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    28 December 2022, Volume 22 Issue 12
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    Cover and Contents
    The Chinese Journal of Process Engineering. 2022, 22(12):  0. 
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    Research Paper
    Water model experiment on the motion, melting, and mixing of scrap in bottom stirred reactors
    Kanghua PEI Chao CHEN Yu ZHAO Yaocheng LIN Rongwang YANG Jiangjun ZHU Tao WANG Kang YANG Wanming LIN
    The Chinese Journal of Process Engineering. 2022, 22(12):  1601-1612.  DOI: 10.12034/j.issn.1009-606X.222053
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    Ice sphere made by saturated KCl solution, which can simulate the heavy scraps, are used in water model experiment to study the mechanism of motion and melting of scrap and mixing of the solute of scrap in bottom stirred reactors. The effects of liquid level in single nozzle stirring mode and gas flowrate in double nozzle stirring mode on the motion, melting, and mixing of scraps are investigated. The results show that in the single nozzle stirring mode, when the liquid level is low (the ratio of liquid level to the diameter is 0.42), the stirring of gas column and the circulation in the reactor is weak. As a result, the salt ice sphere moves up and down in the gas column, and the melting of the sphere is relatively slow. With the increase of liquid level (the ratio of liquid level to the diameter is 1.04), the salt ice sphere moves with the circulation. Hence, the melting process is accelerated. However, the mixing time of KCl solution, which is obtained according to the 98% standard, in the reactor is even lower than the melting time of sphere. In the double nozzle stirring mode, the gas flowrate of nozzle A remains unchanged at 0.8 m3/h, and the gas flowrate of nozzle B is 0.5 and 1.0 m3/h, respectively. In the two cases, after the salt ice sphere is added above from nozzle A, the sphere stays at the bottom of the reactor for a period of time. After 60~70 s, the sphere moves to the top and moves along the circulation. When the gas flowrate of nozzle B increases to 1.5 m3/h, the salt ice sphere will not stay at the bottom. It moves with the gas column to the plume area formed by nozzle B and its melting process is accelerated. In all the double nozzle stirring mode cases, it is also found that the mixing time of KCl is lower than the melting time of sphere, which is related to the small mass of sphere and less salt released at the end of melting process. In this study, the effect of double nozzle stirring mode on the acceleration of melting of salt ice sphere is not as good as that of single nozzle stirring with large gas flowrate.
    Dynamic characteristic of single CCl4 droplet underwater on concave-wall
    Jing ZHANG Hao ZHANG Bin GONG Yaxia LI Siyuan LIU Jianhua WU
    The Chinese Journal of Process Engineering. 2022, 22(12):  1613-1622.  DOI: 10.12034/j.issn.1009-606X.221408
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    The impact behavior between discrete phase and concave-wall was complex and changeable in cylindrical section equipment and pipeline, which directly affected the mass transfer efficiency of inter-phase. In this work, the dynamic characteristic of CCl4 single droplet with iodine containing under water impacting the concave-wall was systematically studied by experiment and image post-processing. The results showed that the settlement velocity of CCl4 droplet under water was relatively stable and only was related to the droplet initial diameter. The process of droplet impacting the concave-wall was divided to five stages, falling stage, spreading stage, relaxing stage, rolling stage, and wetting stage, respectively. The droplets stretched along the circumferential direction of concave-wall and contracted along the normal direction of concave-wall. The effect of the impact angle between droplet and concave-wall θ on the droplet stretching property was greater than the droplet initial diameter and concave-wall curvature radius. The droplet vertically impacted at the lowest point of the concave-wall, then bounced rapidly and contracted strongly when θ=90°. The spreading time was shorter and the deformation rate was the smallest, there was no rolling stage. At the range of θ=100°~150°, the droplet deformation rate increased with the increase of impact angle, the sliding deformation rate was less than the rolling deformation rate. The travel distance, times and duration of droplet oscillation at the concave-wall lowest point increased. At the same time, the oscillation amplitude of droplet velocity increased in the gravity direction. The droplets were mainly sliding and spreading at the range of θ=110°~130°. The phenomenon of droplet rolling along the concave-wall was more likely to occur at θ>130°. The droplet was close to the pure rolling state when θ=154.2°, the droplet diffusing and relaxing stages were very short, the droplet earlier got into the wetting state. The impact angle was increased for the droplet rolling along the concave-wall, effectively reducing the wall adhesion and droplet breakage.
