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Table of Content
28 August 2021, Volume 36 Issue 8
    Separation Science and Engineering
    Meltblown fabric vs nanofiber membrane, which is better for fabricating personal protective equipments
    Junwei Wu, Hongjia Zhou, Jingyi Zhou, Xiao Zhu, Bowen Zhang, Shasha Feng, Zhaoxiang Zhong, Lingxue Kong, Weihong Xing
    2021, 36(8):  1-9.  doi:10.1016/j.cjche.2020.10.022
    Abstract ( )   PDF (2768KB) ( )  
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    The coronavirus disease 2019 (COVID-19) pandemic has led to a great demand on the personal protection products such as reusable masks. As a key raw material for masks, meltblown fabrics play an important role in rejection of aerosols. However, the electrostatic dominated aerosol rejection mechanism of meltblown fabrics prevents the mask from maintaining the desired protective effect after the static charge degradation. Herein, novel reusable masks with high aerosols rejection efficiency were fabricated by the introduction of spider-web bionic nanofiber membrane (nano cobweb-biomimetic membrane). The reuse stability of meltblown and nanofiber membrane mask was separately evaluated by infiltrating water, 75% alcohol solution, and exposing under ultraviolet (UV) light. After the water immersion test, the filtration efficiency of meltblown mask was decreased to about 79%, while the nanofiber membrane was maintained at 99%. The same phenomenon could be observed after the 75% alcohol treatment, a high filtration efficiency of 99% was maintained in nanofiber membrane, but obvious negative effect was observed in meltblown mask, which decreased to about 50%. In addition, after long-term expose under UV light, no filtration efficiency decrease was observed in nanofiber membrane, which provide a suitable way to disinfect the potential carried virus. This work successfully achieved the daily disinfection and reuse of masks, which effectively alleviate the shortage of masks during this special period.
    Concentration of mixed acid by electrodialysis for the intensification of absorption process in acrylic acid production
    Hanxiao Du, Lixin Xie, Jie Liu, Shichang Xu
    2021, 36(8):  10-18.  doi:10.1016/j.cjche.2020.07.020
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    The absorption process in acrylic acid production was water-intensive. The concentration of acrylic acid before distillation process was low, which induced to large amount of wastewater and enormous energy consumption. In this work, a new method was proposed to concentrate the side stream of absorption column and thus increase the concentration in bottom product by electrodialysis. The influence of operating conditions on concentration rate and specific energy consumption were investigated by a laboratory-scale device. When the voltage drop was 1 V·cP-1 (1 cP=10-3 Pa·S), flow velocity was 3 cm·s-1 and the temperature was 35 ℃, the concentration rates of acrylic acid and acetic acid could be 203.3% and 156.6% in the continual-ED process. Based on the experimental data, the absorption process combined with ED was simulated, in which the diluted solution from ED process was used as spray water and the concentrated solution was feed back to the absorption column. The results shown that the flow rate of spray water was decreased by 37.1%, and the acrylic acid concentration at the bottom of the tower was increased by 4.56%. The ions exchange membranes before and after use 1200 h were tested by membrane surface morphology (scanning electron microscope), membrane chemical groups (infrared spectra), ion exchange capacity, and membrane area resistance, which indicated the membrane were stable in the acid system. This method provides new method for energy conservation and emission reduction in the traditional chemical industry.
    Eco friendly adsorbents for removal of phenol from aqueous solution employing nanoparticle zero-valent iron synthesized from modified green tea bio-waste and supported on silty clay
    Shaimaa T. Kadhum, Ghayda Yassen Alkindi, Talib M. Albayati
    2021, 36(8):  19-28.  doi:10.1016/j.cjche.2020.07.031
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    The present research investigated a novel route for the synthesis of nanoparticle zero-valent iron (NZVI) utilizing an aqueous extract of green tea waste as a reductant with ferric chloride. Also, the supported nanoparticle zero-valent iron was synthesized using natural silty clay as a support material (SC-NZVI). The NZVI and SC-NZVI were characterized by infrared spectroscopy (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), and zeta potential (ζ). The interpretation of the results demonstrated that the polyphenol and other antioxidants in green tea waste can be used as reduction and capping agents in NZVI synthesis, with silty clay an adequate support. Additionally, the experiments were carried out to explore phenol adsorption by NZVI and SC-NZVI. To determine the optimum conditions, the impact of diverse experimental factors (i.e., initial pH, adsorbent dose, temperature, and concentration of phenol) was studied. Langmuir, Freundlich, and Tempkin isotherms were used as representatives of adsorption equilibrium. The obtained results indicated that the adsorption processes for both NZVI and SC-NZVI well fitted by the Freundlich isotherm model. The appropriateness of pseudo_first_order and pseudo_second_order kinetics was investigated. The experimental kinetics data were good explained by the second-order model. The thermodynamic parameters (ΔH0, ΔS0, and ΔG0) for NZVI and SC-NZVI were determined. The maximum removal rates of phenol at optimum conditions, when adsorbed onto NZVI and SC-NZVI, were found to be 94.8% and 90.1%, respectively.
