Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1:~04978
METHOD FOR DECAFFEINATING COFFEE
WITH A SUPERCRITICAL FLUID
Technical Field
05 The present invention relates to a method of
extracting caffeine from green coffee beans with a
supercritical fluid. More particularly, the inven-
tion involves continuously feeding an essentially
caffeine-free supercritical fluid to one end of an
extraction vessel containing green coffee beans and
continuously withdrawing a caffeine-laden super-
critical fluid from the opposite end. A portion of
decaffeinated beans is periodically discharged while
a fresh portion of undecaffeinated beans is
essentially simultaneously charged to the extraction
vessel. Substantially all the caffeine is then
removed from the caffeine-laden supercritical fluid
stream in a countercurrent water absorber. The
method of the present invention is more efficient
and produces a better quality decaffeinated coffee
than prior art batch processes.
Backqround Art
Various coffee decaffeination methods are
well-known in the art. The most common techniques
involve first swelling the coffee beans with water
1304978
-- 2 --
and then extracting the caffeine with an organic
solvent or a caffeine-deficient solution of green
coffee solubles which solution is then itself con-
tacted with a solvent to remove the caffeine there-
oS from. In either case, at least some of the solventtypically contacts the beans, leaving minute traces
therein. The most useful solvents are halogenated
hydrocarbons, but it is becoming increasingly desir-
able to avoid such solvents so as to leave the
coffee free of any trace solvent.
One of the more promising, although costly,
alternative techniques is the use of a supercritical
fluid, preferably supercritical carbon dioxiae, to
extract the caffeine from green coffee beans. Such
a technique is disclosed in U.S. Pat. No. 4,260,639
to Zosel wherein green coffee is contacted with
water-moist supercritical carbon dioxide in order to
extract the caffeine. The caffeine may be absorbed
from the caffeine-laden supercritical carbon dioxide
by bubbling the carbon dioxide through a water
reservoir, said reservoir being replaced by fresh
water every 4 hours, as disclosed in U.S. Pat.
No. 3,806,619 to Zosel. However, such a recovery
system is highly inefficient because the water
reservoir fails to provide a continuous driving
force for caffeine recovery and the periodic replace-
ment of the reservoir results in an undesirable
discontinuity in the process. In still another
technique, disclosed in U.S. Patent ~o. 4,247,570 to
Zosel, the green coffee is mixed with a caffeine
adsorbent prior to contact of the coffee and the
1304978
3 --
supercritical fluid. Then, as the caffeine is extracted
by the supercritical fluid, it is adsorbed by the
caffeine adsorbent, eliminating the need for a separate
caffeine removal step. The prior art methods are batch
techniques which tend to be less efficient than would be
more nearly continuous methods.
It is a feature of one embodiment of the present
invention to provide a more nearly continuous method of
extracting caffeine from green coffee beans with a
supercritical fluid.
Another feature of an embodiment of the present
invention produces a decaffeinated coffee of improved
quality by limiting the loss of non-caffeine solids
during decaffeination.
