Fluidized Bed Photoreactor Research Articles

Carrier modification and its application in continuous photo‐hydrogen production using anaerobic fluidized bed photo‐reactor

AbstractPoor hydrogen production performance and low biomass limit the practical application of photo‐fermentation. To improve the immobilization capability of bacteria and hydrogen production performance, activated carbon fibers (ACFs) were modified by acidic, alkaline, and neutral solutions. The modified ACFs were further used in the anaerobic fluidized bed photo‐reactor (AFBPR) to explore its continuous operation characteristics. Results showed that among the three reagents, nitric acid was the most efficient for ACF modification, and the maximum yield and production rate of hydrogen increased between about 33.6% and 65.8% compared to the control. Furthermore, with the optimal influent glutamate concentration (10 mmol L−1) and light intensity (4000 lux), the AFBPR gave efficient and stable performance with hydrogen yield of 2.26 mol H2 mol−1 acetate and hydrogen production rate of 25.8 mL L−1 h−1. The results showed the potential of using the AFBPR with HNO3‐modified ACF carriers for the large‐scale production of bio‐hydrogen.

Cyclohexane photocatalytic oxidation on Pt/TiO2 catalysts

Gas-solid heterogeneous photocatalytic oxidation (PCO) of cyclohexane in humidified air over TiO2 and Pt/TiO2 catalyst was studied.Pt/TiO2 photocatalysts were synthesized by photodeposition method at different Pt loadings (0.5–2wt.%). The addition of 0.5wt.% Pt does not significantly modify the TiO2 properties. The increase in Pt loading induces to an aggregation of metallic particles on TiO2 surface.The cyclohexane PCO was performed in a fluidized bed photoreactor at 60 and 100°C. Pure TiO2 was more active than 1 and 2wt.% Pt/TiO2 samples at 60°C. Nevertheless, the conversion level increases with temperature on Pt/TiO2 photocatalysts. The cyclohexane was mineralized into CO2, water and low amount of CO. A beneficial effect of Pt addition was found, since total CO2 selectivity was obtained. The Pt/TiO2 photocatalysts prepared by photodeposition provide the total cyclohexane PCO without CO production. Photocatalysts deactivation was not observed in any performed test. Evidence of an opportune tuning of temperature is highlighted.

A complete multi-scale simulation of light absorption within a fluidized bed photoreactor using integrated particle, fluid and photon behaviour models

Photocatalysis is a process that offers the ability to degrade a wide range of pollutants through a non-intensive process using renewable light sources. Despite this promise, in practice the take-up of photocatalysis has been slow, in part because little work has been done on the optimal design of photocatalytic reactors. The use of fluidized beds for photocatalytic applications has many advantages through their high illuminated surface area, reduced mass transfer constraints and retention of the photocatalyst. However this photoreactor design has received little attention compared to other possible designs, especially in regards to modelling and simulation. The models that have been developed simplify the behaviour of the fluidized bed, and in doing so lose much of the dynamic behaviour of the system that would be present in most realistic operations. This report details the development of a fully simulated fluidized bed photoreactor, where the movement of the particle and fluid phases was determined by discrete element modelling and computational fluid dynamics, respectively, and the behaviour of the photons was modelled using geometric optics. The accuracy of the model was assessed comparing it to the light transmitted through an experimental fluidized bed. Previously unreported photon absorption behaviour was found, particularly in regards to how the photons are absorbed throughout the space. At lower heights of the bed the photons are overwhelmingly absorbed at the walls of the reaction volume, while higher up the bed there is a broad zone of relatively even absorption throughout the entire space. This has implications for the design of this class of reactor. Two possible fluidized bed photoreactor designs are discussed based on this effect, one having a very small reaction volume and having a very dense particle phase, while the other has large reaction volume with a more distributed particle phase.

