Jun 2007, Volume 1 Issue 2

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  • ZHOU Xiaopeng, SU Xueli, SUN Yan
    A study of nonlinear competitive adsorption equilibria of proteins is of fundamental importance in understanding the behavior of preparative chromatographic separation. This work describes the nonlinear binary protein adsorption equilibria on ion exchangers by the statistical thermodynamic (ST) model. The single-component and binary protein adsorption isotherms of bovine hemoglobin (Hb) and bovine serum albumin (BSA) on SP Sepharose FF were determined by batch adsorption experiments in 0.05 mol/L sodium acetate buffer at three pH values (4.5, 5.0 and 5.5) and three NaCl concentrations (0.05, 0.10 and 0.15 mol/L) at pH 5.0. The ST model was found to depict the effects of pH and ionic strength on the single-component equilibria well, with model parameters depending on the pH and ionic strength. Moreover, the ST model gave acceptable fitting to the binary adsorption data with the fitted single-component model parameters, leading to the estimation of the binary ST model parameter. The effects of pH and ionic strength on the model parameters are reasonably interpreted by the electrostatic and thermodynamic theories. Results demonstrate the availability of the ST model for describing nonlinear competitive protein adsorption equilibria in the presence of two proteins.
  • FU Xiaoguo, CHEN Hongzhang, LI Hongqiang, MA Runyu
    The effect of different extraction and purification conditions on the microbial protein obtained from solid-state fermentation (SSF) and the effect of periodical dynamic changes of air on protein have been studied. The mechanism of solid-state fermentation with periodical dynamic changes of air is also discussed. Compared with static solid-state fermentation, periodical dynamic changes of air afford a higher protein mass; from 1 g of the fermentation microbe, 5.3 mg of the intracellular protein (an increase of 34.63%) and 9.09 mg of the extracellular protein (an increase of 17.8%) were obtained on the sixth day of fermentation. The filter paper activity and carboxymethyl cellulose activity (FPA and CMCase) of the extracellular protein are 1.739 μmol/s and 109.592 μmol/s, respectively, which represent increases of 60.1% and 21.2% over the corresponding values for static solid-state fermentation. The FPA and CMCase of the intracellular protein are 0.245 μmol/s and 6.392 μmol/s, respectively, which represent decreases of 22.2% and 38.7% over the corresponding values for static solid-state fermentation. The enzyme activity of the microbial extracellular protein in solid-state fermentation with periodical dynamic changes of air on the fifth day is nearly equal to that on the sixth day without periodical dynamic changes of air, so the period of fermentation can be shortened. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) experiments suggest that pulsating air pressure stimulation leads to a decrease in the amount of protein component with molecule mass of about 80400Da, and an increase in the amount of protein component with molecule mass of about 28520Da.
  • GONG Yanwen, REN Defeng, YUAN Yingjin
    Quantitatively describing the signal transduction process is important for understanding the mechanism of signal regulation in cells, and thus, poses both a challenge and an opportunity for chemical and biochemical engineers. An artificial neural network (ANN), in which we took the signal molecules as neural nodes, was constructed to simulate the generation of active oxygen species (AOS) in Taxus chinensis cells induced by a bio-elicitor. The relative contents of AOS in cells predicted by the ANN model agreed well with the experimental data and three notable stages of AOS increase were observed from the 3D figure of AOS generation. The robustness of AOS trajectories indicated that signal regulation in vivo was an integral feedback control model that ensured the adaptation of Taxus chinensis to environmental stress. The artificial neural network was able to predict taxol production as well as determine the optimal concentration of oligosaccharides needed for it.
  • LIU Rui, QI Wei, SU Rongxin, ZHANG Yubin, JIN Fengmin, HE Zhimin
    The effects of temperature, ionic strength, and enzymatic hydrolysis on the average hydrodynamic radius (Rh) of casein micelles in phosphate buffer were studied by using dynamic light scattering. The results showed that the average Rhvalue of casein micelles decreased irreversibly during the heating, decreased with the increase of ionic strength in lower ionic strength solution (less than 0.05 mol/L), but opposite in higher ionic strength solution (above 0.1 mol/L). The Rh value of casein increased rapidly during the process of enzymatic hydrolysis, and the structural model of casein micelles in the enzymatic hydrolysis process was also proposed, i.e. the casein micelle changed from compact sphere into unfolded and regularly flocky peptides.
