10.11949/j.issn.0438-1157.20180712
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Low cost heat charge and discharge can be realized by immersion arrangement of a helically coiled heat exchanger in molten salt single storage tank. Heat removal modes of the helically coiled heat exchanger will directly affect the heat discharge process of the storage system. Simulations were performed for two heat removal modes which include upper-lower path and lower-upper path. For different heat removal modes in the heat discharge process, the law of heat discharge performance of the molten salt single storage tank is given, and the change of flow field of molten salt side is analyzed. The results show that upper-lower path for the helically coiled heat exchanger can improve the transient out temperature, transient heat transfer rate and heat discharge efficiency. The research results provide a theoretical basis for the design of the molten salt single tank heat storage and discharge system.

Evaporation characteristics of water film over collecting electrode in high-voltage electrical field
Jingcai CHANG, Xiang WANG, Peng WANG, Lin CUI, Jun LI, Xin ZHANG, Chunyuan MA
2019, 70(3):  865-873.  doi:10.11949/j.issn.0438-1157.20180546
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Based on the polarization and force characteristics of water molecules in the electrostatic field, the transport process of water molecules in the liquid film on the surface of the plate in hot dry flue gas is analyzed. Besides, the effect of electrical field parameters on the evaporation characteristics and the dominant influence factors in the evaporation process under multi-field coupling effect (temperature, velocity and electrical field) were all studied. Eventually an evaporation model was proposed. The results showed that the ion wind is the main power source in the process of water film evaporation and the electric evaporation rate is 6.7 higher than the natural evaporation rate (25 kV). Water film evaporated at a constant rate and there was a positive relationship between evaporation rate and electrical field intensity. Evaporation process can be inhibited by the dissolved solute in the water film and the process was divided into two periods: constant rate period and falling rate period. The solute precipitated firstly on the water film surface. Under the coupling effect of velocity and electrical field, the evaporation rate increases slowly (U＜20 kV) and then increases rapidly (U＞20 kV) with increasing the voltage, velocity and voltage is the main influence factor in this two processes respectively. Under the coupling effect of temperature and electrical field, the evaporation rate is higher than the superposition of these two single fields. All these results can provide a theoretic support for the water film forming and consumption, humidity distribution in the unsaturated flue gas.

Heat transfer performance of pulsating heat pipe with hygroscopic salt solution
Hang ZHANG, Jianhua WENG, Xiaoyu CUI
2019, 70(3):  874-882.  doi:10.11949/j.issn.0438-1157.20180661
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The heat transfer characteristics of the 10% (mass) concentration LiCl hygroscopic salt solution as the oscillating heat pipe of the working fluid were studied. The 10% LiCl salt solution was prepared to test the PHP evaporator section temperature and the thermal resistance at 45%—90% filling rate and 10—100 W heating power. Besides, that of deionized water PHP was compared. The results show that at the low filling rate of 45% and 55%, when the heating power reaches over 50 W, the thermal resistance of LiCl solution pulsating heat pipe is obviously lower than that of the deionized water PHP. LiCl solution can effectively delay the occurrence of dry-out phenomenon and reduce the thermal resistance of the PHP. At the filling rate of 62%, when the heating power reaches over 35 W, the evaporator section temperature curve of LiCl solution PHP has higher oscillation frequency and smaller oscillation amplitude. The thermal resistance of LiCl solution PHP at different heat power is lower than that of the deionized water PHP. At the high filling rate of 80% and 90%, the temperature curves of the evaporator section of the two types of PHP are similar for the average temperature, the oscillation frequency and the amplitude. The thermal resistance is relatively close.

Effect of cooled cylindrical surface on droplet dynamic behavior
Xin ZHOU, Ledong DENG, Hong WANG, Xun ZHU, Rong CHEN, Qiang LIAO, Yudong DING
2019, 70(3):  883-891.  doi:10.11949/j.issn.0438-1157.20181168
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The prevention and control of ice accumulation has important applications in aviation, building construction and power grid construction. A deep physical insight of the ice forming on the cylindrical surface would give an instruction to the ice-removal strategies for energy conversion devices. Simulations were performed using CLSVOF (coupled level-set and volume of fluid) to track the air-water interface and an enthalpy-porosity method to capture the phase transition. The effects of learning behavior and phase transition characteristics are mainly concerned with the variation of two important parameters: the change of liquid film height and the wetting characteristics of droplets on the wall. The results showed that improve the wall hydrophobicity performance, which could effectively reduce the spreading wetted area of the droplet impact cylinder, thereby reducing the frozen area and decreasing the damage degree of icing. Due to the curvature of the cylinder, the liquid film breaks when the droplet hits the hydrophobic cylindrical wall. However, at extremely low temperature, it can inhibit the splitting of the liquid film on the circular wall surface, resulting in an increase in the spreading area of the liquid film on the wall surface, and the icing phenomenon becomes more serious.

Character of sessile gold-water nanofluid droplet evaporation with solar heating on superhydrophobic surface
Xin YAN, Jinliang XU
2019, 70(3):  892-900.  doi:10.11949/j.issn.0438-1157.20180818
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The evaporation characteristics of gold nanofluid by solar heated on superhydrophobic surfaces were investigated experimentally. The evaporation process of 2 μl gold nanofluid droplets on the superhydrophobic surface was recorded simultaneously by high-speed camera and IR camera. Through a series of experiments, the evaporation dynamic characteristics of volume, contact angle, contact diameter, droplet surface temperature and evaporation rate of gold nanofluid with different concentrations were studied. Combined with the water vapor diffusion model and the IR temperature distribution, the characteristics of evaporation flux and surface temperature change of droplets on the superhydrophobic surface were analyzed. It is found that the evaporation rates of nanofluid droplets with different concentrations are almost the same. The droplets evaporation on the super-hydrophobic surface is the normal contact angle mode, and the mixed evaporation mode occurs in the final stage. During the droplets evaporation process, the evaporation flux of the upper part of the droplets is large, resulting in the lower surface temperature.

Behavior characteristics of bubble formation under various nozzle immersion modes
Xuan WU, Xiaorui LI, Jun MA, Mengzhu QIN, Yahui ZHOU, Haiguang LI
2019, 70(3):  901-912.  doi:10.11949/j.issn.0438-1157.20180804
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The visual experiment and three-dimensional numerical simulation of the bubble generation behavior process under three nozzle immersion modes were carried out. The impacts of nozzle immersion modes, nozzle diameters and gas flow rates on the bubble formation, the bubble detachment diameter, the bubble expansion and detachment time, and the velocity of the gas-liquid flow are analyzed. Good agreement between the experimental and numerical simulation results is obtained. The results indicate that the bubble formation process can be categorized into two modes: single bubble generation and double bubbles generation, and there exists a critical point indicating bubble detachment form. The bubble detachment diameter increases with the increase of nozzle diameter and gas flow rate under all three different nozzle immersion modes. The bubble expansion and detachment time increases with the enlargement of nozzle diameter. However, with the increase of gas flow rate, it decreases sharply at the beginning and then tends to be gentle gradually. With bottom-submerged and side-submerged nozzles, the major to minor axis ratio (C) of bubble fluctuates near the values of 0.75 and 1.1, respectively. And the bubble detaches in spherical shape. While with top-submerged nozzle, the bubble detaches in the form of ellipsoidal shape with the C value fluctuates around 1.5.

