Note: Descriptions are shown in the official language in which they were submitted.
037
~ DESCRIPTION
C~RBON-CAFFEINE SEP~RATION
Technical Field
The present invention relates to decaffeination,
05 and particularly to an improved process ~or recovering
caffeine from an activated carbon adsorbent.
The decaffeination of vegetable materials and
vegetable material extracts is of major commercial
importance. Also significant is the recovery and
sale of the caffeine removed from ~egetable sources
such as coffee and tea. It is known that activated
carbon is a good adsorbent in caffeine recovery and
purification procedures, but the carbon tends to
hold the caffeine so tenaciously that, often,
significank quantities of caffeine are lost or
reduced in commercial value. None of the techniques
currently available to the art for separa~ing the
caffeine from the carbon has been wholly satisfactory
; in terms of both degree and quality of caffeine
recovery.
~.~
- 2 - ~ ~61~7
Back~ound Art
The recovery of caffeine from decaffeinating
solvents has been an active area of concern for many
years. For example, in U.S. 2,508,545, Shuman
Q5 discloses that activated carbon and other adsorbents
had been used to remove impurities from solutions of
caffeine extracted from coffee. Shuman indicates
that until the time of his invention caffeine losses
due to adsorption onto the carbon ran as high as 10
to 14%. To rectify this, Shuman disclosed alternate
use of organic and agueous extractions with the
final aqueous extraction being done at a pH of at
least 7. While activated carbon is employed to
remove impurities from the aqueous extract, the
~5 amounts employed are apparently small and no mention
of separating caffeine from the carbon is made.
Similarly, in U.S. 2,472,881, Bender employs activated
carbon to remove impurities from an agueous caffeine
solution but does not discuss the steps taken to
recover the caffeine adsor~ed on the carbon.
Recently, an improved decaf~eination method was
disclosed in U.S. 3,879,569 wherein ~uantitative
extraction of caffeine -from raw coffee beans is
achieved with moist supercritical carbon dioxide.
This process produces an extract from which
essentially all of the caffeine can be removed by
activated carbon. Unfortunately, the prior art
techniques do not economically provide good levels
of recovery of caffeine or they reguire the use of
chlorinated hydrocarbon solvents which are o~herwise
avoided by the use o~ carbon dio~ide as an extracta~t.
Disclosu_e of Invention
The present invention now enables improved recovery
of caffein~ from an activated carbon adsorbent, by an
improved process which comprises: contacting activated
~.~.6~
-- 3 --
carbon having caffeine adsorbed thereon with a
li~uid, food-grade caffeine solvent which comprises
an organic acid or an alcohol, and which is capable
of displacing at least a portion of the caffeine
05 from active sites on the carbon; maintaining the
contact for a period of time and at a temperature
effective for th~ solvent to displace at least a
portion of the caffeine from the carbon and dissolve
the displaced caffeine; and separating the caffeine
10 from the solvent.
The present invention takes ad~antage of the
discovery that ~ome liguid, food-grade caffeine
solvents which have the ability to effect desorption
both by -~heir strong solvent ability and their
ability to displace the adsorbed material from
active sites on the adsorbent, are extremely effective
in separating caffeine from carbon adsorbents. The
strong solvent effect causes a partitioning between
the activated carbon and the solvent. The site
displacement effect is achieved by the solvent
molecules themselves competing for the active adsorbent
sites. Once a caffeine molecule is displaced, it is
then taken into solution by ~h~ solvent which is a
strong solvent for caffeine.
The solvents employed according to the present
invention are employed in their liquid state and
preferably at temperatures in excess of 100 C to
obtain the greatest rates of recovery. Temperature
has a strong effect on desorption and should therefore
be as high as possible, consistent with maintaining
the solvent as a liquid. Where temperatures higher
than the boiling point of the solvent are desired,
it will be necessary to employ pressures in excess
of atmospheric. It is preferred, however, to maintain
~ 3
-- 4 --
the pressure at no gxeater than ahout atmospheric.
Therefore, the higher boiling solvents are pre~erred.
Because the caffeine is valuable for food and
pharmaceutical use, the soIvents must be food-grade.
05 By this, it is meant that the materials are on the
Generally Recognized As Safe (GRAS) list maintained
by the Food and Drug Administration to this type of
use. This is important because where any measurable
quantity of a non GRAS material works its way into
either the product caffeine or the product tea or
coffee, the value of the product will be seriously
diminished, if not wholly lost.
