FR2756196A1 - Granule preparation process - Google Patents

Abstract

New method (I) of preparing granules (II) containing at least one solid substance (III) from a mother-composition (IV) comprising (III) and at least one diluent comprises: breaking (IV) up into (II); freezing (II) by exposing them to a liquid cryogenic liquid (V); recuperating; and drying frozen (II). Also claimed are (II). Also claimed is a device to put (I) into operation comprising: a means of breaking (IV) up; at least one recipient containing (V); and a means of recuperating and drying (II). (IV) is zeolite, alumina, silica, coal, an organic polymer, or a cosmetic or food product. The diluent in (IV) is water. (IV) also comprises a binder (e.g. a glue, clay, resin, wax or cement). (II) are of diameter 0.07-2 cm. In an example, a mixture of alumina powder and water is injected into liquid nitrogen. The resulting frozen granules are recuperated and dehydrated under gaseous nitrogen at -20 deg C and atmospheric pressure.

Description

Method and device for manufacturing aggregates
The present invention relates to the field of the manufacture of aggregates, from a composition comprising at least one dry extract, that is to say a solid substance and at least one diluent, typically an aqueous diluent, such as water.

 I1 exist in the prior art many techniques for manufacturing aggregates.

 Indeed, depending on the application, an aggregate presentation is sometimes preferred to a presentation in powder form. Thus, depending on the case, a visual quality of presentation can be sought, ease of handling, protection of the atmosphere against the flight of fine particles, ease of dosing, etc. Furthermore, for solid products intended for be brought into contact with a gas, or a mixture of gases, for a catalysis or adsorption operation, the pulverulent form is not suitable, since the powder is entrained by the gas. It is therefore customary to shape the solid in the form of aggregates, balls or sticks, which have an appropriate particle size, and are intended to constitute beds (fixed, fluidized or circulating) through which the gas can circulate. , and react, without attrition and without significant loss of active substance by training.

 Mention may be made of document GB-A-2092880 which describes a process and a device for manufacturing frozen aggregates of a liquid or semi-liquid substance, in which said substance is introduced dropwise into a cryogenic fluid in the state liquid, having a boiling point below -300C, which causes instant freezing of said substance in the form of aggregates; said aggregates then being recovered.

 However, it appears that this process has several drawbacks.

 In fact, the aggregates frozen by this process must be stored and kept permanently at temperatures below -200C to avoid any liquefaction of said aggregates, due to thawing thereof.

 Therefore, the possible applications of this process are essentially limited to the food sector and to certain products, such as ice creams, yogurts, cheeses ...

 In addition, frozen aggregates must be kept permanently at a temperature below -200C, their handling, sieving, transport and storage pose problems and generate unacceptable costs.

 Finally, this process is limited to the freezing of liquid or semi-liquid substances.

The object of the present invention is therefore to propose a method for manufacturing aggregates which does not have the abovementioned drawbacks and which allows, in particular:
- To manufacture aggregates from a mother composition containing at least one dry extract or solid substance, and at least one diluent, typically an aqueous diluent, such as water;
- Obtain aggregates essentially free of the diluent (s) present in the mother composition, or comprising a determined residual content in said diluent (s);
- Obtain aggregates that can be stored, handled, used and transported, as the case may be, at a temperature below OOC or above O "C, and preferably at room temperature;
- to manufacture aggregates of various compositions which can find, according to their composition, their structure, and more generally their own characteristics, an application in various sectors of industry, in particular in the chemical sector, in particular catalysis or adsorbents, for example in the field of separation or purification of gases, such as air, by means of catalysts or adsorbents, as well as in other sectors such as the agro sectors -food, pharmacy, cosmetics ...;
- To obtain aggregates of rounded shapes, that is to say spherical, ovoid, or the like.

In the context of the invention, the following are called:
- mother composition: the starting composition comprising at least one dry extract or solid substance and at least one diluent, that is to say a mixture of one or more solid products with at least one diluent, preferably a aqueous diluent, such as water;
- granulate: a grain form of the mother composition by a granulation technique. The terms granulate, granule, granule, grain, ball, particles substantially spherical or ovoid are used interchangeably;
- dry extract: a solid substance, such as a mineral or organic powder, or a mixture of several solid substances, for example the mixture of a particular mineral powder (alumina, zeolite, etc.) and a binder (clay, etc.) .);
- diluent: a liquid or a liquid phase which has the property of suspending the aforementioned dry extract, such a diluent being able to be aqueous, that is to say for example water.