Photocatalytic Degradation of Humic Acid by Fe-TiO2Supported on Spherical Activated Carbon with Enhanced Activity

Fe-TiO2supported on spherical activated carbon (Fe-TiO2/SAC) with different Fe contents was prepared by heat treatment process after ion exchange method. The prepared Fe-TiO2/SAC was characterized by SEM, EDS, and BET. Batch experiments for photocatalytic degradation of humic acid by Fe-TiO2/SAC were carried out in the fluidized bed photoreactor. It was found that 0 wt% Fe-TiO2/SAC had high photocatalytic activity in the wavelength range of 100~280 nm. However, Fe-TiO2/SAC with Fe contents of 0.4, 0.6, and 0.8 wt% exhibited higher photocatalytic activity than 0 wt% Fe-TiO2/SAC in the wavelength range of 315~400 nm compared to that of 100~280 nm. The optimum Fe content was 0.6 wt% for maximum photocatalytic degradation of humic acid. Moreover, Fe-TiO2/SAC does not require an additional process step for separation of photocatalyst from treated water after photocatalysis.

Application of TiO2-containing mesoporous spherical activated carbon in a fluidized bed photoreactor—Adsorption and photocatalytic activity

A TiO2-containing mesoporous spherical activated carbon (meso-TiO2/SAC) with high adsorption capacity and photocatalytic activity was prepared using ion-exchange method and heat-treatment process. The prepared meso-TiO2/SAC was characterized by SEM, TEM, EDS, XRD, and BET analysis. Results obtained showed that meso-TiO2/SAC had a smooth spherical shape (0.30–0.45mm) and TiO2 with crystalline size of 10–30nm was well dispersed on the spherical activated carbon. XRD study confirmed that TiO2 existed in a mixture of anatase (83%) and rutile (17%) phase. The meso-TiO2/SAC presented a high specific surface area of 1649m2/g. The meso-TiO2/SAC was used for the removal of humic acid (HA) in a fluidized bed photoreactor, the rate of adsorption reaction of HA by meso-TiO2/SAC followed the pseudo second-order kinetic, the adsorption isotherm fitted well to the Freundlich and Langmuir isotherm models. The maximum adsorption capacity of meso-TiO2/SAC determined from Langmuir isotherm was 2.92mg/g. The effect of the photocatalysis of HA by meso-TiO2/SAC under UV irradiation was investigated under various conditions of varying catalyst dosage, initial HA concentration, and coexisting anion. HA was mineralized up to 80.3% under optimal experimental conditions for a catalyst dosage of 9g/L and at an initial HA concentration of 20mg/L. In the presence of coexisting anions, the degradation efficiency of HA was reduced to 72.1% and 72.8% for SO42− and NO3−, respectively. In the cyclic reuse experiment, over 85% of the initial TOC and COD were removed after the eighth cycles, indicating the relatively high photocatalytic stability of meso-TiO2/SAC. TiO2 was not released from the spherical activated carbon during the photocatalytic reaction. The meso-TiO2/SAC developed, therefore has potentials for practical applications in water treatment.

Innovative structured VOx/TiO2 photocatalysts supported on phosphors for the selective photocatalytic oxidation of ethanol to acetaldehyde

In this work, an innovative and effective formulation of photocatalysts is presented. The highly selective photocatalysts at 5wt% of nominal V2O5 on TiO2 for the photoconversion of ethanol to acetaldehyde was supported on the surface of commercial ZnS based phosphors (ZSP), on the base of the evidence that the addition of these phosphors, physical mixed with the photocatalysts, as light carriers inside a gas-solid fluidized bed photoreactor resulted in a significantly improved photoefficiency. Structured vanadia-titania catalysts in the form of micropellets were successfully synthesised by sol–gel method on the UV activated luminescent phosphors microparticles. The catalysts were investigated by TG-MS analyses, Raman and UV–vis spectroscopy, X-ray diffraction, as well as adsorption of N2 at −196°C.A progressive increase of the amount on titania on the phosphors was realized to get the well dispersed nanoparticles of TiO2 on ZSP surface, able to absorb the UV light needed by the photoreaction in the proximity of light source. The residual UV light can penetrate up to the phosphors core, leading to their excitation and emission of further radiation at 440nm useful to proceed the photoreaction in darker zones. The performances of structured VOx/TiO2/ZSP have been compared to physical mixtures of VOx/TiO2 catalyst with phosphors in the partial photooxidation of ethanol to acetaldehyde with the gas-solid fluidized bed photoreactor at high illumination efficiency. The ethanol consumption rate increased linearly with the ethanol initial concentration and at given alcohol concentration, its value was significantly higher on VOx/TiO2/ZSP with respect to the case in which the photocatalyst was only mixed with them. The results underlined as the higher capture of the structured photocatalyst, due to the additional light harvesting of support, gives enhanced activity in the selective oxidation of ethanol to acetaldehyde already dramatically improved by the innovative use of light emitting phosphorescent particles.

