WO2013041750A1 - Method and device for improving material transfer in low-temperature processes using high-intensity ultrasound - Google Patents

Abstract

The present invention relates to a method for accelerating and improving the transfer of at least one solvent, occluded in a solid, semi-solid or liquid matrix, to a gaseous medium at an absolute pressure equal to or greater than 0.5 atm and at a temperature equal to or less than 15ºC, which is characterized in that it comprises the application of a high-intensity ultrasonic field, equal to or greater than 150 dB. A further subject matter of the invention is the device for implementing said method and the use thereof in the agrifoodstuff, chemical, cosmetic and/or pharmaceutical field.

Description

 PROCEDURE AND DEVICE FOR IMPROVING THE TRANSFER OF MATTER IN LOW TEMPERATURE PROCESSES THROUGH THE USE OF HIGH INTENSITY ULTRASOUNDS Technical sector

The present invention relates to a method and device based on the application of ultrasound of high intensity (equal to or greater than 150 dB) to accelerate processes of transfer of matter that are carried out at low temperature (equal to or less than 15 ° C) between a solid, semi-solid matrix (such as high concentration suspensions, purees, pastes, etc.) or liquid and a gaseous medium (such as air, CO ₂ , N ₂ , etc.). Due to the low temperature used, the transfer of matter is done without affecting the quality properties of the matrix. The process can be carried out at absolute pressures equal to or greater than 0.5 atm, that is, close to atmospheric or higher. This procedure has applications in the agri-food, chemical, cosmetic and pharmaceutical fields.

State of the art

Matter transfer processes between solid, semi-solid or liquid matrices and gases are common at the industrial level in the agri-food, chemical, cosmetic and pharmaceutical fields. Thus, the processes of dehydration of agri-food products or residues (EP1821054; WO2005092109) or the elimination of organic solvents from chemical, cosmetic or pharmaceutical products (US5630911; EP0723127; JP1245804) can be cited. In all these processes, there is a high concern in the literature to accelerate the transfer of matter and thus increase energy efficiency and production capacity, so that the process is accelerated and reduced. In addition, in some cases it is very difficult to eliminate the molecules that are most strongly retained in the matrix, so that substances are never free of traces of said molecules. The transfer rate of a solvent occluded in a matrix to a gas can be increased by increasing the matrix temperature, either by heating directly or by application of technologies with high thermal capacity, such as infrared radiation (US3883958; WO2006020749) and microwaves (GB2343502B; US2008179318). The increase in the temperature of the matrix entails a degradation of the quality properties, so it is necessary to find other alternatives to improve the transfer of matter without inducing a degradation of the quality properties.

In the processes of transfer of matter in which it is tried to avoid the degradation of the quality properties of the matrix, the use of low temperatures (equal or inferior to 15 ° C) is an alternative of great interest. Due to the low temperature used, the matter transfer process occurs without practically affecting the quality properties of the matrix (WO2006068499). In these cases, the rate of transfer of matter is very low, and should not be increased by increasing the temperature of the product (US3883958) if you want to preserve its quality properties. The processes of transfer of matter at low temperature can be accelerated by working at pressures below atmospheric (GB2343502; US2008179318). Thus, lyophilization processes of agri-food, chemical, cosmetic and pharmaceutical products are common (US3648379, US4590687). The main problems of the processes of transfer of matter carried out under vacuum are the high costs of the installation and that it is difficult to work in continuous (US3883958), so that it is normally operated in batch (loads). In this context, the application of power ultrasound can be enormously interesting because ultrasound in gaseous media produces mechanical effects that improve the transfer of matter and produce a low thermal effect. In addition, it is not necessary to lower the pressure of the gaseous medium. It is necessary to indicate that in gaseous media the transmission of acoustic energy is very difficult due to the large difference in impedances between the ultrasonic emitting systems and the gases and the high sound absorption of the latter. Therefore, to obtain an efficient transmission of energy and produce high intensity acoustic fields it is necessary to achieve a good impedance adaptation between the emitter and the gas, large amplitudes of vibration and a high concentration of energy. In addition, for industrial applications where large volumes need to be treated, it is necessary that the application system has high power capacity and an extensive radiant surface.

 So far, the application of power ultrasound in gaseous media constitutes a potential area that has not been sufficiently exploited. This is probably due to problems related to the complexity of the basic mechanisms involved and the difficulties in the efficient generation of high intensity ultrasound under these conditions.