The present invention therefore relates to a process for the manufacture of aggregates containing at least one solid substance, from a mother composition comprising at least said solid substance and at least one diluent, in which:
a) fractionating said mother composition into aggregates;
b) freezing said aggregates by contacting with a cryogenic fluid;
c) the frozen aggregates are recovered;
d) drying said frozen aggregates.

 According to a first embodiment of the invention, the fractionation of step a) of the mother composition into aggregates and the freezing of step b) of said aggregates are carried out simultaneously by injection of the mother composition in contact with the cryogenic fluid in liquid state.

 In other words, the coming into contact of the "jet" of mother composition with the cryogenic fluid, will cause the fractionation, that is to say the partition of the mother composition, with the formation of "particles" or substantially spherical aggregates of various sizes.

 Preferably, the injection of the mother composition is carried out at a flow rate of between 0.1 m, s-1 and 0.5 m. -1. In fact, injection at too high or too low flow rates results in aggregates of irregular shapes, and often unusable industrially.

 According to a second embodiment of the invention, the fractionation of step a) is carried out prior to step b) and using a fractionation technique chosen from the group formed by soft distribution, atomization and 11pot-vibrating technique ".

 By soft distribution, it is meant that the distribution of portions, that is to say of predetermined quantities, of mother composition on the surface of the cryogenic fluid is carried out so as to minimize and even eliminate any fractionation of the portions of mother composition when coming into contact with the cryogenic fluid, and this, unlike the embodiment by injection.

 By atomization is meant spraying the mother composition into fine droplets, that is to say portions of mother composition with a diameter between 100 and 500 μm.

 By "pot-vibrating" technique is meant the emission of a calibrated jet by a nozzle or a needle and the fractionation of said jet by vibration of said nozzle or needle at a preset frequency. In other words, the head of the nozzle is animated by a vibrator with periodic oscillations, which makes it possible to regularly break the flow of mother composition and to obtain beads or droplets of regular sizes. The desired size of the droplets, and therefore of the aggregates, to be produced can be controlled by adjusting the ratio between the frequency of the vibrator and the flow rate of the mother composition.

 The mother composition is divided into aggregates of 3 predetermined volumes, preferably between 0.01 mm and 100 mm3; the fractionation being carried out by means of a nozzle or a nozzle.

 Advantageously, the end of the dispensing means has an internal diameter between 0.10 mm and 4.5 cm, preferably between 0.5 mm and 2.1 cm.

 Depending on the case, in step c), the frozen aggregates are recovered on the surface and / or under the surface of the cryogenic fluid.

 Preferably, the mother composition contains at least one aqueous diluent, preferably water.

 Preferably, the cryogenic fluid is liquid nitrogen.

According to a preferred embodiment, the frozen aggregates are dried by lyophilization; said lyophilization being carried out:
- Either by conventional vacuum freeze drying techniques using any commercially available vacuum freeze dryer;
- Either by lyophilization using a cryogenic gas at a temperature below OOC, preferably less than or equal to -20OC. Advantageously, the cryogenic gas is nitrogen gas, however, using dry air is also possible.

 Depending on the case, the mother composition may comprise at least one solid substance chosen from the group formed by zeolite, alumina, silica, activated carbon, catalyst supports, bases of adsorbent materials or a substance chosen from the group formed by mineral powders, organic polymers, drugs, natural, cosmetic, pharmaceutical and food products and / or an organic or mineral binder, for example, chosen from the group formed by glues, clays, resins , waxes, cements and, in general, any organic or mineral adjuvant allowing, by drying, curing and / or subsequent polymerization, to reinforce the mechanical properties of the aggregate.

 The addition of an adhesive or binder type product generally makes it possible to facilitate the formation of aggregates or balls of the solid substance and / or the improvement of the mechanical properties of the balls (resistance to attrition, etc.) .