  • CHEN Gufeng, ZHANG Yi, XU Jiarui, ZHU Yafei
    Linear low-density polyethylene (LLDPE) was melt and blended with styrene-maleic anhydride copolymer (SMA). The blending films were then immersed in poly(ethylene glycol)400 (PEG400) at room temperature. The surface composition of the blend films was determined by Fourier transform infra-red spectroscopy coupled with a variable incidence angle attenuated total reflection accessory (ATR-FTIR). Results show that PEG400 can be grafted onto the surface of the films via esterification with SMA. The immersion of PEG promotes the enrichment of SMA onto the surface of the films. The water contact angle data show that grafting of PEG400 onto PE can greatly improve the hydrophilicity of the PE surface. These experiments show that surface functionalization of polyethylene films by blending SMA and then surface grafting of PEG is feasible, which suggest an effective and simple route for PE surface modification via blending and grafting.
  • FENG Jian, HUANG Yongmin, LIU Honglai, HU Ying
    Diblock copolymers with ordered mesophase structures have been used as templates for nano-fabrication. Unfortunately, the ordered structure only exists at micrometer-scale areas, which precludes its use in many advanced applications. To overcome this disadvantage, the diblock copolymer confined in a restricted system with a patterned surface is proved to be an effective means to prohibit the formation of defects and obtain perfect ordered domains. In this work, the morphologies of a thin film of diblock copolymer confined between patterned and neutral surfaces were studied by dissipative particle dynamics. It is shown that the morphology of the symmetric diblock copolymer is affected by the ratio of the pattern period on the surface to the lamellar period of the symmetric diblock copolymer and by the repulsion parameters between blocks and wall particles. To eliminate the defects in the lamellar phase, the pattern period on the surface must match the lamellar period. The difference in the interface energy of different compartments of the pattern should increase with increasing film thickness. The pattern period on the surface has a scaling relationship with the chain length, which is the same as that between the lamellar period and the chain length. The lamellar period is also affected by the polydispersity of the symmetric diblock copolymer. The total period is the average of the period of each component multiplied by the weight of its volume ratio. The morphologies of asymmetric diblock copolymers are also affected by the pattern on the surface, especially when the matching period of the asymmetric diblock copolymer is equal to the pattern period, which is approximately equal to the lamellar period of a symmetric diblock copolymer with the same chain length.
  • YU Tao, WANG Yun, LU Dairen, BAI Ruke, LU Weiqi
    Dimethyl 4, 6-bis (bromomethyl) isophthalate was synthesized by bromomethylation, oxidation, esterification and bromination of 1, 3-dimethylbenzene. This was used to initiate the atom transfer radical polymerization of styrene successfully. Results showed that the process had some of the good characteristics of controlled/living free radical polymerization. The molecular weight of the obtained polymer increased linearly with monomer conversion, its molecular weight distribution was very narrow, and a linear relationship between ln([M]0/[M]) and polymerization time was found. A well-defined novel structural polystyrene containing two ester groups in the mid-main chain was prepared with controlled molecular weight and narrow polydispersity. The structure of the polymer was confirmed by 1H-NMR spectra. After being hydrolyzed, dicarboxy polystyrene was obtained and used to form ionic-bonded supramolecules with 1-dodecanamine as a model of the star-shaped supramolecules. The supramolecules formed were characterized by Fourier transform infrared (FTIR) spectrum.
  • WANG Hongxing, CAO Pengzhen, WANG Yuxin
    The performance of the polymer electrolyte membrane fuel cell (PEMFC) is greatly controlled by the structure of the catalyst layer. Low catalyst utilization is still a significant obstacle to the commercialization of the PEMFC. In order to get a fundamental understanding of the electrode structure and to find the limiting factor in the low catalyst utilization, it is necessary to develop the mechanical model on the effect of catalyst layer structure on the catalyst utilization and the performance of the PEMFC. In this work, the structure of the catalyst layer is studied based on the lattice model with the Monte Carlo simulation. The model can predict the effects of some catalyst layer components, such as Pt/C catalyst, electrolyte and gas pores, on the utilization of the catalyst and the cell performance. The simulation result shows that the aggregation of conduction grains can greatly affect the degree of catalyst utilization. The better the dispersion of the conduction grains, the larger the total effective area of the catalyst is. To achieve higher utilization, catalyst layer components must be distributed by means of engineered design, which can prevent aggregation.
