The Chinese Journal of Process Engineering

Oxygen Mass Transfer in the Liquid Phase of a Three-phase Continuous Loop Reactor

GU Kui-qing;HUANG Hai;LI Hong-xing;LIU Hui;LI Jian-wei;LI Cheng-yue

. 2007, 7(5): 847-852.

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Liquid phase oxygen mass transfer characteristics in a three-phase continuous loop reactor were studied by a dynamic oxygen dissolution method with glass beads (dp=59, 200 mm; rs=2460 kg/m3) as the solid phase, air as the gas phase and tap water as the liquid phase, respectively. Liquid phase oxygen mass transfer coefficient (kLa) was measured in the range of superficial gas velocity (Ug=0.01~0.13 m/s), superficial slurry feeding velocity (USL=0.001~0.011 m/s), solid holdup (es=0~30%, w) and two different particle diameters. It is found that kLa value increases with increasing superficial velocity, but decreases with increasing particle size. It is also demonstrated that variation of USL has no significant effect on kLa in the range of the investigated operation conditions. And a maximum kLa is found when the solid holdup increases at given Ug and USL, but the effect of solid hold-up is negligibly small when es is larger than 10%(w). Finally, an empirical correlation of kLa is presented for designing such type reactors.

Numerical Simulation of External Heat Transfer Coefficient of Vertical Heating Tubes in a Stirred Tank

QIAN Xiao-jing;WANG Zhi-feng;HUANG Xiong-bin

. 2007, 7(5): 853-858.

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The commercial software CFD code CFX was used to simulate temperature profiles in a f500 mm stirred vessel with a pitched-blade turbine (PBT). The liquid (glycerol) was heated by four sets of vertical heating tubes symmetrically fixed in the tank and the tubes also served as baffles. The simulation of liquid flow field at the Reynolds number of 232 was used to compute the local external heat transfer coefficient on the outer surface of vertical heating tubes (hL) at different heights. The results showed that hj at the downwind side surface was the smallest，and hLmax/hLmin reached 6.23 at different off-bottom clearances of the same position on the same tube. hL varied greatly along the axis, and hLmax/hLmin reached 4.48 at the same off-bottom clearance of different positions on the same tube, it decreased as the off-bottom clearance increasing. The ratio of the maximum and minimum average surface heat transfer coefficient values of the tubes was 2.35. The CFD predictions were in good agreement with the literature.

Measurement of Temperature Field in a Fast Liquid-Liquid Mixing Process by PLIF

DU Run-ping;LIU Zhe;CHENG Yi;LUO Pei-cheng

. 2007, 7(5): 859-864.

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Two-dimensional temperature distributions were instantaneously visualized in a liquid-liquid cross-flow mixing process with flow channels at millimeter scale using planar laser induced fluorescence (PLIF) technique, where the excited fluorescence strength of Rhodamine B dye had linear relationship with the temperature. The mixing process of two liquids with different temperatures could then be characterized by the measured temperature fields. The intensity of segregation (IOS) was applied to quantify the non-uniformity of the mixing process along the flow development. The effect of momentum ratio of two liquid flows on the mixing process was studied. Larger momentum ratio between the jet and bulk flow benefited the mixing efficiency of the two liquids. Meanwhile, the heat transfer coefficient of water in the liquid sheets impingement process was compared with the turbulent heat transfer coefficient calculated by an empirical formula. The results show that the impingement process can promote the heat transfer between the two liquids with different temperatures. Higher momentum ratio of two liquid flows leads to better mixing performance in terms of the transport phenomenon of temperature.

CFD Analysis and Experimentation on Gas Turbulent Mixing Process in a Jet Mixer

CHEN Yi;ZHANG Lin-jin;YE Xu-chu

. 2007, 7(5): 865-870.

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The carbon dioxide-air jet mixing process is simulated with commercial CFD software. The simulated concentrations of CO2 in different section planes with the standard k-e model and the RNG turbulent model are compared with experimental data. The results indicate that the numerical results agree well with the experiments, CFD simulation is reliable in predicting the turbulent diffusing process, the CO2 concentration by the side of the lateral-inlet is generally higher than the other side, and the concentration range in the first section plane (d=100 mm) reaches 6%, while the CO2 average concentration is 6%. The influence of turbulent model on CFD simulation is not significant in gas jet mixing process. The velocity field and concentration field of a T-type symmetrical jet mixer and the original single-lateral-inlet jet mixer are then simulated with the standard k-e model, showing that the uniformity of the T-type symmetrical jet mixer is much improved as compared with the original single-lateral-inlet jet mixer.

Numerical Simulation of Flow Field in a Cyclone Separator under High Temperature

WAN Gu-jun;WEI Yao-dong;SHI Ming-xian

. 2007, 7(5): 871-876.

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In the temperature range from 293 K to 1273 K and the inlet gas velocity at 20 m/s, the flow field in a volute cyclone separator with 300 mm diameter has been numerically simulated using a modified non-isotropy RSM model on the platform of commercial CFD software package, FLUENT 6.1. The predicted results are in agreement with the experimental data. The computational results show that temperature increase affects gas velocity vector much, especially tangential component. The temperature increase results in the tangential velocity decrease. This tendency, however, becomes smooth when the temperature is above 1000 K. The correlation between tangential velocity and temperature is expressed as . The influence of temperature on the axial velocity can contribute to the change of rotation intensity of the tangential velocity. The downward axial velocities decrease when the rotation intensity becomes small at high temperatures, but the upward ones increase a little. The increase of temperature affects the separation performance of cyclone separator by changing the gas viscosity and tangential velocity. When temperature is to 1273 K, the increase of gas viscosity increases the cut-size diameter 1.58 times and the decrease of gas tangential velocity increases the cut-size diameter 1.23 times. The effect of gas tangential velocity on the separation performance of cyclone is approximately equal to the effect of gas viscosity.

