Performance of immobilized photocatalytic reactors in continuous mode

Abstract

) A packed-bed PBR , fiber FR , membrane MR , and tubular TR photocatalytic reactor ha®e been modeled to compare their performance on a pilot scale. The influence of radial dispersion in the PBR and mass-transfer limitation in the PBR, FR, and TR has been taken into account. The oxygen concentration in the liquid has a large influence on the performance and, therefore, air or pure oxygen should be added. The MR and PBR ha®e a better performance than the TR and FR. Only a small degree of mass-transfer limitation occurs in the PBR. Radial dispersion hardly influences the performance of the PBR. External mass-transfer limitation influences the con®ersion in the TR and FR se®erely. The PBR, MR, and TR show a much better energy efficiency than the FR. Introduction Ž. Like other advanced oxidation technologies AOTs , heterogeneous photocatalysis is an emerging technology for water purification. Almost any organic pollutant present in water can totally be degraded to carbon dioxide, water, and mineral acids. Heterogeneous photocatalysis for water purification is based on a semiconductor, usually TiO , and UV-A 2 Ž . radiation -385 nm . The light activates the semiconductor by generating electron᎐hole pairs. These charge carriers can participate in redox reactions at the surface and form hy-Ž droxyl radicals, which can degrade the pollutant Halmann, 1996;Hoffmann et al., 1995;Mills et al., 1997;Bahnemann, . 1999;Serpone and Pellizetti, 1989;Schiavello, 1997 . In the field of heterogeneous photocatalysis, much research has been performed on the laboratory scale, but no industrial application exists to our knowledge. One of the reasons that prevented this technology from being established in industrial installations is the absence of efficient re-Ž actors, proper reactor design, and reactor optimization Ollis et al., 1991;Legrini et al., 1993; Rajeshwar, 1995;Maurino et . al., 1999 . Reactors presented in the literature can be divided into two categories: reactors using solar light, and those using artificial light. The solar reactors will not be discussed, since our project focuses on reactors using artificial light. A sumCorrespondence concerning this article should be addressed to. M. F. J. Dijkstra. mary of the most important reactor designs in the artificiallight reactor category is given in Table 1. Ž Slurry reactors have often been investigated Cassano et . al., 1995 : in the laboratory, an immersed annular reactor is the type most used. A promising design is that using a thin flowing film of a titanium dioxide suspension over an illumi-Ž nated glass plate or annulus Ollis and Turchi, 1990;Yue, . 1997 . The cocurrent downflow contactor reactor has two sections. In the top part, the pollutants adsorb onto the catalyst; in the lower part the slurry is irradiated to degrade the Ž . pollutants Winterbottom et al., 1997 . Several designs are meant to enhance the mixing of the suspension so that all of Ž the catalyst can be illuminated for example, by using a rotat-. Ž ing glass tube Karpel Vel Leitner et al., 1996;Sczec...

Three-phase photocatalysis using suspended titania and titania supported on a reticulated foam monolith for water purification

“…A literature review of reactor configurations tabulating photocatalytic research using slurry reactors and immobilised catalyst reactors can be found in [9], while a literature review tabulating methods of immobilisation of TiO 2 and support substrates coated can be found in [10,11]. Some researchers have reported that the efficiency of the slurried photocatalyst is larger than the supported form [8,10,12] while others have reported that the catalytic activity of TiO 2 is not affected when it is immobilised [13].…”

Design, Mass Transfer Studies, and Optimization of an Air-Sparged Tubular Photocatalytic Reactor for the Degradation of Methylene Blue

“…Various studies have identified the existence of mass transfer limitations in many immobilized systems, such as tubular reactors [7], [8], annular reactors [9]- [11], rotating disc reactors [9], [12], and packed-bed reactors [7], [13], among others [14]. A commonly used model equation derived from first principles is a Langmuir-type equation based on volumetric flowrate Q [15], [16]:…”

Design of an Air-Sparged Tubular Photocatalytic Reactor for the Degradation of Methylene Blue: Mass-Transfer Limitation Studies

“…Various studies have identified the existence of mass-transfer limitations in many immobilized systems, such as tubular reactors [7][8], annular reactors [9][10][11], rotating disc reactors [9,12], and packed-bed reactors [7,13], among others [14]. A commonly used model equation derived from first principles is a Langmuir-type equation based on volumetric flowrate Q [15][16]:…”