GRANULAR THERMAL INSULATION MATERIAL AND METHOD FOR PRODUCING THE SAME

Abstract

The present invention relates to a granular thermal insulation material comprising hydrophobized silicon dioxide and at least one IR opacifier, having a tamped density of up to 250 g/l and a compressive strength according to DIN EN 826:2013 at 50% compression of 150 to 300 kPa or greater than 300 kPa, to processes for production thereof and to the use thereof for thermal insulation.

Claims

1-15. (canceled)

16. A granular material comprising hydrophobized silicon dioxide and at least one IR opacifier, wherein said granular material comprises: a) a tamped density of up to 250 g/l; and b) a compressive strength according to DIN EN 826:2013 at 50% compression of 150 to 300 kPa, wherein the compressive strength is measured on a bed with a square face having an edge length of 200 mm and bed height 20 mm.

17. The granular material of claim 16, wherein the IR opacifier is selected from the group consisting of: silicon carbide; titanium dioxide; zirconium dioxide; ilmenites; iron titanates; iron oxides; zirconium silicates; manganese oxides; graphites; carbon blacks; and mixtures thereof.

18. The granular material of claim 16, wherein said granular material comprises a BET surface area of 50 to 400 m.sup.2/g.

19. The granular material of claim 16, wherein said granular material comprises a tamped density of 100 to 240 g/l.

20. The granular material of claim 16, wherein said granular material comprises a thermal conductivity of less than 50 mW/(m*K) according to EN 12667:2001, measured in the bed, at a mean measurement temperature of 10 C., a contact pressure of 250 Pa under an air atmosphere and at standard pressure.

21. The granular material of claim 16, wherein the silicon dioxide has been produced by pyrogenic means.

22. The granular material of claim 16, wherein said granular material comprises a methanol wettability of methanol content 10% to 60% by weight in a methanol/water mixture.

23. A granular material comprising hydrophobized silicon dioxide and at least one IR opacifier, wherein said granular material comprises: a) a tamped density of up to 250 g/l; and b) a compressive strength according to DIN EN 826:2013 at 50% compression of greater than 300 kPa, wherein the compressive strength is measured on a bed with a square face having an edge length of 200 mm and bed height 20 mm.

24. The granular material of claim 23, wherein the IR opacifier is selected from the group consisting of: silicon carbide; titanium dioxide; zirconium dioxide; ilmenites; iron titanates; iron oxides; zirconium silicates; manganese oxides; graphites; carbon blacks; and mixtures thereof.

25. The granular material of claim 23, wherein said granular material comprises a BET surface area of 50 to 400 m.sup.2/g.

26. The granular material of claim 23, wherein said granular material comprises a tamped density of 100 to 240 g/l.

27. The granular material of claim 23, wherein said granular material comprises a compressive strength according to DIN EN 826:2013 at 50% compression of up to 2000 kPa, wherein the compressive strength is measured on a bed with a square face having an edge length of 200 mm and bed height 20 mm.

28. The granular material of claim 23, wherein said granular material comprises a thermal conductivity of less than 50 mW/(m*K) according to EN 12667:2001, measured in the bed, at a mean measurement temperature of 10 C., a contact pressure of 250 Pa under an air atmosphere and at standard pressure.

29. The granular material of claim 23, wherein the silicon dioxide has been produced by pyrogenic means.

30. The granular material of claim 8, wherein said granular material comprises a methanol wettability of methanol content 10% to 60% by weight in a methanol/water mixture.

31. A process for producing a granular material comprising hydrophobized silicon dioxide and at least one IR opacifier, comprising the following steps: a) mixing a hydrophilic silicon dioxide with at least one IR opacifier; b) densifying the mixture obtained in step a) to give a granular material; c) either: i) subjecting the granular material produced in step b) to thermal treatment at a temperature of 200 to 1200 C.; or ii) treating the granular material produced in step b) with ammonia; d) hydrophobizing the granular material produced in step c) with a hydrophobizing agent.