Radial distribution modeling of liquid-phase phenol concentration in a liquid–solid fluidized bed photoreactor

A fluidized bed photoreactor with titanium dioxide-immobilized spherical activated carbon particles was examined. The light intensity profile was modeled using the Lambert-Beer rule for the modeling of the radial distribution of liquid-phase phenol concentration in the fluidized bed photoreactor, when considering the reactor composed of numerous differential annular drums and no mass transfer between drums. The model could be well matched with the experimental data which indicated the liquid flow rate of 13.8 L/min was the optimum in the balance of flow rate-related light penetration and photocatalyst concentration. By integration of liquid-phase phenol concentration along the radius, photocatalytic oxidation performance of the photoreactor was evaluated in comparison with the experimental data and model prediction. The results showed that the errors were less than 30% for most of the predictions. It is suggested that mass transfer and flow rate difference along the radial direction should be considered to obtain more precise prediction.

Continuous photo-hydrogen production in anaerobic fluidized bed photo-reactor with activated carbon fiber as carrier

Download options Please wait... Supplementary files Supplementary information PDF (59K) Article information DOI https://doi.org/10.1039/C2RA20420G Article type Communication Submitted 07 Mar 2012 Accepted 29 Apr 2012 First published 30 Apr 2012 Download Citation RSC Adv., 2012,2, 5531-5535 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Continuous photo-hydrogen production in anaerobic fluidized bed photo-reactor with activated carbon fiber as carrier H. Ren, B. Liu, J. Ding, G. Xie, L. Zhao, D. Xing, W. Guo and N. Ren, RSC Adv., 2012, 2, 5531 DOI: 10.1039/C2RA20420G To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Hong-Yu Ren Bing-Feng Liu Jie Ding Guo-Jun Xie Lei Zhao De-Feng Xing Wan-Qian Guo Nan-Qi Ren

Photocatalytic degradation of 2,4-dichlorophenoxyacetic acid in a fluidized bed photoreactor with composite template-free TiO 2 photocatalyst

The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) was degraded in a photocatalytic fluidized bed reactor with template-free TiO 2 photocatalytic spheres in the presence of UV irradiation at 254 nm. The photocatalyst was prepared by binding together pre-calcined commercial TiO 2 particles (Degussa P-25) in an aqueous sol of TiO 2 nanoparticles (composite sol–gel) by the assistance of a polymeric matrix. The photocatalytic spheres had a considerable degree of consistency in their size and shape. X-ray diffraction (XRD), scanning electron microscopy (SEM), and BET specific surface area were used to characterize the photocatalyst. The effects of the initial contaminant concentration, its adsorption on photocatalyst surface, and the fluence rate on the herbicide degradation were studied. 2,4-D showed significant adsorption on the composite TiO 2 spheres. Depending on the initial concentration of 2,4-D, between 50% and 70% was adsorbed on TiO 2 spheres. In all the cases, adsorption equilibrium was reached within 75 min of contact in the fluidized bed reactor with the UV lamps off. After the UV lamps were turned on, 2,4-D was completely degraded within 45 min of irradiation with a fluence rate of 4.16 mW cm −2. Experimental results were fitted with a simplified kinetic model that takes into account the initial concentration of 2,4-D and the fluence rate. A comparison of photocatalytic degradation of 2,4-D with commercial particulate TiO 2 (Degussa P-25) showed that the composite spheres have a photocatalytic activity 26% higher than that obtained with Degussa P-25. The TiO 2 spheres were mechanically robust and demonstrated a high attrition resistance with only 0.014% of TiO 2 released from the spheres due to attrition after 3 h of continuous operation.

