WO2003045541A2 - Device and method for producing foam - Google Patents

Abstract

The invention relates to a method and a device for producing foam. According to the invention, a fluid (Fl1) passes through a channel-shaped feeding chamber. Said fluid (Fl1) exits via an opening on one end of said chamber and arrives in a formation chamber surrounding the opening in order to form fluid deposits (Fl1). A second fluid (Fl2) is introduced into the formation chamber in such a way that it passes the opening. Fluid deposits are formed in the second fluid passing the opening when the first fluid (Fl1) exits from the feeder chamber via the opening. An expansion of the deposits is limited by the size of the formation chamber in the region of the opening, said size of the formation chamber in the region of the opening being smaller or equal to an expansion of a bubble/drop of the first fluid (Fl1) in a free-flow of the second fluid (Fl2). In order to form the foam, the second fluid (Fl2) flows with the deposits in a collecting chamber.

Description

 Device and method for producing a foam

The invention is in the field of foam production.

Foams are used as raw materials for a variety of different materials. To produce a foam, at least two fluids are mixed with one another that are limited or cannot be mixed at all. When the two fluids are mixed, bubbles or drops of one fluid form in the other fluid. The term foams in the meaning used here includes foams of any kind, in particular also emulsions, which can be produced with the aid of the mixing of at least two fluids. The fluid that forms the bubbles / drops can be, for example, a gas, water, an alcohol, ether or CC1. The other of the two fluids is, for example, an aqueous solution, a silicate brine, an aluminosilicate brine, a polymerizable liquid, a paste, a slurry of metal-containing pastes, a cream, an oil, a silicone oil, a fat, etc. The mixing of the Both fluids to the foam take place in such a way that, for example, there is a hexagonal, densest packing of the bubbles / drops. Apart from the typical crystal defects of each “real crystal”, such crystalline bubble / drop packs should have practically no structural defects, which leads to a high chemical, mechanical, hydrodynamic and thermodynamic stability of the foam formed. However, these positive properties of the foam formed depend on it to what extent it is possible to achieve a size distribution of the droplets / bubbles forming the pores of the foam that is as uniform as possible. Usually, foams have a fairly broad distribution of the pore sizes. This shows the positive properties with regard to the chemical, mechanical properties , hydrodynamic and thermodynamic stability of the foam formed is therefore adversely affected. It is therefore desirable to form the foams with a defined size distribution of the drops / bubbles. The drops / bubbles can generally be closed as inclusions with at least one This surface can be defined. Of particular importance in this context are monoporous or monomodal foams, in which the deposits have an essentially uniform size. The object of the invention is therefore to provide an improved method and an improved device for producing a foam, in particular a monoporous foam.

This object is achieved by a method according to independent claim 1 and a microreactor device according to claim 10.

The essential idea of the invention comprises the introduction of a fluid into another flowing fluid. In this case, the fluid passes through a feed space in the form of a channel, which has an opening at one end through which the fluid exits the feed space and arrives in an education chamber surrounding the opening to form deposits of the fluid. The other fluid, in which the deposits are to be introduced for foam formation, flows through the formation chamber, so that the other fluid flows past the opening. When the fluid emerges from the supply space through the opening, deposits of the fluid are formed in the other fluid flowing past the opening. The deposits arise due to the formation of bubbles / drops in the area of the opening, through which. the fluid enters the formation chamber from the feed chamber. To form deposits (bubbles / drops) of the fluid in the other fluid, an expansion of the deposits is limited by a dimension of the formation chamber in the region of the opening, the dimension of the formation chamber in the region of the opening being less than or equal to an extension of a bubble / drop of the fluid is in a free flowing fluid stream of the other fluid. Such a design of the education chamber in the area of the opening leads to the formation of deposits with a defined size. When the fluid exits the opening, drops / bubbles form, the size of which is limited by the size of the formation chamber in the area of the opening. If the deposit forming in the area of the opening has a maximum size, which is defined by the formation chamber in the area of the opening, the deposit, that is to say the drop / bubble, is torn off by the other fluid flowing past the opening. In this way, deposits of the fluid of a defined size are formed in the other fluid, which form a so-called “one-dimensional” foam, that is to say a sequence of bubbles / drops of the fluid flowing in the formation chamber. The foam thus produced then flows in for further processing a collecting room, where the two or three-dimensional "crystalline" structure of the foam is created. With the help of the invention it is possible to produce foams in which the deposits (drops / bubbles) have a defined size. If the size of all the deposits is essentially the same, it is a monoporous foam which has high chemical, mechanical, hydrodynamic and thermodynamic stability. As mentioned above, the term foam in the meaning used here includes foams of any kind, in particular emulsions, which can be produced with the aid of the bubble / drop formation process described above.

