Packed-bed Photocatalytic Reactor Research Articles

Photocatalytic sol-gel/P25 TiO2 coatings for water treatment: Degradation of 7 selected pharmaceuticals

The effect of different water matrices on the photocatalytic degradation of dissolved pharmaceuticals was explored. The focus was on the degradation efficiencies in wastewater effluent from a bioreactor and water effluent from a central wastewater treatment plant and comparing the results with degradation in deionized H2O. The compounds tested included: oxytetracycline, marbofloxacin, ibuprofen, diclofenac, phenytoin, ciprofloxacin, sulfamethoxazole. For the experiments performed in this study, a compact packed-bed photocatalytic reactor was used in which the hybrid TiO2 photocatalyst (sol-gel/P25) was deposited on ∼3 mm glass beads. As expected, the reactions proceed more slowly in wastewater than in deionized water, yet it is shown that removal of the compounds from the water is still possible even when other organic molecules are present. Total organic carbon measurements have shown that complete mineralization takes place albeit at slower rates than the initial degradation of parent compounds. The results show that an acidic pH can increase the reaction rates and the adsorption on the photocatalyst surface. Analyses of the degradation intermediates were performed using tandem liquid chromatography triple-quadrupole mass spectrometry system. Additionally, X-ray absorption spectroscopy was applied to get insight into the local structure of the photocatalyst before and after use. Understanding the effects that different wastewater compositions have on photocatalytic reactions will help to refine the potential applications of the technology.

Solar photocatalysis at semi-pilot scale: wastewater decontamination in a packed-bed photocatalytic reactor system with a visible-solar-light-driven photocatalyst

Particles of natural volcanic ashes as photocatalyst configured in a packed-bed photocatalytic reactor were studied for the photodegradation of wastewater pollutants under solar light. The photocatalytic system was equipped with a cylindrical parabolic sunlight concentrator, and the photocatalytic treatment has been developed with a continuous flow of wastewater under sunlight irradiation. The influence of incident radiation, amount of photocatalyst, and several configurations in the photoreactor hydrodynamics were studied. Moreover, results obtained were compared with those obtained from the photolysis and adsorption studies. Good photocatalytic activities have been observed, and this allows concluding that heterogeneous photocatalytic system in a packed bed is an effective method for wastewater pollutants removal. In a sunny day, more than 90% of the contaminant can be removed after 5 h by the continuous-flow photocatalytic treatment of the wastewater in the packed-bed reactor under sunlight. The possibility of combining the renewable energy (solar energy) and the photocatalytic technology, by means of a sustainable photocatalytic material, offers a powerful alternative in the wastewater treatment sector.

Bare, gold and silver nanoparticle decorated, monodisperse-porous titania microbeads for photocatalytic dye degradation in a newly constructed microfluidic, photocatalytic packed-bed reactor

Abstract Monodisperse porous titania microbeads were synthesized by a sol-gel templating protocol. Gold nanoparticles (AuNPs) synthesized by Turkevich and Martin methods 16 and 5 nm in size, respectively and silver nanoparticles (AgNPs) 12 nm in size were decorated onto the primary amine attached titania microbeads. Both size and porous properties of bare or AuNP/AgNP decorated monodisperse-porous titania microbeads were suitable for using them as a photocatalyst in a “Microfluidic, Photocatalytic Packed Bed Reactor (MPPBR)” with reasonable pressure drops in the microflow rate range. Then, a MPPBR system for “continuous photocatalytic dye degradation” was first constructed by slurry packing of bare or AuNP/AgNP decorated titania microbeads into a fused silica capillary 320 μm in diameter. The photocatalytic activities of bare and AuNP/AgNP decorated titania microbeads were determined in MPPBR using a textile dye, Remazol Black 5 (RB5). The complete removal of RB5 was achieved in continuous mode and an appreciable enhancement in the photoremoval rate of RB5 was observed with the MPPBR containing Martin AuNP decorated titania microbeads. The system constructed can be evaluated as a promising tool for both pre-column and post-column applications involving the removal of coloured contaminants in the assays conducted in micro-liquid chromatography systems.