Photocatalytic Degradation of Acid Red G by Bismuth Titanate in Three-phase Fluidized Bed Photoreactor

AbstractThe objectives of this study were to prepare a high-performance bismuth titanate photocatalyst and to develop a novel photocatalytic reactor with three-phase internal circulating fluidized bed photoreactor (TPICFBP). Bismuth titanate photocatalyst was hydrothermally prepared under optimum operating parameters such as hydrothermal temperature, reaction time and molar ratio of Bi to Ti. The photocatalytic activity of bismuth titanate using TPICFBP was evaluated for the photocatalytic degradation of Acid Red G (ARG). The photodegradation of ARG over Bi

Avoiding the deactivation of sulphated MoO x/TiO 2 catalysts in the photocatalytic cyclohexane oxidative dehydrogenation by a fluidized bed photoreactor

Since the relevance of deactivation phenomena in heterogeneous gas–solid photocatalytic processes, a study on the deactivation of MoO x /TiO 2 catalysts in the oxidative photodehydrogenation of cyclohexane has been carried out in a fixed bed reactor and compared to the behaviour of catalysts used in a two-dimensional fluidized bed photoreactor. Superior photocatalytic performances were obtained in the fluidized bed reactor with respect to the fixed bed reactor both in terms of cyclohexane conversion and benzene yield. At the opposite of the fixed bed, in the fluidized bed reactor, catalyst did not deactivate. Characterization performed on catalysts after photocatalytic tests evidenced that the deactivation of the catalysts is correlated to the accumulation of carbonaceous species on catalyst surface and the sulphur disappearance. The catalysts used in fluidized conditions remained active as they maintained their initial sulphur content at the surface.

Photocatalytic oxidation of gaseous toluene on titania/mesoporous silica powders in a fluidized-bed reactor

The photocatalytic degradation of toluene was carried out on titania/mesoporous silica photocatalysts in a self-constructed gaseous fluidized-bed photoreactor equipped with UVA light source. The powder photocatalysts were synthesized by incorporation of aqueous titania sol (as a photoactive component), into silica mesoporous materials (as a high-surface-area support), via the sol–gel impregnation method. SBA-15 was used as an ordered and KIL-2 as a disordered mesoporous silica support. The Ti/Si nominal molar ratio was adjusted to 1/2, 1/1 and 2/1. The photocatalysts were characterized by X-ray diffraction (XRD), nitrogen sorption (BET), UV–vis–NIR diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FT-IR) and high-resolution transmission electron microscopy (HR-TEM). The effects of Ti/Si molar ratio and of the mesoporous silica structure were investigated measuring adsorption capacity and photocatalytic degradation of toluene. The rates of photocatalytic degradation reactions were found to be similar for photocatalysts with the same Ti/Si molar ratio independently of the mesoporous structure of silica. The adsorption capacity was decreasing as a function of the increasing Ti/Si molar ratio in the case of both types of mesoporous silica support. However, the photocatalytic degradation proceeded faster for the Ti/Si molar ratio 1/1 while, in the case of the other investigated Ti/Si molar ratios 1/2 and 2/1, the degradation rates were lower. In general, the photocatalytic activity was considerably improved by using supported titania–silica catalyst compared to an unsupported titania powder prepared from the same nanocrystalline titania sol.

Parameter effect on photocatalytic degradation of phenol using TiO2-P25/activated carbon (AC)

P25 powder embedded and TiO2 immobilized on activated carbon (TiO2-P25/AC) was prepared by P25 powder modified sol-gel and dip-coated method. The photocatalysts were characterized by XRD, BET, SEM and their photocatalytic activities were evaluated through phenol degradation in a fluidized bed photoreactor. The addition of P25 in the photocatalysts could significantly enhance the photocatalytic activity, and the optimum loading of P25 was 3g L −1 . The operating parameter results indicated that the optimum pH for phenol degradation was 5.2; the effect of air flow rate gave an optimal value of 2 L min −1 ; the increasing of UV light intensity led to an increase of degradation efficiency due to more photons absorbed on the surface of the photocatalyst. The kinetics of the phenol degradation fitted well with the Langmuir-Hinshelwood kinetics model. Finally, the photocatalytic ability of TiO2-P25/AC was re- duced only 10% after five cycles for phenol degradation.