The organic acids and alcohols which are food-
grade, liquid at the proposed processing temperature
and preferably at room temperature, excellent solvents
~or caffeine, and capable of displacing caffeine
from the ac~ive sites on the carbon, are effective
; solvents for use accordiny to the invention. Preferably,
the solvent will comprise a member selected from the
group consisting of acetic acid, propionic acid,
butyric acid, ethanol, isopropanol, benzyl alcohol,
butanol, amyl alcohol, and azeotropes comprising at
least one of these. Among the co-solvents which can
be employed in forming the azeotropes are water,
n-hexane, n-heptane, n-octane, toluene, benzyl acetate,
me~hylene chloride, ethyl acetate and other food-~rade
solve~ts. The pre~erred solvents are those which
have boiling points over 100 C, and of these glacial
acetic acid and acetic acid azeotropes are the most
preferred. The azeotropes of acetic acid with butyl
alcohol, iso-amyl alcohol, toluene, and n-octane all
have boiling points above 100 C as can be see~l from
the following table:
,
- 5 - ~6~L~3~
Acetic _cld Azeotropes Boilin~ Point ( C~
Acetic Acid 43% wt.
Butyl Alcohol 57% wt. 120.3
Acetic Acid 16% wt.
05 Iso-Amyl Alcohol 84% wt. 133.0
Acetlc Acid 65% wt.
Toluene 35% wt. 105.4
Acetic Acid 53% wt.
n-Octane 47% ~t. 105.0
10 Other azeotropes suitable for use in the process
of the invention, but re~iring the use of superatmospheric
pressures when temperatures of 100 C or more are
employed, are:
Acetic Acld Azeotropes Boilinq Point ~ C~
15 Acetic Acid 6% wt.
n-Hexane 94% wt. 68
Acetic Acid 33% wt.
n-~eptane 67% wt. 95
Other Azeotropes
. ,
20 Ethanol g6% wt.
Water 4% wt. 78.2
Isopropanol 88% wt.
Water 12% wt. 80.1
" : :
.
,,
~:~6~ ~3>~
Benzyl Alcohol 9~ wt.
Water 91% wt 99-9
Non-Azeotropes
Ethyl Acetate 10-50% wt.
Acetic Acid 50-90% wt. Non-Azeotropic
Methylene Chloride 10-50% wt.
Acetic Acid 50-90% wt. Non-Azeotropic
Benzyl Acetate 10-30% wt.
Acetic Acid 70-90% wt. Non-Azeotropic
Based on economy, effect on final product quality and
effectiveness, glacial acetic acid is the most efficient of all
the solvents. It will be appreciated, however, that care must be
taken when using glacial acetic acid due to its low flashpoint
in the order of 104F - 110F. (open cut test~ and burn causing
properties well known in the literature for example in The Con-
densed Chemical Dictionary-Rose-Reinhold Publishing Corporation -
1966.
The solvent is maintained in contact with the carbon
having caffeine adsorbed thereon for a period of time and at a
temperature effective for the solvent to displace at least a por-
tion of the caffeine from the carbon and dissolve the displacedcafEeine. As noted above, preferred temperatures will be above
100C., but the specific temperature for any particular process
will be selected on its own set oE economic considerations and
may be below this. Practical contact times will be determined
on the basis of the desired degree of recovery and the desorption
rate for a particular system. Preferably, the contact time should
be sufficient to permit displacernent of at least 75% by weight
of the caffeine from the carbon and into solution with the solvent.
Because the caffeine is valuable as a product, and if not
37
- 7
removed from the carbon, decreases the adsorbent
capacity of the carbon, still higher ra-tes of dis-
; placement, on the order of 90% by weight or more,
are desired.
05 As the activa~ed carbon adsorbent can be any of
those types commercially available which are effective
caffeine adsorbents and capable of withstanding the
riyors of recycling permitted by the invention.
Preferred activated carbons are those prepared from
coconut, coal and lignite, particularly those available
commer~ially from Calgon Corporation, ICI, Carborund~m
and Union Carbide Corporation.
After contact for the requi~ite period of time,
the activated carbon is preferably separated from
the solvent prior to separation of the caffeine from
the solvent. The simplest and most effective manner
or removing the carbon from the solvent is by
filtration.
The caffeine can be separated from the solvent
in any suitable manner such as steam distillation or
simply evaporating the solvent. In a preferred form
o~ recovery, steam is passed through the caffeine-
containing solvent in a vented vessel until the
solvent concentration is reduced to about zero, most
preferably about Cl ppm, leaving an a~ueous caffeine
solution. The caffeine is then precipitated from
the a~ueous solution by cooling to form pure white
needle-shaped crystals.
Best Mode for Carrying Out the_Invention
The following examples are for the purpose of
illustraiing and explaining the best mode for carrying
out the irivention, but are not meant to be limiting
in any regard. Unless otherwise indicated, all
parts and percenta~es are by weightO
3~
8 -
Example 1
One hundred parts of glacial acetic acld and 10
parts of ~ctivated carbon pellets co~taining 10% by
weight caffeine, obtained from the process of
05 U.S. 3,879,569, were admixed and then raflu~ed in a
vessel at atmospheric pressure and 117 C for two
~ hours. The acetic acid was decanted from the carbon
and found to contain 0 . 801% caffeine. The carbon
had 9.5 parts of acetic acid remaining on it. The
caffeine was recovered from the solukion by evaporation.
