PROCESS AND EQUIPMENT FOR THE EXTRACTION OF TCA FROM NATURAL CORK STOPPERS WITH ORGANIC LIQUID SOLVENT

Technical field of the Invention

The invention described in this document refers to a process and an equipment to extract 2 , 4 , 6-trichloroanisole, usually called TCA, from natural cork stoppers or other pieces made of cork. The presence of contaminants in cork, such as TCA, has been one of the biggest problems in the cork industry in recent years. At concentrations as low as 5 ng/L, it can release an unpleasant flavour to wine, easily detectable by consumers. As a result of this problem, wine producers began requiring strict quality control solutions from cork stopper manufacturers to ensure that stoppers are not contaminated. The present invention discloses a solution for this problem, based on the use of liquid solvents with adequate solubility for TCA.

Background of the Invention

Various solutions have been proposed to ensure that stoppers contain amounts of TCA below the detection threshold. One of the strategies has been the stopper-by-stopper analysis with rapid detection methods. However, this solution is time- consuming and has high costs, which limits its extensive use. Another strategy has been to subject cork to vacuum thermal desorption extraction processes. However, this option requires the use of sophisticated vacuum equipment. A third approach has been the use of heated vapours to produce the TCA solubilisation and its removal. However, it is known to any expert in this area, that these technologies have a very limited effectiveness, especially when applied to natural cork stoppers. It is also described in the literature the use of highly pressurized fluids, such as supercritical CO2, used to clean cork granulates. However, this solution cannot be applied to natural corks as it produces permanent deformation.

The technologies closest to the present invention are those that use heated vapours. W02004014436 describes a process with superheated water vapour able to reduce by 90% the concentration of TCA in granulate, but resulting in a smaller reduction for natural cork stoppers. W003041927 describes a similar method, but in this case, with a mixture of water vapour, ethanol vapour and air at 60° C, the method is able to reduce the TCA content up to 80%. W02010040949 describes a process wherein cork is subjected several times to rapid pressurization periods with water vapour followed by periods of vacuum decompression. Although the results seem to be good, the example presented is applicable to granulates of reduced granulometry, without indication of the degree of contamination, which leaves unknown its effectiveness in natural cork stoppers. In these technologies, the solubilisation of the TCA is done in gaseous phase by steam, which then also produces its removal.

The patent FR19990012003 describes the use of CO2 in the supercritical state applied to granulates of small pieces of cork. Although the extraction efficiency is excellent, the required high pressures produce the irreversible deformation of cork, so it can only be used in granulates of reduced size .

EP2396153 also describes a process based on supercritical fluids that can be applied to natural cork stoppers. It contains a separating device that prevents the stoppers from coming onto contact with each other during the compression and decompression cycles and that, allegedly, reduces the final deformation of the stoppers. A co-solvent can be added to the supercritical fluid to increase the solubility of the contaminants. The results on three corks indicated degrees of extraction greater than 90%. Stoppers showed an increase in dimensions of some millimetres after the process, indicating that they needed to be rectified to restore the initial measurements. The extraction depth is unknown as well as whether the rectification has again revealed any TCA inside the stopper.

ITBA20120015A1 describes a process wherein the corks are soaked in a liquid solution of 2% to 25% of an organic solvent in water, preferably ethanol, and then heated by microwaves (hyper frequencies) . According to the authors, the contact of the TCA with the liquid solubilizes the TCA, which is then removed when it is heated by the microwaves, passing to the gas phase and then being dragged by a flow of air. The extraction process is associated with microwave heating and not with the immersion phase in the liquid solution. Furthermore, the solution is not renewed in order to perform the extraction by the liquid medium. It is known that the immersion of contaminated stoppers in a 12% ethanolic solution at room temperature does not reduce the concentration of TCA in a contaminated stopper. Herve and his co-workers [1] demonstrated that repeated immersion or maceration of stoppers during 24 hours in consecutive solutions with that concentration did not reduce the concentration of releasable TCA. The TCA released to the solution was more or less constant; no matter how many times the stoppers were immersed in this solution, indicating that the degree of extraction was negligible. It is also known that heating with microwaves causes permanent deformations in cork, so its application to corks is questionable. No results were found on the degree of extraction of the ITBA20120015A1 patent, so its effectiveness cannot be compared .

Reference should also be made to the scientific article (reference [2]) where the authors describe the use of acetone to perform TCA extraction for analytical purposes from cork stoppers and from samples of wooden barrels. In that study, a comparison of acetone with pentane found that the extraction efficiency of acetone was superior. It was also found that if extraction is assisted by ultrasound, its efficiency is even greater.