Summary of the Invention
In accordance with an embodiment of the present
invention there is provided a method of extracting
caffeine from green coffee comprising: (a) continuously
feeding essentially caffeine-free supercritical carbon
dioxide containing non-caffeine solids and saturated with
water to the lower end of an elongate, substantially
vertical extraction vessel containing green coffee beans
having a moisture content of 25-50% by weight,
continuously countercurrently contacting the
supercritical carbon dioxide and the green coffee beans
in the extraction vessel to affect extraction of caffeine
from the coffee into the supercritical carbon dioxide,
and continuously withdrawing supercritical carbon dioxide
containing caffeine and non-caffeine solids from the
upper end of the extraction vessel; (b) discharging a
portion of the coffee b~ans in the vessel from the lower
end of the extraction vessel, the discharged portion
comprising decaffeinated coffee beans; (c) moving the
B
1304978
- 3a -
remaining coffee beans downwardly in the extraction
vessel to an extent corresponding substantially to the
amount of decaffeinated cof~ee beans discharged from the
extraction vessel; (d) introducing moist green coffee
beans having a moisture content of 25-50% into the upper
end of the extraction vessel in an amount corresponding
substantially to the amount of decaffeinated coffee beans
discharged from the extraction vessel; (e) maintaining
the temperature in the extraction vessel at from 80-
140C; (f) feeding the supercritical carbon dioxide
containing caffeine and non-caffeine solids withdrawn
from the upper end of the extraction vessel to an
absorber; (g) continuously countercurrently contacting
the supercritical carbon dioxide containing caffeine and
non-caffeine solids with water in the absorber at a
temperature and pressure substantially the same as in the
extraction vessel to extract substantially all of the
caffeine contained in the supercritical carbon dioxide
but extracting no appreciable amount of the non-caffeine
solids therefrom; (h) withdrawing caffeine-laden water
from the absorber; (i) withdrawing substantially
caffeine-free supercritical carbon dioxide containing
non-caffeine solids from said absorber; (j) recycling the
substantially caffeine-free supercritical carbon dioxide
containing non-caffeine solids to the lower end of the
extraction vessel as required by step (a); and (k)
periodically repeating steps (b), (c) and (d) while
carrying out steps (a) and (e) through (j) to effect
extraction of caffeine from the green coffee beans.
13049~8
Brief Description of the Drawings
Figure l is a schematic illustration showing an
extraction vessel.
Figure 2 is a schematic illustration showing a
05 system for decaffeinating green coffee in an extrac-
tion vessel and recovering caffeine from the caffeine
solvent in a liquid absorber.
Detailed DescriPtion of the Invention
According to the present invention, caffeine is
extracted from the green coffee beans with a super-
critical fluid. A supercritical fluid is a fluid,
typically one wh7ch is gaseous at æmbient conditions,
which is maintained at a temperature above its
critical temperature and at a pressure above its
critical pressure. Suitable supercritical fluids
for use in the present invention include carbon
dioxide, nitrogen, nitrou~ oxide, methane, ethylene,
propane and propylene Carbon dioxide, having a
critical temperature of 31C and a critical pressure
of 72.8 atmospheres, is particularly preferred.
Carbon dioxide i~ abundantly available, relatively
inexpensive, non-explosive and thoroughly safe for
use in food proces~ing. The supercritical fluid5
may be used either individually or in combinations,
as mixed supercritical solvents.
In addition, a so-called enhancer may be added
to the supercritical fluid to improve the solvent
characteristics of the supercritical fluid. The
most useful enhancers are the low to medium boiling
alcohols and esters. Typical enhancers include
methanol, ethanol, ethyl acetate and the like. The
enhancers may be added to the essentially caffeine-
free supercritical fluids at proportions of between
about 0.1% and 20.0% by weight. The enhancers
,~
,
1304978
contemplated for use herein are most typically not
supercritical fluids at the disclosed operating
conditions but rather, the enhancers are simply
dissolved in the supercritical fluid, improving its
05 solvent properties.
In one embodiment the chosen enhancer is
combined with the essentially caffeine-free super-
critical fluid at the described proportions prior to
feeding the supercritical fluid to the extraction
vessel. Alternatively, the essentially caffeine-
free supercritical fluid is fed to the extraction
vessel without the enhancer. The enhancer is then
introduced into the extraction vessel and thereby
combined with the supercritical fluid at a point at
which the supercritical fluid has progressed through
between one-quarter and one-third of the length of
the column. Operation in this manner provides for
some washing of the beans with enhancer-free super-
critical fluid so as to remove any residue of the
enhancer from the coffee beans.
The extraction vessels intended for use herein
include those which provide for efficient contact of
the green coffee beans and the supercritical fluid,
and which are capable of withstanding the necessarily
elevated pressures involved with the use of super-
critical fluids. The preferred extraction vessel is
an elongated column, having a length between four
and ten times the diameter, so that the green coffee
beans are maintained as a bed as the supercritical
fluid passes therethrough. The extraction vessel,
particularly an elongated column, is most typically
situated vertically so as to take advantage of
gravity in providing the movement of the beans
through the vessel.