Dehumidification performance experiment of hydrophilic non-woven PVC composite structured packing
Zhijia HUANG, Liang LUO, Rui KE, Feifei ZHUO, Liang ZHONG
2019, 70(3):  913-921.  doi:10.11949/j.issn.0438-1157.20181029
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The hydrophilic non-woven PVC composite structured packing is used as the core of the solution dehumidification tower, and the dehumidification performance test of the hydrophilic non-woven PVC composite structured packing is carried out. The change of dehumidification rate, dehumidification efficiency, mass transfer coefficient and heat transfer coefficient of hydrophilic non-woven PVC composite structured packing under different air flow, liquid flow and liquid temperature were analyzed. Under experimental conditions, the maximum values of the dehumidification rate, dehumidification efficiency, mass transfer coefficient, and heat transfer coefficient are 11.05 g·kg-1, 86.7%, 12.95 g·(m2·s)-1, 10.33 W·(m2·℃)-1, respectively. Compared with the CELdek structured packing and plastic corrugated-hole plate packing, the hydrophile non-woven PVC composite structured packing has the best dehumidifying performance. The experimental data were regressed to obtain a dehumidification efficiency correlation formula of a hydrophilic non-woven PVC composite structured packing.

Catalysis, kinetics and reactors
Continuous synthesis of anisole in microreactor system
Hanlin WANG, Deqiang WANG, Kai WANG, Guangsheng LUO
2019, 70(3):  922-928.  doi:10.11949/j.issn.0438-1157.20181246
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Anisole is an important solvent and organic synthesis inter20181246te. In the past, it was synthesized by batch reaction, which has problems such as low production efficiency and long operation cycle. A continuous synthesis device and technology for anisole is highly required. A continuous-flow microreaction method using sodium phenolate solution and dimethyl sulfate as reactants was proposed. The microreactor employs micromixer and locally constructive reaction tube to enhance reactant mixing and the reaction was carried out at approximately adiabatic condition. The influences of sodiumphenolate concentration, reactant flow rate and molar ratio of phenolatetodimethyl sulfate on the sodium phenolate conversion and dimethyl sulfate utility were reported. A comparison with the batch reaction in the literatures was provided to show the advantage of microreaction technology.

Copper catalyst supported on cross-linked phenanthroline for oxidative synthesis of 2,3,5-trimethyl-1,4-benzoquinone
Wanwan GUO, Ruyue LI, Jun HUANG
2019, 70(3):  929-936.  doi:10.11949/j.issn.0438-1157.20181322
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Alkyl-substituted benzoquinones were versatile building blocks for a variety of biologically active compounds. The catalytic oxidation of 2,3,6-trimethylphenol (TMP) to 2,3,5-trimethyl-1,4-benzoquinone (TMQ, vitamin E precursor) with oxygen gas was proposed under mild conditions. The cross-linked porous polymer (PPhen) was synthesized by Friedel-Crafts alkylation of 1,10-phenanthroline, and the related Cu catalysts (Cu/PPhen) were prepared. The prepared Cu/PPhen catalysts were characterized by nitrogen adsorption and desorption isotherms, scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) .The basic structure of the Cu/PPhen catalysts were obtained. Reaction conditions, such as catalyst loading, solvent, oxygen pressure, reaction temperature and reaction time were studied, and 2,3,5-trimethyl-1,4-benzoquinone was obtained in 99% yield with the optimized reaction conditions. The optimized reaction conditions were achieved as 136 mg 2,3,6-trimethylphenol with 150 mg the Cu/PPhen-4 catalyst in 2 ml acetonitrile, under 0.5 MPa O2 at 40℃ for 4 h. The Cu/PPhen-4 catalyst has good stability and can be recovered at least five times with almost no decrease in activity.

Preparation of palladium-based catalysts by complexing-solvothermal method and catalytic oxidation of m-xylene
Shuai HE, Feng GUO, Guojun KANG, Jian YU, Xuefeng REN, Guangwen XU
2019, 70(3):  937-943.  doi:10.11949/j.issn.0438-1157.20181083
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The Pd/Al2O3 catalysts with a loading of 0.6% (mass fraction) were prepared by complexation-solvent thermal method, hydrothermal method and impregnation method. The effect of different preparation methods on the performance of the catalyst was evaluated by using m-xylene as the representative of volatile organic compounds (VOCs). The results showed that the most effective catalyst Pd/Al2O3-com was prepared by complexing-solvothermal. The m-xylene with volume fraction of 0.002% can completely converted to CO2 and H2O (T100) at 130℃ over Pd/Al2O3-com catalyst from the complexing-solvothermal method, which was lower about 30℃ than the catalyst (Pd/Al2O3-imp) from the impregnation method. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) and scanning electron microscopy (SEM) techniques were performed to characterize the physico-chemical properties of synthesized Pd/Al2O3 catalysts. The results indicated that the Pd element of Pd/Al2O3-com was mainly dispersed on the surface of the support at the reduction state Pd0, while the Pd element of Pd/Al2O3-imp and Pd/Al2O3-hyd catalyst was at the form of Pd2+ with poor dispersion. Combined with the catalytic activity performance and evaluation results, a highly dispersed and reduction state form of Pd active component on the surface of the carrier resulted in a remarkable catalytic activity on m-xylene conversion. The Pd/Al2O3-com catalyst with these features exhibit good activity for removing VOCs under high concentration (0.02%－0.07%, vol) and wide space velocity (5$×$104－10$×$104 h-1) conditions, and thus meet well the requirements of industrial application.

Catalytic combustion of propane over PdxPty-ZSM-5/Cordierite monolithic catalyst
Quan TANG, Yanglong GUO, Wangcheng ZHAN, Yun GUO, Li WANG, Yunsong WANG
2019, 70(3):  944-950.  doi:10.11949/j.issn.0438-1157.20181110
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PdxPty-ZSM-5/Cordierite monolithic catalysts were prepared on the surface of the cordierite honeycomb supports, via vacuum extraction and one coating method, in which ZSM-5 molecular sieve, alumina sol, platinum or palladium nitrates and water were used as raw materials to prepare molecular sieve slurry. Effects of Pd loading, Si/Al ratio of ZSM-5, the mass ratio of Pd/Pt on the catalytic performance of the monolithic catalysts for the catalytic combustion of propane were investigated. The monolithic catalysts were characterized by ultrasonic oscillation, SEM, XRD, H2-TPR and C3H8-TPD. When the ball milling time is 60 min and the molecular sieve slurry solid content is 38%, the coating amount of the monolith catalyst can reach 178 g?L-1, and the coating detachment rate is less than 0.5%. Pd2Pt3-ZSM-5/Cordierite catalyst (total loading of noble metals of 1.2 g?L-1 ) exhibits better catalytic activity and stability (T50=259℃, T90=323℃) for the catalytic combustion of propane, which has better industrial application prospect. Lower Si/Al ratio of ZSM-5 and the interaction between Pd and Pt increase the amounts of adsorbed propane and surface active oxygen species, thus increases the catalytic performance of the monolithic catalyst.