An expedient development of the invention provides that an inflow speed of the fluid is set through the opening into the formation chamber. In this way, the process parameters during the generation of the foam can be adjusted depending on the application in order to achieve a desired size of the deposits of the fluid in the other fluid.

Alternatively or additionally, it can be provided in an advantageous embodiment for the same purpose that an inflow pressure is set when the fluid flows in through the opening of the feed space into the formation chamber.

It can advantageously be provided in one embodiment of the invention that the feed space is formed in a feed device, the feed device is made of an electrically conductive material and a time-varying electrical voltage is applied to influence a size of the deposits of the fluid in the other fluid. With the aid of the electrical voltage, the formation process of the deposits (drops / bubbles) in the region of the opening when exiting the feed space into the feed chamber can be influenced. In this way, depending on the foam material to be formed, a desired size of the inclusions can be set. In particular, oligoporous foams can be produced in this way if the applied electrical voltage is varied during foam generation.

In order to be able to adapt the proposed method to the various requirements when manufacturing materials based on the foam produced, a preferred embodiment of the invention provides that the foam is post-treated in the collecting space.

In an expedient development of the invention, the step of post-treating the foam in the collecting space can be a light treatment, a temperature treatment, a removal gassing, predrying, gel formation and / or polymerisation. Aftertreatment is provided, for example, when ceramic foams are produced from a sol. The foamed sol phase must first be converted into the gel phase, which corresponds to a polymerization. This gel is dried in the collecting room before it can be fired in an oven to avoid tearing the resulting ceramic.

Finishing of a material based on the foam is made possible in an expedient embodiment of the invention in that the foam is finished in the collecting space. Depending on an application, the step for the final treatment of the foam in the collecting space can include drying, heating small areas of the foam and / or polymerizing out.

In an advantageous embodiment of the invention it can be provided that the foam is formed taking into account an external shape specification. In this way, it is possible to take into account the shape requirements of an object that is to be produced on the basis of the foam material when producing the foam material.

The method for producing a foam can expediently be carried out with the aid of a microreactor device. In order to produce a foam that has deposits of different sizes and / or deposits of different fluids, a device can be formed in which a fluid can flow through at least two formation chambers, in each of which drops / bubbles are formed, the deposits in form the fluid. The flowing fluid with the deposits then passes from the at least two formation chambers into a common collection chamber. The process of forming the deposits (drops / bubbles) in the two education chambers can differ with regard to the size of the deposits. It can also be provided that drops / bubbles of different fluids are generated in the two formation chambers, which are then incorporated in the fluid flowing past. In this way, foams can be produced in which the deposits are formed by different fluids and / or have different pore sizes.

Mineral foams can expediently be produced with the aid of the invention. Using the described method for generating the deposits in a fluid for

Foaming and a subsequent sol-gel process and a subsequent vacuum vacuum drying can produce a monoporous ceramic. For example, silicates, aluminosilicates or analogs can be used. The foams produced are characterized by a regular arrangement of inclusions with a delta function-like radius distribution that can be varied in a targeted manner. Materials created in this way can be used in filters, sieves or as thermal insulation foams for the lining of devices.

The invention can also be used to produce foamed supports for supported catalysts. The described process for generating the deposits is coupled with a sol-gel process, subsequent metal ion impregnation and subsequent vacuum drying and heating. In this way, ceramic supported catalysts can be produced. The foam materials are in turn characterized by a regular arrangement of the deposits with a delta-function-like radius distribution that can be varied in a targeted manner. The moldable foamed supported catalysts can be used in various applications, for example heterogeneous catalysis, CH ₄ oxidation or CO → CO ₂ on supported Pd catalysts.

The method for foam formation can also be used expediently to produce metallic foams, in particular metallic microfoams, for example for zinc or aluminum foams.

In addition, the foam formation described can be used to produce oxidic foams. In a system in which the two fluids used for foam formation are liquids, monomodal emulsions can be produced with the aid of oxidic slurries. If the fluid forming the deposits is evaporated or dried, a framework of the fluid in which the deposits are formed can be solidified into an oxidic foam with the aid of subsequent “burning” or “glazing”. A foam formed here is characterized by a regular arrangement of the deposits with a delta-function-like radius distribution of the deposits that can be varied in a targeted manner. Such oxidic foams are resistant to high temperatures and can be used as inert foams for linings in furnaces or combustion chambers, for example based on ZrO ₂ , HfO ₂ or Al ₂ O ₃ ).

