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Table of Content
28 April 2020, Volume 28 Issue 4
    Recent advances of pharmaceutical crystallization theories
    Jingyun Weng, Yiping Huang, Dule Hao, Yuanhui Ji
    2020, 28(4):  935-948.  doi:10.1016/j.cjche.2019.11.008
    Abstract ( )   PDF (1312KB) ( )  
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    As a technology of separation and purification, crystallization plays a vital role in diverse industries such as inorganic salt, pharmaceutical, and food industries, which has a huge impact on purity, crystal polymorph, crystal morphology, and particle size distribution of final products. In the past few decades, with the rapid advancement of experimental approaches and molecular simulation methods, considerable advances in the interpretation of crystallization mechanisms have been obtained, promoting the investigation and understanding of crystallization theories greatly. In this review, the advances of pharmaceutical crystallization theories in recent years from the perspectives of nucleation and crystal growth are summarized and discussed. Two thermodynamic models that are helpful in the study of the crystallization mechanisms will be introduced. In this section, the perturbed-chain statistical associating fluid theory (PC-SAFT) and a chemical-potential-gradient model will be introduced, which have been successfully applied in pharmaceutical solubility prediction, the research of dissolution mechanism as well as dissolution kinetics analysis. These two models are expected to be applied to the study of pharmaceutical crystallization process and mechanism. Furthermore, molecular simulation based on the interaction between particles can provide structural information, thermodynamics, and dynamics properties of complex systems at the molecular level, like intermolecular interaction and surface adsorption energies. Application and some shortcomings of molecular simulation, especially molecular dynamics simulation, in the field of pharmaceutical crystallization will be expounded.
    Metastable state of gas hydrate during decomposition: A novel phenomenon
    Ronghui Sun, Zhen Fan, Lei Yang, Yuanping Li, Xin Lü, Yang Miao
    2020, 28(4):  949-954.  doi:10.1016/j.cjche.2020.02.003
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    Natural gas hydrates are solid compounds with cage-like structures formed by gas and water. An intriguing phenomenon that gas hydrates can dissociate at a low rate below the ice freezing point has been viewed as the metastability of hydrate. The mechanisms of hydrate metastability have been widely studied, and many mechanisms were proposed involving the self-preservation effect, supercooled water-gas-hydrate metastable equilibrium, and supersaturated liquid-gas-hydrate system etc. The metastable state of hydrate could be of crucial significance in the kinetics of hydrate formation and decomposition, heat and mass transfer during gas production processes, and the application of hydrate-based technique involving desalination, energy storage and transportation, and gas separation and sequestration. Few researches have systematically considered this phenomenon, and its mechanism remains unclear. In this work, various mechanisms and hypothesis explaining the metastable state of gas hydrates were introduced and discussed. Further studies are still required to reveal the intrinsic nature of this metastable state of gas hydrate, and this work could give some implications on the existing theory and current status of relevant efforts.
    Fluid Dynamics and Transport Phenomena
    The weeping characteristic of submerged multi-orifice plate
    Jiming Wen, Ruifeng Tian, Sichao Tan, Qiunan Sun, Haifeng Gu
    2020, 28(4):  955-968.  doi:10.1016/j.cjche.2019.12.024
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    Weeping is an adverse phenomenon which results in higher pressure drop and poorer aeration performance. Visual experiments have been conducted to study the mechanism by which weeping impairs the work performance of multi-orifice plate. A theoretical model is improved to analyze the weeping phenomenon of multiorifice plate based on potential flow theory. The relations of different bubbling conditions and weeping rate are analyzed. Weeping condition and average weeping rate have relation with the driven pressure differential and dynamic variation of gas chamber pressure. In addition, a set of experiments are designed to study the influence of various factors on weeping rate. The bubble coalescence during bubble formation is a fatal factor determining weeping rate, so the relation between weeping rate and gas flow rate is concerned with the pitch of orifices and orifice diameter. There is a critical plate thickness which is in favor of weeping.
    Experimental investigation and theoretical modeling on scale behaviors of high salinity wastewater in zero liquid discharge process of coal chemical industry
    Kai Lu, Yang Lü, Youxiang Bai, Jueru Zhang, Nanxi Bie, Yongsheng Ren, Yulong Ma
    2020, 28(4):  969-979.  doi:10.1016/j.cjche.2020.01.001
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    Zero liquid discharge (ZLD) treatment and reuse equipment of high salinity wastewater in coal-chemical industry often occur in various types of blockage problems because of high salt content, affecting the long-term stability of the device. In this study, the effects of solution temperature, steel, reaction time and wall roughness on fouling were investigated. The changes in the contents of fouling and fouling substances were qualitatively and quantitatively analyzed by XRD and EDS respectively, and the formation of scale was observed by SEM. The results show that with temperature increasing, Q235 steel is the most difficult to scale. Scaling rate of all salt scales reaches a maximum after 12 h, and the fouling rate decreases significantly from 12 to 48 h. It gradually stabilizes at 48 to 96 h. With the roughness increasing, the thickness of fouling layer increases, and a linear relationship is presented for 1 to 10 h. By comparing actual and simulated wastewater scaling rates, the relationship between actual and simulated wastewater scaling rates is y=ax-0.494. The composition of the scale was analyzed, calcium carbonate is the main product and increases with fouling time. Based on the above-mentioned results combining literatures, the hybrid prediction model with calcium carbonate as the main product is put forward. It is discussed microscopically that calcium carbonate is converted from aragonite and vaterite in a thermodynamically metastable state to calcite in a thermodynamically stable state.