1304978
-- 6 --
Inasmuch as the supercritical fluid extraction
method is countercurrent, the end of the vessel from
which the decaffeinated coffee beans are discharged
is also the end to which the essentially caffeine-free
05 supercritical fluid is fed, and the end of the
vessel to which the undecaffeinated green coffee is
charged is also the end from which the caffeine-laden
fluid is withdrawn. For the vertical elongated
vessel, it is preferable to discharge the portion of
decaffeinated coffee from the bottom of the vessel
so as to best use gravity in assisting the movement
of the green coffee through the column. The progres-
sion of the green coffee bed through the vessel
arises from the periodic discharging and charging of
the portions of green coffee. When the portion of
decaffeinated green coffee is periodically discharged,
the weight of the coffee bed causes said bed to
shift downward, with the void created at the top of
the column being filled by the portion of undecaffein-
ated coffee which is simultaneously charged to thevessel. The net effect is the progression of the
green coffee charged to the extraction vessel downward
through the column whereupon the decaffeinated
coffee is eventually discharged. Of course, it is
not necessary to situate the column vertically nor
to discharge the decaffeinated green coffee from the
bottom of the vessel, but such a scheme is the most
convenient, particularly with respect to charging
and discharging of the green coffee beans.
In view of the high pressures involved, the
periodic charging and discharging of the coffee is
most easily accomplished through the use of inter-
mediate pressure vessels known as blow cases. Blow
cases are merely smaller pressure vessels of about
~304978
the same volume as the portions of coffee that are
peri~dically charged and discharged, and which are
isolated on both ends by valves, typically ball
valves. A blow case is situated both immediately
05 above and below the extraction vessel and each
connects therewith through one of the valves. Prior
to the time for the periodic charging and discharging,
the upper blow case (for the embodiment of a vertical
elongated vessel) is filled with the desired volume
of beans, which blow case is then isolated. The
remaining void space in the blow case is then filled
with the supercritical fluid so as to increase the
pressure to that maintained in the extraction vessel.
When it is time for the periodic charging and discharg-
ing, the valve connecting the lower and otherwiseempty blow case with the extraction vessel is opened.
Similarly, the valve connecting the upper blow case
and the extraction vessel is opened, charging the
undecaffeinated coffee beans to the vessel. Both
valves are then shut. The upper blow case is essen-
tially empty but for a small amount of supercritical
fluid. The lower blow case contains the decaffeinated
coffee and some supercritical fluid. The supercritical
fluid in the lower blow case may be vented to a
holding vessel or the upper blow case prior to
emptying the beans therefrom so as to conserve the
costly fluid. Al~ernatively, rotary locks of the
sort known for use on pressure vessels may be used
to provide smoother, more easily automated operation.
However, such rotary locks tend to be more mechani-
cally complex, costing more initially and generally
requiring more maintenance.
1304978
- 8 --
The discharging of the portion of decaffeinated
green coffee beans and charging of the portion of
undecaffeinated beans is carried out periodically,
after a period of time established as hereinbelow
05 described. The portion of decaffeinated beans
periodically discharged most preferably r~nges
between 5% and 33% of the volume of the green coffee
contained in the extraction vessel. Similarly, the
portion of undecaffeinated coffee beans periodically
charged to the vessel is also measured as against
the volume of the coffee bed. A height about equal
to the portion of discharged decaffeinated beans is
simultaneously charged to the opposite end, usually
the top, of the elongated vessel. For instance, if
15% of the volume of the green coffee bed i5 discharged,
the equivalent 15% of the volume is then simultaneously
charged to the vessel as undecaffeinated green
coffee beans.
Particular operating conditions are obviously
related to the configuration of a gi~en system, but
the invention is most preferably operated so as to
maximize productivity while providing sufficient
decaffeination of the green beans, from which
it is typically desired to extract at least 97% of
the caffeine initially present. Two of the more
important operating conditions are the weight ratio
of supercritical fluid to coffee and the frequency
of the periodic discharging and charging of the
coffee beans. There are competing aims in choosing
the optimal weight ratio. It is, of course, prefer-
able to use the least possible amount of the super-
critical fluid so as to minimize operating expense.