    Coalescence separation of oil water emulsion on amphiphobic fluorocarbon polymer and silica nanoparticles coated fiber-bed coalescer
    Qian Zhang, Lei Li, Lixia Cao, Yanxiang Li, Wangliang Li
    2021, 36(8):  29-37.  doi:10.1016/j.cjche.2020.07.034
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    Discharging untreated oily wastewater into the environment disrupts the ecological balance, which is a global problem that requires urgent solutions. Superhydrophilic and superoleophilic fibrous medium (FM) effectively separated oil-water emulsion as it was hydrophobic underwater. But its separation efficiencies (SEs) first increased to 98.9%, then dropped to 97.6% in 10 min because of oil-fouling. To tackle this problem, FM deposited with 0%-10% silica nanoparticle (NPsFMs), then coated by fluorocarbon polymer (X-[CH2CH2O]nCH2CH2O-Y-NH-COOCH2C4F9) (FCNPsFMs), was used to enhance its roughness and regulate its initial wettability to improve the anti-fouling property. FCFM and FCNPsFMs were hydrophobic and oleophobic in air and oleophobic underwater. Their water contact angles, oil contact angles and oil contact angles were 115.3°-121.1°, 128.8°-136.5°, and 131.6°-136.7°, respectively, meeting the requirement of 90°-140° for coalescence separation. FCNPsFM-5 had the best separation performance with a constant value of 99.8% in 10 min, while that of FCNPsFM-10 slightly decreased to 99.5%. Theoretical released droplet (TRD) diameter, calculated by the square root of the product of pore radius and fiber diameter, was used for the evaluation of coalescence performance. Analyzed by two ideal models, TRD diameter and fiber diameter showed a parabola type relationship, proving that the separation efficiency was a collaborative work of wettability, pore size and fiber diameter. Also, it explained the SEs reduction from FCNPsFM-5 to FCNPsFM-10 was revelent to the three parameters. Moreover, FCNPsFMs effectively separated emulsions stabilized by cationic surfactant CTAB (SEs:97.3%-98.4%) and anionic surfactant SDBS (SEs:91.3%-93.4%). But they had an adverse effect on nonionic surfactant Tween-80 emulsion separation (SEs:94.0%-71.76%). Emulsions made by diverse oils can be effectively separated:octane (SEs:99.4%-100%), rapeseed oil (SEs:97.3%-98.8%), and diesel (SEs:95.2%-97.0%). These findings provide new insights for designing novel materials for oil-water separation by coalescence mechanism.
    Enhanced extraction of essential oil from Cinnamomum cassia bark by ultrasound assisted hydrodistillation
    Guanghui Chen, Fengrui Sun, Shougui Wang, Weiwen Wang, Jipeng Dong, Fei Gao
    2021, 36(8):  38-46.  doi:10.1016/j.cjche.2020.08.007
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    Cinnamon essential oil with many bioactivities is an important raw material for the production of various chemicals, and the conventional hydrodistillation (HD) for cinnamon oil extraction always require a longer extraction time. In this work, ultrasound-assisted hydrodistillation extraction (UAHDE) technique was employed to enhance the extraction efficiency of essential oils from cinnamon barks. The parameters with significant effects on the essential oil extraction efficiency (ultrasound time, ultrasound power, extraction time, liquid-solid ratio) were optimized, and the proposed UAHDE was compared with the conventional HD extraction in terms of the extraction time, extraction yield, and physicochemical properties of extracted oils. Compared to the HD extraction, the UAHDE resulted in a shorter extraction time and a higher extraction yield. Using GC-MS analysis, the UAHDE provided more valuable essential oil with a high content of the vital trans-cinnamaldehyde compounds compared with the HD. Scanning electron micrograph (SEM) confirmed the efficiency of ultrasound irradiation for cinnamon oil extraction. In addition, the analysis of electric consumption and CO2 emission shows that the UAHDE process is a more economic and environment-friendly approach. Thus, UAHDE is an efficient and green technology for the cinnamon essential oil extraction, which could improve the quantity and quality of cinnamon oils.
