JPS6247043B2 - - Google Patents

Description

[Detailed description of the invention]

The use of hydrophobic adsorption media to remove dissolved compounds from aqueous solutions is well known and is a relatively simple method when separating binary mixtures. If the adsorbed soot body is exclusively selective for one component of a multicomponent system, adsorption methods that seek to selectively remove one component from a multicomponent system will likewise be relatively uncomplicated. Unfortunately,
This is rare, if ever, and
And if it is desired to remove a single compound in relatively concentrated form from a complex mixture of compounds in an aqueous solution, such as an aqueous extract of food, a variety of new processing methods must be developed and used. When aqueous coffee extract was contacted with currently available high surface area adsorption media capable of adsorbing caffeine, a number of other compounds, most significantly chlorogenic acids, were also adsorbed by this adsorbent, and caffeine was adsorbed. It was found that it constituted only a small amount of the total solids. Such methods will be economically unattractive unless techniques are developed to recover and re-add a significant portion of the non-caffeine solids that would be lost using classical adsorption methods alone. Will. The present invention relates to an improved countercurrent adsorption process that essentially removes one component from a multicomponent aqueous solution while minimizing loss of other components. In particular, the present invention is suitable for removing caffein from aqueous extracts of green or aged coffee while minimizing loss of non-caffein solids. Although the present invention is described with respect to the removal of caffeine from aqueous coffee extract in a multi-stage fixed bed adsorption system, the method disclosed herein allows selected compounds from a multi-component solution to be relatively concentrated by a hydrophobic adsorption medium. It will be apparent to those skilled in the art that it has applicability to a wide variety of processes and systems, including continuous countercurrent adsorption systems, which seek to remove oxidized particles in the form of oxidation. An adsorbent is any material effective for adsorbing dissolved components from an aqueous liquid stream, such as an industrial effluent or process stream, including a stream containing edible substances and/or biologically active or therapeutic substances. can be. Examples of suitable adsorbents are macroreticular acrylic and/or styrene and/or
Or divinylbenzene adsorption resin. This resin can be an ion exchange resin, or it can lack ion exchange capacity; however, the present invention relates to an adsorption method and thus the use of an ion exchange resin as an adsorbent as well as an ion exchange resin. It should be understood that only applicable Removing caffeine from aqueous coffee extracts (typically 15-30% soluble solids), such as the caffein-containing aqueous extract of green coffee described in U.S. Patent No. 2,309,092 to Berry et al. Useful adsorbents are known commercially available non-ionogenic macroreticular resins. Particularly useful are high surface area, water-insoluble, cross-linked particulate polymers, such as divinylbenzene, trivinylbenzene, alkyl-benzene substituted with 1 to 4 alkyl groups of 1 to 2 carbon atoms. prepared by suspension polymerization of ethylenically unsaturated molecules consisting of about 2 to 100% by weight, preferably at least 50% by weight, of at least one poly(vinyl)benzene monomer selected from the group consisting of divinylbenzene; , and the polymer has a porosity of at least 10% and a surface area of at least 10 m ² /g and does not swell appreciably with caffeine. In addition to homopolymers and copolymers of these poly(vinyl)benzene monomers, one or more of these monomers may be used as (1) monoethylenically unsaturated monomers, or (2) poly(vinyl)benzene monomers as just defined above. 98% of a polyethylenically unsaturated monomer other than (vinyl)benzene or (3) a mixture of (1) and (2)
(based on the weight of the total monomer mixture). Divinylbenzene polymers and styrene/divinylbenzene copolymers are particularly effective in the process of the present invention. Adsorbent resins of the aforementioned type are known and commercially available, and Gustafson
(Rohm & Haas Company) US Patent No.
Further details are provided in issue 3531463. Other high surface area hydrophobic adsorbents, such as molecular sieves, may be equally effective in the process of the invention. Suitable adsorbents will exhibit a dipole moment of less than 2.0 debye, preferably less than 0.5 debye. The method of the invention will now be described with reference to the accompanying drawings. In the countercurrent multistage adsorption method, multiple columns are connected in series. Each column or stage contains a fixed bed of adsorbent, and the coffee extract to be treated passes successively through a plurality of beds, and these beds are used in stages in countercurrent relation to the flow of liquid. This causes the caffeine-containing extract to enter the system (line 10).