However, use of an insufficient amount of the fluid
impairs productivity and raises the caffeine concen-
tration of the caffeine-laden supercritical fluid to
1304978
its maximum obtainable level prior to reaching the
de~ired level of decaffeination, thereby eliminating
the overall driving force for the extraction of
caffeine from the green coffee beans. It has been
05 found that the weight ratio of supercritical fluid
to coffee is most preferably between 30 and 100 kg.
supercritical fluid/kg. coffee processed through the
vessel .
The frequency of the periodic charging and
discharging is also a significant operating condi-
tion related to decaffeination efficiency. It is
desirable to maximize productivity but it is also
important to extract the desired amount of caffeine
from the beans and 50 the frequency of the discharg-
ing and charging must be balanced between the twoobjects. The most preferable frequency will depend
on a given system, but it has been found that the
portions of substantially decaffeinated coffee beans
are conveniently discharged between about ever~ 10
and 120 minutes. Considering that the charging of
the portion of undecaffeinated green coffee bean~ is
most preférably concurrent with the discharging of
the beans, the frequency of the charging of the
portions of undecaffeinated beans is also between
about every 10 and 120 minutes. The total residence
time of the green coffee beans in the extraction
vessel is established by the frequency of the periodic
discharging and charging in addition to the size of
the portion periodically discharged and charged.
Thus, if 15% of the volume of an elongated column is
discharged (and the corresponding portion charged)
every 54 minutes, the total residence time of the
beans in the vessel is 6 hours. According to the
limits hereinbefsre set, the total residence time of
the green coffee beans in the elongated vessel is
between about 2 and 13 hours.
1304978
- 10 -
In addition, the temperature and pressure main-
tained in the extraction vessel are also significant
operating variables because both temperature and
pressure must be above the critical constants so as
05 to give the supercritical fluid. Although there is
no corresponding upper limit on the temperature or
pressure, the temperature should not be so high as to
damage the quality of the beans nor the pressure so
high as to require excessively expensive equipment.
The green beans are sensitive to the effects of
temperature with different types of beans having
varying degrees of tolerance for increased tempera-
ture. A temperature in excess of about 100C may
tend to degrade the f}avor of some green bean type~.
The rate of decaffeination, though, is favored by a
relatively high temperature and so it is not desirable
to feed the supercritical fluid to the ve~sel precisely
at the critical temperature. It is preferable to main-
tain the temperature in the extraction vessel between
about 70C and 140C, and more preferable to maintain
the temperature between about ~0C and 100C, depending
on the green bean tolerance to temperature. The
pressure in the vessel must be maintained at at least
the critical pressure in order to provide for the
supercritical fluid. It has long been known that
increasing pressure increases the solvent capacity of
the supercritical fluid. However, a point is reached,
typically at around 400 atmospheres, where the
increased capacity does not justify the added expense
of maintaining such pressures.
It may be desirable to introduce moisture into
the system to facilitate decaffeination. The undecaf-
feinated green coffee beans may be moisturized prior
to charging the beans through the extraction vessel,
solubilizing the caffeine contained in the beans,
thereby making the solubilized caffeine more easily
13049~ 8
extractable. The undecaffeinated beans are typically
moisturized to between about 2S% and 50% by weight
moisture In addition, the essentially caffeine-free
supercritical fluid may be saturated with water
05 prior to being fed to the extraction vessel. Such
saturation of a supercritical fluid is typically
between about 1% and 3% by weight moisture. Decaf-
feination efficiency is thus increased by introducing
moisture into the system.