32. The process of claim 31, wherein step c) is conducted at 800-1000 C.

33. The process of claim 31 wherein, step b) and/or c) and/or d) is followed by a separation of fractions of the granular material of different size from one another.

34. The process of claim 31, wherein the hydrophobizing agent used in step d) is selected from the group consisting of halosilanes, alkoxysilanes, silazanes and siloxanes.

35. The process of claim 31, wherein said process is used to produce a granular material comprising a tamped density of up to 250 g/l and a compressive strength according to DIN EN 826:2013 at 50% compression of either: a) 150 to 300 kPa; or b) 300 to 2000 kPa, wherein the compressive strength is measured on a bed with a square face having an edge length of 200 mm and bed height 20 mm.

Description

EXAMPLES

Comparative Examples 1-3

[0054] Mixing

[0055] Silcar G14 silicon carbide (ESK-SiC GmbH), 20% by weight, and AEROSIL R974 dimethyldichlorosilane-hydrophobized silica (BET=200 m.sup.2/g, manufacturer: EVONIK Resource Efficiency GmbH), 80% by weight, were mixed by means of a Minox PSM 300 HN/1 MK ploughshare mixer.

[0056] Densification

[0057] The mixture of AEROSIL R974 with silicon carbide produced above was densified with a Grenzebach densifying roll (Vacupress VP 160/220). The tamped density of the product was adjusted via the contact pressure, the roll speed and the reduced pressure applied.

[0058] Compaction

[0059] By means of the Bepex Pharmapaktor L200/50P roll compactor, the mixture densified beforehand was then compacted once again to give granules that are easy to handle. The speed, contact pressure and vacuum here were adjusted correspondingly.

[0060] Sieving/Fractionation

[0061] In order to obtain desired fractions, the compacted granular material was first fed to an oscillating sieve mill with mesh size 3150 m (manufacturer: FREWITT), in order to establish an upper particle limit and hence remove the particles larger than this upper limit. This was followed by the desired fractionation of the particle fractions, for example from 200 to 1190 m or from 1190 to 3150 m. This was done using a vibrating sieve from Sweco, model LS18S.

[0062] The sieved granules thus obtained were not subjected to any further treatment and had the tamped densities and other parameters reported in Table 1.

Comparative Example 4

[0063] A commercial hydrophobized granular aerogel material (manufacturer: Cabot, product name: Enova IC3120, particle size from 0.1 to 1.2 mm), in untreated form, was analysed under the same conditions as the other materials; see Table 1.

Examples 1-2

[0064] Mixing

[0065] 1000F silicon carbide (Carsimet), manufacturer: Keyvest, 20% by weight, and AEROSIL 300 hydrophilic silica (BET=300 m.sup.2/g, manufacturer: EVONIK Resource Efficiency GmbH), 80% by weight, were mixed by means of a Minox PSM 300 HN/1 MK ploughshare mixer.

[0066] Densification

[0067] The mixture of AEROSIL 300 with silicon carbide produced above was densified with a Grenzebach densifying roll (Vacupress VP 160/220). The tamped density of the granular material obtained was adjusted via the contact pressure, the roll speed and the reduced pressure applied. The vacuum applied was less than 300 mbar, absolute. The roll speed was 5 rpm, and the pressure was 2000 N.

[0068] Sintering/Hardening

[0069] The subsequent thermal hardening was effected in an XR 310 chamber kiln from Schrder Industriefen GmbH. For this purpose, multiple layers with a bed of height up to 5 cm were subjected to a temperature programme. The temperature ramp was 300 K/h up to the target temperature of 950 C.; the hold time was 3 hours; then the samples were cooled (without active cooling) until removal.

[0070] Hydrophobization

[0071] The final hydrophobization of the thermally hardened granules was effected at elevated temperatures over the gas phase. For this purpose, hexamethyldisilazane (HMDS) as hydrophobizing agent was evaporated and conducted through by the reduced pressure process in accordance with the process from Example 1 of WO 2013/013714 A1. The specimens were heated to more than 100 C. in a desiccator and then evacuated.

[0072] Subsequently, gaseous HMDS was admitted into the desiccator until the pressure had risen to 300 mbar. After the sample had been purged with air, it was removed from the desiccator.