    CFD investigation of the feasibility of polymer-based microchannel heat sink as thermal solution
    Yue Seong Ong, KuZilati KuShaari
    2020, 28(4):  980-994.  doi:10.1016/j.cjche.2020.01.007
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    Microchannel heat sinks (MCHSs) are promising thermal solutions in miniaturized or compact devices. Lightweight aspect has been given huge emphasis in recent years. Metal-based materials are commonly used to fabricate MCHSs due to their high thermal conductivity. Consequently, MCHSs are heavy due to the high density of these materials albeit the small footprint of MCHSs. Polymer-based materials are interesting alternatives. Despite their poor thermal conductivity, lightweight feature attracts the interest of researchers. Heat transfer is a conjugate process of heat conduction and heat convection. Poor heat conductions aspect may be compensated through enhancement of heat convection aspects. Although polymer-based materials have been used in microscale heat transfer studies, their focus was not on their feasibility. The present study aims to evaluate the feasibility of polymer-based MCHSs as thermal solutions. The effect of thermal conductivity of fabrication materials, including polymer-based PDMS, PTFE, PDMS/MWCNT, and metal-based aluminum, on the thermal performance of MCHSs was investigated and compared at various inlet flow rate, fluid thermal conductivity, and microchannel ratio at different constant heat fluxes using three-dimensional CFD approach. Results showed that the thermal performance of MCHSs was greatly affected by the heat conduction aspect in which poor heat conduction limited the thermal performance improvement due to enhanced heat convection aspects. This suggests polymer-based materials have the potential for heat transfer applications through thermal conductivity enhancement. This was confirmed in the further analysis using a recently proposed high thermal conductivity polymer-based graphite/epoxy MCHS and a hybrid-based PDMS/aluminum MCHS.
    Structural optimization of a settler via CFD simulation in a mixer-settler
    Sishi Ye, Qiao Tang, Yundong Wang, Weiyang Fei
    2020, 28(4):  995-1015.  doi:10.1016/j.cjche.2020.01.010
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    This work is aimed at optimizing a settler structure in a mixer-settler. Two different aspects have been considered. Firstly, the flowcharacteristics of a settler have been examined by computational fluid dynamics (CFD) simulation with various agitation speeds of the mixer, as well as organic phase volume fractions ranging from 0.075 to 0.6. The aqueous and organic phase turbulent flow fields were measured by particle image velocimetry (PIV) technique to verify the CFD simulation. Two organic phases with different physical properties were assessed in the CFD simulation to simulate the liquid-liquid systems related to rare earth element extraction, i.e., 0.072 mol·L-1 P507/kerosene and 1.8 mol·L-1 P507/kerosene. Secondly, the CFD simulation was carried out in a settler equipped with baffles. The effects of number and location of the baffle in the settler on flow features and entrainments of the aqueous and organic outlet were analyzed. Meanwhile, different settler/mixer volume ratios were also examined. By analyses and comparisons, an optimal design for settler was proposed. CFD can provide a significant guidance to better mixer-settler design.
    Parametric study of droplet size in an axisymmetric flow-focusing capillary device
    Mostafa Rahimi, Sajad Yazdanparast, Pouya Rezai
    2020, 28(4):  1016-1022.  doi:10.1016/j.cjche.2019.12.026
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    A conventional technique for microfluidic droplet generation is Co-axial Flow Focusing (CFF) in which a contraction zone is placed downstream of the dispersed phase nozzle. In this contraction zone, the dispersed-phase (dphase) fluid is pinched off by continuous-phase (c-phase) fluid to generate micro-droplets. Studying the influence of multiple parameters such as the fluids velocities and viscosities, the interfacial tension, and nozzle and orifice diameters on the droplet size is of great importance for the design and application of CFF devices. Thus, development of more complete numerical models is required. In this paper, we show our model is compatible with experimental data and then numerically investigate the effects of aforementioned parameters on the droplet generation in a CFF microfluidic device. Simulation results showed that the c-phase flow rate, viscosity and the interfacial tension had great impacts on the droplet size. The effect of the nozzle diameter on the generated droplet size was small compared to that of the orifice in a CFF device. Using the simulation results, a correlation was also developed and suggested which predicts the droplet size with less than 15% error in a wide range of the introduced dimensionless parameters.
