WO2006108292A1

WO2006108292A1 - Decaffeination method and apparatus

Info

Publication number: WO2006108292A1
Application number: PCT/CA2006/000569
Authority: WO
Inventors: Sasha Omanovic; Wayne Brown
Original assignee: Mcgill University
Priority date: 2005-04-15
Filing date: 2006-04-13
Publication date: 2006-10-19

Abstract

A batch method for decaffeinating a liquid is provided comprising the steps of: inserting into the liquid an electrochemical apparatus comprising at least one working electrode and at least one counter electrode that are suitable to cause degradation of caffeine; and supplying power to the electrodes for a period of time sufficient to cause the desired degree of decaffeination.

Description

DECAFFEINATION METHOD AND APPARATUS

FIELD OF THE INVENTION

[0001] The present invention relates to a novel electrochemical method for decaffeinating a liquid in which the caffeine is degraded to form by-products. An apparatus for conducting such a method of decaffeination is also provided.

BACKGROUND OF THE INVENTION

[0002] Caffeine (1,3,7-trimethylxanthine) is an alkaloid that is produced naturally in more than 60 varieties of plants. It is a potent chemical that is known to illicit a number of physiological responses in both unicellular and higher order organisms including toxicological effects, cardiovascular effects, and neurological stimuli. Of the plants that produce caffeine, the Coffea genus is of great commercial importance as it accounts for the majority of coffee cherries grown. For many countries coffee is a significant export. In 1994, the world production of green coffee was 5,430,000 metric tonnes, with 99.9% of this production coming from developing nations. In the United States and Canada, coffee is grown only in the state of Hawaii. However, since 1980 there has been a steady increase in the overall coffee trade in these countries. Between the years of 1980 and 1993, the amount of green, unroasted coffee beans imported by Canada increased by 55%. In fact, the coffee industry is second only to oil with associated revenues of $60 billion worldwide.

[0003] Coffee is often consumed for the neurological effects derived from caffeine. As a result the primary source of caffeine in adults is derived from coffee. While half of the adult population drinks coffee, the number of children that consume the beverage is much lower. Caffeine enters the younger population mainly through other beverages and food sources including tea, cocoa and soft drinks.

[0004] Driven by health concerns, the number of consumers that avoid caffeine ingestion is significant. As a result, the decaffeinated coffee market accounts for roughly [0005] The demand for decaffeinated beverages is currently addressed through the marketing of decaffeinated versions of their caffeinated analogues. With respect to coffee, all commercial decaffeination methods target the bean itself. Decaffeination methodologies can be grouped into two broad categories: liquid extraction and genetically modified plants. Most of the commercial methods for decaffeinating coffee involve the principle of liquid extraction. In general the beans are contacted with an appropriate liquid solvent for which the caffeine molecule has a strong affinity. Caffeine is thus extracted from the solid coffee cherry into the liquid. Liquid extraction methods incorporating methylene chloride, ethyl acetate, water, and carbon dioxide have all been demonstrated commercially. Although economically viable, these methods suffer from a lack of selectivity, removing chemicals from the coffee bean that affect the taste. Thus, the resulting beverage does not have the same flavour as its caffeinated analogue. Complete removal of the extracting solvent is also difficult, and residual levels of solvent have been detected in the decaffeinated product. While there is no adverse effect in the case of water extraction, this is undesirable where chlorinated solvents are employed.

[0006] Advances in molecular biology have made it possible to modify the genome of the coffee plants so that the coffee cherry itself contains no caffeine. A number of plants have been produced in this manner using both natural selection and genetic engineering. The beverage produced from these plants is indistinguishable in taste from the equivalent caffeinated product. However, this product will be difficult to market in Europe, where genetically modified foods have not been accepted by the general public.

[0007] In general, the following issues are associated with decaffeination methods that target the coffee cherry;

• On the manufacturing side, two parallel lines of cherries must be processed in order to accommodate both caffeinated and decaffeinated. This also applies to roasting and distribution. This adds additional complexity as the markets associated with both decaffeinated and caffeinated coffee consumers must be anticipated. As a result, the selection offered to decaffeinated coffee consumers is limited, in proportion to market share, and the decaffeinated coffee drinker has dramatically less selection; • In the case of genetically modified coffee plants, additional farm land must be committed to growing these plants. World markets are also limited for these genetically modified products;

• Solvent extraction methods affect the taste of the final beverage. Residual solvents may also be retained in the decaffeinated bean;

• The level of decaffeination cannot be selected, as roasts are either caffeinated or decaffeinated. Recently, partially decaffeinated products prepared by traditional solvent extraction decaffeination methods have been introduced into the marketplace, attesting to consumer demand for such products; and

• The approaches currently used to decaffeinate whole coffee cherries cannot be applied to soft drinks and many other caffeinated beverages.

