Showing papers on "Packed bed published in 2001"

Microfabricated multiphase packed-bed reactors : Characterization of mass transfer and reactions

Abstract: A microchemical device has been built in silicon and glass by using microfabrication methods including deep-reactive-ion etch technology, photolithography, and multiple wafer bonding. The microchemical system consists of a microfluidic distribution manifold, a microchannel array, and a 25-μm microfilter for immobilizing solid particulate material within the reactor chip and carrying out different heterogeneous chemistries. Multiple reagent streams (specifically, gas and liquid streams) are mixed on-chip, and the fluid streams are brought into contact by a series of interleaved, high-aspect-ratio inlet channels. These inlet channels deliver the reactants continuously and cocurrently to 10 reactor chambers containing standard catalytic particles. The performance of the microfabricated “packed-bed” reactor is compared to that of traditional multiphase packed-bed reactors in terms of fluid flow regimes, pressure drop, and mass transfer. The hydrogenation of cyclohexene is used as a model reaction to measure t...

Microfabricated packed‐bed reactor for phosgene synthesis

Abstract: A silicon micropacked-bed reactor for phosgene synthesis is demonstrated as an example of the potential for safe on-site/on-demand production of a hazardous compound. Complete conversion of chlorine is observed for both a 2:1 CO/Cl 2 feed at 4.5 std.cm 3 /min and a 1:1 feed at 8 std.cm 3 /min. The latter gives a projected productivity of ∼100 kg/yr from a 10-channel microreactor, with the opportunity to produce significant quantities through operating many reactors in parallel. The versatility of silicon microfabrication technology for producing reactors for corrosive gases is demonstrated by a protective oxide coating formed during reactor fabrication. The increased heat and mass transfer inherent at the submillimeter reactor length scale provides a larger degree of safety, control, and suppression of gradients than is available in macroscale systems. These advantages are also explored in the extraction of chemical kinetics from microreactor experiments. The preexponential factor and apparent activation energy for phosgene formation are determined demonstrating the utility of micropacked-bed reactors as laboratory research tools.

Pressure‐Flow Relationships for Packed Beds of Compressible Chromatography Media at Laboratory and Production Scale

Abstract: Pressure drop across chromatography beds employing soft or semirigid media can be a significant problem in the operation of large-scale preparative chromatography columns The shape or aspect ratio (length/diameter) of a packed bed has a significant effect on column pressure drop due to wall effects, which can result in unexpectedly high pressures in manufacturing Two types of agarose-based media were packed in chromatography columns at various column aspect ratios, during which pressure drop, bed height, and flow rate were carefully monitored Compression of the packed beds with increasing flow velocities was observed An empirical model was developed to correlate pressure drop with the aspect ratio of the packed beds and the superficial velocity Modeling employed the Blake-Kozeny equation in which empirical relationships were used to predict bed porosity as a function of aspect ratio and flow velocity Model predictions were in good agreement with observed pressure drops of industrial scale chromatography columns A protocol was developed to predict compression in industrial chromatography applications by a few laboratory experiments The protocol is shown to be useful in the development of chromatographic methods and sizing of preparative columns

Gas-Phase Mass Transfer in a Centrifugal Contactor

Abstract: The liquid-side mass transfer rate in a centrifugal gas-liquid contactor has been reported to be several times higher than that in conventional packed beds. However, no direct measurement of the gas-side mass transfer coefficient has been reported. We present experimental studies on gas-side mass transfer in a rotating packed bed with wire-gauze packing. Contrary to expectations, the gas-side mass transfer coefficient was much lower than that in conventional packed columns. An analysis of the gas flow, based on the equations of motion, revealed that the gas undergoes solid-body-like rotation in the rotor because of the drag offered by the packing. Therefore, the mass transfer coefficient should be in the same range as that in conventional packed columns. The lower value of the coefficient found experimentally is attributed to liquid maldistribution. The possibility of enhancing the mass transfer coefficient by enhancing the slip between the gas and the packing was explored by using a stack of closely spaced disks as the packing. Mass transfer studies with a pair of disks were conducted. Higher throughputs and mass transfer rates than those with the wire-gauze packing were obtained. A stack of disks as packing appears to hold promise.