    Predictive models for characterizing the atomization process in pyrolysis of methyl ricinoleate
    Xiaoning Mao, Qinglong Xie, Ying Duan, Shangzhi Yu, Xiaojiang Liang, Zhenyu Wu, Meizhen Lu, Yong Nie
    2020, 28(4):  1023-1028.  doi:10.1016/j.cjche.2020.02.007
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    Pyrolysis of methyl ricinoleate (MR) can produce undecylenic acid methyl ester and heptanal which are important chemicals. Atomization feeding favors the heat exchange in the pyrolysis process and hence increases the product yield. Herein, predictive models to characterize the atomization process were developed. The effect of spray distance on Sauter mean diameter (SMD) of atomized MR droplets was examined, with the optimal spray distance to be 40-50 mm. Temperature mainly affected the physical properties of feedstock, with smaller droplet size obtained at increasing temperature. In addition, pressure had significant influence on SMD and higher pressure resulted in smaller atomized droplets. Then, a model for SMD prediction, combining temperature, pressure, spray distance, and structural parameters of nozzle, was developed through dimensionless analysis. The results showed that SMD was a power function of Reynolds number (Re), Ohnesorge number (Oh), and the ratio of spray distance to diameter of swirl chamber in the nozzle (H/dsc), with the exponents of -1.6618, -1.3205 and 0.1038, respectively. The experimental measured SMD was in good agreement with the calculated values, with the error within ±15%. Moreover, the droplet size distribution was studied by establishing the relationship between the standard deviation of droplet size and SMD. This study could provide reference to the regulation and optimization of the atomization process in MR pyrolysis.
    CFD study of non-premixed swirling burners: Effect of turbulence models
    Erfan Khodabandeh, Hesam Moghadasi, Mohsen Saffari Pour, Mikael Ersson, Pär G. Jönsson, Marc A. Rosen, Alireza Rahbari
    2020, 28(4):  1029-1038.  doi:10.1016/j.cjche.2020.02.016
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    This research investigates a numerical simulation of swirling turbulent non-premixed combustion. The effects on the combustion characteristics are examined with three turbulence models: namely as the Reynolds stress model, spectral turbulence analysis and Re-Normalization Group. In addition, the P-1 and discrete ordinate (DO) models are used to simulate the radiative heat transfer in this model. The governing equations associated with the required boundary conditions are solved using the numerical model. The accuracy of this model is validated with the published experimental data and the comparison elucidates that there is a reasonable agreement between the obtained values from this model and the corresponding experimental quantities. Among different models proposed in this research, the Reynolds stress model with the Probability Density Function (PDF) approach is more accurate (nearly up to 50%) than other turbulent models for a swirling flow field. Regarding the effect of radiative heat transfer model, it is observed that the discrete ordinate model is more precise than the P-1 model in anticipating the experimental behavior. This model is able to simulate the subcritical nature of the isothermal flow as well as the size and shape of the internal recirculation induced by the swirl due to combustion.
    Separation Science and Engineering
    Reducing active layer thickness of polyamide composite membranes using a covalent organic framework interlayer in interfacial polymerization
    Meidi Wang, Weixiong Guo, Zhongyi Jiang, Fusheng Pan
    2020, 28(4):  1039-1045.  doi:10.1016/j.cjche.2019.11.007
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    Polyamide (PA)-based thin-film composite membranes exhibit enormous potential in water purification, owing to their facile fabrication, decent performance and desirable stability. However, the thick PA active layer with high transport resistance from the conventional interfacial polymerization hampers their applications. The controllable fabrication of a thin PA active layer is essential for high separation efficiency but still challenging. Herein, a covalent organic framework TpPa-1 interlayer was firstly deposited on a polyethersulfone (PES) substrate to reduce the thickness of PA active layer in interfacial polymerization. The abundant pores of TpPa-1 increase the local concentration of amine monomers by adsorbing piperazine molecules, while hydrogen bonds between hydrophilic groups of TpPa-1 and piperazine molecules slow down their diffusion rate. Arising from those synergetic effects, the PA active layer is effectively reduced from 200 nm to 120 nm. By optimizing TpPa-1 interlayer and PA active layer, the water flux of resultant membranes can reach 171.35 L·m-2·h-1·MPa-1, which increased by 125.4% compared with PA/PES membranes, while the rejection rates of sodium sulfate and dyes solution remained more than 90% and 99%, respectively. Our strategy may stimulate rational design of ultrathin PA-based nanofiltration membranes with high performances.
