Showing papers in "Journal of The Chinese Institute of Chemical Engineers in 2005"

Fluidization of fine cohesive powders and nanoparticles - A review

Abstract: Fluidization of fine cohesive powders, generally classified as the Geldart's group C powders, and fluidization of nanoparticles less than 100 nm were reviewed. Fundamentals on cohesiveness among particles and their extension to prediction of agglomerate size and effects on fluidization phenomena were introduced. Methods for improving fluidization, which include flow conditioners, mechanical vibration, sound-assisted fluidization, fluidization with magnetic/electric fields, pulse fluidization, and centrifugal fluidization, were investigated. Finally, the potential application of fluidization in handling and processing of cohesive powders, especially for nanoparticles, were explored.

Transport of Zidovudine-and Lamivudine-Loaded Polybutylcyanoacrylate and Methylmethacrylate-Sulfopropylmethacrylate Nanoparticles across the In Vitro Blood-Brain Barrier: Characteristics of the Drug-D

Abstract: Transport study of zidovudine (AZT) and lamivudine (3TC) loaded on polybutylcyanoacrylate (PBCA) and methylmethacrylate-sulfopropylmethacrylate (MMA-SPM) nanoparticles (NPs) across the in vitro blood-brain barrier (BBB) model system was presented. Through primary culture, confluent monolayer of bovine brain-microvascular endothelial cells (BBMECs) with the feature of cellular homogeneity and tight intercellular junction was demonstrated by immunocytochemical fluorescent method. Besides, for the colloidal drug-carrier system, average diameters of the two nearly monodispersed PBCA and MMA-SPM nanospheres were, respectively, about 92 nm and 78 nm. The amount of AZT and 3TC across the current BBMEC monolayer in carrier-incorporated system was much higher than that in non-carrier system, suggesting sufficient amelioration in drug transport by employing the NP carriers for brain-targeting delivery. Comparing PBCA NPs with MMA-SPM NPs, the amount of drug (AZT and 3TC) across the in vitro BBB system for the former was in excess of 1.5 times that for the latter.

Preparation and Characterization of TiO2-Coated Optical-Fiber in a Photo Reactor

Abstract: An optical-fiber photo reactor (OFPR) was designed and assembled to provide uniform light distribution inside the reactor, which spread light energy more efficiently than a traditional fixed-bed reactor. TiO2 films were coated on optical fibers using the dip-coating method. Titania solutions were prepared through the thermal hydrolysis of titanium butoxide, commercial Hombikat XXS100 solution, and Degussa P25 suspension for comparison. The thicknesses of the films ranged from 60 to 600 nm after calcination at 500℃, and the sizes of the nanocrystals in the TiO2 films were 15-25 nm, as estimated from SEM micrographs. Anatase phase was found from the XRD patterns in all the TiO2 films. The profilemeter and ASTM D3359 adhesion test results showed that uniform TiO2 films were formed with strong adhesion using the thermal hydrolysis and Hombikat XXS100 solutions, while those coated with P25-suspension exhibited poor adhesion on a glass surface. The contact angle of the water decreased to almost zero within 30 minutes under UV-light irradiation and then recovered to the initial contact angle in darkness, implying super hydrophilicity and perfection of the TiO2 films. Ammonia was photocatalytically decomposed in the OFPR under artificial light irradiation, indicating good photocatalytic reactivity of the TiO2-coated fibers.

Biodegradable Polymeric Nanoparticles Bearing Stealth PEG Shell and Lipophilic Polyester Core

Abstract: PEGylated particles are considered to be macrophage-resistant in blood circulation following intravenous injection. Therefore, drug-loaded particles in blood stream can extend its lifetime. In this study, we utilized PEG-PCL block copolymers designed to avoid attacking from macrophages. We used MTT assay to evaluate the cytotoxicity of nanoparticles formed by self-assembly of the block copolymers. The flow cytometry was utilized to analyze the interaction of the polymeric nanoparticles with a macrophage cell line (RAW264.7). It was found that the cell granularity did not change significantly in PEG-PCL block copolymer yet increased substantially in PCL-PAA (non PEG grafted copolymer). The preliminary results in this study suggested that the macrophage cells were not activated by PEG-PCL nanoparticles.

