“PROCESS AND SYSTEM FOR DECONTAMINATING CORK MATERIAL”

FIELD OF THE INVENTION

The present invention relates to a process and system for decontaminating cork material by using a cycle comprising one step of extracting contaminant compounds from cork material and only one step of regeneration of the extraction fluid. The invention applies to the cork industry.

BACKGROUND OF THE INVENTION

Decontamination of cork material is of paramount importance in the cork industry, particularly in connection with the production of cork stoppers to be used to close bottles of beverages, and specially bottles of wine.

It is well known that cork is a natural product originated from a cork oak that possesses desirable natural characteristics for a number of different uses and it is nowadays world widely spread under a plurality of different commercial products, namely from the food, aeronautics, floor and construction industries, among many others.

Cork stoppers to close or seal wine bottles are a main application for cork material. Its hydrophobicity, elasticity and impermeability to liquids in addition to its low permeability to gases make it a unique eco-friendly material for this application.

In addition to provide an efficient closing/sealing of the bottles, stoppers made of cork also contribute to an adequate wine maturation or aging when bottles are stored for long times. This is not accomplished by other material stoppers.

However, in view of its nature, cork material naturally contains some natural compounds acting as contaminants in food articles, in particular wine. In fact, these substances are responsible for adulterating the taste and aroma of food articles. These detrimental effects are known by “cork taint” of wine. Examples of such contaminant compounds are 2,4,6-trichloroanisole (TCA), 2,4- di chi oroani sole, 2,6 dichloroanisole, 2,4,6-tribromoanisole (TBA), 2,3,4,6-tetrachloroanisole (TeCA), pentachloroanisole (PCA), 2,4,6-trichlorophenol (TCP), 2-methylisoborneol (MIB), geosmine, 2-isobutyl-3-methoxypyrazine (IBMP), 2-isopropyl-3-methoxypyrazine (IPMP), 2- m ethoxy-3, 5 -dimethylpyrazine (2M35DP), guaiacol, l-octen-3-ol, and l-octen-3-one, just to mention some.

Since the presence of such contaminants is quite detrimental to the organoleptic properties of beverages, affecting specially the wine, the cork industry has taken considerable efforts in developing appropriate solutions to remove said contaminants from the cork material.

One widely used solution is to use cycles of dense fluids circulation, particularly under supercritical conditions, which is known in the art by “Supercritical Fluid Extraction” or “SFE”.

Commonly, conventional processes relying on SFE resort to a) circulate an extraction fluid at supercritical or near-critical conditions through a cork bed, thereby solubilizing the contaminant extractable compounds; then b) the contaminants-loaded extraction fluid is subjected to a decompression well below the critical pressure, such that the fluid becomes a compressed gas wherein its solubility decreases drastically and, by this reason, the solutes (contaminants) precipitate in a collection vessel (in some cases, after precipitation, the extraction fluid is further circulated through a filter medium, for example, an adsorbent material like activated carbon, to better regenerate the extraction fluid); then c) the already regenerated extraction fluid is cooled to condensate to the liquid state and pumped and heated to the desired (supercritical or near-critical) conditions of step a) and the cycle continues by undergoing steps a) to c) again. The cycle is performed for a certain amount of time depending on the amount and type of cork material to be treated (Fig. 2 illustrates a conventional cycle of this type).

This conventional cycle presents a number of important drawbacks:

• Intensive energy consumption due to the cooling and heating steps included in each cycle;

• Intensive energy consumption due to the pressure drop and recompression steps needed in each cycle;

• High capital costs due to the necessary heat exchangers, condenser, separator and pump needed inside the cycle; and • High maintenance costs derive from the complex systems which are inevitably needed to carry out the process.

A number of variants to this solution may include more or less extraction fluid regenerating steps, and more complicated fluid compression-decompression and/or heating cooling steps, while keeping the main core steps above-mentioned.

European patent EP 1216123 B2, entitled “Method For Treating And Extracting Cork Organic Compounds, With A Dense Fluid Under Pressure”, discloses a method for treating cork or a cork-based material, for extracting therefrom contaminating organic compounds which consists in contacting the cork or said cork-based material with a dense fluid under pressure, at a temperature between 10 and 120 °C and under a pressure of 10 to 600 bars.