    Entrainment and elutriation of particles in a gas-solid fluidized bed
    Qi WANG Zhunzhun MA Hongfang MA Weixin QIAN Qiwen SUN Haitao ZHANG Weiyong YING
    The Chinese Journal of Process Engineering. 2022, 22(12):  1623-1632.  DOI: 10.12034/j.issn.1009-606X.222004
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    The experimental work on the entrainment and elutriation of glass beads and white fused alumina powder with a wide particle size distribution was carried out in a fluidized bed with an inner diameter of 0.5 m and a total height of 6 m. The two powders were passed through the sieve distribution ratio to obtain experimental materials with different particle size distributions belonging overall to the Geldart groups A or B particles. Fluidization tests were carried out in a steady state at velocities of 0.25~0.76 m/s, the effects of superficial gas velocity, bed material particle size distribution and particle size on particle entrainment and elutriation rate were investigated. The elutriation rate constant of the powders under different conditions was obtained. In order to ensure that the transport disengaging height (TDH) was reached under various conditions, the entrained particles in the fluidization column were sampled axially and analyzed for particle size distribution. The experimental results showed that an increase of the concentration of fine particles in the experimental materials increased the total entrainment flux, but reduced the elutriation rate constant (Ki*). The total entrainment flux and the elutriation rate constant increased exponentially with increases of the superficial gas velocity. In addition, at a given superficial gas velocity, the elutriation rate constant first increased with the decrease of particle size, until reaching a critical particle size (dcrit), after which the elutriation rate constant would tend to flatten or decrease, that changes in the elutriation rate may be attributed to the interparticle adhesion forces. A new empirical correlation was proposed based on the experimental results and theory of dimensional analyses to estimate the elutriation rate constant of particles below the critical particle size. The correlation could agree well with the experimental data. The proposed empirical correlation can be used to scale up fluidized beds.
    Numerical investigation of gas-assisted sludge atomization and breakup based on VOF-DPM coupled model
    Haihong FAN Zhou LI Binbin LI Lin LI Shuo SHANG Jiayang WANG
    The Chinese Journal of Process Engineering. 2022, 22(12):  1633-1642.  DOI: 10.12034/j.issn.1009-606X.221412
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    Sewage sludge is an unavoidable by-product in the process of sewage treatment. Due to its characteristics of high pollution and difficult to treat, the efficient and harmless treatment of sludge is still facing certain challenges. A new sludge treatment technology, spray drying technology with relatively simple process and high value-added utilization after sludge atomization has a great promotion effect on sludge treatment. The gas-assisted atomizer has a good atomization effect on high-viscosity fluids, and can ensure a better atomization quality at a faster atomization rate. In the study of sludge atomization, many scholars have carried out certain researches, but there is no numerical simulation study of sludge atomization, and numerical simulation can be low-cost, more intuitive study of sludge atomization breakup, has certain advantages. In order to realize the numerical simulation of sludge atomization and breakup, computational fluid dynamics software is used to explore the influence of gas-assisted sludge atomization characteristics and operating parameters (gas velocity, gas-liquid ratio, spray angle) on the effect of sludge atomization. The results show that the density and viscosity of sludge gradually decrease with the increase of moisture content. Gas velocity, gas-liquid ratio and spray angle are the three most important operating parameters that affect sludge atomization and breakup. During the atomization process, the high-speed airflow makes the sludge vibrate and unstable at the front end of the atomizer, resulting in the tearing of the sludge and the breaking of the droplets. The density of droplets in the center area is greater than that in the edge area and there are a few large particles agglomerated. For sludge with moisture content of 87% and a density of 1.065×103 kg/m3, the atomization effect is the best when the gas velocity is 180 m/s, the gas-liquid ratio is 126.3, and the spray angle is 55°. The average particle size of the droplets is about 0.193 mm, and the experimental results are in good agreement with the simulated particle size, and the maximum relative error is 5.80%.
