Fluidized Bed Photocatalytic Reactor Research Articles

Effects of KBr and KI on Photocatalytic Degradation of Dye W-7G with Nano-TiO2 as Catalyst

To investigate the influence of inorganic salt on the photocatalytic degradation, the effects of KBr and KI at various concentrations and pH values on the photocatalytic degradation of dye W-7G using nanoscaled titanium dioxide as photocatalyst in a bubbling fluidized bed photocatalytic reactor (BFBPR) were studied. The results indicated that the degradation apparent rate constant ( K app ) of the system with KI was clearly higher than that with KBr under acidic or alkaline conditions. And the maximum value of K app (0.01127) appeared at the KI concentration of 0.075 g L-1 with a pH value of 9.37, meaning the highest degradation efficiency. Furthermore, the possible mechanism of photocatalytic degradation of W-7G in the presence of KBr and KI was proposed, which could provide a theoretical support for the further study of inorganic salt effects on the photocatalytic degradation of dyes.

Photocatalytic Removal of NO on Sulphated TiO2 in a Photocatalytic Fluidized Bed Reactor

Photocatalytic Removal of NO on Sulphated TiO₂ in a Photocatalytic Fluidized Bed Reactor

Impact of pH on the kinetics of photocatalytic oxidation of 2,4-dichlorophenoxy acetic acid in a fluidized bed photocatalytic reactor

The impact of pH on the kinetics of photocatalytic oxidation of 2,4-dichlorophenoxy acetic acid (2,4-D) was investigated. Experiments were performed in fluidized bed photocatalytic reactor using TiO2 photocatalyst spheres. The rate of oxidation was affected by the solution pH. In acidic medium, according to the kinetic model, the rate of oxidation was higher because the rate constant was directly related to UV intensity (I); whereas this relationship reduced to a functional square root (i.e., I1/2) at pH 7. In addition, pH resulted in changing the photocatalytic oxidation mechanism. At pH 7, the photocatalytic oxidation took place away from the photocatalyst surface, the oxidation rate followed first order kinetics. Under acidic condition, on the other hand, the oxidation mostly took place on the surface of photocatalyst and the rate of oxidation followed a combination of the Langmuir-Hinshelwood and first order kinetic models.

Impact of natural organic matter on the degradation of 2,4-dichlorophenoxy acetic acid in a fluidized bed photocatalytic reactor

The effect of natural organic matter (NOM) on the photocatalytic oxidation of 2,4-Dichlorophenoxy acetic acid (2,4-D) was investigated in a fluidized bed photocatalytic reactor (FBPR), utilizing template free photocatalytic spheres. Changes in solution pH were used to decouple the effects of NOM on adsorption and major oxidative mechanisms, e.g., reactions on the surface of the photocatalytic spheres via positive hole (h+) mediation as well as in the solution via hydroxyl radicals (OH) reaction. At pH 3, highly electrostatic attraction between solutes (2,4-D and NOM) and photocatalyst surface caused increasing adsorption and consequently photocatalytic oxidation which mostly occurred via charge transfer on the surface of the spheres. At pH 7, on the other hand, electrostatic repulsion between solutes and photocatalyst surface reduced the adsorption and the process was primarily driven by hydroxyl radical attacks. With the aid of methanol as an OH scavenger, it was determined that at neutral pH, due to higher aromatic moieties concentration and lower NOM adsorption, the effect of NOM on scavenging OH was considerable. This effect dramatically decreased at low pH due to high adsorption of NOM.

Solar light mediated photocatalytic degradation of phenol using Ag core – TiO2 shell (Ag@TiO2) nanoparticles in batch and fluidized bed reactor

Ag@TiO2 nanoparticles were synthesised using one pot method followed by calcination at 450°C for 3h and were tested for their photocatalytic efficacy in degradation of phenol both in free and immobilized form under solar light irradiation through batch experiments. Ag@TiO2 nanoparticles were found to be effective in solar photocatalytic degradation of phenol. The effect of factors such as pH, initial phenol concentration and catalyst loading on phenol degradation were evaluated and these factors were found to influence the process efficiency. The optimum values of these factors were determined to maximize the phenol degradation. The efficacy of nanoparticles immobilized on cellulose acetate film was inferior to that of free nanoparticles in solar photocatalysis due to light penetration problem and diffusional limitations. The performance of fluidized bed photocatalytic reactor operated under batch with recycle mode for solar photocatalysis of phenol with immobilized Ag@TiO2 nanoparticles was evaluated for large scale application. The performance was found to be dependent on catalyst loading and the optimum is governed by active catalyst sites and light penetration limitations. The photocatalytic degradation of phenol by Ag@TiO2 nanoparticles was only marginally influenced by the presence of small traces of chloride ions. Ag@TiO2 showed a better efficacy as solar photocatalyst than as UV photocatalyst in degradation of phenol. Solar light irradiation is recommended because solar energy, a readily available form of energy can be effectively harnessed for energy efficient, environment friendly and cost effective process. The kinetics of degradation of phenol was found to follow the nth order kinetics with order, n=2.19 for solar photocatalysis.

