Photo-CREC-air reactor

Development of the Photo-CREC-Air reactor also involved the characterization of fluid flow patterns in the unit and the assessment of the UV radiation reaching the impregnated mesh. The fluid flow pattern calculation and the fluid flow visualization can be developed using CEX-4.3 software for fluid flow simulation. A plane of symmetry in both the x and y directions can be assumed by simulating the flow patterns in the Venturi section. Hiis enables the sub-division of the reactor s physical volume into 4 quarters. This makes possible the use of smaller cell sizes and an improved convergence (Ibrahim, 2001). 

Ibrahim, H., and de Lasa, H., 2003, Photo-catalytic degradation of air bonre pollutants apparent quantum efficiencies in a novel photo-CREC-air reactor, Chem. Eng. Sci., 58(3-6) 943-949. 

For photocatalytic conversion of model pollutants in air (refer to section 2.10.5), model pollutants such as iso-propanol, acetone, and acetaldehyde are recommended to be used. Acetone and iso-propanol injections of 40, 50, and 60/xl of the liquid pollutant can be employed in the 14.7 L Photo-CREC-Air reactor. For acetaldehyde 30,40, and 50 /xl liquid injections can be used to get the desired initial pollutant concentrations. A gas chromatograph (HP 5890) equipped with a HP-3393A integrator, a TCD and aPoropak Q packed column are adequate to identify and quantify chemical species, including product intermediates and carbon dioxide. Examples of this type of photocatalytic experiments for the photoconversion of model pollutants in air are provided in Chapter VIII. 

The debate still remains regarding which configurations are the most adequate for the photocatalytic reactors to photoconvert air borne pollutants (Ollis and Al-Ekabi, 1993). Several options have been described (Chapter 11) fluidized bed (Brucato et al., 1992 Dibble and Raupp, 1992 Yue et al., 1983 ), annular packed bed (Raupp et al., 1997), coated honeycomb (Sauer and Ollis, 1994 Suzuki et al., 1991 Suzuki, 1993), fixed powder layer (Formenti et al., 1971 Peral and Ollis, 1992) and fiber optic reactor (Peill and Hoffmann, 1995). The Photo-CREC-Air reactor (Ibrahim and de Lasa, 2002) optimizes TiOa-mesh iiradiation and air contacting the supported TiOa. As reported in the upcoming section, this configuration yields model pollutant conversions with high apparent quantum efficiencies. 

APPARENT QUANTUM EFFICIENCY IN PHOTO-CREC-AIR REACTORS... 

In order to establish a kinetic model, a number of assumptions regarding the operation of the photocatalytic reactor should apply (Ibrahim, 2001). Consideration of the applicability of model assumptions is relevant for any type of photocatalytic reactor model. In the specific case of Photo-CREC-Air, and given the special design of this unit, the following model simplifications can be adopted ... 

FIGURE 2.11. Schematic representation of the Photo-CREC Water-II Reactor (1) MR or BL lamp, (2) replaceable 3,2-cm-dianieter glass inner tube, (3) replaceable 5.6-cm-diameter glass inner tube, (4) fused-silica windows, (5) UV-opaque polyethylene outer cylinder, (6) stirred tank, (7) centrifugal pump, and (8) air injector, (Reprinted with permission from Ind. Eng. Chem. Res., 40(23), M. Salaices, B. Seiraiio and H.l. de Lasa, Photocatalytic conversion of organic pollutants Extinction coefficients and quantum efficiencies, 5455-5464. Copyright 2001 American Chemical Society). 

Air decontamination is another potential innovative application of photocatalysis. Chapter VIII focuses on air decontamination using Photo-CREC reactors. Several examples are provided by examining the photoconversion of acetone, iso-propanol, and acetaldehyde. Special attention is paid to the quantum efficiencies for air decontamination, exceeding 100% in many cases, which demonstrates the distinctive chain mechanism character of the photoconversion of organic pollutants in air. 

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