    CFD-DEM and experimental research on sedimentation process of columnar particles
    Jiajun LIU Xuedong LIU Shengnan LÜ Huaxin GAO Jiawei SHAO Honghong ZHANG
    The Chinese Journal of Process Engineering. 2022, 22(12):  1643-1651.  DOI: 10.12034/j.issn.1009-606X.221386
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    Solid-liquid two-phase flow widely existed in daily life. It was widely used in petrochemical, medical, environmental protection and other fields. The common particles in solid-liquid two-phase flow were spherical, cylindrical and rectangular. According to the elongated shape characteristics and particle orientation of cylindrical catalyst particles relative to spherical particles, five cylindrical particles with diameters of 2 mm and different lengths were selected to study. The computational fluid dynamics coupled discrete element method (CFD-DEM) was used to simulate the motion behavior of cylindrical particles during the settlement of tubular containers. Cylindrical particles were constructed by the combination of spherical element method and multi sphere method. A cylindrical particle sedimentation test-bed was established, and the sedimentation process of cylindrical particles in tubular container was verified by high-speed camera. The results showed that the particles near the wall were affected by the wall effect. When cylindrical particles with the same diameter and length were released at different positions, the particles drifted to the center in the process of sedimentation. The settling velocity of particles near the wall was slower and the settling time was longer. When releasing the columnar particles at the same position of the circular tube by only changing the angle between the cylindrical particle's principal axis and the horizontal plane, the particles would eventually rotate to a state where the principal axis was parallel to the horizontal plane. In the process of sedimentation, the greater the angle between the particle principal axis and the horizontal plane, the greater the resistance on the windward surface of the particle, and the particle rotation time would also increase. The Stokes equation for the settlement of cylindrical particles was derived, and the resistance coefficient in the Stokes equation was modified through the experimental data. The resistance coefficient corrected by the experiment was introduced into user defined function (UDF), and the end velocity of particle settlement was simulated and calculated. When using the resistance coefficient of spherical particles, the error was 40.6%. After correction, the relative error was reduced from 50% to less than 17%.
    Discrete relaxation model for coarse-grained CFD-DEM
    Yaxiong YU Fan DUAN Yu ZHANG Qiang ZHOU
    The Chinese Journal of Process Engineering. 2022, 22(12):  1652-1665.  DOI: 10.12034/j.issn.1009-606X.222036
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    Direct application of computational fluid dynamics and discrete element method (CFD-DEM) in industrial applications is unfeasible due to the enormous number of particles. As a result, the coarse-grained CFD-DEM (CFD-CGDEM) is proposed, which could save time and money by lumping a cloud of real particles into a coarse particle. However, due to its under-prediction of collisional energy dissipation, CFD-CGDEM typically over-predicts granular temperature and solid stresses when compared to CFD-DEM. As a result, in CFD-CGDEM simulations, a coarse-grained model capable of increasing energy dissipation is necessary. This work developed a coarse-grained model called discrete relaxation model based on the granular kinetic theory in the homogeneous cooling system (HCSs). By putting dissipation forces on the particle-pair, the discrete relaxation model could increase the energy dissipation between them. The proposed model eliminates errors in the estimation of local average solid phase velocity and granular temperature, as compared to Yu et al.'s relaxation model (Ind. Eng. Chem. Res., 2021, 60(15): 5651-5664). A posteriori simulations on homogeneous cooling systems and bubbling fluidized beds were used to assess the proposed model. It was discovered that CGDEM with the proposed model produced a more accurate forecast of the instantaneous granular temperature in HCSs than CGDEM with the usual coarsening model which was unable to improve energy dissipation. Furthermore, when compared to CFD-CGDEM with Yu et al.'s model and that with usual coarsening model, CFD-CGDEM with the proposed model better reproduced the time-averaged fields generated by CFD-DEM simulation for the considered bubbling fluidized bed. This emphasized the significance of increasing energy dissipation in CFD-CGDEM simulations, as well as the potential of the proposed model to considerably increase simulation accuracy.
    Research on influence of meshing clearance and number of rotor blades on pump performance
    Qin LI Hui WANG Zhiqiang HUANG Yachao MA
    The Chinese Journal of Process Engineering. 2022, 22(12):  1666-1675.  DOI: 10.12034/j.issn.1009-606X.221438
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    In recent years, the demand for oil has increased year by year. In petroleum engineering, oil transportation is an important process. As an important power equipment for oil transportation in the oil field, the oil rotary pump has the advantages of a wide range of medium viscosity and strong self-absorption, but the fluid flow in the rotary pump cavity is not stable. In order to further improve the performance of the oil rotary pump, numerical simulations by the Fluent software were carried out on oil transfer rotor pumps with 5 meshing clearances and 3 rotor blade numbers. The influence of meshing clearance and rotor blade numbers on the performance of oil transfer rotor pumps was analyzed. The results showed that as the meshing gap increases from 0.1 mm to 0.3 mm, the high-speed flow area in the cavity of the 2-blade oil delivery rotor pump was enlarged, the vortex intensity in the rotor cavity increased, and the smoothness and volumetric efficiency of fluid flow in the pump cavity decreasd. The number of blades increased from 2 blades to 4 blades, the variety of pressure changes in the rotor cavity increased, the fluid flow stability in the rotor pump cavity was improved, and the fluid flow in the 3-leaf rotor pump cavity was the most stable. After the optimized design, the smoothness of the flow in the cavity of the oil transfer rotor pump was improved, and the volumetric efficiency increased by 2.1%, which can better meet the needs of oil transportation in the oil field, and can provide a reference for the further optimization of the oil transfer rotor pump.