[0008] While the coffee cherry has been the target for all commercial decaffeination methods, methods for removing caffeine from the aqueous coffee solution produced from the roasted coffee bean have been proposed. A number of fungi and bacteria are capable of producing enzymes that afford selective removal of the caffeine molecule. The reaction involves the transfer of electrons from the caffeine molecule to an electron accepting species, a method known as a "redox" reaction. These enzymes, referred to as caffeine demethylases, are all from the same general class, and hence transform caffeine by the same general reaction pathway. While most of the research has suggested the application of these enzymes for the decaffeination of the carbohydrate-rich coffee pulp by-product for use in animal feed, a few have also mentioned the possibility of using these enzymes to decaffeinate the coffee beverage. A major impediment to this approach is the requirement of a particular biological co-factor for the chemical reaction to occur. This co-factor, nicotinamide adenine dinucleotide (NADH), is relatively expensive, and therefore must be regenerated in order for the method to be feasible. There are currently no easy methodologies for accomplishing this, and no sustainable method has been developed that can accomplish decaffeination without the aid of the whole cell. In addition, demethylases show little activity at the normal drinking temperature of coffee, making the application of such methods difficult. [0009] Other less selective redox reaction pathways are possible for the destruction of caffeine. Of significance are those that can be carried out in an electrochemical cell. In these methods, the electrons required for the oxidation or reduction of caffeine are provided from a power source. A working electrode and a counter electrode are immersed in the solution of interest. Through application of the appropriate potential or current between the electrodes, electrons can be exchanged between the caffeine molecule and electrode thus initiating its destruction. The method disclosed in French patent application no. 2,761,235 is based on this principal for the decaffeination of coffee and tea. This patent describes a continuous method in which the coffee is decaffeinated during the brewing method. The brewing method involves allowing the coffee to flow by gravity through the decaffeinating device. The zone of influence in such a method is limited to the region where the electrodes are located. Once the solution has passed this zone and has entered the coffee receptacle, no further decaffeination can occur. The flow rate is set by the brewing method, and hence the decaffeination rates must be adjusted to accommodate. As a result, it appears that high current densities are required for this proposed methodology, with very low current efficiency. It is unlikely that appreciable levels of decaffeination could be achieved at the conditions disclosed in this patent application.

[0010] Given the foregoing, there is clearly a need for a decaffeination method and apparatus that provide not only efficient decaffeination of a beverage, but that also provides controlled decaffeination of any caffeinated liquid. An "ideal" decaffeination method and apparatus, thus, would:

• provide the consumer with the flexibility to choose the level of decaffeination;

• eliminate any incremental costs associated with the production and distribution of decaffeinated coffee; and

• be applicable to a wide variety of caffeinated liquids. SUMMARY OF THE INVENTION

[0011] The present invention provides a novel electrochemical batch method for the controlled decaffeination or reduction of caffeine levels in a caffeinated liquid, such as a beverage.

[0012] In one aspect of the invention, an electrochemical batch method for decaffeinating a liquid is provided comprising the steps of: inserting into the liquid an electrochemical apparatus comprising at least one working electrode and at least one counter electrode that are suitable to cause degradation of caffeine; and supplying power to the electrodes for a period of time sufficient to cause the desired degree of decaffeination.

[0013] A significant advantage of the present decaffeination method is that it is a batch decaffeination method which is time-controllable based on the degree of decaffeination desired. This is different from prior continuous gravity flow-through or one-pass methods in which a caffeine-containing liquid is simply passed over a decaffeinating apparatus. The present batch approach circumvents many of the difficulties associated with a continuous gravity flow-through or one-pass method. For example, the present batch decaffeination method provides a flexible method that may be applied to any caffeinated liquid since it is not linked to the manufacture of the liquid. In addition, the present batch method can be carried out until a desired level of decaffeination is attained including complete decaffeination. In contrast, in a continuous gravity flow-through, one-pass method, the level of decaffeination is generally more difficult to control because it is limited by the flow rate of the liquid through a decaffeinating device. Moreover, adjusting the flow rate of a liquid may affect the concentration of the final beverage, particularly in the case of a decaffeinating device that functions in conjunction with a beverage brewing method.

DESCRIPTION OF THE DRAWINGS

[0014] The advantages of these and other aspects of the present invention will become apparent in the following description and drawings in which: Figure 1 graphically illustrates the effect of varying the surface area of the working electrode (WE) on the rate of decaffeination of pure caffeine in a buffer solution using a method in accordance with one embodiment of the present invention;

Figure 2 graphically illustrates the effect of varying the chemical composition of the counter electrode (CE) on the rate of decaffeination of pure caffeine in a buffer solution using a method in accordance with one embodiment of the present invention;

Figure 3 graphically illustrates the effect of varying the applied current density on the rate of decaffeination of pure caffeine in a buffer solution using a method in accordance with one embodiment of the present invention;

