Showing papers on "Packed bed published in 2016"

Photocatalytic degradation of binary mixture of toxic dyes by HKUST-1 MOF and HKUST-1-SBA-15 in a rotating packed bed reactor under blue LED illumination: central composite design optimization

Abstract: A new composite of mesoporous materials, HKUST-1 metal organic framework and SBA-15, was synthesized and applied to the simultaneous visible light photodegradation of a binary mixture of safranin O and malachite green. Structural and electronic properties of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), Brunauer–Emmett–Teller (BET), Barrett–Joyner–Halenda (BJH), photoluminescence (PL) and diffuse reflectance spectroscopy (DRS). In the photodegradation process, a rotating packed bed reactor was used to enhance mass transfer and the distribution of irradiance. In the rotating packed bed reactor, by creating a rigorous centrifugal field due to high rotational speed, thick liquid films are converted into thin layers and small droplets, therefore the interfacial area between pollutants and photocatalyst particles increases and mass transfer is improved dramatically. The benefits of visible-light-emitting diodes (LED) compared to UV lamps are economically significant. In the reactor applied here, a blue LED strip with high mechanical flexibility was wrapped around the reactor vessel for uniform irradiance distribution. The influence of the initial dye concentration, rotational speed, solution flow rate, photocatalyst dosage and irradiation time on the photodegradation efficiency and the relationship among these parameters were investigated to find the optimum operational conditions using response surface methodology based on a central composite design (CCD). The results showed that applying HKUST-1-SBA-15 is cost-effective, due to less rotational speed and irradiation times. Investigation on the kinetics of the photodegradation reaction showed that the experimental data follow a pseudo first order reaction, based on the Langmuir–Hinshelwood model.

Fluid modelling of a packed bed dielectric barrier discharge plasma reactor

Abstract: A packed bed dielectric barrier discharge plasma reactor is computationally studied with a fluid model. Two different complementary axisymmetric 2D geometries are used to mimic the intrinsic 3D problem. It is found that a packing enhances the electric field strength and electron temperature at the contact points of the dielectric material due to polarization of the beads by the applied potential. As a result, these contact points prove to be of direct importance to initiate the plasma. At low applied potential, the discharge stays at the contact points, and shows the properties of a Townsend discharge. When a high enough potential is applied, the plasma will be able to travel through the gaps in between the beads from wall to wall, forming a kind of glow discharge. Therefore, the inclusion of a so-called 'channel of voids' is indispensable in any type of packed bed modelling.

Plasma-catalytic degradation of benzene over Ag–Ce bimetallic oxide catalysts using hybrid surface/packed-bed discharge plasmas

Abstract: Plasma-assisted catalysis has been employed for the degradation of benzene by hybrid surface/packed-bed discharge (HSPBD) plasmas over a series of Agx Ce1−x/γ-Al2O3 catalysts in in-plasma catalysis (IPC) and post-plasma catalysis (PPC) configurations. In order to study the influence of catalysts placement on discharge characteristics and the consequent synergetic effect in plasma-catalysis process, the catalysts were introduced inside and downstream the surface discharge region (region I) and packed-bed discharge region (region II), respectively, and the benzene degradation performance was investigated in these systems. The effects of the Ag/Ce molar ratio and water vapor have also been investigated in terms of benzene degradation efficiency and CO2 selectivity. Compared with the plasma-only process, the combination of plasma with Agx Ce1−x/γ-Al2O3 catalyst significantly improved the reaction performance, and the combined degradation efficiency is a synergistic effect rather than simply an additive effect. Besides, the emission of discharge products (O3 and NOx) and hazardous intermediates (formic acid and CO) was markedly suppressed with the introduction of catalyst. The highest benzene degradation efficiency of 96.2% and CO2 selectivity of 77.3% can be achieved with Ag0.9Ce0.1/γ-Al2O3 catalyst at the SIE of 400 J/L. This result suggests that the interaction between a certain proportion of Ag and Ce species over the catalyst is capable of activating the surface lattice and generating more surface adsorbed oxygen (Oads), which favors the plasma-catalytic oxidation reaction. PPC processes can decompose O3 and destroy benzene more effectively than IPC processes, especially when the catalyst was introduced downstream the region II. Adding a small amount of water vapor into plasma-catalysis system enhanced the catalyst activity, however, further increased the water vapor caused an obvious negative impact on the catalyst activity.