    Degradation mechanism of mechanical properties for CO2 adsorbed coal
    Chuanqu ZHU Heyi MA Pengtao ZHAO
    The Chinese Journal of Process Engineering. 2022, 22(12):  1676-1682.  DOI: 10.12034/j.issn.1009-606X.221382
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    It is necessary to understand accurately mechanical properties of coal seam induced by CO2 adsorption for the safe and successful implementation of CO2 storage. Through the triaxial compression test of coal samples (long flame coal and anthracite) under different CO2 adsorption equilibrium pressure, the change law of coal mechanical properties after CO2 adsorption is revealed. The research results show that the triaxial stress-strain curves of coal with CO2 adsorption is similar to that of coal without CO2 adsorption, however, after CO2 is adsorbed in coal, it causes the structural reorganization and expansion of the coal, which reduces the surface energy of the coal, and then leads to the obvious reduction of the compressive strength. The higher the CO2 adsorption equilibrium pressure, the greater the reduction of surface energy, and the smaller the tensile strength leading to the formation of coal cracks. CO2 adsorption causes the plastic effect of coal. This plasticization is due to the increase of segment mobility in coal polymer structure caused by CO2 adsorption, which softens the coal, and then leads to the decrease of elastic modulus of coal with the increase of CO2 adsorption equilibrium pressure. In addition, the rearrangement of polymer structure after CO2 adsorption leads to the free volume expansion of coal, the toughness of coal structure is enhanced and the elastic modulus is reduced. The degradation of mechanical properties (strength and elastic modulus) of coal caused by CO2 adsorption can be described by Langmuir curve, and the correlation coefficients are all above 0.99. In the same stress environment, the strength and elastic modulus of high rank coal are higher than that of low rank coal, it is mainly due to the existence of developed cleat system in high rank coal, which provides more conditions for CO2 adsorption. And the decrease percentage of strength and elastic modulus of high rank coal is larger than that of low rank coal after CO2 adsorption.
    Numerical investigation on the turbulent mixing and reaction characteristics in the static mixer with Lightnin insert
    Yanfang YU Yuanyuan HE Peng YANG Yunjuan YAO Huibo MENG Jianhua WU
    The Chinese Journal of Process Engineering. 2022, 22(12):  1683-1690.  DOI: 10.12034/j.issn.1009-606X.222066
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    Using the computational fluid dynamics (CFD) component transport model and SST k?ω turbulence model, A series competitive nitride reaction between naphthol (component A) and para aminobenzene sulfonic acid (component B) was used as the working system to determine the concentration distribution of materials in the range Re=3000~9000 in the Lightnin static mixer. The concentration distribution, turbulent flow, and micromixing characteristics of each component in the chemical reaction field were analyzed. The Lightnin insert can promote the efficient process of the main reaction in the tube. The by-product S was small and its concentration was between 0.0004 and 0.03 mol/L, while the concentration of the main product R was two orders of magnitude higher than that of the by-product S. The turbulence intensity increased obvously with the increasing of Re. The peak value of turbulence intensity reached 2.95, which was 2.02 times than the minimum value at the exit when z/l=2 and Re=3000. The critical value of turbulent kinetic energy appears when wA=0.7, and the turbulent kinetic energy increases with the increase of concentration when wA<0.7, and turbulent kinetic energy decreases with the increase of concentration when wA>0.7. The turbulent dissipation rate decreases gradually with increasing of radial distance and concentration. Compared with wA=0.5, the turbulent dissipation rate of z/l=10 decreases by 2.43%, 8.86%, 19.80%, and 42.25% under wA=0.6~0.9. The radial-flow number is distributed periodically which is formed a small peak value in an even number of the swirl element, while a concave trend in the odd number at Re=6000~9000. Under the condition of the same mole ratio and concentration of components A and B, the micromixing characteristics at the outlet increased by 18.22%, 30.38%, 38.91%, 45.52%, 50.97%, and 55.34% respectively at Re=4000~9000 compared with Re=3000.