Separation engineering
Long LI, Tianshu GE, Xuannan WU, Yanjun DAI
2019, 70(3):  951-959.  doi:10.11949/j.issn.0438-1157.20180746
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Simulation and analysis of reactive dividing-wall column for methylal production process
Jie YANG, Jiangyu QI, Yong SHA
2019, 70(3):  960-968.  doi:10.11949/j.issn.0438-1157.20180623
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Methylal is an important raw material used for the production of chemical intermediates, solvents, paints and fuel additives, etc. At present, reactive distillation technology is the main method for preparing methylal from methanol and formaldehyde. In this work, the reactive distillation with a dividing-wall column for producing methylal was proposed and simulated. The results show that the preparation of methylal by such a process can avoid the back mixing effect of the middle component in the column and reduce the total cost by 8.09% annually, then significantly improve the economics of the process.

Experiment and simulation of PSA process for small oxygen generator with two adsorption beds
Tao TIAN, Bing LIU, Meisheng SHI, Yaxiong AN, Jun MA, Yanjun ZHANG, Xinxi XU, Donghui ZHANG
2019, 70(3):  969-978.  doi:10.11949/j.issn.0438-1157.20180729
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A small two-bed pressure swing adsorption oxygen generator was designed and a series of experiments were carried out in the low-pressure cabin. The influences of structure and operating parameters were investigated simultaneously. The mathematic model of oxygen production process was established. The model was matched with the experiment results to verify the accuracy of the model. Numerical simulation and simulation researches were carried out to determine the relevant intrinsic parameters and external factors on the process of oxygen production and the effect of oxygen production. Performance of oxygen generator at different altitudes with different operating conditions, design parameters and operating parameters were studied to improve the oxygen production efficiency and reduce the manufacturing and operating costs of oxygen generator.

Process system engineering
Optimal control strategies combined with PSO and control vector parameterization for batchwise chemical process
Bowen SHI, Yanyan YIN, Fei LIU
2019, 70(3):  979-986.  doi:10.11949/j.issn.0438-1157.20181140
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As a gradient search algorithm for dynamic optimization of chemical process, the efficiency of control vector parameterization depends on the initial given trajectory deeply. At present, the initial trajectory is usually set at the boundary value or the intermediate value, which does not have enough scientific reason and it affects the convergence speed of the algorithm. To solve this problem, a hybrid strategy combined with particle swarm optimization and control vector parameterization method is proposed in this paper, it uses particle swarm optimization to achieve the value of control variables before employing the method of control vector parameterization to reoptimize the process. The two-layer optimization hybrid strategy improves the convergence speed of the control vector parameterization method and the precision of the particle swarm optimization. The hybrid strategy is applied to two examples of batch chemical process optimization control, and the simulation results show that the algorithm is feasible and effective for solving dynamic optimization problems of chemical process.

Separation engineering
Dynamic monitoring of chemical processes based on latent variable auto-regressive algorithm
Junmiao TANG, Haizhen YU, Xuhua SHI, Chudong TONG
2019, 70(3):  987-994.  doi:10.11949/j.issn.0438-1157.20181180
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From the viewpoint of constructing auto-regressive (AR) models for latent variables, the current paper proposed a dynamic modeling and monitoring approach for chemical processes based on latent variable auto-regressive (LVAR) algorithm. With respect to the requirement of minimizing AR model residual, the LVAR algorithm simultaneously searches for projecting vectors and AR coefficient vectors, so as to extracting dynamic latent variables and their corresponding AR models. In addition, the LVAR algorithm can efficiently distinguish the auto-correlated and cross-correlated relations inherited in the sampled data, by extracting the dynamic latent variables first and then the static component information. In the comparisons, the superiority and validity of the LVAR method are demonstrated by comparing the fault monitoring results in a classical chemical plant with other three counterparts.

Surface and interface engineering
Unified model and geometrical optimization of bi-directional groove of dry gas seal based on genetic algorithm
Qichao XU, Jinbo JIANG, Xudong PENG, Jiyun LI, Yuming WANG
2019, 70(3):  995-1005.  doi:10.11949/j.issn.0438-1157.20181075
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The steady-state performance of bi-directional groove dry gas seal can be enhanced by new proposed geometrical model with strong representational capability and new introduced optimization method with strong global search ability. On the basis of analyzing the structural characteristics of typical bi-directional grooves of dry gas seals, a new type of unified model of bi-directional groove with variable spiral angle of hydrodynamic groove was proposed. The geometrical model and mathematical model of dry gas seal with unified model groove were established. The gas film pressure control equations were resolved by use of finite difference method, and the steady-state performance, such as opening force and film stiffness, were obtained. The effect of spiral angle of upstream and downstream hydrodynamic groove on steady-state performance was analyzed, and effect of three typical optimization methods, including single factor optimization, iterative optimization and genetic algorithm optimization, on the enhancement of steady-state performance of bi-directional groove under different working conditions were compared numerically. The results show that compared with the single-factor optimization of the two-way tree-shaped groove dry gas seal, the opening force and film stiffness obtained by the unified model groove dry gas seal based on genetic algorithm are significantly improved, and the maximum increase is 6% and 55% respectively. The bi-directional groove shaped like an aircraft wing with upstream spiral angle equals to 0°—90° and downstream spiral angle equals to 90°—180° possesses the maximum opening force and film stiffness under high-speed condition.

Performance study of arc groove dry gas seal based on orderly micro-structure
Qiong HU, Yan WANG, Rong DAI, Jianjun SUN, Xiaoqing ZHENG
2019, 70(3):  1006-1015.  doi:10.11949/j.issn.0438-1157.20180820
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Based on the dry gas sealing and grooving method of laser technology, it is proposed to establish an orderly micro-shape of roughness level at the bottom of the circular arc groove dry gas seal (A-DGS) to improve the grooving efficiency and reduce the cost. Simulation based on the finite volume method was validated by comparing with other researches. After analyzing and filtering, it can be known there is little difference of seal performance between the windward micro-structure and leeward micro-structure, and then the opening force and leakage with different geometry and operation parameters of A-DGS based on the leeward-structure was studied, and the influence degree of all parameters was finally obtained and analyzed by a design of experiment based on Taguchi approach. The results show that the opening force is improved by orderly micro-structure, especially under low speed, high pressure and small groove depth conditions. Under given conditions, the influence of ratio of micro-structure depth and width on the opening force is greater than the film thickness and speed. The optimal parameters of arc groove structure are not affected by the micro-structure design. Based on Taguchi approach, the influence degree of different impact factors could be easily and accurately obtained, which is helpful for engineering design.

