Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Case 2931
DESCRIPTION
SEPARATE RECOVERY OF CAFFEINE AND
COFFEE SOLIDS ADSORBED ON ACTIVATED CARBON
Technical Field
This invention is directed to separately re-
05 covering caffaine and non-caffeine solids adsorbed
on activated carbon. Specifically, the non-caffeine
solids are Pluted from the activated carbon by
contacting said carbon with an aqueous basic solution.
Caffeine is subseguently eluted from the activated
carbon in relatively pure form by contacting said
carbon with a concentrated aqueous acidic solution.
The non-caffeine solids in the basic solution
may be re-adsorbed onto the activated carbon subse-
quent to the caffeine elution. The aqueous acidic
solution is refined whereby ess~ntially pure
crystalline caffeine is obtained.
Background Art
Much activity has been directed towards finding
a suitable adsorbent for removing caffeine from an
aqueous coffee extract. Activated carbon has long
been known as a caffeine adsorbent but use of such
carbon has been limited by the concurrent adsorption
of non-caffeine coffee solids during decaffeination,
making the process uneconomical. A process
directed to overcoming the problem is
disclosed in European Patent 0,008,308.
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05 Decaffeination with activated carbon, even by
the methods disclosed above, is still hampered by
the tenacity with which the caffeine adsorbs to the
activated carbon, which tenacity makes regeneration
of said carbon extremely difficult. Two recent
disclosures, U.S. Pat. No. 4,298,736 to Katz et al.
and commonly assigned U.S. Pat. 4,513,136 to
Katz et al., describe effective techniques for
removing adsorbed caffeine from activated carbon.
The inventions call for contacting activated carbon
containing both caffeine and non-caffeine solids
with an organic acid or aqueous solution of an
organic acid or an alcohol. The effect of the
contact is to strip the activated carbon of sub-
stantially all material contained thereon. Though
the caffeine is indeed removed, the resulting solution
is low in caffeine purity; roughly 25% by weight of
the total solids in solution is caffeine. The low
purity renders the mixture diff:icult to refine.
Additionally, the non-caffeine solids are rendered
somewhat unusable by the refining process and can
not generally be re-adsorbed onto the activated
carbon bed.
It is an object of the present invention to
separately recover the caffeine and non-caffeine
solids adsorbed on activated carbon. A further
object is to recover the caffeine in relatively pure
form. Another object of the present invention is to
recover the non-caffeine solids in a form suitable
for re-adsorption onto the activated carbon.
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Disclosure of the Invention
The present invention permits the separate
recovery of caffeine and non-caffeine solids adsorbed
on activated carbon by the initial contact of the
05 carbon with an aqueous basic solution followed by
contact of the activated carbon with an aqueous
acidic solution. The non-caffeine solids in the
basic solution may, with minor treatment, be
re-adsorbed onto the activated carbon.
Re-adsorption of the non-caffeine solids is
advantageous in lowering the cost of decaffeinating
an aqueous extract with a treated adsorbent. For
instance, the Pfluger et al. patent applications
describe a process of coating fresh activated carbon
with a carbohydrate solution in order to reduce
non-caffeine coffee solids losses during decaffeina-
tion. The present invention eliminates the use of
the carbohydrate solution by providing for the
re-adsorption of the non-caffeine solids. The
invention is not limited to a process such as
disclosed by Pfluger et al. Decaffeination of an
aqueous coffee extract by an untreated activated
carbon leads to the adsorption of a large amount of
non-caffeine solids. These solids may also be
recovered by the present invention and re-adsorbed
onto the activated carbon to prevent subsequent
non-caffeine solids losses.
The activated carbon contemplated for use in
this invention is the spent carbon as may be obtained
by operation of decaffeination processes similar to
those set orth above. Said activated carbon thusly
contains adsorbed caffeine, non-caffeine coffee solids
and may contain carbohydrates (the carbohydrates and
non-caffeine coffee solids are hereinafter together
referred to as non-caffeine solids). A limited
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amount of non-caffeine coffee solids are adsorbed
onto the activated carbon in an exchange with
adsorbed carbohydrates during the decaffeination
operation of the Pfluger et al. applications. As a
05 result of the carbohydrate treatment and the limited
exchange of non-caffeine coffee solids, the activated
carbon contains valuable non-caffeine solids which
solids are very desirable for recovery and re-adsorp-tion
onto the activated carbon.