 The permanent effects produced in the medium treated with high intensity ultrasonic waves are mainly due to a series of mechanisms, such as: radiation pressure, acoustic currents, agitation, instability at the interfaces, diffusion, etc., which are linked to the non-linear phenomena produced by ultrasonic waves of great amplitude. Some of these phenomena and mechanisms are briefly described below:

 1. Radiation pressure. When a high intensity ultrasonic wave propagates in a medium in the presence of obstacles, continuous radiation forces that act on these obstacles and give rise to what is known as radiation pressure become apparent. The radiation pressure is linked to any wave process and has its origin in the change of momentum experienced by the wave when acting on the obstacle. These forces are weak for waves of infinitesimal amplitude, and intense for acoustic waves of high power (macrosonids) giving rise to drag and interaction processes;

2. Acoustic currents. As a consequence of the effects of acoustic absorption on high intensity ultrasonic waves radiation forces are generated that they induce movements of the irradiated fluid causing transfer of matter and heat;

 3. Instability at the interfaces. High intensity ultrasound produces pressure variations at the solid-gas or liquid-gas interfaces that can influence the evaporation / sublimation rate (depending on the temperature) of the solvent molecules retained in the matrix. During the negative phase of the pressure cycle, the partial pressure of the solvent on the surface decreases and therefore the loss from the matrix surface is accelerated. On the other hand, high intensity acoustic energy also causes oscillating and microcurrent velocities at the interface that can contribute to the reduction of the thickness of the diffusion boundary layer, and therefore, reduce the external resistance to matter transfer and increase the matter transfer coefficient. The effects of ultrasound on the interfaces can also influence the internal resistance to the transport of matter when they affect the intercellular spaces inside the particle. These phenomena will be more intense in those materials with a wide network of intercellular spaces such as solid matrices of high porosity;

 4. Structural diffusion: When the ultrasonic energy crosses the solid, semi-solid or liquid matrix, it causes rapid series of contractions and alternative expansions. The process could be assimilated to what happens when a sponge squeezes and relaxes, which is why it is usually referred to as the "sponge effect." These alternating stresses facilitate the movement and elimination of solvents through microscopic channels created by the propagation of the wave, increasing the diffusion coefficients.

In this way, the mechanical effects produced by ultrasound can induce an improvement (US20100199510; WO2009102679; US20090007931) in the phenomena of matter transfer, which entails the corresponding acceleration of the process without affecting the quality of the product and without the need to perform empty. This makes without Decrease product quality, installation costs are reduced and continuous processes are feasible.

 No background has been found in the existing patent literature that contemplates the application of high intensity ultrasonic waves in processes of matter transfer at low temperature and at near atmospheric or higher pressures. The only method currently published in which high intensity ultrasound is used to improve the processes of transfer of matter at low temperature refers to the improvement of the nucleation process during vacuum lyophilization (WO2004090446). This invention, however, has different objectives than those set forth in the process proposed herein, since it refers to the improvement of the formation of ice crystals by the ultrasonic vibration generated by a transducer in direct contact with the particles in the freezing process In addition, it is necessary to indicate that in this process the application of ultrasound is performed in a vacuum and by direct contact, so that the effects of ultrasound on the processes of transfer of matter in the gaseous medium are non-existent, because the waves Acoustics need a material medium for transmission.

 Based on the foregoing, in the process of the present invention it is proposed to apply ultrasound of high intensity to accelerate and improve the efficiency of processes of transfer of matter at low temperature in gaseous media, by taking advantage of the effects that ultrasound produces both at the interfaces as in the structure of the matrix. One of the main disadvantages in the processes of transfer of matter that are carried out at low temperature is the slowness of the kinetics of the process, which cannot be improved with technologies that lead to an increase in temperature if you want to preserve quality properties of the matrix.

As just indicated, the application of high intensity ultrasound produces both an increase in solvent diffusion due to structural effects that occur within the matrix, as a decrease in the boundary layer, which leads to an increase in the external coefficient of matter transfer. The increase in the transfer coefficients of matter occurs with a low thermal effect, so that the efficient application of high intensity ultrasound translates into a decrease in processing time without increasing the temperature of the matrix. Description of the invention

A first object of the invention is a process for accelerating and improving the transfer of matter from at least one solvent occluded in a solid, semi-solid or liquid matrix to a gaseous medium (such as air, CO ₂ , N ₂ , etc.) to a pressure close to atmospheric or higher (equal to or greater than 0.5 atm) and at a temperature equal to or less than 15 ° C, by applying a high intensity ultrasonic field (equal to or greater than 150 dB).

 Thus, the transfer of matter occurs as a result of the difference in solvent leakage (preferably water and organic solvents) in the matrix and in the gas. This transfer of matter is accelerated by the mechanical phenomena produced by the efficient application of high intensity ultrasonic waves both in the structure of the matrix and at the interfaces, for which an acoustic field with an intensity equal to or greater than 150 is required. dB These phenomena can lead to a reduction in processing times of up to 70-80%. Due to the low temperature used, the quality properties of the matrix are not affected.