Effect of friction pair interface micro-texture sequence on gas sealing performance
Chuangang CHEN, Xuexing DING, Junjie LU, Weizheng ZHANG, Jinlin CHEN
2019, 70(3):  1016-1026.  doi:10.11949/j.issn.0438-1157.20181062
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The microstructures between the relatively sliding friction pair surface-interface can reduce attrition and improve lubricity. Computational domain model of cross scale lubrication film with micro-holes and micro-grooves on static and move rings were established. The lubrication film structured grids were meshed by the software ICEM with unique block mapping technology. Then the Fluent was used for numerical simulation. Taking the working conditions of the seal as the starting point, combined with the size of the micro-modeling structure, the paper discusses the four factors: the film opening force, the leakage amount, the friction coefficient of the lubricating film and the wall shearing force. The results showed that under the same medium pressure and rotational speed, the coverage ratio of micro-holes have a greater impact on the performance of gas sealing, and the increase is 5% to 8%, the gas sealing performance can achieve the best level when the coverage ratio of micro-holes is 50%. After that, the density, depth and diameter of the friction pair interface of the model were changed according to this criterion. It was found that the density and diameter of the micro-hole could significantly improve the sealing performance by 7% to 8%. And the gas seal performance can reach the best level when the micro-hole density is 12.5%, the depth is 10 μm and the diameter is 400 μm.

Mechanism prediction of flow-induced corrosion and optimization of protection measures in overhead system of atmospheric tower
Changchun HE, Lei XU, Wei CHEN, Xiaofeng XU, Pengwei OUYANG
2019, 70(3):  1027-1034.  doi:10.11949/j.issn.0438-1157.20180785
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Corrosion failures often occur at the overhead cooling system in the atmospheric tower in a domestic oil refinery. Based on the material balance principle, this study uses the reverse derivation method and process simulation to analyze the flow corrosion failure mechanism of the atmospheric pressure overhead cooling system, including dew point corrosion, ammonium salt crystal deposition scale corrosion, and multiphase flow erosion. Generally, water injection is a convenient and efficient measure to eliminate dew-point corrosion and under-deposit corrosion caused by ammonium salt crystallization. Nevertheless, due to the restricted water injection flow rate and various water injection modes for the heat exchangers, corrosion failure still occurred in the overhead cooling system of the atmospheric tower. By simulating the overhead system, the suitable one of three water injection modes (in the main process pipe, in the heat exchangers and by a programming controller) can be determined to realize the long-term stable operation of the overhead cooling system in the atmospheric tower according to a given injected water flow rate.

Mechanism of deterioration for dry barrier material in aluminum electrolysis cells
Yaowu WANG, Jianping PENG, Yuezhong DI, Pengcheng HAO
2019, 70(3):  1035-1041.  doi:10.11949/j.issn.0438-1157.20180662
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A component analysis and an X-ray phase analysis of spent dry barrier material were used to reveal the mechanism of deterioration for dry barrier material in aluminum electrolysis cells. The results show that both NaF and cryolite in the osmotic electrolyte react with the dry anti-seepage material to form a glass matrix of nepheline (NaAlSiO4), which can prevent the electrolyte from further penetrating downward. The Na3AlF6 continuously penetrating from the carbon cathode can react with the nephelite to form β-Al2O3, and the formation of β-Al2O3 is one major cause for deterioration of dry barrier materials. It can also produce SiF4 gas in the process of electrolyte reacts with dry barrier, which makes the silicon migrate to the lower part and results in the decrease of silicon in the upper layer.

Energy and environmental engineering
Microscopic measurements on methane hydrate dissociation
Xuebing ZHOU, Chanjuan LIU, Jinqiong LUO, Deqing LIANG
2019, 70(3):  1042-1047.  doi:10.11949/j.issn.0438-1157.20180821
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The decomposition process of methane hydrate was measured by laser Raman and X-ray powder diffraction (PXRD) at 253 K under normal pressure. The results showed that the methane hydrates at the surface dissociated into Ⅰh ice in the initial 30—50 min and then the ice film covered the hydrate phase which triggered the “self-preservation” effect and finally led to a dramatic decrease in dissociation rate of methane hydrate. During the dissociation, the ratio of methane content in large and small hydrate cages obtained from Raman spectra remained stable at around 3.2 which was generally in accord with the ratio of large to small cages in methane hydrate, while the characteristic peaks of hydrate lattice planes in the powder X-ray diffraction patterns decreased in the same profile, suggesting that the methane hydrate dissociated as a whole crystal unit. However, the characteristic peaks of Ⅰh ice lattice planes increased in different ways. The intensity of (002) plane was found to increase linearly up to 370% of its original value in 60 min while the intensity of (100) plane kept steady at about 200% of its original value after the first 20 min, indicating that the ice inclined to grow into horizontal plates instead of columnar growth. Combining with the transport characteristics of water molecules on the ice surface under low temperature, the growth of ice film covered on the inner hydrate cores was suggested to cultivate the “self-preservation” effect.

NOx emission characteristics of high-N fuel combustion in atmospheres rich in O2 and steam
Chuanqiang ZHU, Shuyuan LIU, Jian YU, Shiqiu GAO, Guangwen XU
2019, 70(3):  1048-1055.  doi:10.11949/j.issn.0438-1157.20181042
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The NOx emission characteristics of the nitrogen-rich fuel distiller's grains in a fluidized bed were studied under oxygen-rich and steam-rich conditions. The effect of steam on NOx emission is competitive with the influence from varying oxygen concentration in the combustion gas at the excessive air ratio of 1.2. When the oxygen concentration was below a value of about 35%, the steam addition decreased the NOx formation to lower the NOx concentration in the flue gas and also the fuel-N conversion into NOx. When oxygen concentration in the combustion gas was above the preceding critical value of about 35%, the addition of steam into the burning atmosphere resulted in higher NOx emission than the case without steam addition, showing the dominance of the enhanced oxidation with raising the O2 concentration. The NOx emission would increase first and finally decrease with raising temperature, and the higher O2 concentration in the combustion gas lowered the occurrence temperature for such a NOx decrease with raising temperature. The presence of steam in the combustion atmosphere delayed the occurrence of such a decrease so that it appeared at higher temperature.

Preparation of red mud-based catalyst and performance for trace ammonia in simulative tail gas
Chao WANG, Changming LI, Lin HUANGFU, Ping LI, Yunquan YANG, Shiqiu GAO, Jian YU, Guangwen XU
2019, 70(3):  1056-1064.  doi:10.11949/j.issn.0438-1157.20181051
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A Fe-based powder catalyst was prepared from red mud (RM) solid waste with acid base neutralization method, which was used to eliminate the trace ammonia thought the proposed process of directly spraying the catalyst into SNCR tail gas. The effects of temperature, space velocity, NH3 concentration and water vapor on ammonia removal capacity of the catalyst were investigated in details, and excellent removal efficiency could be achieved with 100% NH3 conversion above 450℃ as well as > 80% selectivity of N2 between 400—500℃. Especially, the trace ammonia in the tail gas can completely be cleared with 0 left between the space velocity of 3×106—6×106 h-1 at 500℃. Meanwhile, the catalytic process is also effective for the removal of NH3 with wide concentration of (40×10-6~800×10-6 mol/L) even in the presence of water. The multiple characterizations further revealed that the strong alkalinity of the original solid waste was removed together with the increase of surface acidity as well as large specific surface area and rich surface microstructure for the obtained red mud catalyst, which accounts for its significant increase of adsorption and activation of NH3. Moreover, it was found the removal process of NH3 follows the internal selective catalytic reduction (iSCR) mechanism, and the NH3 was eliminated through both the NH3-SCR and NH3-SCO reactions, which mainly function below 400℃ and between 400-500℃, respectively.

