EP3573798A1 - Process for the extraction of volatile contaminants from cork by thermal desorption - Google Patents
Process for the extraction of volatile contaminants from cork by thermal desorptionInfo
- Publication number
- EP3573798A1 EP3573798A1 EP18709071.7A EP18709071A EP3573798A1 EP 3573798 A1 EP3573798 A1 EP 3573798A1 EP 18709071 A EP18709071 A EP 18709071A EP 3573798 A1 EP3573798 A1 EP 3573798A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- cork
- mbar
- temperature
- pressure
- tca
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B67—OPENING, CLOSING OR CLEANING BOTTLES, JARS OR SIMILAR CONTAINERS; LIQUID HANDLING
- B67B—APPLYING CLOSURE MEMBERS TO BOTTLES JARS, OR SIMILAR CONTAINERS; OPENING CLOSED CONTAINERS
- B67B1/00—Closing bottles, jars or similar containers by applying stoppers
- B67B1/03—Pretreatment of stoppers, e.g. cleaning, steaming, heating, impregnating or coating; Applying resilient rings to stoppers
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
- B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
- B27K7/00—Chemical or physical treatment of cork
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
- B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
- B27K5/00—Treating of wood not provided for in groups B27K1/00, B27K3/00
- B27K5/001—Heating
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
- B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
- B27K5/00—Treating of wood not provided for in groups B27K1/00, B27K3/00
- B27K5/007—Treating of wood not provided for in groups B27K1/00, B27K3/00 using pressure
- B27K5/0075—Vacuum
Definitions
- the present invention relates to a process for the extraction of volatile contaminants from cork by thermal desorption, i.e., by supplying thermal energy to break the bond between the volatile contaminant and cork.
- This process has its application namely in cork pieces, more specifically natural cork stoppers and granulates.
- This process is able of removing volatile contaminants, namely 2,4,6-trichloroanisole, commonly referred as TCA, as well as other contaminants with similar properties.
- the removal is based on a temperature stimulated desorption process in which the bond between the volatile contaminant and cork is broken followed by its release from the surface of the cork cells into the gas phase and subsequently removed by vacuum pumps.
- cork is heated to a well-determined temperature range to provide sufficient energy to the contaminant molecules to break their bond with cork.
- This process is carried out under vacuum for a specific time length in order to allow desorption and removal of contaminants even if present in the innermost cells of each piece of cork.
- this process is applied to whole natural corks, it allows to simultaneously decontaminate large quantities of whole natural corks, typically ranging 10.000 to 50.000 per day, per equipment. In this way, the present process becomes an economically competitive alternative to individual cork stopper analysis.
- Cork is a cellular material whose cells are filled with air.
- the volume of air inside the cells occupies 70% to 80% of the total volume. Being a natural material, it is expected that under certain conditions of temperature and humidity it can house several microorganisms.
- metabolites having intense aromas are produced, which may remain in the cork even after their disinfection.
- These metabolites are the main source of cork contaminants.
- Cork contaminants may be present in cork at room temperature in the gas phase inside the inner cell volume, in the solid phase in the form of micro or nanocrystals and adsorbed on the inner surface of the cork cells. The exposure of cork to vacuum is able to remove contaminants in the gas phase.
- any solid or liquid contaminant will change phase to vapour and may also be removed by vacuum. This process is often incorrectly mistaken as thermal desorption, but in reality it is only a thermal evaporation, eventually assisted by vacuum.
- the bonds between adsorbed molecules and the surface may be stronger than the bonds between similar molecules when they are in the solid or liquid phase. Therefore, in order to describe the mechanism of thermal desorption of contaminants in cork, it is necessary to know which is binding energy to the surface in order to heat the system to a temperature which provides sufficient energy to break this bond at a rate high enough to produce desorption of the all contaminants within a reasonable time length.
- the process of thermal desorption is not the same as a process of phase change.
- Different compounds may be adsorbed on surfaces without coexisting in the solid phase or in the liquid phase.
- a surface has about 10 15 adsorption sites per cm 2 . If only 10% of these adsorption sites receive one contaminant molecule, then only 1 cm 2 can adsorb as many molecules as the equivalent of 35 ng of TCA.
- a cork stopper for example, has a total area in the order of 5 m 2 . Therefore, it is understandable that one cork can be contaminated with TCA without having two molecules of TCA together that would enable the condensation or crystallization process.