It enters the system, passes through the most depleted adsorbent bed (stage 2), and exits the system through the most recent or least depleted adsorbent bed (stage 4) (line 14). Typically, the coffee extract is continuously fed to stage 2 where the coffee extract is the most loaded (most adsorbed, i.e. most depleted) until the capacity of the adsorbent bed to adsorb caffeine reaches saturation. or close to it, i.e., the caffeine concentration of the coffee extract leaving this column (stage 2) (line 12) continues until the caffeine concentration of the coffee extract entering this column (line 11) is the same or close to it. supply. Of course, the supply of extract to stage 2 can be stopped at any time before saturation. When the desired amount of caffeine has been adsorbed onto the resin bed in stage 2, the extract supply is switched to the second stage.
Switch to the second depleted but not yet fully loaded bed and add a new bed (not shown) to the downstream end of the system. The loaded bed or column located in stage 2 is immediately and completely regenerated by drawing all of the adsorbed solids out of the system with a desorption or elution medium in a conventional countercurrent adsorption process, and the present invention According to , it is retained for retrieval operations until regeneration is achieved. It is of course possible to supply the loaded bed of stage 2 with sufficient water to displace the extractant contained in the column and to displace the trapped but unadsorbed solids. Additional amounts of water sufficient to wash out the adsorbent bed may also be used.
The displaced extract and aqueous wash solution could then be fed to the adsorption column apparatus along with the fresh feed extract. However, this addition of water is usually not necessary. This is because this introduces an amount of water into the decaffeination system that would normally have to be removed later by energy-intensive steps such as evaporation. Preferably, the loaded bed or column is placed in processing stage 1 immediately upon removal from the adsorption column apparatus, and is passed through line 20 to the bed or column that was recovered or eluted in the previous regeneration cycle, as detailed below. An aqueous solution containing adsorbed solids will be provided. Of course, in the first cycle, stream 20 must be replenished and freshly injected into the system; however, once steady state is reached, there is no need for replenishment. When operating a countercurrent system according to the technique of the present invention,
Additional adsorbent bed capacity can be obtained by means of a loaded column; and surprisingly, this additional capacity is different from that obtained during the contact between the adsorbent bed and the feed stream. Moreover, it was found to be effective in adsorbing solids according to a more desirable distribution pattern. Without wishing to be limited to any particular theory, it is believed that most, if not all, of the non-caffeine solids adsorbed prior to stream 20 as stream 20 is fed through stage 1 leave the feed bed without being reabsorbed. (exiting via line 21), whereas most of the previously adsorbed caffeine solids appear to be readsorbed onto the resin bed. A portion of the non-caffeine solids adsorbed onto the resin bed of stage 1 passing through the countercurrent adsorption system (stages 4-2) can also be replaced by adsorbed caffeine solids from stream 20 from the resin. As a result, the stage 1 bed contains adsorbed solids in a fresh and more favorable distribution, and that distribution contains a higher percentage (by weight) of caffeine, eventually It will contain a low percentage of non-caffeine. The desirability of a low weight percentage of non-caffeinated solids in the adsorbent bed to be regenerated makes it easy to and/or remove these non-caffeic solids in a manner that allows them to be reintroduced into the decaffeinated system. Based on the fact that it cannot be economically separated from caffeine. Chemical treatments that can separate these adsorbed solids during or after elution or desorption alter and/or degrade the non-caffeinated solids so that government regulations do not allow reintroduction of non-caffeinated solids into the decaffeinated system. will. Eventually the non-caffeinated solids present on the pre-elution adsorption bed will be removed from the decaffeinated system and constitute an economic loss as well as a waste disposal problem. As is clear to experts in this field, flow 2
0 will contain a higher weight percent caffein (on a solids basis) and a lower weight percent non-caffeine solids than is present in the feed to stage 2 (line 11). The solids concentration of stream 20 may be adjusted, for example, by evaporator 8 such that it has a higher caffeine concentration (based on the weight of the solution) and a lower total solids concentration than the respective concentration of stream 11. Dew. Under these critical conditions, during contact between stream 20 and the adsorbent bed of stage 1, there is a significant positive driving force for additional caffeine to be adsorbed onto the bed and additional non-caffeine solids. There appears to be a slight or possibly negative driving force for adsorption to the bed. This discovery is surprising. This is because, although the total non-caffeic solids concentration in stream 20 is lower than that of stream 11, all of the non-caffeic solids in stream 20 can be adsorbed. The concentration of a large number of previously adsorbed non-caffeine solids in stream 11