In an expedient embodiment of the invention, the method for foam formation can be used to produce a foamed glass. Here is the deposit raging fluid forms a gas so that a gas / liquid system is used to form the foam, with kaolinic / silicate slurries flowing. A subsequent micro-glass melt leads to the formation of the foamed glass. A foamed glass produced in this way can be used as a glass foam for frits, filters and sieves.

With the aid of the foam formation process described, stable, flowable emulsions can be produced which are suitable for depositing, for example, cosmetic active ingredients. For example, this can be a cream in which the fluid is a fat or an oil and the other fluid is water. Depending on the solubility, both fluids can contain suitable active substances or combinations of active substances, which can be used, for example, for cosmetic or medical applications. It can be vitamins in skin creams. Furthermore, other substances such as stabilizers, emulsifiers, surfactants, preservatives or abrasives can be introduced in one fluid or distributed over several fluids and in this way the emulsion can be defined in the foam. With the help of size-controlled bubbles / drops in the foams, the active substance contents in the size-controlled deposits can be defined in an advantageous manner.

The invention is explained in more detail below using exemplary embodiments with reference to a drawing. Here show:

FIG. 1A shows a schematic illustration of a microreactor for producing a one-dimensional monoporous foam;

FIG. 1B shows a schematic representation of a microreactor for producing monomodal encapsulated deposits;

FIG. 2 shows a schematic illustration of a microreactor for producing a two- or three-dimensional monoporous foam; FIG. 3 shows a schematic illustration of a microreactor for producing a three-dimensional monoporous foam;

FIG. 4A shows a schematic illustration of a microreactor for producing a monodisperse foam with an electrode arrangement for decomposing a fluid; FIG. 4B shows a representation for a time-dependent voltage curve when using the electrode arrangement in FIG. 4A; and Figure 5 is a schematic representation of another microreactor for generating a monocrystalline foam using a hydrodynamic surface instability.

FIG. 1A shows a schematic illustration of a microreactor 1 for producing a crystalline foam. The term foam in the meaning used here also includes emulsions which can be produced in an analogous manner with the aid of the microreactor 1. In Figure 1, the microreactor 1 is shown in cross section. A feed device 3 is at least partially arranged in a hollow body 2, which is preferably tubular. To generate a foam, a fluid F is introduced through a feed space 4 formed in the feed device 3. Here, the fluid F ^ flows through the feed chamber 4 and enters via an opening 5 at one end 6 of the feed device 3 from the feed chamber 4 into a formation chamber 7, which begins in the hollow body 2 in the region of the opening 5 and downstream in the hollow body 2 continues from the opening 5 away.

According to FIG. 1A, another fluid F1 is introduced into the hollow body 2 via a feed device 8, which in the simplest case is a hose coupling to the microreactor 1. Here, the other fluid is introduced Fl ₂ in the hollow body 2 so that it flows along the supply means 3 by a portion 9 and flows past the opening 5 in the forming chamber. 7

When the fluid Fli emerges from the opening 5, a bubble or a drop forms in the region of the opening 5, depending on whether the fluid Fli is a gas or a liquid. The potting / blistering is particularly effective if the feed device 3 is a capillary. The bubble / drop is designated in FIG. 1A in an initial size and an end size by reference numerals 10a and 10b, respectively. The expansion of the bubble / drop at the opening 5 increases continuously up to the final size 10b. The final size 10b is limited by a dimension 11 of the formation chamber 7 in the area around the opening 5. The dimension 11, which in the case of a tubular formation chamber 7 can be the radius or the diameter, is less than or equal to the diameter of a bubble / drop of the fluid F ^ in a free-flowing fluid stream of the other fluid Fl ₂ . The value for the expansion of a bubble / drop for a specific fluid is known or can be determined experimentally. In this way it is ensured that the bladder / drop does not tear off from the opening 5 due to the flow of the other fluid Fl ₂ as a rule only when the bladder / drop has the final size 10b has reached. In order to achieve this goal, the flow velocities of the fluid F and the other fluid Fl _{2 must} be coordinated. With the help of the definition of the dimension 11, the size of the deposits can be predefined on the basis of the drops / bubbles formed in the opening 5 in the other fluid F1 ₂ .

After tearing off the opening 5, the bubbles / drops form deposits 12 in the fluid Fl ₂ , so that a foam is formed. The one-dimensional foam produced in this way then passes into a collecting space 13, in which a crystalline structure of the foam can form. The crystalline foam can be formed in the collecting space 13 or in a downstream container (not shown in FIG. 1A). A foam formed in this way has a monoporous structure. Such a foam has a high chemical, mechanical, hydrodynamic and thermodynamic stability because it has a crystalline foam lattice. Any gases, water, alcohol, ether, CC1 ₄ etc. can be used as the fluid Fh. The other fluid F1 can be, for example, an aqueous solution, a silicate brine, an aluminosilicate brine, a polymerizable liquid, a paste, a slurry of a metal-containing paste, a cream, an oil, a silicone oil, a fat or another solution. The foams formed in the manner described have no or only negligible construction defects with regard to the distribution of the deposits which are formed with the aid of the drops / bubbles.

