CONTRIBUTIONS TO PLASMA PHYSICS, Issue 6-7 2010
N. Yanagi
Abstract Configuration optimization is examined for the heliotron fusion energy reactor FFHR in order to find sufficient clearances between the ergodic region outside the nested magnetic surfaces and blankets at the inboard side of the torus. The standard configuration of FFHR, which is similar to that of LHD, has a relatively large major radius of the helical coils in order to satisfy this requirement. It has been found, as an alternative design, that equivalent clearances are obtained with a shorter major radius both by employing a lower helical pitch parameter and splitting the helical coils in the poloidal cross-section at the outboard side. Splitting the helical coils also provides another configuration that ensures magnetic well formation in the fairly large nested magnetic surfaces with outward shifted configurations. Optimization is being carried out for these configurations by adjusting the pitch modulation parameter to improve the particle confinement (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Integrated Enzymatic Synthesis and Adsorption of Isomaltose in a Multiphase Fluidized Bed Reactor

ENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 5 2006
M. Ergezinger
Abstract Dextransucrase catalyzes the formation of dextran, but also of numerous oligosaccharides from sucrose and different acceptors, if appropriate conditions are chosen. A process on a technical scale with immobilized enzyme was established to produce isomaltose, a disaccharide of industrial interest. Isomaltose is also a reactant for dextransucrase and has to be quickly taken out of the reaction solution. This was realized by integrated adsorption of isomaltose on zeolites. In the case of biotransformation the reactor works with a fluidized bed of immobilized enzyme and the in situ separation is realized with a suspension flow of adsorbent. This process was investigated experimentally and theoretically. With a design model consisting of hydrodynamics, kinetics of enzymatic synthesis, and thermodynamics of adsorption, a comparison was made between experimental and calculated data. [source]

Acclimation Strategy of a Biohydrogen Producing Population in a Continuous-Flow Reactor with Carbohydrate Fermentation

ENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 4 2006
Q. Ren
Abstract Poor startup of biological hydrogen production systems can cause an ineffective hydrogen production rate and poor biomass growth at a high hydraulic retention time (HRT), or cause a prolonged period of acclimation. In this paper a new startup strategy was developed in order to improve the enrichment of the hydrogen-producing population and the efficiency of hydrogen production. A continuously-stirred tank reactor (CSTR) and molasses were used to evaluate the hydrogen productivity of the sewage sludge microflora at a temperature of 35,°C. The experimental results indicated that the feed to microorganism ratio (F/M ratio) was a key parameter for the enrichment of hydrogen producing sludge in a continuous-flow reactor. When the initial biomass was inoculated with 6.24,g of volatile suspended solids (VSS)/L, an HRT of 6,h, an initial organic loading rate (OLR) of 7.0,kg chemical oxygen demand (COD)/(m3,×,d) and an feed to microorganism ratio (F/M) ratio of about 2,3,g COD/(g of volatile suspended solids (VSS) per day) were maintained during startup. Under these conditions, a hydrogen producing population at an equilibrium state could be established within 30,days. The main liquid fermentation products were acetate and ethanol. Biogas was composed of H2 and CO2. The hydrogen content in the biogas amounted to 47.5,%. The average hydrogen yield was 2.01,mol/mol hexose consumed. It was also observed that a special hydrogen producing population was formed when this startup strategy was used. It is supposed that the population may have had some special metabolic pathways to produce hydrogen along with ethanol as the main fermentation products. [source]

Optimization of Operating Temperature for Continuous Immobilized Glucose Isomerase Reactor with Pseudo Linear Kinetics

ENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 5 2004
N.M. Faqir
Abstract In this work, the optimal operating temperature for the enzymatic isomerization of glucose to fructose using a continuous immobilized glucose isomerase packed bed reactor is studied. This optimization problem describing the performance of such reactor is based on reversible pseudo linear kinetics and is expressed in terms of a recycle ratio. The thermal deactivation of the enzyme as well as the substrate protection during the reactor operation is considered. The formulation of the problem is expressed in terms of maximization of the productivity of fructose. This constrained nonlinear optimization problem is solved using the disjoint policy of the calculus of variations. Accordingly, this method of solution transforms the nonlinear optimization problem into a system of two coupled nonlinear ordinary differential equations (ODEs) of the initial value type, one equation for the operating temperature profile and the other one for the enzyme activity. The ODE for the operating temperature profile is dependent on the recycle ratio, operating time period, and the reactor residence time as well as the kinetics of the reaction and enzyme deactivation. The optimal initial operating temperature is selected by solving the ODEs system by maximizing the fructose productivity. This results into an unconstrained one-dimensional optimization problem with simple bounds on the operating temperature. Depending on the limits of the recycle ratio, which represents either a plug flow or a mixed flow reactor, it is found that the optimal temperature of operation is characterized by an increasing temperature profile. For higher residence time and low operating periods the residual enzyme activity in the mixed flow reactor is higher than that for the plug flow reactor, which in turn allows the mixed flow reactor to operate at lower temperature than that of the plug flow reactor. At long operating times and short residence time, the operating temperature profiles are almost the same for both reactors. This could be attributed to the effect of substrate protection on the enzyme stability, which is almost the same for both reactors. Improvement in the fructose productivity for both types of reactors is achieved when compared to the constant optimum temperature of operation. The improvement in the fructose productivity for the plug flow reactor is significant in comparison with the mixed flow reactor. [source]

