Showing papers on "Packed bed published in 1989"

Reactive bed plasma air purification

Abstract: The Reactive Bed Plasma is a novel air purification and material processingevice which may efficiently treat both toxic chemicals and hazardous aerosols. The Reactive Bed Plasma device embodies an active alternating current discharge plasma permeating a dielectric packed bed. Advantages of this device include an increased power efficiency by the elimination of dielectric barriers (characteristic of ozonizer devices); a selectively increased residence time of contaminants in the active plasma zones through interaction with the packing material (analogous to chromotographic separations); also a reduced size and power consumption while maintaining high processing efficiency. Further advantages include greatly increased operating lifetime without failure due to electrical arcing (problematic with ozonizers) or poisoning of the packing surfaces (problematic with adsorbents and catalysts); an achievement of a high processing efficiency at low temperature; a control over plasma air by-product formation; and the promotion of chemical and physical reactions simultaneously in a single device heretofore requiring several vastly different devices (promoting photoionoization, catalytic oxidation, plasma-induced decomposition, combustion, electrostatic precipitation, or plasma etching processes).

Use of an oxygen gas diffusion cathode and a three-dimensional packed bed anode in a bioelectrochemical fuel cell

Abstract: An oxygen gas diffusion electrode was successfully used as a cathode in a bioelectro-chemical fuel cell with 2-hydroxy-1,4-naphthoquinone as redox-mediator and Escherichia coli as biocatalyst. On addition of bacteria to the anode compartment of the fuel cell a rapid increase in the electricity output was observed. With the use of a three-dimensional packed bed anode the electricity output of the cell could be considerably increased.

Periodic separating reactors: Experiments and theory

Abstract: The novel combination of a pressure swing adsorber (PSA) with a periodic flow-forced packed-bed reactor is explored. The device provides integral component separation and reaction. Feed sequences studied for the periodic separating reactor (PSR) were those of rapid, single-bed pressure swing adsorption (RPSA). The experimental investigation employed CO oxidation over a packed bed of supported platinum catalyst and molecular sieve adsorbent. A reaction rate limited model is formulated and solved for a variety of irreversible and reversible reactions. The presence of irreversible chemical reaction is shown to greatly enhance the separation achievable by RPSA alone. For a wide range of inlet CO/O, ratios, CO, production could be increased up to two times over steady-state plug-flow reactor operation, while providing a recycle stream without phase change or extractive procedures. Selectivity and conversion improvements were predicted for multiple reaction systems. Other unusual features of operation, such as separation reversals, were also predicted and observed.

Thermal response of a packed bed of spheres containing a phase-change material

Abstract: A computational model of the transient thermal response of a packed bed of spheres containing a phase-change material (PCM) is presented. A one-dimensional separate phases formulation is used to develop a numerical analysis of the dynamic response of the bed which is subject to the flow of a heat transfer fluid, for arbitrary initial conditions and inlet fluid temperature temporal variations. Phase-change models are developed for both isothermal and nonisothermal melting behaviours. Axial thermal dispersion effects are modelled, including intraparticle conduction (Biot number) effects. Regenerative thermal storage applications involve flow reversals to recover the stored energy; this aspect of operation is included in the present model. Results from the model for a commercial sized thermal storage bed for both the energy storage and recovery periods are presented. Experimental measurements of transient temperature distributions in a randomly packed bed of uniform spheres containing a PCM for a step-change in inlet air temperature are reported for a range of Reynolds number.

Microwave-Induced Plasma as an Elemental Detector for Packed-Column Supercritical Fluid Chromatography

Abstract: The direct introduction of supercritical fluid chromatography effluent from a packed DeltaBond 300 phenyl column with the MIP as an elemental detector, using a high efficiency TM010 cavity, has been employed for SFC separations. A toroidal plasma is sustained in the cavity by using an ICP type torch and an argon auxiliary flow (2 L/min) over all pressures (1500-5000 psi). Methanol modifier concentrations (0-5%) have also been studied. Studies of the effects of CO2 on excitation temperature, electron number density, and analyte emission signals are presented. In addition, the background broad-hand emission signal with 100% CO2 and a methanol modifier up to 5% are presented.