It would be expected that the net result would be a relatively constant percentage (on a solids basis) of non-caffeine solids present on the Stage 1 resin bed. Another surprising aspect of the process of the present invention is that, particularly when relating to decaffeinating coffee extracts, the caffeine present in both stream 10 and stream 20 is complexed with non-caffeinic material, most significantly chlorogenic acid. It is known to do. It was unexpected that these caffeine-complexing solids appeared to be able to pass through the stage 1 caffeine-loaded adsorbent bed without complexing with the adsorbed caffeine. Stream 21 exiting the bottom of stage 1 contains non-caffein solids and a small amount of caffeine that would have been lost in conventional adsorption processes while stream 20 was fed to the top of this column. The amount of solution fed back to the adsorption device (via lines 21 and 31) can be adjusted to limit the total amount of caffeine introduced into the adsorption device (stages 2-4), as described below. Probably. After the flow from line 20 has stopped, collection stage 1
The column can be washed with a sufficient amount of water to displace the solution present in the column and to wash the adsorption bed of trapped solids, especially if not done beforehand. However, it will usually be preferable to avoid adding water to the system again and subsequent dilution of process streams 21 and/or 23. The stage 1 adsorption bed is regenerated by a suitable desorbent (line 19). This desorbent may consist of recycled desorbent (line 17) and fresh replenishment desorbent (line 16). Typically, regeneration is carried out with an organic solvent that is easily separated from water by means such as distillation, or with an aqueous solution of the solvent, such as an aqueous alcohol solution. Particularly in food processing applications, it is then desirable to remove all elution media from the adsorbent bed. The resin could be steam treated to remove all or a portion of the adsorbent. Preferably, however, the adsorbent is subjected to one or more water rinses (line 30).
preferably at least once in the opposite direction (not shown). Fresh displacement water is fed into the system (line 26) and together with other possible water streams such as evaporative condensate of evaporator 8 (line 27) and recycled displacement water (line 29). Can be done. It is generally desirable to pass the initial portion of the displacement water leaving the column to the separator 7 (line 28), where the solvent that may be contained therein can be recovered and recycled. The forward flow of displacement water, which may contain only very low levels of solvent and is generally approximately half of the latter, is recycled without treatment (line 29) to provide displacement water for the displacement step of the subsequent cycle. You can configure the initial part of The eluent (line 23) is at a higher level (typically Approximately 35
~65%) of caffeine, which is treated to remove the organic solvent from the aqueous solution of solids, for example in separator 7. This essentially solvent-free solution of the solid is then reduced to an appropriate concentration (evaporator).
or through a dilution step to produce an aqueous solution (line 24) having a higher concentration than was present in the feed to the adsorption column apparatus (line 11). A portion of this high caffeine solution is withdrawn from the system as a byproduct stream (line 25) and the remainder of this solution (line 20) is used to concentrate the caffeine onto the next loaded column removed from the adsorption device. As an alternative to simply separating a portion of stream 24 as a caffeine-rich by-product, all or a portion of stream 24 may be subjected to a fractionation process (not shown), such as fractional crystallization, membrane separation, fractional sublimation, electrodialysis, etc. A byproduct stream with an elevated caffeine level can then be formed and the resulting stream (eg, mother liquor, etc.) can be fed to line 20. The method of the present invention operates when the caffeine concentration of the high caffeine stream (stream 20) fed to the loaded bed of stage 1 is at least twice, preferably at least about 4 times, the caffeine concentration of feed stream 11. , was found to be the most effective. Adding relatively pure caffeine material to stream 20 to achieve this high caffeine concentration is specifically contemplated in the present invention. Preferably the total solids concentration of stream 20 (typically about 6-15% by weight) will be close to that of stream 11, usually about half or less.
Furthermore, it has been found that the amount of caffein returned from recovery stage 1 to the adsorption device (via lines 21 and 31) should not significantly exceed the amount of caffein present in the feed extract (line 10).
Preferably, line 1, defined herein as reflux ratio
Caffeine supplied to stage 2 via line 3
The weight ratio of the amount of caffeine supplied via 1 is
0.01:1-5:1, preferably 0.1:1-2.5:
1, typically about 0.5:1 to 1.5:1. Those skilled in the art will appreciate that a number of holding tanks, valves and similar standard equipment (not shown) can be provided in accordance with standard chemical process design techniques. Preferred embodiments of the invention are described in the examples below, all percentages are by weight, and the examples describe the systems shown in the figures, operated in countercurrent mode at equilibrium conditions. The various streams described in the examples have the parameters shown in Table 1.

