Table of Content

22 February 2021, Volume 21 Issue 2

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Contents

Cover and Contents

Chin. J. Process Eng.. 2021, 21(2):  0. 

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Flow & Transfer

Lattice Boltzmann simulation of mass transfer process affected by a moving particle

Rui HE Chongzhi QIAO Limin WANG Shuangliang ZHAO

Chin. J. Process Eng.. 2021, 21(2):  125-133.  DOI: 10.12034/j.issn.1009-606X.220323

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In the catalytic reaction system, the internal and external diffusion have a great impact on the total reaction rate through the influence on the mass transfer process. The internal diffusion in porous channels has been well investigated by statistical mechanics on the influence of wettability, roughness, and electric properties of channel walls. By contrast, the influence of external diffusion needs to be further studied such as, how the active motion of particles impacts the mass transfer. Herein, by using the lattice Boltzmann method coupled with mass transfer process, the influence of the forced rotation or vibration of the catalyst particle was studied. A circular particle with constant interfacial boundary concentration was considered, and the immersed moving boundary and non-equilibrium extrapolation methods were chosen to treat the liquid?particle interface. The effects of rotational speed, vibrational amplitude, and frequency on mass transfer were investigated. The simulations indicated that when only considering diffusion, particle rotation inhibited mass transfer. The higher the rotation speed, the worse the mass transfer, while the overall suppression effect was not significant. The particle streamwise vibration enhanced mass transfer significantly. The lock-on frequency was about 1.9, and the enhancement amplitude reached 10%. Increasing the amplitude and Reynolds number strengthened the mass transfer, and the lock-on frequency moved towards the low frequency direction, while the Schmidt number had little effect on the value of the lock-on frequency. The transverse vibration was also compared with the streamwise one and showed greater enhancement of Sherwood number at a lower frequency. This numerical results not only demonstrated the feasibility of the lattice Boltzmann method for simulating the forced convection mass transfer process but also provided a route for enhancing mass transfer.

Reaction & Separation

Gas separation performance of [Emim][BF₄]-supported ionic liquid membranes prepared by supercritical fluid deposition

Yuqing WANG Jutao LIU Qinqin XU Jianzhong YIN

Chin. J. Process Eng.. 2021, 21(2):  134-143.  DOI: 10.12034/j.issn.1009-606X.220100

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Supported ionic liquid membrane (SILM) technology is an attractive way for CO2 separation and capture, because of its combined advantages of both ionic liquid and membrane. The supercritical fluid deposition is a novel and promising preparation method to improve the CO2 permeation of the SILMs by confining ionic liquid only in the thin effective layer of support, leaving the large pores in the substrate open. To improve the preparation efficiency and the gas separation performance, the ionic liquid, [Emim][BF4], was confined into the asymmetry alumina supports to prepare SILMs by supercritical fluid deposition. The performance of SILMs was evaluated by analyzing the IL addition, the N2 and CO2 permeance and the ideal CO2/N2 selectivity. And the influences of deposition time, IL and ethanol addition were investigated. Comparing to those prepared with other ILs, [Emim][BF4]-SILMs can achieve better CO2 separation performance in a shorter time. The SILM prepared under the optimum condition, exhibited the IL addition of 2.6 mg/g, the CO2 and N2 permeance of 6.4 and 0.14 GPU, the CO2/N2 selectivity of 45.3. It was close to the upper limit of CO2/N2 selectivity of [Emim][BF4], and reached the Robeson upper bound as well, showing both high permeance and selectivity. It was found that higher surface tension of IL and higher IL concentration in supercritical CO2 improved the preparation efficiency significantly, while the IL concentration was mainly determined by IL type, ethanol and IL addition. Besides, using ILs with low viscosity, high CO2/N2 selectivity was conductive to obtaining SILMs with both high CO2 permeance and CO2/N2 selectivity.