European patent EP 1701775 B2, entitled “A Method And Process For Controlling The Temperature, Pressure And Density Profiles In Dense Fluid Processes And Associated Apparatus”, discloses a method of treating a material contained in a vessel. This method involves a fluid present in the vessel and comprises at least one pressurization step in which the pressure in the vessel is increased and at least one depressurization step in which the pressure in the vessel is decreased. The invention further relates to an apparatus for executing this method and the products obtained therefrom.

European patent EP 2396153 Bl, entitled “Method For Direct Treatment Of Cork Stoppers, Using Supercritical Fluids”, discloses a method which permits direct treatment of natural cork stoppers, using supercritical fluids with the aim to eliminate or significantly reduce the quantity of cork contaminants, namely 2, 4, 6-trichloroanisole. The process uses a separating device which permits natural cork stoppers to go through compression/decompression cycles without losing their shape and maintaining their sealing properties.

European patent EP 2404647 Bl, entitled “Method For Extracting Organic Compounds From Granulated Cork”, discloses extraction of organic compounds present in granulated cork by dispersively applying a supercritical fluid comprising at least two different gases in a supercritical state. This can be combined with a previous extraction using vapor continuously performed in another extractor. Each extractor is further supported on a vibratory base, whereby a more uniform contact of the vapor or supercritical fluid with the granulated cork is obtained. The gases coming from the extraction are recirculated through several recirculation circuits to make the most use of gases. One of the components in which the recirculation consists is a condenser with conical body, providing a higher surface for evaporating the coolant fluid and thereby increasing the condensation of gases.

European patent application 2799199 Al, entitled “Method For Removing Various Undesirable Compounds From Cork”, discloses a method for removing compounds that are responsible for undesirable flavours and/or odours, such as phenolic compounds or anisol derivatives, the method comprising maintaining the cork to be treated at a pressure of between 64 and 450 bar, a temperature of between 27 °C and 90 °C and doing so for a period of time of less than 60 minutes, solely in contact with a dense gas, without cosolvents or additional coagulant substances other than said dense gas. The method may include several regeneration steps for regenerating the fluid.

International application published as W02005025825, entitled “Method For The Extraction Of Cork-Containing Material”, discloses a method for extracting cork-containing material with the aid of a compressed gas at temperatures ranging between 10 and 120 °C and pressures ranging between 10 and 600 bar. Extraction takes place in isobaric conditions while the compressed gas flows through the charge in a radial or axial direction and the charge that is to be extracted is combined with an adsorbing material. The inventive method allows cork plates, cork granules, bottle cork, or agglomerated cork, for example, to be quantitative removed from organic compounds such as pentachlorophenol, tri chi oroani sole, and tetrachloroanisole as well as waxes and fats such that the purified cork-containing materials can be used without reservation in the food sector and particularly in the beverage sector.

Although the above-mentioned processes may be more or less effective as to the removal of contaminants from cork, they all suffer from the drawback of needing complex systems to be implemented. At an industrial scale, such complexity implies great-deals of equipment, energy and maintenance costs.

On the other hand, the compression-decompression cycles of the conventional treatment continuously dry the cork material along the cycle operation time, with serious consequences for the structural integrity thereof. In fact, the imposed pressure drop may decrease the water solubility in the extraction fluid, giving rise to its condensation in the collection vessel. In this way, the water that is transferred from cork material to the extraction fluid (cork drying) is subsequently eliminated in the collection vessel by condensation.

Also, the particular elimination of large molecules (e.g., long-chain aliphatic alcohols, waxes and fats) from the extraction fluid requires dedicated equipment and specific thermodynamic conditions to reduce their solubility and promote their precipitation, thus turning the process and respective systems complex to implement and maintain.

Therefore, a need exists in the art for an SFE-based process and system that overcome the above-mentioned drawbacks.

SUMMARY OF THE INVENTION

The present invention relates to a process for decontaminating cork material, the process comprising the steps of: a) circulating a supercritical or near-critical extraction fluid through a batch of cork material so as to extract contaminant compounds from cork by solubilizing them in the extraction fluid; followed by b) circulating at supercritical or near-critical conditions of pressure and temperature the contaminants-loaded extraction fluid from step a) through an adsorbent means so as to free up the extraction fluid of contaminants by adsorption; followed by c) repeating step a) with the regenerated extraction fluid from step b); and d) repeating steps b) and c) for a predetermined amount of time.