 Advantageously, the porosity of the aggregates is controlled by the content of the mother composition in its various constituents.

 Thus, when it is desired to obtain, after drying, a dry extract of low density and high porosity, the diluent content of the mother composition will be increased.

 Conversely, when one wishes to obtain, after drying, a dry extract of high density and low porosity, the diluent content will be reduced, while taking care to keep a mother composition sufficiently liquid or fluid, this is that is to say containing the minimum diluent content allowing it to be fractionated by means of one of the abovementioned fractionation modes.

 Depending on the case, the aggregates dried in step d) undergo a subsequent baking step, which usually makes it possible to give them their physicochemical properties and to improve or strengthen their mechanical properties.

 The invention also relates to the use of aggregates obtained in a process for the separation or purification of gas mixtures using at least one step of adsorption of at least one constituent of said gas mixture on said aggregates and / or at least one step of catalysis of at least one constituent of said gaseous mixture by means of said aggregates used as supports for at least one catalyst.

 The invention also relates to the aggregates obtained by said process, which have a diameter between 0.1 mm and 3 cm, preferably between 0.7 mm and 2 cm.

The invention also relates to a device for implementing the method of the invention and for manufacturing aggregates, comprising:
means for fractioning the mother composition into aggregates;
- means for freezing the aggregates, comprising at least one container containing a cryogenic fluid in the liquid state;
- means for recovering frozen aggregates,
- and means for drying frozen aggregates.

 The invention will now be described in more detail with the aid of figures and examples given by way of illustration, but in no way limit the invention.

FIGS. 1 to 4 schematically represent different modes of fractionation of the mother composition into aggregates and, more precisely:
- Figure 1 shows an injection fractionation;
- Figure 2 shows a fractionation by soft distribution;
- Figure 3 shows a fractionation by the technique of the "vibrating pot";
- And Figure 4 shows an atomization fractionation.

 Furthermore, FIG. 5 represents the diagram of a device according to the invention.

 In FIG. 1, a jet 2 ′ of mother composition 2 is injected by means of a nozzle 1 in the direction (direction of the arrows 7) and in contact with a liquid cryogenic fluid 3, here liquid nitrogen, circulating in the direction indicated by arrow 4.

 The coming into contact of the jet 2 'of mother composition 2 with said cryogenic fluid causes, on the one hand, a fractionation of said jet 2' into aggregates 5 and a simultaneous freezing of said aggregates. The aggregates or frozen beads are then removed by the flow of liquid nitrogen 3; these aggregates can have a diameter of between 0.6 mm and 3 mm.

 FIG. 2 represents a fractionation by gentle distribution of a controlled amount of mother composition 2 by means of a dispensing nozzle 1. I1 is formed, first of all, at the end of the nozzle 1, a "drop" 5 'of mother composition 2, which detaches and falls by gravity to the surface of the flow of liquid nitrogen 3, where it undergoes freezing to form an aggregate 5 of substantially ovoid shape, which is then evacuated by flow 3.

 Preferably, the composition 2 is fractionated near the surface of the cryogenic liquid 3, so as to avoid or minimize any deformation of the "drop" in contact with the cryogenic flow 3 due to a fall from a height that is too great. The aggregates obtained have a diameter in the range of 2 mm to 5 mm.

 FIG. 3 represents a fractionation by the "pot-vibrating" technique where the size of the balls 5 "is varied by playing, on the one hand, on the diameter of the nozzle 1 and, on the other hand, on the frequency oscillations imparted to nozzle 1.

 When a 5 "drop of mother composition 2 forms at the end of the nozzle 1, the oscillations imparted to said nozzle 1 (shown diagrammatically by the arrow 6) cause the drop 5" to detach and fall by gravity into the flow of liquid nitrogen 3 where it is frozen into a granulate 5, which is discharged by the flow 3. The beads obtained by this technique generally have a diameter of between 0.5 mm to 2 mm.

 FIG. 4 represents a fractionation by atomization by means of an atomizer shown diagrammatically by a reservoir 9 of mother composition 2, which reservoir 9 is connected to atomization means, such as an atomization nozzle 8, making it possible to fractionate the composition mother 2 in fine droplets which will then fall, by gravity, into the flow of liquid nitrogen 3 and be frozen there in the form of aggregates or beads 5.

