FR2819996A1 - Dehydration of liquid, semisolid or water-containing products comprises sealing the product in a semipermeable bag and heating it in a vacuum chamber - Google Patents

Abstract

Process for dehydrating a liquid, semisolid or water-containing product comprises sealing the product in a bag that is permeable to water vapor and air but not to liquid water; placing the bag in a chamber whose internal walls are at least 5[deg]C hotter than the desired product temperature; and evacuating the chamber. Independent claims are also included for the following: (1) apparatus for carrying out the above process, comprising a chamber (1) having internal walls or plates (2) with means for circulating hot liquid or steam produced in an external oil-liquid heat exchanger in which the oil is heated by external means or by heat generated by the adsorption of water on a zeolite and the sensible heat of regeneration of the zeolite; (2) a product dehydrated by the above process without any additives.

Description

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PROCESS AND DEVICE FOR DEHYDRATION OR VACUUM DRYING OF LIQUID, PASTY PRODUCT CONTAINING ROOM TEMPERATURE WATER.

 The present invention relates to a process for dehydrating liquid or pasty products containing water. It makes it possible to obtain a solid product containing only a proportion of water which may be less than 1%. Subsequent storage of the residual product can be several years if it is protected from light and moisture. In most of the applications of this present invention, it is the residual product which is sought for industrial or food uses. The same process can be applied to the concentration or drying of wet waste of all kinds.

 A liquid is a product which tends to flow, or is a state of matter presented by bodies which do not have their own shape, but whose volume is practically invariable. Dehydration or drying consists in removing water from a solution in which the generally solid residual product is contained, which may or may not crystallize when the water content becomes low. This residual product is the desired product. Separation from the solvent or more generally from the water contained or containing the product will ensure the possibility of easier conservation, or of a different use from that possible in the presence of water or solvent. Drying indicates that the solvent of the solution can be water but also any other liquid.

 By "under vacuum" we understand a partial pressure of incondensables (nitrogen, oxygen ...) lower than that of the solvent. In most uses of this phrase, we understand a partial pressure of air or gas less than 1 millibar.

 The airtightness required for our applications is understood to be sufficient when, without pumping, closed on itself, a so-called hermetic enclosure, after being placed under vacuum of the order of 0.8 to 0.9 bar (by

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 compared to atmospheric pressure), does not have a pressure rise (global leak) greater than 1 millibar per 24 hours.

 It is known that to dry a solution containing a solid product, it is sufficient in most cases to heat to obtain the departure of the solvent.

 Another variant resides in the lyophilization techniques which consists in freezing the product before sublimation of the water or the solvent.

This sublimation is obtained by fixing the steam on a cold surface maintained at a temperature lower than that of the product. To allow an almost constant departure of the water vapor, the product is maintained at temperature between two heating plates thus ensuring heating by radiation.

 For example, today, there is no known technology for dehydrating honey without additives. The known and used technologies do not allow certain labels to be obtained.

 Another difficult example is the dehydration of eggs, especially white. It is a product which foams under vacuum and also presents significant risks of contamination.

 The technologies in use today make it possible to obtain acceptable products, the drawbacks of each of these technologies which are dehydration with hot air, dehydration by atomization, lyophilization and the various technologies of dehydration of liquids without freezing. are set out below.

 The dehydration by hot air of liquid food causes that they lose most of the most interesting products of the liquid first; most of them are flavors and alcohols which evaporate before water. They have a vapor pressure higher than that of water at the temperatures usually used.

 For dehydration by hot air, the enclosure in which this type of operation is practiced is generally not waterproof, so the departure of all these products is absolutely not controlled.

 In the case of atomization, the problem is the same, but the manufacturers using this technology seek to overcome the drawbacks of simple hot air by drying very quickly. Inside the enclosure

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d'atomisation le liquide coule en sens inverse de l'air chaud. La température d'air à l'entrée est dans la plupart des cas supérieure à 120 cl. A cette température, non seulement il y a départ d'arômes, mais une partie non négligeable des éléments nutritifs (vitamines, protéines, lipides...) sont modifiés par la température.

atomizing liquid flows in the opposite direction from the hot air. The air temperature at the inlet is in most cases above 120 cl. At this temperature, not only does the flavor start, but a non-negligible part of the nutrients (vitamins, proteins, lipids, etc.) are modified by the temperature.

