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Table of Content
28 May 2013, Volume 21 Issue 5
    Transport of Wetting and Nonwetting Liquid Plugs in a T-shaped Microchannel
    YONG Yumei, LI Sha, YANG Chao, YIN Xiaolong
    2013, 21(5):  463-472.  doi:10.1016/S1004-9541(13)60523-6
    Abstract ( 4186 )   PDF (846KB) ( 45 )  
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    The transport of liquid plugs in microchannels is very important for many applications such as in medical treatments in airways and in extraction of oil from porous rocks. A plug of wetting and non-wetting liquids driven by a constant pressure difference through a T-shaped microchannel is studied numerically with lattice Boltzmann (LB) method. A two-phase flow LB model based on field mediators is built. Three typical flow patterns (blocking, rupture and splitting flow) of plug flow are obtained with different driving pressures. It is found that it becomes difficult for a plug with short initial plug length to leave the microchannel; the flow pattern of plug transport varies with the contact angle, especially from wetting to nonwetting; with the increase of interfacial tension, the front interface of plug moves faster; the front and rear interfaces of the plug with small viscosity ratio move faster in the microchannel than those of the plug with large viscosity ratio. The study is helpful to provide theoretical data for the design and scale-up of liquid-liquid reactors and separators.
    Surface Modification of Commercial Aromatic Polyamide Reverse Osmosis Membranes by Crosslinking Treatments
    WEI Xinyu, WANG Zhi, XU Jun, WANG Jixiao, WANG Shichang
    2013, 21(5):  473-484.  doi:10.1016/S1004-9541(13)60507-8
    Abstract ( 5785 )   PDF (898KB) ( 47 )  
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    Crosslinking treatments for a commercially available aromatic polyamide reverse osmosis membrane were carried out to improve its chlorine resistance. The crosslinking agents including 1,6-hexanediol diglycidyl ether, adipoyl dichloride and hexamethylene diisocyanate ester with long flexible aliphatic chains and high reactivity with N-H groups were used in the experiments. Attenuated total reflective Fourier transform infrared spectra verified the successful preparation of highly crosslinked membranes by crosslinking treatments. It was suggested that the crosslinking agents were connected to membrane surface through the reactions with amine and amide II groups, which is confirmed by surface charge measurements. Based on contact angle measurements, crosslinking treatments decreased membrane hydrophilicity by introducing methylene groups to membrane surface. With increasing amount of crosslinking agent molecules connected to membrane surface, the hydrolysis of unconnected functional groups of crosslinking agent produced polar groups and increased membrane hydrophilicity. The highly crosslinked membranes showed higher salt rejections and lower water fluxes as compared with the raw membrane. Since the active sites (N-H groups) vulnerable to free chlorine on membrane surface were eliminated by crosslinking treatments, the chlorine resistances of the highly crosslinked membranes were significantly improved by slighter changes in both water fluxes and salt rejections after chlorination.
    A Method to Obtain Gas-PDMS Membrane Interaction Parameters for UNIQUAC Model
    LIN Dongjie, DING Zhongwei, LIU Liying, MA Runyu
    2013, 21(5):  485-493.  doi:10.1016/S1004-9541(13)60513-3
    Abstract ( 4460 )   PDF (310KB) ( 691 )  
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    The recovery or capture of one or more components from gas mixture by membrane separation has become a research focus in recent years. This study investigates the gas-membrane solution equilibrium, for which Henry’s law is not applicable if the gas phase is a mixture. This problem can be solved by using UNIQUAC model to calculate the activity coefficient of gas dissolved in the membrane. A method was proposed in this study to obtain the gas-membrane interaction parameter for UNIQUAC model. By the experiments of gas permeation through polydimethylsiloxane PDMS membrane, the solubility coefficients of some gases (N2, CO2, CH4) were measured. Through non-linear fitting UNIQUAC model to the experimental results from this study and in literature (H2, O2, C3H8), the gas-membrane interaction parameters for these gases were obtained. Based on these parameters, the activity coefficients of the dissolved gas were calculated by UNIQUAC model, and their values agree well with the experimental data. These results confirm the feasibility and effectiveness of the proposed method, which makes it possible to better predict gas-membrane solution equilibrium.