Synthesis and Hydrolysis of Methyl Acetate by Reactive Distillation Using Structured Catalytic Packings: Experiments and Simulation

Abstract: Reactive distillation experiments have been performed for the synthesis and hydrolysis of methyl acetate using the structured catalytic packing Katapak-S with an acidic ion-exchange resin (Amberlyst 15) as the heterogeneous catalyst. Three different setups were used: one-feed and two-feed setups for the methyl acetate synthesis and another two-feed setup for the hydrolysis reaction. The influence of several variables, such as reaction kinetics, separation efficiency, residence time distribution, and heat loss, on the simulation results has been studied. Most important is the use of an adequate reaction kinetics, that is, an adsorption-based kinetic model that takes into account the selective swelling of the polymeric catalyst. Only using this model can the synthesis as well as the hydrolysis experiments be simulated within experimental accuracy. With pseudohomogeneous kinetics, only the experiments performed for the synthesis of methyl acetate can be modeled. An equilibrium-stage model is capable of desc...

Catalytic distillation in structured packings: Methyl acetate synthesis

Abstract: Catalytic distillation can improve process design, the design of column internals requires special attention. The catalytic packing MULTIPAK facilitates effective catalysis, high separation efficiency, and a wide loading range simultaneously. In this work the main characteristics of MULTIPAK - pressure drop, loading range, and separation efficiency - are determined experimentally. The developed nonequilibrium stage model developed reflects the complexity of catalytic distillation processes and comprises correlations describing pressure drop and separation efficiency of MULTIPAK as a function of the operating conditions. The model has been implemented in the simulation environment Aspen Custom Modeler, and the simulation results are compared with experimental data for the synthesis of methyl acetate. This model reflects the process behavior, but differences between simulated results and experimental data can still be observed.

Dynamic discharge and performance of a new adsorbent for natural gas storage

Abstract: Performance of a new highly conductive adsorbent matrix for ANG systems was evaluated. The adsorbent composite block (ACB) was a mixture of superactivated carbon, labeled MAXSORB and expanded natural graphite (ENG), followed by consolidation. ENG was used both as a very high conductive matrix and as support for adsorbents. Thermal conductivity is 30 times higher than that of activated carbon packed bed. Dynamic methane discharges were studied experimentally with a 2-L vessel filled with ACB. The influence of both the discharge flow rate and heat-exchange conditions at the reactor wall on the delivered methane capacity was investigated. The modeling of the discharge process, validated from experimental results, shows the efficiency of this ACB with a 100-V/V delivered methane capacity under various working conditions.

Absorption of H2S in NaOCl caustic aqueous solution

Abstract: Pilot plant experimental data were collected to study the feasibility of H 2 S removal from air streams utilizing aqueous solutions. Solutions of NaOCl/NaOH were tested in a packed bed scrubber and found to be effective. An efficiency of 99.2% H 2 S removal was achieved at a gas flow rate of 790 lb/ft 2 -hr and liquid-gas ratio of 5.06. Sodium hydroxide was found to be the active ingredient in the absorption process. A minimum alkalinity of pH 11 in the scrubbing solution was required for the H 2 S to be efficiently absorbed in the packed bed scrubber. For gas flow rates up to 2100 lb/ft 2 -hr, the height of a transfer unit (HTU) varied from 1.8 ft to 2 ft with different proportions of NaOCl and NaOH in the solution.

Anion-exchange capillary electrochromatography with indirect UV and direct contactless conductivity detection.

Abstract: Conductivity detection is applied to ion-exchange capillary electrochromatography (IE-CEC) with a packed stationary phase, using a capacitively coupled contactless conductivity detector with detection occurring through the packed bed. Columns were packed with a polymeric latex-agglomerate anion-exchanger (Dionex AS9-SC). A systematic approach was used to determine suitable eluants for IE-CEC separations using simultaneous indirect UV and direct conductivity detection. Salicylate and p-toluenesulfonate were identified as potential eluant competing anions having sufficient eluotropic strength to induce changes in separation selectivity, but salicylate was found to be unsuitable with regard to baseline stability. It was also found for both indirect UV and direct conductivity detection that homogenous column packing was imperative, and monitoring of the baseline could be used to assess the homogeneity of the packed bed. Using a p-toluenesulfonate eluant, the separation of eight common anions was achieved in 2.5 min. Direct conductivity detection was found to be superior to indirect UV detection with regard to both baseline stability and detection sensitivity with detection limits of 4-25 g/L being obtained. However, the calibration for each anion was not linear over more than one order of magnitude. When using conductivity detection, the concentration of the eluant could be varied over a wider range (2.5-50 mM p-toluenesulfonate) than was the case with indirect UV detection (2.5-10 mM), thereby allowing greater changes in separation selectivity to be achieved. By varying the concentration of p-toluenesulfonate in the eluant, the separation selectivity could be manipulated from being predominantly ion-exchange in nature (2.5 mM) to predominantly electrophoretic in nature (50 mM).

