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Archives (2004)
Silica gel from rice hull?
by Ma. Lizbeth J. Baroña |
January-March
2004
|
 It
comes with your new pair of shoes, inside your vitamin bottles,
your new bag, and with just about anything new you buy. "It"
would be that quaint little packet of "something"
that accompanies your newbies, the silica gel pack. If you
think the dry and exciting environment of your new buy is
something that will not occur in the same thought as rice
hull, think again.
Utilizing the potentials of an agricultural
waste like rice hull as a component in silica gel is the objective
of a study conducted by the Natural Science Research Institute(NSRI)
and the Bureau of Agricultural Research(BAR).
Rice hull, an abundant agricultural waste,
is usually burned in the field contributing to air pollution.
With proper methods, however, this agricultural waste can
be an effective energy source, and more importantly, can be
a source of silica gel.
What is silica gel?
Not to be mistaken for a "silicon gel", the silica
gel is not really a "gel" in form. It is in a porous,
granular form of silica. Inside each small silica gel granule
is a vast network of inter-connecting microscopic pores, which
attract and hold moisture by processes known as physical adsorption
and capillary condensation.
To graphically describe how silica gel works,
a single teaspoon of hydrosorbent silica gel has an internal
adsorptive area equivalent to a football field. Silica gel
is inert, non-toxic and safe to use to protect foods, medicines,
sensitive materials, electronics, films, etc., from humidity.
Even when saturated with adsorbed moisture, silica gel looks
and feels dry to the touch. It can also be "reactivated"
after it is saturated with moisture so it can be used over
and over again.
Most damage to stored valuables, like leather
and pharmaceutical products, is caused by humidity trapped
in the storage area. Humidity trapped within enclosed space
undergoes undetectable condensation, which causes the damage.
This damage comes in the form of rust, corrosion, oxidation,
mildew, fungus, mold, odor, spoilage, shortened "shelf-life"
of photographic film, batteries, and deterioration of foods
and medicines.
Silica gel prevents these moisture-related
problems, that's why manufacturers often include a small packet
of silica gel in shipments of leather goods and pharmaceuticals.
Silica gel creates a protective shield of dry air within any
enclosed storage area and it remains the highest adsorbent
capacity available today.
Waste not, want
not
Scientists at NSRI burned rice hull resulting to high silica
(87%) ash. The ash was used to prepare four samples of rice
hull silica gel(RHSG). These four samples, a commercial silica
gel, and silica gel prepared by the Industrial Technology
Development Institute(ITDI) were compared and characterized
for chemical and physical structure, drying properties, and
elemental impurities. The first sample, RHSG 1, is composed
of 21 g rice hull ash (RHA) boiled in 1liter of sodium hydroxide,
and was made into gel after 18 hours. RHSG 2 was made up of
the same components like the first sample, except that the
gel was aged for a week. RHSG 3 was of the same component
as the first two samples, except that the resulting gel was
soaked in hydrochloric acid overnight. The fourth sample was
made of 16 g RHA mixed with 6.7g sodium hydroxide and 65.6
g water.
The study found that rice hull silica gels,
RHSG 2 and 4, have properties comparable to the commercial
silica gel, and the gel prepared by the ITDI. Depending on
the method of preparation, the RHSG has dessicant properties,
which can be applied in both high and low humidity environment.
The microstructure of the rice hull silica
gel were also observed to have a more uniform particle size
and distribution, compared to the commercial and ITDI manufactured
silica gel samples. As for the RHSG elemental composition,
results show significant lower levels of impurities for the
RHSG samples compared to the commercial and ITDI samples.
Rice hull, even as it is regarded as agricultural
waste, can be used both as energy source, and as silica gel
component. Since the country imports most of the components
in manufacturing silica gel, utilizing the potentials of rice
hull will also lessen the economic burden brought about by
importation.
Sources:
"Silica gels from rice hull: Structure, composition and
water vapor adsorption behavior" 2002 by Leni Quirit
and Elma Llaguno, Natural Sciences Research Institute (NSRI),
Diliman, Quezon City.
www.dehumidity.com/FAQ.html
www.howstuffworks/science/questions206.html
Photo: www.dehumidity.com
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Silica gel from rice hull?
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