In an embodiment, the steps a) and b) of the process comprise circulating the extraction fluid at a same pressure in both steps a) and b).

In a preferred embodiment, steps a) and b) of the process comprise circulating the extraction fluid at a same pressure and at a same temperature in both steps a) and b).

Preferably, step b) of the process of the invention comprises circulating the contaminants- loaded extraction fluid through an adsorbent means selected from the group comprising activated carbon, bleaching earth, diatomaceous earth, a zeolite material, silica gel, resins, and combinations thereof; more preferably circulating the contaminants-loaded extraction fluid through activated carbon. In another preferred embodiment, the step b) of the process of the invention comprises circulating the contaminants-loaded extraction fluid through an amount of activated carbon in the range of 1.5 % to 8 % by weight of the cork material, preferably 2 % to 5 %, more preferably 2.5 %.

Preferably, steps a) and b) of the process of the invention comprise circulating CO2 as the extraction fluid, more preferably steps a) and b) comprise circulating water mixed with the CO2, the water in the range of 0.05 % (w/w) up to saturation.

In a further embodiment, steps a) and b) of the process of the invention comprise circulating CO2 at a pressure in the range of 60 to 300 bar, preferably 70 to 150 bar, more preferably 100 bar.

In other embodiment, steps a) and b) of the process of the invention comprise circulating CO2 at a temperature in the range of 20 °C to 160 °C, preferably 30 °C to 90 °C, more preferably 50 °C to 80 °C, most preferably 60 °C.

In a further preferred embodiment, the process of the invention comprises: a) circulating a mixture of CO2 saturated with water, at 100 bar and 60 °C, through a batch of granulated cork followed by b) circulating the contaminants-loaded CO2 saturated with water through a bed of activated carbon under the same pressure and temperature conditions of step a); followed by repeating step a) with the contaminants-free CO2 saturated with water from step b); and repeating the cycle during 30 minutes, wherein the mass of activated carbon is 2.5 % of the mass of granulated cork, and the mass of the granulated cork is 14 % of the mass of circulated CO2.

The invention also relates to a system for carrying out the process of the invention, the system comprising:

• an extraction chamber (1);

• a pump means (2) for circulating an extraction fluid;

• an adsorbent means support (3) for supporting an adsorbent means; and

• a cork material supporting means (4) arranged inside the extraction chamber (1), characterized in that said pump means (2) is arranged inside the extraction chamber (1). Preferably, said adsorbent means support (3) is also arranged inside the extraction chamber (1).

In an embodiment, the system further comprises three compartments inside the extraction chamber (1), the said compartments interconnected for fluid circulation but separated for solids, wherein each compartment contains respectively the pump means (2), the adsorbent means support (3), and the cork material supporting means (4).

Preferably, said three compartments are arranged in series in any order, more preferably the said compartments are arranged in the order of pump means compartment, adsorbent means support compartment and cork material supporting means compartment.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, a detailed description of the invention is provided making reference to the appended drawings, in which:

Fig. 1 illustrates an example of a phase diagram in which the pressure-temperature equilibrium is shown in terms of reduced properties;

Fig. 2 is a schematic representation of a prior art common supercritical fluid extraction (SFE) process, showing a conventional operating cycle and respective pressure and temperature variations along the cycle, the horizontal patterned strip represents the possible range of pressure and temperature conditions in which the extraction fluid remains in a supercritical or near-critical state;

Fig. 3 is a schematic representation of the SFE process of the present invention, showing the operation cycle of the invention and respective pressure and temperature variations along the cycle, the horizontal patterned strip represents the possible range of pressure and temperature conditions in which the extraction fluid remains in a supercritical or near-critical state;

Fig. 4 is a schematic illustration of a preferred embodiment of an inventive system to carry out the process of the invention. DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a process and system for extracting contaminant compounds from cork material.

The invention is directed specifically to a supercritical fluid extraction (SFE) process that makes use of a cycle of an extraction fluid operating under its supercritical or near-critical conditions of pressure and temperature, thus operating in a supercritical or near-critical state.

In the context of the present invention, an extraction fluid in a supercritical or near- critical state is hereinbelow simply designated “supercritical extraction fluid”, unless explicitly mentioned otherwise.