Extraction of Ag(I) and Tl(I) by thiacrown ether

Xiankun CHENG Yanhang XIONG Xue HOU Huan TIAN Yongpan TIAN Liang XU Zhuo ZHAO

Chin. J. Process Eng.. 2021, 21(2):  144-152.  DOI: 10.12034/j.issn.1009-606X.220076

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Based on the coordination chemistry of crown ether and soft and hard acid-base theory (HSAB) of crown ether, five kinds of thiacrown ethers were designed and synthesized. And their complexation abilities to two soft acid ions-Ag(I) and Tl(I) were systematically investigated. Firstly, the five crown ethers and their complexes with Ag(I) and Tl(I) complexes were optimized by Gaussian 16 software. On this basis, the Gibbs free energy change (ΔG), enthalpy change (ΔH), internal energy change (ΔU) and other thermodynamic parameters of the complexation process of five sulfur crown ethers with Ag(I) and Tl(I) at 298.15 K were calculated. The simulation results showed that the five thiacrown ethers had changed after being complexed with Ag(I) and Tl(I), and the ΔG and ΔU of the five crown ethers after structural optimization were negative in the complexation process with Ag(I), showing a certain coordination ability. However, during the complexation with Tl(I), ΔG and ΔU were close to 0, and the coordination ability was relatively poor. On the basis of simulation calculation, the extraction ability of five crown ethers on Ag(I) and Tl(I) was investigated by solvent extraction. The experimental results showed that the complex constants of five thiacrown ethers for Ag(I) were 3.97, 6.58, 20.61, 9.76, 13.40, respectively in the single system. In the multi-system, thiacrown ethers 2, 3, 4, and 5 had higher extraction rate and selective recognition ability for Ag(I), while thiacrown ether 1 exhibited poor selective recognition ability for Ag(I), this may be due to the small cavity of thiacrown ether 1. However, the five thiacrown ethers had almost no selectivity for Tl(I), this may be related to the coordination properties of Tl(I). Finally, combined with the simulation results and extraction experiments, the extraction mechanism of five crown ethers on Ag(I) and Tl(I) was analyzed in detail.

Comparison of the influence of Ca²⁺ and Mg²⁺ on floatability of molybdenite

Shuai SHI Tingshu HE Hui LI

Chin. J. Process Eng.. 2021, 21(2):  153-159.  DOI: 10.12034/j.issn.1009-606X.220028

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Ca2+ and Mg2+ are inevitably introduced into the production backwater when the mineral processing plants treat wastewater with precipitation agent, both of them would affect the flotation effect of molybdenite. The different influence of Ca2+ and Mg2+ on the flotation of the molybdenite was compared and investigated by flotation experiments of pure minerals, measurements of zeta-potential, X-ray photoelectron spectroscopy (XPS) and solution chemistry of Ca2+ and Mg2+. The results showed that both Ca2+ and Mg2+ could be adsorbed on the surface of the molybdenite, which changed the surface zeta-potential of the molybdenite and inhibited the floatability of the molybdenite. The inhibition was stronger with the increase of the pH value. Under the alkaline condition, the inhibition of Mg2+ on floatability of the molybdenite was stronger than that of Ca2+. And when the pH value was more than 9.0, the inhibition difference between the two ions was observed. When pH=11.0, the recovery of Mg2+ with a concentration of 800 mg/L decreased by about 34 percentage points compared with that of Ca2+ with a concentration of 800 mg/L. Both Ca2+ and Mg2+ could combine with MoO42– on the “edge” of molybdenite and form precipitation of molybdate salt, which existed on the surface of molybdenite in the form of chemical adsorption. When pH value was more than 9.15, calcium still existed in the form of Ca2+ and Ca(OH)+ and adsorbed on the surface of molybdenite, and the zeta-potential of the molybdenite in slurry containing Ca2+ showed an increasing tendency with the increase of the pH value. While magnesium deposit on the surface of molybdenite in the form of Mg(OH)2, and the zeta-potential of the molybdenite in pulp containing Mg2+ decreased rapidly with the increase of the pH value. This is the main reason for the difference between Ca2+ and Mg2+ in molybdenite?s floatability inhibition.