    Potential-aided recovery of iodide using 2-D nanosheet CuxO coating polymer/graphene/carbon fibers composite
    Yexiao Yu, Guanping Jin, Yuhong Fang, Zheng Xu, Xiaoyuan Lü, Chunnian Chen
    2020, 28(4):  1046-1054.  doi:10.1016/j.cjche.2019.11.010
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    2-D nanosheet Cu2O doped CuO coating poly m-phenylenediamine and melamine/graphene/carbon fibers composite (CuxO/MPM/GFs) was firstly fabricated by compound electrochemical method. CuxO/MPM/GFs was successfully used to the recovery of iodide (I-) from salt water by lower potential-aided sorption and desorption processes. The potential-aided recovery of I- at CuxO/MPM/GFs was characterized by FE-SEM, XRD, IR, Raman, XPS, UV-vis and electrochemical techniques in detail. The maximal adsorption capacity of 86.82 mg·g-1 could be obtained with a pseudo-second-order model at 0.8 V for 210 min in pH 5.0, 0.1 mol·L-1 NaCl, and the process accompanied the generation of CuI, CuO and I5-. The I- could be quickly desorbed from the electrode with a transfer of CuI to Cu2O by cycle voltammetry from -1.0 to 0.5 V for 90 cycles in pH 9.0, 0.1 mol·L-1 KNO3. Thus, CuxO/MPM/GFs was renewable in the continuous electrochemical-adsorption-desorption processes.
    Simple separation method of Zn(II) and Cd(II) from brine solution of zinc plant residue and synthetic chloride media using solvent extraction
    Ali Asghar Balesini Aghdam, Hossein Yoozbashizadeh, Javad Moghaddam
    2020, 28(4):  1055-1061.  doi:10.1016/j.cjche.2019.12.003
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    In this work, the possibility of separation of Zn2+ and Cd2+ metal ions from chloride (brine) solutions was examined. For this purpose, simple solvent extraction (SX) experiments by di-2-ethylhexyl phosphoric acid (D2EHPA) in kerosene as a diluent was performed on synthetic and industrial chloride solution obtained from brine leaching of zinc filter cakes (by-product of zinc hydrometallurgical processing). The optimal conditions for separation were determined. The zinc extraction efficiency was 99% with negligible co-extraction of cadmium. Therefore, a high ΔpH0.5 value for Zn(Ⅱ) and Cd(Ⅱ) was achieved. FT-IR and slope analysis indicated that ZnClA·3HA and CdClA·3HA species were probably extracted.
    Effect of pore size on CH4/N2 separation using activated carbon
    Gaofei Chen, Yaxiong An, Yuanhui Shen, Yayan Wang, Zhongli Tang, Bo Lu, Donghui Zhang
    2020, 28(4):  1062-1068.  doi:10.1016/j.cjche.2019.12.018
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    In this paper, a model of activated carbon was established by molecular simulation and the separation performance of N2 and CH4 on activated carbon was studied. In order to evaluate the adsorption selectivity and diffusion selectivity of N2 and CH4, Grand Canonical Monte Carlo and molecular dynamic methods were used to obtain equilibrium adsorption isotherms and mean square displacements of N2 and CH4 on activated carbon with different pore sizes. Research results showed that the difference in adsorption isosteric heat of N2 and CH4 at the pore size of 0.46 nm is the largest, which is 5.759 and 7.03 kcal·mol-1 (1 cal=4.184 J), respectively. Activated carbon with pore size of 0.46 nm has the best N2 and CH4 adsorption selectivity, while its diffusion selectivity is not obvious.
    Adsorption of congo red on mesoporous activated carbon prepared by CO2 physical activation
    Mingjie Ma, Huijuan Ying, Fangfang Cao, Qining Wang, Ning Ai
    2020, 28(4):  1069-1076.  doi:10.1016/j.cjche.2020.01.016
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    This research demonstrates the production of mesoporous activated carbon from sargassum fusiforme via physical activation with carbon dioxide. Central composite design was applied to conduct the experiments at different levels by altering three operating parameters. Activation temperature (766-934 ℃), CO2 flow rate (0.8-2.8 L·min-1) and activation time (5-55 min) were the variables examined in this study. The effect of parameters on the specific surface area, total pore volume and burn-out rate of activated carbon was studied, and the influential parameters of methylene blue adsorption value were identified employing analysis of variance. The optimum conditions for maximum methylene blue adsorption value were: activation temperature = 900 ℃, activation time = 29.05 min and CO2 flow rate = 1.8 L·min-1. The activated carbon produced under optimum conditions was characterized by BET, FTIR and SEM. The adsorption behavior on congo red was studied. The effect of parameters on the adsorbent dosage, temperature, PH and initial congo red concentration was investigated. The adsorption properties of the activated carbon were investigated by kinetics. The equilibrium removal rate and maximum adsorption capacity reaches up to 94.72%, 234 mg·g-1, respectively when initial congo red concentration is 200 mg·L-1 under adsorbent dosage (0.8 g·L-1), temperature (30 ℃), PH7.
