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Table of Content
28 December 2016, Volume 24 Issue 12
    Fluid Dynamics and Transport Phenomena
    Effect of the shaft eccentricity and rotational direction on the mixing characteristics in cylindrical tank reactors
    Houari Ameur
    2016, 24(12):  1647-1654.  doi:10.1016/j.cjche.2016.05.011
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    Strategy of the shaft eccentricity is introduced to enhance the mixing characteristics in a flat bottomed cylindrical vessel without baffles. The mixing is ensured by a six-curved blade impeller. Three solutions which are models of food emulsions are used as working fluids. These solutions have a shear thinning behavior modeled by the power-law. The effects of fluid properties, stirring rates, impeller rotational direction and impeller eccentricity on the 3D flow fields and power consumption are investigated. Three values of impeller eccentricity are considered, namely 0%, 24% and 48% of the vessel diameter. It is found that the opposite clockwise rotational direction reduces the power consumption, compared with the clockwise rotational direction. Also, the obtained results show that an impeller placed at an eccentric position between 24% and 48% of the vessel diameter and at the third of the vessel height may ensure the best mixing characteristics.
    Modeling and experimental studies of methyl methacrylate polymerization in a tubular reactor
    Mohamad-Taghi Rostami, Ali Daneshgar
    2016, 24(12):  1655-1663.  doi:10.1016/j.cjche.2016.05.049
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    In this study, rheological examination of the mixture of a tubular reactor in which methyl methacrylate was polymerized has been studied. The n (flow behavior index) value of Power Law Model of mixture contained in the reactor has been determined within the span of 0.3492 to 0.9889 by curve fitting. Employing these numerical data for velocity profile, the reactor has been modeled. Moreover, the functions of the reactor have been compared in the three modes of plug, mixed and laminar flow. The results obtained in this research indicate that the polymethyl methacrylate mixture contained in the reactor is pseudo-plastic. Moreover, as the conversion grows, the velocity profile starts as a parabolic profile and approaches the plug mode; although it never reaches the plug. The other conclusions borne in this study indicate that when the reactor's radius is decreased, the conversion rate grows. However, as decreasing the radius would also reduce the productions rate, this procedure is not economical. Finally, in this modeling, the amount of conversion is equal to 56.47% at the end and according to its laboratory proportion which is 55.88%, it has reached the conclusion that the modeling duly undertaken is applicable and valid.
    Design factors affecting the dynamic performance of soil suspension in an agitated, baffled tank
    M. Moayeri Kashani, S. H. Lai, S. Ibrahim, P. Moradi Bargani
    2016, 24(12):  1664-1673.  doi:10.1016/j.cjche.2016.07.011
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    The effects of particle size, impeller clearance and impeller speed are assessed to show how condition variations influence power consumption in the water-solid slurry suspension in an agitated tank. The energy efficiency of slurry height variation, impeller type and diameter, and solid movement speed has been investigated with six soil series stirred in a soil-water slurry. Coarser sand particles are observed to significantly increase power consumption, while finer particles, for instance clay, decrease the stirring power requirement. The 3-blade HR100 SUPERMIX® impeller manufactured by SATAKE generally performs more efficiently than a conventional 4-pitched blade turbine. The impeller's geometric design, including diameter and number of blades influences the impeller's energy efficiency, and HR100 impellers with greater diameters remarkably reduce power consumption. The tests demonstrated that the power required to provide off-bottom solid suspension and solid dispersion can be reduced dramatically by increasing the slurry height rather than by accelerating the impeller, if this option is possible.
    Separation Science and Engineering
    Optimal design of nanofiltration system for surface water treatment
    Fei Bi, Haiyang Zhao, Zhijun Zhou, Lin Zhang, Huanlin Chen, Congjie Gao
    2016, 24(12):  1674-1679.  doi:10.1016/j.cjche.2016.05.012
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    Both reverse osmosis (RO) and nanofiltration (NF) membranes have been increasingly used for water purification and desalination. However, the salt rejection of NF membranes is quite different from that of RO membranes, which makes a significant distinction in their process designs. This work started from the performance investigation of a single NF membrane element and then focused on the process design of the NF system for surface water treatment. In experimental tests, it was found that the observed rejection of the NF element becomes nearly constant when the concentrate flow is large enough, while the membrane flux of the NF element is quite stable regardless of the water flow across the membrane surface. These findings can be used to instruct the process design of the NF system for surface water treatment. In process design, a two-stage arrangement is sufficient for the NF system to reach the highest water recovery, while the RO system requires a three-stage arrangement.