- the phase change may occur either by changing the temperature, by changing the pressure, or by a combined effect of changing temperature and pressure.
- the phase change is achieved only by decreasing the pressure.
- the decrease in pressure alone has no effect on desorption, only has the surface temperature, or also irradiation with electrons or other forms of radiation.
- Pressure is only related to the adsorption process, or to reabsorption, so it is important to be kept low in order to control this effect.
- TCA contaminant in cork are in the range of 10 to 200 ng per stopper, it is very questionable that it can exist in the solid phase in the form of tiny crystals in the interior.
- the rate of sublimation of a solid contaminant at ambient temperature can be calculated based on its vapour pressure, considering that all released molecules do not return to the condensed phase, for example by being adsorbed on another part of the material.
- the vapour pressure is 1,5 Pa which results in a sublimation rate of 5,6 g/m 2 /s or 5,6 pg/mm 2 /s.
- TCA is in the liquid state and its evaporation rate is 600 times higher than the sublimation rate at 20°C.
- a stopper has a contamination in the range of 10 to 200 ng, even if at some point the TCA exists in the form of micro or nanocrystals, in a very short time it will sublimate at room temperature or evaporate if heated above the triple point. But, after its sublimation, TCA molecules will remain in the cork, spread on the cells surface in the adsorbed phase. A surface of 1/50.000 of the total inner surface of a stopper with only 10% of the adsorption sites filled is enough to adsorb 35 ng of TCA. This adsorption is thermodynamically stable since it is known that a contaminated stopper remains so for an indeterminate period of time.
- Cork stoppers are the main product of the cork industry. Since cork stoppers are a natural product and a closure with suitable permeability for bottling wine, it is the material of choice for most wine producers and consumers.
- FR2884750 discloses a device for decontamination of cork stoppers in which the stoppers are introduced into a rotary drum inside a vacuum chamber. While referring to the use of heaters inside the vacuum chamber, it only describes preheating at temperatures of 40 °C or 50 °C. To control the decontamination process, it describes the use of a mass spectrometer to monitor the concentration of TCA in the gas phase. When the TCA intensity, as indicated by the mass spectrometer, reaches a value considered sufficiently low, then the decontamination process can be ended.
- EP2639025 (Bl) discloses not only an apparatus but also a process for the el imination of contaminants. According to this document, after a recrystallization stage of the haloanisols, the cork is reheated in a vacuum so that the desorbed contaminants, are removed by the vacuum pumps. However, unlike the process in the present patent application, the process described in EP2639025 (Bl) requires a recrystallization stage which precedes the desorption stage, and which supposedly facilitates subsequent contaminants removal. Although this document refers to a wide temperature range, it recommends a temperature between 100°C and 135°C and links the treatment temperature with the contaminant boiling temperature as a function of the pressure.
- the present invention disclosures a process for the extraction of volatile contaminants from cork through vacuum desorption, suitable to reduce significantly, or even to eliminate, the presence of contaminants.
- the process of the present invention results from the concerted combination of 3 variables: temperature, pressure and time. These variables are combined in well defined intervals to assure the effective reduction of the amount of contaminants in cork, to below the sensory detection limit, and close to, or below, the current quantification limit of the SPME GC / MS technique.
- TCA its removal occurs at a temperature above 120°C.
- the heated cork surface provides to TCA molecules the required energy to break their bond to the cork surface at a rate, which allows the release of all TCA molecules rapidly.
- the temperature is adjusted in proportion to their desorption energy.
- the process time is typically between 6 and 24 hours. With this time, it is possible to generate a pressure of at least 1 mbar within all cork cells and desorb the majority of the contaminant amount in cork.
- the pressure of 1 mbar corresponds to approximately 1% of the TCA vapour pressure at 160°C.
- the process time is adjusted by the ratio of the square of the smallest distance to the innermost point of the piece of cork.
- the external pressure must be of the order of 0,1 mbar or less in order to achieve a pressure less than or equal to 1 mbar within the cork after 24 hours for an ideal cork stopper without defects (lenticular channels), with a permeability close to the known average permeability of cork.
- the typical combination recommended for the three variables is a temperature from 120°C to 190°C, for 6 to 24 hours and a chamber pressure lower than 0,1 mbar.
- the heating technique is not relevant as long as it does not damage the cork pieces. Heating may be produced by radiation using an infrared lamp or by conduction through an oven with holes of dimensions close to the diameter of the stopper. The uniformity of the heating process must be ensured, as well as sufficient space to allow the vacuum to reach on all sides of the stopper.