If the other fluid F1 is due for polymerization, it is possible, for example, to produce solid foams with very special thermal insulation properties or crystalline foams which form excellent electrical insulators. In particular, materials with which ceramics or glasses can be produced permit the production of a monoporous ceramic or a monoporous glass with the aid of the described method. Monoporous ceramics form a new carrier material for catalysts. For example, the fluid Fli can be air, and the fluid Fl ₂ is a sol of silicates and aluminumates with a surface-active reagent, for example long-chain, tertiary ammonium compounds. In this way, a wide variety of foamed aluminosilicate gels can be obtained, which can then be processed into ceramics or glasses.

Monoporous metallic foams produced with the aid of the described method are very light in comparison to compact metals and have a higher mechanical stability than foamed metals, in particular a higher resistance to breakage. she form materials that can be used in the field of lightweight metal construction.

After leaving the formation chamber 7, a targeted aftertreatment of the foam produced can be carried out in the collection chamber 13. The aftertreatment can include, for example, predrying, gel formation (sol-gel process) and or anpolymerization. In the phase of such an aftertreatment, the resulting foams remain plastically deformable so that they can be led out of the collecting chamber 13 of the microreactor 1. Aftertreatment can be followed by a final treatment, including shaping for a foam workpiece. The final treatment includes, for example, drying, vigorous heating in a very small area (burning, sintering, metallizing) and / or polymerization, for example with the aid of photo-curing by exposure to light.

Mineral foams can be produced on the basis of the described method with the aid of the microreactor 1 shown in FIG. 1A. Here the fluid is Fli. a gas which flows into the other fluid Fl ₂ , so that the bubble formation process described with reference to FIG. 1A takes place. As part of an aftertreatment, the foam is then subjected to a sol-gel process and subsequent vacuum drying, so that a monoporous ceramic can be produced therefrom in a final treatment (firing). This can be done, for example, using silicates, aluminosilicates or analogs. The monoporous ceramic has a regular arrangement of deposits (bubbles or pores). Materials produced in this way can be used for filters, sieves or thermal insulation foams for the lining of devices.

In another embodiment, the foam formation process described can in turn be coupled with a sol-gel process in order to produce foam-borne catalysts. The sol-gel process is followed by metal ion impregnation and subsequent vacuum drying. Alternatively, in-situ catalyst impregnation and subsequent vacuum drying can be provided. In this way, after the final treatment (firing of the shaped body), a ceramic supported catalyst material is formed, which can be used as a starting material for supported catalysts in various applications. The method of foam formation described in connection with FIG. 1A can also be used to produce metallic foams. In this case, the fluid Fli is preferably an inert gas, for example an inert gas, and the fluid Fl ₂ is a liquid. The process for foam formation described in connection with FIG. 1A can also be used to produce another type of metallic foam. These purely metallic foams are produced in such a way that both the fluid Fli and the fluid Fl _{2 are} in the liquid state. These fluids are, for example, molten metals, slurries, pastes or pasty fluids. With the help of a subsequent laser metallization and combustion of organic residues, a metallic foam with a regular arrangement of deposits can be generated. Metallic microfoams are created in this way.

It is also possible to produce oxidic foams using the method described. When using different liquids for the fluid Fli and the other fluid Fl ₂ , using oxidic slurries, a monomodal emulsion can be generated. If the fluid F is evaporated in the process, the framework of the other fluid F1 _{2 can} be solidified into an oxidic foam by means of subsequent firing or glazing. With the aid of this embodiment, high-temperature-resistant, inert foams for linings of furnaces or combustion chambers can be produced.

Appropriate use of the method described can be provided in connection with the production of foamed glasses. Here, the fluid Fli is introduced in the form of a gas in the other fluid Fl ₂ , which is a liquid. For example, kaolinic / silicate slurries are used as another fluid F1. A subsequent micro-glass melt leads to the formation of foamed glasses. In this way, glass foams for frits, filters or sieves can be produced.

With the aid of the foam formation process explained with reference to FIG. 1A, stable, flowable emulsions can also be produced which are suitable for depositing, for example, cosmetic active ingredients in the deposits (bubbles / drops 12). In this way, suitable monoporous emulsions can be produced for the production of cosmetic products or foods.

FIG. 1B shows a schematic representation of a microreactor for producing a slurry of encapsulated bubbles / drops. For the same characteristics, the same Zugszeichen as used in Figure 1A. The formation of the bubbles / drops in the region of the opening 5 of the hollow body 2 was described in detail above with reference to FIG. 1A.

