Chemistry Reference
In-Depth Information
O
N
N
Ca
eine
N
O
N
H
+
O
O
O
N
+
N
N
N
N
N
Protonated
ca
eine
+
+
N
O
N
N
N
O
N
O
N
FIGURE 2.9
Caffeine extraction: The addition of sodium carbonate converts the protonated
form of the caffeine back to its free form.
Extraction Procedure II: Supercritical carbon dioxide extraction.
There
are advantages to this method: eliminating the use of flammable and
toxic solvents, and the caffeine is easily removed from the final product.
In this process, the caffeine diffuses into supercritical CO
2
with water.
In a continuous extraction to remove the caffeine, the beans enter at
the top of an extractor vessel, with fresher CO
2
entering at the bottom.
Recovery is achieved in a separate absorption chamber with water. In
this manner, greater yields are obtained at higher pressures and tem-
perature. The process requires a pretreatment step. The addition of polar
cosolvents affects cosolvent-solute specific chemical or physical interac-
tions. The solvent-cosolvent interaction accelerates the extraction and
makes the extraction easier. For prewetting, the material is humidified
with ultrapure water. In this manner, the hydrogen bonds linking the
caffeine to its natural matrix are ruptured. Cell membrane swelling
enhances solute diffusion. Subsequently, the quality of caffeine can
reach a purity >94%, and this is usually the acceptable criteria for use in
the soft drink and drug industries.
Extraction Procedure III: Activated charcoal
. There are some advantages to
using charcoal: it is economical, “green,” and easily regenerated by heat
and steam. By choosing activated carbon with the appropriate numbers of
micropores and a surface area up to 1000 m
2
per gram, it is possible to
achieve good performance of adsorption. Cleaned green coffee beans are
first soaked in water, and the caffeine and other soluble content will migrate
to the aqueous phase. The water is filtered through the active charcoal and
only caffeine will continue to migrate in water. These recovered and dried
coffee beans are now decaffeinated.
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