- One embodiment is achieved by placing the stoppers in a rotating drum with holes or openings and horizontal axis, which rotates slowly inside a cylindrical vacuum chamber, with radiative heating inside the drum. Corks will roll over one to another while being heated and, at the same time, exposed to the vacuum produced by a two-stage rotary pump.
- a i m 3 vacuum chamber can simultaneously treat 10.000 corks or more, which makes the process described in this invention an economically viable solution for processing all stoppers without pre-selection, i.e., contaminated stoppers and uncontaminated stoppers.
- the process is able of reducing the concentration of contaminants in cork stoppers, namely TCA, by an average value between 10 and 100 times if it is applied with a temperature of 180 °C for 24 hours and a pressure in the chamber in the order of 0,1 mbar.
- the process is effective in extracting not only the releasable fraction of the contaminant in the hydro-alcoholic solution but also the total contaminant spread within the cork volume even if it is well inside cork. - In the case of stoppers, it is an economically competitive process compared to the individual stopper analysis because it is capable of processing all stoppers without the need for pre-selection.
- this process can advantageously replace the stage of drying cork in an oven.
- Figure 1 shows a graph with the experimental result of the TCA desorption rate during heating of contaminated cork in vacuum with a heating rate of 0,5 K per minute.
- the TCA desorption rate was measured by a mass spectrometer, through the ion of mass 195 dalton, which corresponds to the most abundant ionization fragment.
- the desorption temperature peak was close to 160 °C.
- the decrease of the desorption rate which is visible after the desorption peak, occurs due to the decrease of the amount of TCA in the cork throughout the heating process. If there is less TCA to desorb, the desorption rate is, of course, lower.
- Zone Zl represents the range of temperatures at which release is very slow
- zone Z2 represents the temperature range suitable for desorption of TCA
- zone Z3 represents the interval at which the change in the mechanical properties of cork becomes very relevant.
- FIG. 2 shows the TCA desorption time constant as a function of temperature. It can be seen that only for temperatures near or above the maximum desorption temperature (160 °C) the time constant is low enough so the desorption process can occur in a time length of practical use.
- the present invention describes a process for removing volatile contaminants from cork through the vacuum desorption mechanism in a well-defined temperature range.
- it is necessary to stress the difference between condensation and adsorption and between the sublimation and vaporization phase changes and the desorption process.
- condensation similar molecules are attached to each other to form a liquid drop or a crystal.
- adsorption molecules are bound directly to a surface. If the concentration is too low (as is the case), the adsorbed molecules do not interact with each other but only with the surface (Langmuir adsorption).
- Adsorption of water in a vacuum system is a good example to illustrate the difference between adsorption on surfaces and their condensation.
- vacuum is generated in a high vacuum system (pressures between 10 "3 mbar and 10 "8 mbar) the composition of the residual gas is dominated by water vapour.
- this pressure range is well below the vapour pressure of water at ambient temperature, which is approximately 20 mbar. Therefore, this pressure range is incompatible with the presence of water in the liquid or even in the solid state (unless the water is at temperatures close to -200°C).
- the water released into the gaseous phase comes mainly from the metal surfaces of the entire vacuum system where the water molecules are adsorbed. Desorption of water from these materials at ambient temperature is very slow.
- the determination of the desorption temperature of a contaminant may be carried out by an experiment called Temperature Programmed Desorption (TPD).
- TPD Temperature Programmed Desorption
- the previously contaminated surface is heated under vacuum (10 "8 to 10 “5 mbar).
- a mass spectrometer measures the relative concentration of the desorbed gas now in the gas phase. This amount of gas is the balance between the gas being released from the surface and that which is being removed by the vacuum pump that run continuously.
- P. A. Redhead demonstrated how to calculate the desorption energy based on the temperature desorption peak.
- the obtained value is 1,39 eV or 134 kJ / mol. Since cork has a very rich chemical composition, it is possible that this energy may have some deviations, related to the type of cork or other variables, namely associated with the cleaning processes.
- This calculation of the desorption energy assumes that the desorption process is of first order, meaning that TCA molecules are desorbed without dissociation. This is compatible with the clear similarity between the fragmentation pattern of the desorption mass spectrum and the spectrum obtained directly from TCA in the gas phase. In order to establish the temperature range to desorb other typical cork contaminants, the same technique should be used in order to determine the desorption peak.