    Low-temperature denitrification activity and water tolerance of Ti/Sn doped CeMn-based catalyst
    Lixin QIAN Long DING Jinchao WEI Bentao YANG Hongliang ZHANG Hongming LONG Hongtao WANG
    The Chinese Journal of Process Engineering. 2022, 22(12):  1691-1701.  DOI: 10.12034/j.issn.1009-606X.221388
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    Sintering flue gas is faced with serious denitrification pressure, traditional vanadium tungsten titanium catalyst can effectively remove nitrogen oxides in industrial flue gas above 280℃, which is 100~150℃ higher than that of sintering flue gas. The purpose of denitrification can be achieved by heating sintering flue gas, but it will undoubtedly cause huge energy consumption, which is inconsistent with the concept of carbon emission reduction proposed by China. Therefore, it is necessary to develop denitrification catalysts with low-temperature activity. At present, the CeMn-based catalyst can achieve efficient denitrification in the sintering flue gas temperature range and has broad application prospects. In this study, the Ti/Sn doped CeMn composite metal oxide catalysts were prepared by a coprecipitation method. The effect of Ti/Sn modification on the denitrification and water resistance of the CeMnOx catalyst was studied. The microstructure, ammonia adsorption state, redox capacity, and surface element valence of CeMnOx catalyst were analyzed by physical and chemical properties characterization. The results showed that both Ti and Sn elements improve the low-temperature NOx conversion activity and water resistance of CeMnOx catalyst, and Ti presented a more significant improvement effect. At 150~250℃, the denitrification efficiency of CeMnTiOx was close to 100%. When the reaction temperature was 200℃ and the mixed gas contained 10vol% H2O, the denitrification efficiency of the catalyst remained above 95%. The results of H2 temperature programmed reduction, NH3 temperature programmed desorption, and X-ray photoelectron spectroscopy showed that the Ce-O-Ti and Mn-O-Ti structures in the modified catalyst improve the redox performance of the catalyst, increase the number of weak acid sites and medium strong acid sites on the surface of the catalyst, and form more oxygen vacancies, which made the catalyst exhibit better low-temperature activity.
    Green oxidation process for synthesis of 2-methyl-1,4-naphthoquinone from β-methylnaphthalene
    Jinwen PAN Suohe YANG Guangxiang HE Xiaoyan GUO Haibo JIN Lei MA
    The Chinese Journal of Process Engineering. 2022, 22(12):  1702-1709.  DOI: 10.12034/j.issn.1009-606X.221426
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    2-methyl-1,4-naphthoquinone (2-MNQ) is an important intermediate of K vitamins, which is widely used in medicine, pesticides, feed additives and other fields. However, this vitamin does not exist in nature, and artificial synthesis is the only way to produce 2-MNQ. In industry, vitamin K3 is prepared using 2-methylnaphthalene (2-MN) as raw material and chromic anhydride as an oxidant. This process produces a large amount of waste residue and wastewater containing chromium, causing irreversible pollution to the environment,and trace amounts of chromium in the product pose a threat to human health. Therefore, a new type of the green oxidation process was used for hydrogen peroxide oxidation. The process used 2-methylnaphthalene (2-MN) as raw material, (NH4)2S2O8 as initiator to prepare peroxygen with 30% H2O2 and glacial acetic acid under the catalysis of sulfuric acid. Acetic acid was added dropwise to the reaction solution to synthesize 2-methyl-1,4-naphthoquinone (2-MNQ) by oxidation, and its structure was characterized by ICIR, GC-MS, and LCMS, and the oxidation reaction mechanism and the type and content of by-products were verified. The main impurities were isomer 6-methyl-1,4-naphthoquinone and its by-products phthalic anhydride and 4-methylphthalic anhydride produced by excessive oxidation. The effects of catalyst, reaction temperature, reaction time, dosage of oxidizer and initiator on the yield and conversion of 2-MNQ were investigated. The conversion rate and yield of 2-MNQ were determined by HPLC (external standard method). The optimum reaction conditions were reaction temperature of 65℃, reaction time of 5 h, n(H2O2):n(2-MN)=26:1. The conversion rate of 2-methylnaphthalene was 99%, and the product yield was 34%. The innovation point of this work was to verify