    A Mathematical Model for Designing Optimal Shape for the Cone Used in Z-flow Type Radial Flow Adsorbers
    ZHANG Xuejun, LU Junliang, QIU Limin, ZHANG Xiaobin, WANG Xiaolei
    2013, 21(5):  494-499.  doi:10.1016/S1004-9541(13)60527-3
    Abstract ( 3871 )   PDF (314KB) ( 33 )  
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    Nonuniform flow distribution along the radial direction usually exists in a Z-flow type radial flow adsorber, which will decrease the utilization of adsorbent and the switching time and may result in operating safety problems in cryogenic air separation. In order to improve the uniformity of the flow distribution along the radial direction in the adsorber, a differential equation is derived through pressure drop analysis in the Z-flow type radial adsorber with a cone in the middle of the central pipe. The differential equation determines the ideal cross-sectional radii of the cone along the axis. The result shows that the cross-sectional radius of the cone should gradually decrease from 0.3 m to zero along the axis to ensure that the process air is distributed uniformly in the Z-flow type radial flow adsorber and the shape of the cone is a little convex. The flow distribution without the cone in the central pipe is compared under different bed porosities. It is demonstrated that the proposed differential equation can provide theoretical support for designing Z-flow type radial flow adsorbers.
    Preparation, Characterization of Dawson-type Heteropoly Acid Cerium (III) Salt and Its Catalytic Performance on the Synthesis of n-Butyl Acetate
    CAO Xiaohua, REN Jie, XU Changlong, ZHANG Kanghua, ZHAN Changchao, LAN Jian
    2013, 21(5):  500-506.  doi:10.1016/S1004-9541(13)60493-0
    Abstract ( 4970 )   PDF (390KB) ( 45 )  
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    A novel cerium (III) salt of Dawson type tungstophosphoric acid (Ce2P2W18O62·16H2O) was prepared by doping cerous nitrate in H6P2W18O62·13H2O powder and characterized by thermogravimetry and differential thermal analyses (TG/DTA), Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), pyridine infrared spectroscopy (Py-IR) and scanning electron microscopy (SEM). Its catalytic activity was evaluated by the probe reaction of synthesis of n-butyl acetate with acetic acid and n-butanol. The effects of various parameters such as molar ratio of n-butanol to acetic acid, reaction temperature, reaction time, and catalyst amount have been studied by single factor experiment. The results show that Ce2P2W18O62·16H2O behaved as an excellent heterogeneous catalyst in the synthesis of n-butyl acetate. The optimum synthetic conditions were determined as follows:molar ratio of n-butanol to acetic acid at 2.0:1.0, mass of the catalyst being 1.44% of the total reaction mixture, reaction temperature of 120 ℃ and reaction time of 150 min. Under above conditions, the conversion of acetic acid was above 97.8%. The selectivity of n-butyl acetate based on acetic acid was, in all cases, nearly 100%. The catalysts could be recycled and still exhibited high catalytic activity with 90.4% conversion after five cycles of reaction. It was found by means of TG-DTA and Py-IR that the catalyst deactivation was due to the adsorption of a complex of by-product on the active sites on catalysts surface or the catalyst loss in its separation from the products. Compared with using sulfuric acid as catalyst, the present procedure with Ce2P2W18O62·16H2O is a green productive technology due to simple process, higher yield, catalyst recycling and no corrosion for the production facilities.
    Preparation of Fe-Mn/K/Al2O3 Fischer-Tropsch Catalyst and Its Catalytic Kinetics for the Hydrogenation of Carbon Monoxide
    F. Fazlollahi, M. Sarkari, H. Gharebaghi, H. Atashi, M. M. Zarei, A. A. Mirzaei, W. C. Hecker
    2013, 21(5):  507-519.  doi:10.1016/S1004-9541(13)60503-0
    Abstract ( 4904 )   PDF (468KB) ( 31 )  
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    A K promoted iron-manganese catalyst was prepared by sol-gel method, and subsequently was tested for hydrogenation of carbon monoxide to light olefins. The kinetic experiments on a well-characterized Fe-Mn/K/Al2O3 catalyst were performed in a fixed-bed micro-reactor in a temperature range of 280-380 ℃, pressure range of 0.1-1.2 MPa, H2/CO feed molar ratio range of 1-2.1 and a space velocity range of 2000-7200 h-1. Considering the mechanism of the process and Langmuir-Hinshelwood-Hogan-Watson (LHHW) approach, unassisted CO dissociation and H-assisted CO dissociation mechanisms were defined. The best models were obtained using non-linear regression analysis and Levenberg-Marquardt algorithm. Consequently, 4 models were considered as the preferred models based on the carbide mechanism. Finally, a model was proposed as a best model that assumed the following kinetically relevant steps in the iron-Fischer-Tropsch (FT) synthesis: (1) CO dissociation occurred without hydrogen interaction and was not a rate-limiting step; (2) the first hydrogen addition to surface carbon was the rate-determining steps. The activation energy and adsorption enthalpy were calculated 40.0 and -30.2 kJ·mol-1, respectively.