Figure 4 graphically illustrates the reaction kinetics of a method in accordance with one embodiment of the invention;

Figure 5 graphically illustrates the effect of varying the temperature of a caffeine- containing solution on the rate of its decaffeination using a method in accordance with the present invention;

Figure 6 graphically illustrates an extrapolated determination of decaffeination reaction time a coffee beverage using a method in accordance with the present invention;

Figure 7 graphically illustrates the effect of varying the chemical composition of the working electrode on the rate of decaffeination of a coffee beverage using a method in accordance with the present invention;

Figure 8 graphically illustrates the rate of decaffeination of a coffee beverage using a multi-pass batch method in accordance with the present invention;

Figure 9 illustrates an apparatus for conducting a batch decaffeination method in accordance with the invention; and

Figure 10 (AJB) each illustrate an apparatus for conducting a multi-pass batch decaffeination method in accordance with the invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present electrochemical batch decaffeination method comprises contacting a liquid to be decaffeinated with an electrochemical apparatus comprising at least one working electrode and at least one counter electrode that are suitable to cause degradation of caffeine in a batch of liquid to be decaffeinated; and supplying power to the electrodes for a period of time sufficient to cause the desired degree of decaffeination within the liquid.

[0016] The term "degradation" as it is used herein with respect to decaffeination refers to any means of decaffeinating including oxidation and/or reduction of the caffeine molecule as well as other forms of breakdown of the caffeine molecule.

[0017] The present method may be applied to the decaffeination of any caffeine- containing liquid including beverages such as coffee, tea, cocoa and soft drinks (eg. cola). The caffeine-containing liquid may also be a non-beverage such as waste water. Caffeine adversely affects plant and animal life; thus, incorporating decaffeination into waste water treatment prior to release into the environment is also desirable.

[0018] In accordance with the present method, decaffeination of a liquid is carried out in a batch-wise manner. The term "batch" is used herein to refer to a decaffeination method in which a given volume of liquid to be decaffeinated is exposed to an electrochemical reaction for an amount of time sufficient to result in the desired degree of decaffeination, ranging from minimal decaffeination to complete decaffeination, i.e. 100% decaffeination. Thus, in the present batch decaffeination method, decaffeination is controlled by varying exposure time of the given volume or batch of liquid to the electrochemical reaction. The period of time sufficient to cause the desired degree of decaffeination will vary depending on the conditions and parameters of the electrochemical reaction.

[0019] The electrochemical reaction occurs on application of a constant current supplied by a power source to a working electrode (WE) and a counter electrode (CE). As will be appreciated by one of skill in the art, the power source may be any power source capable of providing constant current including means to connect to any power source. Thus, the power source may be an electrical outlet, and the means to connect a plug. The power source may also be a battery. Alternatively, the reaction can be powered to operate at a constant potential rather than a constant current.

[0020] An "electrochemical method" is a reaction that occurs upon the application of electrical power to a pair of electrodes, a working electrode and a counter electrode. The WE and CE electrodes must be spaced from one another, i.e. not touching, in order for an electrochemical reaction to occur.

[0021] The term "working electrode" (WE) refers to an electrically conducting surface at which a defined (targeted) electrochemical reaction occurs upon application of an appropriate potential difference between the working electrode and a counter electrode. A "counter electrode" (CE) refers to an electrically conducting surface that serves to complete the electric circuit of an electrochemical cell - power supply system. An electrochemical reaction occurring at these electrodes can be controlled, if desirable, upon application of an appropriate current, potential or material selection.

[0022] The electrodes (WE and CE) may be made of or coated with any material suitable to cause degradation of caffeine in the electrochemical cell. Examples of suitable materials include, but are not limited to, platinum, ruthenium, rhodium, iridium, gold, stainless steel, titanium, palladium, graphite, boron-doped-diamond, and metal- oxides and their alloys, provided that they are electrically conducting or semiconducting.

[0023] In order to optimize the present decaffeination method, the specifications of both the working and counter electrodes, including surface chemistry and surface area, can be varied.

[0024] Surface chemistry of the electrodes used in the present method can be altered by altering the transition metal-based oxide content of the electrode body, or by applying variable transition metal-based oxide, boron-doped diamond or carbon coatings to an electrode body. Electrodes of different surface chemistries will vary with respect to decaffeination time and may also affect the quality of the decaffeinated end product. For example, the use of electrodes with a certain surface chemistry may result in a slight taste difference in a liquid beverage decaffeinated by the present method, and thus, may be undesirable for use in decaffeinating beverages but desirable for use in the decaffeination of waste water.

[0025] The electrochemical reaction rate of the present method is directly proportional to the electrode surface area available for the reaction. Thus, the rate of decaffeination using the present method is increased as the surface area of the electrodes utilized is increased. It is desirable, thus, to design and employ electrodes having a high surface area/unit volume ratio. Electrodes made of mesh, porous materials, a flat material and beads/particles, for example, achieve a high surface area/unit volume ratio, although other configurations exist. In preferred embodiments, electrodes used in the present method have a surface area in the range of about 10 to 1000 cm².