Biofilm Growth and Bed Fluidization in a Fluidized Bed Reactor Packed with Support Materials of Low Density,

ENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 2 2004
R.A. Saucedo-Terán
Abstract Support materials of low-density for fluidized bed reactors provide several operational advantages, including lower energy requirements and proper biofilm growth balance. The aim of this investigation was to study the extent of biofilm growth and bed fluidization in an experimental reactor, using polyester resin (,pr,=,1220,kg/m3) and vitrified expanded perlite (,vep,=,1710,kg/m3) as alternative support materials to conventional silica sand. A noteworthy amount of biofilm was observed to be attached to both support materials from the very beginning of the bioreactor operation. Nevertheless, there were significant variations in biofilm growth and activity over the course of the experimental trials. For both perlite and polyester beds, the highest biofilm mass and the highest total number of mesophilic bacteria were observed between the 7th and the 10th day, showing a steady state trend at the end of the experimental runs. The chemical oxygen demand (COD) removal levels were concomitant with biofilm mass and total mesophilic bacteria changes, although the polyester bed efficiency was slightly higher than that for the perlite bed. As expected, the polyester bed was fluidized at a lower re-circulation flow compared to the perlite bed. Reactor back-washing was not required for these support materials since biomass excess was adequately separated by means of a special internal device. The efficiencies of removal of organic matter achieved were acceptable (up to 78,%) despite the low volume of the support material (25,%) and the low hydraulic retention time (30,min). [source]

Combined Treatment of Perchlorate and RDX in Ground Water Using a Fluidized Bed Reactor

GROUND WATER MONITORING & REMEDIATION, Issue 3 2007
Mark E. Fuller
A bench-scale study was conducted to assess the effectiveness of biological treatment of comingled perchlorate and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in ground water using fluidized bed reactors (FBRs). In addition, the ability of FBRs to treat low concentrations of perchlorate was examined. Pilot-scale FBRs were fed either acetic acid or molasses as an electron donor to facilitate simultaneous perchlorate and RDX reduction. The acetic acid-fed FBR consistently removed perchlorate from an influent level of 100 ,g/L to below 6 ,g/L, and values below the method detection limit of 1 ,g/L occurred approximately 70% of the time. RDX breakthrough from all FBRs was minimal due to sorption of the explosive on the granulated activated carbon media, but mass balance calculations indicated that more than 99.5% of the total RDX entering the acetic acid-fed FBR was biologically degraded. Approximately 80% of the RDX fed to the control FBR (i.e., no substrate addition) was accounted for at the end of the study; the remainder was assumed to have been degraded. Molasses was much less effective than acetic acid as an electron donor for treatment of perchlorate and RDX. This work demonstrates that combined treatment of perchlorate and RDX is feasible using FBR technology, and that very low levels of perchlorate (less than 100 ,g/L) can be effectively treated in an FBR. [source]

Atomic Layer Deposition of UV-Absorbing ZnO Films on SiO2 and TiO2 Nanoparticles Using a Fluidized Bed Reactor,