 Manufacturers using freeze-drying advertise this technology as giving products of incomparable quality. However, it has many drawbacks. Indeed, the sublimation of the water does not allow the aromas to be left in place. The temperature of the cold surface of the lyophilization device being necessarily at least ten degrees centigrade lower than the product, therefore, the partial pressure of most of the flavors being stronger than that of water, the latter fix more easily than water on the cold surface for the duration of the drying operation.

 For the dehydration of liquids containing invert sugars, atomization or any other process obliges to carry out dehydration with an additive. In most cases it is maltodextrin or gum arabic which generally have a different origin from the product. This job removes the possibility of using an advertisement announcing a local or pure product unless this malto-dextrin is extracted from the basic product.

 Many of these products require very low water contents, often less than 1%.

 In the dehydration of liquid not frozen under vacuum, the biggest difficulty lies in the bubbling of the liquid. This technique is generally used only for products of which no component has a partial pressure greater than water. Splashes due to violent boiling and to the foam often generated jointly cause a significant quantity of the product to be lost and do not allow '' use technologies other than freeze-drying. Generally this dehydration takes place in a tank with a scraped wall, the product often being in the form of gum as soon as it has lost part of its water. This wall-mounted tank, also heated, is connected to a condenser, and the condenser to a ring pump.

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d'eau ; ces deux derniers dispositifs travaillent souvent en eau perdue ce qui représente souvent quelques inconvénients pour l'environnement.

water; these last two devices often work in waste water which often represents some disadvantages for the environment.

 The present invention eliminates the various drawbacks listed above. It makes it possible to dehydrate products which can either foam considerably, or quickly lose aromas if their partial pressures are strong at low temperature, or either boil very violently at low pressure. The present invention relates to a new dehydration process.

- ce volume étant lui-même placé dans une enceinte hermétique résistante à la pression atmosphérique dont les parois sont maintenues à au moins 5 C au dessus de la température à laquelle sera maintenu le produit, - la mise sous vide de l'enceinte est réalisée avec des moyens de pompage compatibles avec la quantité de vapeur d'eau à extraire du volume enfermant le produit, - un chauffage du volume et donc du produit contenu est assuré pour permettre la mise en pression interne de la vapeur d'eau et maintenir la température du produit pour que l'évaporation de l'eau du produit puisse perdurer jusqu'à déshydratation partielle ou complète, l'humidité résiduelle dans le produit pouvant être comprise entre 1 et 50 %, la durée pouvant aller de 1 à plus de 24 heures et la température comprise entre 0 et 120 C sont fonction de la nature et de la qualité du produit à obtenir. The process of the present invention with which the product is maintained at a temperature and a pressure or it appears that very little physical and organoleptic degradation of the liquid, pasty or water-containing product in cells or molecules is characterized in that it has the following stages: - the product is placed in a closed volume or bag having all or part of the walls having a high permeability to water vapor and to air gases but negligible to liquid water, i.e. an almost total seal against sugars, mineral salts, vitamins, amino acids and other components of pharmaceutical and agrifood products,

- this volume itself being placed in an airtight enclosure resistant to atmospheric pressure, the walls of which are maintained at least 5 ° C. above the temperature at which the product will be maintained, - the enclosure is evacuated with pumping means compatible with the quantity of water vapor to be extracted from the volume enclosing the product, - heating of the volume and therefore of the product contained is ensured to allow the internal pressure of the water vapor to be put under pressure and to maintain the temperature of the product so that the evaporation of water from the product can continue until partial or complete dehydration, the residual humidity in the product can be between 1 and 50%, the duration can range from 1 to more than 24 hours and the temperature between 0 and 120 C depend on the nature and quality of the product to be obtained.

 The method of the present invention is preferably carried out in the device characterized in that it comprises at least the following elements:

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 - an enclosure which can be evacuated comprising at least two plates in which a circulation of a hot liquid or of vapor can be established; - a hot liquid or vapor obtained in an oil-liquid exchanger, - this heat transfer oil is heated by the heat produced during the adsorption of water on the zeolite and the sensitive heats during the regenerations of said zeolite, - Other pumping or heating means can be used, they are available to those skilled in the art and are only means for using this invention.