    Numerical simulation of low-concentration CO2 adsorption on fixed bed using finite element analysis
    Yonghou Xiao, Shuang Qiu, Qidong Zhao, Yuhao Zhu, Chirag B. Godiya, Gaohong He
    2021, 36(8):  47-56.  doi:10.1016/j.cjche.2020.08.012
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    Accurately predicting distributions of concentration and temperature field in fixed-bed column is essential for designing adsorption processes. In this study, a two-dimensional (2D), axisymmetric, nonisothermal, dynamic adsorption model was established by coupling equations of mass, momentum and energy balance, and solved by finite element analysis. The simulation breakthrough curves fit well with the low-concentration CO2 adsorption experimental data, indicating the reliability of the established model. The distributions of concentration and temperature field in the column for CO2 adsorption and separation from CO2/N2 were obtained. The sensitivity analysis of the adsorption conditions shows that the operation parameters such as feed flow rate, feed concentration, pellet size, and column height-to-diameter ratio produce a significant effect on the dynamic adsorption performance. The multi-physics coupled 2D axisymmetric model could provide a theoretical foundation and guidance for designing CO2 fixed-bed adsorption and separation processes, which could be extended to other mixed gases as well.
    Ethylene absorption in N-methyl-2-pyrrolidone/silver nano-solvent: Thermodynamics and kinetics study
    Mohammad Yousefi, Shima Azizi, S. M. Peyghambarzadeh, Zoha Azizi
    2021, 36(8):  57-66.  doi:10.1016/j.cjche.2020.08.017
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    The effect of presence of silver nanoparticles in pure N-methyl-2-pyrrolidone (NMP) solvent for ethylene gas absorption in an experimental pressure decaying setup has been investigated. All experiments were performed at temperatures of 278.15 K, 298.15 K and 328.15 K and different pressures (up to ethylene dew point) as well as different concentrations of silver nanoparticles (0.05 g·L-1 and 0.1 g·L-1). The kinetic data of absorption, Henry's law constants, and heat of absorption were calculated. Comparison of the pure solvent and the nanofluids absorption results revealed that the presence of small amounts of nanoparticles could improve the absorption performance between 1.5%-18%. Finally, the effect of temperature, pressure, and nanoparticle concentration on the equilibrium results were investigated.
    Fabrication of Pd-Nb bimetallic doped organosilica membranes by different metal doping routes for H2/CO2 separation
    Hengfei Zhang, Yibin Wei, Shufeng Niu, Hong Qi
    2021, 36(8):  67-75.  doi:10.1016/j.cjche.2020.09.003
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    Monometallic doping has proved its superiority in improving either permselectivity or H2 permeability of organosilica membranes for H2/CO2 separation, but it is still challenging to break the trade-off effect. Herein, we report a series of Pd-Nb bimetallic doped 1,2-bis(triethoxysilyl)ethane (Pd-Nb-BTESE, PNB) membranes with different metal doping routes for simultaneously improving H2 permeance and H2/CO2 permselectivity by the synergetic effects of Pd and Nb. The doped Pd can exist in the BTESE network as nanoparticles while the doped Nb is incorporated into BTESE network forming Nb-O-Si covalent bonds. The metal doping routes significantly influence the microstructure of PNB networks and gas separation performance of the PNB membranes. We found that the PNB membrane with Pd doping priority (PNB-Pd) exhibited the highest surface area and pore volume, comparing with Nb doping priority (PNB-Nb) or Pd-Nb simultaneous doping (PNB-PdNb). The PNB-Pd membrane could not only exhibit an excellent H2 permeance of ~10-6 mol·m-2·s-1·Pa-1 but also a high H2/CO2 permselectivity of 17.2. Our findings may provide novel insights into preparation of bimetallic doped organosilica membranes with excellent H2/CO2 separation performance.
    Simultaneous CO2 capture and thermochemical heat storage by modified carbide slag in coupled calcium looping and CaO/Ca(OH)2 cycles
    Chunxiao Zhang, Yingjie Li, Zhiguo Bian, Wan Zhang, Zeyan Wang
    2021, 36(8):  76-85.  doi:10.1016/j.cjche.2020.09.026
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    The simultaneous CO2 capture and heat storage performances of the modified carbide slag with by-product of biodiesel were investigated in the process coupled calcium looping and CaO/Ca(OH)2 thermochemical heat storage using air as the heat transfer fluid. The modified carbide slag with by-product of biodiesel exhibits superior CO2 capture and heat storage capacities in the coupled calcium looping and heat storage cycles. The hydration conversion and heat storage density of the modified carbide slag after 30 heat storage cycles are 0.65 mol·mol-1 and 1.14 GJ·t-1, respectively, which are 1.6 times as high as those of calcined carbide slag. The negative effect of CO2 in air as the heat storage fluid on the heat storage capacity of the modified carbide slag is overcome by introducing CO2 capture cycles. In addition, the CO2 capture reactivity of the modified carbide slag after the multiple calcium looping cycles is enhanced by the introduction of heat storage cycles. By introducing 10 heat storage cycles after the 10th and 15th CO2 capture cycles, the CO2 capture capacities of the modified carbide slag are subsequently improved by 32% and 43%, respectively. The porous and loose structure of modified carbide slag reduces the diffusion resistances of CO2 and steam in the material in the coupled process. The formed CaCO3 in the modified carbide slag as a result of air as the heat transfer fluid in heat storage cycles decomposes to regenerate CaO in calcium looping cycles, which improves heat storage capacity. Therefore, the modified carbide slag with by-product of biodiesel seems promising in the coupled calcium looping and CaO/Ca(OH)2 heat storage cycles.
