Batch-recirculated Photoreactor Research Articles

Non-linear regression analysis of the kinetics of photocatalytic degradation of phenol using immobilised mesoporous TiO2 nanoparticles on glass beads

ABSTRACT The kinetics of photocatalytic degradation of phenol in batch re-circulated photo reactor packed with immobilised TiO2 nanoparticles on glass beads was estimated under UV light process using non-linear regression analysis. TiO2 nanoparticles are immobilised on glass beads by a simple and inexpensive method. The photocatalytic degradation of phenol using immobilised TiO2 followed pseudo-first-order kinetics. A model was established using non-linear regression analysis for first-order rate constant (k app) as a function of parameters like volumetric flow rate, phenol concentration, intensity of UV light and volume of phenol as the following expression: k app = 0.26 [v o] p [Phenol]o q [I o] r [V] s . This rate equation can be used for predicting k app for various other conditions in batch re-circulated photo reactor.

Photodegradation of lignin from pulp and paper mill effluent using TiO2/PS composite under UV-LED radiation: Optimization, toxicity assessment and reusability study

In the present study, the photodegradation of lignin was studied using TiO2/Polystyrene composite under UV-LED irradiation in a batch-recirculated photoreactor as a supplementary treatment for pulp and paper industries. TiO2/PS composite was synthesized by the solvent-casting method and was characterized by scanning electron microscopy (SEM) and EDX analysis. The 3-level, 3-factor Box-Behnken design was applied to study the effects of main operating parameters and optimization of process circumstances. Besides, COD reduction efficiency, toxicity assays, and reusability were also investigated. The predicted model had R2 and R2adj correlation coefficients of 0.97 and 0.99 respectively, which showed experimental results were very close to the predicted values. Furthermore, under the optimal conditions (reaction time = 72.5, volumetric flow rate = 230 mL/min and lignin = 51.8 mg/L) the lignin degradation efficiency was 93.98%. The maximum COD removal (89%) obtained by 250 mL/min volumetric flow rate and lignin concentration of 50 mg/L after 120 min reaction time. Bioassay using D. Magna exhibited that at the beginning of the process, the toxicity of solution increased but continuously decreasing after then to very low values achieved within 120 min of photodegradation. In addition, the reusability tests demonstrated that the TiO2/PS composite after 5 cycles has a good stability and photocatalytic activity.

Optimization of photocatalytic activity of immobilized TiO2–P25 nanoparticles in the removal of phenazopyridine using response surface methodology

The photocatalytic degradation of phenazopyridine (PhP) as a model contaminant from pharmaceutical compounds was studied using batch-recirculated photoreactor packed with immobilized TiO2–P25 nanoparticles on glass beads. The effects of operational parameters (irradiation time, initial concentration of PhP, volume of solution, and volumetric flow rate) were evaluated by the response surface methodology (RSM). The proposed model of the RSM is a second order mathematical model. According to the results of ANOVA, initial concentration of PhP, volumetric flow rate, irradiation time, volume of solution, mutual effects of initial concentration of PhP × irradiation time, irradiation time × volume of solution and quadratic effects of initial concentration of PhP, and volume of solution are significant model parameters. The optimization process by RSM offers the following optimal conditions: PhP concentration 24 mg L–1, liquid volumetric flow rate 230 mL min–1, irradiation time 30 min, and volume of solution 300 mL. Under these conditions, the proposed removal percent of RSM is 90.28% which have good correspondence with experimental removal percent (87.36%).

Efficiency of a Photoreactor Packed with Immobilized Titanium Dioxide Nanoparticles in the Removal of Acid Orange 7.

In this paper, the removal efficiency of Color Index Acid Orange 7 (AO7) as a model contaminant was investigated in a batch-recirculated photoreactor packed with immobilized titanium dioxide type P25 nanoparticles on glass beads. The effects of different operational parameters such as the initial concentration of AO7, the volume of solution, the volumetric flowrate, and the light source power in the photoreactor were investigated. The results indicate that the removal percent increased with the rise in volumetric flowrate and power of the light source, but decreased with the rise of the initial concentration of AO7 and the volume of solution. The AO7 degradation was followed through total organic carbon, gas chromatography/mass spectroscopy (GC/MS), and mineralization products analysis. The ammonium and sulfate ions were analyzed as mineralization products of nitrogen and sulfur heteroatoms, respectively. The results of GC/MS revealed the production of 1-indanone, 1-phthalanone, and 2-naphthalenol as intermediate products for the removal of AO7 in this process.

Mathematical Kinetic Modelling and Representing Design Equation for a Packed Photoreactor with Immobilised TiO2-P25 Nanoparticles on Glass Beads in the Removal of C.I. Acid Orange 7

In this work, a design equation was presented for a batch-recirculated photoreactor composed of a packed bed reactor (PBR) with immobilised TiO2-P25 nanoparticle thin films on glass beads, and a continuous-flow stirred tank (CFST). The photoreactor was studied in order to remove C.I. Acid Orange 7 (AO7), a monoazo anionic dye from textile industry, by means of UV/TiO2 process. The effect of different operational parameters such as the initial concentration of contaminant, the volume of solution in CFST, the volumetric flow rate of liquid, and the power of light source in the removal efficiency were examined. A rate equation for the removal of AO7 is obtained by mathematical kinetic modelling. The results of reaction kinetic analysis indicate the conformity of removal kinetics with Langmuir-Hinshelwood model (kL-H = 0.74 mg L-1 min-1, Kads = 0.081 mg-1 L). The represented design equation obtained from mathematical kinetic modelling can properly predict the removal rate constant of the contaminant under different operational conditions (R2 = 0.963). Thus the calculated and experimental results are in good agreement with each other.