the reaction mechanism and the intermediate process in detail using the original external infrared, that was, the raw material 2-methylnaphthalene was oxidized by peracetic acid, the epoxidation reaction generated the intermediate, and then rearranged to generate 2-methylhydroxyquinone, and the oxidation continued to generate the target product 2-methyl-1,4-naphthalene quinone. The process has the characteristics of environment friendly, simple technology, mild operating conditions and easy availability of raw materials.The process uses 2-methylnaphthalene (2-MN) as raw material, (NH4)2S2O8 as initiator to prepare peroxygen with 30% H2O2 and glacial acetic acid under the catalysis of sulfuric acid. Acetic acid was added dropwise to the reaction solution to synthesize 2-methyl-1,4-naphthoquinone (2-MNQ) by oxidation, and its structure was characterized by ICIR, GC-MS, and LCMS, and the oxidation reaction mechanism and the type and content of by-products were verified. The main impurities were isomer 6-methyl-1,4-naphthoquinone and its by-products phthalic anhydride and 4-methylphthalic anhydride produced by excessive oxidation. The effects of catalyst, reaction temperature, reaction time, dosage of oxidizer and initiator on the yield and conversion of 2-MNQ were investigated. The conversion rate and yield of 2-MNQ were determined by HPLC (external standard method). The optimum reaction conditions were obtained reaction temperature 65℃, reaction time 5h, n(CH3COOOH):n(2-MN) = 26:1. The conversion rate of 2-methylnaphthalene was 98%, and the product yield was 35%. The innovation point of this paper is to verify the reaction mechanism and the intermediate process in detail using the original external infrared, that is, the raw material 2-methylnaphthalene is oxidized by oxyacetic acid, the epoxidation reaction generates the intermediate, and then the rearranges to generates 2-methylhydroxyquinone, and the oxidation continues to generate the target product 2-methyl-1, 4-naphthalene quinone. The process has the characteristics of environment friendly, simple technology, mild operating conditions and easy availability of raw materials.
    Synthesis of high-qualified pseudo-boehmite by NaAlO2 sulfuric acid method
    Ling LUO Ping LI Kai HUANG Hailin ZHANG Xing CHEN Wenke LIU Shili ZHENG
    The Chinese Journal of Process Engineering. 2022, 22(12):  1710-1718.  DOI: 10.12034/j.issn.1009-606X.221339
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    Pseudo-boehmite, as a catalyst carrier, molecular sieve, and raw material for the production of activated alumina, is widely used in petrochemical, nitrogen fertilizer, environmental protection, and other industries. In recent years, China's petrochemical industry has faced severe challenges such as heavy and inferior crude oil, lighter, and high costs. The traditional synthesis of pseudo-boehmite includes the neutralization method and alcohol aluminum hydrolysis method, which the former has low cost and easy industrial practice, but the pore structure is poor. The latter can produce high-purity γ-AlOOH, but it has high cost and technical barriers, and there is an urgent need for low-cost production of pseudo-boehmite. Based on the controlled colloidal precipitation dissolution equilibrium of Al(OH)3 micelles, γ-AlOOH could be prepared by adding H2SO4 into NaAlO2 solution. This manuscript aimed at synthesizing γ-AlOOH with purified phase and specific pore structure by NaAlO2 and H2SO4 method combined with the pH swing technique. The γ-AlOOH was characterized by XRD, BET, SEM, NMR, etc., in which the specific surface area, pore volume, and average pore diameter were 341.01 m2/g, 0.41 cm3/g, and 4.78 nm, respectively, was synthesized by adding H2SO4 into NaAlO2 solution at 75℃, pH=7 and 30 min. It was also found that extreme synthesis temperature and terminal pH value lead to the formation of Al(OH)3 in γ-AlOOH, and the pH swing technology could effectively promote the transformation of the Al(OH)3 to γ-AlOOH, with the Al(OH)3 phase decreased from 28.2% to 3.1%. The crystallinity of pure γ-AlOOH increased during the swing process, and 27Al exists in the form of six ligands. Finally, the specific surface area, pore volume, and average pore diameter of γ-AlOOH were increased to 358.88 m2/g, 0.70 cm3/g, and 7.83 nm, respectively, with the temperature of reaction at 70℃, the addition rate of NaAlO2 and Al2(SO4)3 of 15 mL/min, reaction and aging time for 10 min.
