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Table of Content
28 June 2013, Volume 21 Issue 6
    Thermohydraulics of Turbulent Flow Through Heat Exchanger Tubes Fitted with Circular-rings and Twisted Tapes
    Smith Eiamsa-ard, Vichan Kongkaitpaiboon, Kwanchai Nanan
    2013, 21(6):  585-593.  doi:10.1016/S1004-9541(13)60504-2
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    The influences of circular-ring turbulators (CRT) and twisted tape (TT) swirl generators on the heat transfer enhancement, pressure drop and thermal performance factor characteristics in a round tube are reported. The circular-ring turbulators were individually employed and together with the twisted tape swirl generators in the heated section of the tube. Three different pitch ratios (l/D1.0, 1.5, and 2.0) of the CRT and three different twist ratios (y/W 3, 4, and 5) of the TT were introduced. The experiments were conducted using air as the working fluid under a uniform wall heat flux condition, for the Reynolds number between 6000 and 20000. The experimental results reveal that the heat transfer rate, friction factor and thermal performance factor of the combined CRT and TT are considerably higher than those of CRT alone. For the range examined, the increases of mean Nusselt number, friction factor and thermal performance, in the tube equipped with combined devices, respectively, are 25.8%, 82.8% and 6.3% over those in the tube with the CRT alone. The highest thermal performance factor of 1.42 is found for the combined device consisting of the CRT with l/D 1.0 and TT with y/W 3. The correlations of the Nusselt number, friction factor and thermal performance factor of the tubes with combined devices are also developed in terms of Reynolds number, Prandtl number, twist ratio and pitch ratio.
    Adsorption and Desorption Behavior of Tannic Acid in Aqueous Solution on Polyaniline Adsorbent
    WANG Jiahong, JI Yanfen, DING Shaolan, MA Hongrui, HAN Xiaojing
    2013, 21(6):  594-599.  doi:10.1016/S1004-9541(13)60516-9
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    Tannic acid is generally considered as one of polyphenolic pollutants, which may cause severe threats to the environment. In this study, polyaniline adsorbent was synthesized by chemical oxidation to remove tannic acid in aqueous solutions. The adsorption amount of tannic acid varied greatly with pH of solution and strong adsorption was at pH 5.8-6.7. Coexisting cations, such as Na+, K+, and Ca2+, can enhance the adsorption of tannic acid on polyaniline, which may be contributed to the electrostatic interaction between tannic acid and polyaniline. The adsorption process could be well described by Langmuir model and the maximum adsorption capacity was 117.65 mg·g-1 at 35℃ and pH 6.0. The thermodynamic parameters calculated from the adsorption isotherms indicate that the adsorption of tannic acid is spontaneous and endothermic process. The polyaniline saturated with tannic acid can be desorbed in alkaline solution and regenerated adsorbent can be used repeatedly with high adsorption capacity, which implies that polyaniline adsorbents have a great potential in water purification for the removal of tannic acid.
    Object-oriented Modular Model Library for Distillation
    CHEN Chang, DING Jianwan, CHEN Liping
    2013, 21(6):  600-610.  doi:10.1016/S1004-9541(13)60519-4
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    For modeling and simulation of distillation process, there are lots of special purpose simulators along with their model libraries, such as Aspen Plus and HYSYS. However, the models in these tools lack of flexibility and are not open to the end-user. Models developed in one tool can not be conveniently used in others because of the barriers among these simulators. In order to solve those problems, a flexible and extensible distillation system model library is constructed in this study, based on the Modelica and Modelica-supported platform MWorks, by the object-oriented technology and level progressive modeling strategy. It supports the reuse of knowledge on different granularities: physical phenomenon, unit model and system model. It is also an interface-friendly, accurate, fast PC-based and easily reusable simulation tool, which enables end-user to customize and extend the framework to add new functionality or adapt the simulation behavior as required. It also allows new models to be composed programmatically or graphically to form more complex models by invoking the existing components. A conventional air distillation column model is built and calculated using the library, and the results agree well with that simulated in Aspen Plus.
