MXPA99009992A - Method for compacting aerogels - Google Patents

Abstract

La inversión se refiere a un método para partículas compactas de aerogeles, de acuerdo con el cual las partículas de aerogel se colocan en un dispositivo a presión y se comprimen.

Description

The object of the present invention is a method of granulating aerogels. Aerogels, particularly those with a porosity greater than 60% and a density of less than 0.5g / cm3 exhibit extremely low thermal conductivity and are therefore used as a heat insulating material, as described in EP-A -0 171 722, as a catalyst or as a catalytic conductor and also as an absorption material. Furthermore, by virtue of its very low refractive index for solid substances, it is also known that they are used for Cernkov detectors. Additionally, due to its particular acoustic impedance, the literature describes a possible use as an impedance matching element, for example in the range of ultrasound. It is also possible to use them as conductors for effective substances in pharmaceuticals or agriculture. Aerogels in the broadest sense, for example in the sense of a "gel with air as the dispersing agent" are produced by drying a suitable gel. The term "airgel" in this sense encompasses aerogels in the narrowest sense, aerogels and cryogels. In this regard, a dried gel is referred to as an airgel in the narrowest sense when the gel liquid is removed above the critical temperature and starting from the pressures above the critical pressure. On the other hand, if the liquid is removed from the gene under subcritical conditions, for example with interphase liquid / flavor formation, then the resulting gel is often referred to as a xerogel. When the term airgel is used in the present invention, these aerogels in the broadest sense, ie in the sense of "gel with air as dispersion medium". The term does not include the aerogels known from the prior literature in which they are obtained, for example, by precipitating the silicic acid (for example DE 3025437, DD 296 898) or occurring as pyrogenic silicic acid, for example Aerosil ™. In these cases, during manufacturing, a three-dimensional lattice is not developed, which is homogeneous over relatively large distances. As far as aerogels are concerned, it is basically possible to differentiate between organic and inorganic aerogels. Aerogels have been known since 1931 (S.S. Kistler, Nature 1931, 127, 741). Since then, "aerogels have appeared from various starting materials, in this respect, for example SiO2-, Al2O2, TiO2-, ZrO2-, SnO2, Li20-, CeO2-, V2Os-aerogels and mixtures were produced (HD). Gesser, OC Boswami, Chem. Rev. 1989, 89, 765 et seq.) For some years, it was also known that organic aerogels that were derived from the broadest and most diverse starting materials, for example melamine formaldehyde (R. Pekala, J. Mater, Sci. 1989, 24, 3221.) Aerogels can therefore be produced in different ways: On the one hand, aerogels Si02 can for example be produced through acid hydrolysis and tetra-ethyl condensation orthosilicate in ethanol During this process, a gel is produced when it can be dried through supracritical drying "while its structure is maintained. Production methods based on this drying technique are known, for example, from EP-A-0 396 076, WO 92/03378 or WO 95/06617. The high pressure technique involved in the supercritical drying of aerogels is, however, an expensive process that involves a high safety risk.

In addition, however, supercritical drying of aerogels is a cost-intensive production method.

An alternative for supercritical drying is available through a method for subcritical drying of Si02 gels. The costs involved in subcritical drying are substantially lower due to the simpler technology, the lower energy costs and the lower safety risk. Si02 gels, for example, are obtained by acid hydrolysis of tetra-alkoxy silanes in a suitable organic solvent by means of water. Once the solvent has been exchanged for an adequate organic solvent, the gel obtained is in a subsequent step reacted with a silylating agent. The resulting Si02 gel can then be dried in air from an organic solvent. Thus, aerogels with densities of less than 0.4 g / cm2 are porosity of more than 60% can be achieved. The production method based on these drying techniques are described in detail in WO 94/25149. In addition, the gels described above can, before drying and in aqueous alcohol solution, be mixed with tetra-alkoxy silanes and aged, in order to increase the lattice resistance of the gel, as disclosed in WO 92/20623. The tetra-alkoxy silanes used as starting materials in the processes described above represent in the same way an extremely high factor in cost. A considerable cost reduction can be achieved that can be achieved through the use of water glass as a starting material for the production of Si02 gels. For this purpose, it is possible, for example, to produce a silicic acid from an aqueous solution of water glass with the aid of a resin ion exchange, the silicic acid is then polycondensed through the addition of a base to produce a gel of Si02. After exchange of an aqueous medium with a suitable organic solvent, it is then possible in a subsequent step to react the resulting gel with a silylating agent containing chlorine. The Si02 gel whose surface is modified for example with methyl silyl groups can then likewise be dried in air from an organic solvent. The production method based on this technique is known from DE-A-43 42 548. Alternative methods with respect to the production of an Si02 airgel on a water glass base with subsequent subcritical drying are described in the Application of German Patent 195 41 715.1 and 195 41 992 8.