- the desorption energy obtained for the TCA is more than twice the enthalpy of vaporization which is 62 kJ/mol. This value reveals that TCA molecules are more strongly bound to cork than to other TCA molecules. Therefore, the energy required to evaporate the TCA is not sufficient to produce its desorption from cork so this invention should not be confused with processes of thermal evaporation or evaporation assisted by vacuum.
- the binding energy is quantized, that is, desorption cannot occur if the energy of the contaminant is not supplied to the molecules of the contaminant, no matter how long we wait.
- the energy of molecules at a given temperature is not singular but follows a Maxwell-Boltzmann distribution. Therefore, there are always some molecules with higher energy. But for temperatures below the maximum desorption rate temperature, its percentage is so low that the desorption process is extremely slow.
- R des The rate of desorption, which we will denote by R des , describes the amount of molecules desorbed from a surface per unit time and is equal to the change in the number of molecules that remain on the surface. As is known, the desorption rate is described by: where:
- This time constant ⁇ describes the time for the adsorbed concentration decrease to 37% and therefore provides a way to evaluate the desorption rate.
- Figure 2 graphically shows the time constant as a function of temperature, using the energy calculated for the TCA.
- Heating cork at lower temperatures only facilitates sublimation of any contaminant that eventually may exist in the solid phase, or its boiling if already liquefied, for later removal by vacuum pumps. However, it produces only a very small effect on adsorbed molecules on the cork, because the energy thermally supplied is not enough to break the bond, which in the case of TCA is « 1,39 eV.
- the contaminant being the TCA should exist predominantly in the adsorbed form, whereby the treatment at temperatures below 120°C will never be able to fully remove the TCA in a useful time.
- the evolution of the temperature inside cork when heated by the outer surface can be easily measured or even calculated based on the thermal diffusivity of cork, which is known.
- the experimental value was 14 minutes for the inner temperature to reach 160°C when the outside was heated to 180 °C. This value is very close to what is theoretically obtained from the Fourier law for heat transfer. Therefore, it does not take much time to establish the thermal equilibrium. However, the stabilization time for the pressure is much longer.
- Cork can be described by a 3 dimensional matrix of small volumes connected by channels with diameters of the order of 40 nm.
- a cork stopper may have 1 billion of these volumes or cells filled with air at atmospheric pressure.
- contamination might be in any position of the cork piece, probably spread by many cells.
- the flow conductance for each channel between cells can be estimated from permeation measurements.
- the mean volume of each cell is known. Based on these two values it is possible to simulate the gas flow from inner cells to boundary, when vacuum is generated outside the stopper.
- Figure 3 represents the result of a simulation of this type, which describes the evolution of the pressure in the innermost cell of a stopper 24 mm in diameter and 45 mm in length. In this simulation an ideal cork without defects having a permeability of 1,85 cm 3 (NPT)/(cm.d.atm) was considered and a cell volume of 2x l0 "8 cm 3 .
- the pressure in the innermost cell of the stopper takes about 16 hours to reach 1 mbar.
- the presence of defects such as the lenticular channels can speed up pumping, because such defects provide higher conductance connections between several points in the cork.
- the time for pumping will be longer.
- the permeability of the uncompressed dry cork can vary greatly, leading one to expect that in some stoppers the pumping time may be even greater.
- the interior of the cork will be ° ⁇ tne a i r f' ow ' which causes a relative enrichment of the TCA inside cork, as well as other volatiles with a high molar mass.
- the flow rate increases with V , which produces an increase by a factor of 1,25 with respect to the flow rate at 20 °C.
- the TCA pressure takes about twice as long to descend the same ratio as the air, that is about 32 h to reach 1 mbar at the innermost point of a perfect stopper (without lenticular channels) having a permeability equal to the average value of the permeability of the non-compressed cork.
- TCA vapour pressure of TCA at 160°C is approximately 100 mbar. Therefore, at a pressure of 1 mbar, there can be no more than 1% of the initial amount of TCA from micro or nanocrystals. This pressure is only reached if the outside pressure is much less than 1 mbar and after several hours of pumping.
- the cork When the cork is subjected to vacuum, some deformation may occur due to expansion of the gas therein or due to the release of some residual stresses on the cell walls. This effect can be minimized if the vacuum generation is performed in steps. In particular, but not exclusively, during the 1 st stage the pressure is maintained at 750 mbar for 20 minutes, in the second step the pressure decreases to 500 mbar during the same time, then to 250 mbar for 20 minutes and finally the pumping is performed at the pump pressure limit up to the end of the planned processing time.