Numerical Simulation on Pressure Distribution and Opening Force of Dry Gas Seal

WANG He-shun;HUANG Ze-pei;WANG Xin-lin

. 2007, 7(5): 877-882.

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For more details about flow field of dry gas seal, the numerical simulation is carried out based on the Navier-Stokes equation, laminar model, and SIMPLEC method, with various face clearances and rotating speeds. The distribution of film pressure and variation of opening force are investigated emphatically. The numerical results shows that at the intersection of groove and stage, there is clear change of film pressure, at the position of gas flow out, pressure increases, hydrodynamic pressure will be formed, at the place gas flows in, pressure decreases, negative pressure (relatively) zone will be formed, gas film stiffness and opening force will be weakened. Through rational groove shape design, enhancement of positive pressure zone and weakening of negative zone, higher opening force and film stiffness will be gained. Comparison analysis shows that opening force will be raised by new groove shape design, and higher stability is gained.

Mathematic Simulation of Heat Transfer in a Petroleum Coke Calcining Rotary Kiln

XIAO Guo-jun;DING Xue-jun;CHEN Han-ping;CHENG Shang-qing;LUO Ming-wen;XIONG Yong

. 2007, 7(5): 883-888.

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Based on the analysis of material motion in the axial direction, heat transfer and mass transport process in a rotary kiln, and comprehensive consideration of the effects of physical change and chemical reaction in the rotary kiln on the heat transfer process, the mathematic model of heat transfer for petroleum coke calcining rotary kiln was built up. The heat transfer mathematic model was solved numerically for an industrial kiln reported in the literature to predict the temperature profiles of the solid bed, the gas phase and the kiln internal wall in the axial direction. The results show that the high temperature region in the kiln is in the zone that volatile matter massively burns. The injection of tertiary air causes obvious drop of gas temperature, but there is no obvious change of solid temperature. In the heat exchange process among material, gas and inwall, the heat convection between the material and the inwall covered with material, and the heat radiation between the gas phase and the surface of solid bed are the principal heat transfer mechanism. The predicted results are in good agreement with the measured data. This model can be used to guide the optimum design and economic operation of petroleum coke calcining rotary kilns.

Numerical Simulation of Production Process of Aluminum Foam by Air Injecting and Melt Stirring

LIU Hong;XIE Mao-zhao;LI Ke;WANG De-qing

. 2007, 7(5): 889-894.

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The production process of aluminum foams by air injecting into molten aluminum composites is a highly complex two-phase flow with mechanical stirring. This work presents the results in Computational Fluid Dynamics simulations of gas-liquid turbulent flows induced by a pitched-blade turbine (four blades, 45 inclined) with a inclined shaft. A two fluid model incorporated with the Multi-reference Frame (MRF) method is used to predict the three-dimensional two-phase flow in the foaming tank. Bubble size distribution is also predicted by solving a transport equation for the bubble number density function, which accounts for break-up and coalescence phenomena. Furthermore, the averaged total and local gas fractions and bubble diameters are predicted by means of volume integration. The influences of impeller rotational speed and gas flowrate on bubble diameter and distribution are examined. Computational results show that gas volumetric fraction increases with increasing gas flowrate and impeller speed, bubble size increases with increasing gas flowrate and decreasing impeller speed.

Application of g-Ray Attenuation Technology in Measurement of Solid Concentration of Gas-Solid Two-phase Flow in a FCC Riser

TAN Hong-tao;DONG Gan-guo;WEI Yao-dong;SHI Ming-xian

. 2007, 7(5): 895-899.

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The solid concentration of gas-solid two-phase flow in a fluid catalytic cracking riser (f186 mm′12 m) is measured with g-ray attenuation technology. The software for processing and analyzing experimental data is programmed and 2-dimensional solid concentration contours are obtained. The solid concentration distribution shows core-annular profile in the riser, lower concentration in the center and higher concentration in the wall, which is in agreement with previous results. But the results indicate that the distribution of concentration is some asymmetric, the solids are concentrated in the area adjacent to the wall, being different from a symmetric pattern published. Comparing the measuring result by g-ray attenuation technology with that of optical fiber method, both are consistent in the distribution, but the value of solid concentration by optical fiber method is about 20% higher. And g-ray attenuation technology is a non-intrusive method, and can obtain the solid concentration profile of cross section, showing the complex characters of gas-solid two-phase flow in whole.

Large Eddy Simulation of Single Loop Flow Field in a Rushton Impeller Stirred Tank

LI Zhi-peng;GAO Zheng-ming

. 2007, 7(5): 900-904.

