Handbook of Solvents - George Wypych - ChemTech - Ventech!

22.4 Application of solar photocatalytic oxidation 1561
Figure 22.4.1. Schematic of the 10 SCFM solar photoreactor system used at McLellan AFB.
Corporation (Golden, CO). The reactor, 1.22 m wide by 2.44 m, consisted of a fiberglass-reinforced
plastic I-beam frame. A transparent fluoropolymer film, treated to accept adhesives,
formed the front and back windows of the reactor. The film windows were attached to
the reactor frame with foam tape coated on both sides with an acrylic adhesive. The catalyst,
titanium dioxide (Degussa P25), was coated onto a structured, perforated polypropylene tubular
packing commonly used in oil-water separators. The TiO 2 was suspended in water as a
slurry and sprayed onto the tubular supports with a new paint sprayer until the supports were
opaque. Fluid modeling of airflow through the reactor showed that a 5.1 cm PVC manifold,
located at the inlet and outlet of the reactor, would provide an even flow distribution. Small
(0.6 cm) holes, drilled into the manifold at one inch intervals, provided the even flow distribution
required for efficient contact of the contaminated air with the catalyst.
A two-inch diameter pipe from the outlet of the air stripper supplied the contaminated
air stream to the reactor. The air stream was first passed through to a tube-in-shell heat
exchanger for partial dehumidification. A chiller circulated 2 o C ethylene glycol through the
tube side of the heat exchanger. Chilling, which reduced the relative humidity of the air
stream from near saturation to less than 20% at 20 o C, was required because high humidity
reduces the TCE destruction rate, likely because of competitive adsorption between moisture
and TCE molecules at the catalyst surface (Fan and Yates, 1996). By lowering the humidity
to less than 20% (@ 20°C), the reaction rate was sufficient to ensure complete TCE
destruction. This effect was observed by Hung and Marinas (1997) in a lamp-illuminated
annular reactor in which TCE conversion was not affected by relative humidity up to 20%;
conversion deteriorated as the humidity level reached saturation. Laboratory tests of the
system demonstrated that at TCE concentrations of near 100 ppmv, less than 15% of the
TCE in the airstream transferred to the condensate formed in the heat exchanger. The condensate
(approx. 1-2 liters per day) could be fed back into the air stripper for treatment.
On the reactor, GC sample ports and temperature and pressure sensors provided monitoring
of reactor inlet and outlet VOC concentrations and temperature and pressure drop
throughout the system. A portable gas chromatograph provided on-line VOC organic anal-