Showing papers on "Packed bed published in 1996"
TL;DR: In this paper, a mass transfer model was proposed for a variety of commercial structured packings for distillation column service with distillation pressures ranging from 0.33 to 20.4 bar.
Abstract: This is the second part of a two-part paper dealing with the fluid mechanics and mass transfer in structured packings for distillation column service. The first part elucidated pressure drop, flooding, and liquid holdup. The second part covers the generation of effective interfacial area and provides a general correlation for predicting the mass-transfer efficiency as a function of surface type, packing geometry, phase flow conditions, and fluid properties. The mass-transfer model has been tested against a variety of commercial structured packings, for distillation pressures ranging from 0.33 to 20.4 bar. In all cases the fit of the data is excellent, with the possible exception of the highest pressures, where additional factors of axial mixing appear to have an effect.
374 citations
212 citations
TL;DR: In this article, a high-gravity vapor−liquid contactor (Higee) was studied under distillation conditions using a semi-works scale system, where the cyclohexane/nheptane test mixture was used at operating pressures of 166 and 414 kPa and under total reflux conditions.
Abstract: A high-gravity vapor−liquid contactor (“Higee”) was studied under distillation conditions using a semiworks scale system. The cyclohexane/n-heptane test mixture was used at operating pressures of 166 and 414 kPa and under total reflux conditions. Rotational speeds ranged from 400 to 1200 rpm. Data were collected on mass transfer efficiency, pressure drop, and hydraulic capacity. As many as six transfer units were achieved in a bed depth of 21 cm, with efficiency being directly proportional to speed of rotation. Models were developed for mass transfer and pressure drop, and the earlier packed bed flooding model of Sherwood, which includes a gravity term, was found to represent the vapor capacity of the contactor. Sufficient information is given to enable the preliminary design of a system containing a high-gravity vapor−liquid contactor. Because the test mixture has been widely used for conventional contactor studies, means for comparing high-gravity contacting with other methods are now available.
203 citations
TL;DR: In this article, a process for simultaneous reaction and separation of desired products in a single unit operation is described, which uses a fixed packed column of an admixture of a catalyst and a sorbent that selectively removes a reaction byproduct from the reaction zone.
Abstract: A process for carrying out simultaneous reaction and separation of desired products in a single unit operation is described. It uses a fixed packed column of an admixture of a catalyst and a sorbent that selectively removes a reaction by-product from the reaction zone. The sorbent is periodically regenerated by using the principles of pressure-swing adsorption. The process steps allow direct production of the desired product at high purity and at the reaction pressure. High conversion of the reactants to products in an endothermic, equilibrium-controlled reaction can be achieved while operating the reaction at a substantially lower temperature than would be necessary by a plug-flow reactor packed with the catalyst alone. The equilibrium-controlled reverse water-gas shift reaction for the production of carbon monoxide is experimentally evaluated as a proof of the concept.
196 citations
TL;DR: A novel column is described that does not require frits to keep packing material within a capillary, and is an alternative to packed capillary columns which have been used previously in CEC.
Abstract: A novel column is described that does not require frits to keep packing material within a capillary. A continuous bed is prepared in situ in aqueous solution by radical copolymerization of N-isopropylacrylamide and 2-acrylamido-2-methylpropanesulfonic acid (the resultant gel is denoted poly(AMPS-co-IPAAm). N,N'-Methylenebisacrylamide is used for cross-linking. On the application of an electrical field, electroosmotic flow (EOF) is developed in the bed along the capillary, where fluid propulsion would be otherwise difficult to achieve. The resultant EOF transports neutral compounds through the column without forcing the gel out of the capillary. Examination of the fluid motion in the continuous bed using a video microscope system and an image processor shows a relatively flat flow profile of EOF. The bed functions as the stationary phase for reversed-phase capillary electrochromatography (CEC). This new approach is an alternative to packed capillary columns which have been used previously in CEC. A high efficiency is obtained for a steroid which is separated on a 4.0% total monomer concentration (T), 10.0% degree of cross-linking (C), and 10.0% mole fraction of AMPS in the total monomer (S), poly(AMPS-co-IPAAm) column. A mixture of polyaromatic hydrocarbons is separated on a 6.9% T, 5.8% C, and 5.5% S poly(AMPS-co-IPAAm) column. The capacity factor of benzo[a]pyrene increases from 0.63 to 1.91 as the acetonitrile content in a Tris-boric acid buffer is decreased from 45 to 30% (v/v). The run-to-run RSD of analyte migration time is less than 0.73%, and the day-to-day RSD is acceptable. Potential benefits of this approach are also mentioned.