ADVANCED FUNCTIONAL MATERIALS, Issue 4 2008
David M. King
Atomic layer deposition (ALD) was used to apply conformal, nanothick ZnO coatings on particle substrates using a fluidized bed reactor. Diethylzinc (DEZ) and water were used as precursors at 177,°C. Observed growth rates were ca. 2.0 Å/cycle on primary particles as verified by HRTEM. ICP-AES and XPS were used to quantify Zn:substrate ratios. Layers of 6, 18, and 30 nm were deposited on 550 nm SiO2 spheres for UV blocking cosmetics particles. TiO2 nanoparticles were coated in the second part of this work by ZnO shells of 2, 5, and 10 nm thickness as novel inorganic sunscreen particles. The specific surface area of powders changed appropriately after nanothick film deposition using optimized conditions, signifying that high SA particles can be functionalized without agglomeration. The ZnO layers were polycrystalline as deposited and narrowing of the FWHM occurred upon annealing. Annealing the ZnO-TiO2 nanocomposite powder to 600,°C caused the formation of zinc titanate (Zn2TiO4) in both oxygen-rich and oxygen-deficient environments. The non-ideal surface behavior of the DEZ precursor became problematic for the much longer times required for high surface area nanoparticle processing and results in Zn-rich films at this growth temperature. In situ mass spectrometry provides process control capability to functionalize bulk quantities of nano- and ultrafine particles without significant precursor waste or process overruns. ZnO overlayers can be efficiently deposited on the surfaces of primary particles using ALD processing in a scalable fluidized bed reactor. [source]

A Palladium Wall Coated Microcapillary Reactor for Use in Continuous Flow Transfer Hydrogenation

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010
Christian
Abstract Herein we describe the preparation of a novel continuous flow multi-channel microreactor in which the internal surface has been functionalised with a palladium coating, enabling its use in catalytic heterogeneous liquid-phase reactions. Simple chemical deposition techniques were used to immobilise palladium(0) on the channel wall surface of a polymeric multi-capillary extrudate made from ethylene-vinyl alcohol copolymer. The Pd coating of the microcapillaries has been characterised by mass spectrometry and light and electron microscopy. The functional activity of the catalytic Pd layer was tested in a series of transfer hydrogenation reactions using triethylsilane as the hydrogen source. [source]

Polyurethane- and Polystyrene-Supported 2,2,6,6-Tetramethyl- piperidine-1-oxyl (TEMPO); Facile Preparation, Catalytic Oxidation and Application in a Membrane Reactor

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2008
Muhammad Afzal Subhani
Abstract In this contribution, the facile synthesis of two new polymer-supported 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) catalysts and their application in the catalytic oxidation of alcohols to carbonyl compounds are described. For attachment of the TEMPO group to the polymer an isocyanate functionalized polymer is chosen. This new approach facilitates the synthesis in comparison with previously existing methods which generally require deprotonation of TEMPO prior to reaction with the polymer. Following this approach, polyurethane (PU)- and polystyrene (PS)-based TEMPO catalysts are prepared in a one-step reaction from commercially available compounds. Both polymer-supported catalysts showed promising yields for a variety of substrates using inorganic and/or organic co-oxidants in biphasic and/or monophasic systems. The recyclability of the corresponding catalysts was studied in repetitive batch experiments using filtration or distillation depending on the support type. Furthermore, application of the homogeneous polyurethane-supported TEMPO for the selective oxidation of benzyl alcohol in a continously operated membrane reactor is demonstrated. [source]

Microstructural investigation of low-dose neutron irradiation effects in martensitic steels for nuclear application by means of small-angle neutron scattering

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007
Rainer Lindau
The microstructural effect of low-dose neutron irradiation and subsequent high-temperature tempering in the reduced activation ferritic/martensitic steel F82H-mod. (7.73 Cr, 0.09 C, 0.08 Mn, 0.19 V, 2.06 W, 0.02 Ta, wt%, bal. Fe) has been studied using small-angle neutron scattering (SANS). The investigated samples were irradiated with thermal neutrons at 523,K, to dose levels of 2.4 displacements per atom then tempered for 2,h at 1043,K. The SANS measurements were carried out at the D22 instrument of the High Flux Reactor at the Institut Max von Laue,Paul Langevin, Grenoble, France. The differences observed in nuclear and magnetic small-angle neutron scattering cross-sections after subtraction of the reference sample from the irradiated one suggest that the irradiation and the subsequent post-irradiation tempering produce the growth of non-magnetic precipitates; the results are also compared with those obtained on other ferritic/martensitic steels, with different chemical composition, irradiated under the same conditions. [source]

Polymer-acid solutions: Their use for the enhancement of oil reservoir stimulation