In addition, DE-A-195 02 453 discloses a use of chlorine-free silylating agents during the production of subcritically dried aerogels. Additionally, an organofunctionalization by means of organofunctionalizing the silylating agents in the production of dried aerogels subcritically is described in DE-A-195 34 198. However, in the field of process technology and manufacturing costs, the production of Airgel particles on a larger industrial scale are limited to the particle size of less than 5 mm and preferably less than 2 mm. In accordance with a particular way of producing aerogels, so that in principle a plurality of washing and solvent exchange steps are required. Since these are diffusion dependent, the time required increases across the square of the radius of the gel particles. Consequently, apart from the drying method, the production costs of the airgel will also be increased considerably by increasing the size of the particles. In the cost areas, the result is an attempt to produce the airgel particles as small as possible.

On the other hand, the handling of such small particles is very complicated and thus also the relative costs are unfavorable and not all industrial applications of aerogels are independent of the particle size. Therefore, from the point of view of handling and for many applications, larger or at least more advantageous airgel particles are needed. Therefore, the aim of the present invention is to provide a method through which smaller airgel particles of 2 mm can be formed into larger airgel particles. This problem is solved through a method in which the airgel particles are taken to a molding apparatus where they are compressed. In this way, it is particularly simple to form small airgel particles in larger airgel particles. The binder can be added to the mixing apparatus before, during and / or after the addition of the airgel particles, it is preferred that the addition be subsequent. The airgel particles are caused to move so as to enjoy a relative movement with each other by means of the mixing apparatus, which is, for example, a binder plate, a mixer or a fluidized bed unit. Advantageously, the binder is incorporated as an aqueous or non-aqueous solution or a suspension or even as a batch, for example by means of a spray. The binder gives rise to a bond together with the airgel particles provided primarily to produce larger agglomerates. During this process, through the chemical reaction, the rigidification, the crystallization, due to evaporation or vaporization of the solvent, the binder results in a binding of the constituents of the mixture. According to a further advantageous embodiment, the binder is added as a solid substance. The agglomeration is then carried out through the chemical reaction of the solid substance with one or more components of the mixture by softening the solid binder, for example, by elevated temperatures, which result in it becoming sticky and the agglomeration of the particles of the mixture. Another embodiment of the invention envisages that in addition to the airgel particles, also the additives and / or filters that are present in the form of particles or fibers are added to the mixing apparatus. According to a preferred embodiment, the agglomerates are separated according to their size. Advantageously, this is carried out in such a way that from the granules produced, the target fraction is screened according to the desired granular range. The granules that are so large, possibly crumble, for example with a cutting apparatus or a cutting head and then are filtered so that they are present in the desired granular range or can be fed back into the agglomerating device after being sprayed. Granules that are too small may possibly be recycled in the binder. According to a further embodiment, the agglomerates are dried before being processed.

Claims (9)

1. CLAIMS 1. A method for the structural agglomeration of airgel particles in which the airgel particles are fed and mixed thoroughly in a mixing apparatus and in which a binder is added to the mixing apparatus.
2. 2. A method according to claim 1, characterized in that the airgel particles are presented to the mixing apparatus and then the binder is added then added.
3. A method according to Claim 1 or 2, characterized in that the binder is incorporated as an aqueous or non-aqueous solution, as a suspension, as a melt or as a solid substance.
4. 4. The method according to at least one of the preceding claims, characterized in that in addition to the airgel particles, also additives and / or filters are fed into the mixing apparatus.
5. 5. A method according to at least one of the preceding Claims, characterized in that the agglomerates are separated according to their size.
6. 6. A method according to claim 5, characterized in that the agglomerates that are below the desired granular range are fed back into the mixing apparatus.
7. 7. A method according to claim 5, characterized in that the agglomerates that are above the desired granular range are sprayed.
8. 8. A method according to claim 7, characterized in that the pulverization and / or the binders that are below the desired granular range are fed to the mixing apparatus.
9. 9. A method according to at least one of the preceding claims, characterized in that the agglomerates are dried in addition to the processing.