    Modeling and Optimization of the Steam Turbine Network of an Ethylene Plant
    LI Zeqiu, ZHAO Liang, DU Wenli, QIAN Feng
    2013, 21(5):  520-528.  doi:10.1016/S1004-9541(13)60530-3
    Abstract ( 4642 )   PDF (359KB) ( 1476 )  
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    In this paper, we developed a hybrid model for the steam turbines of a utility system, which combines an improved neural network model with the thermodynamic model. Then, a nonlinear programming (NLP) model of the steam turbine network is formulated by utilizing the developed steam turbine models to minimize the total steam cost for the whole steam turbine network. Finally, this model is applied to optimize the steam turbine network of an ethylene plant. The obtained results demonstrate that this hybrid model can accurately estimate and evaluate the performance of steam turbines, and the significant cost savings can be made by optimizing the steam turbine network operation at no capital cost.
    PID Controller Design Based on the Time Domain Information of Robust IMC Controller Using Maximum Sensitivity
    JIN Qibing, LIU Qie, WANG Qi, TIAN Yuqi, WANG Yuanfei
    2013, 21(5):  529-536.  doi:10.1016/S1004-9541(13)60522-4
    Abstract ( 4707 )   PDF (223KB) ( 75 )  
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    The IMC (Internal Model Control) controller based on robust tuning can improve the robustness and dynamic performance of the system. In this paper, the robustness degree of the control system is investigated based on Maximum Sensitivity (Ms) in depth. And the analytical relationship is obtained between the robustness specification and controller parameters, which gives a clear design criterion to robust IMC controller. Moreover, a novel and simple IMC-PID (Proportional-Integral-Derivative) tuning method is proposed by converting the IMC controller to PID form in terms of the time domain rather than the frequency domain adopted in some conventional IMC-based methods. Hence, the presented IMC-PID gives a good performance with a specific robustness degree. The new IMC-PID method is compared with other classical IMC-PID rules, showing the flexibility and feasibility for a wide range of plants.
    A Hybrid Algorithm Based on Differential Evolution and Group Search Optimization and Its Application on Ethylene Cracking Furnace
    NIAN Xiaoyu, WANG Zhenlei, QIAN Feng
    2013, 21(5):  537-543.  doi:10.1016/S1004-9541(13)60531-5
    Abstract ( 4476 )   PDF (230KB) ( 42 )  
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    To find the optimal operational condition when the properties of feedstock changes in the cracking furnace online, a hybrid algorithm named differential evolution group search optimization (DEGSO) is proposed, which is based on the differential evolution (DE) and the group search optimization (GSO). The DEGSO combines the advantages of the two algorithms: the high computing speed of DE and the good performance of the GSO for preventing the best particle from converging to local optimum. A cooperative method is also proposed for switching between these two algorithms. If the fitness value of one algorithm keeps invariant in several generations and less than the preset threshold, it is considered to fall into the local optimization and the other algorithm is chosen. Experiments on benchmark functions show that the hybrid algorithm outperforms GSO in accuracy, global searching ability and efficiency. The optimization of ethylene and propylene yields is illustrated as a case by DEGSO. After optimization, the yield of ethylene and propylene is increased remarkably, which provides the proper operational condition of the ethylene cracking furnace.