[0026] The efficiency of decaffeination using the present method may also be optimized by using a working electrode with a low selectivity for oxygen production since oxygen evolution competes for the surface area of the electrodes resulting in lower rates of caffeine degradation. Accordingly, in order to optimize the caffeine degradation reaction, the working electrode is preferably made of a material that does not catalyze the production of oxygen at the conditions under which the decaffeination reaction occurs. These materials include, for example, doped and undoped transition metal oxides and their alloys in the form of dimensionally stable electrodes. Boron doped diamond, graphite, glassy carbon, platinum, titanium, palladium and stainless steel are, thus, examples of preferred working electrodes.

[0027] Similarly, the efficiency of decaffeination may also be optimized by using a counter electrode with a low selectivity for hydrogen production. This will increase peroxide production which also functions to oxidize caffeine. Counter electrodes made of glassy carbon, for example, function to produce hydrogen peroxide during an electrochemical reaction.

[0028] The present batch decaffeination method may be conducted using a single pair of electrodes, one working electrode and one counter electrode, or may be conducted using multiple electrodes, for example, multiple working or counter electrodes or multiple of both electrodes. As one of skill in the art will appreciate, multiple electrodes could be arranged such that the active surface of each working electrode faces the active surface of a counter electrode to ensure uniform electric field and potential/current distribution. The use of a single working electrode and a single counter electrode is illustrated in both Figure 9 and Figure 1OA; while the use of multiple counter electrodes and a multi-sided working electrode is illustrated in Figure 1OB. The use of multiple electrode pairs, as shown in Figure 1OB, results in a greater degradation rate of caffeine due to an increase in the reactive electrode surface area.

[0029] For electrochemical methods, reaction rates are directly proportional to the current density. Thus, the current density applied in the present method may also be varied to optimize decaffeination. The smaller the current, the longer the time for the desired level of decaffeination to be reached. For the purposes of the present method, a current density in the range of 5 to 2000 mAcm^'2 may be used. Preferably, the current density for the present method is in the range of 30 to 1100 mAcm^'2.

[0030] The temperature of the liquid to be decaffeinated also affects the rate of decaffeination in a directly proportional way. The rate of decaffeination is increased as the temperature of the liquid to be decaffeinated is increased. At atmospheric pressure, the reaction can be carried out at any temperature between 0 and 100⁰C, with the optimum decaffeination temperature being between 50 and 7O⁰C. As one of skill in the art of thermodynamics will appreciate, the range of operating temperatures that can practically be utilized, may be increased by changing the operating pressure.

[0031] While not wishing to be bound by any particular theory, the present method of decaffeination is believed to occur, at least in part, by anodic oxidation of caffeine indirectly through interaction with hydroxyl radicals ("OH)₃(_J8 formed at the electrode surface and/or chemically adsorbed oxygen (MO_x+i). The first step involves the oxidation of water at the electrode surface to form hydroxyl radicals that are adsorbed onto the electrode surface (equation (I)):

( 1 ) MO_x + H₂O → MO_x(.OH)_ads + H⁺ + e^"

[0032] In the second step of the method, caffeine is believed to be oxidized through interaction with the adsorbed hydroxyl radicals (equation (2)):

(2) 2MO_x(«OH)_ads + Ri-C → H₁-C + CH₂O + H₂O + 2MO_x where Ri represents a methyl group (CH₃) on the caffeine molecule.

[0033] MO_x represents a metal oxide film formed on the WE surface at high anodic potentials. As one skilled in the art will appreciate, the absolute value of the overpotential necessary for reactions (1 and 2) to occur varies greatly from one surface to another and cannot be generalized. The mechanism described in equation (2) is associated with metal electrodes that do not change their oxidation state at high anodic currents and potentials such as, but not limited to, PtO, SnO₂, PbO₂, carbon, glassy carbon, AuO and Boron-Doped-Diamond and combinations thereof.

[0034] If the degradation of caffeine is carried out using metal electrodes that change their oxidation state at high anodic currents and potentials (e.g. IrO, RuO), the reaction mechanism is changed. In a first step, active MO_x+] is formed by electrolysis of water according to:

(3) MO_x + H₂O -> MO_x+, + 2H⁺ + 2e^~

[0035] The degradation of caffeine then follows as:

(4) MO_x+I + Ri-C → MO_x + H₁-C + CH₂O

[0036] There is also a direct method in which the electrode does not change, but only 2 electrons are transferred directly from the caffeine molecule to the electrode. This occurs at low overpotential, with a first step that may involve adsorption of caffeine onto the electrode surface (5), and a second step involving degradation of the adsorbed caffeine molecule (6):

(6) M-(R, -C)_ads + H₂O → M + H, -C + CH₂O + 2H⁺ + 2e^~

[0037] In all three methods involving degradation of caffeine at high current densities, the method of oxygen evolution exists as competitive side reaction (equations

(7) and (8)): (7) MO_x(^OH) → MO_x + V- O₂ + H⁺ + e^"

O₂

[0038] Oxygen evolution competes for the surface area of the electrodes, and hence decreases the energy efficiency of the caffeine degradation reaction. However, other parameters such as larger electrode surface areas, higher current densities and electrode surface chemistry may be used in order to achieve the desired reaction time as previously described.