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2008
Mohammed M. Amro
Abstract A reduction in permeability occurring around the wellbore resulting from drilling, completion and/or workover fluids increases the flow resistance to the petroleum reservoir fluids and is defined as formation damage. Acidizing process removes near-wellbore damage and enhances hydrocarbon production from producing wells. This study investigates the effect of adding polymer as a retarding agent to acid solutions to slow and control the reaction in matrix acidizing treatment of carbonate rocks. Two different polymers, polyacrylamide (PAA) and polysaccharide (xanthan) and two different acids, acetic acid and formic acid, were used through this study. The results revealed that the presence of PAA did not change the viscosity of the acid solution significantly, while the viscosity of xanthan-acid solutions was decreased with increasing the acid concentration. Additionally, the reaction of polymer-acid solutions with the rock material was monitored under microscope. Original rock samples obtained from Saudi reservoirs containing mainly carbonate were used in the reaction. The PAA-acid solution did not show any decrease in the reaction rate compared to that of acid solution. Thus, the PAA solution applied in this study is not recommended as a retarder. However, xanthan-acid solutions showed a significant decrease in the reaction time. Therefore, xanthan was selected to perform further investigations in Rotating Disk Reactor at different pressures. Scanning electronic microscopy (SEM) was conducted on pretreated and posttreated rock samples. This provides the opportunity to perform a detailed description of the rock surface and facilitates the identification of the changes occurring due to polymer-acid treatment. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Hydrodynamic Cavitation to Improve Bulk Fluid to Surface Mass Transfer in a Nonimmersed Ultraviolet System for Minimal Processing of Opaque and Transparent Fluid Foods

JOURNAL OF FOOD SCIENCE, Issue 9 2007
P.J. Milly
ABSTRACT:, Ultraviolet (UV)-induced chemical reactions and inactivation of microorganisms in transparent and opaque fluids are strongly dependent upon the homogenous exposure of the target species to the UV irradiation. Current UV technologies used in water disinfection and food preservation applications have limited efficacy due to suspended particles shading target species. An Ultraviolet-Shockwave PowerÔ Reactor (UV-SPR) consisting of an inner rotating rotor and a stationary quartz housing and 2 end plates was used to induce ,controlled cavitation.' Eight UV low-pressure mercury lamps spaced uniformly were installed lengthwise around the quartz housing periphery. A KI to I3,chemical dosimeter for UV was used to quantify photons received by fluid in the annular space of the SPR. UV dose (J/m2) increased from 97 J/m2 at 0 rpm to over 700 J/m2 for SPR speeds above 2400 rpm. Inactivation of E. coli 25922 in apple juice and skim milk in the UV-SPR at exit temperatures below 45 °C was greater than 4.5 and 3 logs, respectively. The UV-SPR system proved successful in increasing the mass transfer of transparent and opaque fluid to the UV irradiated surface. [source]

Application of a Plasma Reactor to Modify Egg Ovalbumin for Improved Solubility

JOURNAL OF FOOD SCIENCE, Issue 1 2001
G.H. Gao
ABSTRACT: A Plasma reactor was used to change the surface structure of ovalbumin and enhance solubility. The gases used to generate the plasmas were air, argon, nitrogen and oxygen. Ovalbumin was exposed to the gases for 10, 20, 30, 60, and 120 min. Unexposed ovalbumin served as the control. Samples were examined by polyacrylamide gel electrophoresis (PAGE), spectrophotometry, fluorometry, differential scanning calorimetry, and circular dichroism. Solubility and hydrophobicity of ovalbumin increased with exposure time, whereas endothermic enthalpy, onset PAGE. No change in CD spectra resulted from the plasma treatment. The structural changes were regarded as conformational adaptability. [source]

99Mo shortage in nuclear medicine: crisis or challenge?

JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 4 2010
James R. Ballinger
Reactor produced 99Mo is the source of 99mTc used in 85% of nuclear medicine studies but the worldwide supply is currently very fragile. This has forced radiopharmaceutical scientists to make more efficient use of available 99Mo, to explore new routes to produce it, and to develop alternative agents such as 68Ga complexes. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Fast and Almost Complete Nitridation of Mesoporous Silica MCM-41 with Ammonia in a Plug-Flow Reactor

