Showing papers on "Packed bed published in 2007"
TL;DR: The chromatographic performance of a new brand of shell particles is compared to that of a conventional brand of totally porous silica particles having a similar size and finds an excellent agreement considering that the internal tortuosity of the particles might be different, affecting the ratio of the effective diffusivities of the proteins in the two materials.
241 citations
TL;DR: In this article, a new reactor concept for chemical-looping combustion (CLC) is proposed, based on dynamically operated packed bed reactors, and it is demonstrated that a constant, very high temperature air stream can be generated efficiently using packed bed CLC reactors to drive a downstream gas turbine.
Abstract: Chemical-looping combustion (CLC) has emerged as an alternative for conventional power production processes to intrinsically integrate power production and CO2 capture. In this work a new reactor concept for CLC is proposed, based on dynamically operated packed bed reactors. With analytical expressions validated with a more detailed numerical model, it is demonstrated that a constant, very high temperature air stream can be generated efficiently using packed bed CLC reactors to drive a downstream gas turbine. The process consists of alternate oxidation and reduction cycles, intermittently alternated with short periods of mild fluidization of the bed after each cycle to level off temperature and concentration profiles. Oxygen carriers based on nickel, iron, and manganese oxide show the highest potential for use in packed bed CLC. Compared to the interconnected fluidized bed system proposed in the literature (Lyngfelt, A.; Leckner, B.; Mattisson, T. A fluidized-bed combustion process with inherent CO2 separation; application of chemical-looping combustion
239 citations
TL;DR: In this paper, the absorption and desorption of carbon dioxide in aqueous monoethanolamine (MEA) was measured in a rotating packed bed of size 398 mm outside diameter, 156 mm inside diameter, and axial depth 25 mm.
Abstract: The absorption and desorption of carbon dioxide in aqueous monoethanolamine (MEA) was measured in a rotating packed bed of size 398 mm outside diameter, 156 mm inside diameter, and axial depth 25 mm. The effect of lean amine temperature (20 and 40 °C), peripheral rotor gravity (31 and 87 g), and various MEA concentrations were investigated. Using MEA concentrations above 30 wt % achieved lower CO2 penetration levels. This is particularly pronounced for the 100% MEA solution. Comparison with conventional columns showed the advantages of using rotating packed beds in terms of saving size and space and efficient operation.
210 citations
TL;DR: In this paper, the thermal performance of a double glass, double pass solar air heater with a packed bed (DGDPSAHPB) was investigated experimentally and theoretically.
143 citations
TL;DR: The thermal performance of a double-glass double-pass solar air heater with a packed bed (DPSAHPB) above the heater absorber plate was investigated experimentally and theoretically as discussed by the authors.
141 citations
TL;DR: The discussion of the contribution to the HETP of the mass-transfer resistances shows that shell particles exhibit much lower plate heights for large molecular size compounds than do fully porous particles, this advantage increasing with decreasing thickness of the shell.
Abstract: The equations of the general rate model of chromatography and those of simple models (the POR, equilibrium-dispersive, and transport-dispersive models) are derived for beds packed with shell particles. Shell particles are made of a solid, nonporous core surrounded by a shell of a porous material that has properties similar to those of the fully porous materials conventionally used in HPLC. These equations have no algebraic solutions, but the moments of the peaks eluted under linear conditions can be calculated, affording the HETP equation for these columns. The discussion of the contribution to the HETP of the mass-transfer resistances shows that shell particles exhibit much lower plate heights for large molecular size compounds (e.g., peptides and proteins) than do fully porous particles, this advantage increasing with decreasing thickness of the shell. In contrast, the efficiencies of columns packed with shell particles and with fully porous particles having the same diameters are nearly the same for lo...
132 citations
TL;DR: Using columns packed with Halo, a new type of porous silica shell particles, the gain achieved with this principle for peptides of moderate molecular weights and for small proteins is assessed.