Document W02009072916 was also found, which describes the use of liquid solvents to extract frideline from cork, which is a compound with potential commercial interest, in which cork is rich.

All cited documents referred here depict technologies or applications that are substantially different from the one described in this document. No document was found describing the use of liquid-phase solvents applied at atmospheric pressure to extract TCA or other contaminants from natural cork stoppers or granulates with the aim of producing a TCA- free product.

However, washing or leaching processes with liquid solvents applied to solid matrices are well known. Good examples are the preparation of a coffee drink or the extraction of sugar from beets. In both cases, a suitable solvent extracts compounds from a complex solid, to be used later. The penetration of the solvent into the solid matrix dissolves the solute, decreasing its concentration in the solid, passing it to the solvent. Another example is the Soxhlet extraction in which the solvent is distilled and reintroduced in the liquid phase over the solid matrix in a closed circuit. No evidence was found that any of these known technologies were industrially adapted to extract TCA from natural cork stoppers or other forms of cork.

In addition, from the documents mentioned, it is not evident that an organic solvent in a liquid state and at atmospheric pressure is able to penetrate into the cork, solubilizing the TCA and transporting it outside, thus reducing the concentration of TCA on the surface and inside the natural cork stoppers, as shown in the present invention.

Advantages of the Invention

The present invention has the following advantages:

• The equipment described is simple and easy to build;

• The equipment can be used to process an amount equal to or greater than 10.000 cork stoppers, or other pieces of cork, at once;

• If the organic solvent is acetone or ethanol, due to its low cost, this process can be applied with an economic advantage over other more sophisticated processes;

• The degree of extraction can achieve a reduction greater than 80 times, from 40 ng/L to less than 0,5 ng/L as shown in the given examples.

Summary of the Invention

The process and the equipment depicted in the present invention are based on the use of a liquid organic solvent that dissolves the TCA and removes it from the cork. The equipment used to extract the TCA consists of a tank where the stoppers are immersed; a filter and a circulation pump that form a closed circuit through which the solvent circulates. Ultrasound transducers are mounted on the tank walls to increase the extraction efficiency. The solvent circulates out of the tank, passes through the filter and is reintroduced back into the tank through the circulation pump. The extraction efficiency depends on the temperature of the solvent and the time of the process. Organic solvents suitable for TCA are acetone and ethanol. Other contaminants similar to TCA can also be removed as long as they solubilize well in the solvent used.

Brief description of the figures

These and other characteristics can be easily understood through the accompanying drawings, which should be considered as mere examples and not restrictive in any way, of the scope of the invention. In the drawings, and for illustrative purposes, the measurements of some of the elements may be exaggerated and not drawn to scale. The absolute dimensions and the relative dimensions do not correspond to the real relationships for implementing the invention .

Figure 1 describes an embodiment of the equipment for processing natural cork stoppers or other pieces of cork.

The figures show the elements and components of the equipment of the present invention:

1. Tank

2. Basket

3. Reservoir 4. Cover

5. Filter

6. Circulation pump

7. Heating resistors

8. Temperature meter and controller

9. Ultrasound transducers

10. Chimney

Detailed description of the invention

The present invention describes a process and the equipment for extracting contaminants from cork, namely 2,4,6- trichloroanisole (TCA) . The tests carried out demonstrate that it is effective for cleaning natural cork stoppers, that is, stoppers made by a single piece of cork. Of course, it will be even more effective for cleaning granules or cork discs due to their smaller dimensions.

Tests carried out with various organic solvents have shown that acetone and ethanol are effective in solubilizing TCA. These solvents easily penetrate the cork, showing a contact angle close to zero. It is expected that some cork waxes are also dissolved, on which the TCA may be deposited or adsorbed, contributing to the extraction process.

According to Charles Hansen in his 2007 book "Hansen Solubility Parameters- a User's Handbook", the solubility can be quantified by three parameters obtained experimentally: the dispersion solubility parameter, the polar solubility parameter and the hydrogen bonding solubility parameter. A good solvent for a given chemical compound is one that has the most similar solubility parameters. The proximity between the parameters of the solvent and the solute can be assessed by another parameter called the RED number. The lower this number, the better the solvent is. If this number is greater than 1, the solvent is considered to be unsuitable.

To apply this theory to TCA, it is necessary to know its solubility parameters. The same book contains a listing of parameters for many chemical compounds, including TCA. Based on these parameters, it is possible to confirm that acetone is a suitable solvent, having a RED number = 0,57. Ethanol is also a TCA solvent with a RED number of 0,75. Chlorinated solvents such as chloroform and dichloromethane are even better solvents, but because they are chlorinated, they can promote the later development of more TCA under possible microbial action. Other theories of solubility can be used in a similar way to find suitable solvents.