Experimental study on effective nitrate removal from sewage by ZVI-based catalyzed reduction
Desheng LI, Chao ZHANG, Shihai DENG, Zhifeng HU, Jinlong LI, Yuanhui LIU
2019, 70(3):  1065-1074.  doi:10.11949/j.issn.0438-1157.20181059
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It remains difficult to achieve effective nitrate removal with conventional biological nitrogen removal processes, for the high $NO3-$-N concentration and low organic carbon in tail water from WWTP. Thus, ZVI-based catalyzed reduction was developed and applied in this study. The influence of catalytic activity of the catalysts, pH and $NO3-$-N concentration on nitrate reduction by ZVI-based catalyzed reduction was studied, and the reaction mechanisms was investigated. The results show that the high-catalytic catalytic denitrification carrier with catalyst D can remove 92.23% of $NO3-$-N, and the $NO3-$-N removal rate can reach 92.09% when the wastewater is acidic to neutral. The $NO3-$-N removal efficiency of above 86.13% was also achieved even under alkaline conditions, and no $NH4+$-N accumulation was found. Increasing in $NO3-$-N concentration (20—70 mg·L–1) showed little impact on nitrate reduction efficiency (remaining ≥96.11%). The nitrogen removal efficiency by ZVI-based catalyzed reduction in the presence of catalyst D obtained the highest speed when compared to catalysts A, B and C, and the reduction reaction was in keeping with the first-order kinetics equation with a calculated reaction rate constant of k=0.0170 min–1.

Difference of fly ash characteristics from PC and CFB boilers and its effect on mercury adsorption capability
Xiaohang LI, Yun LIU, Yinjiao SU, Yang TENG, Yanjun GUAN, Kai ZHANG
2019, 70(3):  1075-1082.  doi:10.11949/j.issn.0438-1157.20180882
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The particle size distribution, surface structure property, unburned carbon content and mercury content of fly ash were investigated to understand the effect of boiler type and mercury adsorption capability on fly ash. Different samples were obtained from a circulating-fluidized bed (CFB) boiler and a pulverized coal (PC) boiler with the capacity of around 300 MW coal-fired power generation units. In this study, the mercury contents in fly ash collected from the CFB and PC boilers are 1584.0ng/g and 503.7ng/g, respectively. The results show that the mercury content in the fly ash from CFB boiler increases with decreasing particle size and reactivity temperature, but increasing surface area and unburned carbon content. For the fly ash from PC boiler, the portion with the diameter of 75—53 μm displays better mercury adsorption capability, the unburned carbon content is much lower than that from CFB boiler, and the surface area is almost independent to particle size. As a result, the adsorption capacity of the sample taken from the ash discharge port of the pulverized coal boiler dust removal equipment is much lower than that of the corresponding position of the circulating fluidized bed boiler.

Optimization of extraction process of inorganic phosphorus in scale of circulating cooling system
Yuling ZHANG, Liping ZHANG, Qian WANG, Xudong LI, Xiaodong LIU, Jinghong ZHANG
2019, 70(3):  1083-1088.  doi:10.11949/j.issn.0438-1157.20181016
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Most of the phosphorus in the reclaimed water is inorganic phosphorus, which is an important factor causing scale corrosion of the circulating cooling system. To explore the migration and transformation of inorganic phosphorus in the system and its influence on the system, the quantitative determination of inorganic phosphorus is particularly important. The feasibility of SMT continuous extraction of inorganic phosphorus in the fouling of the circulating cooling system was carried out, the inorganic phosphorus SMT was optimized and improved, and a qualitative and quantitative analysis method for inorganic phosphorus was established. The results showed that the majorization of SMT extraction method was able to extract the inorganic phosphorus in the scale completely, the recovery rate was close to 100%， and weakly adsorbed phosphorus (NH4Cl-P), aluminum-bound phosphorus (Al-P), iron-bound phosphorus (Fe-P) and calcium-bound phosphorus (Ca-P) in the scale can be completely separated.

Transformation of Fe3+ and its effect on anoxic sludge flocculation in A2O process
Lanhe ZHANG, Mingshuang ZHANG, Jingbo GUO, Yanping JIA, Zheng LI, Zicheng CHEN
2019, 70(3):  1089-1098.  doi:10.11949/j.issn.0438-1157.20180793
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To study the effect of iron on the flocculation of A2O process sludge, the distribution and migration and tranformation of Fe3+ in sludge supernatant, extracellular polymeric substances (EPS) and sediment (Pellet) were investigated. A large amount of wastewater containing Fe3+ was generated in the rapidly developed industries such as metallurgy, electroplate and mineral separation. Fe3+ entered the sewage biological treatment system and could affect the sludge biological flocculation and the removal of COD, TN and TP. Information on the morphology, structure change, migration and conversion of iron ions in the anaerobic, anoxic and oxic sludge was scrace. The occurrence form and structural characteristics of iron ions were analyzed and the interaction mechanism between Fe3+ and microbial metabolites was revealed based on the analyses of three-dimensional excitation (3D-EEM), atom absorption and X-ray diffraction (XRD). The effect of Fe3+ on the denitrification and phosphorus removal was explored. The results showed that low concentration of Fe3+(<10 mg·L-1) could improve COD and TN removal, promote microbial activity and enhance the biological flocculation of sludge. When Fe3+ increased from 0 to 10 mg·L-1, the removal efficiency of COD and TN increased from 42% and 37% to 60% and 45%, respectively, while the dehydrogenase activity increased from 20.09 mg·(L·h)-1 to 31.91 mg·(L·h)-1. The flocculation ability (FA) increased from 30% to 53% and the maximum sludge particle size was 43.3 μm. High concentration of Fe3+ could inhibit microbial activity, increase EPS content and induce sludge deflocculation. When Fe3+ concentration increased from 10 mg·L-1 to 40 mg·L-1, the removal efficiency of COD and TN decreased by 28% and 34%, respectively. Protein (PN)/polysaccharide (PS) in loosely bound EPS(LB) and tightly bound EPS(TB) was the key factor affecting the flocculation of sludge. Fe3+ addition could enhance TP removal efficiency and it was 93% when Fe3+ was 40 mg·L-1. Fe3+ concentration distribution in the sludge was TB>supernatant>LB>soluble microbial products(SMP), and the main form of Fe element in the sludge was Fe3+. The iron content of different forms changed with the increase of Fe3+ concentration. In addition, Fe3+ could enrich and accumulate in the microorganism cells and could change the composition of EPS layers.