Abstract: A shell particle consists of a solid, nonporous core that is surrounded with a shell of a porous solid having essentially the same physicochemical properties as those of the conventional porous particles used as packing media in chromatography. The diameter of the solid core and the thickness of its shell or the external diameter of the particle characterizes the chromatographic properties of the packing material. The potential advantage of this particle structure would be the shorter average path length experienced by solute molecules during their diffusion across the particles of packing material when they are retained. Compounds having slow pore diffusion would exhibit higher efficiencies on columns packed with shell than with conventional, fully porous particles. Using columns packed with Halo, a new type of porous silica shell particles, we assess the gain achieved with this principle for peptides of moderate molecular weights and for small proteins.
121 citations
TL;DR: The hold-up volumes, V(M) of two series of RPLC adsorbents were measured using three different approaches, which consist in weighing the masses of the chromatographic column filled with two distinct solvents of different densities, and the dynamic minor disturbance method (MDM) with binary eluents.
111 citations
TL;DR: Monitoring of pH in the effluent of the column presented the simultaneous release of H+ with the uptake of heavy metals; hence, ion exchange was confirmed to be one of the main biosorption mechanisms.
106 citations
TL;DR: In this paper, the catalytic perovskite hollow fiber membrane (HFMR) was designed and tested for the methane oxidative coupling reaction, and a maximum C2 yield close to 21% can be achieved in the packed hollow fibre membrane reactor.
90 citations
TL;DR: In this paper, the Eley-Rideal (ER) formulation was used for modeling and simulation of the carbon dioxide reforming of methane (CDRM) in a catalytic packed bed reactor over a new Ni/ CeO 2 -ZrO 2 catalyst.
TL;DR: In this article, the impact of using a porous media approximation, neglecting intraparticle gradients, for modeling fixed bed combustion has been investigated by comparing the results from a bed model using the porous media approximations with the results of the same model, where the intraparticles gradients have been taken into account by a two-dimensional particle model.
TL;DR: In this article, the authors investigated the thermal effects during high-pressure charging of a packed bed hydrogen storage tank, where the column is packed with activated IRH3 carbon, which has an average surface area of 2600 m 2 g - 1 and is fed with hydrogen or helium from an external high pressure source, and the temperature at six locations in the storage tank and the pressure value at the bottom of the tank are recorded during the charging stage.
TL;DR: In this paper, the authors present simulations for a 120 ∘ segment of an N = 4 packed tube for the endothermic methane steam reforming reaction and show that the usual assumption of symmetric species and temperature fields inside spherical catalyst particles holds for particles away from the tube wall, but particles placed in the strong temperature gradient near the tube walls show significant deviations.
TL;DR: In this paper, a transient analytical model has been presented to study the new concept of a solar crop dryer having reversed absorber plate type collector and thermal storage with natural airflow.
TL;DR: In this article, the authors examined pressure drop and mass transfer of a rotating packed bed (RPB) equipped with blade packings using stripping of oxygen from water and absorption of isopropyl alcohol from gas.
TL;DR: Production of l -DOPA was investigated by using tyrosinase enzyme in batch and packed bed reactors using method of entrapment in copper-alginate gels to find out the concentration and productivity of this compound.
TL;DR: In this paper, a model based on Langmuir-Hinshelwood-Hougen-Watson and Eley-Rideal approaches was proposed to describe the kinetics of hydrogen production by the catalytic reforming of concentrated crude ethanol over a Ni-based commercial catalyst at atmospheric pressure, temperature range of 673-863 K, ratio of weight of catalyst to the molar rate of crude ethanol 3472-34722 ǫ s/kmol, in a stainless steel packed bed tubular microreactor.
TL;DR: Production of lactic acid from glucose by immobilized cells of Lactococcus lactis IO-1 was investigated using cells that had been immobilized by either entrapment in beads of alginate or encapsulation in microcapsules ofAlginate membrane and microencapsulation proved to be the better method of immobilization.