It has been found that said non-caffeine solids
may be recovered from the activated carbon separately
from adsorbed caffeine by contacting the carbon with
an aqueous basic solution which solution is confined
to a specific range of pH. The critical range for
the pH of the basic solution is between pH 8 and pH
13. A solution having less than pH 8 is not particu-
larly effective for non-caffeine solids removal.
The use of a basic solution with a pH greater than
13 will cause non-caffeine solids elution, but the
2~ caffeine remaining on the carbon tends to be destroyed
by reactions well known in the art.
Provided the proper pH is maintained, a wide
variety of basic solutions may be used in the present
invention. For instance, aqueous solutions of
potassium carbonate, potassium hydroxide or ammonium
hydroxide have been discovered to work well. The
concentration of any of the respective aqueous basic
solutions is adjusted such that the solution is of a
pH within the prescribed range. Ammonium hydroxide
is convenient because any residue is easily steam
stripped from the activated carbon subsequent to the
contact of the basic solution and said carbon. So
too, ammonium hydroxide is easily recovered from the
aqueous basic solution which contains the non-caffeine
solids by steam stripping prior to re-adsorption of said
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solids onto the activated carbon. Potassium-containing
bases are preferred though because potassium is a
natural constituent of coffee. Speciically, potassium
hydroxide is the preferable base owing to its strength
05 which minimizes the amount and hence, cost of the
preparation of the a~ueous basic solution.
Contact of the activated carbon and the a~ueous
basic solution is carried out in any manner providing
solid-liquid contact, such as circulation of the
basic solution through a bed of spent activated
carbon contained in an elongated column. As noted,
the pH of the aqueous solution is the critical
parameter, but the temperatur~ of the contact between
said carbon and baæic solution is significant as
well. It has been found that the temperature of the
contact should be at least 65C if the non-caffeine
solids are to be properly eluted. Operation within
the described conditions provides for removal o~ up
to 65% by weight of the non-caffeine solids with
concurrent desorption of approximately 5% by weight
of the caffeine initially present on the activated
carbon.
The bulk of the caffeine may be desorbed from
the activated carbon by the process described in the
hereinabove referred to Katz et al. patent and the
hereinabove referred to ~atz et al. patent application.
The preferred process is set forth in the Katz et
al. application wherein the activated carbon is
contacted with a concentrated aqueous acetic acid
solution comprising between 50% by weight and 80% by
weight acetic acid. Preferably, the aqueous acid
solution is at a concentration of 70% by weight
acetic acid.
Use of an alkali metal base and acetic acid
presents a difficulty in that an acetate salt tends
to form when the two constituents are mingled. The
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salt has the effect of lowering the purity of the
caffeine in the aqueous acidic solution. Ik is
desirable, then, to introduce a flush step between
the contact of the aqueous basic and acidic solutions
05 with the activated carbon. Said flush step comprises
contacting the activated carbon with an aqueous
solution of approximately 5% by weight acetic acid.
The dilute acid mingles with any basic solution
which may remain on the carbon, forming the acetate
salt which is then flushed from the activated carbon
and subsequently discarded.
The contact of the activated carbon and the
concentrated aqueous acidic solution occurs in any
manner providing for good solid-liquid contact;
slurrying said carbon in the concentrated acid
solution is one example. The temperature at which
said contact is carried out should be at least 85C.
Operation in the manner described herein permits
recovery of up to 70% by weight of the caffeine
initially present on the activated carbon, which
caffeine has a purity of roughly 60% by weight in
the aqueous acidic solution.
Regeneration of the activated carbon which has
been contacted by both the basic solution and acidic
solution is completed by two further processing
steps. The carbon is first contacted with a quantity
of fresh wash water to displace any non-adsorbed
acid. Said activated carbon is subsequently steamed
for a period of time whereby the remaining acid is
volatilized. The regeneration steps are as described
in the Katz et al. patent application.