Since TCA may be in internal cavities of cork, the ultrasound-assisted solubilisation increases the penetration capacity of the solvent as well as its agitation at the microscopic level. Ultrasounds produce shock waves within the liquid that result in cavitation (production of microbubbles) that help the solubilisation of TCA and possibly its matrix, even in deep parts of the stopper. In addition, the use of ultrasound also avoids the need for a stirrer .

Acetone in low concentration is considered a non-toxic solvent, which is even present in small amounts in the human body. It quickly evaporates from corks after they are removed from the tank, leaving no trace or any significant smell. Both acetone and ethanol are easily available in large quantities and at an affordable price. Its greatest danger lies in the fact that these solvents are flammable, requiring special care in their handling as well as in the operation of machines and electrical devices in their proximity. The use of other suitable should also take these aspects into account .

After immersion in the solvent, the cork pieces can be centrifuged to recover some solvent and rinsed in water to reduce the amount of solvent in the cork. If necessary, they can then be air-dried or oven-dried. In the case of stoppers, if they have any increased roughness, they can be polished again in order to recover the initial dimensions.

The solvent, after contacting the cork, can be reused if its concentration in TCA is reduced. This can be achieved by passing the solvent through an appropriate filter. Several tests were carried out with absorbent materials and acetone contaminated with TCA, measuring the degree of reduction in the concentration of TCA after passing through the filter. In this regard, it was found that activated carbon gave good results. Thus, after the solvent has passed through this type of filter, it can be reintroduced into the tank where the cork is immersed. For this purpose, a circulation pump made of materials chemically compatible with the solvent is required. Activated carbon has a very affordable price and after saturation, it can be regenerated in an oven at high temperatures where the retained compounds are released.

An embodiment of the equipment is shown in figure 1. The tank (1) is filled with the liquid solvent at atmospheric pressure. A metal basket (2) loaded with stoppers is inserted into it. The solvent level is adjusted from the reservoir (3) . The tank (1) is closed with the cover (4) to limit the evaporation of the solvent. The small chimney (10) in the cover (4) ensures that the pressure in the tank (1) remains constant, releasing some solvent vapours. The solvent flows through the filter (5) via the circulation pump (6) . The tank (1) is heated by the resistive heaters (7) and its temperature is monitored and kept constant by the temperature meter and controller (8) . Ultrasound transducers (9) are used to promote TCA solubilisation and solvent agitation. At the end of the desired process time, the heating, ultrasound and circulation pump are switched off and the cork stoppers are removed, concluding the cycle.

All sealing materials and non-metallic elements must be chemically compatible with the solvent. For example, if the solvent is acetone, elastomers made of EPDM (ethylene propylene diene monomer) or Teflon can be used.

The extraction efficiency depends on the temperature of the solvent and the time of the process. As the examples demonstrate, excellent results were obtained in natural stoppers with acetone at a temperature between 45°C and 55°C, more precisely at a temperature of 50°C, or ethanol at a temperature between 60°C and 70°C, more precisely at a temperature of 65°C for 14 hours to 16 hours with the ultrasound transducers (9) connected for 50% of the time, in cycles of 30 seconds on and 30 seconds off. In an embodiment, the organic solvent is a 50% solution of the organic solvent in water.

The referred tests were carried out after hundreds of contaminated stoppers were processed, demonstrating that the solution and the filter were not saturated with TCA.

Examples

Example 1 Ten natural cork stoppers 44 mm x o24 mm with natural contamination were analysed by SPME-GC to determine their initial concentration in releasable TCA. Then, they were subjected to an extraction process for 4 hours in the equipment of the invention with acetone. The ultrasound transducers (9) were on for 50% of the time, in cycles of 30 seconds on and 30 seconds off. The temperature was 35°C. After the process, the stoppers were analysed again. The results obtained were as follows:

After 4 h at 35°C

Before

with acetone

(ng/L)

(ng/L)

1 1,1 <0,5

2 43, 8 1,4

3 1,2 2, 8

4 2,3 2.3

5 1,0 <0,5

6 6, 3 <0,5

7 5, 8 <0,5

8 48, 0 3.4

9 5,9 <0,5

10 5,7 <0,5

Average 12, 82 1, 1

'Assuming values '<0,5' as zero

Example 2

Ten natural cork stoppers 44 mm x o24 mm with natural contamination were analysed by SPME-GC to determine their initial concentration in releasable TCA. Then, they were subjected to an extraction process in the equipment of the invention with acetone for 15 to 17 hours, more precisely for 16 hours. The ultrasound transducers (9) were on for 50% of the time, in cycles of 30 seconds on and 30 seconds off. The temperature was 50°C. After the process, the stoppers were analysed again. The results obtained were as follows:

After 16 h at 50°C

Before

in acetone

(ng/L)

(ng/L)

1 1,4 <0,5

2 1.7 <0,5

3 1,4 <0,5

4 1,4 <0,5

5 2.7 <0,5

6 37, 6 <0,5

7 40, 6 <0,5

8 41, 8 <0,5

9 2,2 <0,5

10 12, 6 <0,5

Average 14,34 0

'Assuming values '<0,5' as zero

Example 3

Twenty 44 mm x o24 mm natural cork stoppers with natural contamination were analysed by SPME-GC to determine their initial concentration in releasable TCA. Then, they were subjected to an extraction process in the equipment of the invention with ethanol for 13 to 15 hours, more precisely for 14 hours. The ultrasound transducers (9) were on for 50% of the time, in cycles of 30 seconds on and 30 seconds off. The temperature was 65°C. After the process, the stoppers were analysed again. The results obtained were as follows:

After 14 h at 65°C After rectification

Before in ethanol of 1 mm

(ng/L)

(ng/L) (ng/L)

1 60, 0 <0,5 <0,5

2 43, 9 <0,5 <0,5

3 21, 6 1, 6 <0,5 4 12,4 <0,5 1,4

5 10,8 1,5 <0,5

6 7,1 <0,5 <0,5

7 6,5 <0,5 <0,5

8 6,2 <0, 5 <0,5

9 5,9 <0,5 <0,5

10 4,5 2,8 <0,5

11 3,7 <0,5 <0,5

12 3,4 <0,5 <0,5

13 3,2 <0,5 <0,5

14 3,1 <0,5 <0,5

15 3,1 <0,5 <0,5

16 3,0 <0,5 <0,5

17 2,8 <0,5 <0,5

18 2,5 <0,5 <0,5

19 2,3 <0,5 <0,5

20 2,1 <0,5 <0,5

Average 10,41 0,29 ^* 0, 07

*Assuming values ' <0 , 5 ' as zero

These results demonstrate that ethanol at 65°C is also effective in extracting TCA resulting in almost all stoppers testing below 0,5 ng/L even after 1 mm rectification.

Example 4

Twenty 44 mm x o24 mm natural cork stoppers with natural contamination were analysed by SPME-GC to determine their initial concentration in releasable TCA. Then, they were subjected to an extraction process in the equipment of the invention with a 50% solution of acetone in water for 13 to 15 hours, more precisely for 14 hours. The ultrasound transducers (9) were on for 50% of the time, in cycles of 30 seconds on and 30 seconds off. The temperature was 50°C. After the process, the stoppers were analysed again. The results obtained were as follows: After 14 h at 50°C After rectification

Before

in 50% acetone of 1 mm

(ng/L)

(ng/L) (ng/L)

1 49, 1 2,1 17, 1

2 30, 6 <0,5 <0,5

3 22, 9 <0,5 <0,5

4 15, 0 <0,5 <0,5

5 10.7 <0,5 1,1

6 7.9 <0,5 <0,5

7 6, 8 <0,5 <0,5

8 5.1 <0,5 <0,5

9 5, 0 <0,5 <0,5

10 4, 6 <0,5 <0,5

11 3.9 <0,5 <0,5

12 3,4 <0,5 <0,5

13 3,4 <0,5 <0,5

14 3,3 <0,5 <0,5

15 3.3 <0,5 <0,5

16 3.1 <0,5 <0,5

17 2.7 <0,5 <0,5

18 2,7 <0,5 <0,5

19 2.4 <0,5 <0,5

20 2,3 <0,5 <0,5

Average 9,41 0, 10 ^* 0, 91 ^*

^Assuming values '<0.5' as zero

The results demonstrate that 50% acetone is also effective in extracting TCA resulting in almost all stoppers going below 0,5 ng/L, even after 1 mm rectification. Only one stopper still revealed some significant amount of TCA after rectification .

References

[1] Herve, E.; Price, S.; Burns, G.; Weber, P. Chemical Analysis of TCA As a Quality Control Tool for Natural Corks, 2000, http://208.201.226.44/ current-research/CorkTaint/ ETS%20CQC-SPME.pdf, consultado em 6/6/2019. [2] Cacho, J. I.; Nicolas, J.; Vinas, P.; Campillo, N.; Hernandez-Cdrdoba, M. Control of halophenol and haloanisole concentration in wine cellar environments, wines, corks and wood staves using gas chromatography with mass spectrometry. Aust. J. Grape Wine Res. 2016, 22, 391-398.