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The single loop hydrodynamic characteristics in a baffled Rushton impeller stirred tank were investigated by using large eddy simulation (LES) method. The dynamic Smagorinsky-Lilly sub-grid scale (SGS) model was used in the simulation and compared with k-e model and experimental data. The results show that the two trailing vortices generated behind the impeller blades move down to the bottom of the tank, the upper one begins to damp at 30o. 800000 non-uniformly distributed grids and 30 impeller revolutions used for statistical analysis can give a more accurate LES prediction. Time-averaged velocities, root mean square velocities and turbulent kinetic energy predicted by the LES approach are in good agreement with the experiment, while the k-e model gives an erroneous estimation. Near the impeller, the flow is highly anisotropic, which is the main reason why the prediction by k-e model is inaccurate. The results confirm that LES is an effective approach for investigation of the complex flow in stirred tanks.

Effect of Solid Acid as Dehydrant on One-step DME Synthesis

XU Qing-li;LI Ting-chen;ZHANG Su-ping;REN Zhen-wei;YAN Yong-jie

. 2007, 7(5): 905-909.

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Hybrid catalysts composed of JC207 methanol synthesized catalyst and dehydrant (HZSM-5 zeolite or g-Al2O3) were prepared for the synthesis of dimethyl ether (DME). Evaluation of catalytic activity on them was conducted in a fixed-bed reactor in order to investigate the effect of solid acid as dehydrant on one-step DME synthesis. The results show that dehydration occurs at B acid site or L acid site, and synergic function exits possibly between the two types of acids. In the experimental scope, when the ratio of L acidity to B acidity is equal to 3.270, the dehydration effect is the best. Besides the total amount of acidity plays a role in the dehydrated step, in the experimental scope, when the total amount of acidity is equal to 0.521, the dehydration effect is the best.

Desulfurization of High Sulfur Coal by Recycling Additional Gases during Coking Process

FU Zhi-xin;GUO Zhan-cheng;WANG Shen-xiang

. 2007, 7(5): 910-915.

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The variation of sulfur content in coke and releasing behavior of H2S in pyrolysis gas were investigated by recycling additional gases during coking process. A high sulfur coal was used in this work to simulate the industrial coking process under different gas atmospheres, gas fluxes and heating rates. The results showed that it was effective to suppress the sulfur in gas returning into coke by recycling additional gases during coking process. Contrasted to the case without gas recycling, the initiation temperature of sulfur releasing was advanced when additional gases were recycled. Under different gas atmospheres, the cumulative sulfur removal of H2 was greater than those of CH4 and N2. The releasing behavior of H2S in pyrolysis gas indicated that the peak stage of sulfur releasing from coal was corresponding to the first peak of coal pyrolysis. In addition, the start releasing temperature of H2S was advanced due to additional gases being recycled. About 90% of the total sulfur removal could be reached when coking temperature was up to 800℃. The sulfur content in gas increased and the sulfur content in coke decreased with increasing gas flux and decreasing heating rate. The result from the sulfur content in coke also showed that the effect of desulfurization was more pronounced than other gases. Compared with the sulfur content in coke without gas recycling, the sulfur content was decreased by 0.36%~0.39% and 0.46%~0.56% at the space velocities of 0.8, 1.3, 2.1 mm/s with two different heating rates of 3.0℃/min and 1.5℃/min, respectively.

Synthesis of P-Zeolite from Alkli-activated Kaolinite and Its Adsoption to K+

CAO Ji-lin;LIU Xiu-wu;JU Yin-xuan;LIU Xiu-fang;TIAN Li-na

. 2007, 7(5): 916-921.

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In order to reduce energy cost in developing new technology of P-zeolite synthesis from kaolinite, the synthesis of P-zeolite from alkli-activated kaolinite was carried out and the activative reaction mechanism was also analyzed. The suitable conditions of activative reaction were that the mixture of kaolinite and sodium hydroxide with mass ratio 1:0.94 was calcined at 400℃ for 2 h. Adding water glass and water to the alkli-activated kaolinite, the suitable composition solution of P-zeolite synthesis was obtained. The mixed compound with molar ratio of Al2O3:SiO2:Na2O:H2O=1:3.2:3.7:220 was firstly aged at 80℃ for 3 h, secondly crystallized with 4A-zeolite as seed at 95℃ for 30 h, and the P-zeolite was obtained. The experimental result of adsorption of K+ on P-zeolite showed that K+ ion exchange capability for simulated seawater was 10.5 mg/g.

Pre-desiliconization of a Bauxite Ore through Leaching by High Concentration NaOH Solution under Atmospheric Pressure

YANG Bo;WANG Jing-gang;ZHANG Yi-fei;ZHANG Yi

. 2007, 7(5): 922-927.

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A leaching process for the pre-desiliconization of bauxite ore by high concentration NaOH solution under the atmospheric pressure was studied. The effects of leaching temperature, initial NaOH concentration, leaching time and mass ratio of alkali to ore on the leaching rates of Al2O3 and SiO2, and the ratio of aluminum to silicon in solid residue were investigated, and the kinetic equation was obtained. The results show that when the mass concentration of NaOH is 50%, the desiliconization temperature 135℃, mass ratio of alkali to ore 2.5 and the desiliconization time about 5~20 min, the ratio of aluminum to silicon of bauxite ore can be increased from 7.6 to 12, so as to meet the grade need of bauxite ore in Bayer process. The pre-desiliconization of bauxite ore can be realized by this process without physical processing. Compared with other chemical processing, the pre-desiliconization treatment can improve the grade of bauxite ore with the advantages of saving energy and reducing production costs, which may provide a new way of exploitation of mid-low grade bauxite ore.

