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Photo-Catalytic Oxidation | |
 Photo-Catalytic
Oxidation (PCO)
The Technology 
In order to fully understand PCO,
we must first learn a little about the metal catalyst involved, Titanium
in this case. Titanium has been stated as being a light, strong, and
anti-corrosive. These characteristics are largely due to its unique, very
thin barrier layer of oxidized film on its surface. This invisible
surface layer, Titanium Oxide (Ti02), is quite remarkable in the fact
that it will if scratched or damaged, immediately restore itself in the
presence of air or water. The Ti02 film layer also has a high refraction
ratio and when it is irradiated by UV light of less than 385nm, the band
gap energy (the level of energy photons needed to be able to free
electrons from their atomic bonds) is exceeded. What is created are
electron/hole pairs, hydroxyl radicals (OH), thus attracting molecules,
i.e. volatile organic compounds and bioaerosols, to the catalyst
Titanium. The contaminants are oxidized by the reaction that takes place
during the process due to the fact that the OH radicals need to attach
themselves to something, and when they do they oxidize it to C02 and H20
primarily.
A good analogy to think of when you are
pondering the concept is electronic air cleaners. Electronic air cleaners
work by charging the large dust particles passing through them with an
electronic charge, either positive or negative. The particles are than
collected on oppositely charged metal plates. With PCO, after the VOC's
and bioaerosols are attracted to the titanium, they are come into contact
with the OH radicals which change the contaminants molecular structure.
PCO will kill and decompose absorbed bioaerosols, as well as toxic VOC's
and the odors they produce.
As can be seen from these charts the oxidation
power of OH radicals is second only to that of fluorine. Looking at the
oxidation power of ozone we can determine that it is not as powerful an
oxidant as singlet oxygen or OH radicals. Therefore an ozone generator,
though a good method of oxidizing VOC's, is not as effective as singlet
oxygen 1.78 or OH radicals 2.06 in oxidizing contaminants.
Advantages of
Photo-Catalytic Oxidation
- High destruction efficiencies at
room temperatures
- No chemical
additives
- No residual
ozone
- High oxidation yields for gas
phase reactants and odors.
- Low energy
requirements
- Complete oxidation of organics to
C02 & H20 is possible (VOC's and
bioaerosols)
- Applies to a large number of
organics (VOC's and bioaerosols)
- Works in humid
conditions
- Long service
life
- Low maintenance
requirements
- Negligible pressure drop in duct
system
- Low system
cost
- Easy to
install
Now that PCO technology can be integrated into new and
existing heating, air conditioning, and ventilating systems everyone
(even the most chemically sensitive) have an effect process for removing
and destroying low-level indoor air pollutants including mold, bacteria,
viruses, and fungi.
There have been numerous scientific studies,
research and applications using PCO technology. The following are a few
exerts from some:
"One effective method to destroy dilute
concentrations of organic and chlorinated organic pollutants in air is
heterogeneous POC, which uses a semiconductor catalyst such as Ti02 and
near-UV radiation to decompose contaminants..." The large number and
variety of chemicals successfully treated by PCO indicates potentially
broad range of application."
John L. Falconer, Ph.D. Professor of Chemical Engineering Univ. of
Colorado, Ph.D (Chemical Engineering), Stanford University 1974, B.E.S.
(Chemical Engineering), The John Hopkins University,
(1967)
"Photocatalysts for the destruction of indoor air
pollutants, including VOC's and gaseous inorganic pollutants such as
nitrous oxides, carbon monoxide, and hydrogen cyanide..." (Heller 1996).
"Report test show the technology capable of rapidly destroying toxic
components of tobacco smoke such as formaldehyde, acrolein and
benzene."
Taken from the American Lung Association webpage
January 24, 2001
"...The PCO technique destroys pollutants in both air and
water..."
NREL National Renewable Energy Laboratory
"...Carbon 13 labeled ethanol (CH3(13)CH20H) was absorbed
on the catalyst and photocatalytically oxidized..."
Darrin S. Muggli; Sheldon A. Larson; John L. Falconer Journal of
Chemistry 1996
"...The purpose of this study is to investigate the
purification of air emissions contaminated with toluene via the
heterogeneous photocatalytic oxidation (PCO) process..." "...Experimental
results indicated that near to 100% conversion ration of toluene are
achieved for the initial 30-minute reaction period..."
Chung-Hsuang Hung Photocatalytic Decomposition of Toluene Under
Various volatile organic
compounds temperatures.
"...Photocatalytic oxidation (PCO), a relatively
new technology, shows promise for economically controlling hazardous air
pollutants and volatile organic compounds from smaller sources, such as
waste water treatment plants, dry cleaning facilities, painting
facilities, carbon regeneration plants, air-stripping towers, soil
venting processes, hazardous waste incinerators, and municipal
landfills..."
Melanie Louise Sattler, Method for
Predicting Photocatalytic Oxidation Rates of Organic
Compounds
"...Potential applications for using
titania-based materials as photocatalysts include...Destroying volatile
organic compounds (trichloroethylene, benzene, formaldehyde, etc.).
Reducing air pollution in homes and industries such as dry-cleaners,
painting booths, and printers..."
Marc A Anderson, Professor Water Chemistry Program and Material Science, University of
Wisconsin
"...In addition to automobile exhaust cleaning,
use of environmental catalysts such as titanium oxide photocatalysts is
rapidly growing for control of residential environments, e.g.,
antimicrobial activity and odor control..."
Katsunori Yogo, Masamichi Ishikawa, Interdisciplinary Department,
Frontier Science Institute, Mitsubushi Research Institute, Inc.
"...Titanium dioxide is
therefore applied for deodorizing, by decomposing substances causing bad
odor, and for prevention of air pollution by absorbing and
oxidizing..."
Japan Chemical Week, August 26, 1999
Those are just a few examples
of the vast research that has been and is being done on PCO technology,
including Second Wind's own testing recently completed at the IAQ labs of
the University at Waterloo on our own photocatalytic air purifiers.
Please view the dramatic results of our testing on the following
page.
Note: Second Wind Air Purifiers have been tested effective in the destruction and reduction of bacteria viruses and fungus under various conditions. The effectiveness of our devices may vary depending upon the size of the area to be treated and the rate of air circulation. Your results may be higher or lower than those presented here. The health aspects associated with Second Wind Air Purifiers were not investigated by U.L..
COMPARATIVE SUMMARY OF
AIR CLEANING TECHNOLOGY
|
|
Second
Wind
PCO
|
Active
Carbon
Filter
|
HEPA
Filter
|
Air
Ozonation
|
Chemical
Biocide
|
High
Energy
UV
|
Electro-
static
Filter
|
Captures
Microorganisms
|
X
|
X
|
X
|
|
|
|
X
|
Destroys
Microorganisms
|
X
|
|
|
X
|
X
|
X
|
|
|
Creates No Hazardous
Waste Products
|
X
|
|
|
|
|
|
|
Generates no
Ozone
|
X
|
X
|
X
|
|
X
|
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Captures
High
Molecular
Weight
VOCs
|
X
|
X
|
|
|
|
|
|
Captures Low
Molecular Weight VOCs
|
X
|
|
|
|
|
X
|
|
Destroys
High
Molecular Weight
VOCs
|
X
|
|
|
X
|
|
X
|
|
Destroys High
Molecular Weight VOCs
|
X
|
|
|
|
|
|
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Unlimited
Capacity
|
X
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