    Optimization on the Conversion of Bamboo Shoot Shell to Levulinic Acid with Environmentally Benign Acidic Ionic Liquid and Response Surface Analysis
    ZHOU Cunshan, YU Xiaojie, MA Haile, HE Ronghai, Saritporn Vittayapadung
    2013, 21(5):  544-550.  doi:10.1016/S1004-9541(13)60509-1
    Abstract ( 4960 )   PDF (383KB) ( 55 )  
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    Levulinic acid (LA) has been identified as a promising green, biomass derived platform chemical. Response surface analysis (RSA) with a four-factor-five-level central composite design (CCD) was applied to optimize the hydrolysis conditions for the conversion of bamboo (Phyllostachys Praecox f. preveynalis) shoot shell (BSS) to LA catalyzed with ionic liquid [C4mim]HSO4. The effects of four main reaction parameters including temperature, time,C[C4mim]HSO4(initial [C4mim]HSO4 concentration) and XBSS (initial BSS intake) on the hydrolysis reaction for yield of LA were analyzed. A quadratic equation model for yield of LA was established and fitted to the data with an R2 of 0.9868, and effects of main factors and their corresponding relationships were obtained with RSA. Model validation and results of CCD showed good correspondence between actual and predicted values. The analysis of variance (ANOVA) of the results indicated that the yield of LA in the range studied was significantly (P<0.05) affected by the four factors. The optimized reaction conditions were as follows: temperature of 145 ℃, time of 103.8 min,C[C4mim]HSO4 of 0.9 mol·L-1 and XBSS of 2.04% (by mass), respectively. A high yield [(71±0.41)% (by mol), triplicate experiment] was obtained at the optimum conditions of temperature of 145 ℃, time of 104 min,C[C4mim]HSO4 of 0.9 mol·L-1 and XBSS of 2% (by mass), which obtained from the real experiments, concurred with the model prediction [73.8% (by mol) based on available C6 sugars in BSS or 17.9% (by mass) based on the mass of BSS], indicating that the model was adequate for the hydrolysis process.
    Pretreatment of Corn Stover Using Supercritical CO2 with Water-Ethanol as Co-solvent
    LÜ Huisheng, REN Miaomiao, ZHANG Minhua, CHEN Ying
    2013, 21(5):  551-557.  doi:10.1016/S1004-9541(13)60508-X
    Abstract ( 4779 )   PDF (516KB) ( 97 )  
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    Supercritical carbon dioxide, with water-ethanol as co-solvent, was applied to pretreat corn stover to enhance its enzymatic hydrolysis. The efficiency of pretreatment was evaluated by the final reducing sugar yield obtained from the enzymatic hydrolysis of cellulose. Under the operation conditions of pretreatment pressure 15 MPa, temperature 180 ℃ and time 1 h, the optimal sugar yield of 77.8℅ was obtained. Scanning electron microscopy (SEM) and chemical composition analysis were applied to the pretreated corn stover. The results showed that the surface morphology and microscopic structure of pretreated corn stover were greatly changed. After the pretreatment, the contents of hemicellulose and lignin were reduced obviously. Thus more cellulose was exposed, increasing the sugar yield.
    Selective Removal of Nitrogen-Containing Heterocyclic Compounds from Transportation Diesel Fuels with Reactive Adsorbent
    YANG Lei, WANG Shengqiang, WANG Ruicong, YU Hongbing
    2013, 21(5):  558-563.  doi:10.1016/S1004-9541(13)60512-1
    Abstract ( 5046 )   PDF (440KB) ( 35 )  
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    This paper presents a new selective adsorbent to remove nitrogen-containing heterocyclic compounds from model and commercial transportation diesel fuels based on characteristic reaction designed to occur in the pores of substrate. This reactive adsorbent is composed of formaldehyde, phosphotungstic acid and Santa Barbara USA (SBA)-15. The experiment was based on assumed hydroxymethylation reaction of nitrogen-containing heterocyclic compounds with formaldehyde using phosphotungstic acid as catalyst in batch and fixed-bed systems. The nitrogen concentration in the model fuel was 237.33 ng·μl-1, carbazole and toluene were used as model nitrogen-containing heterocyclic compound and solvent, respectively. The effectiveness of reactive adsorbent for removal of nitrogen-containing heterocyclic compounds from commercial 0# diesel fuel containing 224.86 ng·μl-1 nitrogen was examined in a fixed-bed reactor at 70 ℃. The results showed that nitrogen in the model fuel was very low and the nitrogen concentration in the commercial diesel reduced to 2.44 ng·μl-1. The demand for transportation fuel with ultra-low nitrogen is satisfied.