[0073] Sieving/Fractionation

[0074] In order to obtain desired fractions, the thermally hardened granular material was first fed to an oscillating sieve mill with mesh size 3150 m (manufacturer: FREWITT), in order to establish an upper particle limit and hence remove the particles larger than this upper limit. This was followed by the desired fractionation of the particle fractions, for example from 200 to 1190 m or from 1190 to 3150 m. This was done using a vibrating sieve from Sweco, model LS18S.

[0075] The values of tamped density, compressive strength at 50% compression and thermal conductivity that are compiled in Table 1 were measured as elucidated above in the description.

[0076] Ultrasound Measurements

[0077] The ultrasound measurements were conducted with the Retsch Horiba LA-950 Laser Particle Size Analyzer from Horiba. Test method: Mie scattering theory, measurement range: 0.5 to 5000 m. A similar process is described in WO 2014001088 A1. The samples were pretreated prior to the measurement by manually sieving off particles larger than 2500 m, in order not to block the gap of the analyser. The amount of sample used was 1 g in each case (guided by the laser attenuation). A double determination for each sample was conducted and then a mean was calculated. The measurements showed good repeatability. The ultrasound intensity of the ultrasound standard finger installed cannot be regulated in terms of power; only the duration can be adjusted. The measurement was effected in intervals at room temperature. The d.sub.50 is evaluated at the start of the test series and after each time interval. The US (20s), d.sub.50 quotient values compiled in Table 1 are the ratios of the d.sub.50 values after 20 seconds of ultrasound treatment (d.sub.50 20 s) to the corresponding d.sub.50 values at the start of the test series (d.sub.50 start):

US(20s),d.sub.50quotient=d.sub.50 20 s/d.sub.50 start

[0078] Accordingly, the higher this d.sub.50 quotient, the more mechanically stable the granules tested.

[0079] FIG. 1 shows the decrease in the d.sub.50 quotient (dimensionless, plotted on the Y axis) during the ultrasound treatment time (in seconds, plotted on the X axis). The individual test series are identified as follows:

[0080] Comparative Example 1triangle (.box-tangle-solidup.);

[0081] Comparative Example 2star ();

[0082] Comparative Example 3X (x);

[0083] Comparative Example 4circle (.circle-solid.);

[0084] Example 1square (.square-solid.)

[0085] Example 2rhombus (.diamond-solid.)

[0086] The test results for granules with comparable particle size fractions compiled in Table 1 show that the inventive granular materials from Examples 1 and 2 have better mechanical stability than the products from Comparative Examples 1 and 4 with tamped density less than 260 g/l. Secondly, the inventive granules have comparable or even better mechanical stability than the materials from Comparative Examples 2 and 3 with tamped densities higher than 350 g/l. Accordingly, the inventive granules have a unique and economically utilizable combination of parameters.

TABLE-US-00001 TABLE 1 Compressive US (20 s) Opacifier, Tamped strength at 50% d50 Thermal Silicon dioxide raw % by density, compression, Fraction, D.sub.50, quotient, conductivity, material, % by weight weight g/l kPa m m* m mW/(m*K) Comparative AEROSIL R974, 80 SiC, 20 256 128 <3150 519 0.11 25.0 Example 1 Comparative AEROSIL R974, 80 SiC, 20 460 1575 250-600 500 0.89 36.9 Example 2 Comparative AEROSIL R974, 80 SiC, 20 360 869 1000-4000 1842 0.53 30.0 Example 3 Comparative Aerogel granules, unknown 105 119 100-1200 1233 0.12 21.0 Example 4 manufacturer: Cabot, Enova IC3120 Example 1 AEROSIL 300, 80 SiC, 20 202 840 200-1190 861 0.74 28.1 Example 2 AEROSIL 300, 80 SiC, 20 200 1018 1190-3150 1936 0.51 30.2 *All the materials tested were sieved prior to the measurement of the d.sub.50 in order to separate off the particles larger than 2500 m; see the description of the ultrasound measurement experiment.