Caffeine recovery from activated carbon

The invention relates to a process for recovering caffeine from caffeine-loaded activated carbon and which is characterized in that the caffeine destroying activity of the activated carbon is reduced before or after loading with caffeine. The activated carbon can to that end be treated with acids, buffers, complexing agents, redox substances, caffeine and other xanthine derivatives. The caffeine recovery yield can be considerably increased by this means.

The present invention relates to an improved process for recovery of 
caffeine from caffeine-loaded activated carbon. 
With a number of decaffeination processes for vegetable products, including 
coffee, activated carbon is used at some stage for selective separation of 
the caffeine. Because the caffeine obtained as a by-product can be used 
for other purposes, efforts are made to separate the caffeine from the 
activated carbon by economical means. 
The desorption of the caffeine from the activated carbon is not easy 
because activated carbon is a very good adsorbent for caffeine. U.S. Pat. 
No. 4,673,743 to Wilkens describes a process for separating caffeine from 
caffeine-loaded activated carbon with which a circulated inert gas 
sweeping stream is passed rectangularly through the activated carbon at a 
temperature of 350.degree. to 450.degree. C., and the caffeine desorbed 
from the activated carbon is precipitated by cooling in the form of solid 
particles and separated. One essential disadvantage of that process is the 
fact that the activated carbon layer thickness or bed depth cannot be more 
than 60 mm. If the layer thickness is increased, the caffeine yield 
decreases considerably. 
A further disadvantage of that process resides in that a considerable part 
of the caffeine cannot be recovered but is lost. 
U.S. patent application Ser. No. 08/092,339 (filed Jul. 15, 1993); 
describes a process for recovery of caffeine from activated carbon which 
permits the successful use of significantly deeper beds for desorption and 
which reduces the process time and the quantity of hot gas or steam 
required per unit of carbon desorbed, thereby making the entire process 
economically attractive. That process uses a circulated inert gas sweeping 
stream held at a temperature of 250.degree. to 460.degree. C. and is 
characterized in that the activated carbon is preheated prior to the 
desorption of the caffeine with external heating means and held during the 
desorption step at a uniform temperature or at a temperature increasing 
from the inlet to the outlet of the inert gas sweeping stream within the 
range of 250.degree. to 460.degree. C. and the caffeine is subsequently 
separated from the inert gas sweeping stream by conventional means. The 
preheating preferably takes place at a temperature of at least 250.degree. 
C., especially at least 320.degree. C. 
It is possible with that process to eliminate a substantial disadvantage of 
the process of the above-mentioned U.S. Pat. No. 4,673,743. It is, 
however, also disadvantageous with that process that a part of the 
caffeine is irretrievably lost. 
It is therefore the object of the present invention to find a process with 
which it is possible to reduce to a minimum the caffeine losses resulting 
upon recovery of caffeine from caffeine-loaded activated carbon. 
It has been found within the scope of the present invention that the losses 
with the recovery of caffeine from caffeine-loaded activated carbon are to 
be attributed to an apparent caffeine destroying activity of activated 
carbon. Consequently, the invention relates to a process for recovering 
caffeine from caffeine-loaded activated carbon and which is characterized 
in that the caffeine destroying activity of activated carbon is reduced 
before or after loading with caffeine. 
It has been established within the scope of the invention that the caffeine 
destroying activity of activated carbon can be reduced by various means. 
The activated carbon can be treated according to the invention with acids, 
buffers, complexing agents, redox substances, caffeine and other xanthine 
derivatives. In all cases, a considerable reduction in the extent of the 
decomposition of the caffeine is achieved during the recovery and the 
yield of caffeine there with considerably increases.

The invention works by treating the activated carbon, either before or 
after loading it with caffeine, prior to thermal caffeine recovery 
processes, in order to reduce the caffeine destroying activity of the 
activated carbon. 
The treatment of the activated carbon with the agent for reducing the 
caffein destroying activity can be carried out, for instance, in an 
apparatus as it is shown in FIG. 1. The meanings of the numerals in FIG. 1 
are 1 a jacketed activated carbon treatment column, 2 the activated carbon 
to be treated, 3 the inlet for the treatment solution and 4 the outlet for 
the treatment solution. 5 and 6 are the inlet and outlet for a heating 
medium optionally to be used. 