    Adsorption equilibrium for Z-ligustilide on C18-bonded silica from supercritical carbon dioxide
    Huisheng Lü, Shuangyan Liu, Yonghui Li, Fanmei Meng, Dawei Yao, Xufei Mo
    2016, 24(12):  1680-1686.  doi:10.1016/j.cjche.2016.04.020
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    Adsorption equilibrium is of great importance for the preparative supercritical fluid chromatography (pre-SFC) in defining supercritical adsorption behavior and the industrial amplification. This paper presents adsorption isotherms of Z-ligustilide from supercritical carbon dioxide (SC-CO2) on C18-bonded silica. Adsorption behavior was studied at 305.15 K, 313.15 K and 323.15 K with SC-CO2 density varying from 0.687 g·cm-3 to 0.863 g·cm-3 with the elution by characteristic points (ECP) method. The adsorption amount of Z-ligustilide from SC-CO2 on C18-bonded silica decreased with the increasing density of the mobile phase as well as the increasing temperature. Adsorption equilibrium data were fitted by Langmuir and Freundlich isotherm models, and the Langmuir isotherm model performed better for describing the whole adsorption process on the column. The monolayer saturation adsorption capacity of Z-ligustilide is in the range of 3.0×10-4 mg·cm-3 to 5.5×10-4 mg·cm-3 with an average value of 4.0×10-4 mg·cm-3.
    CO2/CH4 and CH4/N2 separation on isomeric metal organic frameworks
    Xiaoqing Wang, Libo Li, Jiangfeng Yang, Jinping Li
    2016, 24(12):  1687-1694.  doi:10.1016/j.cjche.2016.05.013
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    Two isomeric metal-organic frameworks (MOFs) with 2-dimensional (2D) and 3-dimensional (3D) topologies both comprised of Cu(II) and OTf (OTf=trifluoromethanesulfonate) ions were synthesized and characterized. The CO2, CH4 and N2 adsorption properties of the two isomeric MOFs were investigated from 263 K to 298 K at 0.1 MPa. The results showed that the 2D MOF exhibited a higher selectivity for CO2 from CO2/CH4 and CH4 from CH4/N2 compared to the 3D MOF, even though it possessed a lower surface area and pore volume. The higher adsorption heats of gases on the 2D MOF inferred the strong adsorption potential energy in the layered MOFs. Dynamic separation experiments using CO2/CH4 and CH4/N2 mixtures on the two MOFs proved that the 2D MOF had a longer elution time than the 3D MOF as well as better separation abilities.
    Characterization of functionalized multiwalled carbon nanotubes and application as an effective filter for heavy metal removal from aqueous solutions
    Emad. M. Elsehly, N. G. Chechenin, A. V. Makunin, H. A. Motaweh, E. A. Vorobyeva, K. A. Bukunov, E. G. Leksina, A. B. Priselkova
    2016, 24(12):  1695-1702.  doi:10.1016/j.cjche.2016.05.017
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    Filtration efficiency of Ni(II) from aqueous solution using pristine and modified MWCNTs filters was investigated as a function of Ni(II) ion concentration, pH, and filter mass. MWCNTs were synthesized by CVD method and modified using two complementary treatments, purification (using a mixture of hydrochloric acid and hydrogen peroxide) and functionalization (using nitric acid). The effect and mechanism of each treatment on the structural integrity of pristine MWCNTs has been studied. Morphology of the pristine and modified filters was investigated by Raman Spectrometry (RS), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Fourier Transform Infrared (FTIR) spectrometry and Thermogravimetric analysis. It was found from Raman spectra that the ratio of the intensity of D-band to that of G-band decreased by purification process, and increased by functionalization process. The adsorption mechanism of Ni(II) onto the surface functional groups of modified MWCNTs was confirmed by FTIR spectrum. The filtration results showed that the removal efficiency of Ni(II) is strongly dependent on pH and could reach 85% at pH=8. Also, modified MWCNT filters can be reused through many cycles of regeneration with high performance. Functionalized MWCNTs filters may be a promising adsorbent candidate for heavy metal removal from wastewater.
