3. WHY PMRs ???
A very promising method
for solving problems
concerning separation of
the photo-catalyst as well
as products and by-
products of photo-
decomposition from the
reaction mixture is
application of
photocatalytic membrane
reactors (PMRs).
PMRs are hybrid reactors
in which photo-catalysis
is coupled with a
membrane processes.
The membrane would
play both the role of a
simple barrier for the
photo-catalyst and a
selective barrier for the
molecules to be degraded.
6. Figure. 1 Schematic of semiconductor excitation by band gap
illumination leading to the creation of “electrons” in the conduction
band and “holes” in the valance band ( Mozia 2010)
MECHANISM OF PHOTOCATALYTIC
OXIDATION
7. CHARACTERISTIC OF
PHOTOCATALYST
A Photocatalyst should possess;
High activity.
Resistance for poisoning.
Mechanical stability and resistance to attiration.
Physical and chemical stability.
Inexpensive.
Able to utilize not only UV light but also visible
light.
11. Reactors with
catalyst suspended
in the feed solution
Irradiation of
membrane module
Irradiation of feed
tank
Irradiation of an
additional reservoir
PMRs with suspended TiO2
12. Figure. 3. PMR utilizing photocatalyst in suspension: irradiation of
the feed tank (Mozia 2010)
13. Figure. 2. PMR utilizing photocatalyst in suspension: irradiation of
the membrane module (Mozia 2010)
14. Figure. 4. PMR utilizing photocatalyst in suspension: irradiation of
the additional reservoir (photoreactor) located between the feed
tank and membrane module ( Mozia 2010).
15. PMRs with suspended TiO2
Reactors with
catalyst suspended
in feed solution
With pressure
driven membrane
techniques
Nanofiltration
Ultrafiltration
microfiltration
With concentration
driven techniques
DCMD
Dialysis
Pervaporation
16. PMRs coupling photocatalysis with
pressure-driven membrane processes
Figure 5. Schematic diagram of laboratory scale slurry PMR with submerged
membranes and internal (immersed) UV lamps [Fu et. al. 2006].
20. Advantages
No need to separate
and recycle the
catalyst
No membrane
fouling
Contaminants
could be
decomposed either
in feed or permeate
Disadvantages
Low photocatalytic
efficiency
Adjustment of
catalyst loading is
impossible
Risk of damage of
polymer
membranes
Necessity of
membrane
exchange