    Catalysis, Kinetics and Reaction Engineering
    Photocatalytic activity of metal nanoparticle-decorated titanium dioxide for simultaneous H2 production and biodiesel wastewater remediation
    Patsakol Prayoonpunratn, Trin Jedsukontorn, Mali Hunsom
    2021, 36(8):  86-100.  doi:10.1016/j.cjche.2020.08.010
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    A set of metal nanoparticle-decorated titanium dioxide (Mx/TiO2; where x is the percent by mass,%) photocatalysts was prepared via the sol-immobilization in order to enhance the simultaneous hydrogen (H2) production and pollutant reduction from real biodiesel wastewater. Effect of the metal nanoparticle (NP) type (M = Ni, Au, Pt or Pd) and, for Pd, the amount (1 %-4 %) decorated on the surface of thermal treated commercial TiO2 (T400) was evaluated. The obtained results demonstrated that both the type and amount of decorated metal NPs did not significantly affect the pollutant reduction, measured in terms of the reduction of chemical oxygen demand (COD), biological oxygen demand (BOD) and oil & grease levels, but they affected the H2 production rate from both deionized water and biodiesel wastewater, which can be ranked in the order of Pt1/T400 > Pd1/T400 > Au1/T400 > Ni1/T400. This was attributed to the high difference in work function between Pt and the parent T400. However, the difference between Pt1/T400 and Pd1/T400 was not great and so from an economic consideration, Pd/TiO2 was selected as appropriate for further evaluation. Among the four different Pdx/TiO2 photocatalysts, the Pd3/TiO2 demonstrated the highest activity and gave a high rate of H2 production (up to 135 mmol·h-1) with a COD, BOD and oil & grease reduction of 30.3%, 73.7% and 58.0%, respectively.
    One-step conversion of syngas to light olefins over bifunctional metal-zeolite catalyst
    Ce Du, Linet Gapu Chizema, Emmerson Hondo, Mingliang Tong, Qingxiang Ma, Xinhua Gao, Ruiqin Yang, Peng Lu, Noritatsu Tsubaki
    2021, 36(8):  101-110.  doi:10.1016/j.cjche.2020.09.004
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    Light olefins (C2-C4) are fundamental building blocks for the manufacture of polymers, chemical intermediates, and solvents. In this work, we realized a composite catalyst, comprising MnxZry oxides and SAPO-34 zeolite, which can convert syngas (CO + H2) into light olefins. MnxZry oxide catalysts with different Mn/Zr molar ratios were facilely prepared using the coprecipitation method prior to physical mixing with SAPO-34 zeolite. The redox properties, surface morphology, electronic state, crystal structure, and chemical elemental composition of the catalysts were examined using H2-TPR, SEM, XPS, XRD, and EDS techniques, respectively. Tandem reactions involved activation of CO and subsequent hydrogenation over the metal oxide catalyst, producing methanol and dimethyl ether as the main reaction intermediates, which then migrated onto SAPO-34 zeolite for light olefins synthesis. Effects of temperature, pressure and reactant gas flow rate on CO conversion and light olefins selectivity were investigated in detail. The Mn1Zr2/SAPO-34 catalyst (Mn/Zr ratio of 1:2) attained a CO conversion of 10.8% and light olefins selectivity of 60.7%, at an optimized temperature, pressure and GHSV of 380 ℃, 3 MPa and 3000 h-1 respectively. These findings open avenues to exploit other metal oxides with CO activation capabilities for a more efficient syngas conversion and product selectivity.