Molecular Dynamics for Thermal Unfolding Behaviors of N-Carbamyl-D-Amino Acid Amidohydrolase

Abstract: The thermal unfolding behaviors of the dimeric N-carbamyl-D-amino acid amidohydrolase (CAA) were investigated by 1 ns molecular dynamics simulations in explicit water system with temperature jump technique. Rather than a symmetrical event, the unfolding of the two subunits of the dimeric CAA follows different pathways. Although these two subunits are structurally identical, subunit A loses its secondary structure integrity from the outermost layer 1 to the innermost layer 4; whereas subunit B unfolds first from its interior layer 3, where the active site pocket is located. Hence, the active site from subunit B is less stable than that from subunit A. Furthermore, the interfacial hydrophobic region is expanded, implying that the dimeric CAA tends to dissociate into the enzymatically inactive monomeric form. It further indicates that the interior layers lose their secondary structure integrity, resulting in the destruction of the active site geometry. Thus, it is suggested to engineer several disulfide bonds to “bind” the interfacial hydrophobic region, such as L218C, A 222C, I301C, and A302C, which is currently being conducted in our group.

Crack Dynamics of Thermally Dried Sludge Cake

Abstract: We examined in this work the dynamics of crack in drying sludge cake using an X-ray micro-computerized tomography scanner (micro-CT). The three-dimensional crack structure model was reconstructed, and the geometric parameters of cracks were evaluated over time. Internal cracks were found to grow fast in the initial phase of drying, and to then develop into shapes that exhibited zigzagging with non-circular cross-sections and fractal-like boundaries. The role of cracks on sludge drying is discussed.

Steady-State Solid-Flux Plot of Blanket in Upflow Suspended Bed

Abstract: We experimentally elucidated the behavior of steady-state blanket produced from raw water of turbidity 100-450 NTU (Nephelometric Turbidity Unit) subjected to underdosed, optimal, and overdosed coagulation. Polyaluminum chloride (PACl) was the coagulant. The blanket heights and effluent turbidities in an upflow suspended bed were recorded at different upflow velocities. Based on the one-dimensional model proposed by Chen et al. (2003a), the steady-state blanket concentration were estimated, whence the three-dimensional solid-flux plot constructed. When the solid flux was plotted against the solid concentration and the ratio of raw water turbidity and PACI dose, a master surface presented all tests in a unified way was noticeable. This plot could be used to predict steady-state blanket behavior at change in water turbidity or in PACl dose.

Axial Solids Distribution and Flow Development in the Risers of Circulating Fluidized Beds with Different Heights

Abstract: The axial apparent solids holdup and flow development is studied in two riser circulating fluidized bed reactors of different heights (10 m and 15.1 m risers), but similar diameter (76 mm and 100 mm). Pressure transducers were used for the measurement of axial solids distribution and flow development. For a higher riser, the axial distribution of solids holdup becomes more uniform along the riser. The apparent solids holdup increases with the increase of solids circulating rate or decrease of superficial gas velocity. However, the influence of these operating conditions on solids holdups at different axial regions have different tendency of change, which is quite different at particle acceleration region and fully developed region. A more accurate correlation is proposed to predict average solids holdup at a fully developed region of CFB riser.

Photocatalytic reduction of NO by CO over TiO2/silica gel in an annulus fluidized bed photoreactor

Abstract: The effects of addition of CO on photocatalytic reduction of NO over TiO2/silica gel photocatalyst have been determined in an annulus fluidized bed photoreactor. The NO reduction efficiency increases with the addition of CO gas in the fluidized bed of TiO2/silica-gel photocatalyst and the optimum molar ratio of CO/NO for the NO reduction is found to be 1.2. The addition of CO gas is an effective means for N2O degradation and reduces unreacted CO gas slip in the annulus fluidized bed photoreactor.

Pressure Fluctuations in Spouted Beds

Abstract: The effects of different kind of particles, different particle sizes, conical angles, and static bed heights on the pressure fluctuations and pressure drop in spouted beds were studied. The results showed that the standard deviation of the pressure fluctuations not only described the transition of the regime but also determined the minimum spouting velocity. After transformation with spectral analysis, the major frequency of the pressure fluctuation data was changed with the variation of the hydrodynamics. In addition, the changes of the special frequency scales corresponded to the hydrodynamic changes.

Foaming and Antifoaming in a Gas-Liquid-Finely Divided Particulate System

Abstract: Foaming in slurries and sludges is of immediate concern because of the environmental hazards posed during the safe disposal of radioactive wastes. The present research studied foaminess in simulated radioactive waste, which is a highly alkaline sludge, during dynamic conditions (i.e. boiling). A maximum in foaminess is observed which is due to two competing effects: Amphiphilic particles promoting foaminess by attachment to the bubble surfaces and foam inhibition due to clustering of particles. The maximum in foaminess was of the order of 400 vol% which is detrimental for the working of the commercial evaporator. The antifoaming action of a commercial antifoam agent was investigated as well as an improved antifoamer recently developed by ⅡT in conjunction with researchers at SRNL.