  • SONG Yun, LI Wei, ZHANG Minghui, TAO Keyi
    NiB/SiO2 amorphous alloy catalyst was prepared by power electroless plating method and characterized by induction coupled plasma (ICP), Brunauer Emmett Teller method (BET), transmission electron microscope (TEM) and X-ray diffraction (XRD) techniques. The catalytic performance of NiB/SiO2 was investigated for the hydrogenation of furfuryl alcohol (FA) to tetrahydrofurfuryl alcohol (THFA). The effects of operational conditions, such as reaction temperature, pressure, and stirring rate were carefully studied. The proper conditions were determined as the following: pressure 2.0 MPa, temperature 120?C and stirring rate 550 r/min. A typical result with FA conversion of 99% and THFA selectivity of 100% was obtained under such conditions, which was close to that over Raney Ni.
  • CHEN Yixia, SHE Yuanbin, XU Jing, LI Yan
    The catalysis of chloridized metalloporphyrins in the oxidation of cyclohexane to adipic acid was systematically investigated. The turnover numbers (TON) data of 19 catalysts were obtained experimentally under optimal reaction conditions, and 2.4?106 TON for T(o-Cl)PP-MnIIICl catalyst at 2.0?10 6 mol/L of dosage was reached under the conditions of dioxygen pressure of 2.5 MPa at 150?C for 4 h. This was the best result reported for this reaction up to now. The QSAR models for each concerned metalloporphyrin were established, where the catalytic activity was significantly correlated with the ELUMO (the energy level of the lowest unoccupied molecule orbit) and LM-N (the bond length between metal-nitrogen atoms). Using the QSAR models, four new metalloporphyrins with substituted nitro group were designed, and their catalytic activities were predicted. The experimental TON data of newly designed porphyrins were in good agreement with the predicted ones, and the square of their correlation coefficient was more than 0.958. The above results demonstrated that the proposed structure-activity relationship model could be applied to design some new metalloporphyrin catalysts, and to predict their catalytic activity in cyclohexane oxidation.
  • YU Guoxian, CHEN Hui, LU Shanxiang, ZHU Zhongnan
    Reaction feed was prepared by dissolving dibenzothiophene (DBT), which was selected as a model organosulfur compound in diesel fuels, in n-octane. The oxidant was a 30 wt-% aqueous solution of hydrogen peroxide. Catalytic performance of the activated carbons with saturation adsorption of DBT was investigated in the presence of formic acid. In addition, the effects of activated carbon dosage, formic acid concentration, initial concentration of hydrogen peroxide, initial concentration of DBT and reaction temperature on the oxidation of DBT were investigated. Experimental results indicated that performic acid and the hydroxyl radicals produced are coupled to oxidize DBT with a conversion ratio of 100%. Catalytic performance of the combination of activated carbon and formic acid is higher than that of only formic acid. The concentration of formic acid, activated carbon dosage, initial concentration of hydrogen peroxide and reaction temperature affect the oxidative removal of DBT. The higher the initial concentration of DBT in the n-octane solution, the more difficult the deep desulfurization by oxidation is.
  • QIU Yejun, CHEN Jixiang, ZHANG Jiyan
    The effects of MgO promoter on the physico-chemical properties and catalytic performance of Ni/Al2O3 catalysts for the partial oxidation of methane to syngas were studied by means of BET, XRD, H2-TPR, TEM and performance evaluation. It was found that the MgO promoter benefited from the uniformity of nickel species in the catalysts, inhibited the formation of NiAl2O4 spinel and improved the interaction between nickel species and support. These results were related to the formation of NiO MgO solid solution and MgAl2O4 spinel. Moreover, for the catalysts with a proper amount of MgO promoter, the nickel dispersiveness was enhanced, therefore making their catalytic performance in methane partial oxidation improved. However, the excessive MgO promoter exerted a negative effect on the catalytic performance. Meanwhile, the basicity of MgO promoted the reversed water gas shift reaction, which led to an increase in CO selectivity and a decrease in H2 selectivity. The suitable content of MgO promoter in Ni/Al2O3 catalyst was ?7 wt-%.