Supercritical state corresponds to the region of a well-known pressure-temperature equilibrium diagram (or phase diagram - see Fig. 1) where the fluid is simultaneously above its critical temperature and critical pressure: T>Tc and P>Pc. When a fluid is in the supercritical state it is commonly referred to as a supercritical fluid. The critical pressure and critical temperature are characteristic of each fluid, for example for carbon dioxide they correspond to 73.8 bar and 31.1 °C. Of course, each fluid has its own phase diagram.

With reference to Fig 1, it is noted that another way to define the supercritical region is in terms of reduced properties, which are the ratios between the values of the properties and their values in the critical point (e.g., Pr=P/Pc and Tr=T/Tc). Thus, a supercritical fluid is defined as a fluid with Pr>l and Tr>l .

Still with reference to Fig. 1, a near-critical fluid is a fluid whose pressure and temperature conditions lie inside the near-critical region. This region may be arbitrarily defined around the critical point in a pressure-temperature diagram as 0.9<Pr<l.l and 0.9<Tr<l.l.

A subcritical fluid or the subcritical region is an arbitrary region where at least the temperature or the pressure is below its critical value, i.e. 0.9<Tr<l and 0.9<Pr; or 0.9<Pr<l and 0.9<Tr.

For simplicity of description, by “supercritical extraction fluid” should be understood that an extraction fluid is in a supercritical or near-critical state according to the above definition. In fact, this means that there is a small range of variation slightly below the so-called critical conditions of pressure and temperature in which the dense fluid still keeps the ability to perform the extraction function and, by this reason, such variation should be considered for and comprised in the operational range of the fluid. This understanding is not new and is well accepted and described in the prior art, namely in some of the herein cited prior art.

Several fluids have been used under supercritical conditions in various applications, both alone and in combination (in case of allowable mixtures). Carbon dioxide (hereinafter simply designated by CO2) is the preferred solvent for supercritical fluid extraction since it has proven to be safe, it is inert, non-toxic, non-flammable, non-explosive, and has a relatively easy-to-reach critical point: 73.8 bar and 31.1°C.

The properties of a pure supercritical fluid, e.g., solvation ability or the selectivity towards target compounds, can be improved by mixing small quantities of an inorganic or organic solvent, which is called cosolvent, modifier or entrainer. Water and ethanol are the most commonly used cosolvents.

If temperature and pressure are above the critical temperature and critical pressure of the binary mixture, the (mixture) fluid is under supercritical conditions and, as such, can be used as extraction fluid.

A mixture of CO2 with small amounts of water, from 0.05 % (w/w) up till saturation, is a preferred extraction fluid of the present invention, since the presence of water will positively impact the maintenance of suitable moisture content in the cork material.

The present invention provides a process for decontaminating cork material.

The cork material to be decontaminated is selected from the group comprising cork powder, granulated cork, cork stoppers, cork slabs and cork plates.

The present invention is directed to decontamination of cork material, thus, in general, any cork-based material or composite material containing cork can be subjected to the process and system of the invention provided that such material can withstand the conditions of pressure and temperature of the process without compromising its structural integrity.

Most common contaminants extracted with the process of the present invention are 2,4,6-trichloroanisole (TCA), 2,4-dichloroanisole, 2,6-dichloroanisole, 2,4,6-tribromoanisole (TBA), 2,3,4,6-tetrachloroanisole (TeCA), pentachloroanisole (PCA), 2,4,6-trichlorophenol (TCP), 2-methylisobomeol (MP3), geosmine, 2-isobutyl-3-methoxypyrazine (IBMP), 2- isopropyl-3-methoxypyrazine (IPMP), 2-m ethoxy-3, 5 -dimethylpyrazine (2M35DP), guaiacol, 1- octen-3-ol, and l-octen-3-one. Also, sterols, triterpenoids, long-chain aliphatic alcohols, waxes and fats present in cork are extracted as well.

For a thorough understanding of the invention, a brief description of the most used conventional prior art process and system is described in the following resorting to Fig. 2.

In order to put the prior art cycle of Fig. 2 in practice, a system is used comprising the following parts: heat exchangers (A, Cl, C2), pump (Bl), extraction vessel (D), decompression valve (E), collection vessel (F) and filtering medium (G).