Adsorption performance of continuous fixed bed column for the removal of methylene blue (MB) dye using Eucalyptus sheathiana bark biomass

Abstract: In this study, the adsorptive effectiveness of sustainable and cost-effective eucalyptus bark biomass in the removal of methylene blue (MB) dye from its aqueous solution has been tested using a packed bed up-flow column experiment. A series of column experiments using raw eucalyptus bark was performed to determine the breakthrough curves with varying inlet MB dye flow rate (10–15 mL min−1), initial MB dye concentration (50–100 mg L−1) and adsorbent bed height (10–15 cm). High bed height, low flow rate and high initial dye concentration were found to be the better conditions for maximum dye adsorption. To predict the breakthrough curves and to determine the characteristic parameters of the column dynamics for industrial applications and for process design, Thomas model, Yoon–Nelson model and bed depth service time model were applied to experimental breakthrough data. All models were found suitable for describing the dynamic behaviour of the column, with respect to MB flow rate, initial dye concentration and adsorbent bed height. The findings revealed that eucalyptus bark biomass has a high adsorption potential for the removal of MB dye from aqueous solutions in a column system, and that it could be used to treat dye-containing effluents.

Metal sorption by algal biomass: From batch to continuous system

Abstract: Algal biomass possesses tremendous metal binding ability and therefore has great potential for gleaning these pollutants from wastewaters. The algal cell wall and exopolymers contain diverse functional groups which confer negative charge to cell surface. Since metal ions in water are generally in cationic form, they are adsorbed onto the cell surface. Biosorption of metal ions from aqueous solution is influenced by various factors, such as, pH, charge density of metal ion, concentration of metal ion, concentration of interfering metal ions, nutrient availability, nature of biomass, culture age, temperature and contact time. Batch studies are very important for collecting information for subsequent application on a large scale. Continuous flow studies, like those conducted in packed bed column, seem more efficient and economically feasible than the batch operation for metal sorption. Various kinds of sorption isotherms have been used for the assessment of maximum sorption capacity. The data of metal sorption obtained from continuous system are generally expressed in the form of breakthrough curves. The shape and size of breakthrough curve is influenced by several factors, such as, metal concentration, flow rate, bed height, size of biosorbent particle, solution composition, and packing of column/density biosorbent in the column. Adam-Bohart, Thomas, mass transfer model, advection–dispersion-reaction equation and bed-depth-service-time model have been developed for elucidating breakthrough curve. However, new approaches, such as artificial neural networking and response surface methodology need adequate attention for modeling of breakthrough curves and metal sorption in multi-metal systems.

BiPO4/Bi2S3-HKUST-1-MOF as a novel blue light-driven photocatalyst for simultaneous degradation of toluidine blue and auramine-O dyes in a new rotating packed bed reactor: optimization and comparison to a conventional reactor

Abstract: BiPO4/Bi2S3-HKUST-1-MOF as a novel blue light active photocatalyst was synthesized and characterized by X-ray XRD, SEM, PL, BET, BJH and DRS. This novel photocatalyst was applied in a new catalytic rotating packed bed reactor for intensification of simultaneous photocatalytic degradation of toluidine blue (TB) and auramine-O (AO). In this reactor, high gravity media generated by a high rotational speed in a porous domain leads to intensification of the external mass transfer rate and significantly increases the mixing and turbulency. The central composite design (CCD) following analysis of variance (ANOVA) was applied to optimize the operational parameters including irradiation time, pH, photocatalyst dosage, rotational speed, solution flow rate, aeration flow rate, and TB and AO concentration. The optimum values were found to be 65 min, 6, 0.25 g L−1, 1300 rpm, 0.40 L min−1, 35 L min−1, 25 and 25 mg L−1 for irradiation time, pH, photocatalyst dosage, rotational speed, solution flow rate, aeration rate and initial concentration of TB and AO, respectively. At these optimum conditions, the photocatalytic degradation percentages of TB and AO were found to be 99.37% and 98.44% respectively with an overall desirability of 1.0. Replication of all experiments at optimum conditions with a conventional photocatalytic reactor shows the requirement of more photocatalyst as well as more irradiation time for operation in comparison to the rotating packed bed reactor. Results showed that the rotating packed bed is more economical, has a higher efficiency and can operate at a higher flow rate. Kinetic studies are an essential step in designing and optimizing photocatalytic reactors during scale-up processes, a pseudo first order kinetics based on the Langmuir–Hinshelwood (L–H) model was able to successfully fit the data concerning the present photodegradation approach.