Photocatalytic degradation of phenol using Ag core-TiO2 shell (Ag@TiO2) nanoparticles under UV light irradiation

Ag@TiO2 nanoparticles were synthesized by one pot synthesis method with postcalcination. These nanoparticles were tested for their photocatalytic efficacies in degradation of phenol both in free and immobilized forms under UV light irradiation through batch experiments. Ag@TiO2 nanoparticles were found to be the effective photocatalysts for degradation of phenol. The effects of factors such as pH, initial phenol concentration, and catalyst loading on phenol degradation were evaluated, and these factors were found to influence the process efficiency. The optimum values of these factors were determined to maximize the phenol degradation. The efficacy of the nanoparticles immobilized on cellulose acetate film was inferior to that of free nanoparticles in UV photocatalysis due to light penetration problem and diffusional limitations. The performance of fluidized bed photocatalytic reactor operated under batch with recycle mode was evaluated for UV photocatalysis with immobilized Ag@TiO2 nanoparticles. In the fluidized bed reactor, the percentage degradation of phenol was found to increase with the increase in catalyst loading.

Typical Application of Sound Field in Wastewater Treatment with Fluidized Bed Photocatalytic Reactor.

The effect of a sound field on wastewater treatment with a fluidized bed photocatalytic reactor (FBPR) was investigated. With Alizarin Green (AG) being the sole infectant, the Fe-doped TiO2 catalyst prepared was used as the fluidized media. According to the Langmuir-Hinshelwood model, the photocatalytic degradation follows the pseudo-first-order reaction kinetics with respect to the concentration of AG. Sound field application allowed the fluidization of the fine powder at high liquid flow rates; thus, the mass transfer rate between organic pollutant and particle photocatalyst was enhanced and the efficiency of degradation was increased. As expected, the degradation rate constant increased with increasing sound pressure level, as well as increased with increasing sound frequency ranging from 50 to 100 Hz, then further decreased with increasing sound frequency from 100 to 200 Hz. In addition, Fe doping is also responsible for the enhanced photocurrent response of the Fe-doped TiO2 nanoparticle in FBPR relative to pure TiO2.

Titanium dioxide sol–gel-coated expanded clay granules for use in photocatalytic fluidized-bed reactor

An experimental research into the titania coatings on granulated expanded clay to be used in fluidized-bed photocatalytic reactor was undertaken. The preparation procedures were performed via sol–gel method using dip coating techniques. Two sol–gel compositions based on tetrabutyl orthotitanate and titanium tetraisopropoxide as well as two commercial TiO2 sols were examined. The impacts of titania precursor concentration, modification of sol–gel by industrially available TiO2 nanoparticles, the substrate withdrawal speed and thermal treatment conditions on the coatings’ properties were studied. The photocatalytic activity of expanded clay-supported titania was evaluated by the degradation of an emerging micropollutant, tetracycline family antibiotic doxycycline. Mechanically stable and active coatings with properties dependent on sol–gel processing parameters were obtained. The application of porous titania sol–gel-coated expanded clays could combine pollutants’ adsorption and their photocatalytic degradation. The compromise between coatings’ improved photocatalytic performance, on the one hand, and their adhesion and attrition properties, significant for fluidized-bed operation, on the other hand, lead to the determination of appropriate processing parameters.