    Modelling-based Optimisation of the Direct Synthesis of Dimethyl Ether from Syngas in a Commercial Slurry Reactor
    Sadegh Papari, Mohammad Kazemeini, Moslem Fattahi
    2013, 21(6):  611-621.  doi:10.1016/S1004-9541(13)60505-4
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    In the present study, we developed a multi-component one-dimensional mathematical model for simulation and optimisation of a commercial catalytic slurry reactor for the direct synthesis of dimethyl ether (DME) from syngas and CO2, operating in a churn-turbulent regime. DME productivity and CO conversion were optimised by tuning operating conditions, such as superficial gas velocity, catalyst concentration, catalyst mass over molar gas flow rate (W/F), syngas composition, pressure and temperature. Reactor modelling was accomplished utilising mass balance, global kinetic models and heterogeneous hydrodynamics. In the heterogeneous flow regime, gas was distributed into two bubble phases: small and large. Simulation results were validated using data obtained from a pilot plant. The developed model is also applicable for the design of large-scale slurry reactors.
    Study on Deactivation by Sulfur and Regeneration of Pd/C Catalyst in Hydrogenation of N-(3-nitro-4-methoxyphenyl) Acetamide
    ZHANG Qunfeng, LÜ Jinghui, MA Lei, LU Chunshan, LIU Wei, LI Xiaonian
    2013, 21(6):  622-626.  doi:10.1016/S1004-9541(13)60497-8
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    Deactivation of Pd/C catalyst often occurs in liquid hydrogenation using industrial materials. For instance, the Pd/C catalyst is deactivated severely in the hydrogenation of N-(3-nitro-4-methoxyphenyl) acetamide. In this study, the chemisorption of sulfur on the surface of deactivated Pd/C was detected by energy dispersive spectrometer and X-ray photoelectron spectroscopy. Sulfur compounds poison the Pd/C catalyst and increase the formation of azo deposit, reducing the activity of catalyst. We report a mild method to regenerate the Pd/C catalyst: wash the deposit by N,N-dimethylformamide and oxidize the chemisorbed sulfur by hot air. The regenerated Pd/C catalyst can be reused at least ten runs with stable activity.
    Surface Acidity of Aluminum Phosphate and Its Catalytic Performance in Benzene Alkylation with Long Chain Olefin
    YUAN Haikuan, LIU Xuru, REN Jie, SHEN Lian
    2013, 21(6):  627-632.  doi:10.1016/S1004-9541(13)60498-X
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    The acidic properties of aluminum phosphate (AlPO4-5) solid acid catalyst were characterized by temperature programmed desorption (TPD) of ammonia (NH3), n-propylamine (n-C3H7NH2), iso-propylamine [(CH3)2CHNH2] and n-dipropylamine [(C3H7)2NH] separately, and its catalytic performance in benzene alkylation with long chain olefin was studied in a fixed-bed reactor. The characterized acid amount of catalyst increased with the basicity of adsorbates. With increase of the activation temperature of catalyst, the acid amount characterized by NH3-TPD decreased, however, it increased when characterized by TPD using three other adsorbates. The desorption kinetics of TPD process and the deactivation kinetics of catalyst were investigated. The acidity and catalytic performance of catalyst was also correlated. The results showed that the acid amount and strength are well correlated with the activity and stability using NH3 as adsorbate, respectively, which indicated NH3 was a better basic adsorbate. It was also found that the catalyst with higher acid amount and lower acid strength on the surface exhibited the better catalytic performance and stability.
    Statistical Monitoring of Chemical Processes Based on Sensitive Kernel Principal Components
    JIANG Qingchao, YAN Xuefeng
    2013, 21(6):  633-643.  doi:10.1016/S1004-9541(13)60506-6
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    The kernel principal component analysis (KPCA) method employs the first several kernel principal components (KPCs), which indicate the most variance information of normal observations for process monitoring, but may not reflect the fault information. In this study, sensitive kernel principal component analysis (SKPCA) is proposed to improve process monitoring performance, i.e., to deal with the discordance of T2 statistic and squared prediction error δSPE statistic and reduce missed detection rates. T2 statistic can be used to measure the variation directly along each KPC and analyze the detection performance as well as capture the most useful information in a process. With the calculation of the change rate of T2 statistic along each KPC, SKPCA selects the sensitive kernel principal components for process monitoring. A simulated simple system and Tennessee Eastman process are employed to demonstrate the efficiency of SKPCA on online monitoring. The results indicate that the monitoring performance is improved significantly.