Process & Technology

The construction of phase diagram for ionic liquid/wool fiber/coagulator ternary systems

Fengjiao PAN Le ZHOU Shaojuan ZENG Xue LIU Yanrong LIU Yi NIE

Chin. J. Process Eng.. 2021, 21(2):  160-166.  DOI: 10.12034/j.issn.1009-606X.220063

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Keratin is one of the natural polymers with abundant reserves, wool fiber consists 95wt% of keratin, which is an important source of natural keratin and has excellent mechanical and biological properties. However, due to the numerous complex inter- and intra-molecular hydrogen bonds, disulfide bonds and other chemical bonds, wool fiber is insoluble in water and common organic solvents. As an emerging green solvent, ionic liquid (IL) shows outstanding performance in dissolving natural polymers such as wool fiber, cellulose, chitin, etc. due to their tunable structure, non-volatile, thermal stability, as well as high solubility for biopolymer. According to the reports, the current researches of ionic liquids on wool fiber are mainly focused on the solubility properties of wool fiber. The studies on the regeneration properties of wool keratin are still limited. There are three components involved in the regeneration process of wool fiber, and thus the thermodynamic behavior of polymer regeneration can be investigated by the ternary phase diagram. In this study, the linearized cloud point (LCP) correlation and ternary phase diagram of IL/wool fiber/coagulator (T) system were constructed by the turbidity method. The effects of coagulator types, coagulation temperatures, and structures of ILs on the properties of wool keratin regeneration were investigated systematically. The regenerated wool keratin was obtained using [Emim]Dep as the solvent with the coagulation temperature of 25℃. In different coagulator systems, the order of wool keratin regeneration capacity is water>ethanol>iso-propanol. The regenerated wool keratin was obtained using [Emim]Dep as the solvent, and water as the coagulator. In different coagulation temperature systems, as the coagulation temperature increased, the regeneration capacity of wool keratin gradually decreased. The regenerated wool keratin was obtained using water as the coagulator with a coagulation temperature of 25℃. In different IL structure systems, the order of wool keratin regeneration capacity was [Emim]Dep>[DBNE]Dep>[DBNH]OAc. The characterization of raw wool fiber and regenerated wool keratin under different regeneration conditions were obtained by FT-IR and XRD, the characterization of the structures and properties showed that the main structure of the regenerated wool keratin basically agreed with the raw wool fiber, and the crystallinity of the regenerated wool keratin had decreased than raw wool keratin. The highest crystallinity of the regenerated wool keratin was obtained from the system of [Emim]Dep/wool fiber/water system at the coagulation temperature of 25℃.

Release of sulfur from roasting the acid leaching tailings of vanadium-bearing stone coal minerals as the raw materials for preparing ceramsite

Chunguang SONG Hongling ZHANG Yuming DONG Lili PEI Honghui LIU Junsheng JIANG Hongbin XU

Chin. J. Process Eng.. 2021, 21(2):  167-173.  DOI: 10.12034/j.issn.1009-606X.220045

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The acid leaching tailings of vanadium-bearing stone coal minerals (hereinafter referred to as “tailings”) is the solid waste discharged in the industry of vanadium extraction from stone coal. Using the tailings as raw materials for the preparation of ceramsite is an important way for the resource ultilization of the tailings. Ceramsite can be widely used in many areas, and the main application is to be used as lightweight aggregate in construction industry. Lightweight aggregate has a critical requirement of sulfur content when it is used as building materials. The total contents of sulfate and sulfide, calculated by SO3, should be no higher than 1.0wt%. Usually, the sulfur content (calculated by SO3) of the tailings is much higher than 1.0wt%, which is much higher than the requirement of lightweight aggregate. So, it is necessary to study the release of sulfur during the preparation of ceramsite using tailings as raw materials. In this work, simultaneous thermogravimetric–Fourier transform infrared spectrometry (TG–FT-IR) analysis were used to investigate the weight loss, the exothermic/endothermic phenomenon, and releasing of gases in the process of roasting the tailings as the raw materials for preparing ceramsite. The sulfur contents of samples prepared by roasting tailings at different temperatures were tested, their crystal phases were characterized, the Gibbs free energies of several reactions were obtained by thermodynamic calculation, and the mechanism of sulfur releasing from tailings was discussed accordingly. The results showed that sulfur-containing substances in the tailings gradually decomposed and SO2 was released with temperature increasing. Consequently, the sulfur content of samples gradually decreased with roasting temperature increasing. The sulfur content (0.44wt%) of samples obtained at 1200℃ can meet the requirements of lightweight aggregate. Intermediated phases such as wollastonite (CaSiO3) might be formed by the reaction of anhydrite and quartz in the tailings, accompanied with the releasing of SO2. SiO2, Fe2O3 and Al2O3 in tailings might be helpful for the releasing of sulfur.