Performance of gas-phase photocatalytic reactors on hydrogen production

Three types of high-performance photocatalytic reactors were developed for gas-phase photocatalytic hydrogen (H2) production from hydrogen sulphide (H2S) and effective photocatalytic decomposition of gaseous H2S at a very low concentration is investigated. In this paper, three lab-scale photocatalytic reactors viz., packed bed photocatalytic reactor, catalyst coated fixed bed photocatalytic reactor and catalyst dispersed photocatalytic reactors were developed to study the performance of reactors on hydrogen production. The novel photocatalyst (CdS + ZnS)/Fe2O3 and the optimized catalyst dosage, H2S gas flow rate, pollutant concentration, light irradiations were used. The experimental result indicates that packed bed photocatalytic reactor can effectively splits the H2S into hydrogen (i.e. 98%) and rapidly decompose H2S toward zero concentration than the other two reactors. Hence the bench-scale photocatalytic reactor was fabricated in packed bed reactor and the maximum hydrogen conversion achieved from hydrogen sulphide was found to be 98%.

Photocatalytic packed bed reactor design for efficient UV light utilization

In this study, TiO2/SiO2 beads packed bed reactor system in which black light was placed at the center of the reactor was developed for a low cost and environmentally–friendly water treatment process. The reactor was designed to achieve efficient utilization of UV light, large contact area with pollutants as well as easier post separation at the same time. As model pollutants, PNP and DNP were used in this study, and the effects of the initial concentration of those substrates and radial thickness of the packed bed for the decomposition properties were examined. The results showed that the decomposition ratio decreased with the increase of the initial concentration and the packed bed radial thickness. The result suggested that the UV light was absorbed by the solution and TiO2/SiO2 beads. To take into consideration the effect of light absorption toward radial direction of the reactor on the decomposition ratio, simple model called “2-boxes model” was developed. The result of reaction kinetics analysis showed that the 2-boxes model could reasonably explain the experimental data. Finally, by using 2-boxes model, the effective diameter of penetrated UV light was examined. The result confirmed that it decreased with the increase of UV absorption caused by the increase of initial inlet concentration and the increase of the radial thickness of the packed bed. This indicates that the simple 2-boxes model can approximately estimate the effective diameter of packed bed for PNP or DNP decomposition, and it will give a design guideline for an efficient TiO2/SiO2 beads packed bed reactor system for water treatment.

A continuous flow packed bed photocatalytic reactor for the destruction of 2-methylisoborneol and geosmin utilising pelletised TiO2

Taste and odour compounds, especially geosmin (GSM) and 2-methylisoborneol (2-MIB), cause major problems in both drinking water and aquaculture industries world-wide. Aquaculture in particular has experienced significant financial losses due to the accumulation of taint compounds prior to harvest resulting in consumer rejection. UV–TiO2 photocatalysis has been demonstrated to remove GSM and 2-MIB at laboratory scale but the development of a continuous flow reactor suitable for use in water treatment has not been investigated. In this study, a pilot packed bed photocatalytic reactor was developed and evaluated for water treatment with both laboratory and naturally tainted samples. A significant reduction of both 2-MIB and GSM was achieved in both trials using the packed bed reactor unit. With the laboratory spiked water (100ngL−1 of each compound added prior to treatment), detectable levels were reduced by up to 97% after a single pass through the unit. When the reactor was used to treat water in a fish farm where both compounds were being produced in situ (2-MIB: 19ngL−1 and GSM: 14ngL−1) a reduction of almost 90% in taint compounds was achieved. These very encouraging promising results demonstrate the potential of this UV–TiO2 photocatalytic reactor for water treatment in fish rearing systems and other applications.