 - in the space defined between two plates, permanently or loaded for each operation, the volumes or bags are maintained, all or part of the surface of the bag or the volume made up of a TERGAL fabric coated with a dimethylpolysiloxane allow the passage of water vapor which can be evaporated by the product contained in these volumes or bags, - by means of regulating physical parameters such as the temperature of the plates is less than 130 ° C., the absolute pressure in the enclosure is between 0.1 and 50 millibars, the pressure in the bags or enclosure can vary from 2 to 2000 millibars.

 This process is therefore characterized by controlled evaporation, through the wall of the bags, osmosis membrane comprising on the surface, by coating, a silicone elastomer or equivalent, for example a fabric coated with a layer of dimethylpolysiloxane with a thickness of 30 to 100 microns water cannot pass directly into this osmosis membrane in the liquid phase. The variation in thickness of the elastomer layer resulting in different permeability for gases, including water vapor. This membrane also having zero or almost zero permeability for the complex molecules making up the flavors, vitamins, etc. Other semi-permeable materials can be used depending on the nature of the solvents to be evaporated.

 The permeability of the membrane is constant, but a function of the partial pressure difference for each product that can pass through it in the gas phase. The duration of the operation is therefore a function of the partial pressure of the water inside the bag, the temperature of the plates and the total pressure maintained in the enclosure.

 In the description of Figures 1 and 2 and examples below we will better understand the process and its device

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La figure 1 représente le dispositif de l'invention adapté à une enceinte ordinaire de déshydratation comme décrite dans le FR 89 17413.

FIG. 1 represents the device of the invention adapted to an ordinary dehydration enclosure as described in FR 89 17413.

 FIG. 2 represents a device specific to the present invention.

Figure 1 shows the enclosure 1 with its loading door, in which an absolute pressure up to 0.1 millibar can be established
Inside this enclosure 1 are arranged the heating plates 2 in which a liquid or vapor circulates, the temperature of which is controlled. These plates 2 have a surface designed to have maximum emissivity. The enclosure 1 has double internal and external walls which can be heated; it has at least the hot liquid inlets and outlets, not shown, for supplying the plates.

 Preferably, a flange 5 provides the connection with the zeolite pumping system equivalent to that described in French patent FR 89 17413.

 The product 4 is, prior to placing under vacuum, placed in a bag or pocket 3 made of a fabric coated with a layer of a silicone compound, preferably a dimethylpolysiloxane, this constitutes the membrane, ensuring controlled permeability for most gases and water vapor. Depending on the pressure difference, therefore the water vapor flow rate per unit of surface area sought, a pressure difference is maintained between the inside of the bag and the inside of the enclosure. A belt, not shown, arranged around said bag, in metallic canvas or in perforated sheet metal ensures that the canvas is not torn in the event of excessive pressure.

 A pressure difference is maintained by adjusting the valve 7, the opening of which, therefore the flow of steam and residual air often due to the degassing of the gases dissolved in the product between the enclosure and the pumping assembly is regulated according to an imposed pressure difference.

 The differential pressures between the inside of the bag and the enclosure and between the enclosure and the pumping unit are a function of the surface temperature of the bag or of the product, of the total pressure maintained by the pumping unit and the partial pressure of water vapor maintained by this same pumping group.

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 It is possible to develop this scheme towards machines with practically continuous operation as presented in FIG. 2.

 It is possible not to place the product directly in contact with the silicone membrane. In addition, this device makes it possible to take out a sterilized or pasteurized dry product.

 We will not describe the pumping group, it consists of vacuum pumps associated with several adsorbers or an adsorber as provided in patent FR 89 17413.

 All of the devices are contained in an enclosure II, an enclosure the walls of which can all be heated by circulation of hot liquid to avoid any risk of intermediate condensation, liquid heated by external means or by the heat produced during adsorption. water on the zeolite and the sensitive heat of said zeolite and its support, so that, depending on the temperatures and pressures necessary for the product 10 which is dehydrated.

 In the lower part of the enclosure, a tube 12 which can be maintained at a precise and regulated temperature receives the product.

 Inside this tube, a device 13 makes it possible to produce agitation of the product to be dehydrated by mechanical means which can be either an alternating movement of scraper half segments, or of an Archimedes screw periodically changing direction of rotation . The Archimedes screw also allows a simpler evacuation of the finished product.