Preparation of a novel phosphorus removal filler and optimization of phosphate removal adsorption bed process
Qian ZHANG, Xiangyang LIU, Wang CHEN, Heng WU, Pengying XIAO, Fangying JI, Chen LI, Haiming NIAN
2019, 70(3):  1099-1110.  doi:10.11949/j.issn.0438-1157.20181054
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Biomass activated carbon loaded with zero-valent iron nanocrystal clusters for direct catalytic reduction of NO
Yanying LI, Xianchun LI
2019, 70(3):  1111-1119.  doi:10.11949/j.issn.0438-1157.20180947
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The nano-iron-based catalysts with biomass activated carbon as carrier were prepared by equal volume impregnation method. The catalysts were characterized by TG, SEM, XPS, Raman and other analytical instruments. The activated carbon was loaded with zero-valent iron and iron oxide under anaerobic conditions. Actively developing a cheap catalyst suitable for coke oven flue gas denitrification at low temperature and no oxygen so that its flue gas emissions meet the national environmental protection standards is one of the research hotspots at the present stage. The mechanism of denitrification of zero-valent iron and iron oxides supported on activated carbon under anaerobic conditions is discussed. The results prove that the Fe-based catalyst prepared by thermal reduction at 750℃ has high activity, and its active center is the homogeneously dispersed zero-valent iron nanocrystalline cluster. The removal efficiency of NO at 280℃ is 100% and the loss of activated carbon carrier was avoided. The fast deactivation of the catalyst is due to the oxidation of zero-valent iron to Fe3O4, thus reducing the activity of the denitrifying agent. The catalyst activity can be completely restored by heat treatment at 750℃ nitrogen atmosphere, but the carbon carrier will be consumed by regeneration method without adding reducing gas. The preparation and regeneration of CO as reducing agent can effectively improve the dispersion of nanocrystalline clusters, prolong the denitrification life and reduce the loss of carbon support, which provides the possibility for the application of zero valent Fe catalyst in practical application.

Performances of waste paper cellulose/SiO2 composite aerogel
Yuhan ZHOU, Xiaoyu CHEN, Cheng ZUO, Qingjie GUO, Jun ZHAO
2019, 70(3):  1120-1126.  doi:10.11949/j.issn.0438-1157.20180916
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The waste paper cellulose was treated, and the cellulose/SiO2 composite hydrogel was prepared by using methyltrimethoxysilane (MTMS) as a silicon source, and freeze-dried to obtain a cellulose/SiO2 composite aerogel having good performance. The prepared aerogels were characterized by scanning electron microscopy (SEM), contact angle measuring instrument and thermogravimetric analysis (TGA). The results show that the material consists of macropores, mesopores, and micropores with a minimum density of 0.107 g/cm3, which has good hydrophobic properties, static hydrophobic contact angle of up to 148.5°, good mechanical properties, and 100% recovery after compression in 50% range. The material has good adsorption performance, and the adsorbed oil can reach 12.7 times of its own quality, and the thermal stability is improved. It has broad application prospects in the treatment of organic wastewater, especially water pollution.

Influencing factors of denitrification of glycans and transformation characteristics of internal carbon sources
Xiaofang LIU, Haiyan GUO, Shengnan ZHANG, Liang HUANG
2019, 70(3):  1127-1134.  doi:10.11949/j.issn.0438-1157.20181076
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The denitrifying glycan bacteria were successfully enriched in the SBR reactor with sodium acetate as the carbon source and $NO3-$-N as the electron acceptor, and the effects of the influent C/N ratio (3.3,6.7,10), electron acceptors ($NO3-$-N, $NO2-$-N), carbon source types (sodium acetate, glucose) on the activity of denitrifying glycans and the conversion characteristics of internal carbon sources were further investigated by batch experiment. The results show that the higher the influent C/N ratio, the higher the $NOx-$-N removal rate of the system, and the more PHB synthesis in the anaerobic section, but the influent C/N ratio is too high, which leads to the predominance of common denitrifying bacteria. The denitrification efficiency of the internal carbon source is suitable for the influent C/N ratio of 6.7. The DGAOs system with $NO3-$-N as the electron acceptor for long-term cultivation is not domesticated by $NO2-$-N, and has good anti-$NO2-$-N. Nitrification performance, after adding the same concentration of $NO2-$-N as $NO3-$-N, the system NOx--N removal rate is 89.6%; when glucose is used as the carbon source, the amount of PHB synthesized by DPAOs in the anaerobic section is only 79.5% of PHB with sodium acetate as the carbon source, and the anaerobic glucose utilization rate is only 72.8%, which is much smaller than the utilization rate of sodium acetate.

Material science and engineering, nanotechnology
Performance of metal-organic frameworks for CO2 capture from large-scale computational screening
Lei WANG, Guiying FANG, Qingyuan YANG
2019, 70(3):  1135-1143.  doi:10.11949/j.issn.0438-1157.20181079
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The global greenhouse effect situation is becoming more and more serious, and there is an urgent need to research and develop high-performance materials that can be used for CO2 capture. Metal?organic frameworks (MOFs) containing an inorganic unit of copper paddle-wheel (Cu2(COO)4) have excellent performance in CO2 capture in low pressure region because of their coordinatively unsaturated Cu sites. However, large-scale computational screening work available so far mainly used conventional molecular force field, which cannot accurately describe the host-guest molecules involved in current study. Thus, on the basis of accurate molecular force fields derived from quantum mechanics calculations, grand canonical Monte Carlo simulation method was adopted to investigate CO2 storage and CO2/N2 separation behaviors of 763 MOFs with Cu-OMS under ambient conditions. Not only were promising MOFs found through large-scale screening, but the established structure-performance relationships and the structural characteristics of high-performance materials were revealed, providing a theoretical foundation for design and synthesis of new materials for targeted applications.

Preparation and lithium storage properties of flexible self-standing PDDA-Si/G nanocomposite film
Yating ZHANG, Kaibo ZHANG, Kaili JIA, Xinfu HE, Guoyang LIU, Wei WANG, Yongling ZHANG, Jieshan QIU
2019, 70(3):  1144-1151.  doi:10.11949/j.issn.0438-1157.20181287
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Silicon is an active electrode material for future commercial lithium-ion batteries with extremely high theoretical specific capacity (4200 (mA·h)/g). However, the large volume change of silicon over charge-discharge cycles weakens its competitiveness in the capacity and cycle life. A flexible self-supporting polydiene dimethylammonium chloride-Si/graphene (PDDA-Si/G) nanocomposite film was successfully prepared by electrostatic self-assembly technique. The composite film can maintain the integrity of electrode structure without adding binder and conductive carbon black. Graphene provides complete conductive network and mechanical toughness. The electrochemical test results show that when the current density was 0.2 A/g, the specific capacity of PDDA-Si/G composite could reach 1439.9 (mA·h)/g and the Coulombic efficiency was above 98%. The specific capacity was 1209.3 (mA·h)/g after 80 cycles. The specific capacity still maintained 499.9 (mA·h)/g at a high current density (2 A/g).