CO2 decomposition in a packed DBD plasma reactor: influence of packing materials

Abstract: Carbon dioxide (CO2) decomposition has drawn significant interest over the years due to its global warming potential. A packed bed dielectric barrier discharge reactor has been designed and tested for the conversion of CO2 into carbon monoxide (CO). The discharge volume was filled with different packing materials (glass beads, alumina, anatase titania, ceria) so as to understand the influence of dielectric constant, porosity and ultraviolet light. Typical results indicated that the packed bed DBD promotes CO2 conversion into CO and oxygen and CeO2 packing showed the highest conversion (10.6%) at a specific input energy of 4.8 J mL−1. The best performance of CeO2 may be due to oxygen vacant sites, which stabilize the atomic oxygen formed in the reaction and thereby promoting CO2 conversion. During the present study, CO2 decomposition has been achieved at ∼0.139 eV per molecule.

Hydrogenation of Levulinic Acid to gamma-Valerolactone in Water Using Millimeter Sized Supported Ru Catalysts in a Packed Bed Reactor

Abstract: γ-Valerolactone (GVL) has been identified as a sustainable platform chemical for the production of carbon-based chemicals. We here report an experimental study on the catalytic hydrogenation of levulinic acid (LA) in water to GVL in a packed bed reactor using supported Ru catalysts (carbon, alumina, and titania) with particle sizes in the millimeter range (CLA,0 = 1.2 mol/L, LA feed = 1 mL/min, H2 feed = 30 mL/min, 90 °C, 45 bar, and WHSV = 30 gfeed/gcat·h). Intraparticle diffusion limitations for hydrogen and LA were confirmed by performing LA hydrogenation experiments with different catalyst particle sizes (0.5 wt % Ru/C) and supported by calculations. The best performance was obtained with Ru/C, showing high LA conversion during 6 h on stream with negligible deactivation. Ru/Al2O3 was found to be less active, and stability was also considerably reduced due to the reactivity of the support. Ru/TiO2 was considerably less reactive, though stability was better than that for the alumina based counterpart. A...

Temperature Swing Adsorption for Postcombustion CO2 Capture: Single- and Multicolumn Experiments and Simulations

Abstract: A mathematical model used to describe cyclic adsorption processes is calibrated and validated for the simulation of temperature swing adsorption (TSA) processes applied to the capture of CO2 from a model flue gas (CO2/N2) using zeolite 13X as sorbent material. Three types of experiments are reported in this work, all of them performed in jacketed columns packed with 13X. During these experiments, the temperature was measured at five positions along the central axis of the column, and the exit composition was measured on line by mass spectrometry. The first series of experiments were breakthrough experiments, used to characterize transport phenomena within the packed bed. The second series were heating and cooling experiments, which were used to study the heat transfer from the heating fluid in the column jacket to the bed. Lastly, cyclic TSA experiments were performed to test the model’s ability to predict the cyclic steady state behavior of the column as well as the separation performance of the process.

Kinetic studies of CO2 methanation over a Ni/γ-Al2O3 catalyst.

Abstract: The production of methane by reacting CO2 with H2 (CO2 methanation) has the potential for producing synthetic natural gas, which could be exported using the existing infrastructure for the distribution of natural gas. The methanation of CO2 was investigated over a wide range of partial pressures of products and reactants using (i) a gradientless, spinning-basket reactor operated in batch mode and (ii) a laboratory-scale packed bed reactor operated continuously. The rate and selectivity of CO2 methanation, using a 12 wt% Ni/γ-Al2O3 catalyst, were explored at temperatures 445–497 K and pressures up to 20 bar. Research with the batch reactor showed that the rate increased with increasing partial pressures of H2 and CO2 when the partial pressures of these reactants were low; however, the rate of reaction was found to be insensitive to changes in the partial pressures of H2 and CO2 when their partial pressures were high. A convenient method of determining the effect of H2O on the rate of reaction was also developed using the batch reactor and the inhibitory effect of H2O on CO2 methanation was quantified. The kinetic measurements were compared with a mathematical model of the reactor, in which different kinetic expressions were explored. The kinetics of the reaction were found to be consistent with a mechanism in which adsorbed CO2 dissociated to adsorbed CO and O on the surface of the catalyst with the rate-limiting step being the subsequent dissociation of adsorbed CO. The ability of the kinetic expressions to predict the results from the continuous, packed-bed reactor was explored, with some discrepancies discussed.