[Table] Example 1 Each stage of the adsorption system consisted of 480 g of a hydrated non-ionodiene macroreticular adsorption resin of the polydivinylbenzene type (Amberlite™ XAD-4, Rohm &
Haas Company), this resin is approximately 50%
Gives a bed volume of 540 c.c. with a void volume of . Stream 10 consisting of an aqueous extract of green coffee (83° C.) as described in the aforementioned U.S. Pat. No. 2,309,092.
(4.34 bed volumes and 82° C.) are combined with stream 31 (vessel 5) and fed as stream 11 to consumable stage 2. As the coffee extract flows through the adsorption column connected by lines 12 and 13, the caffeine solids are mixed with non-caffein solids in the resin beds 2, 3.
and 4, respectively. The extract exited the system and stream 14 was found to contain substantially no caffeine and had a lower non-caffein solids concentration than stream 10 (by 11.37 g). Stream 25 exiting the system was found to contain 37% caffeine on a dry basis, 11.37g non-caffein solids.
This stream was then processed to recover pure caffein and discard non-caffeinated solids as solids loss from the decaffeinated coffee. The stage 2 resin bed containing about 73 g of adsorbed solids, of which 23% is caffeine and of which 15.5% is chlorogenic acid, is then transferred to the stage 1 position for a downflow adsorption cycle, while the new A typical resin bed 4 was placed and the beds of previous tiers 3 and 4 were removed to tier 2 and 3 positions, respectively. Stage 1 was then initially fed stream 20 with a high caffeine concentration (3.99%) in an amount of about 2.0 bed volumes (1080 g) and the resulting effluent stream 21 was concentrated in evaporator 6. This concentrated stream 31 is transferred to stream 1 in tank 5.
0 and feed the resulting mixture stream 11 to stage 2. Stage 1 is then diluted with about 8.0 bed volumes of dilute (40% water) ethanol (stream 19) at a temperature of about 77°C and the resulting eluent stream 23 is first fractionated at 7 to form an aqueous ethanol solution. is removed and recovered and then concentrated in evaporator 8 to obtain a solids level of 10.8% in stream 24. Part of flow 24 (approximately 19%)
is passed through the caffeine purification process as stream 25 and the remainder (stream 20) is retained and fed to stage 1 of the downflow cycle. Stage 1 is then fed with water (stream 30) to displace the alcohol contained therein, thereby preparing the resin bed for reuse in a multi-stage adsorption device. Example 2 Using the three-stage adsorption train of the figure, but without using recovery stream 20 or reflux 31, if stage 2 is eluted and placed on stage 1 immediately after removal from the adsorption device, the upstream is at equilibrium conditions. can get.