    Catalysis, Kinetics and Reaction Engineering
    A granular adsorbent-supported Fe/Ni nanoparticles activating persulfate system for simultaneous adsorption and degradation of ciprofloxacin
    Jiwei Liu, Yufeng Du, Wuyang Sun, Quanchao Chang, Changsheng Peng
    2020, 28(4):  1077-1084.  doi:10.1016/j.cjche.2019.12.019
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    In this work, Fe/Ni nanoparticles were produced through Fe(Ⅱ) and Ni(Ⅱ) reduction by NaBH4 and they were stabilized by a kind of prepared granular adsorbent (Fe/Ni@PGA). Fe/Ni@PGA as an environment-friendly activator was used to activate persulfate (PS) for the removal of ciprofloxacin from aqueous solution. Fe/Ni@PGA was systematically characterized via Brunauer-Emmett-Teller (BET) method, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The effects of PS concentration, initial solution pH, Fe/Ni@PGA dosage, initial ciprofloxacin concentration, reaction temperature, anions, and natural organic matters on the removal of ciprofloxacin by Fe/Ni@PGA/PS were analyzed. The removal efficiency of ciprofloxacin by Fe/Ni@PGA/PS was 93.24% under an initial pH of 3.0, PS concentration of 10 mM, Fe/Ni@PGA dosage of 0.1 g, and reaction temperature of 30 ℃. Fe/Ni@PGA could still exhibit high catalytic activity after nine cycles of regeneration. The removal mechanisms for ciprofloxacin by the Fe/Ni@PGA/PS system were proposed. In summary, the Fe/Ni@PGA/PS system could be applied as a promising technology for ciprofloxacin removal.
    Interaction between Pd and Cu nanoparticles in bimetallic CuPdx nanoparticles and its impact on oxidation of 1,2-propanediol to aliphatic acids
    Wei Tao, Aili Wang, Hengbo Yin
    2020, 28(4):  1085-1094.  doi:10.1016/j.cjche.2020.02.005
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    Bimetallic CuPd x nanoparticles synthesized by the wet chemical reduction method were used as the catalysts in the catalytic oxidation of 1,2-propanediol with gaseous oxygen to aliphatic acids. The palladium and copper nanoparticles in the bimetallic CuPdx nanoparticles had an alloying trend. The catalytic activity of the palladium nanoparticles in the bimetallic CuPdx nanoparticles was enhanced by the interaction between the palladium and copper nanoparticles. When the bimetallic CuPd7 nanoparticles catalyzed the oxidation of 1,2-propanediol in an alkaline aqueous solution at 100 ℃ for 3 h, lactic, formic, and acetic acids were dominantly produced with the total selectivity of above 99% at the 1,2-propanediol conversion of 85.9%. The simulation of the reaction kinetic equation on the CuPd7 catalyst showed that the reaction activation energy was 29.4 kJ·mol-1, indicating that the bimetallic CuPd7 nanoparticles had a high catalytic activity in the oxidation reaction between 1,2-propanediol and gaseous oxygen.
    Coupling non-isothermal trickle-bed reactor with catalyst pellet models to understand the reaction and diffusion in gas oil hydrodesulfurization
    Xingqiang Zhao, Changfeng Yang, Mengke Lu, Yao Shi, Gang Qian, Xinggui Zhou, Xuezhi Duan
    2020, 28(4):  1095-1106.  doi:10.1016/j.cjche.2020.02.013
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    In this work, a trickle-bed reactor coupled with catalyst pellet model is employed to understand the effects of the temperature and catalyst pellet structures on the reaction-diffusion behaviors in gas oil hydrodesulfurization (HDS). The non-isothermal reactor model is determined to be reasonable due to non-negligible temperature variation caused by the reaction heat. The reaction rate along the reactor is mainly dominated by the temperature, and the sulfur concentration gradient in the catalyst pellet decreases gradually along the reactor, leading to the increased internal effectiveness factor. For the fixed catalyst bed volume, there exists a compromise between the catalyst reaction rate and effectiveness factor. Under commonly studied catalyst pellet size of 0.8-3 mm and porosity of 0.4-0.8, an optimization of the temperature and catalyst pellet structures is carried out, and the optimized outlet sulfur content decreases to 7.6 wppm better than the commercial level at 0.96 mm of the catalyst pellet size and 0.40 of the catalyst porosity.
    Process Systems Engineering and Process Safety
    Removing contaminants from tannery wastewater by chemical precipitation using CaO and Ca(OH)2
    Adriana Reyes-Serrano, Joel E. López-Alejo, Manuel A. Hernández-Cortázar, Ignacio Elizalde
    2020, 28(4):  1107-1111.  doi:10.1016/j.cjche.2019.12.023
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    The removal of Cr, sulfates and Chemical Oxygen Demand (COD) from industrial tannery wastewater by chemical precipitation was carried out using Calcium oxide (CaO) and Calcium hydroxide (Ca(OH)2). Different doses of alkalis, ranging from deficiency to excess hydroxyl species over the stoichiometric necessary, were used to remove theoretically the 100% of Cr [0.3-3.2 g alkali·(g Cr3+)-1]. The precipitation was carried out at room temperature, 10 min of vigorous stirring, 200 r·min-1 and a settling time of 24 h, followed by separation and characterization of liquid product. As result of addition of alkalis, pH underwent increase as did the alkali concentration. The removal of Cr, and sulfates also increased as alkali concentration did, although for first species the changes at higher alkali contents were less evident. COD removal on the other hand, did not follow a unique trend, instead exhibited a maximum. Based on our results, selection of a specific dose of alkali was carried out taking as reference the efficiency on total chromium removal, keeping the pH in the range 7 to 9 to ensure Cr precipitation as chromium hydroxide. With those conditions, jar test was used to produce enough liquid product in order to determine the removal percent of several other species. The removal percent of the species was as follows: Cr, SO42-, ZnSO4, FeSO4, CN-1, NiSO4, Fe2[Fe(CN)6] at 99.8%, 66.9%, 99.6%, 21.4%, 70.9%, 52.8% and 76.4% with CaO, and 99.8%, 61.6%, 99.9%, 7.1%, 84.0%, 54.4% and 90.5% with Ca(OH)2, respectively.