The settling behavior of scaling ions in brine purification process by NaOH–flue gas method

Xingguo LUO Jianbo PENG Sanqiang ZHENG Mingyu ZHANG Xingbin LI Chang WEI Zhigan DENG

Chin. J. Process Eng.. 2021, 21(2):  174-182.  DOI: 10.12034/j.issn.1009-606X.220002

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The scaling ions (Ca2+, Mg2+ and CO32–) in raw brine are easy to form calcium carbonate and calcium sulfate deposit in the process of vacuum evaporation. Because of their poor thermal conductivity and their good adherence to the walls, these mineral compounds decrease the heat transfer ratio and even shorten equipment life by corrosion. The brine purification method of NaOH–flue gas can utilize the flue gas from a power plant and low concentration waste alkali from chlor-alkali enterprises, which has absolute advantages and broad application prospects in energy conservation and environmental protection. In order to analyze the behavior of scaling ions in the process of brine purification by NaOH–flue gas method, the experiment of brine purification by CO2 instead of flue gas was carried out. The effects of CO2 feeding time and pH value on the behaviors of Ca2+, Mg2+ and CO32– in brine were investigated. The behavior of scaling ions and the mineralogical characteristics of precipitates were studied by thermodynamic calculation (Factsage), XRD and SEM–EDS. The thermodynamic and experimental results showed that when pH=11.5 and CO2 introduction time was 60 min, Ca2+ in raw brine was reduced to 6.0~8.0 mg/L, and Mg2+ concentration was reduced to 0.65 mg/L when the time was extended to 80 min. There was a linear relationship between the concentration of CO32– and CO2 entry time. Besides, the dissolution amount and ratio of CO2 in brine were the largest, and the equilibrium constant (K) was the largest at the pH=11.5. Then, the results of XRD and SEM showed that the precipitated vaterite type of calcium carbonate crystals was obtained when the pH of the process was controlled at 9.5. When the pH value increased to 10, the crystal form of calcium carbonate transformed from vaterite to aragonite crystals, and its morphology changed from a regular spherical shape to an oval shape. When the pH was 11 or 11.5, the precipitation was a eutectic of calcium and magnesium, and the crystal form of calcium carbonate was converted from vaterite to calcite crystals, which was more thermodynamically stable.

Materials Engineering

Preparation and physicochemical properties of cyclopropyl methyl ketazine

Wenzhao ZHAO Peng ZHAO Long LIU Yangfeng XIA, Yanqiang ZHANG

Chin. J. Process Eng.. 2021, 21(2):  183-192.  DOI: 10.12034/j.issn.1009-606X.220091