Determination of optimum conditions for removal of Acid Orange 7 in batch-recirculated photoreactor with immobilized TiO2-P25 nanoparticles by Taguchi method

This study investigated the optimum conditions in the removal of model contaminant C.I. Acid Orange 7 (AO7) in batch-recirculated photoreactor with immobilized TiO2-P25 nanoparticles. The effect of different operational parameters such as initial concentration of AO7, volume of solution, volumetric flow rate, time of the reaction, and power of light source were studied and optimized by Taguchi method. Sixteen experiments were performed to examine the effect of the parameters on the removal of AO7. To reduce the error, each experiment was repeated three times and the signal/noise (S/N) was calculated. Results indicated that the power of light source was the most effective parameter in comparison to others. Based on the S/N ratio, the optimized conditions for the removal of AO7 in batch-recirculated photoreactor were initial concentration of AO7 (20 mg L−1), volume of solution (500 mL), volumetric flow rate (140 mL min−1), time of reaction (60 min), and power of light source (13 W).

Combination of Design Equation and Kinetic Modeling for a Batch-Recirculated Photoreactor at Photooxidative Removal of C.I. Acid Red 17

In this work, a design equation has been presented for a reactor composed of an annular photoreactor and a continuous stirred tank reactor (CSTR) with a batch-recirculated current. In this reactor the removal of a contaminant namely C.I. Acid Red 17 (AR17) that is a monoazo acidic dye by means of UV/H2O2 process has been investigated. AR17 kinetics in all cases follows pseudo-first-order kinetics. The effects of the operational parameters such as liquid volume inside the CSTR, volumetric flow rate and initial concentration of H2O2 in the removal efficiency have been surveyed. The results indicate that the increase in volumetric liquid rate increases the removal rate; also, the increase in the experimental liquid volume inside the CSTR decreases the removal efficiency. H2O2 concentration has a critical effect in the removal efficiency. A rate equation for removal of AR17 was achieved by kinetic modeling. Resulted equation was combined with mole balance equation for achieving final equation. The presented final design equation is thoroughly able to predict the reaction rate constant (kap1) under various conditions so that calculated and experimental results are in good agreement.

Photochemical heterogeneous catalytic reaction at recirculated reactor system

A study was undertaken to examine the possibility of combining a batch-recirculated photoreactor with a ceramic membrane filter for heterogeneous photocatalysis applications. D-cargo red GS (GS) was used as the test substrate and titanium dioxide was used as photocatalyst for this study. The dark adsorption of GS on the TiO2 particle surface was also analyzed. The adsorption trends of GS at various initial concentrations followed the Langmuir isotherm trend. The GS were decolorized from 20% to 70% by the dark adsorption with various concentrations. The photodegradation of GS after the dark adsorption showed the behavior of Langmuir-Hinshelwood model. The variation of recirculation flow rate did not much influence photocatalysis. Variation tendencies of GS concentration were almost similar after about 90 minutes illumination in spite of the flow rate change. The values ofk (apparent first order rate constant) also varied with increase of the recirculation flow rate, but there were no observable significant differences between them.

An integrated flow reactor-membrane filtration system for heterogeneous photocatalysis. Part II: Experiments on the ultrafiltration unit and combined operation

A batch-recirculated photoreactor was combined with a hollow-fibre membrane ultrafiltration (UF) unit for heterogeneous photocatalysis applications. This paper focuses on the operation and modelling of the UF process component and on the performance of the integrated photoreactor–UF process assembly. Methylene blue and titanium dioxide (Degussa P-25) were used as the test pollutant and photocatalyst, respectively. The influence of cross-flow velocity, transmembrane pressure, and TiO2 dose on the permeate flux through the hollow fibre membrane is described. These data are modelled on the basis of concentration polarization and gel layer formation at the membrane surface/feed slurry boundary. The operation of the integrated photoreactor–UF assembly over ten repeat cycles is described. Photocatalyst separation was complete as gauged by nephelometric turbidity measurements. However, a systematic degradation in the photocatalyst performance was noted with each repeat cycle. Dynamic laser light scattering data are consistent with agglomeration of the TiO2 particles as a result of the UF process, and suggest a possible factor in the degraded photocatalytic activity. Possible solutions to this problem are finally presented.

An integrated flow reactor-membrane filtration system for heterogeneous photocatalysis. Part I: Experiments and modelling of a batch-recirculated photoreactor

A two-part study was undertaken to examine the feasibility of combining a batch-recirculated photoreactor with a hollow-fibre membrane based ultrafiltration unit for heterogeneous photocatalysis applications. Methylene Blue (MB) and titanium dioxide (Degussa, P-25) were used as the test substrate and photocatalyst respectively for this study. This paper, which forms Part I of this study, describes the influence of MB concentration, recirculation flow rate, TiO2 dose, solution volume in the reservoir and solution pH on the photocatalytic reaction rate. The dark adsorption of MB on the TiO2 particle surface was also analysed. The combination of the reservoir and the annular reaction vessel could be modelled as a continuous flow stirred tank in series with a plug-flow reactor. This model predicts that the reaction rate should increase with a decrease of solution volume in the reservoir, both in the low and high substrate concentration regimes of the Langmuir–Hinshelwood kinetics formalism. This prediction was borne out by the experimental data for the low concentration regime. Part II of this series will describe experiments and modelling of the UF unit, and the operation of the combined system, respectively.