 This tube containing the product is connected by a pipe 14 containing devices 22 avoiding the projection of droplets or foam depending on the nature of the product to be dehydrated, to a tube 15 carrying the bags 16 of coated fabric identical to that of the bags of the description in Figure 1 above. The valve 21 provides the connection with the pumping group.

 Through the orifice 17 it is possible to introduce a liquid product aseptically.

Similarly, through the orifice 18, it is possible to have the opening for the discharge of the dehydrated product take place in a sterile medium.

 The patent FR 78 14549 can be used in this assembly to sterilize the interior of the machine in the absence of air as provided in FIG. 2. The vapor will then be introduced by the valve 19 for the exterior of the device, and the valve 20 for the part of the machine containing the product. The use of the process of this patent makes it possible to obtain the sterilization of

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l'ensemble du dispositif par vapeur d'eau, et de laisser les parois sèches à la fin de l'opération.

the entire device by steam, and leave the walls dry at the end of the operation.

 The product, cold introduced into the tube 12 is placed under an air vacuum through the wall of the bags 16, this osmosis membrane also being permeable to gas, the pressure drop of the enclosure It is produced so as not to destroy coated fabrics 16; as soon as the pressure of 10 millibars is reached, the heating of the wall of the enclosure 11 is carried out, as well as the heating of the tube 12 containing the product. The walls of the parts 11, 14 and 15 are maintained at a temperature slightly (about 5 ° C.) higher than the temperature of the tube 12 containing the product. The total and partial pressure of the water in the enclosure 11 are maintained below the partial pressure of water corresponding to the temperature of the tube 12 by the pumping unit and the pressure regulation imposed on the valve 21.

 Those skilled in the art can vary the devices without changing the meaning of the present invention.

EXAMPLE 1 Drying of egg whites
In a sleeve made with a membrane produced by coating with dimethylpolysiloxane placed on a Tergal support, these products being compatible with food contact, having a diameter of 50 mm, we introduced fresh egg white. This sleeve was closed with pliers. It was then placed in an enclosure or vacuum oven connected to the following pumping system: a vane and oil vacuum pump, an adsorber containing more than fifteen kilograms of dry zeolite, and the appropriate valves. The wall of the vacuum oven was brought to 80 oc. the total pressure in the enclosure was less than 10 mb, the sleeve inflates as soon as the temperature corresponds to a water vapor pressure higher than the pressure prevailing in the enclosure. When the temperature inside the sleeve is 50 C, the pressure is 150 mb the permeability of the silicone coated fabric ensures the passage of water vapor. After six hours of keeping under these conditions, we obtained a dry, white product with the scent of egg white. When the same amount of water is added to it

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 than that previously removed, the whole set up "in snow" or behaves exactly like fresh egg white.

EXAMPLE 2 Drying of honey
In the same membrane we introduced rapeseed honey particularly loaded with water (about 12%) and invert sugars, we proceeded in the same way as for the egg whites mentioned above.

In a few hours we got a perfectly crushable honey stick in a cutter. As soon as it is ground, a rehumidification of the invert sugars causes the honey ground to stick in the minutes following the grinding.

 In these two examples we specify that no additive has been put in the products.

EXAMPLE 3 Dehydration of a product presenting a risk of contamination.

surchauffée assurant une température supérieure à 130 oC sur les parois du tube. La température maximum admissible est de 150Oc. Nous avons fermé sous vapeur le tube. Nous avons introduit du lait stérilisé ne contenant donc pas d'éléments vivants. Nous avons introduit l'ensemble fermé dans l'enceinte à vide utilisée pour les autres exemples, sans désinfection préalable de l'enceinte. Nous avons déshydraté le lait. La poudre obtenue fût dans des conditions de stérilité garantie, réhydratée avec de l'eau stérile, aucun comptage n'a décelé de produit de contamination. We sterilized an identical tube by heating with steam

superheated ensuring a temperature higher than 130 oC on the walls of the tube. The maximum admissible temperature is 150Oc. We closed the tube under steam. We have introduced sterilized milk therefore containing no living elements. We have introduced the closed assembly into the vacuum enclosure used for the other examples, without prior disinfection of the enclosure. We dehydrated the milk. The powder obtained was under guaranteed sterility conditions, rehydrated with sterile water, no count detected any contamination product.