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Ketazines as useful intermediates have been extensively applied in many industrial fields, including dyes, pharmaceuticals, aviation fuels, photosensitive materials, as well as polymerizable monomers. In this work, a new ketazine derivative (cyclopropyl methyl ketazine, C10N2H16) was prepared from cyclopropyl methyl ketone and hydrazine hydrate. Under the atmospheric pressure, the reaction was studied under different mole ratios of cyclopropyl methyl ketone to hydrazine, reaction temperatures, and reaction times. With the optimized reaction conditions of 2.0:1, 363.2 K, 101.3 kPa and 7 h, the yield of cyclopropyl methyl ketazine was up to 93.6% through the chromatograph measurements. The structure of cyclopropyl methyl ketazine was characterized by IR and NMR spectra after it was purified through distillation. In order to prove the existence of isomers, Gaussian 09 program to optimize the structures was used and the energy values (single point energy) of cyclopropyl methyl ketazine was calculated. Furthermore, a comprehensive set of the physicochemical parameters for cyclopropyl methyl ketazine was provided, including density [ρ=0.884~0.947 g/cm3], dynamic viscosity (η=1.39~2.88 mPa?s), liquid heat capacity [Cp=2.03~2.32 J/(g?K)] and surface tension (σ=22.1~25.0 mN/m) in temperature range (280?400 K). The data of ρ, η and σ exhibited the negative correlations with temperature, while Vm, α and Cp showed the positive correlations with temperature, which all had a good fitting degree for equations. Considering the cyclopropyl methyl ketazine reaction systems, the vapor?liquid equilibria (VLE) of binary system (cyclopropyl methyl ketone?cyclopropyl methyl ketazine) was measured and correlated with NRTL model to acquire the binary interaction parameters. The obtained data and correlations are valuable for industrial processes, and could be the good references for industrial design.

Catalytic wet peroxide oxidation of methyl orange in a fixed bed with Fe⁰-NaA-SSFSF

Jian LIU Yini HUANG Xi CHEN Zhengji YI

Chin. J. Process Eng.. 2021, 21(2):  193-201.  DOI: 10.12034/j.issn.1009-606X.220066

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Stainless steel fiber sintered felt supported Fe0-NaA molecular sieve membrane (Fe0-NaA-SSFSF) was prepared by the secondary growth and liquid-phase reduction method. The catalytic wet peroxide oxidation performance of methyl orange in a fixed bed with Fe0-NaA-SSFSF was studied. The effects of pH, bed height, temperature and inlet concentration on the conversion rate of methyl orange, COD removal rate and iron leaching concentration were investigated. The stability of Fe0-NaA-SSFSF catalyst was determined. The results showed that when the pH of the solution was 2.5, the conversion of methyl orange fluctuated in the experimental time range. With the decrease of pH to 2.0, the conversion of methyl orange tended to be stable. When the pH continued to decrease to 1.5, the conversion of methyl orange remained basically unchanged. With the increase of bed height from 0.45 cm to 0.90 cm, the conversion rate of methyl orange remained almost the same and the COD removal rate increased from 21.2% to 85.0%. With the decrease of reaction temperature from 70℃ to 50℃, the conversion rate of methyl orange remained almost unchanged and the COD removal rate decreased from 85.0% to 42.4%. Both the conversion rate of methyl orange and COD removal rate had no obvious change with the increase of inlet methyl orange concentration. Under the conditions of pH=2.0, bed height of 0.90 cm, reaction temperature of 70℃, methyl orange concentration of 50~200 mg/L, the conversion rate of methyl orange was greater than 97% in the experimental time range, the maximum iron leaching concentration was lower than 10.2 mg/L, and the COD removal rate was above 85% when the fixed bed was running continuously for 240 min. When the Fe0-NaA-SSFSF catalyst was reused three times, the conversion rate of methyl orange kept basically the same.

Preparation and characterization of graphene oxide modified n-dodecanol phase change microcapsules

Jinli LU Li WU Yafang HAN Yang LI

Chin. J. Process Eng.. 2021, 21(2):  202-209.  DOI: 10.12034/j.issn.1009-606X.220022