It ha~ been found according to the present
invention that countercurrent operation of the
supercritical fluid caffeine extraction step achieves
an improved decaffeination efficiency and allows the
production of a decaffeinated coffee of improved
quality over prior art systems. The contact of a
supercritical fluid with caffeine-containing green
coffee beans results in a partitioning of caffeine
between the fluid a~d the beans regardless of the
system design. It is, of course, desirable to
partition as much caffeine from the beans into the
fluid as is possible. However, said partitioning is
limited by the relative solubility of the caffeine
in the supercritical fluid versus its solubility in
the green coffee bean. A partition coefficient may
be calculated based on experimental measurements at
a given set of conditions, said partition coefficient
being defined as the concentration of caffeine in
the supercritical fluid divided by the concentration
of caffeine in the green coffee beans, at an
equilibruim point. The conditions which generally
effect a partition coefficient include temperature,
pressure, and moisture level of the green beans.
For example, the partition coefficient for super-
critical C02 as a caffeine solvent for green coffee
beans has been calculated to be 0 026 at a tempera
1304978
ture of about 85C, a pressure of about 250 barr,
and a green bean moisture level of about 35 to 40%
by weight.
It has been found that the continuous counter-
05 current system of the present invention offers a
tremendous advantage over prior art batch systems
because the caffeine-laden supercritical fluid, just
before it exits the extraction vessel, is then in
contact with fresh green coffee beans having the
green coffee's naturally occurring caffeine level.
The naturally occurring caffeine level differs
depending on the type of green beans being decaf-
feinated. For example, Robusta coffees typically
have a caffeine level of about 2.0% by weight whereas
Colombian coffees are typically about 1.1% by weight
caffeine, as is. Because the exiting supercritical-
fluid is in contact with fresh green beans, the
caffeine concentration in the exiting supercritical
fluid increases to its asymptotic limit, or nearly
Z0 thereto, based on the caffeine partition coefficient
for the given fluid. It has been found that with
counter-current operation the caffeine concentration
in the supercritical fluid exiting the extraction
column is typically at least S0% of the maximum
obtainable caffeine concentration and preferably at
least 70% of the maximum obtainable caffeine concen-
tration, the maximum obtainable caffeine concentra-
tion being defined by the partition coefficient and
the naturally occurring caffeine level in the green
coffee being decaffeinated. Such a high caffeine
concentration is very desirable because it reflects
an efficient decaffeination system and it enables
efficient recovery of the caffeine from the super-
critical fluid as a valuable by-product.
1~04978
13 -
In a batch system, however, as caffeine is
partitioned from the green coffee beans contained
therein, the maximum caffeine concentration obtain-
able in the supercritical fluid drops dramatically.
OS Thus, a much larger amount of supercritical fluid is
necessary in a batch syste~ as compared to the
countercurrent extraction system of the present
invention to achieve the same degree of decaffeina-
tion. For example, to achieve 97% decaffeination
of green coffee with supercritical carbon dioxide,
approximately 33 times as much carbon dioxide is
needed to decaffeinate the beans in a batch system
as compared to the countercurrent system of the
present invention. Further, the caffeine concen-
tration of the caffeine-laden supercritical carbon
dioxide exiting the countercurrent extraction system
of the invention, said extraction system containing
Milds coffee bean~, is on the order of 280 ppm as
compared to a batch system wherein the carbon dioxide
exits at a caffeine concentration of about 8 ppm.
This increased caffeine concentration ac~ieved by
the countercurrent extraction of the invention is
particularly important in allowing efficient recovery
of the caffeine from the supercritical fluid.
Several caffeine removal techniques are known
in the art. For example, the caffeine-laden super-
critical fluid may be passed through an absorbent
bed, such as a bed of activated carbon, to absorb
the caffeine. Alternatively, the caffeine may be
recovered by lowering the pressure of the caffeine-
laden supercritical fluid so as to precipitate out
both the caffeine and any enhancer that might be
used. However, it has been found that supercritical
fluids are not entirely selective for caffeine, but
1304 97 8
rather typically extract both non-caffeine solids
and caffeine. For example, supercritical carbon
dioxide typically extracts non-caffeine solids and
caffeine at a weight ratio of about 1.5:1 to 3: 1
05 non-caffeine solids to caffeine. Thus, if super-
critical carbon dioxide extracts caffeine from green
coffee so as to increase its caffeine concentration
to 220 ppm, said fluid will also contain about 300
tO 660 ppm non-caffeine solids. It has been found
that the two methods described above for caffeine
recovery, namely absorption and depressurization,
fail to selectively recover caffeine. Rather,
non-caffeine solids which are important to the
flavor quality of coffee are lost from the super-
critical fluid with the caffeine during caffeinerecovery.