[0039] The present decaffeination method is also useful to produce theophilline and theobromine as by-products of the degradation of caffeine. These products have utility in the pharmaceutical industry as well-known medications or drug precursors for the treatment of breathing-related and coronary-related conditions.

[0040] The present method may be applied to individual or family-sized portions of a liquid, or large volumes of a liquid, for example, vats of a liquid prior to packaging in cans or bottles for retail, or prior to release into the environment in the case of treated water. The electrochemical apparatus used in each case to conduct the method will be appropriately sized to accommodate the volume of liquid to be decaffeinated.

[0041] In order to maximize the efficiency of the method, the solution to be decaffeinated may be stirred to cause the mass transport of caffeine to the electrode surface. The solution may be stirred manually during application of the decaffeination method. Manual stirring is most applicable in the case of decaffeination of a small beverage volume, for example, an individual serving or even a pot comprising multiple servings. In the case of bulk decaffeination in which a vat of liquid is to be decaffeinated, a more sophisticated mixing arrangement may be employed, including mechanically driven stirring devices such as drive stirrers, or recirculation pump systems. Magnetic stirring devices driven by a magnetic stir plate can also be used in the case of both large scale and small scale decaffeination.

[0042] In practice, for the decaffeination of, for example, an individual or family- sized portion of a caffeinated liquid, the liquid (3) is exposed to an electrochemical reaction suitable to degrade caffeine by contact with an electrochemical apparatus (1) as shown in Figure 9. The apparatus (1) is placed in a vessel (2) containing the liquid (3). For the decaffeination of bulk volumes of liquid, a similar apparatus may be used that is appropriately scaled up. The apparatus comprises an appropriate working electrode (5) and counter electrode (6). The apparatus (1) is powered by connection to an electrical power source (4) and hydroxyl radicals are formed as set out above. Caffeine is then degraded as set out above on interaction with the hydroxyl radicals. A magnetic stirring device (8) with magnet (7) may be utilized to increase efficiency of the reaction. As previously described, current density, electrode surface chemistry and surface area and beverage temperature can each be altered to vary the rate of decaffeination. Depending on the selected conditions for the decaffeination method, for example, electrode specifications, caffeine may be degraded by more than one type of reaction if multiple oxidizing entities are formed during the method, or if other caffeine-degrading entities are present. Thus, the period of time sufficient to cause the desired degree of decaffeination will vary depending on the conditions and parameters of the decaffeination.

[0043] In another embodiment of the invention, a multi-pass batch method may also be implemented. In this embodiment, the method is still a batch decaffeination as a single batch or given volume of liquid is decaffeinated; however, the batch of liquid is circulated and passed through the electrochemical cell at least twice, and preferably multiple times, until the desired degree of decaffeination has been achieved. This multipass method may advantageously decrease decaffeination times, particularly in connection with the decaffeination of large volumes of liquid. In a multi-pass batch decaffeination system, the hydrodynamic regime may also be controlled by parameters described above. In addition, flow rate and cell design to increase turbulence of the liquid at the electrode surface may also be used to control decaffeination.

[0044] Reaction rates can be determined or at least estimated by reference to standards that can readily be generated in which the effects of changing one variable, such as current density, can be determined. The specific examples that follow provide exemplification of this.

[0045] The present decaffeination method can be controlled with respect to not only the rate of decaffeination, but also with respect to the level or degree of decaffeination due to the fact that it is conducted in a batch-wise manner. For example, if only 50% decaffeination of a beverage is desired, then given a set of conditions (e.g. current density, electrode specifications, liquid volume and beverage temperature) and based on standards, the time required to achieve 50% decaffeination can readily be determined and applied.

[0046] In another aspect of the present invention, a batch decaffeination apparatus (1) is provided as illustrated in Figure 9. The apparatus comprises at least one working electrode (5), at least one counter electrode (6) and a power supply (4) which is connected to each electrode. The electrodes must be spaced from one another. The working electrode (5) is made of a material which is appropriate to cause degradation of caffeine when current is applied thereto by the power supply. The counter electrode (6) may or may not be made of a material capable of causing degradation of caffeine on application of a current. The apparatus is suitable for batch decaffeination of a caffeinated liquid and does not require flow of the liquid in order for decaffeination to occur. Thus, the electrode portion of the apparatus can simply be submerged in a batch of liquid to be decaffeinated, i.e. placed in a cup or pot of the liquid. Upon activation of the power supply, current is provided to the electrodes and decaffeination occurs.

