The Decaffeination Process
Decaffeination usually describes the process of removing caffeine from coffee or tea in order to
create an enjoyable beverage without the presence of the caffeine. Companies who produce coffee or
tea should always consider making decaffeinated versions of their products because the process does
not just give one new type of product but two new products, caffeine and decaffeinated coffee or tea.
Caffeine is marketable to pain relief companies such as Excedrin. According to WebMD, caffeine makes
pain relievers, with anti-inflammatory properties medication such as aspirin, ibuprofen, and sodium
naproxen 40% more effective. Also caffeine pills such as Vivarin are sold over the counter. People buy
caffeine all the time. Caffeine can be extracted using various methods and they are all similar yet require
toxic substances in the process. That is until cheap, simple, and safe supercritical CO2 extraction was
developed.
Organic Solvent Extraction
It is easy to understand supercritical CO2 extraction, by first understanding organic solvent
extractions. Organic solvent extraction was the first method used for getting the caffeine out of coffee,
it’s one of the easiest ways to make decaffeinated coffee and can even be done in small scale
operations. Also it’s not recommended to decaffeinate tea using this method because many of the
flavor compounds will be soluble in the organic solvent. Organic solvent extraction is done in three main
steps. The first step is to make coffee with hot water, then the second step mix the water with an
organic solvent, creating two layers of liquid. The caffeine is more soluble in an organic solvent than it is
in water so most of the caffeine goes into solution with the organic liquid. After, the layers are
separated and the organic solvent is left to evaporate, leaving close to pure caffeine. The water layer
can also dry and what results can be used as an additive to decaffeinated coffee beans.
Add Solvent
Coffee
Most of the caffeine is drawn
up into the organic solvent
because of its higher solubility
in the solvent.
Step 1: Brewing the Coffee
The first step is to brew the coffee in hot water. This form of extraction is called solid/liquid
extraction. This step is necessary because the organic solvent cant ionize the caffeine but water can.
When the caffeine is ionized the C=O bonds become (C=O-H)+ bonds but not all the caffeine does this at
once and therefore takes flow of the water through the coffee beans to continually remove the caffeine
from the solids. This can be looked at as a process that breaks loose the caffeine and allows the organic
solvent to reach the caffeine particles.
Sigmaaldrich.com
+
H
Non Ion Form
Ion Form
(This product is favored and
can exist in an organic solvent)
(This is the only for that can
exist in water.)
Step 2: Adding the Organic Solvent to the Water
The second step is adding an organic solvent. Caffeine would be more soluble in any type of
organic solvent, for example gasoline could be used as the organic solvent described in the process.
Though any solvent will work the best solvents for this process would be benzene, or toluene using the
“like dissolves like” property, which is simple as it sounds, since they both contain a ring structure they
look similar, and it can be assumed that benzene will disolve caffeine. When the organic solvent is
added it allows caffeine which is more stable in the non ion form (especially when it is left to cool for
awhile). Therefore the caffeine goes into solution with the benzene and leaves the water phase. If only
pure caffeine is desired and not decafe coffee, then table salt (NaCl) is be added to the water layer,
which is more soluble in water than caffeine and therefore drives the caffeine out of solution of the
water resulting in a higher percent yeild. In summary an organic chemical is used to pull caffeine from
the water.
Benzene
Step 3: Final Sepparation
During this step the organic layer is sepparated from the water layer by siphoning off the top
layer. The bottom layer would normally be the water layer which, most of the time more dense than
organic materials. This is not always the case because the amount caffeine that is in solution changes
the density of the liquid it is contained in. Therefore when the liquids are separated it is verified that the
product stream is infact still the organic phase. This is done by a person who drops a drop of water into
a test of the solution for every new batch of coffee or tea being processed. If the drop does not for a
bubble in the solution it can be verified that the process is still running smoothly. If not then the organic
layer needs to be diluted before it can finish processing. This problem is rare though, because most
coffee’s and teas have a set amount of caffeine that can be considered beforehand. Therefore when the
liquids are separated it is verified that the product stream is infact still the organic phase. Also if only
pure caffeine is desired the extraction can be done multiple times over the water layer. In plants this is
done by having a flowing organic layer over a flowing water layer going in opposite directions through a
recycled stream this will result in what can be considered 99.9% yeild of pure caffeine plus other
chemicals after evaporation. Because of cost concerns and enviormental concerns the evaporated
organic solvent is recollected and recycled to use again by cooling the gas in a cooling chamber after it
evaporates. To completely purify the caffeine this is heated to 235 degrees celcius which causes
caffeine to sublimate into a gas, the caffeine goes up into the air to hit a coolant where it recrystalizes
into virtually pure caffeine. Otherwise you only want a one time pass of organic layer over the caffeine
to preserve the flavor of the coffee which still removes about 80% of the caffeine. The flavors remain in
the water and can be mixed back into the ground coffee beans that were used to brew the coffee in.
Super Critical CO2 Extraction
Now that you understand what an extraction process entails, it will be easier for you to
understand a supercritical extraction. The super critical extraction uses CO2 as both the water and the
organic solvent. The CO2 acts like water in that it will dissolve organic chemicals, yet it will not dissolve
things like dirt, or combusted parts of the coffee bean. It breaks lose the caffeine from the bonds that
hold it to the coffee bean but a lot the other things that are absorbed during a water extraction are left
in the bean, some of these in which give the bean flavor which is imported for decaffeinated coffee.
Supercritical extraction is a great way to ensure there are no poisonous chemicals present in the process
of decaffeination, though high pressures are necessary which can also be somewhat dangerous but as
long as proper safety valves are in place the process is very safe. Not only is it safe, but it is also a simple
two-step process. CO2 is added to a chamber with coffee in it, then a lower pressure chamber is opened
causing the caffeinated CO2 to flow into the chamber where it is allowed to evaporate (which is a very
fast process, CO2 is a gas at room temperature and atmospheric pressure, which leaves just pure
caffeine. Super critical extraction can be done with any polar chemical including water, yet the
thermodynamic properties of the substance need to be considered. The easiest supercritical condition
to make is to pressurize CO2 to about 250-300 bar at room temperature. Supercritical fluids are
essentially gases that act like liquids (they dissolve things) yet retain they still flow through objects like
fabric easily without adsorbing to the surfaces. These properties make the caffeine easy to get out of
the solid form of the bean; also what is good is that CO2 dissolves polar molecules, (molecules that
contain hydrogen), which makes it better at dissolving caffeine. The only problem is that it still dissolves
the natural acids and alcohols (though at a much slower rate) that are present in the coffee and
extracting all the caffeine will result in loss of flavor. Thus this is fixed by making the process a relatively
fast process.
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Caffeine is released from
the solid under high
pressure CO2.
Caffeine saturated CO2 is
drawn into a separate
chamber.
The chamber is set to
atmospheric pressure, and
the caffeine falls out.