Abstract: Production of lactic acid from glucose by immobilized cells of Lactococcus lactis IO-1 was investigated using cells that had been immobilized by either entrapment in beads of alginate or encapsulation in microcapsules of alginate membrane. The fermentation process was optimized in shake flasks using the Taguchi method and then further assessed in a production bioreactor. The bioreactor consisted of a packed bed of immobilized cells and its operation involved recycling of the broth through the bed. Both batch and continuous modes of operation of the reactor were investigated. Microencapsulation proved to be the better method of immobilization. For microencapsulated cells at immobilized cell concentration of 5.3 g l(-1), the optimal production medium had the following initial concentrations of nutrients (g l(-1)): glucose 45, yeast extract 10, beef extract 10, peptone 7.5 and calcium chloride 10 at an initial pH of 6.85. Under these conditions, at 37 degrees C, the volumetric productivity of lactic acid in shake flasks was 1.8 g l(-1) h(-1). Use of a packed bed of encapsulated cells with recycle of the broth through the bed, increased the volumetric productivity to 4.5 g l(-1) h(-1). The packed bed could be used in repeated batch runs to produce lactic acid.
TL;DR: In this article, the authors investigated the steam reforming of methanol considering both heat and mass transfer of the species in a packed bed microreactor, and showed that for the constant wall temperature condition, steam reforming results in a nearly uniform temperature throughout the micro reactor over the range of operating conditions.
01 Jan 2007
TL;DR: In this article, the photocatalytic degradation of gas phase toluene (used as a model VOC) over illuminated titanium dioxide (TiO2) was investigated at room temperature using continuous flow annular reactor.
Abstract: The photocatalytic degradation of gas phase toluene (used as a model VOC) over illuminated titanium dioxide (TiO2) was investigated at room temperature using continuous flow annular reactor. The dependence of the overall process efficiency upon operating variables such as initial concentration of toluene and water in air stream and total flow rate of gas mixture was analyzed. Results of kinetic analysis showed that photocatalytic oxidation of toluene obey Langmuir-Hinshelwood kinetics. Deactivation of TiO2 catalyst was observed and attributed to adsorption of the partial oxidation products on the active sites of the catalyst. The presence of the benzaldehyde and benzoic acid on the surface of the deactivated photocatalysts was confirmed by using FT-IR spectroscopy. Different matematical model of the photocatalytic reactor were developed and experimentally verified. Introduction Volatile organic compounds (VOCs) are an important class of pollutants usually found in the atmosphere of all urban and industrial areas. Photochemical oxidation, PCO (also referred to as advanced oxidation processes, AOP) have become increasingly popular as alternative for environmental VOC decontamination purposes [1, 2]. Photocatalysis on TiO2 is advantageous compared to other oxidation methods because it takes place at room temperature, so no thermal activation is necessary and only low-intensity UV lights are needed. Moreover, TiO2 is relatively stable and an inexpensive photocatalyst. While most relevant studies have been concerned with photodegradation in the liquid phase, the degradation of gaseous organic compounds has gained importance recently, predominantly for air purification [3]. Recently, important research area becomes investigation of optimal reactor configurations. There are numerous laboratory reactor designs, such as batch reactor [4], fixed bed annular reactor [5], a microchannel reactor [6], etc. The objective of this work is investigation of the photocatalytic oxidation of toluene in the gas phase with particular emphasis on presentation of the methodology for photoreactor analysis and design based on chemical reaction engineering and mass transfer fundamentals. Experimental The commercial catalyst used in this work was supplied by Degussar (P-25). The TiO2 layer was coated onto the internal glass surface of reactor using TiO2 isopropanol slurry. The TiO2-coated tube was heated at 110oC for 2 hours. A TiO2 loading density of 22.3 m g cm-2 was obtained by weighting the tube before and after the coating. The physico-chemical properties of the TiO2 catalyst were studied by different techniques, such as SEM, XRD, FT-IR spectroscopy, TG/DSC and nitrogen adsorption/desorption measurements. An annular photoreactor was constructed using a Pyrex glass tube with a 53.8 mm internal diameter of outer tube and 23, 8 of