2. Material that been used to absorb water
from wet food to produced dried food.
Function- to make sure that the food can
used in long time.
drying agents are materials, the water
extract. The water can be chemically bound,
e.g. with sulfuric acid or phosphorus
pentaoxide, or the drying process can take
place via adsorption, e.g. with calcium
chloride or Bentonit.
3. hereare various ways of removing water and
other impurities from a solution. This can
become a major task once the used reagents
are also sensitive towards water e.g.
Grignard reagents or enolates.
4. One differentiates between static and
dynamic drying process. During the static
drying process the drying agent is added to
the material which can be dried and again
removed, with the dynamic drying process
flows through the gaseous or liquid substance
the drying agent which can be dried.
5. If water is one of the products, it also has a
detrimental effect on the yield and/or
reaction rate. In those cases, drying agents
like activated alumina¹, calcium hydride
(CaH2), sodium metal (in combination with
benzophenone which forms a dark blue ketyl
radical), lithium aluminum hydride (LiAlH4)
or phosphorous pentoxide (P4O10) are used to
chemically destroy the water
6. The drying agents commonly used in the
organic laboratories are calcium chloride
(CaCl2), sodium sulfate (Na2SO4) Calcium
sulfate (CaSO4, as Drierite (R)) and
magnesium sulfate (MgSO4), all in their
anhydrous form.
Listed below are the drying agents that are
commonly used.Organic liquids are
considered to be wet if they contain water.
Realize that the organic liquid will still be a
liquid after it is dried.
7. Activated alumina ¹ is a very porous form of
aluminum oxide of high surface area which
adsorbs liquids and gases without any change in
form. Activated alumina will not soften or
disintegrate when immersed in liquids. Activated
alumina may be regenerated to its original
adsorption efficiency by heating to a
temperature between (177-316°C).
Reconditioning of mineral oils like transformer or
insulating oils. Removal of oil vapor mist from
compressed air. Drying of organic liquids to a
moisture level of 10 ppm or below. Drying of
various liquids such as Benzene, Carbon,
Tetrachloride, Chlorobenzene, Ethyl Acetate,
Transformer oil, Vegetable oils etc.
8. There are 3 types of drying methods:
•Air drying either wind or blowers; it is used for solid and
semisolid foods.
•Spray and vacuum drying are used for liquids.
•Freeze drying the food is first frozen and then dehydrated, is
used for a variety of foods, including coffee, meat, vegetables,
and fruits. The advantage of this method is that the product
retains its original volume and shape and re-hydrates easily.
9. • Most of the disease-causing organism only can multiply and
survive in wet and moist state.
• Drying is the natural technique to prevent spoilage.
• Indeed, the act of simply leaving foods out in the sun and wind to
dry out the moisture.
• For example, the traditional way to preserving rice is allow it to
dry naturally in the field or drying racks in bam for two weeks.
After a period of time, the native rice is threshed and dried again
on straw mat under sunlight for three days.
• Modern drying technique now apply for controlled environment
such as fan and heater. This method avoid uncertainties from arise
when the crops leaved in the field in traditional way.
• Controlled temperature air drying is especially popular for the
preservation of grains such as maize, barley, and bulgur.
10. In hot air dryers, the heat required for the drying process is
supplied by hot air which cycles through the dryer and
contacts the product. For an example making dried fruit.
11. Freeze-drying is used to preserve food and
make it very lightweight.
The process has been popularized in the
forms of freeze-dried ice cream, an example
of astronaut food.
It is also popular and convenient for hikers
because the reduced weight allows them to
carry more food and reconstitute it with
available water
12. Instant coffee is sometimes freeze-dried,
despite the high costs of the freeze-driers
used. The coffee is often dried by
vaporization in a hot air flow, or by
projection on hot metallic plates.
Freeze-dried fruit is used in some breakfast
cereal. Culinary herbs are also freeze-dried,
although air-dried herbs are far more
common and less expensive. However, the
freeze-drying process is used more commonly
in the pharmaceutical industry.
13.
Spray drying is a method of producing a dry powder
from a liquid by rapidly drying with a hot gas.
This is the preferred method of drying of many
thermally-sensitive materials such as foods and
pharmaceuticals.
Air is the heated drying media; however, if the
liquid is a flammable solvent such as ethanol or the
product is oxygen-sensitive then nitrogen is used.