    Study on the formation behavior of phosphorus containing solid solution phase in BOF slag
    Yunjin XIA Heng CAO Xiaopan LI Jie LI Dingdong FAN Qi HUANG
    The Chinese Journal of Process Engineering. 2022, 22(12):  1719-1728.  DOI: 10.12034/j.issn.1009-606X.222028
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    Fully utilizing the solid in the slag is relatively helpful to improve the dephosphorization capacity of the slag. There are a large number of 2CaO?SiO2 solid phases in the actual steelmaking slag, and the steelmaking operation is usually carried out under the condition of dicalcium silicate saturation. However, the effect of the existing 2CaO?SiO2 in the slag on the formation of the solid solution has not been well clarified. In this work, the dissolution behavior of dicalcium silicate and the formation of phosphorus-containing solid solution phase in CaO-FeO-SiO2-P2O5 system BOF (basic oxygen furnace) slag were studied by putting dicalcium silicate of the average size of about 450 μm into the slag at 1400℃. The results showed that three regions were formed around the dicalcium silicate particles, namely the unmelted dicalcium silicate region, the coexistence region of the liquid phase and the solid phase (2CaO?SiO2 solid phase and 2CaO?SiO2-3CaO?P2O5 solid solution), and the substrate slag layer. The formation mode of the phosphorus-containing solid solution phase in converter slag was the coexistence of the precipitation mechanism and diffusion mechanism. The phosphorus content in the solid solution formed by the precipitation mechanism was high and the content of other elements was low. The phosphorus content in the solid solution formed by the diffusion mechanism was relatively low and the content of other elements was relatively high. The dissolution of dicalcium silicate particles and the formation of a solid solution showed that after the dicalcium silicate particles were added to the slag, Fe2+ and PO43- in the slag diffused to the dicalcium silicate particles, and Ca2+ and SiO32- in the dicalcium silicate diffused to the slag, forming a solid solution of 2CaO?SiO2-3CaO?P2O5; After that, dicalcium silicate particles were further dissolved and completely transformed into 2CaO?SiO2-3CaO?P2O5 solid solution. With the extension of time, the solid solution particles gradually grew up.
    Comparison of hydrogen production from methane steam reforming in different microreactor configurations
    Junbo LIU Xin GUO Shuoxin ZHANG Bang WU
    The Chinese Journal of Process Engineering. 2022, 22(12):  1729-1738.  DOI: 10.12034/j.issn.1009-606X.221327
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    Microchannel reactors are currently one of the most promising technologies in the field of portable hydrogen production. In order to improve the effectiveness of methane steam reforming for hydrogen production in microreactors, three geometrical models of microreactors with different structures are designed, namely, pipe model, FCC model, and Tri-g ISB model. Numerical simulations of three different microreactors are carried out using Ansys Fluent fluid simulation software in conjunction with the CHEMKIN reaction mechanism file of hydrogen production from methane steam reforming. By studying the gas composition changes at the outlet of microreactors under different conditions, it can be seen that the smaller the inlet velocity is, the higher the CH4 conversion and H2 volume fraction are; When S/C>3, the higher the conversion rate of CH4 increases to more than 80%, and the content of H2 increases to more than 73vol%; The higher the temperature is, the more stable the CH4 conversion can be at 99.9%, almost completely transformed, and the H2 content increases to more than 77vol%. However, the higher the temperature is, the lower the H2 output will be, and the higher the CO content will be. By calculating the time required for the microreactor to reach stability under different conditions, it can be seen that with the increase of inlet velocity and S/C, the stability time gradually decreases and tends to be stable, and with the increase of wall temperature, the stability time first decreases and then increases. By comparing the three kinds of microreactors, it can be seen that the complex structure can enhance the performance of the micro reactor, but will increase the time required for the microreactor to reach stability. In terms of microreactor performance, FCC model is the best, and pipe model is the worst; In terms of stability time, the stability time increases with the increase of structural complexity. The pipe model is the shortest and the Tri-g ISB model is the longest; The complexity of the microreactor structure is different, and the performance improvement is also different. The overly complex structure will inhibit the performance of the microreactor.