In particular, the application of the ultrasonic field can be carried out by air and without the need to modify the pressure of the gaseous medium. Preferably, this application of the ultrasonic field can be carried out from selected systems so that they have a good adaptation of impedance with the gas, large amplitudes of vibration (preferably, equal to or greater than 10 μπι), large capacity of power (preferably, equal or greater than 50 W), a large radiant surface (preferably, equal to or greater than 750 cm ² ), as well as a capacity to generate an acoustic field with a high concentration of energy (preferably, equal to or greater than 0.1 W / cm ² ) .

 A further object of the invention is a device for carrying out a method as previously described, characterized in that it comprises a cylindrical or vibrating plate radiating element integrated in a chamber to contain the solid or semi-solid matrix, as well as a system for circulating a gas flow around the matrix.

 This device may additionally comprise an electronic excitation system of at least one piezoelectric transduction element, wherein said electronic system can in turn comprise a resonant frequency control and monitoring system.

 Likewise, the use of the process for the elimination of a solvent (water or organic solvent) retained in a solid, semi-solid matrix (such as high concentration suspensions, purees, pastes ...) or liquid of interest in fields is also object of the invention. , among others, such as agri-food, chemical, cosmetic or pharmaceutical.

 Although in any case the temperature at which the procedure is carried out is equal to or lower than 15 ° C, this temperature may be above the freezing point of the organic compound, or it may be below the point of freezing of said organic compound. In this way, the elimination of the organic compound in one case or another is carried out by different physical processes (evaporation versus sublimation).

Brief description of the figures

 Figure 1 shows a scheme

Ultrasonic vibrating cylinder.

 Figure 2 shows a scheme

Ultrasonic vibrating plate. Figure 3 shows kinetics of water removal from apple cubes (10 mm side). Air (RH = 7%) at -13 ° C and 2 m / s and absolute pressure 1 atm.

 Figure 4 shows kinetics of ethanol removal from apple cubes (10 mm side). Air (RH = 7%) at -13 ° C and 2 m / s and absolute pressure 1 atm.

List of references:

 1. Gas duct;

 2. Low temperature gas (equal to or less than 15 ° C);

 3. Matrix;

 4. Cylindrical radiator;

 5. Mechanical amplifier;

 6. Piezoelectric power or transduction element;

7. Electronic system for generating, controlling and adapting the electrical signal of the piezoelectric element excitation;

 8. Computer;

 9. Coupling material;

 10. Continuous or perforated surface for product placement and conduction;

 11. Vibrating plate radiator.

Detailed description of the invention

 Two particular ways of carrying out the invention are described in detail below. This description is carried out in reference to the figures accompanying the description, by way of illustration and with no limitation of the invention.

 Thus, FIG. 1 and FIG. 2. represent a first and a second configuration of the device for carrying out the process object of the invention.

The main difference between the two devices lies in the element that radiates (emits) the acoustic energy to the gaseous medium, that is, in the ultrasonic application system, whose different design influences its possible applications. Thus, an ultrasonic device with a cylindrical radiator (FIG. 1) has been used that can be used mainly in mobile bed treatment chambers, and an ultrasonic device with vibrating plate radiator (FIG. 2), usable in any type of treatment chamber.

 These devices can be designed to work in the frequency range of 20-50 kHz. The currents generated in the gaseous medium, due to the high amplitudes of the acoustic wave characteristic of an acoustic field of an intensity equal to or greater than 150 dB, cause a decrease of the boundary layer reducing the external resistance to the transfer of matter. When the acoustic wave reaches the matrix, it causes cycles of compressions and decompressions that favor the elimination of the solvent due to an increase in the diffusion coefficients.

 In both devices, for the excitation of the piezoelectric power or transduction elements (6), an electronic system for generating, controlling and adapting the electrical signal (7) has been designed and built, consisting of a power generator with low impedance of output, a power amplifier, an impedance coupling circuit and a resonance frequency control and monitoring system that keeps the power applied to the piezoelectric element constant. For the remote control from a computer (8), a specific software for measuring and controlling the parameters of the electrical signal and resonance frequency has been designed.

 In this way, the transfer of energy between the power generator and the irradiated gas is maximized. The ultrasonic device with vibrating plate radiator (11), as well as the electronic system for generating, controlling and adapting the electrical signal (7) are of the same type as those included in the International Application

PCT / ES2005 / 070113.

The electrical signal is piezoelectrically converted into a mechanical vibration that is amplified by the mechanical amplifier (5) and that excites the radiating element in the form of a cylinder (4) or vibrating plate (11). Additionally, the electrical excitation signal of the piezoelectric power or transduction element (6) is isolated from the gaseous medium low temperature outside to avoid moisture or condensation problems in the piezoelectric elements that could lead to a short circuit.