  • ZHANG Xiongfu, WANG Jinqu, LIU Hai′ou, WANG Anjie
    The present study investigates the formation of silicalite-1 seed layers on a porous carbon support of 0.5 μm pore size and α-A12O3 supports with different pore sizes (0.1 μm and 4 μm) via the slip-casting technique. The effects of support property, seed size and solvent on the formation of seed layers were investigated in detail. The growth of silicalite-1 membranes on different seeded supports by hydrothermal synthesis was also evaluated. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) characterizations indicate that a continuous seed layer can be obtained on the smooth support of 0.1 μm pore size by using any seed of 100 nm, 600 nm or 2.2 μm in size, whereas, on the coarse supports with either 0.5 μm or 4 μm pore size, a continuous seed layer cannot be formed using the above seed sizes and the same seeding time. At a longer contact time, a seed layer can also be formed using 100 nm seed on the supports with larger pore size. However, the layer is not uniform and smooth. For a hydrophobic porous carbon support, seeding ethanol suspension, which has weak polarity, favors the formation of a continuous seed layer. The seed layers and membranes grown from the smaller seed are more uniform and continuous and possess smoother surfaces than those from the larger seed. The seed layer and respective grown membrane formed from nanosized seed (100 nm) are the most uniform and compact. With this method of seeded secondary synthesis of zeolite membranes, the quality of a membrane mainly depends on the quality of the seed layer.
  • XIAO Xinyan, ZHANG Huiping, CHEN Huanqin, LIAO Dongliang
    TiO2 nano-particles were synthesized by sol-gel technique and characterized by X-ray diffractometer (XRD) and transmission electron microscope (TEM). Their photocatalytic activities for formaldehyde (FA) and methyl orange (MO) degradation were tested using degradation rate (η) as an evaluation index. Based on the orthogonal test results, the optimal condition for TiO2 preparation was obtained. Results showed that particle sizes were in the range of 10 40 nm, and that prepared TiO2 had better photocatalytic activity than P25. A simplified model was developed to evaluate the apparent quantum efficiency (Φapp) of this photocatalytic reaction system.
  • CHEN Yunhua, ZHU Xuedong, WU Yongqiang, ZHU Zibin
    The pressure drop of a cross-flow moving-bed was investigated in a two-dimensional rectangular apparatus. The effects of the particle velocity, the superficial gas velocity, the formation and development of cavity/raceway and voidage of particles on the pressure drop were investigated experimentally under the operational conditions of 0.09 1.35 m/s of the superficial gas velocity and 0.95 9.68 cm/min of the particle velocity. The experimental results show that the particle velocity has little influence on the pressure drop, while the phenomena of cavity and pinning occur when the cross-flow velocity is high enough. The development of a cavity or a raceway can result in three types of variations of pressure drop with time: stabilization, slight fluctuation and severe fluctuation. A cavity appears in a process cycle of formation-growing up-collapsing-fluidization  at a high gas velocity. On the basis of experimental results, a model for calculating the pressure drop after a cavity occurs and a dimensionless relationship of cavity size is developed, which gives a good qualitative account of the experimental data.