Leaching Kinetics of Calcined Magnesite from Glycol Solution Dissolved with Ammonium Chloride

OU Teng-jiao;LU Xu-chen;LIANG Xiao-feng;YAO Sheng-yong

. 2007, 7(5): 928-933.

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The calcination conditions of magnesite and the leaching kinetics of calcined powder in glycol solution dissolved with ammonium chloride were systematically studied. It was found that MgCO3 was decomposed completely under 750℃ for 2 h, but CaCO3 was not. Over calcination of magnesite could obviously lower down the leaching rate of calcined powder due to the growth of its particles. Without the effect of outer diffusion, the leaching process accorded with unreacted shrinking core model at the stoichiometric proportion of NH4Cl-MgO and initial concentration of NH4Cl between 0~1.23 mol/L. Furthermore, the leaching rate reached the maximum value with 1.23 mol/L initial concentration of NH4Cl. It was concluded that the leaching rate was controlled by surface chemical reaction. The activation energy was calculated as 44.74 kJ/mol by the model on the basis of experimental data.

Kinetics of Replacement Reaction between Potassium Chloride and Sodium Pentaborate for Preparing Potassium Pentaborate

ZHANG Jin-ping;SUN Yong;YANG Gang;LI Zuo-hu

. 2007, 7(5): 934-938.

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The preparation method of potassium pentaborate (KB5O8) was studied with the replacement reaction between potassium chloride and sodium pentaborate solution. The effects of sodium pentaborate concentration, reaction temperature and reactant mole ratio (KCl:NaB5O8) on the crystallization rate of KB5O8 were investigated. The results show that sodium pentaborate concentration is the most influential factor for affecting the reaction, while reaction temperature and reactant mole ratio (KCl:NaB5O8) are secondary factors. The reaction kinetics was studied by selecting control-step method as well as modified Debye-Hückel activity coefficient model and Bromley osmotic coefficient model. The results show that the reaction order is 2 and apparent reaction activation energy 85.8 kJ/mol, and the reaction is mainly controlled by precipitation of KB5O8×4H2O.

Conversion of HCl to Cl2 by Coupling Oxidation Reaction and Dewatering

CHEN Xian;QIAO Xu;WANG Yong;TANG Ji-hai;CUI Mi-fen

. 2007, 7(5): 939-943.

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Based on thermodynamic calculation and analysis of equilibrium conversion rate of HCl oxidation, the reaction-dewatering coupling technique was applied to the oxidation process of hydrogen chloride, and the process simulation was studied in this work. The results show that the conversion rate of HCl was increased effectively by coupling dewatering in continuous HCl oxidation process. And the cyclic process for multi-dewatering steps under the condition of non-excessive oxygen was also studied. The results show that the conversion rate of HCl was evidently enhanced by increasing secondary oxidation temperature. And the mixture gas which could be used directly in organic chlorination process was obtained through multi-dewatering steps under the condition of the molar ratio of HCl/O2 at 8:1 with the total conversion rate of HCl at 49.3% and the volume content of oxygen in the mixture gas under 0.2%.

Particle Growth in the Flame Synthesis of Titanium Dioxide Nanoparticles

CHEN Bo;CHENG Yi;DING Shi;HU Rong-rong

. 2007, 7(5): 944-951.

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During the flame synthesis of titanium dioxide (TiO2) nanoparticles by oxidation of titanium tetrachloride (TiCl4), transmission electron microscope (TEM) grids were used to collect particle samples at different heights of the flame reactor. The particle diameters and morphology were obtained in the particle growth process. The influences of reactant concentration, reaction temperature and gas velocity on the particle growth process were studied. A TiO2 particle experienced nucleation, growth, agglomeration and sintering processes. Higher precursor concentration produced more primary particles in the early stage so that more colliding chances between particles were allowed for, which resulted in larger particles in the end. Primary particle size changed from 17 to 85 nm when the precursor concentration was adjusted from 7.9′10-5 to 5.7′10-3 mol/L. The reaction temperature depended on the gas flow rates of methane and oxygen. Higher reaction temperature generated mono-dispersed but large primary particles of 63 nm, while low reaction temperature caused small but seriously sintered particles of 35 nm. The increase of the gas velocity decreased the particle diameter from 63 to 36 nm due to the shortened residence time.

On-line Dynamic Model Correction Based Fault Diagnosis in Chemical Processes

TIAN Wen-de;SUN Su-li

. 2007, 7(5): 952-959.

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A novel fault detection and diagnosis method was proposed, using dynamic simulation to monitor chemical process and identify faults when large tracking deviations occur. It aims at parameter failures, and the parameters are updated via on-line correction. As it can predict the trend of process and determine the existence of malfunctions simultaneously, this method does not need to design problem-specific observer to estimate unmeasured state variables. Application of the proposed method is presented on one water tank and one aromatization reactor, and the results are compared with those from the traditional method.

Analysis of Pore Structure Evolution of Ore Granular Media during Leaching Based on X-ray Computed Tomography

WU Ai-xiang;YANG Bao-hua;LIU Jin-zhi;ZHANG Jie

. 2007, 7(5): 960-966.