Parametric studies of carbon dioxide absorption into highly concentrated monoethanolamine solutions

Abstract: Carbon dioxide (CO 2 ) absorption into highly concentrated solutions of monoethanolamine (MEA) was studied. The effect of operating parameters on the overall mass transfer coefficient (K G a v ) was determined in a pilot-plant scale absorption unit. The (K G a v ) increased at low solution concentrations, decreased at intermediate concentrations, and increased as the concentration became high (54 wt%). The (K G a v ) increased with an increasing liquid flow rate, decreased with an increase in either the CO 2 loading or the CO 2 partial pressure, and was not affected by the inert gas flow rate. Finally, structured 4A Gempak packing produced (K G a v ) values twice as high as randomly packed IMTP#15 or 16-mm Pall Ring systems.

Porosity distribution in random packed columns by gamma ray tomography

Abstract: Gamma ray tomography experiments have been carried out to detect any spatial patterns in the porosity in a 0.6 m diameter packed column. Three different sizes of stainless steel Pall rings (16, 25 and 38 mm) have been examined. The primary objective is to detect spatial patterns and statistical information on porosity variation in packed distillation columns. Such data are needed in the computational fluid dynamics simulators based on volume averaged equations. Horizontal scans, at different vertical positions of the packed bed, were made for each size of Pall rings. A tomographic reconstruction algorithm has been used to calculate the spatial variation over the column cross section. Radial porosity variation within the packed bed has been determined. The variation of the circumferentially averaged porosity in the radial direction indicates that the porosity in the column wall region is a somewhat higher than that in the bulk region, due to the effect of the column wall. The probability density function for porosity variation has been constructed from the experimental data and it can be represented by a normal distribution.

Holdup, pressure drop, and flooding in packed countercurrent columns for the gas extraction

Abstract: The hydrodynamic behavior, i.e., flooding, liquid holdup, and pressure drop of countercurrent columns with two random packings, Raschig rings and Berl saddles, and two gauze packings, Sulzer CY and Sulzer EX, is scrutinized at temperatures between 313 and 373 K and pressures between 8 and 30 MPa using carbon dioxide as the supercritical solvent and water and olive oil deodorizer distillate as liquid phases. Two models are employed to correlate the experimental data: a sophisticated mechanistic approach based on the liquid holdup and a well-known empirical approach for the flooding point. The experimental data for the dry pressure drop and the liquid holdup below the loading point are successfully correlated using modified models from normal pressure operation. The flooding points can be correlated with good accuracy as well.

Electrodeionization 1: Migration of Nickel ions absorbed in a rigid, Macroporous Cation-exchange Resin

Abstract: The removal of nickel ions from a packed bed of ion-exchange material under an applied potential is studied. This process involves the use of an electrodialysis type cell in which the centre compartment is filled with a packed bed of ion-exchange particles. The bed width, concentration of nickel in the resin and electrolyte concentration were varied. Emphasis was placed on the rate of nickel migration, current efficiency and the effective mobility of nickel in the system. The purpose of the study is to aid in the development of a system for the continuous removal of heavy metal ions from dilute solutions.

Esterification of Acetic Acid with Ethanol Catalysed by an Acidic Ion-Exchange Resin

Abstract: The esterification of acetic acid with ethyl alcohol catalysed by an acidic ion-exchange resin (Amberlyst-15) was carried out in a batch reactor at temperatures between 323 and 353 K at various starting compositions ranging from stoichiometric regime to the dilute regions. The resultant kinetic model fitted the experimental data well. The activation energy was found to be 104129 kJ.kmol-1 for the formation of ethyl acetate. The ethyl acetate production was also carried out in a packed bed reactive distillation column operated in batch and continuous modes. The effects of the variables such as the reflux ratio, vapour rate and feed flow rate on ethyl acetate production were studied experimentally. A packed bed reactive distillation column operated in continuous mode gave the highest ethyl acetate composition, far surpassing the chemical equilibrium at operating conditions.