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2010
Fumitaka Hayashi
The title reaction proceeded well to yield silicon (oxy)nitride at 973,1323 K using a plug-flow reactor. The degree of nitridation was studied as a function of temperature and time of nitridation, the sample weight, and the flow rate of ammonia. It was dependent on the reaction temperature and the amount of ammonia supplied per sample weight. The nitridation at 1273 K for 10,25 h yielded the oxynitride with 36,39 wt% nitrogen, which was very close to 40 wt% of Si3N4. Characterization with X-ray diffraction, field-emission scanning electron microscopy and transmission electron microscopy measurements, and nitrogen adsorption revealed the conversion of MCM-41 to the corresponding oxynitride without essential loss of the mesoporous structure, the decrements of the lattice constant and the pore diameter by 20,35%, and the increments of the wall thickness by ca. 45%. Solid-state 29Si nuclear magnetic resonance spectra during the nitridation clearly showed fast decrease in SiO4 species and slow in SiO3(OH). Various intermediate species, SiOxNy(NH2 or NH)z, were observed to be formed and finally, ca. 70% SiN4 species, ca. 20% SiN3(NH2 or NH), and ca. 10% SiON2(NH2 or NH) were produced, being consistent with the results of the above mentioned elemental analysis. [source]

Synthesis of Zirconia Nanoparticles in a Continuous-Flow Microwave Reactor

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2008
Federica Bondioli
Monodispersed zirconia colloidal spherical nanoparticles were synthesized from the hydrolysis and condensation of tetra- n -propylzirconate by using a continuous microwave synthesis process. The flow rate was varied from 50 to 100 mL/min in order to establish the optimum conditions required to obtain unagglomerated zirconia nanopowders. The results were compared with those obtained in batch systems. In particular as the flow rate is decreased from 100 to 50 mL/min the particle became spherical with a mean particle size of about 100 nm. [source]

Biological Treatment of Sludge from a Recirculating Aquaculture System Using a Sequencing Batch Reactor

JOURNAL OF THE WORLD AQUACULTURE SOCIETY, Issue 4 2005
Ramaraj Boopathy
[source]

Nitroxide-Mediated Bulk and Miniemulsion Polymerization in a Continuous Tubular Reactor: Synthesis of Homo-, Di- and Triblock Copolymers

MACROMOLECULAR REACTION ENGINEERING, Issue 3-4 2010
Thomas E. Enright
Abstract In previous work, a modified nitroxide-mediated miniemulsion polymerization was demonstrated in a continuous tubular reactor to prepare a latex of polystyrene homopolymer dispersed in water. There, the initial reaction step (low conversion bulk polymerization to prepare the macroinitiator) was done in a batch reactor while the miniemulsion polymerization step was done in a continuous tubular reactor. The present paper describes an extension of that work in which all the reaction steps have been achieved in the continuous tubular reactor. Chain extension of the polystyrene latex to give polystyrene- block -poly(butyl acrylate) diblock and polystyrene- block -poly(butyl acrylate)- block -polystyrene triblock copolymers is also described. [source]

Design and Implementation of a Novel Quench Flow Reactor for the Study of Nascent Olefin Polymerisation

MACROMOLECULAR REACTION ENGINEERING, Issue 2 2007
Audrey Di Martino
Abstract A novel stopped flow reactor system is described in the current work, along with the underlying design philosophy. While the concept of stopped flow technology is not recent, this system is the first to be designed with the objective of studying particle morphology, and to work at extremely short (40 ms) residence times. It is shown that traditional chemical engineering principles are required to properly design and operate this type of reactor, and that when correctly design, it is a very flexible tool for the study of nascent polymerisation of olefins. [source]

How Can the United States Take the Initiative in the Current North Korean Nuclear Crisis?

PACIFIC FOCUS, Issue 2 2005
Jin H. Pak
On September 19, 2005, the last day of the fourth round of six-party talks, a deal was announced in which North Korea pledged to end its nuclear program in return for a number of concessions. Within 24 hours of that announcement, North Korea clarified its position by stating that the United States "should not even dream" it would dismantle its nuclear weapons until it receives a light-water nuclear reactor. Despite four rounds of six-party talks over a three year period, it seems that almost no real progress has been made, except for North Korea; US intelligence officials estimate that North Korea could have made as many as 8 or 9 nuclear weapons already. So it seems North Korea has cleverly increased its bargaining position vis-à-vis the United States. As lengthy negotiations over the provision of a Light Water Reactor (LWR) will undoubtedly ensue, it can use that time to steadily increase its nuclear deterrent. Why did the United States agree to this sub-optimal outcome? Why was it so difficult for the United States to exert more influence on North Korea and the other countries in the six-party talks? The answer to these questions lies in the changing trends affecting Northeast Asian security dynamics. For various reasons that this article will explain, these trends affect the ability of the United States to take the initiative in the ongoing North Korean nuclear crisis. As long as the United States fails to account for various changes in Northeast Asian regional dynamics, its strategy will to deter North Korea from continuing its nuclear program will not succeed. [source]

Deposition of Cubic Boron Nitride in a Supersonic Plasma Jet Reactor with Secondary Discharge