As already mentioned above, the most varied treatment agents have proven to 
be useful. That gives rise to the assumption that the caffeine destroying 
activity of activated carbon is to be attributed to various causes. Acids, 
buffers, complexing agents, redox substances and also the additional 
loading with caffeine or other xanthine derivatives have proven to be 
useful. 
Inorganic and/or organic acids come under consideration as suitable acids 
for carrying out the process of the invention. For instance, phosphoric 
acid, sulfuric acid, nitric acid, hydrochloric acid, acetic acid, citric 
acid, gluconic acid, formic acid, perchloric acid, phytic acid, lactic 
acid, ascorbic acid, isoascorbic acid, etc., are suitable. 
The strength of the acids used as well as their amounts vary depending both 
on the type of activated carbon to be treated as well as the contacting 
apparatus used. Acid concentration will generally vary between 0.001N to 
10N and more, preferably be between 0.01 and 5N. Usage ratios will be 0.5 
to 30 1/1 of carbon and more, preferably between 1 and 10. 
The increase in the caffeine yield with the recovery from caffeine-loaded 
activated carbon by means of the treatment according to the invention with 
acid is surprising because other tests in respect of the recovery of 
caffeine had shown that pure caffeine readily sublimes, on the other hand, 
crude caffeine from coffee decaffeination decomposes but can readily be 
brought to sublimation when it is made alkaline with CaO or MgO. 
A possible explanation for the mode of operation of the acids could 
possibly be seen in that the metal content of the carbon has a causal 
influence on the decomposition of the caffeine and the treatment according 
to the invention with acid leads to a reduction in the metal content of 
the activated carbon. 
For instance, practically the most diverse buffers which regulate pH in the 
acid range (as, for example, HCl/KCl, citric acid/NaCl, citric acid/NaOH, 
acetic acid/Na acetate, etc.) and especially those on the basis of the 
aforementioned acids and their salts, especially some of their 
combinations with ammonia (as, for example, citric acid/NH.sub.4 OH, 
acetic acid/NH.sub.4 OH, etc.), can be quoted as buffers suitable 
according to the invention. Strengths and amounts correspond to those used 
for acids. Solutions based on metaphosphates, pyrophosphates, 
polyphosphates and other phosphates are also suitable. 
The sodium salt of ethylenediaminetetraacetic acid (EDTANa.sub.2), 
phytates, gluconic acid, and practically all the numerous well-known heavy 
and transition metal complexing agents, under also well-known suitable 
conditions, are to be quoted as complexing agents suitable according to 
the invention. 
Suitable redox compounds are, for example, nitric acid, perchloric acid, 
ascorbic acid, isoascorbic acid, etc. Strengths and amounts of complexing 
agents and redox compounds correspond to the ones to be used for the 
acids. 
Combinations of acids and/or buffers and/or complexing agents and/or redox 
compounds can also be used within the scope of the invention. 
Even caffeine itself showed a positive effect on recovery yields. A more 
fully loaded carbon shows not only-a definitive yield improvement in 
percent but also an absolute lower caffeine loss. The same effect was able 
to be achieved by "uploading" the carbon before subjecting it to the 
recovery process. Xanthine derivatives other than caffeine can also be 
used successfully. 
The carbon coming from the decaffeination process as a rule has a degreee 
of caffeine loading of 15 to 19% by weight (dry basis). In accordance with 
the invention, the carbon 20% should be loaded to the extent that the 
loading is at least 20% by weight, preferably at least 24% by weight, 
caffeine and optionally other xanthine derivatives 
Uploading the activated carbon with caffeine and other xanthine derivatives 
can be effected in very diverse forms. One of the preferred ways is to 
reload the used activated carbon into the adsorber section of the 
decaffeination plant in such a way that it is in contact with the caffeine 
rich stream just prior to its separation from caffeine with fresh carbon. 
Another possibility for effecting the uploading is to contact it with a 
partial caffeine solution recycle just prior to the recovery unit or with 
a xanthine derivative solution. This, of course, has the disadvantage of 
increase in the content of water which has to be dried off in the 
immediately following step, but avoids the need for a larger (for example, 
high-pressure) adsorbing unit in the decaffeination plant. 