Improved Performances of a Fluidized Bed Photoreactor by a Microscale Illumination System

The performances of a gas‐solid two‐dimensional fluidized bed reactor in photocatalytic selective oxidation reactions, irradiated with traditional UV lamps or with a microscale illumination system based on UV emitting diodes (UVA‐LEDs), have been compared. In the photocatalytic oxidative dehydrogenation of cyclohexane to benzene on MoOx/TiO2‐A12O3 catalyst the use of UVA‐LEDs modules allowed to achieve a cyclohexane conversion and benzene yield higher than those obtained with traditional UV lamps. The better performances with UVA‐LEDs are due to the UVA‐LEDs small dimensions and small‐angle emittance, which allow photons beam be directed towards the photoreactor windows, reducing the dispersion outside of photoreactor or the optical path length. As a consequence, the effectively illuminated mass of catalyst is greater. We have found that this illumination system is efficient for photo‐oxidative dehydrogenation of cyclohexane to cyclohexene on sulphated MoOx/γ‐A12O3 and ethanol to acetaldehyde on VOx/TiO2.

Photocatalytic cyclohexane oxidehydrogenation on sulphated MoO x/γ-Al 2O 3 catalysts

The photocatalytic oxidative dehydrogenation of cyclohexane on sulphated MoO x /γ-Al 2O 3 catalysts has been studied in a two-dimensional fluidized bed photoreactor. The influence of Mo loading at similar sulphate content and the effect of catalyst preparation method have been investigated. Considering the influence of Mo loading at similar sulphate content, the highest photoactivity at 2.4 SO 4 wt% was found at MoO 3 loading of 8 wt%. Selectivity to cyclohexene was 100%, irrespective of the Mo content. At fixed MoO x content, in particular at 50% of theoretical monolayer coverage, the preparation method of catalysts strongly affected the photocatalysts performances, showing in addition a slight decrease in selectivity to cyclohexene due to side-production of benzene. All the catalysts showed a similar equivalent band gap energy. Thermogravimetric analysis evidenced the presence of surface sulphate species of different thermal stabilities. A linear correlation of photoactivity with the surface sulphates amount of lower thermal stability has been found for all sub-monolayer MoO x sulphated catalysts. The neighboring of surface sulphates to octahedral polymolybdate species appears to be a key parameter for the photoactivity of the catalysts. The catalyst selectivity was related to surface acidity. Higher acidity resulted in increased cyclohexene dark adsorption and consequently in enhanced benzene formation.

Highly Thermostable Anatase Titania-Pillared Clay for the Photocatalytic Degradation of Airborne Styrene

Airborne styrene is a suspected human carcinogen, and traditional ways of mitigation include the use of adsorption technologies (activated carbon or zeolites) or thermal destruction. These methods presenttheir own shortcomings, i.e., adsorbents need to be regenerated or replaced regularly, and relatively large energy inputs are required in thermal treatment. Photocatalysis offers a potentially sustainable and clean means of controlling such fugitive emissions of styrene in air. The present study demonstrates a new type of well-characterized, highly thermostable titania-pillared clay photocatalysts for airborne styrene decomposition in a custom-designed fluidized-bed photoreactor. This photocatalytic system is found to be capable of destroying up to 87% of 300 ppmV airborne styrene in the presence of ultraviolet (UV) irradiation. The effects of relative humidity (RH: 0 or 20%) are also studied, together with the arising physical structures (in terms of porosity and surface characteristics) of the catalysts when subjected to relatively high calcination temperatures of 1000-1200 degrees C. Such a temperature range may be encountered, e.g., in flue gas emissions (1). It is found that relative humidity levels of 20% retard the degradation efficiencies of airborne styrene when using highly porous catalysts.