    Effect of Ferric Chloride on the Properties of Biological Sludge in Co-precipitation Phosphorus Removal Process
    ZHANG Zhibin, LI Yi, WEI Leilei, LÜ Yufeng, WANG Meng, GAO Baoyu
    2013, 21(5):  564-568.  doi:10.1016/S1004-9541(13)60511-X
    Abstract ( 4874 )   PDF (207KB) ( 40 )  
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    This paper studied the effect of ferric chloride on waste sludge digestion, dewatering and sedimentation under the optimized doses in co-precipitation phosphorus removal process. The experimental results showed that the concentration of mixed liquid suspended solid (MLSS) was 2436 mg稬-1 and 2385 mg稬-1 in co-precipitation phosphorus removal process (CPR) and biological phosphorous removal process (BPR), respectively. The sludge reduction ratio for each process was 22.6% and 24.6% in aerobic digestion, and 27.6% and 29.9% in anaerobic digestion, respectively. Due to the addition of chemical to the end of aeration tank, the sludge content of CPR was slightly higher than that of BPR, but the sludge reduction rate for both processes had no distinct difference. The sludge volume index (SVI) and sludge specific resistance of BPR were 126 ml穏-1 and 11.7?1012 m穔g-1, respectively, while those of CPR were only 98 ml穏-1 and 7.1?1012 m穔g-1, indicating that CPR chemical could improve sludge settling and dewatering.
    Porous TiO2-coated Magnetic Core-Shell Nanocomposites:Preparation and Enhanced Photocatalytic Activity
    LIU Hongfei, JI Shengfu, ZHENG Yuanyuan, LI Ming, YANG Hao
    2013, 21(5):  569-576.  doi:10.1016/S1004-9541(13)60521-2
    Abstract ( 5210 )   PDF (753KB) ( 49 )  
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    The core-shell structured TiO2/SiO2@Fe3O4 photocatalysts were prepared using Fe3O4 as magnetic core, tetraethoxysilane (TEOS) as silica source and tetrabutyl titanate (TBOT) as titanium sources. The as-obtained structure was composed of a SiO2@Fe3O4 core and a porous TiO2 shell. The diameter of SiO2@Fe3O4 core was about 205 nm with thickness of porous TiO2 of about 5-6 nm. The 9%TiO2/6% SiO2@Fe3O4 microspheres possess the highest BET surface area and the BJH pore volume, which are 373.5 m2-1 and 0.28 cm3-1, respectively. The 9%TiO2/6%SiO2@Fe3O4 photocatalyst exhibited an excellent performance for the degradation of methyl orange and methylene blue dyes. Two different dyes were completely decolorized in 60 min under UV irradiation. The photocatalytic activity and the amount of catalyst were almost not decrease after recycling for 6 times by using external magnetic field.
    Recycling and Reuse of Ionic Liquid in Homogeneous Cellulose Acetylation
    HUANG Kelin, WU Rui, CAO Yan, LI Huiquan, WANG Jinshu
    2013, 21(5):  577-584.  doi:10.1016/S1004-9541(13)60524-8
    Abstract ( 5119 )   PDF (289KB) ( 650 )  
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    Molecular distillation was used to recover ionic liquid (IL) 1-allyl-3-methylimidazolium chloride (AmimCl) in homogeneous cellulose acetylation. The five factors that affect the separation efficiency of molecular distillation, namely, feed flow rate, distillation temperature, feed temperature, wiper rotating speed, and distillation pressure, are discussed. The optimal recovery condition was determined via orthogonal experiments using an OA9(34) design. The IL was recycled and reused 5 times in the homogeneous cellulose acetylation system under optimal conditions. The purity of recycled IL the 5th time reached 99.56%. FT-IR (Fourier transform infrared spectroscopy) and 1H NMR (nuclear magnetic resonance) spectroscopy showed that the structure of the recovered IL is not changed. This work proves that AmimCl has excellent reusability, and that molecular distillation is an effective method for recovering IL in homogeneous cellulose acetylation.