Steam Regeneration of Polyethylenimine-Impregnated Silica Sorbent for Postcombustion CO2 Capture: A Multicyclic Study

Abstract: Steam regeneration of polyethylenimine (PEI)-impregnated commercial grade silica was investigated in a packed bed reactor. Adsorption was performed at 75 °C under 10% CO2/N2, and desorption was carried out under steam at 110 °C for 20 consecutive cycles. CO2 adsorption capacity was found to decrease by 9 mol % over the period of 20 cycles. No evident signs of sorbent degradation due to PEI leaching or changes in surface morphology and amine functionalities were observed upon characterization of the sorbent after the cyclic study. Most of the loss in adsorption capacity was associated with thermal degradation of the sorbent during drying under N2 after steam stripping at 110 °C. The desorption kinetics during steam stripping was found to be much faster than during N2 stripping. Over 80% of the total CO2 was released within the first 3 min of steam injection into the reactor. A separate packed bed study was conducted to investigate the influence of moisture content (5.3–14.7 vol %) in flue gas on the CO2 ad...

Polytetrafluoroethylene Wire Mesh Packing in a Rotating Packed Bed: Mass-Transfer Studies

Abstract: Polytetrafluoroethylene (PTFE) material, which is well-known for its excellent anticorrosion properties, was used as wire mesh packing in a rotating packed bed (RPB). The effective interfacial area (ae) and the volumetric liquid-side mass-transfer coefficient (kLae) of the RPB with PTFE packing was studied experimentally by a NaOH–CO2 chemical absorption system and an oxygen–water physical desorption system, respectively. Experimental results showed that both ae and kLae increased with decreasing fiber diameter and pore size. As for material, mass-transfer performance of the PTFE packing was lower than that of the stainless steel wire mesh packing but is applicable in some high-corrosion and -viscosity environments. Moreover, correlations for ae and kLae were proposed.

Thermal performance of double pass packed bed solar air heaters – A comprehensive review

Abstract: The present work intended to conduct a comprehensive review on the thermal performance of double pass packed bed solar air heaters. Various aspects that govern the thermal performance of such solar air heaters has been highlighted and discussed in detail. A comprehensive review of reported studies indicate that the use of porous packed bed material in the upper channel of double pass solar air heaters significantly increases the thermal performance as compared to solar air heaters without packed bed and with packed bed when porous material is provided in the lower channel. Moreover, studies revealed that employment of parallel, counter and recyclic double air pass increases the thermal performance of the packed bed solar air heater as well by increasing the heat extraction rate of the flowing air through the packed bed duct. Although, it has been obtained that sufficient work using parallel and counter double air pass has been reported on packed bed solar air heaters, only few studies were reported using recyclic double air pass. However, results show that employment of recycle operation to the double pass packed bed solar air heaters momentously increases the thermal performance and can be used as an alternative thermal performance enhancement technique. Therefore, more investigations are required to be conducted using recyclic double pass packed bed solar air heaters.

Removal of ammonia from wastewater by air stripping process in laboratory and pilot scales using a rotating packed bed at ambient temperature

Abstract: In this study, a continuous-flow rotating packed bed (RPB), functioning as an efficient gas–liquid contactor, was employed for the ammonia stripping from wastewater in laboratory-scale and pilot-scale systems at ambient temperature. The effects of major operating variables, such as rotational speed (ω), liquid flow rate (QL), and gas flow rate (QG) on the volumetric liquid mass-transfer coefficient (KLa) and stripping efficiency (η) were elucidated. The results show that the KLa values demonstrate the greatest increase with increasing gas flow rate (QG), followed by liquid flow rate (QL) and rotating speed (ω). Although changes in KLa would be expected to directly reflect in the η values, the increased QL results in considerable compensation effects leading to the decreased η, predominantly due to the decreased liquid hydraulic retention time. The dimensionless models used in this study describe the relationships of KLa and η with the major parameters for ammonia stripping in the RPB, and demonstrate good agreement with the experimental data. Moreover, in the continuous-flow pilot-scale RPB, an η of 95% was achieved at 4.6 min. while KLa values of approximately 0.017–0.027 1/ s and height transfer unit (HTU) values of 2.2–4.8 cm were obtained at a QL of 5 L/min, QG of 1,500 L/min, and ω of 480–1000 rpm, suggesting that the RPB is a viable alternative technology for stripping large loadings of ammonia from wastewater.