    Chemical Engineering Thermodynamics
    Accelerated methane storage in clathrate hydrates using surfactantstabilized suspension with graphite nanoparticles
    Liang Yang, Xin Wang, Daoping Liu, Guomin Cui, Binlin Dou, Juan Wang, Shuqing Hao
    2020, 28(4):  1112-1119.  doi:10.1016/j.cjche.2019.12.009
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    In this study, enhanced kinetics of methane hydrate formation in the sodium dodecyl sulfate (SDS) solution with different concentrations of suspended graphite nanoparticles (GNPs) were investigated at 6.1-9.0 MPa and 274.15 K. The GNPs with rough surfaces and excellent thermal conductivity not only provided a considerable number of microsites for hydrate nucleation but also facilitated the fast hydrate heat transfer in the suspension system. At a relatively low pressure of 6.1 MPa, the suspension with 0.4 wt% of GNPs exhibited the minimum induction time of 22 min and maximum methane uptake of 126.1 cm3·cm-3. However, the methane storage performances of the suspensions with higher and lower concentrations of GNPs were not satisfactory. At the applied pressure, the temperature increase arising from the hydrate heat in the suspension system with the optimized concentration (0.4 wt%) of GNPs was more significant than that in the traditional SDS solution. Furthermore, compared with those of the system without GNPs, enhanced hydration rate and storage capacity were achieved in the suspensions with GNPs, and the storage capacities were increased by 3.9%-17.0%. The promotion effect of GNPs on gas hydrate formation at low pressure is much more obvious than that at high pressure.
    Biotechnology and Bioengineering
    Salt-tolerant mechanism of marine Aspergillus niger cellulase cocktail and improvement of its activity
    Linian Cai, Shengnan Xu, Tao Lu, Dongqiang Lin, Shanjing Yao
    2020, 28(4):  1120-1128.  doi:10.1016/j.cjche.2019.11.012
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    The cellulase cocktail produced by marine Aspergillus niger exhibits a property of salt-tolerance, which is of great potential in cellulose degradation in high salt environment. In order to explain the mechanism on the salttolerance of the cellulase cocktail produced by marine A. niger, six cellulase components (AnCel6, AnCel7A, AnCel7B, AnEGL, AnBGL1 and AnBGL2) were obtained by directed expression. Studies on their enzymatic properties revealed that one β-glucosidase (AnBGL2) and one endoglucanase (AnEGL) exhibited an outstanding salttolerant property, and one cellobiohydrolase (AnCel7B) exhibited a certain salt-tolerant property. Subsequent study revealed that the salt-tolerant AnEGL and AnCel7B endowed the cellulase cocktail with stronger salttolerant property, while the salt-tolerant AnBGL2 had no positive effect. Moreover, after overexpression of AnCel6, AnCel7A, AnCel7B and AnEGL, the activity of cellulase cocktail increased by 80%, 70%, 63% and 68%, respectively. However, the activity of cellulase cocktail was not improved after overexpression of AnBGL1 and AnBGL2. After mixed-strain fermentation with cellobiohydrolase recombinants (cel6a, cel7a and cel7b recombinants) and endoglucanase recombinant (egl recombinant), the the activity of cellulase cocktail increased by 114%, 102% and 91%, respectively.
    Fabrication and characterization of epoxylated zwitterionic copolymergrafted silica nanoparticle as a new support for lipase immobilization
    Ning Chen, Chunyu Zhang, Xiaoyan Dong, Yan Sun
    2020, 28(4):  1129-1135.  doi:10.1016/j.cjche.2019.12.006
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    Our previous work proved that the thermal stability of Candida rugosa lipase (CRL) immobilized on zwitterionic polymer (poly(carboxybetaine methacrylate)) grafted silica nanoparticle (SNP) was much higher than that on poly(glycidyl methecrylate) (pGMA) grafted SNP, while the latter showed significantly increased activity. Inspired by the research, we have herein proposed to synthesize copolymers of zwitterionic sulfobetaine methacrylate (SBMA) and GMA for CRL immobilization. The copolymers were grafted onto SNP surface at three GMA/ SBMA (G/S) molar ratios (G100/S0, G50/S50, G10/S90), followed by the covalent coupling of CRL to the surface copolymers. The immobilized CRLs on the corresponding supports were denoted as p(G100-S0)-CRL, p(G50-S50)-CRL and p(G10-S90)-CRL. The enzyme loading increased with the increase of GMA content in the copolymer, while the activity varied with the grafted copolymer composition. Kinetic study proved the improvement of enzyme-substrate affinity after immobilization. In comparison to p(G100-S0)-CRL, p(G50-S50)-CRL and p (G10-S90)-CRL presented remarkably enhanced thermal stability and pH tolerance, and p(G10-S90)-CRL showed the highest stability. These results suggest that the copolymer design is promising for development as a versatile platform for enzyme immobilization.