139 citations
TL;DR: In this paper, the mass transfer and pressure drop of a rotating packed bed were investigated under 13−273 equiv of gravitational force with two packings, and the results indicated that the mass-transfer coefficient (KGa) was enhanced due to the centrifugal force as compared to a conventional packed bed.
Abstract: The mass transfer (stripping of ethanol) and pressure drop (water−air) of a rotating packed bed were investigated under 13−273 equiv of gravitational force with two packings. The results indicated that the mass-transfer coefficient (KGa) was enhanced due to the centrifugal force as compared to a conventional packed bed. An empirical correlation was also proposed, suggesting that the KGa value depends on the GrG number to the power of 0.25. As to pressure drop, the gas rate seems to be a more important factor than the liquid rate because of less liquid holdup under centrifugal force. A semiempirical equation was also developed to correlate the pressure drop data with good agreement.
137 citations
TL;DR: The monolithic medium proved to be superior for high-speed separations using very steep gradients at a flow-rate of 20 ml/min and the separation in the column packed with non-porous beads was poor, while higher flow-rates led to an unacceptably high back pressure.
119 citations
TL;DR: In this article, random and structured packings were compared for their efficiency in dehumidification of air in a packed column using lithium chloride solutions, and experiments were conducted with cross corrugated ce...
Abstract: Random and structured packings were compared for their efficiency in dehumidification of air in a packed column using lithium chloride solutions. Experiments were conducted with cross corrugated ce...
112 citations
TL;DR: In this article, the authors evaluated the performance of packed capillary electrochromatography under both pressure and electrically driven conditions and found that the performance was excellent for 5 μm reversed-phase particles.
106 citations
TL;DR: In this article, column efficiencies and van Deemter coefficients were compared for fused silica capillary liquid chromatography columns with inner diameters between 12 and 33 μm with 5 μm octadecylsilane-modified silica particles.
Abstract: Fused silica capillary liquid chromatography columns with inner diameters between 12 and 33 μm were slurry packed with 5 μm octadecylsilane-modified silica particles. Column efficiencies and van Deemter coefficients were compared. A linear decrease of the A term as column diameter was decreased was the most significant contributor to a lower overall plate height at the optimum velocity.
98 citations
TL;DR: The axial and transverse apparent dispersion coefficients of three solvents in two packed chromatographic columns were determined by pulsed-field-gradient nuclear-magnetic resonance in a range of mobile phase velocity as mentioned in this paper.
Abstract: The axial and transverse apparent dispersion coefficients of three solvents in two packed chromatographic columns were determined by pulsed-field-gradient nuclear-magnetic resonance in a range of mobile phase velocity. The column beds were packed with 5-{micro}m particles of porous C18 silica or 30-{micro}m particles of silica. The solvents used were methanol and acetonitrile (in an 80:20 ACN/water solution) in the former and acetone in the latter. The coefficients were determined over a range of particle Peclet numbers from less than 0.1 to approximately 10 in the former case and 40 in the latter. The data obtained with short dispersion times were fitted to the correlations suggested by Giddings, Horvath and Lin, Huber, and Knox. These data agreed well only with the Giddings equation.
TL;DR: In this article, the internal and external pore volumes (hence, porosities) of the columns can easily be determined with accuracy from the plots of the logarithm of the molecular mass of the probes versus their retention volume.
TL;DR: In this article, the mass balance and the use of a packed bed reactor for the electrochemical incineration of human wastes were investigated, and the effect of anodic particle size, flow rate of faeces/urine mixture, height of packed bed, current density and cathode to anode spacing arrangement, on the rate of oxidation of human waste were investigated.
