Monolith Reactors for Intensified Processing in Green Chemistry - Process Intensification for Green Chemistry - page 187

supports [59]. A significant challenge in the area of multiple pollutant reduction is
finding a catalyst that can simultaneously reduce NO x and N 2 O. Centi et al.[60]found
that a combination of Fe-ZSM-5 and Co-ZSM-5 is effective for reducing both pollutants
by over 80%. Dhanushkodi et al. [9] modelled NO x removal in a honeycomb monolith
reactor by SCR with ammonia, utilizing a 2D reactor model and encompassing mass and
momentum balances, with suitable inclusion of SCR reaction kinetics. This model
indicated that ammonia is mainly consumed by the desired reaction at a temperature of
655 K, and under these conditions the conversion of NO is predicted to be 85%. Future
developments in this area could include improved monolith preparation procedures and
fluid distributor design [58].
The compact design of monolith reactors also makes them highly suitable for
miniaturized applications in air purification, such as indoors or in aircraft cabins.
Kalluri et al. [46] prepared microfibrous entrapped catalysts (MFECs) by entrapping
small gamma alumina particles (150-180 m m) within sinter-locked networks of metal
microfibres (8-12 m m)andformedthemintothinflexible sheets (0.5-2.0mm thickness)
(Figure 6.8). Pleated structures of MFEC containing Pd/ g -Al 2 O 3 , conventional mono-
liths and packed beds were tested for the purification of air in aircraft cabins (ozone
decomposition). It was found that packed beds gave too high a pressure drop, while mass
transfer in monoliths was not as high as in MFEC mesh. However, Figure 6.9 shows
that similar overall conversion levels of ozone were achieved in monoliths and in
MFEC mesh.
An emergent area of research in monolith reactors is their application as bioreactors.
Ebrahimi et al. [61] have asserted that as bioreactors require gas-liquid mass transfer for
substrate supply, monoliths could be an attractive alternative, providing a reduction in the
Figure 6.8 Micrograph of 150-250mm g-Al 2 O 3 entrappedin4and8mm(1:1ratio)
stainless-steel microfibres. Reprinted from Kalluri et al # 2009, with permission from
Elsevier.