    Reaction kinetics for the heterogeneously resin-catalyzed and homogeneously self-catalyzed esterification of thioglycolic acid with 2-ethyl-1-hexanol
    Xiaoda Wang, Wenkai Li, Shiwei Wang, Qinglian Wang, Ling Li, Hongxing Wang, Ting Qiu
    2021, 36(8):  111-119.  doi:10.1016/j.cjche.2020.08.052
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    Producing 2-ethyl-1-hexyl thioglycolate (ETE) via esterification reaction with thioglycolic acid (TGA) aqueous solution as raw material by reactive-separation coupling technology is a promising process intensification method. To choose suitable reactive-separation coupling strategy, the kinetic studies of the esterification of TGA with 2-ethyl-1-hexanol (EHL) were carried out in a batch system. The commercial ion exchange resin was employed as an eco-friendly catalyst. The effects of temperature, catalyst concentration and molar ratio were determined. It was interesting to observe that the equilibrium conversion of TGA increased with the increase of catalyst mass fraction due to the adsorption of product water onto resin surface. The activity-based pseudo-homogeneous (PH), Eley-Rideal (ER) and Langmuir-Hinshelwood-Hougen-Watson (LHHW) models were used to fit the kinetics data of the resin-catalyzed reaction. The models of ER and LHHW performed better than the PH model. The kinetics of the TGA-self-catalyzed reaction was also determined. An activity-based homogeneous kinetics model could well describe this self-catalyzed reaction. These results would be meaningful to the selection and design of an appropriate reaction-separation strategy for the production of ETE, to realize the process intensification.
    Reactive extraction for synthesizing long chain ester butyl hexanoate intensified by deep eutectic solvent
    Yishan Zhou, Hao Qin, Hongye Cheng, Lifang Chen, Bingjian Zhang, Zhiwen Qi
    2021, 36(8):  120-127.  doi:10.1016/j.cjche.2020.10.005
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    Butyl hexanoate (BuHE) is an important long-chain ester that is widely used in the food, beverage and cosmetic industries. In this work, reactive extraction concept was proposed to intensify the BuHE formation in a biphasic system, in which deep eutectic solvent (DES) comprising 2-methylimidazole (2-MIm) and p-toluenesulfonic acid (PTSA) was used as dual solvent-catalyst. First, the effect of 2-MIm to PTSA molar ratio on esterification was investigated to determine the optimum DES of[2-MIm:2PTSA], which was characterized by FT-IR and TGA. Then, the liquid-liquid equilibrium (LLE) and esterification experiments were carried out to confirm the extraction and catalytic effect of[2-MIm:2PTSA], respectively. Afterwards, the pseudo-homogeneous kinetic model was employed to describe the esterification kinetics. Finally, the intensification mechanism of reactive extraction for BuHE formation was proposed according to the experiments and interaction effect analysis.
    Process Systems Engineering and Process Safety
    Balanced multiple weighted linear discriminant analysis and its application to visual process monitoring
    Weipeng Lu, Xuefeng Yan
    2021, 36(8):  128-137.  doi:10.1016/j.cjche.2020.10.032
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    Visual process monitoring is important in complex chemical processes. To address the high state separation of industrial data, we propose a new criterion for feature extraction called balanced multiple weighted linear discriminant analysis (BMWLDA). Then, we combine BMWLDA with self-organizing map (SOM) for visual monitoring of industrial operation processes. BMWLDA can extract the discriminative feature vectors from the original industrial data and maximally separate industrial operation states in the space spanned by these discriminative feature vectors. When the discriminative feature vectors are used as the input to SOM, the training result of SOM can differentiate industrial operation states clearly. This function improves the performance of visual monitoring. Continuous stirred tank reactor is used to verify that the class separation performance of BMWLDA is more effective than that of traditional linear discriminant analysis, approximate pairwise accuracy criterion, max-min distance analysis, maximum margin criterion, and local Fisher discriminant analysis. In addition, the method that combines BMWLDA with SOM can effectively perform visual process monitoring in real time.
    Testing and validation of a self-diffusion coefficient model based on molecular dynamics simulations
    Xia Chen, Yan Wang, Lianying Wu, Weitao Zhang, Yangdong Hu
    2021, 36(8):  138-145.  doi:10.1016/j.cjche.2021.04.036
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    In our previous work, we endowed a new physical meaning of self-diffusion coefficient in Fick's law, which proposed that the diffusion coefficient can be described as the product of the characteristic length and the diffusion velocity. To testify this simple theory, in this work, we further investigated the underlying mechanism of the characteristic length and the diffusion velocity at the molecular level. After a complete dynamic run, the statistical average diffusion velocity and the characteristic length of molecules can be obtained by scripts, and subsequently the diffusion coefficient was determined by our proposed theory. The diffusion processes in 35 systems with a wide range of pressure and concentration variations were simulated using this model. From the simulated results, diffusion coefficients from our new model matched well with the experimental results from literatures. The total average relative deviation of predicted values with respect to the experimental results is 8.18%, indicating that the novel model is objective and rational. Compared with the traditional MSD-t model, this novel diffusion coefficient model provides more reliable results, and the theory is simple and straightforward in concept. Additionally, the effect of gas pressure and liquid concentration on the diffusion behavior were discussed, and the microscopic diffusion mechanism was elucidated through the distribution of diffusion velocity and the characteristic length analysis. Moreover, we suggested new distribution functions, providing more reliable data theoretical foundations for the future research about the diffusion coefficient.