After tearing off the opening 5, the bubbles / drops form deposits 12 of the fluid Fli in the fluid Fl ₂ , which form a three-dimensional foam in the hollow body 2. When the bubbles / drops leave the hollow body 2 via an opening 19 at one end 18, the deposits 12 of the fluid Fli in the fluid Fl enter a further fluid Fl ₃ , that through a further supply space 14 past the hollow body 2 into an encapsulation space 16 streams. A chemical reaction with the fluid Fl _{3 then} takes place in the encapsulation space 16 at the phase interface between the fluid F, from which the bubbles / drops are formed, to the fluid Fl ₂ , which results in a dense, movable or firm, rigid skin 15 of the deposits 12 leads so that “encapsulated” deposits 17 are formed. The bubbles / drops 17 encapsulated in this way do not form a well-ordered foam in the collecting container 13 but a loose slurry of monomodal encapsulated bubbles / drops 17.

Using hydrodynamic interface instabilities when the foam formed in the formation chamber 7 flows, it is possible to isolate individual deposits or groups of deposits from the flowing foam. If a medicament has been added to the fluid Fh before being introduced into the other fluid Fl ₂ , microdepots in the form of isolated spherical shells for medicines can be produced in this way. This enables, for example, a very precise microdosing of long-term medication. The formation of the microdepots is possible with the aid of the microreactor 1 according to FIG. 1B, since a defined configuration of the inclusions and an encapsulation of the fluid Fli can be set with regard to the size in the other fluid F1.

FIG. 2 shows a schematic illustration of another microreactor 20. In contrast to the microreactor 1 according to FIG. 1, in the case of another microreactor 20, a plurality of formation chambers 21a, 21b, 21c, 21d are arranged side by side. An opening 22a-22d of a feed space 23a-23d is arranged in each of the formation chambers 21a-21d, so that a different fluid Fl ₂ , Fl ₃ , Fl ₄ or Fl ₅ can flow into the formation chamber 21a-21d. When the respective other fluid Fl ₂ -Fl _{5 flows in} , the bubble A drop formation process described in connection with FIG. 1 takes place in the area of the opening 22a-22d. Fluid F flows past opening 22a-22d as described with reference to FIG. Foam is then generated in the formation chamber 21a-21d. The Foam then passes from the formation chamber 21a-21d into a common collection chamber 24. The flows of the fluids Fl ₂ , Fl ₃ , Fl ₄ and Fl ₅ must be decoupled before entering the feed spaces 23 a - 23 d so that feedback occurs can be avoided via the education chamber 21a-21d.

A dimension 25a-25d of the formation chamber 21a-21d in the area of the opening 22a-22d is in each case smaller or equal to the diameter of a drop / bubble of the respective other fluid Fl, Fl ₃ , Fl ₄ or Fl ₅ in a free-flowing fluid stream of the other Fluids Fli. This ensures that the same size is generated in the education chamber 21 a-21 d.

It can be provided that the respective formation chambers 21a-21d have different cross-sectional dimensions, so that bubbles / drops of different sizes are generated. This enables the production of oligoporous foams. The parameters of the bubble / drop formation can also be influenced by the fact that the other fluids Fl ₂ -Fl ₅ flow through the respective feed space 23a-23d at different flow rates. In addition, it can be provided that the other fluids Fl ₂ , Fl ₃ , Fl ₄ , FI ₅ each flow into the other fluid Fh at a defined pressure.

In one embodiment it can be provided that the feed device 3 or the respective feed devices in which the feed spaces 23a-23c are formed are made of an electrically conductive material so that they can be subjected to an electrical pulsed voltage. A defined frequency spectrum can be selected for the applied voltage in order to influence the formation of drops / bubbles in the area of the opening 5 or 22a-22d. The size of the drop / bubble and the frequency of their formation can be influenced. The pulsed voltage used here is expediently chosen so that polarity, the selected frequency spectrum and the voltage level support a predetermined detachment of bubbles / drops from the opening 5 or 22a-22b.

FIG. 3 shows a schematic illustration of a further microreactor 30 which, in a manner analogous to the other microreactor 20 according to FIG. 2, has a plurality of feed devices 31a, 31b with feed spaces 32a, 32b, which via a respective opening 33a, 33b to a respective education chamber 34a and 34b. The feed device 31a, 31b can also be designed as a respective capillary in this exemplary embodiment. The Bla- Sen / drops enter at the openings 35 a, 35 b of the formation chambers 34 a, 34 b into a common bubble collection chamber 36.