Steady state and dynamic modelling of a packed bed reactor for the partial oxidation of methanol to formaldehyde i. model development

Abstract: Several levels of mathematical models involving one and two dimensions as well as single and multiple phases are used to predict the steady state and dynamic behavior of a packed bed reactor for the partial oxidation of methanol to formaldehyde. Parametric sensitivity is examined for several heat and mass transfer parameters, kinetic parameters, and operating conditions. Yield is compared for various models, and significant differences are observed between the one-dimensional and two-dimensional models. The dynamic behavior after step changes in the operating conditions is found to be qualitatively similar for different models.

Synthesis of methanol in a reactor system with interstage product removal

Abstract: This paper reports the synthesis of methanol carried out in a high-pressure miniplant consisting of two packed tubular reactors in series with a high-temperature interstage product removal. In this way, high per-pass conversions can be achieved, even so high that recycle of nonconverted reactants is not necessary anymore. Methanol was absorbed at reaction temperatures in a countercurrently operated packed bed absorber with tetraethylene glycol dimethyl ether as the solvent, which proved to be efficient and selective. Solvent vapors have no influence on the activity or durability of the cooper catalyst used. A closed absorption-desorption loop has been used for the solvent system. Significant earnings savings and raw material savings are expected for large-scale applications of this system.

Scanning electron microscopic examination of Thiobacillus ferrooxidans on different support matrix materials in packed bed and fluidized bed bioreactors

Abstract: Thiobacillus ferrooxidans was used in fixed-film bioreactors to oxidize ferrous iron to ferric iron. The test support matrix materials included activated carbon particles, glass beads, and ion-exchange resin particles. The experimental systems included a fluidized bed approach, which was evaluated with activated carbon only, and a packed bed approach which was tested with each of the support matrix materials. The colonization of the matrix surface was examined with scanning electron microscopy. There were contrasting differences in the bacterial colonization and accumulation of Fe(III) precipitates on the matrix surface among the test materials. The packed bed activated carbon bioreactor displayed the fastest kinetics and the highest amount of cell sorption as well as the roughest and most porous matrix surface.

Steady state and dynamic modelling of a packed bed reactor for the partial oxidation of methanol to formaldehyde ii. experimental results compared with model predictions

Abstract: Heterogeneous and pseudohomogeneous two-dimensional models are compared to steady state and dynamic experimental data from a packed bed reactor for the partial oxidation of methanol to formaldehyde over an iron oxide-molybdenum oxide catalyst. Highly effective parameter estimation software was used to fit selected model parameters to large sets of experimental data so as to obtain small residuals. Heat transfer parameters which were successful in matching data from experiments without reaction were not capable of fitting data from experiments with reaction, and it was necessary to increase the radial heat transfer for higher temperatures or reaction rates. Axial composition profile data was represented by estimating the preexponential factors and activation energy in a half-order redox rate expression for methanol oxidation. After some decline in catalyst activity, a time-varying axial catalyst activity profile was determined from the data. A redox-type rate expression for the oxidation of formal...

Packed bed thermal dispersion models and consistent sets of coefficients

Abstract: Previous experimental and theoretical work has shown that the numerous one- and two-phase packed bed dispersion models can be regarded to be equivalent in describing important aspects of fixed bed behaviour. This paper is concerned with the problem of how thermal model coefficients for any other model are obtained if a set of reliable coefficients is known for one particular model from experimental results. The results of this analysis agree with observations made during the past decades that the Nusselt numbers are particularly sensitive to small changes of the axial dispersion coefficients and that—depending on the model—they differ considerably. While this is the case for the range of lower Reynolds numbers (say Re

Effective Thermal Conductivity Within Packed Beds of Spherical Particles

Abstract: Five beds of different materials were evaluated to determine the effective thermal conductivity as a function of the mechanical load on the bed, the conductivity of the bed material, and the interstitial gaseous environment surrounding the bed particles. The effective thermal conductivity of the packed beds were found to be dependent upon the thermal conductivity of the bed material and the axial load

Retention of acidic and basic compounds in packed column supercritical fluid chromatography

Abstract: Retention behaviour in supercritical fluid chromatography (SFC) with packed columns has been investigated using various model compounds of different polarity. Capacity ratios and selectivities were determined for basic compounds (xanthine bases), fat-soluble vitamins and carboxylic acids. Many of these compounds are difficult to elute from packed columns when a nonpolar supercritical fluid is used. In this work mobile phases of carbon dioxide and nitrous oxide with alcohol modifiers (methanol and 2-propanol) were used. The dependence of capacity ratios and selectivites on the modifier content of the mobile phase was measured. Retention behaviour of the model compounds was compared for stationary phases of unmodified and chemically modified silica particles. The results can be summarized in some general guidelines for stationary phase selection in packed column SFC.