    Estimation of Formation Enthalpies of Organic Pollutants from a New Structural Group Contribution Method
    Mehdi Bagheri, Afshin Bakhtiari, Masoume Jaberi
    2013, 21(6):  644-653.  doi:10.1016/S1004-9541(13)60517-0
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    Chemical stability and reactivity of organic pollutants is dependent to their formation enthalpies. The main objective of this study is to provide simple straightforward strategy for prediction of the formation enthalpies of wide range organic pollutants only from their structural functional groups. Using such an extended dataset comprising 1694 organic chemicals from 77 diverse material classes benefits the generalizability and reliability of the study. The new suggested collection of 12 functional groups and a simple linear regression lead to promising statistics of R2=0.958, QLoo2=0.956, and δAEE=57 kJ·mol-1 for the whole dataset. Moreover, unknown experimental formation enthalpies for 27 organic pollutants are estimated by the presented approach. The resultant model needs no technical software/calculations, and thus can be easily applied by a non-specialist user.
    Entropy Analyses of Droplet Combustion in Convective Environment with Small Reynolds Number
    ZHANG Xiaobin, ZHANG Wei, ZHANG Xuejun
    2013, 21(6):  654-662.  doi:10.1016/S1004-9541(13)60526-1
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    This paper analyzes the entropy generation rate of simple pure droplet combustion in a temperature-elevated air convective environment based on the solutions of flow, and heat and mass transfer between the two phases. The flow-field calculations are carried out by solving the respective conservation equations for each phase, accounting for the droplet deformation with the axisymmetric model. The effects of the temperature, velocity and oxygen fraction of the free stream air on the total entropy generation rate in the process of the droplet combustion are investigated. Special attention is given to analyze the quantitative effects of droplet deformation. The results reveal that the entropy generation rate due to chemical reaction occupies a large fraction of the total entropy generated, as a result of the large areas covered by the flame. Although, the magnitude of the entropy generation rate per volume due to heat transfer and combined mass and heat transfer has a magnitude of one order greater than that due to chemical reaction, they cover a very limited area, leading to a small fraction of the total entropy generated. The entropy generation rate due to mass transfer is negligible. High temperature and high velocity of the free stream are advantageous to increase the exergy efficiency in the range of small Reynolds number (<1) from the viewpoint of the second-law analysis over the droplet lifetime. The effect of droplet deformation on the total entropy generation is the modest.
    Separation of Recombinant Geranylgeranyl Diphosphate Synthase of Deinococcus radiodurans from Expressed Strain Cell Homogenate by Immobilized Metal Affinity Chromatography on a Characterized Monolithic Cryogel Column
    SHEN Shaochuan, WANG Liangyan, SUN Zongtao, LI Mingfeng, LIU Chengzhi, TIAN Bing, YUN Junxian, HUA Yuejin
    2013, 21(6):  663-669.  doi:10.1016/S1004-9541(13)60514-5
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    Geranylgeranyl diphosphate synthase (GGPPS) plays a key role in the biosynthesis of antioxidative carotenoid from the extremely radioresistant bacterium Deinococcus radiodurans. In this work, the recombinant GGPPS expressed in Escherichia coli by cloning and transforming the gene dr1395 of D. radiodurans was isolated rapidly by an immobilized metal affinity supermacroporous cryogel, i.e., Cu2+-iminodiacetic acid (IDA)-cryogel. The properties of the Cu2+-IDA-cryogel were characterized using capillary-based mathematical model and experimental measurements. The obtained protein samples were analyzed by the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The porosity of the present Cu2+-IDA-cryogel is 90.4% and the water permeability is 5.04×10-12 m2. From the capillary-based model, this cryogel presents a slightly wide normal pore (capillary) size distribution with the mean diameter of 55.2 μm, the standard deviation of 28.0 μm and the half of skeleton wall thickness of 2.8 μm. The pore size distribute from about 10 to 141 μm and the effective tortuosity of these capillary pores increases from 2.60 to 9.05. The isolation of the GGPPS from cell homogenate can be achieved at the flow velocity of 3.40×10-4 m·s-1 by the Cu2+-IDA-cryogel bed. High-purity GGPPS (about 91.4%) is obtained according to the SDS-PAGE analysis of the elution samples, indicating that the present method is a promising, simple and effective approach to isolate GGPPS from cell homogenate of engineering strains.