Abstract: There is an increasing interest in the use of electrochemical methods for dealing with pollution problems. This paper deals with the mass balance and the use of a packed bed reactor for the electrochemical incineration of human wastes. Parametric studies were carried out to determine the effect of: (i) anodic particle size, (ii) flow rate of faeces/urine mixture, (iii) height of packed bed, (iv) current density and (v) cathode to anode spacing arrangement, on the rate of oxidation of human waste. It is shown that particles of Ebonex™ (0.5–1.0 mm diam.) coated with a catalyst layer, comprising SnO2/Sb2O3, a solution flow rate of 0.9–1.4 cm s−1 through the packed bed based on the cross sectional area of the reactor, a bed height of 5–8 cm and a current density based on the geometric area of the particles of 5 mA cm−2 comprise an optimum set of parameters for the scale-up of a packed-bed electrochemical reactor system. A preliminary design for the further scale up of the process is also described.
TL;DR: In this paper, the authors compared the destruction efficiency of either borosilicate or zirconia oxide (ZrO2) packing materials in dry and moist air, and nitrogen buffer gases.
Abstract: The destruction of low concentrations (<1000 ppm) of gas‐phase carbon tetrachloride (CCl4) using a low‐temperature, dielectric barrier/packed‐bed corona reactor was studied. We compare, in particular, the destruction efficiencies using either borosilicate or zirconia oxide (ZrO2) packing materials in dry and moist air, and nitrogen buffer gases. Measurements of contaminant removal in the effluent gas were made at atmospheric pressure as a function of energy dissipated in the reactor. In dry N2, destruction of CCl4 was most efficient using ZrO2 beads, whereas, in dry air, contaminant removal was approximately equal for borosilicate glass and ZrO2. The presence of water in the gas stream reduced the CCl4 destruction efficiency under all conditions. This reduction was likely a synergistic effect that involves changes in the plasma density, scavenging of low energy secondary electrons, and possible surface passivation. Assuming the primary step in CCl4 destruction is dissociative electron attachment, an estimate of the average density of low energy electrons as a function of input energy was made. We relate the enhancement in CCl4 destruction using the ZrO2 beads in N2 to a slight increase in the number density of low energy secondary electrons. A discussion of the importance of energy density measurements and a useful phenomenological kinetic model consistent with the observed results are presented.
TL;DR: In this article, random and structured packings were studied with varying bed depths in the regenerator and the dehumidifier of a solar-assisted liquid-desiccant system, and the slopes of the log−log plots of mass transfer rate vs solution flow rate were found to be close to 0.8.
Abstract: Random and structured packings were studied with varying bed depths in the regenerator and the dehumidifier of a solar-assisted liquid-desiccant system. The slopes of the log−log plots of mass-transfer rate vs solution flow rate were found to be close to 0.8, which indicated that the conditions for the liquid phase were turbulent for the operating conditions in both contactors. The small intercepts obtained for the Wilson plots indicated that the gas-phase mass-transfer resistance was negligible compared to the liquid-phase mass-transfer resistance. Liquid-phase mass-transfer coefficients for the packed bed alone were obtained by separating the contributions of the other mass-transfer regions in the contactors. The random packing mass transfer coefficients varied from 0.48 to 2 mol/(s m2), while the double-layer, structured packing mass-transfer coefficients varied from 0.018 to 0.035 mol/(s m2). These mass-transfer coefficients were converted into a dimensionless form, utilizing experimentally obtained d...
TL;DR: In this article, a column for capillary electrochromatography may be prepared by packing reversed phase silica-based material using a supercritical fluid carbon dioxide carrier, and the repeatability of retention time, peak area and peak height was measured.
Abstract: Columns for capillary electrochromatography may be prepared by packing reversed phase silica-based material using a supercritical fluid carbon dioxide carrier. Procedures for the in-situ manufacture of frits and UV detection windows, and the wetting of columns are described. The columns were employed in two commercial instruments (and a home-built system), and their properties investigated during the separation of standard mixtures of test compounds. The columns are highly efficient and durable, with reduced plate heights of 1.0–1.4. The repeatability of retention time, peak area and peak height was measured. The influence of applied voltage and column temperature and of electrokinetic injection parameters was explored, along with other practical considerations.