Xanthine derivatives which can be used here are compounds with chemical, 
structural and behavioral similarity to caffeine. Examples are 
isocaffeine, all dimethylxanthines (theobromine, theophylline, 
paraxanthine), diverse monomethylxanthines, etc., all very similar in 
their chemical structure, adsorption behavior with respect to activated 
carbon, sublimability, etc. 
In a preferred embodiment of the invention, the activated carbon is treated 
with acids, buffers, complexing agents and/or redox compounds and 
additionally--either fully high level loaded or uploaded--with caffeine or 
other xanthine derivatives. 
As already mentioned, the treatment according to the invention can be 
carried out in a simple batch vessel as shown in FIG. 1, stirrer or 
pumping devices optionally being used to improve intimate contact between 
the treatment agents and the activated carbon. 
The treatment duration can be from a few to several hours and preferably 
from 10 minutes to 3 hours. The treatment normally takes place at room 
temperature but can also be at elevated temperatures, for instance in the 
range from 40.degree. to 180.degree. C., preferably in the range from 
60.degree. to 110.degree. C. 
After the treatment according to the invention, the activated carbon can 
optionally be washed with water in order to remove excess treatment agents 
(acid, buffer, etc.). 
In the case of treatment with HCl, there should at any event be washing 
with water. It has proven necessary that chloride ions be removed as far 
as possible. Washing is preferably at elevated temperatures of, for 
example, 80.degree. to 100.degree. C. The disturbing chloride ions can, 
however, also be removed by displacement with other ions, e.g. NO.sub.3 
--or OH--. A thermal treatment in an oven at about 500.degree. to 
700.degree. C. can also be used for this purpose. 
The treatment of the activated carbon according to the invention can take 
place before or after loading it with caffeine within the scope of the 
decaffeination process. The caffeine adsorbing properties (loading levels 
and kinetics) are not negatively influenced by a treatment beforehand. To 
the contrary, unusually high caffeine recovery yields are possible with 
the process of the invention. The process thereby has the additional 
advantage that the activated carbon can be used again immediately after 
the recovery of the caffeine without need of a reactivation of the 
activated carbon. 
EXAMPLE 
The treatment according to the invention was carried out with an apparatus 
as shown in FIG. 1. 500 g of activated carbon were washed with 3250 ml of 
0.1N agents (H.sub.3 PO.sub.4, HCl, EDTANa.sub.2) in a one-way through 
fashion at a flow rate of 2.5 1/hr followed by removing excess agents by a 
2 hr hot (80.degree. C.) water wash. 
The activated carbon treated by this means was then introduced into an 
apparatus as it is shown in FIG. 2. That apparatus works according to the 
process which is described in U.S. patent application Ser. No. 08/092,339 
(filed Jul. 15, 1993). and is similar to the apparatus described there but 
has a fluidized bed (with externally heated walls). With that process, the 
activated carbon loaded with caffeine and treated according to the 
invention is, as already mentioned above, rapidly brought to a uniform 
temperature suitable for the desorption of the caffeine from the activated 
carbon with the aid of an external heating and a hot inert gas sweeping 
stream before desorption of the caffeine is commenced. 
The individual reference numerals in FIG. 2 have the following meanings: 
1. activated carbon desorption vessel with electrically heated walls, an 
internal diameter of 100 mm, perforated plates for producing a fluidized 
bed and with a total height of about 900 mm. 
2. fluidized carbon bed (static bed heights 100 to 120 mm) 
3. inert gas sweeping stream (N.sub.2), 380.degree. C., 9 st m.sub.3 /hr 
4. gas heater 
5. gas source 
6. caffeine-loaded inert gas sweeping stream, 380.degree. C., exiting from 
1 
7. caffeine-loaded inert gas sweeping stream, 380.degree. C., entering the 
caffeine collection vessel 8 
8. caffeine collection vessel 
9. 20 .mu. sintered metal filter 
10. caffeine solution wash sprays (aqueous, 60.degree. C.) 
11. caffeine solution 
12. recirculation pump 
13. heat exchanger 
14. exiting inert gas sweeping stream freed of caffeine 
15. caffeine solution drain 
16. make-up water. 
The desorption vessel 1 was in each experiment first filled with 500 g of 
material and rapidly brought to a temperature of 380.degree. C. with the 
aid of external heating and the inert gas sweeping stream. The flow rate 
of the inert gas sweeping stream (N.sub.2) was 9 st m.sub.3 /hr, and its 
temperature was 380.degree. C. The residence time was 3 hrs in all cases. 