【table】

Table 2 As can be seen from Table 2 above, by-product stream 25 (same as 24) leaving the system contains only 16% caffeine solids on a dry basis. For every gram of caffeine removed from the system in this manner, 5.25 grams of non-caffein solids are lost. Since the amount of non-caffeinated solids lost directly impacts the overall economics of the decaffeinated system, it is desirable to minimize this loss. A comparison of non-caffeine solids loss in Examples 1 and 2 is provided in Table 3.

Comparable results may be obtained when attempting to decaffeinate an aqueous extract of bitter coffee; however, prior to contacting the extract with the adsorbent resin, the extract may be subjected to such means as steam stripping. It may therefore be preferable to remove volatile substances from the extract. The volatile substances are retained and added back to the decaffeinated coffee extract in subsequent processing steps.

[Brief explanation of the drawing]

The drawing is operated at steady state conditions3
A stage countercurrent (stages 2-4) adsorption device is shown. 1, 2, 3, 4... stage, 5... tank, 6, 8...
Evaporator, 7...Separator, 10, 11, 12, 1
3, 14, 16, 17, 19, 20, 21, 2
3, 24, 25, 26, 27, 28, 29, 3
0,31... line.

Claims (1)

[Scope of Claims] 1. In a countercurrent adsorption method for separating preferentially adsorbed components from a multicomponent aqueous solution that also contains other adsorbed compounds, the method is characterized in that (a) a predetermined amount of the preferentially adsorbed component is , passing the multicomponent aqueous solution through the most depleted section of the flow of the countercurrent adsorption system until adsorption onto the adsorbent with the highest adsorption capacity; (c) Pass the solid aqueous solution through the adsorbent taken out in step (b) above to obtain an effluent, and the solid aqueous solution is passed through step (a).
has a higher concentration of preferentially adsorbed components than the multicomponent aqueous solution of (d), but has a lower total solids concentration, and the solids consist of solids adsorbed during the subsequent adsorbent regeneration process in step (f): (d) Adding fresh adsorbent to the least depleted zone of the countercurrent adsorption system; (e) Adding a certain amount of the effluent from step (c) along with a certain amount of the multicomponent aqueous solution to the least depleted zone of the countercurrent adsorption system; (f) replacing the desorbent with the adsorbent of step (c); a method comprising the steps of: removing the adsorbed solids having a relatively high proportion of preferentially adsorbed components on a dry basis; 2. The method according to claim 1, wherein the adsorbent comprises non-ionogenic giant reticular cross-linked resin particles. 3. The method according to claim 2, wherein the desorbent in step (f) is an organic solvent or an aqueous solution thereof. 4 Separating the adsorbed solids of step (f) from the organic solvent and feeding a portion of these solids in the form of an aqueous solution to the adsorbent on which the adsorption of step (c) was carried out The method described in Section 3. 5. The method according to claim 2, wherein the adsorbent is an acrylic and/or styrene and/or divinylbenzene resin. 6. The method of claim 2, wherein the adsorbent resin is a divinylbenzene polymer or a styrene/divinylbenzene copolymer. 7. The method according to claim 1, wherein the countercurrent adsorption system is a multistage fixed bed adsorption train. 8 The solid content concentration of the multi-component aqueous solution in step (a) is 15 to 30
% by weight, and the solids concentration of the solution in step (c) is from 6 to 15% by weight. 9. The method of claim 1, wherein the reflux ratio is about 0.5:1 to 1.5:1. 10. With respect to the adsorption of preferentially adsorbed components, feeding the stream containing the multicomponent solution to the most depleted compartment in step (a) until substantially the capacity of the most adsorbed adsorbent is reached; The method described in Section 1. 11. The method of claim 8, wherein the multicomponent solution is an aqueous extract of green coffee or cold coffee.