Investigation into adsorption and photocatalytic degradation of gaseous benzene in an annular fluidized bed photocatalytic reactor

The adsorption and photocatalytic degradation of gaseous benzene were investigated considering the operating variables and kinetic mechanism using nano-titania agglomerates in an annular fluidized bed photocatalytic reactor (AFBPR) designed. The special adsorption equilibrium constant, adsorption active sites, and apparent reaction rate coefficient of benzene were determined by linear regression analysis at various gas velocities and relative humidities (RH). Based on a series of photocatalytic degradation kinetic equations, the influences of operating variables on degradation efficiency, apparent reaction rate coefficient and half-life were explored. The findings indicated that the operating variables have obviously influenced the adsorption/photocatalytic degradation and corresponding kinetic parameters. In the photocatalytic degradation process, the relationship between photocatalytic degradation efficiency and RH indicated that water molecules have a dual-function which was related to the structure characteristics of benzene. The optimal operating conditions for photocatalytic degradation of gaseous benzene in AFBPR were determined as the fluidization number at 1.9 and RH required related to benzene concentration. This investigation highlights the importance of controlling RH and benzene concentration in order to obtain the desired synergy effect in photocatalytic degradation processes.

A novel fluidized-bed-optical-fibers photocatalytic reactor (FBOFPR) and its performance

The key in designing a photocatalytic reactor lies in resolving the problems of mass transfer, light transmission and light scattering. Especially, the light scattering of catalyst is very acute, which makes the accurate quantification of light irradiation difficult. In this study, a novel fluidized-bed-optical-fibers photocatalytic reactor (FBOFPR) with easy quantification of light irradiation was designed by combining fluidized-bed photocatalytic reactor with optical-fiber light source that its optical fibers were fixed by an aluminum fixed jacket for UV total reflection, and its performance was tested by using trichloroethylene (TCE) as a target pollutant. The results show that, under the condition of water vapor content at 0.25%, oxygen content at 20.8%, initial concentration of TCE at 303.32ppm, input light amount at 3.07×1017s−1 and residence time at 1.6s, the apparent photon quantum efficiency is 26.31%, the turnover frequency is 12.44μmol/(g TiO2min) and the removal efficiency is 86.66%. Compared with the conventional flat plate fluidized-bed photocatalytic reactor, FBOFPR exhibits many advantages in the aspect of effective use of photon, sufficient exertion of catalyst activity, effective removal of TCE and easy quantification of light irradiation.

Photocatalytic Hydrogen Production from Refinery Gas over a Fluidized-Bed Reactor I: Numerical Simulation

Photocatalytic technology has received increasing attention owing to its various advantages. In this work, we designed a fluidized-bed photocatalytic reactor using H2S simultaneously as the bubbling gas for catalyst suspension and as the feed for hydrogen production. The photocatalyst distribution was simulated by CFD with a Eulerian model. The simulation results indicated that the fluidizing time showed a linear relationship with the inlet gas velocity and that the optimal inlet gas velocity was between 30 and 50 mL/min. Further, light energy absorption characteristics, in both homogeneous and heterogeneous media, were simulated by the Monte Carlo method. Our study showed that light energy absorption is affected by the nonuniform distribution of the catalyst particles and that finding the optimum optical thickness in chemical reaction space and the optimal height for catalyst fluidization is essential for reactor design. The simulation results and the related predictions are helpful for the design and optimization of fluidized-bed photocatalytic reactors.

Photocatalytic Hydrogen Production from Refinery Gas over a Fluidized-Bed Reactor II: Parametric Study

Based on the numerical simulation results in our previous article, experimental studies were conducted. Under our reaction conditions, the selected nano-Cd0.5Zn0.5S photocatalyst could be homogenously suspended by 40 ± 5 mL/min H2S bubbling, as predicted. A homogenous distribution of photocatalyst ensured efficient absorption of the incident light. Hydrogen production with Na2S/Na2SO3 solution in a batch photocatalytic reactor (BPR) and in a fluidized-bed photocatalytic reactor with H2S bubbling (FBPR) were compared. The activity of the FBPR was obviously higher than that of the BPR. The reaction rate constant was 1.12 for the FBPR, whereas it was only 0.083 for the BPR case. The similar hydrogen productions and significant difference in reaction rate constants for the two reactors indicates that an increase in the effective initial reactant concentration in FBPR is essential. In this regard, a circulating fluidized bed with recycling use of H2S gas is preferred. Our study is expected to provide useful guidance for the development of a direct photocatalytic H2S decomposition technology.