Modeling of a TiO2-coated quartz wool packed bed photocatalytic reactor

A fixed-bed, photocatalytic laboratory reactor aimed to degrade pollutants from water streams was designed and built. Quartz wool coated with a thin film of TiO2 was employed as the reactor filling. The photocatalyst was placed in the reactor forming a loose packing to guarantee the intimate contact among reactants, photons, and the photocatalytic surface. This reactor was employed to study the photocatalytic decomposition of a model pollutant (formic acid). A reactor–radiation–reaction model was developed, which was comprised of the reactor mass balance, radiation model, and kinetic model for the degradation of formic acid. The local superficial rate of photon absorption, which was necessary to evaluate the kinetic, was obtained from the results of a radiation model. The Monte Carlo approach was employed to solve the radiation model, where the interaction between photons and the TiO2-coated fibers of the packing was considered. The kinetic model was derived from a plausible kinetic scheme. Experimental results obtained in the packed-bed reactor, operating in a differential mode and without mass transfer limitations, were used to estimate the parameters of the kinetic model. A satisfactory agreement was observed between model simulations with the derived parameters and experimental results, with a root mean square error less than 8.3%.

Performance of a Bench-Scale Annular-Type Packed-Bed Photocatalytic Reactor for Decomposition of Indigo Carmine Dissolved in Water

A bench-scale annular-type packed-bed photocatalytic reactor with TiO2-coated glass beads as the photocatalyst was designed; the performance of the reactor was evaluated by using it for the photocatalytic decomposition of indigo carmine (IC) dissolved in water. The reactor was operated in a recirculation batch mode, and the dye solution in the reservoir was recirculated through the photocatalyst bed in the annular space of the reactor. The concentration of the dye in the reservoir decreased gradually with an increase in the operation time. The time course of the change in the IC concentration was calculated numerically by assuming first-order kinetics, and the overall rate constant of photocatalytic decomposition was determined by fitting the calculated time course to the experimental value obtained for various treatment times. The overall decomposition rate constants decreased with an increase in the initial concentration of the IC solution. The rate-controlling step in the photocatalytic decomposition was the mass transfer of IC from the bulk of the solution to the catalyst surface when the flow rate was less than 1 dm3/min; however, when the flow rate exceeded the transition flow rate, the reaction occurring at the catalyst surface was the rate-controlling step.

Photocatalytic Degradation of Methanol Using Silica–Titania Composite Pellets: Effect of Pore Size on Mass Transfer and Reaction Kinetics

Nanostructured silica-titania composites (STC) synthesized with varying pore sizes (45, 134, and 299 angstroms) were tested for the removal of methanol from a humid air stream. The STC pellets were characterized for surface area and pore size distribution and tested in a packed-bed photocatalytic reactor for methanol removal and oxidation. While the pore size distributions for all STC were unimodal, STC with larger average pore sizes exhibited a broader pore size distribution. The efficiency of methanol oxidation was dependent on the surface area of the STC and the space time of the gas in the reactor. For all STC tested, the rate of methanol oxidation was not limited by resistances to external or internal mass transfer. For 134 and 299 angstroms STC, a lag time of 1.0 and 1.2 s, respectively, was observed before mineralization began. After this lag time, which was zero for the 45 angstroms STC, the data followed pseudo first-order reaction kinetics and the rate constant, k, was 0.40 s(-1) for all pore sizes.

Photocatalytic degradation of volatile organics on TiO 2 embedded glass spherules

This work investigates the feasibility of applying photocatalytic technology for removal of volatile organic compounds (VOCs) over TiO 2. A photocatalytic packed bed reactor (PPBR) was employed to determine the oxidation rates of VOCs (bezene, toluene, o-, m-, p- xylenes). TiO 2 Degussa P25 was used to prepare a nanocrystalline titania paste, where glass spherules were embedded. The photocatalyst was extensively characterized by means of spectroscopy (Raman, XRD) and microscopy (SEM, AFM). Experiments were conducted under ‘real world setting’ condition of temperature (25 °C ±2) and humidity (60%) while the irradiation was provided by 15 W near UV lamps. The dependence of the reaction rate on light intensity as well as the deactivation of the catalyst were determined. The results indicate that the rate of the photo-oxidation process increased while increasing the intensity of UV irradiation. Using two (2) UV-A lamps, the destruction rate of benzene and toluene was 0.0429 and 0.1960 μg m −2 h −1 respectively, while with four (4) UV-A lamps values of 0.6775 and 1.5301 μg m −2 h −1 correspondingly were obtained. The stabilized photocatalysts present remarkable stability (no deactivation and excellent repeatability). Reproducibility tests proved that the photocatalytic activity of the photocatalyst remains intact even after thirty consecutive experiments of new added VOCs quantities.