Influence of Agitation Intensity on Mycelium Aggregation of Ganoderma lucidum

Abstract: Previous work has shown that in many filamentous fungi fermentations the morphology of the fungi influence both biomass and metabolites. The formation of large pellet is the main characteristic of the mushroom mycelium submerged culture. In this paper the dynamic change of mycelium aggregation process was investigated in 5L fermentor. Low agitation intensity resulted in large loose mycelium aggregates rapidly and the mycelium fragment concentration (mfc) dropped to 20% of the initial value at 100 rpm at 4th h. In contrast, high agitation intensity led to small compact mycelium aggregates. A novel scheme using intermittent agitation could maintain a higher level of mfc for more than 24 h and also enhanced the production of mycelium biomass.

Separation Efficiency of a Centrifugal Fluidized Bed Classifier in the Micron Range

Abstract: Solid liquid separation is a standard task in modern chemical industry. Therefore various different technologies and equipment exist for this task. However, especially for cut sizes in the micron range all of the existing devices show drawbacks, e.g. regarding separation sharpness, throughput, yield of fines, etc. This article describes a novel device for solid-liquid separation with cut sizes in the micron range which was built to close the gap of solid-liquid separation equipment in the micron range. The operating principle and design concept of the device are explained, its separation performance for standard slurries and different operating conditions as well as degrees of freedom and optimisation strategy are outlined.

Molecular Dynamics Simulations to Investigate the Thermal Unfolding Behaviors of the Tetramerization Domain of Shaker and Kv1.1 Potassium Channels

Abstract: In our previous study, a set of homology models of the tetramerization (T1) domain of six eukaryotic potassium channels Kv1.1-Kv1.6 from Homo Sapiens was constructed based on the crystal structure of the Shaker T1 domain from Aplysia californica. The results reveal that the T1 domains of these Kv channels exhibit similar folds as those of Shaker K(superscript +) channel. In this study, several molecular dynamics (MD) simulations towards the Shaker and Kv1.1 T1 domains were conducted at various temperatures. Our results show that the Shaker T1 domain exhibit higher structural integrity than the Kvl.1 T1 domain at all temperatures examined. In addition, the thermal unfolding of the Shaker T1 domain begins at layer 3. In contrast, layers land 2 exhibit higher structural stability because layer 1 remains more hydrogen bonding interactions at elevated temperatures and layer 2 is located in the highly conserved hydrophobic core. Ile121 in the Shaker T1 domain plays an important role in disrupting the loop between helices 4 and 5. During the thermal unfolding process, the newly formed hydrophobic interactions between A1a120, Ile12l, Leu122, Leu13l, and Leu151 may distort the native contact between layers 2 and 3 of the T1 domain.

Mercury Emission Control from Combustion Flue Gas Employing Semi-Fluidized Bed Activated Carbon Adsorption

Abstract: Control of mercury emissions from various combustion sources has attracted great attention due to the toxic nature of mercury and the current and potential regulations. The proposed Clear Skies Act of 2003, introduced in the US House of Representatives as House bill HR 999 and the US Senate as Senate bill S. 485 on February 27, 2003, would create a mandatory program that would dramatically reduce power plant emissions of SO2, NO(subscript x) and Hg by setting a national cap on each pollutant. In this study, a process model was developed to simulate mercury sorption by activated carbon in three distinct beds, namely a confined bed, a semi-fluidized bed, and a fluidized bed. The simulation results have suggested that the confined bed has the best mercury control performance; however, it generates the highest pressure-drop across the bed. A semi-fluidized bed offers acceptable performance with affordable pressure-drops and can be a practical candidate for the process.

Kinetic study of the reaction of carbon disulfide and basic compounds

Abstract: The reaction of carbon disulfide and basic compounds, including potassium hydroxide (KOH), tetrabutylammonium hydroxide (QOH), and tertiary amine (TBA ), to form CS2-X in a homogeneous solution was studied. A UV detector was used to measure these reactions. The concentration of the active intermediate CS2-X (X: basic compounds), which was not purified from the solution, was measured using a UV instrument. It is found that the reactions did not follow a pseudo first order rate law when potassium hydroxide or tetrabutylammonium hydroxide was used as the basic compound. Nevertheless, a pseudo first order rate law is proposed to describe the kinetics of reactions involving carbon disulfide and tertiary amine. In the reaction of carbon disulfide and tertiary amine, the rate constant of the forward reaction (k1) was obtained through UV absorbance of the product. The effects of organic solvents, temperature, and the concentration of the reactants on the rates of reactions were investigated.