    Influence of TiB2 dispersion behavior on the performance of inert cathode materials for aluminum electrolysis
    Ziyang ZHANG Wei WANG Weibin WANG
    The Chinese Journal of Process Engineering. 2022, 22(12):  1739-1746.  DOI: 10.12034/j.issn.1009-606X.221404
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    Due to its good wettability to molten aluminum and good corrosion resistance to the molten electrolyte, TiB2 is a promising cathode material. Recently, a number of studies on TiB2-C composite cathode materials have been undertaken by researchers. Yet, the mechanism of TiB2 reducing sodium and electrolyte penetration is reported scarcely. In order to understand the effect of TiB2 on the performance of cathode materials for aluminum electrolysis, TiB2-C composite cathode materials were prepared by the hot press sintering process, and experimental investigation of sodium expansion of cathode samples was conducted in laboratory aluminum electrolysis cells. By virtue of detailed SEM, TEM, and XRD analyses, the interfacial behavior between TiB2-C composite material and the substrate, the effect of TiC on the performance of the cathode material, and sodium penetration were investigated elaborately. The results showed that TiC generated in the process of firing can increase the degree of graphitization and coherence length of La by converting the disordered carbon into graphite crystals during aluminum electrolysis. This catalysis process, which was called dissolution-precipitation mechanism, can improve the performance of cathode materials and reduce the penetration of electrolytes and sodium to the cathode. The electrical resistivity with TiB2-C composite cathode was 55.6 μΩ?m at 950℃, and that with the carbon cathode was 96.7 μΩ?m applied on the same temperature. As a result, the cathode voltage drop can be effectively reduced by using a TiB2-C composite cathode, which reduced energy consumption in production. The composition and structure of the cathode were changed in a gradient by inserting a transition layer so that the properties and functions of the cathode also were changed in a gradient along the gradient direction. Generally, cracking would initiate and propagate between the composite layer and carbon base because of a large mismatch of their thermal expansions. But the interface bonding between the TiB2-C composite and the substrate was significantly improved by inserting a transition layer, which can remarkably decrease sodium penetration. This work is useful for increasing the service life of cathodes and reducing the energy consumption of aluminum electrolysis.
    Preparation technology optimization and performance characterization of AZI-RHL micelles
    Yuning ZHANG Jingyuan FU Shiyu LIN Xiaojuan LI Wei ZHANG Hualin FU
    The Chinese Journal of Process Engineering. 2022, 22(12):  1747-1754.  DOI: 10.12034/j.issn.1009-606X.221425
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    The azithromycin-rhamnolipid (AZI-RHL) micelles were prepared by thin film hydration method. Taking encapsulation efficiency and drug loading as evaluation indicators, the optimal preparation technology was obtained through single factor test and orthogonal test, and then the physical and chemical properties of AZI-RHL micelles were investigated. The critical micelle concentration (CMC) of RHL aqueous solution was determined before preparing the AZI-RHL micelles. The results showed that the CMC of RHL aqueous solution was about 0.25 mg/mL. The optimized preparation technology conditions were as follows: RHL dosage was 100 mg, methanol dosage was 12 mL, and the stirring time was 20 min. The AZI-RHL micelles prepared under the optimized preparation technology conditions were spherical when observed under transmission electron microscope (TEM), with a hydrodynamic diameter of 136.3±68.5 nm, a Zeta potential of -23.1±6.8 mV, an encapsulation efficiency of 80.34%±0.60%, and a drug loading of 19.42%±0.48%. Infrared spectroscopy revealed that AZI was embedded in micelles. The in vitro cumulative release test showed that AZI-RHL micelles had a certain sustained release effect compared with bulk drugs. The cumulative release curve of AZI-RHL micelles in vitro conformed to the Ritger-Peppas equation, and the release of drugs was dominated by Fick diffusion. To sum up the above, the preparation technology of AZI-RHL micelles was stable and reliable; the AZI-RHL micelles had small particle size, high encapsulation efficiency and high drug loading. AZI-RHL micelles achieved synergistic delivery of RHL and AZI by means of formulations. RHL had good anti-biofilm properties, and in combination with AZI, AZI-RHL micelles can exhibit greater anti-biofilm potential. In addition, rhamnolipids, as small-molecule biosurfactants, had the characteristics of low toxicity and easy degradation compared with other types of surfactants. AZI-RHL micelles enriched the research on surfactant micelles as drug carriers, and provided a certain reference for the preparation of subsequent surfactant micelle drug delivery systems.