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With the characteristics of high energy storage density, constant temperature in phase change process and convenient storage/transportation, the microencapsulated phase change material (MPCM) has a broad application prospect in the fields of thermal storage, transportation and utilization such as solar energy thermal utilization, waste heat recovery and utilization, refrigeration and air conditioning, and so on. However, the traditional MPCM particles use formaldehyde as the shell material, which releases harmful substances during application process. In addition, the MPCM application fields is restricted because of low thermal conductivity of polymer shell. Therefore, it is necessary to develop a new type of formaldehyde-free MPCM. In this work, the MPCM particles of n-dodecanol as core material and acrylic resin copolymers as shell were prepared employing the method of suspension polymerization under the condition of ultrasound exposure. Furthermore, in order to enhance the thermal performance of MPCM particles, the graphene oxide (GO) was introduced to modify the MPCM. Then the characteristics of MPCM and GO-MPCM were tested by scanning electron microscope (SEM), Fourier transform infrared spectrometer (FT-IR), differential scanning calorimetry (DSC), thermal gravimetric analyzer (TG–DTA). The results showed that there was no effect on basic chemical organization of MPCM with introduce the graphene oxide nano-particles. However, under the same preparation conditions, the introduction of graphene oxide nano-particles increased the MPCM particles size and greatly affected their appearance and morphology. The thermal conductivity of MPCM particles was improved. The encapsulation rate increased to 62%, and the latent heat of phase change was 135.6 kJ/kg, which was 45% higher than that of unmodified phase change microcapsules. The study results in this work can provide data support for the preparation and performance improvement of MPCM particles, and also provide theoretical basis for its engineering application.

Giant dielectric properties and mechanism of Ca and Ta co-doped TiO₂ ceramics

Bing CUI Ji CHEN Zaizhi YANG Weiyu ZHAO Yujun DENG Qian YU Juan LIU Dong XU

Chin. J. Process Eng.. 2021, 21(2):  210-218.  DOI: 10.12034/j.issn.1009-606X.220023

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With the rapid development of the society, ceramic materials are being studied more and more. Recently, most of the studies on co-doping TiO2 ceramics are about trivalent acceptor and pentavalent elements which exhibit good dielectric properties, while the studies on divalent elements are relatively few. However, the mechanism, preparation process and the effects of different doped ion combinations on the dielectric properties are still unclear. Further research on the microstructure, dielectric properties and mechanism of co-doped TiO2 ceramics is of great significance. In this work, (Ca, Ta) co-doped TiO2 ceramics were prepared by a solid state reaction process. The effects of different components on their morphology, crystal structure and dielectric properties were studied. The sample with high viscosity needs to be sintered at 1400℃ for a minimum of about 4 h. When (Ca1/3Ta2/3)xTi1?xO2 ceramic with x≥7%, the second phase appeared in the (Ca1/3Ta2/3)xTi1?xO2 ceramic sample. Compared with pure TiO2, (Ca1/3Ta2/3)xTi1?xO2 ceramics all had giant dielectric constant, which roughly increased by two orders of magnitude. With the continuous increase of doping, the dielectric constant increased first and then decreased, while the dielectric loss was completely opposite. (Ca1/3Ta2/3)xTi1?xO2 ceramic with x=3% showed better dielectric and pressure-sensitive properties of ceramics. Ta doping led to the generation of electrons in the material, but Ca doping can produce vacancy and the defective dipole cluster can improve the dielectric performance.

Biochemical Engineering

Molecular dynamics simulation and calculation of binding free energy of a HBc-VLP

Yanyan MA Zhengjun LI Songping ZHANG Wei CHEN Ying REN

Chin. J. Process Eng.. 2021, 21(2):  219-229.  DOI: 10.12034/j.issn.1009-606X.220085

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Hepatitis B core antigen virus-like particles (HBc-VLPs) are widely used as vaccine vectors due to their good stability and easy modification, and the investigations of VLPs is one of the hot spots in the field of bio-pharmaceutical engineering. However, VLPs may disassemble or aggregate due to their sensitivity to temperature, pH and other factors, which becomes the bottleneck hindering the widely application, and the underlying mechanisms which governs the structure and thus stability of VLPs is still ambiguous. In this work, molecular dynamics simulation was utilized to investigate the stability of the dimer, pentamer and hexamer formed by protein subunits in HBc-VLP. Instead of using empirical values in previous studies, the parameters of protein dielectric constant in aqueous solution were obtained by molecular dynamics simulations, and the results suggested that both the aqueous solvent and the arrangement of protein subunits in the complex could significantly change the dielectric constant, which further affected the binding free energy. Furthermore, with the dielectric constant of protein subunits, the binding free energy between protein subunits were calculated by the molecular mechanics-Poisson Boltzmann solvent accessible surface area (MM-PBSA) method. Finally, according to the calculation results, it was speculated that the stability of the hexamer was better than the pentamer, and the dimers formed between two adjacent hexamers or between a pentamer and a hexamer can further lead to a more stable structure. These understandings could provide theoretical guidance for the modification of candidate vaccine with HBc-VLPs as the carrier.