Visible-light photoresponsive heterojunctions of (Nb–Ti–Si) and (Bi/Bi-O) nanoparticles

The increasing motivation to seek alternative sources of clean and sustainable energy has intensified, due to a growing awareness that fossil fuels are finite in quantity, and that the combustion products of such fuels contribute to global warming. Solar energy is considered one of the most readily available alternatives, but materials which are able to harness this form of energy need to be developed. This study details the development of a novel composite material, of the form of Bi/Bi-O nanoparticles supported on a (Nb–Ti–Si) oxide. Characterized using electrochemical and other methods, this material generates a photocurrent, and is capable of photo-oxidizing airborne-styrene in a fluidized-bed photoreactor when exposed to visible-light.

Effects of Liquid and Gas Flow Rates on the Performance of a Fluidized Bed Photocatalytic Reactor

Titanium dioxide was immobilized onto spherical activated carbon particles via the sol-gel coating method. The photo-catalyst, annealed at 500 °C, was found to posses the highest activity according to the results of a bench-scale test. The photocatalytic performance of the immobilized photocatalyst was studied in a three-phase fluidized bed photoreactor, with the use of phenol as the model pollutant. Effects of both liquid and air flow rates on the phenol degradation rate were examined. The experimental results showed that the increase of liquid and air flow rates may enhance the phenol degradation rate. However, very high liquid and air flow rates could lead to the decrease in the performance of the three-phase fluidized bed photoreactor. The results on the effect of initial phenol concentration on the degradation rate indicated that the photocatalytic reaction in the three-phase fluidized bed followed the first order kinetics and could be reasonably fitted by the Langmiur-Hinshelwood kinetics model. Compared to the three-phase fluidized bed in which air is introduced into the bed from the distributor, the liquid-solids fluidized bed in which oxygen is provided by injecting air into the freeboard region of the reactor showed a better phenol destruction performance and is thus preferred for photodegradation of water contaminants.

Fluorine and Carbon Codoped Macroporous Titania Microspheres: Highly Effective Photocatalyst for the Destruction of Airborne Styrene under Visible Light

Airborne styrene is a suspected human carcinogen commonly present in industries where resins are used. Traditional ways of abating this pollutant include the use of various adsorbents (activated carbon or zeolites) or thermal treatment. The earlier method is simply a temporary containment of the pollutant, requiring spent-adsorbents to be regenerated frequently, while the latter is energy-intensive. Work involving the photodegradation of airborne styrene is limited in recorded literature. This study uses a well-characterized combined fluorine/carbon codoped macroporous-titania catalyst, capable of destroying airborne styrene using irradiation in the visible range. A fluidized-bed photoreactor, combined with high-flow rates relative to the minimum fluidization velocity (Umf) of the catalysts, is utilized in the photooxidation process. The effects of varying relative humidity (RH, 0 or 20%) are investigated in using both UV (248nm) and visible (400−700nm) irradiation. It is found that RH levels of 20% promote the complete degradation of 300 ppmV airborne styrene under both types of irradiation. Reaction intermediates on the surface of the used catalysts are probed by high-performance liquid chromatography (HPLC).

Fluidized-bed photocatalytic degradation of airborne styrene

Monomeric styrene, an aromatic compound present in many industries involved in the processing of fiberglass reinforced plastic products, is potentially carcinogenic. Based on current literature, studies on the breakdown of styrene via photocatalysis are limited. This study aims to develop suitable photocatalysts to be used in the mineralization of styrene. In particular, two specific objectives are of interest: first, the development of photocatalysts which are able to work under ultraviolet (UV) radiation and potentially visible/solar light irradiation; secondly, the design of an efficient fluidized-bed photoreactor. Preliminary work done using titania-based catalysts incorporated into a designed bench-scale UV photoreactor indicates that up to 80% of styrene can be degraded to water and carbon dioxide, based on an effective concentration ( C 0) of 300 ppm.