[0047] The apparatus can be provided as a portable unit with an appropriate portable power supply that can be used at home, at the office or even on the go. It is an independent unit that need not be used in conjunction with any other appliance, such as for example, a coffee maker. This makes it suitable for the decaffeination of not only coffee, but other caffeinated liquids including tea, cocoa and soft drinks such as cola.

[0048] In another embodiment, a decaffeination apparatus (10) is provided as shown in Figure 1OA which permits multi-pass batch decaffeination. This apparatus comprises a decaffeination chamber (12) which houses the electrodes, for example at least one working electrode (15) and at least one counter electrode (16). The electrodes are connected to a power supply (14). This chamber (12) is connected by an inlet (13A) at a bottom end thereof and an outlet (13B) at a top end thereof to a reservoir (20). The apparatus also includes a circulating means, such as a pump (18), to continuously circulate liquid within the apparatus, from the reservoir (20) through the inlet (13A) into the decaffeination chamber (12) and out through the outlet (13B) back into the reservoir (20). A fixed volume or batch of liquid is, thus, continuously circulated through the decaffeination chamber (12) until the desired degree of decaffeination is achieved.

[0049] Figure 1OB illustrates a modified apparatus (100) for multi-pass batch decaffeination in which a two-sided working electrode (25) is flanked on either side with a counter electrode (25).

[0050] The apparatus, either for batch or multi-pass batch decaffeination as set out above, may include a single working electrode and a single counter electrode. Alternatively, the apparatus may include multiple working or counter electrodes or multiple of both electrodes. As one of skill in the art will appreciate, multiple electrodes in a single decaffeination apparatus are preferably arranged such that the active surface of each working electrode faces the active surface of a counter electrode. Figure 9 illustrates a batch decaffeinator comprising a single working electrode and a single counter electrode. Figure 1OA illustrates a multi-pass batch decaffeinator comprising a single working electrode and a single counter electrode, while Figure 1OB illustrates such a decaffeinator comprising more than one counter electrode (26) spaced around a two- sided working electrode (25). The nature of the electrodes is previously described. A decaffeinating apparatus comprising multiple electrodes may also advantageously decrease decaffeination times, particularly in connection with the decaffeination of large volumes of liquid.

[0051] An apparatus in accordance with the present invention may be incorporated into a coffee maker such that the brewed coffee may optionally be collected in a decaffeination chamber within the coffee maker for decaffeination. The chamber includes at least one working and counter electrode suitable to cause degradation of caffeine, and are linked to a power source. As outlined above, decaffeination using the present batch method can be achieved to any desired degree, the degree of decaffeination being time-dependent such that decaffeination time increases with greater degrees of decaffeination. The coffee maker, thus, may incorporate not only means to activate within the chamber the electrochemical reaction required to decaffeinate the coffee, but may also include a timer or means to select the desired degree of decaffeination which is linked to a timer. Following decaffeination, the decaffeinated product is dispensed into a pot or mug in the usual manner for consumption. [0052] The present apparatus may also be incorporated into other beverage dispensing machines or appliances, including vending machines, to decaffeinate the caffeinated beverages dispensed by the machine as set out above. The machine will incorporate a decaffeination chamber which includes at least one working and counter electrode suitable to oxidize caffeine which are linked to a power source. When decaffeination is selected, the beverage will dispense first into a decaffeination chamber and then, following the amount of time required to result in the desired degree of decaffeination, will be dispensed into a cup for consumption. One of skill in the art will be well familiar with the means to incorporate the decaffeinating apparatus into coffee makers, vending machines and the like.

[0053] It may also be desirable to incorporate the present apparatus into water treatment and/or water purification systems for the purpose of decaffeinating the water prior to its release into the environment, or release for other uses, as noted above. Again, incorporation of the present apparatus into such systems would be within the purview of one of skill in the art.

[0054] It may also be desirable to incorporate the present apparatus into a chemical reactor for the production of theobromine and/or theophilline based drugs. Again, incorporation of the present apparatus into such systems would be within the purview of one of skill in the art.

[0055] Embodiments of the present invention are described by reference to the following specific examples which are not to be construed as limiting.

[0056] A batch electrochemical cell (Figure 9) was used in Examples 1 to 7.

Example 1 - Decaffeination utilizing electrodes of variable surface area

[0057] An aqueous solution volume of 120 mL containing 5mM of caffeine was used as these parameters are typical of the coffee beverage. The temperature of the solution was 22 ⁰C. This experiment was conducted using a platinum (Pt) working electrode and a stainless steel counter electrode. The surface area of the working electrode was varied. [0058] In a first experiment, a working electrode of surface area 15 cm² (WEl) was utilized; while a working electrode of surface area 6 cm² (WE2) was utilized in a second experiment. The electrodes were each placed in the solution and a current density of 28 mA/cm was applied.