The relatively pure caffeine in the aqueous
acid solution may be recovered in any suitable
manner such as steam distillation or simple evaporation
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of the acid. The preferred method i9 to first fully
evapora-te the solvent, leavin~ an aqueous caffeine
solution. Caffeine may then be precipitated from
said solution by cooling the same to form pure white
05 needle-shaped crystals.
The aqueous basic solution which contains the
non-caffeine solids may be made suitable for
re-adsorblng said solids onto -the activated carbon
with only minor manipulation. Alternatively, the
basic solution may be neutralized and the coffee
solids contained therein may be returned to the
aqueous coffee extract used in decaffeinating green
coffee beans. In the case of re-adsorption, the
basic solution must ~enerally be concentrated to
roughly 25% by weight non-caffeine solids because
the basic solution as obtained above is typically of
lower concentration. Then, the solution may be
contacted directly with the activated carbon at the
elevated pH in order to effect non-caffeine solids
readsorption provided the temperature of said contact
is sufficiently low. Another possibility is to
neutralize the concentrated basic solution prior to
contacting the activated carbon. Such a neutralization
step eliminates the need for contact at a reduced
temperature. Similarly, an ion exchange resin may
be used to reduce the pH of the concentrated basic
solution prior to contact with the carbon.
Whatever the manner of treatment of the basic
solution chosen, contact with the activated carbon
is again carried out in any vessel providing solid-
liquid contact. The operating temperature depends
on the pre-treatment of the basic solution. Re-
adsorption of the non-caffeine solids substantially
eliminates the use of the carbohydrate solution
described in the previously referred to Pfluger et
.
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al. patent applications, representing a significant
cost savings for the present invention.
The following examples are illustrative of
certain e~bodiments of the present invention. The
05 methods and results shown are not intended to limit
the invention beyond what is claimed.
Example 1
1. 76.8 g of activated carbon loaded with
about 20% by weight non-caffeine solids and about 5%
by weight caffeine was charged into an elongated
glass coiumn.
2. 1980 ml of 1.0% by weight potassium hydroxide
solution (pH 12.7) was passed through the column at
a rate of 4 ml/min. and a temperature of about 88C.
3. About 1500 ml of water at a temperature of
about 93C was passed through the column subsequent
to the passage of the basic solution. 97.6% by
weight of the non-caffeine solids initially loaded
on the carbon was removed whereas 11.6% by weight of
the caffeine initially loaded was removed from the
carbon.
4. 2100 ml of 70% by weight acetic acid
solution (pH 1.3) was then passed through the column
at a rate of 4 ml/min. and a temperature of about 88C.
The discharged acetic acid solution contained 70.9%
by weight of the caffeine initially loaded on the
carbon which caffeine was at a purity of 86.5% by
weight.
Example 2
A laboratory scale multi-column system run was made
with six columns on stream a all times after the
system reached equilibrium. The activated carbon
used was from the same source as that used in Example 1.
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g
The conditions for the run were as follows:
Contact with Basic Solution
. _
basic solution: 1% by we~ght potassium
hydroxide
05 pH: 12.7
temperature: about 93C
flow rate: 2.8 ml/min.
wt. of basic
solution/wt of carbon: 9.0
10 cycle time: 4 hours
Intermediate Flush
flush solution: 5% by weight acetic acid
temperature: about 93C
flow rate: 4 ml/min.
15 wt. of flush solution/
wt. of carbon: 3.0
cycle time: l hour
Contact with Acidic Solution
acidic solution: 70% by weight acetic acid
20 pH: 1.3
temperature: about 93C
flow rate: 3 ml/min.
wt. of acidic solution/
wt. of carbon: 10.0
25 cycle time: 4 hours
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Approximately 75 g of activated carbon was loaded
into the column each cycle. Contact of the basic
solution removed better than 60% of the non-caffeine
solids initially present on the activated carbon.
05 Subsequent cont:act of the acidic solution removed an
average of nearly 70% of the caffeine initially
pres~nt on the carbon. The caffeine was at an
average purity of 67% in the acetic acid solution.
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