Photocatalytic degradation intrinsic kinetics of gaseous cyclohexane in a fluidized bed photocatalytic reactor

The special photocatalytic degradation intrinsic kinetics of gaseous cyclohexane were investigated in a designed fluidized bed photocatalytic reactor (FBPR). A series of photocatalytic kinetic reaction equations were developed to explore the relationship of degradation efficiency and operating variables based on photocatalytic mechanism and particle fluidization hydrodynamic characteristics. The corresponding results indicated that the initial concentration has influenced the photocatalytic degradation reaction conversion, and having a concentration inflexion point which theoretically divided the photocatalysis into a first-order apparent kinetic rate equation at low concentrations and a zero-order kinetic rate equation at high concentrations. Furthermore, these results were validated theoretically by the intrinsic kinetic models of photocatalytic degradation conversion developed according to variation of cyclohexane concentration and gas velocity. Based on the experimental results, the optimal operating gas velocity range was determined. The multi-factors synergy effect resulting from gas velocity on photocatalytic degradation efficiency was explored and proved by mass transfer, illumination transmission and adsorption models. Finally, the degradation pathways of the cyclohexane and deactivation mechanism of the photocatalyst were studied according to the intermediates degraded on TiO2 surface, and a feasible method presented for catalyst regeneration.

Adsorption and Photocatalytic Oxidation of Methanol–Benzene Binary Mixture in an Annular Fluidized Bed Photocatalytic Reactor

Adsorption and photocatalytic degradation kinetics of a gaseous benzene–methanol binary mixture in an annular fluidized bed photocatalytic reactor (AFBPR) were investigated. On the basis of a series of adsorption and photocatalytic degradation kinetic equations developed, the influences of molar ratios of benzene–methanol and relative humidity (RH) on adsorption efficiency, degradation efficiency, and half-life were explored. The results indicated that the molar ratio of benzene–methanol and RH has obviously influenced the adsorption/photocatalytic degradation and corresponding kinetic parameters. In the adsorption process, the coadsorption mechanism of methanol–benzene not only was related to competition adsorption but also involved penetrating the multi- or mono-water layer formed on the surface of catalyst particles as well. On the basis of the photocatalytic degradation kinetics of the benzene–methanol binary component, a new mechanism occurred in the photocatalytic oxidation of the methanol–benzene binary mixture due to competitive adsorption of them and some new radicals produced on the same photocatalyst surface was deduced. The special complex relationship between the photocatalytic degradation efficiency and the molar ratio of benzene–methanol with various RH demonstrated that there was an obvious synergy effect between benzene, methanol, and water molecule in photocatalytic degradation processes. This investigation highlights the importance of controlling RH and molar ratio in binary mixture in order to obtain the desired synergy effect in PCO processes.

Photocatalytic degradation of bisphenol A using an integrated system of a new gas-liquid-solid circulating fluidized bed reactor and micrometer Gd-doped TiO2 particles

A new gas-liquid-solid circulating fluidized bed photocatalytic reactor (GLSCFBPR) with internally placed multi-layered UV lamps was developed. Micrometer Gd-TiO2 particles and commercial nanometer P25-TiO2 were chosen as the photocatalysts, and the hazardous substance bisphenol A (BPA) was chosen as the model pollutant to investigate the performance of this new photocatalytic system. The results showed that the photocatalytic degradation efficiency of the micrometer Gd-TiO2 particles was similar to that of the nanometer P-25 particles at their respective optimum dosage but the former could be easily separated out by gravity. After investigating the effects of process parameters on the photocatalytic BPA degradation, the response surface method (RSM) was further used for process optimization. The interactions among process parameters, i.e., TiO2 concentration, superficial gas velocity and superficial liquid velocity were discovered and a related analysis was carried out to explore the underlying mechanism. A quadratic mathematic model was established and performed satisfactorily when used for prediction. The optimum conditions for this new process were as follows: TiO2 concentration 4.5 g/L, superficial gas velocity 7.83 × 10−3 m/sec and superficial liquid velocity 8.65 × 10−3 m/sec.