The design and photoreaction kinetic modeling of a gas-phase titania foam packed bed reactor

The design and testing as well as theoretical and experimental study involving kinetic modeling and photooxidation reactions of a gas-phase photocatalytic packed bed reactor (PBR) based on a porous titania foam is reported. The photoreactor was designed to incorporate a nanoporous titania foam photocatalyst for volatile organic compound (VOC) remediation in the gas-phase. Theoretical and experimental studies based on the photodegradation of model volatile organic compounds (VOCs), have been carried out and results show that 90% degradation can be achieved in the photoreactor which has been designed at low cost and to provide increased efficiency at elevated pollutant feed. The reactor represents an inexpensive design and can be applied to the remediation of various pollutants of biological, organic or inorganic origin. In addition, the reactor can accommodate the photocatalyst in the form of a thin film and porous foams. © 2007 Elsevier B.V. All rights reserved.

Kinetic modeling of promotion and inhibition of temperature on photocatalytic degradation of benzene vapor

This study investigated the effects of temperature, humidity, and benzene concentration on the photocatalytic oxidation of benzene vapor over titanium dioxide. An annular packed-bed photocatalytic reactor was employed to determine the intrinsic oxidation rates for the photocatalysis of benzene. Degussa P-25 TiO 2 was used as the photocatalyst and a 15 W near-UV lamp (350 nm) was used as the light source. The experiments were conducted at influent benzene concentrations of 250–450 ppmv, water vapor concentrations of 13,500–27,500 ppmv, and reaction temperatures ranging from 100 to 200 °C. Benzene oxidation rates increased with temperature below 160–180 °C, but decreased with temperature above 160–180 °C. Raising the reaction temperature increased the chemical reaction rates but reduced the reactant adsorption rate on TiO 2 surfaces. The overall reaction rate increased with temperature, indicating that the reduction of reactant adsorption rate did not affect the overall reaction, and thus the chemical reaction was the rate-limiting step. As the chemical reaction rate gradually exceeds the reactant adsorption rate with temperature, the rate-limiting step was shifted from the chemical reaction to the reactant adsorption. Additionally, the competitive adsorption between benzene and water for the active sites on TiO 2 resulted in the promotion and inhibition of reaction rate by humidity. This study developed a modified bimolecular Langmuir–Hinshelwood kinetic model to simulate the temperature and humidity related promotion and inhibition of the photocatalysis of benzene. The correlation developed here was used as a basis for determining the apparent activation energy of 0.76 kcal/mol and adsorption enthalpies of benzene and water of −20.1 and −13.7 kcal/mol.

Design and theoretical study of a packed bed photoreactor

The design and fabrication of a new gas-phase photocatalytic packed bed reactor (PBR) is described. The photoreactor was conceived for incorporating porous, foaming titania photocatalysts for volatile organic compounds (VOCs) destruction. The PBR is optimized by theoretical prediction of the conversion factor x as a function of the molecular feed, volume and reaction rate.

Preliminary analysis of a tellerette packed-bed photocatalytic reactor

A novel tellerette packed bed photoreactor (TPBP), in which titanium dioxide was immobilized on stainless steel tellerette packings, was developed to provide a combination of good light and mass transfer. The experiments revealed that mass transfer limitations in this packed bed photoreactor were insignificant, such that the reaction appeared to be kinetically controlled even in regions closest to the illumination sources. A combination of measurements and simple modelling suggests that the TPBP may have potential use due to the effective mass transfer and UV light penetration characteristics.