PLASMA PROCESSES AND POLYMERS, Issue S1 2007
Jami McLaren
Abstract We have deposited cubic boron nitride thin films with a supersonic plasma jet chemical vapor deposition system with bipolar pulsed substrate bias. Deposited films were characterized by Fourier transform infrared spectroscopy, micro-X-ray diffraction, and scanning electron microscopy. The cubic boron nitride content is observed to scale well with the degree of ion bombardment of the substrate and growing film, which is affected most drastically by the substrate bias pulse frequency, and positive and negative duty cycle. The magnitude of the negative substrate bias was also critical in depositing cubic boron nitride, with a threshold voltage of approximately 90 V necessary for cubic boron nitride deposition. [source]

Numerical Simulation of Fluid Flow and Enzyme Catalysed Substrate Conversion in a Packed-bed Enzyme Reactor

PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003
Ö. Özmutlu M. Sc.
This numerical study evaluates the momentum and mass transfer in an immobilized enzyme reactor. The simulation gives detailed information of the local substrate and product concentrations with respect to external and internal transport limitations. The flow field characterization of the system makes it possible to understand fluid mechanical properties and its importance on transport processes. With the obtained data it is also possible to detect zones of high, low and latent enzymatic activity and to determine whether the conversion is limited due to mass transfer or reaction resistances. [source]

A Study on Hydrodynamics and Heat Transfer in a Bubble Column Reactor with Yeast and Bacterial Cell Suspensions

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2005
Nigar Kantarci
Abstract Hydrodynamics and heat transfer experiments were carried out in a slurry bubble column with air-water-yeast cells and air-water-bacteria cells systems to investigate gas hold-up, bubble characteristics and heat transfer coefficients with cell concentrations of 0.1% w/w and 0.4% w/w and superficial gas velocity up to 0.20 m/s. The gas hold-ups and heat transfer coefficients were found to increase with increasing gas velocity and cell concentration. The heat transfer coefficients were higher at the centre of the column as compared to the near wall region. The development of empirical correlations to predict the heat transfer coefficient in two- and three-phase systems was carried out with ±15% confidence interval at most. On a réalisé des expériences d'hydrodynamique et de transfert de chaleur dans une colonne triphasique gaz-liquide-solide avec des systèmes de cellules air-eau-levure et de cellules air-eau-bactéries afin d'étudier la rétention de gaz, les caractéristiques des bulles et les coefficients de transfert de chaleur avec des concentrations de cellules de 0,1 % en poids et 0,4 % en poids et des vitesses de gaz superficielles jusqu'à 0,20 m/s. On a trouvé que les rétentions de gaz et les coefficients de transfert de chaleur augmentaient avec la vitesse de gaz et la concentration en cellules. Les coefficients de transfert de chaleur sont plus grands au centre de la colonne que dans la région proche de la paroi. Des corrélations empiriques pour prédire le coefficient de transfert de chaleur dans des systèmes bi et triphasiques ont été établies avec un écart de confiance inférieur ou égal à ± 15%. [source]

Decolorization of RR-120 Dye Using Ozone and Ozone/UV in a Semi-Batch Reactor

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2004
Mohammad Kazemi
Abstract Treatability of RR-120 aqueous dye solutions using O3 and O3/UV was studied in a bench scale set-up. Reduction in colour and chemical oxygen demand (COD) under various pH and initial dye concentrations were investigated. Pseudo first order reaction rate was satisfactorily used for kinetic interpretations in destruction of the dye. The results showed that decolorization with O3 was faster at neutral pH values. While use of UV had a small effect on ozonation at low pH values, UV radiation had a considerable effect at pH values of 7 and above. It was found that ozone utilization efficiency of higher than 95% could be attained in the experimental set up. On a étudié la possibilité de traitement de solutions aqueuses de colorant RR-120 à l'aide d'O3 et O3/UV dans un banc d'essai. La réduction de la demande chimique en oxygène (DCO) et en colorant a été étudiée pour différentes concentrations initiales de colorant. La vitesse de réaction du pseudo-premier ordre a été utilisée avec succès pour les interprétations cinétiques de la destruction du colorant. Les résultats montrent que la décoloration avec l'O3 est plus rapide à des valeurs de pH neutres. Alors que le recours aux UV a un faible effet sur l'ozonation à de faibles valeurs de pH, la radiation par UV a un effet considérable à des valeurs de pH de 7 et au-dessus. On a trouvé qu'une efficacité d'utilisation de l'ozone supérieure à 95% pouvait être atteinte dans l'installation expérimentale. [source]