inner tube. Illumination was provided by a 8 W fluorescent lamp. The high purity synthetic air was used as a gas carrier. The concentration of toluene and moisture in the contaminated atmosphere was obtained by vaporization of organic compound and water using predetermined values of flow rate applying mass flow controllers (Cole Parmerr ). Prior to switching on the UV or visible light illumination, the catalyst was first exposed to the polluted air stream until dark adsorption equilibrium was reached. Toluene concentrations were measured on-line by a gas chromatograph equipped by Carbowax 20M packed column (Restekr ) and FID detector. Results and discussion The photocatalytic oxidation of toluene was carried out over TiO2 in an annular reactor that had been developed to study the treatment of organic pollutants in gas phase. The experiments were performed at different initial concentration of toluene (0.8-8.9 g m-3) and water content in the air (10-60 %) as well as at different total flow rate of gas mixture. It was observed that conversion of toluene decreased with the increase of initial concentration of toluene. As expected, toluene conversion increased with increase of the space time in the reactor. On the other hand, water content had only small influence on the observed conversion. After several hours of using in the reaction, the TiO2 catalyst was deactivated. Additional FT-IR analysis of surface species was confirmed the presence of small quantities of the benzaldehyde and benzoic acid. However, assumption of the constant catalyst activity was taken into consideration during reactor analysis and modeling, due to the fact that kinetic experiments were performed in the relativelly small time intervals. Generally, approach to the modeling of an annular photocatalytic reactor is not different of modelling other similar configuration, for example of a monolithic catalyst structure. In this study reactor models were derived based on the physical picture, especially regarding on hydrodynamics of gas phase inside the reactor and mode of transfer of toluene from gas to the catalyst surface. The main assumptions made during deriving of the models were: a) reactor was considered as steady-state tubular reactor, i.e. inlet and outlet characteristic variables were independent of time ; b) isothermal conditions ; c) catalyst was deposited on the inner wall of outer tube of annular reactor in very thin layer and therefore intraphase diffusion was neglected in the overall reaction path. Following such approach, several mathematical models were used, ranging from the simple 1D heterogeneous model, based on assumption of the ideal flow conditions to the complex 2D heterogeneous model taking into account the radial concentration gradients due the mass transfer by diffusion and laminar flow of gas mixture. The proposed models were verified by comparing the experimental data with theoretical predictions. The most realistic situation was achieved using the last one, which is based on the fact that imaginary boundary layer between gas and solid phase is broadened to the whole space between two concentric tubes of the annular reactor. The mass transfer in this region is due to diffusion. This model is very complex but it's very important advantage in comparison with other models is in the fact that the diffusion coefficient of toluene in gas mixture, mainly consisted of air, can be easily calculated. Accuracy of the empirical calculation of mass transfer coefficient is much lower in the case of the 1D heterogeneous model. Therefore, much better approximation and estimation of kinetic constants can be made using 2D heterogeneous model. Obviously, 2D model with laminar flow is the best approximation of physical nature of the photocatalytic annular reactor. Thus, it is useful to optimize by this model the operating conditions and design parameters of the photocatalytic reactor. References [1] H. d. Lasa, B. Serrano, M. Salaices, Photocatalytic Reaction Engineering, Springer, London, 2005. [2] G. Ertl, H. Knozinger, J. Weitkamp, Handbook of Heterogeneous Catalysis, Wiley-VCH, Weinheim, 1997. [3] J. Zhao, X. Yang, Building and Environment, 38, 645-654 (2003). [4] S. B. Kim, H. T. Hwang, S. C. Hong, Chemosphere 48, 437-444 (2002). [5] R. M. Alberici, W. F. Jardim, Applied Catalysis B: Environmental, 14, 55-68 (1997). [6] H. Ge, G. Chen, Q. Yuan, H. Li, Catalysis Today, 110, 171– 178 (2005).
TL;DR: In this article, a mathematical model is presented to simulate the multiple heterogeneous reactions with complex set of physicochemical and thermal phenomena in a moving bed of porous pellets, including chemical reactions at interfaces whose areas vary during the conversion.