    Chemical looping catalytic gasification of biomass over active LaNixFe1-xO3 perovskites as functional oxygen carriers
    Jingchun Yan, Weidong Liu, Rong Sun, Shouxi Jiang, Shen Wang, Laihong Shen
    2021, 36(8):  146-156.  doi:10.1016/j.cjche.2020.09.038
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    Oxygen carriers (OCs) with perovskite structure are attracting increasing interests due to their redox tunability by introducing various dopants in the structure. In this study, LaNixFe1-xO3 (x=0, 0.1, 0.3, 0.5, 0.7, 1.0) perovskite OCs have been prepared by a citric acid-nitrate sol-gel method, characterized by means of X-ray diffraction (XRD) analysis and tested for algae chemical looping gasification in a fixed bed reactor. The effects of perovskite types, OC/biomass mass ratio (O/B), gasification temperature and water injection rate on the gasification performance were investigated. Lower Ni-doped (0 ≤ x ≤ 0.5) perovskites crystalized in the rhombohedra system which was isostructural with LaNiO3, while those with composition 0.5 ≤ x ≤ 1 crystalized in the orthorhombic system. Despite the high reactivity for LaNiO3, LaNi0.5Fe0.5O3 (LN5F5) was found to be more stable at a high temperature and give almost as good results as LaNiO3 in the formation of syngas. The relatively higher syngas yield of 0.833 m3·kg-1 biomass was obtained under the O/B of 0.4, water injection rate of 0.3 ml·min-1 and gasification temperature at 850℃. Continuous high yield of syngas was achieved during the first 5 redox cycles, while a slight decrease in the reactivity for LN5F5 after 5 cycles was observed due to the adhesion of small grains occurring on the surface of OCs. However, an obvious improvement in the gasification performance was attained for LN5F5 compared to raw biomass direct gasification, indicating that LN5F5 is a promising functional OC for chemical looping catalytic gasification of biomass.
    Effect of different organic compounds on the preparation of CaO-based CO2 sorbents derived from wet mixing combustion synthesis
    Tong Luo, Shaolong Liu, Cong Luo, Xiaolei Qi, Bowen Lu, Liqi Zhang
    2021, 36(8):  157-169.  doi:10.1016/j.cjche.2020.09.039
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    CaO based sorbents have great potential for commercial use to capture CO2 of power plants. In the demand of producing sorbents with better cyclic performance, CaO-based sorbents derived from different kinds of calcium precursors, containing calcium carbonate (CC-CaO), calcium gluconate monohydrate (CG-CaO), calcium citrate (CCi-CaO) and calcium acetate monohydrate (CA-CaO), were tested cyclically and compared using simultaneous thermal analyzer (STA). And further study was conducted on the sorbents modified with citric acid monohydrate and 50% gluconic acid solution by wet mixing combustion synthesis. The modified sorbents showed better performance and higher pore parameters as well as porous microstructure with more organic acid added. After 20 cycles of carbonation and calcination, the C2CCi8 (CaO:citric acid=2:8 by mass ratio) and C2G8 (CaO:gluconic acid=2:8 by mass ratio) sorbent possess CO2 capture capacity of 0.45 g·g-1 (g CO2 per g sorbents) and 0.52 g·g-1 respectively. The citric acid was more effective for modification than gluconic acid for extended 50 cycles. Furthermore, good linear relationship between CaO conversion and specific surface area as well as pore volume were determined, of which the specific surface area showed closer correlation with CaO conversion.
    Calcium looping heat storage performance and mechanical property of CaO-based pellets under fluidization
    Zhangke Ma, Yingjie Li, Boyu Li, Zeyan Wang, Tao Wang, Wentao Lei
    2021, 36(8):  170-180.  doi:10.1016/j.cjche.2020.10.002
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    The CaO-based pellets were fabricated using extrusion-spheronization method for calcium looping thermochemical heat storage under the fluidization. The effects of adhesive, biomass-based pore-forming agent, binder and particle size on the heat storage performance and mechanical property of the CaO-based pellets were investigated in a bubbling fluidized bed reactor. The addition of 2% (mass) polyvinylpyrrolidone as an adhesive not only helps granulate, but also improves the heat storage capacity of the pellets. All biomass-templated CaO-based pellets display higher heat storage capacity than biomass-free pellets, indicating that the biomass-based pore-forming agent is beneficial for heat storage under the fluidization. Especially, bagasse-templated pellets show the highest heat storage conversion of 0.61 after 10 cycles. Moreover, Al2O3 as a binder for the pellets helps obtain high mechanical strength. The CaO-based pellets doped with 10% (mass) bagasse and 5% (mass) Al2O3 reach the highest heat storage density of 1621 kJ·kg-1 after 30 cycles and the highest crushing strength of 4.98 N. The microstructure of the bagasse-templated pellets appears more porous than that of biomass-free pellets. The bagasse-templated CaO-based pellets doped with Al2O3 seem promising for thermochemical heat storage under the fluidization, owing to the enhanced heat storage capacity, excellent mechanical strength, and simplicity of the synthesis procedure.