 Therefore, both the piezoelectric part and the mechanical amplifier (5) are placed inside a sealed metal housing that also protects the piezoelectric element from power or transduction (6) from possible shocks or impacts due to improper handling. Ultrasonic radiators, cylindrical (4) or vibrating plate (11), produce a vibration that is transmitted through the gaseous medium to the matrix. The dimensions of the application systems may vary depending on the volume of the treatment chamber. In the vibrating cylinder application system, the samples are placed inside the treatment chamber, through which a stream of gas is circulated at low temperature (2), without the need to control its pressure. In the vibrating plate application device, the samples are placed at a certain distance from the radiating plate radiator (11) and the low temperature gas flow (2) can be parallel or perpendicular to the plate surface.

 In the vibrating cylinder application system, the structure of the acoustic field of the transducer inside the radiator is that of a stationary field with cylindrical geometry. The designed ultrasonic devices are conditioned to work at low temperatures, so that both the piezoelectric power or transduction element (6) and the ultrasonic radiators will operate in those conditions with good electroacoustic performance.

 The developed / used ultrasonic devices have high performance (greater than or equal to 60%) for gas generation. To obtain the maximum efficiency and to be able to act in any volume of work, it is possible to use transducers of wide surface (PCT / ES2005 / 070113, EP0450030A1; US5299175).

Examples of embodiment of the invention

Example 1. Elimination of water in apple By way of example, they are included in FIG. 3, the results of the experimentation carried out to remove water (dehydration process) from fresh apple cubes (10 mm side). The apple cubes were frozen at -20 ° C 24 hours before the beginning of the experiences. The samples were placed inside the cylindrical ultrasonic radiator (4) through which a stream of air was circulated at relative humidity (7%), absolute pressure (1 atm), temperature (-13 ° C) and speed (2 m / s) controlled. Given these experimental conditions, solvent removal was performed by sublimation. It can be seen that in the experiences where high intensity ultrasound (156 dB) were applied, the dehydration time was drastically reduced compared to the experiences that were performed without ultrasound application. Thus, to achieve a moisture content of 1 kg water / kg dry product the drying time was reduced from 60 hours to 20 hours by the application of ultrasound. This means a decrease in process time close to 70%.

Example 2. Elimination of ethanol in a solid matrix. Examples are included in FIG. 4, the results of the experimentation carried out to remove ethanol (organic solvent) from a solid matrix. The dehydrated apple cubes of Example 1, which were impregnated in vacuo for 2 hours with ethanol (96% purity), were chosen as the solid matrix. Thus, the apple cubes impregnated with ethanol, were placed inside the cylindrical ultrasonic radiator (4) through which a stream of air was circulated at relative humidity (7%), absolute pressure (1 atm) temperature (-13 ° C) and speed (2 m / s) controlled. Given these experimental conditions, solvent removal was performed by evaporation. Similar to example 1, the application of high intensity ultrasound (156 dB) significantly reduced the treatment time. To achieve an ethanol content of 125,000 ppm, the treatment time was reduced from 225 to 45 minutes. This means a decrease in process time close to 80%.

Claims

Claims 1. Procedure to accelerate and improve the transfer of at least one solvent occluded in a solid, semi-solid or liquid matrix to a gaseous medium at an absolute pressure equal to or greater than 0.5 atm and at a temperature equal to or less than 15 ° C, characterized in that It includes the application of a high intensity ultrasonic field, equal to or greater than 150 dB. 2. Method according to claim 1, wherein the application of the ultrasonic field is carried out by gas. 3. Method according to claim 1 or 2, wherein the transfer of the solvent is carried out by evaporation when the temperature of the gaseous medium is higher than the freezing point of the solvent. 4. Method according to claim 1 or 2, wherein the transfer of the solvent is carried out by sublimation when the temperature of the gas is below the freezing point of the solvent. 5. Device for carrying out the application of a high intensity ultrasonic field, equal to or greater than 150 dB, according to a method according to any one of claims 1 to 4, wherein said device is characterized in that it comprises an extensive radiating surface , equal to or greater than 750 cm ² and a good impedance adaptation with the gaseous medium. Method according to any one of claims 1 to 4, characterized in that the application of the high intensity ultrasonic field is carried out from a device according to claim 5, wherein said device operates with equal performance. or greater than 60%, vibration amplitudes equal to or greater than 10 μπι and a power capacity equal to or greater than 50 W. 7. Device for carrying out a method according to any one of claims 1 to 4, characterized in that it comprises a cylindrical radiator (4) or vibrating plate (5) connected to an element for containing the matrix, as well as a system to circulate a gas flow around said matrix. Device according to claim 7, characterized in that it additionally comprises an electronic excitation system of at least one piezoelectric transduction element, wherein said electronic system in turn comprises a resonance frequency control and monitoring system. 9. Use of a method according to any one of claims 1 to 4 in the agri-food, chemical, cosmetic and / or pharmaceutical field.