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The experiments of the column leaching and percolation of ore granular media were conducted by using the home-made multifunctional equipment simultaneously and the pore structure images of the ore granular media were obtained by X-ray computed tomography before and after leaching. Based on the image processing operations, the spatial distribution of the porosity and the change rule of the pore connectivity before and after leaching were investigated, and the reasons of pore structure evolution during leaching were analyzed. The results indicate that the porosity of ore granular media during leaching has spatial and temporal variability, which decreases as height decreasing. The trend is more obvious after leaching and the average porosity lowers by 1.71% than that before leaching. The connectivity of the pores also has spatial and temporal variability. After leaching, the connectivity of upper zone has been improved. However, the lower zone has been weakened seriously. The evolution of the pore structure makes the percolation coefficient decrease gradually by 31.37%. The main reasons for the evolution are the subsidence of the whole ore granular body and the transportation and accumulation of the smaller ore particles from top to bottom under the influences of multi-factors.

Behavior of Al and Si in Red Mud from Leaching Process of Diaspore Bauxite with NaOH Sub-molten Salt

WANG Shao-na;ZHENG Shi-li;ZHANG Yi

. 2007, 7(5): 967-972.

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The behavior of Al and Si in red mud in the leaching process of diaspore bauxite with NaOH sub-molten salt was investigated. The effects of reaction temperature, mass ratio of alkali to ore and CaO addition on the behavior of diaspore bauxite in NaOH sub-molten salt were investigated by experiment. The results show that high temperature leads to the total leaching of diaspore bauxite. Silicon-containing ore is the most common impurity in bauxite. In the process of alumina production with NaOH sub-molten salt, almost all the Si in bauxite is transformed into aluminosilicate. AlOOH disappears in red mud under the conditions of the ratio of alkali to ore 2, leaching temperature 180℃ and leaching time 2 h. Al and Si coexist in the resulting red mud in the forms of Na8Al6Si6O24(OH)2(H2O)2 and Na9Al9Si15O48(H2O)27 after leaching. The addition of CaO in the leaching process does not prevent Si from entering liquid phase under the temperature of 180℃. The leaching rate of Al2O3 is reduced under the condition of CaO addition in the sub-molten salt process. But the addition of CaO can reduce the loss of NaOH, it is beneficial to the leaching of middle grade bauxite.

Bioleaching of Covellite Concentrate and Process Enhancement

WEN Jan-kang;RUAN Ren-mang;ZHOU E;ZHANG Ming-ming;WANG Dian-zuo

. 2007, 7(5): 973-978.

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The influential factors of bioleaching of covellite concentrate collected from Zijinshan copper ore in Fujian Province with bacteria were investigated. As a result, the optimal influential parameters of bioleaching process were determined, which are concentration of inoculum 100%, pulp density less than 5%, and initial Fe2+ concentration 4.0 g/L. Within 20 d, the copper recovery rate reached 60%. In order to enhance the redox potential (Eh) level in the bioleaching process, several efforts such as the additions of Fe3+, pyrite and hydrogen peroxide were attempted in the experiments. The results show that the optimal choice to increase Eh level is the addition of pure pyrite. This condition can effectively raise the Eh of bioleaching process while the impact of environmental change is negligible. It can quicken the leaching process and enhance the final copper recovery through the addition of pyrite by 1:1 or 1:2 mass ratio of covellite concentrate to pyrite.

Process Analysis for Direct Catalytic Disproportionation of Gum Oleoresin

WANG Lin-lin;LIANG Jie-zhen;CHEN Xiao-peng;SUN Wen-jing;XU Xu;TONG Zhang-fa

. 2007, 7(5): 979-983.

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On-line tracking analysis for the changes of major chemical components during catalytic disproportionation of gum oleoresin over Pd/C catalyst was studied by the gas chromatography (GC) and gas chromatography-mass spectrometry-detection system (GC-MS-DS), and the reaction mechanism of catalytic disproportionation from gum oleoresin has been discussed. The results showed that the disproportionated rosin and high content of p-cymene could be obtained using the novel process from oleoresin. At reaction temperature 250℃ and reaction time 90 min, and the quantity of catalyst 0.05% (based on oleoresin weight), the contents of dehydroabietic acid and abietic acid were 79.15% and 0 of the acid fractions, respectively, and p-cymene was 62.52% of the neutral oil. The reaction rate of the resin acids was faster than that of turpentine, and dehydrogenations of resin acids and turpentine were main reactions during intermolecular hydrogen transfer reaction of oleoresin. Meanwhile, the tracking analysis indicated that the disproportionation rate of resin acids from oleoresin was faster than that of resin acids from rosin, and the conversion rate of abietic-type resin acids was 89.32% and the content of dehydroabietic acid was 63.20% when reaction time was 15 min. During one-step catalytic disproportionation of oleoresin, the viscosity of reaction system was reduced and liquid-solid mass transfer was improved by the solvent effect of turpentine, so the aromatization of abietic acid was intensified, and the double ring monoterpene in the turpentine was transformed into monocyclic ring monoterpene by ring-opening isomerization reaction, then converted into p-cymene by catalytic dehydrogenation under the resin acids. The present work may provide a reference for research of relevant reaction kinetics and optimization of process.

Synthesis and Characterization of ZnS Nanoparticles Modified with Mercaptoacetic Acid in Aqueous Solution

SUN Wei;ZHONG Jiang-hua;ZHANG Can-ying;JIANG Hong;JIAO Kui

. 2007, 7(5): 984-988.

