Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2/00—Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic
  • B01J2/20—Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic by expressing the material, e.g. through sieves and fragmenting the extruded length
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B9/00—Making granules
  • B29B9/12—Making granules characterised by structure or composition
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B9/00—Making granules
  • B29B9/08—Making granules by agglomerating smaller particles

Definitions

• the present invention relates to a method for compacting aerogels.
• Aerogels in particular those with porosities above 60% and densities below 0.6 g / cm 3 , have an extremely low thermal conductivity and are therefore used as heat insulation material, as described in EP-A-0 1 71 722, as catalysts or Catalyst carrier, as well as an adsorbent material.
• the use for Cerenkov detectors is known due to their very low refractive index for solids.
• the literature describes a possible use as an impedance matching, for example in the ultrasound range, due to its special acoustic impedance.
• Aerogels in the broader sense ie in the sense of "gel with air as the dispersion medium" are produced by drying a suitable gel.
• airgel in this sense includes aerogels in the narrower sense, xerogels and cryogels.
• a dried gel is referred to as an airgel in the narrower sense if the liquid of the gel is largely removed at temperatures above the critical temperature and starting from pressures above the critical pressure. If, on the other hand, the liquid of the gel becomes subcritical, for example with the formation of a liquid-vapor boundary phase removed, the resulting gel is often referred to as xerogel.
• aerogels in the broad sense, i.e. in the sense of "gel with air as a dispersion medium”.
• the term does not include xerogels known from the older literature, which e.g. obtained by precipitation of silica (e.g. DE 3025437, DD 296 898), or as pyrogenic silica, e.g. Aerosil TM. In these cases, a homogeneous three-dimensional gel network is not formed over large distances during production.
• Inorganic aerogels have been known since 1 931 (SS Kistler, Nature 1 931, 1 27.741). Since then, aerogels have been made from a wide variety of starting materials.
• z. B. SiO 2 -, Al 2 O 3 -, TiO 2 -, ZrO 2 -, SnO 2 -, Li 2 O-, CeO 2 -, V 2 O 5 -Aerogels and mixtures of these can be prepared (H .D. Gesser, PCGoswami, Chem. Rev. 1 989, 89.765ff).
• organic aerogels made from a wide variety of starting materials, e.g. from Meiamine formaldehyde, known (R.W. Pekala, J. Mater. Sci. 1 989, 24, 3221).
• Inorganic aerogels can be produced in different ways.
• SiO 2 aerogels can be produced, for example, by acid hydrolysis and condensation of tetraethyl orthosilicate in ethanol. This creates a gel that is obtained by supercritical drying while maintaining the structure can be dried. Manufacturing processes based on this drying technique are known, for example, from EP-A-0 396 076, WO 92/03378 or WO 95/0661 7.
• An alternative to supercritical drying is a method for subcritical drying of SiO 2 gels.
• the SiO 2 gel can be obtained, for example, by acid hydrolysis of tetraalkoxysilanes in a suitable organic solvent using water. After replacing the solvent with a suitable organic solvent, the gel obtained is reacted with a silylating agent in a further step. The resulting SiO 2 gel can then be dried in air from an organic solvent. This enables aerogels with densities below 0.4 g / cm 3 and porosities above 60% to be achieved. The manufacturing process based on this drying technique is described in detail in WO 94/25149.
• the gels described above can also be mixed with tetraalkoxysilanes and aged in the alcohol-aqueous solution before drying in order to increase the gel network strength, as disclosed in WO 92/20623.
• the tetraalkoxysilanes used as starting materials in the processes described above also represent an extremely high cost factor.
• a not inconsiderable cost reduction can be achieved by using water glass as the starting material for the production of the SiO 2 gels.
• a silica can be produced from an aqueous water glass solution with the aid of an ion exchange resin, and this polycondenses into an SiO 2 gel by adding a base. After replacing the aqueous medium with a suitable organic solvent, the gel obtained is then reacted with a chlorine-containing silylating agent in a further step. The resulting, on the surface z. B. modified with methylsilyl groups SiO 2 gel can also be dried in air from an organic solvent. The manufacturing method based on this technique is known from DE-A-43 42 548.