    Immobilization of laccase from Myceliophthora thermophila on functionalized silica nanoparticles: Optimization and application in lindane degradation
    Jelena Bebić, Katarina Banjanac, Marija Ćorović, Ana Milivojević, Milica Simović, Aleksandar Marinković, Dejan Bezbradica
    2020, 28(4):  1136-1144.  doi:10.1016/j.cjche.2019.12.025
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    This work is focused on immobilization of laccase from Myceliophthora thermophila expressed in Aspergillus oryzae (Novozym 51003® laccase) on amino modified fumed nano-silica (AFNS) and the possible use in bioremediation. Hereby, for the first time, factors affecting the immobilization of Novozym 51003® laccase on AFNS were investigated for defining the immobilization mechanism and optimizing the utilization of AFNS as support for laccase immobilization. The highest specific activity (13.1 IU·mg-1 proteins) was achieved at offered 160 mg per g of AFNS and for the same offered protein concentration the highest activity immobilization yield, reaching 68.3% after the equilibrium time, at optimum pH 5.0, was obtained. Laccase immobilization occurs by adsorption as monolayer enzyme binding in 40 min, following pseudo-first-order kinetics. The possible use of obtained immobilized preparation was investigated in degradation of pesticide lindane. Within 24 h, lindane concentration was reduced to 56.8% of initial concentration and after seven repeated reuses it retained 70% of the original activity.
    Energy, Resources and Environmental Technology
    DBU-based CO2 absorption-mineralization system: Reaction process, feasibility and process intensification
    Cong Luo, Kejing Wu, Hairong Yue, Yingying Liu, Yingming Zhu, Wei Jiang, Houfang Lu, Bin Liang
    2020, 28(4):  1145-1155.  doi:10.1016/j.cjche.2019.12.008
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    Amine-based carbon dioxide (CO2) capture is still limited by high desorption energy consumption. Fixing CO2 into carbonate is a safer and more permanent method. In this work, calcium oxide (CaO) is introduced to perform chemical desorption instead of thermal desorption on 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU) aqueous solution after CO2 absorption. The X-ray diffraction (XRD) patterns of solid products show the formation of calcite calcium carbonate (CaCO3), which prove the feasibility of this method. The effects of reaction temperature, reaction time and Ca2+/CO32- molar ratios on the related reactions in CO2 absorption-mineralization process and CaCO3 precipitation are discussed, and purer CaCO3 is obtained by ultrasonic treatment. The CaCO3 content can be increased to 95.8% and the CO2 desorption ratio can achieve 80% by 30 min ultrasonic dispersion treatment under the conditions (40 ℃, 180 min, Ca2+/CO32- molar ratio = 1.0). After five cycles, DBU aqueous solution shows stable CO2 absorption and mineralization ability. Fourier transform infrared spectroscopy (FT-IR) spectra of the reaction process also indicate the regeneration of the solvent. Compared with thermal desorption, this process is exothermic, almost without no additional heat.
    Solid oxide fuel cells in combination with biomass gasification for electric power generation
    Huangang Shi, Qianjun Li, Wenyi Tan, Hao Qiu, Chao Su
    2020, 28(4):  1156-1161.  doi:10.1016/j.cjche.2020.01.018
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    Biomass, a source of renewable energy, represents an effective substitute to fossil fuels. Gasification is a process that organics are thermochemically converted into valuable gaseous products (e.g. biogas). In this work, the catalytic test demonstrated that the biogas produced from biomass gasification mainly consists of H2, CH4, CO, and CO2, which were then be used as the fuel for solid oxide fuel cell (SOFC). Planar SOFCs were fabricated and adopted. The steam reforming of biogas was carried out at the anode of a SOFC to obtain a hydrogen-rich fuel. The performance of the SOFCs operating on generated biogas was investigated by I-V polarization and electrochemical impedance spectra characterizations. An excellent cell performance was obtained, for example, the peak power density of the SOFC reached 1391 mW·cm-2 at 750 ℃ when the generated biogas was used as the fuel. Furthermore, the SOFC fuelled by simulated biogas delivered a very stable operation.