Preparation of polyvinyl alcohol-graphene aerogel by emulsion method and its adsorption on pure organics
Zhenyou WANG, Hui’e LIU, Jiameng ZHU, Shuang CHEN, Anran YU
2019, 70(3):  1152-1162.  doi:10.11949/j.issn.0438-1157.20180995
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A polyvinyl alcohol-graphene aerogel was prepared by using a graphene oxide (GO)-stabilized Pickering emulsion as a soft template. The effects of GO concentration, homogenization speed, oil/water ratio, the amount of ethylenediamine (EDA) and polyvinyl alcohol (PVA) on the stability, particle size distribution of the emulsion and the formation of aerogel were investigated. It was found that the drop size of the emulsion could be controlled by changing the emulsion composition ratio. Then, the density and porosity of the aerogel also could be controlled. The polyvinyl alcohol-graphene aerogel (PGA) prepared under optimal preparation conditions was characterized by SEM, FT-IR, Raman and XRD. It was found that GO had been reduced and assembled to form a three-dimensional network structure (PGA) after the hydrothermal reaction and the pore size of the PGA was substantially the same as the particle size of the emulsion. The extrusion test of PGA was carried out and it was observed that PGA had both longitudinal and lateral bidirectional extrusion resilience. And the PGA still had good elasticity after more than 200 times repeated extrusion. The adsorption amount of pure organics by PGA was up to 280 g·g?1, and the volume of organics adsorbed per gram of PGA was constant value.

Preparation and characterization of electrostatic-assisted porous liquid
Lisha SHENG, Zhenqian CHEN
2019, 70(3):  1163-1170.  doi:10.11949/j.issn.0438-1157.20181183
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Electrostatic-assisted hollow silica porous liquid was here obtained. First, nano-hollow SiO2 particles were prepared by hard template, which took the role of pore structures of porous liquid. Then the surface of SiO2 particles was positively charged by the electrostatic action of the polymeric imidazolium cation. Finally, sulfonated polyethylene glycol was added on the surface of hollow SiO2 particles to obtain the fluidity. As the characterizations of properties revealed, porous liquid had a spherical cavity with a uniform pore size of about 10 nm and the content of hollow SiO2 in porous liquid was about 13% by mass. Porous liquid had a viscosity of 2.25 Pa·s at room temperature, which revealed a good fluidity. Simulation results showed that the physisorption energy of the most stable optimized structure was 279.55 kJ/mol, which indicated a strong interaction between hollow SiO2 and polymeric imidazolium cation. The method of electrostatically assisted surface modification provides a new idea for designing and preparing porous liquids.

Mechanical properties of basalt fiber-reinforced polylactide matrix and aging resistance properties
Lu HAN, Fangwu MA, Shixian CHEN, Yongfeng PU, Liang SHEN
2019, 70(3):  1171-1178.  doi:10.11949/j.issn.0438-1157.20180912
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With tests, the tensile properties, impact properties and aging resistance of PLA composites with basalt fibers as reinforcement were investigated. With DSC, crystallininty of the basalt fiber composites are obtained. With the mass fraction increasing, tensile strength and tensile modulus reach 141 MPa and 5 GPa respectively which are the best. However, the tensile properties decrease. The impact strength reach 20.76 kJ/m2 and 6.7 kJ/m2 respectively when the mass fraction is 30%. The results of DSC test show that the crystallinity of polylactic acid composite increases from 34.6% to 54.6% with the increase of basalt fiber content, and the increase of crystallinity can slow down the degradation rate of polylactic acid. After 48 h accelerated aging, the tensile modulus maintains 77% of the value before the aging test. Stable functional relationships that are not affected by aging between the tensile properties and mass fraction are found. Second linear fitting relationship is found between tensile strength and mass fraction. Near linearity is found between the tensile modulus and mass fraction.

Preparation of BaSO4 nanoparticles in microchannel reactor and its application in multifunctional layers of medical slices
Feifei YE, Baodan ZHANG, Haibo JIN, Xiaoyan GUO, Guangxiang HE, Rongyue ZHANG, Qingyang GU, Suohe YANG
2019, 70(3):  1179-1187.  doi:10.11949/j.issn.0438-1157.20180779
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BaCl2 and Na2SO4 were used as raw materials to prepare cubic nano-BaSO4 particles by microchannel reactor, and characterized by SEM and XRD. The effects of different reaction methods and microchannel reactor structures, volume flows of reactants, the concentration, temperature, volume flow ratio on size and morphology of BaSO4 nanoparticles were investigated. The suitable reaction condition applied to multifunctional layer of amylase medical dry film was obtained with volume flow of 2.5 ml/min, reactant concentration of 0.1 mol/L, the temperature of 25℃ and volume flow ratio of 5. At the same time, compared with the direct precipitation method, the nano-BaSO4 particles prepared in the microchannel reactor had a regular morphology with particle size from 25 nm to 55 nm. The prepared BaSO4 multi-functional layers were applied to the amylase medical slides with an obvious color gradient. The signal value decreased in turn using the densitometer, and the repeatability and stability of signal value curve were better, which indicated that the prepared BaSO4 particles could be applied to the multi-functional layer of the amylase in vitro diagnostic reagent.

Preparation and heat transfer characteristics of GO/paraffin composite phase change emulsions
Xiaoshi LIU, Deqiu ZOU, Ruijun HE, Xianfeng MA
2019, 70(3):  1188-1197.  doi:10.11949/j.issn.0438-1157.20180895
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To improve the heat transfer performance of paraffin phase change emulsion, GO/paraffin composite phase change emulsion was prepared by adding graphene oxide (GO) and its properties were characterized. The flow resistance and convection heat transfer test rig were set up, and the flow resistance characteristics and convective heat transfer characteristics of paraffin phase change emulsion and GO/paraffin composite phase change emulsion were comparatively studied. The results show that the composite phase change emulsion shows good stability due to the hydrophilicity of GO. When the mass fraction of GO is 0.01%, 0.02%, and 0.03%, the thermal conductivity of the composite phase change emulsion increases by 20.01%, 30.50%, and 35.18%, respectively. The flow resistance of the GO/paraffin composite phase change emulsion increases slightly compared to that of paraffin phase change emulsion. The straight pipe section increased by 6.70%, and the 90°elbow section increased by 13.20%.The convective heat transfer coefficient increases with the increase of GO concentration. The maximum convective heat transfer coefficient was increased by 43.90% at the GO addition amount of 0.03%.