    Immobilization of Papain in Biosilica Matrix and Its Catalytic Property
    ZHOU Liya, WANG Cui, JIANG Yanjun, GAO Jing
    2013, 21(6):  670-675.  doi:10.1016/S1004-9541(13)60528-5
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    A novel method was developed for papain immobilization through a biomimetic silicification process induced by papain. By incubating papain in a silica precursor solution, the papain-silica composite formed rapidly and papain was encapsulated. The encapsulation efficiency and the recovery activity were 82.60% and 83.09%, respectively. Compared with enzymes and biomolecules immobilized in biosilica matrix in the presence of additional silica-precipitating species, this papain encapsulation process, a biomimetic approach, realized high encapsulation efficiency by its autosilification activity under mild conditions (near-neutral pH and ambient temperature). Furthermore, the encapsulated papain exhibits enhanced thermal, pH, recycling and storage stabilities. Kinetic analysis showed that the biomimetic silica matrix did not significantly hinder the mass transport of substrate or the release of product.
    Comparison on Thermal Conductivity and Permeability of Granular and Consolidated Activated Carbon for Refrigeration
    JIN Zhequan, TIAN Bo, WANG Liwei, WANG Ruzhu
    2013, 21(6):  676-682.  doi:10.1016/S1004-9541(13)60525-X
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    This paper focuses on the development of three types of activated carbon (AC) adsorbents, i.e. granular AC, consolidated AC with chemical binder, and consolidated AC with expanded natural graphite (ENG). Their thermal conductivity was investigated with the steady-state heat source method and the permeability was tested with nitrogen as the gas source. Results show that the thermal conductivity of granular AC with different sizes almost maintains a constant at 0.36 W·(m·K)-1, while the value modestly increases to 0.40 W·(m·K)-1 for the consolidated AC with chemical binder. The consolidated AC with ENG at the density of 600 kg·m-3 shows the best heat transfer performance and their thermal conductivity vary from 2.08 W·(m·K)-1 to 2.61 W·(m·K)-1 according to its fraction of AC. However, the granular AC and consolidated AC with chemical binder show the better permeability performance than consolidated AC with ENG binder whose permeability changes from 6.98×10-13 m2 to 5.16×10-11 m2 and the maximum occurs when the content of AC reaches 71.4% (by mass). According to the different thermal properties, the refrigeration application of three types of adsorbents is analyzed.
    Effect of Hydrogen Reduction of Silver Ions on the Performance and Structure of New Solid Polymer Electrolyte PEI/Pebax2533/AgBF4 Composite Membranes
    WANG Yanbei, REN Jizhong, LI Hui, DENG Maicun
    2013, 21(6):  683-690.  doi:10.1016/S1004-9541(13)60515-7
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    In this paper, the effect of hydrogen reduction of silver ions on the performance and structure of new solid polymer electrolyte polyetherimide (PEI)/Pebax2533 (Polynylon12/tetramethylene oxide block copolymer, PA12-PTMO)/AgBF4 composite membranes is investigated. For PEI/Pebax2533/AgBF4 composite membranes prepared with different AgBF4 concentration, the permeances of propylene and ethylene increase with the increase of AgBF4 concentration due to the carrier-facilitated transport, resulting in a high selectivity. But for propylene/propane mixture, the mixed-gas selectivity is lower than its ideal selectivity. The hydrogen reduction strongly influences the membrane performance, which causes the decrease of propylene permeance and the increase of propane permeance. With the increase of hydrogen reduction time, the membranes show a clearly color change from white to brown, yielding a great selectivity loss. The data of X-ray diffraction and FT-IR prove that silver ions are reduced to Ag0 after hydrogen reduction, and aggregated on the surface of PEI/Pebax2533/AgBF4 composite membranes.