In short, this prior art cycle comprises (see Fig. 2):

• circulating the supercritical extraction fluid through the extraction vessel (D) containing the cork to be treated, the extractable (contaminant) compounds are solubilized in the extraction fluid; then

• the fluid circulates through a decompression valve (E) where it significantly reduces its pressure well below the critical pressure. At this point the fluid may be also heated in a heat exchanger (C2) to compensate the drastic cooling from decompression in order to avoid freezing and pipe clogging;

• at this lower pressure, the fluid changes its state into a compressed gas, whose solubility decreases drastically, and the solutes (contaminant compounds plus other extractives like the above-mentioned sterols, triterpenoids, long-chain aliphatic alcohols, waxes and fats) precipitate in the collection vessel (F). Optionally, in some cases, after the precipitation step, the extraction fluid is further passed through a filtering medium (G), for instance an adsorbent bed of activated carbon, to remove non-precipitated contaminants that may still exist, so as to further purify the extraction fluid; then

• the regenerated extraction fluid is cooled and liquified by means of a heat exchanger (A); the liquified fluid is then pumped by a pump (Bl) to the desired high extraction pressure (above the critical pressure); and finally, the extraction fluid is heated (Cl) to the operating temperature (above the critical temperature);

• at this point the fluid is again at the supercritical state and the cycle restarts.

When the set cycle time is over, the whole system is depressurized to remove the (decontaminated) cork material and load it with another cork bed to be decontaminated.

In this prior art process, the step of (fluid expansion for) the precipitation of the contaminant compounds is a key-factor for the continuity of the cycle, since the extraction fluid must be regenerated (purified) before a new solubilization step of the contaminant compounds takes place, otherwise the efficiency of the process does not fit with the requirements of said industrial process. Further steps of regeneration, like the one using an adsorbent medium, for example, activated carbon, were considered supplementary in the art and have been used so as to further improve the fluid regeneration.

Important drawbacks in connection with the above prior art process are mentioned in the background art section above. It is obvious that significant energy and equipment costs are involved in the fluid repressurization and reheating steps to its operating conditions.

The process of the present invention does not resort to a step of fluid expansion (involving a major pressure drop) for the precipitation of the contaminant compounds to regenerate the extraction fluid.

The process of the present invention for decontaminating cork material comprises the steps of: a) circulating a supercritical or near-critical extraction fluid through a batch of cork material so as to extract contaminant compounds from cork by solubilizing them in the extraction fluid; followed by b) circulating at supercritical or near-critical conditions of pressure and temperature the contaminants-loaded extraction fluid from step a) through an adsorbent means so as to free up the extraction fluid of contaminants by adsorption; followed by c) repeating step a) with the regenerated extraction fluid from step b); and d) repeating steps b) and c) for a predetermined amount of time.

Surprisingly, it has been found that a cycle process comprising a single step of regeneration of the fluid at supercritical (or near-critical) conditions for the extraction fluid, followed by the extraction step, provides similar or even better decontamination results when compared to the prior art process resorting to fluid expansion for the precipitation of contaminants and further subsequent regeneration steps before the extraction step is carried out.

In the present invention, to accomplish the fluid regeneration step, the said adsorbent means operates at such supercritical (or near-critical) pressure and temperature conditions for the extraction fluid, thereby preventing the need of phase changes of the extraction fluid in the process of the invention. In this way, no need exists to restore supercritical conditions of the fluid during the cycle operation itself. Only to start the process, the extraction fluid must be set at supercritical or near-critical state. This leads to significant energy savings and to simplified systems for carrying out the process at an industrial scale, as it is apparent from comparison between Fig. 2 and Fig. 3.

Of course, during the cycle of the invention, some variations in the pressure and temperature of the extraction fluid are allowed as long as the fluid remains in the supercritical (or near-critical) state until the cycle time is over.

When the cycle time is over, the process is stopped and the batch of decontaminated cork is removed and switched by another batch of cork to be treated. These switching tasks are performed around room conditions of pressure and temperature.

To start a new cycle, the extraction fluid must be set only once to the desired supercritical or near-critical conditions of pressure and temperature and the above-mentioned step a) starts the new cycle. Then, during the cycle itself, as no major pressure and/or temperature variations will occur, it is easy and costly efficient to keep the extraction fluid at its supercritical or near-critical state. As to costs improvement of the present invention in relation to the conventional prior art process, a comparative experimental study has been performed regarding energy consumption and CO2 usage. The results are shown in the following Table 1.