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A simple synthesis method of ZnS nanoparticles for biological probe application in aqueous solution was proposed by using mercaptoacetic acid (RSH) as modifier. The conditions for the synthesis of ZnS nanoparticles were carefully investigated and the optimal conditions were obtained as pH at 8.0 and [Zn2+]:[S2-]:[RSH] at 1:1.34:2. ZnS nanoparticles were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), size distribution instrument and FT-IR spectra. The results showed that ZnS nanoparticles were mono-dispersed face-centered cubic b-sphalerite with average size of about 11 nm.

Thermodynamic Equilibrium Analysis on Release Characteristics of Chlorine and Alkali Metals during Combustion of Biomass Residues

CHEN An-he;YANG Xue-min;LIN Wei-gang

. 2007, 7(5): 989-998.

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The transformation characteristics of chlorine and alkali metals, such as potassium and sodium, during combustion have been investigated by using thermodynamic equilibrium analysis (TEA) technique for five kinds of biomass residue samples, i.e. straw, bark, wood chips, waste wood and olive residue in the temperature range of 400~1600 K with excess air coefficient of 1.0, 1.2 and 1.4. The TEA results show that changing excess air coefficient can not obviously affect the released amount of chlorine and potassium or sodium. The major gaseous and solid existing species of chlorine, potassium and sodium are found to be KCl(s), HCl(g), KCl(g), (KCl)2(g) and NaCl(g) for five kinds of biomass residues samples studied during the combustion. A great amount of chlorine contained species can be released as gaseous species at the temperatures above 800~1000 K while alkali metals, potassium and sodium can be transformed into the following gaseous species KOH(g), KCl(g), (KCl)2(g), K2SO4(g), Na(g), NaOH(g), Na2SO4(g) and NaCl(g) at temperature above 850 K. Hence, the least release of chlorine, potassium and sodium as gaseous species can be realized at the temperatures less than 850 K in the viewpoint of TEA. As practical biomass combustion reactors are performed far from real thermodynamic equilibrium, the combustion operation temperature of practical reactor can be controlled a bit greater than the critical condition mentioned above.

Enhanced Production of Tyrosine Phenol Lyase by Recombinant E. coli M15 (pQTPL) through Controlling Nutritional and Environmental Conditions

SHI You;LIU Li-ming;DUAN Zuo-ying;LI Hua-zhong

. 2007, 7(5): 999-1003.

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The effects of nutritional and environmental conditions on production of tyrosine phenol lyase (TPL) were investigated in flask and 4 L fermentor. The optimal concentrations of glucose and corn steep liquor for recombinant strain growth and TPL production were 20 g/L and 1.0 g/L, respectively. When the level of dissolved oxygen was kept at 30%, a high cell concentration and TPL activity reached 4.78 g/L and 52.8 U/g (DCW), which were 21% and 36.1% higher than those without dissolved oxygen control, respectively. The cell concentration reached 31.5 g/L when the strategies of dissolved oxygen feedback regulation and restrictive supplement of nutrients were used. By using a bi-stage pH and temperature control strategy, in which pH value and temperature were controlled at 7.0 and 37℃ in the first 8 h and then switched to pH 8.0 and 30℃, a high cell concentration and high TPL activity [154.4 U/g (DCW)] were achieved.

Mechanism of Effects of Allyl Compounds on Asymmetric Reduction of Baker￠s Yeast

LI Yan;NI Hong-liang;YAO Shan-jing

. 2007, 7(5): 1004-1008.

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In the process of asymmetric reduction of b-ketoesters by baker￠s yeast, the enantioselectivity of yeast cells could be controlled by allyl compounds added in the reaction system. 4-Chrolo-3-oxobutanoate (COBE) was used as the model substrate. After yeast cells were pretreated with acrylamide and allyl alcohol, the enantiomeric excess (e.e.) of S-CHBE increased to 94%, while pretreated with allyl bromide, R-CHBE could be detected. The allyl compounds were proved to be toxic to the cells and intracellular enzymes by DNS and API ZYM system respectively. Furthermore, the toxicity was determined by the groups the allyl carried. Washed with PBS buffer for several times, the activity of pretreated yeasts could be recovered gradually. As the concentration of substrate increased, the e.e. of S-CHBE catalyzed by ally alcohol-pretreated yeast remained at 90%. On the other hand, the e.e. of R-CHBE catalyzed by allyl bromide-pretreated yeast dropped from 90% to 45%. These results suggested that allyl compounds acted as competitive enzyme inhibitors adsorbed on the active site of enzymes, and different groups of allyl compounds determined the types of subjected enzymes. The result in pretreatment of the yeast with inhibitor analogs showed that the enzymes had steric hindrance for both inhibitor and substrate.

Immobilization of Sulfate Reducing Bacteria

CAO Jun-ya;ZHANG Guang-ji;MAO Zai-sha;FANG Zhao-heng;HAN Bao-ling

. 2007, 7(5): 1009-1013.