According to the present invention, the
caffeine-laden supercritical fluid removed from the
caffeine extràction vessel is continuously fed to a
countercurrent liquid absorber. Continuous counter-
current liquid absorption systems aré impractical
and uneconomical for use in prior art supercritical
fluid decaffeination systems because of the low
caffeine concentration in the caffeine-laden super-
critical fluid exiting the batch extractor. However,not only is a countercurrent absorber efficient and
economical as used in the present invention, but it
has additionally been found that polar fluids exhibit
an excellent selectivity for caffeine when contacting
caffeine-laden, non-caffeine solids containing
supercritical fluids. As such, as the essentially
caffeine-free supercritical fluid exits the absorber,
it typically contains very nearly the same level of
non-caffeine solids as it did upon entering the
absorber. Thus, if this fluid is recycled to the
1304978
caffeine extraction vessel, it extracts no measurable
amount of non-caffeine solids from the green beans
then being decaffeinated. As a result, the decaf-
feinated beans produced by the present invention are
05 of a better flavor quality. Additionally, the yield
loss generally associated with non-caffeine solids
loss is eliminated by the process of the present
invention.
According to the invention, the liquid absorber
is operated under supercritical conditions. Typically,
the temperature and pressure within the absorber are
identical, or very nearly identical, to the temperature
and pressure conditions- in the extraction vessel.
As discussed hereinabove, the critical temperature
and pressure will vary depending on the fluid employed.
Absorber design is considered to be well within the
ordinary skill of one in the art Tgpically, the
abosrber is operated with a packing selected from
those readily available in the art. Generally, the
polar fluid i8 contacted with the supercritical
fluid at a weight ratio of about 5:I to 25:1, and
typically about 10:1 to 20:1, supercritical fluid to
polar fluid. Water is the preferred polar fluid for
use in the continuous countercurrent absorber of the
present invention. It is preferred that the polar
fluid of the invention remove at least 90% by weight
of the caffeine contained in the caffeine-laden
supercritical fluid, and more preferably 95% of the
caffeine by weight.
The invention is further described by reference
to the figures. Figure 1 shows a preferred embodiment
of the caffeine extraction vessel. At steady state
conditions, the extraction vessel 5 is filled with a
bed of green coffee beans. An essentially caffeine-
free supercritical fluid is fed to the first end of
3 0 4 9 7 8
- 16 -
the extraction vessel 6 and caffeine-containing
supercritical fluid is withdrawn from the second end
of the extraction vessel 4. Green coffee is periodi-
cally admitted through valve 1 into blow case 2.
OS Valves 3 and 7 are simultaneously ~pened intermit-
tently so as to charge the green coffee from blow
case 2 to the second end of the extraction vessel 4
and discharge a portion of substantially decaffeinated
green coffee beans from the first end of the extrac-
tion vessel 6 to blow case 8. Valve3 3 and 7 are
then closed. Valve 9 is then opened to discharge
the substantially decaffeinated green coffee from
blow case 8. Additional green coffee is admitted
through valve 1 into blow case 2 and the procedure
is repeated.
Figure 2 is a schematic illustration of adecaffeination system according to the invention
wherein green coffee (12) is fed to an extraction
vessel (L0) and is removed therefrom as decaffeinated
green coffee (14). An essentially caffeine-free
supercritical fluid is fed countercurrently to the
green beans as stream 16 into the extraction vessel,
and exiting as a caffeine-laden fluid stream (18).
The caffeine-laden stream (18) is then fed to a
water absorber (20) and exits as an essentially
caffeine-free supercritical fluid stream (16).
Countercurrently, water is fed as stream 22 to the
water absorber and exits as an aqueous caffeine-
containing stream (24).