Opportunities for Improving the Plant Cell Culture Processes for Secondary Metabolite Production

Abstract: This article illustrates some methods and approaches which improve the performances of plant cell culture processes and relevant bioreactors. The focus is placed on the promotion of cell growth and enhancement of secondary metabolite production. Production of L-DOPA (3,4-dihydroxyphenylalanine) by Stizolobium hassjoo is the primary cell culture system encountered in this article. For suspension cell cultures, the key points for inductions of pertinent callus and cell line are described. Hydrodynamic effects on cell aggregate and secondary metabolite production are demonstrated. Strategy for elicitation, control of gaseous composition in a reactor, measurements of power consumption in shake flasks laboratory-scale agitated reactor are exemplified. For transgenic hairy roots, the medium optimization through statistical experimental design is employed to promote the hairy root weight, L-DOPA content in the roots and L-DOPA productivity. The results show that the root weight, L-DOPA content and L-DOPA productivity promoted 1.8-, 2.2- and 2.8 folds of basal B5 medium control runs. Mist trickling reactor (MTR) is promising for proliferating the hairy roots. The features of hairy root growth on a Petri-dish suggested that the bridging of the lateral roots and exertion of an appropriate hindrance to root tips are favorable to the profuse growth of roots and L-DOPA production. The mode of replenishment of nutrients, especially the nitrogen and carbon sources in the late of the cultures is justified.

Heparin Modulates Human Osteosarcoma (MG-63) Activities on Collagen-Coated Substrata

Abstract: Collagen, the major extracellular matrix component, is a popular biomaterial due to its excellent biocompatibility. Collagen is widely used in sutures, corneal bandages, drug delivery gels, and as wound dressings, as well as in a newly emerging interdisciplinary biomedical field, tissue engineering. A better understanding of the interaction between cells and collagen substrata combining other ECM components should allow for a more rational scaffold design for tissue engineering. In this study, we explored the effects of heparin on the behavior of osteoblast-like cell lines (MG-63) on collagen-based substrates. Collagen mixture (0.1mg/mL) with heparin at different concentrations (0.02mg/mL, 0.1mg/mL, and 0.5mg/mL) was coated onto tissue culture polystyrene plates. We found that low concentration of heparin (0.02mg/mL) enhanced cell adhesion and spreading on collagen-coated plates, but did not influence cell growth and alkaline phosphatase activity. On the other hand, high doses of heparin (0.1 and 0.5mg/mL) decreased cell adhesion and spreading, as well as cell proliferation. Our results suggest that a small amount of heparin might support osteoblast attachment and spreading although high heparin concentration is not suitable for cell culture.

Reaction Kinetics and Mechanism of Nickel Fiber Synthesis

Abstract: Nickel fibers were chemically synthesized from three different processes and their respective mechanisms and kinetics were investigated in this work. In the three processes, four reaction pathways were discovered indicating four different nickel precursors, which were Ni(N2H3COO)3(superscript -), Ni(NH3)6(superscript 2+), Ni(N2H4)3(superscript 2+), and Ni(OH)2 respectively. The activation energy of each reaction was determined to be 189.4kJ/mol, 96.3kJ/mol, 51.3kJ/mol, and 13.4kJ/mol. From SEM analysis the morphologies were found to be different in size and structure according to the reaction conditions. Since the nickel fibers were basically formed by the connection of nickel particles under the magnetic field, the variation in thickness of the fiber could therefore be explained by the rate of nucleation and subsequent growth. For stable nickel complexes such as Ni(N2H3COO)3(superscript -) and Ni(NH3)6(superscript 2+), the nucleation rate was relatively slow, and there were fewer nuclei generated, so the diameter of nickel fibers became larger. On the contrary, when more nuclei were generated, the diameter of nickel fiber was smaller. At the same time, the structure of nickel fibers was also affected by growth rate. Excessively high growth rate would cause weak connection between nickel particles and hence a loose structure. In the most extreme case, only nickel powder was obtained.

A Simpler Plasmid Loss Rate Model with Less Assumption

Abstract: A simpler mathematical model with less assumption to measure plasmid loss rate is developed in this study. The plasmid loss rate is defined as the probability of a division of a plasmid-containing cell dividing into one plasmid-containing and one plasmid free daughter cell. The model proposed here allows one to estimate value for plasmid loss rate without forcing it to be constant. The plasmid loss rate is determined by parameters including specific division rate of host cells, the ratio of plasmid bearing cells to total cells and incubation time.