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In view of the difficulty in treating the bioleaching solutions, the selective precipitation of metals using H2S produced biologically by sulfate reducing bacteria (SRB) was as an alternative process. At first, the initial COD/SO42- ratio and pH value were determined, and then the capability of different immobilized carriers was investigated by batch experiments. The results showed that high removal rate of SO42- was achieved when the initial COD/SO42- ratio was 3 and the initial pH value was 7. In the experiments, it was found that two factors were important for influencing the formation of biofilm and the reducing capability of SRB, the roughness of the immobilized carriers and the pore volume. There was no biofilm found when glass beads were immobilized carrier, and the reducing capability of SRB was low, the removal rate of SO42- was only 50%. Furthermore, the removal rate of SO42- increased with the pore volume of immobilized carriers. So, in view of the stability of process and the removal rate of SO42-, polyurethane foam was top priority as the immobilized carrier in the experiments, the removal rate of SO42- with it reached 95%, and the process was easily operated.

Improvement of 1,3-Propanediol Production with a Recombinant Strain Klebsiella pneumoniae F-1 by Regulating Redox Potential

HUANG Zhi-hua;ZHANG Yan-ping;DU Chen-yu;HUANG Xing;CAO Zhu-an

. 2007, 7(5): 1014-1017.

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Redox potential (also called oxidoreduction potential, ORP) is one of important indicators to monitor the anaerobic fermentation of Klebsiella pneumoniae. In this report, the preferred ORP of a recombinant strain K. pneumoniae F-1 was investigated by controlling the ORP of broth into four levels of -190, -210, -240 and -290 mV. The results showed that in the fermentation of ORP at -240 mV, the highest final 1,3-propanediol concentration and molar yield of were achieved, being 81.5 g/L and 0.423 mol/mol, respectively. This preferred ORP to the genetic modified strain was different from those of both the wild strain K. pneumoniae M5aL (-190 mV) and the mutant K. pneumoniae M5aL YMU2 (-280 mV). It is demonstrated that the modification of the metabolic pathway in the K. pneumoniae F-1 exerted effects on the preferred ORP of the strain. The effect of ORP on re-distribution of the metabolites was also investigated. The results demonstrated that the reduction environment facilitated the pathways from glycerol to reduction end-metabolites, such as 1,3-propanediol, ethanol and 2,3-butanediol. This work is the first investigation on the ORP regulation method in a recombinant strain, which will provide insight into the mechanism of ORP regulation in anaerobic fermentations.

Application of Silver Nanoparticles in Immobilization of Papain

ZONG Jing;WANG An-ming;WANG Hua;SHEN Shu-bao

. 2007, 7(5): 1018-1021.

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Silica spheres with amine groups were synthesized in a one-step process by synchronous hydrolysis of tetraethylorthosilicate (TEOS) and N-(2-aminoethyl)-3-aminopropy-triethoxysilane (APTES) under a ultrasound condition, and then silver nanoparticles were deposited on the surface of spheres. These silica spheres coated with silver nanoparticles were used as the carrier in immobilization of papain. The influence of silver nanoparticles on immobilized papain was studied. The highest activity recovery rate was obtained using carrier with 0.68% silver nanoparticles, and it increased 188% than that using the carrier without silver nanoparticles. The performance of the fixed enzyme was also examined. This immobilized papain was more resistant to heat than free enzyme. It maintained 43% activity after using by 20 times repeatedly, and the activity dropped exiguously after it was preserved at 4℃ for 2 months.

Preparation and Photoelectrochemical Performance of Potassium Hexatitanate Nanofilm

QIAN Qing-hua;LIU Chang;HU Yu-yan;YANG Zhu-hong;FENG Xin;LU Xiao-hua

. 2007, 7(5): 1022-1028.

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Nanostructured K2Ti6O13 film photoelectrode produced in situ was prepared on indium-tin oxide (ITO) glass substrate by a sol-gel process and characterized by thermogravimetry (TG) and differential scanning calorimetry (DSC), X-ray diffraction (XRD), atomic force microscopy (AFM), UV-Visible diffuse reflectance and Raman spectrometry. The photoelectrochemical performance of K2Ti6O13 film was assessed by electrochemical method. The analytical results showed that the K2Ti6O13 film had a strong and wide absorption in the ultraviolet and visible light range. The band gap energy (Eg) of the film shifted from 3.45 eV (bulk) to 3.05 eV (film). The flat-band potential (Efb) of K2Ti6O13 film was -0.67 V [vs. saturated calomel electrode (SCE)]. The transport of photogenerated electrons and holes was better in K2Ti6O13 film electrode than that in TiO2 film electrode. The photoelectrochemical response of K2Ti6O13 photoelectrode was increased in electrolyte solution with KOH, compared with that in the solution without KOH. The adsorption of OH- on the nanofilm acted as the surface activity center. The mechanism of photolysis was analyzed in terms of photoelectrochemical behavior.

Preparation of Macroporous Polymer Microspheres by Double-emulsion Method

SONG Wei;MA Guang-hui;SU Zhi-guo

. 2007, 7(5): 1029-1034.

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Amphiphilic copolymer, monomethoxy-poly(ethylene glycol)-b-poly-dl-lactide (PELA), was used to prepare macroporous microspheres without adding any emulsifier or porogen, and the necessary preparation conditions for formation of macroporous microspheres and their effects on pore diameter were studied. The results indicated that stable emulsions and macroporous structure were prepared by PELA, but hydrophobic poly(lactic acid) and poly(lactide-co-glycolide) could only produce microcapsules. It was found that macroporous microspheres with the pore diameters more than 100 nm could be produced while the volume ratio of inner water phase to the volume of oil phase was between 1:4~1:2, and the microspheres were solidified through two steps. The results showed that the pore diameters of macroporous microspheres decreased as the primary emulsification rate increased. In addition a possible mechanism of the formation of macroporous microspheres was proposed.