TL;DR: In this article, the performance of laboratory trickle-bed and upflow reactors over a range of operating conditions was compared using the hydrogenation of α-methylstyrene to cumene in hexane solvent.
Abstract: This study compares the performance of laboratory trickle-bed and upflow reactors over a range of operating conditions, using the hydrogenation of α-methylstyrene to cumene in hexane solvent over 2...
TL;DR: In this article, different heat removal mechanisms (conductive, convective and evaporative) were studied in a SSF process using a packed bed reactor with an inert support (Amberlite IRA-900) previously inoculated.
TL;DR: In this paper, a packed bed of 150×3 mm I.D. columns, packed with 1-μm nonporous spherical silica particles, was used to separate soluble synthetic polymers by hydrodynamic chromatography.
01 Jan 1996
TL;DR: In this paper, the self-sustaining combustion wave, occurring when a methane-air mixture is filtered through a porous media, is examined theoretically in a two-temperature model in which external heat losses are taken into account.
Abstract: The self-sustaining combustion wave, occurring when a methane-air mixture is filtered through a porous media, is examined theoretically in this paper. Such processes are characterized by an intense thermal interaction between the gas and the porous material. Due to the interfacial heat transfer, the solid phase is able to redistribute heat absorbed from reaction products to the unburned mixture. In the case of combustion waves cocurrent with the filtration flow, this results in peak temperatures exceeding the adiabatic one for the air-methane mixture. Theoretical treatment is conducted within a two-temperature model in which external heat losses are taken into account. The ignition temperature as the main parameter used in analytical solutions is determined for experimental conditions typical for methane-air mixtures burning under filtration in a packed bed. Analytical expressions predicting the combustion wave velocity and temperature distributions in the wave are derived. The results obtained are confirmed by numerical calculations and compared with related experimental data.
TL;DR: In this paper, the thermohydraulic performance of packed-bed solar air heaters has been investigated and the effective efficiency has been employed to express the net useful thermal energy gain taking into account the equivalent thermal energy required to produce the work energy necessary to overcome the additional friction or hydraulic losses as a result of packing the solar air heater duct with absorber matrices.
TL;DR: In this article, a new UT-3 process has been developed in which all four reactions are carried out adiabatically using a heat carrier vector (steam or an inert gas).
TL;DR: In this paper, axial dispersion coefficients of squalene, benzoic acid, and oleic acid were measured in packed beds using supercritical carbon dioxide as a solvent over the temperature range 313−333 K, pressure range 100−300 bar, and Reynolds number range 2−80.
Abstract: Axial dispersion coefficients of squalene, benzoic acid, and oleic acid were measured in packed beds using supercritical carbon dioxide as a solvent over the temperature range 313−333 K, pressure range 100−300 bar, and Reynolds number range 2−80. Measurements were performed under both horizontal and vertical flow conditions, using a variety of particle sizes, bed diameters, and bed lengths. The axial Peclet numbers obtained for small particles ( 1 mm) could be satisfactorially predicted by literature correlations.
TL;DR: In this paper, a packed bed membrane reactor (PBMR) with Pd/SS-316L composite membranes and Pt-Sn/alumina catalyst pellets was used for de-hydrogenation.
Abstract: Dense Pd/SS-316L composite membranes were prepared using conventional electroless plating and a new synthesis procedure based on electroless plating with osmosis. Membranes from the new synthesis technique have about five times higher hydrogen permeation rate and exhibit better thermal stability. Ethane dehydrogenation reaction was conducted in a packed bed membrane reactor (PBMR) with Pd/SS-316L membrane and Pt-Sn/alumina catalyst pellets. Supra-equilibrium conversions were obtained with a better than 95 % selectivity towards ethylene. The effect of non-uniform distribution of catalyst in pellets was also investigated.
TL;DR: The feasibility of a continuous ethanol fermentation process with immobilizedSaccharomyces cerevisiae cells in a magnetically stabilized bed (MSB) was demonstrated and higher ethanol concentration, ethanol production, and glucose uptake rates than in conventional packed bed reactor were reached.