    MCM-36 zeolites tailored with acidic ionic liquid to regulate adsorption properties of isobutane and 1-butene
    Hongxia Li, Tao Zhang, Shaojun Yuan, Shengwei Tang
    2016, 24(12):  1703-1711.  doi:10.1016/j.cjche.2016.05.033
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    Adsorption properties of an adsorbent or a catalyst towards adsorbates are crucial in the process of adsorption separation or catalytic reaction. Surface morphology and structure of adsorbents have a significant impact on the adsorption properties. In this study, a novel acidic ionic liquid, 1-butyl-3-(triethoxysilylpropyl)imidazolium hydrogen sulfate (i.e.,[BTPIm] [HSO4]), was synthesized and subsequently grafted onto the MCM-36 zeolite for the regulation of its adsorption properties towards isobutane and 1-butene. The resultant[BTPIm] [HSO4]-immobilized MCM-36 (i.e., MCM-36-IL) was characterized by FT-IR, XPS, XRD, SEM, TG/DTG and N2 adsorption-desorption measurement. It was found that the specific surface area, micropore volume and mesopore volume of the MCM-36 support underwent a reduction upon the immobilization of ionic liquid, while the surface density of acid increased from 0.0014 to 0.0035 mmol·m-2. The adsorption capacity of isobutane and 1-butene on the MCM-36-IL was determined by a static volumetric method. Results demonstrated that the interaction between isobutane and MCM-36-IL was enhanced and the interaction between 1-butene and MCM-36-IL was reduced. As a result, a tunable adsorption ratio of isobutane/1-butene on MCM-36 was achieved. With the increase in surface density of acid and the tunable adsorption ratio of isobutane and 1-butene on the functionalized MCM-36, the acidic ionic liquid-immobilized zeolites are beneficial to obtain an improved reaction yield and a prolonged catalyst life in the reactions catalyzed by solid acid.
    Catalysis, Kinetics and Reaction Engineering
    Degradation of phenol in industrial wastewater over the F-Fe/TiO2 photocatalysts under visible light illumination
    Yandong Liu, Shijian Zhou, Fu Yang, Hua Qin, Yan Kong
    2016, 24(12):  1712-1718.  doi:10.1016/j.cjche.2016.05.024
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    F-Fe/TiO2 composite photocatalyst was synthesized by a facile one-step hydrothermal method and then characterized by XRD, XPS and UV-Vis DRS. The catalyst of F-Fe/TiO2 exhibited the highest photodegradation rate for phenol as compared with pure TiO2, F/TiO2, Fe/TiO2, F0.38-Fe0.13-TiO2 and Fe(III)/F-TiO2 under visible light irradiation. The simulated conditions of industrial phenolic wastewater including initial phenol concentration, visible light intensity, pH and different anions were investigated in the presence of F-Fe/TiO2 photocatalyst. In addition, as expected, the F-Fe/TiO2 photocatalyst displayed excellent stability, showing a potential industrial application for the treatment of phenolic wastewater.
    Kinetic effects of nanosecond discharge on ignition delay time
    Xingqian Mao, Guoxiu Li, Qi Chen, Yujun Zhao
    2016, 24(12):  1719-1727.  doi:10.1016/j.cjche.2016.05.014
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    The effects of nanosecond discharge on ignition characteristics of a stoichiometric methane-air mixture without inert diluent gas were studied by numerical simulation at 0.1 MPa and an initial temperature of 1300 K. A modified non-equilibrium plasma kinetic model was developed to simulate the temporal evolution of particles produced during nanosecond discharge and its afterglow. As important roles in ignition, path fluxes of O and H radicals were analyzed in detail. Different strength of E/N and different discharge duration were applied to the discharge process in this study. And the results presented that a deposited energy of 1-30 mJ·cm-3 could dramatically reduce the ignition delay time. Furthermore, temperature and radicals analysis was conducted to investigate the effect of non-equilibrium plasma on production of intermediate radicals. Finally, sensitivity analysis was employed to have further understanding on ignition chemistries of the mixture under nanosecond discharge.
    Modification and sequential treatment of EU-1 zeolite in mild alkali and alkaline-acid conditions
    Xiaofeng Li, Xiaotao Sun, Yanting Zhang, Junliang Zhang, Pengchao Ren, Xiaozhen Liu, Tao Dou
    2016, 24(12):  1728-1734.  doi:10.1016/j.cjche.2016.08.020
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    EU-1 zeolites were sequentially treated with low-concentration sodium carbonate (Na2CO3) and hydrochloric acid (HCl) solutions. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption/desorption, temperature programmed desorption of NH3 (NH3-TPD), solid state 27Al nuclear magnetic resonance (27Al NMR), and the catalytic performances of the treated samples were tested in the xylene isomerization reaction. The results showed that the external surface area and mesoporous volume of the sample sequentially treated with 0.05 mol·L-1 Na2CO3 and 0.1 mol·L-1 HCl solutions reached 73.9 m2·g-1 and 0.162 cm3·g-1, respectively. The catalytic performances of EU-1 zeolites were significantly improved, that the activity of the probe reaction increased from 23.03% to 23.61% and the selectivity increased from 85.09% to 87.14% compared with those of parent sample. Furthermore, it was found that only amorphous silica and alumina species was dissolved during the post-treatment process, but the framework structure and the acidic properties of EU-1 zeolite remained intact.