All carbon samples had been loaded with caffeine in an industrial 
supercritical CO.sub.2 decaffeination plant, except the EDTANa.sub.2 one 
which was loaded in a respective pilot plant. 
The results of the experiments are set forth in the following Tables 1 to 
4. The treatment process according to the invention, the caffeine loading 
of the activated carbon at the beginning of the experiments and the 
recovery yield are quoted. Absolute loss values are additionally contained 
in Table 2. 
The results of experiments with activated carbon treated according to the 
invention (H.sub.3 PO.sub.4, HCl) and untreated activated carbon are 
compared in Table 1. The recovery yield values show that considerable 
increases are possible with the process of the invention. 
The result of an experiment is given in Table 2 with which the caffeine 
loading of the activated carbon had been purposively increased, and it is 
shown that substantially higher recovery yields, namely about twice as 
high, are possible in comparison with normally loaded activated carbon. 
Experiments are described in Table 3 with which two measures according to 
the invention have been combined, namely, on the one hand, the treatment 
with acid or, resp., complexing agent and, on the other hand, a purposive 
additional caffeine loading, with yields of more than twice as high, 
reaching to almost 100%, being possible. 
It is shown in Table 4 that the activated carbon treated according to the 
process of the invention has reattained its original adsorbing properties 
after recovery of the caffeine so that a reactivation of the activated 
carbons prior to their renewed use is not necessary. The caffeine 
adsorbing activity was measured according to a test where a certain amount 
of activated carbon adsorbs pure caffeine from a standard aqueous 
solution, two different caffeine/carbon contact times (2 and 16 hours) 
being used to represent both the kinetics of adsorption influence and the 
maximum absolute loading capacity of the material. The test is run at 
25.degree. C. and the results are expressed as percentage caffeine on dry 
caffeine + carbon basis. From the two values, it is possible to infer the 
behavior of the activated carbon under super-critical CO.sub.2 
decaffeination conditions, as experience shows. 
TABLE 1 
______________________________________ 
Effects of carbon pretreatment on recovery yield 
Caffeine load on 
Experiment 
Carbon carbon at start, 
Recovery 
No. Quality % dry basis yield 
______________________________________ 
1 untreated 15.2 43% 
2 H.sub.3 PO.sub.4 /H.sub.2 O 
14.6 67% 
3 HCl/H.sub.2 O/temp.*) 
14.3 74% 
______________________________________ 
*)temp. means a treatment of the HCl treated carbon in an oven at a 
temperature between 500.degree. and 700.degree. C. 
TABLE 2 
______________________________________ 
Effects of caffeine levels (uploading) on recovery 
yields, also illustrating absolute caffeine losses. 
Caffeine load on 
Re- 
Exper. 
Carbon carbon at start, 
covery Absolute 
No. Quality % dry basis yield loss 
______________________________________ 
1 untreated 
15.2 43% 38 g from 80 g 
4 untreated 
21.8 82% 17 g from 96 g 
______________________________________ 
TABLE 3 
______________________________________ 
Effects of both treatments and caffeine 
levels (uploading) on recovery yields 
Caffeine load on 
Experiment 
Carbon carbon at start, 
Recovery 
No. Quality % dry basis yield 
______________________________________ 
1 untreated 15.2 43% 
5 H.sub.3 PO.sub.4 /H.sub.2 O 
24.1 99% 
6 HCl/H.sub.2 O/temp. 
23.3 94% 
7 EDTANa.sub.2 /H.sub.2 O 
21.0 97% 
______________________________________ 
TABLE 4 
______________________________________ 
Caffeine adsorbing properties of activated carbon 
after caffeine loading in an industrial supercritical 
CO.sub.2 decaffeination plant and subsequent thermal 
desorption/sublimation with inert gas sweeping stream 
Experiment 
Carbon Caffeine adsorbing activity 
No. Quality in 2 hrs in 16 hrs 
______________________________________ 
typical untreated fresh 
20-22 28-29 
typical treated fresh 
20-22 28-29 
1 untreated 19.7 28.2 
5 H.sub.3 PO.sub.4 /H.sub.2 O 
21.2 29.4 
6 HCl/H.sub.2 O/temp. 
20.8 28.6 
______________________________________