Method for making a non-extractable stationary phase of polymer within a capillary column

Abstract: A method for coating interior capillary column surfaces, or packing material of a packed column, used for gas chromatography, with a stationary polymer phase that is cross-linked by exposing it to a low-temperature plasma that is uniformly distributed over the column or packing material for a predetermined period of time to effect the desired degree of cross-linking of the coating.

Packed bed gradient generator for high performance liquid chromatography

Abstract: Solvent composition gradients in high performance liquid chromatography (HPLC) are generated with a packed bed gradient generator. Natural dispersion occurs in flow through a bed of particles due to eddy and molecular diffusion. This dispersion changes a sharply defined front between two solvents into a desirable error function type gradient profile at the interface between the solvents. The packed-bed gradient generator is a cylindrical tube filled with chemically inert glass beads. Other axial column contours such as a double taper column or bell-shaped entrance and exit regions can be used to tailor the gradient profile. The static packed-bed gradient generator can be placed either on the low pressure inlet side of the high pressure pump, or the high pressure outlet side of the pump. While low pressure operation may provide added convenience, high pressure operation provides additional pulse dampening ability. The high pressure placement of the packed-bed generator would be the only option for use with syringe pumps common in microbore HPLC.

Solventless injecction for packed column supercritical fluid chromatography

Abstract: The adverse effects of injection solvent strength on microbore packed column SFC band broadening are demonstrated and a solventless injection system that eliminates these effects is introduced. The injection system removes solvent in a GC-like manner using a retention gap and an on-column capillary GC syringe. The analyte is delivered to the analytical column in a solvent-free plug of supercritical fluid mobile phase.

Local solid-liquid mass transfer coefficients in a three-phase fixed bed reactor

Abstract: Experimental data are presented concerning the local solid-liquid mass transfer coefficients in a packed column operated with a cocurrent downflow of gas and liquid. The experiments were carried out for two diameters of spherical particles, with the flow rates of both phases and the physicochemical properties of the liquid varied over a wide range. The experimental results are correlated and compared with the appropriate literature data.

Reduction of volatile organic compounds in aqueous solutions through air stripping and gas‐phase carbon adsorption

Abstract: Aqueous solution of volatile organic compounds (VOC's) is a waste stream of many chemical process industries. Conventionally, it is treated with a costly liquid-phase activated carbon adsorption process. An alternative process is studied, which is the combination of air stripping and gas-phase activated carbon adsorption. The removal of VOC's from waste-water can be as high as 99.8%, using a packed column for air stripping at room temperature. These VOC's include vinyl chloride, carbon tetrachloride, trichlorethylene, 1,1-dichloroethane, toluene, chloroform, 1,1,1-trichloroethane, benzene and xylene. These VOC's are separated from air and recovered through a carbon adsorption-regeneration cycle. The cost of VOC removal and recovery is in the range from $0.457 to $0.899 per 1000 liters.

Inner wall coating of micro-LC columns. Wall effects in LC

Abstract: An elastic inner wall coating in the fused silica capillaries used for Micro-LC (LC on packed fused silica capillary columns) stabilizes the packed bed and thus increases column efficiency and life expectancy. Probably the particles of packing material are partly forced into the elastic polymer layer which thus holds the packing in position. Bonded polymers of very different chemical polarity can be used with equally good results. Variation of the coating layer thickness shows that there is an optimum value around 0.3 μm. A discussion of various wall effects in LC columns is presented. The i.d. of the columns is a most important parameter in this respect.

Continuous Cell Debris Filtration Using A Magnetically Stabilized Fluidized Bed

Abstract: The magnetically stabilized fluidized bed (MSFB) is capable, unlike most column operations, of handling streams with suspended particles The MSFB has the contacting properties of a packed bed and the fluidity of a fluidized bed When cell debris is fed into the column, either filtration or passage of the debris can be obtained depending on the bed height, solids velocity, pH, and liquid composition Removal rates from as high as 99% to as low as 5% have been observed The controlling mechanism of filtration appears to be an electrostatic adsorption of the debris onto the surface of the support Debris/debris adhesion also affects filtration