    Directional assist (0 1 0) plane growth in LiMnPO4 prepared by solvothermal method with polyols to enhance electrochemical performance
    Qian Xie, Jihua Zhu, Chengyun Wang, Kaibin Fang, Wei Yang, Quanbing Liu, Yali Wang, Shengzhou Chen
    2021, 36(8):  181-189.  doi:10.1016/j.cjche.2020.10.027
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    Phosphate material LiMnPO4 is popular for its high energy density (697 W·h·kg-1) and safety. When LiMnPO4 crystal grows, the potential barrier along b and c axis is strong, which makes the crystal grow along b axis to form a one-dimensional chain structure. However, the main migration channel of lithium ions in olivine structure is plane (0 1 0). By shortening the growth in the direction of b axis and enhancing the diffusion along the directions of a and c, two-dimensional nanosheets that are more conducive to the migration of lithium ions are formed. The dosage of polyols is the key factor guiding the dispersion of the crystals to the (0 1 0) plane. X-ray diffraction (XRD), Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and other means are used to characterize the samples. After experiments, we found that when the ratio of polyol/water was 2:1, the morphology of the synthesized sample was 20-30 nm thick nanosheets, which had the best electrochemical performance. At 0.1C, the discharge specific capacity reaches 148.9 mA·h·g-1, still reaches 144.3 mA·h·g-1 at the 50th cycle. and there is still 112.5 mA·h·g-1 under high rate (5C). This is thanks to the good dispersion of the material in the direction of the crystal plane (0 1 0). This can solve the problem of low conductivity and ionic mobility of phosphate materials.
    Energy and economic analysis of a hydrogen and ammonia co-generation system based on double chemical looping
    Xin Pan, Jingjing Ma, Xiude Hu, Qingjie Guo
    2021, 36(8):  190-198.  doi:10.1016/j.cjche.2020.10.007
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    In this work, a model of hydrogen production by double chemical looping is introduced. The efficiency benefit obtained was investigated. The chemical looping hydrogen generation unit is connected in series to the downstream of a chemical looping gasification unit as an additional system for 100 MW·h coal gasification, with the function of supplementary combustion to produce hydrogen. Using Aspen Plus software for process simulation, the production of H2 and N2 in the series system is higher than that in the independent Chemical looping gasification and Chemical looping hydrogen generation systems, and the production of hydrogen is approximately 25.63% and 12.90% higher, respectively; The study found that when the gasification temperature is 900℃, steam-carbon ratio is 0.84 and oxygen-carbon ratio is 1.5, the hydrogen production rate of the system was the maximum. At the same time, through heat exchange between logistics, high-pressure steam at 8.010×104 kg·h-1 and medium-pressure steam at 1.101×104 kg·h-1 are generated, and utility consumption is reduced by 61.58%, with utility costs decreasing by 48.69%. An economic estimation study found that the production cost of ammonia is 108.66 USD·(t NH3)-1. Finally, cost of equipment is the main factors influencing ammonia production cost were proposed by sensitivity analysis.