Selectivity, Hydrodynamics and Solvent Effects in a Monolith Cocurrent Downflow Contactor (CDC) Reactor

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003
Mike Winterbottoma
Abstract The liquid phase hydrogenation of 2-butyne-1,4-diol (B) to cis-2-butene-1,4,-diol (C) was studied in a Monolith (CDC) Reactor. The effect of temperature, pressure, different solvents and gas and liquid feed rates on reaction rate and selectivity was determined. RTD measurements were made under different hydrodynamic conditions. The liquid flow was largely laminar with evidence of a stagnant wall film. Selectivity to C was observed to increase with hydrogen pressure and approaches 1 at high superficial gas velocities and conversion of B (>95%) as plug flow is approached. The flow regime was of influence on selectivity and kinetics, which was described by a dual site Langmuir-Hinshelwood mechanism. L'hydrogénation en phase liquide du butyne-2-diol-1,4 B en cis-butène-2-diol-1,4 C a été étudiée dans un réacteur à monolithe (CDC). On a déterminé l'effet de la température, de la pression, des différents solvants et des vitesses d'alimentation de gaz et de liquide sur la vitesse de réaction et la sélectivité. Des mesures de distribution de temps de séjour ont été effectuées pour différentes conditions hydrodynamiques. L'écoulement du liquide est largement laminaire avec un film de paroi stagnant évident. On a observé que la sélectivité pour C augmentait avec la pression de l'hydrogène et s'approchait de 1 à des vitesses de gaz superficielles élevées et à conversion de B élevée (>95%) quand l'écoulement piston devient piston. Le régime d'écoulement a une influence sur la sélectivité et la cinétique, et celle-ci est bien décrite par un mécanisme à site double de Langmuir-Hinshelwood. [source]

Oxidative Coupling of Methane in a Negative DC Corona Reactor at Low Temperature

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2003
Faezeh Bagheri-Tar
Abstract Oxidative coupling of methane (OCM) in the presence of DC corona is reported in a narrow glass tube reactor at atmospheric pressure and at temperatures below 200°C. The corona is created by applying 2200V between a tip and a plate electrode 1.5 mm apart. The C2 selectivity as well as the methane conversion are functions of methane-to-oxygen ratio, gas residence time, and electric current. At CH4/O2 ratio of 5 and the residence time of about 30 ms, a C2 yield of 23.1% has been achieved. The main products of this process are ethane, ethylene, acetylene as well as CO and CO2 with CO/CO2 ratios as high as 25. It is proposed that methane is activated by electrophilic oxygen species to form methyl radicals and C2 products are produced by a consecutive mechanism, whereas COx is formed during parallel reactions. On décrit le couplage oxydant du méthane (OCM) en présence d'une couronne CC dans un réacteur tubulaire étroit en verre à la pression atmosphérique et à des températures en dessous de 200°C. La couronne est créée en appliquant 2200 V entre une pointe et une électrode plate distantes de 1,5 mm. La sélectivité du C2 ainsi que la conversion du méthane sont des fonctions du rapport méthane-oxygène, du temps de séjour du gaz et du courant électrique. À un rapport de CH4/O2 de 5 et un temps de séjour d'environ 30 ms, un rendement de C2 de 23,1 % est obtenu. Les principaux produits de ce procédé sont l'éthane, l'éthylène, l'acétylène, ainsi que le CO et le CO2 avec des rapports de CO/CO2 aussi élevés que 25. On propose l'idée que le méthane est activé par des espèces d'oxygène électrophiles pour former des radicaux de méthyle et que les produits du C2 sont produits par un mécanisme consécutif, tandis que les COx se forment lors de réactions parallèles. [source]

Carbon Monoxide Mass Transfer for Syngas Fermentation in a Stirred Tank Reactor with Dual Impeller Configurations