Instead of the feed devices, electrodes of different shape, size and material can be used for the formation of bubbles / droplets which, for example due to an electrochemical reaction on their surfaces, generate a fluid from a surrounding fluid, which in the form of bubbles or droplets in a capillary designed as a formation chamber other fluid flowing past. With pulsed operation of the electrodes, bubbles / droplets of uniform size can be generated, which are arranged in the flow of the other fluid flowing past the electrodes to form a crystalline foam / emulsion. If several electrodes are used, different pulsed voltages with different frequency spectra can also be applied to the electrodes. When using different diameters of the formation capillaries, which are smaller than the diameters of the bubbles in a free-flowing fluid, bubbles / drops of different sizes can be generated on the plurality of electrodes. The pulsed voltages used here are advantageously selected / regulated so that the polarity, the selected frequency spectrum and the selected voltage level support the desired detachment of bubbles.

FIG. 4A shows a schematic representation of a further microreactor 100 for producing a crystalline / monodisperse foam in cross section. An electrode 300 is at least partially arranged in a hollow body 2, which is preferably tubular. The electrode 300 is made of a conductive material, for example metal, which was selected in accordance with one for the electrolysis of the liquid fluid Fl ₂ and a desired electrochemical reaction. The electrode 300 can be partially (not shown in FIG. 4A) provided with an electrically non-conductive coating, which makes it possible to limit the surface of the electrode 300 on which the reaction takes place. An electrochemical half cell is formed on the electrode 300. Depending on the desired reaction, the electrode 300 can be operated as an anode or as a cathode of the electrochemical half cell. If the electrode 300 is operated as an anode and an aqueous medium is decomposed, oxygen is generated at the electrode 300 if the aqueous medium has a suitable pH value and a suitable voltage is present. So-called Pourbaix diagrams or pH potential diagrams provide an indication of suitable voltages depending on the fluid composition. To generate the foam, a fluid F1 is passed through the hollow body 2. A constant or even to the desired reaction matched by means of applying, varying over time, periodic or chaotic voltage between the electrode 300 and a counter electrode 301 formed on the electrode 300 by the decomposition of the fluid Fl ₂ interlining wrung 12 in the fluid Fl. ₂ The initial size of the inclusions 12 is designated 10a, the final size 10b. The deposits 12 are filled with a further fluid Fli, for example with gas, which is hydrogen when the electrode 300 is operated as a cathode for water decomposition. The counter electrode 301 is electrically conductive and is formed from a suitable material, for example metal, in accordance with the desired reaction. The fluid Fl ₂ is fed in via a feed device 8 and flows through an area 9 past an electrode tip 306, at which the further fluid Fli is formed by the decomposition reaction of the fluid Fl, into the formation chamber 7. The droplet formation at the electrode tip 306 takes place in such a way that that the expansion increases from the initial size 10a, which is shown enlarged in FIG. 4A for better illustration, to the final size 10b. The extent is limited by the dimension 11 of the formation chamber 7 in the area around the electrode tip 306.

After the bubbles have been torn off from the electrode tip 306, the deposits 12 form in the formation chamber 7, so that a one-dimensional foam is formed. This is collected in the collecting space 13, in which the crystalline foam structure is formed, and shaped in a suitable manner, provided that a solid foam is sought as a product.

To apply a constant or a time-varying voltage, the electrode 300 and the counter electrode 301 are electrically conductively connected to a voltage source 307 via connecting lines 308 and 309. FIG. 4B shows an example of the course of a time-varying current at the voltage source 307. Here, a positive voltage is present during a time interval ti, so that, for example, oxygen is formed on the electrode 300, which forms an anode during the time interval ti. In order to interrupt the formation of oxygen and to influence a tear-off condition for the bubbles / drops in a suitable form, the polarity is reversed during a time interval t ₂ . During a further time interval t ₃ , a potential is applied, for example a weakly positive potential, in which no bubbles arise.

The method described with reference to FIGS. 4A and 4B is the production of a foam, in particular a monoporous foam, in which the Inclusions 12 are generated with the aid of an at least partial decomposition of a fluid Fli on an electrode arrangement, the extent of the inclusions being limited by the dimension in the area where the inclusions (bubbles / drops) 12 are formed.