Synthesis of Fe3+-doped ZnO nanostructures by antisolvent precipitation method and their visible photocatalytic activity
Yunbiao DUAN, Cunying XU, Xiang WANG, Hai LIU, Mengting HUANG
2019, 70(3):  1198-1207.  doi:10.11949/j.issn.0438-1157.20181233
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Fe3+-doped ZnO (Fe-ZnO) nanostructures with different dopant concentrations were successfully synthesized by a simple antisolvent precipitation method from the choline chloride-oxalic acid deep eutectic solvent (ChCl-OA DES). The structure and morphology of the prepared Fe-ZnO were characterized by SEM, XRD, Raman spectroscopy and XPS. The as-prepared Fe3+-doped ZnO sample was micro-rods that were composed of nanoparticles with diameter of 20—30 nm. All of Fe3+-doped ZnO samples with various Fe3+-doping concentration were hexagonal wurtzite structure and the Fe3+ ions were well incorporated into the ZnO crystal lattice. In addition, the optical properties and photocatalytic activities of the samples were investigated based on ultraviolet-visible (UV-Vis) spectra analysis as well as the degradation of Rhodamine B in aqueous solution under visible light. Compared with ZnO catalysts, the threshold wavelength of Fe3+-doped ZnO nanostructure was shifted to the full visible light region (red shift) and their absorption in the visible region increased with increasing of Fe3+-doping concentration from 0 to 5.0%(atom). The content of iron ion was found to be significant to the photocatalytic efficiency of Fe-ZnO nanostructures. The results demonstrated that the most optimal Fe3+-doping concentration was 1.0% (atom), and its photocatalytic activity was increased by 102% compared with ZnO under visible light. The enhanced photoactivity of the Fe3+-doped ZnO nanostructure was mainly due to the improved visible photon harvesting achieved by Fe3+ doping.

Foam phase preparation of porous poly(methyl methacrylate-co-butyl acrylate) microspheres in continuous process
Qiang ZHOU, Junzheng HAO, Linhua ZHU, Hong WANG, Tian SI, Yanping HE, Yanlin SUN
2019, 70(3):  1208-1219.  doi:10.11949/j.issn.0438-1157.20181012
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Porous polymeric microspheres have been widely used since their characteristics in the structure. However, the reported methods are less efficient, especially no continuous process was reported to prepare porous polymeric microspheres. Therefore, there is a need to develop a time-saving method with high yield for producing porous polymeric microspheres. This paper reports a continuous process to prepare porous polymeric microspheres via the solvent evaporation method in foam phase, being efficient and of high yield. Preparation of porous poly(methyl methacrylate-co-butyl acrylate) [P(MMA-BA)] microspheres was carried out in a customized continuous reaction device. At a certain stirring rate and reaction temperature, the oil phase and the aqueous phase were pumped continuously into the reactor. Foam phase gradually generated and flowed out from the outlet of the reactor. Porous P(MMA-BA) microspheres were obtained after collecting the bubble phase followed by defoaming, washing, filtration and drying. The average foam flow rate, the microspheres’ yield, the average particle size and the pore structure were investigated as a function of the experimental conditions including the feed rate of the oil phase, the reaction temperature, the stirring rate and the concentration of PVA. The results showed that the reaction temperature was 45℃, the stirring rate was 500 r/min, the oil phase solution feed rate was 30 g/min, the PVA concentration was 1.0% (mass), and the oil phase solution P (MMA-BA): DCM∶HT is 10∶53∶6 respectively, the yield of the porous P(MMA-BA) microspheres was up to 92% and the average particle size is 130 μm. The temperature and the residual amount of the aqueous phase left in the customized continuous reaction device are critical for the foam behavior and the yield of the porous P(MMA-BA) microspheres. This work validates that the customized continuous reaction device is capable to produce porous polymeric microspheres continuously, based on the method to prepare porous polymeric microspheres via solvent evaporation method in foam phase, with improved efficiency and yield. In addition, the method reported in this work is able to use continuously on an industrial scale potentially.

Fabrication process of MEMS print head based on silicon-silicon low temperature direct bonding
Yanzhao ZHAI, Anjiang CAI, Dongpeng ZHANG, Chao HAN, Li LI
2019, 70(3):  1220-1226.  doi:10.11949/j.issn.0438-1157.20180919
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Aiming at the processing of complex chamber structure of MEMS piezoelectric integrated print head, a set of fabrication process based on ICP etching combined with silicon-silicon low temperature direct bonding was proposed. Firstly, the upper and lower chamber structures of the print head are separately fabricated by the ICP bulk silicon dry etching process, and then the two silicon wafers with the chamber structures are directly bonded at a low temperature to form a complete print head chamber. Through bonding experiments on the upper and lower chamber structures of the print head, the mechanism of silicon-silicon low temperature direct bonding was further explored and verified. Besides, the effects of different activation methods and annealing time on bonding quality were analyzed, and the bonding process was optimized. The low temperature direct bonding process lays the foundation for the fabrication of MEMS devices with complex three-dimensional structures. The test results show that the finished MEMS print head has a high bonding strength, and the chamber flow channel has good integrity and sealing.

Process safety
Experimental study on flame propagation characteristic of polyethylene dust explosion under confined chamber
Jianliang YU, Yujie HOU, Xingqing YAN, Wentao JI, Xiaozhe YU, Yibo WANG
2019, 70(3):  1227-1235.  doi:10.11949/j.issn.0438-1157.20181072
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An experimental apparatus which could withstand high pressure and with good visibility was modified. PIV technology was applied to measure the distribution of cold pulverized flow field. Flame propagation characteristics of polyethylene dust explosion were investigated in closed vessel. In experiments, flame structure, flame brightness, flame front location, flame propagation speed and other parameters variation were analyzed. The results show that in the concentration range of 200—1000 g/m3, the low-concentration polyethylene dust explosion flame has a discontinuous fin-like structure, and the flame front is discrete star-shaped. On further increasing the dust concentration the flame continuity as well as the luminance increased and reached the top at the concentration of 400 g/m3. The velocity fluctuated obviously during the flame propagation process of polyethylene dust explosion at different concentrations, which increased at first and then decreased. The velocity-fluctuation of the flame was more obvious when it was close to the optimum explosion concentration range. The RMS turbulent velocity equation was adopted to quantify overall pulsation amplitude. Dust concentration was close to the optimal explosion concentration of 400 g/m3 and the RMS turbulent velocity was 3.21 m/s.

Analysis of fire suppression effectiveness of ultra-fine water mist containing iron compounds additives in cup burner
Tianshui LIANG, Zongying WANG, Kun GAO, Runwan LI, Zheng WANG, Wei ZHONG, Jun ZHAO
2019, 70(3):  1236-1242.  doi:10.11949/j.issn.0438-1157.20180654
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To evaluate the fire suppression effectiveness of ultra-fine water mist containing iron compounds additives qualitatively and quantitively, a small-scale experiment platform was set up to explore the minimum extinguishing concentration of the water mist under different fuels. Ethanol and n-heptane were separately used as fuels. Air flow was kept as 60 L/min during experiments. The water mist content in the air was gradually increased by adjusting the power of atomizer. The critical fire suppression concentration was obtained until fire was extinguished. Furthermore, to understand the fire suppression mechanisms deeply, structures formed by iron oxides and H radicals were relaxed based on the density functional theory. The results show that ferrocene and ferrous sulfate can obviously reduce the minimum extinguishing concentration of ultra-fine water mist. The decreasing degree of minimum extinguishing concentration is not linear with the content of additives. There are optimal concentrations of iron compounds additives match to fire suppression effectiveness of the water mist. The optimal concentrations of ferrocene and ferrous sulfate are 0.01% and 1% respectively. The fire suppression effectiveness is affected by the type of fuels. Its order is as following in this experiment: ethanol > n-heptane. Fe(OH)2 formed by the reaction of iron oxide with H radical is an active catalytic substance capable of eliminating H radicals by chain reaction.