Eggshell as a Novel Biomimetic Reactor for in vitro Tissue Culture

Abstract: In this study, a biomimetic eggshell reactor capable of highly efficient gas transfer was developed for in vitro tissue cultures. The reactor consisted of a natural eggshell (working volume≈50-60mL) for the containment of medium and a chamber-stirrer assembly for the containment of tissue constructs and for agitation. The pores on the eggshell allowed for gas transfer; thus, no air sparging was required. Compared with commercial spinner flasks, the eggshell reactor resulted in slightly better oxygen transfer rates at low agitation speeds, but significantly higher volumetric mass transfer coefficients at high agitation speeds. The highly efficient gas transfer in the eggshell reactor enabled the in vitro cultivation of actively growing E. coli and long-term cultivation of tissue engineered cartilage-like constructs. Taken together, our results implicate the potential application of this reactor as a low-cost alternative for cell and tissue cultures.

Controlling Bed Solids Inventory and PSD during Fluidized Bed Combustion of Solid Fuels: The Role of the Primary Ash PSD

Abstract: The paper addresses the establishment of a steady inventory of bed inert material in a fluidized bed combustor when the bed consists of fuel ash only. The analysis is based on the concept of the primary ash particle size distribution (PAPSD), defined as the PSD of primary ash particles liberated by fuel particles upon complete burn-off. An experimental procedure for the quantitative assessment of the rate of primary ash generation and of the size distribution of primary ash particles (PAPSD) is presented. The application of the procedure is demonstrated with reference to a set of solid fuels, including coals and biogenous fuels. The reliability and accuracy of the technique was satisfactorily tested, with the exception of two biomass fuels which gave rise to bed agglomeration making the application of the test procedure unsuccessful. A simplified theoretical analysis is presented, based on material balances on lumped classes of primary ash particles around the CFBC. The analysis aims at clarifying the role of the PAPSD and of the cyclone efficiency to the establishment of bed inventory, particle size distribution and solids circulation rate. Lower and upper bounds to the solids circulation rate that can be established in the steady operation of a CFBC are related to the PAPSD and to the cyclone performance.

Effects of Carica papaya Lipase Pretreatments on Enantioselective Hydrolysis of (R,S)-Arylpropionic Thioesters

Abstract: The hydrolytic resolution of (R,S)-naproxen 2,2,2-trifluoroethyl thioester in water-saturated isooctane was employed as a model system to study the pretreatment effect of Carica papaya lipase on the enzyme performance. In comparison with the result of using deionized water in the pretreatment, improvements in lipase activity and enantioselectivity were achieved when polar organic solvents, pH 8 phosphate buffer, or aqueous solution containing methyl-β-cyclodextrin, but not NaCl or 18-crown-6, was employed. The lipase pretreated with isopropyl ether was selected as the best lipase and further employed to resolve 2,2,2-trifluroethyl thioesters of (R,S)-fenoprofen, (R,S)-flurbiprofen and (R,S)-ibuprofen.

Using Aniline as an Adductive Agent for Separation of an m-Chlorophenol + p-Chlorophenol Mixture

Abstract: The experimental solid-liquid equilibrium data of ternary mixtures consisting of m-chlorophenol, p-chlorophenol, and aniline, and those of the constituent binary pairs were determined using the solid-disappearance method. The isomer mixture consisting of m-chlorophenol + p-chlorophenol exhibits one eutectic point at 276.0 K with 0.52 mole percentage of m-chlorophenol. The binary mixture of aniline + m-chlorophenol exhibits two eutectic points, 278.7 K and 257.2 K, at aniline compositions of 0.22 and 0.85, respectively , and one congruent point at aniline mole fraction of 0.5. And another pair of aniline + p-chlorophenol also exhibits two eutectic points, 286.2 K and 259.2 K, at aniline compositions of 0.28 and 0.87, respectively , and one congruent point at aniline mole fraction of 0.5. Ternary mixtures with designated mole ratios of m-chlorophenol to p-chlorophenol exhibit two eutectic points and one congruent point also at aniline mole fraction of 0.5. All the experimental SLE data were fitted by the empirical equation of Ott and Goates with an optimization technique. The results showed the equation of Ott and Goates represents the experimental data fairly well with the average absolute deviation of temperature less than 1.0 K. All the parameters were given and can be used for interpolation purpose. Based on the experimental data and the ternary phase diagram showing all the eutectic and congruent points, three conceptual feasible processes using aniline as an adductive agent for separating m-chlorophenol from p-chlorophenol are proposed.