Table 1

The savings provided by the present invention over the prior art are rather significant.

To preserve the quality of the cork material, an appropriate moisture content [usually up to 20 % (w/w), preferably between 2 and 15 % (w/w), more preferably between 5 and 10 % (w/w)] should be kept in the cork material. In the prior art processes, a continuous stream of cosolvent (i.e., water) must be fed to mix with the extraction fluid at supercritical state, because in the expansion (depressurization) step the cosolvent also condensates, thus separating from the extraction fluid. Another advantage of the invention is that it does not need such a continuous stream of cosolvent (i.e., water) to maintain the moisture content of cork, because the absence of depressurization step eliminates the problem of cosolvent condensation. In this way, it is much easier to preserve the appropriate moisture conditions of the cork material.

Preferably, the adsorbent means of the invention is selected from the group comprising activated carbon, bleaching earth, diatomaceous earth, zeolite material, silica gel, resins, and combinations thereof; more preferably the adsorbent means is activated carbon.

In fact, it is quite surprising that the process of the invention is able to effectively perform the decontamination of cork material resorting to a single fluid regeneration step that is carried out at the supercritical (or near-critical) conditions for the extraction fluid, without the need of further extraction fluid filtering steps, by a number of reasons, namely because it is not expected that:

• an adsorbent means like the activated carbon used in the prior art as optional and complementary to the main usual filtering step (resorting to precipitation by pressure drop) would suffice to perform alone the fluid regeneration; • the adsorbent means would be able to work under such supercritical (or near- critical) conditions of pressure and temperature without losing its adsorption ability or decreasing the thermodynamic distribution coefficients of the contaminants to be adsorbed, thus reducing even further a fluid regenerating action that was believed insufficient if taken alone;

• the problem of removing also large molecules like long-chain aliphatic alcohols, waxes and fats from the extraction fluid could be overcome without a precipitation step, since it was believed that an adsorbent means would rapidly become saturated or blocked by said large molecules.

Despite the above-mentioned expectations of the skilled person, the present invention is able to perform an efficient decontamination of cork material while allowing considerable savings in extraction fluid quantity and energy per unit weight of cork material and in maintenance costs.

In an embodiment of the invention, the extraction fluid circulation of step a), to extract the contaminant compounds from cork and the contaminants-loaded fluid circulation of step b), to regenerate the extraction fluid, are performed at a same isobaric pressure.

In a preferred embodiment, said steps a) and b) are performed both at a same isobaric and isothermal conditions. In other words, the supercritical or near-critical extraction fluid is circulated in both steps a) and b) at same conditions of pressure and temperature.

It has been surprisingly found that running the regeneration of the extraction fluid under the same supercritical (or near-critical) conditions does not penalize contaminants elimination because, in fact, the adsorbent means maintained its high adsorption capacity, and the favourable thermodynamic distribution coefficients of the contaminants between the adsorbent and the extraction fluid were preserved.

The weight proportion of adsorbent means to cork material that is required for total cork decontamination depends on the operating conditions of the process and the initial contaminants concentration in the cork. In the particular case of activated carbon, it was surprisingly found experimentally that amounts of activated carbon as low as 1.5 % by weight of cork material were sufficient to regenerate the extraction fluid even for initial TCA contents in the cork as high as 25 ng.L ¹ . This finding adds even further to the significant savings at industrial scale provided by the present invention over the prior art. On the other hand, it provides the technical improvement of allowing to keep the adsorbent means together with the cork bed in the same extraction chamber without a negative impact on the process productivity that would result from the sacrifice of useful space for the cork material inside the extraction chamber, if larger amounts of adsorbent had to be used there inside.

With reference now to the particular embodiment of Fig. 3, in step a) - the extraction fluid, at the desired supercritical or near-critical conditions, is circulated through the extractor (D) containing the cork bed and solubilizes the extractable compounds of cork. At this stage a very small continuous pressure drop (from 0.001 % to 1 % of the operation pressure per meter of cork bed) occurs as the fluid percolates the cork bed; then in step b) - still under supercritical or near-critical conditions, the extraction fluid circulates through an adsorbent means (G), preferably an adsorbent bed, more preferably activated carbon, where fluid suffers a small continuous pressure drop (from 0.01 % to 5 % of the operation pressure per meter of adsorbent bed). At this step, the adsorbent bed removes by adsorption the extracted contaminants from the extraction fluid, ensuring that clean extraction fluid is recycled to the extractor (D). A small heat exchanger (C3) is used to compensate for the heat losses from the equipment to the environment. A blower (B2) is used to recirculate the extraction fluid and to compensate for the mentioned small pressure drops caused by the percolation through the cork and adsorbent beds. This cycle is repeated for a predetermined amount of time that usually depends on the amount and type of cork material to be decontaminated.