The total amount of caffeine in the acetic acid was
0.725 parts, nearly 73% recovery in a single stage.
Example 2
The procedure of Example 1 was repeated but
this time the components were introduced into a
Soxhlet extraction tube and refluxed at 117 C for
four hours. Total recovery of caffeine based on the
10% initial caf~eine was 99%.
Example 3
The procedure of Example 2 was repeated, but
this time employing a solvent containing 57 parts of
n-butyl alcohol and 43 parts of glacial acetic acid.
After four hours contact a~ 120 C, 82% o~ the caffeine
was recovered. On evaporation, white crystals of
caffeine precipit~ted from the solution.
Exam~le 4
In this example, green coffee beans are contacted
with methylene chloride solvent to obtain a caffeine
extract as described in U.S~ 3,671,263. The solvent
is removed from the extract by evaporation, leaving
a brown, crude~ caffeine sludge containing lar~e
amounts of impurities in addition to caffeine. The
sludge is preliminarily dissolved in water. Then
the caffeine e~tract is contacted with DARCO powdered
- 35 activated carbon which adsorbs mos~ of the impurities
g
from the extract to prepare it for crystallization
into pure, white caffeine crystals. The carbon
picks up about 10% caffeine in addition to the
impurities. The caffeine is removed from the carbon
05 by contacting the charcoal with glacial acetic acid
for 4 hours at 100 C in a vessel. The carbon is
separated from the acetic acid solution by filtration
--- and the acid is evaporated to leave rela~ively pure
cxystals of caffein~. The acetic acid is condensed
and recycled. The carbon is regenerated for recycle
by thermal reactivation.
The above description has been for the purpose
of teaching a person skilled in the art how to
practice the invention. It is not intended to
describe in detail each and every modification and
variation of the invention which will become apparent
to those skilled in the art upon study. It is
applicant's intention, however, that all such
modifications and variations be included within the
scope of the invention as defined by the following
claims.
-10~ 33~
SUPPLEMENTARY DISCLOSURE
' - -
he preceding disclosure relates to a process of
recovering caffeine from activated carbon by contacting the
carbon having caffeine adsorbed thereon with a liquid, food-
grade caffeine solvent which comprises an organic acid or an
alcohol and azeotropes thereof and which is capable of displacing
at least a portion of the caffeine from actlve sites on the car-
bon, while maintaining -the contact for a period of time and at a
temperature effective for the solvent to displace at least a por-
tion of the caffeine from the carbon and dissolve the displaced
caffeine, and separating caffeine from the solvent.
Acetic acid and acetic acid azeotropes are preferred
solvents but when glacial acetic acid (which is the most efficient
of the solvents) is employed it will be appreciated that care must
be taken because of the low (104F) flashpoint of glacial acetic
acid and its skin burning effect.
It has been determined that acetic acid water mixtures,
preferably having a concentration of between about 50% and 80%,
20 by weight, may be employed to elute either batchwise or contin-
uously in a countercurrent manner the caffeine and other solids
frorn the spent activated carbon. Although acetic acid-water mix-
tures are usually less efficient than pure glacial acetic acid
they offer the advantage of being totally non-fIammable with no
flashpoint. Glacial acetic acid is flammable with a flashpoint
of 104F. requiring the use of equipment providing operational
safety and this increases the capital costs for the process.
By adding water to glacial acetic acid or using acetic acid-
water mixtures this re~uirement is eliminated and thereby dram-
atically reduces capital ccsts. Most preterably, acetic acid cr
:
37
70% concentration which is commercially available is used.
The aqueous acetic acid solution is liquid at the pro-
posed processing temperature a~d at room temperature, is an ex-
cellent solvent for caffeine, is capable of displacing caffeine
from the active sites on the carbon and is an especially effect-
ive solvent for use according to the invention. As indicated,
the acetic acid solution preferably has a concentration of about
50 to 80~, and most preferably 70%, by weight.
The recovery of caffeine is of commercial importance,
and the carbon itself is of commercial value for upon regenera-
tion it may again be employed in caffeine recovery and purifi-
cation processes.
EXAMPLE 5
One hundred parts of 70% acetic acid solution and 10
parts of activated carbon pellets containing 9.1% by weight caf-
feine, obtained from the process of U.S. 3,879,569, of Vitzthum
et al. were introduced into a Soxhlet extraction tube and then
refluxed at atmospheric pressure and 110C. for 16 hours. The
caffeine was recovered from the solution by evaporation. The
total amount of caffeine recovered was ~.91 parts, 100% recovery.