In order to carry out the process of droplet formation of a fluid in another fluid described in various embodiments, which process makes it possible to produce monodisperse droplet distributions of the one fluid in the other fluid, a method can be provided which is carried out alternatively and is also used for the various described use cases can be used to produce a monodisperse or an oligodisperse foam. In the alternative method, two immiscible liquid fluids, which have a very different viscosity, are guided past each other in lamellar fashion at different speeds. The one fluid can be, for example, water, alcohol, ether, CC1 ₄ , etc. The other fluid is, for example, a silicate brine, an aluminosilicate brine, a polymerizable liquid, a paste, a slurry, a slurry of metal-containing pastes, a cream, an oil, a silicone oil, a fat, etc. The hydrodynamic interface instabilities (waves) that occur when flowing past rise as they flow past and form a regular pattern of the drops of the one fluid enclosed in the other fluid. Due to the characteristic modes of the hydrodynamic system, this leads to a very narrow, for example monomodal or bimodal, size distribution of the radii of the drop-like deposits of one fluid in the other fluid. A prerequisite for the formation of the characteristic modes is a sufficient distance along which the two fluids flow past one another in a narrow education area.

FIG. 5 shows a schematic illustration of another microreactor 500 for producing a monocrystalline foam from two immiscible liquid fluids Fli, Fl ₂ . The other microreactor 500 is shown in cross section. For the same features, the same reference numerals are used as in Figures 1A and 1B. A feed device 3, which in turn is a tubular hollow body, is at least partially arranged in a preferably tubular hollow body 2. To generate the foam, a fluid Fli is introduced through a feed space 4 formed in the feed device 3. In this case, the fluid Fli flows through the feed chamber 4 and enters via an opening 5 at one end 6 of the feed device 3 from the feed chamber 4 into a "virtual" education chamber 70 delimited by another fluid Fl ₂ , which is located in the hollow body 2 in the region of the opening - 5 begins and continues in the hollow body 2 downstream of the opening 5 away. The liquid other fluid Fl ₂ is inserted into the hollow body 2 via a further supply space 504th

The fluid and the other fluid Fl ₂ flow through the microreactor 500 in the same direction, the respective flow rates being coordinated with one another in such a way that hydrodynamic interface instabilities of defined modes form at an interface 516 of the fluids Fli, Fl. A wavelength 514 of the developing interface instabilities 516 is in the order of a diameter 511 of a virtual education room 505. The (real) education room 7 preferably has a durometer 513, which is only slightly larger than the diameter 511 of the virtual education room 505. It these are flow velocities that result in a slow flow. Depending on the diameters 513, 512, 511, which are selected as a function of the fluids Fli, Fl ₂ and the flow velocities, and on the flow velocities of the fluids Fli, Fl, defined modes are formed, and bubbles / drops are formed accordingly defined, essentially uniform diameter. The diameter 511 of the virtual education space 505 can differ from the diameter 512 of the feed space 4. The bubbles 12 then have a diameter which corresponds to the diameter 511 of the virtual education space 505 / the wavelength 514 of the interface instability 516. The flow velocities of the fluids Fli, Fl ₂ to be mixed are regulated by means of regulating devices (not shown in FIG. 5).

The method described with reference to FIG. 5 is the production of a foam, in particular a monoporous foam, in which the deposits are generated as a result of hydrodynamic instabilities at the interface between two fluids Fli, Fl ₂ flowing past one another in a narrow formation chamber.

The features of the invention disclosed in the above description, the claims and the drawing can be of importance both individually and in any combination for realizing the invention in its various embodiments.

