Applied Catalysis B: Environmental 105 (2011) 95–102
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Applied Catalysis B: Environmental
journal homepage: www.elsevier.com/locate/apcatb
Solar/lamp-irradiated tubular photoreactor for air treatment with transparent
supported photocatalysts
R. Portela
a,∗
, S. Suárez
a
, R.F. Tessinari
a,b
, M.D. Hernández-Alonso
a
, M.C. Canela
b
, B. Sánchez
a
a
CIEMAT-PSA, Environmental Applications of Solar Radiation, Madrid, Spain
b
UENF-CCT, Chemical Sciences Laboratory, Campos dos Goytacazes, RJ, Brazil
article info
Article history:
Received 14 December 2010
Received in revised form 24 March 2011
Accepted 30 March 2011
Available online 12 April 2011
Keywords:
Photoreactor
Pilot-plant
Solar
UV-lamp
Supported photocatalyst
Monolith
H
2
S
abstract
A novel versatile tubular reactor that may use both types of radiation, solar and/or artificial, and dif-
ferent types of suspended or immobilized photocatalysts is proposed. The photocatalytic reactor was
evaluated for air treatment at laboratory scale and semi-pilot-plant scale. UV-A transparent immobilized
photocatalysts were employed, which allowed an efficient use of radiation. Two different types of photo-
catalytic modules were tested: (a) TiO
2
-coated PET monoliths and (b) TiO
2
-coated glass slides, arranged
in monolith-like units with the help of especially designed star-shaped polygonal structures. Both types
of units were easy to handle and assured the adequate distribution of the photocatalyst inside the tubular
reactor. The efficiency of the photocatalytic system with both solar and artificial radiation to oxidize the
H
2
S contained in an air stream was demonstrated at the laboratory roof and in the treatment of real air
of a wastewater treatment plant located in Madrid (Spain). As a consequence of the chemical nature of
the pollutant, the photocatalytic activity decayed over time due to the accumulation of sulfate on the
surface, but easy regeneration of the exhausted photocatalyst was achieved by washing with water.
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
In gas phase heterogeneous photocatalysis, the advantages of
working with immobilized instead of suspended catalysts are clear.
These include no need for fluidization – the fluidization would
entail reducedoperationalflexibility and difficulty in the scaling-up
– and easy recovery and reuse of the catalyst, avoiding a separa-
tion stage after treatment. Due to the small particle size of TiO
2
,a
conventional sedimentation process would require high residence
times; hence more complex and expensive separation systems
would be necessary, such as sedimentation accelerated by coagula-
tion [1], magnetic separation [2] or membrane filtration [3]. There
are, however, some disadvantages of working with immobilized
photocatalysts that must be overcome: decreased exposed surface
per unit mass – compared with the catalyst in suspension; reduced
catalyst mass to fluid volume ratio; mass transfer limitations at
low flow rates and difficulty in achieving efficient irradiation of
the entire photocatalyst surface without casting shadows, espe-
cially in the case of solar radiation. Therefore, most photocatalytic
reactors are designed for liquid phase and employ photocatalysts
in suspension. For these applications tubular reactors are usually
selected. These systems can operate with adequate flow regimes
and greater quantum yield may be obtained, since practically all
∗
Corresponding author.
E-mail address: raquel.portela@ciemat.es (R. Portela).
the radiation affects the reaction medium. Moreover, the radia-
tion source may be either artificial – surrounding the reactor [4]
or placed in the reactor axis [5] – or the sun, and the reactor may be
placed in the focus of reflectors that collect the radiation efficiently
[6]. Non concentrating Compound Parabolic Collectors (CPCs) have
been widely used for photocatalytic water treatment applications
[7–9] because all the incident radiation on the aperture area, diffuse
radiation included, is directed to the reactor without a significant
temperature increase and no tracking system is required.
Until the first solar pilot plants for polluted water treatment
were constructed in the late 1980s at the National Renewable
Energy Laboratory (NREL) and the Sandia National Laboratories
(USA), photoreactor designs were not optimized for photocatalytic
processes. Since then, different concepts have been proposed with
a variety of designs, in an effort to increase efficiency and reduce
costs [10]. The first solar photocatalysis industrial pilot-plant was
installed in 1999 in Arganda del Rey (Madrid, Spain) for the treat-
ment of non-biodegradable chlorinated hydrocarbon solvents [8].
However, water treatment by photocatalysis seems to be not com-
petitive with other technologies – such as biological treatment or
photo-Fenton [11,12] – and recent efforts in applied research of this
technology are increasingly focused on the treatment of air [13–15].
There have been several attempts to use fluidized reactors for
air treatment [16–18]. However, due to the advantages already
mentioned, the vast majority of gas phase photoreactors are fixed
or packed bed, where the catalyst, the irradiation and the flow
requirements strongly condition the system design and perfor-
0926-3373/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcatb.2011.03.039