Ethanol partial photoxidation on Pt/TiO2 catalysts as green route for acetaldehyde synthesis

Heterogeneous photocatalytic partial oxidation of ethanol was studied over different Pt/TiO2 as an alternative green process for acetaldehyde production.The catalysts were synthesized through the photodeposition of Pt over sol–gel TiO2 with platinum loads of 0.5 and 1wt.%. The effect of some experimental conditions during photodeposition, such as deposition time and Pt loading, was investigated. A short deposition time at 0.5wt.% Pt nominal loading led to small average particle size of platinum (2–3nm) homogeneously distributed all over the TiO2 surface.Ethanol partial oxidation was tested in a gas–solid photocatalytic fluidized bed reactor at high illumination efficiency, using different reaction temperatures. Activity results have been correlated with characterization results of the different samples. Platinized samples prepared with short deposition times showed high conversion levels and high selectivity to acetaldehyde. Materials prepared at longer times, 120min, showed selectivities >98%, although with lower ethanol conversion.Sample with 1wt.% Pt loading prepared with 15min deposition time combined a good compromise between a relevant ethanol conversion and a very high selectivity to acetaldehyde at a selected reaction temperature of 80°C, with an acetaldehyde yield higher than 80%, which make of this catalyst a good candidate for acetaldehyde production by photocatalysis.

Photocatalytic Ethanol Oxidative Dehydrogenation over Pt/TiO2: Effect of the Addition of Blue Phosphors

Ethanol oxidative dehydrogenation over Pt/TiO2photocatalyst, in the presence and absence of blue phosphors, was performed. The catalyst was prepared by photodeposition of Pt on sulphated TiO2. This material was tested in a gas-solid photocatalytic fluidized bed reactor at high illumination efficiency. The effect of the addition of blue phosphors into the fluidized bed has been evaluated. The synthesized catalysts were extensively characterized by different techniques. Pt/TiO2with a loading of 0.5 wt% of Pt appeared to be an active photocatalyst in the selective partial oxidation of ethanol to acetaldehyde improving its activity and selectivity compared to pure TiO2. In the same way, a notable enhancement of ethanol conversion in the presence of the blue phosphors has been obtained. The blue phosphors produced an increase in the level of ethanol conversion over the Pt/TiO2catalyst, keeping at the same time the high selectivity to acetaldehyde.

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.

Photodegradation of benzene, toluene, ethylbenzene and xylene by fluidized bed gaseous reactor with TiO2/SiO2 photocatalysts

The photodegradation of BTEX (benzene, toluene, ethylbenzene and xylene) in a photocatalytic fluidized bed reactor with TiO2/SiO2 was investigated. The TiO2 film was prepared using the sol-gel method and coated onto silica-gel powder. The effects of the superficial gas velocity and SiO2 size on the photodegradation of BTEX were examined in a fluidized bed reactor. At steady-state operation, above 79, 79, 99, 98, and 98% removal efficiencies were achieved for benzene, toluene, ethylbenzene, m, p-xylene and o-xylene, respectively, under optimal conditions (2.0 Umf of superficial gas velocity and 1.43 of height/diameter ratio). The reaction product such as CO2 was detected and intermediate products such as benzaldehyde, malonic acid, acetaldehyde, and formic acid were identified from the photocatalytic reaction. Also, small amounts of benzoic acid and benzyl alcohol were found through analyzing the intermediate species adsorbed on the photocatalysts. The experimental results can lead to the development of an efficient photocatalytic treatment system that utilizes solar energy and TiO2/SiO2 photocatalysts.

Adsorption and degradation of model volatile organic compounds by a combined titania–montmorillonite–silica photocatalyst

A series of adsorptive photocatalysts, combined titania–montmorillonite–silica were synthesized. The resultant photocatalysts consisted of more and more spherically agglomerated TiO 2 particles with increasing of TiO 2 content, and anatase was the only crystalline phase with nano-scale TiO 2 particles. With increasing of the cation exchange capacity to TiO 2 molar ratio, specific surface area and pore volume increased very slightly. In a fluidized bed photocatalytic reactor by choosing toluene, ethyl acetate and ethanethiol as model pollutants, all catalysts had relatively high adsorption capacities and preferred to adsorb higher polarity pollutants. Langmuir isotherm model better described equilibrium data compared to Freundlich model. Competitive adsorptions were observed for the mixed pollutants on the catalysts, leading to decrease adsorption capacity for each pollutant. The combined titania–montmorillonite–silica photocatalyst exhibited excellent photocatalytic removal ability to model pollutants of various components. Almost 100% of degradation efficiency was achieved within 120 min for each pollutant with about 500 ppb initial concentration, though the efficiencies of multi-component compounds slightly decreased. All photocatalytic reactions followed the Langmuir–Hinshelwood model. Degradation rate constants of multi-component systems were lower than those for single systems, following the order of toluene < ethyl acetate < ethanethiol, and increased with the increase of adsorption capacities for different pollutants of various components.