Claims

Mi - nem tάrnon 17M60088PCTA Claims 1. A method of making a foam in which: - A fluid (Fli) flows through a channel-shaped feed space; - The fluid (F ^) exits the feed space through an opening at one end of the feed space and arrives in a formation chamber surrounding the opening to form deposits of the fluid (¥ \); - Another fluid (Fl ₂ ; Fl ₂ -Fl ₅ ) is introduced into the formation chamber so that the other fluid (Fl ₂ ; Fl ₂ -Fl ₅ ) flows past the opening; - When the fluid (Fli) emerges from the supply space through the opening, deposits of the fluid (Fli) are formed in the other fluid flowing past the opening (Fl ₂ ; Fl ₂ - Fl ₅ ), with an expansion of the deposits by a dimension of the Education chamber is limited in the area of the opening and the dimension of the education chamber in the area of the opening is less than or equal to an expansion of a bubble / drop of the fluid (Fh) in a free-flowing fluid stream of the other fluid (Fl; Fl - Fl ₅ ); and - To form a foam, the other fluid (Fl; Fl ₂ -Fl ₅ ) with the deposits flows into a collecting space. 2. The method according to claim 1, characterized in that an inflow speed of the fluid (Fli) is set through the opening in the formation chamber. 3. The method according to claim 1 or 2, characterized g e ke nnz e i chne t that an inflow pressure is set when the fluid (Fli) flows through the opening in the formation chamber. 4. The method according to any one of the preceding claims, characterized geke nnz eic hn et that the feed space is formed in a feed device, the feed device is made of an electrically conductive material and to influence a size of the insert of the fluid (Fli) in the other fluid (Fl ₂ ; Fl ₂ -Fl ₅ ) is subjected to a time-varying electrical voltage. 5. The method according to any one of the preceding claims, characterized in that the foam is post-treated in the collecting space. 6. The method according to claim 5, characterized in that the step for post-treating the foam in the collecting space comprises predrying, gel formation and / or a polymerization. 7. The method according to any one of the preceding claims, characterized in that the foam is finished in the collection room. 8. The method according to claim 7, characterized in that the step for the final treatment of the foam in the collecting space comprises drying, heating small areas of the foam and / or a polymerization. 9. The method according to any one of the preceding claims, characterized in that the foam is formed taking into account an external shape specification. 10. The method according to claim 1, characterized in that the fluid (Fh) is generated by electrochemical decomposition of the other fluid (Fl ₂ ) in this. 11. The method according spoke 1, characterized by a virtual education space (505), which is formed by a hydrodynamic boundary instability (516) between two liquids (Fli and Fl ₂ ) in the education chamber (7). 12. Microreactor device for producing a foam with: - A feed device with a channel-shaped feed space through which a fluid (Fli) can flow; - an education chamber which is connected to the feed space via an opening at one end of the feed space and surrounds the opening so that the fluid (Fli) can pass through the opening from the feed space into the education chamber; a feed device (8) for introducing another fluid (Fl ₂ ; Fl -Fl ₅ ) into the education chamber so that the other fluid (Fl ₂ ; Fl ₂ -Fl ₅ ) flows past the opening and absorbs deposits, which are formed in the region of the opening when the fluid (F) emerges from the opening from the fluid (Fli); and - A collection space, which is in communication with the formation chamber, so that to form a foam, the other fluid (Fl ₂ ; Fl -Fl ₅ ) with the inclusions of the fluid (Fli) can flow into the collection space; wherein a dimension of the formation chamber in the region of the opening, which limits an expansion of the deposits in the region of the opening, is less than or equal to an expansion of a bubble / drop of the fluid (Fli) in a free-flowing fluid stream of the other fluid (Fl; Fl ₂ -Fl ₅ ) is. 13. Microreactor device according to claim 12, characterized by: - Another feed device with a further channel-shaped feed space through which a further fluid (Fl ₂ -Fl ₅ ) can flow; - Another formation chamber, which is connected via a further opening at one end of the further feed space to the further feed space and surrounds the further opening, so that the further fluid (Fl-Fl ₅ ) through the further opening from the further feed space into the further Chamber of Education can get there; and - Another feed device to introduce the fluid (Fli) in the further education chamber, so that the fluid (F ^) flows past the further opening and receives further deposits, which in the region of the further opening at Emergence of the further fluid (Fl ₂ -Fl ₅ ) from the further opening are formed by the further fluid (Fl ₂ -Fl ₅ ); wherein the further education chamber is connected to the collecting space, so that to form the foam, the fluid (Fli) with the inclusions of the further fluid (Fl - Fl ₅ ) can flow into the collecting space, and wherein a dimension of the further education chamber in the area of the further Opening which is an extension of the further Deposits in the region of the further opening are limited, less than or equal to an expansion of a bubble / drop of the further fluid (Fl ₂ -Fl ₅ ) in a free-flowing fluid stream of the further fluid (Fl ₂ -Fl ₅ ). 14. Microreactor device according to spoke 13, characterized in that the dimension of the further education chamber in the region of the further opening is different from the dimension of the education chamber in the region of the opening. 15. Microreactor device according to one of claims 12 to 14, characterized in that the channel-shaped feed space and / or the further channel-shaped feed space are formed in a capillary. 16. Microreactor device according to one of claims 12 to 15, characterized in that the feed device and / or the further feed device are made of an electrically conductive material and can be subjected to a time-varying electrical voltage with the aid of voltage means. 17. Microreactor device according to one of claims 12 to 16, characterized in that the collecting space is formed as a shaping space for the foam. 18. Use of a method according to one of claims 1 to 11 or a device according to one of claims 12 to 17 for producing a ceramic foam. 19. Use of a method according to one of claims 1 to 11 or a device according to one of claims 12 to 17 for producing a foam-borne catalyst material. 20. Use of a method according to one of claims 1 to 11 or a device according to one of claims 12 to 17 for producing a metallic micro foam. 21. Use of a method according to one of claims 1 to 11 or a device according to one of claims 12 to 17 for producing an oxidic foam. 22. Use of a method according to one of claims 1 to 11 or a device according to one of claims 12 to 17 for producing a foamed glass material. 23. Use of a method according to one of claims 1 to 11 or a device according to one of claims 12 to 17 for producing a monodisperse emulsion.