    Catalytic kinetics of dimethyl ether one-step synthesis over CeO2-CaO-Pd/HZSM-5 catalyst in sulfur-containing syngas process
    Ruizhi Chu, Wenxin Hou, Xianliang Meng, Tingting Xu, Zhenyong Miao, Guoguang Wu, Lei Bai
    2016, 24(12):  1735-1741.  doi:10.1016/j.cjche.2016.09.008
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    CeO2-CaO-Pd/HZSM-5 catalyst was prepared for the dimethyl ether (DME) one-step synthesis in a continuous fixed-bed micro-reactor from the sulfur-containing syngas. The catalytic stability over hybrid catalyst of CeO2-CaO-Pd/HZSM-5 was investigated to ensure that the kinetics experimental results were not significantly influenced by induction period and catalytic deactivation. A large number of kinetic data points (40 sets) were obtained over a range of temperature (240-300℃), pressure (3-4 MPa), gas hourly space velocity (GHSV) (2000-3000 L·kg-1·h-1) and H2/CO mole ratio (2-3). Kinetic model for the methanol synthesis reaction and the dehydration of methanol were obtained separately according to reaction mechanism and Langmuir-Hinshelwood mechanism. Regression parameters were investigated by the method combining the simplex method and Runge-Kutta method. The model calculations were in appropriate accordance with the experimental data.
    Process Systems Engineering and Process Safety
    Development of a bifurcation analysis approach based on gPROMS platform
    Xueqing Kang, Hongye Cheng, Liwei Tong, Lifang Chen, Zhiwen Qi
    2016, 24(12):  1742-1749.  doi:10.1016/j.cjche.2016.05.025
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    A bifurcation analysis approach is developed based on the process simulator gPROMS platform, which can automatically trace a solution path, detect and pass the bifurcation points and check the stability of solutions. The arclength continuation algorithm is incorporated as a process entity in gPROMS to overcome the limit of turning points and get multiple solutions with respect to a user-defined parameter. The bifurcation points are detected through a bifurcation test function τ which is written in C++ routine as a foreign object connected with gPROMS through Foreign Process Interface. The stability analysis is realized by evaluating eigenvalues of the Jacobian matrix of each steady state solution. Two reference cases of an adiabatic CSTR and a homogenous azeotropic distillation from literature are studied, which successfully validate the reliability of the proposed approach. Besides the multiple steady states and Hopf bifurcation points, a more complex homoclinic bifurcation behavior is found for the distillation case compared to literature.
    Chemical Engineering Thermodynamics
    A comprehensive fractal char combustion model
    Yuting Liu, Rong He
    2016, 24(12):  1750-1760.  doi:10.1016/j.cjche.2016.05.048
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    The char combustion mechanisms were analyzed and a comprehensive fractal char combustion model was developed to give a better understanding and better predictions of the char combustion characteristics. Most of the complex factors affecting the char combustion were included, such as the coupling effects between the pore diffusion and the chemical reactions, the evolution of the char pore structures and the variation of the apparent reaction order during combustion, the CO/CO2 ratio in the combustion products and the correction for oxy-char combustion. Eleven different chars were then combusted in two drop tube furnaces with the conversions of the partly burned char samples measured by thermogravimetric analysis. The combustion processes of these chars were simulated with the predicted char conversions matching very well with the measured data which shows that this char combustion model has good accuracy. The apparent reaction order of the char combustion decreases, stabilizes and then increases during the combustion process. The combustion rates in the oxy-mode are generally slower than in the air-mode and the effect of the char-CO2 gasification reaction becomes obvious only when the temperature is relatively high and the O2 concentration is relatively low.