  • ZHU Jiqin, YU Yanmei, CHEN Jian, FEI Weiyang
    The separations of olefin/paraffin, aromatic/aliphatic hydrocarbons or olefin isomers using ionic liquids instead of volatile solvents have interested many researchers. Activity coefficients γ at infinite dilution of a solute in ionic liquid are generally used in the selection of solvents for extraction or extractive distillation. In fact, the measurement of γ by gas-liquid chromatography is a speedy and cost-saving method. Activity coefficients at infinite dilution of hydrocarbon solutes, such as alkanes, hexenes, alkylbenzenes, styrene, in 1-allyl-3-methylimidazolium tetrafluoroborate ([AMIM][BF4]) and 1-butyl-3-methyl imidazolium hexafluorophosphate ([BMIM][PF6]), 1-isobutenyl-3-methylimidazolium tetrafluoroborate ([MPMIM][BF4]) and [MPMIM][BF4]-AgBF4 have been determined by gas-liquid chromatography using ionic liquids as stationary phase. The measurements were carried out at different temperatures from 298 to 318 K. The separating effects of these ionic liquids for alkanes/hexane, aliphatic hydrocarbons/benzene and hexene isomers have been discussed. The hydrophobic parameter, dipole element, frontier molecular orbital energy gap and hydration energy of these hydrocarbons were calculated with the PM3 semi-empirical quantum chemistry method. The quantitative relations among the computed structure parameters and activity coefficients at infinite dilution were also developed. The experimental activity coefficient data are consistent with the correlated and predicted results using QSPR models.
  • ZHOU Xiantao, PAN Jiazhen, CHEN Liqing, SHI Yan, CHEN Wenmei, CHU Liangyin
    Turbulent Taylor vortex flow, which is contained between a rotating inner cylinder and a coaxial fixed outer cylinder with fixed ends, is simulated by applying the development in Reynolds stress equations mold (RSM) of the micro-perturbation. This resulted from the truncation error between the numerical solution and exact solution of the Reynolds stress equations. Based on the numerical simulation results of the turbulent Taylor vortex flow, its characteristics such as the fluctuation of the flow field, the precipitous drop of azimuthal velocity, the jet flow of radial velocity, the periodicity of axial velocity, the wave periodicity of pressure distribution, the polarization of shear stress on the walls, and the turbulence intensity in the jet region, are discussed. Comparing the pilot results measured by previous methods, the relative error of the characteristics predicted by simulation is less than 30%.
  • GAO Sujun, SUN Yaqin, XIU Zhilong
    The separation of 1,3-propanediol from the glycerol-based fermentation broth of Klebsiella pneumoniae plays an important role during the microbial production of 1,3-propanediol. In this paper, the separation of 1,3-propanediol from fermentative broth by a combination of ultrafiltration and alcohol dilution crystallization was investigated. The broth was first filtered by ultrafiltration, and 99% of cells, 89.4% of proteins and 69% of nucleic acids were removed. The obtained broth was further condensed by vac uum distillation, and then alcohol was added. The macromolecular impurities, such as nucleic acids, polysaccharides and proteins, were precipitated, and inorganic and organic salts were crystallized. The optimal volume ratio of alcohol added to the condensed fermentation broth was determined to be 2:1. As a result, proteins, nucleic acids and electric conductivity decreased by 97.4%, 89.7% and 95.8%, respectively, compared with the fermentative broth. The influences of pH and water content in condensed broth on alcohol precipitation and dilution crystallization were also investigated. The experimen tal results indicated that alcohol precipitation and dilution crystallization was feasible and effective for the separation of 1,3-propanediol from actual fermentation broth.
  • SHANG Weijuan, WANG Daxin, WANG Xiaolin
    Although there is a voluminous literature on the determination of structural parameters (the pore radius, the ratio of membrane porosity to membrane thickness) of a nanofiltration (NF) membrane and its separation performance (such as the rejection and the permeation flux) by the simplified Teorell-Meyer-Sievers (TMS) model, little of this research comments on other theories and the consequences of linking modeling evaluation to technological application. Theories used to predict the separation performance of an NF membrane usually include: the non-equilibrium thermodynamic model, the pore model, the space charge model, the TMS model, the electrostatic and steric-hindrance model, and the semiempirical model. In the article, we briefly trace the origins or the general ideas of the above-mentioned theories. From there, recent researches on the characterization of membrane structural parameters and electrical properties (such as the surface charge density qw) are reviewed. We then turn to research on the separation performance of an NF membrane for single-component solutions of inorganic electrolytes, neutral organic solutions, and a mixture solution of electrolytes or that of an electrolyte and neutral organic solute. Afterwards, we outline the applications of NF technology in the processes of product separation and conclude with a discussion on the role of models in such applications.