Role of Rcs phosphorelay system on capsule synthesis of Klebsiella pneumoniae

Shaoqi SUN Yike WANG Yang YANG Chenguang ZHU Jiping SHI Jian HAO

Chin. J. Process Eng.. 2021, 21(2):  230-239.  DOI: 10.12034/j.issn.1009-606X.220104

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Klebsiella pneumoniae, capsulated bacterium, is an important industrial microorganism. Roles of the Rcs phosphorelay system on K. pneumoniae capsular polysaccharide synthesis were investigated in this work. In this research, rcsA and rcsB in K. pneumoniae were knocked out individually with the Red recombinase assisted gene replacement method. Capsule synthesized by K. pneumoniae ΔrcsA and K. pneumoniae ΔrcsB were both weak, therefore the transformation efficiency of cells was significantly increased. When these two strains were cultured with glucose or glycerol as a main carbon source, the yields of 2,3-butanediol or 1,3-propanediol produced by the cells were both higher than that of the wild-type strain. Cells of the two strains were more likely to agglutinate in the broth, which is favored for the downstream process. rcsA and rcsB over-expression strains were constructed, and the growth of the two strains were both slower than the wild-type strain. The transformation efficiency of rcsA and rcsB over-expressing strains both decreased compared with the wild-type strain. The titer of extracellular polysaccharide and the viscosity of fermentation broth of rcsA or rcsB over-expression strains increased. Especially, 10.33 g/L of extracellular polysaccharide was produced by the rcsA over-expression strain, which was five times of that of the wild type strain. On the whole, the regulation of rcsA and rcsB expression provides a novel way to influence the performance of K. pneumoniae.

Environment & Energy

Numerical simulation of combustion of CH₄ mixed H₂ and rationality analysis of premixed ratio

Ke WANG Yindi ZHANG Chengjing WANG Yue XIN

Chin. J. Process Eng.. 2021, 21(2):  240-250.  DOI: 10.12034/j.issn.1009-606X.220058

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The hydrogen-blended combustion technology is a new technology that mixes a specific proportion of hydrogen, in the fuel, to improve combustion efficiency and reduce pollutant emissions. This technology is considered to be an effective method in improving the overall energy produced. The principle of “power to gas” technology is to take advantage of the intermittent nature of both wind-generated and solar energy, by using the surplus energy for the production of hydrogen by the electrolysis of water. The hydrogen can then be combined with carbon dioxide to produce methane, or by direct addition to natural gas in the pipeline network, thus enabling large-scale utilization of hydrogen energy. The rationality of the application of hydrogen-blended combustion technology in gas boilers is based on a simplified mechanism of GRI-MECH 3.0 of methane combustion. This reaction contains 24 elementary reactions involving 17 components. In this work, a numerical simulation experiment was designed, where atmospheric air was the oxidant, and the oxygen excess coefficient was maintained as a constant. A total of eleven groups of methane/hydrogen premixing ratios Rf (0~1) were considered and the effects of differing hydrogen blending ratios on fuel combustion temperature, combustion rate, and main pollutant emission concentrations were studied. The results showed that, by increasing the hydrogen blending ratio, both the combustion temperature and the reaction rate increased. Similarly, the concentration and the total emissions of soot and CO decreased, while the concentration of NOx increased, however, the total emissions decreased first then increased. The mechanisms relating to the effect of hydrogen mixing on the combustion process and the resultant pollutant formation were also analyzed, concerning China's urban fuel gas interchangeability regulations and industrial pollutant emission standards, the optimal hydrogen blending ratio was determined to be 23%.