Application of Ni(OH)2-Activated Carbon Composite in the Hybrid Supercapacitors

HUANG Qing-hua;WANG Xian-you;LI Jun;DAI Chun-ling;LI Na

. 2007, 7(5): 1035-1039.

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Nickel hydroxide/activated carbon (AC) composite was prepared by a chemical precipitation method. The structure and morphology of nickel hydroxide-AC composite were characterized by X-ray diffraction (XRD) and the measurements of nitrogen gas adsorption isotherm (BET). The results showed that b-nickel hydroxide was loaded into the activated carbon. Electrochemical performance of the composite electrodes with different loadings was studied by cyclic voltammetry and galvanostatic charge-discharge measurement. It was demonstrated that the introduction of small amount of nickel hydroxide could promote the specific capacitance of composite. The composite electrode had good electrochemical performance and high charge-discharge properties. Moreover, when the optimal loading nickel hydroxide was 6%(w), the electrode showed better electrochemical behavior. A hybrid supercapacitor was fabricated using an Ni(OH)2-AC composite as positive electrode and an activated carbon as negative electrode. The electrochemical properties of the electrodes and the capacitive behavior of the resulting supercapacitor were studied by cyclic voltammetry and constant current charge-discharge tests. The specific capacitance of activated carbon supercapacitor was 245.6 F/g, while the hybrid supercapacitor had a higher specific capacitance of 330.7 F/g, which was increased by 34.6%. Moreover, the hybrid supercapacitor had better charge-discharge and cycling performance in 6 mol/L KOH electrolyte.

Performance of YCo0.6Mn0.4O3 Coating Material for Metallic Interconnects of Intermediate Temperature Solid Oxide Fuel Cells

TAO Ling;ZHU Qing-shan;XIE Zhao-hui;XIN Xian-shuang;ZHANG Tao;PENG Tong-an

. 2007, 7(5): 1040-1044.

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High-temperature oxidation-resistant alloys are considered to be one kind of the most promising candidate materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) due to their excellent electrical conductivity, low cost and superior mechanical properties. However, poorly conductive chromium oxide scales forming on the surface of the alloy at high temperature lead to rapid degradation of stack performance. In this work, YCo0.6Mn0.4O3 was initially adopted as the protective coating material for SS410 alloy by screen-printing. The microstructure, mass gain and electrical conductivity of the coated and uncoated samples after oxidation were investigated. The results revealed that an uniform and dense YCo0.6Mn0.4O3 coating formed on the surface of the SS410 and bonded well to the alloy substrate after the thermal cyclic tests owing to well matched thermal expansion between the coating material and the alloy. The parabolic rate constant of the coated alloy was about ten times lower than that of the uncoated alloy after the oxidation test at 800℃. The YCo0.6Mn0.4O3-coated alloy obviously showed a lower area specific resistance of 17 mW×cm2 as compared with that of 72 mW×cm2 for the bare-alloy.

Modification of Spinel LiMn2O4 Electrode with SnO2

LIU Tao;DU Rong-bin;JIANG Xiao-jun

. 2007, 7(5): 1045-1049.

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In order to improve electrochemical performance of spinel LiMn2O4 for positive electrode material of lithium ion battery at high temperature (60℃), the stable SnO2 film was coated on the surface of LiMn2O4 positive electrode material by sol-gel method with Sn(OCH2CH2OCH3)4. The structures of the coated and uncoated LiMn2O4 were characterized by XRD and SEM techniques. The results show that the SnO2 layer can reduce the direct contact between LiMn2O4 and electrolyte, and thus effectively restrains the harmful interactions between them at elevated temperature and reduces the dissolving of manganese in electrolyte. Although the initial electric volume of positive electrode material LiMn2O4 decreases slightly after modification, its cycling stability of charge/discharge increases remarkably, in this work, the capacity loss decreases from 31% for pure LiMn2O4 to 12% at 60℃ after 40 times cycling, and the self-discharge rate of the battery is largely reduced. As a cathode material of lithium-ion battery, this modified spinel is one of the most competitive substitutes for LiCoO2.

Synthesis of Aliphatic Weak Acid Cation Exchange Resin with Double Bonds

ZHOU Yuan;WEI Rong-qing;LIU Xiao-ning;ZHANG Xiao-xiao

. 2007, 7(5): 1050-1054.

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A kind of aliphatic weak acid cation exchange resin with double bonds was prepared with crosslinked polystyrene and cis-butenedioic anhydride by Friedel-Crafts acetylation reaction. The double bonds derived have active property, and can react with other functional monomers to introduce multiple functional groups to the poly(styrene-co-divinylben-e) resin. Consequently, this method can expand the application fields of the resin and lead to a new functional approach of polystyrene. This weak acid cation exchange resin has a long chain connected with carboxyl and is easier to react with other compounds because its steric hindrance is weak. In this work, the effects of the kind and amount of solvent, reaction time, amount of catalyst and acylating reagent on the reaction result were studied. By optimizing and controlling the reaction conditions, the quantitative loading of the aliphatic weak acid cation exchange resin could be attained. The maximum carboxyl loading and double bonds loading could be up to 3.54 and 3.16 mmol/g, respectively. The filling material of chromatographic column could be prepared by this method.

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