- Exposure of cork to high temperatures for a long time may reduce some of the mechanical properties of cork, such as torsion resistance or the ability to recover after compression. This effect can be minimized if the time at which the cork piece is at the desorption temperature (approximately 120°C to 190°C for TCA) is not the total treatment time.
- the temperature may be programmed to be, namely, 120°C for 80% of the treatment time in order to pump the interior of the cork.
- the temperature is then raised above the maximum desorption rate (160°C for TCA) for an hour or more. In this way, the contaminant is desorbed and removed and the temperature impact on the cork structure is minimized.
- a mixture of air and water vapour can be introduced in order to restore the moisture content of the cork and recover the mechanical properties.
- Bleaching agents such as hydrogen peroxide, or active reagents to degrade the remaining contaminants, for example by means of advanced oxidation processes, may also be added.
- the present invention describes a process for extracting volatile contaminants which takes into account a concerted combination of the three variables: temperature, time and pressure outside the stopper. Temperature is the most critical variable since has to be close to the desorption peak, so the process may be viable and find an industrial application. For example, for the extraction of TCA, the temperature should reach values between 120°C and 190°C. The total time length should be between 6 h and 24 h so that it is possible to generate a pressure of the order of 1 mbar inside high quality corks (having little defects). Finally, the outside pressure should be less than 0,1 mbar so that it is possible to reach the pressure of approximately 1 mbar inside the stopper.
- the present invention has been validated with artificially contaminated samples and with naturally contaminated samples, as described in the following examples:
- Detection limit of TCA is 0,5 ng/L in this labora tory Second example
- the stoppers were then analysed all together by SPME GC/MS in a reference laboratory, which measured the concentration of TCA released after maceration of 24 h in hydro-alcoholic solution.
- the result of the releasable TCA was 0,8 ng/L for all 25 stoppers, well below the human detection threshold.
- the corks were then grounded and the total TCA was analysed, giving a value of 4,0 ng/L corresponding to a mean value of 0,2 ng/stopper.
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- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Forests & Forestry (AREA)
- Mechanical Engineering (AREA)
- Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
- Processing Of Solid Wastes (AREA)
- Chemical And Physical Treatments For Wood And The Like (AREA)
Abstract
Description
Claims
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
PT10987817A PT109878B (en) | 2017-01-26 | 2017-01-26 | 2,4,6-TRICHLOROANISOL (TCA) EXTRACTION PROCESS FROM COMPLETE NATURAL CORK STOPPERS |
PCT/IB2018/050259 WO2018138599A1 (en) | 2017-01-26 | 2018-01-16 | Process for the extraction of volatile contaminants from cork by thermal desorption |
Publications (1)
Publication Number | Publication Date |
---|---|
EP3573798A1 true EP3573798A1 (en) | 2019-12-04 |
Family
ID=61569297
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP18709071.7A Pending EP3573798A1 (en) | 2017-01-26 | 2018-01-16 | Process for the extraction of volatile contaminants from cork by thermal desorption |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP3573798A1 (en) |
PT (1) | PT109878B (en) |
WO (1) | WO2018138599A1 (en) |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CH666886A5 (en) * | 1986-04-28 | 1988-08-31 | Raoul Guy Renz | PROCESS FOR TREATING CORK STOPPERS. |
FR2884750A1 (en) | 2005-04-25 | 2006-10-27 | Jean Paul Obrecht | Cork stopper decontamination device, has vacuum tank in which stoppers are placed and maintained under vacuum using vacuum pumps that are suitable to obtain high pumping speed, where stoppers are put in rotation inside tank |
ES2423255B1 (en) | 2012-03-13 | 2014-10-01 | Universidad De Salamanca | Procedure for the elimination of haloanisols and halophenols present in the cork and installation to carry out said elimination |
-
2017
- 2017-01-26 PT PT10987817A patent/PT109878B/en active IP Right Grant
-
2018
- 2018-01-16 WO PCT/IB2018/050259 patent/WO2018138599A1/en unknown
- 2018-01-16 EP EP18709071.7A patent/EP3573798A1/en active Pending
Also Published As
Publication number | Publication date |
---|---|
PT109878A (en) | 2018-07-26 |
WO2018138599A1 (en) | 2018-08-02 |
PT109878B (en) | 2021-10-28 |
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