 This technique makes it possible to produce balls or aggregates of small diameter, for example from 0.1 to 0.5 mm.

 We will therefore choose, as appropriate, the most suitable technique for obtaining beads of a desired size.

FIG. 5 represents a device making it possible to implement the method according to the invention, which consists of:
- A reservoir 9 of mother composition 2 provided with an agitator 10 allowing perfect homogenization solid phase / liquid phase;
- A loop circuit 12 for routing the mother composition 2 to the distribution means 13 or, if necessary, the return of the mother composition to said tank 9;
- a pump 11 for circulation of the mother composition 2;
- distribution means 13, making it possible to implement, for example, one of the techniques shown in FIGS. 1 to 4, and generally provided with distribution nozzles 1;
- a reservoir of cryogenic fluid in the liquid state 14, such as liquid nitrogen, conveyed along a channel 15, such as a U-shaped channel, in the form of a stream 3, conveying the frozen aggregates 5 of mother composition in the direction of arrow 4;
- Means 16 and 18 for recovering and separating liquid nitrogen 3, on the one hand, and frozen aggregates 5, on the other hand;
- drying means 19, such as a vacuum freeze dryer (not detailed), frozen aggregates 5;
- Means for conveying, such a pipe 17, the liquid nitrogen 3 recovered to a tank 20 of liquid nitrogen;
- And means 20, 22 for conveying the liquid nitrogen stored in the tank 20 to the tank 14, provided with a pump 22.

 The cryogenic liquid circuit 3 is therefore there too, preferably, a loop circuit.

 After freezing the beads obtained by one of the previous techniques, they are removed by the cryogenic fluid 3 and then recovered in order to then undergo a drying step, that is to say elimination of all or part of the phase liquid or diluent that they contain, preferably by lyophilization under vacuum, and possibly other subsequent treatments, such as a cooking step.

Example 1
This example illustrates the production of aggregates or alumina beads by implementing the method of the invention.

 Alumina is an adsorbent material used in particular in many gas purification processes.

 A mother composition was produced from the mixture of an equal amount (by weight) of alumina powder and water.

 The stable mother composition obtained, in the form of a "milk" of low viscosity, is injected into a stream of liquid nitrogen by means of nozzles or needles whose minimum diameter is approximately 0.4 mm, preferably from 0.8 mm to 1.2 mm.

 The aggregates or beads of frozen mother composition are recovered and then subjected to dehydration, that is to say to elimination of water, by lyophilization by means of a flow of dry nitrogen gas at a temperature of approximately -200C. and at atmospheric pressure.

 The alumina beads dehydrated by lyophilization are recovered and handled at room temperature; in particular, they have been sieved and observed using a binocular microscope: their average diameter is approximately 1 mm and their shape is substantially spherical.

 These balls can then undergo sintering in order to consolidate them and make them suitable for industrial use.

Example 2
This example 2 relates to the production of aggregates or zeolite beads.

Zeolite beads are commonly used in many processes, such as PSA type gas separation processes (for Pressure Swing
Adsorption in English). Indeed, materials of the zeolite type have adsorption properties making it possible to effectively separate, in particular the various major constituents of air, nitrogen and oxygen, or others, such as carbon mono- and dioxide and hydrogen. , or to dry the gases.

 The synthesis of the zeolite beads was carried out in a manner analogous to Example 1.

 A mother composition (100 g) was produced by mixing approximately 35 g of zeolite powder, approximately 5 g of a binder, such as a clay (attapulgite or Kaolin), and approximately 60 g of water.

 The homogeneous mother composition obtained underwent the process of the invention by giving zeolite beads with a diameter of between 0.8 mm and 1.2 mm.

 The beads were collected and then subjected to a subsidiary baking step in order to strengthen their cohesion, to give them a given porosity and their physico-chemical properties.

 It is possible to control the porosity of the zeolite ball by varying the amount of dry extract (zeolitic powder and binder) relative to the amount of water, that is to say, in other words, on the quantity of dry extract in a bead of given diameter.

Example 3
This example aims to illustrate the production of colored beads or aggregates.