Abstract: This paper is focused on the possibility to apply the magnetic stabilization technique in bioprocessing. The feasibility of a continuous ethanol fermentation process with immobilizedSaccharomyces cerevisiae cells in a magnetically stabilized bed (MSB) was demonstrated. The fermentation processes were carried out in an external magnetic field, transverse to the fluid flow. The flexibility to change the bed expansion owing to the independent change of the fluid flow and the field intensity (the “magnetization FIRST” mode) permitted the creation of fixed beds with different particle arrangements, which affected the bed porosity, the effective fluid-particle contact area, and the mass transfer processes on the particle-fluid interface. As a result, higher ethanol concentration, ethanol production, and glucose uptake rates than in conventional packed bed reactor were reached.
TL;DR: In this paper, the effects of flow direction of solvent on the fluid-to-particle mass transfer were studied for packed beds of sintered porous pellets of two sizes (diameters of 1 and 2 cm) at conditions supercritical with respect to carbon dioxide using toluene and 1,2-dichlorobenzene as the impregnating solutes.
Abstract: The effects of flow direction of solvent (CO{sub 2}) on the fluid-to-particle mass transfer were studied for packed beds of sintered porous pellets of two sizes (diameters of 1 and 2 cm) at conditions supercritical with respect to carbon dioxide using toluene and 1,2-dichlorobenzene as the impregnating solutes. Dynamic extraction experiments were performed in the laminar flow regime (Re = 8--90) where both free and forced convection modes of mass transfer were found to be significant. Measured mass transfer coefficients showed an almost linear dependence on the Reynolds number (Re{sup {approx}0.9}). Downflow of fluid had a strong effect on accelerating extraction rates, in particular at lower Reynolds numbers and for conditions near the critical point of CO{sub 2}, where natural convection is dominant. Experimental mass-transfer coefficients were well correlated using a single general equation that accounts for both modes of mass transfer (free and forced convection) as well as for upflow or downflow operation (i.e., with gravity opposing or assisting forced convection).
TL;DR: A quantitative analysis of mass transfer combined with biochemical reaction and correlation of experiment with theory is carried out for immobilized cell packed bed reactors for the first time, of use in making realistic engineering estimates of the effect of external mass transfer on the observed reac- tion rates in immobilizedcell bioreactors.
Abstract: A quantitative analysis of mass transfer combined with biochemical reaction and correlation of experiment with theory is carried out for immobilized cell packed bed reactors for the first time. Experimental data on flow rates and pseudo first-order rate constants, k,, , for the continuous bioconversion of sugars to ethanol in an immobilized cell reactor using Saccharornyces cereuisiae cells on activated bagasse chips has been analyzed and compared with theory. Theoreti- cally, first-order reaction kinetics was considered and various external film diffu- sion models of the type jD = K Re-('-") evaluated. The effects of external film diffusion in immobilized cell reactors have been quantified. Various mass transfer correlations were systematically tested and the mass transfer correlation j, = 5.7 R~-0'59 correctly predicted experimental data. Use of this correlation is recom- mended to quantify external film diffusion effects for the continuous bio- conversion of sugars to ethanol in immobilized cell packed bed reactors. Finally, the mass transfer coefficient, k, , was calculated as a function of the mass veloc- ity, G, and the Reynolds number, Re. This study will be of use in making realistic engineering estimates of the effect of external mass transfer on the observed reac- tion rates in immobilized cell bioreactors.
TL;DR: In this article, the authors investigate hydrodynamics and radial heat transfer in packed column with cocurrent downflow of gas and liquid, and propose simple predictive relations for each regime, based on physical phenomena.
TL;DR: In this paper, an experimental and theoretical study of a parallel passage adsorbent contactor is reported, and an expression for the HETP (height equivalent to a theoretical plate) analogous to the van Deemter equation for the packed bed is derived and verified experimentally for the adsorption of several light gases from a helium carrier in an adsorber consisting of parallel sheets of activated carbon fibre adsorbents.
TL;DR: In this article, the authors compared the performance of a single porous hollow-fiber membrane and a gel bead-packed bed under identical conditions from a viewpoint of flow resistance and breakthrough behavior.