Example 1
An elongated pressure vessel having a height
about five times its diameter was loaded with 100%
Colombian green coffee which was prewet to a moisture
~304978
- 17 -
of about 30% to 40% by weight. Approximately
120 pounds of green coffee were contained in the
pressure vessel. To the bottom of the pressure
vessel was continuously fed essentially caffeine-free
05 supercritical carbon dioxide at a pressure of about
250 atm. and a temperature of about 130C. The
carbon dioxide extracted caffeine and non-caffeine
solids from the green coffee as it moved upwardly
through the pressure vessel. The caffeine-laden
supercritical carbon dioxide which also contained
non-caffeine solids continuously exited the top of
the pressure vessel. Each nineteen minutes,
approximately 10% of the volume of the coff~e bed
was discharged into a bottom blow case while the
same volume of prewet Colombian coffee was simul-
taneously charged from a previously loaded top blow
case into the top of the pressure vessel. The total
residence time of the green coffee in the pressure
vèssel was about 3 hours. The weight ratio of
supercritical carbon dioxide to coffee was about
50 kg. carbon dioxide/kg. coffee.
The caffeine partition coefficient for super-
critical carbon dioxide and green coffee beans has
been measured to be about 0.026 at these operating
2S conditions. The average caffeine concentration for
Colombian Milds coffee is about 1.22% by weight on a
dry basis or about 1.08~o by weight as is. Thus, the
maximum obtainable caffeine concentration in the
supercritical carbon dioxide is about 280 ppm. The
caffeine-laden supercritical carbon dioxide exiting
the top of the pressure vessel was found to have a
caffeine concentration of about 200 ppm, or about
71% of the maximum obtainable caffeine concentration.
The caffeine-laden supercritical carbon dioxide was
also found to contain about 350 ppm non-caffeine
3 0497 8
- 18 -
solid~. The coffee discharged to the bottom blow
case wa~ found to b~ at least 97~ decaffeinated by
weight.
05 ExamDle 2
The caffeine-laden supercritical carbon dioxide
from Example 1 was continuously fed to the bottom of
an ab~orber mea~uring 4.3 inches in diameter, 40 feet
in height, and with 32 feet packing height. The
carbon dioxide was fed at a rate of 1350 lb~/hr.
Water wa~ fed to the top of the absorber at a rate
of 110 to 120 lbs/hr. The absorber was operated at
a pressure of about 250 atm. and a temperature of
about 130C. The following Table demon~trates the
excellen~ selectivity for caffeine exhibited by the
water, yielding a caffeine purity of about 88~.
TABLE
Non-Caffeine
Rate Caffeine Solids
(lb/hr) Conc. (PPM) Conc. (PPM)
C0Feed To 1350 200 348
~ sorber
CO Exit From 1350 19 332
~bsorber
Water Feed To 110-120 0 171*
Absorber
Water Exit From 110-120 2,450 340*
Absorber
*Includes 171 ppm non-caffeine solids attributable
to hardness of water.
30 497 8
- 19 -
Tbe essentia}ly caffeine-free supercritical
carbon dioxide exiting the abo~rber was recycled to
the extraction vessel of Example l. The decaffe~nated
green coffee beans produced by recycling the eGsen-
05 tially caffeine-free carbon dioxide containing
non-caffeine solid~ was u~ed to prepare a coffee
brew (A). A control coffee brew (B) wa~ prepared
from identical bean~ tecaffeinated with super-
critical carbon dioxide which was e~sentially free
of carbon dixoide and non-caffeine solid~. Thig
supercritical carbon dioxide strea~ had passed
through an activated carbon bed which had a~sorbed
caffeine and non-caffeine solids from a caffeine-
laden supercritical carbon dioxide ~trea~ generated
by the process of Example 1. Coffee brew A was
judged by a panel of expert coffee tasters to be of
superior flavor quality as compared to coffee brew
8. The improved flavor quality of brew A wa~
attributed to the presencc of non-caffeine solid~ in
the recycled carbon dioxide which prevented the loss
of valuable flavor compounds from the green bean~
during decaffeination.
,.