    Amination of biochar surface from watermelon peel for toxic chromium removal enhancement
    Mohamed A. El-Nemr, Ibrahim M. A. Ismail, Nabil M. Abdelmonem, Ahmed El Nemr, Safaa Ragab
    2021, 36(8):  199-222.  doi:10.1016/j.cjche.2020.08.020
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    Watermelon peel residues were used to produce a new biochar by dehydration method. The new biochar has undergone two methods of chemical modification and the effect of this chemical modification on its ability to adsorb Cr(VI) ions from aqueous solution has been investigated. Three biochars, Melon-B, Melon-BO-NH2 and Melon-BO-TETA, were made from watermelon peel via dehydration with 50% sulfuric acid to give Melon-B followed by oxidation with ozone and amination using ammonium hydroxide to give Melon-BO-NH2 or Triethylenetetramine (TETA) to give Melon-BO-TETA. The prepared biochars were characterized by BET, BJH, SEM, FT-IR, TGA, DSC and EDAX analyses. The highest removal percentage of Cr(VI) ions was 69% for Melon-B, 98% for Melon-BO-NH2 and 99% for Melon-BO-TETA biochars of 100 mg·L-1 Cr(VI) ions initial concentration and 1.0 g·L-1 adsorbents dose. The unmodified biochar (Melon-B) and modified biochars (Melon-BO-NH2 and Melon-BO-TETA) had maximum adsorption capacities (Qm) of 72.46, 123.46, and 333.33 mg·g-1, respectively. The amination of biochar reduced the pore size of modified biochar, whereas the surface area was enhanced. The obtained data of isotherm models were tested using different error function equations. The Freundlich, Tempkin and Langmuir isotherm models were best fitted to the experimental data of Melon-B, Melon-BO-NH2 and Melon-BO-TETA, respectively. The adsorption rate was primarily controlled by pseudo-second-order rate model. Conclusively, the functional groups interactions are important for adsorption mechanisms and expected to control the adsorption process. The adsorption for the Melon-B, Melon-BO-NH2 and Melon-BO-TETA could be explained for acid-base interaction and hydrogen bonding interaction.
    Combined pretreatment using CaO and liquid fraction of digestate of rice straw: Anaerobic digestion performance and electron transfer
    Ruolin Guan, Hairong Yuan, Liang Zhang, Xiaoyu Zuo, Xiujin Li
    2021, 36(8):  223-232.  doi:10.1016/j.cjche.2020.08.036
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    To improve anaerobic digestion (AD) efficiency of rice straw, solid alkaline CaO and the liquid fraction of digestate (LFD) were used as pretreatment agents of rice straw. The results showed that AD performance of rice straw with CaO -LFD pretreatment was optimal in different pretreatment methods of the CaO + LFD, CaO -LFD, LFD + CaO, CaO, and LFD. The maximum methane yield (314 ml·(g VS)-1) and the highest VFAs concentration (14851 mg·L-1 on day 3) of the CaO -LFD pretreatment group were 81% and 118% higher than that of the control group, respectively. Under the action of solid alkaline CaO, the bacteria of Clostridium, Atopostipes, Sphaerochaeta, Tissierella, Thiopseudomonas, Rikenellaceae, and Sedimentibacter could build up co-cultures with the archaeal of Methanosaeta, Methanobacterium, and Methanosarcina performing direct interspecies electron transfer (DIET) and improving AD performance of rice straw. Therefore, the combined pretreatment using CaO and LFD could not only pretreat rice straw but also stimulate co-cultures of microorganism to establish DIET enhancing AD efficiency.
    Chemical looping gasification of maceral from low-rank coal: Products distribution and kinetic analysis on vitrinite
    Bo Zhang, Bolun Yang, Wei Guo, Song Wu, Jie Zhang, Zhiqiang Wu
    2021, 36(8):  233-241.  doi:10.1016/j.cjche.2020.11.021
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    The product distribution and kinetic analysis of low-rank coal vitrinite were investigated during the chemical looping gasification (CLG) process. The acid washing method was used to treat low-rank coal, and the density gradient centrifugation method was adopted to obtain the coal macerals. By combining thermogravimetric analysis and online mass spectrometry, the influence of the heating rate and oxygen carrier (Fe2O3) blending ratio on product distribution was discussed. The macroscopic kinetic parameters were solved by the Kissinger-Akahira-Sunose (KAS) method, and the main gaseous product formation kinetic parameters were solved by the iso-conversion method. The results of vitrinite during slow heating chemical looping gasification showed that the main weight loss interval was 400-600℃, and the solid yield of sample vitrinite-Fe-10 at different heating rates was 64.30%-69.67%. When β=20℃·min-1, the maximum decomposition rate of vitrinite-Fe-10 was -0.312%·min-1. The addition of Fe2O3 reduced the maximum decomposition rate, but by comparing the chemical looping conversion characteristic index, it could be inferred that the chemical looping gasification of vitrinite might produce volatile substances higher than the pyrolysis process of vitrinite alone. The average activation energy of the reaction was significantly reduced during chemical looping gasification of vitrinite, which was lower than the average activation energy of 448.69 kJ·mol-1 during the pyrolysis process of vitrinite alone. The gaseous products were mainly CO and CO2. When the heating rate was 10℃·min-1, the highest activation energy for CH4 formation was 21.353 kJ·mol-1, and the lowest activation energy for CO formation was 9.7333 kJ·mol-1. This study provides basic data for exploring coal chemical looping gasification mechanism and reactor design by studying the chemical looping gasification process of coal macerals.