EXAMPLE 4 Dehydration of apple pieces.

We are fully aware of the possible results of dehydrating apple pieces by the method described in patent F. R. 89 17413.

We enclosed pieces of apples in the same type of tube.

The product in the bag was placed in the enclosure used for the other examples. After four hours of vacuum maintenance with a radiation temperature of 70 C the apples were taken out with humidity

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 residual less than 5%. It seems that the products obtained are slightly whiter than in the case of usual dehydration according to the process described in the patent cited at the beginning of this paragraph.

EXAMPLE 5 Coffee dehydration We made French-style coffee using traditional equipment. We put the liquid equivalent of a cup in one of the bags described above and proceeded to the most complete dehydration possible. The residual product represents approximately less than 1 gram of dry extract. When the same amount of water is returned, a coffee is obtained which it seems impossible to differentiate from the original drink. This was done without any addition of dextrin or other malto.

EXAMPLE 6 Dehydration of a polysacharrides A polysacharrides containing water having a dry extract of approximately 1% is placed in the device of FIG. 1, it is maintained at a temperature below 30 and a transparent gum is obtained.

Claims (9)

 that it has the following stages: - the product (4, lao) is placed in a closed volume or bag (3, 12) having all or part of their walls having a high permeability to water vapor and to air gas but negligible in liquid water, i.e. an almost total seal against sugars, mineral salts, vitamins, amino acids, and other components of pharmaceutical and food products, - this volume (3.12) is itself placed in an airtight enclosure (1,11) resistant to atmospheric pressure, the internal walls of which are kept at least 5 oC above the temperature at which the product will be kept (4, 10), - vacuum is produced with pumping means compatible with the quantity of water vapor to be extracted from the volume enclosing the product, - heating of the volume (3, 12) and therefore of the product (4,10) contained is ensured to allow the internal pressurization of water vapor and maintain l at product temperature (4, 10) so that the evaporation of water from the product can continue until partial or complete dehydration, the duration and the temperature depend on the nature and the quality of the product to be obtained.

CLAIMS 1 / Dehydration process in which the product is maintained at a temperature and a pressure or it appears that very little physical and organoleptic degradation of the liquid, pasty product, or product containing water in its cells or molecules , characterized in  2 / A method according to claim 1 characterized in that the volume containing the product consists of a fabric made with fibers including "Tergal", fibers coated by coating with dimethylpolysiloxane with a thickness of the order of 30 to 100 microns.  3 / A method according to claim 2 characterized in that, the thickness of the coating can vary to allow different permeability characteristics for water vapor.  4 / A method according to claim 1 characterized in that the wall of the volume (3.12) with controlled permeability can be made of different materials adapted to the solvents used.  5 / Device used for the method according to any one of claims 1 to 4 characterized in that it consists of an enclosure (1, 11) which can be evacuated having internal walls or plates (2) comprise means ensuring the circulation of hot liquid or vapor, said hot liquid or vapor is obtained in an oil-liquid exchanger external to the device, this thermal transfer oil heated by <Desc / Clms Page number 12>  external means or by the heat produced during the adsorption of water on the zeolite and the sensitive heats of regeneration of said zeolite

6 / Device according to claim 5 characterized in that between said plates (2) or the tube (12) are loaded with the product to be dehydrated in bags (3) between the plates (2), or in the volume (12), the temperature of the plates or the inner wall of (12) will be less than 130OC, the absolute pressure in the enclosure will be between 0.1 and 50 millibar, the pressure in the bags (3) or the tube (12) may vary from 2 to 2000 millibars.  7 / Device according to claims 1 to 6 characterized in that the product container can be a container; the fabric of the bag (3) or (16) with controlled permeability being fixed or connected to the container.  8 / Device according to claims 1 to 7 characterized in that the enclosure (ll) has walls heated to a temperature sufficient to avoid any intermediate condensation, the product (10) is kept in a tube (12) heated and kept at programmed temperature and in which the product (10) is agitated by mechanical means (13).  9 / Product obtained using the process according to Claims 1 to 4 and the devices produced according to Claims 5 to 8 characterized in that the product is dehydrated without any additives, even those extracted from the waste of the plant, in particular coffee , honey, egg, polysaccharides.