    Preparation of Mesoporous Carbons from Acrylonitrile-methyl Methacrylate Copolymer/Silica Nanocomposites Synthesized by in-situ Emulsion Polymerization
    BAO Yongzhong, ZHAO Wenting, HUANG Zhiming
    2013, 21(6):  691-697.  doi:10.1016/S1004-9541(13)60493-1
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    Acrylonitrile-methyl methacrylate (AN-MMA) copolymer/silica nanocomposites were synthesized by in-situ emulsion polymerization initiated by 2,2'-azobis(2-amidinopropane) dihydrochloride absorbed onto colloidal silica particles, and the mesoporous carbon materials were prepared through carbonization of the obtained AN-MMA copolymer/silica nanocomposites, followed by HF etching. Thermogravimetric analysis of AN-MMA copolymer/silica nanocomposites showed that the carbon yield of copolymer was slightly decreased as silica particle incorporated. N2 adsorption-desorption, scan electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the structure and morphology of the mesoporous carbon materials. Both SEM and TEM results showed that disordered mesopores were formed in the obtained carbon material mainly through templating effect of silica nanoparticles. The diameter of mesopores was mainly distributed in the range from 5 nm to 15 nm. The mean pore diameter and total pore volume of the material increased as the mass fraction of silica in the nanocomposites increased from 0 to 24.93%. The significant increase of the mean pore diameter and the decrease of surface area for the carbon material prepared from the nanocomposite with 24.93% silica were caused by partial aggregation of silica nanoparticles in the polymer matrix.
    Supercritical Fluid Extraction of a Novel Template from Mesoporous Zirconia and the Effect on Porous Structure
    MA Fu, ZHAO Hongjian
    2013, 21(6):  698-700.  doi:10.1016/S1004-9541(13)60493-2
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    Mesoporous zirconia was synthesized by a new and simple method. Zirconium n-propoxide was used as the zirconium source. A small, inexpensive nonsurfactant, triethanolamine, was used as the template. The template was removed by thermal treatment in air and supercritical fluid extraction using CO2. The structure of the resulting materials was characterized by X-ray diffraction, transmission electron microscopy, and N2 adsorption-desorption analyses. The materials are found to have narrowly distributed average pore diameters and wormhole-like pore channels. However, higher surface area and larger pore volume are exhibited after supercritical fluid extraction with CO2. The removal of the template by thermal treatment also leads to condensation and mild shrinkage of the zirconia framework.
    Synthesis of 2-Methyl-4-methoxyaniline from o-Nitrotoluene Using Pt/C and Acidic Ionic Liquid as Catalyst System
    LIU Yingxin, LI Xiying, FANG Yanyan, ZHANG Lin
    2013, 21(6):  701-704.  doi:10.1016/S1004-9541(13)60499-X
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    2-Methyl-4-methoxyaniline (MMA) was synthesized by one-pot method through the hydrogenation and Bamberger rearrangement of o-nitrotoluene in methanol using acidic ionic liquid and 3% Pt/C as catalyst system. The effects of ionic liquid type, dosage of ionic liquid and 3% Pt/C, reaction temperature and reaction pressure on o-nitrotoluene conversion and MMA selectivity were investigated. The results indicated that the imidazolium-based acidic ionic liquid which contains SO3H-functionalized cation showed higher selectivity to MMA than other acidic ionic liquids used in this work. Using 1-(propyl-3-sulfonate)-3-methylimidazolium hydrosulfate ([HSO3-pmim][HSO4]) as the acid catalyst, the selectivity to MMA was as high as 67.6% at 97.8% of o-nitrotoluene conversion. As 3% Pt/C increased from 0.01 g to 0.025 g, the selectivity to MMA decreased from 73.4% to 62.5%, because of the hydrogenation of intermediate o-methyl-phenylhydroxylamine to o-toluidine becoming more dominant. An increase in hydrogen pressure also had obviously dramatic effect in lowering the MMA selectivity. After easy separation from the products, the catalyst system could be reused at least 3 times.