 The procedure is the same as in Example 1 above, except that 1 to 2% (by weight) of a pigment of the desired color are added to the mother composition.

 Colored balls of substantially spherical shape are thus obtained.

Claims (23)

 1. Process for the manufacture of aggregates containing at least one solid substance, from a mother composition comprising at least said solid substance and at least one diluent, in which:  a) fractionating said mother composition into aggregates;  b) the said aggregates are frozen by contacting with a cryogenic fluid in the liquid state;  c) the frozen aggregates are recovered;  d) the frozen aggregates are dried.  2. Method according to claim 1, characterized in that steps a) and b) are carried out simultaneously by injection of the mother composition in contact with the cryogenic liquid.  3. Method according to claim 2, characterized in that the injection of the mother composition is carried out at a flow rate of between 0.1 m.s and 0.5 m.s  4. Method according to claim 1, characterized in that the fractionation of step a) is carried out prior to step b) and using a fractionation technique chosen from the group formed by soft distribution, atomization and the "pot-vibrating" technique.  5. Method according to claim 4, characterized in that the mother composition is fractionated into aggregates of predetermined volume preferably between 0.01 mm3 and 100 mm3.  6. Method according to claims 1 to 5, characterized in that the fractionation of the mother composition is carried out by means of a nozzle or a nozzle.  7. Method according to claim 6, characterized in that the end of the nozzle or of the nozzle has an internal diameter between 0.10 mm and 4.5 cm, preferably between 0.5 mm and 2.1 cm.  8. Method according to claim 1, characterized in that in step c) the frozen aggregates are recovered on the surface and / or under the surface of the cryogenic fluid.  9. Method according to one of claims 1 to 8, characterized in that the mother composition contains at least one aqueous diluent, preferably water.  10. Method according to one of claims 1 to 8, characterized in that the cryogenic fluid is liquid nitrogen.  11. Method according to one of claims 1 to 10, characterized in that in step d), the frozen aggregates are dried by lyophilization.  12. Method according to claim 11, characterized in that the lyophilization is carried out by means of a vacuum freeze dryer.  13. The method of claim 11, characterized in that the lyophilization is carried out by means of a cryogenic gas at a temperature below OOC, preferably less than or equal to -200C.  14. Method according to claim 13, characterized in that the cryogenic gas is nitrogen gas or dry air.  15. Method according to one of claims 1 to 14, characterized in that the mother composition comprises at least one solid substance chosen from the group formed by zeolite, alumina, silica, activated carbon, carriers for catalysts, the bases of adsorbent materials.  16. Method according to one of claims 1 to 14, characterized in that, the mother composition comprises at least one substance chosen from the group formed by mineral powders, organic polymers, drugs, natural products, cosmetics, galenical and food.  17. Method according to one of claims 15 or 16, characterized in that the mother composition further comprises an organic or inorganic binder, preferably a binder chosen from the group formed by glues, clays, resins , waxes, cements or organic or mineral additives.  18. Method according to claims 1 to 17, characterized in that the porosity of the aggregates is controlled by the content of the mother composition in its various constituents.  19. Method according to one of claims 1 to 18, characterized in that the dried aggregates in step d) undergo a subsequent cooking step.  20. Aggregate obtained by the process according to one of claims 1 to 19.  21. The aggregate according to claim 20, characterized in that its diameter is between 0.1 mm and 3 cm, preferably between 0.7 mm and 2 cm.  22. Use of aggregates according to one of claims 20 or 21 in a process for the separation or purification of gas mixtures using at least one step of adsorption of at least one constituent of said gas mixture on said aggregates and / or at least one step of catalysis of at least one constituent of said gaseous mixture by means of said aggregates used as supports for at least one catalyst.  23. Device for implementing the method according to one of claims 1 to 19 and for the manufacture of aggregates according to claims 20 or 21, comprising:  - Means for fractionation (1, 13) of the mother composition (2) into aggregates;  - means for freezing (3, 15) the aggregates (5), comprising at least one container (15) containing a cryogenic fluid (3) in the liquid state;  - recovery means (18) of the frozen aggregates (5),  - And drying means (19) of the frozen aggregates.