It is noted that the mentioned small pressure drops result naturally from physics of the fluid percolation through the cork material and through the adsorbent means. Usually such pressure drops are in the range of 0.001 % to 5 % of the operation pressure per meter of solid bed. While these pressure drops must be compensated all the times, the energy involved to do so is proportionally low. Thus, in the context of the invention, when reference is made to isobaric and/or isothermal conditions, it is considered that such inevitable pressure or temperature variations are negligible in comparison with the absolute operation conditions.

As to the cycle time, it is noted that decontamination of granulated cork can be done in significantly lesser times than cork materials of bigger size, such as for example cork stoppers or pristine cork slabs/boards. Since these latter materials imply bigger thicknesses, the diffusion of solutes from their most inner locations to the external surface of the material can make the extraction time to be much longer than those required to decontaminate granulated cork.

Therefore, the decontamination cycle times are comprised in the range of 10 to 480 minutes, preferably 10 to 240 minutes, more preferably 15 to 100 minutes, most preferably between 20 and 60 minutes.

In an embodiment, the extraction fluid comprises at least 50 % by weight of CO2.

Preferably, the extraction fluid supply is at least of 2 kg. kg ¹ of cork, preferably between 5 kg. kg ¹ of cork and 20 kg. kg ¹ of cork material.

Preferably, the amount of activated carbon used as adsorbent means is between 1.5 % and 25 % by weight of cork material, more preferably between 1.5 % and 8 %, even more preferably between 2 % and 5 %, most preferably 2.5 % by weight of cork material. Of course, higher amounts than 25 % of activated carbon would work, but it is technically and economically advantageous to use as low as possible amounts of activated carbon, as already mentioned.

Preferably, the operation temperature ranges between 20 °C and 160 °C, more preferably between 30 °C and 90 °C, even more preferably between 50 °C and 80 °C, most preferably 60 °C.

Preferably, the operation pressure is higher than 40 bar, more preferably between 60 and 300 bar, even more preferably between 70 and 150 bar, most preferably 100 bar.

In a further preferred embodiment, the process of the invention comprises: a) circulating a mixture of CO2 saturated with water, at 100 bar and 60 °C, through a batch of granulated cork followed by b) circulating the contaminants-loaded CO2 saturated with water through a bed of activated carbon under the same pressure and temperature conditions of step a); followed by repeating step a) with the contaminants-free CO2 saturated with water from step b); and repeating the cycle during 30 minutes, wherein the mass of activated carbon is 2.5 % of the mass of granulated cork, and the mass of the granulated cork is 14 % of the mass of circulated CO2. The present invention relates also to a system designed to carry out the process of the invention above described.

Fig. 4 shows schematically a preferred embodiment of the system of the invention, whereby should not be considered limitative, since different embodiments may be designed to practice the invention. In Fig. 4, the arrows schematically illustrate the circulation of the extraction fluid.

The system for decontaminating cork material of the invention comprises an extraction chamber (1); a pump means (2) arranged inside the extraction chamber (1) for circulating an extraction fluid; a adsorbent means support (3); and a cork material supporting means (4) arranged inside the extraction chamber (1).

In the preferred embodiment of Fig. 4, also said adsorbent means support (3) is arranged inside the extraction chamber (1).

In the context of the present invention, the pump means (2) is any means that is able to perform the circulation of the extraction fluid through the cork bed and through the adsorbent means, ensuring the continuity of the cycle of the present invention. It should be able to overcome small to moderate pressure drops that may occur during the process, which however are not sufficient to remove the fluid from its supercritical or near-critical state. Preferably, the pump means (2) is a blower or a positive displacement or centrifugal pump.