    Chemical dehydration coupling multi-effect evaporation to treat waste sulfuric acid in titanium dioxide production process
    Hongyin Pang, Ruifang Lu, Tao Zhang, Li Lü, Yanxiao Chen, Shengwei Tang
    2020, 28(4):  1162-1170.  doi:10.1016/j.cjche.2020.02.009
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    In order to concentrate the diluted sulfuric acid from the titanium dioxide (TiO2) production of sulphate process, a new concentration process was proposed by coupling chemical dehydration and multi-effect evaporation. The ferrous sulfate monohydrate (FeSO4·H2O), as the dehydrant, was added to the diluted sulfuric acid to form ferrous sulfate heptahydrate (FeSO4·7H2O) according to the H2SO4-FeSO4-H2O phase diagrams, which partially removes the water. This process was named as Chemical Dehydration Process. The residual water was further removed by two-effect evaporation and finally 70 wt% sulfuric acid was obtained. The FeSO4·H2O can be regenerated through drying and dehydration of FeSO4·7H2O. The results show that FeSO4·H2O is the most suitable dehydrant, the optimal reaction time of chemical dehydration process is 30 min, and low temperature is favorable for the dehydration reaction. 45.17% of the entire removed water can be removed by chemical dehydration from the diluted sulfuric acid. This chemical dehydration process is also energy efficient with 24.76% saving compared with the direct evaporation process. Furthermore, 51.21% of the FeSO4 dissolved originally in the diluted sulfuric acid are precipitated out during the chemical dehydration, which greatly reduces the solid precipitation and effectively alleviates the scaling in the subsequent multi-effect evaporation process.
    Materials and Product Engineering
    Studies on batch adsorptive removal of cadmium and nickel from synthetic waste water using silty clay originated from Balochistan- Pakistan
    Abdul Samad, Muhammad Imran Din, Mahmood Ahmed
    2020, 28(4):  1171-1176.  doi:10.1016/j.cjche.2019.12.016
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    The potentials of silty clay (SC), acquired from Chaman, Balochistan, were investigated as adsorbent for Ni (Ⅱ) and Cd (Ⅱ) removal from contaminated media. The influence of different operating factors like dose, pH, temperature, and time of contact was explored, and optimum values were noted under batch adsorption method. Isothermal study was conducted with varying concentrations of solutions on optimized conditions and different adsorption models i.e., Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) isotherm, which were employed to interpret the process. The isothermal data of both Ni (Ⅱ) and Cd (Ⅱ) were well fitted to Langmuir isotherm suggesting the formation of monolayer of metal ions on silty clay. The values of adsorption capacity noted for Ni (Ⅱ) and Cd (Ⅱ) were 3.603 mg·g-1 and 5.480 mg·g-1, respectively. Kinetic studies affirmed that pseudo second order (PSO) kinetics was being obeyed by the removal of Ni (Ⅱ) and Cd (Ⅱ). Thermodynamic variables like free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) were calculated. The negative value of ΔG° and the positive values of ΔH° and ΔS° unfolded that the removal process of both metal ions of by SC was spontaneous, endothermic and feasible.
    Preparation of graphite nanosheets in different solvents by sand milling and their enhancement on tribological properties of lithiumbased grease
    Jin Zhang, Aili Wang, Hengbo Yin
    2020, 28(4):  1177-1186.  doi:10.1016/j.cjche.2020.01.013
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    Graphite nanosheets with the average thicknesses ranging from 24.4 to 48.9 nm were prepared with the use of expanded graphite as the raw material by sand milling in deionized water, anhydrous ethanol, glycerol, and 1,4-butanediol, respectively. Anhydrous ethanol favored the formation of graphite nanosheets with a smaller average thickness. When the graphite nanosheets with the content of 2 wt% were added in lithium-based grease, the average friction coefficient decreased by 27% as compared with the pure lithium-based grease. The weld point and load wear index were 1.6 and 1.4 times those of the pure lithium-based grease, respectively. The tribological properties of the graphite nanosheet-containing lithium-based grease were comparable with those of the graphene-containing lithium-based grease.
    Preparation of graphene oxide/natural rubber composites by latex cocoagulation: Relationship between microstructure and reinforcement
    Yingyan Mao, Chao Wang, Li Liu
    2020, 28(4):  1187-1193.  doi:10.1016/j.cjche.2020.01.015
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    Graphene oxide (GO) has recently attracted substantial interest as a possible reinforcing agent for next generation rubber composite materials. In this research, GO was incorporated in natural rubber (NR) composites through latex co-coagulation technique. The microstructures of GO/NR composites were characterized through a combination of transmission electron microscope, scanning electron microscope, X-ray diffraction, Fourier transform infrared spectroscopy, and Differential scanning calorimeter. The results showed that highly exfoliated GO sheets were finely dispersed into NR rubber matrix with strong interface interaction between GO and NR. The mechanical properties of the GO/NR composites were further evaluated. The results showed that the tensile strength, tear strength and modulus can be significantly improved at a content of less than 2 phr. Especially, GO exhibited specific reinforce mechanism in NR due to the stress-induced crystallization effects of NR. The stress transfer from the NR to the GO sheets and the hindrance of GO sheets to the stress-induced crystallization of NR were further displayed in stress-strain behavior of GO/NR composites. These enhanced properties were attributed to the high surface area of GO sheets and highly exfoliated microstructures of GO sheets in NR.