[0059] The rate of destruction (oxidation) of caffeine was seen to depend upon the surface area of the WE as shown in Figure 1. Complete decaffeination using WEl occurred in 120 minutes, while complete decaffeination using WE2 occurred in about 240 minutes. Hence, by increasing the surface area of the WE two times, the initial caffeine degradation rate increases two times, and the time to completely oxidize caffeine decreases by about 50%.

Example 2 - Decaffeination utilizing counter electrodes of different composition

[0060] This experiment was conducted using an aqueous solution similar to that described in Example 1 above. The working electrode was platinum. The counter electrode was varied. Results with three counter electrodes, namely, glassy carbon, stainless steel and platinum, were obtained.

[0061] The results in Figure 2 indicate that rate of decaffeination varied with the composition of the counter electrode. Complete decaffeination using the glassy carbon CE (CEl) occurred after a charge of 0.42 Ah passed through the system, while 0.85 Ah of charge was required for complete decaffeination using either a platinum (CE2) or a stainless steel (CE3) counter electrode.

[0062] These results can be explained as follows. When glassy carbon is integrated into the cell, hydrogen peroxide is produced at the surface of the CE by reduction of dissolved oxygen according to:

(9) O₂ + H₂O + 2e^" → H₂O₂

[0063] Since hydrogen peroxide is itself an oxidizing agent, degradation of caffeine in solution also occurred according to:

(10) H₂O₂ + Ri-C -> H₁-C + CH₂O + H₂O [0064] Thus, when glassy carbon is used as the CE, caffeine is oxidized both at the surface of the WE, and in solution by hydrogen peroxide generated at the CE.

Example 3 - Decaffeination at variable current densities

[0065] This experiment was conducted using a working electrode (WE2) and an aqueous solution of similar composition to that described in Example 1. The counter electrode was a glassy carbon electrode. In this case, the current density at the working electrode was varied. Currents of 12, 23, 35 and 58 mA/cm² were applied.

[0066] As illustrated in Figure 3, an increase in current density resulted in reduced decaffeination times. Increases in current density from 12 mA/cm² to 58 mA/cm² reduced the time required for the complete degradation of caffeine from 240 minutes to 120 minutes. This reduction in decaffeination time occurred because increased current density causes an increase in the number of hydroxyl radicals formed (equation (I)) or active oxygen adsorbed at the WE surface (equation (3)) resulting in higher rates of caffeine degradation (equations (2) and (4)).

[0067] The increase in the degradation rate is not linearly proportional to the increase of current density due to the occurrence of the parasitic oxygen evolution reaction (equations (7) and (8)), a more thermodynamically favourable reaction. In order to minimize the occurrence of this reaction, the working electrode must comprise a material that offers higher overpotential for oxygen evolution reaction. For example, use of an SnO₂-modifϊed electrode or a boron-doped electrode reduces generation of parasitic oxygen.

Example 4 — Reaction kinetics of decaffeination method

[0068] The influence of the initial caffeine concentration on the degradation time was studied to determine the order of the reaction. This experiment was conducted using the electrode WEl of Example 1 above as the working electrode, a glassy carbon CE and a current density of 28 mA/ cm². [0069] The results shown in Figure 4 indicate that increasing the initial caffeine concentration resulted in a proportional linear increase in initial removal rate. This dependence is characteristic of a first order reaction.

Example 5 - Decaffeination at variable temperatures

[0070] This experiment was conducted using an aqueous solution of caffeine similar to that described in Example 1, a working electrode WEl, a counter electrode as described in Example 3 above, and a current density of 28 mA/cm². In this case, the solution temperature was varied. Temperatures of 22⁰C, 6O ⁰C and 7O⁰C were utilized.

[0071] As shown in Figure 4, an increase in solution temperature increases the rate of decaffeination that occurs using the present method. An increase in solution temperature from 22⁰C to 7O⁰C, results in a decrease of the time to completely remove caffeine by approximately 2.5 times, e.g. from 60 minutes to 25 minutes.

[0072] With knowledge of the reaction order as justified in Example 4, rate constants were extracted from the data. The temperature dependence of these constants were found to follow an Arrhenius dependence (inset to Figure 5). An activation energy of 9.4 kJ/mol^"1 was estimated for the reaction which is quite low.