    Statistical mechanics and artificial intelligence to model the thermodynamic properties of pure and mixture of ionic liquids
    Fakhri Yousefi, Zeynab Amoozandeh
    2016, 24(12):  1761-1771.  doi:10.1016/j.cjche.2016.05.003
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    In this paper, the volumetric properties of pure and mixture of ionic liquids are predicted using the developed statistical mechanical equation of state in different temperatures, pressures and mole fractions. The temperature dependent parameters of the equation of state have been calculated using corresponding state correlation based on only the density at 298.15 K as scaling constants. The obtained mean of deviations of modified equation of state for density of all pure ionic liquids for 1662 data points was 0.25%. In addition, the performance of the artificial neural network (ANN) with principle component analysis (PCA) based on back propagation training with 28 neurons in hidden layer for predicting of behavior of binary mixtures of ionic liquids was investigated. The AADs of a collection of 568 data points for all binary systems using the EOS and the ANN at various temperatures and mole fractions are 1.03% and 0.68%, respectively. Moreover, the excess molar volume of all binary mixtures is predicted using obtained densities of EOS and ANN, and the results show that these properties have good agreement with literature.
    Investigation on molar heat capacity, standard molar enthalpy of combustion for guaiacol and acetyl guaiacol ester
    Changshuai Shen, Wenli Li, Cairong Zhou
    2016, 24(12):  1772-1778.  doi:10.1016/j.cjche.2016.05.004
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    The molar heat capacities (Cp) of guaiacol (CAS 90-50-1) and acetyl guaiacol ester (AGE, CAS 613-70-7) were determinated from 290 K to 350 K by differential scanning calorimetry (DSC), and expressed as a function of temperature. Two kinds of group contribution models were used to estimate the molar heat capacities of both guaiacol and AGE, the average relative deviation is less than 10%. The standard molar enthalpies of combustion of guaiacol and AGE were -3590.0 kJ·mol-1 and -4522.1 kJ·mol-1 by a precise thermal isolation Oxygen Bomb Calorimeter. The standard molar enthalpies of formation of guaiacol and AGE in a liquid state at 298.15 K were calculated to be -307.95 kJ·mol-1 and -448.72 kJ·mol-1, respectively, based on the standard molar enthalpies of combustion. The thermodynamic properties are useful for exploiting the new synthesis method, engineering design and industry production of AGE using guaiacol as a raw material.
    Molar volume of eutectic solvents as a function of molar composition and temperature
    Farouq S. Mjalli
    2016, 24(12):  1779-1785.  doi:10.1016/j.cjche.2016.05.047
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    The conventional Rackett model for predicting liquid molar volume has been modified to cater for the effect of molar composition of the Deep Eutectic Solvents (DES). The experimental molar volume data for a group of commonly used DES has been used for optimizing the improved model. The data involved different molar compositions of each DES. The validation of the new model was performed on another set of DESs. The average relative deviation of the model on the training and validation datasets was approximately 0.1% while the Rackett model gave a relative deviation of more than 1.6%. The modified model deals with variations in DES molar composition and temperature in a more consistent way than the original Rackett model which exhibits monotonic performance degradation as temperature moves away from reference conditions. Having the composition of the DES as a model variable enhances the practical utilization of the predicting model in diverse design and process simulation applications.
    Biotechnology and Bioengineering
    Hemicellulose in corn straw: Extracted from alkali solution and produced 5-hydroxymethyl furfural in HCOOH/HCOONa buffer solution
    Yan Li, Hongxian Fan, Xueqing Yu, Songmei Zhang, Gang Li
    2016, 24(12):  1786-1792.  doi:10.1016/j.cjche.2016.05.016
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    Hemicellulose in corn straw is a group of complex heteropolysaccharides which are composed of different sugar units, including mannans, xylans, arabinans and galactans. This study developed a simple and practical process for production of 5-hydroxymethyl furfural (HMF) using hemicellulose that was extracted from corn straw. In the hemicellulose degradation process HCOOH/HCOONa was used as buffer solution, and the optimum conditions for maximum HMF yield were explored. Various extraction conditions including NaOH concentration, reaction time, temperature, solid-to-liquid ratio and precipitant were tested for hemicellulose obtaining, giving the optimum condition of 55℃, 4 h, solid-to-liquid ratio of 1:10, 1.5 mol·L-1 NaOH solution and ethanol as precipitant with the yield of 34.16%. Dehydration of hemicellulose under HCOOH/HCOONa buffer solution process, using solution medium of pH=0.8 hydrolyzed hemicellulose in corn straw at 190℃ after 190 min and 82% of HMF yield was achieved.