Photocatalytic Reactor Employing Titanium Dioxide: From a Theoretical Model to Realistic Experimental Results

Abstract

The performance of a reacting system for degradation of trichloroethylene (TCE) in a pilot-size annular photocatalytic reactor having a tubular lamp located at its centerline was studied. The reactor operation was carried out with commercial catalytic particles of titanium dioxide (Aldrich) in a water suspension. The description of the reactor performance was made by employing a kinetic model developed in a laboratory reactor of different size and configuration, irradiated with similar lamps of lower output power. The annular reactor was operated in the continuous mode but inside the loop of a recirculation system.The performance of the annular reactor was modeled by assuming three different behaviors: (i) a well-stirred tank reactor, (ii) a pseudo-steady-state laminar flow reactor in a batch recycle, and (iii) a transient-state laminar flow reactor in a recycle. Case iii produced the best representation of the experimental data. Along with the experimental validation of the developed theoretical models, three practical features were unveiled that had to be taken into account in any subsequent design: (a) an important change in the pH, from 6.5 to 3.5, along the reaction time; (b) a significant titanium dioxide deposition on the reactor walls; and (c) an appreciable catalyst agglomeration produced by the recirculation system and magnified by the change in pH. Only after the first 120 min of reaction time, the reactor conditions became almost stabilized; thus, the observed transformations had to be incorporated into the modeling.

Photoreactors for Wastewater Treatment: A Review

“…XeL [17,29], FL [30], ML [23] UV: pesticide photolysis [29] UVA 315 -400 Ultraviolet A HPML [31,32], FL [30,33], Bl [34], BlB [35,36], XeL [17], MVL [37], BLFL [38], MPML [39], ML [23], TL [40] UV/TiO2:organic and inorganic pollutants [41][42][43], dyehouse effluents [33], phenol [17,32], 4-CP [32], 4-NP [32], salicylic acid [38], chloroform [44], chloroorganic pesticides [45][46][47], cyanide [48], BSA [30], dodecane [49]; Fe +3 /H2O2/UV-vis: fenitrothion [50] Microwave 1 -15 mm Microwave-induced oxidation, e.g. microwave-induced ClO2-CuOx/Al2O3 process for phenol removal [82] should be fixed, e.g.…”

“…Another purpose of black box (often wooden, inside covered with black material or painted black), dark room, covering reactor walls with black adhesive tape [40], aluminum foil [107] or closing reactor with a mirror cover [52] is to avoid the influence of stray light (natural or artificial), often unfavorable (e.g. UVrays for testing the activity under visible light irradiation of modified titania photocatalysts), which can reach a reactor.…”

“…during photocatalytic oxidation of salicylic acid in a pilot-scale LFFS photocatalytic reactor [111] and in a pilot plant "fountain" photocatalytic reactor [119], during degradation of 4-chlorophenol in a cylindrical slurry reactor [117], for hydrodynamic calculation by computational fluid dynamics (CFD) with visualization data by particle image velocimetry (PIV) [120]. However for long reaction time (>120 min), realistic reactors may have a performance very different than predicted one by theoretical calculation [40]. Romero et.…”

“…al. examined an annular, tubular reactor inside a recycle for three different modes: (i) perfectly mixed, (ii) operating at pseudo-steady-state, and (iii) operating at transient state, and only the third one, after consideration of deposition and agglomeration effects, fitted to the experimental results [40]. It is thought that insufficient amount of research on photoreactor modeling, and thus a lack of readily applicable mathematical models to reactor design and scale-up, is the reason of impeding application of photocatalytical method for wastewater treatment on an industrial scale [116].…”

“…-Shape: cylindrical [117,[133][134][135], annular [24,40,134], round-shaped [101], vertical [30], horizontal [30], flat [136], rectangular [51], tubular [137,138], roundbottom [35], flat-surfaced [54,139] and round flask [140] reactor,…”