Abstract: A mathematical model is presented to simulate the multiple heterogeneous reactions with complex set of physicochemical and thermal phenomena in a moving bed of porous pellets. This model is based on both heat and mass transfer phenomena of gaseous species in a porous medium including chemical reactions at interfaces whose areas vary during the conversion. This model accounts for both the exothermic and endothermic reactions which can be equimolar or nonequimolar. Furthermore it considers simultaneously the reactions in the nonisothermal transient condition. A powerful technique based upon finite volume fully implicit approach has been implemented to solve the complicated governing equations numerically. The model has been validated by comparing with various experimental and analytical results in two cases: the single pellet scale as well as the counter current moving bed reactor.
TL;DR: An alternative method to determine the interstitial void volume and the external porosity inside a packed or a monolithic column was developed based on the total blocking of the mesopores of a porous support by filling them with a hydrophobic solvent.
TL;DR: The analysis of elution peaks with model proteins (packed bed mode) indicated that the mass transfer kinetic inside the macroporous beads prepared was enhanced, which might certainly benefit the chromatographic operation under high flow rate and the prepared beads showed good expansion and stability in expanded bed, and are thus suitable for expanded bed applications.
TL;DR: In this article, the effective thermal conductivity of a Li2TiO3 pebble bed was measured as a function of the average bed temperature, and the experimental results showed that the effectiveness of this bed decreased from 1.40 to 0.94 W/m K with the increase of the bed temperature from 50 to 500 °C.
TL;DR: In this article, a nonthermal, atmospheric pressure plasma utilising a dielectric packed bed was used to study the destruction of dichloromethane, CH2Cl2, (DCM) in gas streams of nitrogen with the presence of catalysts.
Abstract: A non-thermal, atmospheric pressure plasma utilising a dielectric packed bed was used to study the destruction of dichloromethane, CH2Cl2, (DCM) in gas streams of nitrogen with the presence of catalysts. The effect of plasma-assisted catalysis was investigated in two configurations; one where the catalyst was incorporated into the packed bed itself and the other where the catalyst was downstream of the plasma. The combination of plasma and a catalyst allowed improved destruction of DCM. γ-Al2O3 in a one-stage reactor configuration was the most successful in terms of the total destruction of DCM as well as providing the best result in the two-stage reactor configuration compared with the eight catalysts chosen which included alumina, TiO2 and various zeolites. Products as detected by FTIR were CO, CO2, HCN, HCl and H2O with the by-product of N2O. The nature of the catalyst plays a vital role with respect to the effectiveness of DCM destruction and the selectivity of the end-products.
Journal Article•
TL;DR: In this paper, the boron removal efficiency from seawater was examined through the packed column experiment and the results showed that the removal rate increased with the initial state of increasing temperature, it was independent of temperature.
TL;DR: Two models, the general rate model taking into account convection, axial dispersion, external and intra-particle mass transfer resistances and particle size distribution and the artificial neural network model, were developed to describe solanesol adsorption process in packed column using macroporous resins and simulated results showed that ANN model could describe present system even better than general rate models.
TL;DR: In this article, a method is described by which a CFD code known as FLUENT, may be adapted to model the reactions that take place inside catalyst structures, and the results of the CFD simulations are compared with solutions obtained from a one-dimensional model using MATLAB.
Abstract: A method is described by which a CFD code known as FLUENT, may be adapted to model the reactions that take place inside catalyst structures. To test the CFD code, simulations of gas flow in a circular tube are performed and compared with analytical solutions. Then the coupled processes of diffusion and chemical reaction, combined with heat and mass transfer effects are modelled in a catalyst pellet. To illustrate the technique, the catalytic combustion of propane is simulated in spherical and cylindrical shaped pellets, at gas temperatures from 500 to 700 K and at atmospheric pressure. To help validate the approach adopted, the results of the CFD simulations are compared with solutions obtained from a one-dimensional model using MATLAB. It is shown that the CFD simulations provide comparable results with MATLAB, and that the CFD code can provide valuable additional information about temperature and concentration gradients in and around the catalyst pellet—this is not available in a simple one-dimensional approach. It is discussed how the technique could be extended to model reactions in a packed bed which would be a valuable design tool.