BIOTECHNOLOGY PROGRESS, Issue 3 2007
Andrew J. Ungerman
This study compares the power demand and gas-liquid volumetric mass transfer coefficient, kLa, in a stirred tank reactor (STR) (T = 0.211 m) using different impeller designs and schemes in a carbon monoxide-water system, which is applicable to synthesis gas (syngas) fermentation. Eleven different impeller schemes were tested over a range of operating conditions typically associated with the "after large cavity" region (ALC) of a Rushton-type turbine (D/T = 0.35). It is found that the dual Rushton-type impeller scheme exhibits the highest volumetric mass transfer rates for all operating conditions; however, it also displays the lowest mass transfer performance (defined as the volumetric mass transfer coefficient per unit power input) for all conditions due to its high power consumption. Dual impeller schemes with an axial flow impeller as the top impeller show improved mass transfer rates without dramatic increases in power draw. At high gas flow rates, dual impeller schemes with a lower concave impeller have kLa values similar to those of the Rushton-type dual impeller schemes but show improved mass transfer performance. It is believed that the mass transfer performance can be further enhanced for the bottom concave impeller schemes by operating at conditions beyond the ALC region defined for Rushton-type impellers because the concave impeller can handle higher gas flow rates prior to flooding. [source]

Hydrogenogenic CO Conversion in a Moderately Thermophilic (55 °C) Sulfate-Fed Gas Lift Reactor: Competition for CO-Derived H2

BIOTECHNOLOGY PROGRESS, Issue 5 2006
Jan Sipma
Thermophilic (55 °C) sulfate reduction in a gas lift reactor fed with CO gas as the sole electron donor was investigated. The reactor was inoculated with mesophilic granular sludge with a high activity of CO conversion to hydrogen and carbon dioxide at 55 °C. Strong competition for H2 was observed between methanogens and sulfate reducers, while the homoacetogens present consumed only small amounts of H2. The methanogens appeared to be more sensitive to pH and temperature shocks imposed to the reactor, but could not be completely eliminated. The fast growth rates of the methanogens (generation time of 4.5 h) enabled them to recover fast from shocks, and they rapidly consumed more than 90% of the CO-derived H2. Nevertheless, steep increases in sulfide production in periods with low methane production suggests that once methanogenesis is eliminated, sulfate reduction with CO-rich gas as electron donor has great potential for thermophilic biodesulfurization. [source]

Xylitol Production from Sugarcane Bagasse Hydrolyzate in Fluidized Bed Reactor.

BIOTECHNOLOGY PROGRESS, Issue 4 2003
Effect of Air Flowrate
Cells of Candida guilliermondiiimmobilized onto porous glass spheres were cultured batchwise in a fluidized bed bioreactor for xylitol production from sugarcane bagasse hemicellulose hydrolyzate. An aeration rate of only 25 mL/min ensured minimum yields of xylose consumption (0.60) and biomass production (0.14 gDM/gXyl), as well as maximum xylitol yield (0.54 gXyt/gXyl) and ratio of immobilized to total cells (0.83). These results suggest that cell metabolism, although slow because of oxygen limitation, was mainly addressed to xylitol production. A progressive increase in the aeration rate up to 140 mL/min accelerated both xylose consumption (from 0.36 to 0.78 gXyl/L·h) and xylitol formation (from 0.19 to 0.28 gXyt/L·h) but caused the fraction of immobilized to total cells and the xylitol yield to decrease up to 0.22 and 0.36 gXyt/gXyl, respectively. The highest xylitol concentration (17.0 gXyt/L) was obtained at 70 mL/min, but the specific xylitol productivity and the xylitol yield were 43% and 22% lower than the corresponding values obtained at the lowest air flowrate, respectively. The concentrations of consumed substrates and formed products were used in material balances to evaluate the xylose fractions consumed by C. guilliermondii for xylitol production, complete oxidation through the hexose monophosphate shunt, and cell growth. The experimental data collected at variable oxygen level allowed estimating a P/O ratio of 1.35 molATP/molO and overall ATP requirements for biomass growth and maintenance of 3.4 molATP/C-molDM. [source]

Influence of Hydrodynamic Conditions on Biofilm Behavior in a Methanogenic Inverse Turbulent Bed Reactor

BIOTECHNOLOGY PROGRESS, Issue 3 2003
S. Michaud
This paper presents a study about the influence of gas velocity on a methanogenic biofilm in an inverse turbulent bed reactor. Experimental results indicate a dynamic response of the growing attached biomass to the changes of hydrodynamic conditions, mainly attrition constraints. Short but intensive increases of gas velocity (Ug) are shown to induce more detachment than a high but constant gas flow rate. Hydrodynamic conditions control the composition of the growing biofilm in terms of cells and exocellular polymeric substances (EPS). The cell fraction within the biofilm (Rcell) was found to be inversely proportional to the gas velocity. The specific activity expressed in methane production rate or COD removal rate is higher in biofilms formed under high hydrodynamic constraints. The control of the hydrodynamic conditions in a biofilm reactor should make it possible to obtain a resistant and active biofilm. [source]