• DE-A-1 95 02 453 also describes the use of chlorine-free silylating agents in the production of subcritically dried aerogels.
• DE-A-1 95 34 1 98 also describes organofunctionalization using organofunctionalized silylating agents in the production of subcritically dried aerogels.
• airgel particles are, however, for the sake of Process engineering and the manufacturing costs on an industrial scale limited to particle sizes smaller than 5 mm, preferably smaller than 2 mm.
• the object of the present invention is therefore to provide a method by means of which small airgel particles below 2 mm can be formed into larger airgel particles.
• This object is achieved by a method in which the airgel particles are placed in a pressing device and pressed. In this way, it is particularly easy to form small airgel particles into larger airgel particles.
• these additives, fillers and / or binders are advantageously added, which may be in particulate and / or fibrous form, optionally also liquid or pasty.
• the starting material is degassed before pressing. This is particularly advantageous if the starting material is a loose bed, since then a certain proportion of the gas located between the airgel particles must be removed before compacting.
• the starting material for degassing is expediently subjected to a negative pressure, and in another embodiment the degassing can also take place during the pressing.
• the airgel particles or the starting material can be pressed into granules, after which they are then advantageously separated according to their size. This can be done, for example, by sieving the desired particle size range in order to obtain the desired target fraction. Granules lying below the desired grain size range are advantageously returned to the pressing device, while granules lying above are expediently comminuted so that they lie in the desired grain size range. After crushing, they can also be fed directly back to the pressing device in order to be compacted again.
• the granulate is then dried before further processing in order to remove undesirable residual moisture or harmful residual moisture for the further course of the process.
• the starting material can also be pressed into a slug, which is then also dried in accordance with a further embodiment before a further process step.
• the airgel particles or the airgel particles with possible additives can be pressed using customary suitable pressing devices.
• Another embodiment provides that the starting material is pressed into a die by a punch.
• the resulting compacts can then optionally be cut to the desired size with a knife, a scraper or the like.
• the starting material is pressed between a die and a roller sliding or rolling over it.
• the die can be perforated, in which case the resulting compacts are advantageously cut off in the desired size on the exit side with a knife, a scraper or the like.
• the starting material is pressed between two rollers, at least one of which rotates, but advantageously both.
• the starting material is then expediently pressed into the roll gap by a stuffing screw.
• At least one of the rolls is designed as a perforated hollow roll.
• the compacts formed here during the pressing are advantageously cut to the desired size on the outlet side using a suitable device, for example a knife or scraper.
• rollers are profiled.
• the starting material can then be pressed directly either into granules or into a coherent product band, a so-called Schülpe.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Dispersion Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Silicon Compounds (AREA)
• Oxygen, Ozone, And Oxides In General (AREA)
• Colloid Chemistry (AREA)

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Citations (2)

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• 1997
  • 1997-05-02 DE DE19718741A patent/DE19718741A1/de not_active Ceased
• 1998
  • 1998-04-29 CA CA002287832A patent/CA2287832A1/en not_active Abandoned
  • 1998-04-29 JP JP54769698A patent/JP2001525721A/ja active Pending
  • 1998-04-29 EP EP98925497A patent/EP0979142A1/de not_active Ceased
  • 1998-04-29 WO PCT/EP1998/002520 patent/WO1998050145A1/de not_active Ceased
  • 1998-04-29 KR KR19997010097A patent/KR20010012152A/ko not_active Ceased
  • 1998-04-29 CN CN98805628A patent/CN1258231A/zh active Pending
  • 1998-04-29 CN CNA2006100048970A patent/CN101015781A/zh active Pending
• 1999
  • 1999-11-01 US US09/430,982 patent/US6620355B1/en not_active Expired - Lifetime

Patent Citations (2)

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