Surprisingly, it has been found that in operation a stabilization of the pressure and temperature conditions inside the extraction chamber (1) is achieved by arranging said pump means (2) inside the extraction chamber (1). Even better results are achieved by also arranging the adsorbent means support (3) inside the extraction chamber (1). These arrangements provide simpler and compact extraction systems over the prior art, allowing significant savings in the equipment costs of such compact embodiments and in energy and maintenance costs of the operation thereof.

The compact embodiment in which both adsorbent means support (3) and pump means (2) are arranged inside the extraction chamber (1) revealed a better performance of the process to operate under isobaric and isothermal conditions for the extraction fluid in the extraction cycle. This stability increase resulted in optimized energy costs.

A possible design of the latter compact embodiment is to arrange three compartments inside the extraction chamber, wherein the compartments are interconnected for fluid communication, but separated for solids, such that the extraction fluid can flow from one compartment to another by means of the pump means. A first compartment contains the pump means, a second compartment contains the adsorbent means support, and a third compartment contains the cork material supporting means.

The said three compartments containing the pump means (2), the adsorbent means support (3), and the cork material supporting means (4) can be arranged in series in any order. Preferably, they are arranged in series by the following order: pump means compartment, adsorbent means support compartment and cork material supporting means compartment.

In operation, when the supercritical (or near-critical) decontamination cycle ends, the extraction chamber is depressurized to remove the decontaminated cork and switch it by a new cork bed to be extracted, and the extraction fluid returns to a storage vessel. The extraction fluid may be stored as it is, or it is firstly percolated through an adsorbent bed (containing activated carbon or other adsorbent) under low pressure in order to remove trace quantities of some remaining volatile compounds, in this way, the extraction fluid can be stored very pure until a new decontamination cycle is set.

EXAMPLES

A number of experiments were carried out based on the decontamination process of the invention and using a prototype of the described preferred system of the invention.

Since it is known from the prior art that supercritical fluid extraction can decontaminate cork material within a large range of (supercritical and near-critical) pressures and temperatures using different extraction fluids, the purpose of these experiments was to demonstrate that it is sufficient to use a single step of extraction fluid regeneration, carried out at supercritical or near- critical conditions for the extraction fluid, and resorting to adsorbent means. As the extraction step and the fluid regeneration step are performed at similar P-T conditions, the energy consumption and the required quantity of the extraction fluid are considerably reduced, thereby largely improving operating costs (opex) over prior art processes, as demonstrated by results of Table 1 above.

Since the wine industry requires cork stoppers with amounts of 2,4,6-trichloroanisole (TCA) below 0.5 ng.L ¹ , the TCA was the reference contaminant measured in these experiments. Thus, upon completion of treatment cycle, the extraction chamber was depressurized, the cork material was removed and submitted to TCA analysis by SPME-GC-MS according to International Standard ISO 20752. Tables 2 and 3 show the levels of TCA, respectively in granulated cork and natural cork stoppers, before and after decontamination by the SFE process of the invention.

Table 2 hereinafter shows different operation conditions used in fifteen experiments with granulated cork and activated carbon as the adsorbent means. The extraction fluid used was CO2, both alone and in combination with water added up to saturation. The extraction results in both cases were similar, since all the trials presented less than 0.5 ng.L ¹ of TCA after decontamination.

Table 2 Six similar batches of fourteen natural cork stoppers (ca. 44 g each batch) were submitted to the decontamination process of the invention using CO2 as extraction fluid (ca. 305 g), both pure and in combination with water added up to saturation, during 480 min at 100 bar and 60 °C, using 1.5 %, 4.0 % and 8.0 % of activated carbon as the adsorbent means. Prior to the decontamination cycle, all the cork stoppers were assessed as to their level of contamination by means of individual analysis by SPME-GC-MS according to International Standard ISO 20752. Upon completion of the decontamination cycle, the extraction chamber was depressurized, the cork stoppers were removed and submitted to TCA individual analysis by SPME-GC-MS according to International Standard ISO 20752. The extraction results were all similar and independent of the water content and adsorbent amount, since all the trials presented less than 0.5 ng.L ¹ of TCA after decontamination.

Table 3 presents the results achieved for the experiment using fourteen cork stoppers (total mass of 43.6 g), 305.7 g of pure CO2, and 1.5 % of activated carbon, while fixing the remaining operating conditions.

Table 3

The description herein should be construed as n on-limitative of the scope thereof which is defined only by the independent claim. The dependent claims define particular embodiments of the invention.