Example 6 - Decaffeination of brewed coffee

[0073] Figure 6 shows the concentration profile of caffeine during the decaffeination of 100 mL of filtered coffee. The WE was a 15cm² Pt mesh, while the CE was stainless steel. Degradation current was 28 mA/cm². It is evident that the concentration of caffeine decreases with time. However, compared to the kinetics of degradation of pure caffeine, the degradation of caffeine in filtered coffee is kinetically a much slower reaction. A total of 2.5 Ah charge was needed for an almost complete removal of caffeine (Figure 6), while 0.85 Ah was needed for a complete removal of caffeine from a pure caffeine solution (Figure 2). This is mostly due to the occurrence of parallel side reactions related to oxidation of other organic compounds present in coffee, oxidation of by-products and also partially due to the fouling of the WE by organic molecules and particulate material present in filtered coffee, decreased conductivity of the aqueous phase. In accordance with the Examples 1 to 5 above, decaffeination time can be reduced by optimizing electrode composition and surface area, current density and beverage temperature. For example, varying the CE from stainless steel to glassy carbon and beverage temperature from 22° C to 70° C, decreases decaffeination charge (time) 5 times, from ca. 2.5 Ah down to 0.5 Ah (ca. 71 minutes), based on the extrapolation results. Further decrease in the decaffeination time could be achieved by employing a WE of even larger surface area. For an example, in accordance with Figure 1, an increase in surface area for 10 times would further reduce the degradation time 7.1 minutes at the same current density as in Figure 6.

Example 7 - Decaffeination of brewed coffee using working electrodes of different composition

[0074] Figure 7 illustrates the effect of varying the composition of the WE on the concentration profile of caffeine during the decaffeination of filtered coffee. The abscissa represents the charge passed through the apparatus, while the ordinate represents the caffeine concentration profile normalized to the initial concentration of caffeine in the beverage. The results demonstrate that the activities of Pt and stainless steel are very similar, while the activity of graphite is lower. In addition, erosion of the graphite electrode was noticed during the decaffeination of the beverage.

Example 8 - Decaffeination of brewed coffee using a multi-pass batch method

[0075] A multi-pass batch method for decaffeinating coffee was also conducted using an electrochemical apparatus as illustrated in Figure 1OA. The working electrode of this apparatus was a Pd-coated Ti plate of area 10 cm and the counter electrode was a Ti plate (10 cm²). Regular-type store-brewed coffee (Van Houtte -130 mL) was decaffeinated using this apparatus. The degradation current applied was 0.11 A/cm . The results (see Figure 8) demonstrate that a complete decaffeination was achieved after charge of approx. 3.3Ah is passed through the cell. Using these conditions, degradation time was 2.9 hours.

Claims

CLAIMS:

1. An electrochemical batch method for decaffeinating a liquid comprising the steps of: inserting into the liquid an electrochemical apparatus comprising at least one working electrode and at least one counter electrode that are suitable to cause degradation of caffeine; and supplying power to the electrodes for a period of time sufficient to cause the desired degree of decaffeination.

2. A method as defined in claim 1, wherein the electrodes have a surface area in the range of about 10 to 1000 cm².

3. A method as defined in claim 1, wherein the electrodes are each made of a material selected from the group consisting of platinum, titanium, palladium, gold, stainless steel, graphite, boron-doped-diamond, metal-oxides and metal-oxide alloys.

4. A method as defined in claim 2, wherein one or more of the electrodes is made of a material selected from mesh, a porous material, a flat material, a particulate and a bead material.

5. A method as defined in claim 1, wherein the method is conducted using a current density in the range of 5 to 2000 mAcm^"2.

6. A method as defined in claim 5, wherein the current density is in the range of 30 to 1100 mAcm^"2.

7. A method as defined in claim 1, which is conducted at atmospheric pressure at a temperature between 0 and 100⁰C.

8. A method as defined in claim 7, wherein the temperature is between 50 and 7O⁰C.

9. A method as defined in claim 1, wherein more than one counter electrode is used.

10. A method as defined in claim 1, wherein more than one working electrode is used.

11. A decaffeination apparatus comprising:

at least one working electrode and at least one counter electrode spaced from one another; and

a power supply connected to the working electrode and the counter electrode for delivering a current thereto;

wherein the working electrode is made of a material suitable to cause degradation of caffeine in a liquid on application of a current thereto.

12. An apparatus as defined in claim 11, comprising more than one working electrode.

13. An apparatus as defined in claim 11, comprising more than one counter electrode.

14. An apparatus as defined in claim 11 , which is portable.

15. An apparatus as defined in claim 11 , additionally comprising:

a decaffeination chamber housing the electrodes, said chamber having a bottom end and a top end;

a reservoir to hold a liquid to be decaffeinated, wherein the reservoir is connected to the decaffeination chamber via an inlet at the bottom end of the chamber and an outlet at the top end of the chamber; and

means to circulate a liquid to be decaffeinated from the reservoir and into the chamber via the inlet and back into the reservoir via the outlet.

16. An apparatus as defined in claim 15, comprising more than one working electrode.

17. An apparatus as defined in claim 15, comprising more than one counter electrode.

18. An apparatus as defined in claim 15, which is portable